Shuttle question: how to unload External Tank?

[astrowikizhang]

Hello,<br /><br />I have a question about Space Shuttle External Tank. I think that is an ET loading test, filling it with LOX and LH2 to the launch level, before count down begins. Is that some way to unload the ET after the test? I am sure there is because after on-pad abort, SSMEs get problems and shut down before SRBs ignition, there should be some way to unload the propellent safely. But I don't know the details. Any information?<br /><br />Thanks,<br /><br />zhang

 

[henryhallam]

Really not sure (there are several people here who will know the answer) but I believe the propellants are removed through the same feed lines used to fill the tanks.

 

[astrowikizhang]

//<br /> the propellants are removed through the same feed lines used to fill the tanks.<br />//<br /><br />LOX and LH2 tank has a forward/up end openess to load the propellent. But I think that will be hard to upload the liquids from the same end.<br /><br />Another question: it is clear that LOX is filled via the retractable arm of FSS accessing the tip of the ET, but where is the LH2 filled? Is that another arm to fill the LH2 tank, but located on the other side of the ET (to the orbiter)?<br />

 

[astrowikizhang]

Thanks shuttle guy for your answer. It is a smart solution to boil the liquid and pump out the gas.<br /><br />"Both the LH2 and LOX are filled from the base of the ET."<br /><br />So the LOX and LH2 are filled by some device on the Mobile Launch Platform, and the nose vent is for retrieve only? So LH2 is loaded from lower end of LH2 tank and LOX is loaded through the 17-inch line to LXO tank? Does the Loading pass the orbiter?<br /><br />"The ground line attachment at the nose of the LOX tank is to capture the Lox boil off gas. "<br /><br />Is there any device like that for the boiled LH2? Or just drain it off as liquid?<br /><br />Just searching for technical details of the ET.

 

[astrowikizhang]

Thanks for your help, shuttle guy. The ET filling process is quite different from my knowledge. It is amazing to pump the ultra-cold propellent through the orbiter and up to the altitude of LOX tank.<br /><br />On more question: ET has its Thermal Protection System to prevent the cold fuel from boiling during filling process for hours. But ice still forms on its foamed skin. Are there other ways to control the temperatures of LOX/LH2 tanks to an acceptable level? How long can the propellent be stored in ET before it is forced to unload?

 

[astrowikizhang]

Just found out that Tail Service Masts provide the umbilical connections for fuel and oxidizer.<br /><br />"In addition the propellants must ke kept at the engine interface for a proper engine start sequence. "<br /><br />I think the SSMEs need the propellent to cool the burners, so running dry will destroy the engines.<br /><br />It is amazing that ET can wait 100% for 12 hours without hard freezing! I mistakenly thought it is urgent to launch once the ET is loaded.<br /><br />I am interested in where are the LOX and LH2 is produced. How to transport the propellent to the pad storage? Pipe or tanker? Is the LOX/LH2 production/transportation/storing quite complex and expensive?<br /><br />I notice a very thin line running along the full length of the ET's outside.<br />http://en.wikipedia.org/wiki/Image:Sts_et.jpg<br />What is the use of the line? <br /><br />Thanks again.

 

[astrowikizhang]

Hi, I have a question about the SSME: what is the white steam keep being vent out of each SSME before launch? Is that gaseous oxygen boiled out and mixed with heated gaseous nitrogen, just like what happened in the "beanie cap"? If it is oxygen, where does the gas come from? Thanks.

 

[astrowikizhang]

Thanks for your answer. Keep venting helium gas out during prelaunch, is that cost a lot helium gas?

 

[astrowikizhang]

I think Helium is also hard to produce because US refused to sell Helium to German in 1930s and German had to fill its giant flying boat with dangerous Hydrogen gas.