Editing Galileo project (section)

===Mission extension===

After the primary mission concluded on December 7, 1997, most of the mission staff departed, including O'Neil, but about a fifth of them remained. The ''Galileo'' orbiter commenced an extended mission known as the ''Galileo'' Europa Mission (GEM), which ran until December 31, 1999. This was a low-cost mission, with a budget of $30 million (equivalent to ${{Inflation|US-GDP|30|1997}} million in {{Inflation/year|US-GDP}}).{{sfn|Meltzer|2007|pp=234–237}} The reason for calling it as the "Europa" mission rather than the "Extended" mission was political; although it was wasteful to scrap a spacecraft that was still functional and capable of performing a continuing mission, Congress took a dim view of requests for more money for projects that had already been fully funded. This was avoided through rebranding.{{sfn|Greenberg|2005|pp=337–338}}

The smaller GEM team did not have the resources to deal with problems, but when they arose it was able to temporarily recall former team members for intensive efforts to solve them. The spacecraft performed several flybys of [[Europa (moon)|Europa]], [[Callisto (moon)|Callisto]] and [[Io (moon)|Io]]. On each one the spacecraft collected only two days' worth of data instead of the seven it had collected during the prime mission. The [[radiation]] environment near Io, which ''Galileo'' approached to within {{convert|201|km|sp=us}} on November 26, 1999, on orbit I25, was very unhealthy for ''Galileo''{{'s}} systems, and so these flybys were saved for the extended mission when loss of the spacecraft would be more acceptable.{{sfn|Meltzer|2007|pp=234–237}}

By the time GEM ended, most of the spacecraft was operating well beyond its original design specifications, having absorbed more than 600 [[kilorad]]s in between 1995 and 2002,{{sfn|Fieseler|Ardalan|Frederickson|2002}} three times the radiation exposure that it had been built to withstand. Many of the instruments were no longer operating at peak performance, but were still functional, so a second extension, the ''Galileo'' Millennium Mission (GMM) was authorized. This was intended to run until March 2001, but it was subsequently extended until January 2003. GMM included return visits to Europa, Io, Ganymede and Callisto, and for the first time to [[Amalthea (moon)|Amalthea]].{{sfn|Meltzer|2007|pp=237–238}} The total cost of the original ''Galileo'' mission was about {{US$|1.39 billion}} (equivalent to ${{Inflation|US-GDP|1.39|2003}} billion in {{Inflation/year|US-GDP}}). Of this, {{US$|892 million}} (equivalent to ${{Inflation|US-GDP|892|2003}} million in {{Inflation/year|US-GDP}}) was spent on spacecraft development.<ref name="galileo-arrival" /> Another $110 million (equivalent to ${{Inflation|US-GDP|110|2003}} million in {{Inflation/year|US-GDP}}) was contributed by international agencies.<ref>{{cite web |url=https://solarsystem.nasa.gov/missions/galileo/overview/#otp_quick_facts |title=Galileo: Quick Facts |publisher=NASA |access-date=January 19, 2021 |archive-date=July 19, 2009 |archive-url=https://web.archive.org/web/20090719111109/http://www2.jpl.nasa.gov/galileo/messenger/oldmess/2Probe.html#otp_quick_facts |url-status=live }}</ref>