fisher@star.DEC (Burns Fisher ZKO1-1/D42 DTN 381-1466) (01/06/86)
>I've been wondering just what determines the length of a delay or >postponement of a shuttle launch when some defect is discovered >while the assembled craft is already fueled and there is only a short >time remaining in the countdown. Sometimes things are slipped a few >hours, other times until the next day, and then there will be abrupt >jumps to much longer delays, like several weeks. > >Could someone in the know post a short summary of what sorts of delays >what kinds of discovered problems will cause? Something like: > >Shuttle computer software bug ..... 1 day for patching & reloading > >SRB Engine Safety-related failure ... 3 weeks for return to vehicle > assembly building & replacement >and so on... ... >Thanks! >Will Martin I don't think it is that simple. For example, the last delay (from December 20-Jan 6) was so long because they had promised KSC workers the Christmas holidays off. At different points in the countdown, there are also different hold times available. These are the amount of time that the count can be held without having to go back and do something over again. There are also recycle times, which are the amount of time it will take to get back to a certain point in the count. And finally (in this note, at least) there are launch windows, which means the absolute time of day before and after which you can't launch. So when a problem comes up, first estimate how long it will take to fix. Then see if it is within the current hold time. If so, will the revised launch time be within the window. If not within the current hold time, will recycling allow a launch within the window? ETc etc etc. BTW, Examples of cause for limited hold times (which came into play in today's launch attempt). APUs: If the APUs have been started (about T-5 min) you can only hold for n minutes (5?) in order to make sure there is enough APU fuel. Furthermore, if you recycle the count back to T-9, you must wait for the APUs to cool down before you restart them. And if you wait too long, you have to back to T-20 in order to realign the inertial measurement units, since they have a limited time that they can remain within tolerance. Burns ...decwrl!rhea!star!fisher