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SpaceX’s Falcon Heavy successfully launches

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Re: SpaceX’s Falcon Heavy successfully launches

#861

Post by thinkcontext »

kuschku wrote: post #792
z3t4 wrote: post #747

Earlier quoted context omitted.

It look cool to have them land on their own, but wouldn't it be much cheaper to use parachutes and drop them in the ocean !? Either way they are going to take them apart down to each bolt and then reassemble again to make sure there are no faults. You don't simply fill it up and relaunch.

SpaceX goal with the Falcon 9 is to be able to land, simply check the core (the engine gets more complicated checkups), and to have it back on the launchpad within of a few days or weeks. Arianespace (a major european launch company, known for the Ariane 5) has developed their own new engine concept for reusability, which is designed to be restarted unlimited times. Once Prometheus flies, they’ll not only have a reus…

> Once Prometheus flies

Sounds like they are not that committed to the project and if it happens at all it will be a long way off. Will it be worth competing with both SpaceX and Blue Origin?

“We could replace Vulcain 2.1 by Prometheus,” Bonguet told SpaceNews. “Or Prometheus can be the first brick to build the next generation. We will see where we are in 2025 or 2030, and then decide on the right time whether to go one way or the other.”

http://spacenews.com/ariane-6-could-use-reusable-prometheus-...

Re: SpaceX’s Falcon Heavy successfully launches

#862

Post by dtparr »

rocqua wrote: post #858
mohaine wrote: post #852

Earlier quoted context omitted.

The plain is to lock down block 5's design so it can be man rated which in itself would make it more reliable. This will probably not happen until they fly them a few times though so that wouldn't mean the first block 5s would be more reliable.

I recall reading or hearing yesterday that space-x no longer plans to man-rate any falcon-9s instead reserving that for the BFR.

I believe that was in reference to the Falcon Heavy, not the F9. The F9 is expected to be man-rated for NASA's commercial crew program.

Re: SpaceX’s Falcon Heavy successfully launches

#863

Post by dtparr »

rocqua wrote: post #860
simonh wrote: post #793

Earlier quoted context omitted.

The rocket ran out of engine igniter fluid. It had enough to light the centre engine, but not the two side engines. That seems to imply they were trying to do a 3-engine landing, which they tested recently in the 'failed to expend the rocket' incident. This might explain why they miscalculated the igniter requirement since they don't have much experience with 3-engine landings.

Is the normal landing a 1-engine landing? If so, is the advantage of a 3-engine landing that it requires less fuel due to having a much shorter 'suicide burn'?

Yes, and yes. The less time you're in the air, the less fuel needed to counter gravity's continual pull, so the most efficient landing burn is basically the highest acceleration you can handle without coming apart such that your velocity hits 0 as your altitude does.

Re: SpaceX’s Falcon Heavy successfully launches

#864

Post by pavel_lishin »

hueving wrote: post #558
pavel_lishin wrote: post #362

Earlier quoted context omitted.

If you know that the person asking you to be a reference is a bad engineer, and they're applying for someplace that builds critical systems - medical devices, say, or rockets - maybe you want to warn their potential employer that they're hiring a liability.

It's pretty presumptuous to make that assertion unless you knew the person for many years in different work environments. I've seen lots of engineers become 'bad engineers' because of a myriad of environmental issues (bad management, bad peers, bad office, bad engineering decisions foisted upon them). If you didn't see them perform well, don't provide a reference. If they are that bad, nobody in a reputable position…

If someone calls me up and asks about Coworker X, and I refuse to provide a reference, isn't that likely to be viewed the same as a negative reference?

Re: SpaceX’s Falcon Heavy successfully launches

#865

Post by mcv »

leetrout wrote: post #139
subway wrote: post #103

Earlier quoted context omitted.

I thought it was interesting that they specifically said the two panels represent the two boosters. I don't think they ever directly claimed each video was from a different booster.

Ah interesting. I don't think that's what they meant. I think they did think it was 2 different views. https://youtu.be/wbSwFU6tY1c?t=37m10s "even though those look very similar those ... are representative of different boosters"

I think they were themselves a bit surprised they were so similar, and weren't yet sure whether they were from different boosters or not, so they kept it vague.

Re: SpaceX’s Falcon Heavy successfully launches

#866

Post by dtparr »

MayeulC wrote: post #834
simonh wrote: post #793

Earlier quoted context omitted.

The rocket ran out of engine igniter fluid. It had enough to light the centre engine, but not the two side engines. That seems to imply they were trying to do a 3-engine landing, which they tested recently in the 'failed to expend the rocket' incident. This might explain why they miscalculated the igniter requirement since they don't have much experience with 3-engine landings.

