Posted by KeighleyAstro on Jun 29, 2024 in Main |

Thursday 27th June 2024 witnessed a very well attended meeting of Keighley astronomical society. The guest speaker was the ever popular Mr Peter Rea FRAS from the Cleethorpes and district astronomical society. Mr Rea’s presentations are always on his love of the exploration of space. The title of this presentation was ‘The Origins of Planetary Exploration – 1961 to 1981’ Mr Rea pointed out that it was during this twenty year period that mankind saw these other worlds in detail for the very first time, and he feels privilege to have witnessed these important forward steps.

Mr Rea introduced the subject by pointing out that communications was the core to successfully exploring our Solar System. The United States established, three deep space communication arrays collectively known as ’The Deep Space Network’; at Goldstone in California, Madrid in Spain and at Canberra in Australia. With these three sites they could receive radio communications from distance space probes 24 hours a day.

The then Union of Soviet Republics had a similar communication system to the Americans but as they only explored the nearer planets of Venus and Mars, it didn’t need to be as sophisticated at the ‘Deep Space Network’.

Soviet planetary exploration:-

Mr Rea explained whereas the United States were to explore all the planets in the Solar System the Soviets concentrated their efforts on just Mars and Venus.

The Soviet Mars programme was a series of spacecraft which were intended to explore Mars, and included flyby probes, landers and orbiters.
Early Mars spacecraft were small, and launched by Molniya rockets. Starting with two failures in 1969, the heavier Proton-K rocket was used to launch larger 5 tonne spacecraft, consisting of an orbiter and a lander to Mars. The orbiter bus design was likely somewhat rushed into service and immature, considering that it performed very unreliably in the Venera variant after 1975. This reliability problem was common to much Soviet space hardware from the late 1960s and early 1970s and was largely corrected with a deliberate policy, implemented in the mid-1970s, of consolidating (or “debugging”) existing designs rather than introducing new ones. The names of the “Mars” missions do not need to be translated, as the word “Mars” is spelled and pronounced approximately the same way in English and Russian.

In addition to the Mars program, the Soviet Union also sent a probe to Mars as part of the Zond program; Zond 2, however it failed on route.

During the two decades covered by this presentation eight Soviet missions were dispatched with only one noticeable success, the Mars 3 probe in 1971. It successfully landed on the surface, making it the first man-made object to achieve this goal. However, it stopped transmitting 20 seconds after the television scan began.

Mr Rea highlighted that the Soviets Union had more success in landing probes of the surface of Venus. Which doesn’t make much sense really as Venus is such an inhospitable world compared to Mars.

The Venera (means “Venus” in Russian) programme:-

Thirteen probes successfully entered the Venusian atmosphere, including the two Vega program and Venera-Halley probes. Ten of those successfully landed on the surface of the planet. Due to the extreme surface conditions on Venus, the probes could only survive for a short period on the surface, with times ranging from 23 minutes to two hours.

The Venera program also had many failures but it did establish a number of precedents in space exploration, among them being the first human-made devices to enter the atmosphere of another planet (Venera 3 on 1st March 1966). Contact with the probe was lost, likely due to overheating, and it crashed into the planet surface.

The first to make a soft landing on another planet was the Venera 7 probe, launched in August 1970, was the first one designed to survive Venus’s surface conditions and to make a soft landing. Massively overbuilt to ensure survival, it had few experiments on board, and scientific output from the mission was further limited due to an internal switchboard failure that stuck in the “transmit temperature” position.

Venera 7’s parachute failed shortly before landing very close to the surface. It impacted at 17 metres per second (56 ft/s) and toppled over, but survived. This caused antenna misalignment making the radio signal very weak, but it was detected (with temperature telemetry) for 23 more minutes before its batteries expired.

The first to mission return images from another planet’s surface was Venera 9, on 8th June 1975.

Many of the instruments began working immediately after touchdown and the cameras were operational 2 minutes later. These instruments revealed a smooth surface with numerous stones. The lander measured a light level of 14,000 lux, similar to that of Earth in full daylight but no direct sunshine.
A system of circulating fluid was used to distribute the heat load. This system, plus pre-cooling prior to entry, permitted operation of the lander for 53 minutes after landing, at which time radio contact with the orbiter was lost as the orbiter moved out of radio range.

Venera 9 measured clouds that were 30–40 km (19–25 mi) thick with bases at 30–35 km (19–22 mi) altitude. It also measured atmospheric chemicals including hydrochloric acid, hydrofluoric acid, bromine and iodine. Other measurements included surface pressure of about,100 kilopascals (90 atm), temperature of 485 °C (905 °F), and surface light levels comparable to those at Earth mid-latitudes on a cloudy summer day.

Venera 9 was the first probe to send back television pictures (black and white) from the Venusian surface, showing no shadows, no apparent dust in the air, and a variety of 30 to 40 cm (12 to 16 in) rocks, which were not eroded. Planned 360-degree panoramic pictures could not be taken because one of two camera lens covers failed to come off, limiting pictures to 180 degrees.

