=--=--=START=--=--= NASA Spacelink File Name:6_2_2_46_3_8.TXT ACTS Overall Description ACTS is comprised of a spacecraft bus with basic housekeeping functions and a payload, known as the multibeam communications package (MCP). At launch, ACTS weighs 6,108 pounds including the propellants and the spacecraft adapter and clamp band which remain with the Transfer Orbit Stage (TOS) upon separation. When in the stowed configuration in the Shuttle payload bay, ACTS' overall height is 15.9 feet (5 m) from the spacecraft separation plane to the tip of the highest antenna. During the transfer orbit phase, the spacecraft is spin stabilized, and the antenna reflectors and solar array panels are retracted and stowed to provide better load support for these appendages. During the on-orbit mission phase, the spacecraft is three-axis stabilized with the large antenna reflectors facing the Earth and the solar array panels rotating once per day to track the Sun. On-orbit, ACTS measures 47.1 feet (14 m) from tip to tip of the solar arrays and 29.9 feet (9 m) across the main receiving and transmitting antenna reflectors. Spacecraft Bus The spacecraft bus structure is a rectangular box with a cylindrical center structure that houses the apogee kick motor (AKM). The multibeam antenna subsystem is mounted to the Earth facing panel of the spacecraft bus. The North and South sides are each divided into three panels. These panels are used to mount most of the spacecraft bus and MCP electronics equipment. The spacecraft bus provides support functions for the MCP such as electrical and mechanical mounting surfaces, attitude control, electrical power, thermal control, command reception, telemetry transmission and ranging and propulsion for station keeping maneuvers. Multibeam Communications Package The multibeam communications package performs receiving, switching, momentary storage, selectable coding and decoding, amplifying and transmitting functions for Ka-band time division multiple access (TDMA) communications signals. The multibeam antenna (MBA) has fixed beams and hopping spot beams that can be used to service traffic needs on a dynamic basis. (A hopping spot beam is an antenna beam on the spacecraft that points at one location on the ground for a fraction of a millisecond. It sends/receives voice or data information and then the beam electronically "hops" to a second location, then a third and so on. At the beginning of the second millisecond the beam again points at the first location.) In addition, the receiving antenna provides signals to the autotrack receiver which generates input error signals to the attitude control system for spacecraft pointing operations. Beam forming networks (BFN) utilize hopping beams to provide independent coverage of the East and West scan sectors, plus coverage for isolated locations outside of either sector. The MBA also has three fixed spot beams. A steerable beam antenna has been incorporated into ACTS to provide antenna coverage of the entire disk of the Earth as seen from l00 degrees west longitude and to any aircraft or low Earth orbit spacecraft, including the Space Shuttle, within view of the ACTS. ACTS Deployment Sequence ACTS will be deployed from Discovery's cargo bay approximately 8 hours after launch on orbit six. The TOS burn which will inject ACTS into a geosynchronous transfer orbit. The spacecraft apogee kick motor will inject ACTS into a drift orbit. Finally, ACTS will be placed in a geostationary orbit at 100 degrees west longitude over the equator, approximately in line with the center of the United States. A geostationary orbit is one where a satellite takes 24 hours to complete one revolution, thus appearing to remain motionless above a single place on the Earth. About 2 hours before deployment from the orbiter, the astronauts perform a sequence of events beginning with preliminary TOS checks, unlatching the TOS cradle and elevating the ACTS/TOS flight element to a 42 degree angle for deployment. The crew will fire the "Super*Zip" separation system, and six springs on the TOS aft cradle will push the flight element out of the cargo bay. The TOS motor firing is controlled by an on-board timer and occurs 45 minutes following deployment from the orbiter or about 8 hours and 45 minutes after STS-51 launch. The approximately two- minute burn will place ACTS in a geotransfer orbit. The apogee kick motor burn to inject ACTS into drift orbit will take place 42 1/2 hours after deployment, approximately 50 1/2 hours into the mission. The 7-day drift will allow ACTS to move toward its final station location of 100 degrees west longitude. Firing of the spacecraft's thrusters will bring the perigee and apogee radii increasingly closer to the geostationary orbit. Upon reaching geostationary orbit, ACTS will transition from a spinning to a three-axis stabilized spacecraft configuration and deploy its solar arrays and antennas. ACTS experiments will begin 12 weeks after launch following the placement of the spacecraft on-station and spacecraft checkout. ACTS is designed to have a minimum life of 2 years but will have enough station keeping fuel for a 4-year-plus mission. ACTS Ground Systems and Support The facilities and support to be used for the ACTS mission phases include the Guam and Carpentersville, N.J., C-band telemetry, tracking and command stations and the ACTS ground segment. Tracking, Telemetry and Command The ACTS mission telemetry, tracking and command (TT&C) control and monitor functions are distributed between two geographically separate locations: Lewis Research Center, Cleveland and the Martin