Beyond_Earth-_A_Chronicle_of_Deep_Space_Exploration_1958-2016.pdf

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In March 1998, NASA announced that data from Lunar Prospector suggested the presence of water ice at both the lunar poles; the neutron spectrometer instrument detected hydrogen, assumed to be in the form of water. The information indicated that a large amount of water ice, possibly as much as 300 million (metric) tons was mixed into the regolith at each pole, the first direct evidence of water ice at the lunar poles. The spacecraft also detected strong localized magnetic fields, mapped the global distribution of major rock types, and discovered signs of a 600-kilometer diameter, iron-rich core. On 10 December 1998, Lunar Prospector's orbit was lowered to 40 kilometers to perform high-resolution studies. A subsequent maneuver on 28 January 1999 changed the orbit to 15 × 45 kilometers and ended the space probe's primary mission but began an extended mission for an additional seven months. Lunar Prospector was deliberately impacted onto the shadowed Shoemaker crater on the lunar surface at 09:52:02 UT on 31 July 1999. Observations of the resulting dust cloud by Earth-based telescopes showed no spectral signature characteristic of water vapor. The vehicle carried part of the cremated remains of geologist Eugene Shoemaker to the lunar surface.

190

NEAR Shoemaker

Nation: USA (68)

Objective(s): asteroid (Eros) orbit and landing

Spacecraft: NEAR

Spacecraft Mass: 805 kg

Mission Design and Management: NASA / GSFC / APL

Launch Vehicle: Delta 7925-8 (no. D232)

Launch Date and Time: 17 February 1996 / 20:43:27 UT

Launch Site: Cape Canaveral Air Force Station / Launch Complex 17B

Scientific Instruments:

• 1. multi-spectral imager (MSI)
• 2. magnetometer (MAG)
• 3. near infrared spectrometer (NIS)
• 4. x-ray/gamma ray spectrometer (XGRS)
• 5. laser rangefinder (NLR)
• 6. radio science and gravimetry experiment

Results: Near Earth Asteroid Rendezvous (NEAR) was the first mission flown under NASA's Discovery program, a series of low-cost (less than c. $150 million in mid-nineties dollar amounts) planetary science projects that were selected competitively and led by a Principal Investigator rather than a NASA manager. NEAR's primary goal was to rendezvous with the minor planet 433 Eros (an S-class asteroid), approximately 355 million kilometers from Earth, and gather data on its physical properties, mineral components, morphology, internal mass distribution, and magnetic field. The spacecraft was the first to rely on solar cells for power during operations beyond Mars orbit. On the way to its primary mission, NEAR performed a 25-minute flyby of the asteroid 253 Mathilde on 27 June 1997. Closest approach to 1,200 kilometers was at 12:56 UT.

