VIKING 75 PROJECT
Viking Lander 1 on Mars, 1976 Description The Viking project consisted of launches of two separate spacecraft to Mars, Viking 1, launched on 20 August 1975, and Viking 2, launched on 9 September 1975. Each spacecraft consisted of an orbiter and a lander. After orbiting Mars and returning images used for landing site selection, the orbiter and lander detached, and the lander entered the Martian atmosphere and soft-landed at the selected site. The orbiters continued imaging and other scientific operations from orbit while the landers deployed instruments on the surface. The fully fueled orbiter-lander pair had a mass of 3530 kg. After separation and landing, the lander had a mass of about 600 kg and the orbiter 900 kg. The lander was encased in a bioshield at launch to prevent contamination by terrestrial organisms. Spacecraft and Instrumentation The lander consisted of a six-sided aluminum base with alternate 1.09 meter (m) and .56 m long sides, supported on three extended legs attached to the shorter sides. The leg footpads formed the vertices of an equilateral triangle with 2.21 m sides when viewed from above, with the long sides of the base forming a straight line with the two adjoining footpads. Instrumentation was attached to the top of the base, elevated above the surface by the extended legs. Power was provided by two radioisotope thermal generator (RTG) units containing plutonium 238 affixed to opposite sides of the lander base and covered by wind screens. Each generator was 28 cm tall, 58 cm in diameter, had a mass of 13.6 kg and provided 30 W continuous power at 4.4 volts. Four wet-cell sealed nickel-cadmium 8 amp-hour, 28 volt rechargeable batteries were also onboard to handle peak power loads. Communications were accomplished through a S-band transmitter and two 20 TWTA's. A 2-axis steerable high-gain parabolic antenna was mounted on a boom near one edge of the lander base. An omnidirectional low-gain S-band antenna also extended from the base. Both these antennae allowed for communication directly with the Earth. A UHF (381 MHz) antenna provided a one-way relay to the orbiter using a 30 W relay radio. Data storage was on a 40 Mbit tape recorder, and the lander computer had a 6000 word memory for command instructions. The lander carried instruments to achieve the primary scientific objectives of the lander mission: to study the biology, chemical composition (organic and inorganic), meteorology, seismology, magnetic properties, appearance, and physical properties of the Martian surface and atmosphere. Two 360-degree cylindrical scan cameras were mounted near one long side of the base. From the center of this side extended the sampler arm, with a collector head, temperature sensor, and magnet on the end. A meteorology boom, holding temperature, wind direction, and wind velocity sensors extended out and up from the top of one of the lander legs. A seismometer, magnet and camera test targets, and magnifying mirror are mounted opposite the cameras, near the high-gain antenna. An interior environmentally controlled compartment held the biology experiment and the gas chromatograph mass spectrometer. The X-ray flourescence spectrometer was also mounted within the structure. A pressure sensor was attached under the lander body. The scientific payload had a total mass of approximately 91 kg. Mission Profile Following launch and a 304 day cruise to Mars, the orbiter began returning global images of Mars about 5 days before orbit insertion. The Viking 1 spacecraft was inserted into Mars orbit on 19 June 1976 and trimmed to a 1513 x 33,000 kilometers (km), 24.66 hour site certification orbit on 21 June. Imaging of candidate sites began and the landing site was selected based from these pictures. The lander and its aeroshell separated from the orbiter on 20 July 08:51 UT. At the time of separation, the lander was orbiting at about 4 kilometers above Mars after separation rockets fired to begin lander deorbit. After a few hours at about 300 km altitude, the lander was reoriented for entry. The aeroshell with its ablative heat shield slowed the craft as it plunged through the atmosphere. During the descent the lander parachutes were deployed. Seven seconds later the aeroshell was jettisoned, and 8 seconds after that the three lander legs were extended. The parachute had slowed the lander to 60 meters per second (m/s). At 1.5 km altitude, retro-rockets were ignited and fired until landing 40 seconds later at about 2.4 m/s. The landing rockets used an 18 nozzle design to spread the hydrogen and nitrogen exhaust over a wide area. The Viking 1 Lander touched down in western Chryse Planitia at 11:53:06 UT (4:13 p.m. local Mars time). Approximately 22 kg of propellants were left at landing. Transmission of the first surface image began 25 seconds after landing. 