Ulysses (spacecraft)

[3][4] To study the Sun at all latitudes, the probe needed to change its orbital inclination and leave the plane of the Solar System.It was renamed Ulysses, the Latin translation of "Odysseus", at ESA's request in honor not only of Homer's mythological hero but also of Dante's character in the Inferno.The box mounted the 1.65 m (5 ft 5 in) dish antenna and the GPHS-RTG radioisotope thermoelectric generator (RTG) power source.The spacecraft used X-band for science return (downlink only), using dual 20 watts TWTAs until the failure of the last remaining TWTA in January 2008.Dual tape recorders, each of approximately 45-megabit capacity, stored science data between the nominal eight-hour communications sessions during the prime and extended mission phases.Documented 1802 usage includes dual-redundant 1802s in the COSPIN, and at least one 1802 each in the GRB, HI-SCALE, SWICS, SWOOPS and URAP instruments, with other possible microprocessors incorporated elsewhere.However, gravity assists are not limited to in-plane maneuvers; a suitable flyby of Jupiter could produce a significant plane change.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 changes delayed launch from February 1983 to May 1986 when it was to be deployed by the Space Shuttle Challenger (boosted by the proposed Centaur G Prime upper stage).However, the 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.[22] ESA's Science Program Committee approved the fourth extension of the Ulysses mission to March 2004 [23] thereby allowing it to operate over the Sun's poles for the third time in 2007 and 2008.As the spacecraft traveled on its outbound trajectory to the orbit of Jupiter, the downlink signal would have eventually fallen below the receiving capability of even the largest antennas (70 meters - 229.7 feet - in diameter) of the Deep Space Network.Once the hydrazine froze, the spacecraft would no longer be able to maneuver to keep its high gain antenna pointing towards Earth, and the downlink signal would then be lost in a matter of days.[29] When the spacecraft was out of contact with a ground station, the S-band transmitter was switched off and the power was diverted to the internal heaters to add to the warming of the hydrazine.Typically, a determination came from comparing: one of several spacecraft orbiting the Earth, an inner-Solar-System probe (to Mars, Venus, or an asteroid), and Ulysses.However, there is a chance that in one of its re-encounters with Jupiter a close fly-by with one of the Jovian moons would be enough to alter its course and so the probe would enter a hyperbolic trajectory around the Sun and leave the Solar System.