The Forgotten Pathfinders. Early Deep Space Probes (By Anton Komarov)

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Luna 2

Luna 3

Kosmos 419

Mariner 9

Mars 2

Mars 3

Pioneer 10

Pioneer 11

Giotto

Vega 1

Vega 2

Sakigake

Suisei

Pathfinders

The Forgotten Pathfinders

By Anton Komarov

Early Deep Space Odyssey

25/12/2021

*References are found at the end of each section

When speaking about space exploration, some names come automatically to mind. I am not speaking about human names like Garry Flandro, Edward Stone, Larry Soderblom, Carolyn Porco, Alan Stern or even Linda Morabito but the names of their robotic emissaries. How can you speak about Pluto without quoting the probe New Horizons? If you succeed in doing so, you will have to use the data of New Horizons, which by itself sums up most of what we know about this astonishing little world and its astonishing system of moons. The same goes for Neptune,and while it is true that Neptune has been observed by different means since the flyby of Voyager 2 in August 1989, the bulk of human knowledge about the eighth planet of the solar system comes from the valiant probe, which reached the vicinity of Neptune after a solitary odyssey of twelve years through the solar system. During this, she visited the realm of the giants Jupiter, Saturn, Uranus, and Neptune and to this date, is the only probe to have visited the four giant planets of the solar system in one mission and the only man-made probe to have flown by Uranus and Neptune.

Thus we readily associate Saturn with the incredible journey of the Probe Cassini-Hugyens while most commentators speaking about Jupiter will quote the Galileo probe or even Juno which is in orbit and still completing its mission around the biggest planet of the system (Dec 2021). But space exploration like most if not all of other human activities is not a fair game. There are probes which have achieved outstanding results and sometimes still hold unbroken records that are rarely spoken about. The purpose of this article is to revisit some of these missions which at their time were an absolute first and which have paved the way to the more recent missions giving them optimal chances of success. It is a random list and we will certainly have missed a few of those key pathfinders.

Luna 3

Luna 3: First picture of the far side of the moon.

Gravity Assist Manoeuvre is a key feature in space exploration because it allows space probes to get to their target at minimal cost with less fuel requirements; they do so by using the gravity of the body they are approaching. This technique can be used either to reduce or increase the speed of a space probe, and it can also be used to redirect the probe’s path [1]. The robotic explorers Galileo, the Voyagers, Cassini and many others made use of this free (almost free as the linear momentum gained by the spaceship is equal in magnitude to that lost by the planet) cosmic bonus to get to their objectives.

The first space probe to employ this useful technique, without which many planets of the solar system would not have yet been explored, is the Luna 3 space probe [2]. We are in 1959, the race to put a first man into space is in full swing and, without any possible doubt, the Russian boosters are far more powerful and reliable than anything that the United States had to propose. However, the US was catching up quickly. Brian Harvey in an interview to Radio Free Europe explains "In what we call the Space Race, there were many subraces, and there were subraces to Venus and to Mars,"

Any first in space also belonged to this subrace and impressed the public as a demonstration of superior technological achievements. After a series of near misses in September 1959, the USSR attempted and succeeded in launching their probe Luna 2 to our natural satellite and entered history as the first manmade object to reach the Moon. It was not a soft landing and was the sixth attempt by the Soviets to impact the Moon. Luna 2 crash landed on the Moon, east of Mare Serenitatis near the Aristides, Archimedes and Autolycus craters deploying the Soviet Pennants [3] of the USSR made of titanium with the more resistant polysiloxane enamels and capable of surviving the explosion intact, an explosion which was designed to scatter the 72 pennants on the surface of the Moon before impact. The Russians were keeping the World’s public engaged while keeping the Americans enraged with their own home-grown failures and the consequent success of their adversaries.

