View source for Engineering:Ulysses (spacecraft)

{{Short description|1990 robotic space probe; studied the Sun from a near-polar orbit}}
{{italic title}}
{{Infobox spaceflight
| name              = ''Ulysses''
| names_list        = Odysseus
| image             = Ulysses spacecraft.jpg
| image_caption     = ''Ulysses'' spacecraft
| image_size        = 300px

| mission_type      = [[Physics:Heliophysics|Heliophysics]]
| operator          = [[Organization:NASA|NASA]] / [[Organization:European Space Agency|ESA]]
| COSPAR_ID         = 1990-090B
| SATCAT            = 20842
| website           = [https://web.archive.org/web/20031226150122/http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Ulysses NASA Page]<br/>[https://www.esa.int/esaSC/120395_index_0_m.html ESA Page]
| mission_duration  = {{time interval|6 October 1990|30 June 2009|show=ymdhm|sep=,}}<ref>{{cite web|url=https://solarsystem.nasa.gov/missions/ulysses/in-depth/ |title=Ulysses |publisher=NASA's Solar System Exploration website |access-date=September 25, 2023}}</ref>

| spacecraft_bus    = 
| manufacturer      = Astrium GmbH, Friedrichshafen<br/>(formerly Dornier Systems)
| launch_mass       = {{cvt|371|kg}}<ref name="Ulysses">{{cite web|url=https://solarsystem.nasa.gov/missions/ulysses/in-depth/ |title=Ulysses |publisher=NASA's Solar System Exploration website |access-date=December 2, 2022}}</ref>
| dry_mass          = 
| payload_mass      = {{cvt|55|kg}}
| dimensions        = {{cvt|3.2 × 3.3 × 2.1|m}} 
| power             = 285 [[Watt|watt]]s

| launch_date       = 6 October 1990, 11:47:16 [[Physics:Coordinated Universal Time|UTC]]<ref name="Ulysses"></ref>
| launch_rocket     = [[Engineering:Space Shuttle Discovery|Space Shuttle ''Discovery'']] ([[Engineering:STS-41|STS-41]]) with [[Engineering:Inertial Upper Stage|Inertial Upper Stage]] and [[Engineering:Payload Assist Module|PAM-S]]
| launch_site       = Kennedy Space Center, [[Astronomy:Kennedy Space Center Launch Complex 39B|LC-39B]]
| launch_contractor = [[Organization:NASA|NASA]]

| disposal_type     = Decommissioned
| deactivated       = 30 June 2009

| orbit_reference   = [[Astronomy:Heliocentric orbit|Heliocentric orbit]]
| orbit_periapsis   = 1.35 AU
| orbit_apoapsis    = 5.40 AU
| orbit_inclination = 79.11° 
| orbit_period      = 2,264.26 days (6.2 years)
| apsis             = helion

| interplanetary    = {{Infobox spaceflight/IP
   | type           = flyby
   | object         = [[Astronomy:Jupiter|Jupiter]] <small>(gravity assist)</small>
   | arrival_date   = 8 February 1992
   | distance       = 440,439 km (6.3 Jupiter radii)
 }}

| insignia          = Ulysses insignia.png
| insignia_alt      = ''Ulysses'' mission insignia
| insignia_caption  = ''Ulysses'' mission patch
| insignia_size     = 200px
}}

'''''Ulysses''''' ({{IPAc-en|j|uː|ˈ|l|ɪ|s|iː|z}} {{respell|yoo|LISS|eez}}, {{IPAc-en|UKalso|ˈ|j|uː|l|ɪ|s|iː|z}} {{respell|YOO|liss|eez}}) was a [[Engineering:Robotic spacecraft|robotic]] [[Engineering:Space probe|space probe]] whose primary mission was to orbit the [[Astronomy:Sun|Sun]] and study it at all latitudes. It was launched in 1990 and made three "fast latitude scans" of the Sun in 1994/1995, 2000/2001, and 2007/2008. In addition, the probe studied several comets. ''Ulysses'' was a joint venture of the [[Organization:European Space Agency|European Space Agency]] (ESA) and the United States' [[Organization:NASA|National Aeronautics and Space Administration]] (NASA), under leadership of ESA with participation from Canada's National Research Council.<ref>{{cite web|quote=The Herzberg Institute of Astrophysics (HIA) of the National Research Council of Canada provided instrumentation and test equipment for the COsmic ray and Solar Particle INvestigation (COSPIN) on the ''Ulysses'' spacecraft. The COSPIN instrument consists of five sensors which measure energetic nucleons and electrons over a wide range of energies. This was the first participation by Canada in a deep-space interplanetary mission.  |archive-url=https://web.archive.org/web/20110817205127/http://hiauly1.hia.nrc.ca/index.html|url=http://hiauly1.hia.nrc.ca/index.html|archive-date=August 17, 2011|title=Welcome to the HIA Ulysses Project |publisher=Herzberg Institute of Astrophysics}}</ref> The last day for mission operations on ''Ulysses'' was 30 June 2009.<ref name="ESA News"/><ref>[http://ulysses-ops.jpl.esa.int/ulsfct/the_odyssey_continues.html#12 The odyssey concludes ...] {{webarchive|url=https://web.archive.org/web/20120224180806/http://ulysses-ops.jpl.esa.int/ulsfct/the_odyssey_continues.html |date=February 24, 2012}}</ref>

