Rocketroll: nuclear-electric spacecraft study
In brief
- The conclusions from an ESA-commissioned study on a nuclear-electric powered spacecraft are available.
- A wide pool of experts from all domains, gathered in three consortia, delivered reports with their design approaches: Tractebel, CNRS and OHB Czech Space.
- All aspects from safety to ground segment, operations and technological requirements were considered.
In-depth
As humans prepare to explore farther from our Sun with more cargo and more versatility, our current space technology is quickly reaching its limits. Nuclear-electric propulsion could provide a large source of power that solar panels or traditional propellants cannot achieve.
The “Rocketroll” study (a loose acronym taking letters from the phrase “pReliminary eurOpean reCKon on nuclEar elecTric pROpuLsion for space appLications”) tasked three consortia to investigate a European approach to nuclear electric propulsion. The study is similar to the Alumni study but focusses on electric propulsion instead of nuclear-thermal propulsion. With nuclear-electric power, controlled fission is used to generate electricity.
The Rocketroll study was conducted because some space missions have high-power requirements which can only be achieved with nuclear power. For example missions to outer planets, or Moon surface missions that need to survive the 14-day lunar night. The Rocketroll designs could provide electrical power ranging from hundreds of kilowatts that would fit with Europe's Ariane 6 heavy-lift rocket, to a few megawatts that could be launched on next-generation rockets.
Three consortia, three designs
Three teams looked at the nuclear-electric designs and proposed their solutions in three reports, the executive summaries are public and are linked below.
Tractebel led a proposal that relied on enriched uranium, CNRS proposed a solution based on a molten salt reactor, and OHB Czech Space suggested a larger spacecraft.
New focus, new possibilities
“The studies show clearly what is possible and how well it all fits inside ESA’s long-term strategy 2040,” explains Valère Girardin, ESA’s programme manager for the study, “We now better understand what technologies are missing and what to target in research and development.”
All studies conclude the use of nuclear-powered propulsion opens new paths for exploration: there are destinations or missions that are simply unattainable with traditional spacecraft propulsion.
Safety is no problem, all designs rely on unirradiated uranium that is not activated until in orbit, meaning no high radiation, even in case of launcher explosion, splashdown to the ocean or other launch failure. The uranium’s chain reaction is only activated –once in space and safely in orbit, until then the uranium is inert.
The tipping point for spacecraft designs is around the 100 kW power level, below that power production a solar-electric propulsion system relying on solar panels is ideal, above that a nuclear-electric design rules. All consortia foresee two launches, one with the payload, and one with the spacecraft that would dock in Earth orbit continue their voyage in space together.
“These studies are kick-starting progress and putting nuclear-powered European spaceflight on the roadmap,” concludes Valère, “the technologies we need fit well with ESA Member States industrial capacities and the political will is gaining traction, we now have a clearer target to work towards.”
The next step is to increase knowledge and experience of each system separately, the nuclear reactor, the radiation shield, the energy conversion system, the thermal heating and cooling system and the electric thrusters. ESA has formed a nuclear propulsion working group that will oversee the design and building of sub-scale hardware and tests in laboratories.