NASA Human Landing System

[tater]

8 minutes ago, Beccab said:

Honestly, I'd pick none of them. Surely not NT for the reasons you stated, but also dynetics was definitely not good. The negative mass margins are a massive problem, and make me doubt they could make a working lander by the 2029, not 2024. They've got a lot of stuff to solve, made little progress as far as we can see since they entered the HLS selection and cost 4 times Starship HLS, and on the top of that they also don't have a random billionaire like Musk or Bezos willing to take part of the costs. This isn't looking good, imo

I wish ULA would have been able to submit something. Except LM is part of NT, and Boeing didn't even make the first down-selection. (so LM/Boeing under the name ULA wasn't gonna bid).

ULA has come up with pretty good cislunar plans over the years.

The Masten/ULA XEUS, for example.

Edited May 12, 2021 by tater

[sevenperforce]

The Source Selection Statement says Dynetics was planning on using cryogens but it's unclear if they were using an existing engine or waiting to design one.

If you were in charge at Dynetics and had an opportunity to re-bid and could use any engine, what engine would you pick and what kind of propellant resupply mode would you pick for reuse?

Assume Gateway has a Canadarm and can grapple replacement tanks.

It would be cool to see something that borrowed a little from the Blok D crasher stage architecture. 

The Rutherford engine might not be a bad fit.

[RCgothic]

So it's not $10B extra after all:

Reeks of corruption as well, IMO.

 

 

[tater]

1 hour ago, sevenperforce said:

The Source Selection Statement says Dynetics was planning on using cryogens but it's unclear if they were using an existing engine or waiting to design one.

If you were in charge at Dynetics and had an opportunity to re-bid and could use any engine, what engine would you pick and what kind of propellant resupply mode would you pick for reuse?

Assume Gateway has a Canadarm and can grapple replacement tanks.

It would be cool to see something that borrowed a little from the Blok D crasher stage architecture. 

The Rutherford engine might not be a bad fit.

NT is stuck using SLS or NG. SLS would make it absurdly expensive (and impossible if cadence was required), NG doesn't exist yet, but regardless limits component size to what they can send to TLI.

An expendable SH with a bare 9m upper stage (per Elon tweet a while ago about deep space probes) can send any of the landers to TLI I think (I got 50-something tons).

Dynetics can pick what LVs they want, so maybe they can close it with SS/SH as the LV (LOL).

I wonder if the initial drop tank idea closed, then in simplifying it by removing them, they lost the mass margin? The trick is if they use cryo  they need larger tanks (which might present a LV issue), and it creates scheduling issues due to boiloff. CH4 sorta splits the difference between great Isp and less concern about boiloff, or there are storables (which becomes a mass problem because Isp is terrible).

Edited May 12, 2021 by tater

[sevenperforce]

1 minute ago, tater said:

An expendable SH with a bare 9m upper stage (per Elon tweet a while ago about deep space probes) can send any of the landers to TLI I think (I got 50-something tons).

Dynetics can pick what LVs they want, so maybe they can close it with SS/SH as the LV (LOL).

I wonder of the initial drop tank idea closed, then in simplifying it by removing them, they lost the mass margin? The trick is if they use cryo  they need larger tanks (which might present a LV issue), and it creates scheduling issues due to boiloff. CH4 sorta splits the difference between great Isp and less concern about boiloff, or there are storables (which becomes a mass problem because Isp is terrible).

Here's an idea.

Two vehicles, a lander and a resupply/transfer vehicle.

First, the lander. Stick with the eight-engine cluster (redundancy is good) but make them simple pressure-fed hypergolic engines instead of cryogens. Same overall low-slung design. However, there are no integral tanks at all. There are three mounting points for tanks, each with propellant flow couplings and a simple load-bearing locking mechanism: two on the "wings" mounted over the engines, and one directly underneath the capsule. The mounting points on the wings are plumbed to the main engines; the mounting point under the capsule is plumbed to the RCS array.

Second, the resupply/transfer vehicle. It will also act as a crasher stage a la N1-Blok D. It can be cryogenic but has its own RCS and power supply.

It carries three tanks: the lander RCS tank in the front with the mounting point exposed and the two wing tanks on either side. The wing tanks have a quick release element that allows them to be dropped quickly without needing to remove the entire load-bearing mounting point attachment, and of course the transfer stage also can drop away from the RCS tank quickly.

Between missions, the lander is docked to Gateway without tanks.

The resupply/transfer stage is launched to TLI on a commercial LV and the efficient cryogenic engine takes it to Gateway, where the station's Canadarm grapples it and attaches it to the base of the lander via the load-bearing mounting point.

