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SpaceX lands rocket at sea second time after satellite launch (phys.org)
814 points by dnetesn on May 6, 2016 | hide | past | web | favorite | 474 comments

For those wondering, this isn't a simple repeat of CRS8 which landed on a drone ship about a month ago. CRS8 was a mission to low earth orbit which left the first stage with plenty of fuel to effect a landing. The landing was made as slow as possible and limited only by how low a single engine could be throttled. The re-entry burn which slows the rocket down before the landing burn was also more agressive.

This mission was to launch JCSAT-14 to geosynchronous orbit which requires the falcon 9 to move the already heavy satellite into a geosynchronous transfer orbit. That meant the first stage had to do a lot more work and was left with a lot less fuel as a result. Therefore, the re-entry burn was less aggressive, the first stage came in with twice the speed, and SpaceX needed to do a far harder landing with three engines lit in the quicker and riskier suicide burn. Somehow, despite playing down expectations, they managed an even more precise landing than last time.

To expand on this slightly the CRS8 (and OG2, the land landing) landing was done using only 1 engine, which even then was presumably throttled. This landing burn was done using 3 engines so they spend less time below terminal velocity, and thus use less fuel. The total deceleration should be ~40 m/s during the burn.

40 m/s is a velocity, not an acceleration (deceleration). I guess that you mean 40 m/s^2

He did say total deceleration, so I believe he meant the landing burn starts at a velocity of 40 m/s and consequently the total ΔV of the landing burn is 40 m/s.

That said, I have no idea where he got that number, whether 40 m/s or 40 m/s^2; both are incorrect.

The best estimate available for the flight dynamics can be found at flightclub.io, specifically for JCSAT-14: https://flightclub.io/results/?id=eeaf889e-f3d8-4f9b-be98-b7...

This shows the landing burn starting at a velocity of 269 m/s and experiencing a peak deceleration of 12.3g = 121 m/s^2

I don't know how accurate these numbers are, but some fans put quite a bit of effort into getting the flightclub.io profiles as close to reality as possible, so they tend to be pretty good.

Oops, you are right, I did miss a ^2.

The approximation I had is almost certainly less reliable than flightclubs, not sure why it was so low, will have to look at the math I did and figure out what I screwed up.

So only about 4Gs? I somehow though it would be more and unsurvivable for humans.

Check out the flight profile on Flightclub.io -- I'm not sure how accurate their instantaneous data is but they're showing ~12g acceleration upon landing the booster. Seems more like what I'd expect.

TheVehicleDestroyer (who makes FlightClub) actually commented [1] to say that the 12G is an error due to how he models the deployment of the landing legs.

The actual force would have been closer to 5.1G

[1] https://www.reddit.com/r/spacex/comments/4htenu/rspacex_jcsa...

Ugh sorry, there's a bug of some sort in Flight Club there. There's no way it was that large. A constant deceleration down from terminal velocity over 6 seconds is

a = (300 - 0)/6 = 50m/s2 = 5.1g

I'll need to look into that


So it looks like that peak is due to the sudden increase in drag during my landing legs deployment. I deploy them at 500m altitude which is a time when the stage is probably still moving a bit too fast. It's a really large increase in cross-sectional area, but I'm probably not treating it correctly. I'll revise before Thaicom-8

Wow, thanks for the update -- the internet can be damn cool sometimes.

Impatient to know if the 1st stage is reusable after a 12g phase. The entire concept hangs on this and it looks like we don't have a firm confirmation yet.

12g but empty. A structure meant to survive being filled with 10+ times (fuel+upper stage) it's own weight will survive 10+Gs without effort. In other words, the stress of a 12g acceleration isn't much different than the stress of the stage sitting on the pad a few minutes previously.

The overall structure actually goes through all sorts of stresses, not all of which are measured in G. The combination of push from the rocket and air resistance compresses the rocket from both ends, something that isn't reflected in G numbers.

I am not a rocket scientist, but:

I think this is only sort of true. Yes, the fueled rocket is much, much heavier. But not all parts of the rocket are load bearing as it sits on the pad waiting for launch. All parts of the rocket experience the 12g (or whatever it was) deceleration.

Also, rocket skins are really, really thin (relative to their size, the forces they endure, etc.) I've read that without the fuel inside to reinforce the rocket, it is quite fragile - think of trying to crush an empty soda can vs a full one. This is part of why rockets which deviate too far from prograde on launch are ripped apart mid-air.

Regarding your last part, some rockets have balloon tanks, which means that the tank requires pressurization to keep its shape.

The Falcon 9 has a sort of partial balloon tank. It's strong enough for ground handling without pressurization, but it requires pressurization to handle flight loads.

Note however that it's pressure, not fuel, that provides the extra strength. These tanks are still pressurized even when almost empty.

From the video it looks like it lands on a ship in rough seas and they do nothing to secure it. Won't it just fall over if the seas are rough enough, and if so, why don't they have some sort of robotic system that locks it down tight the moment it lands?

If the sea is still enough to land, it's still enough to take time securing. The previous stage was secured by tying down the thrust structure ("octaweb") to tack-welded fixings on the deck with hoofing big chains. There may also have been shoes, we couldn't see clearly.

Tack-welding fixtures to a steel deck is apparently SOP in big shipping, so it's not as radical as it sounds.

Securing is purely a safety precaution, it's not actually required.


With respect to Musk, that is total bunk. Any structure like this will have to be secured to the deck. The fact that it is a rocket doesn't matter. He may think that it is safe from falling over, but the insurance company and/or the health and safety people will tell him that cargo that tall needs to be secured. Ropes, chains, welding ... it cannot just sit there. A Volvo station wagon, on that deck at sea, would be tied. A box of onions would at least be secured so that it doesn't shift onto someone's foot. Boats move, cargo cannot.

I suspect he is in a unique situation to know the numbers for this much better than you do, because he runs the company that has successfully done this.

Bonus points that the overwhelming majority of ships lack the giant oil rig thrusters that all of the ASDS armada contain to keep them as stable as feasible and prevent listing too much in normal ocean condiditons.

It is amusing that you insist your speculation about something you've never done is more valuable than the experience of someone that has pioneered it.

Ya, because SpaceX is the only company to have ever transported something on the deck of the ship. It was a rocket until the moment it landed. Now it's cargo.

This isn't my area of expertise and what you've said certainly makes sense, however from my understanding ship-to-ship, or in this case ship-to-barge, boardings at sea aren't without their own inherent risks.

It could be that having the first stage untethered is deemed less risky to personnel than having a team of welders board the barge and tie it down.

The key is movement. Doing something like moving objects from one ship to another is pretty standard, but only in good conditions and normally not when the ship is moving. The rocket may well be safe to stand on the ship at the moment it lands. The conditions at that moment are good enough to make the choice to do the move. Once it is on the ship, that choice is over. Conditions change, most dramatically in that the stationary ship is going to drive away to port. Not bringing the object aboard is no longer an option, as it was prior to the rocket landing. Under those conditions the cargo has to be secured not against current conditions, but against all possible conditions.

Thanks for the clear explanation.

If they don't need it, they don't need it, but I wonder if there would be any other way do the secure the rocket without requiring welders to board the barge. Coat the deck with solder and put heaters in the feet to attach? A robotic Roomba-style welder? Giant arms that rise up to clasp the rocket regardless of the exact landing position? Fun to think about...

Maybe something with magnets?

