Cornell boffin explains Galileo hack

PATIENCE may be a virtue, but impatience has led to a lot of technical breakthroughs.

In January, Mark Psiaki, professor of mechanical and aerospace engineering at Cornell University in Ithaca, NY, and his team of researchers were impatient. Galileo had sent up its first prototype satellite, and Psiaki wanted the codes that would let his team begin testing receivers they hoped would work with the new system.

"We thought we were all ready to go with a receiver design, and we wanted to present it at a conference in September," he said.

Psiaki was working on a receiver intended to work with both GPS and its European civil successor, Galileo, which together will considerably expand today's global navigation satellite systems. Galileo will deploy some 30 satellites between 2008 and 2010. GPS satellites, which nominally last seven years, will gradually be replaced and upgraded. "It will be at least 2014 or 2015 before they have anywhere near the new capabilities that Galileo will have," said Psiaki.

By then, the market should be filled with receivers that work with both systems to give better coverage than is possible now with GPS alone.

"Even next year," said Psiaki, "when more satellites are launched, it would probably be an advertising plus for a receiver manufacturer to say 'this is a Galileo-capable receiver'. Why would you want to buy a receiver that in three years won't do more than it does now?"

So you want your designs to be ready. And despite requests to the Galileo folks, Psiaki couldn't get the codes the team needed to test the receiver.

Navigation satellites use codes known as pseudo-random numbers (PRNs) to identify themselves so that multiple satellites can transmit on the same frequencies without interfering with each other - think an ADSL microfilter, or perhaps two conversations over the same phone conversation, one in Chinese and one in English. The PRN codes also, said Psiaki, "allow precise timing of when a part of the signal left the satellite and when it gets to the receiver." The length of the interval gives you a range of locations; when you repeat the exercise with three satellites, you know where you are. But you have to know the PRN codes in order to identify the signal you want - and Galileo wasn't revealing them even for the supposedly free part of the service.

Colleagues in Europe were having no better luck.

So his team cracked them and published the codes and the details of how they did it on April 1. Within a couple of days other researchers had downloaded the codes and begun using them. "We were worried that they'd change the codes after we cracked them," he said. But so far, that hasn't happened.

Even so, "Everyone knows this is not the final version," said Psiaki, "but we can test a lot of difficult and important stuff with this signal."

Such as: monitoring the ionosphere, for which Psiaki has a contract from NASA. "There are scintillations where the ionosphere becomes turbulent over Brazil or over the Equator after dark. We have known this for a while, but we're starting to uncover more aspects of how that happens, so we're working on using Galileo and GPS to develop techniques whereby we might image it. We have to develop receivers, Galileo has to launch all its satellites. These are projects that will take years to see fruition. For the man in the street, space weather can affect power networks, communications, and GPS itself. Oil rigs in Brazil use GPS to maintain the right positioning and stay hooked up to the wellhead on the sea floor, and sometimes after dark it just goes bananas."

The upshot is that despite cracking and publishing the codes, Psiaki really doesn't want anything bad to happen to Galileo as a result. "I and a lot of people want Galileo to succeed," he says. "But we don't want to be shut out." µ