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103-511: SNAP-10A ( Systems for Nuclear Auxiliary Power , aka Snapshot for Space Nuclear Auxiliary Power Shot , also known as OPS 4682 ) was a US experimental nuclear powered satellite launched into space in 1965 as part of the SNAPSHOT program. The test marked both the world's first operation of a nuclear reactor in orbit, and the first operation of an ion thruster system in orbit. It is the only fission reactor power system launched into space by

206-519: A Thor-Ablestar rocket carrying the Transit 5BN-3 satellite failed to reach orbit, destroying the satellite in re-entry over the southern hemisphere. Its one kilogram of plutonium-238 fuel within the SNAP-9A RTG was released into the stratosphere. A 1972 Department of Energy soil sample report attributed 13.4 kilocuries of Pu-238 to the accident, from the one kilogram's 17 kilocuries total. This

309-462: A resistor in series with a diode (or series of diodes). Due to the logarithmic shape of diode V-I curves, the voltage across the diode changes only slightly due to changes in current drawn or changes in the input. When precise voltage control and efficiency are not important, this design may be fine. Since the forward voltage of a diode is small, this kind of voltage regulator is only suitable for low voltage regulated output. When higher voltage output

412-410: A (somewhat noisy) voltage slightly above the ultimately desired output. That is followed by a linear regulator that generates exactly the desired voltage and eliminates nearly all the noise generated by the switching regulator. Other designs may use an SCR regulator as the "pre-regulator", followed by another type of regulator. An efficient way of creating a variable-voltage, accurate output power supply

515-480: A 2 Hz change in generator frequency, which is very large, results in an output voltage change of only 4%, which has little effect for most loads. It accepts 100% single-phase switch-mode power-supply loading without any requirement for derating, including all neutral components. Input current distortion remains less than 8% THD even when supplying nonlinear loads with more than 100% current THD. Drawbacks of CVTs are their larger size, audible humming sound, and

618-408: A Rand Corporation study of reconnaissance satellites completed in 1954. As some of the proposed satellites had high power demands, some as high as a few kilowatts, the U.S. Atomic Energy Commission (AEC) requested a series of nuclear power-plant studies from industry in 1951. Completed in 1952, these studies determined that nuclear power plants were technically feasible for use on satellites. In 1955,

721-501: A cesium ion thruster as a secondary payload, the first test of an electrically powered spacecraft propulsion system to operate in orbit (following the SERT-1 suborbital test in 1964). The ion-beam power supply was operated at 4500 V and 80 mA to produce a thrust of about 8.5 mN. The ion engine was to be operated off batteries for about one hour, and then the batteries were to be charged for approximately 15 hours using 0.1 kW of

824-511: A compact fission reactor that generates heat, (2) an energy converter that transforms some of the heat into electricity, and (3) a radiator that radiates away heat that cannot be used. The reactor measures 39.62 cm (15.6 in) long, 22.4 cm (8.8 in) diameter and holds 37 fuel rods containing U as uranium-zirconium-hydride fuel. The SNAP-10A reactor was designed for a thermal power output of 30 kW and unshielded weighs 650 lb (290 kg). The reactor can be identified at

927-544: A higher input than the output. If the input voltage approaches the desired output voltage, the regulator will "drop out". The input to output voltage differential at which this occurs is known as the regulator's drop-out voltage. Low-dropout regulators (LDOs) allow an input voltage that can be much lower (i.e., they waste less energy than conventional linear regulators). Entire linear regulators are available as integrated circuits. These chips come in either fixed or adjustable voltage types. Examples of some integrated circuits are

1030-431: A model of Stirling radioisotope generator (SRG)) produces roughly four times the electric power of an RTG per unit of nuclear fuel, but flight-ready units based on Stirling technology are not expected until 2028. NASA plans to utilize two ASRGs to explore Titan in the distant future. Radioisotope power generators include: Radioisotope heater units (RHUs) are also used on spacecraft to warm scientific instruments to

1133-435: A modern AVR uses solid-state devices. An AVR is a feedback control system that measures the output voltage of the generator, compares that output to a set point, and generates an error signal that is used to adjust the excitation of the generator. As the excitation current in the field winding of the generator increases, its terminal voltage will increase. The AVR will control current by using power electronic devices; generally

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1236-416: A negative feedback control loop; increasing the open-loop gain tends to increase regulation accuracy but reduce stability. (Stability is the avoidance of oscillation, or ringing, during step changes.) There will also be a trade-off between stability and the speed of the response to changes. If the output voltage is too low (perhaps due to input voltage reducing or load current increasing), the regulation element

1339-485: A power-distance drop-off of P ∝ R − 4 {\displaystyle P\propto R^{-4}} , comparatively low Earth orbits are desirable. The Soviet Union did not launch interplanetary missions beyond Mars, and generally developed few RTGs. American RTGs in the 1970s supplied power in the 100 W range. For the RORSAT military radar satellites (1967–1988), fission reactors, especially

