Mission Overview ================ The Viking mission to Mars consisted of four spacecraft: the two orbiters VO1 and VO2, and the landers VL1 and VL2 [SOFFEN1977]. During cruise to Mars the landers were attached to the orbiters; the combined spacecraft were then known as Viking 1 and 2. The role of the orbiters was to transport the landers to Mars, to carry reconnaissance instruments for certifying the landing sites, to act as relay stations for lander data, and to perform their own scientific investigations. The initial orbit periapses were placed over the candidate landing sites to allow for maximum viewing resolution and relay of the lander data. After the primary lander missions were completed, the orbiters' orbits were allowed to drift so that the entire planetary surface could be systematically mapped by the three remote sensing experiments. The Viking 1 spacecraft was launched August 20, 1975, and arrived at Mars on June 19, 1976. Lander 1 was deployed to the Mars surface on July 20, 1976. The VO1 orbital inclination of 38-39 degrees was chosen to optimize communication with VL1. Viking 2 was launched September 9, 1975 and arrived at Mars August 7, 1976. VL2 landed on September 3, 1976, at a more northerly site than VL1. The VO2 orbit was correspondingly more inclined than VO1; initially 55 degrees, it was later adjusted to 80 degrees, providing particularly good coverage of polar regions. The areocentric locations of VL1 and VL2 have since been determined to be (22.270N, 48.264W) and (47.669N, 226.032W), respectively [YODER&STANDISH1997]. Mission Phases ============== The timeline for the Viking Mission is divided into a number of mission phases in terms of the types of observations and level of activity. The references [SNYDER1977], [SNYDER1979], [MOOREETAL1987], and [SNYDER&MOROZ1992] provide detailed descriptions of these mission phases. A summary of the mission phases and the relevant dates are described below. Before Mars encounter and orbit insertion the orbiter and lander spacecraft are considered as one spacecraft with the same mission phases. The primary missions for all four spacecraft (VL1, VO1, VL2, and VO2) are listed separately because each has a different starting date. All mission phases after the primary mission are listed only once because all four spacecraft operated together. VIKING 1 MARS LAUNCH -------------------- The Viking 1 spacecraft was launched on August 20, 1975 on a Titan Centaur 3 booster from Cape Canaveral, Florida. Spacecraft Id: : VO1, VL1 Target Name : MARS Mission Phase Start Time : 1975-08-20 Mission Phase Stop Time : 1975-08-20 Spacecraft Operations Type : ORBITER, LANDER VIKING 1 MARS CRUISE -------------------- The Viking 1 spacecraft, consisting of the VO1 orbiter and VL1 lander, cruised to Mars for about 10 months, during which time the spacecraft was checked periodically. Spacecraft Id: : VO1, VL1 Target Name : MARS Mission Phase Start Time : 1975-08-20 Mission Phase Stop Time : 1976-06-19 Spacecraft Operations Type : ORBITER, LANDER VIKING 2 MARS LAUNCH -------------------- The Viking 2 spacecraft was launched on September 9, 1975 on a Titan Centaur 3 booster from Cape Canaveral, Florida. Spacecraft Id: : VO2, VL2 Target Name : MARS Mission Phase Start Time : 1975-09-09 Mission Phase Stop Time : 1975-09-09 Spacecraft Operations Type : ORBITER, LANDER VIKING 2 MARS CRUISE -------------------- The Viking 2 spacecraft, consisting of the VO2 orbiter and VL2 lander, cruised to Mars for about 11 months, during which time the spacecraft was checked periodically. Spacecraft Id: : VO2, VL2 Target Name : MARS Mission Phase Start Time : 1975-09-09 Mission Phase Stop Time : 1976-08-07 Spacecraft Operations Type : ORBITER, LANDER VIKING ORBITER 1 PRIMARY MISSION -------------------------------- The Viking Orbiter 1 spacecraft entered Mars orbit on June 19, 1976. Operations commenced by supporting the selection of a landing site for VL1. Throughout the Primary Mission, the VO1 spacecraft supported communications with the landers and made observations of the Martian surface and atmosphere. The Primary Mission ended at the start of the solar conjunction in November, 1976. Spacecraft Id: : VO1 Target Name : MARS Mission Phase Start Time : 1976-06-19 Mission Phase Stop Time : 1976-11-15 Spacecraft Operations Type : ORBITER VIKING LANDER 1 PRIMARY MISSION ------------------------------- The Viking Lander 1 spacecraft separated from the VO1 orbiter and descended to the Martian surface on July 20, 1976. The Primary Mission focused on the collection and analysis of soil samples and the characterization of the landing site and atmosphere. The Primary Mission ended at the start of the solar conjunction in November, 1976. Spacecraft Id: : VL1 Target Name : MARS Mission Phase Start Time : 1976-07-20 Mission Phase Stop Time : 1976-11-15 Spacecraft Operations Type : LANDER VIKING ORBITER 2 PRIMARY MISSION -------------------------------- The Viking Orbiter 2 spacecraft entered Mars orbit on August 7, 1976. Operations commenced by supporting the selection of a landing site for VL2. Throughout the Primary Mission, the VO2 spacecraft supported communications with the landers and made observations of the Martian surface and atmosphere. The Primary Mission ended at the start of the solar conjunction in November, 1976. Spacecraft Id: : VO2 Target Name : MARS Mission Phase Start Time : 1976-08-07 Mission Phase Stop Time : 1976-11-15 Spacecraft Operations Type : ORBITER VIKING LANDER 2 PRIMARY MISSION ------------------------------- The Viking Lander 2 spacecraft separated from the VO2 orbiter and descended to the Martian surface on September 3, 1976. The Primary Mission focused on the collection and analysis of soil samples and the characterization of the landing site and atmosphere. The Primary Mission ended at the start of the solar conjunction in November, 1976. Spacecraft Id: : VL2 Target Name : MARS Mission Phase Start Time : 1976-09-03 Mission Phase Stop Time : 1976-11-15 Spacecraft Operations Type : LANDER VIKING EXTENDED MISSION ----------------------- The Viking Extended Mission began after solar conjunction. The two orbiters continued to observe the surface and atmosphere of Mars. The two lander spacecraft analyzed additional soil samples and dug three deep holes in the surface. All four spacecraft monitored the planet through the cycle of seasons. During the winter season, the landers operated in an automatic manner designed to allow the spacecraft to survive the cold temperatures and still return some data. Spacecraft Id: : VO1, VL1, VO2, VL2 Target Name : MARS Mission Phase Start Time : 1976-11-15 Mission Phase Stop Time : 1978-05-31 Spacecraft Operations Type : ORBITER, LANDER VIKING CONTINUATION MISSION --------------------------- Primary objectives of the Continuation Mission were to make orbital observations at times of the Mars year that were missed due to landing site selection and solar conjunction and to collect high resolution surface images when the atmosphere was clear. A radio science solar conjunction relativity experiment was also done during the Continuation Mission. Lander activities consisted of measurements by the imaging, meteorology, and XRFS instruments operating in a fully automated manner. Viking Orbiter 2 developed a leak in its propulsion system and lost its attitude control gas. VO2 was turned off on July 25, 1978 after 706 orbits around Mars. Spacecraft Id: : VO1, VL1, VO2, VL2 Target Name : MARS Mission Phase Start Time : 1978-05-25 Mission Phase Stop Time : 1979-02-26 Spacecraft Operations Type : ORBITER, LANDER VIKING INTERIM PERIOD --------------------- The Interim Period mission phase occurred during the time of the Voyager 2 encounter with Jupiter. Thus, communications to and from the Viking spacecraft were limited. The landers continued to operate in an automated manner making imaging and meteorology observations. A final VL2 surface sampler sequence was conducted during this mission phase as an engineering test in the cold temperatures of mid winter. Orbital data stored on spacecraft tape recorders and not returned during the Continuation Mission were downlinked during the Interim Period. Spacecraft Id: : VO1, VL1, VL2 Target Name : MARS Mission Phase Start Time : 1979-02-26 Mission Phase Stop Time : 1979-07-19 Spacecraft Operations Type : ORBITER, LANDER VIKING SURVEY MISSION --------------------- The prime scientific objective for VO1 during the Survey Mission was to obtain high resolution images of possible future landing sites. The plan for the landers was to collect image and meteorology data for as long as possible. Because VL2 no longer had a direct downlink capability, it meant that VL2 could return data only as long as VO1 provided a relay link, once every seven weeks. Communications with VL2 ended on April 11, 1980 after its batteries could no longer hold a charge. VL2 operated on the surface of Mars for 1281 sols. VO1 consumed the last of its attitude control gas on August 7, 1980 and was turned off after 1485 orbits around Mars. Spacecraft Id: : VO1, VL1, VL2 Target Name : MARS Mission Phase Start Time : 1979-07-19 Mission Phase Stop Time : 1980-08-07 Spacecraft Operations Type : ORBITER, LANDER VIKING COMPLETION MISSION ------------------------- Viking Lander 1 continued to operated in its automatic mode during the Completion Mission. The observation sequences were cyclic. VL1 returned via direct downlink image and meteorology data about once a week with image sequences repeating every 37 sols. The VL1 high-gain antenna was programmed to track the Earth until December, 1994. However, communications were lost in November 1982 after a command sequence uplink. Spacecraft Id: : VL1 Target Name : MARS Mission Phase Start Time : 1980-08-07 Mission Phase Stop Time : 1982-11-19 Spacecraft Operations Type : LANDER