.jpeg)
By Dr Sitakanta Mishra
‘Outer space’ is fast becoming the new economic and strategic high ground. During the last few decades, prominent countries have ventured into outer space and many of them dream of interplanetary missions. However, the biggest challenge for interstellar travel is the availability of reliable power sources for spacecraft propulsion, and onboard spaceship systems in the harsh environment of space. The great astronomer Carl Sagan once said that “one cannot travel fast into space without travelling fast into the future;” truly, without futuristic energy sources and propulsion technology, deep-space exploration would not be feasible. Radioisotope and nuclear-based propulsion technology is the promising gateway to outer space.
Today, spacecraft propulsion, power for onboard spaceship systems, and energy generation in extra-terrestrial voyages are mainly based on chemical and solar energy. But long-term space missions such as establishing and maintaining space stations, Lunar bases, Mars missions, deep-space exploration, or interplanetary missions require huge and uninterrupted power supply. For such missions, nuclear fusion propulsion is the next-generation energy solution as the atom is a source of high energy density and inexhaustible.
Technically, there are three possible key nuclear technologies for space propulsion: (1) Nuclear Pulse Propulsion (NPP) used for shorter trips with high acceleration but with lower propellant efficiency [currently not in use]; (2) Nuclear Thermal Propulsion (NTP); and (3) Radioisotope Electric Propulsion (REP). NTP uses a fission reactor to heat a liquid propellant: the heat converts the liquid propellant into gas, which expands through a nozzle to provide thrust to propel the spacecraft. With REP, the thrust is produced by converting the thermal energy from a nuclear reactor into electrical energy. Currently, space programs are using the eighth generation of nuclear batteries called the Multi-Mission Radioisotope Thermoelectric Generator or MMRTG.
Interstellar or interplanetary voyages have long been a matter of science fiction, but it would not be far from a reality soon given the growing interest and research in harnessing nuclear technology for space application. Many countries today have deep-space exploration programs with nuclear propulsion technology experiments. Nuclear pulse propulsion was first developed as Project Orion by the Defense Advanced Research Projects Agency (DARPA), U.S. Department of Defense, in 1947. Between 1955 and 1972, the United States spent more than $1.4 billion on developing nuclear rockets and related technologies.
So far, NASA has only sent one nuclear reactor to space, on a satellite in 1965. Since 1965, the United States has been using only Radioisotope Thermoelectric Generators (RTGs) in space exploration and not nuclear reactors. The high decay heat of Plutonium-238 or Strontium-90 enables its use as an electricity source in the RTGs of spacecraft. So far over 45 RTGs have powered 25 US space vehicles including Apollo, Pioneer, Viking, Voyager, Galileo, Ulysses, Cassini and New Horizons space missions, as well as many civil and military satellites. NASA’s Mars rover was equipped with nuclear power-induced technology, which allowed its detectors to analyze the composition of Martian rocks. Also, NASA aims to test a 40-kilowatt microreactor on the moon by 2030.
Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society (BIS) to design a plausible interstellar spacecraft that could reach Alpha Centauri in more than four decades. A year ago the UK Space Agency (UKSA) awarded funding to the rocket company Pulsar Fusion to develop nuclear fission-based power systems. Meanwhile, the European Space Agency (ESA) is funding several studies such as the RocketRoll that will explore the use of nuclear propulsion for deep space exploration.
The former USSR had a long history of successfully deploying “33 military reconnaissance and targeting spacecraft with nuclear reactors into low-Earth orbit from 1969 to 1988.” In the post-Soviet era, Russia renewed its interest in the space application of nuclear energy, not only for propulsion systems but also for other equipment aboard large spacecraft for military requirements. The KB Arsenal design bureau, the prime contractor in Russia’s military spacecraft project, is known for its Soviet-era nuclear-powered satellites. Reportedly, Russian space agency Roscosmos is considering using the Zevs (Zeus) nuclear tug by 2030 to propel heavy cargo through deep space (Nuklon project) estimated at more than 4.17 billion rubles – to the Moon, then Venus and Jupiter, and also clean up space debris. The scheduled space tug, featuring a 500-kilowatt nuclear reactor and weighing up to 22 tons, will first fly to the Moon, where it will release a spacecraft that will go on to Venus, and “then use Venus as a gravity assist to deliver yet another spacecraft, which will make its long journey to Jupiter.” The “Zeus” module would advance those efforts by using a 500-kilowatt nuclear reactor to propel inter-planetary missions.
So far, Russia has flown more than 30 fission reactors in space. Its independent efforts in space nuclear power systems traced back to 1998, and during the presidency of Dmitry Medvedev, these efforts were proclaimed among the Kremlin’s key priorities. Russia continues a special nuclear space programme “Through The Atom To The Stars” and Rosatom has played a crucial role ever since. Its expertise and technology could aid Moscow to develop a new space station by 2025. Today Russia, a leader in the global nuclear space race, is much ahead of all others.
China is aggressively investing and working on a wide range of space technologies including nuclear propulsion designs to speed travel times in outer space, and to protect its various “cislunar” assets. Mainly China has relied on Russia for radioisotope units for its Chang’e-3 and 4 Lunar lander and rover missions, including an RTG for Yutu-2. However, China is now exploring breakthroughs and has proposals for indigenous reactors in its space missions, including the uranium-powered ACMIR.
India, on the other hand, is no way behind in the unfolding nuclear-propelled space race. The Chandrayaan-3 propulsion module orbiting the Moon is powered by nuclear technology. After its success, ISRO in collaboration with BARC has begun work on nuclear engines for its upcoming space missions. On January 28, 2021, ISRO’s UR Rao Satellite Centre issued a call for proposals outlining a three-phase plan to create a 100-watt RTG.
Gradually peaceful uses of atomic propulsion for space exploration are gaining momentum. To overcome the limitations of spacecraft speed and power demand for deep-space voyages, nuclear is undoubtedly the next space frontier. First, nuclear-based propulsion could speed up space travel ten times faster than light. Second, if harnessed for propulsion, nuclear fusion could revolutionize interstellar travel by providing a nearly limitless supply of energy, efficiency and cost-effectiveness. Third, the space flights would need to lift less fuel and reduce trip times. With this type of propulsion technology, the thrust may be lower but continuous, and the fuel efficiency is far greater, resulting in a higher speed and potentially over 60% reduction in transit time to Mars compared to traditional chemical rockets. Moreover, reduced time in space would also reduce the exposure of astronauts to cosmic radiation.
From all counts, the world is entering a new age of ‘space geopolitics’ and the “pathway to the stars runs through the atom”, rightly says Michail Chudakov, head of the Department of Nuclear Energy at IAEA. Spaceborne fission would enable a single spacecraft to explore multiple targets in the outer solar system and even beyond which humans have always remained fascinated. Nuclear energy has the potential to fulfil this dream; it is just a matter of time and with the maturing of nuclear space technology, the sky won’t be the limit for human beings.
