Optical links connect Earth to deep space

April 1, 1998
PASADENA, Calif. - Scientists at the NASA Jet Propulsion Laboratory (JPL) in Pasadena, Calif., plan to use lasers to speed the flow of data from future satellites and deep-space probes. These optical links are to boost data rates by 100 times with no additional mass or power consumption than today`s radio frequency systems, JPL officials say.

By John McHale

PASADENA, Calif. - Scientists at the NASA Jet Propulsion Laboratory (JPL) in Pasadena, Calif., plan to use lasers to speed the flow of data from future satellites and deep-space probes. These optical links are to boost data rates by 100 times with no additional mass or power consumption than today`s radio frequency systems, JPL officials say.

The JPL plan calls for an Earth-based laser beacon to establish initial communications with the spacecraft, and for the spacecraft to answer via laser along the beacon`s path. Systems designers say the beacon will reduce spatial interference and improve accuracy.

Unlike radio waves, laser links are susceptible to interference from clouds, tropical storms, and other weather conditions, says James Lesh, chief engineer for JPL`s Optical Communications program. Plans call for using several different ground stations to bypass threatening weather, he says.

Enabling technologies include a charge-coupled device to measure the angle between transmit and receive beacon and close the tracking loop, and a steering mirror to stabilize the transmit beam`s line-of-sight, Lesh explains. The ground laser does not need to be stabilized, he adds.

JPL engineers plan to use green lasers operating at wavelengths between 500 and 1,550 nanometers for space-to-Earth transmission. "Some specific candidates operate at 860 nanometers, 980 nanometers, 1,064 nanometers, and 1,550 nanometers," Lesh explains.

"Among the candidates, the 860-nanometers and 980-nanometers lasers are diode lasers," Lesh says. "The 1,064-nanometer lasers can be either diode-laser-pumped fiber lasers for near-Earth applications, or diode-laser-pumped solid-state lasers for deep-space. The 1,550 laser would be a diode-laser-pumped fiber laser."

The 532-nanometers uplink laser - for transmissions from ground to space - would be a frequency-doubled, diode-laser-pumped solid-state laser operating at 1,064 nanometers, he says.

A telescope on the spacecraft will receive the beacon signal and focus it onto a focal plane detector array. Then a two-axis steering mirror bounces the fiber-coupled transmit signal off a dichroic beamsplitter and out of the telescope.

A dichroic beamsplitter can "either combine optical signals of different wavelengths, or separate the components of a beam consisting of multiple wavelengths in the two bands," Lesh says.

The JPL-designed power- conditioning unit provides all operating voltages and currents. Engineers from Hytek Microsystems Inc. in Carson City, Nev., are building a laser transmitter capable of sending data at 500 megabits per second.

A demonstration terminal at JPL will use only one fine-beam-steering element and one detector to acquire, track, point and transmit a received beacon signal.

The Optical Communications System is part of the X-2000 Advanced Deep Space System Development program, which is a candidate for several new proposed missions in the New Millennium Program, also at JPL.

"The goal is to push technology that may not be necessary, but if available could enhance the mission," says Tony Spears, program manager for the X-2000 program.

NASA engineers performed optical communications demonstrations with a laser communications terminal on the Japanese ETS VI satellite in 1995 and 1996. The four-beam transmission helped reduce the effects of atmospheric turbulence on received beam at the spacecraft.

The JPL Optical Communications System also has applications for data return from commercial remote sensing systems, for data relay in space-based personal and mobile communications networks, and for military data relay and data return applications in space, JPL experts say.

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NASA scientists plan to use the laser system pictured above to provide Earth-to-space communications links that are 100 times faster than the RF links used today.

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General Dynamics designers shift to modular vetronics approach

By John Rhea

STERLING HEIGHTS, Mich. - General Dynamics vetronics designers are shifting to a new architectural approach that will help them blend improved electronic components into armored combat vehicles as soon as new electronic technologies become available.

Experts from the General Dynamics Land Systems (GDLS) Division in Sterling Heights, Mich., are demonstrating this new design approach in the first of six prototype upgraded M1A2 Abrams main battle tanks for the U.S. Army. These prototypes incorporate the system enhancement package (SEP) of advanced vehicle electronics.

This new approach represents a departure from the Army`s traditional method of major tank block changes every six years or so, and General Dynamics engineers are doing it by mixing and matching standard off-the-shelf vetronics subsystems across several kinds of military vehicles.

The M1A2 SEP not only shares modules with the United Defense LP M2A3 Bradley fighting vehicle, but also reuses 89 percent of the software from the Army Wolverine heavy assault bridge and 40 percent from the U.S. Marine Corps Advanced Amphibious Assault Vehicle (AAAV), both from GDLS.

In addition, the M1A2 SEP reuses 43 percent of the software from the future Crusader advanced field artillery system, on which GDLS teams with United Defense LP in York, Pa., as the vetronics supplier.

The M1A2 SEP shares at least three subsystems with the Wolverine, AAAV, and Crusader: the commander`s display unit (modified), the processors (Motorola PowerPC), and the power management system. The mass memory unit from the General Dynamics Information Systems Division (formerly Computing Devices International) in Minneapolis, is common to the Wolverine and AAAV.

At the unveiling ceremony Feb. 19, GDLS officials stressed the cost effectiveness of the continuous upgrade process, noting that $1 million per SEP represents one-fifth of the $5 million price tag for the M1A2s when they went into production in 1993.

The original M1 main battle tank entered production in 1979. It was next upgraded to the M1A1 configuration in 1985 at a cost of $3 million a copy.

GDLS leaders are under contract to the Army to upgrade 1,150 early model M1 tanks to the M1A2 configuration. This effort will run in to the year 2003. Army officials plan to make a production decision on SEP in September 1999. GDLS officials say the believe it is essential to phase in SEP as soon as possible to prevent a disruption of tank production.

In the meantime, GDLS engineers are delivering six SEP prototypes, three for company systems integration testing (including the one on display at the unveiling) and three for Army tests at the Yuma Proving Grounds in Arizona.

The idea is to achieve economies of scale and cut electronics costs by building combat vehicles with common subsystems, such as the various Abrams configurations, AAAV, and Wolverine. The principal production facility will be the General Dynamics government-owned, contractor-operated plant at Lima, Ohio.

Research, engineering, and integration are in the Sterling Heights facility, which was part of the package the General Dynamics leaders took over when they acquired Chrysler Corp.`s defense operations in 1983.

General Dynamics is the country`s only supplier of tanks and has produced more than 8,500 main battle tanks for the U.S. Army and for international sales.

Enhancements incorporated in the SEP to date include the Army`s Single Channel Ground and Airborne Radio System, the second-generation forward-looking infrared gunner`s sights and commander`s thermal viewers, color digital terrain maps, and provision for future use of video.

The SEP also has the embedded Force-21 Applique command and control software from TRW and uses the 1553 digital data bus and VME modules.

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The open-systems modular architecture of the M1A2 tank system enhancement package, depicted above, will provide COTS vetronics subsystems across a broad range of combat vehicles.

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