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SpaceX Soft Lands Falcon 9 Rocket First Stage (spacex.com)
561 points by cryptoz on July 22, 2014 | hide | past | web | favorite | 189 comments

The video is pretty cool, but make sure to read the rest of the page. Most exciting of all is this last note: "We will attempt our next water landing on flight 13 of Falcon 9, but with a low probability of success. Flights 14 and 15 will attempt to land on a solid surface with an improved probability of success."

That "solid surface" will presumably be a barge. Very exciting stuff.

Edit: The "loss of hull integrity" also answers a common question of "why not use parachutes". Even if they could land the stage softly enough with a reasonable amount of parachutes, the stage has trouble surviving tipping over in the ocean after landing. It needs to land and remain upright, but using parachutes you will often get some lateral velocity that would cause a tip-over. They need more control than parachutes can provide (and that's all ignoring the problems of salt water).

> common question of "why not use parachutes"

My typical answer to this is to mention Mars and the very thin atmosphere. There's no point in SpaceX developing technology that they can't use on Mars.

Moon landings, too. While Musk has his sight set on Mars, I can't imagine he'd turn down the opportunity to beat NASA to a lunar return.

Yeah, he said: "Loop around the moon, possibly land on the moon - just to prove the capability" - http://www.youtube.com/watch?v=thKMqN-2E4s#t=50

It's not about the rocket tipping over. The use of parachutes would require the loss of landing accruacy. They want to be able to guide the first stage to a specific location (like a launch pad), and parachutes would not allow them to do this.

Powered landings mean precise, highly controlled landings. You land exactly where you want with minimum damage to the vehicle and you go out and put the stage on a truck so you can bring it inside and begin processing it for reuse in a matter of hours.

Parachute landings mean you have a recovery zone, you need a recovery team, you need to find the rocket and bring it back. Whether landing in the ocean or land with a parachute there's a high probability of significant damage from impact and/or seawater intrusion. So now you have a huge amount of effort just to get the rocket back, then you have to clean it up. And the parachute landing likely means much lower chance of being able to fly even one additional flight, let alone many, unless you develop some sort of cushioning system like airbags, in which case you have to add that complexity, cost, and weight to the system. And all of that is aside from having to repack the parachutes for every flight.

SpaceX is planning powered landings for the same reasons that commercial airlines do powered landings. It's safer, it's more controllable, it's a smoother operational experience. It just makes sense.

There are precisely steerable parawings. They looked at recovering Saturn stages by glidinng back to Florida with a Rogallo wing.

It all factors in. SpaceX has performed grasshopper tests on windy days that would be a problem for a parachute landing. There is also the issue that parachutes sufficient to slow down the stage to a soft land-landing would be far too heavy.

> That "solid surface" will presumably be a barge. Very exciting stuff.

I get nerd chills from the level of precision needed to bring a launch vehicle from hypersonic->subsonic speeds to a target that size, and land to reuse the vehicle.

I'm impressed with the barge concept if only from the wave action the'd have to compensate for. Anyone know wave amplitude in the area they'd be landing in? That's a flat surface that's coming up to meet you or dipping away, making for a pretty heavy drop...

You could use a SWATH style ship - http://en.wikipedia.org/wiki/Small_waterplane_area_twin_hull

They get very little wave loading due to having semi-submersible hulls, much like an oil rig.

It's apparently called "Active Heave Compensation":


It's used at sea for winches, but I'm sure platforms can compensate just as well with the proper force actuators and motion reference units.

It's actually much cheaper and easier to sink some anchors and winch the barge down a bit than to try and do active compensation. It's one thing to compensate a crane or a winch, it's another to compensate an entire vehicle. The anchor thing is one way that they handle off-shore drilling rigs.

Another is to use a semi-submersible rig. What that means is that you fill the bottom half or 2/3 of the vessel with water making it much heavier. That changes the way it rides in the waves and can dampen the effects that a wave has substantially.

Maybe use an old oil rig? Its legs would bolted to the seabed, which I would assume is sturdy enough.

Depends on the rig. There are plenty of rigs in 5000' feet of water and I assure you that they are not mile-high building. They are semi-submersible.


Oil rigs are really only for drilling, not for getting the oil out of the ground and into whatever container there is. So that means they move around all the time. Like every couple of weeks.

What you're thinking of is called a jack up rig. They go in water up to a few hundred feet deep. Nothing over 1000 feet for sure. That's because the entire truss has to come out of the water when the barge is being moved from one location to the other.


An old oil rig has the right level of Bond-villain-ness about it. Gets my vote.

The Glomar Explorer, which was custom built by the CIA to raise a sunk russian nuclear submarine (https://en.wikipedia.org/wiki/USNS_Glomar_Explorer_(T-AG-193...),used heave compensation for the entire crane/rig that lifted the submarine from the sea floor.

> "We will attempt our next water landing on flight 13 of Falcon 9, but with a low probability of success."

I'm wondering why the next water landing has a low probability of success?

This is not confirmed by SpaceX, but has been floating around the internet as the suspected reason.

Last year, SpaceX attempted a first stage water landing, but was not successful. Their two most recent successes on this front had at least two hardware differences from that old attempt: landing legs and heavier duty RCS thrusters. However, due to some combination of manufacturing and launch scheduling, an old core without these improvements, similar to their attempt last year, will be flying on flight 13.

Flight 13 will be a flight to ISS on a core without landing legs and other modifications for landing. Apparently, they swapped cores earlier, and now they have a rocket left without legs.

I believe it is because of this:

> However, our next couple launches are for very high velocity geostationary satellite missions, which don’t allow enough residual propellant for landing.

Based on the press release they plan on using Falcon Heavy for this type of launch in the future but it sounds like that project isn't ready for primetime yet.

I took that statement to mean they can't even attempt a landing on the next couple of launches because there will not be enough residual propellant for landing.

