I can only imagine solid hydrogen being something like a metal. Keep it under argon or oil for circuits etc and it would be fine...
As far as combustion driven propulsion goes, I've always wondered why lighter fuels are chosen... I would imagine that "combustion" impulse engines with heavier "combustion"/reaction products would be better, no? (perhaps depending on the size and range of ship) Maybe controlled decomposition of tetrasulfur tetranitride or something like that would be more appropriate.
I like what I see of "ion" drives... plasma torches make perfect sense to me as an impulse engine, only problem is the excess gas required to sustain the torch that would vent (somewhat) wasted to space... hmmm, how to keep the neutral species and allow the charged ones to "push off"... a micro dc plasma might be the best approach... but then perhaps the standard inductively coupled plasma configuration would be better suited for recovery of unconsumed gas... then there's the energy source for the RF to power the plasma...
Perhaps a heavier product decomposition would make a better "ion" impulse engine. It might prove easier than managing plasmas.
There was another post (of yours?) recently about using a microwave beam to boil volatiles off a "sail" thus producing an impulse engine... problem is the beam and line of sight... (limiting).
I just had an interesting idea for a micro (to prototype it) impulse engine.. very simple, safe and practical (?). Think of it as a solar powered light bulb creeping through space. Not sure of the actual feasibility, but I like the idea: The idea is to take a standard light bulb filament (tungsten or similar rhenium) apply a current to it collected by solar panels, and direct the electrons boiled off the filament with a small field to acheive propulsion... you'd need a slow steady supply of filament.. (on a reel? an array?) hehe, I like this idea... worth exploring...
Again, thanks for the interesting post, got me thinking...
Solid hydrogen is (in theory) a metal. Metallic hydrogen (liquid phase) circulating on Jupiter is what is believed to give the planet its magnetic field. Just as the circulating iron and nickel in the Earths core is believed to give the magnetic fields here.
It is not the density that is relevant in the efficiency of a rocket fuel but the energy release. The oxygen/hydrogen combo is the best to date. In theory the metallic hydrogen/cyclic ozone beats that hands down. The fact that the major result of the combustion is water, not a pollutant is a useful side benefit.
The problem of ion drives is simple. To date no ion drive can expell mass quick enough to achieve liftoff from the Earh. Not even close. I'm not totally up to date on the ion drive but as I recall .01 g is considered a good acceleration for them. Ion engines also tend to use cesium. Not something that you want to throw around in bulk. Get an ion engine that can feed on Oxygen or Nitrogen in volume and you will really have something.
The microwave sail post was mine. The line of sight need not be a major problem. Place 3 arrays on the moon (6 would be better). One of the arrays will always be able to target the sail.
If you really want to see some interesting info you should look at some SciFi novels by Robert L. Forward. Particularly his Rocheworld series. Forward is (was R.I.P.) a phyiscist and "rocket scientist" with several related patents to his credit. In the appendices to his novels he goes over the science behind his propulsion systems. He gives a great deal of information on laser driven light sails and antimatter rockets.
I would like to see a magnetic catapault system, such as described by Heinlien in The Moon is a Harsh Mistress. Segments of such a catapault have been made at lab scale and the design can work. Cheap metallic hydrogen super conductors would make it very affordable. Add a cheap fusion power plant that can be turned on and off quickly and you have a winner.
There are other designs such as a (ground based) laser driven jet for launch with the onboard rocket not igniting until after the atmosphere is already behind you.
Imagine a 20 mile long catapault system accelerating a 100 ton craft at 6g for the length of the track until after leaving the track the laser jet system is activated and continues until the atmosphere is left behind when the (metallic hydrogen/cyclic ozone) rocket finally ignites carrying the single stage rocket high enough to deploy the microwave sail and go off to Mars 30 days later.
There are
many theoretical systems that are one or two engineering/science breakthroughs away from revolutionizing space travel.