PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = "CREATED: 1998-05-18, J. MAFI; UPDATED: 2001-08-01, J. MAFI" OBJECT = MISSION MISSION_NAME = "ULYSSES" OBJECT = MISSION_INFORMATION MISSION_START_DATE = 1990-10-06 MISSION_STOP_DATE = NULL MISSION_ALIAS_NAME = "INTERNATIONAL SOLAR POLAR MISSION" MISSION_DESC = " Mission Overview ================ Introduction ------------ Launched in October 1990, Ulysses was an exploratory mission carried out jointly by ESA and NASA and had as its primary objective the study of the inner heliosphere in three dimensions. The importance of such a mission was recognized even at the dawn of the space era (e.g., [SIMPSONETAL1959]), since it was generally accepted that the conditions found in the narrow band of heliographic latitudes available to observers in the ecliptic plane were not representative of the global structure of the inner heliosphere. Nevertheless, prior to Ulysses, attempts to understand the basic physical processes occurring within this environment had, by necessity, been based for the most part on observations made in or near the ecliptic plane. The Ulysses mission provided, for the first time, comprehensive in-situ measurements of the heliospheric particles and fields at distances from 1 to 5 AU from the Sun, and at essentially all solar latitudes. Within the framework of the Ulysses project, ESA was responsible for the operation of the European-built spacecraft, while NASA provided the launch, the spacecraft's radioisotope thermoelectric power source, and was responsible for acquisition of data using the Deep Space Network of tracking stations. The scientific payload comprising nine hardware investigations was provided by international teams of scientists from Europe and the United States. The mission provided results addressing many aspects of solar and heliospheric science. In addition to numerous individual publications, as of 1996 seven collections of papers had appeared as special issues or sections of journals, each one focusing on a specific part of the mission ([GRLV19N121992], [SCIENCEV257N50761992], [JGRV98NA121993], [PSSV41N11/121993], [SSRV72N1/21995], [SCIENCEV268N52131995], [GRLV22N231995]). General aspects of the mission ------------------------------ Following launch by the Space Shuttle, a combined IUS/PAM-S upper-stage was used to inject Ulysses into a direct Earth/Jupiter transfer orbit. A gravity-assist maneuver at Jupiter in February 1992 placed the spacecraft in its final Sun-centered out-of-ecliptic orbit, with a perihelion distance of 1.3 AU and an aphelion of 5.4 AU. The orbital period was 6.2 years. Ulysses' trajectory took the spacecraft literally into the uncharted third dimension of the heliosphere. The prime mission, covering the period from launch up to the end of September 1995, included two polar passes, which are defined to be the parts of the trajectory when the spacecraft was above 70 degrees heliographic latitude in either hemisphere. The first polar pass (over the south solar pole) commenced on 26 June 1994 and ended on 5 November, the second pass (north) occurred one year later (19 June - 29 September), making a total of 234 days (or approximately 9 solar rotations) above 70 degrees latitude. The maximum heliographic latitude reached by Ulysses was the same in both hemispheres, namely 80.2 degrees. Based on the scientific success of the mission in the first solar orbit, and the excellent health of the spacecraft and its payload, both ESA and NASA undertook to continue operating the spacecraft for a second orbit of the Sun. Constituting what was essentially a new mission, the so-called Second Solar Orbit brought Ulysses back over the solar poles in 2000 and 2001. In contrast to the high-latitude phase of the prime mission, which took place under quiet solar conditions, the second set of polar passes occurred close to solar maximum. Scientific investigations ------------------------- Phenomena studied by Ulysses include the solar wind, the heliospheric magnetic field, solar radio bursts and plasma waves, solar and interplanetary energetic particles, galactic cosmic rays, interstellar neutral gas, cosmic dust, solar X-rays and gamma-ray bursts. The prime goal of all of these studies was to characterize the heliographic latitude dependence of the physical parameters involved. In addition, however, Ulysses' unique interplanetary orbit was highly suitable for carrying out measurements that are difficult to perform from the relative proximity of the Earth's orbit to the Sun. An important example of such measurements was the detection of interstellar pick-up ions (atoms of interstellar gas that have become singly ionized). Other investigations carried out by Ulysses included detailed interplanetary-physics studies during the in-ecliptic Earth-Jupiter phase, measurements in the Jovian magnetosphere during the Jupiter encounter, and radio-science investigations of the Sun's corona and the Io Plasma Torus using the spacecraft and ground telecommunication systems. Scientific highlights --------------------- Summaries of the key findings from the southern polar pass and pole-to-pole transit have been reported elsewhere (e.g. [SMITH&MARSDEN1995], [MARSDEN&SMITH1996A], [MARSDEN&SMITH1996B]). The papers in [A&AV316N21996], in addition to addressing new aspects of the data obtained during these periods, also focus on the results from the first northern polar pass. Of particular interest in this context are the north-south asymmetries reported by various authors. Nutation Anomaly ---------------- About two hours following deployment of the 7.5 meter axial boom on 4 November 1990, a small nutation of the spacecraft was observed. This gradually grew until it reached a half-cone angle of 3 degrees with a pronounced periodicity. At that distance from Earth, data transmission was still in S-band with its wide-angle beam. If significant nutation had occurred at larger geocentric distance, with the narrowbeam (2 degree beamwidth) X-band system operating, data transmission would have been seriously hampered. Investigations to find the cause of the nutation and to find ways to reduce and control it showed that the principal, but not the only, cause was solar energy entering the axial boom as the spacecraft rotated at 5 rpm. This induced a periodic bending of the boom which coupled into the entire spacecraft to cause nutation. As the spacecraft traveled further from the Sun and the solar aspect angle diminished (putting the boom into the shadow of the spacecraft), the effect was reduced and on 17 December 1990 the nutation disappeared completely. In the period when nutation was still active, it was experimentally established that use of the automatic earth seeking attitude control system (closed loop CONSCAN) was extremely efficacious in keeping nutation at very low levels (see [WENZELETAL1992]). Correct interpretation enabled the preparation for the return of nutation in 1994 to be carried out in an orderly manner followed by the successful control of nutation during a period of over one year. These activities stretched to the limit the NASA and ESA ground facilities used for the task as well as the operational staff located at JPL and at the ground stations. The fact that the acquired scientific data were not degraded is proof of success of these operations. In 1995, as expected, the joint ESOC-JPL Mission Operations Team located at JPL had to contend with a renewed build-up of the nutation disturbance. Following the procedures developed during previous periods when nutation was present, the onboard Conscan system was operated in closed-loop mode in order to keep the spacecraft's high gain antenna pointed at the Earth. In line with predictions, the nutation, which peaked in early May, had decayed by early September. The cooperation of NASA's Deep Space Network in providing the round-the-clock tracking support needed to operate Conscan throughout this period is gratefully acknowledged. Nutation is not expected to return until January 2001. Mission Phases ============== Launch ------ The spacecraft was launched on Oct. 6, 1990 by the shuttle Discovery with two upper stages. To reach high solar latitudes, the spacecraft was aimed close to Jupiter so that Jupiter's large gravitational field would accelerate Ulysses out of the ecliptic plane to high latitudes; no man-made launch vehicle could by itself provide the needed velocity for Ulysses to achieve high latitudes. Spacecraft ID : ULY Mission Phase Start Time : 1990-10-06 Mission Phase Stop Time : 1990-12-03 Spacecraft Operations Type : LAUNCH/CHECK-OUT Earth-Jupiter Cruise -------------------- Spacecraft ID : ULY Mission Phase Start Time : 1990-12-04 Mission Phase Stop Time : 1992-01-24 Spacecraft Operations Type : CRUISE Jupiter Encounter ----------------- Ulysses arrived at Jupiter 16 months after departing from Earth, having traveled nearly 1 billion kilometers in the ecliptic. Closest approach to the planet occurred at 12:02 UT on 8 February, 1992. The inbound trajectory was rather similar to those of the four spacecraft which flew past Jupiter previously: Pioneer 10, 11 (1972, 1973) and Voyager 1, 2 (1979). In contrast to these missions, however, Ulysses reached high latitudes (40 degrees north of Jupiter's equator) near closest approach. Ulysses' outbound flight path was through the hitherto unexplored dusk sector (18:00 hours local time) of the magnetosphere, this time at high southern latitudes. Another unique aspect of the flyby was the penetration of the Io Plasma Torus (IPT), a few hours after closest approach, in a basically north-south direction which contrasted with the nearly equatorial traversals of the Voyager 1 and Galileo spacecraft. In addition to this direct penetration, the spacecraft radio signal passed through the IPT for a significant length of time making it possible to probe the electron density distribution in the Torus. Spacecraft ID : ULY Target Name : JUPITER Mission Phase Start Time : 1992-01-25 Mission Phase Stop Time : 1992-02-17 Spacecraft Operations Type : FLYBY Sequence of Events during the Ulysses Jupiter Flyby. Event Time Distance (Day/Hour/Min) (Rj) ------------------------------------------------------------- Bow Shock Crossing (In) 033/17:33 113 Magnetopause Crossings (In) 033/21:30-035/04:00 110-87 Magnetodisc/Plasmadisc 036/06:30-037/22:00 67-36 Crossings High Latitude