And then the next statement, I assume, refers to the next launches where they can attempt a landing.

EDIT: my assumption is confirmed here http://en.wikipedia.org/wiki/List_of_Falcon_9_launches

Next up are flights 11 and 12, which can't be landed.

Then 13 has the "low probability of success".

Funny that you cite Wikipedia, which is citing... the link that this HN discussion points to.

Yeah, I actually made that particular edit to Wikipedia about 20 minutes before seeing it cited as a _verification_ of that article, here. Funny to see one of those infamous internet self-confirmation loops get established in near-realtime...

Might be the flight path or payload limitations.

probably because it's another water landing

The last 2 water landings have been successful.

Parachutes also hit a lot harder. Powered landing you can touch down with ~0m/s. Parachutes you'd get something like 10 m/s (~22mph.) Not necessarily nice on your equipment.

Yup. The Soyuz landing capsule uses solid fuel retro-rockets at the very last second to slow down, but even then it is apparently a rather unpleasant bump.

What's interesting here is the difference:

Soyuz uses a 'suicide burn' that releases a ton of delta-V in a short amount of time.

From the video, it seems that Falcon uses a progressive burn as it approaches. They also mention that they can restart it up to 3 times in atmosphere.

The third burn here is also a suicide burn. The first one is to change its path and the second is to prevent it from falling too fast.

Not particularly nice on your astronauts / cosmonauts / 赵里昱 either, though they have training, preparation, and (according to an interview with Cmdr. Hadfield awhile ago) specially-poured per-backside crash seats to ameliorate it somewhat.

What i don't understand is how are they going to solve the problem of landing precision. The stage is passive from the retroburn (just after the stage separation) for the several hundreds seconds it is flying back, and large part of that trajectory is in atmosphere, and stage has a high sail factor: it is big and, being almost empty, lightweight. So it might be dragged by wind too far from the landing site to compensate in hover mode which is i assume only 100-200 meters or so, even if original entry trajectory is perfect. Ballistic missile warheads for example, accumulate about 100 meters or error due to this factor despite they are much smaller/have higher density and fly several times as fast. A an additional short mid-flight engine burn to compensate may be a solution but so far i haven't heard of that. Anyone has an idea?

I believe that's what the new grid fins they've been testing out on the Grasshopper are for. Those are there to let the rocket steer even at the speeds it comes in at.


They are! And they work well at both subsonic and supersonic speeds, just not transonic speeds.

No, these things are just for improvement of stability when descending.

But it seems that answer is aerodynamic control by partially (and differentially) extending the LEGS. Which appears brilliantly smart and should work. Same hardware, zero additional weight or cost, additional function.

"stability" = "steering"

"This test confirms that the Falcon 9 booster is able consistently to reenter from space at hypersonic velocity, restart main engines twice, deploy landing legs and touch down at near zero velocity."

They are restarting main engine twice. First time is for trajectory correction I assume.

Ballistic missile warheads aren't slowing down for a soft landing. Try landing a helicopter at Mach 1 and see how accurate it is compared to a normal landing.

Better video from the first landing, despite the data corruption, than this one, due to the ice fouling. Wonder why this one got iced? Clouds?

But even so, it certainly shows success. Can't wait to see 'em get a stage back. That'll be amazing.

Icing is caused by supercooled raindrops freezing on the airframe. In this case the spacecraft came from a very high altitude so I'd expect the airframe to already be very cold and even if droplets aren't supercooled, they might just freeze on the cold surface of the lens. Pireps (pilot reports) are available globally where pilots report icing conditions they encounter. I suspect the SpaceX engineers anticipated this possibility and decided that they didn't want to add the extra weight and complexity of a heating or deicing system to the lens.

I have a feeling someone is working there right now to come up with a quick and dirty deicing system - considering how disappointing this video is. The fluid system the Cirrus SR22 uses comes to mind.

I think some kind of disposable multi-layered lens cover that peels off automatically would work well. Pretty cheap, and easily replaceable. Effective against more than just ice.

I propose a revolutionary solution: a lens cap.

I'm assuming that they only need the video from when they get close to landing so the lens cap can be ejected once the rocket is low enough in the atmosphere that icing is not a problem.

or some kind of heating element would work, too.

I speculate that this one iced up because the vehicle flew a much higher trajectory than the previous vehicle, as visually noticed from the launch webcast. This meant that the first stage spent more time higher in the atmosphere.

I was wondering that as well. Three possibilities come to mind;

1) Atmospheric conditions are right for it (flying a subzero steel device through clouds with moisture in them, same problem that airplanes have)

2) The burning of the cryo-propellants lead to additional ice formation (as they burn they expand from liquid to gas and pull heat out of the tanks/body)

3) "snow" which is a variation on #2 which is that ice crystals that are forming on the rocket as it burns propellant in ascent the camera is accelerating away from them, but in descent the crystals are coming towards the camera.

Either way its an 'easy' fix, whether you heat the cover, add a wiper (ala nascar) or change the position.


No, it wasn't clouds - it passed through a chemtrail.

For all the rocket science, why can't they get a lens that deices itself?

They will. It's not been seen to be a problem before, so they went with the simplest solution. In rockets, every ounce counts. Now they know it happens (at least sometimes) in this very novel flight regime, they'll do something about it--the linked post even says so explicitly.

I've been super impressed with how efficient SpaceX is in getting launches into orbit. I did a visual comparison to the Space Shuttle program. It looks like SpaceX will overtake the Space Shuttle launch efficiency by the end of the year.





That graph might be a little more intuitive if you swapped the axes, FWIW.

It would be a lot more intuitive. Even knowing exactly what was being described and how - It still is difficult for me to understand a graph in which Time is on the Y-axis. I considered for a few moment that I was actually being trolled with that graph.

Definitely. Also choose colours that aren't almost identical.

The blue and black don't look very close to me, and they're pretty color-blind safe. Odd.

