Microwave Augmented Rocket System (M.A.R.S.) Starship Concept - (Preliminary)

By Kevin Houston -- August 96.

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 with the ground crew. 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.  It would work well between settled starsystems, but it can't be the first ship to stop there.  

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 most famous concept was used by Robert Forward in his 'Dragon's egg' serries.  Forwards Idea was to drop a large reflecting outer ring sail.  This outer sail would reflect the microwave beam (or laser beam in Forwards case) back at the ship and its smaller retro-mirror/sail.  Though elegant from a physics standpoint (Forward is a physisit by training) the concept would be hellishly complicated to implement. Since the reflector 'sail' would have to be tissuepaper thin, hundreds to thousands of miles across, and have to 'surf' the beam presure while precisely curving itself to focus the beam reflection on the fast moving ship.  A target that (given the relative relativistic distences) it couldn't even see in real time.  

The M.A.R.S. is trying to get around this problem by converting the microwaves to reverse rocket thrust.  The problem of course is that to convert them, the microwaves must be absorbed, which would also absorb their forward momentum.  About the only semi practical idea we have come up with to deal with that is a plasma mirror.  Basically the microwaves are focused backwards by the main sail.  Then caught and reflected forward by a drag sail, into a heavy ionized plasma cloud.  The plasma would reflect the beam backwards, as it is blasted forward by the beam presure.  The reflected microwaves can then be absorbed and used to accelerate a reaction mass forward (such as the already accelerated plasma) or simply use the drag sail for reverse thrust.

The two primary problem with this are that the energy level nessisary to move a heavy ship are staggering.  Some of our estimate are up to the 10 to the 18th power of watts, or joules per secound.  Current Earth electric grid estimates are about 10 to the 12th or 13th.  How this much power can be safly handeled or reflected, and what amount of mass flow will be needed to reflect it is still to be determined.  To put it mildly it would be a serious engineer chalenge, but not nessisarily and impossible one.  

If it could be made to work a M.A.R.S. type system would allow the ship to fly to, and stop at, comparativly distent stars at fairly high speeds.  It would not need to carry the fuel or power generators for this system, and might not need to carry a prohibative reaction mass.  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.  Current information follows:

Ships Mass 500,000 kg (5E5)
Ships acceleration 1 ship-G (10 M/S^2)
Sail density 50g/km^2
Sail reflection efficency   99%

Km g/m^2
Sail Mass in Kg Total Mass

(sail + ship)

Maser Energy in Watts Excess Energy KW/m^s Stress Pascals
10 1.57E+07 1.6E+07 2.43E+16 773.8 0.515915
100 1.57E+09 1.6E+09 2.36E+18 750.2 0.500159
500 3.93E+10 3.9E+10 5.89E+19 750.0 0.500006
1000 1.57E+11 1.57E+11 2.36E+20 750.0 0.500002
5000 3.93E+12 3.93E+12 5.89E+21 750.0 0.5
10000 1.57E+13 1.57E+13 2.36E+22 750.0 0.5
100000 1.57E+15 1.57E+15 2.36E+24 750.0 0.5

The listed thermal load of 750 KW on .05 Kg is a big worry, and needs to be analysed.  For example, the heat capacity and black body radiation have to be understood and delt with.

Since much of the ships systems and concepts (habitation deck structure, food consumption numbers, aukilury power reactors, etc.) are assumed to be similar to those developed for 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


Last revision.  August 15 1996

mail Author Kelly Starks

mail Administrator David Levine