* Astronomy

Travellers have relied on accurate timekeeping for navigation since the development of the marine chronometer in the eighteenth century. Galileo, Europes twenty-first century navigation system, also relies on clocks but they are millions of times more accurate than those earlier timepieces.
 The operational Galileo satellites will carry two types of clocks passive hydrogen masers and rubidium atomic frequency standards. Each satellite will be equipped with two hydrogen masers, one of which will be the primary reference for generating the navigation signals, with the other as a cold (non-operating) spare.
 Every operational satellite will also carry two rubidium clocks, one of which will be a hot (permanently running) backup for the operational hydrogen maser, instantly taking over should the maser fail and allowing signal generation to continue uninterrupted. The second rubidium clock will act as a cold spare.
 
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Earlier this week, GIOVE-A successfully transmitted its first navigation message, containing the information needed by user receivers to calculate their position. Prior to reaching this milestone, the satellite had been broadcasting only the data needed for measuring the receiver-to-satellite distance.
The first Galileo navigation message was created by the navigation signal generator unit on board GIOVE-A, using content prepared by the GIOVE Mission Segment. This week-one navigation message was uplinked to GIOVE-A on 2 May from the Guildford ground station operated by Surrey Satellite Technology Ltd (United Kingdom) and then transmitted from the spacecraft to the users. The objective of the test was to demonstrate an end-to-end link between the Mission Segment and the user receivers. The navigation message is being generated for demonstration purposes only no service guarantee is provided.

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India’s participation in the Galileo project, a satellite navigation system being developed by EU and European Space Agency, expected to rival the United States’ GPS (global positioning system), has run into the hard ground realities of security concerns. India fears that sharing of sensitive data may not be adequately firewalled from individuals and other nations participating in the enterprise.

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Members of Cornell's Global Positioning System (GPS) Laboratory have cracked the so-called pseudo random number (PRN) codes of Europe's first global navigation satellite, despite efforts to keep the codes secret. That means free access for consumers who use navigation devices -- including handheld receivers and systems installed in vehicles -- that need PRNs to listen to satellites.

The codes and the methods used to extract them were published in the June issue of GPS World.

Because GPS satellites, which were put into orbit by the Department of Defence, are funded by U.S. taxpayers, the signal is free -- consumers need only purchase a receiver. Galileo, on the other hand, must make money to reimburse its investors -- presumably by charging a fee for PRN codes. Because Galileo and GPS will share frequency bandwidths, Europe and the United States signed an agreement whereby some of Galileo's PRN codes must be "open source." Nevertheless, after broadcasting its first signals on Jan. 12, 2006, none of GIOVE-A's codes had been made public.

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