Propellant Depot - Heavy Lift Versus Depot Centric Architectures

Heavy Lift Versus Depot Centric Architectures

In the heavy lift architecture, propellant, which can be 2/3s or more of the total mission mass, is accumulated in fewer launches and possibly shorter time frame than the depot centric architecture. Typically the transfer stage is filled directly (coined refueling) and no depot is included in the architecture. For cryogenic vehicles and cryogenic depots; additional boiloff mitigation equipment is typically included on the transfer stage, reducing payload fraction and requiring more propellant for the same payload unless the mitigation hardware is expended.

Heavy lift advocates state that the total mass to orbit required for a mission can actually increase because of the need to launch more propellant tanks and boil-off mitigation hardware. Heavy launch vehicles are not developed, so these costs are added to the trade, rather than use existing smaller rockets. Heavy lift advocates question the cost model for propellant depots and cite the need for development and demonstration.

Depot advocates claim this increase in mission mass would be offset by a decrease in the cost per launch and the elimination of the fixed costs of the heavy lift launch vehicle when not required in given year. Further, long life components including insulation and power and cryocoolers could be placed on the depot and not expended, further reducing the mass per mission and hence costs.

Heavy Lift is compared with using Commercial Launch and Propellant Depots in this power point by Dr. Alan Wilhite given at FISO Telecon.