Shuttle launch scrubbed

"Pat Flannery" wrote in message
dakotatelephone...
Trouble with the APU heaters:
http://spaceflightnow.com/shuttle/sts134/110429scrub/
The APU's use hydrazine for fuel, and they need to have their fuel lines
heated to make sure it doesn't freeze up while in orbit.
This is a minimal 72 hour scrub, and NASA is saying don't be surprised if
it's longer that that.

Pat


Interesting way it's described - two heaters, cause may be a blown fuse. So
if one fuse takes out both they're obviously not primary and backup, and no
backup mentioned. Blown fuse is usualy not a cause - it's something caused
by some real circuit failue like a short. Brings back childhood memories of
Vanguard. I wonder how many folks will hang around the extra days in hopes
of a quick resolution.

Val Kraut

Trouble with the APU heaters:
http://spaceflightnow.com/shuttle/sts134/110429scrub/
The APU's use hydrazine for fuel, and they need to have their fuel lines
heated to make sure it doesn't freeze up while in orbit.
This is a minimal 72 hour scrub, and NASA is saying don't be surprised
if it's longer that that.

Pat

On 4/29/2011 9:45 AM, Val Kraut wrote:

Interesting way it's described - two heaters, cause may be a blown fuse. So
if one fuse takes out both they're obviously not primary and backup, and no
backup mentioned. Blown fuse is usualy not a cause - it's something caused
by some real circuit failue like a short. Brings back childhood memories of
Vanguard. I wonder how many folks will hang around the extra days in hopes
of a quick resolution.

According to Spaceflight Now:
"Launch director Mike Leinbach says the team believes there's an
electrical short in one of the shuttle's load control assemblies (LCA)
or one of the lines going to that box. The LCA routes power to the two
heaters that exhibited problems on Auxiliary Power Unit No. 1, forcing
today's scrub."
They think that caused a fuze to blow (they don't use circuit breakers?).
They're pretty sure this will mean going inside the engine compartment
to find out what went wrong and fix things.
I don't think they generally do this with hydrazine aboard for safety
reasons, so it well be interesting how they handle it.

Pat