Design of Molecular Traps for the High-Speed Pumping of Directional Low-Density Nozzle Flow

Abstract

In the testing of rocket nozzles for space applications, the simulation criterion is determined by the test objectives. These objectives normally fall into one of two general categories: those tests requiring accurate exhaust-gas plume development for adjacent structure cooling problems and exhaust-gas radiation studies, and tests concerning rocket system reliability in a vacuum and thermal space environment. In the latter type of test, the rocket system is maintained for long time periods in a simulated space vacuum and thermal environment with interspersed rocket firings to ascertain the system reliability. For this purpose the exhaust flow external to the physical nozzle is of no interest and can be intercepted before it has fully expanded and be pumped from the system at a relatively high backpressure. The J-2A Test Facility at the Arnold Engineering Development Center, Tennessee, is designed for this type of test [¹]. A facility for a similar test is described by Barkdoll and Anderson [²], who have presented the results of their investigation on the use of staged cryopumps to pump rocket exhaust products. In their case the mean free path in the flow was small compared to the dimensions of the cryopump, and the flow could be analyzed using continuum concepts.