History Making First Recovery for SpaceX - Orbcomm-2 Launch

[pmadflyer]

Don't know why that website is named that way - quite crass. But has lot of interesting Elon quotes and transcripts.

It's because the site was originally supposed to mainly feature weird stuff that he said. The home page has a humorous picture of Elon and top quotes.
Examples:

I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact.

I went to Russia three times to negotiate purchasing an ICBM.

Technically, if somebody were to stow aboard the cargo version of Dragon, they'd actually be fine. I mean, hopefully.

the idea of lying on a beach as my main thing, just sounds like the worst - it sounds horrible to me. I would go bonkers. I would have to be on serious drugs.

So, unless you're a mushroom, you're out of luck.

I'm trying to get back to my home planet, ya know.

I can whistle Pachelbel's Canon, which is a tricky one, but I'm not going to whistle for you now because that'd be too embarrassing.

Some very interesting things to consider:

SpaceX has a very long term mission. We want to just keep improving our technology until there's a city on Mars. Well, that could take a long time.

I've gone on record as saying I think we could do a super heavy development for on the order of two and a half billion, other estimates are about 10 times that. And the super heavy that I'm alluding to would have about a 160 ton to orbit capability, so way more than a Saturn V. In fact, I've even gone as far as to say that I will guarantee that personally. And stake everything on SpaceX that it will happen. So, I mean we'll see.

we're looking at launches to be in the five to seven million dollar range - Gwynne Shotwell

 

[doug]

We must search for another explanation for the interesting soot pattern on the paint.

Are we sure it's not mostly from the initial launch?

 

[evp]

There had to have been a very small fuel margin for the landing. This site claims that 160 seconds of first stage burn are used out of an available 185 seconds when a return to launch site maneuver is attempted, so no more than 14% remaining fuel or about 53,500kg. The second stage and propellant weigh less than 100,000kg, and the payload to LEO is about 13,000kg. So even raising fuel for the return to 17% would completely wipe out the payload capacity.

Actually, it's probably less fuel than that, since the engines are throttled down during the last minute or so to reduce acceleration as the stack gets lighter.

172 kg *12 = 2064 kg, that's quite heavy satellite dispenser you have there...

Good point, this flight used nowhere near the final useful load of the vehicle. But I think my math still stands - even with no net payload at LEO, there cannot be more than about 17% fuel left in the first stage if the second stage is going to make it into orbit, certainly not 50%. We must search for another explanation for the interesting soot pattern on the paint.

But the other side of the equation is, of course - how much fuel do they need to make it back to land? Does 17% constitute "a lot of extra fuel"? We know the speed down-range and altitude at staging. We know the time in flight after staging, the mass of the stage, the specific impulse of the engines. I think that's enough to calculate the total delta-vee and thus the necessary mass-fraction of fuel. I'll have to pull out Wolfram Alpha and see if I can get a good estimate. It's only rocket science, after all.

Reviewing the video and checking the math, the scenario here plays out as follows:

First stage cutoff was at about 5988km/h or 1663m/s at T+2:26 (146 seconds, somewhat less than the website suggests probably due to low payload weight). That gives us (180-146)/180 seconds of fuel left or 18.8% (somewhat more than my previous estimate).

Boostback burn: 30 seconds to kill forward velocity and end up at 1300m/s towards launch site: delta vee 1300+1663 = 1963m/s
Entry burn: 20 seconds to slow from 1300m/s to 250m/s between 70 and 40km altitude: 1300-250 = 1050m/s
Fall from 40km adds 885m/s in vacuum minus an unknown amount for drag. But in the video, the boostback burn starts at about 8:10 (ends 8:30) and landing is at 9:46 so it covers 40km in 76 seconds for 526m/s
Landing burn: 526m/s
Total delta vee: 1963+1050+526=3539m/s
The first stage weighs 25600kg empty
Rocket equation says m0 = m1*exp(dv/ve), where m0 is starting mass, m1 is ending mass, dv is delta vee, and ve is exhaust velocity.
ve can be calculated by the engine Isp*g, 311s*9.8m/s = 3050m/s.
so, to touch down with zero fuel remaining, m0 = 25600*exp(3539/3050) = 81689
subtract the mass of the stage: 81689-25600 = 56089kg of fuel burned
Fuel load is 395700kg, so the required fuel at MECO is 56089/395700 or 14.9%.

18.8% fuel remaining (from video timing), 14.9% required (from rocket equation); therefore fuel margin 3.9%

 

[lolachampcar]

Ben,

Fantastic job.
Would you or someone with access to Elon's twitter feed kindly post the pic? I think his followers would enjoy the added historical reference to the existing logo.

Here's an attempt...

View attachment 105446

 

[AudubonB]

evp: Initial Delta vee is 2963 m/s; you used 1963, for a total Delta vee of 4539 m/s. Best re-do your numbers.

 

[Johan]

evp: Initial Delta vee is 2963 m/s; you used 1963, for a total Delta vee of 4539 m/s. Best re-do your numbers.

