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By
Wikipedia,
the free encyclopedia,
http://en.wikipedia.org/wiki/Viking_1
Viking 1 was the first of two spacecraft sent to Mars as part of NASA's Viking program, and holds the record for the longest Mars surface mission of 6 years and 116 days (from landing until surface mission termination, Earth time).
Mission
Following launch using a Titan/Centaur launch vehicle on August 20, 1975 and a 10 month cruise to Mars, the orbiter began returning global images of Mars about 5 days before orbit insertion. The Viking 1 Orbiter was inserted into Mars orbit on June 19, 1976 and trimmed to a 1513 x 33,000 km, 24.66 h site certification orbit on June 21. Landing on Mars was planned for July 4, 1976, the United States Bicentennial, but imaging of the primary landing site showed it was too rough for a safe landing. The landing was delayed until a safer site was found. The lander separated from the orbiter on July 20 08:51 UT and landed at 11:53:06 UT. It was the first attempt by the United States at landing on Mars.
Orbiter
The instruments of the orbiter consisted of two vidicon cameras for imaging (VIS), an infrared spectrometer for water vapor mapping (MAWD) and infrared radiometers for thermal mapping (IRTM). The orbiter primary mission ended at the beginning of solar conjunction on November 5, 1976. The extended mission commenced on December 14, 1976 after solar conjunction. Operations included close approaches to Phobos in February 1977. The periapsis was reduced to 300 km on March 11, 1977. Minor orbit adjustments were done occasionally over the course of the mission, primarily to change the walk rate — the rate at which the planetocentric longitude changed with each orbit, and the periapsis was raised to 357 km on July 20, 1979. On August 7, 1980 Viking 1 Orbiter was running low on altitude control gas and its orbit was raised from 357 × 33943 km to 320 × 56000 km to prevent impact with Mars and possible contamination until the year 2019. Operations were terminated on August 17, 1980 after 1485 orbits.
Lander
The lander and its aeroshell separated from the orbiter on July 20 08:51 UT. At the time of separation, the lander was orbiting at about 4 km/s. The aeroshell's retrorockets fired to begin the lander deorbit maneuver. After a few hours at about 300 km altitude, the lander was reoriented for atmospheric entry. The aeroshell with its ablative heat shield slowed the craft as it plunged through the atmosphere. During this time, entry science experiments were performed by using a retarding potential analyzer, a mass spectrometer, and pressure, temperature and density sensors. At 6 km altitude, traveling at about 250 m/s, the 16 m diameter lander parachutes deployed. Seven seconds later the aeroshell was jettisoned, and 8 seconds after that the three lander legs were extended. In 45 seconds the parachute had slowed the lander to 60 m/s. At 1.5 km altitude, retrorockets on the lander itself were ignited and, 40 seconds later at about 2.4 m/s, the lander arrived on Mars with a relatively light jolt. The legs had honeycomb aluminum shock absorbers to soften the landing.
The landing rockets used an 18 nozzle design to spread the hydrogen and nitrogen exhaust over a large area. NASA calculated that this approach would mean that the surface would not be heated by more than one degree Celsius, and that it would move no more than 1mm of surface material. Since most of Viking's experiments focused on the surface material a more straightforward design would not have served.
The Viking 1 Lander touched down in western Chryse Planitia ("Golden Plain") at 22.697° N latitude and 48.222° W longitude at a reference altitude of −2.69 km relative to a reference ellipsoid with an equatorial radius of 3397.2 km and a flatness of 0.0105 (22.480° N, 47.967° W planetographic) at 11:53:06 UT (16:13 local Mars time). Approximately 22 kg of propellants were left at landing.
Transmission of the first surface image began 25 seconds after landing and took about 4 minutes. During these minutes the lander activated itself. It erected a high-gain antenna pointed toward Earth for direct communication and deployed a meteorology boom mounted with sensors. In the next 7 minutes the second picture of the 300° panoramic scene (displayed below) was taken. On the day after the landing the first color picture of the surface of Mars was taken. This first color image has since been lost or misplaced, The seismometer failed to uncage, and a sampler arm locking pin was stuck and took 5 days to shake out. Otherwise, all experiments functioned nominally. The lander had two means of returning data to earth: a relay link up to the orbiter and back, and by using a direct link to earth. The data capacity of the relay link was about 10 times higher than the direct link.
The lander had two facsimile cameras, three analyses for metabolism, growth or photosyntheses, a gas chromatograph-mass spectrometer (GCMS), an x-ray fluorescence spectrometer, pressure, temperature and wind velocity sensors, a three-axis seismometer, a magnet on a sampler observed by the cameras, and various engineering sensors.
The Viking 1 Lander was named the Thomas Mutch Memorial Station in January 1982 in honor of the leader of the Viking imaging team. The lander operated for 2245 sols (about 2306 earth days or 6 years) until November 11, 1982, when a faulty command sent by ground control resulted in loss of contact. The command was intended to uplink new battery charging software to improve the lander's deteriorating battery capacity, but it inadvertently overwrote data used by the antenna pointing software. Attempts to contact the lander during the next four months, based on the presumed antenna position, were unsuccessful. In 2006 the Viking 1 lander was imaged on the Martian surface by the Mars Reconnaissance Orbiter. First panoramic view by Viking 1 from the surface of Mars.
Viking 1 image gallery
Test of General Relativity | |
High-precision test of general relativity by the Cassini space probe (artist's impression) |
Gravitational time dilation is a phenomenon predicted by the theory of General Relativity whereby time passes differently in regions of different gravitational potential. Scientists used the lander to test this hypothesis, by sending radio signals to the lander on Mars, and instructing the lander to send back signals. Scientists then found that the observed signals matched the predictions of the theory of General Relativity.
See also
External links
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Published in July 2009.
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