Editing Galileo project (section)

===Preparation===
To enhance reliability and reduce costs, the project engineers decided to switch from a pressurized [[Galileo Probe|atmospheric probe]] to a vented one, so the pressure inside the probe would be the same as that outside, thus extending its lifetime in Jupiter's atmosphere, but this added {{convert|100|kg}} to its weight. Another {{convert|165|kg}} was added in structural changes to improve reliability. This required additional fuel in the IUS, but the three-stage IUS was itself overweight with respect to its design specifications, by about {{convert|7000|lb|order=flip}}.<ref name="Hurdles">{{cite news |title=More Hurdles Rise In Galileo Project To probe Jupiter |first=Thomas |last=O'Toole |author-link=Thomas O'Toole |newspaper=[[The Washington Post]] |date=11 August 1979 |url=https://www.washingtonpost.com/archive/politics/1979/08/15/more-hurdles-rise-in-galileo-project-to-probe-jupiter/a30ddbe5-d805-418f-8a93-5d8deaa69f93/ |access-date=11 October 2020 |archive-date=May 23, 2021 |archive-url=https://web.archive.org/web/20210523182517/https://www.washingtonpost.com/archive/politics/1979/08/15/more-hurdles-rise-in-galileo-project-to-probe-jupiter/a30ddbe5-d805-418f-8a93-5d8deaa69f93/ |url-status=live }}</ref>{{sfn|Finley|1988|p=23}}{{sfn|Meltzer|2007|pp=41–43}} Lifting ''Galileo'' and the three-stage IUS required a special lightweight version of the [[Space Shuttle external tank]], the [[Space Shuttle orbiter]] stripped of all non-essential equipment, and the [[Space Shuttle main engine]]s (SSME) running at full power level—109 percent of their rated power level.{{sfn|Heppenheimer|2002|pp=368–370}}{{efn|The rated power level (RPL) is the power at which an engine can be normally operated. In the case of the Space Shuttle, the specification called for 27,000 seconds operation at 100 percent of the RPL, or 14,000 seconds at 109 percent of the RPL, which was designated full power level (FPL).{{sfn|Jenkins|2016|p=II-158}} }} Running at this power level necessitated the development of a more elaborate engine cooling system. Concerns were raised over whether the engines could be run at 109 percent by the launch date, so a gravity-assist maneuver using Mars was substituted for a direct flight.{{sfn|Meltzer|2007|pp=41–43}}

[[File:Galileo Preparations - GPN-2000-000672.jpg|thumb|left|In the Vertical Processing Facility (VPF), ''Galileo'' is prepared for mating with the [[Inertial Upper Stage]] booster.|alt=High gain antenna is folded. ]]
Plans called for the {{OV|Columbia}} to launch ''Galileo'' on the [[Canceled Space Shuttle missions#STS-23 (Columbia)|STS-23 mission]], tentatively scheduled for sometime between January 2 and 12, 1982,<ref>{{cite magazine |last=Portree |first=David S. F. |title=What Shuttle Should Have Been: The October 1977 Flight Manifest |date=March 24, 2012 |magazine=[[Wired (magazine)|Wired]] |issn=1059-1028 |url=https://www.wired.com/2012/03/what-shuttle-should-have-been-the-october-1977-flight-manifest/ |access-date=October 30, 2020 |archive-date=March 17, 2014 |archive-url=https://web.archive.org/web/20140317100957/http://www.wired.com/wiredscience/2012/03/what-shuttle-should-have-been-the-october-1977-flight-manifest |url-status=live }}</ref> this being the launch window when Earth, Mars and Jupiter were aligned to permit Mars to be used for the gravity-assist maneuver.{{sfn|Finley|1988|p=23}} By 1980, delays in the Space Shuttle program pushed the launch date for ''Galileo'' back to 1984.<ref>{{cite web |title=STS Flight Assignment Baseline |publisher=John H. Evans Library Digital Collections |url=https://digcollections.lib.fit.edu/items/show/45381 |access-date=October 31, 2020 |archive-date=November 30, 2021 |archive-url=https://web.archive.org/web/20211130095340/https://digcollections.lib.fit.edu/items/show/45381 |url-status=live }}</ref> While a Mars slingshot was still possible in 1984, it would no longer be sufficient.{{sfn|Meltzer|2007|pp=46–47}}

