The next phase of work is under way for my long-term project to model the Viking '75 Mars lander: the fuel tanks and associated supports and fuel-system plumbing. I recently completed the fuel tanks and their supporting struts.
Published reference material is scant for the lander’s fuel system, but I was fortunate to be able to study in detail lander test units that are exhibited at the California Science Center, the Virginia Air and Space Center, and the Smithsonian National Air and Space Museum. It has been a challenge to reconcile differences between these test units, to decide what is representative of the Flight units that were launched to Mars in 1975. A few press photos of the actual landers during assembly (bought on eBay in recent years) have been helpful.
Here are a few more views (including just the bare-bones lander body for context). All the components are solid.
The fuel tanks (23.5 inches inside diameter) held sterilized hydrazine propellant. This powered the lander’s three Terminal Descent Engines which provided the force to slow the spacecraft during the final 45 seconds or so before touchdown on Mars. The hydrazine was also used to power four small roll-control thrusters that oriented the (immobile) lander such that it would face in the desired direction at landing. The TDEs and roll thrusters will be a future modeling effort.
Next to be modeled will be all the fuel and pressurant plumbing lines (tubes) and valves. I’ve captured many dozens of measurements from the test unit seen below, but it’s still going to be a challenge to make it as accurate as I can. The plumbing for the two tanks are somewhat mirror images of each other, which helps a bit.
Earlier posts on this project are linked below: