I wanted to enter the discussion on HYDROS a bit and explain it a bit more
in a separate thread.
HYDROS is actually commercially available right now in a microsat class
size, and we have already delivered the first flight unit. The smallest
'base' configuration for the CubeSat version is about 1U, with a flexible
amount of water storage capacity. Our anchor customer happened to have 2U
of volume. I'm away from my models right now, but in a 1.5 U linear
configuration we could probably do over 1000 Ns. (These are BOTE
estimates). Freeze-tolerance requirements usually cause us to dedicate ~10%
of the tank volume to ullage space.
HYDROS is completely unpressurized on launch, and the first generation
systems operate at pressures which are considered low by most rocketry
standards. It doesn't require any pumps to pressurize.
We have found a robust method of keeping the gases separated. In case of
accidental mixing it is quickly detectable and we also have catalyst which
will allow the hydrogen and oxygen to combine in a safe way in case of
leakage. We have found It takes a pretty serious leak to reach the 4% lower
explosive limit, and because we are using the gases that are generate,
leaks wouldn't have enough time to build up to dangerous levels. I wouldn't
describe it as more dangerous than a conventional bipropellant.
It does take more energy to run than a butane thruster or steam rocket, but
an advantage of storing gaseous propellants is that the power requirements
are low. It is happy to run at a constant, low power rate throughout the
orbit, and doesn't need to rely on batteries during maneuvers. There are
now a lot of companies developing CubeSat and Microsat electric propulsion
systems, like hall thrusters and electrospray. These consume several times
more power, but isn't deterring their development. Our customers haven't
found our energy consumption to be an issue.
Thanks,
Lars Osborne
