Index Fission, the splitting of atoms, is not a new idea. It has actually been around since World War 2.

Researchers are looking at fission as a form of propulsion because of its large amount of power. If

Field Drives one were to take a chunk of uranium the size of a twelve ounce can, and fission it, the resulting amount

of energy would release 8*10¹⁰ joules per gram of fuel. That is fifty times the amount energy in

Collision Sails 750,000 kilograms of fuel stored in the massive external tank of the space shuttle. As of right now fission systems have not been used in any deep space missions, inter-planetary missions, or even in any

ASTP space flights to the moon. The reason fission propulsion has not been used outside the Earth's orbit is

because of the danger created by using it. A team of researchers at NASA's Marshall Space Flight

Bibliography Center are conducting a Safe Affordable Fission Engine (SAFE) test series that will simulate a safer

and more cost effective fission engine (http://www.highway2space.com/sciresearch/nuclear_prop.html). If the engine passes the test, the design may be used to power spacecraft on missions outside the Earth's orbit.

If one were to look for the reaction that releases the highest amount of energy per unit of mass, they would find a matter/antimatter reaction. Antimatter consists of antiparticles that are the same as a normal particle, except that it's spin and charge are opposite. Instead of protons, neutrons, and electrons, antimatter has antiprotons, antineutrons, and positrons. Whenever a matter particles comes in contact with its antimatter counterpart the two are completely destroyed and all their mass is converted to energy. Antimatter propulsion is not very far along in the research department but is getting attention because of the high energy in antimatter. 0.6 cubic centimeters of antiprotons contain the same amount of energy that is in the external tank of one of the space shuttles (http://www.highway2space.com/sciresearch/nuclear_prop.html).