Cargo shifting is a big deal. The yearly casualty rate for Bering Sea crab fishing used to be over 1% per year, because the shifting weight of crab pots on overloaded vessels in heavy seas. I saw a training film when I was aboard a tender boat in Alaska. Those boats could look fine one minute then capsize and be as good as sunk in the next 2. Shifting weight on vessels has and does cause rapid capsizing and deaths at sea.

This is pretty light cargo relative to the weight of the ship. It's a few tons of rocket and thousands of tons of ship. I don't think it's going to matter to the ship if it shifts, the only risk is losing the rocket over the side.

What you say is True. My comment explains why the shipping industry and regulatory bodies seem paranoid about shifting weights at sea. There are good reasons to be conservative about certain things and brook no exceptions.

Somehow I suspect they have run the numbers.

What numbers? Unsecured cargo is unsecured cargo. A metal object sitting on a flat metal deck gets tied/braced/chained.

Just to elaborate: due to wave action and leverage on the underside of the hull, parts of the deck of a ship can accelerate downward faster than the acceleration from Earth's gravity, and while the deck underneath the rocket has fallen faster than the rocket and its heavy engines it can also lurch to a side. Even if the center of gravity makes it equivalent to a sheet of rolled steel, so that it wouldn't tip over, it could become displaced, then go overboard or cause unwanted damage.

While I suppose that the rocket could be heavy enough to lower the center of gravity of the entire vessel below the troughs of any waves enough to make it incredibly unlikely, it isn't just the prospect of tipping over that makes it important to secure cargo.

Of course if there is any chance of the rocket moving, it isn't even safe to pull up alongside, let alone send people onto the deck to secure it.

There are protocols for securing unsecured cargo. Whether delivered by rocket or crane, things land on decks every day and are tied down by hand.

In conditions where it's going to be sliding around on the deck?

I think you're trying to apply rules designed to govern shipping in general to a very specialised and controlled situation.

A lot of rules around shipping actually have to do with physics. See my other comment. Shifting cargo can be very bad news. It has caused a lot of deaths. It's probably not a big deal in this case, except that booster is worth about (I'm guessing) 20 million dollars, SpaceX's cost? It's tall, but the center of gravity is low and it's on a barge.

Engineering is conservative "just in case." So are a lot of practical activities that happen on the sea. In neither case, is this irrational or a waste of time.

They will of course have modelled the cargo scenario, and I suspect that Musk means that it's nice and stable when they do that -- but then shipping norms come into play because, like you say, unsecured cargo is unsecured cargo.

It needs to be both stable and secured, because only one is inviting woe.

They mentioned multiple times that because the stage is empty, its center of gravity is much lower than what you'd expect.

By whom? The drone ship has no on-board crew.

... which means there's nobody around to be injured or killed if the rocket falls post-landing. Maybe it's a precaution worth taking when they intend these stages for commercial re-use; for now, the whole thing is one big experiment.

There is a ship a few miles away with engineers on it. Once the stage has vented all excess liquid oxygen and is safe to approach, they can return to the ASDS and secure it.

By the time the rocket lands, there's very few fuel left, basically you see a near empty Pepsi can. It's as stable as it can get.

Ever see an empty pepsi can in a stiff breeze?

More like a Pepsi can with a bloody big brick in the bottom 9*470 kg merlins). Main threat to stability would seem to be wind, but doesn't seem to be the case in practice

how much money and time would a robotic lashing system cost? hint: a shitload.

how much money would a few ditched rockets cost, in comparison? hint: less than a shitload

would a recovery crew approach this platform in rough seas, even if a robotic lash were in place? hint: nope

then what exactly is the point of securing this 'cargo'? hint: there isn't one.

problem solved.

The point of securing the cargo is to prevent it being lost to toppling, sliding off the side, or being catapulted off the side of a rolling deck.

And yes, it will be secured. The previous recovered rocket was secured, this one will be too.

i'm talking about the landing pad.

What port will let them in with giant explosive unsecured cargo? Hint no port.

and yet, they seem to be doing just fine.

Everything I've seen says they secure their load. Is there something I'm missing?

i'm referring to the landing platform.

Hence the phrase "purely a safety precaution"

Before it landed, the most likely scenario was that the rocket was going to crash into the deck and be destroyed. (That's happened several times before.) If they can deal with that, they can deal with the rocket landing safely and then falling over.

They can until it gets to a busy port with other ships and people around. Then it becomes a huge safety issue.

Copying my other comment:

Apparently they do secure to the deck after landing.

Discussed here: http://space.stackexchange.com/q/6403/574

All of the centre of gravity is low down with the engines. The rest is basically just a thin empty tube.

To add to above: In the previous barge landing they did weld the landing legs to the barge using some kind of bracket. But they discovered that the centre of gravity is low enough to not need any welding. During the previous attempt the sea was heavier than this time.

Maybe they still weld it this time, but that is done by having someone go to the barge and do it.

Actually no they did not weld anything to the legs. Elon said that they realize it wasn't needed. They did use octojack though to support the weight off the legs.

What's octojack? Can't seem to find any other references to that.

Sorry meant Octoweb jacks


To add to the other comment.


Everyone seems worried about waves and tilting, but you are saying the rocket is pretty much a metal sail. Can wind blow it over?

Plus the platform has four computer controlled engines on basically universal joints to stabilize it. A crew then boards the barge and puts 'shoes' over the landing legs then welds them to the deck.

Apparently they do secure to the deck after landing.

Discussed here: http://space.stackexchange.com/q/6403/574

From the last landing, Elon said (on twitter), that the ASDS can list up to 8% and the rocket can still land or stay upright.

And they did this in the dark! ;) (yes I know it does not matter)

What's notable about this attempt (as opposed to the last) is that the first stage rocket was traveling twice as fast (4x the energy to overcome on landing), and didn't have enough propellant to do a 'boostback' burn.

Instead, coming in very hot, the rocket had to use three engines (instead of one) to slow for landing. The last time this was attempted, the first stage put a nice hole in the deck of the drone ship.

Seeing the rocket dead-center on the barge was quite a sight!

One of my favorite facts is that merely relighting the engine provides enough thrust to lift the rocket (at its minimum throttle of 60%).

This means that it must slow to a standstill, cut the engines and hit the platform at exactly the same time or it will either start going up again or be dropped onto the platform from a less than ideal height.

This maneuver (powered descent with high deceleration right before impact) is called a "suicide burn"!

Slow to a standstill and cut the engines at the exact point where it pushes enough on the platform that when the engine stops thursting, the platform bumps back exactly to the bottom of the rocket.

Mind boggling.

I suppose this is why people say "it's not rocket science".

Slightly off topic but I was watching a television show the other day and someone said they worked at NASA. The host then said "So you're literally a rocket scientist?"

And the guy said emphatically "Rocket engineer, there is a big difference"

I'm sure this particular task probably was a little bit of both. After all, they had to run several real world experiments to prove their calculations.

It's important to know the difference: https://i.imgur.com/r6oEhvS.jpg?1

The most interesting work is right in the intersection of the two disciplines, though. :)

xkcd needs to make one for that too https://xkcd.com/435/

I guess "purity" is just another word for "lack of immediately applied practicality"

Coincidentally, today's smbc is on the distinction http://www.smbc-comics.com/index.php?id=4102

Here's a reason why that guy answered it that way. Note these are my definitions but I've heard it before.

Scientist: Studies and uncovers mysteries of the universe and natural world

Engineer: Applies what scientists discovers

One thing I'd point out is that your model ought to include that engineering also quite often is forced to run ahead of science, too. Engineers don't have the luxury of waiting until science nails down every last parameter, Julius Ceasar wants his aqueduct now, and materials science isn't going to be around to help for another 1800 years or so.... and that's just an example, it happens all the time even today.

