An Integrated Cryogenic Helium System for extended duration balloon flights

Abstract

ICHS SYSTEM NEED AND HISTORY The Integrated Cryogenic Helium System (ICHS) described by this paper is designed to address a number of needs in large, long duration scientific balloons. These include the provision of helium gas for leakage and diffusion makeup, the ability to provide cooling power for onboard scientific instrumentation or other cooling needs, and to provide a tool for altitude and trajectory control. Besides the new Superpressure balloons being developed for the NASA Ultra Long Duration Balloon (ULDB) missions, it is anticipated that the ICHS will find application in any long duration high altitude balloon system, including NASA’s traditional zero pressure and the Over-pressure Zero Pressure (OZP) designs. Included in this paper are the definitions of hardware requirements involved in an on-board helium replenishment system. A detail design for the complete on-board helium replenishment system is described, including elements such as state of the art low heat leak liquid helium storage dewars, low heat leak plumbing, controllable valving, heat exchangers, a rotator fitting bypass, and a microprocessor based control system. The mission life of a high altitude scientific research balloon has been determined by the leakage, diffusion, and/or diurnal venting losses. The present state of the art is to accept these losses, compensating for them by dumping hard ballast. This approach leads to significant payload capacity reduction and gives only limited extra mission lifetime for the balloon vehicle system. Even with the ballastless superpressure balloon systems, lifetime is determined by unknown levels of leakage and diffusion of helium gas through the pressurized envelope. The effect of small unexpected leaks may be ameliorated by having a helium gas makeup available. As an example, Figure 1 shows the advantages of having a helium gas replenishment system for a ULDB type superpressure balloon (95.4 m diameter, 3262 kg initial system mass, 20% initial superpressure, and an a/c of 0.2): --5m’Z;;;;;;;.Ra,e t%,day --lOJO Ltter System. Rate l%Jdry -0-502 Uer System. Rots 5%/day 0 10 20 32 40 50 50 70 90 90 Duration (days) [GURE 1: EFFECT OF LEAKAGE/GAS REPLENISHMENT ON BALLOON LIFETIME (EXAMPLE) Copyright 01999 by GSSL Inc. Published by the American Institute of Aeronautics and Astronautics, Inc. , with permission.