Rockets have been operating for a century in a similar manner. There is a tank that stores chemical fuels. These are ignited and they spit out a nozzle at high speed to create thrust. Space journeys require a lot of fuel as there are no refills available in outer space. Major portion of the tonnage of rockets putting weather and communication satellites in space is accounted by fuel.
In the 1950s, scientists thought of an alternative fuel. There can be a small nuclear reactor to heat up a propellant, say liquid hydrogen, to high temperatures (higher than what could be achieved in a chemical rocket). That will make rocket engine efficient — twice as efficient as a traditional rocket and faster too. A chemical engine will burn out at such high temperatures.
This is in essence nuclear thermal propulsion (NTP). There was research on this till the early 1970s. Such rockets cannot be used as launch rockets, since an NTP system lack the thrust to leave the earth’s surface. Instead, an NTP rocket could be carried into space on a traditional rocket and then make it operate there. So far no such experiment has been conducted but there are tests on the ground which demonstrate that the concept could work.
NTP as a concept has never been forgotten. There are issues of safety. However, tech advancements have placed it on the agenda of space authorities.
National Aeronautics and Space Administration (NASA) has partnered with the department of defense. It has given Lockheed Martin $500 million to build and test superfast nuclear-powered engine by 2027. If this is not done, NASA cannot compete with private companies like SpaceX and cannot realise its dream of putting its mark on more parts of the solar system and make US the leader in outer space.
The immediate objective for NASA is the journey to Mars. By 2030s, there should be manned flight to the Red Planet. Traditional rockets take seven months to reach Mars. A round trip mission would take two to three years. If an efficient rocket is used, Mars could be reached in 45 days. It augurs well for the physical and psychological well-being of the astronauts. It is an incentive to make more trips.
It is a competition among the US, China and Russia. The other countries try to neutralise the US.
A nuclear powered rocket is an untested entity in space. There are issues of its performance in extreme conditions. If there is an accident at the time of launch, there could be an environmental and health catastrophe.
The comforting part is that such a rocket is easier to build new than it was in the past. Material science has made rapid advances. It has come to a stage where an entity could be engineered that can withstand outer space and a heat of a nuclear reactor. Computers have advanced, so that complex reactor designs can be subjected to simulations, and redesigns very quickly.
Success is not guaranteed but the effort is worth.