To study the Sun at all latitudes, the probe needed to change its [[Astronomy:Orbital inclination|orbital inclination]] and leave the [[Astronomy:Ecliptic|plane of the Solar System]]. To change the orbital inclination of a spacecraft to about 80° requires a large change in heliocentric velocity, the energy to achieve which far exceeded the capabilities of any [[Engineering:Launch vehicle|launch vehicle]]. To reach the desired orbit around the Sun, the mission's planners chose a [[Astronomy:Gravity assist|gravity assist]] maneuver around [[Astronomy:Jupiter|Jupiter]], but this Jupiter encounter meant that ''Ulysses'' could not be powered by solar cells. The probe was powered instead by a [[Physics:Radioisotope thermoelectric generator|radioisotope thermoelectric generator]] (RTG).

The [[Engineering:Spacecraft|spacecraft]] was originally named '''''Odysseus''''', because of its lengthy and indirect trajectory to study the solar poles. It was renamed ''Ulysses'', the [[Social:Latin|Latin]] [[Philosophy:Translation|translation]] of "Odysseus", at ESA's request in honor not only of [[Biography:Homer|Homer]]'s mythological hero but also of Dante's character in the [[Unsolved:Inferno (Dante)|''Inferno'']].<ref>"Inferno of Ulysses' urge to explore an uninhabited world behind the Sun. In ''Jane's Spaceflight Directory'' 1988, {{ISBN|0-7106-0860-8}}</ref> ''Ulysses'' was originally scheduled for launch in May 1986 aboard the [[Engineering:Space Shuttle|Space Shuttle]] ''Challenger'' on STS-61-F. Due to the 28 January 1986 [[Engineering:Space Shuttle Challenger disaster|loss of ''Challenger'']], the launch of ''Ulysses'' was delayed until 6 October 1990 aboard [[Engineering:Space Shuttle Discovery|''Discovery'']] (mission [[Engineering:STS-41|STS-41]]).

== Spacecraft ==
[[File:Parts of Ulysses.jpg|thumb|upright=1.0|right|''Ulysses'' spacecraft]]

The spacecraft was designed by ESA and built by Dornier Systems, a German aircraft manufacturer. The body was roughly a box, approximately {{cvt|3.2 × 3.3 × 2.1|m}} in size. The box mounted the {{cvt|1.65|m}} dish antenna and the [[Engineering:GPHS-RTG|GPHS-RTG]] [[Physics:Radioisotope thermoelectric generator|radioisotope thermoelectric generator]] (RTG) power source. The box was divided into noisy and quiet sections. The noisy section abutted the RTG; the quiet section housed the instrument electronics. Particularly "loud" components, such as the preamps for the radio dipole, were mounted outside the structure entirely, and the box acted as a [[Physics:Faraday cage|Faraday cage]].

''Ulysses'' was [[Engineering:Spin-stabilisation|spin-stabilised]] about its z-axis which roughly coincides with the axis of the dish antenna. The RTG, [[Engineering:Whip antenna|whip antenna]]s, and instrument boom were placed to stabilize this axis, with the spin rate nominally at 5 [[Revolutions per minute|rpm]]. Inside the body was a [[Chemistry:Hydrazine|hydrazine]] fuel tank. Hydrazine [[Chemistry:Monopropellant|monopropellant]] was used for course corrections inbound to Jupiter, and later used exclusively to repoint the spin axis (and thus, the antenna) at Earth. The spacecraft was controlled by eight thrusters in two blocks. Thrusters were pulsed in the time domain to perform rotation or translation. Four [[Astronomy:Sun sensor|Sun sensor]]s detected orientation. For fine attitude control, the S-band antenna feed was mounted slightly off-axis. This offset feed combined with the spacecraft spin introduced an apparent oscillation to a radio signal transmitted from Earth when received on board the spacecraft. The amplitude and phase of this oscillation were proportional to the orientation of the spin axis relative to the Earth direction. This method of determining the relative orientation is called [[Engineering:Conical scanning|conical scanning]] and was used by early radars for automated tracking of targets and was also very common in early infrared guided missiles.

