Launched as the first of NASA’s Discovery missions, the Near Earth Asteroid Rendezvous (NEAR) spacecraft was both the first spacecraft to orbit a small body and, although not actually designed to do so, to land on one successfully. In spite of difficulties during the mission, the NEAR spacecraft accomplished all objectives and more, obtaining unprecedented images and data of a near-Earth asteroid.
Although the Near Earth Asteroid Rendezvous (NEAR) spacecraft was not launched until 1996, the general concept for its mission had actually been born many years earlier. In the early 1980’s, the National Aeronautics and Space Administration (NASA) Solar System Exploration Committee suggested that a rendezvous mission with a near-Earth asteroid was a worthwhile goal. Various groups explored the idea, but it was not until NASA introduced the Discovery program, which was developed under the objective of carrying out “faster, better, cheaper” scientific missions, that the concept gained the necessary momentum.
In 1991, the Applied Physics Laboratory (APL) at The Johns Hopkins University in Baltimore, Maryland, was awarded primary oversight of the NEAR mission. Robert W. Farquhar was named as the mission director, while Andrew Francis Cheng and Joseph Veverka were appointed project scientist and leader of the imaging team, respectively. Spacecraft construction began two years later, and it was initially planned that the spacecraft would be launched in 1998. However, it was then discovered that a mission to Asteroid 433 Eros would be possible if the team could meet a 1996 launch date. Eros, which had been independently discovered in 1898 by Gustav Witt and Auguste Charlois, was considered an attractive target because of its large size and unusual brightness. In addition, at the time of its discovery, Eros was the first asteroid known to come within the orbit of Mars; all of the 432 asteroids discovered before Eros were further away, located primarily in the asteroid belt between Mars and Jupiter.
On February 17, 1996, the NEAR spacecraft (renamed NEAR Shoemaker in March, 2000, in honor of the late scientist Eugene Merle Shoemaker) was successfully launched on board a Delta II rocket, with an encounter at Eros planned for late 1998. Along the way, the spacecraft successfully completed a flyby of Asteroid 253 Mathilde, and in January, 1998, it performed a gravity-assist flyby of Earth in order to achieve the trajectory and speed necessary to reach Eros. In December, 1998, however, when the NEAR team began maneuvers to insert the spacecraft into orbit around Eros, the spacecraft began behaving erratically and contact was lost. Fortunately, contact and control were resumed approximately twenty-seven hours later, although a great deal of fuel had been expended. The spacecraft team hastily revised its mission strategy, and in January, 1999, performed a maneuver that would achieve a rendezvous in February, 2000. Although the encounter would be much later than originally planned, and little margin for error remained, the NEAR team still hoped to accomplish its mission.
On February 14, 2000, history was made when the NEAR team completed the final, complex series of maneuvers that successfully placed the spacecraft into orbit around Eros, the first time a spacecraft had orbited a small body. The spacecraft was already transmitting images and data collected by its payload of instruments, which included a multispectral imager, a near-infrared spectrometer, an X-ray/gamma-ray spectrometer, and a magnetometer. It quickly became apparent that the mission would produce more detailed information about an asteroid than had ever been obtained before.
Over the next several months, refining maneuvers were used to gradually move the spacecraft’s orbit closer and closer to Eros, until in April, 2000, it settled for a time at a distance of approximately 50 kilometers from the asteroid. During this time, the spacecraft recorded and transmitted data continuously. By tracking features on the asteroid’s surface from different angles, for instance, the spacecraft allowed the NEAR team to create a three-dimensional model of the asteroid’s shape, which eventually was fine-tuned to an amazing level of detail. Similarly, several of the spacecraft’s instruments were designed to investigate the asteroid’s composition. In particular, the near-infrared spectrometer measured the sunlight reflected off Eros, allowing scientists to identify the presence of specific minerals. The X-ray/gamma-ray spectrometers identified the presence and amounts of different chemical elements.