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 Viking 1 Lander was named the Thomas Mutch Memorial Station in January 1981 in honor of the original leader of the Viking imaging team. Life expectancy was about a month. It operated until 13 November 1982 when contact was lost. The total cost of the Viking project was roughly one billion dollars. Launch Date: 1975-08-20 Launch Vehicle: Titan IIIE-Centaur Launch Site: Cape Canaveral, United States Mass: 572 kg Nominal Power: 70 W But that is only part of the story. During the design and testing phase at the Martin Marietta Corporation (MMC), the on-board 40 mega-bit tape recorder began to experience “cave in’s” during “Thermal Vacuum” testing. Because, you see, the “tape” recorder wasn’t a tape recorder at all. It was a “plated wire” recorder that had “tunnels” that routed the wire that was running through the recorder (reel to reel)for protection from the severe environment the vehicle may/would/probably,” experience during its 10 month journey to Mars. And, wire is obviously a more substantial medium than tape for the environment the recorder and the vehicle would experience in flight. Remember that in 1975 sending a lander to Mars was science fiction stuff. It had never been done before and it was certainly further than the moon. In light of the difficulties, it was decided by NASA-Langley and MMC engineers that we should design, build and test a “core memory (think very small donuts of carbon with wire tightly looped through the donuts). If 5 volts was applied to the wire the core became a “1”. The absence of 5 volts returned the core to a “0”. Hence, the computer was capable of being programmed with 1’s and 0’s to create “words” that turned into commands, and data. It’s more complicated than that, but that is the essence of the Viking on-board computer. It not only recorded Mars data from the planet, but received updates on the spacecraft programs to modify data collection tasks. Core memory uses toroids (rings) of a hard magnetic material (usually a semi-hard ferrite) as transformer cores, where each wire threaded through the core serves as a transformer winding. Three or four wires pass through each core. Each core stores one bit of information. Core Memory Array There was a company- Severe Environment Product Division (SEPD) in Hawthorne CA that specialized in core memory units used in guided munitions (as in ‘bombs”) that could survive large “gforces”- high speed acceleration changes that a bomb experiences when dropped from altitude. They were chosen as the builder of the Core Memory Computer. Generalized specifications for the Viking Core Memory Computer prepared by MMC and NASA with a schedule that frankly was thought not to be achievable from a schedule perspective and perhaps technically as well in conventional projects.The idea was not to get bogged down in the seemingly endless document deliverable lists and build and test to redlined existing specs as much as possible. “As Built” documents would be prepared to document what we built and tested and delivered with the units (2). I recall to this day the arrival in Hawthorne, CA of the NASA Project Manager for the Core Memory Recorder. “My name is Bill Deal and I’m from NASA Langley Virginia. I am responsible to NASA for the success of this project,” he said. “This project is vitally important to the overall Mars Lander project and achieving a successful launch of the spacecraft in 1975. If we miss the launch window, we will have to delay the launch by one year due the position of the two planets. We will reduce the paper and concentrate on building and testing the two recorders. We expect the team of SEPD, MMC and NASA to use the experience you have all brought to this project to GET THE JOB DONE and get it done correctly the first time. Cooperation is not only expected, but mandatory. If any of you, ANY OF YOU, have problems that slow you down you can call me directly and I will resolve them.” “Any questions?” There were none. Two Core Memory units were built, environmentally tested successfully and accepted. They were hand carried to Denver in padded aluminum carrying cases, tested again, and placed in storage. They didn’t fly. The Plated Wire Memory units were flown on Viking 1 and 2 in 1976. They performed well in both vehicles well beyond their expected life cycle.
Gleason.Associates 