The United States has started taking steps to place a nuclear powered thermal rocket in orbit by the year 2025, which can pave the way for improved navigation in space.The Defense Advanced Research Projects Agency (DARPA) has planned to turn the long-studied concept of a nuclear thermal rocket into a reality. The technology isn’t powerful enough to launch a rocket from Earth, but could provide a spacecraft propulsion for an extended period once in space. This will make it ideal for prolonged maneuvering in orbit or in deep-space missions requiring acceleration and deceleration.

Nuclear thermal rockets use nuclear power to heat cold propellants to high temperatures, which causes the propellant to expand and supply thrust. The thought for such propulsion was developed by the US Air Force in 1946, and also later by Qian Xuesen at the Massachusetts Institute of Technology in 1947. The engine will run as long as the supply of propellant – typically hydrogen – holds out (probably for a few weeks).

This project is being facilitated partially by a 2019 US presidential memorandum, which makes it simpler to get approval for launches of spacecraft containing material. To suit in with the rules set out by the memorandum, the project will have a less radioactive power source than the previous ones, like NASA’s Nuclear Engine for Rocket Vehicle Application program in the 1960's, which helped in developing the concept of nuclear powered thermal rockets but never got tested in space. Contracts to design both, a demonstration system and a full-blown operational spacecraft, have now been awarded to the General Atomics, Blue Origin and Lockheed Martin.

The project will focus on satellites in orbits of up to 400,000 kilometres above Earth, which is far higher than current space operations administered by military spacecraft. With this technology, military operators will be able to move nuclear-powered communications or spy satellites, at their own will, to an area of interest. It can also open up new possibilities, like tracking and identifying rival stealth satellites.

Launching nuclear rockets comes with its own challenges. In 1983, a reactor on the Soviet Kosmos 1402 Spy Satellite caused major concerns when it malfunctioned and spiraled towards the Earth. Fortunately, it burned up harmlessly in the atmosphere as it had been designed to do.To avoid such happenings, the DARPA reactor won’t be activated until it's in space. “If the reactor hasn’t been operated, then it’s basically just a quantity of low-enriched uranium,” says Laurence Williams, a specialist in nuclear safety at Imperial College London. “It has nothing like the toxicity of plutonium, which has been used for radio thermal power plants on a number of space missions” for example, NASA’s Perseverance rover that's currently exploring Mars gets its electricity from a plutonium-238 power source.

Williams says that an in-depth safety analysis would still be needed before any launch, assuming what might happen if the rocket failed at take off or blew up in the atmosphere afterwards.The US has been increasingly specializing in expanding its military strength in space after the founding of the US Space Force in 2019.

If the DARPA project succeeds, we could soon see an entire generation of nuclear spacecraft in Earth's orbit and beyond. NASA has long been curious about nuclear thermal propulsion for missions to Mars and elsewhere, and has its own less ambitious program working on the technology.

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