The United Launch Alliance Delta IV launch vehicle is set to make another launch attempt on Monday night, following the telemetry signal issue which caused the scrub during Friday’s countdown, along with a late delay to Sunday’s rearranged launch. With the GPS IIF SV-1 spacecraft – the first of a new generation of GPS satellites for the US Air Force – riding as the passenger, the Delta IV’s 18 minute launch window at Cape Canaveral opens at 11:13pm Eastern on Monday night.
The GPS IIF SV-1 satellite is the first of twelve GPS IIF satellites, built by Boeing under a contract which was signed in 1996. Thirty three were originally planned, but this was scaled back in 2001. GPS IIF will be followed by GPS IIIA, which is expected to see its first launch no earlier than 2014. GPS IIF satellites have a mass of around 1,630 kilograms, and are expected to operate for at least twelve years each.
GPS IIF satellites are expected to provide navigation signals which are twice as accurate as those broadcast by their predecessors thanks to the digitalisation of the caesium-based atomic clocks used for timing. Currently only ten of the twelve GPS IIF satellites have been allocated launches.
The new IIF satellites will also broadcast two new signals. One of these will be used for military navigation, known as “M-code”, which is designed to be more resistant to signal jamming. The other is the L5 signal, which was tested aboard the USA-203 satellite last year. Although USA-203 has been able to successfully demonstrate the L5 signal, and hence reserve the band for use by later spacecraft, interference from transmitting L5 data has affected its other signals, and it has still not been declared operational for navigation.
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