Eh, I think it's simpler than that:

Scientist: Unknown outcome (e.g. hypothesis -> experimentation)

Engineer: Known (or should be) outcome

"In science if you know what you are doing you should not be doing it. In engineering if you do not know what you are doing you should not be doing it. Of course, you seldom, if ever, see the pure state." - Richard Hamming

Aristotle put it this way:

Science is the knowing of things by their causes. Science is the putting into knowledge what is in reality.

Engineering [which he would call techne, from which we get the word 'technology'] is the art of putting ideas into reality. It is putting what is in our knowledge into the real world.

Thus they are perfectly complementary things, one bringing the world into ideas, the other ideas into the world.

There's also experimentation to generate hypotheses. I.e., let's sequence the genomes of healthy people and the genomes of people with some disease and see if there is a difference.

It's possible to argue that the implicit hypothesis there is that there is some sort of difference, but that is a particularly weak hypothesis compared to the specificity of hypotheses that can be formed once we have this pile of data -- i.e maybe X, Y, Z differences are important in this disease.

I think it's more...

Sciencing: Uncovering mysteries about the world. Engineering: Applying such discoveries.

Scientist: Predominantly sciences. Engineer: Predominantly engineers.

There's so much overlap it would make sense for C.V.s of either to include a % science/engineering to suss out their own feel for both history and preference of activity.

if the devil is in the details isn't the devil an engineer?

A friend of mine in Houston Texas had a bumper sticker that said, "Yes, I'm literally a Rocket Scientist!" He had a degree in physics and maintained the software that tracked the Space Shuttle's trajectory.

Hosted webcast: https://youtu.be/L0bMeDj76ig

Landing at 38:18mins https://youtu.be/L0bMeDj76ig#t=38m18s

Great info on the thrusters on the first stage at 19:37. https://youtu.be/L0bMeDj76ig#t=19m37s

Edit: Thank you and sorry about the time stamp link, I posted quickly from my phone. Hopefully it works on shortlinks.

Seems like the landing is now around 29min: https://youtu.be/L0bMeDj76ig?t=28m58s

You link directly a specific place by adding this to the URL: #t=38m18s

you can also make it a query parameter, which often works better. E.g. https://youtu.be/L0bMeDj76ig?t=38m18s

Webcast - https://youtu.be/L0bMeDj76ig

First stage landing is just after 38 minutes - https://youtu.be/L0bMeDj76ig?t=38m

Doing it one time is a technological leap.

Doing it twice in such a small window of time is a logistical/programmatic leap.

In a way this time was a first as well, considering that they only recovered boosters for LEO missions so far. GTO is much less fuel to work with for landing and higher velocities.

Were they different rockets? If so I don't see the logistical leap.

Different use cases. This was a GTO launch which means the first stage had way more energy and therefore way tighter margins than the last attempt. This attempt used three engines to land and had a more difficult landing trajectory.

Looks like the landing was perfectly centered on the barge this time as well. Does anyone know when they plan on reusing one of these recovered first stages?

Good question - Elon tweeted this https://twitter.com/elonmusk/status/728459808270000128 - sounds like they could end up with a backlog ;)

They said at the beginning of the live stream that they plan to do a test fire on the first recovered first stage "sometime soon".

The first recovered stage, F9-021, has already been static fired and will likely end up as a monument outside of SpaceX HQ as they've filed an FAA request to do so.


The second recovered rocket, F9-023, will be relaunched. It has already been static fired with no announced problems. Elon said it'd be a few months before a customer was announced, but the general feeling is that it will be an SES satellite as SES has already publicly expressed interest.

Based on that FAA application it looks like someone will be losing their prime parking spot.

In all seriousness though, I'm not sure how I feel about this monument. It's going to be really crammed next to the main building and I don't think it will have a very strong visual presence with a giant grey wall directly in the background. There isn't really a good vantage point for viewing either. I suppose it will look ok from the opposite corner of Crenshaw.

You probably know best here, but I'm seeing a first stage height of 135 ft. Perhaps they're thinking of placing it on the roof of the main building? Though I do totally agree that it would look better elsewhere, like over by one of the onramps to the 105. Just a shame that the Western Museum of Flight moved, a nice little rocket garden in that museum would have been a nice touch.

Do customers get a discount for launching on a used rocket?

The first one definitely will (unless negotiations break down and they decide to launch without a customer, but that seems unlikely). Eventually when it becomes routine maybe not.

"This ones been up and back, it works. This one hasn't flow yet but we think it's good"

When it becomes routeine all clients get a discount as price per launch goes down.

Or not, because the next best alternative is much more expensive than SpaceX's current pricing.

We're dealing with a corporation -- I'm not sure we can count of them to "pass on the savings".

We're dealing with a group of people with strong ideas about space. They probably won't pass on much of the savings, but for a different reason - they need the budget for Mars project. That's the whole purpose this company exists in the first place.

If they're smart (and they are) they'll figure out ways to reduce the price of launch in the right way to maximize an increase in their margins. They could more than double the number of customers using secondary space in the "trunk" and cube-sats. The secondary customers will pay far less than the primary ones, but there will be many more of them.

If they're smart, they're figuring out ways they can own a big part of the infrastructure for an emerging market.

Aren't they passing on the savings by bidding lower prices than their competitors?

Only marginally - if none of their competitors can reuse a rocket then they only need to undercut the cost of a non-reusable rocket. The reward for innovation is that you get a temporary monopoly on that innovation and so can extract something very like a monopoly rent.

The demand seems to be quite inelastic at the current price levels, but the comsat industry has been gearing up for reusability. It is possible that there will be some price elasticity at radically lower prices, and the increased demand makes up for the lower unit margin. SpaceX need to kickstart a whole new trans-lunar economy for the Mars colonisation project to work, so it is within their interest to stimulate long-term demand.

If Musk wanted to maximize his risk-adjusted profit, SpaceX would never have started. Remember, he financed the cashflow out of his own pocket, and went from a 100-millionaire to not being able to afford rent during the process. He himself said SpaceX had less than even chance of success, and he is known to be both very meticulous in preparation, and an incurable optimist.

Its more favorable for SpaceX to lower prices as much as possible to crush incumbents (ULA). Extracting maximum profits just gives time for other competitors to catch up.

That may be favourable in the short term but a monopoly position stagnates R&D due to lack of need. Plus Elon Musk doesn't strike me as the type to avoid innovating.

The thing is they're already able to bid lower than all their competitors.

Assuming SpaceX gets to the point where they are re-flying stages a dozen or more times, I might expect to see a discount on a "new" rocket, as opposed to a "tried and true" rocket.

Would you rather be on the first flight an aircraft makes after leaving the factory, or the tenth?

I would make the decision based on the data available at the time.

It could easily be the case that the initial launches have the lowest failure rate.

The rumor mill says that they're asking about $40m (the usual cost is $62m). SES are said to be interested, for $30m. Discussions are ongoing.

Amusing... I was wondering why they needed to get FAA permission to park the rocket, but the application says it'll be 160 feet tall. So they're standing it up, as opposed to the NASA methodology of positioning their monuments horizontally.

Normally a 160 foot tall object wouldn't need FAA permission, but SpaceX is located right next to Hawthorne Municipal Airport.

And fairly close to LAX too. Another stop for star tour buses!