The spacecraft used S-band for uplinked commands and downlinked telemetry, through dual redundant 5-watt transceivers. The spacecraft used [[Physics:X band|X-band]] for science return (downlink only), using dual 20 watts TWTAs until the failure of the last remaining TWTA in January 2008. Both bands used the dish antenna with prime-focus feeds, unlike the [[Astronomy:Cassegrain reflector|Cassegrain]] feeds of most other spacecraft dishes.

Dual tape recorders, each of approximately 45-megabit capacity, stored science data between the nominal eight-hour communications sessions during the prime and extended mission phases.

The spacecraft was designed to withstand both the heat of the inner Solar System and the cold at Jupiter's distance. Extensive blanketing and electric heaters protected the probe against the cold temperatures of the outer Solar System.

Multiple computer systems (CPUs/microprocessors/Data Processing Units) are used in several of the scientific instruments, including several radiation-hardened RCA CDP1802 microprocessors. Documented 1802 usage includes dual-redundant 1802s in the COSPIN, and at least one 1802 each in the GRB, HI-SCALE, SWICS, SWOOPS and URAP instruments, with other possible microprocessors incorporated elsewhere.<ref>[http://ppi.pds.nasa.gov/archive1/ULY_5001/DOCUMENT/ Ulysses NASA Documentation Archive] {{Webarchive|url=https://web.archive.org/web/20130317151658/http://ppi.pds.nasa.gov/archive1/ULY_5001/DOCUMENT/|date=March 17, 2013}} {{PD-notice}}</ref>

Total mass at launch was {{cvt|371|kg}}, of which 33.5&nbsp;kg was [[Chemistry:Hydrazine|hydrazine]] propellant used for attitude control and orbit correction.

== Instruments ==
[[File:Ulysses cut picture.gif|thumb|upright=1.0|right|''Ulysses'' instruments]]
[[File:Ulysses radial boom test.jpg|thumb|upright=1.0|right|''Ulysses'' radial boom test]]

The twelve different Instruments came from ESA and NASA. The first design was based on two probes, one by NASA and one by ESA, but the probe of NASA was defunded and in the end the instruments of the cancelled probe were mounted on ''Ulysses''.<ref>{{cite web|title=Ulysses factsheet|url=http://www.esa.int/Science_Exploration/Space_Science/Ulysses_factsheet|access-date=2021-05-07|website=esa.int}}</ref>