[1] Gravity Assist(P) [2] Luna 3 Wikipedia [3] Soviet Pennants

A Millenia Old Enigma

The revolutionary technique of gravity assist would be developed for the flight of Luna 3 by Mstislav Keldysh at the Steklov Institute of Mathematics. Despite its usefulness, the gravity assist technique was not the focal point of the mission. Since time immemorial, humanity has wondered [4] what the Moon was hiding at what is sometimes wrongly called, the dark side of the moon. Jules Verne in his book ‘Around the Moon’described it through the eyes of his explorers as a place where the remnants of a past atmosphere and vegetation would still prevail. In 1959, the scientific community was still convinced that the far side of the moon fairly resembled the one we are used to seeing in the night sky but they were in for a surprise. Launched on a highly elliptical Earth Orbit, Luna 3 used its own onboard lab [5] to take a picture of the far side of our natural satellite, process the picture and convert the photographic negatives into a radio broadcast to send it back to the Earth bound stations.

[4] Lunar Perception.

Sven Grahn describes the process in detail in an astonishing review of the adventure of Luna 3 while not omitting the pioneering three-axis stabilisation system. Also included was the inevitable spy story of the cold war in the revelation that the Soviets ‘borrowed’ the film used in the space probe from American spy balloons.

[5] Luna 3 Story

Luna 3 took a total of 29 pictures over a period of 40 minutes and what they revealed, despite being of poor quality, was a mystery that has not been solved completely to date, why do the two sides of the moon look so very different? For instance, Luna 3 observed only two Maria (large, dark, basaltic plains caused by lava flows) on the far side, which were baptised Mare Moscoviense (Sea of Moscow) and Mare Desiderii (Sea of Desire), which are the features everyone can see with the naked eye and are commonly observed on the near side.

What Happened On The Moon [Before Apollo]

Mars 2 & 3: The Red Planet’s Race.

Aficionados of space exploration know that the first surface picture of Mars was taken by Viking 1 in July 1976. And by extension, one could easily conclude that the first Martian soft landing was achieved by the same lander but that’s a mistake. Mars 3, another Soviet emissary, holds this record for achieving a soft landing on Mars and made history for a mere 114.5 seconds.Considering that the EAU, India, and China succeeded in their maiden attempts to reach the orbit of Mars with China performing a mind blowing Hat Trick of Orbiter, Lander and Rover during their first trip to Mars, one could be led to think that it is an easy task. The three countries quoted took the road to the red planet on the back of the experience and both the successes and the failures of the United States and the USSR and, of course, the hardware used by the new space faring nations is much more reliable than the relics used in the early space age. The road to Mars is paved with a hecatomb of failed space probes. Why then speak about a failure? Simply because Mars 3 was not a total failure at all.

Let’s set up the context to illustrate how tense were those subraces. The race was now on to achieve the first to orbit Mars and it would be a close run. The year is 1971, after having lost the race to put a first satellite and a first man into space,the United States scored a monumental victory by landing manned crews on the Moon with the famed Apollo missions which lasted from 1969 to 1972. On May 10, 1971, a Proton rocket successfully launched the Soviet space probe Kosmos 419 into a low earth parking orbit before attempting to beat the US space probes Mariners 8 and 9 to orbit Mars. The chances were pretty good because one day before May 9,a launch failure of an upper stage of an Atlas Centaur resulted in the loss of Mariner 8. The Soviets knew their own failure when the block D failed to ignite and thus prevented Kosmos 419 from leaving its parking orbit for Mars. A rather stupid mistake is at the origin of the ignition failure; instead of the timer initializing the sequence being set for 1.5 hours after launch, it was set by mistake at 1.5 years. Kosmos 419 was in a low orbit with an apogee (highest altitude) of 174 km and its orbit rapidly decayed, burning up in the atmosphere only two days after launch so Mariner 9 was still in the race. The Soviets did not abandon the launching of Mars 2 and Mars 3 on May 19 and 28 in the same year. Despite being launched after the Russian probes on May 30, Mariner 9 successfully achieved Mars orbital insertion on November 14, making her the first manmade object to orbit Mars. Mars 2 and Mars 3 only arrived in orbit on November 27 and December 2, respectively. The orbital race may have been lost but there were others ahead, notably, who would be the first one to land on Mars? Mars 2 and Mars 3 both carried a lander and in that sense the USSR space probes were more ambitious than Mariner.

