Czech scientists working on nuclear powered electric engines for use in space

The project “RocketRoll” - illustration of NEP tug

The European Space Agency (ESA) is looking for ways by which its future spaceships and probes could use nuclear-powered engines in order to travel across the extreme distances of outer space. Scientists at the Czech Technical University in Prague are among the many institutions involved in the effort, specifically a project called “RocketRoll”. I spoke to Jan Frýbort from the university’s Department of Nuclear Reactors to find out more.

“There are essentially two technologies that we can use for the utilisation of nuclear reactors when it comes to space missions.

“One of them is based around thermal propulsion. That means directly heating a medium such as hydrogen in the reactor. This method works in a similar way to that in which chemical propulsion is used in rockets.

“Our study focuses on the other method. Namely, that of using electric engines or thrusters that use the nuclear reactor to produce the electricity that propels them.”

Could you tell me what the benefits of nuclear propulsion instead of the currently used chemical propulsion for rockets are? I understand that it would, for example, enable us to travel further than is currently possible.

“Exactly. The electric engines or thrusters that are currently in use are powered either by batteries or solar power. The later gets weaker the further we travel from the sun. For longer distances we therefore need to use other power sources.

“The other benefit of nuclear power or fuel is that its power density is much greater than that of classical chemical fuel. This means that we can essentially run those engines for longer periods. So even though the acceleration would be lower, one can achieve a higher velocity at longer distances.

“Therefore, when we think about missions to Mars and beyond, nuclear power becomes inevitable. We have no other choice then to use nuclear power to bring humans to Mars.”

Photo: ESA

Scientists have of course come up with many different ideas of how to travel long distances in space, whether they be electric engines or those solar sales for example. If you had to compare your project to other similar methods that are being developed right now around the world, how does it compare?

“We certainly aren’t the first ones who are trying to achieve this. During the 1960s through to the 1980s, more than 30 nuclear reactors were sent into the Earth’s orbit, so it’s definitely not a new idea.

“However, what is new is that we are now aiming to design the whole vehicle. That means the nuclear reactor, its radiation shielding, the conversion cycle and the way of how to eject heat into space, including the electric propulsion engines.

“So this is the stage that we are at and it is really important for the European Space Agency now because next year, in 2024, they should be deciding on whether they will use nuclear thermal propulsion method or that of electric propulsion.

“Both directions have some advantages and disadvantages and they will decide in which direction to go based off of these findings. After choosing the right direction, we will then need to go beyond the calculation and simulation stage and start with real experiments.”

Tell me why you think your method would be optimal.

“Speaking strictly from my own opinion, these electric propulsion engines have the benefit that you can use them for other purposes, such as for powering bases on the Moon or on Mars. You will need a nuclear reactor to power those bases.

“So, once you have this nuclear reactor with this conversion cycle to produce electricity, you will be able to find other applications outside of it being a space propulsion engine.”

Nuclear reactor | Photo: Don McCullough,  Flickr,  CC BY-NC 2.0

I am guessing that you would have to shoot these nuclear reactor powered objects into space using chemical propulsion. We often see rockets exploding during launches. How would you ensure no nuclear accidents occur?

“Safety is one of the primary objectives of this project. We need to be sure that there is as low a possibility of an accident as possible. Obviously, we cannot start this nuclear reactor before it reaches the orbit.

“If something were to go wrong and what we call ‘re-entry’ were to occur, meaning the rocket were to fall down, it would just be the fresh fuel without any dangers of nuclear active material.

“That means that we would only start the reactor once it is in orbit and it must be safely stored during the launch in order to avoid an accident.”

Aside from your institution, there is also the Czech company OHB Czechspace and two parties from Germany – OHB System and the University of Stuttgart – that are taking part in the RocketRoll study. What exactly is your part in this effort?

“We are focused on the nuclear reactor part of the study, the conversion cycle of how to produce electricity and on the technology of how to produce those electrical engines that I spoke about earlier.

“The companies serve as the primary investigators in this regard and they contribute through their general experience of ESA space missions.

“This is also the case when it comes to our colleagues from Stuttgart because they have also participated in past European projects that have investigated the use of nuclear engines in space, so they help us with their expertise.”

Solar system | Illustrative photo: Efraimstochter,  Pixabay,  Pixabay License

You were saying earlier that a final decision is to be made on which propulsion system to use. Is this also the time limit for your study?

“It has to be finished within a year because the European Union is behind the United States and possibly also China and Russia when it comes to this research.

“We are in a real hurry so to say. ESA would like to take the decision next year, so we have both projects – the exploration of nuclear thermal and of electric propulsion – running at the same time.”

Are you able to take inspiration from those similar projects that are running in other countries, especially the United States, or is this a secret that each country tightly guards?

“Luckily, the main ideas are available in specific journals where scientists publish their work, so we have sources of information.

“However, the assignment from ESA is to investigate the European capability. That means that the study should be based off technologies that are available in the EU or in countries that are participating in ESA. This is also part of the project – to investigate European capabilities to build such rockets.

“We can certainly take inspiration from other projects, but we need to be sure that the necessary components can be made in Europe.”