An American professor explains why nuclear rocket engines are more efficient than chemical ones. Therefore, they are the ones who will help explore Mars and everything beyond it. But he does not think about the question of whether NASA will have enough money to develop such engines, if the Pentagon is also engaged in them, and he is given first.
NASA and Elon Musk dream of Mars, and manned deep space missions will soon become a reality. You will probably be surprised, but modern rockets fly a little faster than the rockets of the past.
Fast spaceships are more convenient for a variety of reasons, and the best way to accelerate is with nuclear powered rockets. They have many advantages over conventional fuel-fueled rockets or modern solar-powered electric rockets, but in the past 40 years, the United States has launched only eight nuclear-powered rockets.
However, in the past year, the laws regarding nuclear space travel changed and work on the next generation of rockets has already begun.
Why is speed needed?
At the first stage of any flight into space, a launch vehicle is needed - it takes the ship into orbit. These large engines run on combustible fuel - and usually when it comes to launching rockets, they mean them. They won't be going anywhere anytime soon - nor will the force of gravity.
But when the ship enters space, things get more interesting. To overcome the gravity of the Earth and go into deep space, the ship needs additional acceleration. This is where nuclear systems come into play. If astronauts want to explore something beyond the Moon, or even more so Mars, they have to hurry. The cosmos is huge, and the distances are rather big.
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There are two reasons why fast rockets are better suited for long-distance space travel: safety and time.
On the way to Mars, astronauts face very high levels of radiation, fraught with serious health problems, including cancer and infertility. Radiation shielding can help, but it is extremely heavy, and the longer the mission, the more powerful shielding will be needed. Therefore, the best way to reduce the radiation dose is to simply get to your destination faster.
But crew safety isn't the only benefit. The more distant flights we plan, the sooner we need data from unmanned missions. It took Voyager 2 12 years to reach Neptune - and as it flew by, it took some incredible pictures. If Voyager had a more powerful engine, these photographs and data would have appeared in astronomers much earlier.
So speed is an advantage. But why are nuclear systems faster?
Today's systems
Having overcome the force of gravity, the ship must consider three important aspects.
Today, the most common chemical propulsion systems are conventional fuel-fueled rockets and solar-powered electric rockets.
Chemical propulsion systems provide a lot of thrust, but are not particularly efficient, and rocket fuel is not very energy intensive. The Saturn 5 rocket, which carried astronauts to the moon, delivered 35 million newtons of force on takeoff and carried 950,000 gallons (4,318,787 liters) of fuel. Most of it went into getting the rocket into orbit, so the limitations are obvious: wherever you go, you need a lot of heavy fuel.
Electric propulsion systems generate thrust using electricity from solar panels. The most common way to accomplish this is to use an electric field to accelerate ions, such as in a Hall induction thruster. These devices are used to power satellites, and their weight efficiency is five times that of chemical systems. But at the same time, they give out much less thrust - about 3 newtons. This is only enough to accelerate the car from 0 to 100 kilometers per hour in about two and a half hours. The sun is essentially a bottomless source of energy, but the further the ship moves away from it, the less useful it is.
One of the reasons why nuclear missiles are especially promising is their incredible energy intensity. Uranium fuel used in nuclear reactors has an energy intensity of 4 million times that of hydrazine, a typical chemical rocket fuel. And it’s much easier to get some uranium into space than hundreds of thousands of gallons of fuel.
What about traction and weight efficiency?
Two nuclear options
For space travel, engineers have developed two main types of nuclear systems.
The first is a thermonuclear engine. These systems are very powerful and highly efficient. They use a small nuclear fission reactor - like the ones on nuclear submarines - to heat a gas (like hydrogen). This gas is then accelerated through the rocket nozzle to provide thrust. NASA engineers have calculated that a trip to Mars using a thermonuclear engine will be 20-25% faster than a rocket with a chemical engine.
Fusion engines are more than twice as efficient as chemical ones. This means that they deliver twice as much thrust for the same amount of fuel - up to 100,000 Newtons of thrust. This is enough to accelerate the car to 100 kilometers per hour in about a quarter of a second.
The second system is a nuclear electric rocket engine (NEP). None of these have yet been created, but the idea is to use a powerful fission reactor to generate electricity, which will then power an electric propulsion system like a Hall motor. That would be very effective - about three times more efficient than a fusion engine. Since the power of a nuclear reactor is enormous, several separate electric motors can work at the same time, and the thrust will turn out to be solid.
Nuclear rocket engines are perhaps the best choice for extremely long-range missions: they do not require solar energy, are very efficient and provide relatively high thrust. But for all their promising nature, the nuclear power propulsion system still has many technical problems that will have to be solved before being put into operation.
Why are there still no nuclear-powered missiles?
Fusion engines have been studied since the 1960s, but they have not yet flown into space.
Under the charter of the 1970s, each nuclear space project was considered separately and could not go further without the approval of a number of government agencies and the president himself. Coupled with a lack of funding for research into nuclear missile systems, this has prevented the further development of nuclear reactors for use in space.
But that all changed in August 2019 when the Trump administration issued a presidential memorandum. While insisting on the maximum safety of nuclear launches, the new directive still allows nuclear missions with low amounts of radioactive material without complicated interagency approval. Confirmation by a sponsoring agency such as NASA that the mission is in compliance with safety recommendations is sufficient. Large nuclear missions go through the same procedures as before.
Along with this revision of the rules, NASA received $ 100 million from the 2019 budget for the development of thermonuclear engines. The Defense Advanced Research Projects Agency is also developing a thermonuclear space engine for national security operations beyond Earth's orbit.
After 60 years of stagnation, it is possible that a nuclear rocket will go into space within a decade. This incredible achievement will usher in a new era of space exploration. Man will go to Mars, and scientific experiments will lead to new discoveries throughout the solar system and beyond.
Iain Boyd is professor of aerospace engineering at the University of Colorado at Boulder