There is no open space to park a 160ft long object horizontally anywhere near spacex HQ.

Not sure why your comment was downvoted but this is true, there really isn't much open space around the SpaceX property.

I wish we had a campus like Raytheon or Northrop have in El Segundo/Redondo Beach. The 60's & 70's were certainly the high points in aerospace campus architecture here in SoCal.

Do you work for SpaceX? You have it in your username and comment like you're part of the company, but also spend your time discussing the merits of the NRA. Do you represent SpaceX or are you just super enthusiastic about them? It's not easy to tell.

I do work for SpaceX although I'm not in engineering or software dev. I work in the technician/skilled labor side of the house.

I don't think I've posted anything specifically discussing the merits of the NRA, although I have posted on the subject of gun control and self defense. In any case I'm not sure why discussing that topic and working at SpaceX would be mutually exclusive.

Obviously it should be said that I don't represent SpaceX and the views I express here are my own and not the company's.

That's the response I was hoping for. My only critique then is please register a personal account. You can't have a name like SpaceX_Tech and not expect us to take everything you say as something that they would endorse. I'd be appalled if a programmer I employed created an account under my company name, for use of expressing every personal opinion under the sun. I hope you understand the position I'm coming from and that others may be thinking the same thing when reading your comments.

Ps: keep up the good work

To be honest, I hadn't considered the ramifications of using the company name as part of my username. You make a good point about the potential of being mistaken for representing the company in some official capacity and I will heed your advice and register under a different username.

I'm curious about the etiquette in regards to identifying myself as a SpaceX employee though. I originally joined to relay some of my personal experiences with the company, is it generally a bad idea to identify myself as an employee, or is the bigger issue in your opinion the use of the company name within my username?

Also, if I do identify myself as an employee, do you think it would be wise to maintain two separate accounts, one exclusively for discussing SpaceX/space related matters and another one for other possibly more controversial topics or is it no longer an issue as long as I have a more generic username?

I certainly understand your position and appreciate the advice.

I wouldn't think twice if you had in your profile something like "I work for SpaceX." Good to know, but not the source of your opinions. Your account is young enough that you can gain all that back without the boss in your name. This isn't my first account.

Plus, and I can't speak for everyone, but as a former would-be astronaut, this kind of stuff is tops to me. Info from insiders is always welcome. Consider starting a blog.

Thanks for taking my opinions into account.

Thanks again for the advice, I certainly value your point of view. This is the last time I'll post from this account, I'll go ahead and start a new one at some point.

I appreciate your sentiment in my starting a blog but I don't think I'd have the time to meaningfully contribute to it and I don't feel comfortable enough in my writing ability to do the kind of long form writing I feel such a topic deserves.

There are certainly many would-be astronauts here as well. Thanks for the kind words in support of the work we're doing.

I'd also advise you to remember that SpaceX isn't taking kindly to employees passing out internal information.

Sick. Hope I helped cuz I'm down for the cause

Stick with your name. You earned it.

023 (Fnord) has been fired? I must have missed that. Got a link?

Did they say anything more specific than that? They have already done a static fire of the first one they recovered.

A few months ago Elon said they were at least initially looking at June or July for a re-fly.

At the presser following the first barge recovery Musk said they would probably re-launch it in June. It sounds like they aren't planning to do much with it beyond test firing.

How are non-US space agencies and companies (like ESA, Russia, Japan, China, etc) reacting to the SpaceX and Blue Origin achievements?

Are they also testing similar things but we aren't hearing? Or they aren't threatened by the advances?

I attended a conference from the head of the CNES (Centre National d'Etudes Spatiales, ~ French NASA) in Paris a week ago and he talked about that.

Ariane 6 is going to be built with a cost effective approach and trying to focus on market needs (3D printing of parts, reusability of the first stage, etc.)

At first, concerning SpaceX, his group of experts told him that the design of the rocket wasn't going to work and was going to explode at high altitude due to fluctuation. They also told him that the first stage would just go through the barge, sinking both the first stage and the barge. Now they are taking new entrants way more seriously.

I can't imagine how anyone with the slightest clue could conclude that the first stage would sink the barge. The scales are just too different; the barge outweighs the rocket by orders of magnitude.

I hope this is one of those "lost in translation" things, because otherwise I fear for that group of supposed experts.

> the barge outweighs the rocket by orders of magnitude

The energy amount the rocket impacts with is dominated by its speed, not its mass. A small, fast-travelling projectile can make a hole in just about any kind of armour. The terminal velocity is quite low, but that's in part because of the way it is engineered — an ICBM would probably be able to put a hole through a ship deck with ease.

There is a lot of reasoning by analogy vs. reasoning from first principles going on, and the latter seems to be winning. But the main driver of the space industry is governmental funding, not commercial. Much of those statements were probably political; SpaceX have prevailed, and indeed found some champions of their own (John McCain is rabidly behind them, and some of the statements he comes up with are ludicrous in their own right, for example), though not before enduring some setbacks.

The energy amount the rocket impacts with is dominated by its speed, not its mass. A small, fast-travelling projectile can make a hole in just about any kind of armour. The terminal velocity is quite low, but that's in part because of the way it is engineered — an ICBM would probably be able to put a hole through a ship deck with ease.

While what you've said is true, in practice it isn't a problem.

If the F9 first stage is out of control and going too fast, it will almost certainly miss the barge to begin with. The barge is small, the ocean is big, and the F9 has to maneuver very precisely to reach it.

If it does reach the barge, it will likely be moving relatively slow, and thus is less likely to sink the barge, even it things go crazy at the last moment.

That brings up an interesting question, can't the range safety officer just scuttle the first stage after separation? I can't imagine that they don't have that capability after separation.

After a certain point in the stage 1 ascent, they disable the FTS (flight termination system). I suppose they could turn it back on for landing.

f = ma.

No, you're looking for

1/2m * v^2

S/He was just one integration off. Let's not be too harsh.

mass != momentum. I'm sure the thinking was that they wouldn't be able to slow the rocket down enough and that the speed of impact would punch through the barge. The autonomous control needed to get the rocket to slow down and stop at just the right time, while accounting for the movement of the barge, the movement of the rocket (eg: unpredictable wind impact), and the difficulty of gathering telemetry through the rocket engine exhaust, is pretty amazing.

They initially aim the rocket to the side, then correct over to the barge after the engine lights, so a failure there doesn't cause a high-speed crash.

Either way, the relative masses matter. It takes a lot more effort to punch a hole through something much more massive than your projectile! It doesn't make much sense that a light, nearly spent rocket stage would punch all the way through a massive barge. And even if it did, the hole still wouldn't be big enough to sink it.

Also the fact that if the rocket has actually lost control its unlikely it would hit the barge anyway at least at any significant amount of speed. The only time that would be likely is if it loses control right at the end where is velocity is low.

> I'm sure the thinking was that they wouldn't be able to slow the rocket down enough and that the speed of impact would punch through the barge.

Would any "expert" really believe SpaceX didn't run the numbers millions of times, and do millions of simulations to confirm they could slow it down before actually spending the money to buy and outfit drone ships, build landing legs onto their rockets, etc. etc. ?

I mean, honestly, while the devil is in the details for an actual landing, they must have been pretty damn sure they could at least slow the thing down sufficiently.

If a one gram bullet hits a 100 kg Athlete what happens?

There are several orders of magnitude there.

The previous attempt literally did make a big hole in the deck.

Pretty sure he means the barge would sink from the big hole he thought the rocket would put in it.

