Ulysses probe
Encyclopedia
Ulysses is a decommissioned robotic
space probe
that was designed to study the Sun
as a joint venture of NASA
and the European Space Agency
(ESA). The spacecraft
was originally named Odysseus, because of its lengthy and indirect trajectory to near Solar distance. 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
. Originally scheduled for launch in 1986 aboard the Space Shuttle Challenger, due to the loss of Challenger, the launch of Ulysses was delayed until October 6, 1990 aboard the Space Shuttle
Discovery
(mission STS-41
). The spacecraft's mission was to study the Sun at all latitudes. To do this required a major orbital plane shift. Due to velocity change limitations of the Shuttle and the Inertial Upper Stage
(IUS), this was accomplished by using an encounter with Jupiter to effect the plane change instead of an engine burn. The need for a Jupiter encounter meant that Ulysses could not be powered by solar cells and was powered by a radioisotope thermoelectric generator
(RTG) instead.
By February 2008, the power output from the RTG
, which is generated by heat from the radioactive decay of plutonium-238
, had decreased enough to leave insufficient power for internal heaters to keep the spacecraft's attitude control hydrazine fuel from freezing.
The end of mission was at one point scheduled for July 1, 2008, but mission scientists came up with a method to keep the fuel liquid by conducting a short thruster burn every two hours, allowing the mission to continue.
The cessation of mission operations and deactivation or hibernation of the spacecraft was determined by the inability to prevent attitude control fuel from freezing.
The last day for mission operations on Ulysses was 30 June 2009.
This was a full year after the most recent previously announced mission end date. The scheduled end of mission in 2009 was the fourth time that the end of the spacecraft's mission had been scheduled.
The last scheduled ground station pass of the mission was over the Madrid Deep Space Network 70m ground station (DSS-63) from around 15:35 to 20:20 UTC. There were no decommissioning engineering tests on the spacecraft.
Until Ulysses, the Sun was only observed from low solar latitudes. The Earth's orbit defines the ecliptic
plane, which differs from the Sun's equatorial plane by only 7.25 degrees. Even spacecraft directly orbiting the Sun do so in planes close to the ecliptic because a direct launch into a high inclination solar orbit would require a prohibitively large launch vehicle.
Several spacecraft (Mariner 10
, Pioneer 11
, and Voyagers 1 and 2
) had performed gravity assist manoeuvres in the 1970s. Those manoeuvres were to reach other planets also orbiting close to the ecliptic, so they were mostly in-plane changes. However, gravity assists are not limited to in-plane maneuvers; a suitable flyby of Jupiter
could produce a significant plane change. An Out-Of-The-Ecliptic mission (OOE) was thereby proposed. See article Pioneer H
.
Originally, two spacecraft were to be built by NASA and ESA, as the International Solar Polar Mission. One would be sent over Jupiter, then under the Sun. The other would fly under Jupiter, then over the Sun. This would provide simultaneous coverage. Due to cutbacks, the US spacecraft was canceled in 1981. One spacecraft was designed, and the project recast as Ulysses, due to the indirect and untried flight path. 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 instruments would be split into teams from universities and research institutes in Europe and the United States. This process provided the 10 instruments on board.
The changes delayed launch from February 1983 to May 1986 where it was to be deployed by the Space Shuttle Challenger
, however, the Challenger disaster
pushed the date to October 1990.
IUS
(Inertial Upper Stage), plus a McDonnell Douglas
PAM-S (Payload Assist Module
-Special). The IUS was inertially stabilised and actively guided during its burn. The PAM-S was unguided and it and the Ulysses spacecraft was spun up to 80 rpm for stability at the start of its burn. On burnout of the PAM-S, the motor and spacecraft stack was yo-yo de-spun
(weights deployed at the end of cables) to below 8 rpm prior to separation of the spacecraft. On leaving Earth, the spacecraft became the fastest ever artificially-accelerated object, and held that title until the New Horizons
probe was launched.
On its way to Jupiter the spacecraft was in an elliptical Hohmann transfer orbit
with perihelion near 1 AU and aphelion near 5 AU, Jupiter's distance from the Sun. At this time Ulysses had a low orbital inclination to the ecliptic.
by 80.2 degrees. The giant planet's gravity bent the spacecraft's flight path southward and away from the ecliptic plane. This put it into a final orbit around the Sun that would take it past the Sun's north and south poles.