The first mission to record sounds on another planet was Venera 13. Launched on 1st March 1982, after launch and a four-month cruise to Venus, the descent vehicle separated from the cruise stage and plunged into the Venusian atmosphere. A parachute deployed once the lander entered the Venusian atmosphere. The parachute detached at about 50 kilometres (31 miles) above the surface; simple air braking was used for the final descent. Venera 13 landed at around 7–8 metres per second

The Venera 13 lander was equipped with cameras to photograph the surface and spring-loaded arms to measure the compressibility of regolith. The quartz camera windows were covered by lens caps that popped off after descent.
The landing area was composed of bedrock outcrops surrounded by dark, fine-grained regolith. After landing, the lander began to take a panoramic photograph while a mechanical drilling arm obtained surface samples. The samples were deposited in a hermetically sealed chamber, maintained at 30 °C (86 °F) and a pressure of about 0.05 atmosphere (5 kPa). Sample composition was determined by the X-ray fluorescence spectrometer to be in the class of weakly differentiated melanocratic alkaline gabbroids.

Although the lander was designed to function for about 32 minutes, it continued to operate for at least 127 minutes in an environment where the temperature was 457 °C (855 °F) and the pressure was 9.0 MPa (89 standard atmospheres). Data was transmitted by the lander to the satellite, which functioned as a data relay as it flew by Venus.

In order to measure surface wind speed, microphones on the probe recorded atmospheric wind noises (the probe also recorded noises associated with the probe’s equipment). This was the first recording of sound on another planet. Venera 14 would also make similar recordings.

United States planetary exploration:-

Mr Rea explained that the experience the NASA had gain with the Ranger programme of missions to the Moon led to the development of the Mariner missions to Venus and Mars.

Mariner missions:-

Mariners 1 and 2 went to Venus. Mariner 3 failed at the launch. Mariner 4 on the other hand was very successful.

On the night of 14th and 15th July 1965, the Mariner 4 spacecraft made history when it completed the first flyby reconnaissance of Mars after a 228-day journey from Earth. Programmatically, Mariner 4’s journey began in November 1962, when NASA approved the Mariner Mars 1964 Project to send two spacecraft to fly by Mars to take photographs and make other measurements during the encounter. The Jet Propulsion Laboratory (JPL) in Pasadena, California, managed the project, building on its experience from the successful Mariner 2 Mariner 4 encounter with Venus in December 1962.

Compared with our deeper yet still incomplete understanding of the Red Planet today, scientists in the 1960s knew relatively little about Mars. In the late 19th century, Italian astronomer Giovanni Schiaparelli claimed to have observed linear patterns on the surface of the planet that he called ‘canali’, which unfortunately were mis-translated into English as canals, leading some to believe they were built by intelligent beings on Mars. Although that idea fell out of favour among scientists by the early 20th century, it did permeate into science fiction as well as popular culture. Notions of a planet with a global climate relatively similar to Earth’s, including the possibility that it harboured some form of extraterrestrial life, remained popular even among scientists into the 1960s. The best Earth-based telescopic images of Mars revealed little surface detail but did show areas that changed size, shape and colour with the Martian seasons, indicative to some observers of at least some form of simple plant-like life forms.

To carry out their observations during their transit from Earth and during their flybys of Mars, each of the 575-pound Mariner Mars 1964 spacecraft carried seven science instruments:-

1) The television imaging system enabled topographic reconnaissance of the Martian surface.

2) The Helium Magnetometer measured magnetic field strength around the planet.

3) The Ionisation Chamber and particle flux detector measured the omnidirectional flux of particle radiation near Mars and in interplanetary space.

4) The Cosmic Dust Detector measured dust particle momentum and mass distribution.

5) The Cosmic Ray Telescope measured charged particles.

6) The Trapped Radiation Detector consisted of three Geiger-Muller detectors to measure any charged particles that may be trapped by a Martian magnetic field.

7) The Solar Plasma Probe measured the density, velocity, temperature, and direction of movement of protons streaming from the Sun.

Each spacecraft generated 310 watts of electrical power at Mars from photovoltaic cells mounted on four solar panels mounted in a windmill-like arrangement around the probe’s octagonal frame. Mounted on the end of each solar panel were steerable pressure vanes to use the solar wind to control the spacecraft’s orientation. The experimental pressure vanes supplemented a set of nitrogen gas thrusters for attitude control.

The spacecraft converted the analogue signal from the camera to digital format, and following the flyby transmitted the photographs back to Earth at a rate of 8 1/3 bits per second, seemingly glacial today but, as the first digital imaging system used beyond Earth, considered state of the art for the mid-1960s. Each photograph took 10 hours to relay to Earth.

