Right now there are at least 5 man made objects that are on course to leave our solar system, two of them Voyager 1 and Voyager 2 have already crossed the heliopause, the boundary where the solar wind and the interstellar wind are in equilibrium which some say is a measurable boundary and therefore one of the possible edges of the solar system.
But whichever way you look at it, all these objects and some others that no one thinks about are all on a one way journey into interstellar space and if the human race never makes it past the outer planets, these will be our emissaries that will outlast, us, the earth and even our sun.
So what are these objects and where do we think they might end up in the future and just how long can they keep going for even when their power supplies have died and they are inactive.
The first of these was Pioneer 10 which was launched on March 3rd 1972 which was sent to investigate Jupiter which it arrived at in November 1973. This was followed by Pioneer 11 which was launched on the 5th of April 1973 to do the same to Saturn and Jupiter. They were 13 months apart to take advantage of favourable launch windows that occurred for only a few weeks every 13 months.
But these were also test probes for what would eventually become the Voyager missions but to find out why these were done in the 1st place we have to spool back almost a decade to 1964.
At this time, American aerospace engineer Gary Flandro at the NASA Jet Propulsion Laboratory noticed an alignment of the outer planets which happened every 175 years would next occur in the late 1970s. This would allow a single spacecraft to visit all the outer planets by using gravity assists something which would allow a complete survey to be conducted in less time and for less money than sending separate space probes to each planet.
This would be called the Grand Tour, initially, this would call for four spacecraft, two of which would visit Jupiter Saturn and Pluto while the other two would visit Jupiter Uranus and Neptune, however, this was an expensive programme with an estimated cost of $1 billion which occurred just as the cost cutting after the Apollo missions started, so it ended up being cancelled and being replaced by what eventually became the two space probe Voyager programme.
Pioneer 10 and 11 were part of the two-part pioneer programme which initially ran from 1958 to 1960 to first explore the moon and then from 1965 to 1992 and sent four spacecraft to measure interplanetary space weather, two to explore Jupiter and Saturn, that was pioneer 10 and 11 and two more to explore Venus.
In February 1970 TRW inc were awarded the contract to build both Pioneer 10 and 11, the design and construction of which required an estimated 25,000,000 man-hours. These were based on spacecraft modules which had already been proven in the pioneer 6 through 9 missions. These would be small lightweight spacecraft weighing about 260 kilogrammes or 570 lbs which would have to be magnetically clean in order to measure the planets magnetic fields and be able to perform an interplanetary mission and take images and other mesurements.
They would also have to withstand high levels of radiation around Jupiter and would need to be made capable of carrying on even if some of the systems were damaged.
They were powered by 4 radioisotope thermoelectric generators or RTG’s mounted on two 3 metre long Trusses, 120° apart and powered by plutonium 238 in a multi-layer protective capsules to shield them from the onboard sensors.
Initially, these were to provide power for just two years in space, but as plutonium 238 has a half-life of over 87 years and in Pioneer 10 they actually kept going for 29 years. The deterioration of the heat output from the plutonium and the thermocouple junctions which generated the electricity caused the final shutdown when the power was not enough to operate the transmitters.
The pioneers used a 2.74 metre or 9 foot diameter high gain antenna and redundant system of twin transceivers with each transmitting 8 watts, with a data transfer of just 256 bits per second. The computer system on board could record up to 6144 bytes of information gathered from instruments which would then be sent back to earth, so we can see just how basic the system was compared to the later voyagers.
As the missions were as much a test as an actual end result, NASA soon discovered that the radiation in Jupiter’s radiation belts was 10 times higher than the designers had predicted. The electron radiation along the magnetic equator of Jupiter was 10,000 times more than the maximum radiation around earth.
Pioneer 10 received an integrated dose of 200,000 rads from electrons and 56,000 rads from protons. To put that into perspective, a whole-body dose of 500 rads is fatal to humans, but the system survived although false commands were generated due to data corruption but pioneer 10 succeeded in obtaining images of the moons Ganymede and Europa.
Pioneer 10 was then put into a trajectory that would take it close to IO and then slingshot around Jupiter and out of the solar system. In 1976 it crossed the orbit of Saturn, then in 1979 the orbit of Uranus, on June the 13th 1983 it crossed the orbit of Neptune becoming the first man-made object to leave the proximity of the major planets of the solar system.
Communications with Pioneer 10 eventually lost contact in January 2003 when is believed it’s power output dropped below that to operate the probe. Its last known trajectory was heading in the direction of Aldebaran, a star 65 light-years away in the constellation of Taurus.
Pioneer 11 flew past Jupiter in 1974 and Saturn in 1979, contact was lost in November 1995. Its last known heading was towards the constellation of Aquila, northwest of the constellation of Sagittarius, which if nothing gets in its way or perturbs its path it will pass near a star in that constellation in about four million years.
The data which Pioneer 10 & 11 discovered would be used to build the Voyager probes which would take on a cut down version of the Grand Tour with the Voyager probes.
Voyager 2 would be launched first In August 1977 on a mission to survey Jupiter which it arrived at in 1979 and then Saturn in 1981, here the decision was made to continue on to Uranus and Neptune.
Voyager One was launched 16 days after Voyager 2, its mission was to visit Jupiter, Saturn and then onto Pluto. However, once it had reached Saturn, NASA realised there was an option to visit Saturn’s moon Titan which was believed to have a considerable atmosphere but if it did this it would not be possible to carry on to Pluto because the trajectory to Titan would take it out of the plane of the solar system and onto interstellar space.
