totm dec 2023 Artemis Discussion Thread

[Exoscientist]

 

My main objection to the Starship HLS is I really don’t like the 8 to 16 refueling flights needed for a single mission. In my mind, a Moon rocket should be A Moon rocket(singular). 

I don’t remember seeing this when it was first announced but Boeing has proposed a single launch architecture for Artemis:

Boeing aims for Moon landing in 'fewer steps'
Published
6 November 2019
https://www.bbc.com/news/science-environment-50322402#

 No $3 billion Starship or $4 billion lunar Gateway required. Of course being Old Space, Boeing would find a way to charge NASA a billion dollars for the lander anyway, no mater how much smaller it was than the Starship lander(see my sig file.)

Robert Clark

 

Edited September 29, 2023 by Exoscientist

[tater]

10 minutes ago, Exoscientist said:

My main objection to the Starship HLS is I really don’t like the 8 to 16 refueling flights needed for a single mission. In my mind, a Moon rocket should be A Moon rocket(singular). 

I don’t remember seeing this when it was first announced but Boeing has proposed a single launch architecture for Artemis:

Boeing aims for Moon landing in 'fewer steps'
Published
6 November 2019
https://www.bbc.com/news/science-environment-50322402#

 No $3 billion Starship or $4 billion lunar Gateway required. Of course being Old Space, Boeing would find a way to charge NASA a billion dollars for the lander anyway, no mater how much smaller it was than the Starship lander(see my sig file.)

Not sure why this text is gray and hard to read. Is the default color changed?

A few points.

1. That article mentions no conops I can see, except it somehow involves Starliner tech—an odd choice because, well, Starliner? LOL. get back to me when it's actually operational and not plagued with problems.

2. Where is this mythical Boeing lander, and how does it get to the Moon, and have the dv for a Gateway RT in 2 stages? Any such lander exceeds what SLS can throw to Gateway—and it's worse because it must use storable props, since There's no possible way 2 SLS launches happen the short distance apart required for a 2 SLS mission and cryos.

The 2 above alone make SLS only a nonstarter—and it's a lie it is single launch. SLS, even the mythical Block 2 cannot do a lunar mission. Not in 2025, not ever. Even if it could, it cannot do the desired mission (long duration, >2 astronauts after the first test landing).

SLS is a rocket to nowhere, nothing changes that, because math.

As to Starship, dunno where you are getting 8-16 refilling operations.

Even a stretched LSS with 1600t of props vs 1200t, and delivery at 200+ tons per tanker sets the max at 6/8 (normal/stretch).

Expended payload is 250-300t. So possibly as few as 3 refills (LSS gets to LEO with 300t residual, then 3 refills). The nominal 1200t props variant can do LEO to Gateway, then a RT to the surface. with residuals.

SLS can do zero lunar surface missions with 1 SLS, 0 with 2 SLS, SLS is useless. And expensive.

[tater]

The NASA estimated mass for a 2-stage, Gateway compliant lander is a min of 41t, a maximum of 50t, and the in between possibilities are between those values.

Block 1B cargo version is now claimed to be 42t to TLI. So it's possible the lowest mass lander might work, unless in order to use the lowest mass ascent stage, you need a higher mass descent stage. Basically this is only possible in that special case of lowest mass everything somehow works.

If this is possible, then you could do an SLS mission in 2 launches. There is no possible way to do it in 1 launch, that's not a thing. The lander would have to have a dwell time at Gateway of many months, possibly over a year. Don't think Starliner is speced out for that.

So now we have the cost an SLS Block 1B, which is presumably higher than B1, so $5+ billion including the lander (no way lander is not at least $1B, as Orion CSM is >$1B), plus a B1 ($4.1B?). So 2 such SLS flights, gets us boots on the Moon for just ~$10B a mission?

 

[SunlitZelkova]

15 hours ago, Exoscientist said:

My main objection to the Starship HLS is I really don’t like the 8 to 16 refueling flights needed for a single mission. In my mind, a Moon rocket should be A Moon rocket(singular). 

I don’t remember seeing this when it was first announced but Boeing has proposed a single launch architecture for Artemis:

Boeing aims for Moon landing in 'fewer steps'
Published
6 November 2019
https://www.bbc.com/news/science-environment-50322402#

 No $3 billion Starship or $4 billion lunar Gateway required. Of course being Old Space, Boeing would find a way to charge NASA a billion dollars for the lander anyway, no mater how much smaller it was than the Starship lander(see my sig file.)

