|Standards in Space
by Clare Coppa
Materials specified to ASTM International standards reinforce two Mars Exploration Rovers scheduled for lift-off in June and July. MER spacecraft will traipse a lofty 33 million miles (53 x 106 km) to probe Mars for past or present life, looking for signs of organic molecules and mapping potential biosignatures. Theyre scheduled to land Jan. 4 and 25 and operate on the surface until May, 2004.
Scientists who built the robotic Rovers and self-propelled spacecraft at the Jet Propulsion Laboratory in Pasadena, Calif., used dozens of ASTM standards in their materials-processing protocols. JPL materials specialists led by Cheng Hsieh referenced ASTM standards to test materials for MER Landers, Rovers, cruise portions, and entry/descent/landing operations. They referenced about 90 sets of materials lists for MER, each list containing 10 to 50 materials, according to a senior engineer.
Hsiehs team tested thermal-coatings for radiators on the Rovers and Landers with ASTM D 3359, Standard Test Methods for Measuring Adhesion by Tape Test. Another frequently-used method was the [ASTM] shore hardness test, Hsieh says. Its part of a program to analyze the structural adhesive to make sure the hardware for entry, descent and landing is cured properly. For example, a structural adhesive for the Rover might have a listed shore hardness of D85. If a situation arose where it had a hardness of D40, theyd say this material is bad, it hasnt cured properly. So its a good cross check, he says.
Among other ASTM standards used by JPL engineers are ASTM specifications A 580, A 313, and A 276 for 300-grade CRES (corrosion-resistant) stainless steel for MER propulsion systems; and ASTM A 582 for cruise-stage hardware. For the payload, they specified aluminum alloy-6061 with B 308; and tantalum with B 575. For the Rovers suspension gears, they tested Teflon® with D 2116. For Rover hardware, they specified Ultem® with D 5205 and Vespel® grade SP-3 with D 6456.
Hsieh is an ASTM standards developer and JPL materials group supervisor. He shared a recent distinction with NASAs Mars Exploration Program scientists who received a number-one rating for effectiveness from the U.S. Office of Management and Budget out of 234 federal programs evaluated. Bolstered by effective methods and ingenious technology, let the countdown to Mars begin. //
Copyright 2003, ASTM