A while back I was chatting with a former astronaut about the future of deep space exploration. I mentioned that SpaceX CEO Elon Musk started his company to make spaceflight more affordable and allow him to try and complete his dream of colonizing Mars.
The space veteran was blunt about Musk’s plan to build a big rocket for carrying cargo and humans to Mars. “We are not getting to Mars with chemical rockets! We need nuclear propulsion,” the former astronaut told me. Eighteen months after that chat, NASA announced it will launch a nuclear thermal rocket (NTR) by 2027.
Time and radiation are the problems astronauts would face traveling to Mars with today’s technology. Earth’s atmosphere protects humans from a lot of radiation. Astronauts are bombarded by radiation, which is why we study the effects of long flights and are looking for radiation protection systems for spacecraft and astronauts.
The time part of this equation is a result of the chemical engines we use for spacecraft. Musk’s current plans for his methane-fueled Starship would mean a six-month journey to Mars. Many believe that’s just too slow, meaning too much radiation exposure for the crew.
A nuclear thermal rocket [also known as nuclear thermal propulsion (NTP)] would be more efficient and therefore faster. An NTR could cut the travel time in half. That’s why NASA and the Defense Department’s science arm, DARPA, are teaming up to build and launch an NTR in five years.
NASA’s Deputy Administrator, Pam Melroy, told an Aeronautics conference, “this is really a tangible step forward for us in getting humans to Mars,” adding, “this will allow us to evaluate the opportunity to move faster. If we have swifter trips for humans, they are safer trips.”
An NTR is a small reactor that is used to heat a liquid into a gas that is then expelled out a nozzle, creating propulsion. Hydrogen is the most likely liquid to be used. NASA is open to using another type of nuclear engine. It’s called nuclear electric propulsion (NEP). An NEP reactor creates electricity, which powers an ion-thrust engine to propel the spacecraft.
The technology is not new. NASA and others were deeply involved in research from the 1950’s through 1972. Twenty-three types of reactor engines were built in that time period. The nuclear propulsion programs were canceled as the US ended the Apollo program and moved forward with the Shuttle. It was also a time of concern over nuclear power. For five decades the research was largely shuttered.
DARPA has been working on the technology for an engine for the past few years. It’s called the Demonstration Rocket for Agile Cislunar Operations (DRACO). Now working together with this announcement, NASA and DARPA say they won’t use highly enriched uranium. Stephanie Tompkins of DARPA says that would create, “regulatory and societal” issues. Instead, what is known as HALEU will be used in the reactor. It is only enriched to between 5% and 20%.
The government officials say the technology will be safe. The exhaust hydrogen from the DRACO will not be radioactive and the test spacecraft will not reenter Earth’s atmosphere until it is no longer radioactive. That will take 300 years.
Under this agreement, NASA will build the reactor engine and DARPA is responsible for the overall effort and building the test spacecraft. Launch is set for 2027. As a long time researcher of space nuclear engines said, “it’s ambitious.”