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Persephone Pluto Orbiter
stevesliva
post Sep 9 2020, 07:40 PM
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Would be a worthwhile use of the space station to bolt two (or any multiple of 2) of these new improved reaction wheels to the outside, and have them apply opposite forces and stress them for a few years, starting as soon as they're ready. If they fail, could actually do PFA. Probably can't isolate them enough. Oh well.

We're headed for Chit-Chat on this one.
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HSchirmer
post Sep 9 2020, 08:06 PM
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QUOTE (stevesliva @ Sep 9 2020, 07:40 PM) *
Would be a worthwhile use of the space station to bolt two (or any multiple of 2) of these new improved reaction wheels to the outside, and have them apply opposite forces and stress them for a few years, starting as soon as they're ready. If they fail, could actually do PFA. Probably can't isolate them enough. Oh well.

We're headed for Chit-Chat on this one.

Eh, whether it's smart to use reaction wheels on a Persephone multi-year missions is on topic.

I like the "hard drives as cubesat reaction wheels" as a possible 2-for-1 (data storage AND attitude control)
Take a couple old hard drives, put in new test bearings, (metal, diamond coated metal, ceramic, magnetic) put them in a RAID array and run to failure while writing the test results to the disk.
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JRehling
post Sep 11 2020, 06:42 PM
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The long timelines for this mission suggest several obstacles beyond those of engineering. When a mission returns science only decades after it launches, one has to consider what the payoff is for the individuals and organizations involved. The true economics of space exploration has always been a little fuzzy – What makes a mission worth a certain amount of cash compared to another mission for another amount of cash? I think a mission like this pushes it beyond the breaking point of philosophy; every person involved with it would be making an investment that would not be repaid. The tenure-track professors would either have their tenure or not. The agency administrators would have moved on. Many people present at the beginning would literally be dead before the main mission commences. And if the agency depends on public goodwill for its sustained support, this is an up-front sink that might do real damage in terms of the opportunity cost. And all of that is to say nothing of the lack of continuity in the operations team and the possibility that future technology could "pass" the probe that's on the long way there and make it possible to get the same science sooner or cheaper or possibly sooner and cheaper.

I think a proposal like this is DOA out of pragmatic considerations. It's not that the science couldn't be lovely and the thought of altruistically giving the gift of that science to future generations is nice and hopeful, but for the price tag, it can't possibly beat out missions that would get some science back in the one-decade timeframe or less.
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Steve G
post Sep 11 2020, 07:19 PM
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I agree! My whole point at the beginning of this discussion, is that new low-cost SpaceX and Blue Origin launch services are game changers. For years we have minimised fuel and weight penalties and took years just to get into orbit around Mercury. Just look at BepiColombo's journey. Having the luxury of massive propellant modules will shorten trajectories, which has a cost reduction right there. Also, the emergence of cube sats offers other opportunities. Look at Rocket Lab's planned Venus mission. We'll know in the next few years how the new generation of super rockets pan out.
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HSchirmer
post Sep 12 2020, 02:43 AM
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QUOTE (JRehling @ Sep 11 2020, 07:42 PM) *
... the possibility that future technology could "pass" the probe that's on the long way there and make it possible to get the same science sooner or cheaper or possibly sooner and cheaper.

There is no paradox. Launch now based on a classic Hohmann transfer orbit.
When (not if) we do eventually develop exponentially better rockets that have torchship levels of specific impulse, we send a "helper" rocket out to dock with the probe. Then blasts along on a brachistochrone trajectory-full throttle acceleration to the half way point, flip 180', full throttle deceleration until the destination.

The next step for space exploration should be to systematically refurbish the defunct US & Russian "Keyhole" class optical spy satellites that are optimized for imaging at 250km, and put them into 250km orbits around Mercury, Venus, the Moon, Mars, large asteroids, Jupiter, Saturn, Uranus Neptune and Pluto. Every planet large circular body orbiting the sun, whether or not it has cleared it's orbit should have a re-purposed spy satellite mapping it at 6 centimeter resolution.
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stevesliva
post Sep 12 2020, 02:55 AM
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Well... the Pluto orbit mission concludes 30 years after launch in 2030, after 3 years in orbit. The additional 20 would probably be the point of substantial debate. Cassini lasted 20 years after launch.

Launch after 2032 means Jupiter's no longer in the right place... for Pluto. Makes me wonder where else direct-to-Jupiter (<1yr) + 26 yrs of electric propulsion can put you.
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