Powering Long-Distance Probes

[ThankQ]

Every once in a while you hear someone talking about sending missions outside the solar system. Our present speed limitations are fairly well discussed, but lets say someone wanted to plan a 300 year Oort Cloud mission using current propulsion technology.
Do we have the technology to power a probe so its instruments would still have energy after all that time? Does anyone know the reasonable maximum battery life we could achieve today? What about the unreasonable maximum battery life, you know, if someone gave you a $10 trillion budget.

 

[Ar-Pharazon]

I imagine, using current tech, it would require nuclear power. Though I don't know what specific kind of fuel might last that long.

 

[Dryson]

I imagine, using current tech, it would require nuclear power. Though I don't know what specific kind of fuel might last that long.

The Curiosity Rover uses nuclear power and is able to operate for fourteen years.

http://science.howstuffworks.com/mars-curiosity-rover4.htm

New Horizons Space Probe

http://www.space.com/27989-new-horizons-pluto-mission-explained-infographic.html

 

[Ar-Pharazon]

Wouldn't a larger amount and/or different type of nuclear fuel last longer?

I mean, the stuff they take out of power plants has to be stored for centuries, right?

 

[ThankQ]

NH has 24 lbs of plutonium for 30 years of life. How long would would it take to produce 250 lbs of Pu-238 (assuming 10x the fuel means 10x the life) it would take for a 300 year mission?

 

[Dryson]

NH has 24 lbs of plutonium for 30 years of life. How long would would it take to produce 250 lbs of Pu-238 (assuming 10x the fuel means 10x the life) it would take for a 300 year mission?

I wasn't able to get an exact measurement but based on the Wiki about Plutonium it would take 2 to 3 years to produce 100kg of plutonium.

https://en.wikipedia.org/wiki/Plutonium-238

 

[Santaman]

https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

It seems the best option is Plutonium-238 which has a half-life of 87.7 years, according to the article it will lose 0.787% per year, for example, the powersources inside the Voyager probes have lost 16.6% since they were launched.

 

[Dryson]

https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

It seems the best option is Plutonium-238 which has a half-life of 87.7 years, according to the article it will lose 0.787% per year, for example, the powersources inside the Voyager probes have lost 16.6% since they were launched.

A 16.6% loss in power source is a lot to lose. I would have to figure that within a few years that the percentage of loss would dwindle close to zero as the loss in power itself is converted into a useable power source.

 

[Asbo Zaprudder]

You've never heard of exponential decay then?
http://mathworld.wolfram.com/ExponentialDecay.html
https://en.wikipedia.org/wiki/Exponential_decay

 

[MacLeod]

Wouldn't we just have to work backwards to determine how much fuel we needed to power the instruments in x years if we laucnhed a probe today?

 

[2takesfrakes]

Perhaps, a solar sail could be used to trap and store solar wind, in some manner? That's a lot of free energy to let go to waste ...

 

[Asbo Zaprudder]

Yeah, just scale up the amount needed or use a longer-lived isotope of Curium or Strontium, or, better than an RTG, use a proper fission reactor as proposed in the cancelled JIMO. Not sure of the potential lifespan of such a reactor though.

https://en.wikipedia.org/wiki/Jupiter_Icy_Moons_Orbiter
https://en.wikipedia.org/wiki/Nuclear_power_in_space
http://www.world-nuclear.org/info/N...ications/Transport/Nuclear-Reactors-for-Space

Even though it'd be a good use of the world's atomic weapons' stockpile, people such as Michio Kaku wouldn't approve of the safety aspects of launching tons of radioactive material into space.

http://atomicinsights.com/michio-kaku-long-history-antinuclear-activism/

ETA: Re the solar wind, that's usable only as far as the heliopause where the solar wind decelerates on encountering the interstellar medium - about 120 AU out from the Sun.

https://en.wikipedia.org/wiki/Heliosphere

 

[Dryson]

Perhaps, a solar sail could be used to trap and store solar wind, in some manner? That's a lot of free energy to let go to waste ...

http://www.planetary.org/explore/projects/lightsail-solar-sailing/
http://www.space.com/29628-lightsail-solar-sail-success-photo.html

That is an interesting concept 2takesFrakes. Trapping solar wind to use later as a source of power is genius.
All you have to do is figure out how to convert solar wind into a storable energy that is then able to be used to power a propulsion system.

Even though it'd be a good use of the world's atomic weapons' stockpile, people such as Michio Kaku wouldn't approve of the safety aspects of launching tons of radioactive material into space.

http://history.nasa.gov/conghand/nuclear.htm

If a way could be found to shield a craft from the the radiation produced then using a nuclear detonation as a propulsion system would be feasible.

http://cygo.com/space-radiation-shielding/

Demron might work as a shielding.

http://cygo.com/space-radiation-shielding/

 

[Ronald Held]

Using Pu for power is still reasonable, as you know the decay rate. You can make certain you have enough power for your encounter snd a plan to turn off equipment as the power generated decreases.

 

[JoeZhang]

If you want to know how far we have got:

http://stuffin.space/

 

[publiusr]

Yeah, just scale up the amount needed or use a longer-lived isotope of Curium or Strontium, or, better than an RTG, use a proper fission reactor as proposed in the cancelled JIMO. Not sure of the potential lifespan of such a reactor though.

https://en.wikipedia.org/wiki/Jupiter_Icy_Moons_Orbiter
https://en.wikipedia.org/wiki/Nuclear_power_in_space
http://www.world-nuclear.org/info/N...ications/Transport/Nuclear-Reactors-for-Space

I heard that JIMO might have been too much for a single Delta IV heavy to carry. Falcon Heavy/SLS could launch it in one shot and send it out of our gravity well--without it having to do a slow spiral up--eating up its service life. I might still put smaller RTGs on it, just in case.

You can never have too much power.

I like radiators better than solar panels. They are not as pickly as to the direction they are pointed--and actually work best edge on the the sun--which is how they would be oriented--heading out at least.

 

[Asbo Zaprudder]

One idea for JIMO was to launch it in two parts and assemble in LEO, which I believe was thought added too much complexity and risk at the time. Anyway, it never got funded.

 

[publiusr]

I hope that changes in the future. I want to see hydrogen pursued with new interest.
Not just for new large engines--as here: http://forum.nasaspaceflight.com/index.php?topic=39413.0
But for NERVA type systems.

Thebig push seems to be for methane--but I want better specific impulse. To reach this new "Planet X" everyone talks about--something even more powerful than JIMO may be needed--even more power.

Say a big DUMBO NTR for a Centaur and a souped up JIMO/TAU type craft