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Optical communications is a rapidly developing technology applicable to future NASA and commercial space missions that desire a communications terminal that provides a higher data rate with lower mass and power.
Free-Space Optical Communications requires precise, stable laser pointing to maintain operating conditions. This paper also describes the software and hardware implementation of Fine Pointing Control based on the Optical Communications Demonstrator architecture.
Over the past decade, the Jet Propulsion Laboratory's Telecommunications and Mission Operations Directorate has invested in a variety of technologies, targeted at both the flight and ground sides of the communications link, with the goal of developing a Ka-band (32 GHz) communications capability for future deep space missions.
Recent work in deep space telecommunication systems has been performed in support of NASA's Mission to the Solar System planning activity. The results show that high bandwidth communications (higher thatn 1 Mbps) are feasible with communication infrastructure investments at targets of high exploration activity. These targets include Mars, Jupiter, and Neptune. Infrastructure improvements must also be made at Earth.
An interface is described that supplies communications between the flight instruments and the analog input of an existing conventional recording unit for the Shuttle Space Acceleration Measurement System (SAMS), a data acquisition unit. The architecture and current implementation of an STD bus/LonTalk communication interface are described.
This paper presents various communication system architectures for Multiple-Link communications with Single Aperture (MULSA) ground station. The proposed architectures are capable of supporting a multiplicity of spacecraft that are within the beamwidth of a single ground station antenna simultaneously. Both short and long term proposals to address this scenario will be discussed. In addition, the paper also discusses the top-level system designs of the proposed architectures and attempts to identify the associated advantages and disadvantages for each system.
This paper presents an overview of the preliminary design of both the flight and ground systems of the Optical Communication Demonstration and High-Rate Link Facility which will demonstrate optical communication from the International Space Station to ground after its deployment in October 2002.
With the impetus towards high data rate communications in inter-satellite and space-to-ground links, the small size, low-mass, and low-power consumption of optical communications is seen as a viable alternative to radio frequency links.
The successful completion of the Galileo Optical Experiment (GOPEX), represented the accomplishment of a significant milestone in JPL's optical communication plan. The experiment demonstrated the first transmission of a narrow laser beam to a deep-space vehicle. Laser pulses were beamed to the Galileo spacecraft by Earth-based transmitters at the Table Mountain Facility (TMF), California, and Starfire Optical Range (SOR), New Mexico. The experiment took place over an eight-day period (December 9 through December 16, 1992) as Galileo receded from Earth on its way to Jupiter, and covered ranges from 1 to 6 million kilometers (15 times the Earth-Moon distance), the laser uplink from TMF covered the longest known range for laser beam transmission and detection. This demonstration is the latest in a series of accomplishments by JPL in the development of deep-space optical communications technology.
Communication over long free space distances is extremely difficult due to the inverse squared propagation losses associated with link distance. That makes communications particularly difficult from outer planet destinations.
This paper describes JPL research in adaptive optics (AO) to reduce the daytime background noise on a Mars-to-Earth optical communications link. AO can reduce atmosphere-induced wavefront aberrations, and enable single mode receiver operation thereby buying back margin in the deep space optical communications link.
An overview of narrow band vs wide band signals is given. Topics discussed included signal transmission, reference distribution and photonic antenna metrology. Examples of VLA, ALMA, ATA and DSN arrays are given. . Arrays of small antennas have become more cost-effective than large antennas for achieving large total aperture or gain, both for astronomy and for communication. It is concluded that emerging applications involving arrays of many antennas require low-cost optical communication of both wide bandwidth and narrow bandwidth; development of round-trip correction schemes enables timing precision; and free-space laser beams with microwave modulation allow structural metrology with approx 100 micrometer precision over distances of 200 meters.
The feasibility of using long wavelength Earth thermal (infrared) images for telescope tracking/pointing application. for both Deep Space Free- pace Optical Communications has been investigated and is reported her. The advantage of this technology rests on using full Earth images in this band, which yield more accurate estimates of geometric centroids than that of Earth images in the visible band. Another major advantage is that these images are nearly independent of Earth phase angle. The results of the study show that at a Mars range, with currently available sensors, a noise equivalent angle of 10 to 150 nanoradians and a bias error of better than 80 nanoradians can be obtained. This enables precise pointing of the optical communications beam for high data rate links.