Of course, but my point is that the barge is so much more massive that the idea of punching a hole all the way through doesn't really make sense, and even if that were possible, such a small hole wouldn't sink it anyway.

I'm a lot bigger than a bullet but it can still punch a hole through me.

and it won't affect your buoyancy at all.

When shot with a bullet all the water leaks out of the organic person.

When shot with a rocket all the air leaks out of the steel barge.

It only leaks out of the compartment that got punctured. The rest will keep it afloat.

Ariane 6 looks like it will be a fine rocket. Should be quite competitive if they can get it to market before, say, 2010, and if SpaceX's reusability efforts come to naught.

Otherwise, I fear it'll be much too little, much t0o late.

I've got $10,000 says they do not get it to market before 2010. :)

(ITYM 2020)

I think he is saying it is already too late as spacex has hit both those milestones.

Well, but SpaceX hasn't. They have not reused any rockets. They've landed a few rockets, they've test-fired one of the landed rockets. But that's far from a track record of reliably recovering their rockets, turning them around and sending them back up that could drive the massive cost benefits that they hope for.

I'm not really playing skeptic here -- SpaceX's progress has been incredible, and I'm inclined to believe them that they can do it -- but it hasn't happened yet.

Newton's approximation for impact depth [1] gives a way to calculate how thick the barge deck would have to be to survive a high speed impact from the rocket stage. The impactor punches through until it has displaced an equal mass. An empty F9 stage masses about 23,100kg and has a diameter of 3.66m. [2] Steel has a density around 7,700 kg/m^3. Doing the math, the deck would need to be about 29 cm thick to survive a high speed impact. Estimates are the actual barge deck is 25-35 mm thick [3], so 1/10th that thickness. If the F9 stage came down onto the barge completely uncontrolled, it probably would punch through!

[1] https://en.wikipedia.org/wiki/Impact_depth

[2] http://spaceflight101.com/spacerockets/falcon-9-v1-1-f9r/

[3] http://space.stackexchange.com/questions/8842/what-is-the-sp...

Punch through the deck. Which we already know can happen, the SES-9 landing attempt punched a nice hole in the deck. But you'd need to punch all the way through the hull to even think about sinking the barge, and of course the barge is built with compartments so even that wouldn't do it.

I expect the hull is thinner than the deck: it isn't designed to hold up to a rocket blowtorching and landing. But good point about compartments: the barge may well be able to survive a rocket-sized hole punched through it!

I'm kind of fascinated -- and not necessarily in a good sense -- with how unbelievably conservative the aerospace industry became right after its greatest moment of glory. That would have been Apollo in 1969. Seems like after the Moon landings everyone just said "welp, that's it, nothing else will ever be done."

NASA didn't become boring because of internal culture. They were planning all sorts of crazy stuff:


NASA became boring because they were ordered to become boring and were defunded.

I agree, I can imagine NASA became complacent, stopped embracing risk, prioritised perfection over practicability and became similar to many public sector departments.

You probably missed the orbital stations programs. :)

Airbus is working on Adeline, which would fly back and recover the first-stage engines and avionics (but not the fuel tanks) on an Ariane rocket.

The Chinese have mentioned an effort to recover and reuse first stages by landing them with parachutes.

So far, the Russians seem to think the effort isn't worthwhile.

Closer to home, ULA's new Vulcan rocket is supposed to recover the first stage engines (but again, not the fuel tanks) using a parachute and helicopter.

It remains to be seen whether any of these schemes will work or how long they'll take. They have a lot of catching up to do in any case.

Wikipedia says Ariane 6's first test flight is scheduled for 2020, and Adeline will arrive between 2025 and 2030.

Meanwhile, SpaceX plans to launch a Mars mission in 2018.

Say what you want about SpaceX's plans for re-usability, nobody can deny they are making progress at an incredible pace. I've just checked on Wikipedia and apparently the first flight of the Falcon was in 2010. That's six years ago.

Compared to that, Arianeespace's target of 2025 (in nine years!) for Adeline is almost ridiculous.

Just checked: Stephane Israël just raised concerned after SpaceX's latest success: http://www.lemonde.fr/economie/article/2016/05/05/face-a-spa...

Could you copy-paste his comments? Google translate worked OK, but the site has a paywall.

Pre paywall ""Europe must take stock of what is happening in the United States , because if nothing is done , in ten years, our launcher sector will be in big trouble. " Faced with the offensive for two and a half years in the space by Elon Musk , who breaks the prices of commercial satellite launches, Arianespace boss Stephane Israel sounds alarm . The distortion of competition will intensify as the founder of SpaceX was awarded on April 28 , its first contract with"

Why should we care. I see no benfit in government funded rockets. I much rather see ESA buy launches on a competitive market. The should invest in innovative new missions instead of an ill fated attempted to beat comercial producers at rocket development.

Other then subsadising your own industry and for military reasons, their is no argument for making your own rockets. Both those are terrible arguments.

I'm not sure Stephane Israël's warning is directed at governments. It's more of a warning call for all European industrials who should increase their efforts to prepare for the present and upcoming US competition.

I mean it's not as if Ariane 6 is being built entirely by government money. It's more complicated than that. As a matter of fact, a new company Airbus Safran Launches[1] has recently been created out of the two big aerospace companies and is working mostly on Ariane 6. As I understand it, the CEO of Arianespace is calling for more initiatives like these.

It's a bit like with aerospace, when Boeing started building big airlines, European companies gathered and formed Airbus. They were not government owned but I supposed the government did intervene some way or an other considering it was a strategically crucial economic sector.

Also, whether the government funds an aerospace company is a bit blurry. SpaceX is privately owned but its major client is the government and, as Stephane Israël often complains about, they get extremely advantageous and arguably unfair contracts notably with the US military. It's kind of a government funding in disguise.

That being said, money is not the only issue here. The big thing SpaceX has is passion : since those guys think they're basically saving the world or something, they work much harder than anyone in Europe. I mean it's surely much easier for an engineer to keep working late at night when he thinks that his work will allow man to walk on mars and save the human race from extinction. That's the only way I can explain the extreme speed at which they're making progress when compared to what is done in Europe.

1. http://www.airbusafran-launchers.com/

As far as I can tell Arian 6 will get tons of government money, almost 3 billion, while private share is only about 0.5 billion. Even with this massive investment the estimated costs are per launch are still quite high.

SpaceX actually has to do a lot of work for those government contracts, and they will lose that money if they can not diliver the capability in the required amount of time. They had to carry most devlopment cost themself and they were also always flighing comercial launches. Governemnts are 70% of the launch market, so I don't think any space company can or will live totally without government contracts.

If they can make the Ariane 6 compete within a decent price, I am not against some government contracts going to them. It makes sense not to give all contracts to one company, but Arianspace (or whoever) has to first devlop a rocket without massiv governemnt investment and show that they are in the 20% range of price. If they can not do that, their are other companies who you can go to. Sure its not fair if the rockets from china or russia are subsidised (not saying the are or ar not) but thats good for Europe because we get cheaper launches that are payed for by other governments.

Are engineers in Europe really less passionate about their job than those in the US? Personally, I'm skeptical. For sure, having a mission to go to Mars is cool, but just working on rockets alone seems like it should be exciting enough to inspire passion and hard work.

I would guess that European rocket engineers are, or could be, just as passionate, and work just as hard as those in the US. But what saps the passion of engineers is bureaucracy, inefficiency and mismanagement that slows them down and interferes with their work, and by most accounts, these problems infest the aeronautical industry, on both sides of the Atlantic.

