RTG operations, I have questions, anyone know the answer?

[gunsandrockets]

Okay, I'm sure most of you are somewhat familiar with the RTG power source, the Radioisotope Thermoelectric Generator, which produces power from the heat generated by the radioactive decay of an unstable isotope, typically Plutonium 238.

http://en.wikipedia.org/wiki/Radioisoto ... _generator

It's clear enough to me how this system operates in a space environment. What I'm wondering about is what about beforehand? When the RTG is crammed into a sealed up launch fairing, or worse sealed up inside an aeroshell for Mars entry such as the Viking spacecraft was or the soon to be launched Mars Science Laboratory. An RTG isn't like a reactor, an RTG has no off switch and it's always on, pumping out heat. So in the crammed environment of a launch vehicle where does that heat go? Does a launch vehicle have to provide some kind of supplemental cooling system to deal with RTG emissions?

If someone knows about this, please provide the answer and I would also appreciate any links to sources of info on the web.

Thanx

 

[aphh]

I'm no expert, but absolutely the heat would need to be vented out from the vehicle. It is just like you said, once the RTG has been sealed, there is no off switch. The heat is produced by the radioactive decay of the element, and also the decay products hitting the container walls.

Element that has also been used for RTG's is Polonium, which has isotopes to last for about six months. Russians used Polonium RTG's on their lunar rovers to keep the rovers from freezing during the lunar nights. Polonium is also relatively safe material to launch to space, the decay products are thermal energy and alpha particles (helium nucleus) producing only alpha radiation, which is relatively harmless (unless ingested, that is).

I have a feeling that Polonium RTG's could be useful in the coming moon projects aswell.

 

[js117]

Element that has also been used for RTG's is Polonium, which has isotopes to last for about six months. Russians used Polonium RTG's on their lunar rovers to keep the rovers from freezing during the lunar nights. Polonium is also relatively safe material to launch to space, the decay products are thermal energy and alpha particles (helium nucleus) producing only alpha radiation, which is relatively harmless (unless ingested, that is).

I think the isotopes will last a lot longer then that ( six month ).
The RTG that is on New Horizons the prube that is going to dwarf planet Pluto


NewHorizon
FROM http://en.wikipedia.org/wiki/New_Horizons
Power
A cylindrical radioisotope thermoelectric generator, or RTG, protrudes from one vertex in the plane of the triangle. The RTG will provide about 240 W, 30 V DC at launch, decaying to 200 W at encounter in 2015. The RTG, model "GPHS-RTG," was originally a spare from the Cassini mission. The RTG contains 11 kg (24 lb) of plutonium-238 oxide pellets. Each pellet is clad in iridium, then encased in a graphite shell.



Voyager program

http://en.wikipedia.org/wiki/Voyager_program

Power

Radioisotope thermoelectric generators for the Voyager program.Electrical power is supplied by three radioisotope thermoelectric generators (RTGs). They are powered by plutonium-238 (distinct from the Pu-239 isotope used in nuclear weapons) and provided approximately 470 W at 30 volts DC when the spacecraft was launched. Plutonium-238 decays with a half-life of 87.74 years,[5] so RTGs using Pu-238 will lose a factor of 1 - 0.5{1/87.74} = 0.78% of their power output per year. In 2006, 29 years after launch, such an RTG would produce only 470 W × 2-(29/87.74) ~= 373 W — or about 79.5% — of its initial power. However, the bi-metallic thermocouples that convert heat into electricity also degrade, so the actual power will be even lower. As of August 11 2006, the power generated by Voyager 1 and Voyager 2 had dropped to 290 W and 291 W respectively, about 60% of the power at launch. This is better than the pre-launch predictions based on a conservative thermocouple degradation model. As the electrical power decreases, spacecraft loads must be turned off, eliminating some spacecraft capabilities.

 

[aphh]

I think the isotopes will last a lot longer then that ( six month ).
The RTG that is on New Horizons the prube that is going to dwarf planet Pluto

Interplanetary probes use Plutonium-238 powered RTG's, that produce energy for years but would be a great hassle and a security risk to launch to space.

Polonium-210 has the half life of 138 days, which would be suitable for missions that last for weeks or a few months. Po-210 is what Russians used on their lunar rovers. The element has great energy density and does not produce highly radioactive decay products, obviously the shelf and operational life of Polonium powered RTG is limited.

 

[dangineer]

I believe the heat is all conducted away from the spacecraft. While it's in the fairing, it's probably connected to the fairing and the fairing is used as a heat sink. I couldn't find any sources on this, but it seems like the most straightforward way.