NEAR Shoemaker

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  NEAR Shoemaker
  •   Eros
  •   Earth
  •   Mathilde
  •   Sun
  • Animation of NEAR Shoemaker's trajectory around Eros from April 1, 2000, to February 12, 2001
NEAR Shoemaker
433 Eros Animation of NEAR Shoemaker trajectory around 433 Eros.gif
    Animation of NEAR Shoemaker's trajectory around Eros from April 1, 2000, to February 12, 2001

    Orbital insertion around Eros occurred on February 14, 2000, at 15:33 UT (10:33 EST) after NEAR completed a 13-month heliocentric orbit which closely matched the orbit of Eros. A rendezvous maneuver was completed on February 3 at 17:00 UT, slowing the spacecraft from 19.3 to 8.1 m/s relative to Eros. Another maneuver took place on February 8 increasing the relative velocity slightly to 9.9 m/s. Searches for satellites of Eros took place on January 28 and February 4 and 9; none were found. The scans were for scientific purposes and to mitigate any chances of collision with a satellite. NEAR went into a 321×366 km elliptical orbit around Eros on February 14. The orbit was slowly decreased to a 35 km circular polar orbit by July 14. NEAR remained in this orbit for 10 days and then was backed out in stages to a 100 km circular orbit by September 5, 2000. Maneuvers in mid-October led to a flyby of Eros within 5.3 km of the surface at 07:00 UT on October 26. [5]

    Orbits and landing

    Eros asteroid from approximately 250 meters altitude (area in image is roughly 12 meters across ). This image was taken during NEAR's descent to the surface of the asteroid. Erosregolith.jpg
    Eros asteroid from approximately 250 meters altitude (area in image is roughly 12 meters across ). This image was taken during NEAR's descent to the surface of the asteroid.

    Following the flyby, NEAR moved to a 200 km circular orbit and shifted the orbit from prograde near-polar to a retrograde near-equatorial orbit. By December 13, 2000, the orbit was shifted back to a circular 35 km low orbit. Starting on January 24, 2001, the spacecraft began a series of close passes (5 to 6 km) to the surface and on January 28 passed 2 to 3 km from the asteroid. The spacecraft then made a slow controlled descent to the surface of Eros ending with a touchdown just to the south of the saddle-shaped feature Himeros on February 12, 2001, at approximately 20:01 UT (3:01 p.m. EST). To the surprise of the controllers, the spacecraft was undamaged and operational after the landing at an estimated speed of 1.5 to 1.8 meters per second (thus becoming the first spacecraft to soft-land on an asteroid). [9] After receiving an extension of antenna time on the Deep Space Network, the spacecraft's gamma-ray spectrometer was reprogrammed to collect data on Eros's composition from a vantage point about 4 inches (100 mm) from the surface where it was ten times more sensitive than when it was used in orbit. [10] This increase in sensitivity was in part due to the increased ratio of the signal from Eros compared to noise generated by the probe itself. [4] The impact of cosmic rays on the sensor was also reduced by about 50%. [4]

    At 7 p.m. EST on February 28, 2001, the last data signals were received from NEAR Shoemaker before it was shut down. A final attempt to communicate with the spacecraft on December 10, 2002, was unsuccessful. This was likely due to the extreme −279 °F (−173 °C, 100 K) conditions the probe experienced while on Eros. [11]

    Spacecraft and subsystems

    NEAR spacecraft inside its Delta II rocket. NEARCraft.jpg
    NEAR spacecraft inside its Delta II rocket.

    The spacecraft has the shape of an octagonal prism, approximately 1.7 m on a side, with four fixed gallium arsenide solar panels in a windmill arrangement, a fixed 1.5 m X-band high-gain radio antenna with a magnetometer mounted on the antenna feed, and an X-ray solar monitor on one end (the forward deck), with the other instruments fixed on the opposite end (the aft deck). Most electronics were mounted on the inside of the decks. The propulsion module was contained in the interior. The decision to mount instruments on the body of the spacecraft rather than using booms resulted in the gamma-ray spectrometer needing to be shielded from noise generated by the craft. [4] A bismuth germanate shield was used although this proved only moderately effective. [4]

    The craft was three-axis stabilized and used a single bipropellant (hydrazine / nitrogen tetroxide) 450 newton (N) main thruster, [12] and four 21 N and seven 3.5 N hydrazine thrusters for propulsion, for a total delta-V potential of 1450 m/s. Attitude control was achieved using the hydrazine thrusters and four reaction wheels. The propulsion system carried 209 kg of hydrazine and 109 kg of NTO oxidizer in two oxidizer and three fuel tanks. [5]

    Power was provided by four 1.8 by 1.2 meter gallium arsenide solar panels which could produce 400  watts at 2.2  AU (329,000,000 km), NEAR's maximum distance from the Sun, and 1800 watts at one AU (150,000,000 km). Power was stored in a nine-ampere-hour, 22-cell rechargeable super nickel-cadmium battery. [5]

    Diagram showing location of NEAR science instruments. NEAR Spacecraft Configuration.jpg
    Diagram showing location of NEAR science instruments.

