Proc. SPIE. 4635, Free-Space Laser Communication Technologies XIV
KEYWORDS: Observatories, Polarization, Signal attenuation, Satellites, Optical communications, Scintillation, Acquisition tracking and pointing, Satellite communications, Space operations, Data communications
ESA and the Instituto de Astrofisica de Canarias (IAC) reached an agreemenet for building the Optical Ground Station (OGS), in the IAC Teide Observatory, in order to perform In Orbit Testing (IOT) of Optical Data Relay payloads onboard communication satellites, the first being ARTEMIS. During its recent launch, ARTEMIS was put into a degraded orbit due to a malfunction on the launcher's upper stage. ESA rapidly adopted a recovery strategy aimed to take the satellite to its nominal geostationary position. After completion of the first manoeuvres, ARTEMIS was successfully positioned in a circular parking orbit, at about 31,000 kilometers, and turned into full operation. In this orbit, its optical payload has been tested with the OGS, before establishing the link with SPOT IV. New tracking algorithms were developed at OGS control system in order to correct for ARTEMIS new orbit. The OGS has established a bi-directional link to ARTEMIS, behaving, seen from ARTEMIS, as a LEO terminal. Preliminary results are presented on the space-to- ground bi-directional link, including pointing acquisition and tracking (PAT) performance, received beam characterization and BER measurements.
The Semi conductor Inter satellite Link EXperiment, SILEX, consists of two terminals, one terminal embarked on the French LEO observation satellite SPOT4 and one terminal embarked on ESA's GEO telecommunication satellite ARTEMIS. The objective of SILEX is to perform optical communication experiments in orbit and on an operational basis transmit SPOT4 Earth observation data to ARTEMIS, which will relay the data to ground via its Ka band feeder link. SPOT4 was successfully launched on 22nd March 1998. The ARTEMIS launch on 12th July 2001 left ARTEMIS in an orbit with too low apogee, necessitating orbit raising to a circular parking orbit, altitude 31000 km, using a large fraction of the chemical propellant on board. The remaining 5000 km to GEO stationary orbit will be achieved using the low thrust innovative electric propulsion system necessitating specific attitude control software. The final orbit raising will last about 6 months and the expected lifetime of ARTEMIS after station acquisition is 5 years. While waiting for the establishment of the new attitude control software and the beginning of the final orbit raising maneuvers a test program has been undertaken to characterize the performances of the SILEX system. Testing was performed every fifth day when ARTEMIS was visible over Europe. The test program involves Optical Ground Station acquisition and tracking, inter-satellite link acquisition and tracking, bit error rate measurements and transmission of Earth observation data. The paper reports on results of the in orbit testing, giving comparisons with predictions. The conclusion of the test program is that the SILEX system has excellent performances qualifying the system for operational use by SPOTIMAGE in parallel with a detailed technological experimentation program involving the two SILEX terminals, ESA's optical ground station on Tenerife, and also NASDA's OICETS, once ARTEMIS has acquired its final orbital position.
This paper presents the qualification history of the Silex flight hardware. The two flight model terminals, the GEO to be flown on ARTEMIS, the LEO to be flown on SPOT 4, have been or are about to be delivered for integration with their host spacecraft. Both terminals have undergone a stringent environmental test program, including optical performance measurements in vacuum, requiring complex test equipment. The flight hardware qualification was supported by development models that demonstrated the structural and thermal integrity of the design, the opto-mechanical stability of all optical paths within the terminals and the communication performances of the optical and electronic equipment. Due to the agreed SPOT 4 and ARTEMIS launch dates SILEX will not be in orbit before 1998 and 2000 respectively, such that the in orbit demonstration of the overall system can, most likely, not start before mid 2000, requiring the storage of the GEO terminal after the completion of the spacecraft testing. In the mean time, the construction of the optical ground station in Tenerife is well advanced. The building with the 1m telescope was handed over to ESA in Summer 1996, the optical bench will be ready in early 1997 and the whole station will be operational by mid 1997. It will first be used for in orbit debris observation. The preparation of the experiment between ARTEMIS and the Japanese spacecraft OICETS is proceeding well. A detailed link simulation has demonstrated the feasibility of the undertakings, the in orbit test plan is agreed, the ground interfaces are defined. This experiment will allow to control a LEO spacecraft via a data relay satellite through a S-band link with the simultaneous bi- directional optical link allowing data transmission at a rate of 50 Megabit per second in the return direction and 2 Mpbs in the forward direction.
The European Space Agency (ESA) is developing an optical inter-orbit communication system enabling a link between a low earth orbiting (LEO) and a geostationary (GEO) spacecraft. The link allows the transmission of 50 Mbps between LEO and GEO in an experimental and pre-operational mode. The system uses laser diodes of typically 100 mW optical power at a wavelength of 830 nanometer. Direct intensity modulation is applied. Telescopes of 25 cm diameter are used on both terminals. The breadboard phase has been completed and the launch of both terminals is scheduled for 1994. Other concepts for optical space communication links using Nd:YAG lasers and heterodyne receive systems are outlined.
The European Space Agency (ESA) is developing an optical interorbit communication system enabling a link between a low earth orbiting (LEO) and a geostationary (GEO) spacecraft. The link allows the transmission of up to 65 Mbps between LEO and GEO in an experimental and preoperational mode. The system uses laser diodes of typically 100 mW optical power at a wavelength of 830 nanometer. Direct intensity modulation is applied. Telescopes of 25 cm diameter are used on both terminals. The breadboard phase has been completed and the launch of both terminals is scheduled for 1994.