From the BBC:

US space agency NASA has named its new manned exploration craft Orion.
The vehicle is being developed to take human space explorers back to the Moon and potentially then on to Mars.

It is hoped the name Orion could eventually mean as much for manned space exploration as Apollo did in the 1960s and 1970s.

Its first manned flight - to the International Space Station - will take place no later than 2014 and its first flight to the Moon no later than 2020.

Don't call it Orion. Say the word Orion to a space-exploration geek and he or she will utter three words; nuclear pulse rocket.

Project Orion was under serious development until 1963 when the PTBT was signed preventing the use of nuclear weapons in space causing the project to be put on hold.

Basically it used nuclear explosions instead of chemical reactions for thrust, by detonating nuclear bombs behind it against an inertial plate. Such a craft would be much faster than chemical rockets and be able to carry much larger cargos. From Wikipedia:

The reference design was to be constructed of steel using submarine-style construction with a crew of more than 200 and a vehicle takeoff weight of several thousand tonnes. This low-tech single-stage reference design would reach Mars and back in four weeks from the Earth's surface (compare to 12 months for NASA's current chemically-powered reference mission). The same craft could visit Saturn's moons in a seven-month mission (compare to chemically-powered missions of about nine years).

Don't use Orion if you want to use the name of a constellation use one that has not been used before like Camelopardalis, now that's good, using a camel to cross the desert of space! But what's wrong with Apollo II? Or hell even Starbuck!? :)