The Interplanetary Internet

Toby Howard

This article first appeared in Personal Computer World magazine, November 1998.

IT'S TWENTY YEARS since Vint Cerf co-invented TCP/IP, the standard data code which made the modern Internet possible. Having watched the Internet grow from a few interconnected academic computers to today's world-circling Web, Cerf now has a bigger idea. He plans to take cyberspace into outer space.

Cerf has just been appointed Distinguished Visiting Scientist at NASA's Jet Propulsion Laboratory in Pasadena, California. Together with Adrian Hooke, manager of NASA's Space Mission Operation and Standardization Program, Cerf's brief is to find a way to merge the work of the space communications and Internet communities. Just as the Web provides an integrated interface to the data moving across the Internet, whether it encodes pictures, sound, text or software, Cerf envisions a solar system-wide Web, unifying space communications.

NASA sees this "Interplanetary Internet", or "InterPlaNet", as the future of outer-space communications. Currently, space comms technology encodes data in different ways to suit particular mission requirements. There are no multimedia standards like on the Internet; no point-and-click interfaces to download video clips or retrieve data files; no standard mechanisms to upload new programs to control spacecraft or planetary landers.

"It took 20 years for the Internet to take off here on Earth," Cerf said recently. "It's my guess that in the next 20 years, we will want to interact with systems and people visiting the Moon, Mars and possibly other celestial bodies". NASA is already convinced: it wants to employ the Interplanetary Internet in its forthcoming Mars missions, and has plans to leave special satellites in orbit as the first step to creating Internet servers in space.

But Cerf's vision is as technically demanding as it's fascinating. Just as the terrestrial Internet brings together smaller networks in cities and countries, the goal of the Interplanetary Internet is to link together Internets on different planets and their moons. Special interplanetary "gateways" will convert the Interplanetary Internet data protocols to conventional TCP/IP, connecting -- in NASA-speak -- dirt-side to space-side.

Like its terrestrial predecessor, the Interplanetary Internet will need a robust data transmission protocol. Traditional TCP/IP won't do, because transferring data across space has its own special problems. First there's interference. As far as man-made radio waves are concerned, empty space is a very noisy place. As well as the natural radio emissions from stars and planets, cosmic rays cause unpredictable distortions in spacecraft transmissions. A more serious problem is the time-lag which results from the vast distances involved, and nature's unbreakable limit of the speed of light. A radio signal transmitted from Mars, for example, takes several minutes to reach Earth, and the transfer time varies constantly as both planets move in their respective orbits around the sun. Move further out and the time lags increase dramatically: a radio signal beamed to Pluto takes at least six hours to get there.

Cerf is confident the technical problems are soluble. "The time has come to think beyond the Earth", he says. But some people worry about taking the Web into space, fearing that we might be exposing ourselves a little too much to scrutiny by extra-terrestrials. It's not quite as daft as it sounds. Suppose aliens spot our planet and want to eavesdrop on us. The Web is a perfect resource for them, far better than fiddly radio and TV transmissions, which bubble out in spheres of ever-decreasing intensity. The Web just sits there with its data intact, surely accessible to any alien with the latest quantum snooping gear. Take the Web into space, and we really start advertising our presence. One day ET will surely say hello. Let's hope the email is friendly.

Toby Howard teaches at the University of Manchester.