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A rocket technology championed by NASA more than 50 years ago could be the future of space travel.
Called nuclear thermal propulsion (NTP), it has the potential to dramatically reduce travel times to distant destinations while increasing launch flexibility and making spaceflight safer for astronauts.
It could also make satellites less vulnerable to enemy attack — and the US plans to demonstrate it in space by 2026.
Nuclear Thermal Propulsion
The propulsion of a rocket is based on thrust, and the easiest way to understand that is to think about releasing the nozzle of a balloon you’ve filled with air – as the air leaves the hole, the balloon flies in the opposite direction. Thrust is the force that moves the balloon.
Most rocket engines Producing thrust by combining fuel (eg, liquid hydrogen) with an oxidizer (eg, liquid oxygen) and igniting the mixture. This creates a gas which is then squeezed out of the engine’s nozzle and propels the rocket in the opposite direction.
However, chemical rocket engines are not the only option.
In the 1950s, NASA began exploring NTP systemswho make use of nuclear fission – the process of splitting atoms – to produce the heat needed to convert a liquid propellant into a gas and produce thrust.
These systems aren’t currently designed to launch spacecraft from Earth’s surface — a chemical rocket would be used for that — but they have huge advantages for space travel.
NTP systems are more powerful and twice as efficient as chemical rocket engines, meaning they can produce twice as much thrust as a chemical rocket with the same amount of propellant.
Experts believe they could reduce the time it takes for a rocket to reach Mars by as much as 25% (about two months after the journey), reducing astronauts’ exposure to threats such as cosmic rays† microgravityand boredom.
NTP engines would also make travel to Mars more flexible.
Because fuel is so heavy, the only launch window for a manned chemical rocket journey to Mars is when the orbits of Earth and Mars are ideally aligned, which only happens once every 26 months†
The efficiency of an NTP system means it needs much less propellant than a chemical rocket to get to Mars, and a volume of uranium barely the size of a marble. The powerful engine allows for trips even when Earth and Mars are not in optimal positions, which is good news if you can’t wait two years for supplies or rescue.
“Once you sent people to Mars under a chemical rocket, you would have to wait… until Mars and Earth are back in the same place [to return]John Horack, the Neil Armstrong Chair in Aerospace Policy at Ohio State University, told Space Times†
†[An NTP system] will allow you to come and go as you please, so to speak, rather than having to wait for the celestial mechanics to queue,” he added.
On an NTP spacecraft, astronauts would have the ability to abort a mission to Mars for months rather than just days.
NASA also plans to equip only a manned chemical rocket with enough fuel to get… until Mars. The fuel for the return journey would either have to be sent to the Red Planet in advance or be made using resources on Mars.
Most of a chemical rocket’s fuel is consumed at the start of the mission, to break free from Earth’s gravity and accelerate to cruising speed.
That means inside a couple of daysa spacecraft aimed at Mars with a chemical propulsion system wouldn’t have enough fuel to return to Earth if the crew had to abort the mission. On an NTP spacecraft, astronauts can: to break down even months into the journey.
NASA’s early research into nuclear propulsion stalled in 1972 due to budget cuts and shifting priorities, but interest in the technology has picked up again in recent years.
“Today’s advances in materials, testing capabilities and reactor development give NASA an impetus to assess” [NTP] as an attractive 21st-century option to propel human exploration missions to Mars and other distant space destinations,” NASA wrote in 2018.
In July 2021, NASA and the DoE awarded three contracts worth approximately $5 million each to US companies to design reactors for NTP systems that could one day be used for: manned missions to Mars or scientific missions to parts of the outer solar system.
“These design contracts are an important step toward tangible reactor hardware that could one day propel new missions and exciting discoveries,” said Jim Reuter, associate administrator for NASA’s Space Technology Mission Directorate.
NASA partners with BWX Technologies to develop NTP fuels that low-enriched uranium instead of highly enriched uranium, which saves costs and reduces proliferation risks.
It is also collaborating with DARPA on the DRACO program. That project (the “Demonstration Rocket for Agile Cislunar Operations”) is developing NTP engines for use in the space between the Earth and the Moon.
DARPA is currently soliciting proposals for: phase 2 and 3 of the program, which aims to demonstrate an NTP system in orbit by 2026. If successful, the DRACO engine could one day give US satellites the ability to quickly evade attacks from anti-satellite weapons.
“To maintain technological superiority in space, the United States needs a forward-thinking propulsion technology that the DRACO program will provide,” said Nathan Greiner, program manager at DARPA’s Tactical Technology Office.
it comes down to
If the DRACO program can demonstrate NTP technology in 2026, it might not be long before the satellites we rely on for communications, defense and more are powered by the systems and better protected from attack.
While shorter flight times would reduce astronauts’ exposure to many space threats, equipping a manned spacecraft with a nuclear reactor comes with its own risks.
“I think it needs to be flown a few times… before someone sells tickets.”
By launching an NTP spacecraft into space aboard a traditional chemical rocket, NASA minimizes the chances of people being injured during takeoff, but the costs and other factors associated with launch a chemical missile would still be applicable to the mission.
NASA should also design the spacecraft to protecting astronauts from the nuclear reactor itself – this can be done by using advanced materials to shield them from radiation or by shielding living quarters as far from the core as possible.
Ultimately, NASA will want to do everything possible to make sure the systems are safe, which means we’ll have to spend years researching NTP engines before seeing manned missions powered by them.
“No one has ever flown with nuclear propulsion,” Jeff Sheehy, chief engineer of NASA’s Space Technology Mission Directorate, told CNN in 2021. “I think it needs to be flown a few times… before someone sells tickets.”
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