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SpaceX lands rocket at sea second time after satellite launch

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Re: SpaceX lands rocket at sea second time after satellite launch

#341

Post by samstave »

cloudwalking wrote: post #313
samstave wrote: post #309

Can someone please explain to me how the falcon orients itself during this total process?? Does it use fins, or simply engines and whatever those little jets are that, say, the space shuttle had around its nose... How does the falcon manage to physically orient its body? Also, is that process completely autonomous? Is there a remote flight engineer steering this to the barge - or is it completely self-guided

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

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

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

Re: SpaceX lands rocket at sea second time after satellite launch

#342

Post by ncallaway »

sandworm101 wrote: post #77
gizmo wrote: post #74

Earlier quoted context omitted.

Securing is purely a safety precaution, it's not actually required. https://twitter.com/elonmusk/status/726218218109444096

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

Hence the phrase "purely a safety precaution"

Re: SpaceX lands rocket at sea second time after satellite launch

#343

Post by nugga »

warrenmiller wrote: post #180
neals wrote: post #28

I always try to watch the webcasts and I can't help but cringe so hard when they start chanting 'USA USA USA', every single time. What is up with that?

Maybe they don't know their CEO is South African?

Actually their CEO is African American..

Re: SpaceX lands rocket at sea second time after satellite launch

#344

Post by stcredzero »

sandworm101 wrote: post #77
gizmo wrote: post #74

Earlier quoted context omitted.

Securing is purely a safety precaution, it's not actually required. https://twitter.com/elonmusk/status/726218218109444096

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

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

Re: SpaceX lands rocket at sea second time after satellite launch

#345

Post by zardo »

rz2k wrote: post #326
sandworm101 wrote: post #90

Earlier quoted context omitted.

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

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

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

Re: SpaceX lands rocket at sea second time after satellite launch

#346

Post by stcredzero »

throwaway2016a wrote: post #118
mabbo wrote: post #99

Earlier quoted context omitted.

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

Slightly off topic but I was watching a television show the other day and someone said they worked at NASA. The host then said "So you're literally a rocket scientist?" And the guy said emphatically "Rocket engineer, there is a big difference" I'm sure this particular task probably was a little bit of both. After all, they had to run several real world experiments to prove their calculations.

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

Re: SpaceX lands rocket at sea second time after satellite launch

#347

Post by ctthill »

mikeash wrote: post #305
grondilu wrote: post #281

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

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

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

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

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

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

Re: SpaceX lands rocket at sea second time after satellite launch

#348

Post by david-given »

Kratisto wrote: post #328
david-given wrote: post #296

Earlier quoted context omitted.

You're getting downvoted into oblivion, but yeah, that's basically how I feel. Cultural differences, I'm sure, because I'm not USian; but every time I see it on the youtube videos it makes me deeply uncomfortable.

I'm an American, and I'm just wondering why it makes you uncomfortable? Does chanting at sporting events make you uncomfortable as well? edit: Reply button showed up finally

I'm fine about sporting events, because it's about something that doesn't matter --- the whole point of sport is to channel the sex-violence-and-tribalism thing in a safe and relatively controlled fashion.

What disturbs me about something like the chanting at SpaceX is that it's something that does matter, and which I feel strongly about. Seeing their great technical achievement turn into exclusionary tribal posturing makes me very sad.

I'm sure there's a long way to go before SpaceX fans and STS fans start beating each other up in the street... but it is one step down that path.

Re: SpaceX lands rocket at sea second time after satellite launch

#349

Post by paulvs »

api wrote: post #295
LocaX wrote: post #171

Earlier quoted context omitted.

I attended a conference from the head of the CNES (Centre National d'Etudes Spatiales, ~ French NASA) in Paris a week ago and he talked about that. Ariane 6 is going to be built with a cost effective approach and trying to focus on market needs (3D printing of parts, reusability of the first stage, etc.) At first, concerning SpaceX, his group of experts told him that the design of the rocket wasn't going to work and…

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

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

Re: SpaceX lands rocket at sea second time after satellite launch

#350

Post by paulvs »

api wrote: post #295
LocaX wrote: post #171

Earlier quoted context omitted.

I attended a conference from the head of the CNES (Centre National d'Etudes Spatiales, ~ French NASA) in Paris a week ago and he talked about that. Ariane 6 is going to be built with a cost effective approach and trying to focus on market needs (3D printing of parts, reusability of the first stage, etc.) At first, concerning SpaceX, his group of experts told him that the design of the rocket wasn't going to work and…

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

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