In June, 2000, only four months into the planned year-long orbit of Eros, NASA and the APL team agreed that they would eventually attempt a landing on Eros, even though the spacecraft was not designed for such a maneuver, having no legs or air bags. Part of this decision was based on the fact that the gamma-ray spectrometer did not have enough sensitivity to return the results the team had hoped for while the spacecraft was still orbiting at a distance. The landing was planned for February 12, 2001, a mere two days before the mission shutdown that was scheduled to take place one year after orbital insertion had been achieved. Although not everyone was in favor of the bold and risky landing attempt, Mission Director Farquhar admitted that he had had just such an idea in mind during the early days of mission planning, and most of the team felt that it was an opportunity for another historic first in space exploration that might also result in additional scientific benefits.
The Near Earth Asteroid Rendezvous (NEAR) spacecraft orbits the asteroid Eros in this artist’s rendering.
Having never attempted such a maneuver before, the NEAR team did not know whether the best they could hope for was a controlled crash, but a series of five deorbit and braking maneuvers resulted in a soft landing, with the spacecraft touching down relatively gently at a speed of around 4 miles per hour. During the descent, the spacecraft continued to transmit images at closer and closer range. Also, although the camera appeared to have been buried during the touchdown, the X-ray/gamma-ray spectrometer was positioned only a few feet away from the surface and was able to transmit higher-quality data than had ever been hoped for. Because of the unprecedented success of its landing, the NEAR mission was extended for an additional fourteen days so that data from the asteroid’s surface could continue to be collected. On February 28, 2001, the spacecraft was put into a deep sleep mode, and the NEAR mission officially ended, although analysis of the data returned by NEAR Shoemaker would continue for years.
The NEAR mission accomplished a number of firsts in space exploration. It was not only the first NASA Discovery program mission, it was also the first spacecraft to achieve the following: operate beyond the orbit of Mars using solar cells; encounter a near-Earth asteroid; orbit a small body; deliver comprehensive scientific measurements of an asteroid’s composition and physical properties; deliver the highest-resolution images ever taken of an asteroid; and land on a small body. Because near-Earth asteroids may have the possibility of making impact with Earth in the future with potentially catastrophic results, NEAR’s contribution to humanity’s understanding of asteroids was invaluable, and the lessons learned during the mission helped ensure the success of future asteroid rendezvous missions.
In addition, the NEAR mission helped demonstrate the concept that smaller and less expensive space exploration missions could nonetheless return astounding scientific results. Other successful Discovery program missions followed NEAR, including Mars Pathfinder, Lunar Prospector, Deep Impact, and Stardust.
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Beatty, J. Kelly. “NEAR Falls for Eros.” Sky and Telescope 101 (May, 2001): 34-37. Describes both the reasoning behind the decision to land the NEAR Shoemaker spacecraft on Eros and the landing itself. -
Bell, Jim, and Jacqueline Mitton, eds. Asteroid Rendezvous: NEAR Shoemaker’s Adventures at Eros. New York: Cambridge University Press, 2002. With chapters written by various NEAR team members and supplemented with photographs and diagrams, this book describes in detail the conception of the NEAR mission, the mission specifics as they occurred, and the knowledge about Eros gained from the mission. -
Graham, Rex. “A NEAR Look at Eros.” Astronomy 29 (March, 2001): 44-47. Discusses how the NEAR mission has both confirmed existing theories about the relationships between asteroids and meteorites and revolutionized scientific understanding of Eros and similar asteroids. -
McCurdy, Howard E. Low-Cost Innovation in Spaceflight: The Near Earth Asteroid Rendezvous (NEAR) Shoemaker Mission. Washington, D.C.: National Aeronautics and Space Administration, Office of External Relations, History Division, 2005. Provides a detailed history of the NEAR mission, including its origins, design of the spacecraft, particulars of the journey to and orbit around Eros, and implications.
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