How feasible are trips by earthmen to other solar systems? They're practically impossible, according to Nobel-prize-winning physicist Edward M. Purcell, Gerhard Gade University Professor.

Purcell's views, which were given national attention over the weekend in a New York Times article on the possibility of communication with other worlds, are based on elementary mechanical considerations which show that preposterous amounts of fuel would be required to propel a rocket to another planetary system and back to the earth within a reasonable period of time.

Using the conservation laws of elementary physics (conservation of energy and momentum) and Einstein's famous mass-energy relationship, the physicist calculated the fuel requirements for a hypothetical round trip to a planet 12 light years distant. He assumed the rocket would accelerate to 99 per cent the speed of light and return to the earth 22 years after leaving.

For such a trip, a rocket driven by a nuclear fusion propellant (much more efficient than the chemical fuels used in today's rockets) would require a mass of fuel about a billion times the mass of the earth.

Purcell then supposed that man could somehow find a way to utilize nature's most efficient energy-producing process--the 100 per cent conversion of mass to energy that occurs when matter and anti-matter annihilate each other. He showed that 200,000 tons each of matter and anti-matter would be needed.

Finally, Purcell noted several radiation hazards. The space traveller would have to be protected by several yards of lead shielding against the lethal radiation produced by interstellar particles striking his ship at 99 per cent the speed of light. The earth would have to be shielded from the tremendous gamma ray exhaust of the matter-anti-matter engine.

Purcell's conclusion: talk of interstellar space travel is "nonsense" and "belongs back where it came from, on the cereal box."