1442-594: A safe and long-lasting space fission reactor system for a spacecraft's power and propulsion, replacing the long-used RTGs. Budget constraints resulted in the effective halting of the project, but Project Prometheus has had success in testing new systems. After its creation, scientists successfully tested a High Power Electric Propulsion (HiPEP) ion engine, which offered substantial advantages in fuel efficiency, thruster lifetime, and thruster efficiency over other power sources. A gallery of images of space nuclear power systems. Voltage regulator A voltage regulator

1545-493: A safety program and led to the inception of the Aerospace Nuclear Safety Program. The program was established to evaluate the nuclear hazards associated with the construction, launch, operation and disposal of SNAP systems and to develop designs to assure their radiological safety. Atomics International had primary responsibility for safety, while Sandia National Laboratories was responsible for

1648-766: A second phase, by early 2022, they would select one company to develop a 10-kilowatt fission power system to be placed on the Moon in 2027. In 2002, NASA announced an initiative towards developing nuclear systems, which later came to be known as Project Prometheus . A major part of the Prometheus Project was to develop the Stirling Radioisotope Generator and the Multi-Mission Thermoelectric Generator, both types of RTGs. The project also aimed to produce

1751-450: A servo control mechanism to advance the movable coil position in order to provide voltage increase or decrease. A braking mechanism or high-ratio gearing is used to hold the rotating coil in place against the powerful magnetic forces acting on the moving coil. Electromechanical regulators called voltage stabilizers or tap-changers , have also been used to regulate the voltage on AC power distribution lines. These regulators operate by using

1854-430: A servomechanism to select the appropriate tap on an autotransformer with multiple taps, or by moving the wiper on a continuously variable auto transfomer. If the output voltage is not in the acceptable range, the servomechanism switches the tap, changing the turns ratio of the transformer, to move the secondary voltage into the acceptable region. The controls provide a dead band wherein the controller will not act, preventing

1957-417: A simple rugged method to stabilize an AC power supply. Older designs of ferroresonant transformers had an output with high harmonic content, leading to a distorted output waveform. Modern devices are used to construct a perfect sine wave. The ferroresonant action is a flux limiter rather than a voltage regulator, but with a fixed supply frequency it can maintain an almost constant average output voltage even as

2060-421: A small part of the generator's output is used to provide current for the field winding. Where a generator is connected in parallel with other sources such as an electrical transmission grid, changing the excitation has more of an effect on the reactive power produced by the generator than on its terminal voltage, which is mostly set by the connected power system. Where multiple generators are connected in parallel,

2163-538: A spacecraft utilizing nuclear-powered propulsion systems (developed at the Keldysh Research Center ), which includes a small gas-cooled fission reactor with 1 MWe. In September 2020, NASA and the Department of Energy (DOE) issued a formal request for proposals for a lunar nuclear power system, in which several awards would be granted to preliminary designs completed by the end of 2021, while in

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2266-535: A spacecraft's heating or propulsion systems. In terms of heating requirements, when spacecraft require more than 100 kW for power, fission systems are much more cost effective than RTGs. In 1965, the US launched a space reactor, the SNAP-10A , which had been developed by Atomics International , then a division of North American Aviation . Over the past few decades, several fission reactors have been proposed, and

2369-422: A specified voltage and will conduct as much current as required to hold its terminal voltage to that specified voltage by diverting excess current from a non-ideal power source to ground, often through a relatively low-value resistor to dissipate the excess energy. The power supply is designed to only supply a maximum amount of current that is within the safe operating capability of the shunt regulating device. If

2472-399: A steady current flow. Greater efficiency is achieved since the pass device is operated as a low impedance switch. When the pass device is at cutoff, there is no current and it dissipates no power. Again when the pass device is in saturation, a negligible voltage drop appears across it and thus dissipates only a small amount of average power, providing maximum current to the load. In either case,

2575-468: A sufficient margin and that the power handling capacity of the transistor is not exceeded. The output voltage of the stabilizer is equal to the Zener diode voltage minus the base–emitter voltage of the transistor, U Z − U BE , where U BE is usually about 0.7 V for a silicon transistor, depending on the load current. If the output voltage drops for any external reason, such as an increase in

2678-472: A varying input current or varying load. The circuit has a primary on one side of a magnet shunt and the tuned circuit coil and secondary on the other side. The regulation is due to magnetic saturation in the section around the secondary. The ferroresonant approach is attractive due to its lack of active components, relying on the square loop saturation characteristics of the tank circuit to absorb variations in average input voltage. Saturating transformers provide

2781-414: Is a system designed to automatically maintain a constant voltage . It may use a simple feed-forward design or may include negative feedback . It may use an electromechanical mechanism, or electronic components . Depending on the design, it may be used to regulate one or more AC or DC voltages. Electronic voltage regulators are found in devices such as computer power supplies where they stabilize

