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Advanced Communications Technology Satellite (ACTS)

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  • Spacecraft G/T and EIRP can be found here (PDF, 170K).


  • Type: 3-axis stabilized experimental communications technology satellite.
  • Application: Testbed of new technology applications available to U.S. users.
  • Launch Vehicle: Space Transportation System (STS)/ Transfer Orbit Stage (TOS).
  • Orbit Position: Geosynchronous, equatorial, 105.2 degrees west.
  • Design Life: 4 Years.

Communications Payload

  • Frequency: 3 Ka-band channels, 30 GHz uplink, 20 GHz downlink.
  • Bandwidth: 900 MHz each channel, 2.7 GHz total.
  • RF Power: 46 Watts/Channel.
  • Redundancy: 1 standby channel (4 for 3 redundancy).
  • Coverage: Two contiguous sectors in north-eastern U.S. plus sixteen isolated spot beams covering selected U.S. locations. Also full visible earth coverage via mechanically-steerable spot beam.
  • Receive Antenna: 2.2-m dish and 1-m steerable.
  • Transmit Antenna: 3.3-m dish and 1-m steerable.
  • EIRP: Isolated spot beams: 65 dBW; contiguous sectors: 60-65 dBW; steerable beam: 57 dBW.
  • Receiver Noise Figure: 3.4 dB High Electron Mobility Transistor (HEMT).
  • On-Board Switching: High speed programmable 3 x 3 switch matrix to provide three input and three output channels with 900 MHz bandwidth. Baseband processor provides demodulation, storage and remodulation of Low Burst Rate (LBR) data using two 110 Mbps TDMA/DAMA data streams assignable in increments of 64 kbits.
  • Fade Beacons: Stable signals radiated from satellite in the uplink (30 GHz) and downlink (20 GHz) frequency bands to permit link fade measurements.

Electrical Power Distribution

  • Solar Array Output: 1418 watts (4 years).
  • Battery System: 2 nickel-cadmium (NiCd) batteries of 19 Amp-hours (AH) each. No payload operations during eclipse.
  • Power Bus: 35.5 (+/- 0.5) volts with full array illumination.

Propulsion and Orbit Control

  • Design: Blowdown hydrazine system with redundant thrusters and four tanks.
  • Propellant: 580 lbs. (at launch).
  • Thrusters: 16 (0.2,0.5, and 1.0 lbf).
  • Stationkeeping: No longer maintained. (+/- 0.05 degrees when it was maintained).

Structure and Thermal

  • Structure: Length: 80", width: 84", depth: 75".
  • Solar Array: With yoke, 46.9' tip-to-tip
  • Antenna Assembly: Height 116" above antenna panel; width: 29.9' deployed.
  • Thermal Control: Passive temperature control: blankets and Optical Solar Reflectors (OSR); active temperature control: solid state controllers and heaters.

Attitude Control

  • Transfer Orbit Control: Autonomous nutation control during spin; initial pointing provided by Transfer Orbit Stage (TOS) booster.
  • On-Orbit Control: 3-axis stabilized via earth and sun sensor and momentum wheel. Autotrack reference used during payload communications usage periods.
  • Pointing Accuracy: 0.025 degree pitch and roll, 0.15 degree yaw using autotrack; 0.1 degree pitch and roll, 0.25 degree yaw using earth sensor.
  • Offset Pointing Control: +/-6 degree pitch; +/-2 degree roll.

Command, Ranging and Telemetry

  • Command Frequency: Ka-band primary; C-band backup and during transfer orbit.
  • Command Rate: 100 pps FSK for bus functions; 5000 pps SGLS for payload.
  • Command Capacity: 379 low rate discretes; 3 serial low rate data streams; 256 high rate discretes; 3 serial high rate data streams.
  • Telemetry Frequency: Ka-band; C-band backup and during transfer orbit.
  • Telemetry Format: 8 nits/word; 256 words/minor frame; 25 minor frames/major frame; 1024 bps.
  • Telemetry Capacity: 312 bilevel words; 364 analog words; 6 serial words; dwell capability on any analog, bilevel or serial word.
  • Tracking Frequency: Ka-band; C-band backup and during transfer orbit.
  • Tracking Tones: 4 from 35.4 Hz to 27.777 kHz.