 Artist's concept ofGalileo at Io with Jupiter in the background. In reality, the high-gain foldable antenna failed to deploy in flight. | |||||||||||||||||||||||
| Names | Jupiter Orbiter Probe | ||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mission type | Jupiter orbiter | ||||||||||||||||||||||
| Operator | NASA | ||||||||||||||||||||||
| COSPAR ID | 1989-084B | ||||||||||||||||||||||
| SATCATno. | 20298 | ||||||||||||||||||||||
| Website | solarsystem | ||||||||||||||||||||||
| Mission duration |
| ||||||||||||||||||||||
| Distance travelled | 4,631,778,000 km (2.88 billion mi)[1] | ||||||||||||||||||||||
| Spacecraft properties | |||||||||||||||||||||||
| Manufacturer | |||||||||||||||||||||||
| Launch mass | |||||||||||||||||||||||
| Dry mass | |||||||||||||||||||||||
| Payload mass | |||||||||||||||||||||||
| Power | |||||||||||||||||||||||
| Start of mission | |||||||||||||||||||||||
| Launch date | October 18, 1989, 16:53:40 (1989-10-18UTC16:53:40) UTC | ||||||||||||||||||||||
| Rocket | Space Shuttle Atlantis STS-34/IUS | ||||||||||||||||||||||
| Launch site | KennedyLC-39B | ||||||||||||||||||||||
| Entered service | December 8, 1995, 01:16 UTC SCET | ||||||||||||||||||||||
| End of mission | |||||||||||||||||||||||
| Disposal | Controlled entry into Jupiter | ||||||||||||||||||||||
| Decay date | September 21, 2003, 18:57:18 (2003-09-21UTC18:57:19) UTC | ||||||||||||||||||||||
| |||||||||||||||||||||||
 Large Strategic Science Missions Planetary Science Division | |||||||||||||||||||||||
Galileo was an American roboticspace probe that studied the planetJupiter andits moons, as well as the asteroidsGaspra andIda. Named after the Italian astronomerGalileo Galilei, it consisted of an orbiter and an entry probe. It was delivered into Earth orbit on October 18, 1989, bySpace Shuttle Atlantis, duringSTS-34.Galileo arrived at Jupiter on December 7, 1995, aftergravitational assist flybys ofVenus andEarth, and became the first spacecraft to orbit an outer planet.[4]
TheJet Propulsion Laboratory built theGalileo spacecraft and managed theGalileo program forNASA. West Germany'sMesserschmitt-Bölkow-Blohm supplied the propulsion module. NASA'sAmes Research Center managed the atmospheric probe, which was built byHughes Aircraft Company. At launch, the orbiter and probe together had a mass of 2,562 kg (5,648 lb) and stood 6.15 m (20.2 ft) tall.
Spacecraft are normally stabilized either by spinning around a fixed axis or by maintaining a fixed orientation with reference to the Sun and a star.Galileo did both. One section of the spacecraft rotated at 3 revolutions per minute, keepingGalileo stable and holding six instruments that gathered data from many different directions, including the fields and particles instruments.
Galileo wasintentionally destroyed in Jupiter's atmosphere on September 21, 2003. The next orbiter to be sent to Jupiter wasJuno, which arrived on July 5, 2016.
