NASA, DOD take the next step in laser communications

NASA and the U.S. Department of Defense (DOD) have a common problem: whether trying to get high-resolution photographs from a Mars orbiter or handle the incredible voice and data traffic from a modern battlefield, traditional radio frequency (RF) technology simply does not have the bandwidth to do the job.

Sep 1st, 2003

By J.R. Wilson

WASHINGTON — NASA and the U.S. Department of Defense (DOD) have a common problem: whether trying to get high-resolution photographs from a Mars orbiter or handle the incredible voice and data traffic from a modern battlefield, traditional radio frequency (RF) technology simply does not have the bandwidth to do the job.

During the second Persian Gulf War in 2003 (Gulf War II), DOD officials relied heavily on commercial satellites to augment overwhelmed military assets, but officials worry those may not always be available — especially if the need covers a larger geographic area than the Gulf War theater or involves two widely separate locations.

As a result, leaders of both government agencies are looking at a technology that has been in various forms of testing and commercial development for at least two decades, but now appears on the verge of becoming a viable government space asset: laser communications (lasercom).

"Lasercom allows us to basically increase what we've been doing by a factor of 1,000," says John Stenbet, chief information officer and assistant secretary of defense for command, control, communications and intelligence. "Where today the most complex systems get 10 megabits per second, in the future, the lowest guy will get one or two megabits per second."

It is no simple task. Those involved say free-space laser communication incorporates a host of diverse, advanced technologies, not only lasers but also quantum and high-speed electronics, advanced optics and optical elements, detectors, controls, fiber optics, signal processing subsystems, and lightweight structures.

Designers then must amalgamate these components into precision tracking, pointing, and acquisition capabilities for communications systems involving deep space, submarine, satellite, aircraft, ground, and maritime applications. It almost goes without saying that these systems must be able to survive rigorous environmental conditions.

"So there are special selection processes and maybe design work-arounds, but, fundamentally, we are using router technology in space that is already being used in the Internet," Stenbet explains. "The requirements of radiation in the space environment may make it somewhat different, but it will be fundamentally a commercial design of the routers. We are in the process of doing accelerated life tests on lasers. We will have to adapt the commercial technology to the environment and that's more than a packaging change but we are not developing how to get it done, just how to put it together."

Even with a lasercom system in space, ground, air-to-ground, and air-to-air communications will continue to use RF, with one major exception — the Global Information Grid Bandwidth Expansion Program, otherwise known as GIG-BEP.

Today's lasers running through fiber-optic lines on the ground can be modulated in as many as 100 different colors 10 gigabits per second of data per color, and modulators that will take that to 10 gigabits per second per color. At those rates, one color in one strand would handle 1,000 times as much data as today's normal broadcast channels. GIG-BEP, which has been funded through 2004, will provide one color of communications capability to each of 100 essential DOD users around the world intelligence, command and control, logistics support, etc.

Stenbet says that will enable the "brains of DOD" to interact via a "smart pull" system, compared to the "smart push" system that has been in place for the past couple of decades. He says "smart push" is based on cheap processing and storage assets, but expensive and limited bandwidth. As a result, someone who has information must determine its value, and then put it into a global broadcast system. This would enable everyone with access and clearance to take what he wants from it.

That makes the system asynchronous in space because the sender and receiver can be anywhere on Earth and need not know each other or where the other is. And it is partly asynchronous in time because the message only needs to be sent once. That is a major improvement from communications prior to the mid-1980s, where the sender not only needed to know the information was important but to whom and how to reach that person with both being available to talk at the same time.

Part of constructing the new DOD system and transforming it from smart push to smart pull will be finding ways to enable allied and coalition forces to communicate with or through it in the battle theater.

"The laser part doesn't really affect our allies; that's more in the backbone part," Stenbet says. "The second part is for us to be able to integrate their data into our system. I expect it will be easier for us to share our data with them than to expect them to present their data in a form we can accept.

"What I'm describing is a DOD intranet, not an Internet. We'll have to connect to others in special purpose ways, and that is really crucial," Stenbet continues. "At one level, it worries the allies because we seem to be running ahead. But every ally can buy a laptop that hooks up to an intranet-type system or works with JTRS (Joint Tactical Radio System). So our question is how much do we share with whom, which is a problem we have to work through every time, but the cost of joining the club will be a lot less."

DOD officials say they expect to begin the process of selecting the right equipment and design by the end of this year, hoping it will be possible to make a build decision by 2005. The goal is to have at least the first two of an eventual five-satellite constellation (including one spare) in orbit and covering part of the planet within 10 years.