The first of the two spacecraft, Mariner 3, launched from Cape Kennedy Air Force Station, Florida, on 5th November, 1964, atop an Atlas-Agena D rocket. Due to the failure of the spacecraft’s payload shroud to jettison, its solar panels could not deploy and Mariner 3 sailed on into solar orbit as an inert spacecraft. Beneath a hastily redesigned payload shroud, the second spacecraft, Mariner 4, successfully launched on 28th November 1964, just two days before the close of the launch window.

During the eight-month cruise phase to Mars, the spacecraft took measurements on the conditions of interplanetary space and relayed the data to Earth. On 14th July 1965, Mariner 4 passed within 6,118 miles of Mars, snapping 22 photographs of the planet and taking scientific measurements. The spacecraft passed behind the planet as seen from Earth, allowing a radio occultation study to estimate the density of the Martian atmosphere. Playback of the flyby imagery began soon after Mariner 4 emerged from behind Mars and continued until 3rd August.

At JPL, a “real-time data translator” machine converted the Mariner 4 digital image data into numbers printed on strips of paper. Too anxious to wait for the official processed image, employees from the Telecommunications Section attached these strips side by side to a display panel and hand coloured the numbers like a paint-by-numbers picture. The completed image was framed and presented to JPL director William H. Pickering.

The radio occultation results indicated a very low surface atmospheric pressure, about 1% that at Earth’s sea level. Scientists estimated the surface temperature at about -100o C and the spacecraft detected no magnetic field or trapped radiation belts around the planet. The photographs revealed a cratered surface resembling the Moon, although the photographs covered less than 1% of the Martian surface and did not represent Mars, as we know it today. By sheer chance, Mariner 4 imaged some of the oldest and most heavily cratered terrain on Mars, missing some of the more diverse and geologically more recent features. All in all, these findings dashed many scientists’ expectations of Mars as a place hospitable to life.

Although the images and data that Mariner 4 returned may have the dashed the hopes of some scientists that Mars harboured some form of life, its results should be placed in proper perspective. The imagery covered about 1% of the planet’s surface and the best resolution achieved was just under a mile per pixel, with significantly less on many of the images. When compared with imagery acquired later by spacecraft with more sophisticated imaging systems, it’s clear that as ground-breaking as Mariner 4 was, it missed a great deal. The photographs below of the same area (southern Amazonia Planitia) on Mars show the progressive improvement in resolution achieved as newer technology became available, beginning with the Mariner 4 photograph, followed by the Viking 1 Orbiter in 1980, the Mars Express orbiter in 2012 and finally the High Resolution Imaging Science Experiment (HiRISE) instrument aboard Mars Reconnaissance Orbiter in 2017 (the yellow rectangle in the preceding three photos), with a resolution of 50 centimeters per pixel.

Having completed the first scientific reconnaissance of Mars, Mariner 4 sailed on in solar orbit, conducting engineering tests of its imaging and propulsion systems, showing no degradation after years in space. In late 1965, the spacecraft passed on the other side of the Sun as viewed from Earth and set a communications distance record of 190 million miles. In October 1967, engineers conducted tests with Mariner 4’s attitude control system to support the Mariner 5 spacecraft then approaching Venus. Finally, after running out of attitude control gas, Mariner 4 could no longer point its solar arrays toward the Sun and contact with the spacecraft was lost on 21st December 1967.

Mariner 5 visited Venus. Two years after Mariner 4. Mariner 6 and 7 travelled to the Red Planet, with much more sophisticated equipment and cameras.

The Mariner 7 spacecraft made a close flyby of Mars just five days after its twin spacecraft, Mariner 6, in 1969.

Although it had the same objective to study the surface and atmosphere of the Red Planet, Mariner 7 benefited from being the second to arrive at Mars. Scientists were able to use the spacecraft’s reprogrammable command system to instruct it to take additional pictures of the Martian south pole, which had piqued their interest during Mariner 6’s flyby. One photo even showed Mars’ irregularly shaped moon, Phobos.

In 1971, the Mariner 9 spacecraft beat the Soviet Mars 2 to the Red Planet to become the first spacecraft to orbit another planet. While in orbit, Mariner 9 mapped 85 percent of the Martian surface, an objective it inherited from the failed Mariner 8 mission, and collected valuable information about Mars’ surface and atmosphere.

Of the more than 7,000 images it transmitted, some of the most significant were the first detailed views of the solar system’s largest volcano, a canyon system that dwarfs the Grand Canyon and the Martian moons Phobos and Deimos.

When Mariner 9 arrived at Mars on 14th November 1971, planetary scientists were surprised to find the atmosphere was thick with “a planet-wide robe of dust, the largest storm ever observed.” The surface was totally obscured. Mariner 9’s computer was thus reprogrammed from Earth to delay imaging of the surface for a couple of months until the dust settled. The main surface imaging did not get underway until mid-January 1972. However, surface-obscured images did contribute to the collection of Mars science, including understanding of the existence of several huge high-altitude volcanoes of the Tharsis Bulge that gradually became visible as the dust storm abated.