Jupiter is the largest planet in theSolar System, with more than twice the mass of all the other planets combined.[5] Consideration of sending a probe to Jupiter began as early as 1959.[6] NASA's Scientific Advisory Group (SAG) for Outer Solar System Missions considered the requirements for Jupiter orbiters and atmospheric probes. It noted that the technology to build aheat shield for an atmospheric probe did not yet exist, and facilities to test one under the conditions found on Jupiter would not be available until 1980.[7] NASA management designated theJet Propulsion Laboratory (JPL) as the lead center for the Jupiter Orbiter Probe (JOP) project.[8] The JOP would be the fifth spacecraft to visit Jupiter, but the first to orbit it, and the probe would be the first to enter its atmosphere.[9]
An important decision made at this time was to use aMariner program spacecraft like that used for Voyager for the Jupiter orbiter, rather than a Pioneer. Pioneer was stabilized by spinning the spacecraft at 60rpm, which gave a 360-degree view of the surroundings, and did not require an attitude control system. By contrast, Mariner had an attitude control system with threegyroscopes and two sets of sixnitrogen jet thrusters. Attitude was determined with reference to the Sun andCanopus, which were monitored with two primary and four secondary sensors. There was also aninertial reference unit and anaccelerometer. This allowed it to take high-resolution images, but the functionality came at a cost of increased weight. A Mariner weighed 722 kilograms (1,592 lb) compared to just 146 kilograms (322 lb) for a Pioneer.[10]
John R. Casani, who had headed the Mariner and Voyager projects, became the first project manager.[11] He solicited suggestions for a more inspirational name for the project, and the most votes went to "Galileo" afterGalileo Galilei, the first person to view Jupiter through a telescope. His 1610 discovery of what is now known as theGalilean moons orbiting Jupiter was important evidence of theCopernican model of the solar system. It was also noted that the name was that of aspacecraft in theStar Trek television show. The new name was adopted in February 1978.[12]
TheJet Propulsion Laboratory built theGalileo spacecraft with anoctagonal prismbus and managed theGalileo mission for NASA.[13]West Germany'sMesserschmitt-Bölkow-Blohm supplied the propulsion module. NASA'sAmes Research Center managed the cone-shaped atmospheric probe, which was built byHughes Aircraft Company.[2] At launch, the orbiter and probe together had a mass of 2,562 kg (5,648 lb) and stood 6.15 m (20.2 ft) tall.[2]Spacecraft are normally stabilized either by spinning around a fixed axis or by maintaining a fixed orientation with reference the Sun and a star;Galileo did both. One section of the spacecraft rotated at 3revolutions per minute, keepingGalileo stable and holding six instruments that gathered data from many different directions, including the fields and particles instruments.[14] Back on the ground, the mission operations team used software containing 650,000 lines of code in the orbit sequence design process; 1,615,000 lines in the telemetry interpretation; and 550,000 lines of code in navigation.[2] All of the spacecraft components and spare parts received a minimum of 2,000 hours of testing. The spacecraft was expected to last for at least five years—long enough to reach Jupiter and perform its mission.[15]
On December 19, 1985, it departed the JPL inPasadena, California, on the first leg of its journey, a road trip to theKennedy Space Center inFlorida.[15][16] Due to theSpace ShuttleChallenger disaster, the May launch date could not be met.[17] The mission was rescheduled to October 12, 1989. TheGalileo spacecraft would be launched by theSTS-34 mission in theSpace Shuttle Atlantis.[18] As the launch date ofGalileo neared,anti-nuclear groups, concerned over what they perceived as an unacceptable risk to the public's safety from theplutonium in theGalileo'sradioisotope thermoelectric generators (RTGs) and General Purpose Heat Source (GPHS) modules, sought a court injunction prohibitingGalileo's launch.[19] RTGs were necessary for deep space probes because they had to fly distances from the Sun that made the use of solar energy impractical.[20][21]
