The Curiosity Rover is part of the Mars Science Laboratory (MSL) mission, NASA’s third generation rover for exploring the red planet. In addition to carrying the biggest and most advanced suite of instruments for scientific studies ever sent to the Martian surface, MSL employed a new entry, descent, and landing (EDL) system. The spacecraft descended on a parachute and then, during the final seconds prior to landing, lowered the upright rover on a tether to the surface.
After landing, Curiosity has relied on a six-wheel rocker-bogie mobility system, which is able to roll over obstacles up to 75 centimeters high and travel up to 90 meters per hour. Additionally, it has a mast with pointable remote-sensing science instruments, and an arm capable of placing contact science instruments and acquiring regolith samples for on-board analysis. The rover’s onboard laboratory was designed to study rocks and soils of the local geology to assess what the Martian environment was like in the past. Currently the rover continues its exploration of Gale crater and the central highlands of Mount Sharp. Below are more detailed descriptions of specific JPL Robotics contributions to this ongoing mission.
EDL Targeting and Simulation
As the Mars Science Lander (MSL) spacecraft approached Mars, a process called "targeting" was used to determine the final aim point for the spacecraft's entry into the Martian atmosphere. This aim point was chosen by running DSENDS, a physics-based EDL simulator. DSENDS used an initial guess at an aim point provided by an inter-planetary trajectory solution, and then propagated the spacecraft trajectory from entry through landing using models of the spacecraft dynamics. Based upon the achieved miss-distance to the desired landing site, DSENDS then adjusted the aim point. The new aim point was fed back to inter-planetary trajectory tools and used to determine the final trajectory correction maneuvers (i.e. thruster firings during planetary approach) needed to achieve the landing target. A high-fidelity Monte-Carlo simulation of the EDL sequence was generated to determine the dispersions of the landing point using parametrically varied models of the multi-body entry system, atmosphere, and aerodynamics, operating in closed-loop fashion with a copy of the on-board flight-software. This dispersion information was used by the MSL mission operators together with a hazard map of the landing terrain to determine the overall probabilistic risk associated with landing. All results of the DSENDS simulation were compared against similar results from another high-fidelity engineering simulation (called POST from NASA Langley) to ensure a high level of simulation data validation.
To complement the EDL targeting, a 3D visualization software framework was also developed. This provides a real-time, multi-mission, 3D visualization playback and geometric reconstruction capability for use by mission engineers and management to view spacecraft and environment states during targeted mission phases, in addition to providing visualization during post event reconstruction. The EDL Reconstruction System can use either real-time telemetry or provided simulation data. MSL mission staff relied on the EDL Reconstruction System to view the state of the spacecraft from the real-time telemetry stream during landing on Mars. Also, for post-EDL reconstruction, MSL analysts use the system in a playback mode to better understand the state of the spacecraft during the EDL phase.
Surface System Software and Rover Navigation
JPL Robotics provided technical leadership, algorithm design, and software engineering for MSL surface system flight software development including robotic motor, drill, and arm control, as well as rover autonomous navigation.
Control of the Rover is achieved through a distributed architecture. At the highest level is the Rover flight software (FSW) resident on the Rover Compute Element (RCE). It receives commands from the sequence engine and generates high level and low level arm motion behaviors designed to achieve the functional requirements of the system. At the lowest level is the Motor Control Flight Software (MCFSW) running on the SPARC processors in the Rover Motor Control Assembly (RMCA). The MCFSW provides PID control and low level motion fault protection operating at a 512 Hz control rate.
To drive on Mars, humans (rover planners) assess the terrain and select a safe driving route through the local terrain imaged with stereo vision camara pairs on the front, back, and mast of the rover. The rover planners can instruct the rover to blindly follow the commanded path, or employ onboard control to navigate to selected waypoints while avoiding specified keep-out zones. In the latter case, auto-navigation uses stereo vision to predictively determine where any Step, Slope, or rough terrain hazards would be encountered. To drive around hazards, the rover stops every 0.5-1.5 meters, takes 4 sets of images, evaluates hazards, and then chooses where to drive. Auto-navigation can also extend directed drives into previously unseen terrain.
Curiosity keeps track of its position and orientation using gyros and accelerometers to measure any attitude (pointing) changes, and combining those attitude changes with wheel rotations to estimate its motion (wheel odometry). Additionally, “visual odometry” is obtained by stopping every meter to take pictures which show how the viewpoint has changed, allowing correction of the onboard position estimate based on a full 6 degrees-of-freedom analysis.
Robotic Arm, Drill and ATLO Rover Integration
JPL Robotics led MSL Robotic Arm (RA) development, drill development, and pre-launch Rover Integration.
MSL RA is the most complex and capable manipulator ever sent to another planetary surface, enabling sample acquisition, processing, and delivery, as well as contact science operations. The robotic arm is a 5 degrees-of-freedom manipulator supporting a 30 kg payload mounted at the end of the arm. The turret mounted payload includes a drill and four contact science instruments.
JPL Robotics engineers managed the development of the manipulator, created the control software for it, and continue to lead the operation of it on Mars. Similarly, JPL roboticists developed the drill control software, performed all the testing and validation of it, and lead in its use for sample collection from Martian rocks.
RSVP for MSL
The Robot Sequencing and Visualization Program (RSVP) for the Mars Science Laboratory Mission (MSL) is built upon prior Mars Pathfinder and Mars Exploration Rover mission operations software. RSVP is comprised of two tools:
- The Robot Sequence Editor (RoSE), which provides efficient graphical user interface (GUI) support to all commands in the mission dictionary, and also interfaces with the JPL spacecraft sequence generation system (SEQGEN) for resource computations and sequence validation. RoSE can be used to create all command sequences sent to Curiosity.
- HyperDrive, which provides multiple 3D graphics interfaces to the stereo images and derived 3D terrain-model data coming from Mars. It is used to plan all rover motions, including driving over the surface of Mars and complex robotic arm actions to place instruments on sites of geologic interest.
For more details on all aspects of the MSL mission, visit the MSL Project website