SNAP-10A, the world’s first operational nuclear reactor in space

Launched on April 3, 1965, SNAP-10A was the world’s first operational nuclear reactor in space. While it still remains in orbit, it was operational for just 43 days. A.S.Ganesh takes a look at SNAP-10A and how it was set up in space…

April 02, 2023 12:26 am | Updated 12:26 am IST

An artist’s impression of the SNAP-10A/ Agena-SNAPSHOT configuration

An artist’s impression of the SNAP-10A/ Agena-SNAPSHOT configuration | Photo Credit: US Department of Energy flickr

Do you know what nuclear reactors are? A class of devices that contain and control sustained nuclear chain reactions, these systems are at the heart of any nuclear power plant. While nuclear power plants produce clean and renewable energy that can then be used to power homes, schools, office spaces, and hospitals, their byproduct is radioactive material, which can be extremely toxic and hence has to be dealt with carefully.

It is no surprise that building nuclear reactors – which releases the nuclear energy in the nucleus or the core of the atom through the process of nuclear fission – needs a high level of technology. Most of the nuclear power plants in the world are, therefore, located in a few countries that possess the necessary technology.

Reactor in Earth orbit

There is, however, a nuclear reactor that is in Earth orbit. The U.S.’ first and only known space nuclear reactor, the SNAP-10A was the result of the government-sponsored System for Nuclear Auxiliary Power (SNAP) programme, also known as SNAPSHOT for Space Nuclear Auxiliary Power Shot.

The objective of this programme, for which considerable effort was spent in the 1950s and 1960s, was to develop compact, lightweight, reliable atomic devices that could then be employed in space, sea, and land. Facilities to support the development and testing of the reactors and related hardware were constructed within Santa Susana Field Laboratory Area IV.

Remotely started and operated

In the case of SNAP-10A, the objective was to produce at least 500 watts of electricity for a year or longer. Designed to be remotely started and operated in space, the entire system weighed less than 431 kg, including the instruments and shielding.

The world’s first nuclear reactor to operate in space, SNAP-10A, was launched into Earth orbit on April 3, 1965.

The world’s first nuclear reactor to operate in space, SNAP-10A, was launched into Earth orbit on April 3, 1965. | Photo Credit: Atomics International contractor to US Atomic Energy Commission Wikimedia Commons

The plan to operate it remotely was put in place so that any radiation hazard associated with nuclear fission does not take place until after the reactor is put into orbit. This not only eliminates radioactive exposure to ground personnel (as byproducts are produced only after operation), but also reduces the overall risk, should there be an accidental reentry during launch.

Using enriched uranium fuel with zirconium hydride as a moderator, the SNAP reactors had liquid sodium potassium alloy as the coolant. A thermoelectric converter was used to directly convert heat from the reactor into electricity.

Placed in polar orbit

The SNAP-10A was launched on April 3, 1965 on an Atlas-Agena D rocket from Vandenberg Air Force Base. A perfect launch meant that the SNAPSHOT spacecraft was placed as planned in a polar orbit.

The startup order was remotely initiated 3.5 hours into the flight and within six hours, the reactor achieved on-orbit criticality (the state in which a nuclear chain reaction is self-sustaining). After 200 hours of reactor operations, it was set to autonomous operation at full power, producing more than 600 watts of electrical power.

On May 16, however, contact was lost with SNAP-10A for about 40 hours. During this blackout, the reactor’s reflectors ejected from the core and the core shut down, bringing an end to the reactor’s operations. The problem, however, wasn’t with the reactor, which shut down as a result of a high voltage failure in the electrical system of the Agena spacecraft.

While all the test flight objectives were met, the only exception was the length of operation, which was just 43 days as opposed to the expected year or more. Once the emergency batteries died five days later, all communications with the spacecraft ceased forever. Data was received from SNAP-10A for only 616 orbits.

Safety concerns remain

SNAP-10A remains the only known nuclear reactor sent to space by the U.S. NASA has considered sending others, but has shelved the idea owing to funding issues and safety concerns. Russia, meanwhile, has sent quite a few of them, including one that crashed and scattered radioactive debris over Canada in 1978.

As for the SNAPSHOT reactor, it continues to be in Earth orbit and NASA expects it to do so for 2,000 years or more. While this means that there is no danger of re-entry in many human lifetimes, at some point, the reactor would have to be moved into a graveyard orbit or needs to be picked up and returned to Earth. That might be a problem worth working on as it has no solution as yet.

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