The launch was delayed twice more: by a faulty main engine controller that forced a postponement to October 17, and then by inclement weather, which necessitated a postponement to the following day,[22] but this was not a concern since the launch window extended until November 21.[23]Atlantis finally lifted off at 16:53:40UTC on October 18, and went into a 343-kilometer (213 mi) orbit.[22]Galileo was successfully deployed at 00:15 UTC on October 19.[17] Following the IUS burn, theGalileo spacecraft adopted its configuration for solo flight, and separated from the IUS at 01:06:53 UTC on October 19.[24] The launch was perfect, andGalileo was soon headed towards Venus at over 14,000 km/h (9,000 mph).[25]Atlantis returned to Earth safely on October 23.[22]
The CDH subsystem was actively redundant, with two paralleldata system buses running at all times.[26] Each data system bus (a.k.a. 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).[27]
The CDH subsystem was responsible for maintaining the following functions:
The spacecraft was controlled by sixRCA 1802 COSMACmicroprocessorCPUs: four on the spun side and two on the despun side. Each CPU was clocked at about 1.6 MHz, and fabricated onsapphire (silicon on sapphire), which is aradiation-and static-hardened material ideal for spacecraft operation. This 8-bit microprocessor was the first low-powerCMOS processor chip, similar to the6502 that was being built into theApple IIdesktop computer at that time.[29]
The Galileo Attitude and Articulation Control System (AACSE) was controlled by twoItekAdvanced Technology Airborne Computers (ATAC), built using radiation-hardened2901s. The AACSE could be reprogrammed in flight by sending the new program through the Command and Data Subsystem.[30] The attitude control system software was written in theHAL/S programming language,[31] which was also used in theSpace Shuttle program.[32]
Memory capacity provided by each BUM was 16K ofRAM, while the DBUMs each provided 8K of RAM. There were two BUMs and two DBUMs in the CDH subsystem and they all resided on the spun side of the spacecraft. The BUMs and DBUMs provided storage for sequences and contain various buffers for telemetry data and interbus communication. Every HLM and LLM was built up around a single 1802 microprocessor and 32K of RAM (for HLMs) or 16K of RAM (for LLMs). Two HLMs and two LLMs resided on the spun side while two LLMs were on the despun side. Thus, total memory capacity available to the CDH subsystem was 176K of RAM: 144K allocated to the spun side and 32K to the despun side.[33]Each HLM was responsible for the following functions:
Each LLM was responsible for the following functions:
The propulsion subsystem consisted of a 400 N (90 lbf) main engine and twelve 10 N (2.2 lbf) thrusters, together with propellant, storage and pressurizing tanks and associated plumbing. The 10 N thrusters were mounted in groups of six on two 2-meter (6.6 ft) booms. The fuel for the system was 925 kg (2,039 lb) ofmonomethylhydrazine andnitrogen tetroxide. Two separate tanks held another 7 kg (15 lb) ofhelium pressurant. The propulsion subsystem was developed and built byMesserschmitt-Bölkow-Blohm and provided by West Germany, the major international partner in ProjectGalileo.[29]
At the time,solar panels were not practical at Jupiter's distance from the Sun; the spacecraft would have needed a minimum of 65 square meters (700 sq ft) of panels. Chemical batteries would likewise be prohibitively large due to technological limitations. The solution was tworadioisotope thermoelectric generators (RTGs) which powered the spacecraft through the radioactive decay ofplutonium-238. The heat emitted by this decay was converted into electricity through the solid-stateSeebeck effect. This provided a reliable and long-lasting source of electricity unaffected by the cold environment and high-radiation fields in the Jovian system.[29][34]
