The launch was originally scheduled for October last year, but was delayed amid speculation that the "engines cannae take it".
Most of Doohan's remains were scattered over Puget Sound but a small proportion of them will boldly go into orbit.
The ashes will make the journey along with the remains of Nasa pioneer L. Gordon Cooper, one of the first pilots of America's Mercury rocket programme, who set new records for being in orbit and was the first astronaut to sleep in space.
"Space remains the domain of the few, the dream of many," said Charles Chafer, chief executive at Celestis, which organises the flights.
"With Celestis, the dream of spaceflight, and the desire to take part in the opening of the space frontier, can be realised and is available to everyone."
The ashes will be mixed with those of 200 other people who have paid to take part in the flight. The ashes will remain in orbit for over 10 years before burning up on re-entry.
Ashes of Star Trek's Scotty set for space
By Iain Thomson on Apr 5, 2007 2:56PM