SpaceX has managed to build a company that doesn't seem to suffer from these problems. From reading Elon Musk's biography, it doesn't sound to me like the SpaceX engineers are driven by some dream of landing on Mars, even if that's Musk's goal. Rather, they just have a no-nonsense, "get stuff done" attitude. They don't spend weeks doing tests when they can get them all done in one day. They don't spend millions of dollars buying outsourced components when they can build them better and cheaper themselves. They don't thoughtlessly replicate inefficient processes because that's how it's always been done, or it's done everywhere else in the industry.

Put Elon Musk and his management staff in charge of the ESA and I bet they'd install the same no-nonsense attitude in European engineers, and it would be Ariane that was delivering reusability before everyone else. As it is, let's just hope that the example SpaceX sets eventually pays off in changes to the way NASA, the ESA, Boeing, Lockheed Martin, etc. are run.

Although I think that the big US defense contractors would rather get out of spaceflight completely than match SpaceX's costs. Because if they can, then it proves they could have done it all along, and that they've been hugely overcharging the US government for years. And if they've been overcharging for access to space, it might make congress ask questions about all the other pork-barrel military contracts they get, and why they can't deliver those cheaper as well?

I did not go through the paywall either, I only just read what you probably did.

There's a lot of skepticism about that 2018 date.

Coming from a lot of the people who have doubted reusable rocket engines...

I don't think so. Engines have been used before. Rockets have been landed on their tails by many organizations. And I don't think too many people doubt SpaceX can go to Mars. The questions are over the date.

Most spacex dates slip. Sure they are wildly optimistic but the end result is still much faster than anyone else.

That's the point, though. They do miss most of their deadlines, and if they miss the 2018 date they're going to have to wait a few years for a comparable launch window.

A white ball of fire. And then there it is...resting! Beautiful!

Love how the autobalance on the cameras cut almost everything to black so you could not see the rocket at first, until it emerged from the darkness.

That was an unexpected and delicious bit of Hollywood drama. My first assumption with the flash followed by darkness is that it had impacted too hard and exploded or wrecked the camera. The autobalance stabilizing was a great big-reveal moment.

The stream I was watching had the video delayed a couple seconds from the audio. Based on the initial crowd reaction I assumed the landing was a failure.

Moon landing deniers will have a field day with that camera's footage.

Much like with the moon landings, then SpaceX will do it another dozen times, and the deniers will pretend there was only one landing so as to fit the narrative better.

SpaceX already have their little cadre of deniers - an offshoot of the "space isn't real" and "moon hologram" berks.

I remain confused about why SpaceX is getting so much fanfare and praise. What have they accomplished that NASA didn't already accomplish during the Apollo missions?

I know SpaceX is doing it all more cost effectively, because we have better technology, but have they actually accomplished anything tangible that NASA didn't a generation ago?

The Apollo missions were one-offs. They left nothing behind that future missions could utilize. Everything was disposed of after use, even Spacelab which had a very short life and completed a specific programme of missions and then burned up.

The shuttle was the first attempt at re-usability but was far too expensive to be viable. Only the space station is genuinely long term re-useable infrastructure. It's something you can actually use as a platform for further missions beyond it's initial purpose but it also has been excessively expensive. We can't go on like this. Nobody is talking about a replacement space station, the appetite just isn't there. Unless somebody does something, the space station might be the last long term repeatedly occupied human habitat in space.

SpaceX is doing something about that. If they really can reduce launch costs by a factor of 100:1, it will change the fundamental economics of everything we do in space. Suddenly going to the moon stops being a pointless gesture and becomes an economically viable long term proposition. Human habitats in space of the scale of the ISS or bigger become affordable. They're even talking about colonizing Mars and plan to do what's effectively a tech demo of that in 2018.

For the first time the rocket man dreams of the 1970s look like they could actually happen. For a lot of people, that's pretty exciting.

P.S. Downvotes for this question? Really? I'm as much a fan of SpaceX as anyone but it's a fair question, SpaceX haven't even launched one of their recovered rockets yet.

> Everything was disposed of after use, even Spacelab which had a very short life and completed a specific programme of missions and then burned up.

Skylab, not Spacelab.

The only two questions I see in your post are in the P.S. What am I missing?

I was referring to the question I was answering, which was getting greyed out. My bad, it was ambiguous and I should have tried to that clearer.

As an Engineer I might be a little biased but I see this is a massive achievement. We are seeing a paradigm shift in space exploration with the rise of the influence of the private sector. Space exploration used to be the domain of government entities. That is gone now. I believe we are seeing a new age of exploration not seen since the 15th and 16th centuries of discovering the "new" world. These new space companies like SpaceX, Blue Origin, Virgin Galactic and others are challenging the norms and will only push each other to new achievements that we haven't dreamed of yet.

As you can tell count me excited.

As an idiot, is is less expensive than asking the NASA or the ESA, or any other providers?

And well, can the "materials" really be recycled without loss of security/quality?

Is the metal more expensive than the carburant/comburant?

Compared to NASA, around a 10x cost reduction. That's before reusability.

>And well, can the "materials" really be recycled without loss of security/quality?

They aren't going to recycle rockets, they're going to refly them. They are aiming for around 100 flights per airframe.

>Is the metal more expensive than the carburant/comburant?

The cost of the metal isn't the major concern, it's the cost of shaping the metal into a working rocket. But yes, fuel costs are a couple hundred thousand, rockets are tens of millions.

Yes, Yes, and Yes.

I'm not sure you and I are following the same news. Granted, I was born in the 80s but I don't think NASA ever landed a first stage on a barge before.

Unfortunately, it's worth noting that while NASA's achievements were extremely laudable, it's an open question whether they could reproduce the results in a short timeframe. Some of the technologies of the Apollo era have been misplaced (either within NASA's large body of hard-copy material or never transferred from private contractors who have gone away).

SpaceX is exciting because they're doing launches and landings right now, reliably and successfully.

NASA accomplished amazing engineering feats while aiming at certain (mostly) one-off goals.

SpaceX (and others) are accomplishing amazing engineering feats aiming at sustainable, repeatable use of their technology, and improving as they go.

Both are amazing accomplishments. But just because "landing a rocket on a barge" is not as sexy as "landing a ship with humans on the moon" doesn't mean it's that much less of an accomplishment. Remember vertical rocket landing is something NASA chose not to attempt because they thought it was going to be too hard. And that's just what SpaceX is doing.

NASA landed a first stage on a barge to be re-used?

NASA reused every engine (not just the first stage) of an orbital payload delivery system, many times, 30 years ago. Runway rather than barge but that's not really an important difference.

(The exciting part will be much cheaper refurbishment than the STS. But SpaceX haven't actually delivered on that component yet)

> Runway rather than barge but that's not really an important difference.

it is an important difference when you look beyond earth

the moon, mars, and any future site that has yet to send robots to pave a runaway that is: 4,500 meters long, 91 meters wide, and 40 centimeters thick(o); will necessarily be vertical take off and landing

(o) https://en.wikipedia.org/wiki/Shuttle_Landing_Facility

Also kinda hard to glide in for a landing when there's little/no atmosphere...

If and when SpaceX land rockets beyond Earth, that will very much be something to get excited about.

This argument makes no sense.

The point is that SpaceX hasn't yet accomplished anything NASA didn't. That SpaceX's approach will be more suitable to future things is not a good counterargument.

They have: they're cheaper, they've developed new technologies, and they're doing it privately.

