totm dec 2023 Artemis Discussion Thread

[tater]

13 minutes ago, sevenperforce said:

Artemis II has to do a multi-translunar injection with two burns (unlike Artemis I) because a free-return is more dV-costly. Artemis III will not be able to do a free-return since it will be setting up to enter NRHO. But sure, let's keep SLS because it is soooooooooooooooo safe.

Yeah... nuts.

Wonder what the apogee is after the first burn... Van Allen territory? Such safety. Much wow.

 

[sevenperforce]

7 minutes ago, tater said:

Yeah... nuts.

Wonder what the apogee is after the first burn... Van Allen territory? Such safety. Much wow.

Per NASA, the first ICPS burn after staging off the SLS core does an insertion to a 185km x 2900km orbit. The second ICPS burn raises the stack to a 378km x 109,400km orbit. Then Orion provides the final burn at perigee for TLI.

A circular LEO at 185 km is 7.80 km/s, and so the initial ICPS orbital insertion is about 640 m/s more than that (velocity at perigee = 8.44 km/s). The second ICPS burn would need to add about 2.21 km/s (velocity at perigee = 10.56 m/s). That puts them in a 42-hour orbit which NASA is saying for "spacecraft checkout" and practice. Then Orion burns about 3 tonnes of its propellant to complete the TLI. Should be a 5-6 minute burn.

So yeah, that's four extra passes through the inner Van Allen Belt and two extra passes through the outer Van Allen Belt. All to get a free-return that Falcon Heavy and Crew Dragon could do with ease.

And then with Artemis III they won't even be able to achieve the safety of a free-return.

[tater]

2 minutes ago, sevenperforce said:

So yeah, that's four extra passes through the inner Van Allen Belt and two extra passes through the outer Van Allen Belt. All to get a free-return that Falcon Heavy and Crew Dragon could do with ease.

Wonder which astronaut gets to be The Thing.

[YNM]

55 minutes ago, sevenperforce said:

Artemis I will enter a distant retrograde orbit. Orion will do a very close flyby -- 100 km -- in order to do a mostly gravitational capture into the distant retrograde orbit. So there will be the nice close-up views that @YNM wants...except for the fact, of course, that there is no one on board.

Ah. So they wouldn't put anyone onboard yet...

idk. We need some way to test the docking IMO...

[Spaceman.Spiff]

Artemis 1 core stage has arrived in Florida!

 

[tater]

What do people think the dry mass of SH is? 200t? Stripped as an expendable, maybe 180?

Looks like a 180t SH with just 24 Raptors can put almost 56t into a 60x185km orbit. Yes, intentionally leaving the SH to go for a swim. That's as a single stage. Every ton saved on the SH is a ton to that orbit. If a LSS is ~85t, then a similarly built SH (~1.5X larger) should be ~130t—meaning as an SSTO, SHe can put ~96t into that orbit. So the payload/upper stage has to do the rest.

With a 40t dry partial SS (half size) with 3 vac raptors, the expendable can throw 53t of additional payload to Earth escape (~TLI). Not sure what the TLI hit is for SH RTLS, if it's still 40%... that's >30t to TLI (<cough> Orion</cough>).

SH is kind of remarkable—and it really is the easy part of the system. SHe with a expendable upper stage can pretty easily hit/exceed SLS Block 2 level payloads to TLI—and SpaceX could still make money selling those launches for 10X less than an SLS launch (1/10th of the very best case SLS cost by the usual SLS fan posters, way less than the actual cost of SLS).

 

 

[RCgothic]

21 hours ago, tater said:

What do people think the dry mass of SH is? 200t? Stripped as an expendable, maybe 180?

Looks like a 180t SH with just 24 Raptors can put almost 56t into a 60x185km orbit. Yes, intentionally leaving the SH to go for a swim. That's as a single stage. Every ton saved on the SH is a ton to that orbit. If a LSS is ~85t, then a similarly built SH (~1.5X larger) should be ~130t—meaning as an SSTO, SHe can put ~96t into that orbit. So the payload/upper stage has to do the rest.

With a 40t dry partial SS (half size) with 3 vac raptors, the expendable can throw 53t of additional payload to Earth escape (~TLI). Not sure what the TLI hit is for SH RTLS, if it's still 40%... that's >30t to TLI (<cough> Orion</cough>).

SH is kind of remarkable—and it really is the easy part of the system. SHe with a expendable upper stage can pretty easily hit/exceed SLS Block 2 level payloads to TLI—and SpaceX could still make money selling those launches for 10X less than an SLS launch (1/10th of the very best case SLS cost by the usual SLS fan posters, way less than the actual cost of SLS).

