Kinkajou : Hey. Star Ship Enterprise stuff here. So what’s the word from Scotty in engineering?
Erasmus :All Scots are engineers and all engineers are Scots at heart, young Kinkajou. But back to the antimatter. Antimatter currently, is just a focus of research. The engineers build and maintain the research equipment. That’s as far as the practical engineering aspects of antimatter go.
Currently, we don’t really need engineers to “work” with antimatter.
WE can produce antimatter only in “atomic” quantities.
WE cannot store it in quantity.
Practically (as opposed to theoretically), we do not know how to use it.
The stuff is dangerous as hell to store.
- The stuff is extra dangerous to burn,
generating lots of hard radiation in violent nuclear reactions and is as unstable as hell.
I really don’t think that I want the stuff in our spaceship, at this time. It’s more likely to take us to heaven or maybe hell, than anyplace else we’d like to go.
Kinkajou : I think all the fuss about antimatter relates to its’ incredible energy density. This looks like being perfect for fuelling a spaceship. Antimatter propulsion is to many people, the Holy Grail of spaceflight.
When matter and antimatter react, the energy produced is many billion billion etc times larger than the thermo-chemical energy resulting from burning a kilogram of a hydrocarbon fuel.
Also, I suppose if it leaks, the danger is not inflicted on the planet-bound people responsible for building the antimatter reaction chamber in the spaceship. Most people really don’t focus on its dangerous aspects. A spaceship vaporising while in space and out of port is not really a problem to lots of people. (Apart from the fact that a lot of money, effort and expertise has been expended and lost in making radioactive fireworks).
Kinkajou : Let’s keep going. Give us an overview of this technology, old dog.
Erasmus :Matter and antimatter particles have the same mass, but opposite charges and spins. When these particles and antiparticles combine, they neutralise or annihilate each other, with consequent release of energy and other secondary particles of matter. This energy usually takes the form of a combination of gamma rays, neutrinos, antineutrinos, and pions. A single gram of antimatter converted to energy, yields energy as predicted by Einstein’s equation: E=mc2. This is a lot of energy. It makes antimatter very attractive as a very concentrated form of fuel/energy.
In 1995, the first anti hydrogen atoms (composed of an antiproton nucleus and an orbiting positron) were created at the CERN collider facility in Europe. Due to its extreme interactiveness, antimatter must needs be trapped and held isolated from ALL normal matter (obviously therefore in a vacuum), usually by electromagnetic fields.
There has been some work in storing nano-balls of antihydrogen in a vacuum at very low temperatures using magnetic field flux as the containment vessel. This is a difficult process. Note that the researchers worked with “cold” antihydrogen. Being “cold” makes the antimatter safer to handle.
The main process whereby antimatter escapes containment relates to the kinetic energy (heat) it contains, allowing it to become electrostatically charged and allowing it to move. The combination of charge and kinetic energy generates random “push” events that allow “hot charged” antimatter particles to push through electrostatic containment fields and then to react with and annihilate the shielding.
My impression is that the scientists have performed wonders to get the technology to the point now where it does work. I think however, that the solution of designing containment fields using a single force such as electrostatic force, is essentially a flawed proposal. There will always be high energy escape events. Random charged particles can combine to form an electrostatic pyramid of energies that add to the kinetic / thermal energy of the antiparticle at the top of the energy pyramid, giving it enough energy to escape containment.
Antimatter does occur in nature. It is a standard by-product of the fusion reactions powering stars. Some authors have suggested that about 10% of a stars energy output is based on the annihilation of antimatter that forms naturally as a by-product of nuclear fusion reactions.
Antimatter is of course difficult and expensive for humans currently to produce. We can only produce it a few elemental particles at a time in specialised nuclear collider facilities. These quantities are far from adequate for industrial usage. Annihilating a few sub-nuclear particles or anti-atoms just does not generate much “total’ energy, because individual particles are so very small. So, an antimatter accident with even say a thousand antimatter particles, does not have enough energy to create even a spark. A sparks’ worth of energy is not an economical proposition.
If humanity can work out a different way of collecting antimatter, the economics could change a lot. For example, consider if we could do “para-dimensional” mining right in the heart of the sun. The sun produces substantial quantities of antimatter as a by-product of solar fusion reactions. If we could ignore space and gravity: perhaps in one of those 13 dimensions of matter that are supposed to exist or through some quantum mechanism, we could collect substantial quantities of antimatter. This would make the use of this resource more commercially viable and applicable to a wider range of situations. Yes, antimatter is costly to produce. But it would be much more practicable and cheaper to “mine” your antimatter directly from the sun for industrial applications requiring commercial quantities of the material.
