RF Subsystem

The RF subsystem enables the SDRs to transmit/receive RF signals from the SN and NEN and receive GPS signals through one of five antennas (3 fixed, 2 movable). The RF Subsystem is comprised of:

  • Traveling Wave Tube Amplifier (TWTA)

  • Three coaxial transfer switches

  • Antennas

  • Diplexers

  • RF isolator

  • RF attenuator

  • Transmission lines to interconnect the RF subsystem components with the SDRs.

The RF subsystem radiates RF signals intended for the TDRS and the ground and receives RF signals from the TDRS, the ground, and the GPS system. The architecture of the SCAN Testbed enables the ability to send RF signals from two separate SDRs to two antennas simultaneously. The RF subsystem interfaces with the avionics subsystem, the flight enclosure, the antenna pointing subsystem, and the three SDRs.

Antenna Pointing System (APS)

The APS allows the Ka-Band High Gain Antenna (HGA) and S-Band Medium Gain Antenna (MGA) to be moved to track TDRSS (or other experimenter-selected targets). The antenna pointing may be done in either open loop or closed loop mode. In the former, the antennas are pointed according to a precomputed track profile. In closed loop mode, the tracking algorithm uses signal strength information from the Ka-band radio to point the Ka-band HGA more accurately to the Ka-band source. The ISS is sufficiently large and flexible that open loop pointing of the Ka-band antenna may have pointing errors, reducing the maximum data rate that can be carried. The gimbaled antennas are locked for launch and deployed on-orbit.

Avionics Subsystem

The Avionics Subsystem provides general control and data handling, as well as supporting network routing. Just like the radios, the software loaded in the Avionics Subsystem will be changed for experiments. The radios are mounted to the Flight Enclosure and functionally interface with the Avionics and RF Subsystems.

Technology Benefits to Society

The ability to track signals from multiple GNSS receivers enables NASA to improve both space operations and science missions that benefit society as a whole, ranging from better observation of Earth for more precise weather forecasting, sea-level height measurements, and climate change monitoring. It also assists in improving understanding of Earth’s crustal movements and allows advanced tsunami warnings.

Some of the technologies developed as part of the SCaN program include a Ground-Based Inflatable Antenna from GATR Technologies that was originally developed as a solar concentrator for power generation as a technical requirement for SCaN. This technology was licensed exclusively and transferred to GATR Technologies to develop the inflatable antenna that was used to support communication efforts in the Haitian earthquake, Hurricane Katrina, and Hurricane Ike.

XCOM Wireless designed lightweight RF microelectromechanical systems (MEMS) that are used to improve satellite communication systems. The RF MEMS have the potential to outperform semiconductor technologies at increased speeds and less power.

General Dynamics Decision Systems’ Multi-Mode Transceiver brings the advantages of SCaN’s Tracking and Data Relay Satellite System to a variety of applications, including university satellite programs, small commercial Earth imaging programs, and Arctic and Antarctic science programs.

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