totm dec 2023 Artemis Discussion Thread

[tater]

1 minute ago, cubinator said:

9348 m/s

Which is lower than what it has with CH₄ and LOX (10,120 m/s with 1200t props, 85t dry, and I_sp of 380)

Low density kills H2 as a good prop to drag up from Earth.

CH4 has an Isp of ~640 with NTP, and the density is 423.8kg/m3. Using your same volume and 85t dry mass, I get a NTR SS using CH₄ having 14,830 m/s.

Surprisingly good. Dump the nose off the front, use as a tug stage, and you could give a full SS with 150t cargo ~2400 m/s of dv, and retain >3500m/s of dv to get back to LEO, etc. SS then only has to use ~1500-2000 m/s for a typical Mars transfer (or 800 m/s for TLI). Such a fully loaded SS only has 6,550 m/s of dv to start. If the cargo mass was reduced to closer to 100t, that SS could land on Mars with enough propellant to come back to Earth with no ISRU required. A huge risk mitigation—perhaps this is an early mission where the cargo IS the ISRU gear, or setting it up having landed a cargo ship that will never return anyway.

[Guest The Doodling Astronaut2]

Just now, tater said:

Which is lower than what it has with CH₄ and LOX (10,120 m/s with 1200t props, 85t dry, and I_sp of 380)

Low density kills H2 as a good prop to drag up from Earth.

CH4 has an Isp of ~640 with NTP, and the density is 423.8kg/m3. Using your same volume and 85t dry mass, I get a NTR SS using CH₄ having 14,830 m/s.

Surprisingly good. Dump the nose off the front, use as a tug stage, and you could give a full SS with 150t cargo ~2400 m/s of dv, and retain >3500m/s of dv to get back to LEO, etc. SS then only has to use ~1500-2000 m/s for a typical Mars transfer (or 800 m/s for TLI). Such a fully loaded SS only has 6,550 m/s of dv to start. If the cargo mass was reduced to closer to 100t, that SS could land on Mars with enough propellant to come back to Earth with no ISRU required. A huge risk mitigation—perhaps this is an early mission where the cargo IS the ISRU gear, or setting it up having landed a cargo ship that will never return anyway.

Whats the approximate amount of d/V for a full lunar mission for the lander then?

[tater]

1 hour ago, The Doodling Astronaut2 said:

Whats the approximate amount of d/V for a full lunar mission for the lander then?

@sevenperforce used 85t for the dry mass I believe. That sounds plausible.

You can throw numbers into a dv calculator and see what you get (or make a spreadsheet):

http://www.strout.net/info/science/delta-v/

If you assume 85t dry, and 15t of cargo/etc, then at the point in LEO where it is tanked up (1200t props), it has a wet mass of 1300t, and 9558 m/s. Surface to LLO is 2km/s, and TEI is ~900 m/s, so it needs to reserve around 2900 m/s to leave (a little less if it is going to Gateway, but margin is good). That 2900 is just 105t of props (calling the dry mass there 85t, cargo left on the surface). That shows us the dv it has reserving the 100t of SS and cargo, plus the 105t of ascent props, for a total of 205t we need on the surface for a round trip.

That leaves 6883 m/s. TLI is 3.2km/s, TLI to LLO is 0.9km/s, and LLO to the surface is 2km/s. 3.2+0.9+2= 6100 m/s. So in fact, SS could take more cargo to the surface.

I know that that vid (with @sevenperforce's help) considered sending LSS to GEO for a retanking op, and it's definitely short for propulsive LEO circularization. Aerobraking seems plausible, but for minimal stress and for a vehicle with crew in it, it's probably too many passes (heading through the Van Allen belts every time, too). Maybe the retanking in GEO is the way to go... The goal there was to dump Orion and use CCVs. As long as Orion is part of the thing, then Orion can deal with that aspect.

Edited April 21, 2021 by tater

[tater]

A tug with an IDA is looking smarter and smarter to me. Take the Commercial Crew vehicle with you. Yeah, decreases payload mass a touch, not a concern. Have another IDA on the side for LSS docking.

Meet CCV, dock, go to the Moon. Transfer crew to LSS, fly mission, return to tug, head home. Tug propulsively enters LEO.

The huge benefit is abort contingencies. You have the crew return vehicle with you. No need for phasing to rendevous, and any vehicle failure en route... leads to some Apollo 13 issue, but you have the tug, and the Dragon/Starliner/Dream Chaser with their own small dv. Options. If the TPS was improved for direct EDL, tug return trajectory can be shaped for direct return, and only altered closer to Earth so an en-route failure means the crew can use the capsule as a lifeboat.

Stick Orion on there if you feel like lighting a billion dollars on fire.

