NASA has successfully tested the first deep-space communications network modeled on the Internet. Part of a NASAwide team, engineers from the Jet Propulsion Laboratory in Pasadena, CA, used software called Disruption-Tolerant Networking (DTN) to transmit dozens of space images to and from a NASA science spacecraft located more than 20 million miles from Earth.
NASA and Vint Cerf, vice president at Google, partnered ten years ago to develop this software protocol. The DTN sends information using a method that differs from the normal Internet’s Transmission-Control Protocol/Internet Protocol (TCP/IP) communication suite, which Cerf co-designed. The Interplanetary Internet must withstand delays, disruptions, and disconnections in space. 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 takes between 3 and 20 minutes at the speed of light.
Unlike TCP/IP, the DTN does not assume a continuous endto- end connection. If a destination path can’t be found, the data packets are not discarded. Instead, each network node keeps custody of the information as long as necessary until it can safely communicate with another node. This store-and-forward method means that information does not get lost when no immediate path to the destination exists. Eventually, the information is delivered to the end user.
Engineers began a month-long series of DTN demonstrations last October. Data were transmitted using NASA’s Deep Space Network in demonstrations occurring twice a week. Engineers used NASA’s Epoxi spacecraft as a Mars data-relay orbiter. Epoxi is on a mission to encounter Comet Hartley 2 in two years.
The 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, a NASA-wide demonstration using new DTN software loaded on board the International Space Station is scheduled to begin this summer. In the next few years, the Interplanetary Internet could enable many new types of space missions. Complex missions involving multiple landed, mobile, and orbiting spacecraft will be far easier to support through the use of the Interplanetary Internet. It could also ensure reliable communications for astronauts on the surface of the Moon.
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