The "Dyson Cap"
In 1960, physicist Freeman Dyson postulated that an exceptionally advanced civilization could surround a star with a spherical shell with a radius of 1 Astronomical Unit (the average distance between the Earth and the sun). This would allow them to harness the practically inexhaustible supply of radiant energy. Such a Dyson Shell will almost certainly remain technologically impossible for our civilization for the foreseeable future, however.
Alternatively, a tiny Dyson Cap (a small section of a Dyson Shell with a radius far less than 1 AU) is much more conceivable. The Dyson Cap could be positioned beyond the bow of the starship so that it would absorb the radiated energy of the Schwarzschild Kugelblitz. This would provide forward thrust for the starship. However, the numbers do not render this option favorable.
Consider a Dyson Cap constructed from, for instance, titanium. The absorbed energy from a SK’s gamma rays would melt such a Dyson Cap out to distances of approximately 30 kilometers (19 miles). However, at a distance of say 33 kilometers (20 miles), the radiation from the SK could be captured by the Dyson Cap without the risk of it melting.
The thickness and diameter of the Dyson Cap would need to be optimized for maximum acceleration. A large diameter and large thickness would increase the amount of absorbed radiation. However, there is a tradeoff here. Too much material, the cap becomes inordinately heavy, and the starship’s acceleration is reduced. Too little material, and insufficient radiation is absorbed to produce appreciable acceleration.
The need to place the cap so far away from the Schwarzschild Kugelblitz means that the Dyson Cap will receive very little radiation, and consequently provide very little thrust.
In fact, over the course of the approximately 5-year lifetime of the above-mentioned SK, a starship the size of a 100-storey office building would increase its speed by only 4 parts in 100,000 above its initial speed; it would have accelerated a distance of only 1.5 AU! Even if the mass of the entire structure could be reduced by a thousand-fold, the starship would reach only 4 percent of the speed of light at the time that the SK evaporated. In contrast, postulated fusion reactors show promise of offering 2-3 times this maximum speed!
The "Dyson Shell"
Alternatively, if all of the accessible energy could be captured and if a significant fraction of it could be used for propulsion, the outcome changes substantially. One approach to accomplishing total energy capture is to surround the Schwarzschild Kugelblitz with a tiny Dyson Shell. The absorbed particle energy is fed to a heat engine, which propels the starship.
When all of the available energy from a typical SK is fed into a 100 percent efficient engine, the starship will reach 72 percent of light speed in the 5 year lifetime of the SK. This formidable subluminal speed would allow a starship to reach, within a human lifetime, a number of stars in the solar neighborhood.
A Few Kugelblitz Challenges
To construct a Dyson Shell (or Cap), an exceptionally light and very absorptive material would be necessary, because a 33 kilometer radius, 1 centimeter thick titanium Dyson Shell would have a mass of more than 1,200 Empire State buildings! Alternatively, a Dyson Cap that absorbs radiation that would be fed into a heat engine, would have a lower mass, but would also deliver an inferior acceleration.
Furthermore, a gamma-ray laser is currently the only conceivable technology that could be used to make a Schwarzschild Kugelblitz. However, such a laser’s output frequency would need to exceed current technology by more than a billion times. Its pulse duration would have to be a hundred billion times shorter than that of lasers today. The total energy of a single laser pulse would need to be equivalent to the energy the sun puts out in 1/10 of a second.
While it’s true that the technical challenges render it unlikely that a SK will be fueling an interstellar starship anytime soon, it’s imperative that we embrace a wide range of theoretical research. SKs can produce many petawatts of useable radiation; therefore, they hold the potential to be an ideal source of power for interstellar starships. Thus, in time, Schwarzschild Kugelblitzes may merit a position of distinction on the vast technology arc that could one day take us to the stars.