2884-471: Is commanded, up to a point , to produce a higher output voltage–by dropping less of the input voltage (for linear series regulators and buck switching regulators), or to draw input current for longer periods (boost-type switching regulators); if the output voltage is too high, the regulation element will normally be commanded to produce a lower voltage. However, many regulators have over-current protection, so that they will entirely stop sourcing current (or limit

2987-434: Is given by where The stability of the output voltage can be significantly increased by using a differential amplifier , possibly implemented as an operational amplifier : In this case, the operational amplifier drives the transistor with more current if the voltage at its inverting input drops below the output of the voltage reference at the non-inverting input. Using the voltage divider (R1, R2 and R3) allows choice of

3090-467: Is highly advantageous for outer solar system exploration i.e. Jupiter and beyond. All spacecraft leaving the Solar System , i.e. Pioneer 10 and 11 , Voyager 1 and 2 , and New Horizons use NASA RTGs, as did the outer planet missions of Galileo , Cassini , and Ulysses . However, in part, due to the global shortage of plutonium-238 , and advances in solar efficiency,

3193-408: Is maximal. The circuit designer must choose a minimum voltage that can be tolerated across R v , bearing in mind that the higher this voltage requirement is, the higher the required input voltage U in , and hence the lower the efficiency of the regulator. On the other hand, lower values of R v lead to higher power dissipation in the diode and to inferior regulator characteristics. R v

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3296-411: Is needed, a zener diode or series of zener diodes may be employed. Zener diode regulators make use of the zener diode's fixed reverse voltage, which can be quite large. Feedback voltage regulators operate by comparing the actual output voltage to some fixed reference voltage. Any difference is amplified and used to control the regulation element in such a way as to reduce the voltage error. This forms

3399-466: Is responsible for the identification and cleanup of the radioactive contamination. (The SSFL was also used for the unrelated testing and development of rocket engines by Rocketdyne primarily for NASA .) The DOE website supporting the site cleanup details the historical development of nuclear energy at SSFL including additional SNAP testing and development information. Atomics International also developed and tested other compact nuclear reactors including

3502-472: Is the SCR shunt regulator which uses the regulator output as a trigger. Both series and shunt designs are noisy, but powerful, as the device has a low on resistance. Many power supplies use more than one regulating method in series. For example, the output from a switching regulator can be further regulated by a linear regulator. The switching regulator accepts a wide range of input voltages and efficiently generates

3605-457: Is to combine a multi-tapped transformer with an adjustable linear post-regulator. In the simplest case a common base amplifier is used with the base of the regulating transistor connected directly to the voltage reference: A simple transistor regulator will provide a relatively constant output voltage U out for changes in the voltage U in of the power source and for changes in load R L , provided that U in exceeds U out by

3708-486: Is typically less than 4%, is independent of any input voltage distortion, including notching. Efficiency at full load is typically in the range of 89% to 93%. However, at low loads, efficiency can drop below 60%. The current-limiting capability also becomes a handicap when a CVT is used in an application with moderate to high inrush current, like motors, transformers or magnets. In this case, the CVT has to be sized to accommodate

3811-561: The BES-5 and TOPAZ-I fission reactors of the Soviet RORSAT program suffered leakages of their liquid sodium–potassium alloy coolant. Each reactor lost on average 5.3 kilograms of its 13 kilogram total coolant, totaling 85 kilograms across 16 reactors. A 2017 ESA paper calculated that, while smaller droplets quickly decay, 65 kilograms of coolant still remain in centimeter-sized droplets around 800 km altitude orbits, comprising 10% of

3914-652: The BES-5 , were developed to supply an average of 2 kW to the radar. At altitudes averaging 255.3 km, they would have rapidly decayed if they had used a large solar array instead. The later United States Lacrosse/Onyx radar satellite program, beginning launches in 1988, operated at altitudes of 420–718 km. To power radar at this range, a solar array reportedly 45 m in length was operated, speculated to supply 10–20 kW. The following technologies have been proposed and in some cases ground or space-tested for propulsion via nuclear energy. process For more than fifty years, radioisotope thermoelectric generators (RTGs) have been

4017-583: The RORSAT program deployed by the Soviet Union. In the case of crewed spaceflight, nuclear power concepts that can power both life support and propulsion systems may reduce both cost and flight time. Apollo 12 marked the first use of a nuclear power system on a crewed flight, carrying a SNAP-27 RTG to power the Apollo Lunar Surface Experiments Package . As active electromagnetic detectors including radar observe

4120-549: The SNAP-10A nuclear reactor in space for 43 days in 1965, with the next test of a nuclear reactor power system intended for space use occurring on 13 September 2012 with the Demonstration Using Flattop Fission (DUFF) test of the Kilopower reactor. After a ground-based test of the experimental 1965 Romashka reactor , which used uranium and direct thermoelectric conversion to electricity,