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During the encounter, the spacecraft photographed 60% of the minor planet from a range of 1,200 kilometers. The collected information indicated that the 4.5 billion-year-old asteroid is covered with craters and less dense than previously believed. After a mid-course correction on 3 July 1997, NEAR flew by Earth on 23 January 1998 at 07:23 UT for a gravity assist on its way to Eros. Closest approach was 540 kilometers. After the Earth flyby encounter, NEAR's previously planned mission profile had to be revised in the light of an aborted engine burn on 20 December 1998 that prevented a critical trajectory correction to meet up with Eros a month later. Instead, NEAR was put on a backup trajectory that afforded a different flyby than that originally planned. As part of this new plan, the spacecraft first flew past Eros on 23 December 1998 at 18:41:23 UT at a range of 3,827 kilometers (distance measured from the center of mass) during which it observed about 60% of the asteroid, and discovered that the minor planet was smaller than expected. NEAR also found that the asteroid has two medium-sized craters, a long surface ridge, and a density similar to Earth's crust. After several more trajectory adjustments, NEAR finally moved into orbit around Eros at 15:33 UT on 14 February 2000, roughly a year later than intended, becoming the first human-made object to orbit a minor planet. Orbital parameters were 321 × 366 kilometers. Through 2000, NEAR's orbit was shifted in stages to permit specific research programs. There were a few problems in the lead up to the landing on the asteroid. For example, on 13 May 2000, controllers had to turn off the Near Infrared Spectrometer due to an excessive power surge. By 30 April the spacecraft was in its operational orbit at an altitude of about 50 kilometers from Eros' center. Later, on 13 July, NEAR entered an even lower orbit at 35 kilometers that brought the vehicle as close as 19 kilometers from the surface. After about 10 days, it moved back into a higher orbit. On 26 October, NEAR performed another close flyby of the surface, this time to just 5.3 kilometers. By the end of the year, the spacecraft had entered a circular 35-kilometer low orbit around the asteroid, and began to make a series of very close passes—on the order of 5 to 6 kilometers—to its surface. Following a slow controlled descent, during which it took 69 high-resolution photos of Eros, NEAR touched down on Eros at a gentle 6.4 kilometers/hour, just south of a saddle-shaped feature named Himeros, on 12 February 2001 at 19:44 UT. This was the first time a U.S. spacecraft was the first to land on a celestial body, having been beaten by the Soviets in landing on the Moon, Mars, and Venus. Remarkably, the orbiter survived contact and returned valuable data, especially from its gamma-ray spectrometer, for about two weeks. Last contact with NEAR was on 28 February 2001, the spacecraft having succumbed to the extreme cold (–173°C). NASA's attempt to contact the probe nearly two years later on 10 December 2002 was unsuccessful. NEAR data showed that Eros had no magnetic field. It mapped more than 70% of the surface using the near infrared spectrometer and provided important data about the asteroid's interior. The spacecraft returned about 10 times more data than originally planned, including 160,000 images. Earlier, on 14 March 2000, a month after entering asteroid orbit, NASA renamed the NEAR spacecraft NEAR Shoemaker in honor of Eugene M. Shoemaker (1928–1997), the renowned geologist.

191

Mars Global Surveyor

Nation: USA (69)

Objective(s): Mars orbit

Spacecraft: MGS

Spacecraft Mass: 1,030.5 kg

Mission Design and Management: NASA / JPL

Launch Vehicle: Delta 7925 (no. D239)

Launch Date and Time: 7 November 1996 / 17:00:49 UT

Launch Site: Cape Canaveral Air Force Station / Launch Complex 17A

Scientific Instruments:

• 1. Mars orbital camera (MOC)
• 2. Mars orbital laser altimeter (MOLA)
• 3. thermal emission spectrometer (TES)
• 4. magnetometer/electron reflectometer (MAG/ER)
• 5. radio science experiment (RS)
• 6. Mars relay antenna for future spacecraft (MR)

