Coming to a satellite near you: broadband optical communications
Posted on: February 4, 2019

Although microwave and light-based optical communications (i.e., lasers) travel at the same speed (that of light), free-space optical (FSO) transmissions offer a huge advantage over microwave transmissions, especially when it comes to satellite communications and deep-space exploration: bandwidth. Lots of bandwidth.

Because light has a much higher frequency than RF/microwave, it can be modulated at a much higher frequency. Microwave frequencies, such as those most commonly used in satellite and space communications, are in the range 1 GHz to 100 GHz, while light is around 200 THz.  The higher frequency also means the light beam spreads less than the microwave beam, so a much greater fraction of the transmitted power gets captured by the receiver.  This means light can transfer much more data per second.

Which comes in pretty handy when you’re on Mars and you need to stream a video to Houston showing how your Laser-Beam Bread Slicer & Simultaneous Toaster[1] has broken (and for Houston to reply with a fix in time for breakfast). Actually, that kind of bandwidth is also very handy for closer-to-home applications, like exploring the Moon or even chatting with Mission Control from low-Earth orbits.

But this bandwidth doesn’t come easy. First, you’ve got to figure out how to embed all that data onto a laser beam, and then how to not only amplify that beam, but also target it so that your video clip from Mars goes to the correct laser signal receiving unit in Houston—and not some cornfield in Iowa (which could easily happen, given your signal has to travel 35 million miles once you hit ‘Send’).

And then you have to figure out how to optimize the size, weight, and power (SWaP) profile of all this technology so that it doesn’t suck up too much energy or floor space on a satellite or spacecraft (where real estate is really expensive).

These are the kinds of challenges that NASA has been tasking us with recently. We’re designing laser amplification and targeting solutions to help NASA’s Deep-Space Optical Communications (DSOC) program send a satellite to explore 16 Psyche, an asteroid about 150 million miles away, and the NASA ILLUMA-T program to power optical communications with the International Space Station.

Most recently, we’re tackling some of the optical communications challenges facing NASA’s Optical-to-Orion (O2O) program. The Orion spacecraft will carry humans on deep-space explorations, beginning with lunar orbits in a few years. LGS-powered optical comms will help the Orion crew to stream high-definition video and data to Earth as they further explore the Moon—and beyond.

As any astronaut or NASA employee will tell you, “Space is hard.” So are space-based and inter-satellite communications. But at LGS, we like challenges! (And we’re hiring!)

[1] We hope these will have been invented by the time we colonize Mars.

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