"In 1961, the first RTG used in a space mission was launched aboard a U.S. Navy transit navigation satellite. The electrical power output of this RTG, which was called Space Nuclear Auxiliary Power (SNAP-3), was a mere 2.7 watts. But the important story was that it continued to perform for 15 years after launch.

Since that initial SNAP-3 mission, RTGs have been an indispensable part of America's space program. They have been involved in more than 25 missions, orbiting Earth and traveling to planets and their moons both nearby and in deep space. (Astronauts on five Apollo missions left RTG units on the lunar surface to power the Apollo Lunar Surface Experiment Packages.)" [USDOE/d, page 6]

The RTG used for the Transit 4A and the Transit 4B missions worked on polonium-210, which has a half-life of 138.4 days. Therefore, it seems rather unlikely that it actually operated for 15 years. This would mean that at the end of its lifetime, 2% of the original heat dissipation would have been sufficient to provide the power for the satellite. See also Transit 4B mission.

The stage used to launch this satellite exploded after the launch. It broke up into 298 pieces, of which appr. 200 were still tracked in orbit according to a 1995 report of NASA's Johnson Space Center [KESSLER].

Contradictory information exists about the operating time of this SNAP. The DoE states "RTG operated for 9 years. Satellite operated periodically after 1962 high altitude test. Last reported signal in 1971." [USDOE/d, pages 15/16] The TRW Space Log 1996 states "In orbit; transmitted until 7/62, SNAP-3 operated 8 months." [TRW, page 71]

This was the first U.S. satellite which used an RTG based on plutonium-238.¹¹

On the use of plutonium RTGs, the DoE says the following: "Although other radioactive fuels have been considered for RTGs, plutonium-238 (Pu-238) has been used most widely. Pu-238 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. ... Longer space missions require a radioisotope with a longer half-life. Pu-238, with its half-life of 87.7 years, fills the need. For example, after five years, approximately 96 percent of the original heat output of Pu-238 is still available. ... Because the nuclear fuel in RTGs is radioactive, safety is a critical issue. ... Only lightweight shielding is necessary because alpha particles cannot penetrate a sheet of paper." [USDOE/d, pages 18-19]

Accident?: Contradictory information exists about the status of this satellite. DoE states: "RTG operated as planned. Non-RTG electrical problems on satellite caused satellite to fall after 9 months." [USDOE/d, pages 15/16] No further information about this incident could be found. The TRW Space Log 1996 [TRW, page 80] as well as the NASA Cassini FEIS [NASA/c] state that the satellite is currently in orbit.

"RTG operated for over 6 years. Satellite lost ability to navigate after 1.5 years." [USDOE/d, pages 15/16, emphasis added]

Accident: "Mission was aborted because of launch vehicle failure. RTG burned up on re-entry as designed." [USDOE/d, pages 15/16] This is the short version of the events on April 21, 1964.

A more detailed account is given by another DoE document: "In 1964, a U.S. Navy Transit navigation satellite failed to reach orbit and disintegrated in the atmosphere. The satellite received its electrical power from a 4.5 pound, grapefruit-sized radiothermal generator that produced energy from the heat of its decaying radioisotopes. The device, known as a SNAP or System for Nuclear Auxiliary Power, disintegrated, scattering plutonium particles in the atmosphere over the southern hemisphere." [USDOE/b] According to a U.S. General Accounting Office report, the Transit 5-BN-3 RTG contained 2.2 pounds of plutonium fuel. [USGOA], page 18]

In the Cassini FEIS, NASA describes the results of this accident: "Since 1964, essentially all of the SNAP-9A release has been deposited on the Earth's surface. About 25 percent ... of that release was deposited in the northern latitudes, with the remaining 75 percent settling in the southern hemisphere. ...The Pu-238 in the atmosphere from weapons tests (about 3.3 x 10¹⁴ Bq [9,000 Ci]) was increased by the 1964 reentry and burnup of a Systems for Nuclear Auxiliary Power (SNAP)-9A RTG, which released 6.3 x 10¹⁴ Bq (17,000 Ci). ... The release into the atmosphere was consistent with the RTG design philosophy of the time. (Subsequent RTGs, including the RTGs on the Cassini spacecraft, have been designed to contain the Pu-238 fuel to the maximum extent possible, recognizing that there are mass and configuration requirements relative to the spacecraft and its mission that must be considered with the design and configuration of the power source and its related safety requirements.) ... Since 1964, essentially all of the SNAP-9A release has been deposited on the Earth's surface." [NASA/c, page 3-44]

The following table from NASA's Cassini FEIS [NASA/c, page 3-44] lists the effect of this SNAP-9A burn-up on the worldwide plutonium-238 distribution.

