PROPELLING ROCKETS

In as many as 17 states in India, governments spend less on health care than their residents

failed to launch. It burned up on re-entry north of Madagascar, ejecting plutonium fuel into the atmosphere over the southern hemisphere. Traces of plutonium-238 were reportedly detected in the area a few months later. Space agencies now seal RTGs inside a hard, radiation-proof shell to prevent radioactive particles from escaping.

Experts also warn that the lack of a robust international regime governing space reactors is troubling as nations increasingly invest in nuclear energy in space. The UN's Office for Outer Space Affairs has provided a set of principles for deploying nuclear power sources in outer space. But it needs to establish guidelines for the safe use of atomic energy.

Countries are also trying to develop spaceships that will use nuclear energy as fuel. In the 1960s, NASA worked on designing rockets that ran on nuclear fuel. The space agency had also planned to launch two crewed nuclear rockets to the Red Planet in November 1981. But budget cuts and changing political priorities meant the space agency had to drop the plan in 1972.

In the meantime, kerosene, alcohol, hydrazine and its derivatives, and liquid hydrogen grew popular as rocket fuel or propellants.

Now, the US and China have once again started focusing on nuclear-fuelled rockets. “We will see the first prototypes of nuclear propulsion systems getting tested sometime in the 2020s,” says Giri, adding that India is also looking at nuclear propulsion. Iain D Boyd, professor at the University of Colorado Boulder, US, says two factors can explain the revival of interest in the US: national security and interplanetary missions. The US military wants to use nuclearfuelled spacecraft to tackle weapons targeting American satellites. Nuclear spacecraft can swiftly jump into action and protect space assets from attacks. According to reports, the US Defense Advanced Research Projects Agency plans to send a spacecraft powered by a nuclear propulsion system into orbit.

One technology showing promise is nuclear thermal propulsion (NTP). According to the US Office of Nuclear Energy, nuclear fission or splitting of uranium atoms releases heat, which converts liquid hydrogen—a fuel—into gas. The gas is expanded through the nozzle, producing the necessary thrust.

The US is also working on rockets with hybrid fuel systems. Such rockets will use the existing chemical fuel to take off and switch to nuclear propellants after leaving the Earth's atmosphere.

Nuclear propellants are twice as efficient as their chemical counterparts. Their energy density, or the amount of energy they can produce, is 4 million times higher than hydrazine, the most commonly used chemical fuel for outer space missions. They are also faster: a round-trip mission to Mars could take more than three years through conventional means. Nuclear propellants might be able to accomplish this in about two years. Faster travel times mean astronauts will be less exposed to harmful space radiation. Giri says nuclear propulsion for spaceflight carrying astronauts could be a distant dream for now. The focus is currently on getting a space-proven tag, which will rely on robots. According to Boyd, nuclear propulsion systems will be used in national security missions before making it into space missions.

Countries are also looking at nuclear alternatives such as solar sails and beam-powered propulsion for deep-space missions in the outer solar system. Solar sails use light made of photons to propel the spacecraft. The idea is quite similar to that of a sailing boat. When light hits the sail—a bright, mirror-like surface—photons transfer their momentum to the sail, giving it a slight push. When photons bounce off the sail, they give it another push. This propels the spacecraft.

In 2010, the Japanese Aerospace Exploration Agency launched IKA

ROS, the first spacecraft to demonstrate that solar sail propulsion technology can work in space. Nine years later, LightSail 2, an experimental spacecraft launched by a private company, also tasted success as it continues to stay in Earth’s orbit to this day. Beampowered propulsion involves using ground-based lasers to propel the spacecraft forward. NASA is studying this technology.

Boyd does not see potential in the new technologies. Safer alternatives, he says, are the existing rocket technologies—but they are much slower than nuclear power. “There is nothing else on the horizon,” he says.

NUCLEAR-POWERED ROCKET ENGINES BEING DEVELOPED BY THE US AND OTHER NATIONS CAN GREATLY REDUCE TRAVEL TIMES AND CARRY MORE PAYLOADS THAN TODAY’S TOP CHEMICAL ROCKETS

PULAHA ROY

NEW DELHI