In the post on the architecture that Doug Plata proposes for the Lunar development, I likely appear as a naysayer as I picked on the sections that I disagreed with or thought that there was a better way forward. Not surprisingly, Doug disagrees with my nitpicking. There is one point that we will not likely agree on which is government involvement. He believes that a Lunar COTS approach can hold costs to roughly a billion a year. I believe that involving NASA at management level brings in baggage that will blow past a billion a year under any contract method due to congressional involvement. There are a lot of talented people in the agency that answer to political reality. As a single example, commercial crew is $6.8 billion to develop two capsules plus a handful of flights. There is a lot of development for a Lunar program that is far more involved than a couple of capsules. On to the technical stuff that I actually like.
Doug thinks that the technical suggestions that I made would delay Lunar settlement, add risk, and drive up costs. It is a series of reasonable concerns that I will try to address. I suggested Lunar hover slam landings, a rotovator, a low gravity research facility in LEO, and propellant depots. Each of these is questionable without more detail on my meanings, and certainly debatable even after I explain. I will be surprised if one or more of them isn’t honestly trashed in comments.
I was one that didn’t see the hover slam landings working, didn’t expect a high percentage success on the barge, and didn’t believe that landings without deep throttling would be possible. You can probably dig up old posts and comments of mine naysaying on all these things. The fact is that SpaceX has succeeded in reliably landing vehicles vertically with a thrust/weight considerably higher than one. It seems to be a matter of having control systems that can accurately decelerate vertical velocity to zero at a specific altitude. It seems to me that that altitude can be regolith zero just as it can be barge or LZ1 zero. The advantage would be that it would become unnecessary to develop a whole new landing stage for the early equipment and supply deliveries. This would be a way of using the second stage all the way to the Lunar surface. While there is risk, I believe a dedicated Lunar lander will also have some element of risk, just later and more expensive. Later on, dedicated landers will be necessary, especially for human landings.
A rotovator is potentially one of the key pieces for Lunar transportation. A 1,600 m/s unit could catch payloads from TLI and soft land them on the surface. The orbital energy gained could be used to pick up payloads from the surface and sling them to TEI. Dougs’ concern on this one is cost, risk, and schedule. A 1,600 m/s rotovator would seem to have a mass ratio of roughly 25. That is a 25 ton unit could handle 1 ton payloads, in theory. I suggest that the testing and development should take place in LEO. At $2K per kilogram launch costs, a 25 ton rotovator would cost $100M to launch and about a quarter of that for the tether material itself. This would be about an eighth of the first year budget. I would not suggest waiting on it to prove itself before starting the settlement missions. In LEO, the operators train, learn, and develop by picking up payloads from 1,600 m/s below orbital velocity and slinging them to 1,600 m/s above orbital velocity. This would be a long way towards a GTO or TLI. Only after proficiency is reached is a unit sent to Lunar orbit. Assuming it works and survives the clutter of LEO of course. Once in Lunar orbit, it roughly doubles the payload of a vehicle in TLI to the Lunar surface. It also allows material from the Lunar surface to be placed in TEI with no propellant or engines. A third function would be pick up and drop off at various points on the Lunar surface for multi-location prospecting without propellant or engines. The rotovator is a risk, a risk with high payoff. And if it doesn’t work, 1/8 of one years’ budget might be an acceptable loss against the potential benefits.
A low gravity research facility in LEO is another point of disagreement. Doug sees no need for the data until actual settlement generates the information needed. I see it as yet another set of information that should be generated in parallel with development. A 50 ton variable gravity facility could be placed in LEO for a similar cost as the rotovator, as long as feature creep and over engineering is avoided. A simple design that can run unmanned most of the time with occasional visits for maintenance, specimen swap, or clean up. Only after a few generations of rodent and primate trials would it be necessary to send permanent human crew to nail down the data points. It may be that Lunar level gravity is enough to maintain health without centrifuges. Or it may be that it is totally inadequate. It would be good to have some realistic data before shipping large scale equipment to the moon that turns out to be unnecessary on one hand or inadequate on the other. The early animal studies could be started by the time the first humans are on the surface with the primate studies completed well before adverse reaction might be expected to show up. A possible benefit would be if the settlers could avoid some of the extreme exercise requirements of LEO. This would be another quarter years budget from his program. It just might more than pay for itself in reduced future equipment and exercise requirements.
To me, propellant depots are almost a no brainer. Not everyone shares my opinion. The way I see it, Lunar development would almost require depot type facilities. The first depot could simply be a repurposed upper stage combined with high sortie rates. A relatively high boil off rate could be acceptable if it means being able to launch the large pieces with the equipment you have instead of the equipment you hope will be available eventually. Refuel the upper stage of the FH and send a 60 ton payload to the Lunar surface in one shot. Propellant can be bought from any delivery including from excess capacity in a given launcher. If a vehicle has the capability of placing 20 tons in LEO and the volume restricted payload is 10 tons, then 10 tons of propellant can be bonus payload. The same applies in Lunar orbit where it would make almost as little sense to send a half loaded vehicle to the surface as it would to send one with insufficient margins. There should be no reason for depots to slow down Lunar development, and the efficiencies should make the system self funding almost from the start. As long as the over specified and over designed techniques of the past are avoided of course.