An Internet available for space

NASA has successfully conducted the first deep-space test of a communication protocol that could serve as the foundation of an interplanetary Internet.

Today, NASA's information superhighway to outer space flows through one major gateway - the Deep Space Network - to a host of space probes, scattered all the way out from Earth orbit to the edge of the solar system. As those probes proliferate, the Deep Space Network has to keep up with an increasingly complex communications schedule.

Hooke's team has been developing new networking tools to cope with the increasing load and the usual glitches and time delays that space missions have to weather. Those tools include a communication protocol known as DTN (which stands for Delay-Tolerant Networking or, more recently, Disruption-Tolerant Networking).

The four-decade-old protocols that rule the Internet, known as the TCP/IP communications suite, are designed to work over a continuous end-to-end connection between the various parts of the network. That isn't well-suited for Earth-to-Mars communications, where the delay between sending a message and having it received can run as long as 20 minutes. And that's assuming that the antennas on both sides of the signal are working.

DTN is designed to accommodate a store-and-forward system, with built-in smarts. If one link in a communication chain is broken, a robot on Mars could decide for itself the next-best way to get its data back to Earth.

"By making the best use of the contacts you've got, you can smooth out the load on the network, and avoid having the network just loitering on one spacecraft," said Hooke, who is manager of space-networking architecture, technology and standards at NASA Headquarters.
For years, engineers on Hooke's team have been working with other network experts to wring the bugs out of DTN, through a series of earthly pilot projects. Hooke said the protocol has been used by Laplanders herding reindeer on snowmobiles, as well as cell-phone users on the bleeding edges of their coverage areas. It's even being deployed by the Pentagon for battlefield communications.

Last summer, the UK-DMC satellite used the protocol to send sensor data down from Earth orbit to a British ground station and onward to NASA's Glenn Research Center in Ohio. That set the stage for October's monthlong deep-space test, involving NASA's Epoxi spacecraft.

The next step would be to install the software on the international space station, creating a permanent DTN node in Earth orbit. "These flight demonstrations are really important, because they show the thing working in a real mission environment," Hooke said.

It's hard to predict exactly when DTN will be needed for deep-space communications. Over the past decade, the "mission density" hasn't been heavy enough to require networks built to tolerate significant disruptions, Hooke said. But that time will come someday. Hooke just hopes that DTN will be fully tested and standardized by the time NASA starts building up networks of landers, orbiters and sensors, all talking amongst themselves.

"With Mars, we've already seen point-to-point-to-point archtecture," he noted, referring to the use of NASA's Mars Odyssey orbiter and Mars Reconnaissance Orbiter as relay satellites for Phoenix Mars Lander.