NGSLR at NASA's GGAO
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The NGSLR is being built to demonstrate that a system using existing COTS technology can satisfy the performance requirements as an autonomous and eye-safe photon-counting Satellite Laser Ranging (SLR) station with normal point precision at the mm level. The system is intended to provide continuous 24 hour tracking coverage of artificial satellites up to GNSS altitudes. NGSLR has already demonstrated much of its new technology and performance capability. Some developmental work remains to be completed to fully demonstrate the technologies can be integrated into a realizable system that meets the required performance criteria. Based on this experience, specifications then need to be written for a production system that can be built by industry.
The NGSLR system is now operating at the optical site at GSFC near MOBLAS-7, one of the early NASA systems still in operation after nearly 30 years. Over the past year, NGSLR has taken over 250 passes of data, over the full range of capability for engineering, diagnostic, and operational testing, during both nighttime and daylight conditions. A few remaining issues need to be resolved, including:
- Automated closure of the tracking loop. With routine star calibrations, NGSLR can track open loop with normal quality predictions Closed-loop tracking, however, is required for cases where the predictions are not good, such as recently launched satellites and satellites at very low altitude with high drag conditions, and to eliminate the need for weekly star calibrations.
- Complete automation of the optical bench. Successful coordination by the software of all the optics, filters, shutters, camera and laser is required for demonstration of automated SLR operations.
- Complete onsite calibration and satellite processors. To be fully automated the system must be able to process calibration data and generate Normal Points in near real-time. Since NGSLR is a single photon system, this processing is somewhat different than for the tradition SLR system.
- Performance testing of the new higher power laser. Completion of this laser has been more challenging and time consuming than anticipated. When it is field-ready, it will be installed and tested on a non-interference basis with the rest of the system. In the meantime, work will proceed with the standard Q-peak laser which can do all of the tasks except perhaps daylight ranging to the GNSS satellites. NGSLR performance with the higher power laser can be extrapolated from the performance of this laser in the lab combined with the system’s performance with the Q-Peak laser. Before the end of the two-year proposal period, this laser will be installed into NGSLR and performance testing will be done with it.
The following will be done to complete the NGSLR prototype and make it part of the prototype next generation space geodetic station at GGAO:
- Stabilize the ranging performance to a level that compares with MOBLAS-7,
- Complete the transceiver bench automation,
- Automate the ground calibration process,
- Complete the automated closed-loop tracking,
- Complete the calibration and satellite post-pass analysis and processing,
- Perform long-term controlled testing of the new higher power laser,
- Conduct and pass a co-location with MOBLAS-7,
- Document the system and the software.