Good catch. Correcting for this gives m0=113385 kg

Subtract mass of the stage 113385-25600 = 87785 kg burnt

Assuming fuel load is correct at 395700 kg then the percentage of fuel required at Main Engine Cut Off would be 87785/395700 = 22,2%

So something doesn't add up with this calculation...

Perhaps the drag when reentering the denser part of the atmosphere is actually quite substantial and helps brake the rocket a lot, perhaps even more so coming down bottom first (the aerodynamics must be quite different to when going up, pointy nose first).

Another thing is these back-of-the envelope calculations may fail to take in to consideration that all these velocity changes are vectors and that they are not completely perpendicular to each other, even though mostly you're going one way then turning back the opposite direction. Another thing, which I'm unsure if has any bearing is the earth's rotation.

 

[SW2Fiddler]

Are we sure it's not mostly from the initial launch?

I'm not sure about anything, but would reason that the biggest opportunity to get carbon "stuck" there would be during the (Entry) Deceleration Burn - air flow has to leave the sooty exhaust far behind in the first and second big burns.
So it could indicate how much LOX was touching tank sides during the "longest a$$-backwards burn." Or on second thought, merely what part was STILL COLD during that and the last landing burn. Hmmmm.

I am still giddy about the whole thing having succeeded so well! Love having people to still discuss it with. Even here in Space City, I'm in a minority with my enthusiasm

 

[Johan]

I'm not sure about anything, but would reason that the biggest opportunity to get carbon "stuck" there would be during the (Entry) Deceleration Burn - air flow has to leave the sooty exhaust far behind in the first and second big burns.
So it could indicate how much LOX was touching tank sides during the "longest a$$-backwards burn." Or on second thought, merely what part was STILL COLD during that and the last landing burn. Hmmmm.

I am still giddy about the whole thing having succeeded so well! Love having people to still discuss it with. Even here in Space City, I'm in a minority with my enthusiasm

Have to agree with this common sense wise. Going away from the exhaust should give way less burn marks than going backwards braking in to the rocket exhaust, right?

Problem is there very little frame of reference at least for us as spectators. They're covering new ground.

One thought I have is if there's any particular reason why space rockets are often white? The soot (however I do prefer carbon scoring) would show a lot less on a black rocket. Elon's Model S and X are black...

 

[Cosmacelf]

I believe the landing legs (or their coating) catch fire a bit after they retract, so that would create some soot.

 

[HVM]

No soot visible, yet.

Reentry burn

Ice and soot.

 

[Ben W]

Ben,

Fantastic job.
Would you or someone with access to Elon's twitter feed kindly post the pic? I think his followers would enjoy the added historical reference to the existing logo.

Thanks! I sent it to him on Twitter: @elonmusk New logo? Congrats on an epic launch/landing!!

Let's hope he notices!

 

[Patrick W]

Bloomberg View: SpaceX's rocket revolution shows power of competition

SpaceXs rocket revolution shows power of competition - Chicago Tribune

 

[Grendal]

Commenting on the soot patterns, the pattern at the base is a perfect line. So perfect that there must be something artificial causing it. It's possible that there is a different coating of paint that resists the soot. Some of the pattern at the top of the booster could have occurred as the second stage ignited. If you watch the video, I believe you can actually see the first stage get hit by the flame wash of the second stage ignition.

Thanks to everyone for the various contributions. All of it is exciting to me.

 

[physicsfita]

One thought I have is if there's any particular reason why space rockets are often white? The soot (however I do prefer carbon scoring) would show a lot less on a black rocket. Elon's Model S and X are black...

When you're trying to keep the oxidizer super-cold it's kind of counter-productive to paint it black and end up fighting the extra heating from the Florida sun because the black paint absorbed the sunlight.

 

[Johan]

When you're trying to keep the oxidizer super-cold it's kind of counter-productive to paint it black and end up fighting the extra heating from the Florida sun because the black paint absorbed the sunlight.

Thanks. Makes a lot of sense.

 

[HVM]

Commenting on the soot patterns, the pattern at the base is a perfect line...

That's the common bulkhead between RP-1 and LOX tanks, and unlike Falcon 1, there isn't any visible insulation on LOX tank wall. And why only paint half of the LOX tank height?

 

[ggr]

That's the common bulkhead between RP-1 and LOX tanks, and unlike Falcon 1, there isn't any visible insulation on LOX tank wall. And why only paint half of the LOX tank height?

My guess is that the part around the LOX tank was still covered with ice during the reentry burns, and it subsequently melted or fell off.

 

[HVM]

Maybe bottom half of LOX tank have more equipment in it, (slosh baffles and helium bottles e.g. COPVs and their struts with the problematic bolts) and those keep the tank walls cold, even if LOX surface is lower.

 

[StephenM]

https://instagram.com/p/_-d28bQEc9/

 

[HVM]

High res. file from SpX Flickr:
https://www.flickr.com/photos/spacexphotos/with/23660653516/

"Elon Musk: Falcon 9 back in the hangar at Cape Canaveral. No damage found, ready to fire again."