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Archive for April, 2004

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)

19-Apr-04 | GP-B scrubbed

SCRUB! The first attempt at launching Gravity Probe B has been called off. Upper level winds had been a constraint for much of the morning, yet had come within acceptable parameters in time to come out of the scheduled T-minus 4 minute hold. But with about 3 minutes remaining in the countdown, Boeing engineers found they had insufficient time to confirm that the proper flight profile for the current upper level wind conditions had been uploaded to the Delta’s RIFCA.  Thus, Boeing manager Rich Murphy called a hold, resulting in a one-day turnaround. The next attempt will be Tuesday, 20 April.

15-Apr-04 | GPS launch moved up

To accomodate the postponement of MESSENGER, the Air Force has moved up the launch of NAVSTAR IIR-12 to early June. This was due to the fact that only SLC-17B has the engineering modifications necessary to allow the use of the larger GEM-46 booster motors of MESSENGER’s Delta II-Heavy.

15-Apr-04 | Aura arrives at VAFB

Also at Vandenberg Air Force Base, NASA’s Aura spacecraft has arrived to begin pre-launch preparations following an overland journey from Northrop Grumman’s Space Park manufacturing facility in Redondo Beach, California.  Aura, the latest addition to the Earth Observing System (EOS) that also includes Terra (launched on an Atlas) and Aqua (Delta 291, 04-May-02), is currently scheduled to launch in mid-June. (NASA Press Release, 06-Apr-04)

15-Apr-04 | Next launch

The next Delta launch will be Gravity Probe B, an intriguing Einsteinian relativity experiment. The spacecraft has been installed atop its two-stage Delta II at Vandenberg’s SLC-2W, and is ready to go on Monday, 19 April. (This is a two-day delay from its previous schedule.) Each launch opportunity is an instantaneous window, so any unexpected hold in the countdown will require a turnaround of at least 23 hours and 56 minutes. Upcoming windows are:

The two-day stand down in the middle of the week would be necessary to replenish the spacecraft’s Dewar tank with cryogenic helium, which is needed to keep GP-B’s highly sensitive gyroscopes cool.



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