Advanced Crew Escape Suit

The Advanced Crew Escape Suit (ACES), or "pumpkin suit", is a full pressure suit that Space Shuttle crews began wearing after STS-65, for the ascent and entry portions of flight. The suit is a direct descendant of the U.S. Air Force high-altitude pressure suits worn by the two-man crews of the SR-71 Blackbird, pilots of the U-2 and X-15, and Gemini pilot-astronauts, and the Launch Entry Suits (LES) worn by NASA astronauts starting on the STS-26 flight, the first flight after the Challenger disaster. The suit is manufactured by the David Clark Company of Worcester, Massachusetts. Cosmetically the suit is very similar to the LES. ACES was first used in 1994 on STS-64.
In 1990, the LES was nearing the end of its service life, so a program to produce a successor was initiated. Favorable crew evaluations of a prototype led to full scale development and qualification that would run until 1992. Production of the completed design began in February 1993, and the first suit was delivered to NASA in May 1994.
After 1998, it became the only suit used during launch and re-entry on the Space Shuttle. The ACES incorporates gloves on disconnecting lock rings on the wrists, liquid cooling and improved ventilation, and an extra layer of insulation. The ACES suit is analogous to the Sokol suits used for Soyuz missions and its functions are virtually the same – the primary differences being the ACES suit having a detachable helmet and survival backpack, while the Russian suit has an integrated helmet and no backpack (due to the limitations in space aboard the Soyuz, and that the spacecraft is an entry capsule, not a winged spacecraft or lifting body).
Each suit is sized individually, although most suits can be worn by astronauts of different heights. No ACES has failed during normal flight operations. The Columbia investigation found that the crews' ACES all failed at some point, but also that none of the Columbia crew had sealed their helmets, and also that several were not wearing suit gloves. By comparison, in 1966 an SR-71 pilot in a similar suit, whose helmet and gloves were sealed, survived similar pressure conditions when his aircraft broke up while flying at approximately Mach 3. The "thermal and chemical environment of the Columbia accident" (the temperature and oxygen concentration) was "much more severe" than in the SR-71 accident, however, and the report recommended that future crew survival suits be evaluated for thermal and chemical resistance as well as (as USAF suits had been evaluated previously) pressure and windblast.
Initially, ACES was intended to be retired after the Space Shuttle program and be replaced by the Constellation Space Suit for Orion missions. The Artemis program instead planned to use a modified ACES called the Orion Crew Survival System (OCSS). This suit will have increased mobility in comparison to its Space Shuttle counterpart and will use a closed-loop system to preserve resources. The OCSS is to be worn inside the Orion spacecraft during launch and re-entry, in case of a depressurization emergency.
Thomas, Kenneth S.; McMann, Harold J. (2006). US Spacesuits. Chichester, UK: Praxis Publishing Ltd. ISBN 0-387-27919-9.