Project SpaceX SuperHeavy

BrianJ

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Hi,
since I did promise to put up something soon, I uploaded a "SpaceX Starship (WIP)" package to OH:
It certainly isn't really finished - autopilot RCS functions need tweaking (can be jittery, unstable with time-acceleration), boostback fuel reserve estimates and ASDS placement not very accurate for steeper ascent profiles, etc.etc.
Upper Stage "Skydive-and-Landing" autopilot works OK with no wind but doesn't always make it home with wind on.
Haven't even started on a Reentry autpilot yet.
BocaChica base needs work, as does the launch tower, etc.etc.

It will put 100T in 200km LEO (booster RTLS mode) and 170T in expendable mode (but would you want to throw away all that hardware? ;-)

You need between 10% and 7% fuel reserve for booster RTLS (depending on ascent profile), and 4% for EDL-only landing on ASDS.

Launch Control panel will be familiar to Falcon9 add-on users, Upper Stage has a lot of functions (see doc/readme).

Anyway, it's there if anyone wants to mess around with it :)

Cheers,
Brian

P.S. In view of the latest NASA HLS proposals, and @francisdrake 's fine Moonship add-on, I figured I'd make a "Tanker" variant asap.
 

4throck

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It's great! I never imagined that it would take that long to clear the tower, but makes perfect sense.
Really nice addon. Can the booster launch francisdrake's Moonship ?

For the tanker my guess is that it will be a normal Starship with a forward docking port.
 

francisdrake

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Went to orbit and back, missing Boca Chica, but at least came to Texas! :)
The belly-first reentry was absolutely spectacular!
Still have to learn all the functions provided by the autopilots.
 

BrianJ

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Went to orbit and back, missing Boca Chica, but at least came to Texas! :)
The belly-first reentry was absolutely spectacular!
Still have to learn all the functions provided by the autopilots.
Cool(y) Sorry about the lack of documentation for autopilots. Skydive-and-Land is for when you have a landing target in sight, Retropulsion will just put you down wherever.
It's great! I never imagined that it would take that long to clear the tower, but makes perfect sense.
Thanks. Yes, I had to increase the Raptor thrust to 2.2MN from 1.9MN, otherwise it doesn't even get off the pad until you have burnt some fuel.
Can the booster launch francisdrake's Moonship ?
I think if you added a docking port at the top(dock to Moonship) and an attachment point at the bottom(attach to launch pad) it might work, but no ascent autopilot. I'll see if I can do that and post here.
For the tanker my guess is that it will be a normal Starship with a forward docking port.
OK - so not the engine-to-engine docking shown in videos, etc? I was going to take out the payload bay and add a docking port at the engines, and some code to transfer fuel to any docked vessel. But I could add a forward docking port mesh as well/instead. @francisdrake - any thoughts about that, re: docking to Moonship?
Landed on the 1st attempt.. Raptors are on the loose!
(y) Heh! You saw that sign at BocaChica too :giggle:

Cheers,
Brian
 

DaveS

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Is there any way to shut down engines and perform a propellant dump for the low altitude hops? I looked through the readme and couldn't find anything.
 

francisdrake

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any thoughts about that, re: docking to Moonship?

Well, the Moonship has a front docking port, but it does not need to re-enter the atmosphere. Even with a high angle-of-attack the nose is very exposed to heating and mechanical forces during re-entry. My guess is the Starship will have a docking port on its back, like the Space Shuttle had.

Docking to tank: This makes me think landing on the Moon is still farther away than 2024. No one has ever demonstrated cryogenic tanking in orbit. Small amounts of hypergolic fuel are transferred to the ISS, using bladder tanks and hoses. But here we talk about 5 x 240 ton of LOX and LCH4.

The aft-to-aft docking seems more reasonable for that. It will probably be rather grabbing the other vessel, plug-in the hoses and the receiving ship activates its nose thrusters, so the fuel flows by acceleration into its tanks.

For the Moonship, I will add an aft docking port, and an attachment point as well.
 

BrianJ

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Well, I couldn't attach the Moonship to the SuperHeavy from my add-on, but francisdrake's launch scenario works fine for me anyway.

Is there any way to shut down engines and perform a propellant dump for the low altitude hops? I looked through the readme and couldn't find anything.
Assuming you're not using the ascent autopilot (it only works for orbital insertion with booster), then you should be able to cut engines in the normal way with NumPad*, dump upper stage propellant is B.
 

DaveS

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Well, I couldn't attach the Moonship to the SuperHeavy from my add-on, but francisdrake's launch scenario works fine for me anyway.


