Weather Forecasts Support Rocket Launches Testing Parachutes for Mars Missions
On a hazy morning at NASA’s Wallops Flight Facility a thin, multi-stage rocket leaps off its launcher. The rocket climbs to an altitude of nearly 50 kilometers (km) and begins pitching back down towards the Atlantic Ocean. As the rocket passes 40 km and is traveling over 1.7 times the speed of sound, a massive parachute is shot out the back of the rocket and begins unfurling. The parachute goes from a cylindrical pack with the density of wood to an inflated shape over 15 meters wide in 0.41 seconds. The parachute carries and slows the descent of a heavy science payload that splashes down gently onto the ocean surface 45 km from the Virginia coastline, where a recovery team is waiting to retrieve the payload and the recorded data onboard.
This September 7 launch was the third flight for the Advanced Supersonic Parachute Inflation Research Experiment (ASPIRE) project aimed at testing parachute designs for future Mars rover missions. Instrumental to planning all three test flights were Global Modeling and Assimilation Office (GMAO) weather forecasts run at the NASA Center for Climate Simulation (NCCS).
From the Viking lander in 1976 to the Mars Science Laboratory’s Curiosity rover in 2012, parachutes have played a role in every successful mission to the Martian surface.
“The Martian atmosphere is so thin that we really don’t have very much time to slow down at all,” explains ASPIRE team member Clara O’Farrell, guidance and control engineer at NASA's Jet Propulsion Laboratory. “When a Curiosity-type vehicle hits the Martian atmosphere it’s traveling at approximately 6 kilometers per second. We rely on our heatshield to help us slow down to below twice the speed of sound, but the supersonic parachute takes us from that speed to where we can start the final powered descent and soft touchdown.”
ASPIRE is testing two candidate supersonic parachute designs for NASA’s Mars 2020 rover and potentially other future missions at conditions simulating Entry, Descent, and Landing (EDL) at Mars. O’Farrell stresses that deploying the parachutes high enough in Earth’s atmosphere is necessary to achieve the right speeds and aerodynamic loads.
The ASPIRE SR01 flight on October 4, 2017 tested a 21.5-meter-wide parachute identical to the one used for EDL of the Curiosity rover. ASPIRE SR02 (March 31, 2018) and ASPIRE SR03 tested a new parachute design with the same geometry but using stronger materials. Each subsequent flight also increased the test conditions and stresses that the parachute encountered.
As with any launch mission, ASPIRE must have reliable weather forecasts. ASPIRE flight planners use data from the GMAO’s Goddard Earth Observing System Forward-Processing (GEOS FP) forecasting system for targeting, range safety, and reconstruction. “Having more confidence in our ability to target the right conditions means we can get more science return with fewer sounding rocket flights,” O’Farrell says.
GEOS FP runs four times per day on the NCCS Discover supercomputer to provide global weather forecasts at 12.5-km resolution. The forecasts range from 1 to 10 days long and use up to 8,400 processor cores on Discover. GMAO and NCCS staff coordinate Discover maintenance downtimes specifically to not interfere with ASPIRE launches.
The NCCS DataPortal hosts GEOS FP forecast data for ASPIRE, other field campaigns, and satellite missions. “In addition to the standard forecast file specification, we created another product exclusively for the ASPIRE campaign,” says Robert Lucchesi, GMAO scientific programmer. “For each forecast timestep, a profile from the top of the atmosphere to the surface at the launch site was extracted from one of the standard 3D gridded forecast products and placed where ASPIRE could see the data.”
Minutes before launch of the Terrier-Black Brant IX sounding rocket, the ASPIRE team loads a model of the atmospheric density and winds at Wallops Island derived from the GEOS FP profile onto their flight computer. “We use that information to compute the dynamic pressure during flight and trigger the mortar that deploys the parachute at the right time,” O’Farrell says.
The science payload includes a suite of high-speed cameras and other instruments for studying the parachute and reconstructing the flight trajectory. Noting that NASA has not run tests like these since the 1970s, O’Farrell says that “the quality and quantity of data that we’re gathering is amazing and allows us to see things we’ve never seen before.”
With three successful launches behind them, the small but dedicated ASPIRE team has “had the privilege of working with excellent people, and the GMAO-NCCS team is no exception,” O’Farrell says. “They’ve enabled us to target conditions with a confidence we didn’t think possible, and they’ve been really helpful in making everything run smoothly.”
Jarrett Cohen, NASA Goddard Space Flight Center
Mars 2020 Parachute a Go
C. O’Farrell, S. Muppidi, J.M. Brock, J.W. Van Norman, and I.G. Clark: Development of Models for Disk-Gap-Band Parachutes Deployed Supersonically in the Wake of a Slender Body. 2017 IEEE Aerospace Conference, Big Sky, MT, 2017, pp. 1–16, doi:10.1109/AERO.2017.7943786.