"The Sails Of Tau Ceti" - читать интересную книгу автора (McCollum Michael)

УNot directly. If they intend to stop inside the Solar System, they have to
decelerate at something around one-thousandth of a standard gravity.Ф
УThat isnТt very much.Ф
УMore than enough to halt short of the sun. Remember, theyТve got one hell of a
long distance to fall.Ф
УIf theyТre slowing, they wonТt arrive as quickly.Ф
УTrue. We now estimate that the sail will reach us in five years rather than
three-and-a-half. A precise figure will have to await a better estimate of their
deceleration constant.Ф
Tory had been reviewing the technology of electrostatic brakes ever since
activating her implant. The idea had a surprisingly long history. An
electrostatic brake was essentially a device for sweeping up hydrogen across a
vast region of space and funneling it into a spacecraftТs path. In effect, the
spacecraft would plow through an artificially enhanced solar wind. Every impact
on the craft robbed it of momentum, causing it to slow.
The literature contained dozens of proposals on how to accomplish the trick. All
relied on the fact that there are some 100,000 hydrogen atoms per cubic meter
even in deep interstellar space. Most used a tuned laser to ionize the hydrogen
over a large region in front of the ship, and then attracted the ions with a
powerful negative electrical charge. The electrical field acted as a giant
invisible funnel that concentrated the interstellar gas onto a collecting device
such as a light sail. If the surface of the sail was then negatively charged,
the ions could be reflected back the way they had come before impact. Reflecting
the ions allowed twice the momentum transfer of merely bombarding the sail,
while protecting the sailТs surface from erosion at the same time.
УElectrostatic brakes work well enough when a ship is moving at high speed,Ф
Tory said, quoting from an encyclopedia article she had just scanned, Уbut their
efficiency drops off drastically with reduced velocity.Ф
УOnce close to the sun, theyТll transition to light pressure braking,Ф Hunsacker
replied.
УI think not,Ф Pierce responded. He, too, had been busy with his implant.
УToryТs right. Electrostatic braking efficiency falls off rapidly as you slow.
Even with optimistic assumptions for both electrostatic and light pressure, they
would still be going too fast to stop by the time they reached the sun. They
must be planning an aerobraking maneuver near the sun to finish the job. That is
a ticklish thing. If they hit that soup too fast, the passengers will be turned
to red mush.Ф
УHow do we know the mush would be red?Ф Ben asked. The question sounded like a
joke and drew him a baleful look from Sadibayan. In truth, he had been
completely serious.
Tory felt a small shiver run up her spine. The aliens were using their light
sail like a giant parachute. If they were to go into solar orbit, they would
practically have to dive into the sun. Whoever had thought up this scheme must
have been truly desperate. After a momentТs thought, however, she chuckled
quietly to herself.
Sadibayan turned his disapproving look from his aide to Tory. УWhatТs so funny?Ф
УWe are,Ф she replied. УHere weТre worried that they will fly too close to the
sun and end up like Icarus. Yet, they launched from out of the heart of an
exploding nova. I doubt they will be frightened by the prospect of diving
headlong into our little star!Ф