With its primary mission now over, Hiten began an unexpected extended mission to experiment with a novel method to enter lunar orbit. After a ninth and tenth flyby of the Moon, the latter on 2 October 1991, Hiten was put into a looping orbit that passed the Earth–Moon L4 and L5 Lagrange Points in October 1991 and January 1991, respectively, where it activated its MDC cosmic dust detector, jointly built with Germany. Circling back to the Moon for its eleventh flyby of the Moon at 13:33 UT on 15 February 1992 at a range of 422 kilometers, Hiten used a portion of its last remaining propellant to fire its engine (for 10 minutes) and insert itself into lunar orbit. This profile to enter lunar orbit that required very little delta-V on the part of the spacecraft was developed by JPL mathematician Edward Belbruno (1951– ). Initial orbital parameters around the Moon were 422 × 49,400 kilometers. A final amount of propellant was then used two months later, on 10 April 1993 to deorbit Hiten, which crashed onto the lunar surface at 18:03:25.7 UT at 55.3° E / 34.0° S.
Ulysses
Nation: ESA and USA (1) Objective(s): heliocentric orbit Spacecraft: Ulysses Spacecraft Mass: 371 kg Mission Design and Management: ESA / NASA / JPL Launch Vehicle: STS-41 Discovery Launch Date and Time: 6 October 1990 / 11:47:16 UT Launch Site: Kennedy Space Center / Launch Complex 39B
Scientific Instruments:
- solar wind plasma experiment (BAM)
- solar wind ion composition experiment (GLG)
- magnetic fields experiment (HED)
- energetic particle composition/neutral gas experiment (KEP)
- low energy charged particle composition/anisotropy experiment (LAN)
- cosmic rays and solar particles experiment (SIM)
- radio/plasma waves experiment (STO)
- solar x-rays and cosmic gamma-ray bursts experiment (HUS)
- cosmic dust experiment (GRU)
Results: The Ulysses mission was an outgrowth of the abandoned International Solar Polar Mission (ISPM) that originally involved two spacecraft—one American and one European—flying over opposite solar poles to investigate the Sun in three dimensions. Eventually, NASA cancelled its spacecraft, significantly eroding the confidence of international partners in the reliability of NASA as a partner, and the mission merged into a single spacecraft, provided by ESA. The scientific payload was shared by ESA and NASA, with the latter providing the RTG power source (similar to one used on Galileo), a Space Shuttle launch, and tracking from its Deep Space Network. Ground control operations were shared by both the Americans and Europeans. The vehicle was designed to fly a unique trajectory that would use a gravity assist from Jupiter to take it below the ecliptic plane and pass the solar south pole and then above the ecliptic to fly over the north pole.
Eventually, 13 years after ESA's science council had approved the mission, and considerably delayed by the Challenger disaster, on 6 October 1990, about 7.5 hours after launch, Ulysses was sent on its way into heliocentric orbit via an Inertial Upper Stage/PAM-S motor combination. Escape velocity was 15.4 kilometers/second, higher than had been achieved by either of the Voyagers or Pioneers, and the fastest velocity ever achieved by a human-made object at the time. After a mid-course correction on 8 July 1991, Ulysses passed within 378,400 kilometers of Jupiter at 12:02 UT on 8 February 1992, becoming the fifth spacecraft to reach Jupiter. After a 17-day period passing through and studying the Jovian system, the spacecraft headed downwards and back to the Sun. From about mid-1993 on, Ulysses was constantly in the region of space dominated by the Sun's southern pole, as indicated by the constant negative polarity measured by the magnetometer. South polar observations extended from 26 June to 6 November 1994, when the vehicle was above 70° solar latitude. It reached a maximum of 80.2° in September 1994. Its instruments found that the solar wind blows faster at the south pole than at the equatorial regions. Flying up above the solar equator on 5 March 1995, Ulysses passed over the north polar regions between 19 June and 30 September 1995 (maximum latitude of 80.2°). Closest approach to the Sun was on 12 March 1995 at a range of 200 million kilometers.
ESA officially extended Ulysses' mission on 1 October 1995, renaming this portion as the Second Solar Orbit. Three times during its mission, the spacecraft unexpectedly passed through comet tails—the first time in May 1996 (Comet C/1996 B2 Hyakutake), the second time in 1999 (Comet C/1999 T1 McNaught-Hartley), and the third time in 2007 (Comet C/2006 P1 McNaught). The spacecraft made a second pass over the solar south pole between September 2000 and January 2001 and the northern pole between September and December 2001. At the time, the Sun was at the peak of its 11-year cycle; Ulysses found that the southern magnetic pole was much more dynamic than the north pole and lacked any fixed clear location. ESA's Science Program Committee, during a meeting on 5–6 June 2000, agreed to extend the Ulysses mission from the end of 2001 to 30 September 2004. In 2003–2004, Ulysses spun out towards its aphelion (furthest point in its orbit) and made distant observations of Jupiter. ESA's Science Program Committee approved a fourth extension of the Ulysses mission so that it could continue investigations over the Sun's poles in 2007 and 2008.
In early 2008, ESA and NASA announced that the mission would finally terminate within the subsequent few months, having operated more than four times its design life. With communications systems failing as well as power depleting due to the decline of the RTGs (and thus allowing the hydrazine fuel in its attitude control system to freeze), the spacecraft was on its last breath at that point. Mission operations continued at reduced capacity until loss of contact on 30 June 2009, more than 18.5 years after launch. Ulysses' principal findings include data that showed that there is a weakening of the solar wind over time (which was at a 50-year low in 2008), that the solar magnetic field at the poles is much weaker than previously assumed, that the Sun's magnetic field "reverses" in direction every 11 years, and that small dust particles coming in from deep space into the solar system are 30 times more abundant than previously assumed.
