NASA Facts the Advanced Communications Technology Satellite (ACTS) a Switchboard in the Sky

8/7/2019 NASA Facts the Advanced Communications Technology Satellite (ACTS) a Switchboard in the Sky

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The Advanced CommunicationsTechnology Satellite (ACTS)

NASAFactsNational Aeronautics andSpace Administration

Glenn Research CenterCleveland, Ohio 44135–3191 FS-2001-05-013-GRC

A Switchboard in the Sky

On September 12, 1993, a new and soon-to-be award-winning on-ramp to the information superhighwaywas opened to heavy traffic: NASA launched one of the most revolutionary breakthroughs in space com-

munications history, the Advanced CommunicationsTechnology Satellite (ACTS).

ACTS is the first high-speed, all-digital communica-tions satellite. It is the first to have sophisticated tele-phone-system-type switching onboard. It can carrydata at standard fiber-optic data rates with the sametransmission quality, added performance, and cost

saving that that a land-based network provides. Itoperates in the uncrowded and rarely used Ka-band(15 to 30 gigahertz) portion of the radio spectrum.ACTS technology integrates well with ground tele-phone network systems, allowing for high-speedtransmission over great distances to even the remotestlocations.

For more than 6 years, ACTS was the testbed whereNASA Glenn researchers demonstrated the abilitiesand reliability of the system they designed. It is alsowhere U.S. companies and institutions tested their

own uses of the technologies.

For all of that, the early intention was to solve anotherexpected problem: crowding of the geosynchronous

orbit where communications satellites fly. Satellites ingeosynchronous orbit fly 22,300 miles above theequator at a speed that matches the rotation of theEarth. Satellites of the same frequency must be posi-tioned, by international agreement, at least 4° apart toavoid interference between signals.

Commercial companies need more and more satellites

to support their many business and consumer ser-vices, such as high-speed and high-security financialtransactions for banks and wireless mobile networksfor consumers. Countries the world over areclamoring for their own satellites, particularly thosecountries without the infrastructure for a reliableground communications network.

ACTS.



As early as the 1970’s, Glenn scientists, and theirindustry collaborators, were aware that the demandfor geosynchronous orbital slots would all too soonexceed capacity. They designed the technology thenlaunched ACTS to test whether their new technology

could meet the growing communications needs of ademanding public. Well before the end of the formaldemonstration project in May 2000, the answer was a

resounding yes.

SPACECRAFT DESCRIPTION

ACTS was launched on September 12, 1993, as theprimary payload of the Space Shuttle Discovery on itsSTS–51 mission. On separation from the Shuttle, atransfer orbit rocket propelled it into a geosynchro-nous orbit. After 7 days, ACTS, guided by spacecraftthrusters, moved into its operations orbit and stabi-

lized (nonspinning) configuration. ACTS remained inits geosynchronous orbit at 100° west longitudethroughout the life of its demonstration project.With the solar arrays and main communications an-tennas deployed, ACTS measures 47.1 feet from tip totip of its solar arrays and 29.9 feet across from itsmain receiving and transmitting antenna. At the be-ginning of its on-orbit life, it weighed 3250 pounds.

ACTS has operated flawlessly, experiencing down-times only during the spring and fall equinoxes whenthe spacecraft’s solar panels are eclipsed. Experimen-tal studies began 12 weeks after launch and continued

through May 2000 when Glenn’s experiments pro-gram came to an end.

TECHNOLOGIES

ACTS’ communications payload includes severaltechnologies through which a full range of voice,video, and data communications services can beprovided on-demand:

• Operation in the Ka-band radio spectrum where the2.5 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 stationantennas.

• Onboard baseband switching, which, like an tele-phony switching station, connects sending and re-ceiving Earth stations. A further innovation insatellite communications is that ACTS makes theuser-to-user connection in a single satellite hop.

• A microwave switch matrix that enables high-speed(billions of bits per second) and high-volume com-munications and data transfer.

