NavList:

There's also coverage and a nice map of the flight plan on the BBC website here. In the photo below, you can see "E3" on the tarmac. Assuming that this photo was taken at "Spaceport Cornwall", this places the 747 carrier aircraft exactly where it should be: right on the "B747 STOP" marker that was visible in the second image of my original post on this topic. Launch is expected around 4-7pm Eastern US time (9pm-midnight in Cornwall). The probability of a scrub (cancellation) tonight is relatively high. There's a lot at stake in terms of commercial and national reputation. I would give only 1-in-3 odds of a launch tonight, meaning making it all the way to "rocket release" from the 747 at high altitude over the Atlantic near Ireland.

If successful this will be the first satellite launch from the UK and the first from western Europe. While many sounding rockets on sub-orbital trajectories have launched successfully from many countries in western Europe for decades, this is a first for an orbital launch. It's also true that the UK launched a single satellite on a British-built rocket in 1971, but its launch site was in Australia. Satellites have been launched by western European agencies for decades (mostly from Kourou in French Guiana) and of course Russia counts as Europe so thousands of satellites have been launched "by Europeans" since the very dawn of the Space Age. And for that matter the first sub-orbital rockets to reach the edge of space were... ahem... German, beginning in 1942.

How do we suppose tonight's rocket navigates after it's dropped from the 747? Just GPS? What happens if the signal is jammed? Early ballistic missiles, like the Polaris submarine-launched nuclear missiles, used celestial-aided inertial navigation. Do such missiles still use celestial? In the early 1950s, there was even speculation about getting position fixes by "lunars" in missile navigation systems (a non-starter in practical terms, but an interesting idea). 

Frank Reed

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