31 July 2012
A new era of space exploration is dawning through the application of nuclear energy for rovers on Mars and the Moon, power generation at future bases on the surfaces of both and soon for rockets that enable interplanetary travel.
NASA has reported the successful tests of power conversion and radiator systems for a nuclear power system it hopes to deploy on the Moon by 2020. It is based on a small fission reactor which would heat up and circulate a liquid metal coolant mixture of sodium and potassium. The heat differential between this and the outside temperature would drive two complimentary Stirling engines to turn a 40 kWe generator. Some 100 square metres of radiators would remove process heat to space.
Using an electric heat source instead of a real reactor, the Stirling engines, generator and a section of the radiator have recently been tested – producing a steady 2.3 kWe. The tests included operation in a vacuum chamber that simulates extreme temperature swings at NASA’s Glenn Research Center, and under elevated radiation levels at Sandia National Laboratory. “It is very efficient and robust,” said Lee Mason of Glenn, “we believe it can last for eight years unattended.”
“Nuclear is a stepping stone to move further out into manned space exploration.”
Sandia National Laboratory
Space missions have so far used a range of power sources: chemical energy for rocket propulsion, solar power with batteries for low-power systems and small radioisotope thermal generators for even lower power applications and to prevent damage from the cold of space. The highest power level so far generated is the 100 kWe of the International Space Station, whereas a satellite or probe might use 25 kWe from solar cells.
Nuclear energy from fission reactors can provide larger constant supplies without reliance on sunlight or the burden of heavy batteries and rocket fuel. “A lunar base needs lots of power for things like computers, life support, and to heat up rocks to get out resources like oxygen and hydrogen,” said Ross Radel of Sandia. The Moon is dark for up to 14 days at a time, and Mars is so much further from the sun that solar power would not be sufficient for life-support. For those reasons, “nuclear is a stepping stone to move further out into manned space exploration,” said Radel.
NASA said that current plans foresee nuclear power employed on the Moon in around 2020. However, a nuclear-powered rover named Curiosity is due to land on Mars in the next ten days.
Atomic batteries to power
The Curiosity rover is in effect a large mobile laboratory that will explore the surface of Mars from a landing point in the Gale Crater. It is about twice as long and five times as heavy as the two previous rovers, Spirit and Opportunity, and powered by a large radioisotope thermal generator instead of solar cells.
Using the 2.7 kWh of electrical power produced each day from the decay heat of 4.8 kg of ceramic plutonium-238 oxide, Curiosity will be the first rover with the power to drill into Martian rocks and analyse the results on-site. The nuclear battery has a minimum lifespan of 14 years.
Next year China is to launch a rover for the Moon powered by a nuclear battery, with a mission to take samples of the surface and survey beneath using radar. Chang’e 3 will follow two previous lunar orbiters, launched in 2007 and 2010, when it begins a three-month mission next year.
Turbines to speed
Most significant of all could be the Russian project for a ‘megawatt-class’ nuclear-powered rocket.
In the 1960s, research into nuclear rockets saw prototypes use small fission reactors to heat and eject hydrogen to propel a craft forward. This came with a number of radiological complications that prevented further development. The idea being pursued now by Russia’s Keldysh Research Centre is to use a small gas-cooled fission reactor aboard the rocket to turn a turbine and generator set and thereby produce electricity for a plasma thruster.
Talking to Interfax, Keldysh chief Anatoly Koroteev said the specific thrust of such a system could be 20 times that of current chemical rockets, enabling heavier craft with greater capabilities to travel further and faster than ever before. According to Koroteev, the advent of nuclear-electric rocketry will be a step-change analogous to the introduction of the jet engine to aviation.
The project to develop the nuclear thrust module began in 2010 with a budget of RUB17 billion ($530 million) and a plan to launch in 2018. The majority of this is allocated to Rosatom’s development of the reactor unit, which should be completed in 2015.
World Nuclear News