> That SpaceX's approach will be more suitable to future things is not a good counterargument.

No one is saying that, they're just being positive and looking forward to the future.

How is that bad?

Doing things cheaper is good, sure. All I'm saying is that zupreme's original point is fair (they haven't (yet) really done anything concrete that NASA haven't (just done it cheaper), and the current enthusiasm is perhaps disproportionate)

We can agree on that!

While that is true, by the time they rebuilt them, you might as well call them new engines.

SpaceX took their landed first stage directly over to the test pad to fire the engines multiple times. It's not really apples to apples.

If SpaceX can deliver what they're claiming in terms of refurb time/cost then that will be something to celebrate. But projects have a way of revealing unexpected challenges right at the last moment. I'm going to hold off the champagne until a refurbished booster actually flies.

That so negative. Of course they don't do this all in one go, it is incremental, step by step to get it to work. And each step is one closer to that goal and something to be happy about. If there are 'unexpected challenges right at the last moment' that's a real pity but those will be met just like all the unexpected challenges along the way. Yes, it's difficult, not it does not seem to be so impossibly difficult or different from what they've done to date that we should assume that it will not work. It will work, the bigger question is when.

Technically, the full SRBs were never (to my knowledge) re-used. Because of the salt water damage, they were parted out and some of those parts were used in new engines.

A shuttle launch cost over an order of magnitude more than a Falcon 9 launch does, though. This is hugely relevant because the biggest factor limiting space travel is cost more than it is anything else. The demand for space travel is absolutely there, and all that is required to satisfy that demand is simply lowering cost.

Quantity has a quality all of its own. Apollo-era NASA consumed 1.5% of the entire federal budget. You're right that SpaceX is still catching up, but they're doing it on a lot less than that to say the least. (Compare: 1980-present NASA has arguably never done anything as exciting as the Apollo programme)

Red Dragon (assuming goes ahead as planned) will be the heaviest payload ever landed on another planet - an incremental improvement to be sure, but a real one. Mars sample return will be a concrete new thing that NASA never managed. Watch this space.

They've done most of the hard work in demonstrating a fully reusable rocket stage of an orbital launch vehicle. That's historic, beating even what the Shuttle managed (the Orbiter was not a full stage).

Nailing down the remaining operational workflow and they'll be able to achieve reusable rocketry, and bring down the cost of spaceflight significantly. It truly is the dawn of a new space age.

Based on some talks the first lunar landings were way more adventurous and lucky than what SpaceX is doing. Making a snooker trick shot is nice, announcing it and doing it twice is another thing.

What about announcing it and doing it six times?

That's the number of times we landed men on the moon.

Let's not try to downplay NASA's previous successes as "lucky" and "adventurous" in order to make SpaceX seem more advanced in an engineering sense.

Announcing it seven times and doing it six times....

Luck did play a pretty big role in Apollo. This is not to discount the huge amount of work and skill that went into making most of those missions a success, but there was sometimes not a whole lot separating them from failure. Apollo 11's landing site ended up being covered with boulders and they nearly had to abort before they found a suitable landing site. Apollo 12 got hit by lightning on the way up, knocking out computers and nearly causing an abort. Apollo 13 came within seconds of exploding on launch, and was saved by a false fuel alarm shutting down the misbehaving engine.

Of course, this is only to be expected when you're doing something so big and new. SpaceX has the benefit of all that experience.

Luck was a significant factor, however. There were _so many_ things that could have gone wrong, that is not an understatement at all. They found bugs in the AGC's software years later that could have sent 3 men to their deaths, had they occurred.

You're right. Funnily my answer was an attempt at not dismissing SpaceX advances too.

The first lunar landings had the resources of an entire nation behind it, and massive motivation to get it done (the cold war).

Did NASA land anything else than the Space Shuttle?

Closest NASA got to this (besides the STS) was DC-X.

This success was unexpected. That means that they can recover a stage from a higher speed than previously thought. Does that mean that the recovery of the second stage from LEO may actually be feasible?

Second stage recovery is a whole different beast. Recovering the first stage on a flight like this is a delicate dance because margins are so small, so everything has to go exactly right. The previous attempt (SES-9) didn't quite go exactly right, and made a big boom, perhaps because the engine burns were slightly mistimed.

Recovering the second stage is difficult because it's coming in from a much higher speed. The first stage came in doing about 2km/s. The second stage would come in doing 8km/s or more. That means 16x more kinetic energy to deal with and 64x more heating. You need a proper heat shield, not just clever engine burns. There's much less extra margin to play with as well. The second stage does most of the work but is much lighter, and one pound on the second stage is worth ten pounds on the first stage.

SpaceX definitely believes second stage recovery to be feasible at some point, but not on the current Falcon 9.

KE = 0.5mv^2, so the second stage would only have 16x the kinetic energy if the two stages had the same mass.

The dry mass of the first stage is approximately 25,600kg. At 2km/s, its kinetic energy is 51.2 terajoules. The dry mass of the second stage is approximately 3,900kg. At 8km/s, its kinetic energy is 125 terajoules.

So the KE of the second stage is actually about ~2.4x that of the first stage.

Here is were I found the masses of the stages: http://spaceflight101.com/spacerockets/falcon-9-v1-1-f9r/

I meant relative to the mass of the stage, since that's what's relevant to the challenge.

The second stage has a smaller ballistic coefficient than the first one, though. Their cross-sectional areas are the same, but an empty second stage has much less mass. If it could survive entry (and that's a big if), it's terminal velocity would be smaller.

Here's the landing from the webcast video on youtube https://youtu.be/L0bMeDj76ig?t=2300

This is one of those turning points in human history.

Not quite "The polio vaccine," but certainly higher up than "laser-based Christmas decorations." ;)

It could be argued that flying to orbit with a first stage that's being reused will be as historical when SpaceX will do it.

The Space Shuttle did reuse SRB casings and the orbiter, it was a bit different but a great achievement too.

However this time there is more potential for cost savings. It can still happen that they can't be realized because of some details or even fundamentals we don't understand from the outside.

Can someone please explain to me how the falcon orients itself during this total process??

Does it use fins, or simply engines and whatever those little jets are that, say, the space shuttle had around its nose...

How does the falcon manage to physically orient its body?

Also, is that process completely autonomous? Is there a remote flight engineer steering this to the barge - or is it completely self-guided

In space it uses nitrogen thrusters to orient. Once in the atmosphere it uses grid fins to orient. The entire liftoff and return is piloted by Falcon's flight computers -- no humans involved.

Thank you - how does the barge communicate with the falcon? And what types of comminucations are they having. I assume the barge is stating its GPS location, but does it also communicate things like sea conditions - and its elevation (what is it called to describe the condition of the sea), as well as wind, north-south orientation, etc...

I am impressed - but I want to know how this works.

Rumor is (https://www.reddit.com/r/spacex/comments/3b0stk/falcon_9_wha...) that the barge does not communicate any information to the booster. Instead, it uses GPS and some ingenious motors to maintain position and orientation, and the Falcon booster uses a radar altimeter to judge accurate vertical distance.

Thats just fucking awesome if true. Its like "how can we maximize the use of some 'cheaper' technology and a shit-ton of math to accomplish this in the technologically simplest way?"


Also, the engines are gimbaled. This is essential for the landing burn.

I wonder if there's coordinate potential with seasteading? Astronauts are gonna want all sorts of goods and services upon landing I imagine. Having someone stationed nearby will mean swifter pickup of equipment and astronauts. And if there's someone stationed nearby they'll want goods and services as well.

