Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!uupsi!pbs.org!pstinson From: pstinson@pbs.org Newsgroups: sci.space.shuttle Subject: Re: Shuttle Status for 04/22/91 (Forwarded) Message-ID: <1991Apr23.115236.12470@pbs.org> Date: 23 Apr 91 11:52:36 EDT References: <1991Apr22.234907.29805@news.arc.nasa.gov> Organization: PBS:Public Broadcasting Service, Alexandria, VA Lines: 14 In article , rose@beowulf.ucsd.edu (Dan Rose) writes: > yee@trident.arc.nasa.gov (Peter E. Yee) writes: > >> The countdown clock entered the T-11 hour planned built-in >> hold this morning at 4:45. The clock will continue to hold until >> resuming the count at 4:45 p.m. today. > > This may be a naive question, but . . . Why do they have these planned > countdown holds? As a hedge against the unexpected. If for whatever reason the countdown work falls behind schedule and there are no built-in holds, you are facing a definite scrub situation. These "built-in" holds allow you to catch up or trouble shoot and still make the target launch time. Unfortunately, sometimes this "extra" time is not enough and you have to scrub anyway.