How nuclear Rockets will get us to mars and beyond.

 How nuclear Rockets will get us to mars and beyond.

Introduction.

A few days ago on the 6th of February2018 SpaceX's first test launch of the Falcon9 heavy the most powerful rocket since the Saturn 5 successfully launched a payload of Elon Musk's own cherry red Tesla roadster complete with a Starman mannequin first into orbit and then on what was meant to be a journey to Mars but now looks more like an elliptical orbit extending out to the asteroid belt between Mars and Jupiter.

 

 Whilst 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. With an average time of nine months to get to Mars the risk from radiation, weightlessness and psychological issues is high, not to mention with supplies they need to carry even if they're going to grow their own food and recycle their own water.

 

But if you can reduce the time it takes to get there all these things become much more manageable, however there is a technology using nuclear power that was developed for about 20 years from the 50s to the1970s 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. Now with 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.

 

 But we have to make a distinction here the nuclear rocket engines are only for use in space because they have a much lower thrust tow eight ratio compared to chemical rockets and so chemical ones will still be doing the heavy lifting from Earth into orbit but once they're an away from a gravity of Earth nuclear engines can be much more efficient. Now as powerful as chemical rockets are they have a problem they need to carry not only the fuel but also the oxygen allow it to burn which makes the Rockets much heavier and also reduces the payload available.

 

The first type of nuclear rocket, the nuclear thermal one does away with the liquid oxygen altogether and instead passes liquid hydrogen fuel through a nuclear reactor to heat it up to a superheated gas, this hot gas has been ejected from the engine in the same way as a chemical rocket and that's where it creates its thrust. The difference is that when a chemical rocket engine burns hydrogen & oxygen the by product which is water vapour is heavy and therefore as a given temperature its velocity is lower and therefore the thrust created is less. Because a nuclear thermal engine doesn't burn the hydrogen it just heats it up it's 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 the thrust is considerably more.

 

A rockets efficiency or how well it makes use of its fuel is measured in seconds of specific impulse sounds complicated but put simply it means 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 test nuclear Rockets had a specific impulse of around 900 seconds twice as efficient. Now couple that to a fact when you don't now need to carry a lot of heavy liquid oxygen around with you and this means you can either go faster or carry greater payloads. From themid-1950s this principle was studied extensively 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 a100 megawatts and then up to a full power rating of 1000 megawatts in 1962the program to turn Kiwi into a working engine was called nuclear engines rocket vehicle applications or NERVA again the tests were successful and in1967 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.

 

Whilst these test engines proved the concept there were still issues 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 launch pad or were to fall back to earth from orbit and spread highly radioactive material over potentially highly populated areas and there was also issues with overheating if the fuel which acted as a coolant ran out before the engine was shut down properly.

 

 But after years of testing they were deemed ready for use in space and NRX seemed to be on track to make it there by the late 1970s. On the other side of the Iron Curtain the Soviet chief rocket designer Sergey Korolyov expected his N1 super heavy lift rocket to carry a nuclear upper stage giving the vehicle a formidable interplanetary capability his team considered several 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 the nuclear thermal engines weren't the only options available on the table Korolev favoured another way of harnessing atomic power pairing a nuclear reactor with an electric ion engine although the system provided much less thrust it was even more efficient and would provide a low thrust for a very long period of time compared to the quick bursts like the nuclear thermal ones.

 

In recent times advances in solar panel design has made nuclear reactor powered iron engines much less likely but for deep space missions beyond Saturn where there is not enough sunlight to operate solar panels successfully nuclear power becomes pretty much the only option. Calculations showed that ion drives will be able to transport 70% more payload than chemical engines on a mission to Mars.

 

After the N1 rocket quite literally fell by the wayside the chief designer Vladimir Chelomei was in pole position to design a rocket for the Soviet manned Mars mission the enormous MK 700 was to be assembled in orbit with multiple launches for the modular UR700 rocket the MK 700 would make its interplanetary burn with a nuclear thermal engine built by Valentin Glushko's design bureau and called the RD-0410 the engine made it as far as testing at the test site in north east kazakhstan demonstrating yet again Glushko's mastery of rocket engine efficiency the RD-0410 showed a capability of 910 seconds of specific impulse.

 

However by 1972 and due to the loss of interest in space by the public and the government in the u.s. funding for nasa's mars mission and NERVA was cancelled by congress as the space shuttle returned to focus to low-earth orbit where nuclear engines weren't required and the soviet priority was to match this capability their research into nuclear-powered spacecraft also stalled.

 

 However things picked up again with President Ronald Reagan's Star Wars initiative in the late 1980s project Timber wind advanced the engines using a pebble bed reactor design and increased the specific impulse to nearly 1,000seconds it also led to the development of modern carbon composite materials but it also faced technical issues which would have made it very difficult to use as a space based engine system and funding was eventually dropped. More recently Russian engineers at the State Energy Corporation ROSATOM are working on a form of nuclear electric propulsion called 'TEM' the acronym translates to transport an energy unit the name indicates a nuclear reactor capable of bimodal operation that is when it's not powering engines it can be switched to a low power mode to power the living quarters and other onboard systems.

 

 According to the designers TEM has a goal of testing a ground-based engine this year and launching a prototype by2025 if funding can be secured. The technology could in theory enable a journey from Earth to Mars in just 45 days. NASA is also conducting new research into rapid transit technologies to mitigate the long-term effects of  interplanetary space on the human body like Russia, NASA sees nuclear thermal propulsion as a solution here the goal of the current research is to reduce for cost and risk of the nuclear fuel by developing a suitable form of low enriched uranium with a concentration of 3-4% uranium-235compared to a 90% concentration of weapons-grade fuel in the earlier designs.

 

 NASA's research may well find its first use in a spacecraft like this the Copernicus mass transfer vehicle conceived as part of the now cancelled constellation program Copernicus B is being considered for an in orbit assembly using NASA's upcoming SLS block 2 launch system. At one end of Copernicus the Orion spacecraft would dock with a manned payload living space Copernicus would then make its interplanetary journey using three nuclear thermal engines each capable of producing 25,000 pounds of thrust the efficiency of the nuclear engines would enable a trip to Mars in a hundred days not quite as quickly as were proposed Russian mission but still a significant improvement over traditional chemical engines and also Copernicus would be capable of by modal reactor operation.

 

So what do you think of using nuclear Rockets for future manned missions let me know in the comments below.