Risk and star travel

Scientists recently discovered that intense photons can interact to create positrons and electrons very efficiently. Others have shown that these materials, even though they interact to produce photons again, can be made into a stable superfluid called a Bose-Einstein condensate that has a density greater than iron - around 8 kg/liter. Furthermore, structured crystals, called electrets, can be fabricated on the nanoscale to store and manipulate positronium superfluids efficiently achieving 10,000 to 1 mass ratios. In this way structures can be placed in sunlight, even on the surface of the sun, or any star, and be used to efficiently absorb sunlight, store it, and regenerate controlled beams of photons to produce thrust effects. Thus, we can class this sort of star drive as near term given recent advances.

A gram of tantalum hafnium carbide (Ta4HfC5)aerogel crystal (with a melting point of 4,488K (7,619F)) equipped with nanoscale computing and equipment for making positronium from sunlight covers a square meter and is 1.25 mm thick. Fully charged the sheet can store up to 10 kg of positronium and regenerate collimated gamma ray beams to produce usable thrust.

This is sufficient to carry the device from Sol to the stars and back at 98% light speed. With recharging on the surface or near the surface, of the target star, this can be upped to 99.98% light speed each way.

For a relativistic positronium fueled rocket we have;

dV/c = tanh(ln(m0/m1))

And if we're carrying positronium we need to do this twice, so we take the square root of the overall mass ratio for a one way journey involving two boosts and we take the fourth root of the overall mass ratio for a two way journey involving four boosts.

At the lower speed time aboard ship moves 20% star time. At the higher speed time aboard ship moves 2% star time. So, 73 days aboard ship at the lower speed covers one light year. One week aboard ship at the higher speed covers one light year.

Accelerating at one gee it takes about a year to get up to relativistic speeds. It also takes about a year to slow down from these speeds to planetary speeds. So at each end it takes about a year and we cover about 1/2 of a light year. So, each journey can be shortened by 1 light year and the result divided by the factors above depending on speed, and 2 years added to the trip.

So, 4.3 light years to alpha centauri would take 2 years and require 3.3 additional weeks at the higher speeds or 0.65 years at the lower speeds - so between 2.06 years and 2.65 years depending on speed.

Of course Dr. Mark Roth's research shows that suspended animation is a solved problem. So, the 2.65 years is really no problem.

The real problem is the risk of exposure to star flight. This scales with distance, regardless of dilation. The risk of running into something is a function of distance.

Now, if star ships were as safe as airliners there would be 1 chance in 3.6 million of it crashing for each hour of exposure. This means that to travel continuously for 6.3 years (the time it takes for the ship to travel 4.3 light years including acceleration time) means that each way the ship will have a 98.5% chance of success. Both ways 97% chance of success.

Check out the chance of success of going out and returning as distance increases;

1 hour = 0.999999726
4.3 ly = 0.984993976 (one way)
4.3 ly = 0.970213132 (out and back)
10.0 ly = 0.891189561 (out and back)
20.0 ly = 0.809614914
50.0 ly = 0.607021015
100.0 ly = 0.375617459
200.0 ly = 0.143823502
500.0 ly = 0.008073877

only 2/3 of the ships going to 50 light years and back will make it. Only 1/3 of the ships going to 100 light years and back will make it. Only 1/7th of the ships going 200 light years and back will make it. Only 1 in 1200 ships going 500 light years and back will make it.

This will constrain the distances we travel to less than 200 light years. It will also constrain population growth if more people than are born each generation elect to travel to the stars.

This is how space travel will restore the stability to the human race.

A black body that was stable up to 4,400K and was 2 sq m in area (front and back) and absorbed over 1 sq m (front only) would be able to radiate away 42.5 MW - and so could absorb that much - and so would survive a distance of only 151,000 km above the solar surface. A system that was 50% efficient in turning solar energy to positronium would be able to operate on the surface of the Sun. Yet, even at this distance - we capture 7.45 grams per year per square meter. At this rate it takes 1,345 years to fully charge the square meter to its full 10 kg. Alternatively, transporting positronium from one region in the collector to another would allow 7.43 sq m to be fully charged per year per hectare of collector area.

Projecting holographic gamma ray images into the solar corona to create self-replicating systems - along the lines of Conway's game of life - and extracting materials from the solar corona, a square meter of collector can grow doubling every minute or so. In this way the output of the Sun can be captured in

A = 4 * pi() * 700e6 ^ 2 = 6.16e18 m2

So,

LN(6.16e+18)/LN(2) = 61.86 doubling periods

So, we could build a square meter of the materials we've been discussing, and let it collect sunlight for a year or so at Earth, and the meter flies to the surface of the Sun and covers it in about an hour!

It could absorb all the output of the Sun over a period in excess of 1,000 years - and let only the light through to the Earth and other bodies of the solar system - so they would see nothing different - even though the vast majority of solar energy were absorbed. 4.59e15 kg of positronium would be generated per year by this process. Only 4,000 kg is required to power human industry.

So, we can imagine an alien species negotiating with Earth, asking for the output of the Sun, saying nothing in the solar system would be adversely affected, and they could solve our energy problem and all other earthly problems - and haul off the energy of the Sun.

At 10,000 to 1 mass ratio 4.59e12 kg per year could be dispatched from the solar system by positronium rocket. At 650 kg per person all of humanity each year could be dispatched from the Sun.

Nanoscale systems put into an array can disassemble materials coming into contact with the surface. The atoms that are extracted are recorded as to type and position. So, not only is the material dissolved and transported to where its needed, but also the information about the material is also recorded if desired.

So, a ham sandwich and beer with chips can be placed on this surface - disassembled into component atoms, and reassembled when desired. So, raw materials can be assembled into desired materials. The cost of 40 MJ per kg. Since a kg of rock contains over 640 MJ of useful energy in the form of Lithium-6 Deuteride - raw material can be processed 8 times. Of course with a store of anti-matter, 10 kg of positronium has the same amount of energy as 372 kg of lithium-6 deuteride which processes 124,000,000 kg of rock.


Humans consume 730 kg of food per year along with another 2,200 kg of consumer products per year. About 3,000 kg per year. So, 10 kg can support 41,000 people for a year.

4.59e15 kg of positronium the output of the sun using the technology we are discussing here could process 5.7e23 kg of rock or waste per year. Enough to support 1.9e20 people. 26.9 billion worlds as populous as Earth.

One way to increase chances of survival to near certainty, is to record the traveller and store the information in the vehicle - replicate the vehicle 1,000x or more - and send the records to the destination - and those that survive, restore the individual - along with all his/her belongings - at the destination - made from local materials. The return works the same way.

A more ambitious program entails sending many recordings to many destinations simultaneously - and then return back to Earth at a predetermined time. Then, to merge all the experiences of all travelers into a single resultant individual.

Of course, Sagittarius A* - the supermassive black hole at the center of the galaxy - has a sizeable ergosphere, the size of the orbit of Mercury. A vehicle can navigate through this ergosphere and emerge at any time traveling in any direction - with very little loss of momentum. Now, we can travel through space and time.

So, a person could form the basis of patterns that are dispatched to all points of interest - in space and time - have a life time of experiences - and return to the point of departure in space and time - to absorb the original traveler and recreate him/her with all the experiences gained - the moment of departure.

This would be less a journey and more a transformative experience.

This is a more advanced method of time/space exploration - and able to reach beyond the constraints imposed by risk.

http://www.youtube.com/watch?v=ryJCirHi4uc