Marietta Satellite Operations Center (SOC), East Windsor, N.J. The SOC is used to control the ACTS housekeeping functions during both the transfer orbit and the on-station phases. During the transfer orbit phases, the SOC controls the ACTS through the C-band ground stations. During the on-station phase, command parameters generated at the SOC are routed via landlines to Lewis to be uplinked to the ACTS via Ka-band. Status information is displayed at the Lewis ACTS master ground station for both the transfer orbit and on-station phases. ACTS Ground Segment The ACTS ground segment is comprised of the ACTS master ground station, the satellite operations center and the experimenter terminals. ACTS Master Ground Station The ACTS master ground station is located at the NASA Lewis Research Center. It includes: * The NASA ground station (NGS), which consists of a Ka-band radio frequency terminal, two traffic terminals and a reference terminal. It up-converts signals for the baseband processor mode of perations to 30 GHz for transmission to ACTS and amplifies and down-converts the 20 GHz baseband processor modulated signals received from ACTS. Modulation and demodulation of the baseband communications signals are performed in the NASA ground station. It also transmits and receives signals in support of the command, ranging and telemetry functions for ACTS. * The master control station provides network control for the spacecraft baseband processor and backup to the satellite operations center for configuring the multibeam communications package. The master control station also enables experiment execution and telemetry collection. * The microwave switch matrix-link evaluation terminal provides the capability for the on-orbit testing of the microwave switch matrix and the multibeam antenna. It also will conduct wideband communications experiments. * The command, ranging and telemetry equipment interfaces with theNASA ground station at intermediate frequency and exchanges command, ranging and telemetry information to and from the master control station, the G.E. SOC and the microwave switch matrix-link evaluation terminal. The SOC has primary responsibility for generating flight system commands and for analyzing, processing and displaying flight system telemetry data. Orbital maneuver planning and execution also are handled by the SOC. The primary housekeeping function is performed at the SOC which is linked via land line to the Ka-band command, ranging and telemetry equipment at the ACTS master control station. The Ka-band experimenter network consists of a variety of ground stations to be operated by industry, universities and government organizations. These ground stations have varying communication services ranging from High Data Rate (HDR) at 1 gigabit per second, to Very Small Aperture Terminal (VSAT) at 1.5 megabits per second, aeronautical and ground mobile voice and data at 500 kilabits per second and Ultra Small Aperture Terminal (USAT) data at 4800 bits per second. Source:NASA Spacelink Modem:205-895-0028 Internet:192.149.89.61 =--=--=-END-=--=--= =--=--=START=--=--= NASA Spacelink File Name:6_2_2_46_3_7.TXT ADVANCED COMMUNICATIONS TECHNOLOGY SATELLITE (ACTS) HARDWARE The Advanced Communications Technology Satellite (ACTS) provides for the development and flight test of high-risk, advanced communications satellite technology. Using advanced antenna beams and advanced on-board switching and processing systems, ACTS will pioneer new initiatives in communications satellite technology. ACTS provides new communications satellite technology for: * Operating in the Ka-band (30/20 GHz) where there is 2.5 GHz of spectrum available (five times that available at lower frequency bands) * Very high-gain, multiple hopping beam antenna systems which permit smaller aperture Earth stations * On-board baseband switching which permits interconnectivity between users at an individual circuit level * A microwave switch matrix which enables gigabit per second communication between users. These technologies provide for up to three times the communications capacity for the same weight as today's satellites (more cost effective), much higher rate communications between users (20 times that offered by conventional satellites), greater networking flexibility and on-demand digital services not currently available from communications systems today. The development and flight validation of this advanced space communications technology by NASA's ACTS will allow industry to adapt this technology to their individual commercial requirements at minimal risk. It also will aid the U.S. industry in competing with European and Asian companies which have, in the last decade, developed significant capabilities for producing communications satellites and associated ground equipment. ACTS technologies, which are applicable for a variety of frequency bands, will potentially lower the cost or technical threshold so that such new services as remote medical image diagnostics, global personal communications, real-time TV transmissions to airliners, direct transmission of reconnaissance image data to battlefield commanders and interconnection of supercomputers will be feasible. Technology spin-off is already occurring. Motorola currently is adapting the ACTS Ka-band and on-board switching technologies for their $3 billion Iridium satellite system, which will provide global voice/data communications services. Norris Communications also is proceeding with a Ka spot-beam communications satellite. Source:NASA Spacelink Modem:205-895-0028 Internet:192.149.89.61 =--=--=-END-=--=--=