The US Seriously Committed to Mars Unveils Cold War Legacy [Tech Talk]

A New Concept Rocket Engine That Can Reach Mars in 40 Days
At Least Twice the Thrust of Commercial Rockets
A Cold War Legacy... Shining Again After Half a Century Ahead of the 'Mars Development' Mission

During the Cold War era, when the arms race between the Soviet Union and the United States was intense, NASA attempted to develop a nuclear-powered space launch vehicle, which was groundbreaking at the time. Codenamed 'NERVA,' the project was researched until the 1960s but was ultimately scrapped without ever flying. It was believed that nuclear rockets, along with other Cold War legacies, would fade into history, but recently NASA has restarted the project. This is because traveling to Mars, which is much farther than the Moon, requires a much more powerful rocket, and nuclear rockets are seen as a potential solution.

A New Concept Rocket Engine That Can Reach Mars in 40 Days

An artist's rendering of NASA's nuclear propulsion rocket, expected to be unveiled in 2027. NASA website

NASA and the U.S. Defense Advanced Research Projects Agency (DARPA) are developing a prototype rocket aimed at reaching Mars by 2027. On the 10th of last month (local time), NASA announced the successful development of a modular heat shield, a core component of the nuclear rocket.

Currently, space launch vehicles use either solid fuel or liquid fuel rockets. Solid fuel rockets have a simple structure and are cost-effective but provide relatively weak thrust, whereas liquid fuel rockets have a more complex structure but deliver much stronger thrust, making them ideal for commercial space launch vehicles.

Even the most advanced liquid fuel rockets today require a considerable amount of time to travel to Mars. According to a NASA presentation released in 2012, the travel time from Earth to Mars using a liquid fuel rocket was estimated to be about 120 days. This is a very long time when considering the need to transport numerous personnel and supplies for future human settlement on Mars.

CAD image of a nuclear rocket engine selected by NASA as a candidate launch vehicle to reach Mars. When the reactor emits heat, the hydrogen oxide fuel expands and is ejected, driving the engine's turbo machinery. NASA Glenn Research Center

However, nuclear rockets can solve this problem. It is estimated that a nuclear rocket, which expels hydrogen oxide, could reach Mars in just 40 to 45 days. Moreover, the reactor onboard the rocket can be landed directly on the Martian surface and repurposed as a power source to supply electricity for up to 20 years.

At Least Twice the Thrust of Commercial Rockets

The mechanism of a nuclear rocket is similar to that of a terrestrial nuclear power plant. When the reactor, which induces nuclear fission reactions, emits intense heat, the hydrogen fuel expands due to the thermal reaction and is expelled through the propulsion nozzle, generating thrust. The specific impulse (the thrust produced per kilogram of fuel burned per second, indicating engine efficiency) theoretically ranges from 900 to 1000 seconds, more than twice that of liquid fuel rockets (450 seconds).

Higher fuel efficiency means the rocket can travel farther with less fuel. Consequently, rockets with higher specific impulse are lighter yet can carry more payload. In aerodynamics, weight is a key factor that determines not only platform performance but also logistics efficiency. This is why nuclear rockets are regarded as game changers for deep space exploration.

SpaceX's Falcon Heavy rocket. The thrust of modern commercial rockets using liquid fuel has practical limitations for reaching Mars. SpaceX

Another advantage is that the reactor can be reassembled into a power generator. For an extraterrestrial base to operate, a generator that runs 24/7 without the need for frequent refueling is essential, and a reactor is perfect for this role. If conventional rockets were used, heavy generators would have to be separately loaded into the cargo bay, increasing the burden of Mars exploration missions. However, with nuclear rockets, the transportation means also serve as the power source, allowing for much more flexible operations.

A Cold War Legacy... Shining Again After Half a Century Ahead of the 'Mars Development' Mission

The idea of nuclear rockets was first proposed shortly after World War II in 1946. British rocket scientist Val Cleaver explored rocket propulsion using nuclear energy. Later, this idea materialized as the 'NERVA rocket,' a joint project by NASA and the U.S. Department of Energy in the late 1960s, but the program was discontinued after only ground testing.

Researchers assembling the nuclear-powered rocket engine NERVA in 1962. NASA Glenn Research Center

At that time, the U.S. federal government was focused on the Apollo program, the world's first lunar landing project, and did not have the budget to allocate large sums to NERVA, which was suitable for deep space launch vehicles. After the Apollo program ended, other departments besides the Department of Defense had to enter austerity due to the Vietnam War. As a result, NASA scrapped most projects related to Mars exploration, including the large Saturn V rocket and NERVA.

It took nearly half a century for NERVA's legacy to shine again. Former U.S. President Donald Trump mentioned in his inauguration speech on the 20th of last month that he would "plant the American flag on Mars," which could accelerate the nuclear rocket development program in the future.

Nuclear propulsion rockets are being researched in advanced countries other than the United States because rocket engines can be used directly as nuclear power generators. The photo shows a mock-up of Rolls-Royce's ultra-small space nuclear reactor. Rolls-Royce website. Photo by Rolls-Royce

Currently, nuclear rocket technology is also gaining attention as a core technology for space development in countries other than the U.S. Rolls-Royce, the world's second-largest aircraft engine manufacturer and a developer of military reactors in the UK, is collaborating with the UK Space Agency (UKSA) to develop a 'micro nuclear space reactor.' This reactor can be mounted on rockets to provide power or reassembled as a power source immediately after landing on the Moon or Mars.