I don't think astronauts would land on the droneship, as that's just for the first stage. When the Crew Dragon lands, it would be coming in from orbit, so I imagine they would just target the landing platform at the Cape as part of their de-orbiting plan.

That being said, would you want to be in the nearby path of the rockets if they were going to be ditched?

Am i missing something, is the need to land vertically a requirement of a fragile fuselage? Seems wasteful to carry extra anything (in this case rocket propellant) to space, just to avoid having to re-right the rocket when you get it back on earth for a subsequent launch. Is extra fuel payload < landing gear or parachutes?

Parachutes aren't massless. The parachutes you'd need to land a rocket like this are actually comparable in mass to the extra fuel and landing legs needed for the vertical landing approach.

You also can't land on a ship with parachutes. You don't have enough control. You can still land at sea, but then you have to actually land in the water, which means getting seawater on all your rocket hardware. That causes lots of problems when you want to use that hardware again.

SpaceX did experiment with this approach. Here's a picture of the second Falcon 9's interstage with parachutes packed inside:


But it turned out not to work so well.

NASA had some success with this approach on the Shuttle SRBs. It's easier with solid fuel rockets, because they're less efficient and built tougher. Even then, the cost of recovery and refurbishment ended up roughly breaking even compared to just building new ones each time.

As far as "wasteful" goes, that depends on what you're looking at. Saving fuel for the landing subtracts from payload capacity, which is wasteful in theory... but in practice, many payloads are smaller than the maximum anyway. If you suffer a 30% payload penalty, but you're launching a satellite which is 40% smaller than your maximum, then who cares? The only waste is some extra fuel, which is super cheap. The full fuel load for a Falcon 9 launch is something like $200,000, compare to the total mission price of around $60 million.

If the problem is simply the seawater, you could use a large plastic liner to create a pool of fresh water floating in the sea, and land in that.

This pool of freshwater would need to be many kilometers in diameter to give a high chance of hitting it with an unpowered parachute descent (thanks to unpredictability of the winds). At this point you are talking about doing something that is much, much more expensive than the current approach of a powered landing. How are you going to get so much freshwater out into the sea, anyway? That's way more water than could be carried in the largest cargo ship that exists.

A freshwater lake would seem easier

There are remarkably few freshwater lakes in the Atlantic Ocean.

Lake Michigan seems like a pretty easy target and it's 100% American territory.

The barge was located about 400 miles downrange of the launch site in this case, so if you're landing in Lake Michigan then you're launching from somewhere around western Iowa/Minnesota or eastern Nebraska/South Dakota. When your rocket goes off course or explodes, you'll rain parts and fuel down on Minneapolis or Chicago or whatever other inconvenient population happens to be in the way.

This is a typical engineer conversation.

"Oh, I'm sure I know a lot better than the accumulated centuries' worth of knowledge from actual rocket scientists, and I can come up with solutions to their problems based on no in-depth knowledge of the field and a minute's thought."

Not at all, it was an observation that bodies of fresh water exist that don't require huge effort to make massive floating ponds on the sea.

It was also an observation that this particular body of fresh water is an "easy target," apparently stated without putting any thought into what makes a target easy or hard for this purpose.

Given the lack of fine guidance control that parachutes imply, your "large" plastic liner would have to be miles in diameter.

That's a lot of complexity to add compared to the current landing which boils down at it's simplest to an inverted pendulum balancing problem, hard but the dynamics are pretty well understood. First parachute landings aren't super accurate without a lot of engineering and controls and would rely on calm or no winds down range wherever you're landing to have any chance of hitting the 'pool'. Second that pool would want to float and to my knowledge no one's made anything like that, so they'd have to invent and build then deploy a huge piece of engineering for every single launch.

Lack of wings. (That's obviously for the landing gear part of the question)

But fragile fuselage is certainly spot on. Parachute-landings still have quite some impact velocity. Strengthening an object the size of a Falcon 9 first stage to survive that impact would require a much stronger and thus prohibitively heavy structure, even if the parachute itself was free. The nice thing about powered upright landing is that all the forces involved are pretty much the same as during launch so that there is little (if any) additional strengthening required.

Note also how the ULA plans for the use of parachutes to recover first stage engine blocks require the parachute to be caught in-flight by a helicopter to avoid any uncontrolled ground contact.

Even if you were sure the engines would survive impact, you wouldn't want your expensive, complex rocket engine to take a dunk in salt water.

This is a good point. Remember that the early "sea landing" experiments ended with the stage breaking up just from falling over into the water.

I believe they did try or at least look into parachutes initially, but gave it up as not feasible.

With the powered landing, you already have the engines there, it's just a matter of leaving a bit more fuel. It's not a lot of fuel because you've already dropped a bunch of mass (the whole second stage and a bunch of fuel), and air is helping instead of hindering.

There's also the fact that, unlike parachutes, you can use a powered landing on Mars and the Moon.

It is partly because they are trying to develop a system which can be used regardless of atmospheric conditions, so reusable in another sense. Parachutes don't do so well on the moon, for example.

But also because a parachute landing actually does a lot more damage than you might expect, and sea water is the last thing you want in your million dollar rocket engine.

IIRC it's the most stable position because it's a big empty tube with some really heavy rocket engines at the base. It's also precise so they can land on a tiny barge in the ocean.

Keep in mind everything SpaceX are doing is with the goal of getting to Mars.

They don't want to use cranes, or parachutes or helicopters or complex landing structures, because none of those things will work on Mars in such a way the rocket just needs to be refueled and can fly again.

Armadillo lost several craft to parachutes. When you add them to a system, you also have to worry about them deploying at the wrong time.

I'm guessing they want a single solution like vector thrusting because it can be used on planets with and without atmospheres.

Elon intends to land rockets on Mars and return them to Earth. Mars is light on facilities for refurbishing rockets.

If it's such a good idea, why don't all airlines use it for airplane landings?

Airliners don't land on their tails either. If that's your model then Adeline is the correct approach.

I think you missed the observation there.

Airliners could certainly land with parachutes. They could even glide in for unpowered landings. And doing so would save a lot of fuel in either case. But that fuel savings would come at the cost of adding huge operational complexities, and risks. Powered landings are more precise, more predictable, and more reliable. They reduce operational complexities, even if they are costly, and for that reason they are more than worth the fuel costs. An airplane could carry more weight a farther distance if it glided into landing unpowered, but effectively all landings would become emergency situations, and it's just not worth the small benefit of increasing payload.

The same is true in orbital rocketry as well. Parachutes may seem like a good idea, but they increase recovery complexity and costs, they increase the likelihood of damage to the rocket, they reduce predictability, and so on. Powered landings are the most dependable way of ensuring the stage can be returned and of doing so within an operational profile that can be streamlined and optimized until its very reliable and efficient, just like landing a plane. The fact that it comes at some cost of payload capacity is comparatively inconsequential, as it substantially increases the likelihood of recovering the tens of millions of dollars worth of launch vehicle hardware (which over its lifetime will service launches worth hundreds of millions of dollars).

I just don't think you can generalize like that. A "powered" landing for an aeroplane is very different from what SpaceX is doing, e.g. an aeroplane can and often does abort and go around, whereas the rocket has no such capability.

Rocket landings are different than plane landings, but that doesn't mean powered landings are less worthwhile. In either case a powered landing means a more precise, more reliable, more repeatable situation. And if you want to maximize the operational lifetime of the equipment, that's what you want.


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