Don't underestimate the damage of bad screens, bad screen settings and people blaming the source rather than their setup.

It's all right to blame the source. Imagine half a population having grayscale screens. Would you pick colors that map to the same shade of gray? I guess not, so why would you pick colors and thickness that can be mistaken on so many setups?

In this case it doesn't matter, as it's obvious which line is which.

Even just laptop screen brightness or glare can play a huge role here. I know it's offtopic, but if anyone is aware of a guide or methodology for picking colors that will be less susceptible to this problem, I would love to see it.

'Cheat' and use something else to differentiatie between the two, in addition to color (line thickness, line dash, markers)

You probably should always do that, as you won't know where your chart will be used (printed in black and white, very lossily converted to JPEG, whatever)

Convert to grayscale.


I cannot tell them apart, other than length.

Be nice to have one solid, the other dashed or dotted.

The space shuttle launches are manned missions. I don't think it's a fair comparison.

good point. I was considering the comparison as resupply missions and (future) re-usability of the vehicle.

can you compare these to the Russian unmanned supply runs to the ISS?

Shuttle was alway fairly low-frequency, far below its design goals, so possibly not a great comparison. Here's 2014 in space launches: http://en.wikipedia.org/wiki/2014_in_spaceflight

At peak, in the 70s, there were about 140 launches per year.

An expendable vehicle should be inherently more efficient in launching frequency than a reusable one. The reusable one is fundamentally limited by the number of reusable vehicles you have on hand and the time it takes to turn each around. The expendable one is only limited by the speed of your manufacturing.

So, since SpaceX is moving to a reusable vehicle, this graph could easily change slope in the future.

Telecoms and the market for satellites has only recently boomed. You cannot compare the two programs in such a way.

The limiting factor of the Shuttle wasn't low demand for its services, I don't think.

Demand was ~1/10 of projected demand which dramatically increased costs not only by increasing overhead by also by extending vehicle lifespans well beyond what they where designed for.

Put another way, scrapping a shuttle mission saved less than 90 million.

PS: It was also horribly compromised based on Airforce requirements yet never flew a single Airforce mission.

> PS: It was also horribly compromised based on Airforce requirements yet never flew a single Airforce mission.

The shuttles flew a few DoD missions, including I believe at least one for the Air Force (a DSCS satellite during STS-51-J I believe? Maybe others, which DoD mission was for who isn't nicely broken down anywhere that I can find. It looks like most were for the NRO).

However none of the Shuttles ever flew a polar orbit mission; an ability that the Air Force demanded but never used. The large cross-range capabilities of the shuttle (necessitating such large wings) was for polar orbit missions, so those massive wings were dead weight caused by the Air Force.

I should have been more clear.

The airforce had two mission profiles outside NASA's goals. Polar orbits AND capturing Russian satilites. Neither of those missions types where ever flown. The Airforce ended up having a huge impact on the design including much larger cargo bay etc but it was those two mission profiles that really fucked up the design.

If NASA had gotten it's way the shuttle would have been more reliable and cost less than 1/3 as much per mission at the cost of significantly lowered cargo capasity. Intact both shuttle disasters can be traced back to these compromises.

Funnily enough, Russia 'copied' the shuttle design for the Buran.

That ship was almost exclusively designed for millitary use. It was speculated that they planned to carry nuclear weapons up in the cargo bay.

Actually, in later years the internal reasoning has been published, so we no longer need to speculate. (This following quotes are taken from the book "Energiya-Buran, the Soviet Space Shuttle" by Bart Hendrickx and Bert Vis). And the actual reason is even more hillarious.

So, first, we now know the US space shuttle was the outcome of some bureaucratic processes in the US (NASA wants a new program to replace Apollo, the Air Force accidentally ends up in a super good negotiating position, Nixon does not want to be responsible for ending manned flight but also doesn't want to pay for a trip to Mars), so in the end it didn't end up a very sensible design. But the Soviets did _not_ known this, and assumed there must be some secret rational reason for building it:

> As TsNIIMash [Central Scientific Research Institute of Machine Building] director Yuriy Mozzhorin later said: "[The Space Shuttle] was introduced as a national program, aimed at 60 launches per year ... All this was very unusual: the mass they had been putting into orbit with their expendable rockets hadn't even reached 150 tons per year, and now they were planning to launch 1,770 tons per year. Nothing was being returned from space, and now they were planning to bring down 820 tons per year. This was not simple a program to develop some space system ... to lower transportation costs (they promised they would lower those costs tenfold, but the studies done at our institute showed that in actual fact there would be no cost savings at all). It clearly had a focused military goal".

So what might this secret military goal be? Apparently the Soviet speculations was that either it might be part of some nuclear fractional-orbit bombardment system, or it might be part of a plan to launch lots of laser weapons into orbit. In any case, we can't have a space shuttle gap, so:

> "[Central Committe Secretary for Defense Matters, Dmitri] Ustinov had made the following argument: if our scientists and engineers do not see and specific use of this technology now, we should not forget that the Americans are very pragmatic and very smart. Since they have invested a tremendous amount of money in such a project, they can obviously see some useful scenario which is still unseen from Soviet eyes. The Soviet Union should therefore develop such a technology so that it won't be taken by suprise in the future".

Let's build it now, and see what it is good for later! And then the Americans started speculating about what the secret military purpose of the Soviet shuttle might be! :D

I know, wouldn't a constellation of nukes in low earth orbit be amazing. It would only take 200 to 300 seconds to deorbit from LEO.

From what I've read, the idea doesn't actually work very well. Since they're in orbit, you only have a relatively small window per orbit to get it to hit any particular place. If you want to be able to hit any particular place with that kind of notice, you need like dozens of them in the same orbit. Maybe a bunch of orbits, depending on how the cross-range capability is. You could well end up with a constellation of hundreds in orbit.