EachGPHS-RTG, mounted on a 5-meter-long (16 ft) boom, carried 7.8 kilograms (17 lb) of238Pu. Each RTG contained 18 separate heat source modules, and each module encased four pellets ofplutonium(IV) oxide, aceramic material resistant to fracturing.[34] The plutonium was enriched to about 83.5 percent plutonium-238.[35] The modules were designed to survive a range of potential accidents: launch vehicle explosion or fire, re-entry into the atmosphere followed by land or water impact, and post-impact situations. An outer covering ofgraphite provided protection against the structural, thermal, and eroding environments of a potential re-entry into Earth's atmosphere. Additional graphite components provided impact protection, whileiridium cladding of the RTGs provided post-impact containment.[34] The RTGs produced about 570 watts at launch. The power output initially decreased at the rate of 0.6 watts per month and was 493 watts whenGalileo arrived at Jupiter.[3]
The spacecraft had a large high-gain antenna which failed to deploy during the mission, so the low-gain antenna was used instead, limiting data transfer to slowerbit rates.[36]
Scientific instruments to measure fields and particles were mounted on the spinning section of the spacecraft, together with the mainantenna, power supply, the propulsion module and most ofGalileo's computers and control electronics. The sixteen instruments, weighing 118 kg (260 lb) altogether, includedmagnetometer sensors mounted on an 11 m (36 ft) boom to minimize interference from the spacecraft; aplasma instrument for detecting low-energy charged particles and a plasma-wave detector to study waves generated by the particles; a high-energy particle detector; and a detector of cosmic and Joviandust. It also carried the Heavy Ion Counter, an engineering experiment to assess the potentially hazardous charged particle environments the spacecraft flew through, and anextreme ultraviolet detector associated with the UV spectrometer on the scan platform.[2]
The despun section's instruments included the camera system; thenear infrared mapping spectrometer to make multi-spectral images for atmospheric and moon surface chemical analysis; the ultraviolet spectrometer to study gases; and the photopolarimeter-radiometer to measure radiant and reflected energy. The camera system was designed to obtain images of Jupiter's satellites at resolutions 20 to 1,000 times better thanVoyager's best, becauseGalileo flew closer to the planet and its inner moons, and because the more modernCCD sensor inGalileo's camera was more sensitive and had a broader color detection band than thevidicons ofVoyager.[2]
The SSI was an 800-by-800-pixelcharge-coupled device (CCD) camera. The optical portion of the camera was a modified flight spare of theVoyager narrow-angle camera; aCassegrain telescope.[37] The CCD had radiation shielding a 10 mm (0.4 in) thick layer oftantalum surrounding the CCD except where the light enters the system. An eight-position filter wheel was used to obtain images at specific wavelengths. The images were then combined electronically on Earth to produce color images. The spectral response of the SSI ranged from about 400 to 1100 nm. The SSI weighed 29.7 kg (65 lb) and consumed, on average, 15 watts of power.[38][39]
The NIMS instrument was sensitive to 0.7-to-5.2-micrometer wavelengthinfrared light, overlapping the wavelength range of the SSI. NIMS used a 229 mm (9 in) aperture reflecting telescope. Thespectrometer used a grating to disperse the light collected by the telescope. The dispersed spectrum of light was focused on detectors ofindium,antimonide andsilicon. NIMS weighed 18 kg (40 lb) and used 12 watts of power on average.[40][41]
TheCassegrain telescope of the UVS had a 250 mm (9.8 in) aperture. Both the UVS and EUV instruments used a ruledgrating to disperse light for spectral analysis. Light then passed through an exit slit intophotomultiplier tubes that produced pulses of electrons, which were counted and the results sent to Earth. The UVS was mounted onGalileo's scan platform. The EUV was mounted on the spun section. AsGalileo rotated, EUV observed a narrow ribbon of space perpendicular to the spin axis. The two instruments combined weighed about 9.7 kg (21 lb) and used 5.9 watts of power.[42][43]
The PPR had seven radiometry bands. One of these used no filters and observed all incoming radiation, both solar and thermal. Another band allowed only solar radiation through. The difference between the solar-plus-thermal and the solar-only channels gave the total thermal radiation emitted. The PPR also measured in five broadband channels that spanned the spectral range from 17 to 110 micrometers. The radiometer provided data on the temperatures of Jupiter's atmosphere and satellites. The design of the instrument was based on that of an instrument flown on thePioneer Venus spacecraft. A 100 mm (4 in) aperture reflecting telescope collected light and directed it to a series of filters, and, from there, measurements were performed by the detectors of the PPR. The PPR weighed 5.0 kg (11.0 lb) and consumed about 5 watts of power.[44][45]
