NASA HLS (Human Landing System) Lunar Landers

[Patchouli]

The deck of charts are now publicly available here: https://www.nasa.gov/directorates/heo/nac-heoc

But these appear to be the most relevant to the current discussion (these are from Crusan’s slides)

With a fuel depot infrastructure the single stage lander would not be too large for SLS or even a smaller vehicle like New Glenn or Falcon Heavy as it could act as it's own departure stage.

[ncb1397]

So, was the landing radar put there because of the planned but never used lunar truck mode or is it simply the best place to put it to allow for lunar surface line of sight in both hoizontal and vertical orientations?

The whole of the LEM was expendable so no consideration was needed for a second landing. The landing radar was not used to help the Ascent Stage rendezvous and dock with the Command Module so there was probably no benefit from attaching the radar to the Ascent Stage. The propellant needed to lift the mass could be saved by fitting it to the Descent Stage.

NASA hopes to make the Ascent Stage of the new lander reusable, so by attaching the landing radar to the Ascent Stage it will not have to buy a new radar for each landing.

Just make it easy for them to unbolt it and stow it in the ascent stage? Anyways, new landing radars are probably in the 8 digit annual expenditure range. Supporting a clean sheet heavy cargo lander is probably in the 9 digit annual expenditure range.

[Coastal Ron]

NASA hopes to make the Ascent Stage of the new lander reusable, so by attaching the landing radar to the Ascent Stage it will not have to buy a new radar for each landing.

So in order to reuse the Ascent Stage, NASA would have to ship a whole new Decent Stage to the LOP-G every time they want to land on the lunar surface?

I guess I'm not understanding why NASA wouldn't want to make the entire lunar lander reusable. If this has already been covered then just point me to that part of the thread.

But if it hasn't been discussed then what possible logic would make it seem better to just reuse the Ascent Stage and STILL have to ship mass to the LOP-G in order to reuse a vehicle? Do that enough times and it sure seems like it's less expensive to just ship propellant to a fully reusable lander, and not ship half a lander AND propellant.

Color me confused... 

[M129K]

I guess I'm not understanding why NASA wouldn't want to make the entire lunar lander reusable.

What's mentioned in the presentation: If you use hypergolic propellants a single stage lander, even when using a space tug for lunar orbital transfers, would be too heavy and physically large to lift on commercial launchers and can't be co-manifested on SLS.

Seeing how NASA limits itself to hypergolics, it seems more likely that NASA instead wants to minimise programme risk and development cost, foregoing the technologies I mentioned earlier that would enable full reuse. With only partial reuse, SLS only flying once a year and no potential for ISRU, there is no actual plan to actually do frequent surface sorties that would justify the added development costs for fully reusable lander. In other words there is no plan to actually turn this into a serious way to do lunar exploration and settlement.

[John Santos]

The descent stage is probably quite cheap.  Just fuel tanks and landing legs.  All the engines, avionics, etc. are on the ascent stage.
Most of the mass associated with it is fuel, which would have to be sent up whether the lander was completely or partially reusable or expendable.
Since the fuel would have to be shipped up in tanks which would have to be mounted in some sort of structure, even with a fully-reusable lander, just ship the descent stage fuel in the (new) descent stage tanks and structure.  The only additional mass is the legs.

[M129K]

Just fuel tanks and landing legs.  All the engines, avionics, etc. are on the ascent stage.

The descent stage is supposed to land autonomously for cargo. It carries its own avionics and engines. Probably more than the ascent stage.

[John Santos]

Just fuel tanks and landing legs.  All the engines, avionics, etc. are on the ascent stage.

The descent stage is supposed to land autonomously for cargo. It carries its own avionics and engines. Probably more than the ascent stage.

I was thinking, based on reply #48, that they were planning to use a single set of engines for both the descent and ascent stages, but on re-reading, I see that Nibb31 was recommending they do that or inquiring why they weren't planning to do that, and that's not the actual plan.

BTW, going further with Nibb31's proposal, for cargo a dumb (no engines or guidance) descent stage could incorporate an expendable 'ascent' stage (just the engines and guidance from the regular ascent stage), but no fuel tanks or crew cabin, or it could incorporate a truncated reusable ascent stage without the crew cabin, life support, etc., and partially filled tanks (since the ascent mass would be much less) and replace the docking system with a grapple fixture which would be much lighter.

Edit: moved a comma for clarity.

[Coastal Ron]

I guess I'm not understanding why NASA wouldn't want to make the entire lunar lander reusable.

What's mentioned in the presentation: If you use hypergolic propellants a single stage lander, even when using a space tug for lunar orbital transfers, would be too heavy and physically large to lift on commercial launchers and can't be co-manifested on SLS.

Maybe as a single assembled vehicle, but if they are already planning on reusing the Ascent Stage, and providing a new Decent Stage, then it sure looks like they could launch them separately on rockets smaller than the SLS and assemble them in space.

