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[New] Space Launch System / Orion Discussion Thread


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On 3/6/2021 at 2:59 AM, SunlitZelkova said:

I agree that if international cooperation is a goal, NASA has a role to play as a "manager" for everyone involved.

And as the backbone for the rest really. No one else have that much funds to throw around for space stuff. The next best thing is on the whim of a billionaire. The next best thing again is one where they don't really need a breakneck speed to do it (but trust me once they get going it'll be normalized at a breakneck speed).

On 3/5/2021 at 5:09 PM, Hannu2 said:

I would not be surprised if US government announced that Artemis has been cancelled and they begin a new manned Mars-program instead.

With the amount of parties it's involved with now it's difficult to try and undo most of the ongoing work.

Although there's always room to keep Gateway as the continuation of the ISS and that's about it for the Moon mission, and then throw most of the stuff there as 'prepping for Mars'.

On 3/6/2021 at 2:06 AM, tater said:

Artemis was Bridenstine making lemonade out of the lemons (SLS and Orion) he was given.

I have to admit that tying international partners in prevents legislators from any color to stop it on a whim. It was a good move.

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1 minute ago, Barzon said:

Important context in a subsequent tweet...

Yeah, but it makes high C3 cargoes (deep space probes) not really a thing, and SLS has always been a booster in search of a use-case.

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10 minutes ago, tater said:

Yeah, but it makes high C3 cargoes (deep space probes) not really a thing, and SLS has always been a booster in search of a use-case.

Indeed. It certainly depends on where the loads are low enough to allow practical (well, as practical as you can get with a rocket that currently can only be launched every 8 months) usage for lower mass spacecraft. Hopefully the loads would be low enough for Europa Lander to be launched on SLS, as I really can't see Starship being ready to launch deep space probes by whenever Europa Lander needs to launch.

Edited by Barzon
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10 minutes ago, Barzon said:

Indeed. It certainly depends on where the loads are low enough to allow practical (well, as practical as you can get with a rocket that currently can only be launched every 8 months) usage for lower mass spacecraft. Hopefully the loads would be low enough for Europa Lander to be launched on SLS, as I really can't see Starship being ready to launch deep space probes by whenever Europa Lander needs to launch.

I'll believe an SLS launch cadence of every 8 months when I see that. It's chicken and egg, though, since they would need payloads every 8 months, and none exist except Orion, and there's no reason to send Orion anywhere every 8 months.

Dunno about expendable Starship, though compared to actual SS, that's pretty trivial, it's literally SS with all the things that are actually difficult to do subtracted.

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2 minutes ago, tater said:

I'll believe an SLS launch cadence of every 8 months when I see that. It's chicken and egg, though, since they would need payloads every 8 months, and none exist except Orion, and there's no reason to send Orion anywhere every 8 months.

Dunno about expendable Starship, though compared to actual SS, that's pretty trivial, it's literally SS with all the things that are actually difficult to do subtracted.

Yea I agree, the 8 month cadence is based off the time needed to build a new core stage, but IDK how the time needed for the rest of the vehicle to be constructed factors in.

and expendable starship still needs refuelling which... I'm not that confident in, not at such a large scale.

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3 minutes ago, Barzon said:

and expendable starship still needs refuelling which... I'm not that confident in, not at such a large scale.

This is OT for SLS/Orion, but any expendable version need not be refilled with propellants.

Any such spacecraft could have a substantial kick stage. So you have some huge probe (20 tons?) and a 130t (more?) kick stage.

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Are you sure? Everything I've heard is that  Starship expendable can't get anything futher than GTO without refuelling? Although yes a kickstage could probably do the job.

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Based on 100t payload to LEO, 30t landing propellant, a regular Starship mass of 80t, and an ISP of 370s, Starship can push ~88t total to TLI.

An expendable starship can ditch all the unnecessary weight, heat shield, fins, fairing. Falcon9 upper stage has a dry weight to propellant ratio of 4%. The square cube law is friendly to Starship. If expendable Starship weighs 4% of 1250t of propellant dry, that's 50t.

So Starship Expendable can send ~38t to TLI without considering expending Superheavy.

 

 

 

 

But that's not the best use of a Starship. Raptors are super-cheap by engine standards. Put a 3t Raptor powered kick stage on top of Starship, and send 38t to TLI without even expending Starship.

 

 

 

 

... And whilst we're at it, 370s ISP and a Methalox mass fraction trump 465s ISP on an EUS. An RVac kick stage weighing 99t wet can put a 1t payload through over an extra 1km/s compared to EUS weighing 130t in LEO.

Assuming the 1t payload could get there on an SLS without being shaken to pieces.

Edited by RCgothic
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