Achieving Safety and Efficiency are Goals of Airborne Radar Recording SystemPhil Brunelle, Conduant Corp., Jerome Vila, CNES
Since 1999, Arianespace Ariane 5, the European Space Agency-developed heavy space launcher, has made successful launches into geostationary, medium and low-Earth and sun-synchronous orbits for commercial and scientific flights. Today, the Ariane 5 continues to launch satellites for communications, Earth observation and scientific research.
The Ariane 5 is designed with two solid boosters, a Main Cryogenic Stage, called EPC, and a storable propellant upper stage. The EPC is left on a controlled reentering orbit after its burnout to avoid any risks of uncontrolled, reentry over inhabited areas.
In order to improve the reentry model and to more accurately characterize the physical phenomena that occur during reentry, CNES (French aerospace agency) on behalf of ESA, decided to conduct observation missions of the EPC reentry.
System Planning Corporation (SPC) of Arlington, Virginia undertook the challenge of observing and measuring the reentry from orbit of the EPC of the Ariane 5. Its Multifrequency Airborne Radar System (MARS) was developed to observe and record debris dispersion over water, allowing CNES to optimize launch trajectories and improve overall safety. The system includes a wide field-of-view narrow-band VHF radar coupled with data acquisition and other subsystems. The data collected by the system allows CNES to further reduce the risks and unpredictability associated with reentering space debris.
SPC launched a search for an enabling technology that allowed for ultra-fast data recording in continuous mode. They needed a data recorder computer that could record on a pulse-to-pulse basis and withstand the rigors of repeated flights over a multi-year project without jeopardizing the data. A real-time computer (RTC) samples incoming video signals while two redundant data recorder computers (DRC) permanently record data. The DRC computers are run in a continuous loop mode, rewriting old data every 52 or 94 minutes, depending on the sample rate. The system includes a National Instruments 4-channel PCI-6110E simultaneous analog to digital card, an IRIG time card for common time stamping and a Conduant recorder card with an array of three target disks. After establishing the parameters, SPC wrote custom-designed software in NI’s LabView.
SPC explored the possibility of using traditional general-purpose analog to digital recorders that passed data through the CPU where the host computer stored the data to disk. They determined that performance characteristics of this configuration were inadequate for recording huge volumes of data and maintaining data integrity.
Searching for a higher performance solution, SPC discovered Conduant Corporation’s StreamStor technology that records direct to disk. SPC learned that it could bypass the operating system, CPU and system memory and was the only solution that could sample data continuously. Situated in a rack mount chassis, it was built to withstand extreme shock and vibration. StreamStor became an integral part of the DRC data acquisition system.
SPC configured a signal generator, transceiver, four 50 kW transmitters, the StreamStor-based data acquisition system and real-time monitoring subsystems to observe fuel tank reentry. The system was initially installed on a Boeing KC-135 tanker, which provided a mobile platform to record and measure the breakup of the reentering fuel tank over the South Pacific. On December 10, 1999, the Ariane 5 504 flight lofted XMM scientific satellite into orbit. Flying from Tahiti, SPC recorded data on the reentry of the EPC. Post-flight analysis of the data allowed CNES to verify and fine-tune re-entry models to narrow the margins and create more efficient trajectories.
“The long VHF wavelength limited us to conformal patch antennas which were custom-designed to fit the curvature of the aircraft cargo door,” said Gary Rubin, Physicist, on the SPC Ariane 5 project. “We were observing at 50 MHz with 2 to 2-1/2 degree per second turns, at a 35 degree bank angle pulling a minimum of 1-1.5 Gs. Regardless of the environmental factors, StreamStor proved to be an extremely valuable device for recording radar signals on debris moving by at 5-7 KM/second. We tracked the volume and size of the debris pieces and their dispersion. We didn’t miss a second of data.”
In 2002 and 2003, SPC transitioned the system to an Airbus A300 operated for the European Space Agency by Novespace of Bordeaux, France. On March 2, 2004, SPC performed another highly successful mission, recording data on the EPC reentry after the launch of the Rosetta space probe by Ariane 5.
The most unique capability of the MARS system is multipath data acquisition. Data collected by StreamStor allowed SPC to resolve multipath returns whereby the path difference from the radar to the EPC and the radar energy bounced off the ocean determined the altitude of the EPC as a function of time. Optimization of future trajectories may be made after land-based analysis of the data.
Conduant continues to contribute to highly successful radar-based data collection missions with additional flights planned for 2005. Today, extensions to Conduant’s real-time digital data capture technology record and playback up to 400 MB/second, the highest performance available today. “Since 1999, StreamStor has been uniquely qualified to perform in environmentally stressful situations with continuous recording and zero data loss,” concluded Gary Rubin. “It has supported multiple generations of our SPC radar technology and offered us a migration path for tomorrow’s demanding requirements.”