Nuclear fusion, solar system

Most schemes that have been proposed to propel starships involve plasmas. Schemes differ both in the selection of matter for propulsion and the way it is energi2ed for ejection. Some proposals involve onboard storage of mass to be ejected, as in modem rockets, and others consider acquisition of matter from space or the picking up of pellets, and their momentum, which are accelerated from within the solar system (184,185). Energy acquisition from earth-based lasers also has been considered, but most interstellar propulsion ideas involve nuclear fusion energy both magnetic, ie, mirror and toroidal, and inertial, ie, laser and ion-beam, fusion schemes have been considered (186—190). 

Resource pessimists counter that this process cannot proceed forever because the eternal persistence of demand for any given commodity that is destroyed by use must inevitably lead to its depletion. I lowever, the eternal persistence assumption is not necessarily correct. The life of a solar system apparently is long but finite. Energy sources such as nuclear fusion and solar energy in time could replace more limited resources such as oil and natural gas. Already, oil, gas, nuclear power, and coal from better sources have displaced traditional sources of coal in, for example, Britain, Germany, Japan, and France. 

At 2000 K there is sufficient energy to make the H2 molecules dissociate, breaking the chemical bond the core density is of order 1026 m-3 and the total diameter of the star is of order 200 AU or about the size of the entire solar system. The temperature rise increases the molecular dissociation, promoting electrons within the hydrogen atoms until ionisation occurs. Finally, at 106 K the bare protons are colliding with sufficient energy to induce nuclear fusion processes and the protostar develops a solar wind. The solar wind constitutes outbursts of material that shake off the dust jacket and the star begins to shine. 

Students often state the laws of thermodynamics this way. You cant win because you cant get any more energy out of a system than you put into it. You can t break even because no matter what you do, some of your energy will be lost as ambient heat. Lastly, you cant get out of the game because you depend on entropy-increasing processes, such as solar nuclear fusion or cellular respiration, to remain alive. 

It is clear, for example from radio-carbon dating of rocks in the earth s surface, that the solar system must be very much older than the Kelvin age of 3 x 107 years. It is now taken for granted that the main source of stellar energy comes from nuclear reactions. The fusion of four protons (hydrogen nuclei) to an alpha-particle (helium nucleus) is associated with the release of energy Q, where Q k, 26 MeV. The total available energy is thus... 

Hydrogai, deuterium and most of the helium atoms in the universe are believed to have bem created some 20 billion years ago in a primary formation process referred to as the Big Bang, while all other elements have been formed — and still are being formed — in nuclear reactions in the stars. These reaction processes can only be understood in an astrophysical context, as briefly outlined in this chapter, which also describes how nuclear sci ce has provided much understanding about the universe, our solar system and our planets. Because the simplest fusion reactions, which created the lightest elements, could... 

As we search for the energy sources of the future, we need to consider economic, climatic, and supply factors. There are several potential energy sources the sun (solar), nuclear processes (fission and fusion), biomass (plants), and synthetic fuels. Direct use of the sun s radiant energy to heat our homes and run our factories and transportation systems seems a sensible longterm goal. But what do we do now Conservation of fossil fuels is one obvious step, but substitutes for fossil fuels must be found eventually. We will discuss some alternative sources of energy here. Nuclear power will be considered in Chapter 21. 

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