The size and shape of the orbit were adjusted to a much smaller degree so that aphelion remained at approximately 5 AU, Jupiter's distance from the Sun, and perihelion was somewhat greater than 1 AU, the Earth's distance from the Sun.
ern solar polar regions, respectively.
(C/1996 B2), revealing the tail to be at least 3.8 AU in length.
carried the cometary material to Ulysses.
ern solar polar regions, which gave many unexpected results. In particular the southern magnetic
pole was found to be much more dynamic than the north pole and without any fixed clear location; instead, it is diffusely located.
, from freezing, instrument power sharing was initiated. Up until then, the most important instruments had been kept online constantly, whilst others were deactivated. When the probe neared the Sun, its power-hungry heaters were turned off and all instruments were turned on.
On February 22, 2008, 17 years 4 months after the launch of the spacecraft, ESA and NASA
announced that mission operations for Ulysses would be likely to cease within a few months. On April 12, 2008 NASA announced that the end date will be July 1, 2008. The spacecraft operated successfully for over four times its design life
. A component within the last remaining working chain of X-band
downlink sub-system failed on January 15, 2008. The other chain in the X-band sub-system had previously failed in 2003.
Downlink to Earth
resumed on S-band
, but the beamwidth
of the high gain antenna on S-band is not as narrow as on X – so the downlink signal was much weaker, thereby reducing the achievable data rate
. 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 m in diameter) of the Deep Space Network
. Even before the downlink signal was lost due to distance, the hydrazine
attitude control fuel on-board the spacecraft was considered likely to freeze
, as the radioisotope thermal generators failed to generate enough power for the heaters to combat the cold of space. 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. The failure of the X-band communications sub-system hastened this, because the coldest part of the fuel pipework was routed over the X-band TWTAs which, when one of them was operating, kept this part of the pipework sufficiently warm.
The previously announced mission end date of July 1, 2008 came and went but mission operations continued albeit in a reduced capacity. The availability of science data gathering was limited to only when Ulysses is in contact with a ground station due to the deteriorating S-band downlink margin no longer being able to support simultaneous real-time data and tape recorder playback. When the spacecraft was out of contact with a ground station, the S-band transmitter was switched off and the power was diverted to keep the internal heaters to add to the warming of the hydrazine. On June 30, 2009 ground controllers sent commands to switch to its low gain antennae which ceased communications with the spacecraft along with previous commands to schedule the shut down of its transmitter entirely.
instrument, Ulysses was an important part of the InterPlanetary Network
(IPN). The IPN detects gamma ray burst
s (GRBs); since gamma rays cannot be focused with mirrors, it was very difficult to locate GRBs with enough accuracy to study them further. Instead, several spacecraft can locate the burst through triangulation
(or, more specifically, multilateration
). Each spacecraft has a gamma-ray detector, with readouts noted in tiny fractions of a second. By comparing the arrival times of gamma showers with the separations of the spacecraft, a location can be determined, for follow-up with other telescopes. Because gamma rays travel at the speed of light, wide separations are needed. 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. When Ulysses crossed the ecliptic twice per orbit, many GRB determinations lost accuracy.
Additional discoveries:
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 is spin-stabilised about its z-axis which roughly coincides with the axis of the dish antenna. The RTG, whip antennas, and instrument boom are placed to stabilize this axis. Spin is nominally 5 rpm. Inside the body is 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 is controlled by eight thrusters, in two blocks. Thrusters are pulsed in the time domain to perform rotation or translation. Four Sun sensors detected orientation. For fine attitude control, the S-band antenna feed is mounted slightly off-axis. This offset feed combined with the spacecraft spin introduces an oscillation to an S-band radio signal transmitted from Earth when received on-board the spacecraft. The amplitude and phase of this oscillation is proportional to the oriention of the spin axis relative to the Earth direction. This method of determining the relative orientation is called CONSCAN and was widely employed in early infra-red guided missiles.
