Viking '75 Mars Lander Construction, Looking for Viking lander design/construction information Options

[Tom Dahl]

Greetings all! I am searching for detailed construction and design information about the NASA Viking '75 Mars project hardware, particularly for the lander, aeroshell, base cover, and bioshield. Can anyone recommend good sources? I am especially looking for engineering drawings and under-construction photographs.

To set the stage, here is an album of about 100 drawings and photos which I've collected so far.

I have already read the "usual" books, such as NASA RP-1027 "Viking '75 Spacecraft Design and Test", the press kits, the scientific papers produced about the mission, a number of industry papers covering various instruments and subsystems, the major Martin Marietta books, etc. I am hoping to find additional sources. Any ideas?

Also, does anyone know if there are aeroshell, base cover, or bioshield components lurking in a museum or in storage somewhere?

FYI, I have visited three of the best landers still on Earth: The Proof Test Capsule in the Smithsonian NASM, the Flight Capsule 3 (backup) in the Museum of Flight near Seattle, and the Science Test Lander in the Virginia Air and Space Center. I've taken nearly 1,000 photos of the three of them (most of which are publicly available in other Picasa Web albums of mine). I've taken a few measurements, but I would dearly love to find more authoritative drawings of more hardware (interior, exterior, everything). I have begun submitting some Freedom of Information Act requests to NASA/JPL which has started to bear some trivial but kind of fun fruit.
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Update as of March 2017: During the past few years I have been fortunate enough to collect a significant amount of information on the Viking lander hardware. My thanks to a number of organizations for providing me access to their resources:

• Viking Mars Missions Education and Preservation Project
• The Museum of Flight in Seattle
• NASA Langley Research Center
• California Science Center
• Virginia Air and Space Center
• Smithsonian Air and Space Museum

Here is a list of on-line albums with Viking information that I have gathered. Essentially all the photographs - about 3500 currently - were taken by me (with the notable exception of those in the "Misc diagrams" album, which come from historic sources). The photos have descriptions that explain the major subject of each image. To see the descriptions with the current Google Photos web album interface, click on an image and then click the small letter i in circle (i) icon in the upper right corner. This displays an information panel that includes the description. You can also zoom and pan to see the full resolution image detail. Many images in a number of the albums show the 1000 or so measurements I have been able to capture from actual Viking hardware, thanks to the kind cooperation of the above folks.

Flight Capsule 3 in Seattle Museum of Flight (756 photos)
Dimensioned diagrams of the FC3 lander

PTC Lander at Smithsonian NASM 2013 (466 photos)
PTC Lander at Smithsonian NASM 2016 (888 photos)

Lander at Virginia Air and Space Center (622 photos)
Dimensioned diagrams of the VASC’s lander

Lander at California Science Center (456 photos)
Dimensioned diagrams of the CSC's lander

Misc diagrams, unusual photos (over 350 images)
Body assembly blueprints

Collector Head Shroud Unit at NASA LaRC (99 photos)
Biology instrument at Cleveland MoNH (36 photos)
Meteorology Sensor Assembly (60 photos)
Meteorology Electronics Assembly (22 photos)
Tape Recorder (53 photos)
High Gain Antenna photos and measurements (96 images)
XRFS Instrument (42 images)

Viking lander contractor historic scale model (14 images)
My Viking project documents collection

The main focus of my efforts during the past few years has been to create an accurate and high-fidelity digital 3D model of the Viking lander. I've chosen to use the SketchUp software to build the model because a near-full-featured free version is available, allowing other people to use my model. The 3D model itself, as a work-in-progress, is available via DropBox. I update that model file periodically as major elements get added. I've created an album containing numerous renderings of digital model components, and I have a YouTube channel with some videos about the modeling project. I have also uploaded the lander core body and the Surface Sampler Collector Head to the SketchUp 3D Warehouse so that other people can easily access those components (the 3D Warehouse can be accessed from within SketchUp, or via web browser). The file on DropBox lister earlier contains those components and others.
-- Tom

[Tom Dahl]

The next Viking lander component 3D models to be completed represent the lander's two thermal switches, which were mounted on the upper surface of the lander's Equipment Plate (the subject of my prior post above). The thermal switches are seen here as green-tinted boxy objects (the contactor assembly) connected to horizontal cylinders (the actuator assembly), on the left and right sides of the rendering. The green coloration represents the fact that I don't have exact measurements for these components.

