Viking '75 Mars Lander High Gain Antenna

Just amazing! Nice weld, by the way. How do you model that?

The weld bead was a lot of work; I suspect it could have been done more easily. Each of the blobs or beads started as a separate solid group, shaped like an asymmetrically-flattened cookie or biscuit. I manually placed a couple dozen of them around the circumference of the joint with slightly uneven spacing similar to the actual weld. For more variation I shifted some of the bead groups left or right or rotated them slightly. The blobs at the bends were stretched a bunch to fill the volume around the bend. Then I exploded all the beads and intersected them with each other and with the shape of the downlock body. Finally, I spent a fair amount of time cleaning everything up and repairing lots of tiny holes (even scaled up via the Dave method). Here’s a view before exploding:


That looks like one of those unusual components that could come in handy for a variety of uses in other models.

I recently completed the Viking '75 Mars lander’s S-Band Low Gain Antenna (LGA), which is an omni-directional (upper-hemisphere) receive-only antenna that picked up signals sent from Earth. This allowed the spacecraft to reliably receive signals regardless of how the lander was oriented on the surface of Mars upon landing (assuming right-side up!). The antenna design consists of two superimposed “turnstile” antennas positioned above a three-wire-grid ground screen reflector. The design and fabrication was done by RCA of Moorestown NJ in the early 1970s. I lack references for physical details of the internal wiring, so it is omitted. The horizontal coax connector on the lower front of the unit (with a dust-cap screwed in place) is for a test circuit, and thus not connected in the Flight configuration.

The model is available in the 3D Warehouse.


Cool stuff and your name looked familiar, from over at FB`s Trimble Group. Would be a good share there as well. Great stuff …!!


I recently completed the third and final communications antenna from the Viking '75 Mars lander, a transmit-only UHF antenna. The UHF antenna relied on either of the two Viking orbiters to relay information sent from the lander to an orbiter, and thence on to Earth.

This relay capability was particularly important during the Entry, Descent, and Landing (EDL) phase of the mission after the lander capsule was released from being piggyback on its paired Orbiter, until landing on the surface of Mars about five hours later (most of that time was spent in final lander on-orbit checkout and de-orbit maneuvering). The lander transmitted a continuous signal via the omni-directional UHF antenna during EDL, which the orbiter relayed to Earth so that waiting Viking team members could get a real-time (though delayed via speed-of-light) stream of information. (To the great worry of team members, Viking 2’s EDL transmissions were not relayed live due to a transient problem on orbiter 2. They were sent later in the day to confirm safe landing of Viking lander 2.)

Each of the antenna’s eight radiator rods is tipped with a metal sphere intended to reduce corona breakdown discharges at high power levels. The low-pressure carbon-dioxide atmosphere of Mars made the antenna particularly susceptible to corona breakdown. The corona balls were surrounded by polyurethane foam within a fiberglass sleeve to further inhibit the problem.

The UHF antenna model is available in the 3D warehouse.


Tom, Congratulations on the progress! I love seeing this project and your attention to detail! Bravo!

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Here are some animation tests that illustrate how the Viking lander’s High Gain Antenna was pulled upright after landing by a set of springs:

The deployment mechanism is driven by two pairs of constant-force springs, each of which consists of nine laminations or layers of heat-treated steel with a powerful tendency to curl up. Here is a photograph of an actual antenna deployment mechanism on the test lander exhibited at the Smithsonian National Air and Space Museum:

The animation was created using a custom SketchUp Ruby script - my first! :slightly_smiling_face: The geometry of the spring laminations is all generated by the script, given a set of points that defines the inner edge of the inner-most lamination, and the thickness and width of the laminations. A moderately simple iterative simulation approach was used to deform the initial geometry frame by frame. The animation was actually created in the reverse of what is seen in the video, because my master definition of the spring laminations is in the upright configuration. It was thus easier to run the simulation from an initial upright position and progressively rotate down. I flipped the video clips in an editor.

It’s pretty cool to generate SketchUp geometry via a program! I’m a professional programmer, and I’ve done a fair amount of graphics and 3D modeling programming in prior decades, but never with SketchUp.


Once more, outstanding in approach, detail and finishing touch !! Deep bow.

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Incredible as usual

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Absolutely marvelous! Incredible dedication.


Here is another short video of some more animation tests:

There are two behaviors being tested, motion-blur and flexible-cable dynamics.

Motion-blur is approximated by creating intermediate image frames that capture motion at a smaller incremental step (in other words, at a higher frame rate), and then selectively blending frames together to form the final still frames. In this case, ten intermediate frames were created for each final still frame. The imagemagick tool was used to compute the average of each set of ten successive intermediate frames, forming the final stills. Then the ffmpeg tool was used to create a video from the final still frames.

Motion-blur is helpful to represent high-speed motion that would otherwise have very odd timing appearances due to stroboscopic effects caused by the discrete sampling of each frame. As an example, look at the governor mechanism on the left side of the fifth clip (0:49 into the video). The larger gears seem to turn at reasonable rates, but the escapement wheel and rocking pallet appear very slow due to discrete sampling, when in fact they are moving very fast; no motion-blur was applied here.

The animation was created with a custom SketchUp script that supports a variable frame-rate. In this case, the frame rate was 4800 FPS at the beginning of the first three short clips (which condenses down to 480 FPS after intermediate frames are average), then gradually changing to 240 FPS near the end of the clips (which condenses down to 24 FPS). The net effect is that the motion speeds up; the simulated behavior goes from a 20x slow-motion start to real-time motion ending.

I wrote a separate SketchUp script that exports the scenes (aka pages) ten to a sub-directory on my computer. A macOS/Linux shell script then repeatedly invokes imagemagick to process the frames in each sub-directory into a final video frame. Then a simple ffmpeg command generates the video from the final frames.

The flexible-cable dynamics are simulated with more custom SketchUp scripting. In essence, the simulation begins with the initial cable path (hand-created of multiple segments), and incrementally computes changes due to movement of one end of the cable. The other end is held fixed. The change experienced by the final segment at the moving end of the cable is gradually propagated to all earlier segments of the cable, with various constraints. The simulation algorithm is re-applied from the fixed end back to the moving end of the cable, to attempt to hold the lengths of each segment constant (my simple hack, without a proper physics engine). With the new path of the cable thus computed, Follow-Me is used by the script to construct the cylindrical outline of the cable. Each successive simulated frame picks up from where the prior frame had evolved the cable shape.


It’s really impressive! I’d love to have this animation tool in my toolbox.

Holy Carp, that’s amazing work! :open_mouth: I can’t believe all the detail you’re putting into this. Awesome job!

Wow! Great work.

I think that @TDahl deserves some sort of special SketchUp award. The purpose, scope, and amount of detail that he has put into this project over the past six years is nothing short of amazing, in my opinion. It is also an excellent example of how SketchUp is not just for architectural work, but can obviously be used for mechanical design as well.

I give him image :slightly_smiling_face:


I was thinking the same thing. Just liking his posts doesn’t seem like enough.


Aww, shucks! Thank you folks. :slight_smile: I am pleased that my efforts have introduced NASA’s Viking '75 project into more people’s awareness, even if only a tiny bit. Sadly, the passage of time fades many important past accomplishments such as the Viking project. Even among professional planetary scientists the project is not very well known anymore. I enjoy researching and re-creating the project hardware very much, and I’m glad others are enjoying following along.