gandalf@pro-canaveral.cts.com (Ken Hollis) (12/05/90)
Greetings and Salutations >From blake@ccwf.cc.utexas.edu (Blake Freeburg) >How do they fill up the big tank attached to the space shuttle? More >specifically, the tank is at ~273K and the hydrogen (liquid) is at <20K, >so how much of it boils off, do they reclaim any of it, and do they precool The ET (External Tank) is loaded with Maximum 143,351 Gallons Of LOX (Top Tank) and 385,265 Gallons Of LH2 (Bottom Tank). Loaded propellant weight is 1,353,452 Lbs LOX & 227,486 Lbs LH2. The process begins at the two large storage spheres on the north side of the pads (LOX on the left side looking north, LH2 on the right side looking north). The LH2 sphere holds 850,000 gallons of LH2. The LOX sphere holds 900,000 Gallons. The LH2 & LOX loading starts at approximately the same time, at about T-Minus 6 Hours and counting. The Pad area is cleared to the BDA (Blast Danger Area) and the loading starts. The LH2 dewar (sphere or storage area) is pressurized by allowing some LH2 to vaporize to a gas, and go back into the tank. The LH2 is then slowly "pushed" uphill to the vehicle all the while chilling down the lines (LH2 Transfer Lines) going from the sphere to the MLP (Mobile Launch Platform) in through the MPS (Main Propulsion System) fill & drain valves into the tank. After LH2 facility & orbiter chilldown are complete (some liquid is onboard, but not "good" liquid) slow fill to the ECO's (Engine Cut-off Sensors) is initiated. The ECO's are a backup system used in flight to tell the engines they are just about to run out of a propellant (LOX or LH2). After the ECO's (inside the ET) show "Wet" then the LH2 fastfill is initiated to the 98% sensors (Sensors showing the tank 98% filled). The level sensors for the ET are 5%, 98% (2 ea), 99.7%, 100% (2 ea.), 100.3% & 102%. After 25 minutes, the MPS recirculation pumps are activated. These pumps push LH2 through the engines to condition them for start (pre-start conditioning). When the 98% sensor is wet, then topping to 100% is started. After topping is complete (at about T-3 Hrs, 30 Minutes) then replenish is initiated, just replenishing the lost liquid. During all this time, all pressurizations (with the exception of the initial dewar pressurization) are done with Helium. All depressurizations (vent valve actuation) goes to the LH2 flare stack where it is burned. If there is a scrub, as much liquid as possible is put back into the LH2 dewar. The LOX is transferred to the vehicle using pumps. It is too heavy just to push around. Once again the transfer line is slowly chilled down, then the MPS system. LOX s then put into slow fill. When the sensors indicate "good" liquid LOX is then started into fast fill to 98%. The LOX tank sensors are 4 ECO's (these ECO's are inside the orbiter) 5%, 98% (2 ea), 99.85%, 100% (2 ea), 100.15% & 102%. After 98%, LOX also goes into replenish. Once again, if there is a scrub the LOX is drained back into the LOX dewar. The LOX that goes to gas is vented out the top of the tank into the "beanie" cap (the arm on top of the tank) to atmosphere. When both LOX & LH2 are in stable replenish the ice crew goes out and inspects the ET for ice buildup & the flight crew is awakened. Ken Hollis ProLine: gandalf@pro-canaveral Internet: gandalf@pro-canaveral.cts.com UUCP: crash!pro-canaveral!gandalf