A journey to Mars can be made relatively safely with acceptable hazards for the crew, but not by conventional means. After nearly a decade of research for my first novel, "Trajectories," I realized that for a "practical" manned mission to Mars, four conditions must be met.
First: The propulsion rockets must involve a nuclear reaction.
The semi-elliptical path between low and high orbits that best economizes fuel, called a Hohmann transfer, will take a chemical rocket at least 8 months to reach Mars from Earth. Once there, the crew will have to wait another 13 months for Earth's solar orbit to re-synchronize with Mars' before the crew can start their return journey, which will take another 8 months to complete.
Such an ordeal will subject the crew to nearly two and a-half years of bone demineralization, severe muscle atrophy and radiation exposure in a confined environment suffered in psychological isolation. And the longest time spent in space so far has only been 438 days on the Russian Mir.
However, if the journey can be made in about 77 days, the crew can turn around and rocket directly back to Earth without waiting for the planetary orbits' to sync-up.
And if the trip can be made in, say, 70 days, the crew will have 14 days to take pictures and collect surface samples. But this not only means a rocket acceleration to 13 kilometers per second (plus Earth's 30 kps, this totals to an escape speed of 43 kps), but this same high-energy burn (270,000 GigaJoules for a 600,000 kg spacecraft) must be done 4 times - the rockets will have to be fired again to brake into Mars' orbit, and two more times for the return journey; a third time to break Mars' orbit, and a fourth to brake into Earth's.
But a chemical rocket able to achieve such energies would have to be the size of four Empire State Buildings, laid end-to-end, and already parked in Earth orbit.
A nuclear rocket would not be so long; maybe the length of a football field.
Such an engine might consist of four stages and would burn hydrogen as a propellant in a reaction so hot that helium might be developed as a fusion by-product.
Second: The mission should be tandem.
By this I mean that, for the further safety of the crew, and until the real hazards of such journeys reveal themselves, two separate spacecraft should make the initial few journeys. At most, these space crews will be 80,000,000 kilometers (50 million miles) distant from Earthly help.
It would be a happy amalgamation of science if the U.S., Europe, Canada and Brazil collaborated on one vessel, and Russia, China, Japan and India built the other. Unfortunately, given the cost overruns and schedule difficulties experienced by the International Space Station (ISS), this condition will be the hardest to realize. Nevertheless, the funding MUST be international; otherwise no one country will be able to afford even one vessel.
Third: A Mars-bound spacecraft must provide its own gravity.
Medical studies in the 70s have indicated that even after a month in space, reintroduction to gravity (by landing on Mars), the astronaut will experience such an abrupt shift in environments that he would initially pose a greater risk to himself than the hazards around him. And two months is quite too much.
Either a strict exercise regimen must be observed, or some way to safely rotate the ship must be found. Obviously, this might render solar power difficult to provide.
Fourth: Radiation shelters must be provided.
If we were to distill the atmosphere above our heads to a liquid, we would be standing under the equivalent of 10 meters (33 ft.) of water. Such is the quality of our terrestrial radiation shielding.
Not only must the crew be protected from engine radiation, but from solar flares both in space and on the surface of Mars, where the near vacuum of its atmosphere is only .7 per cent of ours. (The ISS crew is afforded good radiation protection by the Van Allen belt, or magnetosphere.)
One possible solution might involve an arrangement of liquid oxygen, liquid hydrogen and liquid nitrogen tanks. These would multifunction as propellant, water source, power source, oxygen-regeneration and refrigeration system. Another scheme might involve a chamber shielded by an electromagnetic field strong enough to deflect most charged particles. Though the provision of low-weight radiation shielding promises to be a unique engineering challenge, I'm told that it's not unattainable.
Obviously, the technology required for such a journey is so complex, and expensive, the world might not see a first expedition to Mars until well into the latter half of the 21st Century.
But, at our level of "pre-Star Trek" technology, the safer one wishes to be in space depends on how quickly one can get in and out of it. Mars can be gained safely. But in space, speed is life.
For a world facing future shortages of everything, it would not be improvident to develop a compact engine capable of liberating great energy, even if only to power a Winnebago-sized bottle rocket crewed by five jet pilots with Ph.D.s from the southeastern U.S. with German-sounding last names.
Even this secular humanist would have to admit it to be one of another of God's little ironies that such a system could only be safely tested in space.