A+Century+of+Physics+1985+GALILEO+SPACECRAFT

Galileo

Work on the spacecraft began at JPL in 1977, while the //[|Voyager 1]// and //[|2]// missions were still being prepared for launch. Early plans called for a launch on [|Space Shuttle] [|//Columbia//] on what was then codenamed [|STS-23] in January 1982, but delays in the development of the Space Shuttle allowed more time for development of the probe. As the shuttle program got underway, //Galileo// was scheduled for launch in 1984, but this later slipped to 1985 and then to 1986.[|[][|2][|]] The mission was initially called the //Jupiter Orbiter Probe//; it was christened //Galileo// in 1978.[|[][|3][|]] Once the spacecraft was complete, its launch was scheduled for [|STS-61-G] on-board [|//Atlantis//] in 1986. The [|Inertial Upper Stage] booster was going to be used at first, but this changed to the Centaur booster, then back to IUS to after //Challenger//.[|[][|2][|]] The [|Centaur-G] liquid hydrogen-fueled booster stage allowed a direct trajectory to Jupiter. However, the mission was further delayed by the hiatus in launches that occurred after the [|Space Shuttle Challenger disaster]. New safety protocols introduced as a result of the disaster prohibited the use of the Centaur-G stage on the Shuttle, forcing //Galileo// to use a lower-powered Inertial Upper Stage solid-fuel booster. The mission was re-profiled in 1987 to use several [|gravitational slingshots], referred to as the "VEEGA" or Venus Earth Earth Gravity Assist maneuvers, to provide the additional velocity required to reach its destination. It was finally launched on October 18, 1989, by the [|Space Shuttle //Atlantis//] on the [|STS-34] mission. [|Venus] was flown by at 05:58:48 UT on February 10, 1990 at a range of 16,106 km. Having gained 8,030 km per hour in speed, the spacecraft flew by [|Earth] twice, the first time at a range of 960 km at 20:34:34 UT on 8 December 1990 before approaching the minor planet [|951 Gaspra] to a distance of 1,604 km at 22:37 UT on 29 October 1991. //Galileo// then performed a second flyby of Earth at 303.1 km at 15:09:25 UT on 8 December 1992, adding 3.7 km per second to its cumulative speed. //Galileo// performed close observation of a second asteroid, [|243 Ida], at 16:51:59 UT on 28 August 1993 at a range of 2,410 km. The spacecraft discovered Ida has a moon [|Dactyl], the first discovery of a natural satellite orbiting an asteroid. In 1994, //Galileo// was perfectly positioned to watch the fragments of the [|comet] [|Shoemaker-Levy 9] crash into Jupiter, whereas terrestrial telescopes had to wait to see the impact sites as they rotated into view. After releasing its atmospheric probe on 13 July 1995, the //Galileo// orbiter became the first man-made satellite of Jupiter at 00:27 UT on 8 December 1995 when it fired its main engine to enter a 198-day parking orbit.[|[][|4][|]] Amalthea //Galileo'// s prime mission was a two-year study of the Jovian system. The spacecraft traveled around Jupiter in elongated [|ellipses], each orbit lasting about two months. The differing distances from Jupiter afforded by these orbits allowed //Galileo// to sample different parts of the planet's extensive [|magnetosphere]. The orbits were designed for close-up flybys of Jupiter's largest moons. Once the prime mission concluded, an extended mission started on December 7, 1997; the spacecraft made a number of flybys of [|Europa] and [|Io]. The closest approach was 180 km (110 mi) on October 15, 2001. The [|radiation] environment near Io 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. //Galileo'//s cameras were deactivated on January 17, 2002, after they had sustained irreparable radiation damage. NASA engineers were able to recover the damaged tape recorder electronics, and //Galileo// continued to return scientific data until it was deorbited in 2003, performing one last scientific experiment —a measurement of the moon [|Amalthea]'s mass as the spacecraft swung by it.

The [|Jet Propulsion Laboratory] built the //Galileo// spacecraft and managed the //Galileo// mission for NASA. [|Germany] supplied the propulsion module. NASA's [|Ames Research Center] managed the probe, which was built by [|Hughes Aircraft Company]. Galileo with its main antenna open At launch, the orbiter and probe together had a mass of 2,564 kilograms (5,653 pounds) and stood seven metres tall. One section of the spacecraft rotated at 3 [|rpm], keeping //Galileo// stable and holding six instruments that gathered data from many different directions, including the fields and particles instruments. The other section of the spacecraft was an antenna, and data were periodically transmitted to it. Back on the ground, the mission operations team used software containing 650,000 lines of programming code in the orbit sequence design process; 1,615,000 lines in the telemetry interpretation; and 550,000 lines of code in navigation. === Command and Data Handling (CDH) [ [|edit source] | [|edit] [|beta] ] === The CDH subsystem was actively redundant, with two parallel [|data system buses] running at all times.[|[][|5][|]] Each data system bus (aka string) was composed of the same functional elements, consisting of multiplexers (MUX), high-level modules (HLM), low-level modules (LLM), power converters (PC), bulk memory (BUM), data management subsystem bulk memory (DBUM), timing chains (TC), [|phase locked loops] (PLL), [|Golay] coders (GC), hardware command decoders (HCD) and critical controllers (CRC). The CDH subsystem was responsible for maintaining the following functions:
 * 1) decoding of uplink commands
 * 2) execution of commands and sequences
 * 3) execution of system-level fault-protection responses
 * 4) collection, processing, and formatting of telemetry data for downlink transmission
 * 5) movement of data between subsystems via a data system bust



RESOURSES

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