By the mids, research had begun in earnest on ways to use nuclear power in space. These efforts resulted in the first radioisotope thermoelectric generators RTGs , which are nuclear power generators built specifically for space and special terrestrial uses. These RTGs convert the heat generated from the natural decay of their radioactive fuel into electricity. Today, RTG-powered spacecraft are exploring the outer planets of the solar system and orbiting the sun and Earth.
They have also landed on Mars and the moon. They provide the power that enables us to see and learn about even the farthermost objects in our solar system. Read more Read less. Kindle Cloud Reader Read instantly in your browser. Product details File Size: April 21, Sold by: Related Video Shorts 0 Upload your video.
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Set up a giveaway. As the material naturally decays, it produces heat. The other main component of the RTG, the thermoelectric generator, converts this heat into electricity. This heat-to-electricity conversion occurs through the thermoelectric principle discovered early in the last century. This principle is a way of producing electric current without using a device that has moving parts.cars.cleantechnica.com/medialengua-moiti-langue-petits-pomes-et.php
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It involves two plates, each made of a different metal that conducts electricity. Joining these two plates to form a closed electrical circuit and keeping the two junctions at different temperatures produces an electric current. These pairs of junctions are called thermocouples. In an RTG, the radioisotopic fuel heats one of these junctions while the other junction remains unheated and is cooled by space. RTGs are reliable because they produce electricity without moving parts that can fail or wear out.
This high degree of reliability is especially important in space applications, where the investment is great, and repair or replacement of equipment is not feasible. Although other radioactive fuels have been considered for RTGs, plutonium Pu has been used most widely. Pu is a radioactive isotope -- a form of plutonium that gives off energy as rays and particles.
It continues to be the radioactive fuel of choice today and in planned future missions. What qualities make Pu a good choice for fuel in an RTG?
Its half-life is one of the most important. Half-life is the time it takes for half of the radioactive material to decay. At the end of that time, the amount of radioactive material remaining is half of the original amount. This means there is only half the heat available for conversion into electric energy.
Longer space missions require a radioisotope with a longer half-life. Pu, with its half-life of For example, after five years, approximately 96 percent of the original heat output of Pu is still available. Because the nuclear fuel in RTGs is radioactive, safety is a critical issue. As it decays, Pu emits radiation mainly in the form of alpha particles, which have a very low penetrating power.
Only lightweight shielding is necessary because alpha particles cannot penetrate a sheet of paper. Radioisotopes producing more penetrating radiation, such as beta or gamma particles, would be more difficult to handle safely and would require heavier shielding, a distinct drawback on space missions. The weight and volume of solar panels can cause problems on some space missions. With RTGs, weight and volume are far less of a concern. Pu has a relatively high power density, and a given volume or weight of Pu can produce a relatively high number of watts of power for long periods of time.
These qualities lead to smaller and lighter heat sources than comparable power levels from other sources. This makes Pu fuel an efficient power producer for the space it occupies and the weight it adds to a mission. Any penetrating radiation that escapes a radioisotope heat source is of potential concern.
RTG safety efforts revolve around containing the radioactive fuel in case of accident during a critical time in the mission, such as launch or re-entry.
Multiple layers of special material enclose the plutonium fuel to contain it under both normal and accident conditions. Extensive testing and analysis are used to demonstrate that safety design criteria are met. Today we design to have the fuel capsule remain intact even after Earth re-entry and impact. The Apollo 13 accident and subsequent re-entry of the RTG, without any material release, provided further proof of this safety principle. The basic heat source unit is the GPHS module.
The pellets are also highly resistant to vaporizing or fracturing into breakable particles following impact on hard surfaces. These capsules about the size and shape of a marshmallow would tend to stretch or flatten instead of ripping open if the GPHS module struck the ground at high speed. This would help keep the capsules intact and contain the fuel. The graphite impact shell is designed to limit damage to the iridium fuel capsules from free-fall or explosion fragments. It serves as a shield designed to with stand the heat of re-entering Earth's atmosphere in case of an accident.
The nuclear fuel in the GPHS faces a variety of possible accidents during a space mission. Launch and re-entry pose many types of risks to the spacecraft and its components. As a result, rigorous testing is conducted to ensure the RTG's nuclear fuel will survive a launch accident or other mishap, remain intact, and contain the fuel. The battery of tests that the GPHS's fuel modules have undergone included the effects of: Fire - Direct exposure to solid propellant fires, such as the GPHS might encounter in a launch accident, produced minimal damage and no nuclear fuel release.
Blast - The modules survived the high temperatures of simulated atmospheric orbital decay entry, as tested in an arc-jet furnace, no fuel was released. Earth Impact - Impact at miles per hour approximate top speed for an aeroshell falling to Earth on sand, water, or soil produced no release of heat source module fuel. Impact on rock and concrete sometimes produced releases, but much of the fuel was retained by the surrounding graphite module, leaving only small amounts of low-level radioactive material to enter the localized environment.
Immersion in Water - Long-term exposure to the corrosive effects of seawater showed the iridium capsule is corrosion-resistant and the fuel itself is highly insoluble. Shrapnel - Researchers used aluminum and titanium bullets to simulate the small fragments that might be present in a launch vehicle explosion. Speeds of test fragments exceeded those predicted for an actual explosion. Large Fragments - In tests representing solid rocket booster failures, steel plates were fired at simulated RTGs.
Some unlikely events, such as impact with the edges of steel plates, caused some release in a few fuel capsules. More likely events, such as impacts with the faces of steel plates, did not produce a release. The safety tests demonstrated that the RTGs are extremely rugged and capable of meeting the design objective to prevent or minimize any fuel release.
Other nuclear generator technologies for space applications have been under investigation. These technologies involve more efficient conversion of heat into electricity. Safety and reliability are key factors in determining the possible value of each technology in space missions. One option is the dynamic isotope power systems DIPS , which are much more efficient in converting heat into electricity than the RTGs used on recent missions. The dynamic systems have moving parts that transform heat into mechanical energy, which is used to generate electricity.
One such engine, the Stirling engine, contains helium that expands by absorbing heat on the hot side of the engine and rejecting it on the cold side. The rapidly changing pressure cycles cause a piston to move back and forth, driving an alternator and producing electricity. The range of technologies under investigation is wide.
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By contrast, the thermo-photovoltaic TPV converter changes infrared radiation emitted by a hot surface into electricity. The higher efficiencies of these new technologies mean that future spacecraft may require less Pu than RTGs typically use. This makes these new space power technologies highly attractive due to lower weight and less radioactive material for the same power output.
The Cassini mission is scheduled to begin in October when a Titan IV launch vehicle lifts its payload into orbit. The mission is a joint U. Like Galileo, Cassini will use gravity-assists from other planets to achieve the necessary speed to reach Saturn. Cassini will employ four flybys: Scientists have an intense interest in the Saturnian system - an interest beyond the planet's vast and beautiful system of rings.
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Saturn's largest and most intriguing moon, Titan, has a dense atmosphere that resembles the Earth's early atmosphere, and some scientists suggest there may be oceans on Titan. National Energy Technology Laboratory. Department of Energy Compilation. Science Applications Intern Corporation. To add more books, click here. Just a moment while we sign you in to your Goodreads account. Department of Energy it was amazing 5. Rate this book Clear rating 1 of 5 stars 2 of 5 stars 3 of 5 stars 4 of 5 stars 5 of 5 stars.
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