Where the solar wind subsides behind us and eternity stands next to us … What awaits those who could break through the heliopause and touch the light of distant stars? The ghostly glow of Kuiper belt particles. Decades of flight without the possibility of replacing failing units. Attempts to establish communication with the Earth from a distance of 200 astronomical units.
Will it be possible with modern technologies to take such distant frontiers? Fly to where the radio signals come from with a delay of a day? Even light gives way to a huge distance, but the human mind goes forward.
Jump through daylight
30 billion kilometers. 70 years of flight with the use of existing upper stages with LPRE. Modern interplanetary stations are not designed for such expeditions. After three to four decades, the radioisotope battery dies. The supply of hydrazine in the AMC orientation engines is running out. Communication is disconnected, and the probe, which has fallen asleep forever, dissolves into endless space.
To date, mankind has managed to build six "starships" that have exceeded the third cosmic speed and have left the solar system forever.
Here are the names of the heroes.
Automatic interplanetary stations of the Pioneer series numbered 10 and 11. Launched in 1972-73. The "pioneers" reached the region of the outer planets, for the first time transmitting photographs and scientific data from the vicinity of Jupiter and Saturn to Earth. Having made a maneuver in the gravitational field of the giant planets, they left the ecliptic region forever and entered into an unequal battle with space and time.
Communication with Pioneer 11 was interrupted in 1995, when it was already far beyond Pluto's orbit. By now, the probe has moved away from the Sun by 90 AU. and continues on its way towards the constellation of the Shield.
Its twin lasted exactly thirty years in outer space: the latest scientific data from Pioneer 10 were transmitted to Earth in 2002. According to calculations, in 2012 it should have been at 100 AU. from the sun. A probe that has fallen asleep forever with a gold plate on board flies towards Alpha Taurus. Estimated time of arrival - 2,000,000 A. D.
The next heroes are participants in the mind-blowing Voyager mission, the largest expedition ever made on interplanetary flights. Two probes hit the road back in 1977 with the hope of visiting the vicinity of all the outer planets. The main Voyager mission ended in complete triumph: the probes studied Jupiter, Saturn, Uranus, Neptune, their rings, and 48 satellites of the giant planets from the flyby trajectory. At the moment of passing over the upper cloud layer of Neptune, after 12 years of flight and 4 billion km of distance traveled, the deviation of Voyager 2 from the calculated trajectory was an incredible 200 meters!
Today, 37 years after their launch, they continue their journey in the interstellar ocean, moving away from the Earth at a distance of 107 and 130 AU. The delay of the radio signal from the Voyager-1 is 17 hours 36 minutes. The transmitter power is only 26 watts, but its signals are still reaching the earth.
The memory capacity of the Voyager onboard computer is 100 times less than that of a modern mp3 player. The unique retro equipment continues its work, through the whirlwinds of electromagnetic storms and decades of work in open space. There are several liters of precious hydrazine left in the tanks, and the power of the radioisotope generator still reaches 270 watts. Already beyond the orbit of Neptune, NASA programmers managed to "reflash" Voyager's on-board computer: now the probe data is encoded with a highly secure double Reed-Solomon code (curiously, during the launch of Voyagers, such a code has not yet been used in practice). By the beginning of the new century, the probes switched to a backup set of attitude control engines (the main set had made 353 thousand corrections by that time), but every day it is more difficult for the Sun sensor to find its dim light against the background of thousands of bright stars. There is a threat of loss of orientation and loss of communication with the Earth.
In the summer of 2012, Voyager 1's equipment recorded a sharp drop in the intensity of charged particles of the solar wind - the probe crossed the border of the solar system, getting out of the heliosphere. Now the probe's signals are distorted by a new, never-before-recorded sound - the plasma of the interstellar medium.
For the ninth year now, the automatic station "New Horizons", launched in January 2006, has been surfacing space. The mission's goal is Pluto, about whose appearance we know almost nothing. Estimated time of arrival at the destination - July 14, 2015. Nine and a half years of flight - and only three days for a close acquaintance with the most distant planet.
New Horizons left the near-earth orbit with the highest speed among all spacecraft - 16, 26 km / s relative to the Earth or 45 km / s relative to the Sun, which automatically made New Horizons a starship.