This unexpected situation made a strong case for the desirability of studying a planet from orbit rather than merely flying past. It also highlighted the importance of flexible mission software. The Soviet Union’s Mars 2 and Mars 3 probes, which arrived during the same dust storm, were unable to adapt to the unexpected conditions, which severely limited the amount of data that they were able to collect.

After 349 days in orbit, Mariner 9 had transmitted 7,329 images, covering 85% of Mars’ surface, whereas previous flyby missions had returned less than one thousand images covering only a small portion of the planetary surface. The images revealed river beds, craters, massive extinct volcanoes (such as Olympus Mons, the largest known volcano in the Solar System; Mariner 9 led directly to its reclassification from Nix Olympica), canyons (including the Valles Marineris, a system of canyons over about 4,020 kilometres (2,500 mi) long), evidence of wind and water erosion and deposition, weather fronts, fogs, and more. Mars’ small moons, Phobos and Deimos, were also photographed.
The findings from the Mariner 9 mission underpinned the later Viking program.

Mariner 10, launched on 3rd November 1973; was the first spacecraft sent to the planet Mercury; the first mission to explore two planets (Mercury and Venus) during a single mission; the first to return to its primary destination for another look; and the first to use a gravity assist to change its flight path. The first to return to its target after an initial encounter; and the first to use the solar wind as a major means of spacecraft orientation during flight. These were no mean feats as Mr Rea explained.

The primary goal of the Mariner 10 was to study the atmosphere (if any), surface and physical characteristics of Mercury. Soon after leaving Earth orbit, the spacecraft returned striking photos of both Earth and the Moon as it sped to its first destination, Venus.

After midcourse corrections 13th November 1973, and 21st January 1974, Mariner 10 approached Venus for a gravity assist manoeuvre to send it toward Mercury. On 5th February 1974, the spacecraft began returning images of Venus, the first picture showing the day-night terminator of the planet as a thin bright line. Overall, Mariner 10 returned 4,165 photos of Venus and collected important scientific data during its encounter. The closest flyby range was 3,584 miles (5,768 kilometers) at 17:01 UT 5th February 1974.

Assisted by Venusian gravity, the spacecraft now headed to the innermost planet, which it reached after another course correction 16th March 1974. As Mariner 10 approached Mercury, photos began to show a very Moon-like surface with craters, ridges and chaotic terrain.

The spacecraft’s magnetometers revealed a weak magnetic field. Radiometer readings suggested night time temperatures of minus 297 degrees Fahrenheit (minus 183 degrees Celsius) and maximum daytime temperatures of 369 degrees Fahrenheit (187 degrees Celsius).
The closest encounter came at 20:47 UT 29th March 1974, at a range of 437 miles (703 kilometers). An occultation experiment as the vehicle crossed behind the nightside of the planet indicated a lack of an atmosphere or ionosphere.

Leaving Mercury behind, the spacecraft looped around the Sun and headed back to its target, helped along by subsequent course corrections on 9th May, 10th May and 2nd July 1974. Mariner 10 flew by Mercury once more on at 20:59 UT 21st September 1974, at a range of about 29,869 miles (48,069 kilometers), adding imagery of the southern polar region. The spacecraft used solar pressure on its solar panels and high-gain antenna for attitude control.

Mariner 10 once again sped away from Mercury before a final and third encounter with Mercury, enabled by three manoeuvres (30th October 1974, 13th February 1975, and 7th March 1975), the last one actually to avoid impact with the planet. The third flyby, at 22:39 UT 16th March 1975, was the closest to Mercury, at a range of about 200 miles (327 kilometers).
Because of the failure of a tape recorder and restrictions in the rate of data reception, only the central quarter of each of 300 high-resolution images was received during this encounter.

Last contact with the spacecraft was at 12:21 UT 14th March 1975, after the spacecraft exhausted its supply of gas for attitude control.
Mariner 10 returned over 2,700 pictures during its three Mercury flybys that covered nearly half of the planet’s surface. Some of the images showed detail as small as 328 feet (100 meters) wide. Perhaps the most impressive surface feature was the Caloris basin, characterized by a set of concentric rings and ridges and about 1,550 miles (2,500 kilometers) in diameter.

The mission was the last visit to Mercury by a robotic probe for more than 30 years.

Pioneer missions:-

Pioneer 10, the first NASA mission to the outer planets, garnered a series of firsts perhaps unmatched by any other robotic spacecraft in the space era: the first vehicle placed on a trajectory to escape the solar system into interstellar space; the first spacecraft to fly beyond Mars; the first to fly through the asteroid belt; the first to fly past Jupiter; and the first to use all-nuclear electrical power (two SNAP-19 radioisotope thermal generators [RTGs] capable of delivering about 140 W during the Jupiter encounter).
After launch by a three-stage version of the Atlas Centaur (with a TE-M-364-4 solid propellant engine modified from the Surveyor lander), Pioneer 10 reached a maximum escape velocity of 32,110 miles per hour (51,682 kilometers per hour), faster than any previous human-made object at that point in time.

