The “base first” decision: crew survival and reusability
by John K. Strickland, Jr.
|Considering the political impact on the lunar program if an an accident were to happen, and the great improvements in technology since Apollo, every reasonable effort should now be made to provide additional redundancy or other means of survival for the crew.|
In the current lunar exploration press conference slide set, a lander design is shown which carries both a hab or cargo container and a crew (ascent) cabin on top of the descent stage. The design is explained as minimizing the mass of the landing stage and crew cabin, to maximize the mass of the cargo. The hab or cargo container, as shown (very close to the crew cabin), would endanger the cabin if it had to separate in an emergency during the descent. This apparent problem could be due merely to inaccurate artwork. However, one of the primary post-Columbia decisions was to separate crew and cargo missions for crew safety reasons. This decision might work for lunar landers also. A smaller amount of cargo could be carried in the crew cabin or on the descent stage, as in the original Apollo Lunar Module. The mass used by the large cargo carrier or module could be used instead for the extra propellant and fuel tank mass needed to return the entire vehicle to orbit. The loss of carrying capacity would be balanced by not needing to launch another entire lunar lander stage from Earth to lunar orbit, and the same vehicle could then carry more crews down to the surface. A cargo-only version with an identical landing stage would replace the entire crew cabin with a cargo container, a habitation module, or other large object. Any non-reusable version of the lander similar to the illustration should separate the crew cabin and any cargo by at least 0.9–1.5 meters for safety reasons.
Developing an autonomous lander first, before a crewed version, would also provide a test period while doing useful work at the same time. The maximum landed cargo mass was given as about six metric tons. This seems like a severe limit, considering that the shuttle can put 20-ton payloads in orbit. If the lunar base is to be built by attaching modules together, a rather large fraction of the module mass would be taken by the connecting structures if they are too small. This also provides little room for radiation and thermal shielding mass. A good question for the engineers would be: what is the practical lower limit to habitation module size?
If you can return the entire lander to lunar orbit, this implies that it could be refueled and reused, which also implies that there is a place (a depot) to dock, refuel, and resupply (and live in during an emergency) in lunar orbit. Having a depot would also allow for larger cargo payloads, since the lander could be refueled after entering lunar orbit. (Current plans call for the lander engines to assist the composite Orion vehicle in entering lunar orbit.) Apparently none of the published results of the otherwise very competently done trade-off studies, such as those done for the ESAS Report, have included reusable landers or lunar orbit infrastructure in their calculations and tradeoffs. I strongly agree with the “base first” decision just announced, but I am totally baffled by the seeming unwillingness of the NASA planners to discuss at all the use of reusable landers.
In the set of slides used during the press conference, there is a diagram of a representative lunar base layout. This particular base would be built on the sunlit rim of Shackleton crater near the lunar south pole, where the nearly-horizontal sunlight would provide almost continuous energy to power and heat the base. At the far right end of the rim section where the base is laid out, there is a large area devoted to landing sites for up to 40 lunar landers—large, expendable landers! Since many of these consist of two modules, each critical to crew survival, I suspect that they will each cost at least a billion dollars a copy, eating up a large portion of the entire lunar exploration budget. Continued use of the landing area will steadily fill it with large, expendable landing stages, creating in effect a very large artificial boulder or obstacle field right next to where they want to land. Successive landers will then have to land further and further away from the base itself. When they have used up all of the allotted area for landing landers, then what do they do? Adjacent areas are sloping or in shadow much of the time.
In attempting to cover category 1B, I acknowledge that it would be very hard and very expensive to send a duplicate crew lander to each sortie site, but quite reasonable to send a single (specially modified) autonomous crew lander to the one lunar base site for crew self-rescue. This is very similar to the method used in Robert Zubrin’s “Mars Direct” method, where everything needed to assure crew survival is landed before the crew arrives. The lander would need to be specially modified to survive by itself intact and with power until the first astronauts arrive. Weight that would be occupied by astronauts could be replaced with additional fuel to power the lander, extra insulation, and so forth.
To cover category 2A, we would need to provide a crew refuge, which could double as a habitation unit for regular use at the lunar base. (A crew refuge in lunar orbit attached to a depot, for category 2B, would also be a good idea.) In the current side set, designs show the habitation modules connected together sitting on the lunar surface with no radiation protection. If we are going to use lunar resources to amplify the base’s capabilities, why not use the unmodified lunar regolith to provide the radiation protection? Power equipment can either dig out a base site and bury the hab modules, leaving the connections exposed, or some means should be found of placing packets of regolith on top of and along the sides of the hab modules without burying them.
