The many paths a message can take through the Internet make that network robust and efficient -- and the envy of those whose job it is to design communications schemes for the far-flung spacecraft leaving Earth each year. After more than a decade of development, NASA is in a rush to have a communications network ready by 2011 that can efficiently carry data between Earth and the multiple probes, rovers, orbiters and spacecraft exploring the solar system -- effectively binding them together to form an interplanetary Internet. Tests performed on the International Space Station last May were the second of three tryouts of the network's key technologies, called Delay Tolerant Networking, or DTN, protocols.
The DTN protocols will extend the terrestrial Internet into space by overcoming a number of obstacles, including the extraordinary length of time it takes packets to move between separate hops in a deep-space network, the intermittent nature of network connections, and bit-scrambling solar radiation.
"The communication delays are huge, and they are variable, because the planets are in orbit around the sun," says Vint Cerf, co-inventor of the Internet's TCP/IP protocol and a key member of a group of computer scientists who began working on DTN in 1998. On Earth, packets move from source to destination in milliseconds. By contrast, a one-way trip from Earth to Mars takes a minimum of 8 minutes. The constant motion of celestial bodies means that packets have to pause and wait for antennas to align as they hop from planet to probe to spacecraft.
So sending communications in space is very different from doing so on Earth, where the stable topology of the Internet is taken for granted.
"What we have to do instead is to tell all the nodes that these are the changes that are going to occur," says Scott Burleigh, a software engineer at NASA's Jet Propulsion Laboratory, in Pasadena, Calif., and one of the original developers of DTN. "You are going to be able to communicate from A to B at this data rate starting at 12:30 and ending at 3:30, and then you are not going to be able to communicate on that link anymore... until next Tuesday."
The DTN protocols will extend the terrestrial Internet into space by overcoming a number of obstacles, including the extraordinary length of time it takes packets to move between separate hops in a deep-space network, the intermittent nature of network connections, and bit-scrambling solar radiation.
"The communication delays are huge, and they are variable, because the planets are in orbit around the sun," says Vint Cerf, co-inventor of the Internet's TCP/IP protocol and a key member of a group of computer scientists who began working on DTN in 1998. On Earth, packets move from source to destination in milliseconds. By contrast, a one-way trip from Earth to Mars takes a minimum of 8 minutes. The constant motion of celestial bodies means that packets have to pause and wait for antennas to align as they hop from planet to probe to spacecraft.
So sending communications in space is very different from doing so on Earth, where the stable topology of the Internet is taken for granted.
"What we have to do instead is to tell all the nodes that these are the changes that are going to occur," says Scott Burleigh, a software engineer at NASA's Jet Propulsion Laboratory, in Pasadena, Calif., and one of the original developers of DTN. "You are going to be able to communicate from A to B at this data rate starting at 12:30 and ending at 3:30, and then you are not going to be able to communicate on that link anymore... until next Tuesday."
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