The loss of Kosmos 419 had another consequence; it would have acted as a radar beacon in orbit to guide Mars 2 and 3 if it had succeeded. Added to that, an unforeseen challenge arose. In 2018, a Martian dust storm killed the Opportunity rover, and when Mariner 9 arrived in orbit, an epic planetary scale storm covered the whole planet with dust. Neither of the Soviet probes were reprogrammable and the operators based on Earth, could only hope that they would nevertheless survive their automatic descent and mission in such horrid conditions. At 4.5 hours prior to reaching Mars, Mars 2 had despatched its descent module, which when fuelled had a total mass of 1210 kg. After penetrating the atmosphere, several systems malfunctioned, notably the descent system arguably because of too steep an entry into the atmosphere by the Martian probe,which lead to the malfunction of the descent sequence and the non-deployment of the parachute. Another record was nevertheless achieved, comparable to the one of Luna 2 but less deliberate, Mars 2 became the first manmade object to reach the surface of Mars albeit with a resounding impact. The Soviets would still do better.

Mars 3 entered the atmosphere at a speed of 5.7 km a second, faster compared tothe 6 km a second entry of her sister probe a few days earlier but contrary to her ill fated twin, the descent sequence of Mars 3 operated perfectly, triggering after areobreaking both the parachutes and the retro rockets. A few days after having crash landed on Mars, the USSR succeeded in soft landing a manmade object on another planet of the solar system and the Russian scientists hoped that there was much more to come which would have dwarfed the recent success of the American probe Mariner 9. Though the probe started operations immediately upon landing and began transmitting to the orbiter after 90 seconds, the transmission was interrupted after 20 seconds and was never recovered. What had happened? Many theories have been put forward to explain the sudden failure of the Mars 3 lander pointing to the wind, which could have blown it around or an object carried by the massive storm could have hit it. It could also have easily been a malfunction of the orbiter communication relay or even the lander itself. Furthermore, storms on Earth are known to disturb radio communications and it could be that the extreme conditions provoked a coronal discharge, knocking out or interfering with the communications. The eventual success could have been more astounding since the Soviets did not realise to what extent the Mars 2 and 3 missions were pioneering ones, and the true story would be known only a few decades later. On November 10, 1970, the Soviet spacecraft Luna 17 delivered Lunokhod 1 onto the surface of the Moon, and if it did not eclipse the Apollo mission, it was nevertheless to become the first remotely-controlled vehicle to wander on another celestial body. The USSR repeated the feat with Lunokhod 2 in 1973 after the crewed Apollo missions had already ended Apollo 17 in 1972. Humanity had to wait for 24 years to see another rover operating out of the Earth-Moon system on a fully fledged planet with the 10 kg US rover Sojourner, well known to the fans of the Martian. The character Mark Watney created by Andy Weir, used the operational station of the lander of Sojourner to establish contact with Earth and used Sojourner as a kind of pet rover.

However, here again history could have been very different.

Unknown to everyone until the 1990’s, Mars 2 and her twin probe Mars 3 each carried a small vehicle weighing 4.6 kg mounted on skis and connected to the lander by a 15 meter power cable, the vehicles named Prop- M even had an inbuilt primitive artificial intelligence which would have allowed them to avoid obstacles on Mars. The rovers were to perform scientific experiments carrying both a dynamic penetrometerand a radiation densitometer.The lander would have delivered the rover with the help of a manipulating arm which would have then moved into the camera’s field of view.

As the whole operation was pre-programmed and would have been automatic, it is unknown to this date if the little rover of Mars 3 Lander was deployed.[7] The television camera of the lander managed to send an image that the Soviet scientists considered to be only radio noise but even now, some argue that Mars 3 lander captured part of the Martian Horizon in the dust storm. The image taken by Mars 3 was only known in the west after the politics of glasnost and perestroika initiated by Michael Gorbatchev, the ex Secretary General of the USSR and the first President of Russia post USSR with the eased scientific transparency between east and west. And it is not the end of the story. In 2007, a crowd-funded search to find the hardware of Mars 3 was initiated by a group of US researchers who shared images from the HIRSE camera mounted onboard the Mars Reconnaissance Orbiter,which was in orbit around the red planet. In 2013, HIRSE announced that photographic evidence showed that the Mars 3 lander was found, as well as a parachute, retrorockets, and the heat shield. All in all, Mars 3 was a great success but only verified retrospectively.