* '''Radio/Plasma antennas:''' Two [[Chemistry:Beryllium copper|beryllium copper]] antennas were unreeled outwards from the body, perpendicular to the RTG and spin axis. Together this [[Physics:Dipole antenna|dipole]] spanned 72 meters (236.2&nbsp;ft). A third antenna, of hollow beryllium copper, was deployed from the body, along the spin axis opposite the dish. It was a [[Engineering:Monopole antenna|monopole antenna]], 7.5 meters (24.6&nbsp;ft) 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&nbsp;MHz.<ref>[http://ulysses.jpl.nasa.gov/spacecraft/inst_urap.html Unified Radio and Plasma Wave Investigation, JPL] {{Webarchive|url=https://web.archive.org/web/20090117094444/http://ulysses.jpl.nasa.gov/spacecraft/inst_urap.html |date=January 17, 2009 }}</ref>
* '''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&nbsp;mm (2 in.) 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 [[Physics:X-ray|X-ray]] instrument, composed of two [[Chemistry:Silicon|silicon]] detectors, to study X-rays from [[Astronomy:Solar flare|solar flare]]s and Jupiter's aurorae; the Gamma-Ray Burst experiment, consisting of two [[Chemistry:Caesium iodide|CsI]] scintillator crystals with photomultipliers; two different [[Physics:Magnetometer|magnetometer]]s, a helium vector magnetometer and a fluxgate magnetometer; and a two-axis magnetic search coil antenna measured AC magnetic fields.
* '''Body-Mounted Instruments:''' Detectors for [[Physics:Electron|electron]]s, [[Physics:Ion|ion]]s, neutral gas, [[Astronomy:Cosmic dust|dust]], and [[Astronomy:Cosmic ray|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<ref>[http://www.sp.ph.ic.ac.uk/~giacomo/Papers/1992AAS.pdf The Gravity Wave Experiment, Astronomy and Astrophysics] {{Webarchive|url=https://web.archive.org/web/20081219053444/http://www.sp.ph.ic.ac.uk/~giacomo/Papers/1992AAS.pdf |date=December 19, 2008 }}</ref> (through Doppler shifts) and to probe the Sun's atmosphere through [[Astronomy:Radio occultation|radio occultation]]. No gravitational waves were detected.
* Total instrument mass was 55&nbsp;kg.
* '''Magnetometer (MAG):''' MAG measured the magnetic field in the heliosphere. Measurements of Jupiter's magnetic field were also performed. Two [[Physics:Magnetometer|magnetometer]]s performed ''Ulysses''{{'}} magnetic field measurements, the Vector Helium Magnetometer and the Fluxgate Magnetometer.<ref>{{cite journal |title=The magnetic field investigation on the ULYSSES mission - Instrumentation and preliminary scientific results |journal=Astronomy & Astrophysics Supplement Series |date=20 August 1991 |volume=91 |issue=2 |pages=221–236 |bibcode=1992A&AS...92..221B |url=https://adsabs.harvard.edu/full/1992A%26AS...92..221B |last1=Balogh |first1=A. |last2=Beek |first2=T. J. |last3=Forsyth |first3=R. J. |last4=Hedgecock |first4=P. C. |last5=Marquedant |first5=R. J. |last6=Smith |first6=E. J. |last7=Southwood |first7=D. J. |last8=Tsurutani |first8=B. T. }}</ref>
* '''Solar Wind Plasma Experiment (SWOOPS):''' detected the solar wind at all solar distances and latitudes and in three dimensions. It measured positive ions and electrons.<ref>Goldstein, Bruce. [http://helio.estec.esa.nl/ulysses/archive/swoops_bae_un.html SWOOPS/Electron{{spaced ndash}}User Notes] {{Webarchive|url=https://web.archive.org/web/20060927051549/http://helio.estec.esa.nl/ulysses/archive/swoops_bae_un.html |date=September 27, 2006 }}, [[Organization:Jet Propulsion Laboratory|Jet Propulsion Laboratory]]</ref>
* '''Solar Wind Ion Composition Instrument (SWICS):''' determined composition, temperature and speed of the atoms and ions that comprise the solar wind.<ref>{{Cite journal|last1=Geiss|first1=J|last2=Gloeckler|first2=G|last3=von Steiger|first3=R|last4=Balsiger|first4=H|last5=Fisk|first5=L.|last6=Galvin|first6=A.|last7=Ipavich|first7=F.|last8=Livi|first8=S|last9=McKenzie|first9=J.|last10=Ogilvie|first10=K.|last11=et|first11=al.|date=1995-05-19|title=The southern high-speed stream: results from the SWICS instrument on Ulysses|url=https://www.science.org/doi/10.1126/science.7754380|journal=Science|language=en|volume=268|issue=5213|pages=1033–1036|doi=10.1126/science.7754380|pmid=7754380|bibcode=1995Sci...268.1033G|issn=0036-8075}}</ref><ref>{{Cite journal|last1=von Steiger|first1=R.|last2=Geiss|first2=J.|last3=Gloeckler|first3=G.|last4=Galvin|first4=A. B.|author-link4=Antoinette Galvin|date=1995-04-01|title=Kinetic properties of heavy ions in the solar wind from SWICS/Ulysses|url=https://doi.org/10.1007/BF00768756|journal=Space Science Reviews|language=en|volume=72|issue=1|pages=71–76|doi=10.1007/BF00768756|bibcode=1995SSRv...72...71V|s2cid=189797680|issn=1572-9672}}</ref>
* '''Unified Radio and Plasma Wave Instrument (URAP):''' picked up radio waves from the Sun and electromagnetic waves generated in the solar wind close to the spacecraft.
* '''Energetic Particle Instrument (EPAC) and GAS:''' EPAC investigated the energy, fluxes and distribution of energetic particles in the heliosphere. GAS studied the uncharged gases (helium) of interstellar origin.
* '''Low-Energy Ion and Electron Experiment (HI-SCALE):''' investigated the energy, fluxes and distribution of energetic particles in the heliosphere.
* '''Cosmic Ray and Solar Particle Instrument (COSPIN):''' investigated the energy, fluxes and distribution of energetic particles and galactic cosmic rays in the heliosphere.
* '''Solar X-ray and Cosmic Gamma-Ray Burst Instrument (GRB):''' studied cosmic gamma ray bursts and X-rays from solar flares.
* '''[[Astronomy:Galileo and Ulysses Dust Detectors|Dust Experiment (DUST)]]:''' Direct measurements of [[Astronomy:Interplanetary dust cloud|interplanetary]] and [[Astronomy:Cosmic dust|interstellar dust]] grains to investigate their properties as functions of the distance from the Sun and solar latitude.

