Centaur Upperstage Applicability for Multi-Day Mission Durations with Minor Insulations Modifications

Abstract

In its stori ed and illustrious past, the Centaur upperstage has flown over 175 military, NASA, and commercial flights, including missions up to 12 hours in duration. With its light weight pressure -stabilized tanks and high ISP of its LO 2/LH 2 propulsion system, the ef ficient Centaur is ideal for maximizing payload capacity. Current thermal protection limits the propellant boiloff to slightly less than 2% of loaded propellants per day. Incorporating thermal enhancements to its existing design, long missi on durations, such as lunar explorative missions, are within the near -term grasp of Centaur. From a vehicle perform ance perspective, reducing boil off of the LO 2 and LH 2 cryogen propellants is essential to extending Centaur’s capability to longer duration flights. This translates into the goal of minimizing the net heating to the pressure -stabilized propellant tanks. With relatively slight modifications/upgrades through the use of existing technology, enhancing its thermal insulation would enable Centaur to fly missions from several days in length up to week -long durations, depending upon payload requirements. By applying several more layers of MLI insulation to the Centaur sidewall acreage, system boiloff rates of slightly more than 1 %/day are realistic and achievable. Going one step further, Variable Density Multiple Layer Insulation (VDMLI) radiation shielding provides the necessary characteristics to enhance Centaur’s thermal insulation via further reduction in acreage heating. VDMLI is both relativ ely mature and demonstrated, where the key challenge is the repeatable application to flight hardware. Projections show that system boiloff can be reduced to 1% of loaded propellants per day, making 3 -day mission durations feasible in the near -term.