You're better off putting those weapons on surface-based ICBMs. It'll take a little longer to get to target than the idea case in orbit, but you can launch all of them at a small area at once if you need to. They're a lot easier to maintain and decommission on the ground too - worth considering, since I think we'd all rather not ever have to use the things.

First strike capability, especially hitting their ICBMs before they could make a decision and launch, was considered very important, and may have been considered worth the additional expense/complication. Probably would have been massively destabilizing to reduce lead time that much, though.

Thinking about some more in strategic terms, I think you'd get the most strategic difference by having a lot of weapons in roughly the same orbit. That would give you the ability to conduct an extremely rapid first strike, but only at the time that they happened to be in the right orbit. The downside is that they'd be a terrible second strike weapon, since it would be obvious where they were and they couldn't do much in the way of armoring them or having them avoid enemy weapons. So yeah, it would be pretty damn destabilizing to build a weapon system so massively good at first strike and so bad at second strike. It would tend to tempt the builder to use it or risk losing it in a tense situation, and the opposing nation would know this and perhaps be tempted to make their own first strike or build their own system.

It's probably better/more stabilizing to do what we did, which is to deploy lots of SSBNs - just okay at first strike, great at second strike since it's almost impossible to destroy them all at once. You're less likely to want to pull the trigger on your own first strike when you know you have a nearly unstoppable second strike capability. The enemy nation is less likely to make a first strike if they believe they can't stop your second strike.

Both sides feared their opponent might obtain first strike, but did not want it themselves.

Problem is that some actions that help prevent your opponent from obtaining first strike move you closer to first strike.

For example, having nuclear missiles in submarines makes it very hard for your opponent to take out most of your nuclear weapons in a first strike, but it also gives you the capability to fire from closer range, giving the opponent less time to launch their missiles before your missiles take them out.

This would be similar, as there would be less time between launch and impact.

You say amazing, I say horrifying and a violation of the treaties against militarisation of space. Also the world's worst maintenance liability.

Grave of Fireflies is the saddest movie I have ever seen.

Space is already militarized, and out of the entire population of HN you were the only one to complain about my comment. I didn't get a single downvote.


Ask the people of Palomares Spain how much they like that idea. They had a couple of nuclear bombs accidentally drop out of the sky there after a mishap in the 60's when the US had nukes in the air at all times.

Not that I disagree with you, but capturing Russian satellites may be the kind of thing you want the ability, but are not actually planning to do it.

Funny because wasn't the shuttle-c used for military missions and it has almost no wings.

What do you mean? The shuttle-c was never built.

I meant its punier newer incarnation, http://en.wikipedia.org/wiki/Boeing_X-37

I am not sure what the rated vehicle lifespans were at the time of building, but the design life was 100 missions per shuttle, and the most-flown shuttle (Discovery) only flew 39.

The initial assumption was 40 missions a year. Based on the estimated risks you might get 100 missions from a shuttle on average. So 5 orbitors * 100 / 40 = 12.5 years or ~ 10 years with an early loss. They where in service for 30 years and averaged 4.5 missions per year.

For comparison compare the matence cycle a low mileage 0 to 10 year old car vs a low mileage 15 to 30 year old car.

I've heard this reasoning before (from NASA personnel), but I have never seen the reasoning behind it. Many of the design life requirements were impossible to meet to begin with, such as the 50-launch design life of the Space Shuttle main engines (because of the high chamber pressures, and problems with bearings). If you have some evidence of the veracity of this claim, I would be very interested to read it.

I wonder if that was "We believe they are capable of 100 missions, because we require 100 missions" or "We believe they are capable of 100 missions, because that is what our test data actually suggests".

See: Feynman's Appendix F. Specifically his criticism of the Shuttle reliability numbers quoted by NASA management and how they differed from the reliability numbers quoted by NASA engineers.

Design life and rated life (as built) are two completely different things. The Space Shuttle requirements stated that it should be capable of 100 missions, but I have never seen any document describing what they were rated for, after they were constructed, and the flight tests were completed.

Nor is it for Falcon 9. They're launching them as fast as they can build them, and have a significant payload backlog.

Are you taking into account inflation adjusted cost?

> Flights 14 and 15 will attempt to land on a solid surface with an improved probability of success.

Anyone know when flight 14 is scheduled?

It is scheduled for October 2014: http://en.wikipedia.org/wiki/List_of_Falcon_9_launches

Flight 15 is scheduled to launch November 2014.

Almost no chance these will fly this year. We will only see 3 more launches this year IMO, and 2 will not attempt stage rescue, 1 will attempt on water as the previous ones. So wait till 2015...

Why do you say that?

Because the 3 launches are densely packed for August-September, and delay in one means delay of following ones, and delays almost always happen. Then there is a big hole and next launch is for late November. That alone is enough to move the 4th launch after the most recent one into 2015. So nah, we will not see attempt of land recovery this year.

I am not a naysayer. I am very enthusiastic about what SpaceX does. Especially the reusability. But i just want to remind that they never stick to their schedule (that's generally hard to do in the rocket business), and their current schedule for the rest of 2014 looks in a way it will be almost certainly broken even if slightest issues arise.

Where do you find a solid surface to land on except in Russia and China? You would like to fly across water or at least unpopulated areas in case a problem develops during flight and range safety needs to go for self-destruct. The USA, Europe, India and Japan all do that, because no one wants a re-run of the Long March desaster in 1996.

Flying back the opposite direction is no good because you are fighting the rotation of the Earth and are paying with extra fuel to carry the fuel needed to go back, besides coastlines are always the most densely settled areas of any country.

I can't imagine that the economics will work out, but perhaps someone else has genuine numbers to prove me wrong.

I would suspect SpaceX has the numbers. I don't think they're just guessing that what they want to do will work. Rocket engineers are big on numbers.

They intend to do a return to launch site--at least eventually. There will be several intermediate steps to prove the system. If it proves unworkable, always landing on a barge is better than not, I guess.