Antimatter could well acquire a role in special situations such as powering spaceships, dangerous as it may be. The attraction is of course in the “concentrated” nature of the energy and the capacity to convert so much to energy so fast: essentially instantaneously.
Kinkajou : But then you have to store it.
Erasmus :Antimatter has been mentioned as powering for example, the Star Ship Enterprise. The creation and storage of a super concentrated and volatile energy source such as antimatter is difficult. Various techniques have been researched to store and to manipulate antimatter in storage, apart from cryonic antihydrogen storage. Making bigger anti-atoms such as anti-Helium allows easier storage. Lasers have been used to manipulate antimatter for containment.
An industrial accident could become a civilisation ending incident if enough antimatter is stored. Antimatter reactors would also be quite dangerous in terms of producing large amounts of radiation: pions, gamma rays and neutrinos. They would require huge levels of shielding and extensive safety protocols to enable their use commercially.
Some of the spaceship designs I have seen, call for long thin spaceships with the antimatter engine as far as possible away from the bulk of the spaceship.
Kinkajou: But if we are able to totally annihilate matter, completely converting it into energy, how can we go past that?
Erasmus :Well firstly, that’s just not true.
The only particle antiparticle annihilation reaction that immediately converts one hundred per cent of the particle mass into energy is the collision of an electron with a positron. When this reaction occurs at low kinetic energy, it must produce two or more gamma ray photons as the output of the reaction. There must be a minimum of two gamma rays emitted with an energy of 0.511 Mev. (This is a requirement dictated by the need to balance momentum and energy in the annihilation reaction). If there is a substantial amount of kinetic energy in each of the particles involved in the collision, other more massive particles can be produced.
Particle antiparticle tracks
When protons and antiprotons react, a variety of particles are emitted. This reaction is much more complex because a proton is a composite particle. Protons consist of two up quarks and one down quark. Antiprotons consist of two anti-up quarks and one anti-down quark. There are also other elementary particles in the proton or antiproton such as gluons which bind the quarks together. These transmit the strong nuclear force which provides the attraction between quarks and anti-quarks. This force operates at distances of less than 1 fm. (fempto-meter) At this distance, the quarks and anti-quarks tend to pair up, a reaction that forms three pions, releasing a substantial amount of energy, as the mass of the output pions is much less than that of the proton-antiproton source.
So in a proton- antiproton collision, a quark may annihilate with anti-quark, but often the remaining quarks and anti-quarks recombine into a number of other particles, namely mesons. Mesons are unstable and rapidly decay into other particles such as pions, kaons, gamma rays, electrons, positrons, and neutrinos. This type of reaction will occur with any of the larger elementary particles. Antiprotons can annihilate neutrons. Similarly anti-neutrons can annihilate protons. These reactions can occur in many different pathways and can be very complex and can also be multistage. This gives a very variable output for this nuclear reaction.
Kinkajou : Yes, I see the problem. Industrialisation is more efficient in simpler more homogenous reactions. The more uniform the reaction by-products, the more susceptible is the industrial reaction to optimisation. I think you could design an antimatter reactor to use many different reaction by-products, but optimisation is best done when the reaction by-products are predictable.
Erasmus :Exactly! But proceeding. When an anti-subatomic particle annihilates a more complex structure such as an atom, the resulting mesons also have a substantial probability of being absorbed by the remaining spectator nuclei, instead of escaping. Energy outputs of up to 2 GeV have been observed. This amount of energy can exceed the binding energy of even large stable nuclei such as inside the nucleus of an atom of metal (e.g. iron) in the reactor shielding.
Iron is classically one of the most stable atoms in terms of nuclear binding energies. Smaller atoms such as hydrogen / Helium atoms and larger atoms such as uranium or plutonium atoms, all have lower nuclear binding energies than is inherent in an iron atom. It is known that atomic nuclei attain maximum stability in energy terms at nuclear sizes approximating that of iron: namely 26 protons and approximately 30 neutrons.)
