This is a follow-up to my previous post at
http://disc.server.com/discussion.cgi?id=131070&article=10766

The previous Mars sample return (MSR) architecture, which involved planning a joint NASA-CNES effort, addressed the issue of Sample Transfer Chain (STC), which is the name given to the process of moving samples from the collection device (the Rover Corer/Cache mechanism and/or Lander-Based Sampler (LBS) Drill) to the Orbiting Sample (OS) Canister in the Mars Ascent Vehicle (MAV) Nose Cone.

The main purpose behind STC is to ensure sample containment and sample integrity through the end of the mission. Two concepts, the Canted Concept and the Magazine Concept, were designed, though no final decision had been made before the new Mars Architecture iteration announced last October.

Under the Canted Concept, the OS inside the MAV Nose Cone would be "canted" rather than opening the entire nose (containing a small cap and plug assembly along with a collection funnel), which had the advantage of requiring less precision in positioning the Rover over the MAV. Also, the only external component that must be decontaminated is a ring where the cap meets the OS body, since it is the only surface of the OS that is exposed to the Martian environment. Various decon designs were considered, including the pyro welding technique (either befor MAV launch or during ascent, though the former was preferred for aerodynamic reasons. Unfortunately, the MSR Project did not favor the Canted Concept due its complexity and tight tolerances, and also because of a reluctance in having the Rover remount the MAV for sample transfer.

The Magazine Concept (aka Chamber of Decontamination) emerged as the better of the two. Under this concept, the Rover parks near the Lander, but does not remount the MAV, and the cached samples are loaded via robotic arm. The MAV thermal enclosure igloo functions as a clean room in that OS loading is performed without being exposed to the Martian environment. Specifically, a Chamber of Decontamination (COD) is built into the wall of the MAV igloo and serves as an airlock. The outer COD door opens and the robotic arm inserts the sample magazine(s) into the COD. Seals form a protective shield around surfaces exposed to the Martian environment that have to be sterilized by gas-sterilization pyro welding. Following a rather complex procedure of sealing/welding the various sides of the magazine (both Earth-clean and Mars-exposed), the magazine is then extracted and inserted into the OS. When the launch window opens, the igloo is opened and the MAV is immediately launched. The outcome of this relatively meticulous process is that the chain of contact with Mars is completely broken before launch.

References:

IAF-00-Q.3.03
William O'Neil, JPL and Christian Cazaux, CNES
The Mars Sample Return Project: A Status Report
51st IAF Congress, Rio de Janeiro, 2000.

"STS Mechanical Subsystem Sample Manipulation and Transfer, Magazine Concept", JPL Internal Peer Review, April 18, 2000, Pasadena, California, USA.

Alex R. Blackwell
University of Hawaii