Robert Clark

Refueling is necessary to reuse the lander, lowering cost. Having a singular Moon rocket would mean building a new spacecraft each time and throwing it away, something unviable in the long term.

Artemis is trying to build a lunar base, and to do that within a realistic budget, you need to reuse stuff.

Is it a little dangerous? Yes, but I don’t think it is any more dangerous than a singular Moon rocket.

It’s just a matter of deciding what is dangerous. With reuse, you leave the lander up there for a long time. You can’t inspect every component after each flight in the same way you can with a Space Shuttle returning to Earth, so something could fail due to prolonged use.

But with a singular Moon rocket, you are building a brand new spacecraft each time. There are bound to be defects eventually, as happened with Apollo 13. Note that most spacecraft have been lost to production defects, like Soyuz 1, Soyuz 11, Apollo 1, and Apollo 13. Challenger and Columbia were not lost due to a problem with the vehicle itself, but rather external damage.

Perhaps someday a lunar dockyard could be built for looking over Starship HLS’ in detail.

[magnemoe]

8 hours ago, SunlitZelkova said:

Refueling is necessary to reuse the lander, lowering cost. Having a singular Moon rocket would mean building a new spacecraft each time and throwing it away, something unviable in the long term.

Artemis is trying to build a lunar base, and to do that within a realistic budget, you need to reuse stuff.

Is it a little dangerous? Yes, but I don’t think it is any more dangerous than a singular Moon rocket.

It’s just a matter of deciding what is dangerous. With reuse, you leave the lander up there for a long time. You can’t inspect every component after each flight in the same way you can with a Space Shuttle returning to Earth, so something could fail due to prolonged use.

But with a singular Moon rocket, you are building a brand new spacecraft each time. There are bound to be defects eventually, as happened with Apollo 13. Note that most spacecraft have been lost to production defects, like Soyuz 1, Soyuz 11, Apollo 1, and Apollo 13. Challenger and Columbia were not lost due to a problem with the vehicle itself, but rather external damage.

Perhaps someday a lunar dockyard could be built for looking over Starship HLS’ in detail.

My issue with Starship is that its way overkill for an 3-4 man moon landing for 14 days. But if that is cheaper go for it. 
Its a but like you are an trucker with an 18 wheeler, your other car is an small car. You need an new sofa so you pick it up in the huge truck. Yes the truck is overkill but renting an wan is more expensive. 

[tater]

2 hours ago, magnemoe said:

Its a but like you are an trucker with an 18 wheeler, your other car is an small car. You need an new sofa so you pick it up in the huge truck. Yes the truck is overkill but renting an wan is more expensive. 

Or flying an airliner on a long haul, then throwing it away and flying a new one back home. If there was a smaller, cheaper aircraft, the smaller cheaper one would make more sense if you were going to throw it away... but buying a ticket—even the most expensive "stateroom" first class—on a reusable airliner, or even renting an entire aircraft for the flight is cheaper than buying 1-2 and throwing them away.

All that matters is cost per seat.

[Exoscientist]

On 9/28/2023 at 3:38 PM, tater said:

The NASA estimated mass for a 2-stage, Gateway compliant lander is a min of 41t, a maximum of 50t, and the in between possibilities are between those values.

Block 1B cargo version is now claimed to be 42t to TLI. So it's possible the lowest mass lander might work, unless in order to use the lowest mass ascent stage, you need a higher mass descent stage. Basically this is only possible in that special case of lowest mass everything somehow works.

If this is possible, then you could do an SLS mission in 2 launches. There is no possible way to do it in 1 launch, that's not a thing. The lander would have to have a dwell time at Gateway of many months, possibly over a year. Don't think Starliner is speced out for that.

So now we have the cost an SLS Block 1B, which is presumably higher than B1, so $5+ billion including the lander (no way lander is not at least $1B, as Orion CSM is >$1B), plus a B1 ($4.1B?). So 2 such SLS flights, gets us boots on the Moon for just ~$10B a mission?

 

 

 Rereading that link about the Being lunar lander I see I took it to be “single launch” because it said the lunar lander would be launched on a single launch of the SLS. But what about the Orion and Service Module? You can not do a second SLS launch to carry them because it would take a full year and more likely two years to do a second launch of the SLS. Perhaps they meant them to be launched separately on the Falcon Heavy? However, they meant to do it that is a major omission in their proposal.

