Dr. Lorne Trottier was in attendance of the recent landing of the Mars Rover, Curiosity. Here, he describes his account of the experience as well as the complexities and nuances of what went into this truly historical event.
The dramatic video “The Seven Minutes of Terror” only begins to describe the complexity of the events that unfolded during entry, descent, and landing (EDL). One of the areas of complexity was communications during the landing. Curiosity carries a transmitter that can send a weak signal directly to Earth with very basic information like parachute deployment, jet pack start up, etc. However, this was cutoff two minutes before landing as the rover site passed to the back side of Mars due to the planet’s rotation. NASA also used three satellites in Mars orbit to capture and record more detailed telemetry during the landing. One of these satellites, Mars Odyssey, had the capability to retransmit the data it received in real time. NASA calls this the “bent pipe”. However, Mars Odyssey had to perform a tricky maneuver at the last minute to configure itself correctly. It had to acquire the signal multiple times from Curiosity as it descended and switched antennas as the back shell and jet pack were successively jettisoned. Curiosity is the first Mars lander to use an inertial navigation system to actively guide it to its landing spot. Previous missions had much larger “landing ellipses” since their EDL was passive. Spacecraft navigators could only target the point of entry in the Martian atmosphere. The rest of the entry trajectory was passive and depended on atmospheric conditions. Curiosity used small jets on its aero shell to maneuver and “fly” the spacecraft. The “seven minutes” (of terror) is an average figure based on nominal atmospheric conditions. This can actually vary from 380 to 460 seconds under control of the guidance system that aims for the targeted landing spot.
The Planetfest was held at the Pasadena Convention Center which has a seating capacity of 2,000. The event was sold out and there was an overflow room with another 1000 people. Various speakers gave talks throughout the day including the NASA administrator Charles Bolden and Charles Elachi the director of JPL. About ¾ of an hour before landing we watched a video feed from NASA TV. Events unfolded quickly and at an accelerating pace. The spacecraft was entirely on its own in the final hours. JPL decided that no course correction was necessary as the trajectory was on “on the money”. All everyone in the control room could do was sit and watch. The first event was the separation from the “cruise stage” used for power and communication during the voyage from Earth. Cheers from the control room and the auditorium we were in sometimes made it difficult to follow each of the following events as they were announced. Then the spacecraft rotated to point its heat shield towards the Martian atmosphere. Next came a report the spacecraft was “feeling” the Martian atmosphere. Then the active guidance system was functioning. Contact was made with the Mars Odyssey orbiter but no data was coming from Curiosity. Finally a stream of data started coming from Odyssey which gave precise information like velocity, altitude, and distance to destination etc. Then parachute deployment. In the confusion and excitement I managed to hear that the jet pack had been activated, then the bridle cord was unspooling, height 40 meters, then a few seconds of silence, and finally touchdown confirmed!! This was immediately followed by more wild cheering. A couple of minutes later the first “thumbnail” image showing a wheel came up on the big screen in the control room. It all happened so quickly. It was all very exciting.
The suite of instruments on Curiosity is very impressive. Given the rich array of geologic exposures that have been detected from orbit, Curiosity will be able to greatly expand our understanding of Mars geologic history. Of greatest interest is the extent of “habitable” periods with conditions that are favorable for the emergence of life. These are: liquid water, a source of energy such as heat, and organic molecules. Curiosity is equipped with a sophisticated chemical laboratory, which includes a mass spectrometer, for detecting organic compounds. But according to Jim Bell, the chances of actually finding organic compounds on this mission are slim since radiation will destroy them to a depth of several feet (Curiosity can only drill a few centimeters). The best chance is if there is a fresh crater in the right type of rock that preserves organics. Curious to know more? For a good web site on Curiosity, check out this NASA site: http://marsprogram.jpl.nasa.gov/msl/news/whatsnew/ A video camera on the bottom of Curiosity filmed a video of the final 2 ½ minutes of its descent (a high definition version will be sent to Earth in the coming days): http://www.nasa.gov/multimedia/videogallery/index.html?media_id=149974611
