totm dec 2023 Artemis Discussion Thread

[tater]

Yeah, think it needs its own thread.

[Nightside]

On 9/25/2019 at 4:17 PM, tater said:

Is this the Artemis thread of record?

Regardless:

 

Is that to scale with the lunar rover and astronaut figures?

On 9/25/2019 at 5:12 PM, Ultimate Steve said:

True. I'd say create a new Artemis thread then or ask nightside to rename this one to something more appropriate for an Artemis discussion thread.

But you're the leading authority on space update threads here, not me, so I'll leave that up to you.

How does “Artemis Discussion Thread” sound?

[Ultimate Steve]

1 hour ago, Nightside said:

Is that to scale with the lunar rover and astronaut figures?

How does “Artemis Discussion Thread” sound?

Sounds pretty good to me!

[YNM]

3 hours ago, Nightside said:

Is that to scale with the lunar rover and astronaut figures?

Maybe, but I still fail to find any direct explanation from JAXA or Toyota. JAXA seems to only put the live press release, while Toyota seems to have put nothing up about it.

[tater]

11 hours ago, Nightside said:

Is that to scale with the lunar rover and astronaut figures?

LOL, no. That thing looks SUV sized. OK, really huge SUV sized.

[kerbiloid]

So, looks like its cabin is much heavier than the rear part.

[RCgothic]

That would be... Weird.

[tater]

 

[RCgothic]

Looks like Gateway just took a step towards not happening?

[kerbiloid]

Spoiler

Orion Direct Ascent

 

[Guest]

Quote

“the agency is leaving open the option for contractors to develop a descent craft that would bypass the planned Gateway mini-space station in lunar orbit, at least for the first landing attempt.”

Hmmm, I wonder if there are any guarantees as to the funding for Gateway after the next election. 

[kerbiloid]

Spoiler

They will decide on KSP-2 release.

 

[tater]

They are leaving it open to non-Gateway solutions, but they are also sending the crew on Orion, which pretty much requires Gateway (because the Orion SM is useless). Orion is apparently capable of a ~500km lunar orbit (with return to Earth from there), so maybe they are making it open to that, instead. The difference of a few hundred m/s might matter.

[sevenperforce]

SpaceX can just send up a cargo Starship and say "Our proposal is to meet Orion in LEO, dock it inside our cargo bay, land on the Moon, and come back."

[RCgothic]

Presumably a meatier SM would weigh more. Is SLS even capable of lofting a heavier Orion & SM to the moon? Does it actually gain you anything?

[sevenperforce]

4 minutes ago, RCgothic said:

Presumably a meatier SM would weigh more. Is SLS even capable of lofting a heavier Orion & SM to the moon? Does it actually gain you anything?

Not without Block 1B.

It's a shame the SM is so lame.

[tater]

Yeah, any increase in SM capability requires more throw weight to TLI. ICPS can't do it, so they need B1b, and any increase in Orion SM decreases comanifested payload. If the payload is something like a metal balloon (a hab), it's no big deal. If the payload is supposed to be a lander stage, packed with propellant... that matters more.

[sevenperforce]

25 minutes ago, tater said:

Yeah, any increase in SM capability requires more throw weight to TLI. ICPS can't do it, so they need B1b, and any increase in Orion SM decreases comanifested payload. If the payload is something like a metal balloon (a hab), it's no big deal. If the payload is supposed to be a lander stage, packed with propellant... that matters more.

Orion was sized for the EOR-LOR lunar landing architecture of Constellation, where the Altair lander's descent module would perform the lunar capture burn and leave Orion's SM topped up in low lunar orbit. Strictly speaking, it's a more efficient architecture than Apollo. The reason the Apollo CSM performed the capture burn in the 60s and 70s was that the AJ10-derived SPS was grossly oversized (it had originally been planned for lunar direct ascent) and so they threw more propellant onto the SM.

[tater]

32 minutes ago, sevenperforce said:

Orion was sized for the EOR-LOR lunar landing architecture of Constellation, where the Altair lander's descent module would perform the lunar capture burn and leave Orion's SM topped up in low lunar orbit. Strictly speaking, it's a more efficient architecture than Apollo. The reason the Apollo CSM performed the capture burn in the 60s and 70s was that the AJ10-derived SPS was grossly oversized (it had originally been planned for lunar direct ascent) and so they threw more propellant onto the SM.

Yeah, but that architecture was distributed launch, with initial EoR, and a cargo vehicle to loft a huge lander with TLI stage, and Orion not lofted by the large LV.

 

[sevenperforce]

1 minute ago, tater said:

Yeah, but that architecture was distributed launch, with initial EoR, and a cargo vehicle to loft a huge lander with TLI stage, and Orion not lofted by the large LV.

Regardless of how you get headed to TLI, isn't it more efficient to dump your expended LOI tankage on the moon than to drag it back with you to EOI?

Hmm, I guess it depends. EOI and LOI both cost 1.31 km/s while lunar landing costs 1.87 km/s. So perhaps keeping that expended tankage on your command module is the better choice, unless you have a way to drop it somehow.

Using the TLI stage for your LOI burn (and for your lander deorbit) probably beats both.

