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A rocket technology championed by NASA more than 50 years ago could be the future of space travel.
It’s called nuclear thermal propulsion (NTP), and 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 United States plans to demonstrate this in space by 2026.
Nuclear thermal propulsion
Rocket propulsion is based on thrust, and the easiest way to understand this is to think of releasing the nozzle of a balloon you’ve filled with air – when the air comes out of the hole, it sends the balloon fly in the opposite direction. Push is the force that moves the ball.
Most rocket engines produce thrust by combining fuel (eg, liquid hydrogen) with an oxidizer (eg, liquid oxygen) and igniting the mixture. This creates gas which is then expelled from the engine nozzle, propelling the rocket in the opposite direction.
Chemical rocket engines aren’t the only option, however.
In the 1950s, NASA began exploring NTP systems, which use nuclear fission – the process of splitting atoms apart – to produce the heat needed to convert liquid propellant to gas and produce thrust.
These systems are not currently designed to launch spacecraft from the Earth’s surface – a chemical rocket would be used for this – 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 using the same amount of propellant.
Experts believe they could cut the time it takes for a rocket to reach Mars by up to 25% (cutting the trip by around two months), which would reduce astronauts’ exposure to threats such as cosmic radiation , microgravity and boredom.
NTP engines would also make travel to Mars more flexible.
Because the fuel is so heavy, the only launch window for a crewed chemical rocket trip 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 that it would need far less propellant than a chemical rocket to get to Mars, and a volume of uranium barely the size of a marble. Trips could happen even when Earth and Mars weren’t in optimal positions thanks to the powerful engine, which is good news if you can’t wait two years for resupply or rescue.
“Once you send humans to Mars under a chemical rocket, you’d have to wait…until Mars and Earth are back in the same place [to return]John Horack, Neil Armstrong Professor of Aerospace Policy at The Ohio State University, told Space Times.
“[An NTP system] will allow you to come and go as you please, so to speak, instead of having to wait for the celestial mechanics to align,” he added.
On an NTP spacecraft, astronauts would have the ability to abort a mission to Mars months after the journey begins instead of just days.
NASA also plans to equip a crewed chemical rocket only with enough fuel to get at March. The fuel for the return trip would either have to be sent to the red planet in advance, or be created using resources on Mars.
Most of a chemical rocket’s fuel is used at the start of the mission, to break free from Earth’s gravity and accelerate to cruising speed.
This means that in a few days, a Mars-bound spacecraft with a chemical propulsion system would not have enough fuel to return to Earth if the crew had to abort the mission. On an NTP spacecraft, astronauts could abort even months into the journey.
NASA’s early research into nuclear propulsion stopped in 1972 due to budget cuts and shifting priorities, but interest in the technology has started to rise again in recent years.
“Current advances in materials, test capabilities, and reactor development are prompting NASA to evaluate [NTP] as an attractive 21st century option for propelling human exploration missions to Mars and other deep space destinations,” NASA wrote in 2018.
In July 2021, NASA and the DoE awarded three contracts worth approximately $5 million each to American companies to design reactors for NTP systems that could one day be used for crewed missions to Mars. or science missions to parts of the outer solar system.
“These design contracts are an important step toward tangible reactor hardware that could one day power exciting new missions and discoveries,” said Jim Reuter, associate administrator for NASA’s Space Technology Missions Directorate.
NASA is working with BWX Technologies to develop NTP fuels that use low-enriched uranium instead of high-enriched uranium, which will reduce costs and proliferation risks.
He also works with DARPA on the DRACO program. This project (the “Cislunar Agile Operations Demonstration Rocket”) is developing NTP engines for use in space between Earth and the Moon.
DARPA is currently soliciting proposals for Phases 2 and 3 of the program, with the goal of demonstrating an NTP system in orbit by 2026. If successful, the DRACO engine could one day give U.S. satellites the ability to rapidly evade anti-satellite weapon attacks. .
“To maintain technological superiority in space, the United States needs the advanced propulsion technology that the DRACO program will provide,” said Nathan Greiner, program manager in DARPA’s Office of Tactical Technology.
The bottom line
If the DRACO program is able to demonstrate NTP technology in 2026, it may not be long before the satellites we rely on for communications, defense, etc. are fed by the systems and better protected against attacks.
However, while shortened 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 we’re going to have to fly a few times…before someone sells tickets.”
By launching an NTP spacecraft into space aboard a traditional chemical rocket, NASA minimizes the risk of harming people during liftoff, but the costs and other factors associated with launch a chemical flare would still apply to the mission.
NASA would also have to design the spacecraft to protect the astronauts from the nuclear reactor itself – this could be done by using advanced materials to shield them from radiation or by placing living quarters as far away as possible.
Ultimately, NASA will want to do everything possible to keep the systems safe, which means years of research into NTP engines before we see crewed missions powered by them.
“No one has flown nuclear propulsion yet,” Jeff Sheehy, chief engineer for NASA’s Space Technology Missions Branch, told CNN in 2021. “I think it’s going to have to fly a few times… before someone sells tickets.”
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