Understanding how a spacecraft flies through the atmosphere is key to the entry, descent and landing phase of any mission. Atmospheric and aerodynamic conditions have a huge effect on flight.
Engineers and scientists analyze data to try to better understand what kind of environment a spacecraft will face just before it lands on Mars or another planet, but just like the weather here in Earth -- there are still plenty of unknowns. Think about it in terms of a meteorologist trying to predict the weather in a specific place, at a certain moment in time - years in advance. Each factor -- temperature, pressure, winds, speed of the spacecraft or other variables - impacts the spacecraft's landing location or footprint.
Previous Mars missions have relied on physics to decide where spacecraft should land on Mars. For the first time Mars Science Laboratory, set to land in August, 2012, will collect up-to-the-minute data about the environment it's flying through and use thrusters to adjust its position if needed.
The HIAD team is looking at additional options for controlling where a spacecraft lands. One alternative, being tested on the Inflatable Reentry Vehicle Experiment (IRVE-3), involves the use of a mechanism to shift some of the payload weight from side to side. That would cause the aerodynamics of the spacecraft to change. Another option involves adding trim tabs surfaces of the spacecraft. Trim tabs -- small surfaces attached to the larger control surfaces -- are currently used on boats and airplanes, but could be useful on spacecraft as well.
Understanding both the aerodynamics of atmospheric entry and having a way to better control the entry, descent, and landing can ultimately lead to more pinpoint landing accuracy. When people land on Mars, controllability and a small footprint will be very important. Robotic missions that can land near the sites they are targeted to study and people arriving close to valuable resources, such as food and transportation, will make missions more effective and efficient.