Dot Mars (The Economist)

Dot Mars

Jun 4th 2009 
From The Economist print edition

http://www.economist.com/research/articlesBySubject/displayStory.cfm?story_id=13725833&subjectID=348963&fsrc=nwl

Computing: A modified version of the internet's communications protocol, devised for interplanetary use, is being tested by spacecraft

Illustration by Belle Mellor

CYBERSPACE is noisy, chatty and well-connected. Space, by contrast, is not. Communication between Earth and spacecraft is clunky and reminiscent of the days when switchboard operators had to plug in telephone lines by hand to connect the people at either end. But that is now about to change. America's space agency, NASA, has been researching what it calls the delay- (or disruption-) tolerant network protocol, or DTN. The idea is to introduce to space the automated protocols that enable seamless communication on the terrestrial internet.

Communicating in space is quite different from the constant flow of information on Earth, where a buzz of greetings, acknowledgments and farewells flits between computers as they locate each other, exchange data and then disconnect. Space communication happens in distinct jumps, and requires a "store and forward" system that can retain information at each step in the process. For example, if a rover on Mars needs to send data to Earth, it would first need to store the data until it was within range of an orbiting satellite. After receiving the data, that satellite would hold the information until it could be sent on the next hop towards Earth.

Sending data from Earth to Mars and back can take anywhere between three-and-a-half and 20 minutes, depending on the positions of the planets and whether they are facing each other in their respective rotations. As a result, scientists have to plan when to send data. The DTN is an attempt to automate that process. "The idea would be that you could send data from France to Mars in a seamless way," says Adrian Hooke, a NASA scientist based in Washington, DC, who has been developing the protocol over the past decade with Vint Cerf of Google, a founding father of the internet, and others.

In November 2008 NASA conducted the first test of DTN. It installed software on EPOXI, a NASA probe orbiting the sun roughly 32m kilometres (20m miles) from Earth, and used it to transfer data between the probe and the planet. NASA is now poised to install newer versions of this software on the same probe and on the International Space Station. The software will be sent to the EPOXI computers using powerful antennas at three bases in California, Canberra and Madrid. Uploading this one-megabyte software update takes around an hour, so its speed is comparable to that of a 1990s modem connection. If all goes well Dr Cerf says that by September there should be three nodes on the interplanetary network—including Earth.

Researchers at Ohio University are already distributing a version of what is known as the DTN protocol stack, so that computer programmers can write programs that will use this new protocol. It will require new e-mail clients, web browsers and file-transfer programs that could be used on the International Space Station or other future manned space missions, and which can interact with other nodes on the interplanetary network and the terrestrial internet. It will also require changes to the internet's domain-naming system, so that scientists can simply send e-mail messages torover@nasa.gov.mars.