simulating FEATURE STORY Only One Chance to REALITYMSC Software Magazine Volume II || Supplemental Issue - Summer 2012 recognized the importance of simulation from not induce particularly high loads on the solver. This made it possible to validate the Get it Right the very beginning and devoted an average rover. However, simulation showed the loads system performance and tune the controller of three people working with multibody were much higher than expected. The original parameters with a detailed mechanical model. dynamics over the life of the project. expectations also were that the rover would be JPL engineers validated and updated the Adams Simulations Help Rover The rover, the most critical part of the in a quiescent state when it touched down on Adams model by correlating the simulation Make Perfect Touchdown on simulation, was modeled to a high level of the surface but the Adams simulation results to the test data. showed that the rover was actually rotating fidelity including many flexible elements some The engineers at JPL were not able to test most Based on an interview with Dr. Chia-Yen Peng, Principal & and swinging as it landed. As a result, the of which incorporated nonlinear stiffness and of the critical mission events on Earth so they Lead Engineer for the Loads and Dynamic Simulation team at JPL. damping. The descent stage model is much rover structure was stiffened to mitigate these had to rely upon simulation to design most of simpler, consisting entirely of rigid bodies. In issues. the critical hardware and control sequences for ONLY ONE the beginning of the project, separate models Later studies provided the additional surprise this mission. The accuracy and thoroughness were used for the rover separation, mobility that the deployment of the rover’s wheels and of the simulation results helped make it ars Science Laboratory is a robotic Complex Sequence At about 1.8 kilometers altitude with the space probe mission that successfully traveling at 100 meters per second, deployment, and touchdown phases. During struts as originally planned generated even possible to successfully and precisely place the M The Curiosity rover is about twice as long the later stages of the project, all of the models greater loads on some of the rover components rover onto the Red Planet. u landed Curiosity, a , in the rover and descent stage dropped out. The CHANCE TO and five times as heavy as previous Mars were emerged into one. The combined model than the touchdown. Simulation showed Crater on Mars on August 5th, 2012. The sky descent stage fired its rocket thruster to slow Image Credit: NASA/JPL-Caltech and rovers. Landing runs between 17 to 93 minutes on a four-CPU that the end of wheel deployment generated crane landing sequence required the rover to to less than 1 meter per second and lowered such a large payload on Mars is challenging Hewlett Packard Unix workstation. hammer-like blows on the rover suspension transform from its stowed flight configuration the rover with a 7.6 meter tether consisting of because the atmosphere on Mars is too thin and frame. to landing configuration while being lowered three bridles and an umbilical cable carrying GET IT RIGHT for and aerobraking to be effective electrical signals to the . As Determining Loads JPL engineers addressed this problem by to Mars wheels down from the descent stage. yet still thick enough to create the potential the bridles unreeled, the rover’s six motorized for Structural Design changing the timing of the wheels and struts ADAMS SIMULATIONS HELP CURIOSITY ROVER The final entry, descent, and sky crane landing for stability and impingement problems when wheels snapped into position to prepare deployment. Changing the timing of the MAKE PERFECT TOUCHDOWN ON MARS phase was called “seven minutes of terror” by decelerating with rockets. Also at 900 kg the Optimizing the design of every component in for landing. After landing, the rover fired wheels and struts deployment also reduced the DATES & LOCATIONS NASA engineers because of its complexity Curiosity rover is too heavy to use to the payload was critical because of the need THE explosive devices activating cable cutters swing rate and swing angle before touchdown. and the fact that human intervention from cushion the shock of landing. One additional to ensure their ability to withstand loads and SAVE DATE to free itself from the descent stage and earth was impossible. challenge is that the 14 minute trip required successfully perform their mission while at the Americas the descent stage crash landed hundreds of Checking Other Aspects Tuesday / Wednesday - May 7/8 same time minimizing their weight because NASA Jet Propulsion Laboratory (JPL) for a radio signal to travel from Mars to earth meters from the rover. At 6:33 a.m., the rover of the Landing Sequence 2013 USER CONFERENCES of the high cost of transporting incremental engineers simulated this final sky crane means that the vehicle must act autonomously confirmed a successful landing. weight to Mars. EMEA without interactive control from Earth for the The most critical aspect of the separation Sweden - Monday / Tuesday - May 13/14 landing sequence using MSC Software’s MSC Software will celebrate its 50th entire landing sequence. Adams was used to predict the loads on between the rover and descent stage is the Germany - Tuesday / Wednesday - May 14/15 Adams multibody dynamics software. The Only One Chance to Get it Right anniversary in February, 2013. Please join us components and subassemblies and these need to avoid contact between the flight UK - Wednesday / Thursday - May 15/16 simulation identified problems with the initial NASA engineers addressed these challenges in celebrating at the 2013 User Conferences. France - Thursday / Friday - May 16/17 There was only one chance to get it right. loads in turn were used as input to structural hardware. The Adams simulation was used to concept design and guided engineers as they by developing a unique entry-descent-landing Russia - Tuesday / Wednesday - May 21/22 The