NASA to demonstrate laser beam communications system

Conceptual image of the Laser Communications Relay Demonstration that is designed to increase the data rate of space communications (Image: NASA)

Since the dawn of the space age, NASA has been relying on radio communications technology to send and receive data to and from spacecraft. Although it has developed higher data-rate radio frequency systems, data-compression, and other techniques to boost the amount of data that its current RF systems can handle, they can't keep pace with the projected data needs of advanced instruments and further human exploration. To break this bottleneck, NASA is turning to optical communications technology that would use lasers to increase data rates over existing systems by anywhere from 10 to 100 times.
NASA's current legacy radio-based network includes a fleet of tracking and data relay satellites and a network of ground stations. At the current limit of 6 Mbps for the Mars Reconnaissance Orbiter (MRO), NASA says it currently takes 90 minutes to transmit a single HiRISE high-resolution image from Mars back to Earth. However, the new optical communications system would reduce the transmission time down to just five minutes and even allow streaming of high definition video from distances beyond the Moon.
The Laser Communications Relay Demonstration (LCRD) is designed to enable NASA, other governmental agencies and the commercial space industry to undertake future, complex missions by providing significantly higher data rates for approximately the same mass, power, and volume as a comparable RF system.
NASA says laser-based space communications will enable missions to use bandwidth-hungry instruments, such as hyperspectral imagers, synthetic aperture radar (SAR), and other instruments with high definition in spectral, spatial, or temporal modes. Laser communication will also make it possible to establish a "virtual presence" at a remote planet or other solar system body.
The LCRD is expected to fly as a hosted payload on a commercial communications satellite developed by Space Systems/Loral, of Palo Alto, California. The experimental payload will include telescopes, lasers, mirrors, detectors, a pointing and tracking system, control electronics, and two different types of modems; one ideal for communicating with deep space missions or tiny, low-power smallsats operating in low-Earth orbit, and another that can handle much higher data rates, particularly from Earth-orbiting spacecraft, including the International Space Station.

A team at the NASA Goddard Space Flight Center in Greenbelt, Maryland, which is leading the development of the system, will encode digital data and transmit the information via laser light from specially equipped ground stations to the experimental payload on the commercial communications satellite. Once the payload receives the data, it would then relay it back to the ground stations that are now scheduled to operate in Hawaii and Southern California.
The multiple ground stations are important, as the optical system requires a clear line of sight between the transmitter and receiver. So if bad weather prevents a signal from being sent or received at one location, the network could hand things over to one of the other ground stations or store it for later transmission.
"Just as the home Internet user hit the wall with dial-up, NASA is approaching the limit of what its existing communications network can handle," said LCRD Principal Investigator Dave Israel. "What we're trying to do is get ahead of the curve. We want to get to the point where communications is no longer a constraint on scientists who want to gather more data, but are worried about getting their data back from space," Israel added. "With the higher-speed modem type, future systems could support data rates of tens of gigabits per second," he said.
NASA plans to demonstrate the LCRD system in 2016, with the demonstration expected to run two to three years. It is one of three proposals NASA has selected as Technology Demonstration Missions because of their potential to provide tangible, near-term products and have high-impact of NASA's future space exploration and science missions.
The other two proposals selected were a Deep Space Atomic Clock designed to provide the unprecedented stability needed for next-generation deep space navigation and radio science and an in-space demonstration of a mission-capable solar sail to enable propellantless in-space navigation for missions such as advanced geostorm warning, economic orbital debris removal, and deep space exploration. More on these later.

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Sc/Lasers Could Be Used to Control Rain, Scientists Say

Lasers could help cause rain, scientists now suggest. The finding may give bone-dry regions of the world much-needed moisture, scientists say.

A laser beam (red) and the cloud of generated particles (illuminated by an auxiliary green laser, which makes each particle shine) in a cloud chamber Photo credit: J.P. Wolf / University of Geneva.

Rainclouds form when airborne pockets of tiny particles condense water vapor around them. With enough of these cloud seeds, you get clouds and then rain.

A number of techniques have long existed to control rain by seeding the atmosphere with small particles of compounds such as dry ice and silver iodide that raindrops can grow around. However, "weather modification techniques have raised quite a lot of skepticism," said physicist Jérôme Kasparian, at the University of Geneva.

This controversy is due to questions of the effectiveness of such cloud seeding. The techniques spread chemicals quite widely, so given the variability of the atmosphere, it can be very difficult to judge how they may have actually affected the atmosphere, Kasparian explained.

Instead, Kasparian and his colleagues now reveal control over moisture using lasers. In experiments with infrared lasers over the Rhone River in Geneva employing a variety of temperatures, humidity levels and other atmospheric conditions, the scientists discovered that beams could trigger the growth of micron-sized water droplets even at a relatively low humidity of 70 percent, though not yet droplets large enough for rain.

"At such humidity, condensation does not occur in natural conditions, where 100 percent relative humidity is necessary," Kasparian told LiveScience.

The secret of these beams lies in how they cause chemicals such as nitric acid — which can serve as cloud seeds — to form in the air. These particles prefer to associate with water molecules, acting as a kind of glue that keeps droplets together in relatively dry conditions that would ordinarily cause them to evaporate away.

The fact that researchers can point their lasers at a well-controlled target and at well-defined times allows comparisons to see just how effective the lasers really are at controlling moisture, unlike current weather modification techniques, Kasparian said.

"We are still far from laser-induced rainmaking," Kasparian said. Lasers can generate watery particles and allow them to grow, "but their size is currently limited to a few microns," he said. "They should be 10 to 100 times larger to produce actual rain."

"Provided the above-mentioned challenges are overcome, rainmaking would not need airborne laser systems," Kasparian said. "The type of lasers we are using can reach working distances of several kilometers, so that the atmosphere can be activated using ground-based lasers."

Kasparian sees no advantage in using lasers in conjunction with other cloud-seeding techniques.

"In fact, producing too many particles can even be counter-productive, since these particles would then compete with each other to condense the moisture available in the atmosphere," he said. "As a result of this competition, each droplet would be restricted to small diameters, insufficient to become raindrops, which fall down to the ground."

One concern regarding such weather control is whether or not one area could use lasers to effectively steal moisture that might ordinarily drift to other areas that need it.

"Let me mention that the laser can condense only a small fraction of the moisture from the air, so that the risk that one country takes all the resource from an air mass is not as serious as what happens with surface water, where it is technically possible to pump most of the water from a river before it crosses a border," Kasparian said.

The scientists detailed their findings online Aug. 30 in the journal Nature Communications.

SOURCE| LiveScience

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