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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Viking program | 1/4 | https://en.wikipedia.org/wiki/Viking_program | reference | science, encyclopedia | 2026-05-05T13:26:24.056801+00:00 | kb-cron |
The Viking program consisted of a pair of identical American space probes, Viking 1 and Viking 2 both launched in 1975, and landed on Mars in 1976. The mission effort began in 1968 and was managed by the NASA Langley Research Center. Each spacecraft was composed of two main parts: an orbiter spacecraft which photographed the surface of Mars from orbit, and a lander which studied the planet from the surface. The orbiters also served as communication relays for the landers once they touched down. The Viking program grew from NASA's earlier, even more ambitious, Voyager Mars program, which was not related to the successful Voyager deep space probes of the late 1970s. Viking 1 was launched on August 20, 1975, and the second craft, Viking 2, was launched on September 9, 1975, both riding atop Titan IIIE rockets with Centaur upper stages. Viking 1 entered Mars orbit on June 19, 1976, with Viking 2 following on August 7. After orbiting Mars for more than a month and returning images used for landing site selection, the orbiters and landers detached; the landers then entered the Martian atmosphere and soft-landed at the sites that had been chosen. The Viking 1 lander touched down on the surface of Mars on July 20, 1976, more than two weeks before Viking 2's arrival in orbit. Viking 2 then successfully soft-landed on September 3. The orbiters continued imaging and performing other scientific operations from orbit while the landers deployed instruments on the surface. The program terminated in 1982. The project cost was roughly US$1 billion at the time of launch, equivalent to about $6 billion in 2024 dollars. The mission was considered successful and formed most of the body of knowledge about Mars through the late 1990s and early 2000s.
== Science objectives == Obtain high-resolution images of the Martian surface Characterize the structure and composition of the atmosphere and surface Search for evidence of life on Mars
== Viking orbiters == The primary objectives of the two Viking orbiters were to transport the landers to Mars, perform reconnaissance to locate and certify landing sites, act as communications relays for the landers, and to perform their own scientific investigations. Each orbiter, based on the earlier Mariner 9 spacecraft, was an octagon approximately 2.5 m (8.2 ft) across. The fully fueled orbiter-lander pair had a mass of 3,527 kg (7,776 lb). After separation and landing, the lander had a mass of about 600 kg (1,300 lb) and the orbiter 900 kg (2,000 lb). The total launch mass was 2,328 kg (5,132 lb), of which 1,445 kg (3,186 lb) were propellant and attitude control gas. The eight faces of the ring-like structure were 0.457 m (18 in) high and were alternately 1.397 and 0.508 m (55 and 20 in) wide. The overall height was 3.29 m (10.8 ft) from the lander attachment points on the bottom to the launch vehicle attachment points on top. There were 16 modular compartments, 3 on each of the 4 long faces and one on each short face. Four solar panel wings extended from the axis of the orbiter, the distance from tip to tip of two oppositely extended solar panels was 9.75 m (32 ft).
=== Propulsion === The main propulsion unit was mounted above the orbiter bus. Propulsion was furnished by a bipropellant (monomethylhydrazine and nitrogen tetroxide) liquid-fueled rocket engine which could be gimballed up to 9 degrees. The engine was capable of 1,323 N (297 lbf) thrust, providing a change in velocity of 1,480 m/s (3,300 mph). Attitude control was achieved by 12 small compressed-nitrogen jets.
=== Navigation and communication === An acquisition Sun sensor, a cruise Sun sensor, a Canopus star tracker and an inertial reference unit consisting of six gyroscopes allowed three-axis stabilization. Two accelerometers were also on board. Communications were accomplished through a 20 W S-band (2.3 GHz) transmitter and two 20 W TWTAs. An X band (8.4 GHz) downlink was also added specifically for radio science and to conduct communications experiments. Uplink was via S band (2.1 GHz). A two-axis steerable parabolic dish antenna with a diameter of approximately 1.5 m was attached at one edge of the orbiter base, and a fixed low-gain antenna extended from the top of the bus. Two tape recorders were each capable of storing 1280 megabits. A 381-MHz relay radio was also available.
=== Power === The power to the two orbiter craft was provided by eight 1.57 m × 1.23 m (62 in × 48 in) solar panels, two on each wing. The solar panels comprised a total of 34,800 solar cells and produced 620 W of power at Mars. Power was also stored in two nickel-cadmium 30-A·h batteries. The combined area of the four panels was 15 square meters (160 square feet), and they provided both regulated and unregulated direct current power; unregulated power was provided to the radio transmitter and the lander. Two 30-amp·hour, nickel-cadmium, rechargeable batteries provided power when the spacecraft was not facing the Sun, during launch, while performing correction maneuvers and also during Mars occultation.
=== Main findings ===