complex sequence either works perfectly analysis that optimized the design to provide check the clearance and ensure that there was The events will take place in May and June. - Wednesday / Thursday - May 22/23 resolved these issues and made the design system. The aeroshell containing the heat th or the entire mission goes up in a cloud the strength to withstand mission loads while no possibility of contact. In the final design Location details coming soon. Turkey - Monday - May 27 shield, rover, descent stage, backshell and more robust. The simulation was also used to of Martian dust as the rover is destroyed. minimizing size and weight. The philosophy there is very small clearance but no contact validate the landing sequence and determine , separated from the cruise stage *Dates and locations are subject to change. Japan Engineers cannot test the landing sequence of the modeling was not to try and predict issues. ten minutes before entering the Martian Thursday - May 30th loads on subassemblies and components. The on Earth because they can’t duplicate every event to 100% accuracy but rather to atmosphere and fired thrusters to orient the The flight control software was written in controls software code that guides the mission Martian gravity, atmosphere, and the determine the bounding limit design loads heat shield facing Mars. The aeroshell slowed C++. The people who wrote the controller APAC through the sky crane landing sequence landing conditions on Earth. They can test that could be expected on every component. Korea - Monday / Tuesday - June 4/5 software required a detailed mechanical model For more information, visit: was integrated into the Adams environment to about 578 meters per second at about individual components but the only way to - Wednesday / Thursday - June 6/7 10 kilometers from Mars at which point a Prior to the Adams simulation, JPL engineers to accurately predict the system performance. www.mscsoftware.com/50years India - Thursday / Friday - September 5/6 to validate and tune its performance. The test the complete sequence and determine believed that the projected 1 meter per second The engineers overcame this issue by accuracy of these simulations was proven by supersonic parachute deployed. the loads on the individual components is maximum speed during touchdown would compiling the controller with the Adams the success of the mission. with simulation. The program engineers

Volume II | Supplemental Issue - Summer 2012 | 2 1 | MSC Software

FL_MSC_50th-A4-1.indd 1 10/2/12 10:49 AM START OF LANDING SEQUENCE 2 Curiosity and its landing , traveling at 13,200 miles per hour, had just seven minutes to slow down to two miles an hour and land safely on the Martian surface, a remarkable engineering turn to entry achievement considering that the complex maneuvers and sequences all had to work to perfection, HEATSHIELD SEPARATION 1 the first time tried! 1 At 5 miles (8 kilometers) above the surface of Mars, the heat shield separated from the spaceraft Curiosity and its landing spacecraft were modeled extensively with MSC’s Adams software, to 7 and plummeted to the ground. With the heat shield off, the Mars Descent Imager started a high level of fidelity, including many flexible elements some of which incorporated nonlinear ENTRY. DESCENT. LANDING. recording the first ever video of a Mars landing. This movie gave us a “rover’s eye” view of the stiffness and damping. rapidly approaching Martian surface as if we were landing with it. To see this video, go to: start of landing sequence Adams Simulations Help Curiosity Rover Make Perfect Touchdown on Mars www.mscsoftware.com/roverview. CRUISE TURN TO ENTRY Nine minutes before entry, the back shell thrusters oriented the spacecraft so the heat shield 3 4 RADAR DATA COLLECTION faced forward, a maneuver called “turn to entry.” After the turn to entry, the back shell jettisoned As Curiosity descended, six independent pulsed-Doppler radar antennas where used to scan the 2 two solid-tungsten weights, called the “cruise balance mass devices.” Ejecting these devices, which guided entry peak heating surface. Distance readings from this radar system were used to signal when the parachute should weigh about 165 pounds (75 kilograms) each, shifted the center of mass of the spacecraft. This 8 be detached, when retro-rockets should fire, and when the rover should be lowered down from allowed the spacecraft to fly through the atmosphere at an angle, generating lift. The lift was used the descent stage. Engineers were able to successfully “lock-on-target” by the time the rover was for “guided entry” to steer out of unpredictable variations in the atmosphere and improve landing about 1.2 miles (3 kilometers) above the surface. While the radar only functioned for two minutes, precision. CURIOSITY it was so important that engineers tested it over 100 hours, dangling it from a helicopter over Mojave and Death Valley. Curiosity was modeled in Adams to a high level 6 GUIDED ENTRY of fidelity including many As the spacecraft initially interacted with the upper atmosphere, thrusters on the back shell flexible elements some BACKSHELL SEPARATION AND POWERED DESCENT 3 parachute deploy adjusted the angle and direction of tilt, letting the spacecraft fly a series of “S” curves. These of which incorporated 5 At this stage, the spacecraft had to perform some of the most technically challenging maneuvers curves reduced the horizontal distances the spacecraft covered as it descended. The guided entry nonlinear stiffness ever accomplished on a space mission. Luckily it was not a total “Leap of Faith” as the sequences maneuvers also corrected for drift to the left or right due to winds. and damping. In the 9 were first analyzed with MSC’s Adams multibody dynamics simulation software. For instance, one beginning of the project, 8 of the most critical aspects of the separation between the rover and descent stage is the need separate models were hypersonic aero-maneuvering to avoid contact between the flight hardware components. Adams simulation was used to