Hi,

after testing in Orbiter, it seems that 481kg is more than the Electron can lift to anywhere near orbit.

This made me take another look at the diagram of the Photon stage and reassess the propellant sphere size, which I think I over-estimated.

[Off-topic]

This led me to wonder - what is the maximum size (radius *r*)for 4 equal spheres packed horizontally in a cylinder of radius *R*, and just touching the cylinder wall? A rough sketch helped me realise: *r* = *R* * sin(45deg) / (1 + sin(45deg))

And in fact, for *n* spheres, it generalises to: *r* = *R* * sin(Pi/*n*) / (1 + sin(Pi/*n*))

Although it doesn't work for *n* = 0 or 1

I don't know why my brain likes to think about these things, really.....

[/Off-topic]

The Electron is only 1.2m diameter, and leaving a bit of room for the fairing means the Photon stage is about 1m diameter.

So the propellant spheres must be ~ 0.2m radius max.

So at the moment, I have given the Photon stage 158kg propellant , ISP 3347Ns/kg , 55kg dry mass (+27kg for Capstone), and a 500N main engine.

Thats 240kg for fully fuelled Photon+Capstone, and leaves enough dV to get to Sun-Earth L1 after LEO insertion (provided you do multiple burns around perigee to keep the burn efficiency up).

I wonder if that's anywhere near reality?

Cheers,

Brian