== Mission ==
=== Planning ===
[[File:Ulysses sits atop the PAM-S and IUS combination.jpg|thumb|upright=1.0|left|''Ulysses'' sits atop the PAM-S and IUS combination]]
[[File:Artist picture-Ulysses after deployment.jpg|thumb|upright=1.0|right|Illustration of ''Ulysses'' after deployment]]
[[File:Artist's conception of NASA solar polar spacecraft.jpg|thumb|upright=1.0|right|Illustration of Solar Polar on IUS]]

Until ''Ulysses'', the Sun had only been observed from low solar latitudes. The Earth's orbit defines the [[Astronomy:Ecliptic|ecliptic]] plane, which differs from the Sun's equatorial plane by only 7.25°. 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 ([[Astronomy:Mariner 10|Mariner 10]], [[Astronomy:Pioneer 11|Pioneer 11]], and [[Astronomy:Voyager program|''Voyagers 1'' and ''2'']]) had performed [[Astronomy:Gravity assist|gravity assist]] maneuvers in the 1970s. Those maneuvers 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 [[Astronomy:Jupiter|Jupiter]] could produce a significant plane change. An Out-Of-The-Ecliptic mission (OOE) was thereby proposed. ''See article'' [[Astronomy:Pioneer H|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 U.S. spacecraft was cancelled 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, {{wipe|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 12 instruments on board.

The changes delayed launch from February 1983 to May 1986 when it was to be deployed by the [[Engineering:Space Shuttle Challenger|Space Shuttle ''Challenger'']] (boosted by the proposed Centaur G Prime upper stage). However, the [[Engineering:Space Shuttle Challenger disaster|''Challenger'' disaster]] forced a two-and-a-half year stand down of the shuttle fleet, mandated the cancellation of the Centaur-G upper stage, and pushed the launch date to October 1990.<ref>[https://arstechnica.com/science/2015/10/dispatches-from-the-death-star-the-rise-and-fall-of-nasas-shuttle-centaur/ A Deathblow to the Death Star: The Rise and Fall of NASA's Shuttle-Centaur, ArsTechnica, October 2015]</ref>

=== Launch ===
[[File:STS-41 Ulysses deployment.jpg|thumb|upright=1.0|right|''Ulysses'' after deployment from STS-41]]

''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.<ref>[http://www.esa.int/esaSC/SEMTDTUG3HF_index_0.html ESA—Space Science—Sun to set on Ulysses solar mission on 1 July]</ref> This upper stage consisted of a two-stage [[Company:Boeing|Boeing]] [[Engineering:Inertial Upper Stage|IUS]] (Inertial Upper Stage), plus a [[Company:McDonnell Douglas|McDonnell Douglas]] PAM-S ([[Engineering:Payload Assist Module|Payload Assist Module]]-Special). The IUS was inertially stabilised and actively guided during its burn. The PAM-S was unguided and it and ''Ulysses'' were 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 [[Engineering:Yo-yo de-spin|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 spacecraft, and held that title until the ''[[Astronomy:New Horizons|New Horizons]]'' probe was launched.

On its way to Jupiter, the spacecraft was in an elliptical non-[[Astronomy:Hohmann transfer orbit|Hohmann transfer orbit]]. At this time, ''Ulysses'' had a low orbital inclination to the ecliptic.

=== Jupiter swing-by ===
[[File:Ulysses 2 orbit.jpg|thumb|upright=1.0|right|''Ulysses''{{'}} second orbit (1999–2004)]]
[[File:Animation of Ulysses trajectory.gif|thumb|upright=1.0|right|Animation of ''Ulysses''{{'s}} trajectory from 6 October 1990 to 29 June 2009<br/>{{legend2|magenta| ''Ulysses'' }}{{·}}{{legend2|Royalblue|Earth}}{{·}}{{legend2|Gold|Jupiter}} {{·}}{{legend2| Cyan |C/2006 P1}}{{·}}{{legend2| Lime |C/1996 B2 }}{{·}}{{legend2| OrangeRed |C/1999 T1 }}]]

It arrived at Jupiter on 8 February 1992 for a swing-by maneuver that increased its inclination to the [[Astronomy:Ecliptic|ecliptic]] by 80.2°. 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. The orbital period is approximately six years.