The slingshot manoeuvres that the Voyager probes used were originally proved by the pioneer probes but the Voyager probes were much more advanced than the pioneers and we’re nearly three times the weight at 773 kilogrammes or 1704 lbs each.
The two Voyager spacecraft were identical and had a larger 3.7 metre or 12 foot diameter dish and also had three radioisotope thermoelectric generators giving more power.
The six computers onboard the voyagers had a total memory of 32K and there was a digital tape recorder that could record about 67 megabytes of data when the voyages were unable to communicate with earth which would then be transmitted later when communications were re-established. Voyager 2 also holds the record for the longest continuous operation of a computer since its mission started on the 20th of August 1977.
Communications were also greatly increased with the data rate sent back from Jupiter at about 115,000 bits per second, by the time it reached Saturn it was half and it’s gone down continuously ever since to try and reduce effects of the inverse square law due to the huge distance that the signal has to travel to reach the radio dishes of deep space network on earth.
The RTG power generators were again powered by plutonium 238 and produced approximately 470 watts at 30 volts DC when the spacecraft were launched.
By 2011, 34 years after the launch the power of the plutonium had reduced to about 76% of the initial output, but the degradation of the thermocouples reduced this to about 57%.
It’s estimated that by turning off various spacecraft loads and eliminating some of its capabilities there may be sufficient power for communications up until around 2032 At which point the probes will be on their own with no further communications with earth.
Voyager one is escaping at a speed of 3.6 AU per year in the general direction of a solar apex in Hercules and in about 40,000 years will be within 1.6 light years of Gliese 445.
Voyager 2 speed is about 3.3 AU per year into the general direction of a star called Ross 248 which it will pass within 1.7 light years of in about 40,000 years and in 296,000 years will pass within 4.6 light years of Delta Sirius the brightest star in the night sky.
The last space probe to be heading out of the solar system is New Horizons, launched in 2006 it flew past Jupiter in 2007 and Pluto on July 14th 2015.
The primary goal of New Horizons West was explore the last remaining unexplored planet, Pluto and its moons, that’s of course before it was downgraded to a dwarf planet, It would also go on explore the Kuiper belt and transformation of the early solar system.
New Horizons has been compared to a piano glued to a cocktail-bar size satellite dish But it took its inspiration from the Ulysses spacecraft which was used to orbit and study the sun. It weighed in at 470kg by the time it reached Pluto and down to 445kg by the time it got to Pluto.
However, communication was actually slower at Jupiter than the voyagers at 38 kilobits per second and by the time it got to Pluto it was down to 1 kilobits per second. From that distance of 4.7 billion kilometres it still took 4 1/2 hours for the signal to travel back to earth at near the speed of light.
The radio transceivers were a dual redundant 12 watt system and the dish was 2.1 metres or seven feet in diameter.
Storage was up to 8 gigabytes for each of the low power solid-state recorders again a dual redundant system.
Being a much newer space probe the computer system was far more powerful being split into two duplicated systems for redundancy it had a total of 4 computers with each one using a Mongoose V12 megahertz radiation hardened version of the MIPS R3000 CPU.
Something which was learned from the Voyager missions when Voyager 2’s photographic scan platform jammed at Saturn due to the grease in the mechanism becoming hard, New Horizons didn’t have any mechanism and instead the whole space probe was turned to point the camera as it went past Jupiter and Pluto.
As it flew by Pluto it came within just 7800 miles from the surface whilst travelling at 30,800 miles an hour or 49,600 kilometres per hour. From there it flew on to explore the kuiper belt and some of the larger asteroids and dwarf planets within it.
New Horizons has been called the fastest spacecraft ever launched because it left earth at 16.26 kilometres per second the equipment to 36,373 miles an hour it was also the first spacecraft launched directly into a solar escape trajectory, although Voyager 1 is still the fastest of space probes because of its gravity assists by Jupiter and Saturn and New Horizons will never catch it up.
Currently New Horizons is in excellent health and is expected to have enough power to last until at least 2050, Which is probably longer than the funding for the ongoing data collection and analysis.
But it’s not just the space probes themselves that are on this one way journey, some of the upper stages of the Rockets which launched them are also on similar trajectories. The New Horizons Star 48B third stage reached Jupiter before the new horizon spacecraft and crossed the orbit of Pluto Three months after new horizons.
The upper stages of pioneer 10, Voyager 1 and Voyager 2 are also on escape trajectories out of the solar system.
In fact the yo-yo despin weights on wires which it used to reduce the spin the New Horizons probe before it’s released from the third stage rocket are also on an escape trajectory out of the solar system.
However, we cannot be certain where they are Or their exact trajectory because they had no way of communicating with the earth or changing course like space probes.
But the space between the stars is so vast it has been calculated that it could take 10 to the power of 20 years or 100 million, trillion years before they would collide with a star even after the merger of the milky way and andromeda galaxies in 4.5 billion years time.
They will come close to stars and maybe other planets as in maybe about a light year or so away from one, But that will be at least 40,000 years to the nearest star and we will be long gone by then, so we won’t be getting any little green men bringing back one of the gold records to prove they found it Anytime soon.
So the five emissaries from earth and some of their associated launch hardware will carry on long after our sun and earth have cooled to be become comic debris, all travelling in different directions orbiting the Galaxy that we know as the Milky Way or whatever it may become in the far distant future.
They will be a lasting legacy of a proto space fairing species from a small blue green planet orbiting a small unregarded yellow sun in the unfashionable end of the western spiral arm.
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