Editing Ulysses (spacecraft) (section)

=== Planning ===
[[File:Ulysses sits atop the PAM-S and IUS combination.jpg|thumb|upright=1.0|left|''Ulysses'' sits atop the PAM-S and IUS combination]]
[[File:Artist picture-Ulysses after deployment.jpg|thumb|upright=1.0|right|Illustration of ''Ulysses'' after deployment]]
[[File:Artist's conception of NASA solar polar spacecraft.jpg|thumb|upright=1.0|right|Illustration of Solar Polar on IUS]]
[[File:ISPM space probes.jpg|thumb|upright=1.0|right|1981 concept showing one of two ISPM probes orbiting the Sun]]

Until ''Ulysses'', the Sun had only been observed from low solar latitudes. The Earth's orbit defines the [[ecliptic]] plane, which differs from the Sun's equatorial plane by only 7.25°. Even spacecraft directly orbiting the Sun do so in planes close to the ecliptic because a direct launch into a high-inclination solar orbit would require a prohibitively large launch vehicle.

Several spacecraft ([[Mariner 10]], [[Pioneer 11]], and [[Voyager program|''Voyagers 1'' and ''2'']]) had performed [[gravity assist]] maneuvers in the 1970s. Those maneuvers were to reach other planets also orbiting close to the ecliptic, so they were mostly in-plane changes. However, gravity assists are not limited to in-plane maneuvers; a suitable flyby of [[Jupiter]] could produce a significant plane change. An Out-Of-The-Ecliptic mission (OOE) was thereby proposed. ''See article'' [[Pioneer H]].

Originally, two spacecraft were to be built by NASA and ESA, as the '''International Solar Polar Mission.''' One would be sent over Jupiter, then under the Sun. The other would fly under Jupiter, then over the Sun. This would provide simultaneous coverage. Due to cutbacks, the U.S. spacecraft was cancelled in 1981. One spacecraft was designed, and the project recast as ''Ulysses,'' due to the indirect and untried flight path. NASA would provide the Radioisotope Thermoelectric Generator (RTG) and launch services, ESA would build the spacecraft assigned to Astrium GmbH, [[Friedrichshafen]], [[Germany]] (formerly Dornier Systems). The instruments would be split into teams from universities and research institutes in Europe and the United States. This process provided the 12 instruments on board.

The changes delayed launch from February 1983 to May 1986 when it was to be deployed by the [[Space Shuttle Challenger|Space Shuttle ''Challenger'']] (boosted by the proposed [[Centaur G Prime]] upper stage). However, the [[Space Shuttle Challenger disaster|''Challenger'' disaster]] forced a two-and-a-half year stand down of the shuttle fleet, mandated the cancellation of the Centaur-G upper stage, and pushed the launch date to October 1990.<ref name="ars-20151009">{{Cite news |last=Carney |first=Emily |date=9 October 2015 |title=A deathblow to the Death Star: The rise and fall of NASA's Shuttle-Centaur |url=https://arstechnica.com/science/2015/10/dispatches-from-the-death-star-the-rise-and-fall-of-nasas-shuttle-centaur/ |url-status=live |archive-url=https://web.archive.org/web/20240210063513/https://arstechnica.com/science/2015/10/dispatches-from-the-death-star-the-rise-and-fall-of-nasas-shuttle-centaur/ |archive-date=10 February 2024 |access-date=22 June 2024 |work=[[Ars Technica]] }}</ref>