Viking '75 Mars Lander High Gain Antenna

I’ve completed another portion of my work-in-progress Viking '75 Mars lander high-fidelity model - the deployment mechanism of the lander’s S-Band High Gain Antenna (HGA). The HGA has a 30-inch parabolic dish that needed to be located above the lander (to avoid line-of-sight obstructions from other components). In order to fit within the lander’s aeroshell capsule during launch and cruise the HGA dish was folded down close to the lander body. The deployment mechanism, seen here, was used to raise the antenna to its final vertical position shortly after landing on Mars. Two sets of curled constant-force springs provide the energy to rotate and raise the HGA. In order to avoid a damaging shock at the end of a potentially fast deployment travel, a governor with escapement mechanism is located in the tear-drop end of the deployment’s horizontal hub.

Here is a comparison between actual Viking lander hardware (photographed at the Virginia Air and Space Center, and the Smithsonian National Air and Space Museum) and the model:

This is the deployment mechanism shown in place on the work-in-progress lander (the actual HGA would be attached to the top-most flange of the short vertical elbow tube):

Close-up of the deployment mechanism hub; the clothespin-like device on the left is the uplock, and the governor is within the right end of the hub:

Close-up of the deployment mechanism, showing the two sets of nine-layer constant-force springs that power the deployment mechanism:

Exploded view of the overall deployment mechanism (green-tinted components are simplified or approximated due to lack of reference material):

Exploded view with governor and escapement in the foreground:


As with all of your previous submissions on this project, the level and fidelity of detail is extremely impressive — and the overall quality of modelling, impeccable.

Amazing work.

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So are you using SketchUp for part / mechanical design?

Do you transfer to other programs?

Hi Jeremy, I use SketchUp for creating 3D models of mechanical parts. I am not designing the parts, I’m merely representing existing actual hardware parts as 3D digital models using SketchUp as the modeling tool. The original parts were design by the engineers at Martin Marietta (now Lockheed Martin) and other contractors back in the 1970s. (The two Flight landers built by Martin Marietta have been sitting on Mars since their successful landings in 1976; lander 1 operated until 1982, lander 2 operated until 1980.)

My 3D representations are about as accurate and high-fidelity as I can manage. I’ve taken somewhere around 1500 detail measurements with high-precision calipers etc. of Viking test hardware units that still remain in museums and collections. Also captured about 3500 detail photographs of the hardware. I have made all my measurements and photos freely available on the web (along with the work-in-progress SketchUp model file). Here is a video I created that describes my process:

I have not really tried to transfer the SketchUp model to other programs, no. About the only thing I’ve done is to export a few small parts as STL files and had them commercially printed. It is rather fun to hold in my hand “almost” a piece of Viking. :slight_smile:


Thanks for that info. Great watch and obviously a load of effort goes into these.

If you don’t mind answering one more question, why do you do this?

Sincere question…don’t want to sound rude. Preserve history? Stay sharp? Enjoyable? I too find some parts of SketchUp modeling somewhat soothing lol.


Ahh, “why” indeed? The space program in general and the Viking '75 project in particular has long held my interest. I’m doing this digital lander project (started modeling it in 2013) both for my own enjoyment and to preserve the engineering legacy and accomplishments of the original “Vikings” as they call themselves. It is quite a lot of fun to work out aspects of the original hardware that seem obscure or pointless, as I reverse engineer the components. I love seeing the lander take shape, piece by slow piece, on the computer screen.

I don’t really know exactly how the result will benefit others. However, I have been working with the founder of the Viking Mars Missions Education and Preservation Project. She is the daughter of one of the meteorologists from the project, and has a keen interest in preserving the legacy and educating young people about the work. I was invited by her to attend and have a table display at the 40th anniversary of the Viking landings event held in Denver CO in July 2016, not far from the former Martin Marietta Aerospace facility where the landers were built. I met a good number of “Vikings” there, which was pretty cool!


Well it is great work, I’m sure modeling a nearly complete lander is an amazing feeling.

Keep it up! I didn’t even really know we sent Mars Landers in '75 and I call my self interested in the space programs!

While not an engineer, I can see these models (and the presentations that you’ve made) as a fantastic basis for a high-school level 'Intro to [Space] Engineering’ course to interest kids in STEM. Starting with posing the biggest problem: making a lander (with 70’s materials and methods!) that can work/survive on the Mars surface, then digging down to each detailed challenge for all of it’s required functions: each one an engineering case-study on its own.

You’ve produced an incredibly well-documented dynamic archive of the engineering challenges that the Viking team faced, and your reverse-engineering sheds light on the problem-solving approach (at each level of scale) that their engineers needed to master. Your models and their animations provide such clear illustration of how the approach taken solves the challenges posed, that even non-expert audiences are able to understand how/why it works, and likely be fascinated by it.