Launched on 2nd March 1972. Controllers carried out two course corrections, on 7th March and 26th March, the latter to ensure an occultation experiment with Jupiter’s moon Io.
There were some initial problems during the outbound voyage when direct sunlight caused heating problems, but nothing to endanger the mission.
On 15th July 1972, the spacecraft entered the asteroid belt, emerging in February 1973 after a voyage of about 271 million miles (435 million kilometers).
During this period, the spacecraft encountered some asteroid hits, although fewer than expected, and also measured the intensity of Zodiacal light in interplanetary space.

In conjunction with Pioneer 9 (in solar orbit), on 7th August, Pioneer 10 recorded details of one of the most violent solar storms in recent record.
At 20:30 UT 26th November, the spacecraft reported a decrease in the solar wind and a 100-fold increase in temperature indicating that it was passing through the front of Jupiter’s bow shock. In other words, it had entered Jupiter’s magnetosphere.

By 1st December, Pioneer 10 was returning better images of the planet than possible from Earth. (It had already begun imaging as early as 6th November 1973). Command-and-return time was up to 92 minutes by this time.

Pioneer 10’s closest approach to Jupiter was at 02:26 UT 4th December 1973, when the spacecraft raced by the planet at a range of 81,000 miles (130,354 kilometers) at a velocity of approximately 78,000 miles per hour (126,000 kilometers/hour).

Of the spacecraft’s 11 scientific instruments, 6 operated continuously through the encounter. The spacecraft passed by a series of Jovian moons, obtaining photos of Callisto, Ganymede, and Europa (but not of Io, as the photopolarimeter succumbed to radiation by that time).

Approximately 78 minutes after the closest approach, Pioneer 10 passed behind Jupiter’s limb for a radio occultation experiment. In addition, the infrared radiometer provided further information on the planet’s atmosphere.

Between 6th November and 31st December, the spacecraft took about 500 pictures of Jupiter’s atmosphere with the highest resolution of about 200 miles (320 kilometers), clearly showing such landmarks as the Great Red Spot.

The Jupiter encounter was declared over 2nd January 1974.
Pioneer 10 fulfilled all objectives except one due to false commands triggered by Jupiter’s intense radiation. Based on the data, scientists identified plasma in Jupiter’s magnetic field.
The spacecraft crossed Saturn’s orbit in February 1976, recording data that indicated that Jupiter’s enormous magnetic tail, almost 800 million kilometers long, covered the whole distance between the two planets.

Still operating nominally, Pioneer 10 crossed the orbit of Neptune (then the outermost planet) on 13th June 1983, thus becoming the first human made object to go beyond the furthest planet.
NASA maintained routine contact with Pioneer 10 for over two decades until 19:35 UT 31st March 1997, (when the spacecraft was 67 AU from Earth) when routine contact was terminated due to budgetary reasons.
Intermittent contact, however, continued, but only as permitted by the onboard power source, with data collections from the Geiger tube telescope and the charged particle instrument.
Until 17th February 1998, Pioneer 10 was the farthest human-made object in existence (69.4 AU) when Voyager 1 passed it.

A NASA ground team received a signal on the state of spacecraft systems (still nominal) on 5th August 2000. The spacecraft returned its last telemetry data 27th April 2002, and less than a year later, on 23rd January 2003, it sent its last signal when it was 7.6 billion miles (12.23 billion kilometers from Earth.

That signal took 11 hours and 20 minutes to reach Earth. By that time, it was clear that the spacecraft’s RTG power source had decayed, thus delivering insufficient power to the radio transmitter.
A final attempt to contact Pioneer 10 on 4th March 2006, failed.
Originally designed for a 21-month mission, the mission’s lifetime far exceeded expectations.

By 5th November 2017, the inert Pioneer 10 spacecraft was roughly 118.824 AUs (about 11 billion miles or 17.7 billion kilometers) from Earth, a range second only to Voyager 1.
The spacecraft is generally heading in the direction of the red star Aldebaran that forms the eye of the Taurus constellation. It is expected to pass by Aldebaran in about two million years.
Pioneer 10 is heading out of the solar system in a direction very different from the two Voyager probes and Pioneer 11, i.e., towards the nose of the heliosphere in an upstream direction relative to the inflowing interstellar gas.
In case it’s intercepted by intelligent life, Pioneer 10 carries an aluminium plaque with diagrams of a man and a woman, the solar system, and its location relative to 14 pulsars. The expectation is that intelligent beings would be able to interpret the diagram to determine the position of the Sun and thus, Earth at the time of launch relative to the pulsars.

Pioneer 11, the sister spacecraft to Pioneer 10, was the first human-made object to fly past Saturn and also returned the first pictures of the polar regions of Jupiter.