 Nevertheless, it is possible to do a single launch of the SLS with a light-weight Apollo-sized lander with all the components of Orion capsule/Service Module/lunar lander all carried on that one single SLS launch.

 The NRHO was chosen because it has a lower delta-v requirement to get there than going to low lunar orbit. Here’s the the delta-v requirements:

 The second group of delta-v’s shows the delta-v to NRHO as 0.45 km/s and the delta-v to and from the lunar surface from NRHO as 2.75 km/s, or 5.5 km/s round trip.

 I’ve seen various numbers for the Orion and service module dry mass and propellant mass. I’ll use 16.5 total dry mass for the Orion+service module together, and 10 tons propellant mass.

 Then using 7 tons of Service module propellant to get the Orion/Service Module/lunar lander to NRHO after placed on TLI trajectory by the EUS, for the 16.5 ton Orion/Service Module dry mass, and 15 tons gross mass Apollo-sized lander with 3 tons left over for the return trip: we get:

320*9.81Ln(1 + 7/(16.5 + 15 + 3)) = 580 m/s, or 0.58 km/s, sufficient for placing in the NRHO orbit.

 Then for 3 tons left over used for the return trip, after the lander is jettisoned, we get:

320*9.81Ln(1 + 3/16.5) = 520 m/s, 0.52 km/s, sufficient for return.

 Now for the  ca. 15 ton gross mass lander, because of the higher delta- v needed from NRHO we’ll use hydrolox rather than storable propellant stage. The Ariane 4 hydrolox upper stage had a 11.8 ton propellant mass and 1.2 ton dry mass. We’ll use a 2 ton dry mass of the crew module:

 Then using the max 465 s Isp of the RL-10 engine we get:

465*9.81Ln(1 + 11.8/(1.2 + 2)) = 7,000 m/s, 7 km/s. This is quite a bit higher than the 5.5 km/s needed for the round trip from NRHO to the lunar surface and back again. But it uses hydrolox propellant so needs extra mass for low-boiloff tech.

 The crew module mass could be higher if we used two hydrolox stages, but this single stage version serves as a proof-of-principle.

 This shows a single launch mission is doable if going to NRHO, but it is not my preferred plan. A complete orbit around the Moon at NRHO altitude takes two weeks. This means the lander has to remain on the Moon for two weeks until the Orion comes back around to be over the landing site.

 If instead the Orion was at low lunar orbit it takes two hours to complete an orbit and the lunar lander could launch every two hours to rendezvous with the Orion.

 

  Robert Clark

Edited September 30, 2023 by Exoscientist

[SunlitZelkova]

47 minutes ago, Exoscientist said:

 

 Rereading that link about the Being lunar lander I see I took it to be “single launch” because it said the lunar lander would be launched on a single launch of the SLS. But what about the Orion and Service Module? You can not do a second SLS launch to carry them because it would take a full year and more likely two years to do a second launch of the SLS. Perhaps they meant them to be launched separately on the Falcon Heavy? However, they meant to do it that is a major omission in their proposal.

 Nevertheless, it is possible to do a single launch of the SLS with a light-weight Apollo-sized lander with all the components of Orion capsule/Service Module/lunar lander all carried on that one single SLS launch.

 The NRHO was chosen because it has a lower delta-v requirement to get there than going to low lunar orbit. Here’s the the delta-v requirements:

 The second group of delta-v’s shows the delta-v to NRHO as 0.45 km/s and the delta-v to and from the lunar surface from NRHO as 2.75 km/s, or 5.5 km/s round trip.

 I’ve seen various numbers for the Orion and service module dry mass and propellant mass. I’ll use 16.5 total dry mass for the Orion+service module together, and 10 tons propellant mass.

 Then using 7 tons of Service module propellant to get the Orion/Service Module/lunar lander to NRHO after placed on TLI trajectory by the EUS, for the 16.5 ton Orion/Service Module dry mass, and 15 tons gross mass Apollo-sized lander with 3 tons left over for the return trip: we get:

320*9.81Ln(1 + 7/(16.5 + 15 + 3)) = 580 m/s, or 0.58 km/s, sufficient for placing in the NRHO orbit.

 Then for 3 tons left over used for the return tip, after the lander is jettisoned, we get:

320*9.81Ln(1 + 3/16.5) = 520 m/s, 0.52 km/s, sufficient for return.