Particle Tracks Physics
Kinkajou : I think I can see the problem. Complex annihilations can generate enough energy to make atomic nuclei decay or transmute. They actually change the visible “structure” of matter. I would imagine that many of these particles may well be radioactive if the resulting proton/neutron packing ratios are not optimal. The reactor shielding would deteriorate with time and the radiation hazards could well be substantial and long lasting.
Kinkajou : But what about the energy itself as the main consideration?
Erasmus :Not all the radiation released from antimatter –matter interactions is usable as energy. Much of it would be lost as complex radiated sub-nuclear particles, making antimatter quite a dirty energy source.
Particles generated by matter- antimatter reactions include: Pions, Neutrinos and Gamma-rays.
Pions are charged particles. When generated in a reactor, they can be organized to push against a like charged electrical field in a reaction chamber. The expansion and contraction of the field provided by the ‘push’ of the pion flux against the field can be used to create electrical current.
Neutrinos: These are small essentially massless particles which can pass through a planet size body of matter without interacting with any of the particles. Any neutrinos produced are essentially lost to power generation. Neutrinos can represent 25-50% of the energy output of an antimatter- matter annihilation reaction.
- Gamma Rays: These are essentially very powerful x-rays. We are familiar with how to generate electrical energy from electromagnetic particles, though the energy of these particles makes them difficult to work with. At the least, they could be used to heat a reactor blanket to generate heat or thermal energy, which could then be used to generate electrical power.
Kinkajou : Antimatter has a long way to go before it becomes a main stream technology even in special (niche) applications. Except maybe of course on the starship Enterprise.
Any other ideas out there for using antimatter?
Erasmus : Some authors have suggested using a material (composing a light sail or parabolic sail) to reflect gamma rays, and to provide propulsion, deriving thrust from the gamma rays produced in the annihilation reaction. However unfortunately, we do not know of any material which is capable reflecting gamma rays.
Kinkajou : Sort of caps the upside on the idea, don’t you think?
Erasmus :Just because it’s not possible today, does not mean that it never will be.
Light energy takes years to exit the solar photosphere. It suggests that very high density matter such as exists within a star may be capable of acting as reflecting or as a lensing media. However, I think it will be some time before you’re using super dense matter as mirror or lensing material in association with nuclear reactions. I can see that if we are able to generate gravity, it may well be possible to maintain compression of atomic or nuclear material to a level similar to that occurring within the sun, and therefore able to act as a lensing material for high-energy photons, such as gamma rays.
Nuclear Fusion in Sun
Kinkajou : Unfortunately, sounds more like a weapon to me, not a spaceship drive. Perhaps same principle but different energy levels. So, any more comments "old one", on the use of antimatter as an energy source and for propulsion?
Energy Momentum Relationship
Erasmus :The other problem derives from the fact that although photons have high energy, photons have low mass. Remember E=mc squared. I have seen someone calculate that it requires someone of the order of 300 MW of energy condensed as photons and collimated into a propulsive beam to provide even a single Newton of thrust. (Newtons are a measure of force or momentum and they relate to mv not mv squared.)
Energy is useful in propulsion but only as providing power for the mechanisms of propulsion. Energy production is based on mc squared (or mv squared)
Propulsion is based on the principle of momentum. M = mv.
Engineering Starship Enterprise
(This equation summarises that momentum is the product of the mass ejected and the speed at which it is ejected.) If momentum is created by ejecting energetic matter from a spaceship drive, this will be imparted to the spaceship, enabling the much larger mass of the spaceship to move forward at a smaller velocity. The situation being that momentum ejected from spaceship drive = momentum given to spaceship: the scientific law being the principle of “conservation of momentum”.
It seems unlikely that you can use much of the energy such as gamma-rays generated from an antimatter reactor as a propulsive force.
Kinkajou : But people have been talking about using complex antimatter reactions as engine fuel.
Erasmus :True. When antiproton is annihilated against a complex nucleus for example such as in copper or lead, many of the reaction products become electrically charged and can be focused into a unidirectional beam by a magnetically operated engine nozzle. This material can then be magnetically accelerated and used to provide thrust and momentum for a spaceship.
A couple of scientists Keane and Zhang decided to redesign earlier models of magnetic propulsive engine nozzles. They were able to do this because our understanding of antimatter reactions and the dynamics of charged particles moving in magnetic fields has progressed considerably over the last few decades. In their model, both positive and negative pions can be focussed and ejected energetically to provide momentum for propulsion.
