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Delta 4-Heavy countdown aborted moments before launch – Spaceflight Now
A dramatic automatic abort 7.5 seconds before the planned liftoff of a United Launch Alliance Delta 4-Heavy rocket Saturday night kept the towering launcher on the pad at Vandenberg Air Force Base, California, with a top secret spy payload for the National Reconnaissance Office.
The 233-foot-tall (71-meter) rocket was counting down to launch at 8:15 p.m. PST Saturday (11:15 p.m. EST; 0415 GMT Sunday), but an automated sequencer detected a technical issue and triggered an abort. "Hold hold hold," a member of the ULA launch team declared on the countdown net.
[...] In the statement, ULA said the abort was "due to an unexpected condition during terminal count at approximately 7.5 seconds before liftoff. "The team is currently reviewing all data and will determine the path forward. A new launch date will be provided when available," ULA said.
takyon: A new date has not been chosen yet.
(Score: 1, Informative) by Anonymous Coward on Thursday December 13 2018, @07:32PM
This is part of the reason why the space shuttle fired up the main engines just under 7 seconds before SRB ignition. During those ~7 seconds the launch can still be aborted if there's a problem detected in the main engines. This actually happened 5 times during the space shuttle program.
After SRB ignition the shuttle had no possible abort modes for just over 2 minutes, which turned out to be a problem once.