Image: Interplanetary Internet
Click to launch a graphic presentation about how the earthly Internet would be adapted to interplanetary communications.
By Alan Boyle Science editor

NASA and network gurus are working together to extend the Internet to other worlds in the next few years. But there are some limits that not even the World Wide Web can route around, such as the speed of light. So the builders of the Interplanetary Internet are going back to the basics, retooling protocols for future communications with Mars and beyond.

For the past two years, the vision of the Interplanetary Internet has been championed by such visionaries as Vinton Cerf, one of the Internet’s founding fathers.

“I started thinking about how long it had taken to get the Internet where it is,” Cerf told MSNBC. “I was reflecting on the fact that it had taken almost 25 years to get to where we are now, and although it’s growing by leaps and bounds, it’s still pretty small compared to the telephone system.

“So I got to thinking, what should I be worried about that might be important 20 years from now?” he said.

Cerf started talking about extending networks to other planets, and soon found that NASA’s Jet Propulsion Laboratory was working on the same challenge. Today, engineers from the space agency and several networking companies are adapting Internet architecture to space communications, with funding from NASA as well as the Defense Advanced Research Projects Agency’s Next Generation Internet project.

Robotic rationale
Why do it? It’s not just so Mars colonists can hear a cheery “you’ve got mail” from their computers in 2040 - although space experts say a sense of connectedness could be important in combating the isolation of long-duration missions. At least in the short term, the frontiers of the Interplanetary Net will belong to robots rather than humans.

In fact, Adrian Hooke of NASA’s Jet Propulsion Laboratory argues that the infant Interplanetary Internet is already in action, just as ARPANET prefigured what we now know as the Internet. More than 100 space missions have signed up to use protocols standardized by the international Consultative Committee for Space Data Systems.

The current studies are defining “how we need to grow and expand these underpinnings over the next 20-odd years, i.e., what new protocols and communications capabilities we will need,” he said in an e-mail exchange.

The road ahead
Standardization is just one of the driving forces behind the Interplanetary Net. NASA is moving toward “faster, cheaper, better” space probes - and more of them. If off-the-shelf technologies can be adapted to those robotic missions, so much the better.

“We steal what we can, bend when we need to, and as a last resort start over and design something from scratch. But that’s so expensive that it’s something we don’t want to do,” said Hooke, who is manager of NASA’s space mission operations standardization program.

Lessons gained from the growth of the Internet - and particularly wireless networking - can keep NASA from having to reinvent the wheel as space missions proliferate, Hooke explained.

Problems and solutions
But there’s a big difference between using the Internet on Earth and connecting with Mars — a minimum of 34.6 million miles of difference, to be specific. Even at the speed of light, it takes radio signals three minutes to travel that far. And since the distance between Mars and Earth is constantly changing, the travel time could be as long as 20 minutes.

Those kinds of time delays would wreak havoc on a classical Internet, said Bob Durst, an engineer at Mitre Corp. who is working on the architecture for the Interplanetary Net, also known as the IPN.

“The Internet suite is pretty heavily based on the notion of interactivity,” he explained. Communicating computers trade signals back and forth on a scale of milliseconds, checking to make sure packets are received intact and re-sending them if necessary.

“That’s real handy for us when you’re in a terrestrial environment, but when you get into round-trip times of 10 minutes, that just doesn’t work,” Durst said. “You can’t take delays much past five minutes or so.”

To cope with this cosmic speed limit, network architects envision a “network of Internets,” linked together with new protocols. They draw comparisons to the Pony Express and United Parcel Service.

“We need to distill out all the interactivity and bundle up all the information into a single transaction that has everything needed to process the information, either interactively or noninteractively, on the other side,” Durst said.

Each planet would have a gateway to manage data traffic over the interplanetary backbone. For example, NASA’s Deep Space Network, which NASA uses now to communicate with distant probes like Galileo, could be the gateway for Earth.

“It’s like dropping a package at UPS,” Durst said. “The notion is that you submit your data in the form of a bundle to a gateway that says, ‘I’m going to accept your data ... here’s a claim ticket, and I’ll let you know when it’s there ... if you want to be notified.’”

