Flight spare
Flight spares are extra copies of spacecraft or spacecraft parts kept in reserve in case they’re needed. They’re built to the same specifications as the original equipment, so they can replace damaged parts quickly and prevent launch delays. The extra cost of making spares is often justified by the high cost of delaying a mission.
Spare parts are made as contingencies. They can be swapped onto a craft before launch, or a complete spare spacecraft can be launched if the flight model is lost. NASA uses two main types: development spares and operational spares. Decisions about what parts to spare depend on whether parts are custom and how long it takes to obtain them; how many spares to stock depends on the part’s importance, failure rate, and expected life.
Spares can also be useful during a mission for testing changes on the ground. Even if unused, spares have value. A 2017 NASA report noted hundreds of millions of dollars in spare inventory, not all of it properly catalogued. Parts built for one mission may end up on another to save money. Some missions, like Magellan, used spare parts extensively. Flight spares may even become museum pieces, since many space probes do not return to Earth. The Mariner 10 flight spare is one example.
This page was last edited on 3 February 2026, at 06:20 (CET).