4223-578: The SP-100 , contracting with General Electric and others. In 1994, the SP-100 program was cancelled, largely for political reasons, with the idea of transitioning to the Russian TOPAZ-II reactor system. Although some TOPAZ-II prototypes were ground-tested, the system was never deployed for US space missions. In 2008, NASA announced plans to utilize a small fission power system on the surface of

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4326-485: The Soviet Union launched 31 BES-5 low power fission reactors in their RORSAT satellites utilizing thermoelectric converters between 1967 and 1988. In the 1960s and 1970s, the Soviet Union developed TOPAZ reactors , which utilize thermionic converters instead, although the first test flight was not until 1987. In 1983, NASA and other US government agencies began development of a next-generation space reactor,

4429-574: The TOPAZ-I nuclear reactors (6–10 kWe) aboard the twin RORSAT test vehicles Kosmos 1818 and Kosmos 1867 affected the gamma ray telescopes aboard NASA 's Solar Maximum Mission and the University of Tokyo / ISAS ' Ginga . TOPAZ-I remains the most powerful fission reactor operated in space, with previous Soviet missions using the BES-5 reactor (2–3 kWe) at altitudes well below gamma ray observatories. The presence of space nuclear sources and

4532-664: The inner solar system i.e. missions to Mercury, Venus, Mars and the asteroid belt. However, nuclear power has been used for some of these missions such as the Apollo program's SNAP-27 RTG for lunar surface use, and the MMRTG on the Mars Curiosity and Perseverance rovers. Nuclear-based systems can have less mass than solar cells of equivalent power, allowing more compact spacecraft that are easier to orient and direct in space. This makes them useful for radar satellites such as

4635-564: The 1965 system failure, the reactor was left in a 1,300-kilometre (700 nmi) Earth orbit for an expected duration of 4,000 years. In November 1979 the vehicle began shedding, eventually losing 50 pieces of traceable debris . The reasons were unknown, but the cause could have been a collision. Although the main body remains in place, radioactive material may have been released. Later research, published in 2008 and based on Haystack data, suggests that there are another 60 or more pieces of debris of size <10 cm. The SNAPSHOT test included

4738-406: The 723 general purpose regulator and 78xx /79xx series Switching regulators rapidly switch a series device on and off. The duty cycle of the switch sets how much charge is transferred to the load. This is controlled by a similar feedback mechanism as in a linear regulator. Because the series element is either fully conducting, or switched off, it dissipates almost no power; this is what gives

4841-634: The AEC began two parallel SNAP nuclear power projects. One, contracted with The Martin Company, used radio-isotopic decay as the power source for its generators. These plants were given odd-numbered SNAP designations beginning with SNAP-1. The other project used nuclear reactors to generate energy, and was developed by the Atomics International Division of North American Aviation . Their systems were given even-numbered SNAP designations,

4944-497: The AVR system will have circuits to ensure all generators operate at the same power factor. AVRs on grid-connected power station generators may have additional control features to help stabilize the electrical grid against upsets due to sudden load loss or faults. This is an older type of regulator used in the 1920s that uses the principle of a fixed-position field coil and a second field coil that can be rotated on an axis in parallel with

5047-558: The Aerospace Safety Independent Review and conducted many of the safety tests. Before launch was permitted, proof had to be obtained that under all circumstances the launch of the reactor would not pose a serious threat. A variety of tests were successfully completed and several videos of the development and tests are available for viewing. The Idaho National Laboratory conducted three destructive tests of SNAP nuclear reactors at Test Area North prior to

5150-504: The DC voltages used by the processor and other elements. In automobile alternators and central power station generator plants, voltage regulators control the output of the plant. In an electric power distribution system, voltage regulators may be installed at a substation or along distribution lines so that all customers receive steady voltage independent of how much power is drawn from the line. A simple voltage/current regulator can be made from

5253-408: The Moon and Mars, and began testing "key" technologies for it to come to fruition. Proposed fission power system spacecraft and exploration systems have included SP-100 , JIMO nuclear electric propulsion , and Fission Surface Power . A number of micro nuclear reactor types have been developed or are in development for space applications: Nuclear thermal propulsion systems (NTR) are based on

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5356-483: The NaK heat transfer medium. The temperature difference between the NaK on one side of the thermoelectric converter and the cold of space on the other created an electric potential and usable electricity. SNAP-10A was launched from Vandenberg Air Force Base by an ATLAS Agena D rocket on 3 April 1965 into a low Earth orbit altitude of approx. 1,300 km. It is in a slightly retrograde polar orbit — this ensured that

