Comdrs. John Young and Robert Crippean conducted the first successful manned "dress rehearsal" into orbit of a space shuttle flight Tuesday. The rehearsal took place at the vehicle assembly building of the National Aeronautics and Space Administration and was a simulated burn of the space shuttle Columbia's three main engines and two solid rocket boosters. After a simulated ejection of the boosters and the external fuel tanks, the astronauts simulated firing a smaller engine system to take them into an elliptical orbit. They also simulated a second firing of the secondary set of engines, which would take them into a circular orbit of about 175 miles. the rehearsals continue Wednesday when backup Astronauts Joe Engle and Vic Truly simulated an emergency situation several minutes into flight and "returned" to the landing site.