text: can a jet plane fly out of earth's orbit? since space starts about 100 km... out of orbit?  not a chance.  (remember that the moon, some thousands of miles away, is in earth's orbit.  so i'll assume that you mean out of the atmosphere.)  the thermosphere surrounding the earth is very hot. imagine that a jet could go fast enough to break out of the atmosphere (mach 5 or so would do it i think)- at this speed even the scattered particles of the thermosphere would generate enough heat to destroy all but the most resilient of vehicles.  the reason this incredible speed is needed is that once the jetplane leaves the dense atmosphere of earth it can no longer run its engines; they are out of air.  the jet could no longer generate forward movement, or lift, and would lose altitude.  essentially for a jet to breach the atmosphere then it would have to fire itself into space like a bullet, requiring high speeds, which would likely result in its destruction in the thermosphere.