The spacecraft uses 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 20W TWTAs until the failure of the last remaining TWTA in January 2008. Both bands use 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, store science data between the nominal 8-hour communications sessions during the prime and extended mission phases.
The spacecraft is designed to withstand both the heat of the inner Solar System and the cold at Jupiter distance. Extensive blanketing and electric heaters protect against cold.
Total mass at launch was 366.7 kg of which 33.5 kg was hydrazine (used for attitude control and orbit correction).
antennas unreeled outwards from the body, perpendicular to the RTG and spin axis. Together this dipole
spanned 72 meters. A third antenna, of hollow beryllium-copper, deployed from the body, along the spin axis opposite the dish. It was a monopole antenna
, 7.5 meters long. These measured radio waves generated by plasma releases, or the plasma itself as it passed over the spacecraft. This receiver ensemble was sensitive from dc to 1 MHz.
Experiment Boom. A third type of boom, shorter and much more rigid, extended from the last side of the spacecraft, opposite the RTG. This was a hollow carbon-fiber tube, of 50 mm diameter. It can be seen in the photo as the silver rod stowed alongside the body. It carried four types of instruments. A solid-state X-ray
instrument, which was composed of two silicon
detectors to study X-rays from solar flare
s and Jupiter's aurorae. The GRB experiment consisted of two CsI
scintillator crystals with photomultipliers. Two different magnetometer
s were mounted: a vector helium magnetometer and a fluxgate magnetometer. A two axis magnetic search coil antenna measured AC magnetic fields.
Body-Mounted Instruments. Detectors for electron
s, ion
s, neutral gas, dust
, and cosmic ray
s were mounted on the spacecraft body around the quiet section.
Lastly, the radio communications link could be used to search for gravitational waves (through Doppler shifts) and to probe the Sun's atmosphere through occultation
. No gravitational waves were detected.
Total instrument mass is 55 kg.
Robotic spacecraft
A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...
space probe
Space probe
A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...
that was designed to study the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
as a joint venture of NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
and the European Space Agency
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
(ESA). The spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
was originally named Odysseus, because of its lengthy and indirect trajectory to near Solar distance. It was renamed Ulysses, the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
translation
Translation
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. Whereas interpreting undoubtedly antedates writing, translation began only after the appearance of written literature; there exist partial translations of the Sumerian Epic of...
of "Odysseus
Odysseus
Odysseus or Ulysses was a legendary Greek king of Ithaca and the hero of Homer's epic poem the Odyssey. Odysseus also plays a key role in Homer's Iliad and other works in the Epic Cycle....
" at ESA's request in honour not only of Homer's mythological hero but also with reference to Dante's description in Dante's
Dante Alighieri
Durante degli Alighieri, mononymously referred to as Dante , was an Italian poet, prose writer, literary theorist, moral philosopher, and political thinker. He is best known for the monumental epic poem La commedia, later named La divina commedia ...
Inferno
Inferno (Dante)
Inferno is the first part of Dante Alighieri's 14th-century epic poem Divine Comedy. It is followed by Purgatorio and Paradiso. It is an allegory telling of the journey of Dante through what is largely the medieval concept of Hell, guided by the Roman poet Virgil. In the poem, Hell is depicted as...
. Originally scheduled for launch in 1986 aboard the Space Shuttle Challenger, due to the loss of Challenger, the launch of Ulysses was delayed until October 6, 1990 aboard the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
Discovery
Space Shuttle Discovery
Space Shuttle Discovery is one of the retired orbiters of the Space Shuttle program of NASA, the space agency of the United States, and was operational from its maiden flight, STS-41-D on August 30, 1984, until its final landing during STS-133 on March 9, 2011...
(mission STS-41
STS-41
STS-41 was the eleventh mission of the Space Shuttle Discovery. The four-day mission with a primary objective to launch the Ulysses probe as part of the "International Solar Polar Mission".-Crew:-Mission parameters:*Mass:...
). The spacecraft's mission was to study the Sun at all latitudes. To do this required a major orbital plane shift. Due to velocity change limitations of the Shuttle and the Inertial Upper Stage
Inertial Upper Stage
The Inertial Upper Stage , originally known as the Interim Upper Stage, is a two-stage solid-fueled booster rocket developed by the U.S...