Thedust-detector subsystem (DDS) was used to measure the mass, electric charge, and velocity of incoming particles. The masses of dust particles that the DDS could detect go from 10−16 to 10−7 grams. The speed of these small particles could be measured over the range of 1 to 70 kilometers per second (0.6 to 43.5 mi/s). The instrument could measure impact rates from 1 particle per 115 days (10 megaseconds) to 100 particles per second. Such data was used to help determine dust origin and dynamics within themagnetosphere. The DDS weighed 4.2 kg (9.3 lb) and used an average of 5.4 watts of power.[46][47]
The energetic-particles detector (EPD) was designed to measure the numbers and energies of ions and electrons whose energies exceeded about 20 keV (3.2 fJ). The EPD could also measure the direction of travel of such particles and, in the case of ions, could determine their composition (whether the ion isoxygen orsulfur, for example). The EPD used silicon solid-state detectors and atime-of-flight detector system to measure changes in the energetic particle population at Jupiter as a function of position and time. These measurements helped determine how the particles got their energy and how they were transported through Jupiter's magnetosphere. The EPD weighed 10.5 kg (23 lb) and used 10.1 watts of power on average.[48][49]
The HIC was, in effect, a repackaged and updated version of some parts of the flight spare of theVoyager cosmic-ray system. The HIC detected heavyions using stacks of single crystal silicon wafers. The HIC could measure heavy ions with energies as low as 6 MeV (1 pJ) and as high as 200 MeV (32 pJ) per nucleon. This range included all atomic substances betweencarbon andnickel. The HIC and the EUV shared a communications link and, therefore, had to share observing time. The HIC weighed 8.0 kg (17.6 lb) and used an average of 2.8 watts of power.[50][51]
Themagnetometer (MAG) used two sets of three sensors. The three sensors allowed the three orthogonal components of themagnetic field section to be measured. One set was located at the end of the magnetometer boom and, in that position, was about 11 m (36 ft) from the spin axis of the spacecraft. The second set, designed to detect stronger fields, was 6.7 m (22 ft) from the spin axis. The boom was used to remove the MAG from the immediate vicinity ofGalileo to minimize magnetic effects from the spacecraft. However, not all these effects could be eliminated by distancing the instrument. The rotation of the spacecraft was used to separate natural magnetic fields from engineering-induced fields. Another source of potential error in measurement came from the bending and twisting of the long magnetometer boom. To account for these motions, a calibration coil was mounted rigidly on the spacecraft to generate a reference magnetic field during calibrations. The magnetic field at the surface of the Earth has a strength of about 50,000 nT. At Jupiter, the outboard (11 m) set of sensors could measure magnetic field strengths in the range from ±32 to ±512 nT, while the inboard (6.7 m) set was active in the range from ±512 to ±16,384 nT. The MAG experiment weighed 7.0 kg (15.4 lb) and used 3.9 watts of power.[52][53]
The PLS used seven fields of view to collectcharged particles for energy and mass analysis. These fields of view covered most angles from 0 to 180 degrees, fanning out from the spin axis. The rotation of the spacecraft carried each field of view through a full circle. The PLS measured particles in the energy range from 0.9 to 52,000 eV (0.14 to 8,300 aJ). The PLS weighed 13.2 kg (29 lb) and used an average of 10.7 watts of power.[54][55]
An electricdipole antenna was used to study the electric fields ofplasmas, while two search coil magnetic antennas studied the magnetic fields. The electric dipole antenna was mounted at the tip of the magnetometer boom. The search coil magnetic antennas were mounted on the high-gain antenna feed. Nearly simultaneous measurements of the electric and magnetic field spectrum allowedelectrostatic waves to be distinguished fromelectromagnetic waves. The PWS weighed 7.1 kg (16 lb) and used an average of 9.8 watts.[56][57]
