14 DAY TRIAL // As the landing date for the Mars Science Laboratory (MSL) rover Curiosity is drawing closer, experts at the NASA Jet Propulsion Laboratory (JPL), in Pasadena, California, are again going through the landing procedure the spacecraft needs to undergo. This involves using 76 explosive charges.
Curiosity is scheduled to land on the slopes of Mount Sharp, inside Gale Crater, on August 6 GMT (August 5 PDT). For this maneuver, it will use the newly developed Sky Crane system, which has never been employed by another mission.
Basically, the actual rover is attached to a platform featuring four thrusters, one at watch corner. Both are encapsulated in a so-called aeroshell, which features a bottom shell (also acting as the heat shield) and a back shell (which features the parachute pack).
After entering the Martian atmosphere at the steepest angle ever taken on by a landing spacecraft, the MSL will eject its heat shield, and deploy its parachutes. After its descent is slowed down considerably, the back shell will separate as well, and the thrusters on the Sky Crane platform will be enabled.
These thrusters would then make the platform hover at a suitable altitude. Curiosity will be lowered via cables to Mars, and then the cables will snap from its surface. The Sky Crane will then increase power to its thrusters and fly away. It will crash a kilometer or so away from the rover.
All of these steps in the intricate MSL landing process will rely on a series of pyrotechnic blasts that need to be synchronized with extreme precision. What makes the problem even more complex is the fact that not all charges have the same yield.
Some produce the energy equivalent of setting a box of matches on fire, whereas others pack the same punch as an entire stick of TNT. All of them are timed to go off within fractions of a second of each other, and there is very little room for error.
“We are definitely coming in with a bang – or a series of them. You only get one shot at a Mars landing, and the pyrotechnic charges we are using are great for reliably providing instantaneous, irreversible actions like deploying a parachute or opening a fuel valve,” expert Pete Theisinger explains.
The JPL scientist holds an appointment as the MSL project manager. He says that pyrotechnic devices are commonly used in spacecraft, highlighting the fact that even the NASA space shuttles have landing gears laced with explosives. The goal was to ensure the wheels would open in case of a malfunction.
“When we need valves to open, or things to move or come apart, we want to be confident they will do so within milliseconds of the time we plan for them to do so,” adds JPL pyromechanical engineer, Rich Webster.
“With pyros, no electrical motors need to move. No latches need to be unlatched. We blow things apart – scientifically,” he concludes.