After many subsequent playback and cooling cycles, the complete transmission back to Earth of all recorded Amalthea flyby data was successful. ===End of mission and deorbit=== When the exploration of Mars was being considered in the early 1960s, Carl Sagan and Sidney Coleman produced a paper concerning contamination of the red planet.
This figure was adopted by the Committee on Space Research (COSPAR) of the International Council of Scientific Unions in 1964, and was subsequently applied to all planetary probes.
The danger was highlighted in 1969 when the Apollo 12 astronauts returned components of the Surveyor 3 spacecraft that had landed on the Moon three years before, and it was found that microbes were still viable even after three years in that harsh climate.
In the late 1970s, NASA was focused on the development of the reusable Space Shuttle, which was expected to make expendable rockets obsolete.
The decision to use magnetic tape for storage was a conservative one, taken in the late 1970s when the use of tape was common.
Pioneer 10 was launched in March 1972 and passed within of Jupiter in December 1973.
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 posed little value when observed from a safe distance, but 29 Amphitrite was one of the largest of the asteroids, and a flyby at even could have great scientific value.
Pioneer 10 was launched in March 1972 and passed within of Jupiter in December 1973.
It was followed by Pioneer 11, which was launched in April 1973, and passed within of Jupiter in December 1974, before heading on to an encounter with Saturn.
It was followed by Pioneer 11, which was launched in April 1973, and passed within of Jupiter in December 1974, before heading on to an encounter with Saturn.
In late 1975, NASA decreed that all future planetary missions would be launched by the Space Shuttle.
They were followed by the more advanced Voyager 1 and Voyager 2 spacecraft, which were launched on 5 September and 20 August 1977 respectively, and reached Jupiter in March and July 1979. ==Planning== ===Initiation=== Following the approval of the Voyager missions, NASA's Scientific Advisory Group (SAG) for Outer Solar System Missions considered the requirements for Jupiter orbiters and atmospheric probes.
The United States Congress approved funding for the Jupiter Orbiter Probe on July 12, 1977, and JOP officially commenced on October 1, 1977, the start of the fiscal year.
A configuration with three stages, two large and one small, would be enough for a planetary mission, so NASA contracted with Boeing for the development of a three-stage IUS. It was estimated that the JOP would cost $634 million (equivalent to $ million in ), and it had to compete for fiscal year 1978 funding with the Space Shuttle and the Hubble Space Telescope.
The new name was adopted in February 1978. ===Preparation=== Early plans called for a launch on on STS-23 sometime between 2 and 12 January 1982, this being the launch window when Earth, Jupiter and Mars were aligned in such a way as to permit Mars to be used for a gravitational slingshot maneuver.
By 1989, plutonium had been used in 22 spacecraft. Activists remembered the crash of the Soviet Union's nuclear-powered Kosmos 954 satellite in Canada in 1978, and the Challenger disaster, while it did not involve nuclear fuel raised public awareness about spacecraft failures.
They were followed by the more advanced Voyager 1 and Voyager 2 spacecraft, which were launched on 5 September and 20 August 1977 respectively, and reached Jupiter in March and July 1979. ==Planning== ===Initiation=== Following the approval of the Voyager missions, NASA's Scientific Advisory Group (SAG) for Outer Solar System Missions considered the requirements for Jupiter orbiters and atmospheric probes.
The scientific community did not want a repetition of the 1979 Morabito incident, when Linda A.
The radiation limits for Galileo computers were based on data returned from Pioneers 10 and 11, since much of the design work was underway before the two Voyagers arrived at Jupiter in 1979. A typical effect of the radiation was that several of the science instruments suffered increased noise while within about of Jupiter.
It noted that the technology to build a [shield] for an atmospheric probe did not yet exist, and indeed facilities to test one under the conditions found on Jupiter would not be available until 1980.
By 1980, delays in the Space Shuttle program pushed the launch date for Galileo back to 1984.
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. By late 1980, the price tag for the IUS had risen to $506 million (equivalent to $ million in ).
