What I could see making sense though is adding drop tanks for bigger missions. Like say you want to land a really big payload, you add some extra drop tanks that you leave behind on the surface. Not sure though. Would have to think about it.

~Jon

Re: reusable lander ascent propellant

I have just carefully re-read the LM documents, and it seems to support my conclusions about ascent propulsion. Storable propellants are a better choice for ascent propulsion.

First off the penalty of storable propellants for short missions isn’t very great. Figure 1 of the “Lunar Lander Configurations…” document shows little mass penalty for storable propellant ascent propulsion. For a two stage system (presumably of no more than 14 day mission duration) the penalty is about 12% (45 tons compared to 40 tons). And that penalty gains the reliability and finer flight control that storable propellants provides, important qualities, even more so for a manned lander.

Secondly the penalty for long-term storage of cryogenic propellants is spelled out pretty convincingly. Even if all the proposed boil-off mitigation systems work as advertised the propellant loss over six months is 18% (0.1% per day). In the same document the description of the all-cryogenic propellant “Concept 3: reusable single-stage lander” states such a lander is likely limited to shorter mission durations.

It seems to me the problem with an all-cryogenic propellant reusable manned lander is it falls into a gap between needs and capabilities. The commitment to a lunar depot infrastructure that the reusable lander needs implies lunar operations that include a permanent lunar base. And an all-cryo lander is most capable of sortie missions instead of long duration lunar base crew rotation missions.

This list can go on and on, but starting with Centaur hugely reduces development risk, system weight, residual mass and uncertainties providing a great efficient foundation for the lander propulsion system.

On the other hand, ULA knows squat about landers, terminal guidance, etc. I think that it would make a lot of sense for ULA to simply provide the basic propulsion system while NASA or Lockheed turn it into a lander.

If you use a 1900m/s base delta-V requirement for landing, with another 90s of hover time (140m/s delta-V) from the secondary propulsion, the Centaur based one-way cargo lander could land over 29mT.

The big difference in this situation is that the Centaur lander isn’t doing the LOI for that big of a payload, and it starts in lunar orbit with a full tank of propellant. That payload would either need to be delivered in smaller pieces using smaller Centaur based transfer stage, or would need a Wide Body Centaur/ACES or EDS-based transfer stage to deliver it to lunar orbit.

If you could tank up the LSAM in lunar orbit, it could deliver a much bigger payload. But that’s kind of my whole point with this article–having a lunar propellant depot gives you far more flexibility and capability than an HLV only non=depot solution.

~Jon

~Jon

Please show how you arrived at the 25 mT payload estimate.

Also, note that several sources give the theoretical deltaV of the Apollo descent stage as 2470 m/s, which suggests that they indeed wanted much larger reserves on a landing mission than a typical satellite launch.

BTW, here’s a good link on statistical numbers for the Apollo lunar landings:
http://www.retro.com/employees/gherbert/Space/LunMil2k/Lunar_DeltaV_PlusStats.html

~Jon

I went back and checked the numbers for the two landers, and it turns out that both of us were off. If you run the numbers on Tables 1 and 2, you get both of them having a landing DV of about 2250m/s give or take. Historically from the Apollo missions they used an average of 2050m/s for descent and landing. That extra 200m/s provides over 2 full minutes worth of hover time. While I could quibble with you on the need for that much hover time, rejiggering the numbers using the higher delta-V requirement *and* the heavier 3-RL10 lander (as per your suggestion) *and* the much bigger LMK (5x bigger because of 5x the landed mass), you still get over 25mT worth of cargo on the surface.

So, no the LM guys aren’t stupid, and yes even if you make pessimistic assumptions a Centaur derived cargo lander could put about the same payload to the lunar surface as the Cargo LSAM.

~Jon