check PEAK HEATING used for the rover radar data collection the clearance and ensure that there was no possibility of contact during the sometimes violent separation, mobility motions. In the final design there was very small clearance but no contact issues. Eighty seconds after entering the atmosphere, the heat shield reached the hottest temperature deployment, and ever for any Mars entry vehicle, about 3,800 degrees Fahrenheit (2,100 degrees Celsius). The touchdown phases but 4 innovative Phenolic Impregnated Carbon Ablator (PICA) thermal protection system, allowed during the later stages SKY CRANE MANEUVER Curiosity to remain at a cozy temperature of 32 to 77 degrees Fahrenheit (0-25 degrees Celsius) of the project all of the inside its aeroshell. The PICA thermal protection materials were subjected to severe thermal and models were emerged At an altitude of about 66 feet (about 20 meters) above the surface, the spacecraft then mechanical loading environments during entry into martian atmosphere. MSC Software’s Marc into one. The combined performed the now infamous “Sky Crane Maneuver” - requiring the rover to transform from was used for the Thermal-Structural Analysis of the PICA Tiles. 7 model runs in between its stowed flight configuration to landing configuration while being lowered to Mars wheels 17 to 93 minutes on a down from the descent stage with suspension cables. JPL Engineers used Adams to predict the Hewlett Packard Unix heatshield separation 10 dynamics of the separation and lowering sequences. For instance, as the bridles unreeled and HYPERSONIC AERO-MANEUVERING workstation with four 10 the rover’s six motorized wheels snapped into position to prepare for landing, Adams simulations showed this “snapping” effect generated even greater loads on some of the rover components central processor units The 7,000 pound spacecraft, traveling at Mach 5, caused the molecules in the atmosphere to than the touchdown. The simulation results showed that, at the end of wheel deployment, severe (CPUs). break apart, creating a layer of hot plasma. Shockwaves caused air density and pressure to waver sky crane maneuver hammer-like blows where generated on the rover suspension and frame. JPL engineers addressed dramatically. Onboard guidance algorithms controlled the direction of lift vector, via bank angle this problem by changing the timing of the wheels and struts deployment. Changing the timing of modulation, to keep the vehicle on the desired trajectory. Specifically, the entry flight path angle DESIGN INSIGHT the wheels and struts deployment also reduced the swing rate and swing angle before touchdown. had to be maintained within a strict margin of only 0.27 deg as the spacecraft slowed to under ADAMS 9 5 Mach 3. 12 Adams was used to predict JPL Engineers dealt with This extreme level of flight accuracy was accomplished with the help of Adams. The flight the loads on components complexities involving Martian TOUCHDOWN control software, written in C++, required a detailed mechanical model to accurately predict the separation & powered descent flyaway gravity, atmosphere, surface system performance. The engineers overcame this issue by compiling the controller with the and sub-assemblies and As Curiosity was gently lowered, it eventually made contact with the Martian surface. Prior to the Adams solver. This made it possible to validate the system performance and tune the controller these loads in turn were slope, and landing velocities SKY CRANE MANEUVER Adams simulation, JPL engineers believed that the projected 1 meter per second maximum speed parameters with a detailed mechanical model. JPL engineers validated and updated the Adams used as input to structural that could not be duplicated 11 during touchdown would not induce particularly high loads on the rover. However, simulations model by correlating the simulation results to the test data. analysis that optimized exactly here on Earth, and showed the loads were much higher than expected. The original expectations also were that the the design to provide the relied on the simulations to rover would be in a quiescent state when it touched down on the Martian surface but theAdams strength to withstand gain the they needed to simulation showed that the rover was actually rotating and swinging as it landed. As a result, the mission loads while feel confident in the execution rover structure was stiffened to mitigate these issues. PARACHUTE DEPLOY minimizing size and weight. of the mission. The series 11 7 miles (11 kilometers) above the Martian surface and traveling at Mach 2, the parachute was The philosophy of the of Adams simulations took modeling was not to try place in parallel with design deployed. This was the largest parachute ever built for a planetary mission to land on the Red One Body Two Body touchdown FLYAWAY Planet. The 64.7 foot (19.7 meter) disk-gap-band style chute was deployed by a mortar. The and predict every event to – but it was insight from the Phase Phase 6 (Vertical Descent) (DRL /Bridle main disk was a dome-shaped canopy with a hole in the top to relieve the air pressure. A gap 100% accuracy but rather simulations that helped guide Deployment) Once the descent stage detected touchdown, pyrotechnic charges cut the bridle and “umbilical below the main canopy allowed air to vent out to prevent the canopy from rupturing. During its to determine the bounding the design to maturity, and to 12 cord.” With this final directive and release, the descent stage no longer had access to the rover’s use, it generated up to 65,000 pounds (almost 29,500 kilograms) of drag force and slowed the limit design loads that prevent any failures resulting Two Body Phase Two Body Phase Fly-Away Phase computer “brains.” Having completed its mission and now “unconscious,” the descent stage flew spacecraft down to 250mph. could be expected on from potentially harsh loading (Constant Velocity) (Touchdown Event) out of the way, coming to rest on Mars several hundred yards from the Curiosity. every component. conditions during the mission.