 Now for the  ca. 15 ton gross mass lander, because of the higher delta- v needed from NRHO we’ll use hydrolox rather than storable propellant stage. The Ariane 4 hydrolox upper stage had a 11.8 ton propellant mass and 1.2 ton dry mass. We’ll use a 2 ton dry mass of the crew module:

 Then using the max 465 s Isp of the RL-10 engine we get:

465*9.81Ln(1 + 11.8/(1.2 + 2)) = 7,000 m/s, 7 km/s. This is quite a bit higher than the 5.5 km/s needed for the round trip from NRHO to the lunar surface and back again. But it uses hydrolox propellant so needs extra mass for low-boiloff tech.

 The crew module mass could be higher if we used two hydrolox stages, but this single stage version serves as a proof-of-principle.

 This shows a single launch mission is doable if going to NRHO, but it is not my preferred plan. A complete orbit around the Moon at NRHO altitude takes two weeks. This means the lander has to remain on the Moon for two weeks until the Orion comes back around to be over the landing site.

 If instead the Orion was at low lunar orbit it takes two hours to complete an orbit and the lunar lander could launch every two hours to rendezvous with the Orion.

 

  Robert Clark

SLS can not do a single launch mission without using a tiny open air lander like Gemini LOR was intended to use, and even then SLS probably would not be able to put it in an orbit where the lander could get to the surface and back.

Yes, NRHO was chosen because of a lower delta v requirement, but only because SLS can’t do anything better.

I’m sure @tater and @sevenperforce can give a much more detailed response breaking down the numbers.

[tater]

A much lighter everything can work with 42t to TLI, but that would take… decades? It’s a nonstarter.

it also results in a short sortie lander, so a totally different mission. If it uses gateway at all, lander  needs to support crew for 6.5 days or more (Phasing for an abort contingency).

[RCgothic]

Want to do it with a Boeing Lander? They don't have a lander.

Want to do it in a single launch? Can't get a meaningful mission through NRHO.

Don't want to go through NRHO? That's the only place SLS Orion can go. 

Want to do a skeletal mission? Why? Also no lander and certainly not safer.

Want to go sooner? That's not what changing the mission parameters gets.

[Meecrob]

2 hours ago, RCgothic said:

Want to do it with a Boeing Lander? They don't have a lander.

Want to do it in a single launch? Can't get a meaningful mission through NRHO.

Don't want to go through NRHO? That's the only place SLS Orion can go. 

Want to do a skeletal mission? Why? Also no lander and certainly not safer.

Want to go sooner? That's not what changing the mission parameters gets.

You don't get it, if we kitbash them all together, it will somehow be the most efficient rocket EVER!

 

Jokes aside, if I had actual solid ideas of how to save Dv or whatever, I'd be calling NASA, not telling some message board.

Edited September 30, 2023 by Meecrob

[RCgothic]

18 hours ago, magnemoe said:

My issue with Starship is that its way overkill for an 3-4 man moon landing for 14 days. But if that is cheaper go for it. 
Its a but like you are an trucker with an 18 wheeler, your other car is an small car. You need an new sofa so you pick it up in the huge truck. Yes the truck is overkill but renting an wan is more expensive. 

It may be overkill for that, but eventually the mission planners start asking "Well what isn't it overkill for?"

And that's when things get exciting. (Even more exciting).

Personally I'm never going to get excited or feel motivated to support downgrading the mission to what SLS can limp into a lunar round trip. Compared to what we could have once mission planners wake up to what we can do with Starship and the BO lander architectures? No thanks.

Even if using the current architectures takes a decade longer than an alternative (and as previously discussed it would only be the other way around), I still wouldn't make that trade. A skeletal mission could only lead to flags and footprints, disappointment, and cancellation. There's no scope for future progression.

The HLS architectures give access to the entire solar system and obsolesce the grossly over expensive SLS/Orion ESM at the same time.

There's one good part of the Artemis Programme and HLS is it.

Edited September 30, 2023 by RCgothic

[RCgothic]

On 9/28/2023 at 8:38 PM, tater said:

Block 1B cargo version is now claimed to be 42t to TLI. So it's possible the lowest mass lander might work

In order to get 41t of lander to NRHO takes ~48.5t to TLI.

