British Aerospace Public Limited Company

British Aerospace Public Lmited Company

David Robson

Michael A Grant

Nicholas F Matthews

Brian L Combridge

Daniel R Timson

A multiple access communications system comprises a node spacecraft GEO and several user spacecraft LEO.sub.1 to LEO.sub.n. Each user spacecraft LEO.sub.1 to LEO.sub.n includes a transmit/receive terminal head 18.sub.1 to 18.sub.n, and the node spacecraft GEO includes n transmit/terminals 22 to 22.sub.n and a single beacon unit 24. The beacon beam may be operated to initiate acquisition phases which allow two-way communication to be established between the transmit/receive terminals 22.sub.1 to 22.sub.n on the node spacecraft and the transmit/receive terminals 18.sub.1 to 18.sub.n on the corresponding user terminals. The acquisition phases include a period during which the beacon scans an uncertainty cone associated with the node spacecraft. This scanning period is reduced for second and subseqeunt acquisitions by using the first and subsequently acquired communication links to provide a more accurate estimate of the angular attitude of the node spacecraft, thus reducing the extent of the uncertainty cone.

Multiple access communication system

A method of processing video image data for use in the storage or transmission of moving digital video images, includes decomposition of each frame image into an equivalent set of sub-images containing information on different length scales, derivation of encoded prediction rules from the decomposed data to approximate each sub-image using data from the immediately preceding compressed sub-image and data from the current sub-image to produce compressed data of an image for subsequent storage or transmission to a receiver and reconstruction, after retrieval or receipt, by comparison of the compressed data received for the current frame image with the reconstruction of the preceding frame image.

Method of processing video image data for use in the storage or

A process and apparatus are provided for controlling the alignment of a transmit laser beam (1a) of a first coherent detection optical communications transmitter/receiver terminal with a further coherent detection optical communications transmitter/receiver terminal relative to a receive laser beam (8). The first terminal incorporates a transmit laser beam generator (1) operable to form and pass the transmit beam (1a) through a point ahead mechanism (2) to a telescope assembly (6) operable to receive the receive laser beam (8). The apparatus includes a detector/receiver unit, means (3) for taking a component (1b) of the transmit laser beam (1a) from the transmit laser beam (1a) for receiving the receive laser beam (8) from the telescope assembly (6) and for feeding the transmit laser beam (8) to the detector/receiver unit (10), and means (16, 17, 18, 19, 20 ,21, 22, 23, 24) for detecting, separating and processing the received transmit laser beam component (1b) and received receive beam (8) at the detector/receiver unit (10) to provide signals indicative of the actual alignment of the transmit and receive beams (1a, 8), means (25) for comparing the actual alignment signals with desired alignment values to generate difference signals and means for operating the point ahead mechanism (2) in dependence upon the generated difference signals variably to control the alignment of the transmit beam (1a) relative to the receive beam (8).

Process and apparatus for controlling the alignment of a transmit laser

This invention relates to mechanisms for steering or pointing transmitted optical radiation beams and/or the look directions from which optical radiation beams are received. It also relates to optical communications systems incorporating such mechanisms, more particularly but not exclusively interspacecraft communications systems.

Beam pointing mechanism

A laser beam communication system for spacecraft in which each communication terminal comprises, for steering the beam projected from that terminal, four mirrors, each mounted on a mechanism capable of rotating the mirror about a constant defined axis. The mirrors and their attached mechanisms are arranged in pairs with one pair on either side of a magnifying telescope. All rotating joints in each mechanism are constructed using flexure pivots. Such a pointing element can provide both the range and accuracy required for an important class of free space laser links without introducing any extra friction into the pointing system.

Laser beam communication between spacecraft

Optical communications apparatus for sending and receiving optical transmissions to and from a plurality of remote stations by a plurality of independent terminals which are multiplexed so that all operate through a single optical system for both transmission and reception of modulated beams containing encoded data.

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Stevenage, United Kingdom

David Robson