Polar Cap 038/22:30 15 (or possibly Cusp) 039/06:30 8.7 Closest Approach 039/12:02 6.31 Observations of Io Plasma 039/13:00-18:00 6.4-9.0 Torus Observation of Field Aligned 041/01:00-043/13:00 35-82 Currents, Electron and Ion Streaming Magnetopause Crossings (Out) 043/13:57-045/21:40 83-124 Bow Shock Crossings (Out) 045/00:37-047/07:52 109-149 First Solar Orbit ----------------- The launch energy provided by the space shuttle and three upper stage rockets, combined with the gravity assist maneuver at Jupiter, placed the Ulysses spacecraft in a Sun-centered, elliptical orbit inclined at 80 degrees with respect to the Sun's equator. Important design requirements for the mission were to maximize the time spent at high solar latitudes and to achieve the highest possible latitude. Owing to the relative positions of the Earth, Sun and Jupiter at the time of the planetary swing-by, a south-going out-of-ecliptic trajectory best met these requirements. Spacecraft ID : ULY Target Name : HELIOSPHERE Mission Phase Start Time : 1992-02-18 Mission Phase Stop Time : 1995-09-30 Spacecraft Operations Type : ORBITER Aphelion (5.40 AU) : 1992-02-15 Perihelion (1.34 AU) : 1995-03-12 Ecliptic Crossing : 1995-03-13 First South Polar Pass: On 26 June 1994, 28 months after leaving Jupiter, Ulysses began its passage over the Sun's southern polar cap. The Ulysses polar passes are defined to be the segments of the trajectory corresponding to solar latitudes greater than or equal to 70 degrees in either hemisphere. The south polar pass lasted 132 days, equivalent to 5 solar rotations. During this time, the distance from the spacecraft to the Sun decreased from 2.8 AU to 1.9 AU (1 AU = 150 million km). The spacecraft reached its most southerly point, 80.2 degrees south of the solar equator, on 13 September 1994, at a distance of 2.3 AU from the Sun. Polar Pass (latitude > 70 deg. S) : 1994-06-26 to 1994-11-05 Max. Latitude (80.2 deg. S) : 1994-09-13 First North Polar Pass: On 30 September, five years after launch, Ulysses completed the first phase of its exploratory mission to study the Sun's environment from the perspective of a solar polar orbit. Between 19 June and 29 September, one year after its south polar pass, the spacecraft flew over the Sun's northern polar regions, reaching a maximum latitude of 80.2 degrees north of the equator on 31 July. Polar Pass (latitude > 70 deg. N) : 1995-06-19 to 1995-09-29 Max. Latitude (80.2 deg. N) : 1995-07-31 Second Solar Orbit ------------------ Ulysses' out-of-ecliptic orbit has a period of 6.2 years, corresponding to approximately half a solar cycle. A consequence of this is that the high-latitude passes of the second solar orbit occurred close to the maximum of solar cycle 23. The conditions in the polar regions are expected to be dramatically different from those encountered during the prime mission. In particular, the rather simple configuration of the corona found at solar minimum, with large coronal holes over the polar caps, will have been replaced by a much more complex arrangement, probably including high-latitude streamers. Transient events (solar flares, coronal mass ejections, etc.) related to the increase in solar activity will dominate, greatly disturbing the underlying structure of the solar wind and influencing the transport of cosmic rays and energetic solar particles. Spacecraft ID : ULY Target Name : HELIOSPHERE Mission Phase Start Time : 1995-10-01 Mission Phase Stop Time : 2001-12-31 Spacecraft Operations Type : ORBITER Aphelion (5.41 AU) : 1998-04-17 Ecliptic Crossing : 1998-05-09 2nd South Polar Pass (Lat.>70 deg. S) : 2000-09-06 to 2001-01-16 Max. Southern Latitude (80.2 deg. S) : 2000-11-27 2nd North Polar Pass (Lat.>70 deg. N) : 2001-08-31 to 2001-12-10 Max. Northern Latitude (80.2 deg. N) : 2001-10-13 Perihelion (1.34 AU) : 2001-05-23 References ========== Text for the MISSION_DESC has been adapted from the following sources: [MARSDENETAL1996] - 'Mission Overview' [MARSDEN&WENZEL1992] - 'Jupiter Encounter' [MARSDEN1995A] - 'First Solar Orbit' [MARSDEN1995B] - 'Second Solar Orbit', 'Nutation Anomaly' [WENZELETAL1992] - 'Nutation Anomaly'" MISSION_OBJECTIVES_SUMMARY = " Mission Objectives Overview =========================== The primary mission of the Ulysses spacecraft was to characterize the heliosphere as a function of solar latitude. The heliosphere is the vast region of interplanetary space occupied by the Sun's atmosphere and dominated by the outflow of the solar wind. The periods of primary scientific interest are when Ulysses was at or higher than 70 degrees latitude at both the Sun's south and north poles. On 26 June 1994, Ulysses reached 70 degrees south. There it began a four-month observation from high latitudes of the complex forces at work in the Sun's outer atmosphere -- the corona. Scientists have long studied the Sun from Earth using Earth- based sensors. More recently, solar studies have been conducted from spaceborne platforms; however, these investigations have been mostly from the ecliptic plane (the plane in which most of the planets travel around the Sun) and no previous spacecraft have reached solar latitudes higher than 32 degrees. Now that Ulysses high