Once secure, the Canadarm moves the two wing tanks from the sides of the transfer stage onto their respective mounting points.

The crew gets in and the vehicle undocks, then performs a checkout to make sure all the propellant is flowing properly to the onboard engines and RCS. Then the transfer/resupply stage takes them from NRHO to LLO and then performs the deorbit burn. It then ignites one remaining time to burn to depletion and scrub as much horizontal velocity as possible.

Once the transfer stage is depleted at ~5 km and <200 m/s, it is jettisoned and the lander engines ignite to scrub off the remaining velocity and land.

On the surface it do what it do. It's a minimalist design, dependent on pre-emplaced resources. But because it is so low slung you could even drive a pressurized rover right up to it and dock with it, if it had a docking port on the opposite side.

At mission conclusion, it's back to orbit. 

Just before circularization is completed, the tanks are jettisoned. The lander uses its RCS to complete circularization and head back to the Gateway.

Upon return to Gateway, Canadarm can be used to carefully remove the RCS tank from its mounting point as well as the stubs remaining on the wing mounting points, and it's ready for the next sortie.

Launched to LEO with all three tanks in place, the lander can perform TLI and reach Gateway on its own. If the cabin is removed, the same superstructure and mission profile can be used to reusably deliver payloads to the moon (the transfer stage would carry the lunar surface payload, like a hab or pressurized rover and mount it to the empty lander in the same way, and the lander would have enough dV to take it to the surface and return to Gateway).

This is good because there's no need for propellant transfer; the tanks provide pressurization. No need for cryogens (other than the crasher stage). All tanks are disposed of in a controlled way and there is no wasted tank space. 

And I'm sure the math would close much more easily.

[tater]

I'm not a super big fan of a crasher stage for sustainable use. The other issue then becomes drop tank disposal.

[StrandedonEarth]

11 minutes ago, tater said:

I'm not a super big fan of a crasher stage for sustainable use. The other issue then becomes drop tank disposal.

It does seem wasteful, but if all the landings are in one place, such as the speculative Shackleton ISRU base, then hopefully it wont be too difficult to arrange to have specific disposal zones crasher stages and drop tanks for future lunar colonists to recover and recycle whatever they can.

Future career  option for Lunatics: cratercomber! Sorry, no wrecked Star Destroyers to salvage (yet ).

Edited May 13, 2021 by StrandedonEarth
details, details

[sevenperforce]

7 minutes ago, tater said:

I'm not a super big fan of a crasher stage for sustainable use. The other issue then becomes drop tank disposal.

Well, unless we’re going fully reusable with Starships, then every payload we send to TLI has to have an independent bus with enough propellant (or, if it’s a HLS component, extra propellant) to brake itself into NRHO, which means you have a bunch of derelict buses floating around the Gateway (and the HLS components arrive with tanks already partly depleted).

You can deliver HLS components to Gateway with a separate transfer stage, of course, but then you have THAT transfer stage floating around Gateway.

If you’re already dumping spent stages in cislunar space, you might as well make them part of the landing architecture. And this architecture drops tanks suborbitally so there’s only one fairly small RCS tank that ends up at Gateway.

[sevenperforce]

It should also be noted that the surface payload delivery scheme involves the exact same architecture but doesn’t require a crasher stage. The resupply stage would be set up the same way but would have the payload mounted between the top of the resupply stage and the bottom of the replacement RCS tank. It would probably use some of its own props to complete TLI (since it would be heavier out of LEO) and expend most of its remaining props braking to NRHO. If you’re dropping something off on the lunar surface that you don’t have to take back to Gateway, the lander can get from Gateway to the lunar surface and back to LLO in a single stage, drop the tanks, and head back to Gateway on RCS.

[tater]

10 minutes ago, sevenperforce said:

You can deliver HLS components to Gateway with a separate transfer stage, of course, but then you have THAT transfer stage floating around Gateway.

So they get removed, put on the bus empty, then sent where ever? That makes more sense.

Of course any architecture combined with SS becomes sorta easy. Stick drop tanks to Starship-tug. Bring a few years worth to Gateway in one trip.

[sevenperforce]

7 minutes ago, tater said:

So they get removed, put on the bus empty, then sent where ever? That makes more sense.

Of course any architecture combined with SS becomes sorta easy. Stick drop tanks to Starship-tug. Bring a few years worth to Gateway in one trip.

Well yes, a Starship tug makes things much easier.