NASA decided to launch ''Galileo'' on two separate missions, launching the orbiter in February 1984 with the probe following a month later. The orbiter would be in orbit around Jupiter when the probe arrived, allowing the orbiter to perform its role as a relay. This configuration required a second Space Shuttle mission and a second carrier spacecraft to be built for the probe to take it to Jupiter, and was estimated to cost an additional $50 million (equivalent to ${{Inflation|US-GDP|50|1979}} million in {{Inflation/year|US-GDP}}), but NASA hoped to be able to recoup some of this through competitive bidding. The problem was that while the atmospheric probe was light enough to launch with the two-stage IUS, the Jupiter orbiter was too heavy to do so, even with a gravity assist from Mars, so the three-stage IUS was still required.<ref name="Deferring">{{cite web |title=NASA Weighs Deferring 1982 Mission to Jupiter |first=Thomas |last=O'Toole |author-link=Thomas O'Toole |newspaper=The Washington Post |date=September 19, 1979 |url=https://www.washingtonpost.com/archive/politics/1979/09/04/nasa-weighs-deferring-1982-mission-to-jupiter/bfe8bb4a-20fe-41f5-af14-d6b1c003b470/ |access-date=11 October 2020 |archive-date=August 27, 2017 |archive-url=https://web.archive.org/web/20170827161312/https://www.washingtonpost.com/archive/politics/1979/09/04/nasa-weighs-deferring-1982-mission-to-jupiter/bfe8bb4a-20fe-41f5-af14-d6b1c003b470/ |url-status=live }}</ref>{{sfn|Meltzer|2007|pp=46–47}}

By late 1980, the price tag for the IUS had risen to $506 million (equivalent to ${{Inflation|US-GDP|0.506|1979|r=3}} billion in {{Inflation/year|US-GDP}}).{{sfn|Heppenheimer|2002|pp=330–335}} The USAF could absorb this cost overrun on the development of the two-stage IUS (and indeed anticipated that it might cost far more), but NASA was faced with a quote of $179 million (equivalent to ${{Inflation|US-GDP|179|1979}} million in {{Inflation/year|US-GDP}}) for the development of the three-stage version,{{sfn|Heppenheimer|2002|pp=368–370}} which was $100 million (equivalent to ${{Inflation|US-GDP|100|1979}} million in {{Inflation/year|US-GDP}}) more than it had budgeted for.{{sfn|Meltzer|2007|p=43}} At a press conference on January 15, 1981, [[Robert A. Frosch]], the [[NASA Administrator]], announced that NASA was withdrawing support for the three-stage IUS, and going with a [[Centaur G Prime]] upper stage because "no other alternative upper stage is available on a reasonable schedule or with comparable costs."{{sfn|Janson|Ritchie|1990|p=250}}

[[File:Model of Centaur G with Galileo probe (upright).jpg|thumb|right|Model of ''Galileo'' atop a [[Centaur G Prime]] upper stage in the [[San Diego Air and Space Museum]] |alt=refer to caption]]
Centaur provided many advantages over the IUS. The main one was that it was far more powerful. The probe and orbiter could be recombined, and the probe could be delivered directly to Jupiter in two years' flight time.{{sfn|Heppenheimer|2002|pp=368–370}}{{sfn|Bowles|2002|p=420}} The second was that, despite this, it was gentler than the IUS, because it had lower thrust. This reduced the chance of damage to the payload. Thirdly, unlike solid-fuel rockets which burned to completion once ignited, a Centaur could be switched off and on again. This gave it flexibility, which increased the chances of a successful mission, and permitted options like asteroid flybys. Centaur was proven and reliable, whereas the IUS had not yet flown. The only concern was about safety; solid-fuel rockets were considered safer than liquid-fuel ones, especially ones containing [[liquid hydrogen]].{{sfn|Heppenheimer|2002|pp=368–370}}{{sfn|Bowles|2002|p=420}} NASA engineers estimated that additional safety features might take up to five years to develop and cost up to $100 million (equivalent to ${{Inflation|US-GDP|100|1979}} million in {{Inflation/year|US-GDP}}).{{sfn|Meltzer|2007|p=43}}<ref name="Deferring" />

In February 1981, JPL learned that the [[Office of Management and Budget]] (OMB) was planning major cuts to NASA's budget, and was considering cancelling ''Galileo''. The USAF intervened to save ''Galileo'' from cancellation. JPL had considerable experience with autonomous spacecraft that could make their own decisions.{{sfn|Meltzer|2007|pp=49–50}} This was a necessity for deep space probes, since a signal from Earth takes from 35 to 52 minutes to reach Jupiter, depending on the relative position of the planets in their orbits.<ref>{{cite web |title=Seeing in the Dark. Astronomy Topics. Light as a Cosmic Time Machine |publisher=PBS |url=https://www.pbs.org/seeinginthedark/astronomy-topics/light-as-a-cosmic-time-machine.html |access-date=12 October 2020 |archive-date=October 26, 2020 |archive-url=https://web.archive.org/web/20201026023044/https://www.pbs.org/seeinginthedark/astronomy-topics/light-as-a-cosmic-time-machine.html |url-status=live }}</ref> The USAF was interested in providing this capability for its satellites, so that they would be able to determine their [[orientation (geometry)|attitude]] using onboard systems rather than relying on [[ground station]]s, which were not "hardened" against [[nuclear weapons]], and could take independent evasive action against [[anti-satellite weapon]]s. It was also interested in the manner in which JPL was designing ''Galileo'' to withstand the intense radiation of the [[magnetosphere of Jupiter]], as this could be used to harden satellites against the [[electromagnetic pulse]] of nuclear explosions. On February 6, 1981 [[Strom Thurmond]], the [[President pro tempore of the United States Senate|President pro tem of the Senate]], wrote directly to [[David Stockman]], the director of the OMB, arguing that ''Galileo'' was vital to the nation's defense.{{sfn|Waldrop|1982|p=1013}}{{sfn|Meltzer|2007|pp=50–51}}{{efn|[[Sandia National Laboratories]] produced 12,000 microprocessor and integrated circuit components for ''Galileo'' that were hardened against radiation.{{sfn|Olmstead|Johnson|2024|p=246}} }}

