Well, as a comparison point, meteors typically occur at approx 100 km = 60 miles. The fastest (Leonids, Perseids, Orionids) have been measured at at 120 km (72 miles). These are however hitting the atmosphere at about 160,000 mph. Orbital velocity is about 18,000 mph, or approx 1/9th, which means that the energy is 1/81 as much (E=1/2*Mass*V^2), so an orbiting object would be much lower in the atmosphere before heating up. However, they are larger than meteors, so that does increase the energy.<br /><br />Taking all that into account on the back of my hand (no envelope handy) I'd estimate about 80 km or 50 miles up would be the start of heating. That is just an educated guess though. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>