Future nuclear thermal propulsion for space explorer

Is the future of space NUCLEAR? Nasa is developing new rockets to send astronauts to new corners of the solar system

• Nasa engineers are planning to build rockets powered by nuclear fission
• The nuclear fuel is used to heat liquid hydrogen to create jets of plasma 
• Researchers say the rockets could halve the time it takes to reach Mars
• They hope it could be used to carry astronauts to the red planet in 2033
• They have proposed a new nuclear powered spacecraft called Copernicus

By Richard Gray for MailOnline

Nasa scientists are developing new nuclear powered rockets that they hope could be used to travel the huge distances needed to take astronauts to Mars and explore the solar system.

They believe the rockets, powered using nuclear fusion rather than traditional chemicals, could dramatically cut the time it takes to travel through the solar system.

Engineers at the space agency have now been drawing up plans to use nuclear thermal propulsion in a mission to Mars in 2033.

The proposed Copernicus spacecraft would use nuclear thermal propulsion to carry astronauts to Mars

NASA'S NUCLEAR HISTORY 

Nasa has been using nuclear material to power spacecraft for decades.

In 1960 a satellite programme called TRANSIT, used to guide missiles from space, was the first to use plutonium isotopes to create batteries.

These work by wrapping the plutonium with thermoelectrics, that turn the heat given off by the decaying isotope into electricity.

Nasa also used plutonium batteries on its failed Nimbus B1 satellite, which blew up on launch.

IN 1972 and 1973 Nasa then launched its Pioneer space probes, which used 155-watt nuclear batteries to keep them powered as they travelled to the very edge of the solar system.

The Viking landers, which touched down on Mars for the first time in 1976, also used plutonium batteries to power their experiments.

The Voyager probes, which have become the first manmade objects to leave the solar system, also relied upon three plutonium-238 batteries that have allowed them to communicate with Earth for 36 years.

The Ulysses sun probe also used a nuclear battery to keep the spacecraft operating while it performed a slingshot around Jupiter.

The Galileo spaceprobe to Jupiter's moons also used two nuclear batteries to give it 570 watts of power.

The cassini space probe to Saturn carried the largest nuclear battery every launched, weighing 72lbs.

The Curiosity mars rover also has a 125 watt battery to help keep the robot moving on the surface of the Red planet.

In 1959, Nasa began work with the US Atomic Energy Commission to develop a nuclear powered rocket to carry astronauts into space, but the project was ended in 1973 at the same time as the Apollo space missions.

 

Nuclear thermal rockets weigh around half as much as chemical rockets for the same amount of thrust, they say.

Their plans were outlined in a series of reports and presentations by Nasa officials and researchers and a presentation given by a senior manager

According to their design, uranium-235 nuclear reactions are used to heat liquid hydrogen inside a reactor, turning it into ionized hydrogen gas, or plasma.

This plasma is then channeled through a rocket nozzle to generate thrust.

Dr Stanely Borowski, an engineer at Nasa's John Glenn Research Centre, outlined how this could then be used to propel a space with its crew through space in a official Nasa paper.

He said the spacecraft, called Copernicus, would consist of separate cargo and crewed transfer vehicles, each powered by a nuclear thermal propuslion stage.

These would be constructed from a 'core' that use three engines each capable of producing thrust of around 25,000 lbs of force.

He estimates that these vehicles could make the 40 million mile trip to Mars within 100 days.

It took the Mars Science Laboratory spacecraft carrying Nasa's Curiosity Rover to Mars 253 days to reach the red planet.

Writing in his paper, Dr Borowski said: 'Recent measurements of the energetic particle radiation environment inside the Mars Science Laboratory spacecraft during it journey out to Mars indicate that astronauts could receive a radiation dose of ~0.66 Sv - the limiting value established by NASA — during a 1-year journey out to Mars and back.

'With the potential for the crew to receive additional dose during the exploration phase of the mission, several questions immediately arise.

'Can nuclear thermal propulstion’s performance capability be used to reduce transit times further and by how much?

'The analysis presented here indicates transit time reductions as much as 50 percent are possible.'

Nasa first began researching nuclear thermal rockets as part of its Nuclear Engine for Rocket Vehicle Application (NERVA) programme in 1959.

However, the project, which was a collaboration between Nasa and the US Atomic Energy Comission, was officially ended in 1973.

During that time, however, engineers produced several prototypes, the most advanced of which was known as a Pewee engine. None of the engines were ever used for flight.

A schematic of the nuclear thermal rocket shows how liquid hydrogen propellant would heated by the reactor

This diagram shows how the Copernicus spacecraft could be adapted to different missions and travel times

Now Nasa appears to be hoping to revive the cancelled programme to provide a new generation of rockets to carry its astronauts and the equipment to support them into space.

As a nuclear rocket weights almost half as much as a chemical rocket carring liquid oxygen and hydrogen propellant without reducing thrust.

This means larger payloads of cargo can be carried on the spacecraft and they can also be made to travel far faster.

Under the plans outlined by Dr Borowski, a mission to Mars in 2033 could use two cargo vehicles to deploy surface and orbital equipment to Mars ahead of the arrival of the crew.

He said that Copernicus coulod easity manage a oneway trip to Mars in around 130 days but by altering the design of the spacecraft to carry more propellant this could be reduded to 100 days.

He says that it may even be possible to make the journey in just 90 days with a crew if equipment and cargo are carried into space in a series of seven launches from Earth.

Engineers have proposed using seven launches (shown above) to carry cargo and crew to Mars in 2033

Nasa's engineers have outlined a number of designs, shown above, for nuclear thermal propulsion rockets

The most powerful nuclear rocket engine ever tested was

 the Phoebus 2a, which was fired for 32 minutes in 

Nevada in 1968 as can be seen in the photo above

Proposals to use nuclear powered rockets were also discussed in a recent presentation by Dr Michael Houts, nuclear research manager at Nasa's Marshall Space Flight Centre.

He said the nuclear propulsion was a 'game changing technology for space exploration'.

He said they hoped to prove the viability and affordability of the technology within the next three years.

He said that radioactive isotopes such as strontium-90, which has a half-life of 28.8 years, or cesium-137, with a half life of 30.1 years, could also be used to power the reactors.

Nasa could use nuclear fission to power future missions to explore Jupiter and its moon Europa, Neptune and the Kuiper Belt, he said.

Dr Houts said: 'Nuclear thermal propulsion is a fundamentally new capability - the energy comes from fission not chemical reactions.

'Initial systems will have specific impulses roughly twice that of the best chemical systems, reduced propellant launch requirements, reduced trip time and beneficial to near-term/far-term missions currently under consideration.

'Advanced nuclear propulsion systems could have extremely high performance and unique capabilities.'

Nasa engineers have proposed the above design for the fuel element for a small nuclear rocket engine using uranium carbide (UC2) particles contained within graphite that could be used within a rover or space probe