Optical communications is a key technology to meet the bandwidth expansion required in the global information grid. High bandwidth bi-directional links between sub-orbital platforms and ground and space terminals can provide a seamless interconnectivity for rapid return of critical data to analysts. The JPL Optical Communications Telescope Laboratory (OCTL) is located in Wrightwood California at an altitude of 2.2.km. This 200 sq-m facility houses a state-of- the-art 1-m telescope and is used to develop operational strategies for ground-to-space laser beam propagation that include safe beam transmission through navigable air space, adaptive optics correction and multi-beam scintillation mitigation, and line of sight optical attenuation monitoring. JPL has received authorization from international satellite owners to transmit laser beams to more than twenty retro-reflecting satellites. This paper presents recent progress in the development of these operational strategies tested by narrow laser beam transmissions from the OCTL to retro-reflecting satellites. We present experimental results and compare our measurements with predicted performance for a variety of atmospheric conditions.
This paper investigates the closed-loop dynamics of systems controlled via parallel estimators. This structure arises in formation flying problems when each spacecraft bases its control action on an internal estimate of the complete formation state. For LTI systems a separation principle shows that the necessary and sufficient conditions for overall system stability are more stringent than the single controller case; the controllers' open-loop dynamics necessarily appear in the closed-loop dynamics. Communication amongst the spacecraft can be used to specify the complete system dynamics and a framework for integrating the design of the communication links into the formation flying control design problem is presented.
The Mars Science Laboratory (MSL) is expected to be a long-range, long-duration science laboratory rover on the Martian surface. MSL will provide a significant milestone that paves the way for future landed missions to Mars. NASA is studying options to launch MSL as early as 2009. There are three elements to the spacecraft; carrier (cruise stage), entry vehicle, and rover. The rover will have a UHF proximity link as the primary path for EDL communications and may have an X-band direct-to-Earth link as a back-up. Given the importance of collecting critical event telemetry data during atmospheric entry, it is important to understand the ability of a signal link to be maintained, especially during the period near peak convective heating. The received telemetry during entry (or played back later) will allow for the performance of the Entry-Descent-Landing technologies to be assessed. These technologies include guided entry for precision landing, a new sky-crane landing system and powered descent. MSL will undergo an entry profile that may result in a potential communications blackout caused by ionized particles for short periods near peak heating. The vehicle will use UHF and possibly X-band during the entry phase. The purpose of this rep0rt is to quantify or bound the likelihood of any such blackout at UHF frequencies (401 MHz) and X-band frequencies (8.4 GHz). Two entry trajectory scenarios were evaluated: a stressful entry trajectory to quantify an upper-bound for any possible blackout period, and a nominal trajectory to quantify likelihood of blackout for such cases.
I. Objective: Deliver video from ISS to optical ground terminal via an optical communications link. a) JPL Phaeton/Early Career Hire (ECH) training project. b) Implemented as Class-D payload. c) Downlink at approx.30Mb/s. II. Flight System a) Optical Head Beacon Acquisition Camera. Downlink Transmitter. 2-axis Gimbal. b) Sealed Container Laser Avionics Power distribution Digital I/O board III. Implementation: a) Ground Station - Optical Communications Telescope Laboratory at Table Mountain Facility b) Flight System mounted to ISS FRAM as standard I/F. Attached externally on Express Logistics Carrier.
The National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) is investigating current and anticipated wireless communications concepts and technologies that the National Airspace System (NAS) may need in the next 50 years. NASA has awarded three NASA Research Announcements (NAR) studies with the objective to determine the most promising candidate technologies for air-to-air and air-to-ground data exchange and analyze their suitability in a post-NextGen NAS environment. This paper will present progress made in the studies and describe the communications challenges and opportunities that have been identified during the studies' first year.