Normally they are only seen in September or October, but Galileo was able to detect them in December, an indication of damage to Earth's ozone layer. ===Remote detection of life on Earth=== The astronomer Carl Sagan, pondering the question of whether life on Earth could be easily detected from space, devised a set of experiments in the late 1980s using Galileo remote sensing instruments during the mission's first Earth flyby in December 1990.
At a press conference on January 15, 1981, NASA Administrator Robert A.
NASA engineers estimated that additional safety features might take up to five years to develop and cost up to $100 million (equivalent to $ million in . In February 1981, the JPL learned that the Office of Management and Budget (OMB) was planning major cuts to NASA's budget, and was considering cancelling Galileo.
On February 6, 1981 Strom Thurmond, the President pro tempore of the Senate, wrote directly to David Stockman, the Director of the OMB, arguing that Galileo was vital to the nation's defense. In December 1984 Casani proposed adding a flyby of asteroid 29 Amphitrite to the Galileo mission.
The new name was adopted in February 1978. ===Preparation=== Early plans called for a launch on on STS-23 sometime between 2 and 12 January 1982, this being the launch window when Earth, Jupiter and Mars were aligned in such a way as to permit Mars to be used for a gravitational slingshot maneuver.
There is probably a separate ring along Amalthea's orbit as well. The Galileo spacecraft identified the global structure and dynamics of a giant planet's magnetosphere. ==Follow-on missions== There was a spare Galileo spacecraft that was considered by the NASA-ESA Outer Planets Study Team in 1983 for a mission to Saturn, but it was passed over in favor of a newer design, which became Cassini–Huygens.
By 1980, delays in the Space Shuttle program pushed the launch date for Galileo back to 1984.
While a Mars slingshot was still possible in 1984, it would no longer be sufficient. NASA decided to split Galileo into two separate spacecraft, an atmospheric probe and a Jupiter orbiter, with the orbiter launched in February 1984 and the probe following a month later.
On February 6, 1981 Strom Thurmond, the President pro tempore of the Senate, wrote directly to David Stockman, the Director of the OMB, arguing that Galileo was vital to the nation's defense. In December 1984 Casani proposed adding a flyby of asteroid 29 Amphitrite to the Galileo mission.
Beggs on December 6, 1984. During testing, contamination was discovered in the system of metal slip rings and brushes used to transmit electrical signals around the spacecraft, and they were returned to be refabricated.
On December 19, 1985, it departed the JPL in Pasadena, California, on the first leg of its journey, a road trip to the Kennedy Space Center in Florida.
The Galileo mission was scheduled for STS-61-G on May 20, 1986, using . ===Reconsideration=== On January 28, 1986, lifted off on the STS-51-L mission.
By April 1986, it was expected that the Space Shuttles would not fly again before July 1987 at the earliest, and Galileo could not be launched before December 1987. The Rogers Commission handed down its report on June 6, 1986.
On June 19, 1986, NASA Administrator James C.
By April 1986, it was expected that the Space Shuttles would not fly again before July 1987 at the earliest, and Galileo could not be launched before December 1987. The Rogers Commission handed down its report on June 6, 1986.
The changes to the Space Shuttle proved more extensive than anticipated, and in April 1987 the JPL was informed that Galileo could not be launched before October 1989.
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 retained as a backup for a time, but in November 1988 the USAF informed NASA that it could not provide a Titan IV in time for the May 1991 launch opportunity, owing to the backlog of high priority Department of Defense missions.
It was delivered into Earth orbit on October 18, 1989 by on the STS-34 mission, and arrived at Jupiter on December 7, 1995, after gravitational assist flybys of Venus and Earth, and became the first spacecraft to orbit Jupiter.
The changes to the Space Shuttle proved more extensive than anticipated, and in April 1987 the JPL was informed that Galileo could not be launched before October 1989.
By 1989, plutonium had been used in 22 spacecraft. Activists remembered the crash of the Soviet Union's nuclear-powered Kosmos 954 satellite in Canada in 1978, and the Challenger disaster, while it did not involve nuclear fuel raised public awareness about spacecraft failures.
