The first man to land on Mars and also beyond, may not fly the way Neil Armstrong went in his chemically powered Apollo 11 spacecraft. Well, he likely will, since we’re not going to be getting rid of restrictions on nuclear propelled rockets before Musk takes us to Mars. But eventually, we’ll shed these chemical thrusters. These old-school chemically powered rockets just don’t provide the required thrust to go to massive distances. Not without exposing their crew to excessively harmful space radiation for months. This is why nuclear propulsion rockets are required.
Nuclear power works perfectly as propulsion technology for spacecraft. The principle behind their working is liquid hydrogen. Liquid hydrogen is heated to a high temperature in a reactor which will eventually expand via the rocket nozzle to provide the required thrust.
Nuclear propulsion based rockets are not new either. The prospect of harnessing nuclear power to propel aircrafts and rockets has been discussed as early as 1942. That was when Enrico Fermi successfully completed fission reactor tests. By 1944, groups at University of Chicago’s Metallurgical Laboratory and the Los Alamos National Lab developed an early model of a nuclear-thermal rocket. The design was based on this principle.
The development of such engines started under the aegis of USA’s AEC (Atomic Energy Commission) in 1955 as Project Rover in the Nevada Test Site. Consequently, four basic designs came from this project: KIWI, Phoebus, Pewee and Nuclear Furnace.
Eventually by 1961, the NERVA (Nuclear Engine for Rocket Vehicle Applications) program was up and running. NERVA’s purpose was to formalise the venture of the nuclear-powered rocket into space exploration. While testing and designing of nuclear reactors were performed by the Atomic Energy Commission, NERVA aimed to design a real engine which could be deployed into outer-space for missions.
It all started with the Project Orion. It was the study of the spacecraft to be launched by nuclear propulsion. Though it offered very high thrust and specific impulse, the idea eventually fell out because of the adoption of Partial Test Ban Treaty in 1963. This treaty prohibited the entry of all kinds of nuclear weapons into orbit. This treaty was officially adopted on October 10, 1963. 123 states are signatories to this treaty.
Another treaty involved here was the Outer Space Treaty (OST). The OST prohibits signatory states from placing weapons of mass destruction onto orbit around Earth. Therefore, if a nuclear propulsion rocket is to be sent into space, you need to prove that it’s not a weapon of mass destruction. Difficult.
The Limited Test Ban treaty signed by the US prevents it from launching an Orion.
These were political factors. In addition, a number of technological factors were also responsible for the death of nuclear propelled rockets.
Firstly – there were grave problems regarding the launch of such rockets from the ground. At most places, the Earth’s magnetic field would interfere and trap the radioactive particles. These would eventually return to Earth. So the launch location would have to be selected carefully, at places with holes in the magnetic field. Secondly – the size and weight were proving to be troublesome. The rockets were turning out to be very heavy to get into space. Test firings would need to take place outside the Van Allen Belts. In 1962, Project Starfish Prime launched a warhead into space to an altitude of 250 miles. Charged particles got trapped in the Van Allen Belts, knocking out many satellites around Earth.
There was also an eminent danger of a catastrophic failure known as a containment breach, discovered during testing. These failures were multi-fold, caused by the orbiter impacting the ground, fission runaways, or design flaws in either the atmosphere or orbit. Accidents could pour down a large amount of radiation covering an enormous stretch of land. As a consequence, a group of researchers deliberately exploded a KIWI reactor in the middle of Jackass Flats, that was a part of the Nevada Test Site. The explosion proved out to be apocalyptic, wiping out everything and anything that came in its way through 600 feet and poisoning the land through 2000 feet.
Why do we still need nuclear propulsion rockets?
Despite all the issues that have occurred in the past, Nuclear propulsion rockets are what we need for the new space age and there are so many reasons why.
The first and foremost advantage is that the size and weight of nuclear propulsion rockets. They have been reduced to half without much reduction in thrust. Much larger loads can now be sent into space.
The large thrust significantly improves travel time. Compared to the conventional 18 months needed to get a spacecraft to Mars, nuclear propulsion systems would require only six weeks.
The heat energy released from fuel is massive. So there’s an advantage in efficiency.
Higher specific impulses are generated as compared to chemical rockets. This is due to the achievement of higher exhaust velocities in nuclear propulsion rockets, which cannot be achieved by their chemical counterparts.
The use of solid core nuclear thermal rockets keeps the radioactive elements of the system away from the propellant, making these rockets safer.
Nuclear energy is also the most enduring source of energy, considering the long lifespan it has.
Nuclear energy does not rely on the Sun’s rays either. This makes it the system of choice for travel into deep space.
The propellant and source of energy do not depend on each other.
After an intermittent few decades, both NASA and Russian Federal Space Agency declared in 2012 that there will be a revival of the nuclear propulsion rocket technology. Consequently, a $600 million joint engine project was initiated, alongside France, Britain, Germany, China, and Japan.
This time, researchers are using Marshall’s Nuclear Thermal Rocket Element Environmental Simulator (NTREES). Nuclear rocket testing remains globally banned. But the newer NTREES can provide an accurately simulated interaction between the multiple parts of the Nuclear Propulsion Engine. This allows scientists to analyze most design and function aspects of the engine, without imposing any potent risk of a nuclear fallout.
Outside of revolutionary cutting edge nuclear technology, NASA is also facing some nuclear fuel shortages. Since America does not have plutonium-238 since the 1980s, stocks are already on all time low. Although there are claims that manufacturing of this fuel will begin in 2017, it will take another 5-6 years to furnish the requisite amounts in order to satisfy planetary science mission.
Nuclear propulsion rockets remain the most efficient system of choice to take us into deep space (unless the impossible EmDrive somehow works). This is because chemical propulsion produces comparatively slower aircrafts with a lower thrust, which is clearly not enough.