For an effective refuge for early base conditions, an excavator or earthmover of some sort would be extremely useful for covering a hab unit with regolith. This also implies that there is a hab unit and an excavator waiting at the base site when the first crew arrives. This then implies that the hardware was landed by an unmanned cargo version of the lander, and that there must be some way to remove the units from the lander and place them on the lunar surface, since a hab sitting six or more meters above the surface would be very difficult to cover with lunar soil. This means that there would also need to be a crane or other lifting device available at the base site when the crew arrives. If payloads can be removed from an unmanned cargo lander, it would be even easier to get it back into lunar orbit to bring another cargo down, since there would be no crew cabin on it.
|Strangely, the topic of reusable spacecraft is again missing from this list. It is as though NASA itself, as a community, does not believe (after a series of failures in this area), that it can be successful in developing a reusable vehicle of any kind.|
All of this means that a lot of careful thought and planning must go into both the complement of equipment that must be landed before any crew arrives, and the order in which it arrives. The first pieces of equipment to arrive would need to be able to withstand months of exposure to lunar polar conditions before any protection provided by humans was available. In terms of thermal extremes, the polar environment is less extreme than most other lunar locations, which is another major reason to pick a polar site for the base. Any kind of teleoperational capability that could be provided in an early cargo flight would be very valuable in protecting and maintaining the landed equipment until the first crew arrives.
Fortunately, the NASA lunar exploration site also had links to the Lunar Exploration Conference held Houston last month. Though not mentioned in the press conference, some significant related documents were put on the conference site. These included an impressive list (in Excel and PDF formats) of over 100 things that various people thought were worth doing on the Moon. A significant number of items that I know have been submitted by at least one person do show up in this list.
Many items included in this list now indicate acknowledgment by NASA of at least some issues which are critical to developing a real, capable lunar base, such as: creating redundant lunar transportation systems; lowering the cost of space transportation; developing an autonomous cargo lander; developing cryogenic propellant depots for lunar surface, lunar orbit, and earth orbit applications with zero propellant loss capability (even though the word “depot” is not used); developing lunar-based power systems, infrastructure, and warehouses for consumables and equipment storage; studying mammalian reproduction and life cycle under low-gravity conditions; providing radiation shielding and thermal protection for lunar astronauts and their equipment; providing emergency infrastructure (such as crew refuges); providing the ability to move propellant, other consumables, equipment and personnel within and without a base site area; and developing equipment to excavate, extract and process lunar resources.
Strangely, the topic of reusable spacecraft (not boosters) mentioned above—which I know has been submitted to NASA—is again missing from this list. Listing or discussing this topic at all currently seems to be forbidden within NASA. It is as though NASA itself, as a community, does not believe (after a series of failures in this area), that it can be successful in developing a reusable vehicle of any kind. The more explicit revelation that NASA is very interested in wide participation by other nations, even to the extent of endorsing the development of other lunar transportation systems, is a very positive sign. However, unless someone bites the bullet and starts developing an affordable lunar transportation system, getting the additional, vital items provided by the international community down on the lunar surface will still be extraordinarily expensive.
Jeff Foust is correct in assessing that the six themes offered as rationales for returning to the Moon are too vague. (See “Moonbase why”, The Space Review, December 11, 2006) He points out that the “general public” would be satisfied with what many of the newspaper editorials referenced in the article usually offer at such a time: a much cheaper robotic program. However, if we had no effective leaders and the general public really did make most of the really important decisions for the human race, we would probably still be sitting in caves, splitting bones for marrow with stone hand-axes. Society cannot and should not depend on polls of the public to make critical decisions. That is what leaders are for.
Surprisingly, a December 6th USA Today editorial (“NASA, The Costly Frontier”) was reasonable and made a valid point: that for a real space frontier and space economy to open up, NASA or someone must work on getting the huge Earth-to-orbit transportation costs down. NASA has abandoned its efforts to do just that, putting its cart before the horse once again. NASA will not need to launch large payloads to the Moon (or land them there) for almost 14 years. You would think that within that long a timeframe, it would be able to devote a portion of the budget to cost reduction, designing the new vehicles right (reusable) the first time.
I am not the only one making this point. Many experts agree that developing reusable spacecraft is crucial to reducing transport costs enough to enable a sustained human presence on the Moon, and is vital to any imaginable kind of lunar commerce. Unmeel B. Mehta pointed out in a Space News op-ed last month, “For leadership in Earth to Orbit Transportation, revolutionary propulsion systems and reusable launch vehicles are required”. NASA is basing its entire lunar program for the next 20–30 years on expendable booster technology and expendable spacecraft.
|Without a good answer to the “Why” question, another, equally undesirable result could unfold: an extravagantly expensive, poorly planned program whose uselessness becomes apparent to Congress only after $100 billion or so has been wasted on it, and then is shut down like Apollo.|
Among the six “themes” or rationales proposed to justify the Lunar program, the rationale of economic expansion is a hollow rationale when NASA is spending virtually zero dollars itself on reducing the cost of space transportation, something utterly necessary for any conceivable lunar commerce to operate. Any economy depends on economic transportation. This was proved 180 years ago when the Erie Canal reduced cargo transport costs between Buffalo and New York by a factor of 100. Without the canal, New York would never have become the “Empire State”.
Foust also points out that without a clear rationale, the lunar program may never materialize. In asking NASA to try again with its answer to the “Why” question, he is dead right. Without a good answer, another, equally undesirable result could unfold: an extravagantly expensive, poorly planned program whose uselessness becomes apparent to Congress only after $100 billion or so has been wasted on it, and then is shut down like Apollo. Can we avoid this fate? We should continue to press NASA for a fair hearing on reusability in any future transport trade-off studies, and get them to at least consider phasing in reusable alternatives for both boosters and spacecraft.