[sevenperforce]

15 hours ago, tater said:

I know that that vid (with @sevenperforce's help) considered sending LSS to GEO for a retanking op, and it's definitely short for propulsive LEO circularization. Aerobraking seems plausible, but for minimal stress and for a vehicle with crew in it, it's probably too many passes (heading through the Van Allen belts every time, too). Maybe the retanking in GEO is the way to go... The goal there was to dump Orion and use CCVs. As long as Orion is part of the thing, then Orion can deal with that aspect.

Well, that concept would do retanking in GTO, not GEO, which means you have phasing concerns and the same Van Allen belt issue. 

There are a lot of mission architectures which would be quite efficient but wouldn't be acceptable to NASA. Nor should they be. You need an intact abort mode at all times -- or, if that's not possible, you need an intact abort mode for as much of the time as possible. And once you have crew on a vehicle, you want as few "mission-critical" steps as possible. So NASA would not be okay with a mission architecture that requires a retanking event before the crew can come home. You wouldn't want to end up with a situation where the crew are stuck for an extra week in a prop-depleted Lunar Starship, floating in GTO, because something went wrong with GSE and the retanking mission got delayed.

That doesn't mean you can't have a retanking event with crew on board. It just means that you have to do it in such a way that an intact abort mode is preserved if the retanking goes wrong. For example, if you want to do Artemis with Crew Dragon and Lunar Starship, you could do this:

1. Launch LS to LEO
2. Retank LS
3. Launch a Tanker Starship (TS) to LEO
4. Retank TS
5. Launch Crew Dragon to LEO on Falcon 9
6. Crew Dragon docks to LS, crew transfers
7. TS and LS both burn for TLI with a free-return
8. Immediately after the TLI burn, TS and LS rendezvous
9. TS retanks LS
10. TS makes its loop around the moon and then re-enters and lands at Boca Chica
11. LS performs lunar mission and propulsive return to LEO
12. Crew Dragon docks to LS, crew transfers
13. Crew Dragon deorbits with crew
14. Return to step 2

This way if there is a problem somewhere in steps 7-9, LS still has more than enough propellant to cancel the landing and just return to LEO propulsively.

15 minutes ago, tater said:

A tug with an IDA is looking smarter and smarter to me. Take the Commercial Crew vehicle with you. Yeah, decreases payload mass a touch, not a concern.

The huge benefit is abort contingencies. You have the crew return vehicle with you. No need for phasing to rendevous, and any vehicle failure en route... leads to some Apollo 13 issue, but you have the tug, and the Dragon/Starliner/Dream Chaser with their own small dv. Options. If the TPS was improved for direct EDL, tug return trajectory can be shaped for direct return, and only altered closer to Earth so an en-route failure means the crew can use the capsule as a lifeboat.

The "retank-after-TLI" option above would work perfectly well with "take-the-CCV-with-you" architecture.

[tater]

2 minutes ago, sevenperforce said:

The "retank-after-TLI" option above would work perfectly well with "take-the-CCV-with-you" architecture.

True, but it looks like such a tug can do it without retanking at all.

An 80t SS tug (including the CCV) has 10,300 m/s dv.

RT to LLO is 8200 m/s.

Make the tug+CCV 100t, and you get the same 9558 m/s as a vanilla SS—which BTW would be a LSS with a CCV on top, too.

[sevenperforce]

3 minutes ago, tater said:

True, but it looks like such a tug can do it without retanking at all.

An 80t SS tug (including the CCV) has 10,300 m/s dv.

RT to LLO is 8200 m/s.

Make the tug+CCV 100t, and you get the same 9558 m/s as a vanilla SS—which BTW would be a LSS with a CCV on top, too.

That's fine if you want the CCV to be the primary vehicle for getting to and from the moon, but neither Starliner nor Crew Dragon are really designed for that. And it requires the creation of a third vehicle. Easier to just use Lunar Starship for everything. 

[tater]

4 minutes ago, sevenperforce said:

That's fine if you want the CCV to be the primary vehicle for getting to and from the moon, but neither Starliner nor Crew Dragon are really designed for that. And it requires the creation of a third vehicle. Easier to just use Lunar Starship for everything. 

It's just a matter of where the tanking gets done I suppose. That said, taking the CCV does provide an abort mode that does not otherwise exist. Using LSS alone—dock in LEO, then go, then return, dock in LEO, and EDL in CCV—means that any LSS failure en-route is a LOM/LOC. If the TPS can actually deal with direct entry, the CCVs could still reenter, or have some % chance of doing so if it is marginal.

TLI on free return, correct and do LLO, return to direct entry trajectory, correct to LEO.

They had said Dragon could deal with that sort of entry speed, too bad they never did a test of it.