The prospect of an inadvertent re-entry into the atmosphere during the VEEGA maneuvers was reckoned at less than one in two million, but an accident might have released up to . ==Launch== The mission to launch Galileo was now designated STS-34, and scheduled for October 12, 1989, in the Space Shuttle Atlantis.
Galileo flew by at 05:58:48 UTC on February 10, 1990, at a range of .
A search for lightning on Venus was conducted using the plasma wave detector, which noted nine bursts which were likely caused by lightning, but efforts to capture an image of lightning with the solid-state imaging system (SSI) were unsuccessful. ==Earth encounters== ===Flybys=== Galileo made two small course corrections on 9 to 12 April and 11 to 12 May 1990.
The spacecraft flew by Earth twice; the first time at a range of at 20:34:34 UTC on December 8, 1990.
Normally they are only seen in September or October, but Galileo was able to detect them in December, an indication of damage to Earth's ozone layer. ===Remote detection of life on Earth=== The astronomer Carl Sagan, pondering the question of whether life on Earth could be easily detected from space, devised a set of experiments in the late 1980s using Galileo remote sensing instruments during the mission's first Earth flyby in December 1990.
This was retained as a backup for a time, but in November 1988 the USAF informed NASA that it could not provide a Titan IV in time for the May 1991 launch opportunity, owing to the backlog of high priority Department of Defense missions.
The scheme was studied in 2004 for a data link to a future Mars orbiting spacecraft. ==Lunar observations== ==High gain antenna problem== Once Galileo headed beyond Earth, it was no longer risky to employ the HGA, so on April 11, 1991, Galileo was ordered to unfurl it.
The Galileo project was able to secure 80 hours of the Canberra's 70-meter dish time between 7 and 14 November 1991, but most of images taken, including low-resolution images of more of the surface, were not transmitted to Earth until November 1992. The imagery revealed a cratered and irregular body, measuring about .
A second flyby of Earth was at at 15:09:25 UTC on December 8, 1992.
Galileo experiments were thus the first ever controls in the newborn science of astrobiological remote sensing. ===Galileo Optical Experiment=== In December 1992, during Galileo second gravity-assist planetary flyby of Earth, another groundbreaking experiment was performed.
The motors were pulsed 13,000 times over a three-week period in December 1992 and January 1993, but only managed to move the ballscrew by one and a half revolutions beyond the stall point. Investigators concluded that during the 4.5 years that Galileo spent in storage after the Challenger disaster, the lubricants between the tips of the ribs and the cup were eroded and worn by vibration during the three cross-country journeys by truck between California and Florida for the spacecraft.
O'Neil, Galileo project manager from 1992 to 1997, expressed confidence that 70 percent of Galileo science goals could still be met.
The Galileo project was able to secure 80 hours of the Canberra's 70-meter dish time between 7 and 14 November 1991, but most of images taken, including low-resolution images of more of the surface, were not transmitted to Earth until November 1992. The imagery revealed a cratered and irregular body, measuring about .
While Galileo was operating, Ulysses passed by Jupiter in 1992 on its mission to study the Sun's polar regions, and Cassini–Huygens coasted by the planet in 2000 and 2001 en route to Saturn.
After data acquisition and processing, Sagan published a paper in Nature in 1993 detailing the results of the experiment.
The motors were pulsed 13,000 times over a three-week period in December 1992 and January 1993, but only managed to move the ballscrew by one and a half revolutions beyond the stall point. Investigators concluded that during the 4.5 years that Galileo spent in storage after the Challenger disaster, the lubricants between the tips of the ribs and the cup were eroded and worn by vibration during the three cross-country journeys by truck between California and Florida for the spacecraft.
Measurements of the solar wind in the vicinity of the asteroid showed it changing direction a few hundred kilometers for Gaspra, which hinted that it might have a magnetic field, but this was not certain. ===243 Ida and Dactyl=== Following the second Earth encounter, Galileo performed close observations of another asteroid, 243 Ida, at 16:52:04 UTC on August 28, 1993, at a range of .