The satellite successfully achieved orbit. According to NASA's Cassini FEIS, the reactor was shut down after 43 days in orbit.

Journalist Michael Bein commented this test flight of a space mission powered by a nuclear reactor as follows: "The only U.S. satellite thus far to carry a nuclear fission reactor failed in 1965 after 43 days aloft and was subsequently boosted into a 4000-year orbit in order that its radioactivity might have time to decay to safer levels before it descends to earth. Injection into higher orbit is the method of reactor 'disposal' preferred by both the American and Soviet programs."¹³ [BEIN]

Some additional information is given in the TRW Space Log 1996: "SNAP-10A operated at more than 500 W for 43 days. Since 1979, many objects separating. The only U.S. space reactor flown, a test flight in 1964, used uranium-235 as the fuel." [TRW, page 90, emphasis added]

Technical information about the SNAP-10A, the amount of U-238 used, or the effect of the continuing disintegration of the satellite mentioned in the TRW Space Log 1996 was not given in the sources available at the time of writing.

See Kosmos 84.

This was the first of the 33 so-called RORSAT missions usually listed as nuclear powered space missions launched by the USSR. RORSAT is the acronym for 'Radar Ocean Reconnaissance Satellite'. According to the Federation of American Scientists (FAS), Kosmos 198 was a "1-day flight test of spacecraft support systems" [FAS]. For more details about the RORSAT reactors, see Section 2.2 The USSR/Russia - RORSAT, Topaz, And RTG

See Kosmos 198. According to the Federation of American Scientists, this was the second 1-day flight test of spacecraft support systems [FAS].

According to information from the DoE, this was the first RTG usage on a non-military, i.e. on a NASA mission. [USDOE/a]

Accident: "Mission was aborted because of range safety destruct. RTG heat sources recovered and recycled." [USDOE/d, pages 15/16] A 'range safety destruct' is a deliberate destruction of a mission by the Range Safety Officer of the mission launch pad when a launch vehicle gets out of control.

A report of the U.S. General Accounting Office describes the event as follows: "In 1968, a NIMBUS-B-1 weather satellite was destroyed after its launch vehicle malfunctioned. The plutonium fuel cells from the spacecraft's two RTGs were recovered intact from the bottom of the Santa Barbara Channel near the California coast." [USGOA, page 18] The plutonium from the RTGs was recycled and re-used for another RTG.

"RTGs operated for over 2.5 years." [USDOE/d, page 15/16] A fact sheet published by the Florida State University, Department of Meteorology states: "The craft was powered by 10,500 solar cells and two SNAP-19 nuclear powered generators." [FSU/b]

See Kosmos 198.

Accident: The TRW Space Log 1996 states, "Decayed Oct. 24, 1969; possible lunar mission test; two modules." [TRW] Proposition One suggests that "radiation was detected as craft burns up in atmosphere." [PROP1]¹⁷

This mission is frequently listed in newspaper articles about accidents which occurred with nuclear powered spacecrafts. However, no details are given. This mission is not contained in the otherwise comprehensive Berlin database [ILR].

"RTG operated for about 8 years until station was shut down." [USDOE/d, page 15/16]¹⁸

It is a little known fact that the seismic stations left on the Moon in the course of the Apollo 12 and Apollo 14 to Apollo 17 missions¹⁹ contain one RTG each. The plutonium heat source was loaded into the SNAP RTGs by the astronauts on the moon. [USDOE/d, page 5]

See Kosmos 198.

See Apollo 12. "RTG operated for over 6.5 years until station was shut down." [USDOE/d, page 15/16]

See Kosmos 198.

See Apollo 12. "RTG operated for over 6 years until station was shut down." [USDOE/d, page 15/16]

See Kosmos 198.

"RTGs still operating. Spacecraft successfully operated to Jupiter and is now beyond orbit of Pluto." [USDOE/d, page 15/16]

Other information sources [NSSDC/c and TRW] give March 3, 1972, as the launch date.

See Apollo 12. "RTG operated for over 5.5 years until station was shut down." [USDOE/d, page 15/16]

See Kosmos 198.

"RTG still operating." [USDOE/d, page 15/16]

See Apollo 12. "RTG operated for almost 5 years until station was shut down." [USDOE/d, page 15/16]

See Nimbus IV. The satellite was deactivated on March 29, 1983 [FSU/d].