I think it could be a treasure-trove for a sufficiently well-motivated teacher (or school board) to base a course curriculum around. (Assuming of course that you’re amenable to extending use rights for such purposes)

Just a thought…


The next part of the Viking '75 Mars lander’s High Gain Antenna (HGA) that I’ve modeled is one of the electrical connector receptacles used to link the antenna to electronics within the lander. Available on the 3D Warehouse.
This is a Malco Microdot MARC 63 series connector receptacle type MD63-00E9-19P (shell size 9, with 19 pins). The right-center photograph shows one of these connectors on the interface bracket of the HGA mast (see the right-most connector; the connector with red-taped cover is a Radio Frequency coax connector for pre-launch testing). This multi-pin connector supplies electric power and signal lines to the antenna’s altitude-azimuth drive head.

Photographed in the upper right is a similar unit with larger diameter shell size 15, supporting 61 pins (compared to 19 pins in the modeled unit). There are four sizes of MARC 63 series connector: shell size 9, 12, 15, and 18 (smallest to largest). Size 18 supports 91 pins. I was able to purchase an unused unit surplus on eBay recently. It is a little treasure. The main body or shell of the unit is just over one and a quarter inches long.

The customer who uses the connector (in this case RCA Astro Electronics, maker of the lander’s radio subsystem) installs their wiring into each pin and then threads the pins through the red and black “inserts”, first through the taller rear insert and then the front insert. The inserts are keyed to orient within the shell in just one way. The inserts are locked into place by a five-piece closure (the left-most components in the exploded view) which threads into the hex-end of the shell, behind the inserts. This is an extremely tight fit; the internally-tapered sleeve of the closure squeezes the tapered red rubber rear insert. It is so tight that I have not attempted to fully assemble my unit for fear of causing damage.

The SketchUp model has more detail than might be warranted for inclusion in the overall Viking lander model; most of it becomes hidden when the connector is installed. However, it was enjoyable to model it fairly completely - and with an actual unit in-hand, I could not resist. Even so, the actual hardware is yet more complicated. The gold pins, for example, have some features I decided not to model. The hollow end of each pin (where the customer’s wire is inserted) has two shoulders each just a few thousandths of an inch high. There is also a tiny inspection hole bored sideways through each pin near the base of the hollow wire-insert end.


Here is a preview of my last few months of working on the Viking '75 Mars lander’s High Gain Antenna. This is an X-ray view of the antenna’s drive head, who’s main L-shaped structure left-of-center is a little over seven inches (about 19 cm) tall. The 30-inch parabolic dish reflector will be attached to the “plus shaped” (+) fitting near top center (with prominent lightening holes), facing away in this view’s orientation. The drive head allows the antenna to track the Earth’s movement across the Martian sky.

I have not managed to find drawings of the elevation and azimuth axis internal drive trains, so the shafts and bearings are simply shown schematically and no gearing is included. The cylindrical drive motors and position encoders are mounted on the outside of the head and are included (on the left and bottom faces). A few coax RF connectors (TNC and SMA types) are also modeled to a moderate degree.


Paired with the connector receptacle modeled in an earlier reply above, I’ve recently completed the mating plug, a Malco Microdot MARC 63 series MD63-06E9-19S. Available on the 3D Warehouse.

The little jewel-like plug is about 1.3 inches long and 0.75 inches in diameter (3 cm X 2 cm). The unit photographed in the upper right is a surplus one I found on eBay. I was not able to fully disassemble the rotating shell from its interior stationary sleeve and O-ring, for fear of causing damage when removing the fine retaining ring wire at the back of the shell.

The overall plug design mimics that of its receptacle mate, with multi-part inserts which retain the 19 wires entering the rear of the plug (i.e., the red end) and the 19 tiny hollow sockets that mate with the receptacle’s pins. When using such a plug and receptacle in an actual application, the customer may omit some wires and sockets (or pins), leaving however many are required to satisfy their application.

This type of plug was used in various places on the Viking '75 Mars lander, including supplying the electrical power and control lines to the lander’s High Gain Antenna (HGA). I haven’t been able to capture any good photographs of these applications because the museum-based test units don’t happen to have the corresponding antenna cable installed, and the other similar connectors used elsewhere on the lander are generally obscured by protective tape. Here is a poorly-focused view of one within the test lander exhibited at the Virginia Air and Space Center in Hampton VA, which I was fortunate enough to spend a long day measuring and photographing in 2014.


I have completed modeling the main portion of the High Gain Antenna (HGA) - the so-called Direct Communications System (DCS) of the radio subsystem that includes the Radio Frequency feed and 30-inch parabolic reflector to transmit and receive signals directly between Earth and the Viking '75 Mars landers. The overall antenna model contains nearly 300 unique components (all of which are solid in the SketchUp model). The DCS antenna model is available on the 3D Warehouse, along with its Deployment Mechanism model.