It was hypothesized that both may have been produced by the breakup of a Koronis parent body. The requirement to use the LGA resulted in a bit rate of 40 bit/s, and that only from August 28 to September 29, 1993 and from February to June 1994.
On 26 March 1993, comet-seeking astronomers Carolyn S.
In 1994, Galileo observed Comet Shoemaker–Levy 9's collision with Jupiter. Jupiter's atmospheric composition and ammonia clouds were recorded.
It was hypothesized that both may have been produced by the breakup of a Koronis parent body. The requirement to use the LGA resulted in a bit rate of 40 bit/s, and that only from August 28 to September 29, 1993 and from February to June 1994.
Calculations indicated that it would crash into the planet sometime between 16 and 24 July 1994.
It was delivered into Earth orbit on October 18, 1989 by on the STS-34 mission, and arrived at Jupiter on December 7, 1995, after gravitational assist flybys of Venus and Earth, and became the first spacecraft to orbit Jupiter.
The NIMS observed one fragment create a fireball in diameter that burned with a temperature of , which was hotter than the surface of the Sun. ===Probe deployment=== The Galileo probe separated from the orbiter at 03:07 UTC on July 13, 1995, five months before its rendezvous with the planet on December 7.
The burn lasted for five minutes and eight seconds, and changed the velocity of the Galileo orbiter by . ===Dust storms=== In August 1995, the Galileo orbiter encountered a severe dust storm from Jupiter that took several months to traverse.
The bow wave was not stationary, but moved to and fro in responses to solar wind gusts, and was therefore crossed multiple times between 16 and 26 November, by which time it was from Jupiter. On December 7, 1995, the orbiter arrived in the Jovian system.
It entered Jupiter's atmosphere with no braking at 22:04 UTC on December 7, 1995.
The Imaging Team controlled the manner in which discoveries were presented to the scientific community and the public through press conferences, conference papers and publications. Observations by the Hubble Space Telescope in 1995 reported that Europa had a thin oxygen atmosphere.
When the orbiter reached its apojove on March 26, 1996, the main engine was fired again to increase the orbit from four times the radius of Jupiter to ten times.
On C3, Galileo conducted a "nontargeted" encounter of Europa on 6 November 1996.
During E4 from 15 to 22 December 1996, Galileo flew within of Europa, but data transmission was hindered by a Solar occultation that blocked transmission for ten days. Galileo returned to Europa on E6 in January 1997, this time at a height of to analyze oval-shaped features in the infrared and ultraviolet spectra.
O'Neil, Galileo project manager from 1992 to 1997, expressed confidence that 70 percent of Galileo science goals could still be met.
During E4 from 15 to 22 December 1996, Galileo flew within of Europa, but data transmission was hindered by a Solar occultation that blocked transmission for ten days. Galileo returned to Europa on E6 in January 1997, this time at a height of to analyze oval-shaped features in the infrared and ultraviolet spectra.
On E11 from 2 to 9 November 1997, data was collected on the magnetosphere.
Galileo returned to Ganymede on orbits G7 and G9 in April and May 1997, and on G28 and G29 in May and December 2000 on the GMM.
It has a primary period of 45 days and the dimming is just visible with the naked eye. ===Mission extension=== After the primary mission concluded on December 7, 1997, most of the mission staff departed, including O'Neil, but about a fifth of them remained.
As Galileo approached Io on I24 at 11:09 UTC on October 11, 1999, it entered safe mode.
Not all of the planned activities could be carried out, but Galileo obtained a series of high-resolution color images of the Pillan Patera, and Zamama, Prometheus, and Pele volcanic eruption centers. When Galileo next approached Io on I25 at 20:40 Pacific Time on November 25, 1999, the JPL were eating their Thanksgiving dinner at the Galileo Mission Control Center when, with the encounter with Io just four hours away, the spacecraft again entered safe mode.
The Galileo orbiter commenced an extended mission known as the Galileo Europa Mission (GEM), which ran until December 31, 1999.
The radiation environment near Io, which Galileo approached to within on November 26, 1999, on orbit I25, was very unhealthy for Galileo systems, and so these flybys were saved for the extended mission when loss of the spacecraft would be more acceptable. By the time GEM ended, most of the spacecraft was operating well beyond its original design specifications, having absorbed three times the radiation exposure that it had been built to withstand.
A change to the software was made in April 1999 that allowed the onboard computer to detect these resets and autonomously recover, so as to avoid safe mode. ===Tape recorder problems=== Routine maintenance of the tape recorder involved winding the tape halfway down its length and back again to prevent it sticking.
Galileo returned to Ganymede on orbits G7 and G9 in April and May 1997, and on G28 and G29 in May and December 2000 on the GMM.
Two years of Jupiter's intense radiation took its toll on the spacecraft's systems, and its fuel supply was running low in the early 2000s.
This data was eventually calibrated to show the particles were predominantly > electrons that were trapped in the Jovian magnetic belts, and released to the Planetary Data System. A second discovery occurred in 2000.
The SSI camera began producing totally white images when the spacecraft was hit by the exceptional 'Bastille Day' coronal mass ejection in 2000, and did so again on subsequent close approaches to Jupiter.
While Galileo was operating, Ulysses passed by Jupiter in 1992 on its mission to study the Sun's polar regions, and Cassini–Huygens coasted by the planet in 2000 and 2001 en route to Saturn.
This was intended to run until March 2001, but it was subsequently extended until January 2003.
While Galileo was operating, Ulysses passed by Jupiter in 1992 on its mission to study the Sun's polar regions, and Cassini–Huygens coasted by the planet in 2000 and 2001 en route to Saturn.
Galileo 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 Amalthea's mass as the spacecraft swung by it.
A successful flyby meant knowing which direction the asteroid was pointed in relative to Galileo at all times. Galileo flew by Amalthea on November 5, 2002, during its 34th orbit, allowing a measurement of the moon's mass as it passed within of its surface.
In November 2002, after the completion of the mission's only encounter with Jupiter's moon Amalthea, problems with playback of the tape recorder again plagued Galileo.
The extent and structure of Jupiter's magnetosphere was also mapped. On September 20, 2003, after 14 years in space and 8 years in the Jovian system, Galileo mission was terminated by sending it into Jupiter's atmosphere at a speed of over , completely eliminating the possibility of contaminating local moons with terrestrial bacteria. ==Background== Jupiter is the largest planet in the solar system, with more than twice the mass of all the other planets combined.
With more data on hand, in 2003 a team led Kevin Zahle at NASA's Ames Research Center arrived at a figure of 30 to 70 million years.
Galileo 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 Amalthea's mass as the spacecraft swung by it.
This was intended to run until March 2001, but it was subsequently extended until January 2003.
On April 14, 2003, Galileo reached its greatest orbital distance from Jupiter for the entire mission since orbital insertion, , before plunging back towards the gas giant for its final impact.
At the completion of J35, its final orbit around the Jovian system, Galileo impacted Jupiter in darkness just south of the equator on September 21, 2003, at 18:57 UTC.
The scheme was studied in 2004 for a data link to a future Mars orbiting spacecraft. ==Lunar observations== ==High gain antenna problem== Once Galileo headed beyond Earth, it was no longer risky to employ the HGA, so on April 11, 1991, Galileo was ordered to unfurl it.
New Horizons passed close by Jupiter in 2007 for a gravity assist en route to Pluto, and it too collected data on the planet.
On December 11, 2013, NASA reported, based on results from the Galileo mission, the detection of "clay-like minerals" (specifically, phyllosilicates), often associated with organic materials, on the icy crust of Europa.
This led to the Europa Clipper being approved in 2015; it is currently planned for launch in the mid-2020s. ===Europa Lander=== A lander concept, simply called Europa Lander is being assessed by the Jet Propulsion Laboratory.
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