Networking deep space should be a priority for future missions. If we can set up robust networking between spacecraft, we relieve the Deep Space Network of a huge burden, that of having to communicate directly with each spacecraft for tasks that are essentially routine. No more maneuvering huge dishes to catch one fleeting signal, at least not for missions to come. Instead, we could rely on spacecraft to create their own file transfers, move their own traffic to astronauts (remember the video mail in 2001: A Space Odyssey?), and manage local operations.
Why not use the Internet we’ve already got? Unfortunately, the TCP/IP (Transmission Control Protocol/Internet Protocol) tools we use today are ‘chatty,’ a term that means the computers that run them exchange data over and over again through the course of a transaction. Suppose you want to send a file through FTP (File Transfer Protocol). Doing so takes eight round trips of data between the computers involved before the file can be sent. Not only that, but FTP will time out after a few minutes of inactivity. Try that on a target that’s ten light hours away and the delay times will stretch a routine file swap into a multi-day event.
Vinton Cerf, the visionary behind the original TCP/IP work (and now a Google vice president), has been developing new protocols to handle this problem for a decade. The term to master is Disruption-Tolerant Networking (DTN), and it’s just been through a successful shakedown. Because DTN assumes no continuous connection, it uses store-and-forward methods to hold data until they can be sent. Says Leigh Torgerson (JPL):
“In space today, an operations team has to manually schedule each link and generate all the commands to specify which data to send, when to send it, and where to send it. With standardized DTN, this can all be done automatically.”
It’s satisfying to learn that the EPOXI spacecraft, part of the extended mission of the original Deep Impact vehicle, is one of the nodes on the nascent network, the other nine being simulated spacecraft run through the Jet Propulsion Laboratory. The goal is to get the technology ready for regular use, with a new round of testing scheduled for the International Space Station next summer. And EPOXI, which runs the EPOCH (Extrasolar Planet Observation and Characterization) observing program, adds a nice touch of interstellar drama to the first round, even though the spacecraft itself is, at 32 million kilometers, relatively close to home.
The first intensive use of interplanetary networking is surely going to occur around Mars, where landers can communicate with rovers and the satellites orbiting above. But it’s interesting from the point of view of pure communications that the DTN techniques could have uses here on Earth, particularly in areas where Internet access is needed but sender and receiver may have entirely different schedules. Until Net access is ubiquitous, there will be many places on this planet that can benefit from a system that knows enough to hold data until a signal is available.