If by “other landers” you mean later Mars spacecraft such as Mars Pathfinder, the apparent roughly $100 million versus $10 million difference for particular components/subsystems is largely because Viking was doing things for the first time, whereas later missions could reuse decades of technology. The total Viking figures were actually much larger than $100 million.
NASA’s 1977 accounting put Viking lander development at about $558 million for the two landers, within a total project cost approaching $1 billion in 1970s dollars.
The main reasons were:
- Almost everything had to be invented. Viking was the first fully successful US Mars landing. NASA had no proven Mars entry, descent and landing system to copy. The lander required a new aeroshell, parachute system, terminal descent rockets, autonomous guidance, landing radar, computers and communications.
- Viking was essentially a laboratory on Mars. It carried two cameras, a robotic sampling arm, meteorology, seismology, X-ray fluorescence, a gas chromatograph-mass spectrometer (GCMS) and, most unusually, a sophisticated biological laboratory specifically designed to look for life. The science package alone was projected in 1969 at $43.4 million per lander payload, enormous money at the time.
- Planetary protection was extraordinarily demanding. Because Viking was looking for Martian life, NASA had to be very sure it wasn’t detecting organisms it had brought from Earth. The assembled landers were sealed in bioshields and subjected to whole-spacecraft dry-heat sterilisation at about 112°C for more than 30 hours. Components therefore had to survive conditions that ordinary spacecraft electronics did not. The National Academies estimates that planetary-protection requirements contributed roughly $400 million to Viking’s overall cost.
- The reliability philosophy was expensive. Viking couldn’t simply use cheap commercial electronics and accept the occasional failure. Subsystems were extensively engineered, duplicated and tested because there was no possibility of repairing the spacecraft once it was on Mars. Even the science experiments were designed so that a single failure should not wipe out multiple experiments.
- It used expensive bespoke hardware. Electronics in the early 1970s were enormous by modern standards. Something that can now be done by a £10 microcontroller might then require boards full of custom components, all individually qualified for vibration, vacuum, radiation and temperature extremes.
- Later missions deliberately changed the philosophy. This is particularly striking with Mars Pathfinder. NASA says Pathfinder was being developed for about one-twentieth the cost of the Viking landers. Engineers deliberately used commercially available hardware where possible rather than reproducing Viking’s expensive custom equipment. This was part of NASA’s 1990s “Faster, Better, Cheaper” strategy.
There is another important point: Viking’s first unit effectively paid for the invention of the technology. Once you’ve spent, say, $50 million designing, qualifying and testing a system, building another copy might cost only $10 million. So comparing the Viking development cost with the later manufacturing cost of a spacecraft can be very misleading.
And Viking was unusually ambitious even by modern standards. It wasn’t simply:
“Land a box on Mars.”
It was much closer to:
“Invent a reliable way of landing on Mars, build two autonomous nuclear-powered laboratories, sterilise them sufficiently to search for extraterrestrial organisms, invent much of the instrumentation, and make everything work the first time.”
That helps explain why Viking remains one of the most expensive robotic planetary programmes ever undertaken. The two complete Viking missions cost about $1.06 billion in 1970s dollars.