RTLS will certainly require a good deal of margin (by rocketry standards), but first stages usually have some margin already, and SpaceX will have a nice range of options once the F9H comes on line so that they don't have to fly a rocket "fully loaded" except for certain extra-large payloads.

I imagine they can also optimize most flight profiles for RTLS, by sending the first stage more than usually straight up--which is close to the case anyway. Lateral velocity is mostly the job of the second stage.

While it's never been done before, it's not an unheard-of concept. One of the potential evolutions for the STS was "fly-back boosters".

Returning to launch site doesn't require that much fuel as the first stage is really light after separation.

Barnaby Wainfan patented an interesting alternative: after staging, re-enter, then do a burn and fly ballistically back to launch site. This kills the horizontal speed with air resistance instead of propulsion, potentially saving fuel. You have to regain the altitude though.

SpaceX owns some land in southern Texas. It seems that the initial idea is to have a spaceport in Brownsville, TX, and use Cape Canaveral, FL, as the landing location. In the mean time, they can practice by using floating platforms in the Atlantic.


It would require significantly more fuel to get the stage to even the Gulf coast of Florida (much less the Atlantic coast) than it would take to return to Brownsville. Additionally, Brownsville launches will almost certainly be aimed between the southern tip of Florida and Cuba, in order to avoid traveling over any populated areas.

oh I am sure there are a few islands out there both inhabited and not so much that would present some opportunities. Much easier to deal land on something that isn't moving up and down, let alone side to side.

If launched from Texas, would they have to move side to side to land the first stage in Florida?

my apologies for not be clearer, while the movement of the Earth is a concern I was replying to the idea of trying to land on a floating platform which I do not see as feasible. Both from the standpoint of trying to find such a small location to the fact it is not going to be a stable landing area because of wave action

Would an old oil rig work?

SpaceX has said that they want to fly the booster back to the launch pad from the first announcement of their reusability plans. Yes, the rocket launches with 30% extra fuel - Falcon 9 v1.1's first stage was made bigger to accommodate that need. Fuel is a small cost relative to everything else.

Fuel is a small cost relative to everything else.

But the extra weight is a concern, it limits payload to orbit. Try flying the first stage back to the launchpad in Kerbal Space Program while delivering a useful payload to orbit! It's instructive. KSP really develops your intuition for rocketry, everyone commenting in this thread ought to buy a copy.

On the topic of KSP: Some guy on /r/spacex modded KSP to hell for realism then recorded a video demonstration of how the boost-back will/could work: http://www.reddit.com/r/spacex/comments/1z6vyt/boostback_dem...

The first video explains the modifications to the game, mainly more realistic aerodynamics, realistic fuels and engine capabilities, a realistic planet and launch site. The second video is him actually performing the mission.

There are a few differences between what he did and what we now know is actually planned, but it's still pretty damn close and demonstrates the feasibility of the concept in a pretty intuitive fashion.

You did note that the OG2 flight 1 payload was about 1/4 of the max? And the next 2 flights aren't going to try landing because they need all the fuel to get a big payload into GTO[1]? SpaceX seems to have all this under control, even if you can't imagine that it will work out.

[1] http://www.spacex.com/news/2014/07/22/spacex-soft-lands-falc...

You also always have the option of just building a heavier lift rocket - which is what SpaceX is starting to spin up for. I'd imagine the F9H's successor/bigger brother is going to be designed with provisions for the same type of return profile.

According to SpaceX the Falcon Heavy will only fly with reusable first stages. That will bring the payload down but the payload was very high before. The Falcon Heavy should still be able to lift more than 20 tonnes to LEO, which is equivalent to the Delta IV Heavy. And with reusability it should be able to do so at a cost comparable to or cheaper than today's expendable Falcon 9s.

Kerbal space program is a fun game, but you cannot use it for budgeting real launches, especially in this case. It only has minimalist physics, especially with fluid dynamics, which governs much of a first stage recovery.

It also "scales down" the universe and the time/thrust needed to leave orbit. still a fantastic educational resource!

Is definitely good educationally, but I wouldn't use it to argue against the plans of people who build rockets for a living any more than I would use experience of playing Risk to lecture an Admiral on international warfare.

I'd argue that KSP holds as an upper limit for what's possible - if it doesn't work in KSP, it won't work in the real world (while the opposite doesn't hold true necessarily).

I wouldn't say that. SSTO's are pretty trivial in KSP (even rocket SSTO's with only classical chemical engines, none of the RAPIER/SABRE stuff).

8 Rockomax 48-7S (little orange engine, stuck on with 8 small cube struts) + 1 Rockomax X200-32 Fuel Tank (the large gray tank, one size below the big orange tank) will put a capsule in orbit around Kerbin pretty easily. No such luck in real life.

Typically KSP engines have worse performance than real engines, but Kerbin is pretty small.

> 8 Rockomax 48-7S (little orange engine, stuck on with 8 small cube struts) + 1 Rockomax X200-32 Fuel Tank (the large gray tank, one size below the big orange tank) will put a capsule in orbit around Kerbin pretty easily. No such luck in real life.

That's what I meant by 'the opposite is not necessarily true'. My argument was that if something does not work in KSP, it probably won't work in real life (which was refuted by another commenter because of missing Lagrange points). IMO it still holds true for basic rocket designs and their capabilities for LEO / GEO. To my knowledge, all real world rocket designs have been replicated in-game (albeit with much lower complexity of course) and demonstrated to work.

That makes no sense. KSP hasn't got proper aeronautics and also hasn't got n-body physics. There are plenty of things that work in the real world that would fail in KSP.

edit - and for the same reason there are also things that would work in KSP that would fail in the real world.

> There are plenty of things that work in the real world that would fail in KSP.

Do you have an example for that?

> edit - and for the same reason there are also things that would work in KSP that would fail in the real world.