They were able to calculate the effective exhaust velocity of the new nozzle design could achieve about 69% of the speed of light. This means the spacecraft using an antimatter magnetic nozzle engine could make a one-way trip at a speed of about 0.7c and with substantially increased payloads. They found that a magnetic nozzle about four meters long and 1.5 meters in diameter having a maximum magnetic field of 12 Tesla would represent an optimal configuration for the general design assumed in the study. Such a magnetic nozzle could be made using today's technology, although some rather special engineering would be needed to attain large values of thrust.
Engineering Starship Drive Engine
Energy losses inherent in this engine are:
Rest mass of the charged and un-charged pions (approximately 36%);
Kinetic energy of the uncharged pions which cannot be deflected for thrust,
And as photon energy losses via neutrinos and gamma rays.
Kinkajou : So what other rocket designs have been proposed for antimatter usage?
Erasmus :A number types of antimatter rocket have been proposed, at various times. We have mentioned the photon rocket. We have mentioned the magnetically accelerated particle engine. Others have proposed using a heat derived from the antimatter engine (derived from gamma-ray photons) as an intermediate energy source to generate electricity. This can then be used to provide propulsion. Alternatively, the heat can be transferred to a gas (directly or indirectly), plasma, or liquid propellant. There have also been other proposals using antimatter to catalyse fission or fusion reactions to again either provide energy or propulsive force.
The thermal antimatter rocket engines propose a number of different models. The antimatter initiated reaction can be used to heat either a solid core or liquid propellant in the antimatter engine.
The plasma core engine proposal is probably the most favoured this point in time.
It allows the propulsive gas to be ionised and hence magnetically accelerated.
It is capable of operating at higher effective temperatures than other models.
Heat losses are suppressed by the usage of magnetic confinement in the reaction chamber and nozzle. The magnetic field insulates the plasma from metallic shell of the engine, which houses the fuelling reaction.
Erasmus :Another model proposed from science-fiction suggests that an electric field is introduced in the proton antiproton plasma to create a pinch discharge magnetic field that can collapse the ion plasma into a very dense state, possibly up to even near atomic nuclear density. This intensely localised reaction squeezes the particle antiparticle combinations into a linear confirmation, generating near laser like gamma ray outputs. Intense magnetic field recoil is generated by the firing of the collimated gamma photon beam with pulsed field strength about 30 to 40 Tesla. The recoil force can be conducted back to the spaceship through the choice of magnetic superconductors surrounding the reaction chamber.
Poul Anderson described such a vehicle’s operation in fiction in his Harvest the Fire (1995), Friedwardt Winterberg proposed this type of reactor technology in his writings.
Kinkajou : Definitely, a weapon I think. A Gamma-ray laser would be any ugly little club in war. Be a shame if the gamma-ray burst ran forward as well as backward.
Erasmus :To avoid that particular problem, just design your spaceship sideways not longitudinally.
Kinkajou : That would do it.
Erasmus :Another proposal is to use ultra-dense deuterium (such as may exist inside small dwarf stars). This material is apparently superconducting at room temperature and can sustain magnetic fields apparently up to 100,000 Tesla. This may form another workaround for the problem of the magnetic confinement of antihydrogen at more sustainable temperatures.
Kinkajou : So summarise some of the difficulties inherent in the use of antimatter rockets!
Erasmus :The problems seem endless.
There is a significant problem with extracting either energy or momentum from the output of an antimatter annihilation reaction.
Much of the energy is in the form of extremely powerful (high-energy) gamma radiation and other currently un-manipulable particles such as neutrinos. Electron-Positron annihilation is the cleanest most efficient option, but the only obvious commercial source of positrons would be to mine them directly from the sun.
There is a substantial amount of waste heat.
Gamma radiation is a problem in that it damages the reactor and rocket hull housing over time. Radiation makes metals harder, more brittle and less deformable.
Gamma radiation is extremely harmful to biological systems. It is carcinogenic and mutagenic. It kills.
There are issues also that may contribute to space background radiation as well as reactor output radiation ionising the rocket’s hull over time. Differential charging of various parts of the spacecraft hull, could lead to the formation of high-strength electric fields which arc between spacecraft components causing damage or injury.
Neutrons and other particles output from the high energy antimatter-matter collisions can cause exposed material to become radioactive and to deteriorate due to transmutation of the nuclei of the atoms.