    Spacecraft guidance was achieved through the use of a sensor suite of five digital solar attitude detectors, an inertial measurement unit (IMU), and a star tracker camera pointed opposite the instrument pointing direction. The IMU contained hemispherical resonator gyroscopes and accelerometers. Four reaction wheels (arranged so that any three can provide complete three-axis control) were used for normal attitude control. The thrusters were used to dump angular momentum from the reaction wheels, as well as for rapid slew and propulsive maneuvers. Attitude control was to 0.1 degree, line-of-sight pointing stability is within 50 microradians over one second, and post-processing attitude knowledge is to 50 microradians. [5]

    The command and data handling subsystem was composed of two redundant command and telemetry processors and solid state recorders, a power switching unit, and an interface to two redundant 1553 standard data buses for communications with other subsystems. NEAR was the first APL spacecraft to use significant numbers of plastic encapsulated microcircuits (PEMs), and the first to use solid-state data recorders for mass storage—previous APL spacecraft used magnetic tape recorders or magnetic cores. [13]

    The solid state recorders are constructed from 16 Mbit IBM Luna-C DRAMs. One recorder has 1.1 gigabits of storage, the other has 0.67 gigabits. [5]

    The NEAR mission was the first launch of NASA's Discovery Program, a series of small-scale spacecraft designed to proceed from development to flight in under three years for a cost of less than $150 million. The construction, launch, and 30-day cost for this mission is estimated at $122 million. The final total mission cost was $224 million which consisted of $124.9 million for spacecraft development, $44.6 million for launch support and tracking, and $54.6 million for mission operations and data analysis. [1]

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    References

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    2. 1 2 "NEAR Shoemaker". NASA. Retrieved April 26, 2021.
    3. 1 2 3 4 Extended-mission opportunities for a Discovery-class asteroid rendezvous mission
    4. 1 2 3 4 5 Trombka, J. I.; Nittler, L. R.; Starr, R. D.; Evans, L. G.; et al. (2001). "The NEAR-Shoemaker x-ray/gamma-ray spectrometer experiment: Overview and lessons learned". Meteoritics & Planetary Science. 36 (12): 1605–1616. Bibcode:2001M&PS...36.1605T. doi: 10.1111/j.1945-5100.2001.tb01852.x .
    5. 1 2 3 4 5 6 7 8 "NEAR Shoemaker". NASA Space Science Data Coordinated Archive. Retrieved February 5, 2019.
    6. Williams, David R. (December 18, 2001). "NEAR Flyby of Asteroid 253 Mathilde". NASA . Retrieved August 10, 2006.
    7. D. K. Yeomans; et al. (1997). "Estimating the mass of asteroid 253 Mathilde from tracking data during the NEAR flyby". Science . 278 (5346): 2106–9. Bibcode:1997Sci...278.2106Y. doi:10.1126/science.278.5346.2106. PMID   9405343 . Retrieved August 29, 2007.
    8. "The NEAR Rendezvous Burn Anomaly of December 1998" (PDF). Final Report of the NEAR Anomaly Review Board. November 1999. Retrieved February 2, 2017.
    9. Siddiqi, Asif A. (2018). Beyond Earth: A Chronicle of Deep Space Exploration, 1958–2016 (PDF). The NASA history series (second ed.). Washington, DC: NASA History Program Office. p. 2. ISBN   9781626830424. LCCN   2017059404. SP2018-4041.
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    PD-icon.svg This article incorporates  public domain material from websites or documents ofthe National Aeronautics and Space Administration .

    NEAR Shoemaker
    NEAR Shoemaker spacecraft model.png
    Model of the NEAR Shoemaker spacecraft
    Mission typeOrbiter (433 Eros)
    Operator NASA  · APL
    COSPAR ID 1996-008A
    SATCAT no. 23784 OOjs UI icon edit-ltr-progressive.svg
    Website Official website
    Mission duration5 years, 21 days
    Spacecraft properties
    Launch mass~800 kilograms (1,800 lb)
    Dry mass487 kilograms (1,074 lb)
    Power1,800 W
    Start of mission
    Launch dateFebruary 17, 1996 (1996-02-17) 20:43:27 UTC
    Rocket Delta II 7925-8
    Launch site Cape Canaveral LC-17B
    End of mission
    Last contactFebruary 28, 2001 (2001-02-28) ~00:00 UTC
    Landing dateFebruary 12, 2001 (2001-02-12) 20:01 UTC
    Landing siteSouth of Himeros crater, 433 Eros
    Flyby of 253 Mathilde
    Closest approachJune 27, 1997 (1997-06-27) 12:56 UTC
    Distance1,212 kilometers (753 mi)