(IUS), this was accomplished by using an encounter with Jupiter to effect the plane change instead of an engine burn. The need for a Jupiter encounter meant that Ulysses could not be powered by solar cells and was powered by a radioisotope thermoelectric generator
Radioisotope thermoelectric generator
A radioisotope thermoelectric generator is an electrical generator that obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples.RTGs can be...
(RTG) instead.
By February 2008, the power output from the RTG
Radioisotope thermoelectric generator
A radioisotope thermoelectric generator is an electrical generator that obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples.RTGs can be...
, which is generated by heat from the radioactive decay of plutonium-238
Plutonium-238
-External links:**...
, had decreased enough to leave insufficient power for internal heaters to keep the spacecraft's attitude control hydrazine fuel from freezing.
The end of mission was at one point scheduled for July 1, 2008, but mission scientists came up with a method to keep the fuel liquid by conducting a short thruster burn every two hours, allowing the mission to continue.
The cessation of mission operations and deactivation or hibernation of the spacecraft was determined by the inability to prevent attitude control fuel from freezing.
The last day for mission operations on Ulysses was 30 June 2009.
This was a full year after the most recent previously announced mission end date. The scheduled end of mission in 2009 was the fourth time that the end of the spacecraft's mission had been scheduled.
The last scheduled ground station pass of the mission was over the Madrid Deep Space Network 70m ground station (DSS-63) from around 15:35 to 20:20 UTC. There were no decommissioning engineering tests on the spacecraft.
Planning
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
plane, which differs from the Sun's equatorial plane by only 7.25 degrees. Even spacecraft directly orbiting the Sun do so in planes close to the ecliptic because a direct launch into a high inclination solar orbit would require a prohibitively large launch vehicle.
Several spacecraft (Mariner 10
Mariner 10
Mariner 10 was an American robotic space probe launched by NASA on November 3, 1973, to fly by the planets Mercury and Venus. It was launched approximately two years after Mariner 9 and was the last spacecraft in the Mariner program...
, Pioneer 11
Pioneer 11
Pioneer 11 is a 259-kilogram robotic space probe launched by NASA on April 6, 1973 to study the asteroid belt, the environment around Jupiter and Saturn, solar wind, cosmic rays, and eventually the far reaches of the solar system and heliosphere...
, and Voyagers 1 and 2
Voyager program
The Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...
) had performed gravity assist manoeuvres in the 1970s. Those manoeuvres were to reach other planets also orbiting close to the ecliptic, so they were mostly in-plane changes. However, gravity assists are not limited to in-plane maneuvers; a suitable flyby of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
could produce a significant plane change. An Out-Of-The-Ecliptic mission (OOE) was thereby proposed. See article Pioneer H
Pioneer H
Pioneer H is an unlaunched unmanned space mission that was part of the US Pioneer program for a planned 1974 launch. Had this mission and spacecraft been launched, it would have been designated Pioneer 12; that designation was later applied to the Pioneer Venus Orbiter.The probe would have been...
.
Originally, two spacecraft were to be built by NASA and ESA, as the International Solar Polar Mission. One would be sent over Jupiter, then under the Sun. The other would fly under Jupiter, then over the Sun. This would provide simultaneous coverage. Due to cutbacks, the US spacecraft was canceled in 1981. One spacecraft was designed, and the project recast as Ulysses, due to the indirect and untried flight path. 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 instruments would be split into teams from universities and research institutes in Europe and the United States. This process provided the 10 instruments on board.
The changes delayed launch from February 1983 to May 1986 where it was to be deployed by the Space Shuttle Challenger
Space Shuttle Challenger
Space Shuttle Challenger was NASA's second Space Shuttle orbiter to be put into service, Columbia having been the first. The shuttle was built by Rockwell International's Space Transportation Systems Division in Downey, California...
, however, the Challenger disaster
Space Shuttle Challenger disaster
The Space Shuttle Challenger disaster occurred on January 28, 1986, when Space Shuttle Challenger broke apart 73 seconds into its flight, leading to the deaths of its seven crew members. The spacecraft disintegrated over the Atlantic Ocean, off the coast of central Florida at 11:38 am EST...
pushed the date to October 1990.