There is contradictory information about the RTG operation: "RTGs still operating. Spacecraft successfully operated to Jupiter, Saturn, and beyond." [USDOE/d, pages 15/16] But: "The Mission of Pioneer 11 has ended. Its RTG power source is exhausted." [NASA/h] The latter is confirmed by another source: "Instrument power sharing began in February 1985 due to declining RTG power output. Science operations and daily telemetry ceased on September 30, 1995, when the RTG power level was insufficient to operate any experiments." [NSSDC/d] DoE states: "The spacecraft contained two [sic?] nuclear electric-power generators, which generated 144 W at Jupiter, but decreased to 100 W at Saturn." [USDOE/a]

As for Pioneer 10, contradictory information is given about the launch date. Other information sources (NSSDC/d and TRW, page 151] give April 6, 1973, as the launch date.

See Kosmos 198.

Accident: The TRW Space Log 1996 lists this mission as "Failed to orbit. Rorsat." [TRW, page 152] Proposition One adds "Location: Pacific Ocean, north of Japan. Radiation released from the reactor was detected." [PROP1] No further details about this accident could be found.

See Kosmos 198.

See Kosmos 198.

See Kosmos 198.

See Kosmos 198.

See Kosmos 198.

See Nimbus IV.

Accident?: Broke up into 236 parts; currently tracked are 190; date of event: May 01, 1991. This is NASA information [JSC/a]. No further information is given, therefore it is not clear whether it is the satellite which broke up and what happened to the RTGs.

See Viking 1. "RTGs operated for over 4 years until relay link was lost." [USDOE/d, page 15/16] According to the TRW Space Log 1996, the lander operated less: "Lander died April 12, 1978." [TRW, page 167]

See Kosmos 198.

"RTGs still operating." [USDOE/d, page 15/16]

"RTGs still operating." [USDOE/d, page 15/16]

See Kosmos 198.

See Kosmos 198.

"RTGs still operating. Spacecraft successfully operated to Jupiter, Saturn, Uranus, Neptune, and beyond." [USDOE/d, pages 15/16]

"RTGs still operating. Spacecraft successfully operated to Jupiter, Saturn, and beyond." [USDOE/d, pages 15/16]

See Kosmos 198.

See Kosmos 198.

Accident: The re-entry of Kosmos 954 is one of the best covered and most serious accidents of a nuclear powered space mission. DoE states: "Decayed Jan. 24, 1978; spread radioactive debris over western Canada at re-entry."; [USDOE/d, pages 15/16] RADNET details the amount of radioactive material which was spread: "Reentry inventories: 3TBq strontium-90; ¹³¹-I: 0.2 Bq; ¹³⁷-Cs: 3TBq (81 Curies.)" [CENTER, quoting Health Physics, No. 47, pages 225-233]

In an article almost ten years after the accident, journalist Michael Bein describes the Canadian efforts to recover part of the radioactive material: "Operation Morning Light continued into October and eventually resulted, according to Canada's Atomic Energy Control Board (AECB), in the estimated recovery of 0.1 percent of Cosmos 954's nuclear core. Tens of millions of pepper-flake sized radioactive particles, comprising a fifth to a quarter of the core, remained scattered over a 124,000 square kilometer 'footprint', stretching southward from Great Slave Lake into northern Saskatchewan and Alberta. The clean-up of these populated and frequented areas and the recovery of a number of large satellite fragments from the more remote bush cost Canada nearly $14,000,000, of which only $3,000,000 was later recovered from the USSR." [BEIN]

He continues: "Within a week after the Cosmos crash, U.S. President Carter called for 'an agreement with the Soviets to prohibit earth-orbiting satellites with atomic radiation material in them.'" [BEIN] Although this request was not enforced afterwards, the incident resulted in broad discussions of the issue. "At the end of the year, in November 1978, the General Assembly of the United Nations authorized its Committee on the Peaceful Uses of Outer Space (UNCOPUOS) to establish a technical working group. The assembly also passed a resolution requesting that a country whose NPS [Nuclear Powered Satellite] is about to fall notify others of the impending danger." [BEIN]

Many years later, in 1992, discussions in the UNCOPUOS resulted in the "Principles Relevant to the Use of Nuclear Power Sources in Outer Space" (resolution 47/68). This document "recognizes that nuclear power sources are essential for some missions, but that such systems should be designed so as to minimize public exposure to radiation in the case of accident." [UN]