Assuming you're not using the ascent autopilot (it only works for orbital insertion with booster), then you should be able to cut engines in the normal way with NumPad*, dump upper stage propellant is B.
Thanks for the propellant dump key command, but I was more thinking of shutting down engines 1-by-1 like SpaceX is doing on the real flights. This is to keep acceleration in check. This also has commands the cut-off engine to move away from the main cluster. They also do this for the landing burn, ignite all three, then shut down the one farthest away from the moment arm and then in the final few seconds, shut down a second engine when the horizontal velocity has been nulled out so that touchdown is only a single engine.

All boils down to inability for the Raptors to throttle low enough to keep acceleration under control. AFAIK, they can only go down to around 30%.
 

BrianJ

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Ah, I see what you mean. Sadly, no, no option for shutting down individual engines - just have to do an unrealistic throttle down, I'm afraid. I was really only using the "hop" scenario for testing the Skydive and Land function (which is very different to how SpaceX do it - I don't know how they cope with high cross winds).
 

francisdrake

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Moonship&Starship1.jpg

High above the Pacific Ocean a Moonship is receiving fuel from a Starship tanker.
The Moonship is firing its linear thrusters to make the fuel flow into its tanks.

Added docking ports to the rear of both vessels.
Will add an attachment point to the Moonship's rear in the next version.
 

BrianJ

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High above the Pacific Ocean a Moonship is receiving fuel from a Starship tanker.
The Moonship is firing its linear thrusters to make the fuel flow into its tanks.

Added docking ports to the rear of both vessels.
Will add an attachment point to the Moonship's rear in the next version.
Top notch! I like the engine-to-engine option since I don't have to do too much hacking of the mesh ;-)
I was thinking I could just add a bit of code to select which of the receiving vessel's tanks to fill, and then start filling if there is +Z acceleration (I see your Moonship has a function for that anyway). I do wonder how long the operation would take given only a small acceleration, and also how many tankers carrying a maximum of 170000kg would it take to satisfy the fuel requirement? (just pondering....)

I'll see if I can do something about DaveS engine selection requirements, too.

Cheers,
Brian
 

francisdrake

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I do wonder how long the operation would take given only a small acceleration?
1618778086659.png

Found this formula on Wikipedia, for low-viscosity fluid like water.
This is for free outflow, so the actual time will be somewhat longer
due to flow resistance in the hoses, tubes and valves.
 

BrianJ

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Ha! Thanks :)
I was just trying to remember if I had done that calculation in Applied Maths at college (rather a lot of years ago, now!).
Yep. I thought it would take quite a while. Might be quite a drain on the RCS tanks (if seperate from main tanks).
I wonder if they might just add a pump? I suppose SpaceX thought about that before making the demo videos etc.
Cheers,
Brian
 

ChrisRowland

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If you use a little ullage acceleration to get the fuel to the bottom of the delivery tank you could increase the flow by pressurising the delivery tank. This will be similar to how they fill a starship on the pad and that takes less than an hour.

The logistics of multiple refuelling trips may be challenging because of the requirement to match the orbit planes. There is only one optimum launch time each day for a tanker launch. Maybe launches from Cape Canaveral and Boca Chica would work for consecutive orbits and you could launch tankers in pairs. Also if it needs significant thrust during the fuel transfer the orbit will be changing. And there will only be one or two opportunities a day for the tankers to return to their base.

Something like this:
1) Lunar Starship and tanker launch from the Cape, they rendevous, transfer fuel and undock in the first orbit. Ideally the tanker returns to the Cape from the first or maybe second orbit. After that it will have to wait a day before the orbit is lined up with the Cape.
2) On the second orbit two tankers launch from Boca Chica to rendevous and transfer fuel.

That should have half filled the Lunar Starship, and that may be enough, otherwise another round of launches and transfer will be needed the next time the bases and orbit planes line up.

Elon's starship concept is crucial for this, it has to be routine to launch and recover the boosters and starship tankers, then refill and relaunch them.

Chris
 

4throck

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One flight a day is realistic. That's the point of the current prototypes, they are working towards such timeframes.
People tend to focus on landing and explosions, and disregard things like swapping an engine overnight! That's the real progress!

Also the timeline for a moon mission is relaxed because you don't have crew. Moonship can stay on LEO for weeks, and then go to the moon using a
low DV trajectory.
 

ChrisRowland

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I was more thinking of the boil off rate for the propellants in uninsulated tanks. You can point the nose or tail towards the Sun to avoid that but you will still have half the rocket facing the warm Earth. Maybe I'm overestimating that but it could be an issue.
 

BrianJ

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Hey guys - thanks for the very interesting insights into the mechanics and logistics of this thing (y)
 

Marijn

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So far I've managed to land the 2nd stage on the pad only once after deploying the payload. It's not easy. But some good fun!
 
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