After boost by the TE-M-364-4 engine, the spacecraft sped away from Earth at a velocity of about 32,000 miles per hour (51,800 kilometers per hour), thus equalling the speed of its predecessor, Pioneer 10.
During the outbound journey, there were a number of malfunctions on the spacecraft; including the momentary failure of one of the RTG booms to deploy, a problem with an attitude control thruster, and the partial failure of the asteroidal dust detector; but none of these jeopardised the mission.
Pioneer 11 passed through the asteroid belt without damage by mid-March 1974. Soon, on 26th April 1974, it performed a midcourse correction (after an earlier one on 11th April 1973) to guide it much closer to Jupiter than Pioneer 10 and to ensure a polar flyby.

Pioneer 11 penetrated the Jovian bow shock on 25th November 1974, at 03:39 UT. The spacecraft’s closest approach to Jupiter occurred at 05:22 UT on 3rd December 1974, at a range of about 26,400 miles (42,500 kilometers) from the planet’s cloud tops, three times closer than Pioneer 10. By this time, it was travelling faster than any human-made object at the time, more than 106,000 miles per hour (171,000 kilometers per hour).
Because of its high speed during the encounter, the spacecraft’s exposure to Jupiter’s radiation belts spanned a shorter time than its predecessor although it was actually closer to the planet.

Pioneer 11 repeatedly crossed Jupiter’s bow shock, indicating that the Jovian magnetosphere changes its boundaries as it is buffeted by the solar wind. Besides the many images of the planet (and better pictures of the Great Red Spot), Pioneer 11 took about 200 images of the moons of Jupiter. The vehicle then used Jupiter’s massive gravitational field to swing back across the solar system to set it on a course to Saturn.

After its Jupiter encounter, on 16th April 1975, the micrometeoroid detector was turned off since it was issuing spurious commands which were interfering with other instruments. Course corrections on 26th May 1976, and 13th July 1978, sharpened its trajectory towards Saturn.

Pioneer 11 detected Saturn’s bow shock on 31st August 1979, about 932,000 miles (1.5 million kilometers) out from the planet, thus providing the first conclusive evidence of the existence of Saturn’s magnetic field.
The spacecraft crossed the planet’s ring plane beyond the outer ring at 14:36 UT 1st September 1979, and then passed by the planet at 16:31 UT for a close encounter at a range of about 13,000 miles (20,900 kilometers). It was moving at a relative velocity of about 71,000 miles per hour (114,000 kilometers per hour) at the point of closest approach.

During the encounter, the spacecraft took 440 images of the planetary system, with about 20 at a resolution of about 56 miles (90 kilometers).
The images of Saturn’s moon Titan (at a resolution of 112 miles or 180 kilometers) showed a featureless orange fuzzy satellite. A brief burst of data on Titan indicated that the average global temperature of Titan was minus 315 degrees Fahrenheit (minus 193 degrees Celsius).

Among Pioneer 11’s many discoveries were a narrow ring outside the A ring named the F ring and a new satellite 124 miles (200 kilometers) in diameter. The spacecraft recorded the planet’s overall temperature at minus 292 degrees Fahrenheit (minus 180 degrees Celsius) and photographs indicated a more featureless atmosphere than that of Jupiter. Analysis of data suggested that the planet was primarily made of liquid hydrogen.

After leaving Saturn, Pioneer 11 headed out of the solar system in a direction opposite to that of Pioneer 10, toward the centre of the galaxy in the general direction of Sagittarius.
Pioneer 11 crossed the orbit of Neptune on 23rd February 1990, becoming the fourth spacecraft, after Pioneer 10, Voyager 1 and 2 to do so.
Scientists expect that during their outbound journeys, both Pioneer 10 and 11 will find the boundary of the heliosphere where the solar wind slows down and forms a “termination shock,” beyond which there would be the heliopause and finally the bow shock of the interstellar medium, the space beyond our solar system.

Mars Viking Missions:-

NASA’s Viking Project found a place in history when it became the first U.S. mission to land a spacecraft safely on the surface of Mars and return images of the surface. Two identical spacecraft, each consisting of a lander and an orbiter, were built. Each orbiter-lander pair flew together and entered Mars orbit; the landers then separated and descended to the planet’s surface.

Viking 1
The first spacecraft to successfully land on Mars, Viking 1 was part of a two-part mission to investigate the Red Planet and search for signs of life. Viking 1 consisted of both an orbiter and a lander designed to take high-resolution images and study the Martian surface and atmosphere.
Operating on Mars’ Chryse Planitia (22.27° N, 312.05° E, planetocentric) for more than six years, Viking 1 performed the first Martian soil sample using its robotic arm and a special biological laboratory. While it found no traces of life, Viking 1 did help better characterize Mars as a cold planet with volcanic soil, a thin, dry carbon dioxide atmosphere, and striking evidence for ancient river beds and vast flooding.

The Viking mission was planned to continue for 90 days after landing. Each orbiter and lander operated far beyond its design lifetime. Viking Orbiter 1 continued for four years and 1,489 orbits of Mars, concluding its mission 7th August 1980. Because of the variations in available sunlight, both landers were powered by radioisotope thermoelectric generators (RTGs) – devices that create electricity from heat given off by the natural decay of plutonium. That power source allowed long-term science investigations that otherwise would not have been possible. Viking Lander 1 made its final transmission to Earth on 11th November 1982.