[6] PROP-M Rover [7] Soviet Mars Shot

Mars 3 USSR Docs

Pioneer 10 & 11

The space probes Pioneer 10 and 11 hold by themselves so many firsts that one could find it arguable that they belong to the category of the forgotten pathfinders. But they are less referred to in popular space exploration websites in new articles to the profit of the legendary Voyager 1 and 2, which did more and better in many orders of magnitude for the same type of planetary mission. But the immense success of the Voyagers would definitively not have been the one we know without the path finder work of the two little US deep space probes, which without doubt deserved and honoured their name of Pioneers.

In 1964, space exploration was triumphing; one year earlier Valentina Tereshkova became the first woman to orbit the planet. In 1962, NASA’s probe Mariner 2 performed the first successful planetary encounter by accomplishing a flyby of our closest neighbour Venus, approaching the planet at a distance of 34,773 km. Still in 1962, the spacecraft Mars 1 from the USSR had managed to flyby Mars but contact was lost. The number of launches of rockets kept on increasing and both successes and failures taught engineers and scientists how to build more robust spacecraft. Optimism was de riguer and everything was possible, fuelled by the competition of the superpowers. In this atmosphere, Garry Flandro a graduate student from Caltech was given a task, working part-time at the Jet Propulsion Laboratory, he was asked to study the feasibility of exploring the outer planets of the solar system beyond the orbit of Mars. Flandro was to propose the most efficient way to use gravity assist, as already proven and tested by Luna 3. The task was not an easy one and only one of the few problems that had to be solved. Solar panels for example are inefficient the further the probe ventures in the outer solar system, therefore what source of energy would power the instruments? How to ensure the longevity of the probe? NASA at this time could not guarantee that any spacecraft would survive more than a few months in the unforgiving interplanetary conditions. Was it even possible to cross the asteroid belt between Mars and Jupiter without risking multiple impacts? All kinds of unknowns would have to be solved by others.In 1961 Michael Minovitch [8], using the fastest computer of the time, the IBM 7090, made a breakthrough proposing a solution to the three body problem which has haunted astronomers for centuries.

Applying the solution to the practical use of visiting the outer realms of the solar system, Flandro started to plot where the planets of the solar system would be found in the following years. To his great astonishment, Garry Flandro would discover a rare alignment occurring only once every 175 years with the giant planets of the solar system all positioned on the same side. This particular alignment would occur at the end of the 70s with a short window of few months. The endeavours of Garry Flandro would ultimately culminate with the triumph of the Voyager 2 flyby of Neptune marking the end of the Planetary Grand Tour, which was described as the most important voyage of discovery of the last century. The road to Neptune would be long and hazardous and uncertain and is the matter of another story since the Voyager space probes having written some of the most glorious pages of space exploration, are certainly far from being forgotten.

Nevertheless, NASA had to answer some questions that only extremely dedicated pathfinders could answer.

Top scientists like Dr. James Van Allen, Dr. Thomas Gehrels, Dr. John Simpson, Dr. Edward Smith, or Dr. Martha Hanner worked under the direction of project Manager Charles Hall, formulating and producing the rationale of the project’s conception and then following and ensuring the probe’s journey throughout the solar system. The Galactic Jupiter probes became a proposal of the Goddard Space Center whose initial ambition was that of two probes crossing the asteroid belt to visit Jupiter. The project was finally attributed to NASA’s Ames Center, dubbed Pioneer F and G. Without passing by the usual bidding process, Ames boldly allocated a contract of 310 million USD to TRW to build the Twin probes Pioneer 10 and 11. As the story goes, an engineer from TRW said "This spacecraft is guaranteed for two years of interplanetary flight. If any component fails within that warranty period, just return the spacecraft to our shop and we will repair it free of charge." (Source Wikipedia)