Launch
Ulysses was deployed into low-Earth orbit from the Space Shuttle Discovery. From there, it was propelled on a trajectory to Jupiter by a combination of solid rocket motors. This upper stage consisted of a two-stage BoeingBoeing
The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
IUS
Inertial Upper Stage
The Inertial Upper Stage , originally known as the Interim Upper Stage, is a two-stage solid-fueled booster rocket developed by the U.S...
(Inertial Upper Stage), plus a McDonnell Douglas
McDonnell Douglas
McDonnell Douglas was a major American aerospace manufacturer and defense contractor, producing a number of famous commercial and military aircraft. It formed from a merger of McDonnell Aircraft and Douglas Aircraft in 1967. McDonnell Douglas was based at Lambert-St. Louis International Airport...
PAM-S (Payload Assist Module
Payload Assist Module
frame|PAM-D with the [[Phoenix |Phoenix]] spacecraft. The [[Star 48|Star 48-B]] engine is shown being spun, fired, [[Yo-yo de-spin|yo-yo de-spun]] and jettisoned.thumb|SBS-3 satellite with PAM-D stage inside the space shuttle...
-Special). The IUS was inertially stabilised and actively guided during its burn. The PAM-S was unguided and it and the Ulysses spacecraft was spun up to 80 rpm for stability at the start of its burn. On burnout of the PAM-S, the motor and spacecraft stack was yo-yo de-spun
Yo-yo de-spin
frame|[[Payload Assist Module|PAM-D]] upper stage with the [[Phoenix |Phoenix]] spacecraft. The [[Star 48|Star 48-B]] engine is shown being spun, fired, yo-yo de-spun and jettisoned....
(weights deployed at the end of cables) to below 8 rpm prior to separation of the spacecraft. On leaving Earth, the spacecraft became the fastest ever artificially-accelerated object, and held that title until the New Horizons
New Horizons
New Horizons is a NASA robotic spacecraft mission currently en route to the dwarf planet Pluto. It is expected to be the first spacecraft to fly by and study Pluto and its moons, Charon, Nix, Hydra and S/2011 P 1. Its estimated arrival date at the Pluto-Charon system is July 14th, 2015...
probe was launched.
On its way to Jupiter the spacecraft was in an elliptical Hohmann transfer orbit
Hohmann transfer orbit
In orbital mechanics, the Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits, typically both in the same plane....
with perihelion near 1 AU and aphelion near 5 AU, Jupiter's distance from the Sun. At this time Ulysses had a low orbital inclination to the ecliptic.
Jupiter swing-by
It arrived at Jupiter February 8, 1992 for a swing-by maneuver that increased its inclination to the eclipticEcliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
by 80.2 degrees. The giant planet's gravity bent the spacecraft's flight path southward and away from the ecliptic plane. This put it into a final orbit around the Sun that would take it past the Sun's north and south poles.
The size and shape of the orbit were adjusted to a much smaller degree so that aphelion remained at approximately 5 AU, Jupiter's distance from the Sun, and perihelion was somewhat greater than 1 AU, the Earth's distance from the Sun.
Solar northern polar regions
Between 1994 and 1995 it explored both the southern and northNorth
North is a noun, adjective, or adverb indicating direction or geography.North is one of the four cardinal directions or compass points. It is the opposite of south and is perpendicular to east and west.By convention, the top side of a map is north....
ern solar polar regions, respectively.
Comet C/1996 B2 (Hyakutake)
On May 1, 1996, the spacecraft unexpectedly crossed the ion tail of Comet HyakutakeComet Hyakutake
Comet Hyakutake is a comet, discovered on January 31, 1996, which passed very close to Earth in March of that year. It was dubbed The Great Comet of 1996; its passage near the Earth was one of the closest cometary approaches of the previous 200 years. Hyakutake appeared very bright in the night...
(C/1996 B2), revealing the tail to be at least 3.8 AU in length.
Comet C/1999 T1 (McNaught-Hartley)
Encounter with a comet tail happened again in 1999 when Ulysses flew through the ion tailings of C/1999 T1 (McNaught-Hartley). A coronal mass ejectionCoronal mass ejection
A coronal mass ejection is a massive burst of solar wind, other light isotope plasma, and magnetic fields rising above the solar corona or being released into space....
carried the cometary material to Ulysses.
