Thursday, March 14, 2013

Now How Long Did This Take?

In 1967 I had designed a star tracking system used on the X 15 to managed updating the gyro for position location. We used a photomultiplier tube to scan and lock on to Polaris, the north star, and the earth's limb. It allowed precision position updates.

The in 1975 I added an optical, infrared, laser link between two Intelsat satellites as an option. We had designed the system and Bob Kennedy had delivered a detailed system design.

Now in 2013 I see the MIT Lincoln is finally adding an infrared link to a satellite to improve communications to earth from the satellite. Eureka states:

The LLCD mission will use a highly reliable infrared laser, similar to those used to bring high-speed data over fiber optic cables into our workplaces and homes. Data, sent in the form of hundreds of millions of short pulses of light every second, will be sent by the LADEE spacecraft to any one of three ground telescopes in New Mexico, California and Spain.

The real challenge of LLCD will be to point its very narrow laser beam accurately to ground stations across a distance of approximately 238,900 miles while moving. Failure to do so would cause a dropped signal or loss of communication.

"This pointing challenge is the equivalent of a golfer hitting a 'hole-in-one' from a distance of almost five miles," said Cornwell. "Developers at the Massachusetts Institute of Technology's (MIT) Lincoln Laboratory have designed a sophisticated system to cancel out the slightest spacecraft vibrations. This is in addition to dealing with other challenges of pointing and tracking the system from such a distance. We are excited about these advancements."

The LLCD mission will also serve as a pathfinder for the 2017 launch of NASA's Laser Communication Relay Demonstration (LCRD). That mission will demonstrate the long-term viability of laser communication from a geostationary relay satellite to Earth. In a geostationary orbit the spacecraft orbits at the same speed as Earth, which allows it to maintain the same position in the sky.

My only comments is that 40 years ago we demonstrated this, yes when I was also working at Lincoln.  I just wonder what took so long.