=== Polar regions of the Sun ===
Between 1994 and 1995 it explored both the southern and [[North|north]]ern polar regions of the Sun, respectively.

=== Comet C/1996 B2 (Hyakutake) ===
On 1 May 1996, the spacecraft unexpectedly crossed the ion tail of [[Astronomy:Comet Hyakutake|Comet Hyakutake]] (C/1996 B2), revealing the tail to be at least 3.8 AU in length.<ref name="Jones 2000">{{cite journal|author=Jones G. H.
|author2=Balogh A.|author3=Horbury T. S.|title=Identification of comet Hyakutake's extremely long ion tail from magnetic field signatures|journal=Nature|volume=404|issue=6778|date=2000|pages=574–576
|pmid=10766233|doi=10.1038/35007011|bibcode=2000Natur.404..574J|s2cid=4418311}}</ref><ref name="esa-tail"/>

=== Comet C/1999 T1 (McNaught–Hartley) ===
An encounter with a comet tail happened again in 2004<ref>{{cite book|url=https://books.google.com/books?id=Sh7UBwAAQBAJ|title=The Sun and the Heliosphere as an Integrated System|isbn=9781402028311|last1=Poletto |first1=Giannina|last2=Suess|first2=Steve T.|date=5 June 2013|publisher=Springer }}</ref> when ''Ulysses'' flew through the ion tailings of C/1999 T1 (McNaught-Hartley). A [[Astronomy:Coronal mass ejection|coronal mass ejection]] carried the cometary material to ''Ulysses''.<ref name="esa-tail">[http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=34612 Ulysses Catches Another Comet by the Tail]</ref><ref name="tail-Gloeckler">[http://www.iop.org/EJ/article/1538-4357/604/2/L121/18096.html G. Gloeckler et al. Cometary Ions Trapped in a Coronal Mass Ejection]</ref>

=== Second Jupiter encounter ===
''Ulysses'' approached aphelion in 2003/2004 and made further distant observations of Jupiter.<ref>[http://ulysses.jpl.nasa.gov/science/jupiter_two.html Ulysses - Science - Jupiter Distant Encounter Selected References] {{webarchive|url=https://web.archive.org/web/20080923065057/http://ulysses.jpl.nasa.gov/science/jupiter_two.html|date=September 23, 2008}} {{PD-notice}}</ref>

=== 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 (1,566,000&nbsp;mph) to less than 400 kilometers per second (895,000&nbsp;mph).<ref>{{cite journal|last=Neugebauer|first=Gloeckle|title=Encounter of the Ulysses Spacecraft with the Ion Tail of Comet McNaught|journal=The Astrophysical Journal|volume=667|issue=2|date=October 1, 2007|pages=1262–1266|doi=10.1086/521019|bibcode=2007ApJ...667.1262N|doi-access=free}}</ref>

=== Extended mission ===
[[File:Ulysses RTG.jpg|thumb|upright=1.0|right|''Ulysses'' [[Physics:Radioisotope thermoelectric generator|Radioisotope thermoelectric generator]]]]

ESA's Science Program Committee approved the fourth extension of the ''Ulysses'' mission to March 2004 <ref>[http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=34647 ESA Science & Technology: Ulysses Mission Extended]</ref> 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 [[Astronomy:Spacecraft attitude control|attitude control]] fuel, [[Chemistry:Hydrazine|hydrazine]], 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.<ref>[http://www.esa.int/esaCP/SEMUHTN2UXE_index_0.html ESA Portal - Ulysses scores a hat-trick]</ref>

On 22 February 2008, 17 years and 4 months after the launch of the spacecraft, [[Organization:European Space Agency|ESA]] and [[Organization:NASA|NASA]] announced that the mission operations for ''Ulysses'' would likely cease within a few months.<ref>{{cite web|url=http://www.esa.int/esaCP/SEM6UE3CXCF_index_0.html|title=Ulysses mission coming to a natural end|date=February 22, 2008|access-date=February 23, 2008|publisher=European Space Agency}}</ref><ref>{{cite news|url=http://www.nasa.gov/topics/solarsystem/features/ulysses-20080222.html|title=International Solar Mission to End Following Stellar Performance|access-date=February 23, 2008 |date=February 22, 2008|publisher=NASA}} {{PD-notice}}</ref> On 12 April 2008, NASA announced that the end date will be 1 July 2008.<ref>{{Cite web |url=https://news.yahoo.com/s/ap/20080612/ap_on_sc/sci_solar_probe |title=RIP: Ulysses solar probe coming to end soon - Yahoo! News |access-date=15 January 2017 |archive-date=17 June 2008 |archive-url=https://web.archive.org/web/20080617110614/http://news.yahoo.com/s/ap/20080612/ap_on_sc/sci_solar_probe |url-status=dead }}</ref>