Results: Mars Global Surveyor was the first spacecraft in NASA's new Mars Surveyor Program, a new generation of American space probes to explore Mars every 26 months from 1996 to 2005, and formulated (in 1994) to economize costs and maximize returns by involving a single industrial partner with the Jet Propulsion Laboratory to design, build, and deliver a flight-worthy vehicle for Mars every two years. (A new Mars Exploration Program was inaugurated in 2000.) The Mars Global Surveyor spacecraft carried five instruments similar to those carried by the lost Mars Observer probe that fell silent in 1993. Among its instruments was a French-supplied radio relay experiment to serve as a downlink for future Mars landers, including for the then-planned Russian Mars 96 mission. After mid-course corrections on 21 November 1996 and 20 March 1997, Mars Global Surveyor entered a highly elliptical orbit around Mars on 12 September 1997 after engine ignition at 01:17 UT. Initial orbital parameters were 262 × 54,026 kilometers. Commencement of its planned two-year mission was delayed because one of its two solar panels (-Y) had not fully deployed soon after launch. The solar panels were designed to act as atmospheric brakes to alter its orbit. As a result, mission planners reconfigured the aerobraking process required to place the vehicle in its intended orbit: the modified aerobraking maneuver began on 17 September 1997 and lasted until 11 October. A second aerobraking phase lasted from November 1997 to March 1998 and a third one began in November 1998 whose goal was to reduce the high point of its orbit down to 450 kilometers. The revised maneuvers were finally completed on 4 February 1999 with a major burn from its main engine. A subsequent firing on 19 February finally put Mars Global Surveyor into a near-circular polar orbit at 235 kilometers—and on 9 March 1999, its mapping mission formally began. The orbit was Sun-synchronous, ensuring that all its images were taken by the spacecraft of the same surface features at different times under identical lighting conditions. Despite the early problems, Mars Global Surveyor, already during its movement to its new orbit, began to send back impressive data and high-resolution images of the surface of Mars. The spacecraft tracked the evolution of a dust storm, gathered information on the Martian terrain, found compelling evidence indicating the presence of liquid water at or near the surface (first announced by NASA on 22 June 2000). During its mission, Mars Global Surveyor also produced the first three-dimensional profiles of Mars' north pole using laser altimeter readings. The spacecraft's primary mission was concluded on 1 February 2001, by which time it had returned 83,000 images of Mars, more than all previous missions to Mars combined. In addition, the laser altimeter essentially mapped almost all of the planet, by firing approximately 500 billion pulses at the surface, providing topographical data that was more detailed than many places on Earth. On 1 February 2001, Mars Global Surveyor's mission was extended for a year, and then again on 1 February 2002, this time continuing 11 months. In the early 2000s, the spacecraft supported other missions to Mars, including that of Mars Odyssey (in 2001) and the Mars Exploration Rovers (in 2004) by providing either atmospheric data or relaying telemetry back to Earth. Between 2004 and 2006, it conducted experiments simultaneously with the European Mars Express. On 1 October 2006, mission planners, based on the recommendations of a Senior Review Board, once again extended its mission by another two years but only a month later, on 2 November, the spacecraft lost contact with Earth when attempting to orient a solar panel. Although weak signals were received three days later, on 21 November 2006, NASA announced that the mission of Mars Global Surveyor was over. The final problem was probably related to a flaw in the system's software.

192

Mars 8 / Mars 96

Nation: Russia (106)

Objective(s): Mars orbit and landing

Spacecraft: M1 (no. 520)

Spacecraft Mass: 6,795 kg

Mission Design and Management: NPO imeni Lavochkina

Launch Vehicle: Proton-K + Blok D-2 (8K82K no. 392-02 + 11S824F no. 3L)

Launch Date and Time: 16 November 1996 / 20:48:53 UT

Launch Site: GIK-5 / Site 200/39

Scientific Instruments:

Orbiter:

• 1. Argus imaging complex
  • TV camera (HRSC)
  • spectroscopic camera (WAOSS)
  • Omega infrared and optical spectrometer
• 2. infrared Fourier spectrometer (PFS)
• 3. Termoskan mapping radiometer
• 4. Svet mapping spectrometer
• 5. Spikam multi-channel spectrometer
• 6. ultraviolet spectrophotometer (UFS-M)
• 7. long-wave radar (RLK)
• 8. Foton gamma-ray spectrometer
• 9. Neytron-S neutron spectrometer
• 10. mass spectrometer (MAK)
• 11. Aspera-S ion and particles power and mass analyzer
• 12. Fonema omni non-scanning energy-mass ion analyzer
• 13. Dimio omni ionosphere energy mass spectrometer
• 14. Mari-prob ionospheric plasma spectrometers
• 15. Maremf electron analyzer/magnetometer
• 16. Elisma wave complex experiment
• 17. Sled-2 low energy charged particle spectrometer
• 18. precision gamma-ray spectrometer (PGS)
• 19. Lilas-2 cosmic and solar gamma-burst spectrometer
• 20. Evris stellar oscillation photometer
• 21. solar oscillation spectrometer (SOYa)
• 22. Radius-M dosimeter
• 23. tissue-equivalent dosimeter (TERS)