How was the external fuel tank filled with LH2 and LOX while the shuttle was on the launch pad? I know there was a gaseous oxygen umbilical on the top of the ET and a gaseous hydrogen umbilical about halfway down the tank. So where were the connections to fill the tank with fuel and oxidiser?

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    $\begingroup$ Are you asking how the Space Shuttle was fuelled or how the External tank was fuelled? Because your title says how the space shuttle was fuelled and the last sentence asks how the ET was fuelled. $\endgroup$
    – Star Man
    Commented Oct 13, 2019 at 21:51
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    $\begingroup$ If you want to have cryogenic liquid propellants in the tanks, you got to fill cryogenic liquid propellants. There would be a lot of gaseous boiloff which should be removed by umbilicals to keep them away from the launch pad to avoid explosions or fire. $\endgroup$
    – Uwe
    Commented Oct 13, 2019 at 22:02
  • $\begingroup$ The vast majority of the shuttle fuel was in the external tank @Starman. So while details of loading the APUs, OMSs and Fuel cells is also interesting, and would make a nice addendum to an answer, the location of the ET filling umbilicals and connectors is interesting on its own -- and asking for just those doesn't risk making the question too broad. $\endgroup$
    – user20636
    Commented Oct 13, 2019 at 23:28
  • $\begingroup$ @JCRM I wasn't sure what the OP was asking for because the title and description don't match. Also I assumed the OP knew that the Shuttle is fuelled by the ET. But I guess the question can work both ways because the Tail Service Masts also provided some fuel (for the Orbital Maneuver Systems I believe). $\endgroup$
    – Star Man
    Commented Oct 14, 2019 at 0:53
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    $\begingroup$ Are you using "space shuttle" to refer to just the orbiter @StarMan? $\endgroup$
    – user20636
    Commented Oct 14, 2019 at 0:56

1 Answer 1


The shuttle external tank held the propellants for the shuttle main engines. It was filled from spherical tanks positioned at the perimeter of the launch pad. Insulated lines ran from the spheres, through the Mobile Launcher, and into the Orbiter through two tombstone-shaped Tail Service Masts.

Then through the Orbiter Main Propulsion System plumbing into the External Tank.

Here is a schematic from the Ascent Pocket Checklist showing how the fill and drain lines from the Masts (highlighted) teed into the lines going to the External Tank.

enter image description here

Here is a paper about the Tail Service Masts.


A picture of the Tail Service Mast (TSM) attached to the Orbiter's main propulsion plumbing system. One service mast delivers LOX (oxidizer on the right) and the other delivers LH2 (fuel on the left).

Tail Service Mast


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    $\begingroup$ That's a really interesting view angle; I don't recall ever noticing the TSMs before! $\endgroup$
    – uhoh
    Commented Oct 14, 2019 at 3:34
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    $\begingroup$ so the fuel flowed through the Orbiter on the way to the ET? I didn't expect that! $\endgroup$
    – user20636
    Commented Oct 14, 2019 at 8:25
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    $\begingroup$ @OrganicMarble No problem. I just asked Why is the Space Shuttle's External Tank fuelled through the Orbiter's main engine plumbing system? $\endgroup$
    – Star Man
    Commented Oct 14, 2019 at 16:30
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    $\begingroup$ So... your brain... is it an encyclopedia of all possible space shuttle design concepts and their locations inside of documents? Quite the impressive person... your answers never fail to incite curiosity. $\endgroup$ Commented Oct 18, 2019 at 19:03
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    $\begingroup$ @MagicOctopusUrn Thanks, I was very lucky to have a long career on shuttle. Tried to pay attention to stuff outside my specialty, kept copious notes. $\endgroup$ Commented Oct 19, 2019 at 0:58

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