Thanks. I worked on Constellation Systems in Requirements/Verification Requirements for the EVA System from February 2007 to November 2010 and had the chance to observe (but not directly participate in) the whole debate over the Altair’s capabilities in the Constellation Systems Architecture Requirements Document (CARD).

You are, of course, correct about introduction of methane into Altair’s propellant system.

The whole thing was driving the engineers working on the Altair “up a wall”.

Understood on the Cislunar 1000 XEUS concept. While I think design changes would occur as development proceeded, I agree it is a good starting point for developing a practical/affordable Lunar Lander.

Thanks for the link to the pitch. Did not have it before, but it is now part of my library.

All correct, to the best of my knowledge. Moreover, the last design iteration of the Altair was to be powered by LOX-methane instead of LOX-LH, so as to better fit the requirements of the “Mars Forward” idea.

I was referring to the XEUS concept described in ULA’s Cislunar 1000 concept.

I believe a factor in the debate is the lack of information on why we should go back to the Moon and the reason behind it.

The mass media simply doesn’t report it, so the public is left with a false impression.

And unfortunately, blogs and articles by popular scientists continue to regurgitate the very things you mention in your article.

We need an aggressive tactic to get the word out that we have a better choice.

https://www.astrobotic.com/configure-mission To me looked like it would not be that expensive.

Some of the existing designs, such as the Masten-ULA Xeus lander concept, based on an RL-10 engine and Centaur stage, would be fine for cargo and propellant but harder to use in a safe manner for crews. The crew cabin would need to leave the lander partly horizontally during an abort, which is much harder to handle during an emergency situation. Building a new, purpose-designed lunar lander might take longer and cost more, but such a lander might be safer for crew members and cheaper to operate, since the crew cabin would leave the lander vertically with a single plane of separation. Safety issues like this become much more important when there are routine (frequent) flight operations underway. Parachutes do NOT work in space.

John

(1) There are more similarities between the Altair and Xeus vehicles than there might seem. Both (for instance) rely on variants of the RL-10 engines.

(2) The problem with the Altair was its constantly changing top level design requirements, because of warring objectives for the Constellation Lunar Mission (as has been well documented by Dr. Spudis on this website).
– One faction wanted a lunar base for which the Altair would be a crew transport only (with its first stage adaptable to support a one way cargo lander). That version could have been a smaller/simpler and thus cheaper lander.
– Another faction wanted a series of sortie missions to various Lunar sites to be selected (fought over) at a later date. After those missions were completed Lunar activities would have again been abandoned in favor of “pushing on” to Mars. The scenario required a larger/more complex and thus more expensive lander that (among other things) had an ascent stage that could serve not only as a transport but a base for weeks at a time in addition to carrying new rovers to each sortie site. Because those discrepancies were never resolved, the Altair ended up with requirements to serve both missions.

(3) Because of the situation described in (2) the first objective of any successful lander program must be to establish a set of very narrowly defined and stable top level requirements (e.g. what do you want the lander to do).

(4) With due respect to Masten, it would a mistake to closely conflate his assertions with ULA’s proposals. Never the less with the right requirements a lander capable of supporting the initial phases of Lunar Base development should be possible faster and cheaper than the Altair model would indicate.

Did you ever see if the GATE I & II proposals by Bigelow Aerospace were ever made public? He had a couple tug designs that looked promising.