Fuel / Sail Starship Concept - (Preliminary)
By Kelly Starks -- August 96.
The Fuel / Sail configuration was developed as a merger of the Explorer Class, and Microwave Sail type of starships. One that I think uses the complementary stregths of each to compensate for the weaknesses of each to make a much more practical system them eiather alone.
The Explorer Class design was a fusion rocket system fueled with Lithium-6. However to get to any acceptable cruise speed, and still carry enough fuel to decelerate into the target system, a fusion powered ship would need to carry over 160,000 times its weight in fuel. The Explorer Class design got around this problem by having its acceleration fuel launched to it in small increments during the acceleration burn. This 'just in time' fuel delivery trick allowed the Explorer class to get to speeds over 30% of light speed while launching with a block of Lithium-6 'only' 400 times the dry weight of the ship. (One of the useful caracteristics of Lithium-6 is its cheap and plentyfull.) However since it is reasonable to assume the ship couldn't get fuel deliveries past a certain distence from the launcher. It was imperative that it accelerate rapidly. I.E. that it get as much speed as possible in the shortest distence. In the case of the Explorer class this assumed it could sustain 1g accelerations while picking up fuel canisters. A tricky manuver, and a fantastic engine system.
Traditional Microwave sail ships use a microwave beam reflected off a wire mesh 'sail', or parachute like structure, to accelerate the ship. This allows the heavy power and drive systems, and fuel ,to be left at home. Which makes for a light simple ship; but a ship that can't slow down since its propulsive force always pushes straight away from the microwave transmiters back home. We here (and in many other places), have argued over many strange and highly questionable ways to get a Microwave sail powered ship to slow down. So far no one has come up with a very workable idea. The M.A.R.S. system project is tring to figure out a way to convert the microwaves to reverse rocket thrust. The Argosey or Tradwinds system is a pure microwave system that assumes that it was precedeed by an expidition sent ahead to build a transmiter array to slow down, and launch back to earth the lighter, faster, pure microwave Tradewinds craft. This of course begs the question of how to get the first ship there.
The Fuel / Sail system uses Lithium-6 as the fusion rocket fuel like the Explorer Class; and like it, carries enough fuel to decelerate into the target starsystem. But to accelerate out of sol I spread out the Lithium fuel into a huge microwave sail (lithium is a structural metal). Since the vast bulk of the weight is spread out in the sail, its a more efficent sail system needing less stregth in the attachment cables. Since the acceleration doesn't require power from the Fuel / Sail ship, the ship doesn't need to be refueled while accelerating. Also the microwave system is simpler, and has greater range than any likly fuel launcher system, so the ship can accelerate longer over a greater distence, avoiding the Explorer Class designs ned for rapid early acceleration.
As soon as the Fuel / Sail ship approaches its cruise speed; the sail is pulled back in, melted and cast into a heavy cylindrical fuel plug in the frount of the ship. As the ship approaches the target starsystem, the fusion motors are detatched from the ship and mounted on the frount of the fuel cylinder and the ship starts its the deceleration burn. As fuel is cut out from the volume of the fuel slug nearest the ships hab and main systems section (and transfered forward to the main engines), these main ship sections will be shifted forward as the fuel is consumed from underneath it.
Note that since this design doesn't need to accelerate and decelerate as rapidly as an Explorer class. It can have a higher fuel ratio, and decelerate from higher cruise speeds. Possibly as high as 40%+ of light speed. Giving it a travel time to Alpha Centauri of under 12 years.
A more detailed evaluation of the sail power requirements and design details has not yet been completed, and will be added as soon as it is avalible. Since most of the design is very similar to the Explorer Class design, the below list shows links to applicable topics in the Explorer Class topic area.
Explorer Class Design Overview
Crew Quarters Centrifuge Design
Food Mass numbers
Mission plan and manifest
Bussard Fusion systems
External fueled Drive
Last revision. August 15 1996