Ka-Band Spectrum

One way to increase the amount of information ordata per unit of time transmitted by a satellite is touse a higher radiofrequency. Until ACTS, the higherfrequency Ka-band was virtually unused—most com-munication satellites operate in the lower frequency

C- and Ku-bands. The Ka-band has a greater band-

width (in other words, it has a higher capacity for datatransfer) and allows smaller spacecraft and ground

Spacecraft onboard characteristics.



stations. Ka-band frequency is capable of carryingsimultaneously a multiple mix of voice, high-speed

data, and teleconferencing transmissions. ACTS’ threetransponders can process over a billion bits of dataper second.

High frequency means short wavelengths, though.And the millimeter wavelength Ka-band signals are

easily degraded by rain, a problem known as rainfade. Using detailed studies from 75 years of weatherpatterns, rain amounts, and their effects on lower fre-quency radio signals, Glenn scientists designed ACTSwith higher signal strength, digital error correction

Satellite systems comparison.

codes, and the ability to slow the transmission rate tocompensate for rain fade. ACTS’ digital access ap-proach to sharing the radio spectrum, known as timedivision multiple access or TMDA, is similar to thatused in many cellular phones. In TDMA, each user is

allocated a very large portion of the available band-width for a very short period of time.

Multiple Hopping Beam Antennas

Until ACTS, communications satellites broadcast asingle beam or “footprint” over a large part of theEarth. This is highly efficient for large-scale, one-way communication such as television broadcasts butnot for on-demand two-way communications.

To accommodate real-time two-way communications

for multiple users, ACTS uses 5 tightly focused spotbeams directed to 51 sites. Each beam has a diameteron the Earth of 150 to 200 miles, and each can be“hopped” from one site to another in milliseconds.

The small spot beams allow the same frequency to beused over and over because the spatial isolation be-tween spots prevents interference between beams.

The tighter, more concentrated beams also permitsmaller and less expensive Earth stations. They

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proved well suited to transmitting data to and frommobile terminals with small, 14-inch antennas.

GROUND SEGMENT

Master Ground Station and Satellite

Operations Center

The ground control segment includes the masterground station at Glenn, the satellite operations centerin Newtown, Pennsylvania, and experimenters termi-nals at industry, university, and government locationsacross the United States.

High data rate terminal

Very small aperture terminal

Ultrasmall aperture terminal

Experimenters terminals.

penetrate rain better and mitigate rain fade. ACTS,with its multiple hopping beams and other technolo-gies, uses less power, provides three times the com-munications capacity, and can transmit data 20 timesfaster than similar weight conventional satellites.

Onboard Digital Processing and Switching

In order to sort and route data transfer at high vol-umes and speeds, ACTS is equipped with a basebandprocessor and a microwave switch matrix. Thebaseband processor interconnects hopping spotbeams. It receives data from one spot beam, stores

the data as necessary, and forwards the message tothe proper spot beam and address-all of this inmicroseconds.

The microwave switch matrix interconnects fixedbeams using three transponders, each with an avail-able bandwidth of 900 megahertz (the total bandwidthof conventional C- and Ku-band satellites is 250 and500 megahertz). The switch is capable of high-speed,

high-volume transmission to terminals, operating at622 million bits per second, linked to supercomputersvia fiber-optic-satellite networks. The switch also

The master ground station controls the spacecraftand the network, manages experiments, and recordsspacecraft and system data. Traffic requests are

processed and set up, and traffic channels are as-signed on-demand. Command, ranging, and telemetryinformation is sent to and from ACTS via the masterground station.

The satellite operations center monitors spacecraft

health and status. The center also handles orbital ma-neuvering and housekeeping functions. It is linked byterrestrial line the master ground station at Glenn.



Experimenter Terminals

NASA Glenn researchers developed three specialground stations, or terminals, for certain types of userapplications or experiments. In addition, some ACTSexperimenters designed terminals suited to theirparticular needs. In all, 53 terminals were built andused by more than 100 experimenters to test ACTS

abilities.

The high data rate (HDR) terminals, equipped with

an 11-foot antenna, were developed to handle high-volume, high-speed traffic toand from the ACTS tran-sponders. The terminals con-nect seamlessly to terrestrialfiber-optic systems and

supercomputers at rates upto 622 million bits per sec-ond. They can transport

high-definition video at upto 520 million bits persecond.