In the U.S., the accident provoked discussions not only on a political but also on a technical level: "Regarding the best form of dispersal upon re-entry, a 1979 DoE-commissioned safety study found that »break-up of the reactor into non-respirable particles ... is preferable to uncontrolled intact re-entry or to high altitude vaporization.« In other words, break-up into pepper-flake sized particles like those produced by Cosmos 954 is the best (as well as the most likely) form of reentry." [BEIN]

In the USSR, the opposite conclusion was drawn from the Cosmos 954 accident. It led to a re-design of the future nuclear powered Kosmos missions as described by the Federation of American Scientists: "Following the reentry of Kosmos 954 over Canada in 1978, the RORSAT reactor underwent several modifications, including the ability to eject the fuel assembly at the end of life, hopefully in the disposal orbit but prior to reentry in the event of accident, e.g. Kosmos 1402 in 1983. Between 1980 and 1988, at least 14 RORSATs did perform fuel assembly ejection in the higher altitude storage orbits. However, not until 1994 did terrestrial-based space surveillance sensors detect what may be large numbers of very small particles of NaK reactor coolant released when the fuel assembly was ejected." [FAS] (For more details see Kosmos 1176.)

See Nimbus IV.

This is the first mission where in addition to lifting the reactor to the higher storage orbit, 'core separation' was introduced, i.e. in a case of a re-entry the 'naked' core would completely burn up in the atmosphere rather than come back to Earth (see description of the FAS quoted for Kosmos 954 above.) This method was demonstrated a few years later, when Kosmos 1402 entered the Earth atmosphere and burned up.

Core separation had an unexpected side aspect which was described by NASA. In its April-June, 1997 edition of the Orbital Debris Quarterly News, NASA gives details about "a large number of small-debris objects injected into orbit with very low velocities relative to one another. ... Times of increased flux at 600 km altitudes were found to be associated with overhead passing of COSMOS 1900, A Radar Ocean Reconnaissance Satellite (RORSAT) orbiting around 720 km - providing a clue about, but not explaining the higher-altitude debris. Specially-configured measurements using the Haystack radar determined the orbital inclination of the debris source between 850 km and 1000 km to be between 63 and 67 degrees, matching that of the remaining orbiting RORSATs. The RORSAT design was examined to determine a possible cause of this debris and was found to contain a significant amount of coolant consisting of the liquid-metal alloy Sodium-Potassium (NaK). The leakage of this coolant from COSMOS 1900 and a number of other RORSATs, producing a large number of orbiting liquid metal spheres, was consistent with all observations." [KESSLER]

See Kosmos 1176.

See Kosmos 1176.

See Kosmos 1176. "Raised Sept. 6, 1981." [TRW, page 208]

See Kosmos 1176. "Raised Sept. 27, 1982." [TRW, page 214]

See Kosmos 1176. "Raised Aug. 11, 1982." [TRW, page 215]

See Kosmos 1176.

Accident: The mission Kosmos 1402 is another one of the often mentioned accidents which occurred with nuclear powered space missions. It "decayed January 23, 1983; reactor core separated; completely burned-up." [ILR] Proposition One adds the following information: "Location: South Atlantic; 68 lbs uranium-238; it is unknown whether any debris reached the ground." [PROP1] According to Harro Zimmer, the reactor casing burned up on January 24, 1983 above the Indian Atlantic, the reactor core burned up on February 7, 1983, above the South Atlantic [ZIMMER, page 113].

See Kosmos 1176.

See Kosmos 1176.

Accident: The TRW Space Log 1996 mentions the following status: "In orbit: Rorsat. Exploded March 11, 1985." [TRW] A NASA report also mentions "Catalogued upon breakup: 158 parts; Currently tracked in orbit: 3 parts." [JSC/a] No information is given about the nuclear reactor. Therefore, it might be assumed that the spacecraft exploded after the reactor had been injected into the higher orbit. This mission is not listed in the Berlin database [ILR].

See Kosmos 1176. "Placed in storage orbit Sept. 27, 1984." [TRW, page 233]

See Kosmos 1176.

See Kosmos 1176.

See Kosmos 1176.

See Kosmos 1176.

See Kosmos 1176.

This was the first development test of a Topaz I reactor in space. For more details about the Topaz reactors, see Section 2.2 The USSR/Russia - RORSAT, Topaz, And RTG.

See Kosmos 1176. "Craft split up July 20; RTG boosted to high orbit on July 28, 1987." [ILR, emphasis added]

See Kosmos 1818. This was the second development test of a Topaz I reactor in space.

