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Terminal Descent Radars (TDR), or landing radars, have been an integral element of Guidance, Navigation and Control (GN&C) sensor suites of robotic exploration missions to the Moon and Mars. As plans for new, exciting exploration missions to the Moon, Mars and other planetary bodies are being developed, there is a need for a new generation of TDRs that are smaller, consume less power and are less expensive than previous sensors. The challenge of designing such a landing sensor is twofold: the first is to have well-vetted software tools that allow us to explore the design space for a particular mission scenario and analyze performance of relevant radar architectures. The second challenge is to reduce mass and power requirements of a landing radar without compromising reliability and performance. New design approaches that address these challenges need to be tested and demonstrated in realistic Entry-Descent-Landing (EDL)/Deorbit-Descent-Landing (DDL) scenarios. In this paper, we describe a TDR testbed developed at the Jet Propulsion Laboratory. The testbed is a closed-loop design, analysis and verification capability used to design and evaluate the next generation of landing radars for a variety of EDL/DDL scenarios.

The ProtoEXIST program was conceived for the development of a highly scalable detector plane architecture utilizing pixilated CdZnTe (CZT) detectors for eventual deployment in a large scale (1–4 m2 active area) coded aperture X-ray telescope. Development is now underway for ProtoEXIST2, which ultimately will be comprised of a closely tiled 8×8 array of 19.9 mm × 19.9 mm, 5 mm thick Redlen CZT crystals, analogous to ProtoEXIST1, but will now utilize the NuASIC which accommodates the direct bonding of CZT detectors with a 32×32 pixilated anode with a 604.8 µm pixel pitch and a guard ring surrounding the perimeter of the anode pattern. Currently 6 prototype detectors have been fabricated and tested. An energy threshold of approximately 6 keV and energy resolutions of 2.5 keV FWHM at 122.0 keV and 2.1 keV at 59.6 keV have been achieved with individual detectors. The performance and energy resolution of the individual prototype detectors is discussed in detail. In addition, during preliminary testing of the prototype ProtoEXIST2 detectors reduced photopeak efficiency and pixel distortions were observed for pixels within approximately 3 mm of the CZT edge. These distortions have been largely corrected with two independent techniques: the application of an 73 mm × 73 mm extended cathode centered directly above the detector and the use of a grounded, 6mm tall, electrostatic side shield surrounding the perimeter of the detector. The effects of the side shield and extended cathode are covered in detail.