The spacecraft operated successfully for over four times its [[Engineering:Design life|design life]]. A component within the last remaining working chain of [[Physics:X band|X-band]] downlink subsystem failed on 15 January 2008. The other chain in the X-band subsystem had previously failed in 2003.<ref>{{cite web|url=http://ulysses-ops.jpl.esa.int/ulsfct/opsfiles/03feb_ops.html|title=February 2003 Operations|publisher=European Space Agency|url-status=dead|archive-url=https://web.archive.org/web/20090703055833/http://ulysses-ops.jpl.esa.int/ulsfct/opsfiles/03feb_ops.html|archive-date=July 3, 2009}}</ref>

[[Astronomy:Downlink|Downlink]] to [[Astronomy:Earth|Earth]] resumed on [[Astronomy:S band|S-band]], but the [[Engineering:Beamwidth|beamwidth]] of the high gain antenna in the S-band was not as narrow as in the X–band, so that the received downlink signal was much weaker, hence reducing the achievable [[Bit rate|data rate]]. As the spacecraft traveled on its outbound [[Physics:Trajectory|trajectory]] to the orbit of Jupiter, the downlink signal would have eventually fallen below the receiving capability of even the largest antennas (70 meters - 229.7 feet - in diameter) of the Deep Space Network.

Even before the downlink signal was lost due to distance, the [[Chemistry:Hydrazine|hydrazine]] attitude control fuel on board the spacecraft was considered likely to [[Physics:Freezing|freeze]], as the radioisotope thermal generators (RTGs) failed to generate enough power for the heaters to overcome radiative heat loss into 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 subsystem hastened this, because the coldest part of the fuel pipework was routed over the X-band traveling-wave tube amplifiers, because they generated enough heat during operation to keep the propellant plumbing warm.

The previously announced mission end date of 1 July 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'' was 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.<ref>[http://ulysses-ops.jpl.esa.int/ulsfct/opsfiles/08may_ops.html#max-512bps Ulysses Mission Ops—No more data playback] {{Webarchive|url=https://web.archive.org/web/20081202042239/http://ulysses-ops.jpl.esa.int/ulsfct/opsfiles/08may_ops.html#max-512bps|date=December 2, 2008}}</ref> When the spacecraft was out of contact with a ground station, the S-band transmitter was switched off and the power was diverted to the internal heaters to add to the warming of the hydrazine. On 30 June 2009, ground controllers sent commands to switch to the low gain antennas. This stopped communications with the spacecraft, in combination with previous commands to shut down its transmitter entirely.<ref name="ESA News">{{cite web|url=http://www.esa.int/esaCP/SEMWHF1P0WF_index_0.html|title=Ulysses: 12 extra months of valuable science |date=June 30, 2009|publisher=European Space Agency|access-date=July 1, 2009}}</ref><ref name="NASA JPL">{{cite web|url=http://www.jpl.nasa.gov/news/news.cfm?release=2009-104|title=Ulysses Spacecraft Ends Historic Mission of Discovery|website=[[Organization:Jet Propulsion Laboratory|Jet Propulsion Laboratory]]|date=June 30, 2009|access-date=July 1, 2009|archive-date=16 July 2009|archive-url=https://web.archive.org/web/20090716200317/http://www.jpl.nasa.gov/news/news.cfm?release=2009-104|url-status=dead}} {{PD-notice}}</ref>

== Results ==
[[File:STS-41 launch.jpg|thumb|upright=1.0|right|STS-41 launches from Kennedy Space Center, 6 October 1990.]]

During cruise phases, ''Ulysses'' provided unique data. As the only spacecraft out of the ecliptic with a [[Physics:Gamma ray|gamma-ray]] instrument, ''Ulysses'' was an important part of the [[Astronomy:InterPlanetary Network|InterPlanetary Network]] (IPN). The IPN detects gamma ray bursts (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 [[Multilateration|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 [[Astronomy:Mars|Mars]], [[Astronomy:Venus|Venus]], or an [[Astronomy:Asteroid|asteroid]]), and ''Ulysses''. When ''Ulysses'' crossed the ecliptic twice per orbit, many GRB determinations lost accuracy.