[[File:Astronauts John Fabian and Dave Walker pose in front of a model of the Shuttle-Centaur.jpg|thumb|left|Astronauts [[John M. Fabian]] and [[David M. Walker (astronaut)|David M. Walker]] pose in front of a model of the [[Shuttle-Centaur]] with ''Galileo'' in mid-1985 |alt=refer to caption]]
In December 1984, Casani proposed adding a flyby of asteroid [[29 Amphitrite]] to the ''Galileo'' mission. In plotting a course to Jupiter, the engineers wanted to avoid asteroids. Little was known about them at the time, and it was suspected that they could be surrounded by dust particles. Flying through a dust cloud could damage the spacecraft's optics and possibly other parts of the spacecraft as well. To be safe, JPL wanted to avoid asteroids by at least {{convert|10000|km|sp=us}}. Most of the asteroids in the vicinity of the flight path like [[1219 Britta]] and [[1972 Yi Xing]] were only a few kilometers in diameter and promised little scientific value when observed from a safe distance, but 29 Amphitrite was one of the largest, and a flyby at even {{convert|10000|km|sp=us}} could have great value. The flyby would delay the spacecraft's arrival in Jupiter orbit from August 29 to December 10, 1988, and the expenditure of propellant would reduce the number of orbits of Jupiter from eleven to ten. This was expected to add $20 to $25 million (equivalent to ${{Inflation|US-GDP|20|1984}} to ${{Inflation|US-GDP|25|1984}} million in {{Inflation/year|US-GDP}}) to the cost of the ''Galileo'' project. The 29 Amphitrite flyby was approved by NASA Administrator [[James M. Beggs]] on December 6, 1984.<ref>{{cite press release |id=1062 |date=January 17, 1985 |title=Asteroid 29 Flyby Approved |publisher=NASA/Jet Propulsion Laboratory |url=https://www.jpl.nasa.gov/releases/80s/release_1985_1062.html |archive-url=https://web.archive.org/web/20081006064236/https://www.jpl.nasa.gov/releases/80s/release_1985_1062.html |archive-date=2008-10-06 |url-status=dead |df=mdy-all}}</ref>{{sfn|Meltzer|2007|pp=66–67}}

During testing, contamination was discovered in the system of metal [[slip ring]]s and brushes used to transmit electrical signals around the spacecraft, and they were returned to be refabricated. The problem was traced back to a [[chlorofluorocarbon]] used to clean parts after soldering. It had been absorbed, and was then released in a vacuum environment. It mixed with debris generated as the brushes wore down, and caused intermittent problems with electrical signal transmission. Problems were also detected in the performance of memory devices in an electromagnetic radiation environment. The components were replaced, but then a [[read disturb]] problem arose, in which reads from one memory location disturbed the contents of adjacent locations. This was found to have been caused by the changes made to make the components less sensitive to electromagnetic radiation. Each component had to be removed, retested, and replaced. All of the spacecraft components and spare parts received a minimum of 2,000 hours of testing. The spacecraft was expected to last for at least five years—long enough to reach Jupiter and perform its mission. On December 19, 1985, it departed JPL in [[Pasadena, California]], on the first leg of its journey, a road trip to the [[Kennedy Space Center]] in [[Florida]].{{sfn|Meltzer|2007|pp=68–69}} The ''Galileo'' mission was scheduled for [[STS-61-G]] on May 20, 1986, using {{OV|Atlantis|full=nolink}}.{{sfn|Hitt|Smith|2014|pp=282–285}}<ref>{{cite press release |title=NASA Names Flight Crews for ''Ulysses'', ''Galileo'' Missions |id=85-022 |date=31 May 1985 |first=Steve |last=Nesbitt |publisher=NASA |url=https://www.nasa.gov/centers/johnson/pdf/83137main_1985.pdf |access-date=17 October 2020 |archive-url=https://web.archive.org/web/20221101030918/https://www.nasa.gov/centers/johnson/pdf/83137main_1985.pdf |archive-date=1 November 2022 }}</ref>