Solar southern polar regions
Between 2000 and 2001 it explored the southSouth
South is a noun, adjective, or adverb indicating direction or geography.South is one of the four cardinal directions or compass points. It is the opposite of north and is perpendicular to east and west.By convention, the bottom side of a map is south....
ern solar polar regions, which gave many unexpected results. In particular the southern magnetic
Magnetism
Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...
pole was found to be much more dynamic than the north pole and without any fixed clear location; instead, it is diffusely located.
Jupiter
Ulysses approached aphelion in 2003/2004 and made further distant observations of Jupiter.Comet C/2006 P1 (McNaught)
In 2007 Ulysses passed through the tail of comet C/2006 P1 (McNaught). The results were surprisingly different from its pass through Hyakutake's tail, with the measured solar wind velocity dropping from approximately 700 kilometers per second to less than 400 kilometers per second.Extended mission
ESA's Science Programme Committee approved the fourth extension of the Ulysses mission to March 2009 thereby allowing it to operate over the Sun's poles for the third time in 2007 and 2008. After it became clear that the power output from the spacecraft's RTG would be insufficient to operate science instruments and keep the attitude control fuel, hydrazineHydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
, from freezing, instrument power sharing was initiated. Up until then, the most important instruments had been kept online constantly, whilst others were deactivated. When the probe neared the Sun, its power-hungry heaters were turned off and all instruments were turned on.
On February 22, 2008, 17 years 4 months after the launch of the spacecraft, ESA and NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
announced that mission operations for Ulysses would be likely to cease within a few months. On April 12, 2008 NASA announced that the end date will be July 1, 2008. The spacecraft operated successfully for over four times its design life
Design life
The design life of a component or product is the period of time during which the item is expected by its designers to work within its specified parameters; in other words, the life expectancy of the item...
. A component within the last remaining working chain of X-band
X band
The X band is a segment of the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of X band is rather indefinitely set at approximately 7.0 to 11.2 gigahertz . In radar engineering, the frequency range is specified...
downlink sub-system failed on January 15, 2008. The other chain in the X-band sub-system had previously failed in 2003.
Downlink to Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
resumed on S-band
S band
The S band is defined by an IEEE standard for radio waves with frequencies that range from 2 to 4 GHz, crossing the conventional boundary between UHF and SHF at 3.0 GHz. It is part of the microwave band of the electromagnetic spectrum...
, but the beamwidth
Beamwidth
In telecommunication, the term beamwidth has the following meanings:1. In the radio regime, of an antenna pattern, the angle between the half-power points of the main lobe, when referenced to the peak effective radiated power of the main lobe....
of the high gain antenna on S-band is not as narrow as on X – so the downlink signal was much weaker, thereby reducing the achievable data rate
Data rate
Data rate can refer to:* Bit rate, or data transfer rate* Data signaling rate* Data rate units-See also:* Baud rate* Channel capacity* Throughput* Bandwidth everything in this page is falsified...
. As the spacecraft traveled on its outbound trajectory
Trajectory
A trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...
to the orbit of Jupiter, the downlink signal would have eventually fallen below the receiving capability of even the largest antennas (70 m in diameter) of the Deep Space Network
Deep Space Network
The Deep Space Network, or DSN, is a world-wide network of large antennas and communication facilities that supports interplanetary spacecraft missions. It also performs radio and radar astronomy observations for the exploration of the solar system and the universe, and supports selected...
. Even before the downlink signal was lost due to distance, the hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
attitude control fuel on-board the spacecraft was considered likely to freeze
Freeze
Freeze may refer to:In liquids turning to solids:*Freezing, the physical process of a liquid turning into a solid*Freeze drying, a method of rapidly removing moisture from food productsIn cessation of movement or change:...
, as the radioisotope thermal generators failed to generate enough power for the heaters to combat the cold of space. 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. The failure of the X-band communications sub-system hastened this, because the coldest part of the fuel pipework was routed over the X-band TWTAs which, when one of them was operating, kept this part of the pipework sufficiently warm.