The purpose of each thermal switch was to permit and regulate the transfer of heat from the Radioisotope Thermoelectric Generator (RTG, not shown) mounted directly above the switch contactor assembly, into the lander interior. The near-surface atmospheric temperature of Mars, as measured by the Viking landers, varied from about 1F during a summer day to -178F during a winter night. Most of the lander's components, including electronics and especially its rechargeable batteries, would not survive well-below-freezing temperatures. The RTG's housing exterior was at a fairly steady temperature of about 330F (thanks to the natural radioactive decay of plutonium contained in the RTG's internal fuel capsule), and the lander was designed to utilize that heat to maintain adequate internal temperatures. During cold periods the thermal switch actuator would close the thermal switch, forming a thermally-conductive path between the bottom of the RTG and the lander's internal Equipment Plate. During relatively warm periods, the actuator would open the switch, interrupting the high-conductivity path and allowing relatively little heat to flow into the lander.

When the RTGs were installed onto the landers prior to launch, Earth's relatively dense sea-level atmosphere provided an excess of available heating during the final months prior to launch. Even with the thermal switches open, there was too much heating. Therefore, a coolant loop was incorporated into the lander which circulated chilled water through End Cap Coolers mounted on top of and below each RTG. The top side of the thermal switch contactor assembly was hard-bolted to the underside of the corresponding RTG's lower End Cap Cooler. The bottom of the contactor assembly was hard-bolted to a platform machined into the Equipment Plate.

Here is a cut-away view of a thermal switch with actuator assembly on the left and contactor assembly on the right, connected via a linkage that transmitted the horizontal movement of a piston within the actuator to the contactor.

Here is an exploded view of a thermal switch. The brown objects in two stacks at center are 0.001 inch thick copper foils, 100 per stack. These foils are the core of the conductive path. In the assembled thermal switch, the stacks are interleaved forming a 200-foil group (visible in the middle of the exploded contactor on the right). The foils are bonded together where they overlap at center, and also at their ends, forming a cross with short flexible arms.

Here is a close-up of the cut-away actuator assembly. Freon gas filled the volume surrounding the two bellows chambers. When warmed, the freon expanded and pushed the central piston to the right. The piston pushed the linkage rod which connects the actuator to the contactor via clevises at both linkage ends.

Here are close-up cut-away views of the contactor assembly, first showing the closed configuration and then as opened. The central area of the stack of copper flexible foils is moved up (when closed) and down (when open) via a bellcrank driven from the actuator assembly by the linkage rod. A layer of highly-conductive tin is cast on top of the foil stack. When the switch is closed, the tin "seat" presses hard against the underside of a very thick block called the platten (at top-center of the images, with a vertical thread hole). The platten is hard bolted to the lower End Cap Cooler, upon which is mounted the hot RTG housing itself. Heat from the RTG flows downward through the lower End Cap Cooler, the platten, the tin seat, and into the center of the stack of copper foils. The heat then flows sideways through the flexible foil arms and into the boxy lower base (tinted green, across the center of the image) of the contactor assembly. Because the base is hard-bolted to the Equipment Plate, heat flows into the plate and spreads throughout the upper part of the lander interior. The lander's internal temperature-sensitive components (computer, batteries etc.) are bolted to the underside of that plate and therefore receive heat.

When the switch is opened the central portion of the stack of copper foils moves downward, causing the tin seat to pull away from the bottom of the platten. While the platten remains permanently warm (as the RTG's plutonium fuel slowly decays over decades), relatively little heat is radiated from the platten to the seat and foils. The switch provides an effective 50:1 heat conductance ratio when closed vs. opened.


Lastly, here is an view of the underside of a thermal switch when mounted on the Equipment Plate.