NASA’s Laser Communication Relay Demonstration (LCRD) will be NASA’s first long-duration demonstration of laser communications (lasercom) in space, providing geosynchronous-satellite-hosted bidirectional relay services between two Earth ground stations. LCRD will leverage and enhance existing ground stations. Ground Station 1 (GS-1) will leverage the Optical Communications Telescope Laboratory (OCTL) built by JPL, while Ground Station 2 (GS-2) will leverage the Lunar Laser Communications Demonstration (LLCD) Ground Terminal (LLGT) built by MIT Lincoln Laboratory. While each ground system has unique telescopes and integrated optics, many of the backend subsystems (e.g., communications, environmental monitoring, control, user simulators) will be common to both terminals. Here we provide an overview of the architecture of the LCRD ground stations, and the planned enhancements to the existing facilities.
We have developed and tested an optical ranging system using a Pseudo-Random Bit Stream (PRBS) modulation
technique. The optical transceiver consisted of an infrared laser transmitter co-aligned with a receiver telescope. The
infrared laser beam was propagated to a retro-reflector and then received by a detector coupled to the telescope. The
transceiver itself was mounted on a gimbal that could actively track moving targets through a camera that was bore
sighted with the optical detector. The detected optical signal was processed in real time to produce a range measurement
with sub mm accuracy. This system was tested in the field using both stationary and moving targets up to 5 km away.
Ranging measurements to an aircraft were compared with results obtained by differential GPS (Global Positioning
JPL in collaboration with JAXA and NICT demonstrated a 50Mb/s downlink and 2Mb/s uplink bi-directional link with the LEO OICETS satellite. The experiments were conducted in May and June over a variety of atmospheric conditions. Bit error rates of 10-1 to less than 10-6 were measured on the downlink. This paper describes the preparations, precursor experiments, and operations for the link. It also presents the analyzed downlink data results.
The OCTL to OICETS Optical Link Experiment (OTOOLE) project demonstrated bi-directional optical
communications between the JAXA Optical Inter-orbit Communications Engineering Test Satellite
(OICETS) spacecraft and the NASA Optical Communications Telescope Laboratory (OCTL) ground
station. This paper provides a detailed description of the experiment design for the uplink optical channel,
in which 4 beacon lasers and 3 modulated communication lasers were combined and projected through the
F/76 OCTL main telescope. The paper also describes the reimaging optical design employed on the
acquisition telescope for receiving the OICETS-transmitted signal and the design of the receiver channel.
Performance tests and alignment techniques of both systems are described.
JPL has developed a series of software and hardware tools to analyze and record data from a 50Mb/s down and 2 Mb/s
up bi-directional optical link with the LUCE terminal onboard the LEO OICETS satellite. This paper presents the data
products for this experiment including the system architecture and analysis of the actual data received.
A free-space optical communication channel suffers degraded performance due to blurring and scintillation of the received signal caused by atmospheric turbulence. Adaptive optics (AO) improves the communication performance of such a channel by concentrating the received power on the detector. The degree of improvement with AO correction depends on the modulation format, and on the modulation order when pulse position modulation is utilized. Gains of up to 6 dB with AO have been experimentally validated in a laboratory test bed under simulated atmospheric conditions involving turbulence and background light. The fade statistics of the turbulent atmospheric channel have also been analyzed with and without AO correction.
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
We describe the current performance of an adaptive optics testbed for free space optical communication. This adaptive optics system allows for simulation of night and day-time observing on a 1 meter telescope with a 97 actuator deformable mirror. In lab-generated seeing of 2.1 arcseconds (at 0.5μm) the system achieves a Strehl of 21% at 1.064μm (210nm RMS wavefront). Predictions of the system's performance based on real-time wavefront sensor telemetry data and analytical equations are shown to agree with the observed image performance. We present experimentally measured gains in communications performance of 2-4dB in the received signal power when AO correction is applied in the presence of high background and turbulence at an uncoded bit error rate of 0.1. The data source was a 100Mbps on-offkeyed signal detected with an IR-enhanced avalanche photodiode detector as the receiver.