Packed with 11 scientific experiments among which 6 would function continuously through the encounter with Jupiter,[9] the space probe weighing 258 kilos had been fitted with RTG (a radioisotope thermoelectric generator), which is basically a nuclear battery without moving parts. It converts the heat released by the decay of a radioactive material to electricity to power the probe’s instruments. Using the RTG’s was NASA’s answer to supply power to the spacecrafts, the pre launch requirements for the RTG was to provide power for at least two years in space. Pioneer 10’s mission lapse time was 30 years, 10 months, 21 days, 22 hours, 10 minutes, 56 seconds and exceeded expectations by more than a quarter of a century.

[8] Michael_Minovitch [9] Pioneer 11_ N.A.S.A_

Pioneer 11 The Mission

The Flight

On March 2, 1972 atop an Atlas-Centaur rocket which would be used for the first time as a third stage booster, Pioneer 10 left earth and crossed the lunar orbit 11 hours later. In only three months, Pioneer 10 had passed the Martian orbit; from there on, it was all uncharted terrain. On July 15, 1972, Pioneer 10 became the first manmade object to pass through the asteroid belt. The space probe did collide with some particles but none of them were of a size which would have threatened the mission. Pioneer’s closest approach to an asteroid in the belt was on December 2, 1972 when she passed at about 8.8 million kilometres of the asteroid Nike but no data was collected. Pioneer 10 proved that the crossing of the asteroid belt posed no serious threat to planetary exploration.

In the mean time, one year after Pioneer 10, on April 6, 1973, her twin probe Pioneer 11 took to the heavens in the direction of Jupiter from Cape Canaveral

Humanity would have its first in situ encounter with Jupiter on November 26 when Pioneer 10 hit the bow shock of Jupiter entering her magnetosphere. The pioneering spacecraft made her closest approach of the biggest planet of our solar system at a distance of 130,354 kilometres. The space probe started imaging the giant planet on November 6 and between that date and December 31, the first outer planetary space probe from the United States took 500 pictures of the king of the planets. This was the very first intrusion into the realm of a planet that has played a great part in the configuration of our solar system and is key to its dynamics.

Pioneer 10 captured images [10] of the icy moons Ganymede, Gallisto, and Europa missing only Io among the four so called Galilean moons. Io was not imaged due to the fact that the photopolarimeter did not survive the intense battering from the radiation belt of Jupiter. Successfully completing the Jupiter encounter and passing out of the dreaded radiation belt of Jupiter without critical damage allowed the redirection of the incoming Pioneer 11 to Saturn and later helped determine safer trajectories for the Voyager space probe. The path to Saturn being wide open, Pioneer 10 would perform the first gravity assist manoeuvre at Jupiter and the impulse gained from this would make her the first man made probe to be put on a trajectory leaving the solar system.

[10] Greetings From Earth

Extraordinary Journey Pioneer 10

PLaque

In May 1974 after the accomplished mission of Pioneer 10, a decision was taken to retarget Pioneer 11 already on its way to Jupiter,to flyby the planet on a North-South trajectory which would allow the first ever encounter with Saturn. The science performed in the vicinity of Jupiter included the imaging of its moons (200 pictures were taken). Interestingly, Pioneer 11 passed the bow shock of Jupiter several times because Jupiter’s magnetosphere changes its boundaries as it is buffeted by the solar wind.