Very small aperture termi-nals (VSAT) were developedto work with the on-demandtraffic to and from thebaseband processor. Using a4-foot antenna, these terminals can provide second-single hop data rates up to 180 million bits per secondfor voice, video, and data.

Ultrasmall aperture terminals (USAT) are similar in

size to today’s 18-inch direct broadcast televisionterminals. But USAT’s can uplink (send data toACTS) data as fast as 1.5 million bits per second anddownlink (receive from ACTS) as fast as 45 millionbits per second. The USAT terminals are ideal forhigh-speed Internet service, electronic banking, andreal-time videoconferencing.

Other experimenters designed mobile terminals small

enough to be placed on ships, airplanes, and landvehicles. Still others designed receive-only terminals

for studying rain fade.

EXPERIMENTS PROGRAM

Since its launch, ACTS has successfully validatedNASA’s vision of future satellite communications andhas demonstrated the ability of its technology to meet

the needs of users applications. Experiments havebeen conducted in such diverse areas as networking,medicine, industry, education, defense, business,emergency response, mobile communications, andastronomy.

Telemedicine

ACTS helped physicians meet the goal of providinghigh-quality, low-cost health care to millions of pa-tients in remote areas of the United States Physicians

at the Mayo Clinic diag-nosed and evaluated pa-tients at the Pine RidgeIndian Reservation in

South Dakota. ACTS real-time voice, video, anddata transfer allowed thephysicians to see andspeak to patients as wellas to receive diagnosticinformation from stetho-scopes, ultrasoundsonograms, and electro-

cardiograms. In one case,a child who had sufferedfor years from a misdiag-nosed skin condition wascured after Mayo physi-

cians, via ACTS, diagnosed the condition as leprosy

and prescribed appropriate treatment.

Early detection and diagnosis of breast cancer is an-other medical area benefited by ACTS. Glenn, theCleveland Clinic Foundation, and the University of

Information Capacity and Frequency

1 second

5 hertz or about 2.5 bits

10 hertz or about 5 bits

100 hertz or about 50 bits

More information can be transmitted at higher frequencies in the

same period of time

Experimenter viewing digitally compressed images.



Virginia participated in a clinical study in whichmammograms were given to women in rural regionswhere there are few or no breast cancer specialists. Inthe first part of the study, mammogram images thatwere digitally compressed and transmitted via ACTS

were judged to be equal in quality and resolution tostandard x-ray mammogram films. In the secondphase, patients’ mammograms were transmitted in

real time to specialists for interpretation. Imagestaken in a local hospital can be interpreted elsewhereand reported back to the local physician immediately

at very little additional cost.

Industry

The demand for new sources of fuel has caused off-shore oil exploration to move into deeper ocean wa-ters and to remote regions of the Earth, sending costs

soaring. ACTS has played a vital role in helping U.S.oil companies demonstrate how to be more costcompetitive through the efficient transfer and man-agement of information. Under the ATM (asynchro-nous transfer mode) research and industrial enterprisestudy, or ARIES project, ACTS helped the petroleumindustry remove time and distance obstacles from itsoperations.

Oil and gas companies use seismic information tochart the subsurface structure of the Earth. Done fromsea vessels, the resulting data, sometimes amountingto billions of bytes, are recorded on magnetic tape

and sent to analysts at distant facilities. Often, by thetime the analysts realize that more data are needed,

the collection ships have traveled miles from the siteand must be sent back. The process to accuratelychart an area can take months.

ACTS was used to demonstrate the real-time trans-mission of these data from offshore oil-drillingplatforms to analysts in Washington, DC. Transferringseismic data via ACTS not only saved months in re-search time at a savings of $200,000 per month, but

also provided higher quality seismic data by givingscientists access to the data in enough time to redirectvessels to more promising areas of the ocean.

Education

ACTS small terminals and higher data rates improved

distance education experiences because the nearlyinstantaneous transmissions made for a more naturalinteraction among the participants. Georgetown Uni-versity used ACTS to provide business educationtraining to companies at universities in Bogota,Colombia, and Quito, Ecuador. By obtaining business

knowledge via ACTS, local employees in these coun-tries are better prepared to conduct business with U.S.companies. Also, the university was able to expand itseducational services into international markets.

