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- It doesn't take a crazy leap of imagination to consider
the solar system sprinkled with astronauts in the coming century. There
may be a permanent base on the moon, mining projects in the asteroid belt,
a fledgling colony on Mars, and exploratory robotic spacecraft probing
Venus, Pluto and the moons of Saturn and Jupiter.
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- An unanswered question is how will all these pioneering
outposts communicate with each other and with folks back home on Earth.
The complications are many. Each station will be whizzing around the solar
system at different speeds in different orbits, separated by distances
that take radio signals anywhere from a few seconds to tens of hours to
cross. Sometimes the points are close, as when Mars and Earth approach
each other on the same side of the sun, other times they are at opposite
sides of the solar system separated by trillions of miles and a giant fiery
sun.
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- Until now NASA missions have always set up radio and,
in some cases, television communications mission by mission. A future where
human projects populate the solar system, though, will require much more
intricate and full-service infrastructures.
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- Enter the Interplanetary Internet -- a futuristic web
of radio-linked computer networks deployed across the solar system.
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- NASA's Jet Propulsion Laboratory embarked last week on
a project to devise standards for the Interplanetary Internet. The plan
will essentially take small pieces of the Internet as it exists on Earth
and deploy them throughout the solar system, linking them together through
gateways, which may be orbiting satellites that function somewhat like
servers.
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- The project is being funded by NASA and the Defense Advanced
Research Projects Agency, the group that in the 1960s pioneered the development
of the Internet. Managed by JPL, the project will incorporate the knowledge
of scientists and engineers from universities, government agencies and
private industry. Vinton Cerf, the computer scientist often called the
"father of the Internet," for his role in developing the TCP/IP
protocol that governs Internet communications, is playing a key role.
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- The protocol is the method computers use to talk with
each other. The Interplanetary Internet will require a new protocol that
overcomes several problems unique to transmitting radio signals through
long distances in space, said Adrian Hooke, manager of NASA's Space Mission
Operations Standarization Program. Hooke plays a leading role in the Interplanetary
Internet project.
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- "Most protocols on the Internet operate in a mode
where you essentially send a bunch of data and then you wait for an acknowledgement
that those data got there, then if they didn't get there you back up and
retransmit them," Hooke explained. Transmitting over the huge distances
of space, this method of communicating becomes completely inappropriate,
because the radio signals take so long to travel from point to point. "You
end up in a stacatto mode of operating," Hooke said.
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- In addition to the long time delay in space, other basic
problems that make the current internet protocol inappropriate for interplanetary
communications are the high noise of radio transmissions, and the fact
that continuous connections are impossible in space.
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- Even a spacecraft orbiting Earth has to use several radio
relay stations to keep in contact with mission control. For a scientist
in a space station on the moon to maintain contact with a spacecraft orbiting
Jupiter would be even more difficult. At one moment the call might need
to be relayed through a station on Mercury, and an hour later It might
pass through a gateway in Mars orbit.
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- The entire network would be a very complex web of relay
stations.
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- "It's kind of like one of those cat's cradle elastic-band
things," Hooke said. "Everything's moving. All these links are
coming and going and seeing each other and getting obscured, and somehow
you want to be able to simplify out of that a reliable communications backbone.
That is a humongous job in terms of scheduling and modeling and planning
how those links become available."
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- While a great deal of research must be done on the subject
of routing signals through the solar system, many of the technologies being
developed on Earth already address some of the communications challenges,
Hooke said.
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- For instance, sending e-mail from a laptop computer in
a moving car, through a cellular phone network to a hard-wired personal
computer is similar to the trouble of communicating with a moving spacecraft.
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- What the new JPL project is trying to do is to take the
technologies that are emerging for wireless and satellite communications
on Earth and move them off the planet. The task is to organize various
research groups to develop standardized procedures and protocols that will
make the Internet work in space, Hooke said. It requires detailed cooperation
between the space communications community and the groups that set standards
for Internet communications.
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- Eventually, Hooke envisions robotic rovers on Mars, surface
landers, orbiting satellites, high altitude balloons and even exploratory
aircraft to be able to exchange information and communicate with all engaged
in scientific studies, will be able to communicate with human controllers
on Mars and back on Earth.
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