Geotail
Nation: USA/Japan (1) Objective(s): high elliptical Earth orbit Spacecraft: Geotail Spacecraft Mass: 1,009 kg Mission Design and Management: ISAS / NASA Launch Vehicle: Delta 6925 (no. D212) Launch Date and Time: 24 July 1992 / 14:26 UT Launch Site: Cape Canaveral Air Force Station / Launch Complex 17A
Scientific Instruments:
- magnetic fields measurement monitor (MGF)
- low energy particles experiment (LEP)
- electric field monitor (EFD)
- energetic particles and ion composition experiment (EPIC)
- high-energy particle monitors (HEP)
- plasma wave instrument (PWI)
- comprehensive plasma instrument (CPI)
Results: The Geotail mission was a joint project of Japan's ISAS (and later, from 2003, JAXA), and NASA, executed as part of the International Solar Terrestrial Physics (ISTP) project, which also included the later Wind, Polar, SOHO, and Cluster missions. This particular mission's goal was to study the structure and dynamics of the long tail region of Earth's magnetosphere, which is created on the nightside of Earth by the solar wind. During active periods, the tail couples with the near-Earth magnetosphere, and often releases energy that is stored in the tail, thus activating auroras in the polar ionosphere. Although technically not a deep space or planetary mission, Geotail, in its extremely elliptical orbit, performed numerous lunar flybys, some closer than the distance at which the Soviet Luna 3 took the first pictures of the farside of the Moon.
<!-- image -->The spin-stabilized spacecraft (20 rpms) was designed with a pair of 100-meter tip-to-tip antennae and two 6-meter-long masts. On its fifth orbit around Earth, near apogee, on 8 September 1992, the spacecraft flew by the Moon at a range of 12,647 kilometers. The flyby raised apogee from 426,756 kilometers to 869,170 kilometers. Such flybys continued almost every month subsequent to that, and ultimately raised the spacecraft's apogee to 1.4 million kilometers. During these orbits, Geotail observed the magnetotail's far region (from 80 to 220 times the radius of Earth or "Re"). Geotail's 14th and last flyby of the Moon occurred on 25 October 1994 at a range of 22,445 kilometers and as a result, placed the spacecraft in orbits with progressively lower apogees. In November 1994, Geotail's apogee was 50 Re and by February 1995, it was down to 30 Re. The lower orbit was designed to allow the spacecraft to begin the second part of its mission, to study magnetotail sub-storms near Earth. During these orbits, perigee was about 10 Re, while the orbital inclination to the ecliptic plane was about –7° in order that the apogee would be located in the magnetotail's neutral plane during the winter solstice. Later in the decade, Geotail's orbit was adjusted so that it passed just inside Earth's magnetosphere's boundary plane on the dayside. In 2012, the spacecraft celebrated twenty years of continuous operation, and in 2014, despite having an original lifetime of only four years, was still sending back data on the formation of auroras, the nature of energy funneled from the Sun into near-Earth space, and the ways in which Earth's magnetic field lines move and rebound, thus producing explosive bursts that affect our magnetic environment.
Mars Observer
Nation: USA (65) Objective(s): Mars orbit Spacecraft: Mars Observer Spacecraft Mass: 1,018 kg Mission Design and Management: NASA / JPL Launch Vehicle: Titan III (CT-4) Launch Date and Time: 25 September 1992 / 17:05:01 UT Launch Site: Cape Canaveral Air Force Station / Space Launch Complex-40
Scientific Instruments:
- Mars Observer camera (MOC)
- thermal emission spectrometer (TES)
- pressure modulator infrared radiometer (PMIRR)
- Mars Observer laser altimeter (MOLA)
- magnetometer/electron reflectometer (MAG/ER)
- gamma-ray spectrometer (GRS)
- radio science experiment (RS)
- Mars balloon relay receiver (MBR)
Results: Mars Observer was designed to carry out a high-resolution photography mission of the Red Planet over the course of a Martian year (687 days) from a 378 × 350-kilometer polar orbit. Building on the research done by the Viking missions, it carried a suite of instruments to investigate Martian geology, atmosphere, and climate in order to fill in gaps on our knowledge of planetary evolution. A mere 31 minutes after launch, the new Transfer Orbit Stage (TOS), using the Orbus 21 solid rocket motor, fired to boost the spacecraft on an encounter trajectory with Mars. After a 725 million-kilometer voyage lasting 11 months, at 00:40 UT on 22 August 1993, just two days prior to planned entry into Mars orbit, the spacecraft stopped sending telemetry (as planned), but then never resumed 14 minutes later. Despite vigorous efforts to regain contact, Mars Observer remained quiet.
When the spacecraft did not reestablish command as a result of a stored program that was designed to do so in case of five days of silence, mission planners finally gave up hope on salvaging the mission. The results of a five-month investigation proved to be inconclusive, but one likely cause of the catastrophic failure may have been a fuel line rupture that could have damaged the spacecraft's electronics, throwing the vehicle into a spin. In addition, the fact that the Mars Observer bus was a repurposed Earth science satellite bus may have also compromised the spacecraft's ability to adapt to the deep space environment. While none of the primary mission objectives were accomplished, the spacecraft did return data during its interplanetary cruise. Scientific instruments developed for Mars Observer were later used on several subsequent Mars probes, including Mars Global Surveyor (launched in 1996), Mars Climate Orbiter (1998), Mars Odyssey (2001), and Mars Reconnaissance Orbiter (2005).