Wednesday, June 7, 2017

Luna's Engines

After some discussion with my learned colleagues (At the Chung, Campbell, McVay and Black Design Group) I worked out the following factoids about the Luna's engines.

R-Ray
The R-ray is the primary propulsion. The Luna's ring generates a protational field. It is similar to gravity but it can attract or repel matter. Even though people call it a ray you can't see it anymore than a magnetic or gravity field. In fact if the R-ray does become visible as the saying goes, "Try to keep up with me."

R-rays are built using the Cepheus Engine table for jump drives. Instead of the rating giving you the maximum distance you jump in parsecs you get the R-ray's range. The range is the distance from the Sun that you can focus a beam accurately and efficiently enough to generate thrust. Read it as follows:

Range
1           Operates as far as Earth's orbit
2           Operates as far as the Asteroid Belt
3           Operates as far as Jupiter
4           Operates as far as Saturn
5           Operates as far as Uranus
6           Operates as far as Neptune/Pluto

Within its range the R-ray provides .1 gee of acceleration. An R-ray can operate up to 1 range further but at .01 gee. Getting to the outer worlds can take a while.

Closer to a world the R-ray is used to lift the ship by setting up a field between the ship and the ground. This is extremely safe. Once you have energized the field and raised the ship to a certain altitude you only need to put a little power into it to offset losses to mechanical inefficiencies and other field effects. A ship that loses power will drift downward very slowly, a few meters a second. The same happens with lift belts. In effect the R-ray has a built in parachute.

Some unscrupulous types with access to advanced technology can also shut down an R-ray from a distance or cause it to lose field strength fast, thus allowing boarding actions or bringing down your space support ships. But ships have reaction drives too allowing them to offset these shenanigans.

The Luna by the way has a drive rating of 3 and can easily make it to Jupiter and in a pinch Saturn.

When a ship is taking off or killing its field to drop quickly the R-ray is drawing back energy out of the field. This has such effects as heat, electrical discharge and looks a lot like a conventional chemical rocket in an atmosphere if a ship is really moving. Generally a lift off of a few meters can be done safely (still not a good idea to be in rifle range of the ship. Your phone and wirstwatch might be messed up. Lifting up to a gee creates heat, a lot of it and a boom like a rocket blasting off. On an airless world the ground under the ship bears the brunt of this with no atmosphere and you may leave a glassy crater behind.

How powerful is the drive? The Luna is 400 dTons. That's 5400 cubic meters. I go with .25 tons per cubic meter for my ship's rough density. That gives us 1350 tons of mass (we're going to leave the tonnage as volume alone from here out.)

The energy to raise the Luna ten meters is given by:

E=m*d*g
m is Luna's mass 1,350,000 kg
d= 10 meters (what we decided for the test flight)
g= 10 meters/s/s

=1,350,000 kg*10m*10 meters/s/s
=135,000,000 kg/m/s/s
=135 megajoules or MW

That's just for ten meters. To get out to say 1000 kilometers we need to use the gravitic constant and the Earth's mass and radius and orbit and such and the answer is in terawatts (trust me I'm saving you a lot of wear and tear on your disbelief's suspension by not getting into actual numbers here.) So if we want to get to orbit in any sort of reasonable time (like a few hours) we need a generator providing gigawatts at least. So yeah if you have as little as a few percent of that being released as static or heat you could kill a lot of people around you. Go look it up on the Boom Table at Atomic Rockets. A discharge of  100Kj is the equivalent of a stick of dynamite. Per second. Gentle lifts are called for in most situations.

Lifting the ship to 1000 km requires 11 terajoules. Assuming the beam emits 1 GW/s it will take Luna 3 hours to reach this altitude. She's still not orbiting. Personnel operating n the hull must remember that. Accelerating to 7000 meters per second (our arbitrary orbital speed chosen) will require 33 TJ and takes 9.1 hours. Acceleration is roughly .12 meters per second.

