300th FLIGHT OF RUSSIA'S PROTON
 Delta 4 click to enlarge Boeing artist concept |
It will be either a Delta 2 rocket carrying the Space Infrared Telescope Facility (SIRTF) to orbit or a Delta 4 ferrying a U.S. Air Force DSCS communications satellite.
The Delta 2 launch is expected August 23 with the Delta 4 on August 28. Whichever actually blasts off first will be number 300 in the Delta series.
The back-up launch dates for SIRTF are August 24 and 25.
Some history. The long line of Delta rockets started with a space launcher derived from the U.S. Air Force's Thor intermediate-range ballistic missile (IRBM).
The Thor weapon had been developed in the mid-1950s for the Air Force and concepts for a space booster version were started shortly thereafter. In 1957, the Soviet Union launched Sputnik, the first space satellite. In response, the U.S. government contracted for the Delta expendable space rocket.
NASA, the U.S. space agency, carried out the first successful space launch of a Delta rocket when it boosted the Echo 1A satellite to orbit on August 12, 1960.
Delta ferried early weather, communications and science satellites to orbit. Those spacecraft bore such names as Tiros, Telstar, Explorer and Pioneer. In fact, before the arrival of reusable space shuttles in the 1980s, Delta was NASA's main launcher for weather, communications and science satellites as well as planet probes.
Delta production actually stopped for a time in the early 1980s as NASA intended to use the space shuttle fleet to carry all satellites to orbit. Unfortunately, the shuttle Challenger exploded during liftoff in 1986 and President Ronald Reagan decided that shuttles no longer would carry commercial payloads. Delta production was restarted.
Through the years, Delta became larger, more advanced and capable of lofting heavier satellites to orbit. A more powerful Delta 2 rocket flew in 1989 and an even more powerful Delta 3 in 1998. The most powerful version to date, Delta 4, flew in 2002.
Before the 300th flight, the Delta family had flown 283 successful launches while suffering only 16 launch failures. Today, the Delta rocket line is manufactured by the Boeing Co.
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