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SpaceX successfully lands a Falcon 9 rocket at sea for the third time (theverge.com)
199 points by manu-chroma on May 28, 2016 | hide | past | web | favorite | 49 comments

The landing video from the rocket[0] really puts into perspective how much this truly is 'rocket science'. They placed a boat 600km away in the ocean, and the rocket moving at 3000+km/h from 80-ish km up landed on it using some grid fins to steer.

I get how it works, how you can do it, but it's still kind of incredible that they actually have 3 times in a row.

[0] https://www.youtube.com/watch?v=4jEz03Z8azc

Edit: it was 8000km/h at MECO, not 3000km/h.

I saw the video some hours ago and I have been wondering since: how did the camera survive the re-entry? And how did the lens stay so clean?

First stage re-entry after the retro burn, isn't going fast enough to burn up due to friction. Even the space Shuttle's or the Soyuz's boosters would simply fall back to earth and with some parachutes land intact.

As for keeping it clean, apparently they added a system after they realized its tendency to fog/ice up. I'd love the details on it too. The technique of using a rolling bit of plastic might work but given the weight penalty you probably wouldn't get more than a couple of lens "changes" in the tank.

With regards to re-entry: the rocket was going much slower than orbital velocity, and the re-entry was therefore much more moderate.

Some ballpark math: The 1st stage was travelling at 8,300 kph at MECO, and almost of that velocity would have been horizontal. There was no boost-back burn, so it would have kept that velocity until re-entry. Furthermore, it would be re-entering with some vertical velocity. They mentioned that apogee -- when the vertical velocity is zero -- was two minutes prior to the start of the re-entry burn. 2 minutes of freefall would add another 4,200 kph of vertical velocity. So that's 12,500 kph, which is less than 1/2 of a typical orbital re-entry of 26,000 kph. Because the energy grows with the velocity squared, it's more like a quarter of the heat of a typical orbital re-entry.

Finally, as I understand it, much of the point of the re-entry burn is to deflect the re-entry shockwave, effectively creating a shield of "cooler" rocket exhaust around the vehicle.

Still not anything you'd want to take a leisurely stroll in, but nowhere near as stressful as a proper orbital re-entry.

It's actually doing an entry burn to slow down before hitting the atmosphere, you can see it starting here: https://youtu.be/zBYC4f79iXc?t=27m34s

Also your calculation is not correct: You add another vertical 4,200 kph of free fall starting from apogee, but didn't factor in that of course the vehicle also slows down as much in the 2 minutes before reaching apogee. Since MECO is at about 65 km height at 8,300 kph, it will also have 8,300 kph at 65 km height when falling down again (minus a little atmospheric drag).

You also can't just add 8,300 kph horizontal (and it's not actually all horizontal, look how quickly the altitude is rising around MECO) and 4,200 kph vertical speed. Those are not scalar values but vectors, so you need to apply pythagoras for vector addition. 8,3 km/s horizontal plus 4,2 km/s vertical speed is just 9,3 km/s total speed.

Thanks, I didn't consume enough coffee today.

If it had 8300 horizontal, and 4200 vertical, the total speed would be the hyponetuse of a triangle made by those, not the sum. sqrt(4200^2 + 8300^2) gives me 9,302 kph, which is a bit more than a third of 26000 (.3578). That squared gives you a bit more than an eighth (.1280) of the heat.

and thats not including the fact that someone else pointed out that it would go with velocity cubed.

Because the energy grows with the velocity squared, it's more like a quarter of the heat of a typical orbital re-entry.

No, the drag force grows with the square of velocity. https://en.wikipedia.org/wiki/Drag_(physics)#Drag_at_high_ve...

Force * distance / time = power, so the heating will scale with the velocity cubed. Therefore at 1/2 the speed, it would experience 1/8 the heating.

You are correct!

They mentioned during the broadcast that there is actually a cleaning system to remove frost, etc. from the lens.

Sort of obvious given the lense gets covered during the clip, then almost instantly clearly up; this wouldn't happen unless something was removing stuff.

