Currently, Mars mission is the hottest topic in the field of space science especially when Elon Musk had decided the deadline of 2024 for sending humans on the red planet. Musk is planning for civilization on Mars, but the 9 months’ time which is currently taken by space crafts is not to mention with supplies they need to carry even if they’re going to grow their own food and recycle their own water on Mars.

On February 6th, 2018 SpaceX had successfully launched Falcon 9 heavy the most powerful rocket. The Falcon 9 heavy proved that it could launch a payload into deep space. Starman and the Roasters journey itself is going to be a pretty leisurely one just like everything else we’ve launched into deep space fine for mannequins, cars and robotic probes but not so good for humans.

Can we reduce the time to reach Mars?

if the time limit to reach on red planet is reduced, many problems could be shorted and becomes much more manageable, however there is a technology using nuclear power that was developed for about 20 years from the 50s to the 1970s originally by the US and the Soviets for Mars missions proposed in the 1970s and 80s but was shelved after the demise of the missions themselves.

Currently, in our revived interest in Mars missions and trips to deep space nuclear-powered rockets are back on the agenda as a way to cut transit time and carry greater payloads. In rocket engineering, we were taught different types of engines like: Solid, liquid, gas, hybrid, electric propellant engines. While Nuclear propellant engines are kept in the category of advanced rocket engines, the only reason is a lot of research are still need to be carried out in this area. The commonly used rocket engines are solid or liquid propellant, which contains liquid oxygen, hydrogen or kerosene, etc.

 As the nuclear rocket engines have much lower thrust to weight ratio compared to chemical rockets thus scientists have said that nuclear rocket engines can only be used in outer space and so chemical ones will still be doing the heavy lifting from Earth into orbit but once they’re away from a gravity of Earth nuclear engines can be much more efficient.

How does a nuclear rocket work?

nuclear rocket diagram

In nuclear thermal rocket (NTR) the heat from a nuclear reaction, often nuclear fission, provides the required energy for thrust. In an NTR, a working fluid, usually liquid hydrogen, is heated to a high temperature in a nuclear reactor and then expands through a rocket nozzle to create thrust. The external nuclear heat source theoretically allows a higher effective exhaust velocity and is expected to double or triple payload capacity compared to chemical propellants that store energy internally.

In chemical rockets, the main problem is they need to carry not only the fuel but also the oxygen, to allow it to burn which makes the Rockets much heavier and also reduces the available payload capacity.

The difference between these two types of rocket engines is that when a chemical rocket engine burns hydrogen & oxygen are the byproducts, which is water vapor. But it is heavy and therefore as a given temperature its velocity is lower and thus the thrust created is less. Because a nuclear-thermal engine doesn’t burn the hydrogen it just heats it up its still pure hydrogen when it leaves the rocket engine and as hydrogen is the lightest element its exit velocity is the highest for a given temperature and therefore generates more thrust.

The efficiency of a rocket is measured in seconds of specific impulse, i.e. how long in seconds one pound of propellant can deliver one pound of thrust, the best chemical rockets have a specific impulse around 450 seconds whereas the early tested nuclear Rockets had a specific impulse of around 900 seconds twice as efficient.

 The other benefit of it is that in nuclear rocket you don’t need to carry an extra weight of liquid oxygen around with you and this means you can either go faster or carry greater payloads.

ntr diagram

In the mid-1950s this concept was at its peak this principle was studied at the Atomic Energy Commission laboratory at Los Alamos in New Mexico through a program called Project Rover by 1959 an experimental reactor called Kiwi who was ready for testing it with jackass flats in Nevada and successfully ran at a power of a 100 megawatts and then up to a full power rating of 1000 megawatts in 1962 the program to turn Kiwi into a working engine was called nuclear engines rocket vehicle applications or NERVA. In the year 1967, the NRX-A6 engine fired successfully for an hour as the tests continued the engine runtime was only really limited by the supplies of liquid hydrogen at the test site.

Although the test engines proved the concept and hope in this field of the nuclear rocket, the main issue is the weight of the shielding to protect for crew and the control electronics from the radiation made the engines very heavy.

There was also the problem of what would happen if a nuclear engine rocket were to fail on a launchpad or were to fall back to earth from orbit and spread highly radioactive material over potentially highly populated areas. Another issue with overheating if the fuel which acted as a coolant ran out before the engine was shut down properly.

How nuclear rockets are more effective than the chemical one?

The Iron Curtain the Soviet chief rocket designer Sergey Korolyov proposed his N1 super heavy-lift rocket which could carry a nuclear upper stage giving the vehicle a formidable interplanetary capability. His team considered several more options either to nuclear other stages on a three-stage rocket or a single nuclear stage on a two or three-stage rocket with any of these options the N1 upper stages would have had to cluster large numbers of nuclear engines together many more than on the American designs.

But a nuclear thermal upper stage was calculated to be able to deliver up to 50% more payload to Mars than a chemical one. However, nuclear thermal engines were not the only option for Korolev. He tried another way of harnessing atomic power by pairing a nuclear reactor with an electric ion engine.

Though the system provided much less thrust, it was even more efficient as it would provide a low thrust for a very long period of time compared to the quick bursts like the nuclear thermal ones.

These type of engines will be more useful in deep space missions beyond Saturn where there is not enough sunlight to operate solar panels successfully nuclear power becomes pretty much the only option.

The US Congress has approved $100 million to NASA for the Nuclear thermal rocket engine. NASA has planned a test of it in 2024. Hope in future we could travel to Mars or deep space. The time and hard work will decide the time limit of 2024 will it be real or take more time. Meanwhile, researches are going on and we will try to get as much information about them as possible.


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