That's what I wanted to say with 'the opposite doesn't hold true'.

All of these take advantage of Lagrangian points, which aren't present in KSP: http://en.wikipedia.org/wiki/List_of_objects_at_Lagrangian_p...

Not really applicable to this discussion, but one instance which is highly applicable is that you can't control two ships in KSP at once. If your lower stage needed to do a powered land which an upper stage was still accelerating into orbit, you couldn't replicate that in ksp.

> If your lower stage needed to do a powered land which an upper stage was still accelerating into orbit, you couldn't replicate that in ksp.

.. Unless your name is Scott Manley ;-). But yes, good point about Lagrangian points [1]. I wasn't aware that KSP is only a two-body-simulation - interesting how the game can hide that with its sphere of influence implementation.


Quick save at stage separation, fly the upper stages to orbit. Go back in time (reload the quicksave) and fly the upper stage back to the landing site.

How about very tight hypersonic atmospheric slingshot maneuvers using aerodynamic lift from the shockwave generated by a flexible waverider lifting body? I think it would have significant problems modeling that without some serious modding. http://en.wikipedia.org/wiki/WaveRider#Hypersonic_Sail_Waver...

Also, my point with the logic is that when looking at the differences between physics in KSP and the real world, we are dealing with overlapping, rather than nesting sets.

> http://en.wikipedia.org/wiki/WaveRider#Hypersonic_Sail_Waver...

First time I've seen this, thanks. You certainly have a point that feasible designs in KSP vs. real world aren't completely nested. When I was arguing about KSP being an upper limit, I didn't really think about the SSTO case - at least the stock simulation certainly doesn't hold up to be able do any kind of feasibility check for horizontally launched vehicles.

Sure, you limit the payload to orbit. But on the other hand you end up with an extra orbital rocket stage in your possession. Given that this is a roughly $45+ million commodity at present, that's a significant savings that justifies the payload reduction.

With a truly cheap reusable system, it may finally make sense to send more smaller payloads and assemble in orbit.

I would imagine if the rocket weren't traveling so fast, they could put wings on it and glide the thing back. That would save a lot of the 30% extra fuel if the weight penalty wasn't that significant. Adding more fuel definitely seems easier.

The trouble is that wings also cost a lot of drag on ascent...

Long furled blades is another way to go, then you can have a heliroc. They work pretty nice as toys.

That sounds like the Roton by Rotary Rocket:


Heh, that would certainly put a positive twist on their spinning problem too. ;)

While it works nicely for recovering balsa and cardboard from a thousand feet or so, I have a sneaking suspicion that it might not scale all that well.

If they launch from their Vandenberg launch complex they can "easily"[1] land in the high deserts of California or Nevada. Although I believe the plan is to return to the existing pad. And in answer to the expense question, 9 merlin engines are pretty pricey compared to just fuel costs.

[1] scare quotes because I know its never easy to land and California or Nevada east of Vandenberg for minimal delta-v requirements.

Vandenburg AFB is used for placing payloads in polar orbits, which means they launch north/south. However, because of the population centers north of the AFB, they generally launch all vehicles south. This mean launches will happen over the Pacific Ocean, and they would not recover the first stage in the high deserts of California or Nevada.

Unless they did something different from what others normally do.

As washedup accurately points out they only launch south because in the event of a scrub they are over the ocean. And while Spacex could request an eastward flight plan, its unlikely the FAA would grant such a request because it is unlikely that SpaceX could assure them adequately that Bakersfield would not be at risk. For grins and giggles I confirmed this with the Air Force (their response was "Safety concerns restrict the available launches from this facility."

Interestingly SpacePort America (http://spaceportamerica.com/) has a similar problem, although if you look (https://www.google.com/maps/place/Spaceport+America/@33.0125...) you will see there isn't much east of it.

I'm pretty sure they're planning to fly the first stage back to the launch site (Cape Canaveral in most cases for now). It wouldn't return to the same tower, but somewhere at the Cape.

Thing is, for orbital flight, you're adding a lot of sideways translation in order to achieve orbital speed.

In the case of the Saturn V, the first stage (S-IC) sequence completed after 2 minutes 41 seconds, at an altitude of 42 miles (68 km) a speed of 6,164 miles per hour (9920 kph). It continued ascending ballistically to an altitude of 68 miles (109 kilometers), ultimately landing 340 mi (550 km) downrange.


Reusability trumps everything.


When you throw away the entire rocket every flight you throw away tens of millions of dollars in hardware. If you can recover and re-fly stages you can get away with a lot of compromises elsewhere. Especially since the first stage, for SpaceX anyway, represents 3/4 of the hardware cost of the launch vehicle.

Even reusing the first stage once means cutting the overall hardware cost of a flight by nearly 1/3. For SpaceX that translates to about $20 million per flight in savings. And that's from one and only one reuse flight of the first stage. In comparison the fuel is nothing. In comparison even a massive payload hit is acceptable. As long as the payload reduction is less than the cost reduction, everything is golden, and the rest is profit margin. For 2 reuses (3 total flights) the hardware cost per launch drops to 1/2 of current costs. For 5 or more uses per first stage the cost drops below 40%.

SpaceX's launches are already cheaper than the competition, dropping below 1/2 of their current cost floor makes it impossible for the competition to keep up and would enable them to own the launch market.

Well, cost trumps.

My comment above wasn't shooting down the concept of reuse, but showing that the lateral range of the stage 1 Saturn V booster was pretty significant. To re-land at Kennedy, you'd likely have to:

1. Change the launch trajectory to gain more initial vertical range.

2. (Possibly) reduce the first stage size to decrease its range. This means increasing comparatively the 2nd and 3rd stage sizes.

3. Use of strap-on boosters (themselves independently recoverable) which would reduce the mass of the remaining recoverable stage 1, and hence the momentum that would have to be re-vectored to KSC.

