Interplanetary Internet

has successfully tested a deep space communications network it's calling the Interplanetary Internet.

Working as part of a NASA-wide team, engineers from NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California used Disruption-Tolerant Networking, or DTN, to transmit dozens of space images to and from a NASA science spacecraft located about 20 million miles from Earth.

NASA and Vint Cerf, a vice president at Google, joined forces 10 years ago to develop the DTN software protocol that sends information using a method that differs radically from the normal internet's transmission-control protocol/internet protocol, or TCP/IP, communication suite, which Cerf co-designed.

Any communications protocol used in space must be robust to withstand delays, disruptions and disconnections. Glitches can happen when a spacecraft moves behind a planet, or when solar storms and long communication delays occur. The delay in sending or receiving data from Mars, for example, takes between three-and-a-half to 20 minutes at the speed of light.

For that reason, the DTN does not assume a continuous end-to-end connection like TCP/IP. In its design, if a destination path cannot be found, the data packets are not discarded. Instead, each network node keeps the information until it can communicate safely with another node. This store-and-forward method means information does not get lost when no immediate path to the destination exists. Eventually, the information is delivered to the end user.

‘In space today, an operations team must manually schedule each link and generate all the commands to specify which data to send, when to send it, and where to send it,’ said Leigh Torgerson, manager of the DTN Experiment Operations Center at JPL. ‘With DTN, this can all be done automatically.’

Engineers began a month-long series of DTN demonstrations in October. Data was transmitted using NASA's deep space network in demonstrations occurring twice a week.

There are 10 nodes on the network: one is the Epoxi spacecraft, which is on a mission to encounter Comet Hartley 2 in two years, and the other nine are on the ground at JPL, simulating Mars landers, orbiters and ground mission operations centres.

The month-long experiment is the first in a series of planned demonstrations to qualify the technology for use on a variety of upcoming space missions. In the next round of testing scheduled to begin next summer, DTN software will be loaded on board the International Space Station.