Mars Global Surveyor: Aerobraking . ... Credit Copyright: MGS , JPL , NASA Explanation: Completing a 10 month journey, another spacecraft from Earth arrives at Mars today . The Mars Global Surveyor (MGS) is scheduled to fire its main rocket engine for 22 minutes at 6:17 p.m. PDT and enter a highly elliptical orbit , with a low point 186 miles and a high point 34,800 miles above the surface of Mars . ... But first MGS must circularize its orbit, lowering the high point to about 250 miles. ...