[tater]

1 minute ago, RCgothic said:

In order to get 41t of lander to NRHO takes ~48.5t to TLI.

Yeah, it depends on if they claim the lander mass is already at NRHO, or that's the TLI mass. Unsure from that chart, tbh.

Even under the optimistic assumption it's TLI mass, it's basically a special case that the lowest possible mass lander might be possible with an SLS launch.

[kerbiloid]

On 9/30/2023 at 10:19 AM, RCgothic said:

Want to do it

at all?

The eccentric refuelling is da thing, if it's still on the table.

[sevenperforce]

On 9/29/2023 at 8:28 PM, Exoscientist said:

 Nevertheless, it is possible to do a single launch of the SLS with a light-weight Apollo-sized lander with all the components of Orion capsule/Service Module/lunar lander all carried on that one single SLS launch.

 The NRHO was chosen because it has a lower delta-v requirement to get there than going to low lunar orbit. Here’s the the delta-v requirements:

Spoiler

 

 The second group of delta-v’s shows the delta-v to NRHO as 0.45 km/s and the delta-v to and from the lunar surface from NRHO as 2.75 km/s, or 5.5 km/s round trip.

Yep, all correct so far. Might even be able to tighten it up slightly here and there if you're lucky.

On 9/29/2023 at 8:28 PM, Exoscientist said:

 I’ve seen various numbers for the Orion and service module dry mass and propellant mass. I’ll use 16.5 total dry mass for the Orion+service module together, and 10 tons propellant mass.

Orion's launch mass is 26.52 tonnes and its service module carries 8.6 tonnes of propellant. Are you just rounding up, or?

On 9/29/2023 at 8:28 PM, Exoscientist said:

 Then using 7 tons of Service module propellant to get the Orion/Service Module/lunar lander to NRHO after placed on TLI trajectory by the EUS, for the 16.5 ton Orion/Service Module dry mass, and 15 tons gross mass Apollo-sized lander with 3 tons left over for the return trip....

Hold up. Let's work backward. To get from NRO to an Earth return, you need 450 m/s of Δv (technically 430 m/s but I'm using your number to account for maneuvering, docking, stationkeeping, and the like). The AJ10-190 used for the Orion ESM pushes 316 seconds of I_sp, not the 320 seconds you claim in your post (the highest-performing AJ10, the 118K variant, only got 319 seconds). By the rocket equation, if you have a final mass of 17.92 tonnes (that's 26.52 less 8.6) tonnes then you'll need an initial mass of 20.72 tonnes, or 2.8 tonnes of propellant. So far so good.

How much mass can Orion brake into NRHO, then? 8.6 tonnes of propellant minus the 2.8 tonnes we'll need later leaves us with 5.8 tonnes for the braking burn. With the same 450 Δv we'll need for the return trip and 316 s I_sp, that gives us an m₁/m₀ of 0.865, meaning that those 5.8 tonnes of propellant were 13.5% of our TLI injection mass. This means our injection mass was 42.96 tonnes. That's slightly more than what Block 1B can send. The max that Block 1B can send to TLI in cargo mode is 42 tonnes, which leaves us with 15.48 tonnes of lander.

Even if we are generous and allow for 10 tonnes of lander, that's simply not enough, even with hydrolox.

(I had originally swapped dry and wet mass for Orion; fixed above and below.)

On 9/29/2023 at 8:28 PM, Exoscientist said:

The Ariane 4 hydrolox upper stage had a 11.8 ton propellant mass and 1.2 ton dry mass. We’ll use a 2 ton dry mass of the crew module....

No, the Ariane 4-3 H10-3 had a dry mass of 1.57 tonnes and carried 10.74 tonnes of props, while the H10+ variant had a dry mass of 1.74 tonnes and carried 11.06 tonnes of props. Also, these stages were powered by an HM7-B engine with a mass of 155 kg, half the weight of the RL10C-2-1 that gets the 465 seconds of specific impulse you are using below. If we go with the H10+ variant but automagically swap in the RL10C-2-1 you seem intent on using despite its high dry mass (trying to land on the moon using an RL10-C-2-1 is left as an exercise for the reader), this brings our propulsion stage mass to 12.95 tonnes. Drop your two-tonne crew module on top of that, and you get a total comanifested mass of 14.95 tonnes and 6.2 km/s of propellant. Seems like an okay start.

