ACTS

Launch data: Designation 22796 / 93058B Launch date 12 Sep 1993 - 11:45 UT Launch site KSC, LC39B/MLP3 Launch vehicle STS 51 Mission NASA experimental communications Geostationary orbit on: Perigee / Apogee  35709 x 35929 km Eccentricity   Inclination  0.2 deg Period   min Experimental satellite intended to develop Ka-band mobile services to VSAT terminals from high-data rate personal and transportable terminals. Deployed from STS-51 on Sept 12, 1993; 100 deg W.

Specifications: Prime contractor GE Astro Space (Lockheed Martin Corporation) Platform GE-4000 modified Operator NASA Mass at launch 2545 kg Mass in orbit 1555 kg Dimensions 2.03 x 2.13 x 1.92 m Stabilization 3-axis DC power BOL: 1770 W (batteries: 2 NiCd of 19 AH each) EOL: 1418 W (no payload operation during eclipse) Design lifetime 4 years Telemetry & Command Ka-band with backup in C-band

ACTS deployment from STS-51

Photo of the ACTS spacecraft (image credit: NASA)

Location

Ka-band

Description:

• ACTS was developed as an experimental on-orbit, advanced communications satellite test bed, bringing together industry, government, and academia to conduct a wide range of technology, propagation, and user application investigations. The ACTS spacecraft was built by Lockheed Martin (formerly RCA Astro Space of East Windsor, NJ) as prime contractor. It has a mass of 1480 kg at the beginning of its on-orbit life; and it measures 14.4 m from tip to tip of the solar arrays and 9.1 m across the main receiving and transmitting antenna reflectors, with a height of 4.6 m from the spacecraft separation plane to the tip of the highest antenna. The main receiving antenna is 2.2 m in diameter; the main transmit antenna is 3.3 m in diameter. ACTS also incorporates beacons at 20.2 and 27.5 GHz. An operations phase of 24 months was planned.

Mission details:

• ACTS (Advanced Communication Test Satellite) is the first high-speed, all-digital communications satellite. It is the first to have sophisticated telephone-system-type switching onboard. It can carry data at standard fiber-optic data rates with the same transmission quality, added performance, and cost savings that a land-based network provides. It operates in the uncrowded Ka-band (18 to 30 gigahertz) portion of the radio spectrum. ACTS technology integrates well with ground telephone network systems, allowing for high-speed transmission over great distances to even the remotest locations.

• ACTS, which was built and operated by Lockheed Martin Corporation, was launched on September 12, 1993, as the primary payload of the Space Shuttle Discovery on its STS-51 mission. After separation from the Shuttle, a transfer orbit stage (TOS-21H) rocket propelled it into a geo-transfer orbit. After 7 days, ACTS moved into its geosynchronous operations orbit and stabilized into a nonspinning configuration. ACTS remained in this orbit at 100° west longitude throughout the life of its demonstration project. With its solar arrays and main communications antennas deployed, ACTS measures 47.1 feet from tip to tip of its solar arrays and 29.9 feet across from its main receiving and transmitting antenna. At the beginning of its on-orbit life, it weighed 3250 pounds.

• ACTS has operated flawlessly, experiencing expected downtimes only during the spring and fall equinoxes when the spacecraft's solar panels are eclipsed. Experimental studies began 12 weeks after launch and continued through May 2000 when Glenn's experiments program came to an end.

• The ACTS communications payload includes several technologies through which a full range of voice, video, and data communications services can be provided on-demand:
  • Operation in the Ka-band radio spectrum where the 2.5 gigahertz of available spectrum is five times that available in lower frequency bands.
  • Multiple, high-gain hopping-beam antennas that permit the use of smaller diameter Earth station antennas.
  • Onboard baseband switching, which, like a telephony switching station, directly connects sending and receiving Earth stations. A further innovation in satellite communications is that ACTS makes the user-to-user connection in a single satellite hop.
  • A microwave switch matrix that enables high-speed (billions of bits per second) and high-volume communications and data transfer.
• In Nov. 1997 a record data rate of 520 Mbit/s TCP/IP (Transmission Control Protocol/Internet Protocol) was achieved using ATM via ACTS and several ground stations. The transmission experiment involved government agencies and commercial partners (the ACTS 118 consortium of researchers) to test their COTS products, all were interested in testing the ability of ATM technology to transfer data at high rates over satellite. ACTS communication capabilities continued to be used by industry, universities, and government to develop new satellite services, including real-time TV transmission to airliners.
• In July 1998 the spacecraft's north/south stationkeeping was discontinued (to conserve the last amount of fuel) and to extend operations in an inclined orbit. The reason: the hydrazine fuel was almost consumed by the ACTS spacecraft to maintain its desired position in space.
• On May 31, 2000 the ACTS experiments program officially came to a close. Experiments were continuously supported for 78 months of operations. The ACTS spacecraft was moved to a new parking orbit location at 105.2º W where it arrived on Aug. 11, 2000.
• Also in May 2000, NASA extended ACTS availability for education and research purposes to an education-based consortium in Ohio, referred to as OCACT (Ohio Consortium for Advanced Communications Technology). OCACT formally assumed control of ACTS, under the provisions of a Space Act Agreement between NASA/GRC, the Ohio Board of Regents, and Ohio University.
• 24-hour availability of spot beams until February of 2001 - decreased slowly after that date (due to pointing limits). The steerable antenna remained fully available.
• The deactivation of ACTS occurred on April 28, 2004 when funding was terminated. At the time, the geosynchronous orbit had an inclination of 1.8º (increasing by 0.8º per year). The ACTS mission lasted 127 months (instead of the originally planned 24-48 months) and provided pioneering communications research during its lifetime.

External links:

• EOportal.org Satellite description