Optical links from a spacecraft at planetary distance to a ground-based receiver presume a cloud free line of site (CFLOS). Future ground-based optical receiving networks, should they be implemented, will rely on site diversity of cloud cover to increase link availability. Recent analysis shows that at least 90% and as high as 96% CFLOS availability can be realized from a cluster comprised of 3-4 nodes. During CFLOS availability variations of atmospheric parameters such as attenuation, sky radiance and “seeing” will determine the link performance. However, it is the statistical distributions of these parameters at any given node that will ultimately determine the data volumes that can be realized. This involves a complex interaction of site-specific atmospheric parameters. In the present work a simplified approach toward addressing this problem is presented. The worst-case link conditions for a spacecraft orbiting Mars, namely, maximum range (2.38 AU) and minimum sun-Earth-probe (SEP) angle of 3-10° is considered. A lower bound of ~100 Gbits/day under the most stressing link conditions is estimated possible.
Communication links with multi-giga-bits per sec (Gbps) data-rates depicting both LEO-GEO and GEO-to-Ground optical communications were characterized in the laboratory. A 5.4 Gbps link, with a capability of 7.5 Gbps, was demonstrated in the laboratory. The breadboard utilized a 13 cm diameter telescope as the transmit aperture that simulates the LEO terminal. The receiver is a 30-cm telescope that simulates the GEO terminal. The objective of the laboratory breadboard development is to validate the link analysis and to demonstrate a multi-gigabit link utilizing off-the-shelf or minimally modified commercially available components (optics and opto-electronics) and subsystems. For a bit-error-rate of 1E-7, the measured required received signal is within 1 to 2 dB of that predicted by the link analysis.
JPL is constructing an Optical Communications Telescope Laboratory (OCTL) at its Table Mountain Facility complex in the San Bernadino Mountains of Southern California. The OCTL will house a 1-m class telescope and serve as an R&D ground station supporting future optical communications demonstrations with Earth-orbiting satellites and deep space probes. It will also support research in adaptive optics, optical receiver technologies, and help in developing spacecraft acquisition and tracking strategies from future optical ground stations. The OCTL building was completed in November 1999, and Brashear-LP of Pittsburgh, PA has been selected to build the telescope. First light is expected in July 2001.
The deployment of advanced hyperspectral imaging and other Earth sensing instruments on board Earth observing satellites is driving the demand for high-data-rate communications. Optical communications meet the required data rates with small, low-mass, and low-power communications packages. JPL, as NASA's lead center in optical communications, plans to construct a 1-m Optical Communications Telescope Laboratory (OCTL) at its Table Mountain Facility (TMF) complex in the San Gabriel Mountains of Southern California. The design of the building has been completed, and the construction contractor has been selected. Ground breaking is expected to start at the beginning of the 1999 TMF construction season. A request for proposal (RFP) has been issued for the procurement of the telescope system. Prior to letting the RFP we conducted a request for information with industry for the telescope system. Several vendors responded favorably and provided information on key elements of the proposed design. These inputs were considered in developing the final requirements in the RFP.
The STRV-2 lasercom terminal (LCT) was designed and developed by AstroTerra Corporation of San Diego, California, under funding from the Ballistic Missile Defense Organization (BMDO). Scheduled for launch in late 1998 it will be used to demonstrate, for the first time, high data rate bi-directional satellite-to-ground optical communications. Concurrently with the development of the STRV-2 lasercom NASA/JPL was assembling the lasercom test and evaluation station (LTES), a high quality test platform for pre-flight characterization of optical communications terminals. The respective development schedules allowed evaluation of the STRV-2 LCT using LTES, for a month, prior to integration of the LCT with the spacecraft palette. Final co-alignment of the transmitter lasers to within plus or minus 20 (mu) rads with respect to the receive axis was achieved. This in turn allowed the specified 76 (mu) rad transmit beam divergence to be realized. However, subjecting the LCT to expected on-orbit temperatures revealed that the co-alignment deteriorated causing beam spreading, a finding which prompted the recommendation to operate the lasers warmed up during ground encounters. The 'bent-pipe' operation bit-error rates (BER) at 155, 194 and 325 Mbps were less than or equal to 1E - 10 over an approximately 20 dB range of irradiance measured at the receive telescope aperture. At 500 Mbps BER's of 1E-6 were achieved over an approximately 6 dB irradiance range, suggesting greater vulnerability to atmosphere induced fades. A pointing offset between the acquisition receivers and transmitter lasers of 1 mrad was measured. The impact of this offset will be to limit acquisition camera framing rates to 87 and 251 Hz, thus limiting the tracking loop bandwidth. Tracking performance test of the lasercom terminal, though planned could not be carried out because the software was not ready at the time of testing with LTES. The test results obtained for STRV-2 lasercom terminal will be used for designing the ground receiver.
