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17-Feb-07 | Delta flight 323 – THEMIS

NASA’s THEMIS mission was successfully launched on a three-stage Delta II rocket on Saturday, 17 February 2007.

Thunderstorms delayed fuelling operations earlier in the week, and extreme wind shear between altitudes of 10,000 and 20,000 feet caused a scrub on Friday evening. For Saturday’s attempt, those upper-level winds continued to be a concern, but never exceeded parameters and the board remained green for weather all evening. An unspecified issue with the third stage was quickly resolved without affecting the countdown.

The Delta 7925 with a 10-foot composite fairing left SLC-17B at an official range liftoff time of 18:01:00.384 EST, the very opening of the window. First and second stage burns completed in 9 minutes 59 seconds, placing the spacecraft in a temporary, elliptical parking orbit of 100.0 nm perigee by 303.78 nm apogee, with an inclination of 28.5 degrees.

After a 53-minute coast phase, the Aerojet AJ10-118K second stage reignited for just under a minute, boosting the apogee to 825 nautical miles. It spun up the third stage and payload, then released the pair, having completed its task. With telemetry being received by a Big Crow tracking aircraft flying off the northeast coast of Australia, the third stage’s Thiokol Star 48B solid motor fired for 86.5 seconds to kick the apogee up to almost 50,000 nautical miles. About five minutes later, the custom carrier system deployed all five THEMIS spacecraft, successfully completing the launch about 73 minutes, 42 seconds after liftoff.

Over the next seven months, THEMIS will remain in an injection or “coast” phase while controllers check out the five satellites’ systems and assign them to their operational orbits. Transfer to those orbits will begin some time in September. All five probes have already been found to be in nominal orbits and in excellent health.

THEMIS, an acronym for Time History of Events and Macroscale Interactions during Substorms, will examine the Earth’s magnetosphere and its interaction with the solar wind from various points along the magnetotail. In particular, the mission hopes to shed light on “how Earth’s magnetosphere stores and releases energy from the sun.” It may help to explain why aurorae (the northern and southern lights) have such a wide variety of colours and appearances. The use of five smaller subsatellites will provide a broader understanding of the phenomena than would a single probe. (Spaceflight Now Mission Status Center, 17-Feb-07, NASA Press Release, 17-Feb-07)

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