Trying to understand the different nuclear powered spacecraft?

Well…what a confuse quote.

There is first of all nuclear electric propulsion, which use a nuclear reactor for producing electricity and then use this electricity for accelerating ions by electrostatic or electromagnetic fields, using these ions as reaction mass for producing a low thrust.

There is still no existing satellite that uses any nuclear reactor for propulsion.

There are two ways to produce electricity with nuclear reactors: Either by a liquid or gas and a turbine, or by thermal ions. The latter requires much higher temperatures, and thus higher radiation and shorter life times of the reactor, but is also much more effective. Nuclear reactors in space don’t need as much gear and shielding around them as you need on Earth – for controlling nuclear reactors in space, it is enough to open windows in the reactor case to eject neutrons into space instead of reflecting and moderating them back into the reactor fuel.

But there are also other forms like nuclear thermal rockets, which directly inject hydrogen into the reactor core, heat the hydrogen into hot gas and then eject this hot gas through a nozzle. The only nuclear propulsion concept that violates the nuclear testing treaties is the Orion drive, a system which fires nuclear warheads at high rate behind the spacecraft and lets the spacecraft ride on the explosion shock wave after every explosion. Nuclear explosions in space are banned.

But nuclear reactors in space are not uncommon, both USA and Russia operated satellites with nuclear power. The Russians operated more of them, and caused thus also more problems with them. Add the end of the lifetime of such a satellite, the satellite had to maneuver into a higher orbit, eject the nuclear reactor core and propel it by solid rocket motor into a graveyard orbit. Which did not always work. One nuclear satellite crashed in Canada some years ago, was a big mess. And even if it worked, the NaK reactor coolant is now forming a big cloud around Earth, which damages satellites in this region.

Nuclear power is really the best option for long-distance manned spaceflight, but not without prizes. The spacecraft with nuclear power are generally much larger than a minimum spacecraft with chemical propulsion, since you need large radiator surfaces for producing power with the nuclear reactors. The rule of thumb is: For each kilowatt of electrical power, you need 6 kilowatt thermal energy. And depending on the radiator temperature, you can eject about 85 W thermal power with one square meter of radiator surface. Higher radiator temperatures allow smaller radiators, but also require higher operation temperatures inside the spacecraft – for using this option for manned spacecraft, you would need to have a high-temperature radiator for the propulsion system and a low-temperature radiator for the crew section. Which makes things more complicated.

One Response

Urwumpe says:

July 2, 2010 at 2:32 pm

Well…what a confuse quote.

There is first of all nuclear electric propulsion, which use a nuclear reactor for producing electricity and then use this electricity for accelerating ions by electrostatic or electromagnetic fields, using these ions as reaction mass for producing a low thrust.

There is still no existing satellite that uses any nuclear reactor for propulsion.

There are two ways to produce electricity with nuclear reactors: Either by a liquid or gas and a turbine, or by thermal ions. The latter requires much higher temperatures, and thus higher radiation and shorter life times of the reactor, but is also much more effective. Nuclear reactors in space don’t need as much gear and shielding around them as you need on Earth – for controlling nuclear reactors in space, it is enough to open windows in the reactor case to eject neutrons into space instead of reflecting and moderating them back into the reactor fuel.

But there are also other forms like nuclear thermal rockets, which directly inject hydrogen into the reactor core, heat the hydrogen into hot gas and then eject this hot gas through a nozzle. The only nuclear propulsion concept that violates the nuclear testing treaties is the Orion drive, a system which fires nuclear warheads at high rate behind the spacecraft and lets the spacecraft ride on the explosion shock wave after every explosion. Nuclear explosions in space are banned.

But nuclear reactors in space are not uncommon, both USA and Russia operated satellites with nuclear power. The Russians operated more of them, and caused thus also more problems with them. Add the end of the lifetime of such a satellite, the satellite had to maneuver into a higher orbit, eject the nuclear reactor core and propel it by solid rocket motor into a graveyard orbit. Which did not always work. One nuclear satellite crashed in Canada some years ago, was a big mess. And even if it worked, the NaK reactor coolant is now forming a big cloud around Earth, which damages satellites in this region.

Nuclear power is really the best option for long-distance manned spaceflight, but not without prizes. The spacecraft with nuclear power are generally much larger than a minimum spacecraft with chemical propulsion, since you need large radiator surfaces for producing power with the nuclear reactors. The rule of thumb is: For each kilowatt of electrical power, you need 6 kilowatt thermal energy. And depending on the radiator temperature, you can eject about 85 W thermal power with one square meter of radiator surface. Higher radiator temperatures allow smaller radiators, but also require higher operation temperatures inside the spacecraft – for using this option for manned spacecraft, you would need to have a high-temperature radiator for the propulsion system and a low-temperature radiator for the crew section. Which makes things more complicated.

Popular Phrases

Categories

One Response

Trying to understand the different nuclear powered spacecraft?