Propellant and changing flight plans

NASA’s October 23 update describes revised proposals. Starship retains orbital propellant aggregation and would meet Orion in Earth orbit before sending their joined vehicles toward low lunar orbit. Blue Origin’s accelerated approach defers propellant transfer and uses three expendable transfer stages to deliver its lander to an elliptical lunar polar orbit. These are planned operations, not completed demonstrations.

The comparison shows two ways to distribute propulsion work across a mission. One concentrates propellant through transfers; another adds stages that perform work and are then discarded. A fair comparison tracks delivered capability, required launches, interfaces and evidence gaps. Counting only the lander’s final engines misses much of the system.

Cryogenic propellants must stay extremely cold to remain in the intended liquid state. Heat from sunlight and spacecraft equipment can cause boiling, while low gravity complicates collecting and measuring the fluid. NASA’s cryogenic technology work addresses storage, transfer and gauging as related but separate tasks.

Transferring liquid is therefore more than bringing two spacecraft close together. A transfer system needs a suitable flow path and temperature conditions, as well as a way to establish how much usable propellant arrived. Successful docking can support the operation without proving that the transfer itself succeeded.

Count usable propellant, then protect the reserve

In an original classroom budget, a receiver starts with 90 usable units, receives 25 and loses 5 during the operation. It then has 110 units. If a protected reserve is 20, only 90 units are available for the planned maneuver. These invented numbers explain accounting; they are not specifications for either commercial lander.

A second teaching plan retains its propellant in separate stages rather than moving it to a receiving tank. That avoids the particular transfer step in the sketch but adds staging and separation requirements. Neither simplified sketch establishes which real design is safer, cheaper or ready sooner. Those conclusions require evidence for the complete system.