|There is more information available on this subject at Extra-Vehicular Activity on the English Wikipedia.|
Extra-Vehicular Activity, often abbreviated simply to EVA, is the term applied to external operations by specialist personnel in a vacuum environment outside of a spaceship.
Pressurized Suits are a necessity during an EVA operations due to the vacuum of space. In addition, Thruster pack are needed for maneuvering when not tethered to a spacecraft. Combat EVAs pose a significantly greater risk to those performing it, due to the chance of suit decompression in the vacuum if hit by bullets, shrapnel, etc. Civilian welders and technicians perform EVAs in order to repair ships, such as that performed upon the UNSC Gettysburg in the Eridanus system. The UNSC also employs specialized EVA Engineers on their warships such as the UNSC Spirit of Fire. Specialized zero-G vehicles are also used to perform EVA, such as the Open Frame 92/Extra-Vehicular Activity.
John-117 has performed five known combat EVAs: At the Battle of Chi Ceti in 2525, he inserted into a Covenant warship with Kelly-087 and Samuel-034, planted a missile warhead and extracted him and Kelly-087; At the Fall of Reach, in 2552, he performed another EVA in order to purge a ship's NAV database on an orbital station in accordance with the Cole Protocol. He performed another aboard the Ascendant Justice while in an anomalous slipspace dimension, the first known slipspace EVA and another at Earth, clearing hostiles off the outside of the Cairo Orbital Defense Platform and removing and repurposing a Covenant antimatter charge. Four years later he repelled Jul 'Mdama's Covenant forces off of the Forward Unto Dawn's outer hall and destroyed a nearby Carrier.
The Covenant also perform EVAs. Sangheili Rangers use specialized vacuum-sealed armor to protect themselves from the effects of a vacuum environment, in order to plant antimatter charges and support boarding parties. Kig-Yar rangers in vacuum suits were also used, though their suits were more easily damaged than Sangheili due to the fact they lacked a personal Energy Shield.