Here are comparisons between the SketchUp model and actual hardware:

Here is an exploded view of the antenna and its Deployment Mechanism (covered in earlier replies to this topic):

Close-up exploded view of the DCS antenna itself:

Cut-away view of the antenna, showing a simplified form of the RF cabling running up inside the mast and to a coax non-contacting rotary joint within the antenna’s drive head:

Next is a close-up of the cut-away view. I haven’t been able to identify the actual rotary joint part, so shown is representational based on other units (along with TNC coax connectors). The small green circuit board within the horizontal cylindrical shell of the dual non-constant-helix RF feed at the focus of the dish reflector is also representational; I have not been able to locate images or drawings of the actual part:

Close-up cut-away of the base of the antenna mast, with the wiring interface between the antenna and its Deployment Mechanism. The electrical connectors are modeled in detail, including internal parts. The multi-strand colored wiring bundle routed along the outside of the mast is wrapped in protective red tape; the RF cable within the mast is simplified:

Here is the antenna mounted on the work-in-progress lander model:

Here is a photo taken by my wife of me using an endoscope to capture details within the dish mounting structure; I am looking at a laptop that is displaying and capturing video from the endoscope’s camera:

A huge thanks to the Viking Mars Missions Education and Preservation Project who enabled me to spend hours photographing and capturing hundreds of detail measurements of an actual antenna, serial number 21. Also thanks to some other institutions with Viking hardware on exhibit, who have allowed me to do research on additional antenna-related artifacts:


Wow amazing work as usual, how big is the full file coming in at now?

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The overall work-in-progress Viking lander model file DropBox link is just shy of 180MB at the moment. That is virtually all geometry; there are no images in the model.

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Wow, incredible!

Amazing dedication!

I did not realise it’s actual size untill I saw the picture of you ‘endoscoping’ :grinning:
In my imagination it was much bigger!

Absolutely incredible!

The 30-inch dish, combined with a 30-watt transmitter and the huge dishes of the Deep Space Network on Earth were enough to get signals direct from Mars in the 1970s. And in reverse, the massive Earth transmitters were powerful enough that the lander’s receiver could reliably pick up command signals. Much of the time, the lander actually used a different antenna to transmit indirectly to Earth. Each lander has an omni-directional UHF antenna which was used to send information to either of the two Viking orbiters that were part of the mission and orbiting mars. The Viking orbiters would use their larger (in dish diameter and power) transmitter to forward the signals on to Earth. But after the first couple of years when the orbiters ran out of maneuvering fuel and were shut down, the lander’s dish was the only way to get signals to Earth.

Sad story: the High Gain Antenna was related to how Viking lander 1 was effectively killed by human accident after six years operating nearly flawlessly on Mars. For electric power, the lander had two Radioisotope Thermoelectric Generators (RTGs) that each produced nominally about 35 watts (a little more at the start of the mission, gradually reducing over time). The RTGs could help to power the lander directly, but usually they charged four large NiCad batteries built by General Electric, which provided power to lander systems. The batteries were kind of amazing because they needed to survive heat-sterilization (to about 240 F) along with every other part of the lander. As with any rechargeable battery, they suffered loss in repeated charge-discharge cycles during the mission. Occasionally, new software was uploaded into the lander’s computer with modified recharge algorithms to try improving battery performance.

In late 1982, a new program was uploaded. Unfortunately, the upload was stored by mistake in the part of the computer’s memory which contained the program for controlling the High Gain Antenna’s Earth tracking. Zonk, the antenna immediately went off-point with some unknown behavior. Despite months of work to reproduce the problem with test hardware and with repeated attempts to contact the lander when Mars’ orbit passed through various possible intercept phases, Viking 1 was never heard from again.


The next portion to be completed of the Viking '75 Mars lander model’s antenna hardware is the downlock mechanism for the High Gain Antenna (HGA) which is featured in earlier replies within this topic (3D warehouse link):

This view shows the HGA when stowed or folded down against the lander body, held in place by the U-shaped downlock (partially obscured by the antenna itself):

The downlock restrains the HGA at three places, seen in the following composite image (which hides all components of the antenna except the main frame of the drive head at center, and the cross-shaped dish support below center). A pyrotechnically-actuated “pin-puller” device (the gold-toned object) is the primary locking contact, via a 1/4 inch diameter rod (the “pin”) which slots through holes in a clevis in the drive head frame and a flange in the dish support. Two stabilizers hold small blue fittings on the sides of the antenna drive head:

The pin-puller model includes the internal components, seen in this cut-away in both the normal and fired or retracted states:

Lastly, an exploded view of the downlock mechanism:

My thanks to the Smithsonian National Air and Space Museum for allowing me to capture close-up photography in 2016 of an actual downlock mechanism on the test lander in their collection.