Video Caption:This miniature documentary was created to highlight the San Diego State Rocket Project’s endeavor to build a dual cryogenic rocket, initially designed to compete in the FAR/MARS rocketry competition. With more than two years of engineering work, Lady Elizabeth launched to an altitude of 13,205 feet, leaving behind a legacy for many rocketeers to come.
Music (in order of appearance):
1901 – Phoenix
Unstoppable Now – The Phantoms
Ring of Fire – Johnny Cash
Should I Stay or Should I Go (Remastered) – The Clash
Fortunate Son – Creedence Clearwater Revival
Afternoon Delight – Starland Vocal Band
I have to be a little picky with this video, the masses given comparing pressure fed to electric fed could have been more detailed. In amongst those numbers, I assume is battery weight which would have been nice to know.
If they intend to use Li-Pos and if they want to reuse these they can only really go down to 3.0 volts per cell, or else damage occurs. Others using Li-Pos to power pumps I have heard go down to 2.8 volts per cell, but as this is in an expendable rocket, it does not matter as much. So a bit more care and extra battery capacity may be required to be able to operate safely, which is, of course, more weight.
There is also no deltaV comparison, which is really the only important number you are designing for when trying to reach space, in this case, 105 km altitude.
Where, Δv = Velocity change (deltaV) Isp = specific impulse g0 = gravity m0 = Initial mass (with propellant) mf = Final mass (without propellant)
The comparison also does not state the chamber pressure of the engine, I assume the electric comparison uses the same chamber pressure as the pressure fed. But as stated, the whole point of a pump is to decrease your tank mass and increase engine chamber pressure which in turn increases your engine Isp, your deltaV and decreases engine mass (theoretically). The question then is, what chamber pressure can you reliably design and manufacture for?
One must take into account the higher heat flux and added cooling requirements also.
The COTS or common of the shelf components I have to also argue, you are never going to be able to buy a pump off the shelf that will match your mass flow and pressure requirements, let alone material compatibility. Electric motors and speed controllers you may be able to, which will speed up development, but you will probably have to make modifications to make these flight-ready anyhow.
All in all, I can definitely see the advantages of looking into this pumping method for such a project, and it is great they are open to it.
I just wish the video lived up to its name more as we do not really get a good comparison between the two systems.