latitude data is available, scientists from the joint National Aeronautics and Space Administration (NASA)-European Space Agency (ESA) mission are obtaining new and better understanding of the processes going on at high solar latitudes. Scientists have long been aware of differences between the polar regions of the Sun and lower latitudes. Sunspots are only seen at lower latitudes, and photographs of the solar corona take during solar eclipses often showed dark regions over the poles. The solar corona consists of hot gasses (over 1,000,000 degrees); at this temperature the gravitational field of the Sun can not prevent escape of coronal gas as the solar wind. However, the Sun has a global magnetic field. Many of the solar magnetic field lines that leave the solar surface return to the surface, but some of the field lines, particularly those over the poles, extend deep into interplanetary space. The solar wind expands into interplanetary space along these field lines, and the regions (known as coronal holes) of the corona from which the hot gas escapes are dark because of the low gas density. The properties of the Sun's polar magnetic field are poorly understood, and they have an important influence on the escape of the solar wind. The complex processes that heat and accelerate the solar wind are not well understood, and Ulysses observations over the poles should provide important new information on how the solar wind expands from the Sun that will aid scientists in understanding these processes. The magnetic field also exerts a crucial influence on matter arriving near the Sun from the Milky Way galaxy and from the nearby interstellar medium. Incoming cosmic rays are subjected to forces exerted by the magnetic field. The structure of the Sun's magnetic field is thought to favor entry of cosmic rays by way of the Sun's polar regions. Scientists hope that Ulysses can shed some light on the extent to which the galactic cosmic rays observed at Earth use this route and on the ways in which their properties are modified as a result. Scientists also hope to gain more knowledge of the intensity and properties of the cosmic rays far from the Sun. Jupiter Encounter ----------------- The primary aim of the flyby was to place the spacecraft in its final heliocentric out-of-ecliptic orbit with a minimum of risk to the onboard systems and scientific payload. Scientific investigations at Jupiter are a secondary objective of the mission. Nevertheless, the opportunity to study Jupiter's magnetosphere was exploited to the greatest extent possible. Jupiter is a strongly magnetized, rapidly rotating planet. Its magnetosphere is the largest object in the solar system, a fact reflected in the long interval of 12 days from 2 to 14 February (days 033 to 045 of 1992) that it took for Ulysses to travel through it. The large Galilean satellites are embedded within the magnetosphere and Io is known to be a prolific source of ions and neutral particles. Ions, predominantly of sulfur and oxygen, are distributed around the orbit of Io to form a large torus. Electrons and ions from Io, Jupiter's ionosphere and the solar wind are all present and are transported throughout the magnetosphere. A substantial fraction of these particles are accelerated to extremely high energies to form intense radiation belts. Upstream of the magnetosphere, in the free-streaming solar wind, a detached bow shock forms which slows the solar wind and allows it to be deflected around the magnetosphere. A wide variety of complex physical phenomena are available for study. References ========== Description of the Jupiter Encounter Mission Objectives adapted from [MARSDEN&WENZEL1992])." END_OBJECT = MISSION_INFORMATION OBJECT = MISSION_HOST INSTRUMENT_HOST_ID = "ULY" OBJECT = MISSION_TARGET TARGET_NAME = "JUPITER" END_OBJECT = MISSION_TARGET OBJECT = MISSION_TARGET TARGET_NAME = "SUN" END_OBJECT = MISSION_TARGET END_OBJECT = MISSION_HOST OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "A&AV316N21996" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "GRLV19N121992" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "GRLV22N231995" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "JGRV98NA121993" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "MARSDEN&SMITH1996A" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "MARSDEN&SMITH1996B" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "MARSDEN&WENZEL1992" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "MARSDEN1995A" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "MARSDEN1995B" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "MARSDENETAL1996" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "PSSV41N11/121993" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "SCIENCEV257N50761992" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "SCIENCEV268N52131995" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "SIMPSONETAL1959" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "SMITH&MARSDEN1995" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "SSRV72N1/21995" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "WENZELETAL1992" END_OBJECT = MISSION_REFERENCE_INFORMATION END_OBJECT = MISSION END