Author Topic: STS-121: July 1 Launch SCRUB (Read 133326 times)

kraisee · « **Reply #21 on:** 07/01/2006 12:29 pm »

From: http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/rcs/heaters.html

Heaters

Electrical heaters are provided in the forward RCS module and the OMS/RCS pods to maintain the propellants in the module and pods at safe operating temperatures and to maintain safe operating temperatures for the injector of each primary and vernier RCS thruster.

Each primary RCS thruster has a 20-watt heater, except the four aft-firing thrusters, which have 30-watt heaters. Each vernier RCS thruster has a 10-watt heater.

The forward RCS has six heaters mounted on radiation panels in six locations. Each OMS/RCS pod is divided into nine heater zones. Each zone is controlled in parallel by an A and B heater system. The aft RCS thruster housing contains heaters for the yaw, pitch up, pitch down and vernier thrusters in addition to the aft OMS/RCS drain and purge panels. The OMS/RCS heater switches are located on panel A14.

The forward RCS panel heaters are controlled by the fwd RCS auto A, B, off switch on panel A14. When the fwd RCS switch is positioned to auto A or B, thermostats on the forward left-side panel and right-side panel automatically control the respective forward RCS heaters. When the respective forward RCS panel temperature reaches a minimum of approximately 55º F, the respective panel heaters are turned on. When the temperature reaches a maximum of approximately 75º F, the heaters are turned off. The off position removes all electrical power from the forward RCS heaters.

The aft RCS heaters are controlled by the left pod auto A and auto B and right pod auto A and auto B switches on panel A14. When the switches are positioned to either auto A or auto B, thermostats automatically control the nine individual heater zones in each pod. Each heater zone is different, but generally the thermostats control the temperature between approximately 55º F minimum to approximately 75º F maximum. The off position of the respective switch removes all electrical power from that pod heater system.

The forward and aft RCS primary and vernier thruster heaters are controlled by the fwd and aft RCS jet 1, 2, 3, 4 and 5 switches on panel A14. When the switches are positioned to auto , individual thermostats on each thruster automatically control the individual heaters on each thruster. The primary RCS thruster heaters turn on between approximately 66º to 76º F and turn off between approximately 94º to 109º F. The vernier RCS thruster heaters turn on between approximately 140º to 150º F and off between approximately 184º to 194º F. The off position of the switches removes all electrical power from the thruster heaters. The 1, 2, 3, 4 and 5 designations refer to propellant manifolds. There are two to four thrusters per manifold.

nacnud · « **Reply #22 on:** 07/01/2006 12:31 pm »

Out of interest if it is the heater strips in the OMS Steven Baxster used a similar senario in his book Titan.

Stardust9906 · « **Reply #23 on:** 07/01/2006 12:32 pm »

LH2 Tank 98% full.

psloss · « **Reply #24 on:** 07/01/2006 12:35 pm »

Sounds like they need to have the ASP in the crew module to do some switch throws before they can make a final decision...

Chris Bergin · « **Reply #25 on:** 07/01/2006 12:36 pm »

Options: Troubleshoot heater on the ground or on orbit.

Nice weather at the moment!

Stardust9906 · « **Reply #26 on:** 07/01/2006 12:38 pm »

LH2 in stable replenish.

psloss · « **Reply #27 on:** 07/01/2006 12:42 pm »

Quote

Chris Bergin - 1/7/2006 8:23 AM

Options: Troubleshoot heater on the ground or on orbit.

Chris, did your sources mention what the LCC is for that system? Is the redundancy mandatory for launch and/or could this be waived?

kraisee · « **Reply #28 on:** 07/01/2006 12:46 pm »

While Chris gets additional info, what I've read so far - the verniers heaters do not have redundancy, (nor do the vernier thrusters themselves) and they are required for finite controls and station-keeping work, so they sound fairly critical to me.

Ross.

psloss · « **Reply #29 on:** 07/01/2006 12:51 pm »

I was referring to the reference you cited which says:

Quote

Each OMS/RCS pod is divided into nine heater zones. Each zone is controlled in parallel by an A and B heater system.

Anyone know if the issue is with one or the other system or if the issue affects both?

Chris Bergin · « **Reply #30 on:** 07/01/2006 12:52 pm »

Quote

psloss - 1/7/2006 1:29 PM

Quote
Chris Bergin - 1/7/2006 8:23 AM

Options: Troubleshoot heater on the ground or on orbit.
Chris, did your sources mention what the LCC is for that system? Is the redundancy mandatory for launch and/or could this be waived?

Asking.

MAF (they have controllers on consoles watching the tank) have been told there's a likely scrub - and are in discussions on how much testing them can do with the tank before recycle. However, while in troubleshooting, that is only an intimation on what's been said.

Hopefully the aforementioned flicking of switches will do the trick.

shuttlefan · « **Reply #31 on:** 07/01/2006 12:55 pm »

Likely will be scrubbed especially if there is no redundancy in the system...

kraisee · « **Reply #32 on:** 07/01/2006 01:02 pm »

From the very end of: http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/rcs/overview.html

"The vernier engines are operable in a steady-state thrusting mode of one to 125 seconds maximum as well as in a pulse mode with a minimum impulse time of 0.08 second. The vernier engines are used for finite maneuvers and stationkeeping (long-time attitude hold) and have an expansion ratio that ranges from 20-to-1 to 50-to-1. The vernier thrusters are not redundant."

Ross.

Chris Bergin · « **Reply #33 on:** 07/01/2006 01:04 pm »

Coming up to the T-3 hour built in hold.

Ice Inspection team will then be on their way to the pad.

Chris Bergin · « **Reply #34 on:** 07/01/2006 01:08 pm »

Lots of chatter on the flight loop (you have to turn up NASA TV really loud).

Stardust9906 · « **Reply #35 on:** 07/01/2006 01:08 pm »

T-3 Hours and Holding. Liquid Oxygen in stable replenish.

kraisee · « **Reply #36 on:** 07/01/2006 01:10 pm »

Q: These checks NASA TV just refered to - this is where the ECO's had their problems on the first attempt for 114 last year, right?

I couldn't hear the coverage last year, so I'm not sure.

Ross.

dutch courage · « **Reply #37 on:** 07/01/2006 01:11 pm »

There is a lot of cloud cover into view.

Chris Bergin · « **Reply #38 on:** 07/01/2006 01:11 pm »

Quote

kraisee - 1/7/2006 1:57 PM

Q: These checks NASA TV just refered to - this is where the ECO's had their problems on the first attempt for 114 last year, right?

I couldn't hear the coverage last year, so I'm not sure.

Ross.

I thought they came later in the count, as the crew were on board, right?

Chris Bergin · « **Reply #39 on:** 07/01/2006 01:11 pm »

Quote

dutch courage - 1/7/2006 1:58 PM

There is a lot of cloud cover into view.

Sea Breeze should blow over, looks pretty nice otherwise.