This is how the Rocketroll project works

Artemis II has been an example of how far space travel can go. So far that there will come a time when the technologies currently used to propel ships will be insufficient. There is no point in using solar energy if we move too far from the Sun or travel to the Moon, with 14-day nights. Nor is it useful to use the best fuel if the trip is going to be so long, so far and with so much load that refueling needs would be unfeasible.

For this reason, nuclear propulsion has been considered for some time to take ships where they cannot go today. The European Space Agency (ESA) has also jumped on that bandwagon and has already carried out its first studies.

An order for three consortia. The ESA just announced the first results of the Rocketroll project, which has asked three independent consortia to design an approach to use nuclear electric propulsion in European space missions. This is something that other space agencies, such as NASA, have already begun to study, but in European territory work had not yet been done on this specific issue.

Thermonuclear propulsion vs nuclear-electric propulsion. In fact, nuclear propulsion for spacecraft had already been studied in Europe. That is the key to the Alumni project, presented by ESA last year. The difference is that in that case a thermonuclear propulsion system was designed. That is, a reactor in which nuclear fission generates heat that is used to heat a fluid that serves as a propellant. What has been studied in Rocketroll is different, since nuclear fission generates electricity, which is supplied to a series of electric motors.

Each one has its advantages. In absolute terms, thermonuclear propulsion is more powerful. However, it is accompanied by technical problems, such as storing a sufficient amount of propellant. Plus, it’s very expensive. The other option is cheaper and, accompanied by some chemical propulsion, is just as powerful. That is why ESA is so interested in having its ships work with this mechanism.

Three consortia, three proposals. Three multidisciplinary consortia have participated in this project: Tractebel, CNRS and OHB Czech Space. Each has made a proposal that would be incorporated into the entire system. For example, the first consortium has proposed using enriched uranium as a generator of nuclear power.

Uranium-238 is the most abundant in nature, but it is not fissile. This means that a nuclear fission chain reaction cannot be maintained from it. Nuclear fission is the process by which energy is obtained in nuclear reactors, so it is of no use to us. On the other hand, Uranium-235 is fissile. Enriched uranium is richer in this isotope, so it can be used in a nuclear reactor. Compared to other options, such as Plutonium-239, Tractebel considers that this is better.

For its part, CNRS proposes using a molten salt reactor. That is, a reactor in which this type of salts are used as coolant and/or fuel to trigger nuclear fission. Finally, the third consortium proposes that the ships be larger to optimize the results.

Scheme of the alumni nuclear thermal propulsion system (Image rotated)

A safe option. All consortia conclude that nuclear-electric propulsion can open new paths for space exploration. This is great news, but we may have doubts about its safety. Before them, they remember that it is a risk-free process. The uranium that would be activated remains inert and is only activated, to trigger nuclear fission, once it is in orbit. There would be no risks while handling the ships on Earth.

In addition, shields are used so that astronauts and spacecraft cargo are not at risk when the reaction is triggered. We must not forget that space is also a large source of radiationso ships must be properly protected.

Next steps. This first step by Rocketroll has been little more than a brainstorm. There is still quite a way to go. For example, each system will have to be studied separately, from the nuclear reactor to the radiation shield, including the energy conversion system, the thermal heating and cooling system and the electric thrusters.

For all this, ESA has already formed a nuclear propulsion working group that will oversee the design and construction of subscale hardware. There will also be laboratory tests to confirm that everything is working properly before even thinking about testing the system in space. This technology may be the future, but it must be tested slowly.

Image | THAT

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