 Diagram of the atmospheric entry probe's instruments and subsystems | |
| Mission type | Atmospheric probe |
|---|---|
| Operator | NASA |
| COSPAR ID | 1989-084E |
| SATCATno. | 43337 |
| Mission duration | 61.4 minutes |
| Distance travelled | 83 million km (52 million mi) |
| Spacecraft properties | |
| Manufacturer | Hughes Aircraft Company |
| BOL mass | 340 kg (750 lb) |
| Payload mass | 29 kg (64 lb) |
| Power | 580 watts |
| Start of mission | |
| Launch date | October 18, 1989, 16:53:40 (1989-10-18UTC16:53:40) UTC |
| Rocket | Space Shuttle Atlantis STS-34/IUS |
| Launch site | KennedyLC-39B |
| Deployed from | Galileo |
| Deployment date | July 12, 1995, 03:07 UTC[2] |
| End of mission | |
| Last contact | December 7, 1995, 23:06:08 UTC |
| Jupiter atmospheric probe | |
| Atmospheric entry | December 7, 1995, 22:04:44 UTC |
| Impact site | 6°30′N4°24′W / 6.5°N 4.4°W /6.5; -4.4[58] |
The atmospheric probe was built byHughes Aircraft Company's Space and Communications Group at itsEl Segundo, California plant.[59][60] It weighed 339 kilograms (747 lb) and was 86 centimeters (34 in) high.[2]
Inside the probe'sheat shield, the scientific instruments were protected from extreme heat and pressure during its high-speed journey into the Jovian atmosphere, entering at 48 kilometers per second (110,000 mph).[61] Temperatures reached around 16,000 °C (29,000 °F).[58] The ablative heat shield was made ofcarbon phenolic.[62] NASA built a special laboratory, the Giant Planet Facility, to simulate the heat load, which was similar to the convective and radiative heating experienced by anICBM warhead reentering the atmosphere.[63][64]
The probe's electronics were powered by 13lithium sulfur dioxide batteries manufactured byHoneywell's PowerSources Center inHorsham, Pennsylvania. Each cell was the size of aD battery so existing manufacturing tools could be used.[65][66] They provided a nominal power output of about 7.2-ampere hours capacity at a minimal voltage of 28.05 volts.[67]
The probe included seven instruments for taking data on its plunge into Jupiter:[68][69]
| Instrument | Function | Mass | Power consumption | Principal investigator | Organizations |
|---|---|---|---|---|---|
| Atmospheric structure instrument | Measuring temperature, pressure and deceleration | 4.1 kg (9.0 lb) | 6.3 W | Alvin Seiff | Ames Research Center andSan Jose State University Foundation |
| Neutral mass spectrometer | Analyze the gas composition of the atmosphere | 13 kg (29 lb) | 29 W | Hasso Niemann | Goddard Space Flight Center |
| Helium Abundance Detector | Aninterferometer supporting atmospheric composition studies | 1.4 kg (3.1 lb) | 1.1 W | Ulf von Zahn | University of Bonn,University of Rostock |
| Nephelometer | Cloud location and cloud-particle observations | 4.8 kg (11 lb) | 14 W | Boris Ragent | Ames Research Center andSan Jose State University Foundation |
| Net-fluxradiometer | Measuring the difference between upward and downwardradiant flux at each altitude | 3.0 kg (6.6 lb) | 7.0 W | L. Sromovsky | University of Wisconsin |
| Lightning and radio emission detector and energetic particles instrument | Measuring light and radio emissions associated with lightning, and fluxes ofprotons,electrons,alpha particles and heavyions | 2.7 kg (6.0 lb) | 2.3 W | Louis Lanzerotti | Bell Laboratories,University of Florida and Federal Republic of Germany |
| Radio equipment | Measuring wind speeds and atmospheric absorption | David Atkinson | University of Idaho |
In addition, the probe's heat shield contained instrumentation to measureablation during descent.[70]
Lacking the fuel to escape Jupiter's gravity well, at the end ofGalileo's life, the main spacecraft wasdeliberately crashed into Jupiter on September 21, 2003, to preventforward contamination of possible life of Jupiter's moon Europa.[71]
The Galileo Probe hadCOSPAR ID 1989-084E while the orbiter had id 1989-084B.[72] Names for the spacecraft includeGalileo Probe orJupiter Entry Probe abbreviated JEP.[73] The related COSPAR IDs of the Galileo mission were:[74]
DSI via Stuttgart University
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