"Today we are asynchronous in space, but must bring along a lot of people and equipment on the ground; we would like to be asynchronous in space with small sets of equipment you can carry on your back," Stenbet says. "And we would like to get rid of the time constraints. Those were still present in Iraq, although when we found a target, we did have turnaround times of less than an hour. But we would like to be able to do that in minutes. The real issue is we could have been more effective in Afghanistan at the same time we were effective in Iraq because we could have done it in both places at the same time."

Tasked with turning that vision into reality is the newly created joint Transformational Communications Office, which also includes NASA, and, on the military side specifically, the next generation of military satellite communications (TC-MILSATCOM). Christine Anderson serves as both the deputy director of TCO and director of the MILSATCOM joint program office (JPO).

"We're interested in applying lasercom to space-based networking, specifically the TC initiative," Anderson says.

An integral part of TC-MILSATCOM is bringing IP (Internet protocol) into it to provide the kind of broad connectivity found in the global Internet to a space-based lasercom network. A major element of that would be a space network, with satellites using lasercom to communicate with each other, helping speed data around the globe at much higher rates than is currently possible.

That will involve several different constellations of new DOD satellites, including an advanced polar-orbiting system for strategic users, an intelligence constellation called ORCA (optical relay communications architecture), TSATs (transformational communications satellites) covering the mid latitudes of 65 degrees north and south, and even laser connectivity between high-altitude aircraft. The TSATs and polar systems are scheduled for operation in 2014-16; the launch schedule for ORCA is classified.

"High power amplifier technology, and modem technology that sits behind the amplifiers are enablers. These have been demonstrated," says TC-MILSATCOM initiative lead Dr. Troy Meink. "There has been a huge investment in the telecom commercial world in the past 15 years that we are now starting to leverage, including a number of demonstrations of lasercom technology at various data rates. We are now in the process of taking the experimental demonstrations and prototyping the technology."

Anderson says the entire TC architecture is much like building an Internet, with several spiral builds as the technology advances.

"The first spiral is fairly low risk, mostly a productization activity. But we also are investing in further maturization for the second, third, and on spirals so this is a robust, not static, architecture," she says. "We envision the same thing for the TC architecture that we have seen on the commercial side in terms of future development."

DOD has allocated about $9.6 billion for the TC-MILSATCOM effort.

Scientists from NASA, primarily through the Jet Propulsion Laboratory in Pasadena, Calif., have been developing lasercom for many years, for applications ranging from cross-linking satellites in orbit to communicating with the ground using geosynchronous and low-Earth orbiting satellites and as a way to provide fast and detailed results from deep-space probes.

"There is a study underway to see the viability of flying a payload on a Mars orbiting satellite and communicating back to Earth using lasers," notes Abhijit Biswas, a senior engineer with JPL's optical communications group. "That satellite would have the usual RF communications, but there would be a piggyback demonstration to see how often a laser communication could be received, how atmospheric parameters would affect it and so on. This probably will go on a 2009 launch called Mars Telesat Orbiter, a JPL effort," although officials from the NASA Goddard Space Flight Center in Greenbelt, Md., will manage the laser system.

That test will be somewhat complicated by virtue of using a ground station to receive the signal on Earth; putting a satellite in orbit only for a deep space lasercom test would be too expensive.

On a lasercom satellite, telescopes take the place of the RF communications antennas. The larger the aperture of the telescope lens, the narrower and more effective the beam. For Mars, NASA is looking at a pulse laser that will support high repetition rates with high peak power, although they say they do not expect to get beyond 1 megawatt.

"Your pointing has to be roughly within one-tenth of your beam width, so you don't want to make it too narrow because it would be too difficult to point and acquire," Biswas says. "The lasers we're talking about flying to Mars were built for other applications and we're just trying to space-qualify them. If the technology proves useful, there undoubtedly will be efforts to improve those lasers, but that hasn't happened yet."

NASA experts are concentrating their own lasercom development efforts on deep space, while looking to cooperate with DOD in developing near-Earth capability.

"We have been briefing DOD on what we can bring to the mix and hope we can play some role in their near Earth and airborne efforts," Biswas says. "A good example would be a one-meter transceiving telescope we developed for the optical communications telescope laboratory and took delivery on 25 July. It is the first dedicated optical communications telescope and the kind of asset we can offer on the ground that would be very helpful to accelerate the DOD effort."


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