Kenichi Araki

Preliminary result on laser communication experiment using (ETS-VI)

This paper shows the most recent result of the laser communication experiment using ETS-VI satellite. The satellite failed into geostationary orbit and it is currently in a high elliptic three- day recurrent orbit, but from December 1994, we have performed laser transmission experiment for both uplink and downlink.

Overview of the Ground-to-Orbit Lasercom Demonstration (GOLD)

The ground-to-orbit Lasercom Demonstration conducted between the ETS-VI spacecraft and the ground station at JPLs 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.

In-orbit measurements of short term attitude and vibrational environment on the Engineering Test Satellite VI using laser communication equipment

Morio ToyoshimaNational Space Development Agency ofJapan2-2-1 SengenTsukuba, Ibaraki 305-8505JapanE-mail: toyoshima.morio@nasda.go.jpKenichi ArakiCommunications Research Laboratory4-2-1 Nukui-KitamachiKoganei, Tokyo 184-8795JapanE-mail: araki@crl.go.jpAbstract. Angular microvibrations of platform jitter on a three-axisattitude-stabilized satellite are measured in space using an onboard la-ser communication terminal. Stable optical tracking control allows themeasurement of relative angular variations from the reference line ofsight of the optical link. The tracking accuracy in this measurement isless than 1 mrad rms. The angular variation and the drift rate on thesatellite are measured at a sampling rate of 500 Hz, and these data aredownlinked to a ground station via a satellite-to-ground optical commu-nication link. The power spectral density of the satellite microvibration iscalculated by a Fourier transform analysis. The frequency spectrum ofthe gimbal mirror’s angular variation is also obtained when the coarsetracking control is operational. The rms value agrees with the residualcoarse tracking error estimated before launch of the satellite. These re-sults will be useful for the future design of a tracking control loop foroptical communication systems.

Measurement of the characteristics of a quadrant avalanche photodiode and its application to a laser tracking system

Masahiro ToyodaKenichi ArakiYoshiaki SuzukiCommunications Research Laboratory4-2-1, Nukuikitamachi, KoganeiTokyo 184-8795, JapanE-mail: toyoda@crl.go.jpAbstract. We measured the characteristics of a quadrant-type ava-lanche photodiode (APD). Its transition region between the adjacent cellshad a narrow width of 35 mm. As the multiplication factor of the quadrantAPD was limited by the variety of that among the quadrant cells, themaximum multiplication factor was about 30. We investigated the perfor-mance on applying the quadrantAPD to a laser tracking system.Anoise-equivalent angle of less than 1 mrad (rms) was achieved at a receivedoptical power of more than 4 pW. The quadrant APD compared favorablywith a photodiode quadrant detector when the received power was lessthan 100 pW.

Preliminary results of the Ground/Orbiter Lasercom Demonstration experiment between Table Mountain and the ETS-VI satellite

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, NASDAs Tsukuba tracking station and NASAs 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 Earths 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.

Performance evaluation of laser communication equipment onboard the ETS-VI satellite

Communications Research Laboratory (CRL) developed laser communication equipment (LCE) onboard the engineering test satellite VI(ETS-VI) and a ground system for establishment of basic technologies in optical intersatellite communications. The experiments using a ground-to-space laser link started on December 1994. In the paper, preliminary evaluation for the performance of LCE is presented based on a part of experimental data. Included in the paper are a brief description of operation and data acquisition system, acquisition, tracking and pointing subsystem performance, and communication subsystem performance.

Far-field pattern measurement of an onboard laser transmitter by use of a space-to-ground optical link

The far-field pattern of an onboard laser transmitter was measured with a transatmospheric optical link with a distance of ~33,000 km between the satellite and the optical ground station. The far-field pattern was acquired with a new method used to analyze statistically downlink irradiance data obtained at the ground station. The statistical tracking and pointing characteristics of the transmitter were taken into account in estimating downlink irradiance, assuming that there were no atmospheric scintillation effects. The peak directive gain of the downlink laser beam was 104.3 dB. The beam width (full width at half-maximum) was 28.5 x 17.5murad. These results were consistent with the results froma laboratory test undertaken before launch of the satellite.

Ground-to-ETS-VI narrow laser beam transmission

Experimental results of laser beam transmission from a ground station to the engineering test satellite VI (ETS-VI) are presented. The ETS-VI that was launched in August last year has onboard laser communication equipment (LCE). A very narrow laser beam with less than 60 (mu) rad divergence was continuously transmitted to the LCE from a ground station, using a highly accurate satellite optical tracking technique. The optical power fluctuation detected at the LCE was very large. Its log-amplitude variance was about 0.5 and the maximum duration for the LCE to be able to receive an optical power more than the LCE communication detector sensitivity was about 50 milli-seconds. Theoretical analysis of laser beam fluctuation at a satellite is described and compared with the experimental results.

Earth-to-geosynchronous satellite laser beam transmission

Some experimental results for detection of a ground-based laser beacon by a geosynchronous satellite are reported. A 50-cm diam telescope and silicon intensifier tube camera were used for optical observation of the satellite. The transmitted argon laser beam was detected by the visible channel of a radiometer on board the Japanese Geostationary Meteorological Satellite. Two activities, (1) orbit prediction correction using optical observation and (2) detection of the earth laser beacon by the radiometer, are described.

Experimental operations of laser communication equipment onboard ETS-VI satellite

The first ground-to-satellite laser communication experiments were performed during December 1994 and July 1996 to demonstrate basic technologies for space laser communication systems. It used an optical communication package onboard the Engineering Test Satellite VI and its companion ground optical terminals. A bi-directional optical communication link over 40000 km was demonstrated with precise transmission control of extremely narrow laser beams at both onboard and ground terminals. In the paper, the experimental operations performed in the demonstration are introduced in context with acquisition method for various technical data useful for evaluating the terminal characteristics.