SNAP-10A
Snapshot ( military designation OPS 4682 ) A started on April 4, 1965 experimental technology satellite of the United States Air Force who had the testing of a nuclear reactor as a power source for the satellite to the target. The on-board reactor SNAP -10A was the first nuclear reactor in space. Also came with this mission, the first American in orbit ion thruster.
Development
The development of a space-qualified compact nuclear reactor took place in the framework of the system for Nuclear Auxiliary Power Program ( SNAP ) of the U.S. Atomic Energy Commission. In this program, in addition to nuclear reactors and radionuclide have been developed. SNAP- models with straight serial number were reactors and those with an odd number were radionuclide.
Prime contractor for the reactor coil was Atomics International, then a division of North American Aviation. The development of the systems and the reactor tests took place in Ventura County, California in special facilities at the Santa Susana Field Laboratory.
The company had previously built in the SNAP program experimental compact reactors and tested - including the SNAP Experimental Reactor (SER ), SNAP -2, SNAP -8 Developmental Reactor ( SNAP8 -DR) and SNAP -8 Experimental Reactor (SNAP - 8ER ) versions. However, these were purely experimental and not yet suitable for application to a satellite. In addition, Atomics International Sodium Reactor Experiment with the built the first nuclear power plant, the power delivered into the public electricity grid.
In addition to the development of space-qualified reactor itself, it was also necessary to develop new security guidelines for dealing with such a device. This was part of the Aerospace Nuclear Safety Program, which examined the hazards associated with the construction, startup, operation and disposal of the SNAP systems. The responsibility for the security was at Atomics International, while the Sandia National Laboratories conducted an independent examination and various tests. Before the start was allowed, had to be proved according to these guidelines, that under no circumstances could a serious danger posed by the reactor.
Construction
The satellite snapshot consists of the SNAP -10A reactor, which is firmly attached to the Agena upper stage of the launch vehicle. The Agena stage took over for the satellite after bullet into orbit position control, so that the payload does not require separate systems for it.
Reactor
SNAP -10A - reactor consisted of three main components:
- A compact reactor
- A controllable neutron reflector
- A heat transfer and energy conversion system
The reactor core had a mass of 290 kg at a height of 39.62 cm and a width of 22.40 cm. It contained 37 fuel rods from uranium -zirconium hydride ( UZrH ), which served both enriched uranium -235 ( 235U ) as a nuclear fuel material and as a moderator. The thermal power of the reactor was 30 kW.
To achieve criticality and to control the power of the reactor neutron reflectors were disposed of beryllium to the reactor core. Some of these reflectors were mounted in a fixed position, but four half cylindrical Berylliummassen were rotatably mounted, so that the amount of reflected neutrons could be altered by rotation of the reflector. At the start of the reflectors were in an open position, so that the arrangement was subcritical. Only in orbit, the tax reflectors turned into a position that enabled the reactor core criticality.
For security reasons, the reflectors could be separated from the reactor core in order to this in a permanently subcritical state. To this end, a retaining band was determined by an explosive bolt severed and the reflector elements repelled by springs. Without the presence of the reflectors, the reactor core can maintain no more chain reactions.
As a cooling agent used was a eutectic alloy of sodium and potassium, which was pumped by means of a thermoelectric pump through the reactor core. The hot liquid is passed through tubes in the structure below the conical reactor, where the heat is discharged via thermocouples of radiators. Due to the temperature gradient between the hot coolant lines and the space a voltage was generated in the thermocouples. The output of the thermocouples was 0.5 kW.
Ion propulsion
As a secondary experiment was located on the satellite a cesium ion propulsion, was its energy supply by the electricity generated in the reactor. The ion engine was the first example of an electric drive, which should be tested in orbit.
The power supply of the ion thruster supplied from a battery, a voltage of 4500 V at a current of 80 mA for a period of one hour. After that, the battery had to be recharged by the SNAP -10A reactor for 15 hours again, for which 0.1 kW were needed. A reaction mass of the engine served ionized cesium which was electrically accelerated. The neutralizer of the engine consisted of a barium oxide coated wire mesh. The engine achieved a thrust of 8.5 mN.
Mission Description
Snapshot started on April 4, 1965 on an Atlas - Agena SLV3 - D rocket from Vandenberg Air Force Base in a low polar orbit. Also on board was also a small secondary payload, the satellite geodetic SECOR 4, which was removed after reaching Earth orbit. Snapshot itself was integrated with the Agena stage and remained thus connected with the intentionally rocket stage. Snapshot successfully reached an orbit with an apogee of 1325 km, a perigee of 1279 km and an inclination of 90.2 °.
The ion engine had already been permanently shut down after only one hour of operation, as there were numerous voltage flashovers. This caused electromagnetic pulses, which interfered with the attitude control system of the satellite massively.
After 43 days in orbit failed a voltage regulator of satellite electronics and thus led to a shutdown of the reactor, which meant the end of the snapshot mission.
Although the basic suitability of a nuclear reactor for power supply of a satellite was demonstrated as was the mission objective to operate the reactor at least one year, failed. The testing of the ion thruster was also a failure.
Aftermath
The orbit of snapshot has a height of 1300 km, so that the satellite will be about 4000 years in orbit. Thus, a short-term risk is not given by the re-entry of radioactive reactor.
In November 1979, it was observed that about 50 objects were released from the satellite snapshot. The cause is unknown, but can not be danger of collision with space debris. Perhaps this also radioactive material was released.
A nuclear reactor was here first and last times used as a power supply from the USA. The Soviet Union continued reactors until 1988 with numerous satellite as part of the RORSAT program, where there were several incidents in which radioactive substances were released into the environment. Nuclear reactors play in both the civil and military aerospace U.S. no more practical role, although further, unrealized projects were considered with this energy source. Nuclear energy, however, continue to play as an energy source for space probes to the outer solar system beyond the orbit of Jupiter and Jupiter's solar cells destructive radiation belts play an important role, for example in the form of the radionuclide or radionuclide heating element, since there the sunlight for photovoltaic power supply is too low, or not possible. For earth satellites and space probes many solar cells are, however, a risk-free to be used, economical and reliable technology.