 

 

34 engines at <$1m each plus tanks so cheap SpaceX can afford to build them as GSE instead of COTS. For 300mt+ to LEO.

And because private capital never has to be paid back, only the interest needs to be included in the launch price. This may be an unfair way of comparing SLS to SSSH, but taxpayers have different standards to private investors.

And whereas STS required rapid reusability to be truly revolutionary, SSSH is already revolutionary even before considering the benefits of reusability.

[tater]

1 hour ago, RCgothic said:

34 engines at <$1m each plus tanks so cheap SpaceX can afford to build them as GSE instead of COTS. For 300mt+ to LEO.

And because private capital never has to be paid back, only the interest needs to be included in the launch price. This may be an unfair way of comparing SLS to SSSH, but taxpayers have different standards to private investors.

And whereas STS required rapid reusability to be truly revolutionary, SSSH is already revolutionary even before considering the benefits of reusability.

Yeah.

Since LSS is a thing (technically part of Artemis now, so this is all on-topic), I supposed some of the $2.9B can be folded in as dev cost from the taxpayer, and added pro-rata to future launches—of course then the SLS/Orion dev costs would then need to also be added in. I am firmly of the belief that for a commercial vehicle, as far as NASA missions are concerned, all that matters is what NASA actually pays. For a vehicle NASA devs like SLS/Orion, NASA "actually pays" every penny they spent on it. How many launches this get amortized would be a good idea, and 10 is certainly easy for math reasons, and I think they have started ordering parts for that many. So total dev/production dollars divided by 10 launches. Note that for Orion this certain needs to include all Constellation funding as Orion flew early in the post-Constellation era on EFT-1 since it was already developed.

So a single crew landing from SpaceX will cost NASA $2.9B. Of course I'm sure the unit cost on further landings would be lower, so if they continued for more it'd be what NASA paid ($2.9B), plus what they pay for each future mission (divided by the number of missions for a better per flight cost).

Honestly, SS/SH is probably cheap enough they can use expendable vehicles to retank a test LSS.

[tater]

 

[RealKerbal3x]

Why do I feel like SpaceX sending an uncrewed Starship test mission to Mars before Artemis astronauts walk on the Moon is entirely possible at this point? There's every chance that the technologies required for Starship to do that are ready by that time - and the date of a crewed return to the Moon seems to be steadily slipping.

Edited May 13, 2021 by RealKerbal3x
less repetitive wording

[tater]

SpaceX is moving forward with SS regardless.

If they succeed at almost any level with it, it makes the other vehicles (both launch and landers) look comical.

The pork must flow.

[YNM]

1 hour ago, RealKerbal3x said:

Why do I feel like SpaceX sending an uncrewed Starship test mission to Mars before Artemis astronauts walk on the Moon is entirely possible at this point?

Or LM-9 based architecture...

[StrandedonEarth]

The Pork is strong with this one...

Oh geez, that just brings up more....

SLS: “The Pork is strong in my family. My predecessor had it, my ULA cousins had it....

[cubinator]

2 hours ago, RealKerbal3x said:

Why do I feel like SpaceX sending an uncrewed Starship test mission to Mars before Artemis astronauts walk on the Moon is entirely possible at this point? There's every chance that the technologies required for Starship to do that are ready by that time - and the date of a crewed return to the Moon seems to be steadily slipping.

SpaceX sending a Starship to land on the Moon requires orbital refueling, yeah? So they're going to top up a Starship fully as part of their refueling tests, and where else to send an uncrewed prototype Starship full of fuel?

[Beccab]

9 hours ago, cubinator said:

SpaceX sending a Starship to land on the Moon requires orbital refueling, yeah?

SpaceX was also awarded a nasa contract to demonstrate large scale in orbit refuelling with cryo propellants before the end of 2022, so it's gonna be quite soon too

[tater]

If the goal is a landing test, with cargo (leaving the test LSS on the surface) and 80t (dry) LSS only needs 340t of props. An 80t cargo LSS could deliver 100t cargo with just 750t  of props (if it's 100t dry, then 80t of cargo).

Bottom line is that a test lander could deliver a huge amount to the Moon with only a few retanks.

Under the assumption that it takes many launches to make SS reuse work, one testing method would be to fly Starlinks. Downside is that it holds so many manufacturing enough might be a problem for any rapid testing cadence.

Another mechanism would be to build a LSS test article (maybe no life support, but cargo, etc). Send that up fairly early, and leave it in LEO.use it as a refilling target, when it gets enough props, send it to the Moon. Having transfered props, it likely hits an HLS milestone, and they get some cash from NASA. Land? More cash. It's a way to retroactively get paid for testing.

