🚀 go-pugleaf

In article <1992Dec10.233907.4549@titan.ksc.nasa.gov>, dumoulin@titan.ksc.nasa.gov (Jim Dumoulin) writes:

Jim provided a good overview of the orbiter cooling.  My comments expand on
what he said.

> 
>   When the payload bay doors are opened, radiator panels attached to
>   the doors radiate heat.  If this is insufficent during orbiter
>   operations, the flash evaporator subsystem is automatically activated.

The radiators consist of four panels mounted on each of the payload bay doors.
The forward two panels on each door can be deployed to provide four additional
cooling surfaces.  Very few missions have flown hot enough attitudes to require
the deployment of the radiators.
> 
>   During orbit operations, a freon loop is used for cooling within the
>   payload bay.  This is connected via the payload heat exchanger to
>   a water loop used for cooling within the crew compartment.  No freon
>   is used in the crew compartment due to safety considerations.

There are separate heat exchangers for the cabin and payload.  Both are located
in the payload bay.  The atmospheric revitalization system (ARS) heat exchanger
provides the cooling for the cabin water loops.
> 
>   In preparations for re-entry, the orbiter is cold soaked and then the
>   flash evaporator is reactivated prior to payload bay door closure.

Actually it is the radiators that are cold soaked.

>   The flash evaporator is used during reentry until the orbiter reaches
>   an altitude of 100,000 feet, at which point boiling water can no longer
>   provide adequate Freon-21 coolant loop temperatures.  Below 100,000
>   feet, the ammonia boiler system is used.

Once there is enough atmosphere that the FES can no longer be used, the cooling
is provided by using the cold soak from the radiators.  On missions where a
good cold soak is achieved and the ground crew encounters no problems in 
connecting the ground cooling the radiators have been able to provide all of
the cooling until the ground cooling has been initiated. 
> 
>   The ammonia boiler system use the low boiling point of ammonia to
>   cool the Freon-21 loops.  There are 2 complete, individual ammonia
>   storage and control systems that feed one common boiler.  Each
>   ammonia boiler storage tank contains a total of 49 pounds of NH3
>   and are pressurized with gaseous helium at an operating pressure
>   between 550psia and 83 psia.  The ammonia boiler is a shell-and-tube
>   system with a single pass of ammonia on the ammonia side and two
>   passes of each Freon-21 coolant loop thru the boiler.  When ammonia
>   is sprayed on the Freon-21 coolant lines in the boiler, it immediately
>   vaporizes and the heat and boiler exhaust is vented overboard in
>   the upper aft fuselage of the orbiter next to the bottom right side
>   of the vertical tail.  The ammonia boiler is usually kept on until
>   the orbiter is re-hooked up to a GSE heat exchanger.
> 
Generally the ABS is only required for a few minutes to make up the time
between the loss of radiator cooling and the initiation of ground cooling.
On STS-53, with the RCS leak delaying the ground cooling hook-up, one set of
ammonia tanks were drained and use of the second set was started.  

> -- 
> --------------------------------------------------------------------------
>    Jim Dumoulin                      INTERNET: DUMOULIN@TITAN.KSC.NASA.GOV
>    NASA / Payload Operations      SPAN/HEPnet: KSCP00::DUMOULIN
>    Kennedy Space Center
>    Florida, USA  32899
>   
>  
-- 

Pat Oliver -  	Lockheed Engineering and Sciences Company at NASA JSC
		OLIVER@vf.jsc.nasa.gov
		All standard disclamers apply.