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''Ulysses'' is a decommissioned robotic space probe whose primary mission was to orbit the Sun and study it at all latitudes. It was launched in 1990, made three "fast latitude scans" of the Sun in 1994/1995, 2000/2001, and 2007/2008. In addition, several comets were studied by the probe. The space probe was a joint venture of NASA and the European Space Agency (ESA). The last day for mission operations on ''Ulysses'' was June 30, 2009.〔〔(The odyssey concludes ... )〕 To study the Sun at all latitudes the probe needed to change its orbital inclination and leave the plane of the Solar System – to change the orbital inclination of a spacecraft a large change in heliocentric velocity is needed. However the necessary amount of velocity change to achieve a high inclination orbit of about 80° far exceeded the capabilities of any launch vehicle. Therefore to reach the desired orbit around the Sun a gravity assist manoeuvre around Jupiter was chosen, but this Jupiter encounter meant that ''Ulysses'' could not be powered by solar cells – the probe instead was powered by a radioisotope thermoelectric generator (RTG). The spacecraft was originally named Odysseus, because of its lengthy and indirect trajectory to study the solar poles. It was renamed Ulysses, the Latin translation of "Odysseus", at ESA's request in honour not only of Homer's mythological hero but also with reference to Dante's description in Dante's Inferno.〔"Inferno of Ulysses' urge to explore an uninhabited world behind the Sun. In Jane's Spaceflight Directory 1988, ISBN 0-7106-0860-8〕 ''Ulysses'' was originally scheduled for launch in May 1986 aboard the Space Shuttle ''Challenger'' on STS-61-F. Due to the loss of ''Challenger'', the launch of ''Ulysses'' was delayed until October 6, 1990 aboard ''Discovery'' (mission STS-41). == Spacecraft == The spacecraft body was roughly a box, approximately 3.2 × 3.3 × 2.1 m in size. The box mounted the 1.65 m dish antenna and the GPHS-RTG radioisotope thermoelectric generator (RTG) power source. The box was divided into noisy and quiet sections. The noisy section abutted the RTG; the quiet section housed the instrument electronics. Particularly "loud" components, such as the preamps for the radio dipole, were mounted outside the structure entirely, and the box acted as a Faraday cage. ''Ulysses'' was spin-stabilised about its z-axis which roughly coincides with the axis of the dish antenna. The RTG, whip antennas, and instrument boom were placed to stabilize this axis, with the spin rate nominally at 5 rpm. Inside the body was a hydrazine fuel tank. Hydrazine monopropellant was used for course corrections inbound to Jupiter, and later used exclusively to repoint the spin axis (and thus, the antenna) at Earth. The spacecraft was controlled by eight thrusters in two blocks. Thrusters were pulsed in the time domain to perform rotation or translation. Four Sun sensors detected orientation. For fine attitude control, the S-band antenna feed was mounted slightly off-axis. This offset feed combined with the spacecraft spin introduced an oscillation to an S-band radio signal transmitted from Earth when received on board the spacecraft. The amplitude and phase of this oscillation was proportional to the orientation of the spin axis relative to the Earth direction. This method of determining the relative orientation is called CONSCAN and was used by early radars for automated tracking of targets and also very common in early infra-red guided missiles. The spacecraft used S-band for uplinked commands and downlinked telemetry, through dual redundant 5-watt transceivers. The spacecraft used X-band for science return (downlink only), using dual 20 W TWTAs until the failure of the last remaining TWTA in January 2008. Both bands used the dish antenna with prime-focus feeds, unlike the Cassegrain feeds of most other spacecraft dishes. 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. The spacecraft was designed to withstand both the heat of the inner Solar System and the cold at Jupiter's distance. Extensive blanketing and electric heaters protected the probe against the cold temperatures of the outer Solar System. Total mass at launch was , of which 33.5 kg was hydrazine (used for attitude control and orbit correction). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ulysses (spacecraft)」の詳細全文を読む スポンサード リンク
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