Aerobraking Mars Orbiter Surprised Scientists Universe Today

The Mars Reconnaissance Orbiter (MRO) has completed aerobraking and its primary science phase will soon begin in earnest. MRO’s Project Scientist and members of the Navigation Team discuss the intricacies and challenges of aerobraking in Mars’ ever-changing atmosphere. Aerobraking is a technique that was first used by the Magellan mission to Venus in 1993, and also used on two other Mars missions, the Mars Global Surveyor (MGS) in 1997 and Mars Odyssey (2001). Aerobraking uses repeated dips into the atmosphere to gradually slow the spacecraft and reduce the size of the orbit. While aerobraking takes time, it saves on the amount fuel required, as in MRO’s case, by 600 kilograms (1,300 pounds). To aid in the aerobraking process, the navigation team employs an atmospheric model called the Mars-GRAM (Global Reference Atmospheric Model), a computer database of information from what previous missions have encountered, combined with a mathematical model that attempts to simulate Mars’ atmospheric dynamics. This provides a prediction of the density of Mars’ atmosphere, giving the navigators an estimate of how far down into the atmosphere the spacecraft should go.
But the atmospheric density that MRO actually experienced was much different than what was predicted by the Mars GRAM.