The previously announced mission end date of July 1, 2008 came and went but mission operations continued albeit in a reduced capacity. The availability of science data gathering was limited to only when Ulysses is in contact with a ground station due to the deteriorating S-band downlink margin no longer being able to support simultaneous real-time data and tape recorder playback. When the spacecraft was out of contact with a ground station, the S-band transmitter was switched off and the power was diverted to keep the internal heaters to add to the warming of the hydrazine. On June 30, 2009 ground controllers sent commands to switch to its low gain antennae which ceased communications with the spacecraft along with previous commands to schedule the shut down of its transmitter entirely.
Results
During cruise phases, Ulysses provided unique data. As the only spacecraft out of the ecliptic with a gamma-rayGamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
instrument, Ulysses was an important part of the InterPlanetary Network
InterPlanetary Network
The InterPlanetary Network is a group of spacecraft equipped with gamma ray burst detectors. By timing the arrival of a burst at several spacecraft, its precise location can be found. The farther apart the detectors, or the greater the timing precision of each detector, the more precise the GRB...
(IPN). The IPN detects gamma ray burst
Gamma ray burst
Gamma-ray bursts are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical...
s (GRBs); since gamma rays cannot be focused with mirrors, it was very difficult to locate GRBs with enough accuracy to study them further. Instead, several spacecraft can locate the burst through triangulation
Triangulation
In trigonometry and geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline, rather than measuring distances to the point directly...
(or, more specifically, multilateration
Multilateration
Multilateration is a navigation technique based on the measurement of the difference in distance to two or more stations at known locations that broadcast signals at known times. Unlike measurements of absolute distance or angle, measuring the difference in distance results in an infinite number of...
). Each spacecraft has a gamma-ray detector, with readouts noted in tiny fractions of a second. By comparing the arrival times of gamma showers with the separations of the spacecraft, a location can be determined, for follow-up with other telescopes. Because gamma rays travel at the speed of light, wide separations are needed. Typically, a determination came from comparing: one of several spacecraft orbiting the Earth, an inner-Solar-system probe (to Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
, Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
, or an asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
), and Ulysses. When Ulysses crossed the ecliptic twice per orbit, many GRB determinations lost accuracy.
Additional discoveries:
- Ulysses discovered that the Sun's magnetic field interacts with the Solar System in a more complex fashion than previously assumed.
- Ulysses discovered that dust coming into the Solar System from deep space was 30 times more abundant than previously expected.
- In 2007-2008 Ulysses determined that the magnetic field emanating from the Sun's poles is much weaker than previously observed.
- That the solar windSolar windThe solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
has "grown progressively weaker during the mission and is currently at its weakest since the start of the Space Age."
Spacecraft
The spacecraft body is roughly a box, approximately 3.2 × 3.3 × 2.1 m in size. The box mounted the 1.65 m dish antenna and the RTGRadioisotope thermoelectric generator
A radioisotope thermoelectric generator is an electrical generator that obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples.RTGs can be...
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
Faraday cage
A Faraday cage or Faraday shield is an enclosure formed by conducting material or by a mesh of such material. Such an enclosure blocks out external static and non-static electric fields...
.
Ulysses is spin-stabilised about its z-axis which roughly coincides with the axis of the dish antenna. The RTG, whip antennas, and instrument boom are placed to stabilize this axis. Spin is nominally 5 rpm. Inside the body is a hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
fuel tank. Hydrazine monopropellant
Monopropellant
Monopropellants are propellants composed of chemicals or mixtures of chemicals which can be stored in a single container with some degree of safety. While stable under defined storage conditions, they react very rapidly under certain other conditions to produce a large volume of energetic gases...
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 is controlled by eight thrusters, in two blocks. Thrusters are pulsed in the time domain to perform rotation or translation. Four Sun sensors detected orientation. For fine attitude control, the S-band antenna feed is mounted slightly off-axis. This offset feed combined with the spacecraft spin introduces an oscillation to an S-band radio signal transmitted from Earth when received on-board the spacecraft. The amplitude and phase of this oscillation is proportional to the oriention of the spin axis relative to the Earth direction. This method of determining the relative orientation is called CONSCAN and was widely employed in early infra-red guided missiles.
