Design and Testing of a Prototype Atmospheric Gas Collection Apparatus for a Mission to Mars

Abstract

A novel spacecraft, the Sample Collection for Investigation of Mars (SCIM), was proposed for the collection and return of atmospheric gas and dust samples from the martian atmosphere. The SCIM mission, part of NASA's Mars Exploration Strategy, would allow scientists to greatly enhance our understanding of Mars' water, climate, and geological evolution by studying the element and isotopic composition of the gas and dust. The SCIM spacecraft was proposed to collect its samples during a single high-speed pass through the martian atmosphere at an altitude of 37 km and return the samples back to earth. For the atmospheric gas sampling aspect the SCIM employs the Atmospheric Collection Experiment (ACE), a dual-component apparatus consisting of a passive and a cryogenic sorption gas collection system. Each of these systems possesses a collection vessel that is initially under high vacuum. At the time of entry into the martian atmosphere, valves on SCIM open and gas flows into the parallel-plumbed passive and cryogenic sorption gas collection systems. The passive system simply allows the incoming gas to fill an initially evacuated 1 Liter vessel. The cryogenic sorption system employs a Joule-Thompson cryocooler and sorption medium that initially condenses and captures the incoming gas. As the SCIM begins to exit the atmosphere isolation valves close and trap the gas samples in their collection systems for the return journey back to earth. The minimum SCIM mission goal was to collect 100 cm3 @STP(≈ 0.2 g) of martian atmospheric gas and the ACE was being designed to gather 1000 cm3 @STP (≈ 2.0 g) using both the passive and cryogenic systems. The volumes referred to above correspond to standard temperature and pressure on Earth (e.g., STP). The goals of this study were to prove the gas collection concepts mentioned above and develop the numerical and experimental tools to allow for the optimization of a flight worthy ACE. This paper discusses the design, analysis, and testing of a prototype ACE. First, more specific details on the design and testing methodology for the prototype are presented. Next, the development of a computational fluid dynamics (CFD) model is discussed. Finally, empirical pressure data from the prototype tests are used to assess the performances of the passive and cryogenic sorption gas collection systems and are compared to numerical pressure predictions to provide a benchmark for the CFD model. Results indicate that the prototype ACE is capable of meeting the design goal of 1000 cm3 @STP (2.0 g) of total gas collection.