In 1994, the space shuttle Discovery held a Wake Shield disk behind it while still attached to its robot arm; the facility produced 5 good semiconductor films

On February 3, 1994, space shuttle Discovery lifted off carrying a strange, disk-shaped machine that had one job: catch the emptiest vacuum humans could find. It was the sixth crewed shuttle flight and the first mission of the Shuttle-Mir cooperation program, carrying cosmonaut Sergei Krikalev as the first Russian to fly on a U.S. shuttle alongside five NASA astronauts — though Discovery itself did not dock with or visit Mir on this flight; that milestone came a year later, on STS-71, according to NASA's official account of the STS-60 mission. That experiment was called the Wake Shield Facility, or WSF, a stainless steel disk about 12 feet wide, shaped almost like a giant satellite dish. The goal was to fly fast enough to create a wake with a vacuum far cleaner than anything achievable in a ground-based lab.

Why scientists wanted a hole in space

Even hundreds of kilometers above Earth, stray gas molecules drift around, mostly atomic oxygen. These can interfere with delicate manufacturing, particularly when researchers are trying to grow semiconductor crystals one atomic layer at a time, a process called epitaxy. At sufficient speed, the spacecraft leaves many of those molecules behind, at least in its wake. The peer-reviewed study, ‘Wake vacuum measurement and analysis for the wake shield facility free flying platform’ published in the journal Vacuum found that the facility's wake could reach vacuum levels many times cleaner than those in Earth-based vacuum chambers. That kind of vacuum is ideal for growing pure crystal films of materials such as gallium arsenide, a compound used in high-speed and high-power electronics and in some solar cells.

The plan hits a snag

According to NASA's own mission history, the plan was for astronaut N. Jan Davis to use the shuttle's Canadian-designed robot arm to deploy the WSF, expose it to atomic oxygen to remove surface contamination, and then release it for two days before retrieving it. That did not happen as planned. NASA's mission history notes that ground teams lost contact with the facility during the release process, and the crew had to keep it attached overnight while engineers traced the problem to radio interference that preflight testing had missed. A computer reboot the next day cleared the communication glitch, but another problem with the WSF's navigation system meant it could never be safely released. So the crew made do. The designers had intended all the semiconductor manufacturing on this flight to be done with the disk floating free in the wake of the shuttle, rather than attached to the robotic arm. Tethered to the arm, the disk still trailed in the orbiter's wake, but closer to the shuttle's own outgassing and turbulence than a true free flight would have allowed, meaning the resulting vacuum was likely less pristine than originally intended. It was a makeshift solution hundreds of kilometers above Earth.

Five good films despite the odds

Even without a proper free flight, the mission was not a failure. NASA's account confirms this, saying that the facility was able to produce five semiconductor films of good quality before packing it away on flight day 7. This suggested that even a partial, tethered version of the experiment could produce usable results and encouraged engineers to try again with a full free flight.

NASA's Spinoff publication reports that the follow-up missions bore that out, flying the Wake Shield Facility two more times on STS-69 in 1995 and STS-80 in 1996, both times as a truly free-flying platform trailing the shuttle at a safe distance, documenting how space research becomes everyday technology. Those follow-up missions produced gallium arsenide films that researchers described as very pure, because space offered a vacuum no factory clean room could match.

Why any of this still matters

A shuttle mission from more than three decades ago might seem like history, but the Wake Shield experiments still matter. They were an early attempt at making high-tech materials in space, where gravity and atmosphere are less of a factor. NASA's Spinoff program has credited WSF-derived gallium arsenide research with applications in solar cells and high-frequency communication components, where performance matters more than cost. Discovery's STS-60 crew never got the clean, free-flying deployment they had trained for, but NASA's own mission summary counts the five semiconductor films produced from the end of the robotic arm as evidence the underlying concept worked. Sometimes scientific progress comes from improvising around setbacks.