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23-Apr-04 | Delta flight 304 – Gravity Probe B

The second attempt at launching Gravity Probe B was a complete success, marking the 57th consecutive successful launch for Delta II.

A perfectly uneventful terminal countdown allowed the two-stage Delta 7920 to leave Pad 2W at Vandenberg at the exact time of its launch window, with an offical range liftoff time of 16:57:23.734 GMT.

All systems functioned nominally, the vehicle carrying its spent ground-lit solid motors for an extra twenty seconds or so in order to put them in the drop zone beyond the offshore oil platforms of central California. The 10-foot-diameter composite payload fairing was dropped soon after second stage ignition, and following a pair of second stage burns with a long intervening coast phase, the spacecraft was deployed into a nearly-circular polar orbit of about 356 nautical miles.

NASA Launch Manager Chuck Duvale said, “The initial predictions seem to be right on — the Delta II put us right where we needed to be.”

Gravity Probe B will spend two years making precise measurements of the effect Earth’s rotating mass has on the orbit of the spacecraft, an effect first predicted by Einstein’s general theory of relativity in 1920. The mathematical explanation of this theorized effect is esoteric and complicated (and this author cannot claim to suss it), but suffice to say that if you understand that mass distorts and warps the fabric of spacetime, you might grasp that a spinning mass can drag that same fabric, ever so slightly, around with it as it spins. Scientists have been waiting over forty years, since the earliest days of spaceflight and orbital science, to have a spacecraft sophisticated enough to measure this effect conclusively. In contrast, getting GP-B from proposal to orbit has taken a “mere” twelve years.

As an aside, the first experimental evidence of “frame dragging” was provided by the LAGEOS satellites and announced by NASA back in 1998. LAGEOS 1 was launched aboard Delta 123 on 4 May, 1976. (27-Mar-98 NASA Press Release)


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