And while reusability is good, it's a bit like Amdhal's Law: your initial gains are the biggest, and likely you're going to see a cost function something like:

    (fixed booster cost + reusability engineering cost) / reuses +
    additional fuel cost + refurbishment costs + launch risk
The first two elements are going to decrease with reuse. The reusibility engineering costs will likely themselves be a function of reuses. And at some point you are below the increased incremental fuel, refurbishment, and launch risk (failure) costs.

Which doesn't say that the exercise is futile. Only that past 3-4 reuses you're gaining little for what's likely a large additional expense, or phrased differently, there's a minimum cost if you want to go to space today.

You could achieve very large savings in many things if you fly a lot and the oparations are routine. Also risk should drop a lot.

It's still not inevitable that such things will happen with reusability automatically. Most likely the first reusables have high maintenance. But they can be improved.

Launch risk does seem to be a function of experience -- the Russians have been flying pretty much the same rocket for nearly 50 years. That provides a lot of opportunity for incremental improvement. Combine this with early Russian practice (based largely on lack of sophisticated testing equipment) of testing rocket designs through live flight.

But risk in general is also a function of use and operational time. This has been borne out in many contexts, including both space flight and aviation. Systems degrade in nondeterministic ways over time, increasing failure risk. Even very minor variations in design -- a few mm of protrusion in a fuel-oil heat exchanger in the Boeing 777, implicated in the British Airways 38 Heathrow crash, given a specific set of circumstances in in-flight ambient temperatures and engine throttle settings resulting in ice-induced fuel starvation -- can have profound impacts.


It'll be interesting to see how re-use, risk, and cost play out with Space-X.

Which would then force anybody else who wants to be in the launch biz to develop their own version of the technology. Sounds like a win for humanity.

You just fly back to the launch area. It's immanently feasible to fly that route and always have a buffer of assurance that the rocket's trajectory will not head towards populated areas. If, for whatever reason, that changes then they press a button, the rocket zips apart and falls in pieces into the Atlantic ocean.

As for cost, fuel is cheap, it's one of the cheapest things in the whole operation. Think about the fact that every commercial airliner has the capability to make an unpowered landing and to save fuel doing so, why don't they? Because operational complexity adds cost much more than using up fuel does. By the same token, the greatest costs in orbital launch come from throwing away the hardware after every flight and operational complexity. If using extra fuel enables them to more easily reuse the stages and get more launches out of them as well as reduce overall operational complexity, then it makes economic sense.

If you can deliver a payload and recover and fully reuse the rocket then your costs drop by an order of magnitude. I can't imagine that the economics won't work out.

Depends on cost of refurb

They're shooting for no refurb on per mission basis and potentially to fly it the next day. Apparently the first stage is about 70% of the total $60M mission cost.

I will cry tears of joy when they send that first stage up in less than 24 hrs, return it and launch again.

I'm willing to bet that this will happen before the end of the decade (i'm guessing 2017)

I think they're talking about a barge or floating platform of some sort out in the Atlantic, at least for the initial tests.

Iceland, Bahamas or Canary Islands?

Keep in mind they have a very aggressive flight schedule planned, with basically 3 weeks between launches. August 4, August 25, Sept 12. Possible, but not probable. And if those are delayed, then the later ones are too.

"it fell over, as planned"... great attribution of the fundamental nature of gravity.

But mad props to SpaceX for working towards recycling their boosters.

I had a laugh at that as well. Idiocracy seems near if things like that need to be mentioned in press releases.

The shuttle SRBs floated vertically after splashdown, so I don't know why someone would be dumb for thinking the Falcon 9 booster might do the same.

"This was a COMPLETE failure! It FELL OVER! THEY'RE JUST TRYING TO SAY IT WAS SUPPOSED TO DO THAT AFTERWARDS! SELL ALL SpaceX STOCK PEOPLE!" We've all seen this sort of crap to one degree or another. Sadly a lot of it right here on HN.

The hardest part is not running out of fuel on the way down. Old-school science fiction often assumed something like nuclear power where that wouldn't be a concern. Seems like for many years most people haven't even attempted this full recovery/landing thing because of fuel and weight issues.

Has SpaceX really cracked that problem? What portion of flights on this smaller rocket can do it? It says some missions won't have enough fuel left over.

Will the Falcon 9 Heavy be able to do all or almost all missions with a landing and full recovery at the end? How much fuel will Heavy have left on average after a return? Theoretically it would not wait until the last possible second to start slowing, and therefore use up almost all of the fuel in order to give the descent a larger margin of error and also reduce the possibility of damage, I assume.

Until now most information out of SpaceX has suggested it needs roughly 30% propellant left in the first stage of Falcon 9 to attempt a retrieval.

Numbers are not yet known for the 2nd stage retrieval or Falcon Heavy. One could probably assume a similar number for the first stage but possibly a bit less given the Falcon Heavy's higher thrust/weight ratio.

From what I've read they need 30% additional fuel at launch (as in a 30% bigger first stage) - that's different than needing 30% left in the rocket after separation. The reason being that to have X [kg] of fuel at Y [m] altitude you'll need (1 + Z(Y)) * X [kg] of fuel at launch, with Z being some function of Y. My gut tells me they'll need 15-20% max for retrieval, the 30% + is just to get it up there. Source: Play KSP.

Ahh good catch, thanks for the additional insight.

30% sounds a bit extreme, especially since it is unloaded. I think they could probably do with 5% or less since the vehicle is unloaded (all the propellant is burnt out) and burns for only a few seconds for soft landing, with most of the braking from peak velocity provided by aero braking.

There's deceleration involved as well. Here's a very nice video of the shuttle boosters on their way down to give you an idea of the velocities involved. https://www.youtube.com/watch?v=2aCOyOvOw5c

An enormous amount of inertia to overcome so 30% doesn't sound so unlikely.

