Liquid level equalization for propellant tanks

1. A method for equalizing fluid levels of a propellant tank that stores a liquid propellant for a rocket engine of a rocket, the propellant tank having a vent line with a vent valve and an equalization valve, the method comprising:

after filling the propellant tank with the liquid propellant to a level above a height of the equalization valve within the propellant tank before launch of the rocket:

using one or more controllers to:

determine the level of the liquid propellant relative the height of the equalization valve within the propellant tank after the launch of the rocket;

in response to the level of the liquid propellant falling below the level of the equalization valve, open and close the vent valve to re-duce pressure of the propellant tank; and

in response to the level of the liquid propellant falling below the equalization valve during or after the launch of the rocket, close the equalization valve.

2. The method of claim 1 , wherein one of the one or more controllers further performs the method by, upon or after receiving a signal from a timer at a designated time after the launch of the rocket, opening the vent valve and closing the equalization valve.

3. The method of claim 2 , wherein the designated time after the launch of the rocket is determined based on calculating a rate of liquid propellant use during the launch of the rocket and the rate of liquid propellant use after the launch of the rocket calculated based on an amount of the liquid propellant used over a given amount of time after the launch of the rocket.

4. The method of claim 2 , wherein the designated time after the launch of the rocket is determined based on calculating an expected rate of liquid propellant based on liquid propellant use data of previous launches, the expected rate of liquid propellant used being calculated based on an average of an amount of the liquid propellant used over a given amount of time of one or more of the previous launches.

5. The method of claim 1 , wherein one of the one or more controllers further performs the method by:

closing the vent valve before the launch of the rocket and after the propellant tank is at least partially filled with the liquid propellant above the equalization valve; and

opening the equalization valve before the launch of the rocket and after the propellant tank is at least partially filled with the liquid propellant above the equalization valve.

6. The method of claim 1 , wherein one of the one or more controllers further performs the method by detecting the level of the liquid propellant based on a signal received from a sensor, the signal including sensed level data of the level of the liquid propellant.

7. The method of claim 1 , wherein one of the one or more controllers further performs the method by causing the vent valve and the equalization valve to close in response to receiving sensed level data, the sensed level data being associated with the level of the liquid propellant being below a physical location of the equalization valve.

8. A vent line, comprising:

a vent valve having a vent pressure range;

an equalization valve structured to cause a liquid propellant to be released from the vent line into a propellant tank; and

a controller configured to:

determine when a level of the liquid propellant within the propellant tank is below a height of the equalization valve within the propellant tank, and

when the level of the liquid propellant falls below the equalization valve, send an instruction to:

cause the vent valve to open from a closed position and to close from an open position, the opening and closing to reduce pressure of the propellant tank, and

cause the equalization valve to close from an open position.

9. The vent line of claim 8 , wherein the controller is further configured to:

before launch of the rocket and after the propellant tank is at least partially filled with the liquid propellant above the height of the equalization valve:

causing the vent valve to close from the open position; and

causing the equalization valve to open from a closed position.

10. The vent line of claim 8 , wherein the controller is electrically connected to a sensor, the sensor configured to detect the level of the liquid propellant within the propellant tank.

11. The vent line of claim 10 , wherein the controller is further configured to determine the level of the liquid propellant based on a signal received from the sensor, the signal including the level of the liquid propellant within the propellant tank.

12. The vent line of claim 10 , wherein the sensor is a rake sensor, a point level measurement sensor, a continuous level transmitter, a reflective level sensor, an ultrasonic level sensor, a flowline level sensor, a submersible sensor, a float level sensor, a vibration fork level, a proximity sensor, or combinations or multiples thereof.

13. The vent line of claim 8 , wherein the controller is electrically connected to an external timer, the external timer being configured to send a signal to the controller at a time after launch of a rocket when the level of the liquid propellant is expected to be below the equalization valve.

14. The vent line of claim 13 , wherein the time after launch of the rocket is determined based on calculations of rate of liquid propellant use or based on rate of liquid propellant use data of previous launches.

15. The vent line of claim 8 , wherein the controller further comprises a timer to indicate a time after launch of a rocket when the level of the liquid propellant is expected to be below the equalization valve.

16. The vent line of claim 15 , wherein the time after launch of the rocket is determined based on calculations of rate of liquid propellant use or based on rate of liquid propellant use data of previous launches.

17. The vent line of claim 8 , further comprising a vent duct including a vent wall having a bottom portion, the bottom portion including the equalization valve.

18. The vent line of claim 17 , further comprising a vent tube including an open end and an output, the output being connected to the vent duct and being an end opposing the open end and lower than the open end.

19. The vent line of claim 8 , wherein the level of the liquid propellant and the height of the equalization valve are measured from a bottom of the propellant tank in which the liquid propellant and the equalization valve are located.