Space Link Extension Return Channel Frames (SLE-RCF) Software Library

NASA's SDR uses Field-Programmable Gate Array (FPGA) technology to enable flexible performance on orbit. A first-generation FM-modulated transceiver is capable of operating at up to 1 Mbps downlink and 50 kbps uplink, full duplex. An FPGA performs Reed-Solomon (255,223) encoding, decoding, and bit synchronization, providing Consultative Committee for Space Data Systems (CCSDS) and Near Earth Network (NEN) telemetry protocol compatibility. The transceiver accepts data from the onboard flight computer via a source synchronous RS422 interface. NASA's second-generation full duplex SDR, known as PULSAR (programmable ultra-lightweight system-adaptable radio, Figures 1 and 2 below) incorporates command receiver and telemetry transmitters, as well as updated processing and power capabilities. An S-band command receiver offers a max uplink data rate of 300 Kbps and built-in QPSK demodulation. X- and S-Band telemetry transmitters offer a max downlink data rate of 150 Mbps and flexible forward-error correction (FEC) using Reed-Solomon encoding (LDPC rate 7/8 and 1/2 convolution in development), and it uses QPSK modulation. The use of FEC adds an order of magnitude increase in telemetry throughput due to an improved coding gain. An onboard FPGA uses high-speed logic for uplink/downlink and encoding/decoding processes. Balloon flight testing has been conducted and is ongoing for PULSAR.

NASA Goddard Space Flight Center has developed a low cost, modular, and flexible space flight laser range finder consisting of optics, electronics, and interfaces for satellite servicing missions (i.e. Restore-L) using customized optics. Built upon previous NASA technologies, the system also consists of a high dynamic range receiver and adjustable laser for a wide range of measurements (i.e. multiples of km to sub-meter).

The circularly polarized antenna features an integrated prime-fed S-band and Cassegrain-based Ka-band reflector system. The Cassegrain primary and secondary reflectors are specially shaped for optimal Ka-band gain, while a frequency selective surface on the secondary reflector provides reflectivity at Ka-band, and acts as a transparent dielectric radome for the S-band feed antenna. Design innovations include an improved S-band feed antenna and cross-polarization compensation, improved Ka-band horn, and special shaping of the secondary reflector for ease of fabrication. The technology improves upon prior S-band feed antenna designs to provide mechanical robustness and low cross-polarization over a wide field of view. It also improves the front-to-back ratio, providing much higher signal radiated forward, over an increased bandwidth as well. The Ka-band feed horn is based on a prior NASA innovation, the standard Potter horn, but in this innovation has significantly lower sidelobe level performance. This is achieved by using a modified smooth s-curved interior horn profile rather the the typical conical/cylindrical form typical of the standard Potter horn design. The smooth interior wall is also easier to fabricate than alternative corrugated wall designs. Additionally, a cross-polarization cancellation cup is integrated with the Ka-band horn geometry, with the cup being placed around the neck of the horn in the form of a collar, allowing the two to be fabricated together.

This invention provides a new method for optical data transmissions from satellites using laser arrays for laser beam pointing. The system is simple, static, compact, and provides accurate pointing, acquisition, and tracking (PAT). It combines a lens system and a vertical-cavity surface-emitting laser VCSEL)/Photodetector Array, both mature technologies, in a novel way for PAT. It can improve the PAT system's size, weight, and power (SWaP) in comparison to current systems. Preliminary analysis indicates that this system is applicable to transmissions between satellites in low-Earth orbit (LEO) and ground terminals. Computer simulations using this design have been made for the application of this innovation to a CubeSat in LEO. The computer simulations included modeling the laser source and diffraction effects due to wave optics. The pointing used a diffraction limited lens system and a VCSEL array. These capabilities make it possible to model laser beam propagation over long space communication distances. Laser beam pointing is very challenging for LEO, including science missions. Current architectures use dynamical systems, (i.e., moving parts, e.g., fast-steering mirrors (FSM), and/or gimbals) to turn the laser to point to the ground terminal, and some use vibration isolation platforms as well. This static system has the potential to replace the current dynamic systems and vibration isolation platforms, dependent on studies for the particular application. For these electro-optical systems, reaction times to pointing changes and vibrations are on the nanosecond time scale, much faster than those for mechanical systems. For LEO terminals, slew rates are not a concern with this new system.

NASA’s reverse-ephemeris lunar navigation system is a concept for determining position on the lunar surface based on known orbits of satellites. In conventional GPS navigation systems, the GPS satellite transmits ephemeris data to a receiver on earth for determining position at the receiver location. Whereas for the reverse-ephemeris approach the receiver becomes the transmitter, and the satellite instead serves more as a fixed reference position with a known ephemeris. This simplifies the satellite requirements and also mitigates potential navigational disruptions that can otherwise arise in navigation systems that utilize satellite-based communications, for example from interference, jamming, etc. The design consists of lunar surface S-Band (2,400 – 2,450 MHz) 10 W transceivers ranging with analog translating transponders on a three-satellite constellation in frozen elliptical orbits to provide continuous coverage with service to 300 simultaneous users over 1.8 MHz of bandwidth at the transponder. Digital bases systems are possible too. As compared to GPS-based navigation requiring four or more satellites costing 100’s of millions of dollars, the new NASA concept is based on using only three smallsats.