There are a total of three burns:

1. Alter the path so the parabolic arc goes back to the launch site.

2. Braking burn during descent to minimize atmospheric stress.

3. Landing burn (AKA "suicide burn") to slow the vehicle enough for the landing legs to absorb the impact.

Indeed. Combined, these all burn quite a large volume, but #1 is the most costly in terms of fuel, I think. It's essentially a reversal of the flight path.

Not quite reversal since it doesn't negate the vertical motion, but yeah. Definitely the most significant of the three burns.

Though it's not quite that simple. Based on the trajectory of last week's launch, they're actually going to use a much steeper trajectory during the first stage launch. The result is that the first stage uses significantly less propellant to make that first burn (since its downrange velocity is much smaller), but it cuts into the payload capacity quite a bit by forcing the second stage to do more work.

Is SpaceX's long term plan to also have 2nd stage retrieval?

(I didn't know that)

Yes; in fact they have videos showing the whole stack re-entering and doing a propulsive landing (one at a time, of course.)

The second stage will need a re-entry heat shield, but otherwise can land like the first. Tricky part is getting enough margin in the second stage for the landing fuel and legs and heat shield. Usually the top stage is the one you optimize most heavily. So plausible, but tricky.

Good news is that the second stage is much cheaper than the first, at least on the F9. Eight fewer engines, for one.

Cool. Where might one find those videos? I can't seem to locate them.

Their website has been changed quite a bit and old linked videos are hard to find. I found a copy uploaded to YouTube in 2011 : https://www.youtube.com/watch?v=sSF81yjVbJE

Edit: Found the original copy on the Web Archive http://web.archive.org/web/20110615000000*/http://www.spacex...

I'm sure that all this information is publicly available. There's nothing wrong with asking these question in a forum, but you probably shouldn't suggest that it's some big unknown and you should probably acknowledge that you're asking people to do research for you.

Far as I know, the answer to this question is by far the most relevant in the entire thread.

Even if I were an expert, the starting point is asking the question, and if I made claims about the answer, someone would come along and say it is still unknown as to whether they can do that.

It should be framed as a question because it is an open question. That's the way technology works. You don't really know you can do something until you do it.

So this question is an attempt to inform you and others of the correct context for discussion. Of course it failed.

Right now there is a bit of a slight impedance mismatch between attempted reusability and the commercial launch offering of the full expendable Falcon 9 capability. On the plus side the dual role nature of the Falcon 9 v1.1 means they can take advantage of expendable launches with sufficient margin to test the reusability features, on the minus side it means that when there isn't that margin they don't get free test flights.

However, once the F9 v1.1 has been thoroughly tested in the reusable configuration they will stop offering the expendable option. Every flight will have the first stage flyback for reuse, and only payloads which allow that flight profile will be flown, leaving more than enough fuel margin to allow return and some contingency.

Larger payloads will simply be flown on the Falcon Heavy, which will reuse the lower stage cores from day one. Even if that means no cross-feed and a massive hit to the payload capacity the Falcon Heavy should still be able to loft payloads larger than the Delta IV Heavy and with reusability it should be able to do so at less than the current cost of the F9.

Don't forget you can do an expendable configuration on the final launch before 'retirement'.

That's expendable launch (at reusable prices!) every 5-10+ launches per vehicle.

I did see a launch north over my town, about 80 miles north of Vandenberg. It looked like the path was over the ocean all the way. The first stage was still burning, so it was pretty spectacular.

Edit: oops. This was supposed to be a reply to the comment below about launches from Vandenberg being mostly to the south.

Will there be a video of the landing, as seen from Earth?

Is the rocket currently aimed "at the Atlantic", or are they operating with the precision they need to land back where they took off from: and in that case, do they have a camera pointing at the landing point from a ship?

Probably no video from the earth.

We won't be getting it for awhile. But I think maybe in about a year or 2 we will get to see the video.

I wish there is someone in the medical domain equivalent to Elon Musk.

Elizabeth Holmes is taking a stab at it: http://seattletimes.com/html/businesstechnology/2024121844_v...

Why does the rocket tipping over cause a loss of hull integrity? Does that mean that it actually exploded, just from going horizontal?

Compare the amount of force it takes to crush an aluminum can from the sides vs. from the top and bottom. A rocket is the same basic shape and material.

Probably not exploded, just that the lateral stresses that the rocket is designed for.

Rockets have to withstand a lot of different types of forces (axial, all sorts of vibrational, probably hoop type stresses), but massive lateral shocks aren't really one of them.

> Probably not exploded

I don't know about that: https://twitter.com/elonmusk/status/488718649515986944

Even with minimal fuel, the tanks are still highly pressurized, a loss in hull integrity would result is a rapid depressurization of those tanks. It may not have been a fiery explosion, but I would bet it made a hell of a bang.

Think belly flops on a rocket scale.

I think it just meant that because it was wholly immersed in water, it's not worth refurbishing.

I'm curious as to why SpaceX, or their competitors haven't utilize Sky Cranes, a la Mars Science Laboratory: http://en.wikipedia.org/wiki/Mars_Science_Laboratory#Sky_cra... - basically, it seems to be a powered parachute.

The sky crane will probably never be used again. It was an engineering marvel but the requirements that brought it into being were a management nightmare. (Requirements to not use any carbon-based propellant directly on the surface of Mars, which probably got violated anyway because you can still see blast marks from the sky crane where MSL landed.) And it was only useful for one very particular mass window -- much lighter and it wouldn't be useful, much heavier and it couldn't work.

The main difference between a sky crane and a soft-landing rocket stage is whether the braking/hovering engines are inside the thing landed (SpaceX) or outside and discarded after landing (sky crane). Since SpaceX is doing their best to not discard things, a sky crane is the opposite of what they want.

The sky crane solves a very particular set of problems with landing a (relatively) small, functional rover on Mars. It's not really a general solution to returning a large payload intact to Earth.

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