Contrary to her sister probe, which was not bound anymore for a particular target, Pioneer 11 had to perform her gravity assist with the greatest accuracy possible. The whole manoeuvre used 8 kg of propellant and lasted a little bit more than 42 minutes propelling the spacecraft towards the incontestable jewel of the solar system. After course corrections on May 26, 1976, and July 13, 1978, the US spacecraft finally arrived at the ringed planet on September 1, 1979. The probe had several main objectives, exploring the rings, the moon system, and Saturn itself. The first conclusive evidence of Saturn’s magnetosphere was made when the probe hit the bow shock of the planet on August 31, 1979, when she was about one and a half million kilometres from Saturn and 440 pictures of the system were taken. Pioneer’s second mission was a little bit trickier; if planetary scientists were confident that both Pioneers could have passed through the asteroid belt without encountering serious danger, it was not the same concerning the passage through the plane of Saturn’s rings. The daredevil manoeuvre was necessary because by this time, the famous twin probes Voyager 1 and 2 had already flown by Jupiter, setting records on their path. Already dwarfing the previous discoveries of the Pioneers by showing the denizens of planet Earth volcanoes on the moon Io and revealing the suspicious surface of Europa so triggering the hypothesis of a hidden global subsurface ocean as well as discovering Jupiter’s ring etc. Both Voyagers were en route to Saturn and if Pioneer 11 failed, the Voyagers would have been redirected taking a safer path. Then, the only encounter to this date of mankind with the Icy giants Uranus and Neptune would have not been possible and our knowledge of the far regions of the solar system today would have been radically different. After Pioneer 11, the passage was judged safe, however, the spacecraft almost collided with a moon that she had discovered the previous day. To this date it is uncertain if the object that almost put an end to the mission of Pioneer was Epimetheus as mentioned above discovered the previous day by the probe, but it was suspected to be it from previous telescopic observations. Or was the near-miss caused by Janus? Later, it was discovered that the similar sized moons Janus and Epimetheus share the same orbit.

Before following her sister probe on a path which would take her out of the solar system, Pioneer 11 discovered another ring and a new small moon. The way to Uranus and Neptune was wide open for Voyager 2 to pass through and make planetary exploration history.

Pioneer 11 last made contact with NASA [11] on November 24, 1995 but some engineering data was received on November 24, 1995. The little Pioneer’s signal became too faint to be heard in 2002. The sister probe’s last successful telemetry was received on April 27, 2002, and the last weak signal before complete silence reigned on January 23, 2003.

There is a final note to the story of Pioneer 10 and 11,which also marks a transition in the way a new generation of scientists approached planetary exploration. The famous science populariser, Carl Sagan met the British journalist and senior science reporter Eric Burgess during a visit to the Jet Propulsion Laboratory and was fascinated by the ideas of the journalist who proposed that the space probes on the journey out of the solar system should carry a message for intelligent aliens who could eventually find them drifting in the vastness of interstellar space. The idea strongly advocated by Sagan was accepted and an engraved message on a gold anodized aluminium plaque was placed onto both probes. Having a delay of only 3 weeks as the time allotted by NASA, the message was conceived by Frank Drake and Sagan. The illustration was done by Linda Sagan, the then wife of the astronomer. It depicts a couple, a naked man and a woman relative to the spacecraft and the location of Earth relative to several Milky Way pulsars.

Pioneer 10 and 11 became the first manmade objects [12] to reach the escape velocity required to leave our solar system and are counted among the only five space probes including Voyager 1 and 2 and the spacecraft New Horizons to do so.

[11] Historical_ Nasa_ [12] Pioneer & Voyager

Pioneer [Anim Site]

Giotto and the armada.

Vega 1 & 2

Designed by the Babakin Space Centre and Built by Lavochkin, the Vega space probes were incredibly successful Soviet space probes [13] — the twin probes Vega 1 and 2 demonstrated brilliantly what international cooperation could achieve in space. On December 15, 1984, Vega 1 was launched from the Cosmodrome of Baikonour using a Proton 8K82K rocket. Vega 1 dispatched her descent module through the deadly clouds of Venus on June 11, 1985. The module entered the atmosphere at 125 km at about 11 km/s around 05:10 Moscow time. After first successfully detaching a Venusian Lander at an altitude of 64 km, the module for the first time in the history of mankind, deployed a balloon at an altitude of 61 km. The height of the balloon was stabilized between 53 and 54 km, some 15 to 25 minutes after entry. While collecting data on the temperature of the atmosphere, speed of wind, etc., the probe flew at an average speed of 248 km per hour on a distance of 11,600 km around some 30 percent of Venus’s circumference.

