Word: thermonuclear
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Quinta seems, from terrestrial observations, a promising target, and getting there is half of Lem's fun. The Eurydice is constructed in orbit around a moon of Saturn; its thermonuclear flowstream engines use hydrogen intake as fuel and can achieve a velocity of 99% the speed of light. While the scout ship Hermes, weighing a mere 180,000 tons, is sent off to reconnoiter Quinta, the Eurydice lingers in the vicinity of a black hole. When Hermes returns, the mother ship will execute an "incomprehensible maneuver called 'passage through a retrochronal toroid,' thanks to which she would reappear...
...refined their views of stellar evolution in general and of how, for some stars, an inevitable violent death occurs. The basic theme: a star performs a continual balancing act between its own immense gravity, which tries to pull all of its matter in toward the center, and the intense thermonuclear energy radiating from its core, which pushes the matter outward, keeping the star in the form of a distended ball of hot gases. For most of a star's lifetime, these forces are in equilibrium...
...long. The instant the remaining silicon in the core is fused into iron, the thermonuclear reactions stop. Without enough radiation pressure to sustain it, the now all-iron core, hidden under the star's outer layers, begins its final, catastrophic collapse. In the incredibly short time of just 1 second, according to University of Arizona Astrophysicist Adam Burrows, the core is compressed to more than the density of an atomic nucleus. "It's as if the earth had suddenly collapsed to the size of New York City," says Burrows. "At this point the rest of the star is oblivious...
...real trouble will begin as the sun nears the 10 billion-year mark, when the thermonuclear fires that have been burning since its birth have fused all the hydrogen fuel in the solar core into helium. As the fuel runs out, the nuclear fire will die down, and the now largely helium core -- which has been kept distended by the heat -- will begin to contract under its own gravitational pull...
Thus the question of nuclear testing is not critical for restraint of the nuclear arms race. The issue of nuclear testing, in my opinion, is of minor, secondary importance in comparison with the other military, technical, political and diplomatic problems involved in preventing thermonuclear calamity. Underground tests are conducted in sufficiently deep chambers with adequate safety measures to prevent ecological damage both in the country performing the tests or beyond its borders. As long as nuclear weapons exist and are not banned, the decision regarding underground testing is the internal, sovereign affair of each nuclear power...