First off it's ok, I'm ok! <Allison wrote: <> FYI the speed attained at <> that point is some 3600mph far from orbital velocity. < <I'm not sure how to parse that. Are you saying that it was traveling at <3600 MPH, which is far from orbital velocity (i.e., a missing comma), or <that it was travelling at 3600 MPH less than orbital velocity? Sorry bout that. I do tend to be a tad graphlexic the comma should have been there. It was velocity of 3600. they need 17500+ to orbit. <(In any case, the use of the word velocity is incorrect. Velocity is <a vector, as I had drilled into me in Physics class.) Their forward speed, velocity. I'm a pilot and am quite used to having vectors influence the direction and speed that is indicated vs ground track. <The NASA reference I posted earlier claims: < At this point in its trajectory, while traveling at a Mach number < of 1.92 at an altitude of 46,000 feet, the Challenger was totally < enveloped in the explosive burn. Downrange groundtrack speed is far lower as the vector is still mostly vertical (still greater than 60degrees) at that part of the mission. If memory serves the debrie field was a rough footprint of 20 wide by 80 miles long (for the greater part of the material). As to what computer... Not sure myself totally. It's my belief that the IBMs are high level systems management computers and they command the engine computers. The engines have their own local computers to handle their realtime needs. Same applies to several other systems. I consider spacecraft/aviation computers to be both classic and of great interest. Most are very system and mission specific thus may be nothing more than sequential controllers. Still, I'm curious. Allison