Friday, January 23, 2015

Why A Jetplane Is Not A Spaceship, Part II

Comparison of the nuclear powered Daedalus spacecraft and Saturn V Moon rocket.
Credit/copyright: Adrian Mann
For more than a century, scientists and sci-fi visionaries have been imagining spaceships traveling to the moon, other planets, and the distant stars. Today, we still conceive of  sleek vessels performing aerodynamic maneuvers in a weightlessness vacuum far above the surface of a planet.

But we shouldn’t casually compare visionary spaceships to existing terrestrial aircraft that are burdened with air breathing engines, smooth surfaces and wing flaps. True spaceships don't soar through the air like birds. A spacecraft needs a tremendous amount of thrust just to get off a planet. It also must travel millions of miles between destinations. The NASA Space Shuttle -- a fantastic piece of equipment -- was mostly an aerodynamic box strapped to a big rocket. After each mission, the Shuttle fell back to Earth like a carefully aimed brick. During its career, the Shuttle had notable achievements, but it was not a true spaceship.

Designing a spaceship requires thinking differently.

For instance, using nuclear energy to power a spaceship has been a concept on drawing boards since the 1950s. There have been many variations of craft that mobilized the atom to fulfill humankind's ambitions to leave the planet. These inventions were not flimsy "airplanes" rising on plumes of burning petroleum-based fuels. A spaceship had to do more than  reach several thousand feet into the sky and glide back to Earth.

Spaceships that carried humans into space were huge mechanical monsters that required the resources of a major superpower. Space agencies relied upon chemical rockets burning tremendous amounts of  liquid fuels to create enough thrust to break the bounds of gravity.

Other ideas came into play.

The "nuclear pulse rocket" was seriously considered by scientists in America, Russia and Great Britain. The force of a series of nuclear explosions could push a vehicle off the planet and into space. Once in orbit, additional nuclear explosions could push the spaceship to other planets.

Project Orion, on paper, would have been more powerful than the Saturn V rocket that took the Apollo program to the Moon. Orion could travel to the planet Mars and back in four weeks. NASA's 21st  century chemically propelled spacecraft need 12 months to get to the Red Planet. Orion would have possessed a crew of 200 and weigh several thousand tons. The technology had been available before the first episode of Star Trek aired in the 1960s. The problem of course was nuclear fallout and protecting the crew from dangerous radiation during flight.  Nuclear treaties and atomic bans prevented such a craft ever being built and flown from Earth.

A better idea was to construct a ginormous nuclear-powered spaceship in orbit and not risk polluting human cities and towns with deadly radiation from nuclear fallout in the exhaust of the engines. Thus, Daedalus was born, almost. Daedalus would use nuclear fusion instead of fission -- thermonuclear "hydrogen" bombs using fusion were much more powerful than "uranium" fission bombs. The Daedalus specifications called for an unmanned spacecraft to reach a nearby star in 50 years. The craft would speed up to a substantial fraction of the speed of light and coast. Robotic probes would detach at the destination and send data back to Earth. Without slowing down, Daedalus would then continue on to other stars. Humans would become an interstellar civilization. However, we haven't mastered the art of controlled nuclear fusion, yet. For this reason, Daedalus is still on the drawing board.

In development are other forms of propulsion using the nuclear forces. For instance, the ion propulsion used by NASA’s Dawn spacecraft couldn’t lift a child’s kite off the ground. In space, ion engines can accelerate a vehicle to astonishing speeds. Dawn is now investigating several large objects in our solar system. Fantastic photos of asteroids and dwarf planets such as Ceres are being beamed back to Earth.

Modern aircraft are great for gliding through the air, performing aero stunts or defending our national interests. Indeed, most sci-fi space opera are recreations of World War II battles in the Pacific Ocean -- aircraft carriers, agile fighter planes, hidden submarines and thundering battleships. This scenario is exciting, high drama. But this not how flight would occur in outer space with our present technologies. Our apologies to Battlestar Galactica; it is doubtful that Viper fighters could operate in outer space, land on a planet and takeoff again in a single engagement -- not enough fuel. Likewise, the Star Wars Millennium Falcon could not execute a perfect barrow roll (no air in space),  then jump into hyperspace (FTL?), survive a fiery reentry onto a planet and park itself on a floating city.  These are fantastic dramas, but not good science as we understand it, today.

The bottom line,  fiction may not adhere to fact, but it inspires us to greater innovations. For this reason, a jet plane is not a spaceship, yet.