Viking 2
Viking 2 landed on Mars at Utopia Planitia (47.64° N, 134.29° E, planetocentric) on 3rd September 1976, immediately following the first successful spacecraft landing on Mars by Viking 1. It was part of NASA’s early two-part mission to investigate the Red Planet and search for signs of life. While neither spacecraft found traces of life, they did find all the elements essential to life on Earth: carbon, nitrogen, hydrogen, oxygen, and phosphorus.

Like its predecessor, the Viking 2 mission consisted of a lander and an orbiter designed to take high-resolution images and study the Martian surface and atmosphere. The Viking Orbiter 2 functioned until 25th July 1978. The last data from Viking Lander 2 arrived at Earth on 11th April 1980.

Besides taking photographs and collecting other science data on the Martian surface, the two Viking landers conducted three biology experiments designed to look for possible signs of life. These experiments discovered unexpected and enigmatic chemical activity in the Martian soil, but provided no clear evidence for the presence of living microorganisms in soil near the landing sites.

Planetary Voyages:-

The twin spacecraft Voyager 1 and Voyager 2 were launched by NASA in separate months in the summer of 1977 from Cape Canaveral, Florida. As originally designed, the Voyagers were to conduct close up studies of Jupiter and Saturn, Saturn’s rings, and the larger moons of the two planets.

To accomplish their two-planet mission, the spacecraft were built to last five years. But as the mission went on, and with the successful achievement of all its objectives, the additional flybys of the two outermost giant planets, Uranus and Neptune, proved possible; and irresistible to mission scientists and engineers at the Voyagers’ home at the Jet Propulsion Laboratory in Pasadena, California.
As the spacecraft flew across the solar system, remote control reprogramming was used to endow the Voyagers with greater capabilities than they possessed when they left the Earth. Their two-planet mission became four. Their five-year lifetimes stretched to 12 and is now near thirty-seven years.

Eventually, between them, Voyager 1 and 2 would explore all the giant outer planets of our solar system, 48 of their moons, and the unique systems of rings and magnetic fields those planets possess.

Had the Voyager mission ended after the Jupiter and Saturn flybys alone, it still would have provided the material to rewrite astronomy textbooks. But having doubled their already ambitious itineraries, the Voyagers returned to Earth information over the years that has revolutionized the science of planetary astronomy, helping to resolve key questions while raising intriguing new ones about the origin and evolution of the planets in our solar system.

History of The Voyager Mission:-

The Voyager mission was designed to take advantage of a rare geometric arrangement of the outer planets in the late 1970s and the 1980s, which allowed for a four-planet tour for a minimum of propellant and trip time. This layout of Jupiter, Saturn, Uranus and Neptune, which occurs about every 175 years, allows a spacecraft on a particular flight path to swing from one planet to the next without the need for large onboard propulsion systems. The flyby of each planet bends the spacecraft’s flight path and increases its velocity enough to deliver it to the next destination. Using this “gravity assist” technique, first demonstrated with NASA’s Mariner 10 Venus/Mercury mission in 1973-74, the flight time to Neptune was reduced from 30 years to 12.

While the four-planet mission was known to be possible, it was deemed to be too expensive to build a spacecraft that could go the distance, carry the instruments needed and last long enough to accomplish such a long mission. Thus, the Voyagers were funded to conduct intensive flyby studies of Jupiter and Saturn only. More than 10,000 trajectories were studied before choosing the two that would allow close flybys of Jupiter and its large moon Io, and Saturn and its large moon Titan; the chosen flight path for Voyager 2 also preserved the option to continue on to Uranus and Neptune.

From the NASA Kennedy Space Centre at Cape Canaveral, Florida, Voyager 2 was launched first, on 20th August 1977. Voyager 1 was launched on a faster, shorter trajectory on 5th September 1977. Both spacecraft were delivered to space aboard Titan-Centaur expendable rockets.

The prime Voyager mission to Jupiter and Saturn brought Voyager 1 to Jupiter on 5th March 1979, and Saturn on 12th November 1980, followed by Voyager 2 to Jupiter on 9th July 1979, and Saturn on 25th August 1981.
Voyager 1’s trajectory, designed to send the spacecraft closely past the large moon Titan and behind Saturn’s rings, bent the spacecraft’s path inexorably northward out of the ecliptic plane (the plane in which most of the planets orbit the Sun). Voyager 2 was aimed to fly by Saturn at a point that would automatically send the spacecraft in the direction of Uranus.

After Voyager 2’s successful Saturn encounter, it was shown that Voyager 2 would likely be able to fly on to Uranus with all instruments operating. NASA provided additional funding to continue operating the two spacecraft and authorized JPL to conduct a Uranus flyby. Subsequently, NASA also authorized the Neptune leg of the mission, which was renamed the Voyager Neptune Interstellar Mission.