There's some trouble in paradise, though. You're going to need extra mass for landing legs, egress support, and low-boiloff systems. That will quickly push our mass budget over the edge. So let's go with the H10-3 stage instead: dry mass of 1.57 tonnes and 10.74 tonnes of propellant, minus the 155-kg HM7-B, plus the 301-kg RL10. To get 5.5 km/s of total Δv, those 10.74 tonnes of propellant will correspond to a total mass of 15.34 tonnes, right under what Orion can comanifest. So, what can we do with the 2.88 tonnes of payload this gives us?

Your idea is to rebuild the Standard-sized Cygnus spacecraft as a repurposed crew lander. The original Cygnus pressurized cargo module was 1500 kg, plus a 1800 kg service module that included 800 kg of hypergolic propellants for maneuvering. Rendezvous with Orion in NRHO isn't going to be possible with the RL10 engine so you'll still need the full service module. That alone is 3.3 tonnes, which is overbudget. Let's get very creative and say that we only need 150 kg of propellants for the rendezvous and we can delete some of the tanks from the Cygnus service module, further reducing its dry weight by 20 kg. That gets us down to 2,630 kg, leaving only 250 kg to work with.

I'm not sure we can get landing legs, egress systems, ECLSS, a low-boiloff system, AND multiple astronauts to fit into a 250-kg payload budget. And, as others have said, that would only be for an extreme bare-bones mission.

Finally, there's one more problem. Cygnus Standard is 5.1 meters. The Ariane H10-3 stage was 11.85 meters, including the 1.8-meter HM7-B which is shorter than the 2.19-meter RL10-C-1 (that's with its nozzle extension collapsed). All together, this frankenlander would have a height of 17.34 meters, more than double the maximum 8.4 meters of space available for co-manifested cargo on SLS Block 1B. Trying to salvage by adding an extra stage is right out.

SLS and Orion are both simply too weak to take the place of Apollo.

On 9/29/2023 at 9:18 PM, SunlitZelkova said:

I’m sure @tater and @sevenperforce can give a much more detailed response breaking down the numbers.

Well I screwed it up on the first attempt but the second edit is much improved.

Edited October 2, 2023 by sevenperforce
Wacky math

[sevenperforce]

If you wanted to do a single-launch moon mission with SLS and Orion, EUS simply doesn't have enough kick; you'd have to have the payload perform part or all of the TLI burn. Block 1B can purportedly send 105 tonnes to LEO, although in practice that's presumed to be largely propellant inside of EUS to use for the burn out of LEO. But let's imagine we did have 105 tonnes in LEO to work with. Let's also assume a lander with the same gross diameter as Cygnus above: 3.1 meters.

The RL10C-2-1 is over 2 meters wide which means you can't fit it on either side of Cygnus, but let's shove it underneath, mounted to a landing leg platform and similar structure. You can't land on an RL10, so let's put 4xBE-7s on the outside to provide for landing and allow redundancy on ascent. Your RL10 will need to burn 53 tonnes of hydrolox in order to get you to TLI, leaving you with a mass of 52 tonnes. We'll go straight to LLO because we're using the RL10 for this as well and Orion has no trouble getting out of LLO if it's dropped off there; the RL10 will burn another 9.5 tonnes of hydrolox to get 900 m/s of Δv. We drop off the 26.5-tonne Orion in LLO, reducing our mass to 16.2 tonnes before we head down to the lunar surface.  The RL10 will burn 5.4 tonnes of hydrolox to get the 1.87 km/s of Δv we need to reach the lunar surface, and our landed mass is 10.8 tonnes. We've burned 68 tonnes of hydrolox, triple the capacity of Centaur, so assuming similar balloon tanks (since the structure is provided by Cygnus and the landing legs) our tankage mass is on the order of 6.7 tonnes. Add the RL10, and we're up to 7 tonnes, leaving us with 3.8 tonnes. Let's pretend the additional structural mass for landing legs and egress system on the descent stage is zero, leaving us with all 3.8 tonnes for our ascent stage. At a presumptive 450 second specific impulse for the BE-7s, we'll need to burn 1.3 tonnes of hydrolox to get back up to Orion, leaving us with 2.5 tonnes for Cygnus, ECLSS, crew, engines, and tank dry mass. But of course Cygnus alone is already over 2.6 tonnes.