I think the most obvious problem is the need to dump mass to create momentum / force for propulsion. Spaceships are closed systems and mass is at a premium. A spaceship could lose 10% of its mass as propulsion fuel just to attain a speed of 0.1c. The same again when it slows down. And double that whole lot again when you come home. Essentially in crude terms, giving an answer that 40% of a spaceship’s mass needs to be discarded as fuel.
Protecting the crew is obviously a deal breaker. In short, the crew needs to have
shielded biological support systems
shielded cooling materials
shielded spacecraft and engine
Spaceship hulls would need shielding.
Shielding is important for several reasons in spaceships.
Spacecraft in general moving at high speed through space would suffer significant erosion of the spacecraft’s hull due to collision with particles of dust gas or micrometeorites. This problem is not the fault of the antimatter drive but a consequence of achieving at least partially relativistic velocities such as 0.1c. This means that success in propulsion generates a need for mechanical shielding.
Shielding needs to be directed against radiation and against heat as well.
Being able to derive electricity from ionic plasma or from thermal energy produced by an antimatter reactor is obviously desirable. Dealing with excess heat and radiation is obviously essential in a successful spaceship.
These competing needs may require the design of different subsystems.
Kinkajou : So you’re not sounding like you really are a fan of using antimatter and spaceship engines.
Erasmus : No I think there are many practical difficulties in using this material and a number of extreme dangers.
I think the most obvious application of antimatter is military situations. An Antimatter drive missile would be a very useful animal indeed. High thrust is critical. High-energy detonation is critical. Radiation could even be a benefit. The ability to miniaturise rocket engines using this technology also allows for very compact payloads.
Many the disadvantages for building spaceships arising from antimatter use are not really a problem in military applications. In fact, the inherent dangers of using antimatter in reactors for propulsion translate into considerable advantages when using antimatter in weapons.
Kinkajou : So what do you see as the future?
Military Antimatter Pulses
Erasmus :I think the most obvious propulsive mechanism for spaceships in the long-term is gravity. Gravity appears to be massless. (In fact, it must be massless and energy-less, because we believe in the equivalence of matter and energy via E= mc squared). Gravity can escape from a black hole because it is massless and eneregy-less. If gravity can be generated, it is likely to be able to be generated using standard energy sources such as nuclear fission to provide energy for its generation. You don’t need mass for propulsion. Because gravity is massless, a spaceship can leave Earth and arrive at a destination at much the same mass, not losing up to 40% of its mass as fuel.
Current propulsive systems demand the emission of mass to create momentum to create propulsion. Gravity drive would bypass this.
The availability of gravity could even make nuclear fusion a practicable energy source. Gravity would be the second stabiliser for the electrostatic containment fields for the plasma fusion fuel. Currently, the generation of effective and stable containment fields is not possible using purely electrostatic forces.
Gravity would be very useful:
As containment mechanism for reactors providing either energy or propulsion,
To provide living environment for biological organisms,( gravity is essential for bone health and muscle fitness)
- As an environmental shield against gas dust and micrometeorites existing in space. Orbital Starship Engine
Kinkajou : What do you think, Goo?
Goo : Obviously moving a spaceship between stars would be extremely difficult. It requires considerable technical expertise. The most obvious problem is the need to inject mass to create propulsion. This means a lot of mass needs to be carried with the spaceship and the spaceship will require refuelling at destination. Gravity as a propulsive mechanism seems a much more obvious choice.
Antimatter I agree, seems to be more suitable for use as a weapon or as a propulsion system for a weapon.
I think the problem of collisions faced by spaceships travelling across interstellar distances, becomes a very serious problem. Even small particles striking a moving spaceship at relativistic speeds can cause substantial damage. There is no one nearby to help repair damage. There are no resources apart from those available in the spaceship, in terms of people or materials or expertise. If the impact crisis is prolonged, you may not even be able to do anything to cope with the situation. For example, flying at a speed of 0.2c into a dust cloud, even a small one, would be a disaster.
It is the energy density of the antimatter that beckons to us. But how to use it wisely and appropriately is a question that may well take as some time to answer.
If we can obtain it cheaply, all bets are off. Positrons mined “cheaply “from the sun could well form the basis of many power and propulsion systems. Finding an antimatter asteroid could also well provide the impetus for the development of skills in using antimatter in many applications. As per usual, what you can do is often about the money or the economics. The science is often the easiest part of a new idea.