Step by step sequence of transferred momentum.
Step 1 Solar sail propelled “Bricks” are launched to LEO. “Bricks” are small <30kg and can accelerate from photons at a rate of ~200 m/s per month at Mars, ~460 m/s per month at Earth and ~1440 m/s per month at Venus distances from the Sun. Functional equivalent average from Earth to Mars is 280 m/s per month. This corresponds to a real world acceleration of 0.175 mm/s^2 which is very conservative.
Step 2 “Bricks” deploy solar sails and navigate to 104 unique positions so that they will be at the correct position and velocity at the correct time to roundevous with the “mothership” This takes roughly 19 months to travel the distance of up to 5200 m/s away from Earth
Step 3 “Mothership” launched to LEO capable of ejecting “bricks” using a 400 meter long electro-magnetic catapult similar to maglev trains at 8Gs of acceleration reaching a final velocity of 250 m/s.
Step 4 “Mothership” is loaded with “bricks” sufficient to give 110 m/s of delta V. 100m/s are used to navigate and 10m/s are used as a reserve to dock.
Step 5 “Mothership” ejects “bricks” at 250m/s which is equivalent to 25.5s Isp. The mass fraction for this stage from the rocket equation is 1.55 of which 0.55 times mothership mass is bricks.
Step 6 The “mothership” arrives at a refueling station consisting of a group of “bricks” that have retracted their solar sails and docked with each other and are in a configuration to dock with the “mothership” The refueling station should be very precisely matched to the position and velocity of the “mothership” making the docking a low delta V maneuver. The mass fraction leaving this station will again be 1.55 because the next station is also 100m/s away.
Step 7 The loaded “mothership” repeats steps 5&6 a total of 51 more times to get to Mars
Step 8 The loaded “mothership” returns from Mars using a similar process as getting to mars. The round trip only uses each “brick” a single time but the bricks are not consumed allowing them to be used for additional voyages.
Step 9 after being used in a transit the bricks return to LEO at a single point and then repeat from step 2-8 for each additional voyage within the lifetime of the “bricks” Because the bricks are only used once per transit they can be used to accelerate as fast as energy permits and will be able to compete with rocket fuel acceleration rates over a round trip Mars trip.
High level reasons why this is efficient before we do the math
- The bricks are not carried on “mothership” the entire journey. This partially defeats the rocket equation.
- The reaction mass used by “bricks” is supplied by the sun in the form of photons
- The the solar sail propelled “brick” has its energy supplied by the sun
- No Earth sourced reaction mass is consumed by dispersion in the way rocket fuel is
- The “mothership” can produce energy efficient acceleration because it is only launching projectiles at 250m/s which is 25.5 Isp
- If the “bricks” and “mothership” had infinite life and the sun had infinite life there would be no need for new reaction mass from Earth ever.
- Even at end of life the “brick” mass can be collected and reused unless there has been a collision or some other dispersive event that threatens all spacecraft.
OK Math time
104 segments each require 0.55 times the “mothership” mass in “bricks” this gives 0.55*104=57.2 times the “Mothership” in bricks for a round trip to Mars. This is a round trip mass fraction of 58.2 This is equivalent to a 261 Isp fuel considering (10400m/s voyage) or 287s Isp (if you consider the extra 10 m/s on each leg).
But the “bricks” are not consumed and can be used for more than one journey. A 30 year lifetime with a 37 month refresh between transits gives a useful transits of 9.73.
So lets consider 453s Isp round trip to mars (10400 m/s) performed 9 times. Each roundtrip consumes 9.4 times the “rocketship” mass. So the total fuel consumed is 9*9.4=84.6 times the “rocketship mass” compared to the “brick” “mothership” that only needs 57.2 times the “mothership” mass.
A round trip to mars needs to eject 57.2 kg of “bricks” at 250 m/s for every kg of “mothership” mass. This amounts to 57.2*0.5*1*250^2=1,787,500 joules/kg for a round trip to Mars. This is 0.057 Watts per kg over a 6 month each way trip. There is no energy limit on achieving much faster acceleration.
Long term implications
- If you can create a infinite life “brick” and an infinite life “mothership” then there is no need to produce the reaction mass because its provided by the sun for the duration of the sun’s lifetime
- Even if your spacecraft life is not infinite its mass is not lost if you posses the technology to melt it down and remanufacture it then it is essentially infinite life in terms of there not being a need to pull mass out of a gravity well.
- “reaction mass free” transit between Mars and Earth, Venus and Earth, Moon and Earth are completely game changing
- Within the operating space of solar sail spacecraft the transferred momentum technique scales to high delta V better than rocket fuel because it doesn’t carry the fuel the entire way. This will allow faster transits and protect astronaughts from radiation.
- Solar system navigation is thus synchronized with interstellar navigation in terms of spacecraft lifetime being essential with lifetimes of 100s and 1000s of years being required.
- Spacecraft will be LARGE in the future. The launcher length of the brick launcher improves the system performance and having high fidelity position knowledge is possible if quasar navigation is used. This is also in alignment with what is probably needed for human travel to nearby solar systems.