With an eye to making future unmanned and manned planetary landing missions safer, NASA has installed the first components of an advanced instrument package aboard the Mars 2020 entry vehicle. Parts of the Mars Entry, Descent and Landing Instrumentation 2 (MEDLI2) sensor suite were attached to the spacecraft's heat shield and aeroshell, where they will monitor pressure and temperature during atmospheric entry.
For all its futuristic, high-tech reputation, landing on another planet is a massive exercise in approximation, if not downright educated guessing. Setting down an autonomous spacecraft on a little-known world hundreds of millions of miles away involves taking into account all manner of unknowns about the place where the craft is landing, and also the performance of the spacecraft itself.
Because of this, landing missions have a very large margin of error built into them. Specifications must be overengineered, systems made double or even triple redundant, and the landing area is defined as a large ellipse plotted over a relatively safe region for setting down.
"Uncertainties in our ability to model and predict the performance of an entry vehicle and the associated thermal protection system mean that large margins (100 percent to 200 percent) need to be included in our predictions to ensure the entry vehicle can survive the worst case conditions," says Henry Wright, MEDLI2 project manager. "Flight data will allow the uncertainties in the models to be further reduced leading to a more accurate prediction of the loads and performance."
MEDLI2, as its name suggests isn't the first of its kind. The original MEDLI rode on the Mars Science Laboratory mission, which delivered the Curiosity rover to the Martian surface. The more advanced MEDLI2 package consists of three types of sensors – thermocouples, heat flux sensors, and pressure transducers. These feed into the data acquisition and signal conditioning Sensor Support Electronics Unit that records the thermal and pressure data measured during atmospheric entry and parachute deployment. Unlike the previous version, MEDLI2 includes sensors connected to the aeroshell as well as the heat shield.
The idea is that five hours before Mars 2020 enters the atmosphere of the Red Planet at a speed of about 12,500 mph (20,120 km/h), the instruments will begin to collect data. They will continue to do so during entry, descent, and parachute deployment, which takes about six minutes. By this time, the craft will be descending at a mere 2 mph.
The hope is that this new data will allow engineers and mission planners to make the heat shield for the next lander 35 percent lighter, which would decrease coasts and allow for a heavier science payload. In addition, the landing ellipse for future missions could be made smaller, allowing missions to explore many more interesting areas.
MEDLI2 has so far finished its vibration and thermal vacuum tests at NASA's Langley Research Center in Hampton, Virginia. In addition, the hardware has been sterilized by high temperatures to ensure that the lander will have a very low probability of contaminating Mars with terrestrial microbes.
Installation is expected to be complete by November of this year.
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