(Ultimate arm chair engineer warning, long but hear me out) Artemis is a mess. I've been working on a very deep dive going over all possible options to get humans on the moon with existing (and near future existing) hardware and I've discovered something quite interesting about the current plans for Starship HLS. Starship HLS should ABSOLUTELY not do it's own Trans Lunar Injection. SpaceX should do a "stubby" HLS which only has enough propellant to get from NRHO down to the surface and back. This only requires about 400 tonnes of propellant because you could remove something like 20 or 25 TONNES of tankage that is currently baked into the design that's ONLY used ONCE to do the TLI. A stubby Starship HLS now has MUCH greater margins too, almost 700 m/s of dV for a round trip between NRHO and the lunar surface. This also means its refueling requires substantially less propellant for the subsequent missions. It makes the refueling trans lunar tanker require much less propellant, which means it requires fewer launches to fuel that up as well. It all works towards much fewer launches all together, a much more efficient lunar lander that isn't carrying around an additional 25 tonnes of dry mass, a shorter vehicle which requires less hardware for the elevator, a lower center of gravity, much lower landed mass since it requires less propellant to get back to NRHO etc etc. It's a win : win. The only drawbacks I've found so far is the trans lunar tanker and HLS would need to be able to dock nose to nose and have heavy bracing to be able to perform the TLI docked with the Trans Lunar Depot, however this would certainly be less mass than the 25 tonnes of parasitic tankage we've removed. The other drawback is a trans lunar refuel depot that has minimal dry mass (and therefore only 2 Rap Vacs) would likely need to expend a booster to be able to get into orbit initially since it would take about 19 minutes for two Raptors to burn through 1,600 tonnes of prop, so you'd have to launch it with less than 600 tonnes of prop which still gives it enough dV to get into orbit if the booster is expended, but also can get the job done with just two Raptor Vacuums, would be be most efficient for all trans lunar refueling operations. BUT, THIS IS TRUE OF THE FULL HLS AS WELL! The numbers BARELY close with little margin for error and boil-off with a full height HLS doing its own TLI. A stubby HLS is almost the only real viable option that has much greater margins and requires far less to refuel once its at the moon. Best of all, cargo and crew volume remain the same for a stubby HLS Starship. There's almost no compromise other than the complication of having to do the TLI with two docked vehicles. Something that's never been done before, but certainly the juice is worth the squeeze over having an inherently inefficient lunar lander. I'm working on a very in depth deep dive on all things Artemis and this is just something that stood out. I can't wait to show you my full rundown. There's some interesting options out there that can help ensure the US beats China back to the moon while also aligning with long term sustainability goals. What're your thoughts @elonmusk?
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