When gravity is absent and the fuel doesn’t naturally stay at the bottom of the bank, other schemes must be used to keep the propellant adjacent to the pickup. I’ve previously examined this issue here and here.
What I love about this blog is it kindles my curiosity. I was inspired to look again at how rocket propellant is managed in microgravity by some new details on the SpaceX mars spacecract. Teslerati ran an article in which they described propellant vessel’s in the spacecraft as follows:
“Header tanks refer to smaller tanks contained within the main propellant tanks that are used to ignite engines in microgravity. It’s easier to pressurize or simply fill the smaller tanks than it is to do so with the massive main tanks.”
It’s not clear from what I’ve found how these header tanks work, but what is clear is that Principle 1 – Segmentation is being applied here, as I speculated on in the previous posts.
In my research on the SpaceX header tanks, I came across another ullage scheme.
Propulsive venting was used successfully on the Saturn V rocket. The third stage would need to do more than one burn and in between it would float weightlessly. As the exterior of the third stage was heated by the sun, gases were produced by the liquid hydrogen and oxygen boiling. This gas had to be vented, so they were vented rearward to maintain a tiny bit of thrust to hold the liquid propellants at the bottom of the tank. Principle 22 – Blessing in Disguise