On the other hand, if you look carefully at the landing video, it looks like they did a three-engine landing boost on the other boosters: https://youtu.be/BBA7su98v3Y?t=517 So they have definitely learned something valuable in that landing incident.

Interesting. Looks like a 1-3-1 burn (start with 1, ignite two more for a bit, then finish on a single one).

I wonder how much longer the '3 engine burn' was for the GovSat launch last week that did a 'water landing'

Re: SpaceX’s Falcon Heavy successfully launches

#867

Post by votingprawn »

jpitz wrote: post #847
votingprawn wrote: post #820

Earlier quoted context omitted.

The SR-71 took off with a small fuel load to reduce stress and improve engine-out performance, that is why it was refuelled immediately after take-off. The mental image of it leaking so much fuel on the ground such that it needed immediate refuelling is a myth propagated extensively on the internet.

The characterization is/was also propagated by people who actually refuelled them, so I'm somewhat unconvinced it is a myth.

I believe if you look for primary sources like pilots and ground handlers/mechanics you'll mostly find reference to small leaks (I think they were referred to as drips caught in cookie trays).

I had a quick search and found the KC135 chap who says the refuelling was needed due to leaks, but without being rude to him I'm not sure he's really a qualified source for that information. It sounds more to me like 2+2=5.

I'm procrastinating so lets do some napkin maths, the claim is

1) a significant amount of fuel is leaking out of the expansion gaps,

2) climbing up to 25,000 ft at 300 knots would heat the airframe enough to seal those gaps,

3) there would still be sufficient expansion room to allow for travelling at M3.2

----

Ignoring that no engineer would be happy with 1.

For 2...Total Air Temp = Static Air Temp + Ram Rise. At 25,000 ft the static air temperature is about -35 C. Ram rise for a true airspeed of 300 kts:

RamRise = V^2 / 87^2 = 300^2 / 87^2 = 12 degrees.

So skin temperature at typical refuelling altitude would be -23 C

Titanium has an expansion coefficient of 9E-69 meters per meter-kelvin. So approximating rather grossly, assuming a s tarting temperature of 20 C over the 33 m length of the plane there would be a contraction of about 1 cm.

----

And for 3:

The aircraft then accelerates up to 1900 knots. RamRise = 1900^2 / 87^2 = 470 degrees

Static air temp at over 60000 ft is roughly -55 C. So skin temperature would be 420 C. So assuming the same length and starting temp, the plane would expand by around 11 cm

----

So to summarise: According to the claims, at ground level and temperature the expansion gaps were large enough to significantly leak fuel. After take-off the aircraft needs to be refuelled immediately. Assuming this is done so (i.e. take-off, climb to 20,000, refuel) then the skin temperature is lower than ground level, and the expansion gaps should have grown ever so slightly. The aircraft then climbs up to its M3.2 cruise point and everything expands significantly "as designed" and the gaps disappear.

----

Perhaps the anecdote we'll see on the internet now is that the SR-71 had to take off and go supersonic to rapidly heat up the skin before briefly decelerating to refuel, but the refuel had to be done super fast to stop the skin cooling down too far...

Re: SpaceX’s Falcon Heavy successfully launches

#868

Post by mcv »

buildbuildbuild wrote: post #61

Love that SpaceX’s own team shoots, announces, and switches the live production in-house rather than hiring a production company. Also love seeing machinists side by side cheering with software engineers, standing by a mission control which is placed feet from where engines are assembled on the shop floor. Open company culture well-executed. Congratulations to all there!

The 4 presenters were also engineers. And by doing it that way, they got to show that some engineers are black women. Let's hope this inspires a generation of black girls to seek a career in space or tech.

Re: SpaceX’s Falcon Heavy successfully launches

#869

Post by mcv »

dobecker wrote: post #844
makkesk8 wrote: post #189

Man next to one of the boosters: https://pbs.twimg.com/media/DVYYekSWAAEHpTa.jpg That's nuts.

they looked so tiny on the video stream: https://pbs.twimg.com/media/DVYWR2IUQAAutMB.jpg

I was also surprised that the Falcon Heavy didn't look all that big, really. Until I saw people next to a booster. Scale is hard.

Re: SpaceX’s Falcon Heavy successfully launches

#870

Post by chasd00 »

elmar wrote: post #769
protonimitate wrote: post #110

Earlier quoted context omitted.

There's something awesome (in the literal sense) and unsettling about watching something and being able to say "I am witnessing history".

I fell this is the most important moment in space exploration since the Apollo landing, but I don't see a big coverage in mainstream media. Elon is probably on the trajectory to be remembered as the biggest entrepreneur ever.

I don't fanoboi much but Elon gets me pretty close. He's done 5 lifetimes of work before hitting 50.
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