PV Gap

Alan Said:

New horizons spacecraft now in a way to fly by Pluto around 2015 is fueled by solar energy alone or what else?

We Answered:

New Horizons is powered by a Radioisotope Thermoelectric Generator. Most spacecraft are indeed powered by solar panels linked to a bank of batteries, but that would not be feasible for New Horizons. The sunlight in the outer Solar System is too feeble for solar cells to be effective. Although they are powered by the decay of Plutonium-238, they are not nuclear reactors. They are pellets of plutonium dioxide encapsulated in a heavily armored container to prevent the plutonium from escaping in the event of a launch vehicle failure that results in a crash or explosion. Plutonium 238 has a half-life of 87 years and because it emits mostly alpha particles, it it not very dangerous unless it was inhaled or ingested from a radiological point of view. Indeed, only lightweight radiation shielding is required for an RTG. Plutonium is however also a very poisonous heavy metal, which is why NASA builds as strong a container for the RTG's as possible to reduce the risk of Plutonium escaping. That is one reason it is put in RTG's in the form of an oxide and that is vitrified to further contain the Plutonium. Inside them are devices called thermocouples. As the Plutonium-238 decays alpha particles and heat are released. The heat is converted by the thermocouples to generate electrical power, which operates all of New Horizon's systems. The advantage of this system over a nuclear reactor is there's no way for it to melt down or go "runaway." They cannot explode, nor can they cause a massive radiation release because the amount of fuel they carry is very small. Plutonium-238 cannot be used to build nuclear weapons either. They are compact, radiation proof and will generate power for decades no matter how the spacecraft is oriented with respect to the Sun. As they Voyagers have shown, they will operate even in interstellar space. They gradually produce less and less electricity over time, and eventually New Horizons will not have enough power to run it's instruments and it's other systems. At that point it's mission will end and New Horizons will become mankind's fifth piece of interstellar space junk as well as time capsule.