From Halopedia, the Halo wiki
A thruster pack, also known as the T-PACK for short, is a UNSC-issue form of propulsion for use by individuals on deep-space missions. Chief Mendez trained the SPARTAN-IIs with this type of equipment but warned them if one thing goes wrong the chance of rescue is non-existent.
T-PACKs are fairly fragile and may fail if struck by weapons or bursts of radiation. One (Unit Serial:
Designed for long-range deep-space operations, M-050978 thruster packs are still some of the riskiest equipment available. They feature triple redundancy NAV systems, stabilizers, redundant shutoff valves and emergency sealant foam. T-PACKs contain two tanks of compressed triamino hydrazine, which, if ruptured, will cause rapid loss of control, for which there is little a person can do. They can be linked up to weapons such as MA5B assault rifles. Should the wearer fire the weapon, the pack will provide enough counter thrust to keep the wearer from spinning out of control. T-PACKS also contain emergency rescue lines of orange and white rope meant to rescue other people who are stranded in deep space.
List of appearances