Neither of these comments answers the question of how did it survive re-entry, which we have all been taught to imagine as the rocket being immersed in a fireball at horrific temperatures.

The particularly high-heat re-entries of manned capsules, the Space Shuttle, and so forth are unpowered; the atmosphere slows the spacecraft down. The Falcon 9 first stage re-entries are powered; three engines light to slow it down. The physics of how this works are complex and a bit counterintuitive, but the upshot is a thermal environment which isn't as brutal as an unpowered re-entry.

Beyond that, the glass in front of that camera's probably formulated to take extreme heat.

And of course, as jdblair points out, it's starting at a slower speed to begin with; faster than just about any aircraft (except maybe the X-15), but well short of orbital velocity.

Its not just re-entry that makes heat, its re-entry at high speed. The first stage wasn't in orbit. I don't think it had reached orbital velocity and it turned around and fired its engines to reduce its speed even further.

Re-entry from orbit wouldn't just destroy the camera, it would burn up much of the craft as there is no heat shield.

Amazing, they cut that angle on the live feed, switching to the barge view which doesn't give you much. I'd love the normal speed version too.

They might not be able to get that angle during landing given they had so much trouble with getting barge video during the first couple landings.

Note that the video has been sped up.

It is incredible, but makes to wonder how many things are possible that we don't do.

Whenever I read a news article where politicians congratulate themselves on almost balancing the budget after raising taxes a bit, I'm struck by just how low the bar is placed, even for important things.

I also keep thinking about the book childhood's end, where aliens land and basically force us to run our things properly, cleaning up the planet's problems in a matter of a few years. I always wonder if we got put to the challenge as a species, whether we could meet it.

Think about the bare minimum it would take a software developer not to get fired. It's actually quite low. Now realize how many people do the bare minimum at their job. Including politicians (bare minimum == get elected).

What would you call a politician's maximum job performance?

Enabling policy that helps citizens inside and outside his/her constituency in life-changing ways. Highly ethical, not afraid to make unpopular decisions if its for the greater good (gay marriage in a conservative region etc.).

It makes me wonder how much does the society suck, or what else could be achieved if more of the humanity's resources were managed the way they are at SpaceX. If Musk had decided to do fusion energy instead of rockets, would it be commercially viable by now? How about curing cancer?

While not to diminish what SpaceX has achieved it's really a far cry from "curing cancer". While what they've done too allot of engineering it's not nearly as complex as identifying all of the biological pathways for even a single form of cancer and finding a reliable cure.

That said we do have good treatments for the vast majority of forms of cancer, the problem is that your survivability is directly tied to how early it's detected, surgical removal, radiation and more notably modern chemo regiments are very effective in early stages of detection.

Many type of cancer today have 90%+ survivability rates if they are detected early enough, detection isn't always easy allot of them can not turn symptomatic till later stages, and many of them won't show up in blood work / body scans clearly either.

Curing cancer? Which one?

Let's not assume that nobody else knows what they are doing.

Does not matter which one, does it? Pick any.

They know what they are doing all right. For instance, ITER's managerial staff surely enjoys the jet-setting between Barcelona and the French Riviera. But their goals are not aligned with making progress.

That's a load of cynical and simplistic crock. Yes ITER is super expensive, and maybe it's not the best use of research money, and maybe it'll never get anywhere. But the project's aims are very ambitious, and potential payoff is huge. Saying the ITER management doesn't deserve the same perks as other management is just wrong.

Musk is doing several things apart from launching rockets. For instance he's trying to make electric cars more common and he has quite some success. His solar ventures is less convincing, though.

I'd say the answer to that is all the things. Excepting, of course, the impossible ones.

I think that's a tautology :)

At the end of the day everything is just putting atoms in the correct positions so given enough energy anything is possible.

Having got the atoms into the right place, a surprisingly large amount of effort seems to then be involved in persuading the electrons to dance around in the right patterns. 'More energy' doesn't yet seem to help us solve that problem.

