Persephone Pluto Orbiter Options

[stevesliva]

From fall 2020 OPAG https://www.lpi.usra.edu/opag/meetings/opag2020fall/

Persephone:
https://www.lpi.usra.edu/opag/meetings/opag...Howett_6005.pdf

There is talk of extended missions out to 2079. Building cathedrals for our grandkids here...

[Explorer1]

The Voyagers have lasted that long, we know.
Slide 40 (Data volume) is particularly poignant and rams home the scale, in time and space, of these endeavors: 584 megabytes of data over a generation; that's not even an hour episode of a TV show today. How much smaller will that seem by the 2070s? I cannot imagine.

[volcanopele]

I think that's supposed to be 584 Gb over the course of the Pluto tour which seems pretty good given the distance.

[Explorer1]

Yes, I missed the digits. Still pretty modest by the next half century's standards, I would guess.

[vjkane]

Biggest problem that I see is finding the plutonium for 5 RTGs. I don't believe that the production rate would allow that in the next decade. And we probably are in game of which mission gets the Pu: Ice giants orbiter, Pluto mission, Enceladus lander, Europa lander, something else?

[Steve G]

About that 27 years trajectory . . . That puts a lot of lifetimes to the wayside when it arrives. With a launch ten years from now, new and better rockets may be available, such as StaceX's Starship should it deliver to expectations, or even Blue Origin's New Armstrong (should it be ever come to pass). If launch costs are reduced by the new (reusable) space rockets along with the massive payloads they are advertising, you could conceivably launch it really fast with loaded with tons of fuel and jam on the breaks hard. That would cut trajectory significantly. Based on the cost per flight, SLS may not even be around by then.

[Steve G]

Posted in error

[Explorer1]

If launch costs are reduced by the new (reusable) space rockets along with the massive payloads they are advertising, you could conceivably launch it really fast with loaded with tons of fuel and jam on the breaks hard. That would cut trajectory significantly. Based on the cost per flight, SLS may not even be around by then.

The trouble is, what sort of fuel will last long enough on the journey to still be available for a Pluto orbit insertion? Cryogenic fuels like liquid hydrogen tend to evaporate, don't they? Would solids be better (like for the Mars Ascent Vehicle being planned?)

[Steve G]

Cassini used a Bipropellant system- Nitrogen Tetroxide (NTO)/Monomethylhydrazine (MMH). Solids would be more reliable, but less flexible.

[HSchirmer]

The trouble is, what sort of fuel will last long enough on the journey to still be available for a Pluto orbit insertion? Cryogenic fuels like liquid hydrogen tend to evaporate, don't they? Would solids be better (like for the Mars Ascent Vehicle being planned?)

IIRC, ESA has been looking at hydrogen peroxide monopropellant for attitude control thrusters; and New Shepherd used hydrogen peroxide and kerosene for their oxidizer and fuel. So some propellant combinations could do double duty.

With RTG supplying electric , more likely an ion drive for long term course correction, and reaction wheels for fine attitude control. Would need a battery to store power for fast slewing at encounter, so you might still need thrusters as a backup if the reaction wheels failed.

IIRC some papers found that eddy currents from solar storm could cause arcing across the bearings that chews them up and causes failure; but until somebody perfects and proves ceramic bearings work on reaction wheels, you'll have redundant systems.

[stevesliva]

I wanted to see if you recalled correctly, because I myself could not recollect this:
https://hackaday.com/2018/09/11/do-space-pr...-space-weather/

[mcaplinger]

With RTG supplying electric , more likely an ion drive for long term course correction, and battery powered reaction wheels for attitude control

Persephone already uses electric propulsion, though the viewgraphs are not terribly clear about exactly how the orbit insertion works -- it takes almost 10 years between the KBO flyby and arrival at Pluto. If you want really fast transit times, electric probably won't help. But you are talking a lot more launch vehicle delta-V than anything available now.

Solids have no particular advantages over storable biprops. A solid motor was used for Magellan; it worked but would not be anyone's first choice.

[HSchirmer]

I wanted to see if you recalled correctly, because I myself could not recollect this:
https://hackaday.com/2018/09/11/do-space-pr...-space-weather/

In 2013, they figured launch shaking or radiation.

Launch damage or radiation are most likely causes, says CEO of reaction wheel company
https://spectrum.ieee.org/tech-talk/aerospa...ght-have-failed

By September 2017 they had research and published a paper

CONCLUSIONS
The anomalous friction increases and failures of ITHACO RWAs on the FUSE, Kepler and other spacecraft are the result of the space environment, and likely space charging. This is based on strong statistical correlation of events with geomagnetic storms, and simultaneity of events on different RWAs during geomagnetic storms. Duplication of friction events in the laboratory by applying small voltages across the rotating bearings supports this conclusion. Finally all metal ball bearing control wheels for satellites may be similarly impacted as discussed, when operated in these adverse space weather conditions
http://esmats.eu/esmatspapers/pastpapers/p...2017/bialke.pdf

About a year later that led to a Youtube episode on reaction wheels that has about 700,000 views.

https://www.youtube.com/watch?v=KibT-P...re=emb_imp_woyt[/url] ]

Time to put up some cubesats for small scale testing of different types of bearings.

Hard Disk Drive Based Reaction Wheels for CubeSat Attitude Control
August 2017 DOI: 10.2514/1.A33866
https://www.researchgate.net/publication/31...de_Control#read

[mcaplinger]

But it was sorta suspected issue that radiation was doing something.

There's no consensus that this has anything to do with the failures as far as I know. But Ithaco has started using ceramic bearings so maybe that will help if this was the root cause.

Note that Persephone would have 5 reaction wheels total, 2 for sparing.

[HSchirmer]

There's no consensus that this has anything to do with the failures as far as I know.

Technically radiation and magnetic/electric fields.

Corrected above, added the reaction wheel company's September 2017 "tech service bulletin."