Since the 1950s, nuclear rockets have been seen as a game-changer for space travel. Now, with the combined efforts of the NASA, the Defence Advanced Research Projects Agency (DARPA) and Lockheed Martin, mankind is close to launching the first nuclear spacecraft into orbit for testing, reports Interesting Engineering (IE).

Their Demonstration Rocket for Agile Cislunar Operations (DRACO) project, aims to launch a nuclear thermal rocket (NTR) into orbit using a Vulcan Centaur rocket by around 2027.

The Vulcan Centaur rocket is a next-generation launch vehicle developed by United Launch Alliance (ULA). It combines the Vulcan booster with the advanced Centaur upper stage, designed to carry heavy payloads into space. The Vulcan booster is the main part of the Vulcan Centaur rocket that provides the initial thrust to launch it into space.

The Centaur upper stage is the second part of the Vulcan Centaur rocket that takes over after the booster, propelling the payload into its final orbit.

Why Have Nuclear-Powered Rockets?

It is no secret that the space race between the United States and China is quickly intensifying. In reality, the technology involved is much more than just a part of this competition for space dominance.

Nuclear rockets might be essential for colonizing the solar system and extending humanity’s reach in space. They could be crucial for any plans to create a ‘Planet B’, which means finding another planet for humans to live on.

Nuclear Propulsion in Rockets

In 1955, scientists at the Los Alamos National Laboratory began working on nuclear thermal engines through Project Rover. They tested the world’s first experimental nuclear rocket engine, KIWI-A, in 1959.

From 1961 to 1973, NASA carried on this research with the Nuclear Engine for Rocket Vehicle Application (NERVA) programme. The engines developed under NERVA were theoretically more powerful than the chemical rocket engines used in the Apollo missions.

However, both KIWI-A and NERVA faced such problems as fuel cracking and shedding, as well as hydrogen corrosion, because of the extremely high temperatures.

Despite its potential, the last NERVA engine, named XE Prime, only achieved technology readiness level (TRL) 6. To reach TRL 7, the engine would have needed to be tested in space. Although the NERVA programme showed promise, budget cuts and a shift in focus to the Space Shuttle programme led to its cancellation.

This means no nuclear thermal rocket engine has ever been tested in space. Technology readiness levels (TRLs) are a way to measure the maturity of a technology. They range from 1 to 9, with 1 being the basic concept and 9 being fully tested and operational.

Decoding Nuclear Rocketry

KIWI-A and NERVA are different, although related. The Kilowatt Isotope Reactor-A (KIWI-A) was one of the early experimental nuclear rocket engines developed under Project Rover, while the NERVA was a later programme by NASA that further developed and refined nuclear thermal rocket engines, building on the work done with such engines as KIWI-A.

Fuel cracking and shedding occur at high temperatures and involve the breaking and separation of fuel materials. This process can release hydrogen gas, which then reacts with materials, causing corrosion and damage.

Nuclear Rocket Technology Readiness

Recently, NASA and DARPA gave Lockheed Martin a $499-million contract to build the Demonstration Rocket for Agile Cislunar Operations (DRACO). The DRACO programme plans to build on the lessons from NERVA and take it further by flying a nuclear rocket engine in space.

The DRACO rocket will be about 49 feet long and 17.7 feet wide, making it suitable for launch on one of the United Launch Alliance’s new Vulcan Centaur rockets. It will incorporate new technologies, including a special coating in the reactor to prevent material from breaking off.

N-Propulsion: Thermal vs Electric

Other companies, such as Ad Astra, are exploring different methods. Ad Astra, founded by former NASA astronaut Franklin Chang Díaz, is working on a nuclear electric engine named VASIMR.

Nuclear Thermal Propulsion: This mode used heat produced from nuclear fission in a reactor — a process where the nucleus of an atom splits into two smaller nuclei — releasing a large amount of energy. This energy can be used to produce heat or electricity, and it is the principle behind both N-reactors and atomic bombs. The heat is used to quickly warm up a liquid fuel, such as liquefied hydrogen. The fuel then turns into gas and is expelled through the rocket nozzle to create thrust.

Nuclear Electric Propulsion: This mode converts heat into electricity. This electricity is then used to turn a neutral gas into ions. These ions are pushed out of the engine using a magnetic field, creating thrust. This method of propulsion is efficient and powerful, making it suitable for long space missions.

Fast Travel to Mars in Just 45 Days

Ad Astra says its nuclear electric VASIMR engine might one day get spacecraft to Mars in just 45 days. In comparison, NASA estimates that current chemical rockets take about 6-7 months to make the same trip.

But, where can working nuclear rockets be found? If nuclear-powered spacecraft are such a great idea, why has man not sent any into space yet? It’s a reasonable question. The reality is that nuclear-powered spacecraft have always been a good idea, but there are two main obstacles that have held them back:

1) Funding. The NERVA programme was cancelled because of budget cuts at NASA—it was estimated to cost $800 million before being discontinued in 1973—forcing them to concentrate on projects that promised quicker returns, such as the Space Shuttle programme.

In a 2023 interview with IE, Ad Astra founder Chang-Díaz mentioned the challenge of attracting investment for such a large-scale project. He said the timing for a VASIMR demonstration in space depended fully on the funds available. About $150 million was now needed to prepare this engine for flight and, to launch it into space, $50-60 million more would be needed, he added. He was hopeful that, if the company got that investment, this engine could be flying in three years’ time.

2) Regulations:Such projects as NERVA needed uranium that was highly enriched to the level used in weapons. This created a big problem because, if a launch failed, it could spread a lot of uranium over a wide area. To solve this issue, DRACO will use a new kind of fuel, called high-assay-low-enriched uranium (HALEU). This fuel is created by mixing highly enriched uranium until it has less than 20% enrichment.

The Rationale for N-rocket Now

Even with these challenges, the US enjoys competing in space technology. China’s quick advancements could be the push needed to start using nuclear rockets. A report from Ars Technica mentioned that, in April 2021, General James Dickinson from US Space Command said China was trying to become the top power in space by developing space weapons.

The report mentioned this as one reason why NASA and DARPA were focusing on the DRACO nuclear rocket project. As the US and China compete to colonize the Moon, fast transportation will be crucial for logistics and defence.

Nuclear Rockets Save Billions

Although launching a nuclear rocket would be expensive, it could also lead to significant savings in the long run. In 2007, Steven Howe, who leads the Center for Space Nuclear Research at the Idaho National Laboratory in Idaho Falls, mentioned that NASA could save billions of dollars because nuclear rockets were much more fuel-efficient.

Howe estimated that, because of this, building a 250-ton lunar base would require only nine rocket launches instead of 12. Considering that NASA’s inefficient Space Launch System costs about $2 billion per launch, using more efficient rockets could lead to significant savings.

Why Faster Space Travel Matters

The advantages of faster space travel are significant. First and foremost, reducing travel time is vital for astronaut health. The quicker astronauts can travel through deep space, the less they are exposed to dangerous cosmic radiation.

The alignment between Mars and Earth is also very important. If travel times are longer, it could mean astronauts have to stay on Mars for extended periods. Mars and Earth come closest to each other every two years and two months. If the journey takes seven months, astronauts may not complete their missions in time for the next launch window.

Nuclear rockets could cut travel time in half. This improvement may one day be as significant as the shift from horse-drawn carriages to cars. They could be essential for a future where space travel is common.

Elon Musk from SpaceX has hinted that the Starship could eventually travel to other stars, indicating that SpaceX may someday explore alternatives to conventional chemical propulsion.

The author of this article is a Defence, Aerospace & Political Analyst based in Bengaluru.