5459-938: The SNAP Experimental Reactor (SER), SNAP-2, SNAP-8 Developmental Reactor (SNAP8-DR) and SNAP-8 Experimental Reactor (SNAP-8ER) units at the Santa Susana Field Laboratory (see Systems for Nuclear Auxiliary Power article). Atomics International also built and operated the Sodium Reactor Experiment , the first U.S. nuclear power plant to supply electricity to a public power system. As of 2010, more than 30 small fission power system nuclear reactors have been sent into space in Soviet RORSAT satellites; also, over 40 radioisotope thermoelectric generators have been used globally (principally US and USSR) on space missions. Nuclear power in space The United States tested

5562-457: The USSR sent about 40 nuclear-electric satellites into space, mostly powered by the BES-5 reactor. The more powerful TOPAZ-II reactor produced 10 kilowatts of electricity. Examples of concepts that use nuclear power for space propulsion systems include the nuclear electric rocket (nuclear powered ion thruster (s)), the radioisotope rocket , and radioisotope electric propulsion (REP). One of

5665-548: The United States jointly recovered 80 radioactive fragments within a 600-kilometer range in the Canadian Northwest Territories. COSMOS 954 became the first example for global emergency preparedness and response arrangements for satellites carrying nuclear power sources. The majority of nuclear power systems launched into space remain in graveyard orbits around Earth. Between 1980 and 1989,

5768-408: The United States. The reactor stopped working after just 43 days due to a non-nuclear electrical component failure. The Systems Nuclear Auxiliary Power Program reactor was specifically developed for satellite use in the 1950s and early 1960s under the supervision of the U.S. Atomic Energy Commission . The Systems for Nuclear Auxiliary Power (SNAP) program developed as a result of Project Feedback,

5871-668: The United States’ main nuclear power source in space. RTGs offer many benefits; they are relatively safe and maintenance-free, are resilient under harsh conditions, and can operate for decades. RTGs are particularly desirable for use in parts of space where solar power is not a viable power source. Dozens of RTGs have been implemented to power 25 different US spacecraft, some of which have been operating for more than 20 years. Over 40 radioisotope thermoelectric generators have been used globally (principally US and USSR) on space missions. The advanced Stirling radioisotope generator (ASRG,

5974-425: The change in load. Power distribution voltage regulators normally operate on a range of voltages, for example 150–240 V or 90–280 V. Many simple DC power supplies regulate the voltage using either series or shunt regulators, but most apply a voltage reference using a shunt regulator such as a Zener diode , avalanche breakdown diode , or voltage regulator tube . Each of these devices begins conducting at

6077-427: The controller from constantly adjusting the voltage ("hunting") as it varies by an acceptably small amount. The ferroresonant transformer , ferroresonant regulator or constant-voltage transformer is a type of saturating transformer used as a voltage regulator. These transformers use a tank circuit composed of a high-voltage resonant winding and a capacitor to produce a nearly constant average output voltage with

6180-451: The current drawn by the load (causing an increase in the collector–emitter voltage to observe KVL), the transistor's base–emitter voltage ( U BE ) increases, turning the transistor on further and delivering more current to increase the load voltage again. R v provides a bias current for both the Zener diode and the transistor. The current in the diode is minimal when the load current

6283-465: The current in some way) if the output current is too high, and some regulators may also shut down if the input voltage is outside a given range (see also: crowbar circuits ). In electromechanical regulators, voltage regulation is easily accomplished by coiling the sensing wire to make an electromagnet. The magnetic field produced by the current attracts a moving ferrous core held back under spring tension or gravitational pull. As voltage increases, so does

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6386-408: The current, strengthening the magnetic field produced by the coil and pulling the core towards the field. The magnet is physically connected to a mechanical power switch, which opens as the magnet moves into the field. As voltage decreases, so does the current, releasing spring tension or the weight of the core and causing it to retract. This closes the switch and allows the power to flow once more. If

6489-713: The duty cycle is varied, the average value of the voltage changes proportionally. Like linear regulators, nearly complete switching regulators are also available as integrated circuits. Unlike linear regulators, these usually require an inductor that acts as the energy storage element. The IC regulators combine the reference voltage source, error op-amp, pass transistor with short circuit current limiting and thermal overload protection. Switching regulators are more prone to output noise and instability than linear regulators. However, they provide much better power efficiency than linear regulators. Regulators powered from AC power circuits can use silicon controlled rectifiers (SCRs) as

6592-417: The event of an accident, monitoring teams equipped with highly specialized support equipment and automated stations are deployed around the launch site to identify potential radioactive material releases, quantify and describe the release scope, predict the quantity and distribution of dispersed material, and develop and recommend protective actions. At the global level, following the 1978 COSMOS 954 incident,

6695-428: The excess current which is not available to the load. When more power must be supplied, more sophisticated circuits are used. In general, these active regulators can be divided into several classes: Linear regulators are based on devices that operate in their linear region (in contrast, a switching regulator is based on a device forced to act as an on/off switch). Linear regulators are also classified in two types: In

