The Ares was a proposed intercontinental ballistic missile

Intercontinental ballistic missile

An intercontinental ballistic missile is a ballistic missile with a long range typically designed for nuclear weapons delivery...

 (ICBM) derived from the Titan II missile. It was a single stage rocket with a high-performance engine to increase the rocket's specific impulse

Specific impulse

Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...

. Both Aerojet

Aerojet

Aerojet is an American rocket and missile propulsion manufacturer based primarily in Rancho Cordova, California with divisions in Redmond, Washington, Orange, Gainesville and Camden, Arkansas. Aerojet is owned by GenCorp. They are the only US propulsion company that provides both solid rocket...

 and Rocketdyne

Rocketdyne

Rocketdyne was a Rocket engine design and production company headquartered in Canoga Park, California, United States. The company was related to North American Aviation for most of its history. NAA merged with Rockwell International, which was then bought by Boeing in December, 1996...

 carried out engine design studies for the project, but Ares was ultimately cancelled in favour of solid-fuel ICBMs, which were safer to store and could be launched with much less notice.

Ares would also have been capable of placing a 4,000 kg payload into low Earth orbit

Low Earth orbit

A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...

 as a single-stage to orbit launch vehicle

Launch vehicle

In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from the Earth's surface into outer space. A launch system includes the launch vehicle, the launch pad and other infrastructure....

.