The Vega 1 lander touched down on the Mermaid Plain north of Aphrodite Terra. Due to the fact it was a night-time landing, no imagery was taken. Some experiments of the lander ultimately initiated operations while descending through the atmosphere to an altitude of 20 km. From the 13 experiments carried by the lander, data was returned only from the mass spectrometer.

The sister probe Vega 2 followed almost the same entry procedure penetrating the atmosphere of Venus at 125 Km altitude four days later on June 15, 1985. The balloon that Vega 2 carried was inflated at an altitude of 54 km whereupon the balloon performed its tasks of measuring the atmosphere’s composition and dynamism along the 11100 km she travelled across the atmosphere of Venus. The Vega 2 lander discovered that the surface north of Aphrodite where she landed was made of anorthosite–troctolite, a rock rare on Earth but present in the lunar highlands. The lander registered a surface temperature of 463 degrees centigrade and the pressure measured 91 atmospheres. The Soviet lander lasted 56 minutes in the infernal conditions on the surface of Venus.

After ejecting their descent module on June 11, and 15, 1985 respectively, the carrier spacecrafts Vega 1 and 2 then executed a gravity assist to escape Venus and were targeted towards their next celestial rendez-vous scheduled for the following year

[13] Vega Missions

Vega Pictures Halley

Halley's Comet

Closing in

1986 was one of the bleakest years of space exploration and on January 28, the space shuttle Challenger exploded shortly after take-off, taking the lives of the whole crew of seven astronauts. America was grounded. Four days earlier however, the mood was celebratory with Voyager 2 flying by Uranus and accomplishing an exploit that has never been repeated since. But for astronomers, historians, space enthusiasts, and the public, 1986 was the year that the most famous comet was due to visit us as after her 75 year orbital period,Halley’s Comet was returning back to the inner solar system. Halley’sComet is a short period comet completing an orbit around the Sun in 75–76 years; it is the only comet that one can observe twice in a life time and the only one that can be observed regularly from Earth. Around 468 to 466 BC, a comet was recorded by the Greeks and the dates and location seem to point to that being one of the earliest observations of the comet, which was also reported by Chinese chronicles the same year. Halley’s Comet has accompanied humanity for eons, Babylonian text from 87 BC recorded the year that the comet appeared, day after day for a month. It was not until 1705, however, that English astronomer, Edmond Halley using the formulas of his friend Isaac Newton understood that the entire recorded apparitions were actually describing the same comet. Astronomers in 1986 knew that Halley would not have displayed a grand show in the night sky as her closest approach to our planet would be 0.42 AU (AU Astronomical Unit 150 mkm) compared to the relative close approach in 1910 of 0.15 AU. This passage was the worst for naked eye observation for the past 2000 years and the light pollution in the cities worsened the situation. But mankind was in the space age and had decided to extract the secrets of the famous visitor. A formidable armada of spacecraft were assembled heading inbound for a closer look.

After having dropped her balloon probe in the atmosphere of Venus, the Vega-1 carrier probe was redirected after gravity assist from Venus to intercept Halley’s Comet, both probes had been modified from the earlier Soviet Venera probes. The need for this mission became even more pressing when NASA cancelled its mission to Halley. Vega 1 with an on board French telescope started imagery on March 4, 1986. On March 6, she made her closest approach crossing Halley at a distance of 8889 km and becoming the first probe to return a picture of a comet’s nucleus. Battered by dust particles, Vega 1 survived the flyby without having any of her instruments disabled. Vega 1 took more than 500 pictures of Halley’s Comet sending back data on the dynamics of the coma, shape of the nucleus and composition. It was determined that Halley’s rotation period was 53 hours while her nucleus was measured at about 14 km. Scientific data and imaging were performed March 7 and 8, 1986. Contact was lost with Vega 1 when she ran out of altitude propellant on January 30, 1987. Her accurate positioning of the nucleus would provide accurate data for the close flyby by the European probe Giotto, scheduled for few days later.

