Many have asked if pointing a rocket engine exhaust against the side walls of a propellant tank will not result in the tank exploding.
It will not.
To understand, there are five remarks to be made:
- Analogy: Rocket engine walls also have to deal with the intense heat of the rocket engine, but only thanks to adequate cooling with rocket propellant, through cooling channels in the engine and rocket nozzle they stay intact, while using a minimum of mass and material keeping them light weight;
- The same principle is also applied to the walls of the propellant drop tank. The mass of the cryogenic propellant mix and the way it is transported against the sides of the wall of the drop tank determines how long they survive the heat. With the high rate of fluid transfer involved in our design they last indefinitely.
- It helps that the heat a couple of meters away from the engine has actually cooled a lot compared to the temperature the engine sees. As a result the use of exotic alloys is not required.
- Duration of exposure: The drop tanks are only exposed to the intense heat for a max duration of 7 to ten minutes. This is not enough time to overheat and damage the drop tank walls given the adequate cooling provided and the order in which the propellant tanks are emptied.
- Our durable Thermal Protection System solution provides additional tricks to cool the side walls of the rocket. The TPS resists both the pressure, vibration and heat coming from the rocket exhaust and does not require refurbishing.
As a result, the answer to the question is: it depends on how well you engineer it.
For a real life analogous example of the operating environment you need to design for, we show you how long it takes for a propane tank to explode if you do not take additional measures. Notice that the video has been edited to be shorter.
For comparison: Notice the cooling loops in the venerable F-1, the Saturn V rocket engine used in the Apollo Moon program:
Sufficient cooling protects any wall.