Pre-launch integrated system characterization of a lasercom terminal's (LCT's) communications and acquisition/tracking subsystems can provide a quantitative evaluation of the terminal and afford a better rigorous assessment of the benefits of any demonstration. The lasercom test and evaluation station developed at NASA/JPL is a high quality optical system that possesses the unique capabilities required to provide laboratory measurements of the key characteristics of lasercom terminals operating over the visible and near- infrared spectral region. Over the past year LTES has been used to provide pre-flight testing of the STRV-2 lasercom terminal developed by AstroTerra Corporation of San Diego, CA, and is currently being used for testing of the Optical Communication Demonstrator (OCD) developed by NASA/JPL. Discussions of performance validation tests carried out on LTES and its diverse capabilities are reported in this paper.
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. Recent NASA/JPL optical communications field demonstrations have shown some of the operational strategies needed for space-to-ground optical links. In preparation for the optical communications demonstrations planned for the turn of the century, NASA/JPL is building an Optical Communications Telescope Laboratory (OCTL) with a 1-m class telescope. The OCTL will be located at JPL's Table Mountain Facility complex in the San Bernadino mountains of Southern California and will be capable of supporting demonstrations with satellites from LEO to deep space ranges. In addition, it will support advanced optical communications research, astrometry and astronomy research.
Full-up pre-launch characterization of a lasercom terminal's communications and acquisition/tracking subsystems can provide quantitative characterization of the terminal and better realize the benefits of any demonstration. The lasercom test and evaluation station (LTES) being developed at NASA/JPL is a high quality optical system that will measure the key characteristics of lasercom terminals that operate over the visible and near-IR spectral region. The LTES's large receiving aperture will accommodate terminals up to 20 cm. in diameter. The unit has six optical channels and it measures far-field beam pattern, divergence, data rates up to 1.4 Gbps and bit-error rates as low as 10-9. It also measures the output power of the laser-terminal's beacon and communications channels. The 1 kHz frame rate camera in LTES's acquisition channel measures the point-ahead angle of the laser communications terminal to a resolution of 1 (mu) rad. When combined with the data channel detection, the acquisition channel measures acquisition and reacquisition times with a 1 ms resolution.
Analyses of uplink and downlink data from recent free-space optical communications experiments carried out between Table Mountain Facility and the Japanese ETS-VI satellite are presented. Fluctuations in signal power collected by the satellite's laser communication experiment due to atmospheric scintillation and its amelioration using multiple uplink beams are analyzed and compared to experimental data. Downlink data was analyzed to determine the cause of a larger than expected variation in signal strength. In spite of the difficulty in deconvolving atmospheric effects from pointing errors and spacecraft vibration, experimental data clearly indicate significant improvement in signal reception on the uplink with multiple beams, and the need for stable pointing to establish high data rate optical communications.
In this part-II of the advanced communications benefits study, tow critical metrics for comparing the benefits of utilizing X-band, Ka-band and Optical frequencies for supporting generic classes of Martian exploration missions have been evaluated. The first of these is the overall equivalent communications system mass on the spacecraft. The second comparison metric is the overall cost impact. This 'overall' cost assessment has considered the costs for both the spacecraft end of the link and the ground end. In both cases the metrics indicate that higher frequency communication bands have favorable mass and cost, particularly at higher data volumes transmitted daily to the earth. The same metrics are also applied to telecommunication for a hypothetical Neptune mission, extrapolating from the designs for the Mars case.
The ground-to-orbit Lasercom Demonstration conducted between the ETS-VI spacecraft and the ground station at JPL's Table Mountain Facility, Wrightwood CA was the first ground-to- space two-way optical communications experiment. The demonstration was conducted over a period of seven months and required simultaneous and cooperative operations by team members in Tokyo and California. A key objective was to measure the atmospheric attenuation and seeing during the demonstration to validate the performance of the optical link. The telemetry downlinked from the laser communications equipment provided information on the in-orbit performance of the onboard laser transmitter. Downlinked PN data enabled measurement of bit error rates. BERs as low as 10-4 were measured on the uplink and 10-5 on the downlink. Measured signal powers agreed with theoretical predictions.
