Until now, no technology was known that would be able to give rocket exhaust at relativistic speed and a high enough momentum for relativistic travel. Here, a useful method for relativistic interstellar propulsion is described for the first time. This method gives exhaust at relativistic speeds and is a factor of at least one hundred better than normal fusion due to its increased energy output from the annihilation-like meson formation processes. It uses ordinary hydrogen as fuel so return travel is possible after refueling almost anywhere in space.
The nuclear processes give relativistic particles (kaons, pions and muons) by laser-induced annihilation-like processes in ultra-dense hydrogen H(0). The kinetic energy of the mesons is 1300 times larger than the energy of the laser pulse. This method is superior to the laser-sail method by several orders of magnitude and is suitable for large spaceships.
Researchers are working on an annihilation-like method. It is well studied in the laboratory and gives initially fast kaons and pions from protons or deuterons by annihilation-like processes. They use the phrase annihilation-like since the practical evidence and use is more important for its characterization than the claim inherent in the strict nomenclature without the -like. The necessary antimatter used is concluded to be formed by oscillations of the quasi-neutrons initially formed in the ultra-dense hydrogen by laser-induced processes from spin state s = 2 to s = 1. Considerable progress in the understanding of these complex nuclear processes has been made already. Thus, a practical solution exists for the annihilation rocket drive, ejecting relativistic massive particles and not only photons.
We can compare this laser-based method with other possible propulsion using lasers.
Laser pushed solar sails have been the main known method for potential travel at significant fractions of light speed. Laser-sails have momentum transfer from photons reflecting off the sails. The lasers used for the annihilation-drive described here have pulse energy of less than half of joule. This means that the total impulse per laser shot with a million trillion photons is of the order of one billionth of joule. Laser-ablation methods can probably not give higher impulse than the laser pulse, since the velocities of the sputtered particles are caused by the photon impact.
In the annihilation method described here, each laser pulse gives of the order of 10 trillion mesons with relativistic velocity. This gives an impulse which is up to 3000 times larger than the photon impulse. Thus, this annihilation-like method is far superior over other laser-based space propulsion methods.
Fusion processes have been the main focus of study for potential future interstellar rockets. However, the energy given to the particles ejected by a fusion process is rather small, in the first step in D + D fusion only around 3 MeV u−1. This corresponds to only 0.08 c.
Even with T + D fusion, the highest energy is only 14 MeV u−1, thus only 0.17 c. This is the maximum velocity that can be expected from nuclear fusion using hydrogen isotopes. This indicates a final velocity from D + D fusion of 55 million meters per second or close to 0.2 c without including any relativistic effects which will give slightly lower velocity. However, just a small part of the total D mass is converted to fast particles moving in the wanted exhaust direction, so far from 90% of the mass is exhausted as wanted. If T + D fusion is used, the final velocity becomes 120 million meters per second (0.4 c).
Nuclear fusion using the D + D or T + D reactions cannot give relativistic rockets (50+% of light speed).
A laser target with ultra-dense hydrogen used in this case is of the form fully described in a recent patent. A reasonable estimate is that 50% of the total initial mass of the protons is lost to neutrinos and photons. Some of the momentum of the photons may however also be useful for the rocket drive. Thus, it is estimated that 50% of the proton mass is converted to useful kinetic energy by such a rocket drive. The total energy from these nuclear processes is roughly a factor of hundred higher than from fusion, so the hydrogen fuel lasts much longer than if fusion was used for the drive. Also, ordinary hydrogen can be used as fuel for the annihilation process, which would not be possible if fusion was the main drive process used.
The energy efficiency is more than a factor of 1000. Over 1000 times more kinetic energy is given to the mesons formed relative to the energy in the laser pulse. Experimental reactors which produce relativistic particles from annihilation are operating in Sweden, Norway and Iceland and a propulsion system for relativistic drive should be feasible within a decade.