Re: Ullage
John C. Broman, Jr. (stingray@wizard.net)
Mon, 26 Jul 1999 19:40:22 -0400
At 03:56 PM 7/26/99 -0700, Randy John wrote:
> I noticed in the Globalstar web pages, reference to
>an 'ullage' event over Australia. A trip to the dictionary
>didn't satisfy me so I am appealing to the list.
Basically, the ullage is the gaseous part of a container when partially
filled with a liquid. A sealed soda bottle has a small ullage of C02 at
the top. Rocket tanks often contain a pressurized ullage of helium to help
deliver the propellant to the engine under pressure. And helium is often
chosen because it's light and non-reactive.
In zero-G, there is no "top" for the ullage to rise to, so prior to an
engine restart, small jets give the rocket a small boost forward which
allows the liquid propellant to settle back to the bottom of the tank.
John Broman
Beginner satellite observer
Professional rocket builder