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Old September 18th 19, 03:48 PM posted to sci.space.policy
David Spain
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Default Meet The Nuclear-Powered Self-Driving Drone NASA Is Sending To AMoon Of Saturn

On 2019-09-17 1:33 PM, wrote:
Which is not to say that the idea of a nuclear-powered drone flying around a moon
of Saturn doesn't sound kind of crazy."

See:

https://www.npr.org/2019/09/17/76064...moon-of-saturn


This is pretty tame nuclear technology. A low power RTG. A quick
websearch (DuckDuckGo don't be evil) to Wikipedia yields three links:

https://en.wikipedia.org/wiki/Dragonfly_(spacecraft)
http://www.lpl.arizona.edu/~rlorenz/jbis.pdf
https://dragonfly.jhuapl.edu/News-an..._03-Lorenz.pdf

From the third link see section titled Power 2.1 (pgs 223-224). The two
main points:

1) Titan is Very Cold (you will need ample energy to heat the probe)
2) Titan is Very Dark (no solar cells)

What is interesting is the analysis of why not just bring O2 to combust
with the abundant methane already in Titan's atmosphere? The problem is
the ambient temperature. Combustion products emitted by an APU like
combuster would freeze quickly and could potentially block an exhaust
port. Monoprop hydrazine has a similar issue. Also the fact that you
need two molecules of oxygen to burn one of methane and thus only 50%
better than bringing both fuel and oxidizer from Earth. Thus a big
oxygen tank is needed, brought all the way from Earth.

The second link to the most recent paper proposes an Multi-Mission
Radioisotope Thermal Electric Generator to recharge an on-board battery
pack with efficiencies similar to the batteries used in a Tesla. Thus I
presume we are talking some type of Lithium-Ion. I'm assuming they are
using a hybrid RTG/Li-Ion battery power system in order to supply the
higher electric energy demand needed to power the quad-copter motors. I
believe this is the weakest link in the proposed design because the
batteries do add a lot of mass to the probe. Both the 2018 and 1999
papers leave the exact RTG technology to be used also somewhat
undefined. IMO I think they need to nail the energy budget first to come
up with the requirements needed of a workable power unit and stop
writing about up-and-coming power technology. Go with what you can have
in hand now or don't commit to a launch date.

I assume the crash scenario would only be for an unintended loss of
control, not because you fly it when power is no longer nominal for
flight. I suspect the RTGs are heavy duty enough likely to survive a
fall in Titan's very low gravity. I doubt the shielding of the device
would even be breached. So effectively, what would happen to any
potential life on Titan should the probe crash? Nothing.

The link to the third paper is quite old (1999). For the purposes of
discussion I challenge other readers to due some research and update the
information I have provided to something more recent. (Gosh! You mean to
actually do some RESEARCH before commenting here?).

Dave