And of course figuring out how to fit a retrofit Cygnus, an RL10-C-2-1, a bevy of BE-7s, AND almost seventy tonnes of hydrolox underneath Orion in a 10m high, 8.4m dia volume is left as an exercise for the reader. Maybe we can do something fancy with drop tanks.

[tater]

1 hour ago, sevenperforce said:

If you wanted to do a single-launch moon mission with SLS and Orion,

Yeah, Orion has to go. This has always been the issue with SLS. It was paired with Orion, which Shelby fattened up so that it could only be launched by Ares I (back in the day). It stayed fat (maybe the F-35 can be called Orion, and Orion can become "Fat Amy," instead), and made SLS useless from the moment it was proposed.

[sevenperforce]

6 hours ago, tater said:

Yeah, Orion has to go. This has always been the issue with SLS. It was paired with Orion, which Shelby fattened up so that it could only be launched by Ares I (back in the day). It stayed fat (maybe the F-35 can be called Orion, and Orion can become "Fat Amy," instead), and made SLS useless from the moment it was proposed.

Well, Orion was designed as a crew ferry with just enough props to return from LLO in the Constellation mission profile, and they never updated it.

Not that they could.

I did the math a few years ago. If you're trying to do a single-launch mission architecture a la Apollo, you should try to use the orbital module for the lunar orbital insertion burn if you possibly can, even if your lander is cryogenic, because the dry mass penalty is just too great. 

[AtomicTech]

14 hours ago, tater said:

Yeah, Orion has to go. This has always been the issue with SLS. It was paired with Orion, which Shelby fattened up so that it could only be launched by Ares I (back in the day). It stayed fat (maybe the F-35 can be called Orion, and Orion can become "Fat Amy," instead), and made SLS useless from the moment it was proposed.

Maybe then they ought to just use the Crew Dragon or something?

(Preferably something that does exist and isn't just a concept somewhere.)

[tater]

5 minutes ago, AtomicTech said:

Maybe then they ought to just use the Crew Dragon or something?

(Preferably something that does exist and isn't just a concept somewhere.)

The margins are so tight with SLS for a lunar mission of any kind, better would have been to design something using it from the start vs trying to make something else work. That or make SLS have a useful throw to TLI, particularly if a modern mission is not defined as "do what Apollo did" but instead, "Do longer missions with more astronauts per mission in a more comfortable habitat."

All this noodling around with SLS at best gives you a lander with a crowded, dirty (inside) surface stay best measured in hours—like Apollo.

[AtomicTech]

23 minutes ago, tater said:

The margins are so tight with SLS for a lunar mission of any kind, better would have been to design something using it from the start vs trying to make something else work. That or make SLS have a useful throw to TLI, particularly if a modern mission is not defined as "do what Apollo did" but instead, "Do longer missions with more astronauts per mission in a more comfortable habitat."

All this noodling around with SLS at best gives you a lander with a crowded, dirty (inside) surface stay best measured in hours—like Apollo.

Maybe then a miniature version of the Hermes is in order? (Read Starship with extra modules docked to it.)

If the margins are so tight, then it would make sense to use the existing/planned SLS rockets as resupply craft to load up the Lunar Transfer Vehicle with supplies and propellants. It would keep Congress happy and get the rest of us to the Moon.

[tater]

27 minutes ago, AtomicTech said:

If the margins are so tight, then it would make sense to use the existing/planned SLS rockets as resupply craft to load up the Lunar Transfer Vehicle with supplies and propellants. It would keep Congress happy and get the rest of us to the Moon.

If Starship wasn't  _this_ close to flying at some level (even expendable), I would say concentrate SLS on sending a habitat ahead. Then the lander can be a sortie lander, crew survival on the surface is in the hab.

[AtomicTech]

Just now, tater said:

If Starship wasn't  _this_ close to flying at some level (even expendable), I would say concentrate SLS on sending a habitat ahead. Then the lander can be a sortie lander, crew survival on the surface is in the hab.

True, true 

Might it be better to expend a few Starships for some crazy habitat?

[tater]

8 minutes ago, AtomicTech said:

True, true 

Might it be better to expend a few Starships for some crazy habitat?

Unfortunately (for SLS), yes.

I can probably come up with a 3 stage Starship variant for this use case, Kerbal-style. Stage 3 in this case is just breaking Starship into 2 parts, the usual tank/engines bit, and the top as it's own vehicle with descent engines—which LSS (as currently shown) already has. Think I might have a while ago.