One more thing the R-ray sucks for lateral movement. While it could pull its rating in gees towards or away from a planet, lateral movement is typically a tenth that so for Luna with her three rating we're talking 3m/s. Not much.

The huge ring I added to the Luna design was originally a stabilizer to make landings safer. The ring now serves another function. Superconductor is looped around the ring. This immense battery holds power, a lot. Just in case the generators fail, the battery can hold enough to get the Luna a thousand miles up or let it hover for a couple of days. It also absorbs some of the power returned to the ship from using the field it established to descend or brake. So we're talking several terajoules at least. Oe TJ has the explosive force of 860 tons of dynamite. If anything seriously wrong occurs that superconductor becomes a not so super conductor and the energy is turned back into heat. In such an emergency the ring can be detached. It messes the ship up a lot less than the ring could if it was attached when it explodes. The ring has multiply redundant systems and is a heavily armored section.

Reaction Drive
Luna's secondary propulsion is a reaction drive, fueled with metallic hydrogen. The reaction is hot as f--- and kept away from material components of the ship with R-fields. This lets us use the nifty tractor rocket design and keeps our engines from going all glow-y and mushy. The repellor effect also supercharges the exhaust allowing very high specific impulse. The engines could lift the ship and let her hover though it will run out of propellant eventually. Luna has enough propellant for a round trip to Mars or Venus though it would take a few weeks.

The reaction drive can lift the ship far quicker than the R-ray. The 3 gee rating is for sustained burns. It could move (briefly) fast enough to break your neck. During evasive maneuvers people are strapped in.

Yes the repellor effect is used for a lot of different purposes. It is very useful. think of all the applications a laser now has. Lasers started out as death rays in common understanding. Now we use them for all manner of IT and sensory purposes. Just don't look into them.

The reaction drive is far less damaging than a nuclear drive and harmless beyond a few kilometers. It's also necessary to get Luna up to orbital speeds once you get to orbital heights. Luna could hover at say 1000 kilometers with the R-ray idling. You wouldn't be in free fall and if you stepped out a lock you'd learn that quickly as you fell to your death. The reaction drive is used to correct that when she arrives in orbit at her destination.

Fuel is metallic hydrogen in pellet form. It's way denser than liquid hydrogen, It also can be dumped easily in a fire or other emergency. You might even be able to use the R-ray drive to head back and retrieve some.

Total number of burns is given by the percentage of ship devoted to fuel propellant.

Ship %                          Gee Burns
of fuel propellant
10                                  4
20                                  10
30                                  15
40                                  20
50                                  25
60                                  35
70                                  50
80                                  60

A gee burn is one turn at one gee, three gee burns could be one turn at 3 gees, or three turns at one gee or any other combination. turns are 1000 seconds, so even one burn is a decent amount of boost.

All of this technology has ripple effects in the rest of the setting. The superconductor technology does require strong magnetic fields, strong materials to contain those fields and doesn't scale down nearly as well as people who favor laser pistols would wish. If a cubic meter of superconductor holds a terajoule, it doesn't mean a liter holds a gigajoule.

The metallic hydrogen also requires storage facilities that don't scale down to the size of rocket pistol rounds (though it works fine for their explosive shells).

Personal weapons would be very nasty though not up to say Star Trek (zap! You're gone!) standards.

Repellors do scale down pretty easily. They can make elevators high speed and ultra safe. Ditto for trains (though I'd keep a fee pneumatic trains for sentimental reasons.) The most notable use is the Lift belt. Lift belts delay falling or allow very high hops but as I said repellors don't do lateral movement well. Lift belts will have a variety of add ons if people really want to move.

As for flying cars ... no. Not really. A dieselpunk setting has electronics out of Mayberry N.C. There are no computerized auto-evasion or traffic control remotes. Pedestrians can definitely use lift belts. In fact they let you cross a street anywhere, anytime (they'll sell out in New York City, trust me.) But flying cars or similar vehicles will remain for emergency service or defense purposes.

Flying fire trucks would be awesome, except they have to carry their own water tankage.