The spacecraft uses S-band for uplinked commands and downlinked telemetry, through dual redundant 5-watt transceivers. The spacecraft used X-band
X band
The X band is a segment of the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of X band is rather indefinitely set at approximately 7.0 to 11.2 gigahertz . In radar engineering, the frequency range is specified...
for science return (downlink only), using dual 20W TWTAs until the failure of the last remaining TWTA in January 2008. Both bands use the dish antenna with prime-focus feeds, unlike the Cassegrain
Cassegrain reflector
The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas....
feeds of most other spacecraft dishes.
Dual tape recorders, each of approximately 45 megabit capacity, store science data between the nominal 8-hour communications sessions during the prime and extended mission phases.
The spacecraft is designed to withstand both the heat of the inner Solar System and the cold at Jupiter distance. Extensive blanketing and electric heaters protect against cold.
Total mass at launch was 366.7 kg of which 33.5 kg was hydrazine (used for attitude control and orbit correction).
Instruments
Radio/Plasma antennas. Two beryllium-copperBeryllium copper
Beryllium copper , also known as copper beryllium, beryllium bronze and spring copper, is a copper alloy with 0.5—3% beryllium and sometimes with other alloying elements. Beryllium copper combines high strength with non-magnetic and non-sparking qualities. It has excellent metalworking, forming...
antennas unreeled outwards from the body, perpendicular to the RTG and spin axis. Together this dipole
Dipole
In physics, there are several kinds of dipoles:*An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some distance. A permanent electric dipole is called an electret.*A...
spanned 72 meters. A third antenna, of hollow beryllium-copper, deployed from the body, along the spin axis opposite the dish. It was a monopole antenna
Monopole antenna
A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane. The driving signal from the transmitter is applied, or for receiving antennas the output voltage is taken,...
, 7.5 meters long. These measured radio waves generated by plasma releases, or the plasma itself as it passed over the spacecraft. This receiver ensemble was sensitive from dc to 1 MHz.
Experiment Boom. A third type of boom, shorter and much more rigid, extended from the last side of the spacecraft, opposite the RTG. This was a hollow carbon-fiber tube, of 50 mm diameter. It can be seen in the photo as the silver rod stowed alongside the body. It carried four types of instruments. A solid-state X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
instrument, which was composed of two silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
detectors to study X-rays from solar flare
Solar flare
A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy . The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day...
s and Jupiter's aurorae. The GRB experiment consisted of two CsI
Caesium iodide
Caesium iodide is an ionic compound often used as the input phosphor of an x-ray image intensifier tube found in fluoroscopy equipment....
scintillator crystals with photomultipliers. Two different magnetometer
Magnetometer
A magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...
s were mounted: a vector helium magnetometer and a fluxgate magnetometer. A two axis magnetic search coil antenna measured AC magnetic fields.
Body-Mounted Instruments. Detectors for electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s, ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s, neutral gas, dust
Cosmic dust
Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...
, and cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
s were mounted on the spacecraft body around the quiet section.
- SWOOPS (Solar Wind Observations Over the Poles of the Sun) measures positive ions and electrons.
Lastly, the radio communications link could be used to search for gravitational waves (through Doppler shifts) and to probe the Sun's atmosphere through occultation
Occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
. No gravitational waves were detected.
Total instrument mass is 55 kg.
See also
- Tom KrimigisStamatios KrimigisStamatios M. Krimigis is a Greek-American scientist in space exploration. He has contributed to the majority of the United States' unmanned space exploration programs of the Solar system and beyond. He has contributed to exploration missions to almost every planet of our solar system...
- WIND (spacecraft)
- Solar and Heliospheric ObservatorySolar and Heliospheric ObservatoryThe Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered over 2100 comets. It began normal operations in May...
External links
- ESA Ulysses website
- ESA Ulysses mission operations website
- ESA Ulysses Home page
- NASA/JPL Ulysses website
- Ulysses Measuring Mission Profile by NASA's Solar System Exploration
- ESA/NASA/JPL: Ulysses subsystems and instrumentation in high detail
- Where is Ulysses now!
- Max Planck Institute Ulysses website
- Interview with Ulysses Mission Operations Manager Nigel Angold on Planetary Radio