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11-Jun-08 | Delta flight 333 – GLAST

NASA’s Gamma-ray Large Area Space Telescope (GLAST) is now in its operational orbit, thanks to a successful launch aboard a Delta II-Heavy today. The Delta II launch record now stands at 81 consecutive successes, an unprecedented testimonial of reliability that began over 11 years ago.

The launch, at first slated for mid-May, was delayed for more than three weeks due to stacking issues with the Delta II launch vehicle. Installation of the second stage was delayed when an H-beam adapter, part of the SLC-17B hoisting system, was fractured during prep work around 5 April. Although the second stage was undamaged, a new H-beam had to be manufactured and tested. Later, a 5 June launch date was postponed when the Delta II’s Flight Termination System battery showed signs of flakiness and was swapped out.

Today there were no major issues with the vehicle or spacecraft, although the tracking station at Antigua went offline for a while, resulting in a 20-minute delay in coming out of the T-minus 4 minutes built-in hold. Although the 115-minute launch window afforded plenty of slack for the extended hold, the weather, partly cloudy and breezy, was threatening to worsen in the early afternoon. Fortunately, no other issues arose and the Delta II-Heavy was able to liftoff at an official range time of 12:05:00.521 EDT.

The two-stage 7920 rocket, the fifth Delta II to use upsized GEM-46 solid motors for extra boost, thundered off the pad and streaked through the scattered cloud deck, passing each of its scheduled flight events with precision. The first and second stage burns totaling about ten-and-a-half minutes were followed by a 55-minute coast phase, and then a fairly brief 64-second burn to circularise the orbit around 300 nautical miles altitude. GLAST was released about 75 minutes after launch while within sight of the Kwajalein tracking station, and shortly thereafter it unfurled its solar panels.

After successfully deploying the spacecraft, the Delta second stage performed a gentle evasion manoeuvre using its helium thrusters, and later completed a pair of additional burns using its primary engine—one for further evasion of the spacecraft, and one to deplete its hypergolic propellants. This final burn left the stage in an elliptical orbit with a 99 nautical mile perigee, which will significantly reduce the time until it reenters the atmosphere and burns up.

GLAST carries the most advanced instrument ever built to study some of the universe’s most dynamic and cataclysmic events—supermassive black holes, merging neutron stars, and other phenomena that produce highly energetic gamma-ray radiation. After a 60-day checkout and calibration period, the $693 million telescope is expected to spend at least five years performing both a full sky survey and in-depth, targeted observations.

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