 

[tater]

35 minutes ago, sevenperforce said:

Regardless of how you get headed to TLI, isn't it more efficient to dump your expended LOI tankage on the moon than to drag it back with you to EOI?

Hmm, I guess it depends. EOI and LOI both cost 1.31 km/s while lunar landing costs 1.87 km/s. So perhaps keeping that expended tankage on your command module is the better choice, unless you have a way to drop it somehow.

Using the TLI stage for your LOI burn (and for your lander deorbit) probably beats both.

I wasn't really debating that. Orion was clearly not designed for lunar operations in anything like the Apollo style, but also, SLS is not really designed for the Constellation model, either (launch cadence if nothing else), so Orion is the wrost of both worlds, lol. I was really pointing out that the current architecture pretty much mandates Orion sent directly to TLI alone. I suppose they could man rate FH, then put Orion into LEO that way, then do a cargo SLS with an Altair like lander, rendezvous, then immediately TLI...

The one place I see the CSM as a better place for the props is maybe contingency operations? Having so much more dv probably gives options, though it's not like they couldn't also use an Altair like lander for contingencies as well, likely comes out in the wash.

Being able to have the TLI stage also do the LOI burn (then dispose of itself) would clearly be huge, but such upper stages are usually hydrolox, then you need to deal with boiloff over multiple days of transit time.

[Barzon]

honestly i wish they had never had the ESM. A US-built SM would most likely be far superior. If eventually they do change, such as after Artemis 3 or 4, by then there will be many options available, including using 1 or 2 of the 10 ton Starship methalox RCS as a MPS. A return to a methalox SM with UltraFlex panels would be very interesting, at the least. 
From what i can see, using the Starship RCS would at least double the thrust (1x SS10 ton methox thruster, Orion MPS has 3 tons of thrust. Thats over triple the thrust) and hopefully capability of Orion's SM. The lighter solar panels would also play into it.

I dont know how well gaseous CH4 and GOX fare in deep space, but surely it wouldnt be that bad.

Edited October 8, 2019 by Barzon

[tater]

2 minutes ago, Barzon said:

honestly i wish they had never had the ESM. A US-built SM would most likely be far superior. If eventually they do change, such as after Artemis 3 or 4, by then there will be many options available, including using 1 or 2 of the 10 ton methalox RCS as a MPS. A return to a methalox SM with UltraFlex panels would be very interesting, at the least. 

Well, so far management on the project has been less than great, so who knows, lol.

Looks like the dv is 1226 for the CSM.

If the SM used a vacuum Raptor (which it wouldn't), that would increase to ~1461. Not much of a change.

LOI and TEI are both around 1000 m/s (LLO), so any SM needs to have about 2000+ m/s dv.

 Assuming hypergolics are still the props for the SM, the Orion SM needs to grow by around 8.5 tons to achieve this capability (basically eating up the entire excess capacity of Block 1b).

 

 

[sevenperforce]

6 minutes ago, Barzon said:

I dont know how well gaseous CH4 and GOX fare in deep space, but surely it wouldnt be that bad.

Huge problems with impulse density, unfortunately.

If you really want to use methane+GOX for some reason, you can always use an electric pump and electric resistance heaters to prime pressure-feeding bottles from a liquid reservoir, but then you have a limited burn duration. Might as well just go ZBO hydrolox tanks with the BE-5 instead.

17 minutes ago, tater said:

Being able to have the TLI stage also do the LOI burn (then dispose of itself) would clearly be huge, but such upper stages are usually hydrolox, then you need to deal with boiloff over multiple days of transit time.

Transit boiloff is not prohibitive. 0.35% per day with hydrolox by NASA's current GR&A's. If you have hot-gas thrusters then you can just route any boiloff into the RCS bottles for a pseudo-ZBO approach. What you want to avoid is having hydrolox in loiter; that's where the third-of-a-percent losses start to accrue.

For a disposable lunar landing architecture I have always preferred using the TLI stage for LOI and deorbit, then as a crasher stage to scrub off everything but the last 300 m/s of the landing burn. You can then do a single-stage lander. Although DLOR has its attractions....

3 minutes ago, tater said:

Looks like the dv is 1226 for the CSM.

If the SM used a vacuum Raptor (which it wouldn't), that would increase to ~1461. Not much of a change.

LOI and TEI are both around 1000 m/s (LLO), so any SM needs to have about 2000+ m/s dv.

 Assuming hypergolics are still the props for the SM, the Orion SM needs to grow by around 8.5 tons to achieve this capability (basically eating up the entire excess capacity of Block 1b).

Closer to 1300 m/s, so 2600 m/s dV. And that's only braking itself into orbit, not braking in a lander.

Orion is too heavy, its service module too light, and SLS is too puny.

[tater]

I just used the actual Apollo numbers I found for the 2 burns, and slopped it up.

Apollo 11 LOI burn was 889.2 m/s. They circularized with another 46.7 m/s.

TEI for Apollo 11 was around 1000 m/s.

But yeah, Orion is too heavy, and the SM is too small (Apollo's SM had to also be much larger because it was doing LOI for the CSM/LM stack, not just the CSM).