6798-538: The exposure of nuclear power sources to extreme physical conditions and the release of radioactive materials into the Earth's atmosphere and surface environment. For example, all Radioisotope Power Systems (RPS) used in space missions have utilized Pu-238. Plutonium-238 is a radioactive element that emits alpha particles. Although NASA states that it exists in spacecraft in a form that is not readily absorbed and poses little to no chemical or toxicological risk upon entering

6901-617: The first being SNAP-2. SNAP-10A was the first Atomics International, nuclear-reactor power system built for use in space. Evolved from the SNAP-10 300 watt design, SNAP-10A fulfilled a 1961 Department of Defense requirement for a 500 watt system. Most of the systems development and reactor testing was conducted at the Santa Susana Field Laboratory , Ventura County, California using a number of specialized facilities. The SNAP-10A has three major components – (1)

7004-405: The fixed coil, similar to a variocoupler. When the movable coil is positioned perpendicular to the fixed coil, the magnetic forces acting on the movable coil balance each other out and voltage output is unchanged. Rotating the coil in one direction or the other away from the center position will increase or decrease voltage in the secondary movable coil. This type of regulator can be automated via

7107-431: The generator's output at slightly more than 6.7 or 13.4 V to maintain the battery as independently of the engine's rpm or the varying load on the vehicle's electrical system as possible. The relay(s) modulated the width of a current pulse to regulate the voltage output of the generator by controlling the average field current in the rotating machine which determines strength of the magnetic field produced which determines

7210-643: The heating power of a fission reactor, offering a more efficient propulsion system than one powered by chemical reactions. Current research focuses more on nuclear electric systems as the power source for providing thrust to propel spacecraft that are already in space. Other space fission reactors for powering space vehicles include the SAFE-400 reactor and the HOMER-15. In 2020, Roscosmos (the Russian Federal Space Agency ) plans to launch

7313-443: The high heat generation caused by saturation. Voltage regulators or stabilizers are used to compensate for voltage fluctuations in mains power. Large regulators may be permanently installed on distribution lines. Small portable regulators may be plugged in between sensitive equipment and a wall outlet. Automatic voltage regulators on generator sets to maintain a constant voltage for changes in load. The voltage regulator compensates for

7416-583: The human body (e.g. in the design of American spacecraft, plutonium dioxide exists in ceramic form to prevent inhalation or ingestion by humans, and it is placed within strict safety protection systems), it cannot be denied that it may be released and dispersed into the environment, posing hazards to both the environment and human health. Pu-238 primarily accumulates in the lungs, liver, and bones through inhalation of powdered form, thereby posing risks to human health. There have been several environmental accidents related to space nuclear power in history. In 1964,

7519-515: The input voltage varies widely. The ferroresonant transformers, which are also known as constant-voltage transformers (CVTs) or "ferros", are also good surge suppressors, as they provide high isolation and inherent short-circuit protection. A ferroresonant transformer can operate with an input voltage range ±40% or more of the nominal voltage. Output power factor remains in the range of 0.96 or higher from half to full load. Because it regenerates an output voltage waveform, output distortion, which

7622-643: The international community recognized the need to establish a set of principles and guidelines to ensure the safe use of nuclear power sources in outer space. Consequently, in 1992, the General Assembly adopted resolution 47/68, titled "Principles Relevant to the Use of Nuclear Power Sources in Outer Space." These principles primarily address safety assessment, international information exchange and dialogue, responsibility, and compensation. It stipulates that

7725-458: The launch of SNAP-10A. The SNAPTRAN-3 destructive experiment, on 1 April 1964, simulated a rocket crash into the ocean, purposely sending radioactive debris across the Idaho desert. The testing and development involving radioactive materials caused environmental contamination at the former Atomics International Santa Susana Field Laboratory (SSFL) facilities. The United States Department of Energy

7828-492: The likelihood and mitigate the consequences of potential accidents. Unlike the 1992 "Principles," the "Safety Framework" applies to all types of space nuclear power source development and applications, not just the technologies existing at the time. In the draft report on the implementation of the Safety Framework for Nuclear Power Source Applications in Outer Space published in 2023, the working group considers that

7931-482: The magnetosphere's flux tubes , which carry them through a range of orbital altitudes, where the positrons can annihilate with the structure of other satellites, again producing gamma rays: e + + e − ⟶ γ   + γ {\displaystyle e^{+}+e^{-}\longrightarrow \gamma \ +\gamma } These gamma rays can interfere with satellite instruments. This most notably occurred in 1987, when

8034-453: The mechanical regulator design is sensitive to small voltage fluctuations, the motion of the solenoid core can be used to move a selector switch across a range of resistances or transformer windings to gradually step the output voltage up or down, or to rotate the position of a moving-coil AC regulator. Early automobile generators and alternators had a mechanical voltage regulator using one, two, or three relays and various resistors to stabilize

