The propellant mass ratio in the Space Shuttle external tank differs from the engine consumption ratio due to operational fuel utilization profiles.
the verdict
SUPPORTED
the evidence backs this
refutedsupported
the weight of evidence
1 source for · 0 against
AS REPORTEDno primary record reached; this is what the reporting says
Available records confirm that the propellant mass ratio packed in the Space Shuttle external tank differs from the engine consumption ratio to avoid running oxygen-rich at the end of combustion.
# Why do the contents of the Space Shuttle External Tank not match the mixture ratio of the engines?
Tags: space-shuttle, fuel, mixture-ratio
- Score: 25
- Views: 3239
- Answers: 2
- Answered: yes
- Asked by: SE - stop firing the good guys (45244 rep)
- Asked: 2020-10-14
- Edited: 2025-09-08
- Site: space
## Question
The Space Shuttle External tank contains:
629,340 kg of liquid oxygen
106,261 kg of liquid hydrogen.
That's an oxidiser to fuel ratio of 5.92
Meanwhile, the Space Shuttle Main Engine has a constant mixture ratio of 6.03
Where is that extra hydrogen going? (or extra oxygen appearing...?)
The Space Shuttle used regenerative cooling and staged combustion, so all the fuel and oxidiser should eventually end up in the combustion chamber despite turbo pumps and engine cooling needs.
## Answers
### Answer by Organic Marble (score: 42 [ACCEPTED])
tl;dr as SF said in a comment "...they always packed a little more hydrogen than oxygen (for that ratio), so that at the end of combustion they wouldn't risk running oxygen-rich (and as result engine-rich)."
If you are interested in details, please refer to this propellant loading table for the following explanation.
The numb