Seeing how NASA limits itself to hypergolics, it seems more likely that NASA instead wants to minimise programme risk and development cost, foregoing the technologies I mentioned earlier that would enable full reuse. With only partial reuse, SLS only flying once a year and no potential for ISRU, there is no actual plan to actually do frequent surface sorties that would justify the added development costs for fully reusable lander. In other words there is no plan to actually turn this into a serious way to do lunar exploration and settlement.

You packed a lot of great info and perspectives into that paragraph, and I think you have highlighted part of the reason why NASA hasn't returned to our Moon - they haven't identified a sustainable way to do it. And I think a reusable lunar lander would greatly help that, but that is not the direction they are planning to go today.

Pity...

[Patchouli]

I guess I'm not understanding why NASA wouldn't want to make the entire lunar lander reusable.

What's mentioned in the presentation: If you use hypergolic propellants a single stage lander, even when using a space tug for lunar orbital transfers, would be too heavy and physically large to lift on commercial launchers and can't be co-manifested on SLS.

Seeing how NASA limits itself to hypergolics, it seems more likely that NASA instead wants to minimise programme risk and development cost, foregoing the technologies I mentioned earlier that would enable full reuse. With only partial reuse, SLS only flying once a year and no potential for ISRU, there is no actual plan to actually do frequent surface sorties that would justify the added development costs for fully reusable lander. In other words there is no plan to actually turn this into a serious way to do lunar exploration and settlement.

Hypergolics do have one advantage they can be easily stored long term in space so a SEP tug could be used to take propellant from LEO to where it's needed.
But it doesn't lend itself to ISRU like hydrogen or methane and LOX which does make it kind of a dead end for Mars and beyond.

[Bob Shaw]

Has anyone ever looked at using solid or hybrid motors for any part of a reuseable system? No (or very few) moving parts, safe to handle, non cryogenic; also heavy, lower ISP and perhaps needing to be actively heated/cooled while in storage; and (for solid) with a huge history of long-term storage.

I'm thinking of solids essentially as SRBs, strapped onto spacecraft elements like a lander/ascender - and used as crasher stages during landing with a throttleable liquid motor for final descent. Also, as abort motors.

[A_M_Swallow]

Hypergolics do have one advantage they can be easily stored long term in space so a SEP tug could be used to take propellant from LEO to where it's needed.
But it doesn't lend itself to ISRU like hydrogen or methane and LOX which does make it kind of a dead end for Mars and beyond.

One thing SEPs give is lots of electrical power. Increasing the solar panels on a 50kW SEP to 53kW would allow 3kW to power a refrigeration unit. A dedicated propellant tanker SEP could be fitted with a sun shield, possibly using the same design as the propellant depots.

[A_M_Swallow]

So, was the landing radar put there because of the planned but never used lunar truck mode or is it simply the best place to put it to allow for lunar surface line of sight in both hoizontal and vertical orientations?

The whole of the LEM was expendable so no consideration was needed for a second landing. The landing radar was not used to help the Ascent Stage rendezvous and dock with the Command Module so there was probably no benefit from attaching the radar to the Ascent Stage. The propellant needed to lift the mass could be saved by fitting it to the Descent Stage.

NASA hopes to make the Ascent Stage of the new lander reusable, so by attaching the landing radar to the Ascent Stage it will not have to buy a new radar for each landing.

Just make it easy for them to unbolt it and stow it in the ascent stage? Anyways, new landing radars are probably in the 8 digit annual expenditure range. Supporting a clean sheet heavy cargo lander is probably in the 9 digit annual expenditure range.

CLPS small lunar landers using a variety of fuels go online within 2-3 years. The development of medium sized landers are due to start soon, these are likely to fly before development of the manned lander bends metal. Are any of these landers able to land and return about 4 tonnes to the LOP-G?

[PhotoEngineer]

CLPS small lunar landers using a variety of fuels go online within 2-3 years. The development of medium sized landers are due to start soon, these are likely to fly before development of the manned lander bends metal. Are any of these landers able to land and return about 4 tonnes to the LOP-G?

In the plans NASA released they have mid size landers for 500 kg in the mid 2020's.  There is a commercial tie in to those landers but the details haven't been released. Its a big step from 500 kg to 4 tonnes.

[A_M_Swallow]

CLPS small lunar landers using a variety of fuels go online within 2-3 years. The development of medium sized landers are due to start soon, these are likely to fly before development of the manned lander bends metal. Are any of these landers able to land and return about 4 tonnes to the LOP-G?

In the plans NASA released they have mid size landers for 500 kg in the mid 2020's.  There is a commercial tie in to those landers but the details haven't been released. Its a big step from 500 kg to 4 tonnes.

An order of magnitude increase is always difficult. People sized equipment including lander cabins, habits and manned rovers weighs tons. So manned landers will be similar in size to the upper stages of launch vehicles.

[TrevorMonty]

Having storable propellants on ascent stage allows for extend stays on surface without havibg to deal with boil off.
Cryo fuels are ideal for descent stage as boil off isn't issue for half day trip to surface.

I don't understand reasoning behind adding  3rd stage, just makes it more complicated.