8137-578: The more explored concepts is the nuclear thermal rocket , which was ground tested in the NERVA program. Nuclear pulse propulsion was the subject of Project Orion . After the ban of nuclear weapons in space by the Outer Space Treaty in 1967, nuclear power has been discussed at least since 1972 as a sensitive issue by states. Space nuclear power sources may experience accidents during launch, operation, and end-of-service phases, resulting in

8240-465: The more recent Jupiter missions of Juno , Jupiter Icy Moons Explorer , and Europa Clipper , as well as the Jupiter trojan asteroid mission of Lucy , all opted for large solar arrays despite a relative 4% solar flux at Jupiter's orbit of 5.2 AU . Solar power is much more commonly used for its low cost and efficiency, primarily in Earth and lunar orbit and for interplanetary missions within

8343-506: The nominal 0.5 kW SNAP system as the power supply. The ion engine operated for a period of less than 1 hour before being commanded off permanently. Analysis of flight data indicated a significant number of high-voltage breakdowns, and this apparently caused electromagnetic interference (EMI), causing attitude perturbations of the spacecraft. Ground tests indicated that the engine arcing produced conducted and radiated EMI significantly above design levels. The SNAP reactor program necessitated

8446-571: The ownership, use, and production of nuclear materials and facilities. The Department of Energy is bound by the National Environmental Policy Act (NEPA) to consider the environmental impact of nuclear material handling, transportation, and storage. NASA, the Department of Energy, and other federal and local authorities develop comprehensive emergency plans for each launch, including timely public communication. In

8549-428: The past, one or more vacuum tubes were commonly used as the variable resistance. Modern designs use one or more transistors instead, perhaps within an integrated circuit . Linear designs have the advantage of very "clean" output with little noise introduced into their DC output, but are most often much less efficient and unable to step-up or invert the input voltage like switched supplies. All linear regulators require

8652-412: The peak current, thus forcing it to run at low loads and poor efficiency. Minimum maintenance is required, as transformers and capacitors can be very reliable. Some units have included redundant capacitors to allow several capacitors to fail between inspections without any noticeable effect on the device's performance. Output voltage varies about 1.2% for every 1% change in supply frequency. For example,

8755-480: The potential consequences of nuclear accidents on humans and the environment cannot be ignored. Therefore, there have been strict regulations for the application of nuclear power in outer space to mitigate the risks associated with the use of space nuclear power sources among governments. For instance, in the United States, safety considerations are integrated into every stage of the design, testing, manufacturing, and operation of space nuclear systems. The NRC oversee

8858-402: The power wasted in the pass device is very little and almost all the power is transmitted to the load. Thus the efficiency of a switched-mode power supply is remarkably high-in the range of 70–90%. Switched mode regulators rely on pulse-width modulation to control the average value of the output voltage. The average value of a repetitive pulse waveform depends on the area under the waveform. If

8961-780: The principles should be revisited by the Committee on the Peaceful Uses of Outer Space no later than two years after adoption. After years of consultation and deliberation, in 2009, the International Safety Framework for Nuclear Power Source Applications in Outer Space was adopted to enhance safety for space missions involving nuclear power sources. It offers guidance for engineers and mission designers, although its effective implementation necessitates integration into existing processes. The "Safety Framework" asserts that each nation bears responsibility for

9064-562: The proper temperature so they operate efficiently. A larger model of RHU called the General Purpose Heat Source (GPHS) is used to power RTGs and the ASRG. Extremely slow-decaying radioisotopes have been proposed for use on interstellar probes with multi-decade lifetimes. As of 2011, another direction for development was an RTG assisted by subcritical nuclear reactions. Fission power systems may be utilized to power

9167-544: The safety framework has been widely accepted and demonstrated to be helpful for member states in developing and/or implementing national systems and policies to ensure the safe use of nuclear power sources in outer space. Other member states and intergovernmental organizations not currently involved in the utilization of space nuclear power sources also acknowledge and accept the value of this framework, taking into account safety issues associated with such applications. Nuclear power systems function independently of sunlight, which

9270-518: The safety of its space nuclear power. Governments and international organizations must justify the necessity of space nuclear power applications compared to potential alternatives and demonstrate their usage based on comprehensive safety assessments, including probabilistic risk analysis, with particular attention to the risk of public exposure to harmful radiation or radioactive materials. Nations also need to establish and maintain robust safety oversight bodies, systems, and emergency preparedness to minimize

9373-459: The same function that the relays perform in electromechanical regulators. Electromechanical regulators are used for mains voltage stabilisation—see AC voltage stabilizers below. Generators, as used in power stations, ship electrical power production, or standby power systems, will have automatic voltage regulators (AVR) to stabilize their voltages as the load on the generators changes. The first AVRs for generators were electromechanical systems, but

9476-523: The series device. Whenever the output voltage is below the desired value, the SCR is triggered, allowing electricity to flow into the load until the AC mains voltage passes through zero (ending the half cycle). SCR regulators have the advantages of being both very efficient and very simple, but because they can not terminate an ongoing half cycle of conduction, they are not capable of very accurate voltage regulation in response to rapidly changing loads. An alternative

