Beyond the Rocket
by David Hallquist
Liquid fuel and solid rocket engines have gotten up to orbit and the Moon, and has sent probes in slingshot paths throughout the Solar System. The technology is well developed, but it still takes years to reach distant planets, and vast boosters to lift any significant mass to a distant world. We will need something more to reach the farther worlds.
NERVA (Nuclear Engine for Rocket Vehicle Application) was a concept for manned exploration in the Solar System. The engine incorporated a nuclear reactor, which would then heat the propellent, providing a level of high velocity thrust far more efficient then a chemical rocket. Project Kiwi in 1955 demonstrated a successful test case for the function of the motor, and a manned mission to Mars had been planned for 1981, before being canceled. http://www.lanl.gov/science/NSS/issue1_2011/story4full.shtml
Ion engines use charged atoms (ions) that are then accelerated though a magnetic field to very high velocity. Since the ions travel at extreme speed, they can provide far more thrust per mass, making them more efficient. This technology was successfully tested in 1964. Dawn used solar powered ion engines for Solar System flight, is currently exploring the asteroid belt. Ion engines may also function when powered by nuclear engines in deep space. Ion engines also help stabilize the ISS.
Mars and the other worlds of the Solar System are not beyond our reach. We can reach these worlds, with proven technology, we will just have to look beyond the rocket.