Three spacecraft heading to Mars this summer

My understanding is that there is a dedicated team for each probe on the ground, so two rovers = two teams, twice the cost to support. Or am I wrong?

The launch cost isn't low. They're using an Atlas V-541 from UAL. The program cost is equivalent to about 10% of NASA's annual budget, which is a lot. Mars and the rovers are just one corner of NASA's focus.

It would cost a minimum of another $2 billion to duplicate this rover and mission, if you can find enough qualified people to task to it so as to not harm (by dilution) your ability to deliver on at least one of them. NASA's resources and talent pool are both very much limited.

I'm pretty sure what makes that stuff so expensive is all the Quality Control for every single part.

Its probably quite a linear cost vector they have.

A major point missed by the other answers is that these rovers are exceptionally specialized for their mission, so building a second rover wouldn't be able to accomplish many additional scientific goals, without major modifications. The Curiosity rover and Perseverance share a lot of components, but pretty much the entire science suite is replaced or upgraded. As such, the expensive parts weren't shared, even though the huge value of the bus/bogie system and the skycrane were shared. Even the EDL systems have been changed a lot; the entry system on Perseverance does localization during some phases with a camera (a first for a spacecraft afaic, maybe the shuttle counts though since a human eyeball steered it to a runway). If you don't have additional science objectives that a second rover could accomplish, it will be very hard to justify that budget, even if it is only 20% more (for example).

This being said, clever mission design might take advantage of this cost structure where multiple units are cheaper to build, intending to build two cheaper spacecraft instead of one expensive one; eggs in two baskets. In this case, we've seen this happen with spirit and opportunity, which was a wildly successful program.

Sometimes NASA does send duplicates, including for Rovers. Spirit and Opportunity were identical. If all missions had a duplicate, we would have spent money to build an additional 15 spacecraft, and that would have only saved zero to two missions.

I'd guess it boils down to the relative expected contributions of random errors/failures vs. systematic errors/failures. Many failures were design flaws that would have created identical failures in any duplicate spacecraft of the same design. In that case, spending the money on two separate missions with unique hardware would have a higher return on investment than spending twice the money on one mission where either both spacecraft succeed and collect somewhat redundant data, or both fail and collect nothing.

Looks like NASA has attempted 28 missions to Mars, and four of these involved Rovers. All 4 Rovers have been successful. If NASA sent two rovers together each time, they'd simply have spent 1.5x money and completed the same # of missions.

Out of all 28 Mars missions NASA attempted, only 6 had some kind of failure:

- Mariner 3 and Mariner 4 were identical probes launched 23 days apart. Mariner 3 failed. We never figured out the root cause of Mariner 3 failure. Mariner 4 worked just fine.

- Mariner 8 and Mariner 9 were identical orbiters launched 21 days apart. Mariner 8 failed due to a botched installation of a diode onto a PCB which damaged that diode. Mariner 9 was successful.

- Mars observer failed. Root cause was never 100% definitively determined but NASA's final report focused on the hypothesis "that 2 grams of nitrogen tetroxide slowly leaked through a valve during the 11 months the Mars Observer was in space. When the fuel system was pressurised, the nitrogen tetroxide mixed with monomethyl hydrazine – an explosive combination....If NASA’s managers had studied the design well enough to understand its limitations, they could have taken steps to prevent the failure by periodically purging the fuel line." It sounds like a duplicate would have had the same problem -- increased costs for no benefit.

- Mars Climate Orbiter failed due to a software bug. Any duplicate mission definitely would have had the same bug and failed in exactly the same way -- increased costs for no benefit.

- Mars Polar Lander failed due to a software bug. It's not 100% certain that the bug would have been triggered by a duplicate mission, but it's reasonably likely. "The Failure Review Board concluded that the most likely cause of the mishap was a software error that incorrectly identified vibrations, caused by the deployment of the stowed legs, as surface touchdown. The resulting action by the spacecraft was the shutdown of the descent engines, while still likely 40 meters above the surface. Although it was known that leg deployment could create the false indication, the software's design instructions did not account for that eventuality."[1] I'd personally chalk a duplicate up to increased costs for no benefit, but an expert's interpretation may vary.

- Deep Space 2 failed, no root cause identified. 2 possibilities identified were design flaws, which could have affected a duplicate as well. 4 possibilities involved bad luck in landing so it's possible a duplicate would have had better luck.

So, if all missions had a duplicate, we would have spent money to build an additional 15 spacecraft, and that would have only saved zero to two missions.

[0] https://www.newscientist.com/article/mg14119080-300-cheap-de...

[1] https://en.wikipedia.org/wiki/Mars_Polar_Lander

This is exactly what they did with Opportunity and Spirit: https://en.m.wikipedia.org/wiki/Mars_Exploration_Rover

I think is is largely due to budget reasons, though.

Yes. Consider the Hubble space telescope. I would expect that building a pair rather than one wouldn't cost that much more than one, especially if they were built side by side.

This would likely have been far, far cheaper than the repair mission sent to fix the sole Hubble.

"First rule in government spending: why build one when you can have two at twice the price? Only, this one can be kept secret. Controlled by Americans, built by the Japanese subcontractors. Who, also, happen to be, recently acquired, wholly-owned subsidiaries..."

https://www.imdb.com/title/tt0118884/quotes/qt1542424

NASA is pretty budget constrained. But they also admit to a risk-adverse culture. Part and parcel of having a safety first mission oriented to human spaceflight. I think your right and they would agree. We'll probably take much more risk very shortly, or fund entrepreneurial partnerships willing to do so. SpaceX has changed the game.

The other thing is if you look at the choice of Jezero Crater as the landing zone for the Mars 2020 Perseverance mission. The quality of high resolution astrogeological maps, atmospheric surveys, and even computer simulations is good enough today that we can predict right here on earth where evidence of fossilized life may be found, where rich deposits of silica aerogel may be located for terraforming, where the mineral deposits of niobium and tantalum are likely to be.

The duplicate is almost always called EDU and stays in a cleanroom on the ground for troubleshooting.

> probably very unlikely

Literally astronomically unlikely. If at all they might want to coordinate radio emissions.

COTS sensors don't work well in a high radiation environment.

isn't transmission bandwidth a bigger concern?