It is expected that after the passage of Pluto, the probe will continue its work in open space until the middle of the next decade, having retired by that time from the Sun by 50-55 AU. The shorter mission duration in comparison with Voyagers is due to the short duration of the radioisotope “battery” operation - by the summer of 2015, the power release of RTGs will be only 174 watts.
Slightly behind the "New Horizons" flies another remarkable object - a solid-propellant upper stage ATK STAR-48B. The third stage of the Atlas-5 launch vehicle, which brought the New Horizons probe to its departure trajectory to Pluto, also gained heliocentric speed and will now certainly leave the boundaries of the solar system. Together with it, for the same reason, two balancing weights will fly off to the stars. The second stage (upper stage “Centaurus”) remained in a heliocentric orbit with an orbital period of 2.83.
According to calculations, in October 2015 STAR-48B will pass 200 million km from Pluto, and then disappear forever into the depths of space.
The ships will fall asleep, and time will lose meaning to them. In hundreds of thousands, maybe millions of years, all these man-made objects will reach the stars. But scientists are interested in the possibility of creating OPERATING spacecraft capable of continuing to work in interstellar space for an extended period of time, moving away from the Sun at a distance of hundreds of astronomical units.
TAU project
TAU (Thousand astronomical units). The 1987 concept, which involved sending an automated station at a distance of 1 / 60th of a light year from the Sun. Estimated travel time is 50 years. The purpose of the expedition: the construction of a grandiose rangefinder with a basis of 1000 AU, high-precision measurement of distances to stars, including those outside our galaxy. Secondary tasks: study of the heliopause region, solution of the problem of ultra-long distance space communication, verification of the postulates of the theory of relativity.
The power supply of the probe is a small-sized nuclear reactor with a thermal power of 1 MW. Ion engine with a 10-year service life. The authors of the TAU project proceeded exclusively from the technologies existing at that time.
Currently, the most detailed and feasible project of an interstellar expedition is the Innovative Interstellar Explorer. A compact-sized probe carrying 35 kg of scientific equipment on board and equipped with three RTGs and a space communication system capable of providing stable communication with the Earth from a distance of 200 AU.
Acceleration using a conventional rocket booster on chemical fuel, gravitational maneuver in the vicinity of Jupiter and ion thrusters, in which the working fluid is xenon. All three of these technologies exist and are well proven in practice.
Marching ion engine of the Deep Space-1 probe
An ion engine requires two things: a working fluid (gas) and several kilowatts of electricity. Due to the negligible consumption of the working medium, the ion engine can operate continuously for ten years. Alas, his thrust is also negligible - tenths of Newton. This is completely insufficient for a launch from the Earth's surface, but in zero gravity, due to continuous long-term operation and high specific impulse, such an engine is capable of accelerating the probe to high speeds.
In the Innovative Interstellar Explorer mission, using three acceleration methods, scientists hope to accelerate the probe to a speed of 35-40 km / s (over 4 AU per year). This is extremely high by the standards of modern cosmonautics (Voyager-1 has a record of 17 km / s), but it is quite feasible in practice using modern electric propulsion engines and high-capacity radioisotope energy generators.
Research under the Innovtive Interstellar Explorer program has been conducted by NASA specialists since 2003. Initially, it was assumed that the probe would be launched in 2014 and reach its target (move 200 AU from the Sun) in 2044.
Alas, the nearest starting window was missed. The interstellar probe program is not a priority program for NASA (unlike the more realistic Mars rovers, interplanetary stations and the Webb space telescope under construction).
Favorable conditions for launching an interstellar probe are repeated every 12 years (due to the need to perform a maneuver in Jupiter's gravitational field). The next time the "window" will open in 2026, but it is far from the fact that this chance will be used for its intended purpose. Perhaps something will be decided by 2038, but the concept of Innovative Interstellar Explorer will probably be infinitely outdated by that time.
Already, engineers are working on electric thermal plasma accelerators (VASIMR), magnetoplasma-dynamic motors and a Hall motor. These variations of the electric rocket motor also have a high specific impulse, comparable to beats. imp. ion thrusters, but they are capable of developing an order of magnitude more thrust - i.e. accelerate the ship to the specified speeds in a shorter time.
