In the mid 1990s this correspondent, in his day job as an aerospace engineer, designed and built a diffusion experiment called LMD (Liquid Metal Diffusion) that flew into space to help determine the effects of gravity on diffusion. Built by the author’s (tiny, sole-proprietorship) engineering consulting business Tomorrowtools under contract with the University of Alabama in Huntsville’s Center for Microgravity Materials Research, the experiment flew in 1997 aboard Space Shuttle mission STS-81 to the Russian Mir Space Station where it was operated for weeks at a time.
The LMD unit itself was literally a black box that was so heavy from the lead radiation shielding it carried that it couldn’t be stored in the standard Space Shuttle storage lockers. Instead, it was put in its own special transport bag and flew in seat 7 on the Shuttle Middeck beside some of the astronauts. Because it contained American radioactive material that was going to a Russian orbital facility, we were told then-Vice-President Gore himself had to review the required White House authorization papers.
So what did this radioactive, heavy black box do and how did it work? LMD had many components of many different materials – mainly aluminum (light blue in the referenced diagram), steel (sky blue), lead (royal blue) and gold (shown as light orange). There were lots of wires and custom electronics boards in there, too. The interior of the box was divided into a radioactive sample storage volume and an experiment volume. These were separated by a steel support plate. The lead formed a hollow cylinder like a resealable nut or coffee can in the storage volume that was used to shield the astronauts from the experiment’s radioactive materials. Inside this lead cylinder was a piece of aluminum shaped like the bullet-holding cylinder of a revolver pistol, which in this case held five radioactive cartridges. Astronauts used a red star-shaped handle outside the box to rotate the aluminum cylinder to the desired experimental cartridge. They then used an aluminum plunger rod to loosen a cartridge from the support cylinder and push it through a hole in the steel support plate, into the gold oven that was the heart of the experiment volume.
The gold oven in the experiment volume was the size and shape of a frozen orange juice can and weighed a couple of pounds, made from the melting of 99.9%+ pure Canadian Gold Leaf coins (It was technically illegal for us to melt U.S. gold coins, so we used Canadian ones. Other Canadian connections to the project was a Canadian grad student, Lyle Jalbert, using the project for his thesis and the use on MIR of the Canadian Space Agency shock-absorber platform called MIM). Gold was chosen as the engineering material of choice for the oven because it had the necessary heat conduction properties of copper and the radioactive shielding properties of lead in a single material. Five tiny holes/shafts were drilled in the gold oven – a big one along the axis where the sample cartridge was inserted, and two others through the walls on each side that connecting the central shaft with the outside. Positioned outside each of these four holes was a solid-state electronic radiation detector, basically a “Geiger counter” that could count every minute how many radioactive particles were coming from the cartridge at that location.
The cartridges contained samples of a metal called indium that were the size and shape of a wooden matchstick, with the “matchhead” part being a radioactive form of indium and the “matchstick” part being non-radioactive. Indium is special because it melts at a very low temperature (170 degrees C) that can easily be reached by a home oven – or a gold oven surrounded by a special heating pad. Once melted, the radioactive speck of indium began to diffuse through the non-radioactive part of the overall indium melt. The progress of this liquid metal diffusion could be monitored by detecting over time when and how much of the radioactive material had reached the holes drilled into the side of the gold oven. With some fancy math and handwaving, a lot can be determined about how diffusion works from such observations.
During its stay on MIR three of the five cartridges were run, although the data from one of the runs was lost due to a computer error. Because of a fire on MIR, the final two runs were not performed. The LMD experiment unit was brought back to Earth in a subsequent Space Shuttle flight. The Russian MIR space station eventually reentered the Earth’s atmosphere too and burned up, and has been replaced by the International Space Station. Overall, the LMD effort was considered a success and in time the author duely received a so-called pat-on-the-head “attaboy” from NASA (look for T-Tools, top right, page 6 – that’s me!). I wish I could say we discovered something truly profound, a new process that’s being used in making the Pentium 4 chip, maybe, but we didn’t. That’s the REAL scoop about how science progresses today and every day – slowly, unspectacularly, one data point at a time.