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Payload for First Falcon Heavy Flight Announced

Posted: Sat Dec 02, 2017 2:35 pm
by OverTheTop
Payload for First Falcon Heavy Flight Announced

He will be flying a used car! Absolutely spectacular :D :D :D


https://twitter.com/elonmusk/status/936782477502246912

Tesla.png

Re: Payload for First Falcon Heavy Flight Announced

Posted: Sat Dec 02, 2017 8:47 pm
by Oldboy
Best place for an electric vehicle.

Re: Payload for First Falcon Heavy Flight Announced

Posted: Sat Dec 02, 2017 9:28 pm
by SpaceManMat
Amusing, but you can’t just decide to do that. Anything going to orbit needs to carefully designed for that part of the trip. You’d have to do a ton of work to make it happen and a non traditional payload would add risk to the mission. Nice PR stunt though, ceartainly get a few people talking.

Re: Payload for First Falcon Heavy Flight Announced

Posted: Sun Dec 03, 2017 10:38 am
by OverTheTop
SpaceManMat wrote:Amusing, but you can’t just decide to do that. Anything going to orbit needs to carefully designed for that part of the trip. You’d have to do a ton of work to make it happen and a non traditional payload would add risk to the mission. Nice PR stunt though, ceartainly get a few people talking.

For sure. I have been pondering what the payload adaptor would be like :D

As to adding risk to the mission, I suspect they have other items in their FMEAs that have much higher RPNs :shock:

Considering this is a rocket designed to loft around 63800kg and it will only have a 1300kg car (plus some other necessary stuff) it should slide off the pad at about 1.5Gs. Interestingly it is such a big rocket that flying with the small payload or full payload the difference in accel is only about 5% in rough numbers!

Re: Payload for First Falcon Heavy Flight Announced

Posted: Mon Dec 04, 2017 6:11 pm
by High Impulse
I guess they might throttle back the engines to reduce gees?

Re: Payload for First Falcon Heavy Flight Announced

Posted: Mon Dec 04, 2017 8:51 pm
by OverTheTop
Probably don't have to. The mass of the Roadster is about 1300kg. Add payload adapter, dashcam interfaces, telemetry sensors and interfaces etc and it will be well up on that. The FH is capable of 63800kg payload (LEO), but even that is such a small percentage of the overall mass (1420788 kg) that it is really neither here nor there for the early stages. I think it works out to about 1.5G accel on takeoff (IIRC, rough numbers in my head yesterday).

Re: Payload for First Falcon Heavy Flight Announced

Posted: Tue Dec 05, 2017 9:45 am
by SpaceManMat
The issue is prior to staging as the tanks empty out the mass of the rocket is greatly reduced so the accelleration starts to run away unless you do something about it such as throttle back. This is why the Saturn V used to cut the inboard motor prior to staging, otherwise to Gs would get extremely high, also it didn’t have throttlable engines.

Re: Payload for First Falcon Heavy Flight Announced

Posted: Tue Dec 05, 2017 1:08 pm
by OverTheTop
Correct SMM. I did say it didn't matter much for the early stages. Later ones are a different story as the true payload is a larger part of the mass fraction.

It is my understanding of the FH that both boosters will be at full throttle, with the central core throttled down until booster separation. That gives the highest amount of fuel lifted by the boosters and optimises the gravity loss as best they can. The were originally going to keep the central core topped up as the flight progresses (until separation) but they went for a simpler system after doing the trade studies.

Re: Payload for First Falcon Heavy Flight Announced

Posted: Tue Dec 05, 2017 5:32 pm
by SpaceManMat
I don’t ever recall hearing any explanation from Space X about dumping cross feed from FH. Just figured they though the complexity and extra equipment wasn’t worth the rewards and throttling Center core engines would be a reasonable alternative.

Re: Payload for First Falcon Heavy Flight Announced

Posted: Tue Dec 05, 2017 6:36 pm
by OverTheTop
I don’t ever recall hearing any explanation from Space X about dumping cross feed from FH. Just figured they though the complexity and extra equipment wasn’t worth the rewards and throttling Center core engines would be a reasonable alternative.


They would have done "trade studies" to figure out what they have to lose in one area to gain in another. It is a more official, informative and extensive way than the WAG* or "wet finger in the air" approach. Gives actual numbers that management can make decisions with. It is a prominent method in the aerospace environment. Trade studies make the decisions defendable at higher levels of management.

A similar example is that just like we mitigate risks, typically based on what knowledgeable people know or we work out ourselves, at the hobby level, companies have a lot more to gain from doing a more thorough approach (FMEAs) to determine what the relative risks are, what needs mitigating and what needs eliminating.

Both systems also leave an audit trail if the decisions are ever called upon to support something unexpected that happens. I can vouch that FMEAs have saved us a lot of work at my employer.

* WAG=Wild Ar#@d Guess