9579-1358: The space debris in that size range. Orbital fission reactors are a source of significant interference for orbital gamma ray observatories . Unlike RTGs which largely rely on energy from alpha decay , fission reactors produce significant gamma radiation , with the uranium-235 chain releasing 6.3% of its total energy as prompt (shown below) and delayed (daughter product decay) gamma rays: 0 1 n   +   92 235 U ⟶   56 141 Ba   +   36 92 Kr   +   3   0 1 n   + γ {\displaystyle {\begin{array}{r}^{1}_{0}{\text{n}}\ +\ _{92}^{235}{\text{U}}\longrightarrow \ _{56}^{141}{\text{Ba}}\ +\ _{36}^{92}{\text{Kr}}\ +\ 3\ _{0}^{1}{\text{n}}\ +\gamma \end{array}}} Pair production occurs as these gamma rays interact with reactor or adjacent material, ejecting electrons and positrons into space: γ + Z ⟶   e + + e − + Z   {\displaystyle \gamma +{\text{Z}}\longrightarrow \ e^{+}+e^{-}+{\text{Z}}\ } These electrons and positrons then become trapped in

9682-620: The spacecraft's service module. Upon reentering the atmosphere, the lunar module equipped with the SNAP-27 RTG exploded and crashed into the South Pacific Ocean, with no leakage of nuclear fuel. This is the only intact flown nuclear system that remains on Earth without recovery. In early 1978, the Soviet spacecraft Kosmos 954 , powered by a 45-kilogram highly enriched uranium reactor, went into an uncontrolled descent. Due to

9785-453: The spent rocket stages landed in the ocean. Its nuclear electrical source, made up of thermoelectric elements, was intended to produce over 500 watts of electrical power for one year. After 43 days, an onboard voltage regulator within the spacecraft – unrelated to the SNAP reactor – failed, causing the reactor core to be shut down, after reaching a maximum output of 590 watts. After

9888-507: The stabilizer must provide more power, the shunt output is only used to provide the standard voltage reference for the electronic device, known as the voltage stabilizer. The voltage stabilizer is the electronic device, able to deliver much larger currents on demand. Active regulators employ at least one active (amplifying) component such as a transistor or operational amplifier . Shunt regulators are often (but not always) passive and simple, but always inefficient because they (essentially) dump

9991-403: The stator. A generator uses a mechanical commutator, graphite brushes running on copper segments, to convert the AC produced into DC by switching the external connections at the shaft angle when the voltage would reverse. An alternator accomplishes the same goal using rectifiers that do not wear down and require replacement. Modern designs now use solid state technology (transistors) to perform

10094-416: The switching design its efficiency. Switching regulators are also able to generate output voltages which are higher than the input, or of opposite polarity—something not possible with a linear design. In switched regulators, the pass transistor is used as a "controlled switch" and is operated at either cutoff or saturated state. Hence the power transmitted across the pass device is in discrete pulses rather than

10197-467: The top of the SNAP-10A unit. Reflectors were arranged around the outside of the reactor to provide the means to control the reactor. The reflectors were composed of a layer of beryllium, which would reflect neutrons, thus allowing the reactor to begin and maintain the fission process. The reflectors were held in place by a retaining band anchored by an explosive bolt . When the reflector was ejected from

10300-479: The unit, the reactor could not sustain the nuclear fission reaction and the reactor permanently shut down. The eutectic sodium-potassium ( NaK ) alloy was used as a coolant in the SNAP-10A. The NaK was circulated through the core and thermoelectric converters by a liquid metal direct current conduction-type pump. The thermoelectric converters (identified as the long white "apron") are doped silicon germanium materials, thermally coupled, but electrically isolated from

10403-408: The unloaded output voltage per rpm. Capacitors are not used to smooth the pulsed voltage as described earlier. The large inductance of the field coil stores the energy delivered to the magnetic field in an iron core so the pulsed field current does not result in as strongly pulsed a field. Both types of rotating machine produce a rotating magnetic field that induces an alternating current in the coils in

10506-452: The unpredictable impact point, preparations were made for potential contamination of inhabited areas. This event underscored the potential danger of space objects containing radioactive materials, emphasizing the need for strict international emergency planning and information sharing in the event of space nuclear accidents. It also led to the intergovernmental formulation of emergency protocols, such as Operation Morning Light , where Canada and

10609-538: Was contrasted to the 11,600 kilocuries of strontium-90 deposited by all nuclear weapons testing. In May 1968, a Thor-Agena rocket carrying the Nimbus B satellite was destroyed by a guidance error. Its plutonium SNAP-19 RTG was recovered intact, without leakage from the Pacific sea floor, refurbished, and flown on Nimbus 3 . In April 1970, the Apollo 13 lunar mission was aborted due to an oxygen tank explosion in

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