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SpaceX Discussion Thread

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20 minutes ago, tomf said:

I feel that staging while plummeting towards the moon might be considered a high risk maneuver. Of course I do it all the time when I have been a bit too conservative with delta-v and don't want to waste it. I'm pretty sure that in real life that would be frowned upon, let along my usual alternative of just landing on the engines of the transfer stage and having the astronauts jet-pack up and down from the capsule.

Why is staging during descent any more risky than staging during ascent? In fact, the N-1 Soviet moon landing program planned to use their Blok D stage as a crasher stage on lunar descent, and the original NOVA direct-ascent lunar lander would have used LOI insertion stage as a crasher as well.

It's not "plummeting" either. The maneuver would be very controlled. After lunar-orbit rendezvous and crew transfer from the command module (likely an unmodified Dragon 2 with a hypergolic propulsion assist pallet mated to the payload mount in the trunk) to the lunar module, the command module's RCS would burn retrograde to place the whole stack on a modified orbit with a periapsis of a few hundred meters. The vehicles would separate, and the command module would flip and gently raise its orbit.

At this point, the Falcon upper stage carries around nine tonnes of propellant. Between 90 and 33 seconds before periapsis, the MVac fires its final TEA-TEB shot to ignite, first at 90% throttle, then quickly dropping to 40-50% throttle. Those nine tonnes of propellant deplete in 33 seconds at full throttle or in 84 seconds at minimum throttle. If the MVac fails to ignite for any reason, the lunar module is still orbital and can simply separate, fire its engines radial-out, and bring itself back up to a rendezvous with the command module. If the MVac performs nominally, then it will shut down at nearly zero velocity, after which the lunar module separates, kills residual velocity using a puff from the SuperDracos, and lowers itself gently to the surface.

For a manned mission, the trunk must carry the same propulsion pallet carried by the command module. At mission end, the SuperDracos fire for initial liftoff and the propulsion pallet kicks in to push into orbit. For a one-way, unmanned mission, there is no lunar-orbit rendezvous; the trunk can carry payload which is dropped out, after which the lunar module lifts itself clear of the payload and dumps itself a safe distance away.

One interesting option: if you don't want to man-rate or expend a Falcon Heavy, you can launch the command module on an RTLS (or perhaps ASDS) Falcon 9, then launch a three-core-recovery Falcon Heavy with nothing but an IDA mated to the PAF. The command module can rendezvous with the naked Falcon Heavy upper stage and dock to the IDA, and the Falcon Heavy upper stage can then perform the TLI and LOI burns before being jettisoned in LLO. The crasher-stage lunar lander approach requires the launch vehicle to be attached to the rear of the lunar module, but you can get away with a reusable Falcon Heavy if you use another separate, nose-docked upper stage for the TLI and LOI burns. Probably cheaper to launch three full-reuse Falcon Heavies and one reusable Falcon 9, at the cost of 4 upper stages, than it would be to launch two expendable Falcon Heavies and have to bother with man-rating it.

53 minutes ago, Technical Ben said:

I'm still of the opinion that if they ever want to do it "proper" for the moon, a cycler for both Luna transfer and Luna take off is going to be required. Else you get a LOT of scrap lying around on the Moon. A refuel/reland/relaunch just has the servicing + fuel to worry about. Though of cause a little loss in efficiency as you cannot drop lots of stages. But depending on how it is setup, you could leave a "stage" that is built into your cargo/habitat etc. To reuse empty fuel tanks as structure.

But as the current falcon shows, sending the empty fuel tanks "back" is not really much of a worry.

Doing it "proper" for the moon requires orbital propellant transfer, full stop. We don't currently have that capability.

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THE HYPE IS REAL

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I never saw so many peoples here before, and we are only 4 hours before the launch!

zpIcnbk.jpg

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Listening to the local radio station CFOX talk about the launch, they figure the Roadster is held on with duct tape and zap straps lol :D

Edited by StrandedonEarth

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1 minute ago, CastleKSide said:

Probably a Muskism. but HYPE

HyperHype!

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Finally the day we have all been waiting for! The time has finally come to test the brilliance of Falcon Heavy, and send a little souvenir with it! :wink: 

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The first MVac burn will perform orbital insertion. Following a coast to establish the argument of periapsis, the second will raise apoapsis about halfway to GTO, in an elliptical orbit with a six-hour period. The third burn, six hours later, will take place at periapsis and burn to depletion for escape.

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Quote

At that point, Musk said he’s not worried about the Roadster’s health. The car has a “tiny, tiny chance” of crashing into Mars, Musk says. “It will be fine. I hope.”

Gotta check the airbags. Just in case.

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3 minutes ago, sh1pman said:

Gotta check the airbags. Just in case.

Airbags, technically, are small monopropellant hydrazine rocket engines.

Per ChrisG, the fairings will not be recovered today, but the fairing recovery testing will continue.

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7 minutes ago, sevenperforce said:

The first MVac burn will perform orbital insertion. Following a coast to establish the argument of periapsis, the second will raise apoapsis about halfway to GTO, in an elliptical orbit with a six-hour period. The third burn, six hours later, will take place at periapsis and burn to depletion for escape.

I want a tracker for this thing. Is it going to get over 40°? 

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3 minutes ago, sevenperforce said:

Launch slipped to 2 PM EST.

Seriously? Kerm bleeping dangit, now I'm going to miss the launch.

EDIT: Source please?

Edited by IncongruousGoat

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Im pretty sure this thread will be SUPHA HOT when the stream is going.

Anyways, they are not doing the Moon Dragon thing anymore. They want to do it using the BFR. So, suggesting by the BFR rush we got recently (they ditched the 12m to the 9m design to fit the current hangar, they said they will be putting alot of money in it, and every cool mission of the Dragon has been changed for the BFR), they must be really desperate, for something...

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1 minute ago, IncongruousGoat said:

Seriously? Kerm bleeping dangit, now I'm going to miss the launch.

EDIT: Source please?

https://spaceflightnow.com/2018/02/05/falcon-heavy-demo-flight-mission-status-center/

Apparently they are going to wait for calmer upper level winds. I'm still going to be able to watch, but it will be in class rather than at lunch.

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3 minutes ago, NSEP said:

Im pretty sure this thread will be SUPHA HOT when the stream is going.

Anyways, they are not doing the Moon Dragon thing anymore. They want to do it using the BFR. So, suggesting by the BFR rush we got recently (they ditched the 12m to the 9m design to fit the current hangar, they said they will be putting alot of money in it, and every cool mission of the Dragon has been changed for the BFR), they must be really desperate, for something...

Lunar Dragon and man-rating FH is still a possibility if BFR slips. If BFR does not slip too badly, FH will not be man-rated.

Personally, I think man-rating BFR will be harder than it would be to man-rate FH.

Dollars to donuts, the first manned flights on BFR launch on Falcon 9 and Dragon 2.

From the mouth of Elon:

DVXbp4NUMAAdXcA.jpg:large

So we have fairing splashdown but no net-catch.

Also note boostback for the core.

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