My point is that the reason people would want something NOT SpaceX is for redundancy if SpaceX can’t make reusable LEO retanking into a thing. And if they can’t, then we have to figure out how to get stuff to Gateway (and, ultimately, the lunar surface) using repeated expendable commercial launches.

Suppose you have an HLS architecture that uses three components, like National Team. Each of those components has to get to Gateway somehow. So either it is launched to TLI by itself and brakes itself into NRHO (and thus has to perform the rest of the mission with partially depleted tanks) or it is launched to TLI with a transfer stage that brakes it into NRHO and is then discarded. It has to be one or the other.

It just makes more sense to me to have an oversized transfer stage that brakes all your sortie propellant into NRHO in one launch, then reduces your (minimalist) lander’s dV requirements so it can return from LLO to Gateway on RCS.

[SpaceFace545]

2 minutes ago, sevenperforce said:

Well yes, a Starship tug makes things much easier.

My point is that the reason people would want something NOT SpaceX is for redundancy if SpaceX can’t make reusable LEO retanking into a thing. And if they can’t, then we have to figure out how to get stuff to Gateway (and, ultimately, the lunar surface) using repeated expendable commercial launches.

Suppose you have an HLS architecture that uses three components, like National Team. Each of those components has to get to Gateway somehow. So either it is launched to TLI by itself and brakes itself into NRHO (and thus has to perform the rest of the mission with partially depleted tanks) or it is launched to TLI with a transfer stage that brakes it into NRHO and is then discarded. It has to be one or the other.

It just makes more sense to me to have an oversized transfer stage that brakes all your sortie propellant into NRHO in one launch, then reduces your (minimalist) lander’s dV requirements so it can return from LLO to Gateway on RCS.

I think for sustainability a dedicated tanker craft should be developed, something that can easily deliver large volumes of fuel. A starship tanker is okay but needs a tanker to refuel the tanker and that tanker needs another tanker to refuel it, etc. 

[sevenperforce]

6 minutes ago, SpaceFace545 said:

I think for sustainability a dedicated tanker craft should be developed, something that can easily deliver large volumes of fuel. A starship tanker is okay but needs a tanker to refuel the tanker and that tanker needs another tanker to refuel it, etc. 

That’s limited by TLI throw. If you set Starship aside (because Starship makes everything easier) and you set SLS aside (because it doesn’t fly enough to be useful) then your max TLI throw is restricted what Vulcan, New Glenn, and Falcon Heavy can do. NG and Vulcan can do something like 9 tonnes to TLI. Falcon Heavy can do a little more. But that’s not a lot to work with. 

[tater]

10 minutes ago, SpaceFace545 said:

I think for sustainability a dedicated tanker craft should be developed, something that can easily deliver large volumes of fuel. A starship tanker is okay but needs a tanker to refuel the tanker and that tanker needs another tanker to refuel it, etc. 

If you have a 100% reusable, cost effective tanker to LEO, the whole prop depot and tanker architecture really becomes plausible.

If SS works—just as this alone, mass to LEO is propellants, with no other capability, no humans aboard, etc—it's completely transformative.

ACES was an ULA idea which leveraged smaller LVs, and makes sense to accomplish missions the small LVs cannot do. Send ACES to LEO, it uses some props to get to LEO. Send another, and dock the 2, then fill one. 1 gets thrown away. You now have a 100% full Centaur, possibly a big one, and you can dock a thing to it, and take it to the Moon. You now have ACES at the moon, but filling it becomes really tough. You probably have to throw a few away to end up with a full one at the Moon.

SS completely changes this. Tank one up, send to the Moon. Offload some, head back to LEO. "Some" for SS is more than the other landers mass by a large margin. Hundreds of tons pf props.

3 minutes ago, sevenperforce said:

That’s limited by TLI throw. If you set Starship aside (because Starship makes everything easier) and you set SLS aside (because it doesn’t fly enough to be useful) then your max TLI throw is restricted what Vulcan, New Glenn, and Falcon Heavy can do. NG and Vulcan can do something like 9 tonnes to TLI. Falcon Heavy can do a little more. But that’s not a lot to work with. 

Or you do something akin to ACES, and use those LVs to send props up to fill some stage that delivers a fraction of it to cislunar.

BTW, a year ago, assuming SS was maybe a fanboy thing, but it's kind of not right now.

If NASA had picked NT, we could absolutely assume NG in planning. So while I might give refilling in LEO a few fistfuls of salt until demonstrated, I think SS is a certainty. Even if reuse takes a LONG time to sort, I think it is clear that SS is inexpensive (for its size, certainly), and as I figured out above, a disposable SS/SH can throw over 50t to TLI.