If the go with LH LOX then there is possibility of refuelling descent on surface in future. As for boil off of LH LOX when transporting between earth and Gateway, its something they just need to deal with. If NASA can't deal with long term storage of LH LOX what is point of ISRU.

[GWH]

I don't understand reasoning behind adding  3rd stage, just makes it more complicated.

It makes perfect sense if one is pessimistic on the gateway and worries it will change to orbit in LLO or direct rendezvous. Remove the 3rd stage and the architecture can stay exactly the same.

[ncb1397]

Just stacking 3 ESMs together almost works for this architecture as long as the cabin + astronauts is 2000 kg. Considering the dry mass of the Apollo LEM ascent stage was 2150 kg and that included fuel tanks and engines, that may not be hard to imagine. I get the following delta-vs for the 3 stages with 4,000 kg ESM dry mass, 9,000 kg propellant load, 316 isp engine:

1st stage (tug): 770 m/s
2nd stage (descent): 1200 m/s
3rd stage (ascent): 2800 m/s

1st stage works, 3rd stage works. 2nd stage has a delta-v shortfall.

edit: the best way I can find to get ESM derived modules to close is with a few caveats. The ascent stage has to have a half fuel load (leaving out 2 of 4 propellant tanks) and mass dry 2 mT vs 4 mT (leaving O2/water tanks/solar panels off). The crew cabin + astronauts needs to be 1,000 kg (super hard, probably not impossible for 2 astronauts). This leads to the following dVs.

1st stage (tug): 970 m/s
2nd stage (descent): 1790 m/s
3rd stage (ascent): 2840 m/s

[M129K]

Considering how changing an in-space stage and service module into a lunar lander would already warrant many changes to the design anyway, like new avionics and landing legs, slightly stretching the tanks to meet additional delta V requirements would be a minor change.

Having storable propellants on ascent stage allows for extend stays on surface without havibg to deal with boil off.
Cryo fuels are ideal for descent stage as boil off isn't issue for half day trip to surface.

Boil-off is an issue for a descent stage, because a fully fuelled descent stage is too heavy for Orion co-manifest, so either the delivery of the stage or the delivery of the propellant would need to happen separately. Considering SLS's launch schedule and commercial capabilities to TLI, that's probably going to be a period of months in which you need to keep your tanks topped up. The design goes for the easy route of using hypergolic propellants, postponing the development of critical technologies to a later date to be solved, hopefully by someone else.

[ncb1397]

Anybody here with inside knowledge on accurate numbers for the ESM?

Its dry mass is 3.5 metric tons and it can carry 8.6 tons of propellant.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20170009574.pdf

Service Module – Propulsion, Electrical Power, Fluids Storage
Mass Properties
Dry mass ...............................................................................13,635 lbs

https://www.nasa.gov/sites/default/files/fs-2014-08-004-jsc-orion_quickfacts-web.pdf

13635 pounds= 6185 kg

Bit confused here. Normally would go with NTRS, but 13635 pounds sounds ultra specific. Don't think it is 2/3s the mass of the fuel it carries though. The ESM manager saying they were "always on diet" doesn't fit. Only asking as 3.5 t even with the slightly lower fuel load compared to what I assumed above would make it a bit more feasible to fit into NASA's 3-stage lander.

[clongton]

A_M_Swallow, MATTBLAK and Coastal Ron, Just FYI back in the day we were also working on an expendable lander. It was designed around an Orion crew of 4, with 3 descending to the lunar surface and 1 remaining in orbit. It was a single stage expendable vehicle, hypergolic powered, but the descent propellant was in drop tanks that would be left on the surface together with the structure that supported them and with ascent propellant in separate tanks. So it would be similar to what Apollo did except for the single stage w/drop tanks. That allowed the crew cabin to be larger and support a 3-crew than a 2-stage lander that had to account for an additional engine and all the associated hardware that required. A cargo only version allowed a significant amount of landed mass on the surface, much larger than anything NASA had in mind for CxP. All the numbers were falling into place nicely and could still work for this new lunar program. The one thing that is standing in the way of that is that NASA wants to build, launch and orbit LOP-G first and then use that as the way station to the surface. That requires a reusable lander to justify that mision profile that can be stored at the station between missions. For the foreseeable future hypergolic propellants are the only ones that can support that which leads to the 3 stages being discussed here because of the low isp of that propellant choice. If NASA wanted to get to the surface first and gradually bring LOP-G online as a continuing development, then the single stage, expendable, hypergolic lander would serve nicely during that time. But once lunar ISRU is functioning for propellant production, a single stage LOX/LH2 reusable lander can be deployed which will change everything, for both crew and cargo-only missions.

TrevorMonty, Boil Off is not going to be a problem on the lunar surface. The main thing that needs to be done is for storage tanks to remain in shadow constantly. Because the lunar atmosphere is so tenuous that it is nearly nonexistent, thermal transfer from direct sunlight does not occur. It can be 260F (127C) in the direct sun, then step into the shadow of a large rock or a structure and the temperature will instantly become around -280F (-173C). Store propellant tanks behind a sun shield and the problem is solved. Heat does not radiate well in a vacuum. It tends to remain within whatever mass has been warmed.