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Comment by jkestner | Hacker News Reader

So the big change seems to be foregoing the usual radiation hardened components. Was the calculation that this was less risky for planetary exploration, or the standard risk was acceptable given that it was not the central thrust of the mission? What would the total cost look like if you could launch several redundant cheap probes instead of an NASA-grade one anytime this is a question?

Interesting to see how the lithium batteries did with such extreme temperature cycling. And here I am bringing my mower batteries inside in a cold snap.

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My guess would be the latter. Ingenuity was primarily a technology demonstration whose failure wouldn't impact Perseverance's main objectives, so the risk was probably acceptable.

As for launching several cheap, redundant probes - I think the biggest issue would be the cost of the scientific instruments. I don't have the background to know how much money could be saved you by using commercially available equipment. The basic scientific requirements might be too specialized for cheap commercial equivalents to exist, though maybe not; I really don't know.

The scientific instruments need to be mass-produced, too, of course. A 7-digit number of rovers would be extremly cheap per piece. Shipping would become a problem though.

Heh. I have long advocated that we attempt dozens of "Deep Impact" style missions against the NEOs - short mission lifetime, perhaps months from launch to impact, a high launch rate - would bring the cycle time from innovation to exploration way, way down.

Unfortunately I think this will have less of an impact than many people think. As expensive as the radiation hardened hardware is, it's still series produced stuff that doesn't need reinventing for every mission. Almost all of the costs are in development of the unique scientific instruments each mission needs, and in keeping the mission teams staffed.

For example NASA's Lucy mission that launched in 2021 had a just under $1 billion budget, in which $560m was spacecraft development and $280m was for keeping a mission team staffed for 12 years. The launch on an Atlas V was $150m. What's $250k for a radiation hardened CPU in that? It's not even peanut crumbs. And as expensive as the launch was, even if SpaceX and other new launch companies drive it down by 90%, the budget for this mission would still be about a billion dollars.

Heck, even if you started series production of probes and their instruments and as such were able to amortize the development costs over a bunch of spacecraft, the fact remains that if you wanna go somewhere interesting it's gonna take years and you're gonna have to have a staff of mission specialists on retainer for most of that time. You can't disrupt away the fact that space is really big, at least not until someone discovers some new physics.

I have long advocated that we attempt dozens of "Deep Impact" style missions against the NEOs - short mission lifetime, perhaps months from launch to impact + a high launch rate - would bring the cycle time from innovation to exploration way, way down. The "Pluto Express" abuse of the word "express" rankled. Not having to fund a team for decades per single mission would be a savings also. If we shift our foci to closer targets, outside LEO, by delta-v and flight time, we will evolve our spaceflight technologies much faster. The moon is a lousy target, because landing on it, and returning from it is so hard, and Mars is too far.

Note, also, that just being on a planetary surface significantly reduces your radiation exposure even if the planet doesn't have magnetic fields. The body of the planet shields you from the sun half the time. A thin atmosphere also has some effect.

In addition, being on a planetary surface greatly reduces the thermal cycling. In free space, the instantaneous thermal gradient on your spacecraft could be several hundred degrees, which the spacecraft either has to mitigate via thermal control or it just has to take; usually it will do some of both, so the electronics do need to survive a not insignificant thermal cycle.

You never get that on Mars. The planet is a huge heat sink.

How about during the journey in space, where there's more radiation? Was any shielding provided during transport? (e.g. even from the position of sensitive components relative to the rest of the mothership).

I notice the two flight control MCU's connected to the Qualcomm CPU were still radiation-hardened.

Sure, there's some radiation, and it's shielded to some extent. But 10 mm of aluminum isn't that great at radiation shielding. The big difference is that deep space missions stay in space for decades. The rovers were in space for about a year.

My weed whacker batteries stay inside because the summer heat makes them nearly unusable.

I am surprised you are mowing the lawn and a cold snap though

Maybe it's usually stored in an unheated shed or similar.

Yeah, I keep the batteries inside in the hottest and coldest weather. That cold snap is bookmarked by spring-like weather, and the grass is lush and wet and not fun to walk in.

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