[RCgothic]

If we're concerned about regolith excavation by engines, are we also concerned about the impact of crasher stages?

[Beccab]

1 minute ago, RCgothic said:

If we're concerned about regolith excavation by engines, are we also concerned about the impact of crasher stages?

If the crasher stage can explode because of the impact then yes definitely, though if it's parts that will just crash and that's it I don't think it should be that much of a problem as long as the trajectory is controllable and vertical enough

[sevenperforce]

10 hours ago, tater said:

ACES was an ULA idea which leveraged smaller LVs, and makes sense to accomplish missions the small LVs cannot do. Send ACES to LEO, it uses some props to get to LEO. Send another, and dock the 2, then fill one. 1 gets thrown away. You now have a 100% full Centaur, possibly a big one, and you can dock a thing to it, and take it to the Moon. You now have ACES at the moon, but filling it becomes really tough. You probably have to throw a few away to end up with a full one at the Moon.

SS completely changes this. Tank one up, send to the Moon. Offload some, head back to LEO. "Some" for SS is more than the other landers mass by a large margin. Hundreds of tons pf props.

Yes, the concern with prop-depot distributed launch was always cadence. Even if the commercial LVs could pull it off, it was still very much time-sensitive. If SLS slips, you could end up with a mission-threatening level of boiloff. So that restricts your tug (ACES or whatever) to the limited role of putting storables into cislunar space. And with storables, you are more likely to want them pressure-fed, which means the value of propellant transfer drops (the tank *is* the turbopump in a pressure-fed regime). 

Starship obviates all that by being so massively overpowered and boasting so much capacity that it can accept extra loiter time. 

5 hours ago, RCgothic said:

If we're concerned about regolith excavation by engines, are we also concerned about the impact of crasher stages?

I wouldn’t imagine so. I mean, we’ve crashed tons of stuff into the moon before. As long as you drop at the proper angle and speed and altitude, it’s no big deal. 

[tater]

31 minutes ago, sevenperforce said:

I wouldn’t imagine so. I mean, we’ve crashed tons of stuff into the moon before. As long as you drop at the proper angle and speed and altitude, it’s no big deal. 

It's more ejecta, dust, etc. Better to avoid it if possible.

[wumpus]

text deleted as redundant.

Edited May 13, 2021 by wumpus
deleted as redundant

[Terwin]

7 hours ago, tater said:

It's more ejecta, dust, etc. Better to avoid it if possible.

I could see an argument that the ejecta of a sub-orbital, fully depleted stage would provide less total hazard than the same stage, mostly depleted and in a lunar orbit(probably not long-term stable)

[tater]

1 minute ago, Terwin said:

I could see an argument that the ejecta of a sub-orbital, fully depleted stage would provide less total hazard than the same stage, mostly depleted and in a lunar orbit(probably not long-term stable)

Oh, undisposed, crashing on its own, later? Yeah, a problem.

One of the reasons for the landing engines up the side on LSS is to mitigate engine plume interactions with the surface, though.

[magnemoe]

On 5/13/2021 at 9:08 AM, Beccab said:

If the crasher stage can explode because of the impact then yes definitely, though if it's parts that will just crash and that's it I don't think it should be that much of a problem as long as the trajectory is controllable and vertical enough

Yes, the problem for SS landing is the power and velocity of the exhaust. Crashing an stage will have much lower velocity and it will crash far from landing site. 

[Codraroll]

The moon is also, famously, peppered with craters. Stuff landing on it at very high velocity and kicking up ejecta is part of the climate, as it were. Sooner or later our lunar infrastructure would have to adapt to that phenomenon anyway. Then again, perhaps one shouldn't try to cause such events if it can be avoided.

[RCgothic]

Robert Zubrin was very critical of Dynetics:

 

 

"3. While clearly better on a conceptual level than the National Team offering, the Dynetics design never really had a chance, because the team behind it was not credible enough to be given responsibility for something of such central importance to the space program. Rather, they were given a nice chunk of change in order to assure a wide base of support for Artemis."

 

 So a better idea, but not credibly going to acheive success due to the team (as was born out in NASA's selection document).

[tater]

2 hours ago, magnemoe said:

Yes, the problem for SS landing is the power and velocity of the exhaust. Crashing an stage will have much lower velocity and it will crash far from landing site. 

Yeah, methalox exhaust is ~3700 m/s, still, depending on how much the crasher drops the lunar orbital velocity (and how long it has to accelerate, it's still up to ~2000 m/s. As least the ejecta won't have lunar orbital velocity.