 

[sevenperforce]

Since we haven't been hating on SLS enough lately....

I was racking my brain to come up with a way to actually make use of the RS-25's abilities. What if you put two RS-25s on a narrower, shorter SLS core and then crossfed them from auxiliary tanks on top of kerolox (or even solid) boosters? You'd get the benefit of the high specific impulse all the way from sea level to orbit but you wouldn't be dragging that heavy empty core almost all the way to orbit.

[RCgothic]

The problem with cross-feed has always been seamless switchover between tanks, and it just occurred to me that there is a company that knows how to do that.

SpaceX swaps the final raptor on starship from main to header tanks before cutoff.

[sevenperforce]

2 hours ago, RCgothic said:

The problem with cross-feed has always been seamless switchover between tanks, and it just occurred to me that there is a company that knows how to do that.

SpaceX swaps the final raptor on starship from main to header tanks before cutoff.

Dumb question, perhaps, but why does it have to cross feed at the engine? Why can’t you have tanks that run pressed feed lines to the other tanks?

[cubinator]

4 hours ago, RCgothic said:

The problem with cross-feed has always been seamless switchover between tanks, and it just occurred to me that there is a company that knows how to do that.

SpaceX swaps the final raptor on starship from main to header tanks before cutoff.

ASPARAGUS STARSHIP

ASPARAGUS STARSHIP

[RyanRising]

6 hours ago, RCgothic said:

The problem with cross-feed has always been seamless switchover between tanks, and it just occurred to me that there is a company that knows how to do that.

SpaceX swaps the final raptor on starship from main to header tanks before cutoff.

They do? I thought the ascent burn was entirely on the main tanks. If that’s true, it would seem they solved one of those huge “just not worth it” things in rocketry totally incidentally.

[Ultimate Steve]

Do you think, if they ever do Mars missions, that they will ship complete spare Raptors there in advance in case they have issues?

Edit: Now that I think about it they could probably also swap with the cargo ships if stuff goes wrong, disregard.

Edited May 15, 2021 by Ultimate Steve

[sevenperforce]

Okay, hear me out.

ROMBUS + New Glenn.

Take a Delta IV common booster core and put two RS-25s underneath it. Yes, you'll need a fairing. No big deal.

Build two Delta IV CBC hydrogen tanks without the corresponding LOX tank and put Delta IV Heavy nosecones on the top and bottom. Mount those on the sides.

Take two New Glenn first stages, add nose cones, and mount them on the sides (at 90 degrees to the hydrogen tanks) with their methane tanks partially empty.

Crossfeed the New Glenn LOX tanks into the Delta IV CBC LOX tanks, and crossfeed the side-mounted Delta IV hydrogen tanks into the Delta IV CBC hydrogen tank.

Centaur V on top with your TLI payload.

What does that send to TLI? Probably nearly as much as SLS Block 1B, with only two RS-25s, only two RL-10s, and recoverable boosters.

Edited May 15, 2021 by sevenperforce

[tater]

20 minutes ago, sevenperforce said:

What does that send to TLI? Probably nearly as much as SLS Block 1B, with only two RS-25s, only two RL-10s, and recoverable boosters.

An expendable SS/SH ("SS" in this case being literally a regular looking 9m upper stage) can throw ~20% more to TLI than the notional SLS Block 2.

Assuming a 40% reduction for RTLS, it can recover the booster and send 86% of Block 1B (~31t). If they could ever land the booster down range, it can equal Block 1B.

That was a quick and dirty calc I did, might be possible to optimize it.

Edited May 15, 2021 by tater

[RCgothic]

50 minutes ago, sevenperforce said:

Okay, hear me out.

ROMBUS + New Glenn.

Take a Delta IV common booster core and put two RS-25s underneath it. Yes, you'll need a fairing. No big deal.

Build two Delta IV CBC hydrogen tanks without the corresponding LOX tank and put Delta IV Heavy nosecones on the top and bottom. Mount those on the sides.

Take two New Glenn first stages, add nose cones, and mount them on the sides (at 90 degrees to the hydrogen tanks) with their methane tanks partially empty.

Crossfeed the New Glenn LOX tanks into the Delta IV CBC LOX tanks, and crossfeed the side-mounted Delta IV hydrogen tanks into the Delta IV CBC hydrogen tank.

Centaur V on top with your TLI payload.

What does that send to TLI? Probably nearly as much as SLS Block 1B, with only two RS-25s, only two RL-10s, and recoverable boosters.

Wow, what a frankenrocket.