First ever shipboard trial was aboard the Geco Diamond

exploration vessel.

Participants in the electronic field trip to the Amazon rainforest.

ACTS “took” U.S. elementary and high school stu-dents to the far reaches of the Amazon rainforest andto Antarctica for Passport to Knowledge electronic

field trip programs. Through live audio and videolinks, students in their own classrooms helped per-

form science experiments and interacted with re-searchers at those exotic sites. Another electronicfield trip, this one to NASA’s Kuiper Airborne Obser-vatory (a 1-meter infrared telescope flown above theclouds in a modified C-140 aircraft), is believed to bethe first Internet transmission to and from a flyingaircraft.



Defense

ACTS has helped the U.S. Armed Forces gain experi-ence with satellite-supported communications. ACTScapabilities were put to one of their toughest tests

during the deployment of U.S. Armed Forces in Op-eration Uphold Democracy in Haiti. During the firstmonth of the operation, ACTS videoconferencingtechnology was the primary command and control

system. ACTS provided the secure audio-video link allowing field commanders to talk to commanders inthe United States including the Army Chief of Staff

and even to then President Clinton. ACTS also func-tioned in the secondary role of connecting soldiers inHaiti to their families in the United States through

live video contact between them.

The U.S. Navy has used ACTS to improve communi-cations to and from ships. A link was establishedbetween the USS Princeton and the San Diego NavalBase using a tracking mobile antenna developed bythe Jet Propulsion Laboratory, Pasadena, California.Unexpectedly, this capability was needed for atelemedicine application in which the captain of a

Greek merchant ship became ill and was taken aboardthe Princeton. He was remotely diagnosed while stillat sea and stabilized until he could be brought ashorefor lifesaving surgery.

Other Applications

Some of the other significant demonstrations thatACTS was used in include

• Huntington Bank connected branch offices to thecentral computers to observe service performanceduring emergency communications restoration viasatellite.

• The National Communications System demon-strated a Public Switch Network Restoral system

using easily transportable and mobile terminals to

restore phone service interrupted by a naturaldisaster.

• Cray supercomputers at the National Center for

Atmospheric Research in Colorado and the OhioSupercomputer Center in Ohio were connected forexperiments that combined meteorological andmarine forecasting.

• The Keck telescope at the Mauna Kea observatoryon Hawaii, was linked to a CalTech data processingfacility for experiments in remote facility controland data analysis.

• Supercomputers at Boeing and Glenn were con-nected to carry out computer simulated wind tunneltests.

• Eighteen organizations from U.S. computing andsatellite industries, academia, and governmentagencies participated in an effort to overcome

U.S. Armed Forces supported with satellite communications.

Space Technology Hall of Fame medal.



B–0991

May 01

For more information visit:

http://acts.grc.nasa.gov

Or contact the

Information and Publications Office, MS 8–1NASA Glenn Research CenterCleveland, Ohio 44135–3191

216–433–5573

technical issues in networking high-speed satellitelinks with the terrestrial network over the Internet.Data from this effort has already been incorporatedinto improving commercial products and expandingthe reaches of the Internet.

CONCLUSION

With the overwhelming success of ACTS, Glenncontinues to demonstrate its world leadership role inpioneering advanced technologies for space commu-nications. The ACTS project has set the stage for the

continuing evolution of the information era intospace. The projects technologies can be used to meetthe expanding need for communications resources byimproving satellite communications capabilities and

integrating satellite and ground communication. Sosignificant and valuable have been the ACTS’ contri-bution to the commercialization of space technology,that the ACTS project was inducted into the SpaceTechnology Hall of Fame in April 1997. In 1995

ACTS was selected for Research and DevelopmentMagazine’s R&D 100 Award for significant technol-ogy and was the winner of the prestigious Federal

Technology Leadership Award.

ACTS technology has shown the world new ways to

use orbital space and radio spectrum resources moreefficiently. It has offered alternatives in voice, data,and video communications networking to more mar-kets regardless of geographic location. The ACTSnational asset has been a benefit to us all.

NASA Facts the Advanced Communications Technology Satellite (ACTS) a Switchboard in the Sky

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