Viking 1 was the first of two spacecraft sent to Mars as part of NASA's Viking program. It was the first spacecraft to successfully land on Mars and perform its mission, and holds the record for the second longest Mars surface mission of 6 years and 116 days (from landing until surface mission termination, Earth time).
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.
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 areocentric 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.
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.
Full article ▸