[sevenperforce]

2 minutes ago, tater said:

It's just a matter of where the tanking gets done I suppose. That said, taking the CCV does provide an abort mode that does not otherwise exist. Using LSS alone—dock in LEO, then go, then return, dock in LEO, and EDL in CCV—means that any LSS failure en-route is a LOM/LOC. If the TPS can actually deal with direct entry, the CCVs could still reenter, or have some % chance of doing so if it is marginal.

TLI on free return, correct and do LLO, return to direct entry trajectory, correct to LEO.

They had said Dragon could deal with that sort of entry speed, too bad they never did a test of it.

I don't mean using the Lunar Starship alone; I mean using the Lunar Starship as the tug.

It merely needs to have one post-TLI retank.

Exactly the same mission architecture as above, except that Crew Dragon remains attached to the Lunar Starship after step 6.

[tater]

3 hours ago, sevenperforce said:

Exactly the same mission architecture as above, except that Crew Dragon remains attached to the Lunar Starship after step 6.

Gotcha.

 

I think the following is right:

A round trip from LLO to the surface for LSS (100t including cargo) needs ~200t of props.

So if a tug could deliver the crew, and ~200t of props to LLO, LSS need never leave that frozen orbit except for a sortie to the surface.

Assume a tug is 70t including a CCV taken for the ride. It needs to reserve ~150t of propellant to propulsively return to LEO from LLO. It starts with 1200t props, burns 850t for TLI and LOI. Arrives at LLO with the crew, CCV, and 350t of props (including the 150 for return). Transfers 200t to the LSS, leaving the tug with 150t for the propulsive return to LEO.

The initial 85t LSS with 15t cargo/etc (100t total, 9558 m/s dv) lands on the Moon with about 150t of propellants left in the tanks. Drops cargo, visits the Moon, leaves with 3789 m/s of dv available. LSS burns about 100t to get to LLO. So LSS is now in LLO with ~50t of props, and the next crew delivery (the tug in  the paragraph above) will add 200t, which puts >5km/s in the tanks. Depending on the down mass of cargo brought on these sorties, the LSS could slowly gain propellant—though the best solution would be to leave all unneeded props in LLO with a depot there.

This seems like a way to get crew to LSS with no extra refilling steps. The crew docks to the already filled tug.

The lower the mass the tug can be made, the better this ends up looking. The tug can be thinner steel, and it can launch with only vacuum Raptors (as many as it needs), also reducing mass. No worry about TWR, it can be sent with the tanks not full.

SS really does enable propellant depots in a substantial way—the trick is to transfer crew and cargo in such a way that each trip leaves some residuals at the depot.

This actually provides a space for alternate landers, as well. Design them to use the methalox infrastructure SS provides. While 50t of props is chump change for LSS, that's more than a full load for other lander options. What's the smallest lander that could taxi 7 people to the surface and back (1 stage)? A 50t lander that is 15t dry mass plus cargo can easily do the round trip. Maybe one of the other contractors comes up with such a lander

 

 

 

Edited April 21, 2021 by tater

[RCgothic]

3 hours ago, Deller said:

I think this mission will be successful overall. But can someone remind me of the silt? Is this mission related to another mission for the next man landing on the moon? Or am I confusing something?

The Artemis Program is about landing the next humans on the moon.

Artemis I will be an uncrewed test flight of the Orion capsule and SLS Block 1 rocket, roughly analogous to Apollo 4/6.

Artemis II will be a crewed flight past the moon, roughly analogous to Apollo 8.

The timeline for the first crewed landing is at this point a little unclear. It might be Artemis III or IV depending on the availability of the lander.

Launches for the Gateway station and lander supporting the crewed missions won't be assigned a main Artemis number as far as we can tell.

 

Edited April 22, 2021 by RCgothic

[tater]

https://caseyhandmer.wordpress.com/2021/03/26/lunar-starship-and-unnecessary-operational-complexity/

He's using some different numbers for dv requirements, which are useful. The NASA numbers are higher, and perhaps include margins, variability in launch timing, or define different altituded for LLO, etc? 3.94 km/s vs the 4.1 on the NASA doc. 1.72km/s to or from the surface vs 2 is a large difference.

 

 

[YNM]

On 4/22/2021 at 9:24 PM, RCgothic said:

Artemis I will be an uncrewed test flight of the Orion capsule and SLS Block 1 rocket, roughly analogous to Apollo 4/6.

Wait... I thought it was straight to Apollo 8 style mission ?

[RealKerbal3x]

48 minutes ago, YNM said:

Wait... I thought it was straight to Apollo 8 style mission ?

Artemis 1 is similar to Apollo 8 (lunar free return trajectory) but uncrewed.

I did a big dumb, see @tater's post below instead.

Edited April 24, 2021 by RealKerbal3x

[tater]

3 minutes ago, RealKerbal3x said:

Artemis 1 is similar to Apollo 8 (lunar free return trajectory) but uncrewed.