Especially those electrons inside politicians brains

Amazing that this is becoming a regular-sh occurrence. Have they announced when they might try re-using one of these rockets? I wonder if the folks putting their payload on will get some sort of discount. I suppose that is the long term strategy.. to lower the price. I wonder if that price discount is already factored into the launch price -- after all they are still sort of a "start-up"

IIRC they plan on re-using one of the landed first stages at the end of the year, but they did not give any precise date or mission.


Please don't post uncivil comments here.

We detached this subthread from https://news.ycombinator.com/item?id=11791424 and marked it off-topic.

My bad. Not the comment that I'm most proud of.

For what it's worth, I didn't know it was sped up, and I have taken calculus and advanced physics. I had no frame of reference for how high the rocket was when the video started. It wasn't that I thought it was realtime, I just didn't know if it was sped up or if the rocket was just way faster than I would've imagined. I was quite glad that someone pointed out it was sped up, and I think as a matter of journalistic integrity folks should generally mark when things are sped up or slowed down.

I am mentally handicapped though, so you got that right.

I am a physicist by background and rocket propulsion engineer by career. I am pretty handy at writing signal processing and control stuff on microcontrollers and FPGAs, and writing physics simulation code in C++. I thought, because I am therefore Really Smart (tm), I must be able to knock up a webpage because how hard can it be? I basically died a death within a week, surrounded by sharks in a pool of confusion about javascript and frameworks and doms and salt and pepper hashbrowns and bcrypts.

Reciprocally, I have visited a few hackspaces and witnessed vignettes along the lines of someone saying 'I know Javascript, therefore I'm an engineer!' before they then cut their hand open in a completely predictable way with an angle grinder, having just rebuked you for trying to 'interfere' with their use of said angle grinder because you could see the wheel nut wasn't tightened down properly (this is a true story).

The moral is: don't assume other's backgrounds, and don't over-assume your own. We all come at this stuff from different directions and a pointer can help some of the audience, even if its redundant for others.

Please somebody justify SpaceX because "Science!" isnt cutting it for me anymore.

How about "Money!".

Glibness aside, it's a private enterprise and is profitable, so even without mentioning Musk's ultimate goal of colonizing Mars, its existence needs no further justification. It makes money and its shareholders are happy.

And before someone jumps in with the "SpaceX-is-propped-up-by-the-government" canard, the U.S. government also saves money when it launches military satellites with SpaceX. According to [1] (among many other sources), SpaceX quotes around $60m, compared to the United Launch Alliance price of about $125m (or even, depending on how you count, $200m).

[1] http://arstechnica.com/science/2016/03/ula-executive-admits-...

I'm asking why a company who hasn't done anything novel in the realm of science garners so much attention for its science. The fanboy-ism for SpaceX seems uneducated. Please tell me how I am wrong.

I wish more space aficionados would admit that it's really about entertainment. SpaceX to Mars is like the world's awesomest reality show. People seem to think it's shameful to admit that something is for entertainment, but I think it's a noble calling to do entertainment well. I think of Elon Musk as a modern day Jacques Cousteau, also a great entertainer.

People always make these super slippery arguments about how space research leads to earth inventions and humans need frontiers to stay mentally healthy, all kinds of strange stories to make space exploration seem like a humanitarian pursuit. I think it's just leftover zeal from the U.S. government story that space exploration was important for the country...

... which it was. We needed to stay up on our rocketry game for national defense reasons.

I feel it just muddies the true rationale for space when you try to make it about something it's not.

Is HN now the SpaceX PR RSS feed? Are we going to have to see this same article and talk about how amazing SpaceX is every time they do anything?

I look forward to the breathless comments on "SpaceX successfully lands rocket for 38th time!"

I'm afraid you'll see an article about SpaceX being awesome every time SpaceX are being awesome.

Which is and will continue to be often.

I'm sure we'll get used to this awesome feat eventually. But three good runs does not a routine make. Hopefully they'll keep it up, and then we can have manned flight success stories instead!

The fact that this is getting boring makes me excited.

I wanted to post same thing but was too bored to type, so thank you.

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