In the mean time Vega 2 started imagery on March 7, at 14 million kilometers from the comet. She made her closest approach at a distance of 8030 km from the comet. She repeated the experiment performed by her sister probe and returned more than 700 images of even better resolution. Vega 2 also acted as the pathfinder for the incoming ESA probe Giotto. The last contact with Vega 2 was received on March 24, 1987. Vega 1 and Vega 2 are currently in heliocentric orbits.

On March 8, 1986, Japan’s Suisei deep [14] space probe made its closest passage of Halley’s Comet at a distance of 151,000 km. As of November 1985, the space probe was returning up to 6 images per day. The main mission of the spacecraft was to take UV images of the hydrogen corona for about 30 days before and after Comet Halley's was descending and crossing the ecliptic plane.

Sakigake, the first interplanetary probe launched by another country other than the USA or the USSR, was a Japanese space probe part of the so called Halley’s armada. Sakigake (in Japanese meaning pioneer or pathfinder) was at the closest flyby at 6,990,000 kilometres from Halley’s Comet. The spacecraft did not carry any imaging instruments in her payload. She acted as a frame reference for data received for the probes that flew closer to Halley’s Comet (source Wikipedia).

[14] The Armada

Giotto

The Daredevil

The stage was set for Giotto which was based on the design of a GEO-Earth orbiting satellite on models which were built by The British Aerospace in Bristol. The 960 kg probe was named after the Early Italian Renaissance painter Giotto di Bondone who depicted the comet in his painting after the observation of its passage in 1301. The spacecraft was launched atop an Ariane 1 Rocket from Kourou, Guiana on July 2, 1985.

Giotto was a small spacecraft with a main [15] cylindrical body of about 2 meters in diameter and 1 meter in height. She differed mainly from her predecessors in orbit around the earth by the incorporation of a protective shield against the high velocity dust particles, which were predicted to batter her during the comet’s flyby. The 190 watts power necessary for Halley’s encounter were generated by 5000 solar silicon cells wrapped around Giotto’s cylindrical exterior. Back-up power for when the probe was in the shadow was insured by four silver-cadmium batteries. Giotto was about 7.8 million kilometers of the comet when her instruments detected the first hydrogen ions on March 12, two days before her closest approach. Two hours and two minutes before closest approach, the first dust particles impacted the probe. At a distance of 1372 km from the comet, the European probe started to transmit the first images as the rate of impact kept on increasing. In total, the little probe was impacted a whopping 12000 times by dust particles — the worst of them a mere 7.6 seconds before the closest approach. Giotto was moving at a relative speed of 68 km/s to the nucleus of Halley’s Comet when a massive (1 gram particle) impact sent her spinning, interrupting the image transmissions and contact was lost.

The closest approach to Halley’s Comet was at a distance of 596 km on March 14, 1986 [16]. Few among the scientists and engineers and even less the TV audience, could have hoped for the probe’s survival and even during mission conception it was considered that if Giotto made it to that point, it would have already been an outstanding success. But the ultra resilient probe against all odds was still alive as bursts of information were received. During the next 32 minutes, the thrusters stabilized the spaceprobe and contact was completely re-established.

At 49 minutes after the closest approach, the spacecraft detected the last dust impact. Giotto continued to send valuable information and data for 24 hours after the closest approach.

Giotto’s instruments were turned off on March 15, 1986 but that would not be the last that we would hear from this extraordinary interplanetary space probe. With 60 kg of propellant still available and the only damage being a camera destroyed by a dust particle, it was decided to reawaken her 1419 days later in February 1990 to perform an Earth Flyby, redirecting the spaceprobe towards the comet Grigg-Skjellerup. On July 9 at about 215 million kilometres from Earth, Giotto’s payload was reactivated and she flew by the comet at a distance of 200 km. [17]

[15] Overview [16] Mission [17] Hunter

Pathfinders

Giotto and all the forgotten pathfinders [18] have added encyclopaedias of information to our knowledge of the cosmos, whether purely as by-products of the cold war or as a demonstration of a new era of cooperation. Their stories deserve to be told as they form an integral part of the continuing drive to explore space and our own Solar System. They are also the witnesses of our humanity trying to make sense of its place in the vastness of the cosmos.

[18] Deep Space Probes 2000's

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