The Ground/Orbiter Lasercomm Demonstration (GOLD) is an optical communications demonstration between the Japanese engineering test satellite (ETS-VI) and an optical ground transmitting and receiving station at the Table Mountain Facility in Wrightwood, California. Laser transmissions to the satellite are performed approximately four hours every third night when the satellite is at apogee above Table Mountain. The experiment required the coordination of resources at CRL, JPL, NASDA's Tsukuba tracking station and NASA's Deep Space Network at Goldstone, Calif. to generate and transmit real-time commands and receive telemetry from the ETS-VI. Transmissions to the ETS-VI began in November 1995 and are scheduled to last into the middle of January 1996 when the satellite is expected to be eclipsed by the Earth's shadow for a major part of its orbit. The eclipse is expected to last for about two months, and during this period there will be limited electrical power available on board the satellite. NASDA plans to restrict experiments with the ETS-VI satellite during this period, and no laser transmissions are planned. Post-eclipse experiments are currently being negotiated. GOLD is a joint NASA-CRL (Communications Research Laboratory) experiment that is being conducted by JPL in coordination with CRL and NASDA.
We have performed a study on telecommunication systems for a hypothetical mission to Mars. The objective of the study was to evaluate and compare the benefits that microwave (X-band and Ka-band) and optical communications technologies afford to future missions. The telecommunication systems were required to return data after launch and in-orbit at 2.7 AU with daily data volumes of 0.1, 1, or 10 Gbits. Space-borne terminals capable of delivering each of the three data rates were proposed and characterized in terms of mass, power consumption, size, and cost. The estimated parameters for X-band, Ka-band, and optical frequencies are compared and presented here. For data volumes of 0.1 and 1 Giga-bit per day, the X-band downlink system has a mass 1.5 times that of Ka-band, and 2.5 times that of optical system. Ka-band offered about 20% power saving at 10 Gbit/day over X-band. For all data volumes, the optical communication terminals were lower in mass than the rf terminals. For data volumes of 1 and 10 Gb/day, the space-borne optical terminal also had a lower required dc power. In all three cases, optical communications had a slightly higher development cost for the space terminal.
Optical communications offer high data rate satellite to ground communications in a small, low mass, and low power consumption package. However, turbulence-induced scintillation degrades the link performance as the zenith angle increases. To investigate the effect of atmospheric turbulence on the optical link at high zenith angles, we performed a 570 Mbps optical communications link across a 42 km horizontal path, and have measured the effects of aperture averaging on the irradiance variance. The variance clearly showed a dependence on the aperture size, decreasing with increasing aperture size. These results were used to calculate the log-amplitude variance and the atmospheric structure constant, Cn2, across the link. The bit error rates across the link were also measured. The results show that the link performance was dominated by burst errors with error rates that ranged from 10-6 to 10-2, increasing with decreasing aperture size.
Adaptive optics can mitigate the turbulence-induced wavefront distortions that limit the minimum practical beam divergence in a ground-to-space optical link, and enable high intensity laser beam propagation through the atmosphere. The CEMERLL experiment will use laser guide star adaptive optics to transmit a near-diffraction-limited laser beam from the Starfire Optical Range to the Apollo lunar retroreflectors. The experiment will validate theoretical models that predict the effect of atmospheric turbulence on uncompensated and compensated laser beam propagation, and explore strategies to compensate for atmosphere-induced wavefront tilt not corrected for by laser guide star adaptive optics.
In the Galileo Optical Experiment (GOPEX), optical transmissions were beamed to the Galileo spacecraft by Earth-based transmitters at Table Mountain Observatory (TMO), California, and Starfire Optical Range (SOR), New Mexico. The demonstration took place over an eight-day period (December 9 through December 16) as Galileo receded from Earth on its way to Jupiter. At 6 million kilometers (15 times the Earth-Moon distance), the laser beam sent from Table Mountain Observatory eight days after Earth flyby covered the longest known range for laser transmission and detection.
The Galileo Optical communications from an Earth-based Xmtr (GOPEX) demonstration is designed to exhibit deep-space optical communications using the Galileo spacecraft. The optical transmitter consists of a Nd:YAG laser coupled to a 24-in. telescope at the Table Mountain Observatory (TMO), and the receiver is the Solid-State Imaging camera on board Galileo. The objectives of the demonstration are to understand the issues involved in blind-pointing to a spacecraft in deep space, and to assess the quality of the optical uplink by comparing the experimental results with theoretical predictions. The demonstration is proposed for December 1992 during the second earth-flyby period of Galileo''s trajectory.