Viking '75 Mars Lander Fuel Tanks

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:


When you think it can’t get better it does ! Epic :+1:

Excellent work. The level of detail is amazing.

Fantastic work Tom! I’m a huge fan of this project.

I’m curious: what would the total part count be for the lander — and do you have a total of how many parts you’ve modelled to-date?

To date, the model consists of just over 1000 unique components. Hard to estimate what the total will be, assuming that I’m able to “finish” it; probably another thousand or two. Note that this is to represent essentially all of the externally-visible piece-parts of the lander hardware, plus selected items that are not visible (such as the two Radioisotope Thermoelectric Generators, hidden under large wind covers).

Regarding the actual Viking lander hardware, there are a lot of internal parts. Much of that consists of electronics assemblies (which mostly consist of discrete electronics components - resistors, capacitors, etc. plus some small 8-pin integrated circuits) and wickedly-complex wiring harnesses. But there are a few super-complex mechanical systems inside, such as the Biology instrument (which has many thousands of internal parts itself) and the Gas Chromatograph Mass Spectrometer. I’m not planning on modeling any of that (lack of energy, time, and reference material).

If I have any modeling energy when the “external” lander is done, the next aspect of Viking that I would model (some future decade) is the two-layer capsule in which the lander was sealed prior to landing on Mars - the inner layer of aeroshell (heat shield) and base cover (top-half), plus the outer layer of bioshield base and cover. Those components have complex mechanical systems, probably on the order of a thousand unique piece-parts. (That doesn’t include what was inside another mass spectrometer and other science instruments mounted on the aeroshell to take readings during the few minutes of descent.)

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I marvel at your persistence and patience — as well as your technical knowledge of the lander, and evident modelling skill.