Accident: The reactor was injected into a storage orbit but reached only an altitude of 720 km. This means the reactor will take considerably less than 600 years to decay.

See Kosmos 1176. This was the last of the Soviet RORSAT missions. The missions were not continued by Russia. See also text for Kosmos 1818.

"[Galileo] will involve the first-time use of the shuttle to transport a RTG power source to low Earth orbit." [NASA/b] This sentence is from the Draft Environmental Impact Statement for Project Galileo from 1985. Galileo actually became the first RTG powered mission to be launched by a shuttle. Before, however, the shuttle Challenger exploded during its January 28, 1986 launch. Seven astronauts died. The shuttle failure was eventually traced back to an O-ring seal. [TRW]

Therefore, two RTG missions, Galileo and Ulysses (see below) were delayed by several years. Finally, Galileo with its 49 pounds of plutonium was "lifted into space in October 1989 aboard the space shuttle Atlantis. Its mission involves a scheduled eight-year, deep-space voyage to the solar system's largest planet, Jupiter, and its four major moons. ... Galileo used a technique called gravity-assist to make the journey to Jupiter, which is nearly 500 million miles from Earth. ... The craft flew by Venus first, then made two passes by Earth. ...

The effectiveness of Galileo's instruments depends not only on RTG power, but also on heat from radioisotope heater units (RHU). Because the journey is far from the sun, these compact, light, and long-lasting RTG and RHU units are the only effective power and heat sources for the Galileo mission.²²

Two RTGs provide electrical power to drive the Galileo spacecraft and its instruments. Each RTG produces about 285 watts of electricity at the beginning of the mission. One hundred and twenty small RHUs protect the craft's sensitive instruments from damage in the cold vacuum of outer space, which can reach -400 degrees Fahrenheit. ... Each heater unit produces about 1 watt of heat - about as much as a miniature Christmas tree bulb. But, it is enough to protect the instruments from the cold. ... None [of the Pioneer, Voyager, Ulysses, and Galileo] missions could have been accomplished without RTGs, which have played a key role in helping the U.S. establish its position as the world leader in outer planetary and space science exploration." [USDOE/d, page 14]

"If you think about it, we run our entire spacecraft on less than half the power of an average hair dryer!" [NASA/d] Without knowing this argument, the protest movement against the Cassini mission of 1997 used the same comparison to oppose the RTG usage: it was thought that 72,3 pounds of plutonium is too much to produce no more than 750 watts - less than an ordinary hair dryer would consume. The argument is valid for Galileo too: "Galileo carried 49 pounds of Pu-238 on board to meet its electricity needs." [ANDERSON]

"The Ulysses mission is a joint enterprise of the European Space Agency and NASA, with the Jet Propulsion Laboratory in California providing major support. The craft was launched in October 1990 aboard the space shuttle Discovery. Its mission is to study the sun, the magnetic fields and streams of particles the sun generates, and the interstellar space below and above it. ... A single RTG provides all the power for instruments and other equipment aboard Ulysses. It is the only available power source capable of meeting the mission's power requirements. Furthermore, the RTG will provide power for many years, enabling mission scientists and program managers to extend the life of the spacecraft by several years and reap more scientific benefits." [USDOE/d, pages 12 - 14]

This is the most recent and also a broadly covered accident of a nuclear powered space mission. Mars-96 was meant to send two penetrators and two launchers to Mars. The spacecraft, however, went out of control and re-entered the Earth atmosphere on November 17, 1996. The US Space Command, which followed the route of the craft, claims that it fell intact into the sea off the coast of Chile. Eye-witnesses, however, report they saw the craft falling down in the Chile/Bolivia border area - disintegrating and burning. So far, no proof for either version has been presented.

"No news stories have appeared that RADNET is aware of since this date. Presumably, if the plutonium had been recovered intact, some type of public relations effort would result to emphasize the safety of the upcoming Cassini mission. In lieu of a public relations news byte on this topic, one may assume the plutonium vaporized upon re-entry." [CENTER, written before the Cassini launch]

This is a joint mission by NASA and the European Space Agency (ESA). After a Venus Venus Earth Jupiter gravity assist (VVEJGA), Cassini will be flung to Saturn, its moons, and its rings. The Earth flyby is scheduled for August 1999. The European probe Huygens shall be released over the Saturn moon Titan and collect information about Titan's atmosphere and surface while parachuting down. Cassini carries three RTGs with a total of 72 pounds of plutonium to produce 750 W of electrical energy for the on-board instruments. ²³