Additional discoveries:<ref>{{Cite web|last=|date=June 12, 2008|title=International Mission Studying Sun to Conclude|url=https://www.jpl.nasa.gov/news/international-mission-studying-sun-to-conclude|access-date=2021-08-01|website=NASA Jet Propulsion Laboratory (JPL)|language=en}}</ref><ref>{{Cite web|title=Missions: Ulysses|url=https://solarsystem.nasa.gov/missions/ulysses/in-depth/|access-date=August 1, 2021}}</ref>
* Data provided by ''Ulysses'' led to the discovery that the Sun's magnetic field interacts with the Solar System in a more complex fashion than previously assumed.
* Data provided by ''Ulysses'' led to the discovery that dust coming into the Solar System from deep space was 30 times more abundant than previously expected.
* In 2007–2008 data provided by ''Ulysses'' led to the determination that the magnetic field emanating from the Sun's poles is much weaker than previously observed.
* That the [[Astronomy:Solar wind|solar wind]] has "grown progressively weaker during the mission and is currently at its weakest since the start of the Space Age".<ref name="NASA JPL"/>

==Fate==
''Ulysses'' will most likely continue in heliocentric orbit around the Sun indefinitely. However, there is a chance that in one of its re-encounters with Jupiter a close fly-by with one of the Jovian moons would be enough to alter its course and so the probe would enter a [[Astronomy:Hyperbolic trajectory|hyperbolic trajectory]] around the Sun and leave the Solar System.<ref>{{Cite news|url=https://www.reuters.com/article/us-space-solar-idINTRE5600A220090701|title = Solar orbiter Ulysses ends mission after 18 years|newspaper = Reuters|date = July 2009}}</ref>

== See also ==
* {{annotated link|Astronomy:Advanced Composition Explorer}}
* {{annotated link|Physics:List of heliophysics missions}}
* {{annotated link|Astronomy:List of missions to the outer planets}}
* {{annotated link|Astronomy:Parker Solar Probe}}
* {{annotated link|Astronomy:Solar and Heliospheric Observatory}}
* {{annotated link|Astronomy:STEREO}}
* {{annotated link|Astronomy:TRACE}}
* {{annotated link|Engineering:Wind (spacecraft)|''WIND''}}
* {{annotated link|Astronomy:Solar Orbiter|''Solar Orbiter''}}

== References ==
{{Reflist|30em}}

== External links ==
* [http://sci.esa.int/ulysses/ ESA ''Ulysses'' website]
* [https://web.archive.org/web/20091225230426/http://ulysses-ops.esa.int/ ESA ''Ulysses'' mission operations website]
* [https://web.archive.org/web/20111009171945/http://helio.esa.int/ulysses/ ESA ''Ulysses'' Home page]
* [https://web.archive.org/web/20020602101414/http://ulysses.jpl.nasa.gov/ NASA/JPL ''Ulysses'' website]
* [https://web.archive.org/web/20070801232006/http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Ulysses ''Ulysses'' Measuring Mission Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [https://web.archive.org/web/20041025102441/http://ulysses-ops.jpl.esa.int/ulsfct/spacecraft/scframe.html ESA/NASA/JPL: ''Ulysses'' subsystems and instrumentation in high detail]
* [https://web.archive.org/web/20060928042857/http://ulysses-ops.jpl.esa.int/ulsfct/rgpCafe/solsys/solsys.html Where is ''Ulysses' now!]
* [https://web.archive.org/web/20061101094503/http://www.mps.mpg.de/de/projekte/ulysses/ Max Planck Institute ''Ulysses'' website]
* [http://www.planetary.org/radio/show/00000303/ Interview with ''Ulysses'' Mission Operations Manager Nigel Angold on Planetary Radio] {{Webarchive|url=https://web.archive.org/web/20120220052841/http://www.planetary.org/radio/show/00000303/ |date=20 February 2012 }}
*[https://thehappykoala.github.io/Harmony-of-the-Spheres/#/scenario/Ulysses%20-%20Leaving%20the%20Ecliptic Interactive 3D visualisation of ''Ulysses'' Jupiter gravity assist and polar orbit around the Sun]

{{Sun spacecraft}}
{{Jupiter spacecraft}}
{{Comet spacecraft}}
{{ESA projects}}
{{Jet Propulsion Laboratory}}
{{Solar System probes}}

[[Category:European Space Agency space probes]]
[[Category:NASA space probes]]
[[Category:Missions to the Sun]]
[[Category:Missions to Jupiter]]
[[Category:Derelict satellites in heliocentric orbit]]
[[Category:Missions to comets]]
[[Category:Derelict space probes]]
[[Category:Solar space observatories]]

{{Sourceattribution|Ulysses (spacecraft)}}