2. They don't end up full of high-pressure gas, whose mass can be high
enough to matter, especially if you're not using helium.
In one Sea Dragon configuration they used GOx and gaseous methane to
pressurize the LOx and RP-1 tanks then burned the ullage for added delta-V.
Liquid methane was injected at the bottom of the RP-1 tank then vaporized
to pressurize the fuel tank.
Sea Dragon was a pressure fed 1KT to orbital rocket. First and 2nd stages
were to be recovered. Brain child of my mentor Bob Truax.
Ken
On Fri, Apr 7, 2023 at 4:22 PM Henry Spencer <hspencer@xxxxxxxxxxxxx> wrote:
On Fri, 7 Apr 2023, mark.spiegl@xxxxxxxxx wrote:
To me... the downside of the pistonless pump is the requirement to have
a tank of high pressure gas drive the pump (N2, CO2, other). Once the
tank/GSE/etc have been designed, does the pistonless pump offer any
advantage over pressure feeding the propellants? Don't know.
It uses about the same amount of gas -- after all, it's pushing the same
volume of liquid out at the same pressure. And there are some extra bits
of hardware, which add mass and cost. However...
1. The propellant tanks don't need to handle high pressure, which makes
them lighter.
2. They don't end up full of high-pressure gas, whose mass can be high
enough to matter, especially if you're not using helium.
3. Gas-liquid contact is brief and the surface area is small, so heating
the gas to reduce its density is more effective, and gas that's soluble in
the liquid (e.g. pressurizing LOX with GN2) causes less trouble.
Henry