ULA Cryogenic Moon Landers paper

[Weaver]

Found this study by Lockheed on the United Launch Alliance website, which provides some interesting concepts for moon landers using cryogenic propellants (LH2 + LO2). All three options are unusual:

https://www.ulalaunch.com/docs/default-source/exploration/lunar-lander-configurations-incorporating-accessibility-2006-7284.pdf?sfvrsn=60ce0dbe_2

The Dual Thrust Axis Lander (Concept 1) has a distinct whiff of Space 1999 Eagle about it....

[Weaver]

Found a postable picture of the Concept 1 Dual Thrust Axis Lander:



Image from here: https://selenianboondocks.com/2008/11/lunar-depot-enabled-multi-sortie-missions-part-ii-centaur-derived-landers/

[NARSES2]

Heat rejection system ? That means they'll probably need an on-board psychologist to help the poor thing get over it ? 

No, seriously. Fascinating concept, most of which is way over my head, but we live and learn, or at least try to 

[Old Wombat]

The figures in the cabin/cockpit look like they're doing the Macarena.

[Weaver]

Heat rejection system ? That means they'll probably need an on-board psychologist to help the poor thing get over it ? 

No, seriously. Fascinating concept, most of which is way over my head, but we live and learn, or at least try to 

Here is the circle they're trying to square, put as simply as I can manage:

The most efficient rocket fuels, by a country mile, are Liquid Hydrogen ('LH2' - fuel) and Liquid Oxygen ('LO2' - oxidiser). BUT (there's always a 'but' in rocketry...) they have two major downsides:

1. They have a very low density, which means that a tank of LH2 is light and powerful, but enormous. This affects spacecraft design due to the sheer size of the tanks.

2. They're 'cryogenic', which means they need to be cooled to extremely low temperatures to keep them liquid. This limits their 'storability' because, once loaded into the spacecraft, they can't be actively chilled (not without a massive weight penalty anyway), so they heat up and expand, which means you either let the pressure in the tanks rise to explosive levels, or you vent the fuel and lose it.

These limitations are why the Apollo lander used Hydrazine and Di-Nitrogen Tetraoxide: hideous chemicals to handle, but small volume and liquid at room temperature. Adopting an Apollo-style layout for an LH2+LO2 powered lander would mean a massive increase in the size of the tankage, which would put the crew cabin a very long way above the ground: one proposal had the astronauts climbing a ladder the height of a four-story house!

The paper attempts to find creative solutions for these problems. The storability issue is mostly addressed by applying lessons learnt in the operation of the Centaur: a cryogenic upper rocket stage that's been widely used, proved highly reliable, and amassed a lot of operational experience since the days of Apollo. They think they can extend the storability of the Centaur's propellants by basically doing more of what they do already in terms of tank design, insulation and thermal control. BUT (told ya...) there's a problem: the Centaur's RL-10 engine is not throttleable, and throttleability is a pre-requisite for a controlled Moon landing.

The paper proposes three solutions:

1. The Dual Thust Axis Lander. This deals with the volume problem by landing the craft on it's side, instead of it's end. This puts the crew and cargo near the ground and keeps the rocket nozzles away from it. The RL-10 is used for most of the deceleration burn neccessary to land, then the craft pitches over and does the last bit of the landing using batteries of small rockets mounted on the sides at 90 deg to the RL-10. For ascent, the front section separates and rises back into the orbit on the power of some of the small rockets alone.

2. The Retro Propulsive Lander. This is basically similar to the Dual Thrust Axis lander, but instead of landing the whole craft, the RL-10 and it's tanks are jettisoned to crash on the Moon after their burn is over. On the one hand, this reduces the amount of stuff that has to be soft-landed, but on the other hand, it does pepper the landscape with crashed rockets, which might be a problem if you're going to and from a Moonbase.

3. The Single Stage Lander. This is based on the idea that a throttleable version of the RL-10 can be developed. If this is possible, then it becomes feasible to make a one-piece conventional lander that takes off in one piece without leaving anything behind. The upside is that it's simpler and probably cheaper than the other two, and since no part of it is discarded, it can potentially be refuelled and re-used. The downside is that it has the lowest amount of payload and the access issues of a tall lander with the crew at the top.

[NARSES2]

Cheers H. That's well put, I actually grasped it 

I'm afraid my "O" Level Chemistry was 51 years ago.

[NARSES2]

The figures in the cabin/cockpit look like they're doing the Macarena.

I hadn't noticed that, but now you mention it.

[Captain Canada]

Nice one Weaver. I don't know alot about the subject but that is a link worth saving and reading !

Cheers !