Apollo 8 was not a free return flyby, they entered LLO, did 10 orbits, then burned for TEI and headed home.

They did a TLI into a free return, but this was altered with a mid course correction to set up for LOI.

At no point will any SLS/Orion mission ever even replicate Apollo 8, it is incapable of it (sadly).

[YNM]

2 minutes ago, tater said:

At no point will any SLS/Orion mission ever even replicate Apollo 8, it is incapable of it (sadly).

So what would they do with Artemis 1 ? Just unmanned launch check ? I mean it'd be better to see if it actually works first...

[tater]

1 minute ago, YNM said:

So what would they do with Artemis 1 ? Just unmanned launch check ? I mean it'd be better to see if it actually works first...

The primary Artemis I goal will be testing EDL direct from the Moon, I expect. The current mission I believe has changed from a flyby to entering a distant lunar orbit (unsure if it is actually NRHO, or a related orbit).

Right now Artemis II is a dumb flyby mission, though that keeps changing. Interestingly, they have to do 2 TLI burns (Oberth) because ICPS is lousy, and Orion is bloated.

[wumpus]

12 minutes ago, tater said:

The primary Artemis I goal will be testing EDL direct from the Moon, I expect. The current mission I believe has changed from a flyby to entering a distant lunar orbit (unsure if it is actually NRHO, or a related orbit).

Right now Artemis II is a dumb flyby mission, though that keeps changing. Interestingly, they have to do 2 TLI burns (Oberth) because ICPS is lousy, and Orion is bloated.

Wouldn't you want to change Artemis II to *anything* but a dumb flyby mission?  Simply to avoid the embarrasment of burning multiple billions of dollars on SLS to do a mission that Falcon Heavy can do without modification (other than whatever human rating FH would take).

[YNM]

18 minutes ago, tater said:

The current mission I believe has changed from a flyby to entering a distant lunar orbit (unsure if it is actually NRHO, or a related orbit).

Ah. Well so only on the "not LLO" part to be "not Apollo 8". I guess expect no close-up views of the Moon and no impressive Earth-rise.

But given they're only going to do NRHO for Gateway it's pretty good to get some idea of what it'd look like from there I suppose.

[RealKerbal3x]

34 minutes ago, tater said:

Apollo 8 was not a free return flyby, they entered LLO, did 10 orbits, then burned for TEI and headed home.

They did a TLI into a free return, but this was altered with a mid course correction to set up for LOI.

At no point will any SLS/Orion mission ever even replicate Apollo 8, it is incapable of it (sadly).

Darnit, looks like I misremembered again. I'll just edit my post to avoid any confusion.

[tater]

4 minutes ago, RealKerbal3x said:

Darnit, looks like I misremembered again. I'll just edit my post to avoid any confusion.

It's changed a few times. Who knows what it will be in a month.

 

[RCgothic]

Well I did say roughly analogous, I didn't mean identical.

Artemis I is basically a high altitude uncrewed test flight of a new system. So were Apollo 4 and 6.

Artemis II takes crew to/past the moon but not to the surface. So did Apollo 8. Apollo 10 had a dress rehearsal with a lander that isn't planned at this stage.

[tater]

2 minutes ago, RCgothic said:

Well I did say roughly analogous, I didn't mean identical.

Artemis I is basically a high altitude uncrewed test flight of a new system. So were Apollo 4 and 6.

Artemis II takes crew to/past the moon but not to the surface. So did Apollo 8. Apollo 10 had a dress rehearsal with a lander that isn't planned at this stage.

Wasn't meant in a snippy way at you, sorry if it came off like that... it's more a snippy response to... SLS/Orion

 

[YNM]

18 hours ago, tater said:

Right now Artemis II is a dumb flyby mission, though that keeps changing. Interestingly, they have to do 2 TLI burns (Oberth) because ICPS is lousy, and Orion is bloated.

Actually, thinking about it, if they're planning to fly them by 2022/2023, couldn't they plan it to test it with Starship HLS in, maybe HEO ? That way at least it's not a repeat of Artemis 1, and it actually test the interface before the actual landing mission...

[sevenperforce]

On 4/24/2021 at 1:42 PM, tater said:

The primary Artemis I goal will be testing EDL direct from the Moon, I expect. The current mission I believe has changed from a flyby to entering a distant lunar orbit (unsure if it is actually NRHO, or a related orbit).

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. After six days in the distant orbit, it will lower its perilune and do another Oberth burn to get to Earth entry interface.

On 4/24/2021 at 1:42 PM, tater said:

Right now Artemis II is a dumb flyby mission, though that keeps changing. Interestingly, they have to do 2 TLI burns (Oberth) because ICPS is lousy, and Orion is bloated.

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.