Statistical Ars Legatus Legionis
15y
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pseudonomous said:
I will presume that both you and the NASA guys got the math right and that for a polar landing NRHO makes sense. But if they are really going to "question all requirements", we have to admit the possibility that they might fly Artemis IV or V as an equatorial region landing, do we not?
For Orion as a crew vehicle it doesn't matter. Orion has 1,300 m/s of DeltaV of which 300 m/s is allocated for docking, station keeping, and course corrections. So it is limited to orbits which require <1000 m/s to enter AND exit (NRHO is about 900 m/s). Even equatorial LLO with a 3.5 day loiter (13 days + surface time for total mission time) is a minimum of 835 m/s * 2= 1670 m/s. Loiters improve the worst case scenario but only make a small impact on the best case ones. Even if you could modify the Centaur V to have 3 day endurance and cryocoolers and use it for part of LOI (which we shouldn't that will end up being a $5B 10 year boondoggle) it has in the ballpark of 500 m/s excess DeltaV so you are likely still short unless you dip into your reserves.
Longer term with a better crew vehicle you might have the option to go to LLO Direct via fast insertion but it still isn't a slam dunk option with reusable landers as your example bring up. If you have reusable crew landers LLO as a staging point is made worse if you change landing locations. There isn't one LLO and as such to move between LLOs you need to do a plane change. The only cost effective way to make a plane change is to burn to a highly elliptical orbit you know like how NRHO is highly elipitcal. Every mission requires more prop, has more boiloff, and when changing landing sites you also pay a plane change tax. One feature of NRHO is due to its high perilune you can reach every spot on the moon with a consistent DeltaV cost. This makes mission planning a lot easier. You could land near Apollo 11 on the 70th anniversary if you wanted to. It is no harder (or easier) from NRHO than the poles or any other landing site.
To be clear these nuanced challenges mostly apply to the staging point for a crewed mission. If you are fine with adding 15+ day loiter time you can drop heavy cargo on the south pole by going LLO quite cheaply. If it is an expendable cargo lander efficiency doesn't really matter because it is a one way trip so Direct LLO without a loiter becomes viable.
The reality though is it is complicated and it depends on exactly what mission, to exactly where, how long you are willing to loiter, is the lander reusable and is it crewed. Another wrinkle is if it is crewed are the crew in their own vehicle or pushed there by the tanker. If the crew is riding on the tanker than fast insertion is required which means your crew made the thousands of tons of prop more expensive as well. Likely to the dismay of people in NASA doing this kind of analysis the public discourse though has largely been "NRHO is stupid derp derp derp".
