What is the purpose of the built in hold times during launches.

[jarmenia]

Why do they stop the count down for say 20 minutes as a planned hold? If the launch is scheduled for 9:00 and at 8:20 you are at T-20 and start a 20 minute hold, the launch is still 40 minutes away. Why don't they just keep the countdown going and just not have any activity for those 20 minutes of the countdown?

[Tommygun]

I could be wrong, but I think it is when they spot a problem and the techs ask for a hold to go fix it or check out the issue to see if it is bad enough to stop the launch.

They then hold the launch, because of all the checks they have to do in the control room have to be stopped as well.

Edited January 30, 2015 by Tommygun

[jarmenia]

Well I've heard them referred to as a planned hold, which is why I am confused about them. If they weren't planned, what you suggest would make sense.

[AeroEngy]

Well I've heard them referred to as a planned hold, which is why I am confused about them. If they weren't planned, what you suggest would make sense.

The reason they are there is mostly to give some padding in the timeline and to target an exact launch window. So they do a bunch of checks, preps, and fueling that might take a variable amount of time if someone is slow to do a step or some other complication pops-up. This is all done as part of the initial count and it is possible to fall behind due to random complications etc. Then they hit the planned hold time which can be extended or shortened. This allows them to catch back up if necessary and pick the count back up so that T-0 hits on the exact time they need to launch to hit their window ... or rendezvous with the ISS or whatever.

So it is basically just some padding in the schedule. IT could be done without a planned hold put the launch procedure would just need to have a little bit of padding here and there instead of one longer hold/ time pad.

Edited January 30, 2015 by AeroEngy

[cicatrix]

This is called a tradition. Despite being highly educated men, rocket engineers and mission control officers are highly superstitious people.

This may sound ridiculous, but this is true. Here:

http://www.bbc.com/future/story/20140610-the-strange-rituals-of-cosmonauts

[RainDreamer]

This is called a tradition. Despite being highly educated men, rocket engineers and mission control officers are highly superstitious people.

This may sound ridiculous, but this is true. Here:

http://www.bbc.com/future/story/20140610-the-strange-rituals-of-cosmonauts

I supposed when you are launching a multi-million dollar vehicle, you need all the help you can get, be it fengshui or rituals.

[Starwhip]

This one's great:

10. A towel

Every space traveller knows that the most massively useful thing to have is a towel. Thanks to the late Douglas Adams’ hugely influential Hitchhiker’s Guide to the Galaxy, alongside tens of thousands of others around the globe, some astronauts now commemorate Towel Day on 25 May.

A new space tradition that would surely make Yuri Gagarin proud.

[jarmenia]

The reason they are there is mostly to give some padding in the timeline and to target an exact launch window. So they do a bunch of checks, preps, and fueling that might take a variable amount of time if someone is slow to do a step or some other complication pops-up. This is all done as part of the initial count and it is possible to fall behind due to random complications etc. Then they hit the planned hold time which can be extended or shortened. This allows them to catch back up if necessary and pick the count back up so that T-0 hits on the exact time they need to launch to hit their window ... or rendezvous with the ISS or whatever.

So it is basically just some padding in the schedule. IT could be done without a planned hold put the launch procedure would just need to have a little bit of padding here and there instead of one longer hold/ time pad.

Ahh, thanks for clearing it up.