materials back to Atlantis (the most materials transferred between the two spacecraft to that date). The STS-81 crew also tested the Shuttle Treadmill Vibration Isolation and Stabilization System (TVIS), designed for use in the Zvezda module of the International Space Station. The shuttle's small vernier jet thrusters were fired during the mated operations to gather engineering data for "reboosting" the ISS. After undocking, Atlantis performed a fly-around of Mir, leaving Linenger aboard the station. During his Increment, Linenger became the first American to conduct a spacewalk from a foreign space station and the first to test the Russian-built Orlan-M spacesuit alongside Russian cosmonaut Vasili Tsibliyev. All three crewmembers of expedition EO-23 performed a "fly-around" in the Soyuz spacecraft, first undocking from one docking port of the station, then manually flying to and redocking the capsule at a different location. This made Linenger the first American to undock from a space station aboard two different spacecraft (Space Shuttle and Soyuz). Linenger and his Russian crewmates Vasili Tsibliyev and Aleksandr Lazutkin faced several difficulties during the mission. These included the most severe fire aboard an orbiting spacecraft (caused by a backup oxygen-generating device), failures of various on board systems, a near collision with a Progress resupply cargo ship during a long-distance manual docking system test and a total loss of station electrical power. The power failure also caused a loss of attitude control, which led to an uncontrolled "tumble" through space. The next NASA astronaut to stay on Mir was Michael Foale. Foale and Russian mission specialist Elena Kondakova boarded Mir from Atlantis on mission STS-84. The STS-84 crew transferred 249 items between the two spacecraft, along with water, experiment samples, supplies and hardware. One of the first items transferred to Mir was an Elektron oxygen-generating unit. Atlantis was stopped three times while backing away during the undocking sequence on May 21. The aim was to collect data from a European sensor device designed for future rendezvous of ESA's Automated Transfer Vehicle (ATV) with the International Space Station. Foale's Increment proceeded fairly normally until June 25, when a resupply ship collided with solar arrays on the Spektr module during the second test of the Progress manual docking system, TORU. The module's outer shell was hit and holed, which caused the station to lose pressure. This was the first on-orbit depressurization in the history of spaceflight. The crew quickly cut cables leading to