Space Data

Your Router Is Out of Range

We're all familiar with the concept of wireless. Cell phones, and wifi routers and such. We connect much of the world this way, but it does have it's limitations just here on earth, like being in the furthest room form your router makes the speed slow to a crawl. So how the hell are we getting High resolution images back from telescopes in space?

Laserwaves!

Microwaves pass straight through the atmosphere and are suitable for communicating with distant geostationary satellites, while radio waves are suitable for communicating with satellites in low orbit. Research is being done on using lasers for communication too! How fast can these things transmit though?

Commercial Satellites

Launched from Baikonur Cosmodrome, Kazakhstan, on 19 October 2011, Viasat-1 holds the current Guinness book record for Highest capacity communications satellite, at a proven throughput of 134 Gbps! At the time of launch, this single satellite possessed greater capacity than all of the other satellites covering North America added together.

Hubble

Believe it or not, Hubble data was initially stored on the spacecraft. When launched, the storage facilities were old-fashioned reel-to-reel tape recorders, but these were replaced by solid state data storage facilities during servicing missions 2 and 3A. About twice daily, the Hubble Space Telescope radios data to a satellite in the geosynchronous Tracking and Data Relay Satellite System (TDRSS), which then downlinks the science data to one of two 60-foot (18-meter) diameter high-gain microwave antennas located at the White Sands Test Facility in White Sands, New Mexico.

The most recent generation of TDRSS satellites provides ground reception rates of 300 Mbit/s in the Ku- and Ka-bands and 800 Mbit/s in the S-band.

Curiosity

So what about communicating with things that aren't nearby? 225m km away, the Mars curiosity rover has 2.5GB of data on board, less than a typical USB thumb drive, and it can send data back to Earth at 256 kbit/s, but only for 8 minutes/day due to orbital alignment. This means it can send 256 * 8 * 60 = roughly 120MB a day. Which means it would take about 20 days to transfer all 2.5GB of Curiosity’s software data.

New Horizons

Distance and thus signal strength clearly adversely affect transmission speed, and yes that's how bad it gets when you're that far out, 1 kiliobit per second. So New Horizons can only transmit about 10 full-resolution LORRI images per day, and that's only because LORRI's images are amenable to lossless compression, especially now when they contain mostly black space; the original 12mbit images can compress to about 2.5 Megabits without any loss of detail.

Most communication sessions only last about 8 hours, so at 1kbps, you're looking at about 42 minutes per image. If you were to only transmit LORRI data, which you're not (there are other instruments on board), you could maybe transmit 11 images. Though they do have a trick to increase transmission rates, by basically running their Traveling Wave Tube Amplifiers (or TWTAs) simultaneously, so they can almost double the speed to a whopping 1.9 kbit/s!

What's Next?

The future of satellite communication might be lasers. The Lunar Laser Space Terminal (LLST) is an optical communications test payload that flew aboard the LADEE Spacecraft, and demonstrated laser communications from lunar orbit, back to the Lunar Laser Ground Terminal (LLGT) which is located in White Sands, NM and was developed by MIT/Lincoln Laboratory and NASA.

The main goal of LLCD is proving fundamental concepts of laser communications and transferring data at a rate of 622 megabits per second (Mbps), which is about five times the current state-of-the-art from lunar distances.