To use another comparison, the Interplanetary Internet would be like e-mail: Mission controllers would entrust their transmissions to the Net gateway, with a “soft expectation” that the bundle of data will eventually get to the right destination.

Some other twists will be required: Bandwidth and memory are extremely limited when you go beyond Earth, so engineers want to avoid having to keep an updated Internet address book on every spacecraft. Instead, data traffic would be routed to the proper gateway (say, “earth.sol” or “mars.sol”). The gateway would then figure out how to get it to the exact address specified by the sender.

Also, since celestial objects are constantly moving in relation to each other, the communication paths between gateways will have to stretch and turn like a cat’s cradle between a child’s moving fingers. That’s where the experience of wireless telecom providers like Iridium and Teledesic will come in handy, Hooke said.

Security is another big concern: What’s to stop someone from hacking into Mars’ interplanetary gateway?

“We’re making assumptions that because the bandwidth is still going to be precious ... access to the Interplanetary Internet is something that needs to be mediated,” replied Howard Weiss, an engineer at Sparta Corp.

That means not everyone will be allowed to send messages to rover@pathfinder.mars.sol, at least in the short term. NASA’s Deep Space Network will still be limited, although one company is working on a secure Web-based system for controlling spacecraft from laptop computers.

Weiss said the lack of interactivity over so-called “bundle space” means that the latest crypto protocols, based on public-key exchange, can’t be used. “We’re going to have to go back to the good old golden days ... and use things like pre-shared keys,” he said.

Other time-honored protocols such as BitNet and UUCP - which provided the foundation for newsgroups - also may be adapted, said Eric Travis, an engineer at Global Science and Technology.

What the net will do
When it comes to putting these networking theories in practice, all eyes turn to Mars. “Think of it as the first stop on the Interplanetary Internet,” said Chad Edwards, manager of the Mars Network Project Office at the Jet Propulsion Laboratory.

NASA’s Hooke said the Mars lander and orbiter, both due to be launched in 2001, would communicate with each other using their own style of “Internet service,” but Edwards’ project would build a real telecom constellation around the Red Planet. The telecom satellites could hitch rides on Mars missions every two years, beginning in 2003.

“As his Mars Network constellation builds up, we will progressively add more IPN-derived standard protocols to his communications suite,” Hooke said. “We will also try to start infusing regular terrestrial Internet capabilities into the Mars rover and lander missions as we get the chance, probably starting about 2005.”

The Mars Network could greatly increase the data flow back to Earth, Edwards said.

Back in 1997, Mars Pathfinder could only send 30 megabits of data per day back to Earth, which averages out to 300 bits per second, he said. In contrast, typical modems on personal computers transmit data at rates up to 56,000 bits per second.

The Mars Network could relay data at more than 30 times Pathfinder’s rate, or an average of 11,000 bits per second. That is enough to send back a full-resolution, 360-degree panorama of the Red Planet every day.

By 2007, Edwards said, there could be a “permanent robotic presence” on Mars, pumping data back and forth using Internet protocols, and communicating with Earth via a central gateway.

He even envisions a relay satellite flying 10,625 miles (17,000 kilometers) above Mars, in an orbit stationary with respect to the Red Planet. Such a satellite could transmit 1 megabit of data per second, enough for a continuous video feed via the Mars Channel.

That kind of bandwidth also could be used to send back a detailed virtual-reality representation of the Martian surface - in a sense, allowing scientists and sightseers to study Mars without leaving Earth.

“The public may just want to go for a walk on Mars. ... And with a gigabit of data, I can bring a rock from Mars to here, plop it in front of a field geologist and let him look at it,” Edwards said.

Although this may sound like blue-sky thinking, it’s not too early to lay the technical foundation for the reality yet to be, Hooke said. And he’s hoping that the next generation will help out with what he views as one of this world’s most intriguing research projects.

“There are some great Ph.D.s to be mined here,” he said. “This is cool technology.”

Hooke already has written the International Organization for Standardization in Geneva to ask what would be required to set up “earth.sol” and “moon.sol” superdomains.

“It provoked an interesting exchange with those guys,” he said. “They said I essentially had to get the sovereign representatives of the moon and the earth to write them a letter.”

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