Voyager 2 encountered Uranus on 24th January 1986, returning detailed photos and other data on the planet, its moons, magnetic field and dark rings. Voyager 1, meanwhile, continues to press outward, conducting studies of interplanetary space. Eventually, its instruments may be the first of any spacecraft to sense the heliopause (the boundary between the end of the Sun’s magnetic influence and the beginning of interstellar space).

Following Voyager 2’s closest approach to Neptune on 15th August 1989, the spacecraft flew southward, below the ecliptic plane and onto a course that will take it, too, to interstellar space. Reflecting the Voyagers’ new transplanetary destinations, the project is now known as the Voyager Interstellar Mission.

Voyager 1 has crossed into the heliosheath and is leaving the solar system, rising above the ecliptic plane at an angle of about 35 degrees at a rate of about 520 million kilometers (about 320 million miles) a year. (Voyager 1 entered interstellar space on 15th August 2012.) Voyager 2 is also headed out of the solar system, diving below the ecliptic plane at an angle of about 48 degrees and a rate of about 470 million kilometers (about 290 million miles) a year.

Both spacecraft will continue to study ultraviolet sources among the stars, and the fields and particles instruments aboard the Voyagers will continue to explore the boundary between the Sun’s influence and interstellar space. The Voyagers are expected to return valuable data for at least another decade. Communications will be maintained until the Voyagers’ power sources can no longer supply enough electrical energy to power critical subsystems.

Mr Rea summarised the Mariner heritage of Solar system exploration missions, as 14 launched with 11 being successful.

The Pioneer Venus missions:-

NASA’s Pioneer Venus 1 was the first of a two-spacecraft orbiter-probe combination designed to study the atmosphere of Venus. It was the first American spacecraft to orbit Venus. The second spacecraft was launched a few months later.

Formally approved by NASA in August 1974, the Pioneer Venus project comprised two spacecraft to explore the atmosphere and surface of Venus. Both spacecraft used a basic cylindrical bus.
Pioneer Venus 1, the orbiter, was designed to spend an extended period in orbit around Venus mapping the surface using a radar package. After a six-and-a-half-month journey, the spacecraft entered an elliptical orbit around Venus at 15:58 UT 4th December 1978.

It was the first American spacecraft to enter orbit around Venus, about three years after the Soviets accomplished the same feat. The initial orbital period was 23 hours, 11 minutes, which was altered within two orbits to the desired 24 hours; a manoeuvre that would allow the orbit’s high and low points (about 99 miles or 160 kilometers) to occur at the same time each Earth day.

Data from the radar mapper allowed scientists to produce a topographical map of most of the Venusian surface between 73 degrees north latitude and 63 degrees south latitude at a resolution of about 47 miles (75 kilometers).

The data indicated that Venus was much more smooth and spherical than Earth. The orbiter identified the highest point on Venus as Maxwell Montes, which rises about 6.5 miles (10.8 kilometers) above the mean surface.

Infrared observations implied a clearing in the planet’s atmosphere over its north pole. In addition, ultraviolet light photos showed dark markings that covered the clouds in the visible hemisphere.

Cameras also detected almost continuous lightning in the atmosphere. The spacecraft confirmed that Venus has little if any magnetic field.
Because of the nature of its orbit, Pioneer Venus 1 passed through the planet’s bow shock twice per revolution, and using its magnetometer, scientists were able to observe how the planet’s ionosphere interacted with the solar wind.

The mapping radar was switched off on 19th March 1981, after having mapped 93 percent of the band between 74 degrees north latitude and 63 degrees south latitude. It was reactivated in 1991, 13 years after launch, to explore the previously inaccessible southern portions of the planet.
In May 1992, Pioneer Venus 1 began the final phase of its mission, maintaining its periapsis between 93 and 155 miles (150 and 250 kilometers) until propellant depletion.

The last transmission was received at 19:22 UT 8th October 1992, as its decaying orbit no longer permitted communications. The spacecraft burned up the atmosphere soon after, ending a successful 14-year mission that was planned to last only eight months.

Pioneer Venus 2, the sister ship to Pioneer Venus 1, consisted of the main spacecraft, a Large Probe (698 pounds or 316.5 kilograms), and three identical Small Probes, all of which were designed to collect data during entry into the atmosphere of Venus. The probes were shaped like cones and were not expected to survive impact with the surface.

Pioneer Venus 2 released the Large Probe (5 feet or 1.5 meters in diameter) on 16th November 1978, while about 7 million miles (11.1 million kilometers) from the planet. Four days later, the bus released the three Small Probes, the North Probe, Day Probe and the Night Probe; while about 6 million miles (9.3 million kilometers) from Venus. All five components reached the Venusian atmosphere 9th December 1978, with the Large Probe entering first.

Using a combination of air drag and a parachute, the Large Probe descended through the atmosphere, entering at a velocity of 7 miles per second (11.6 kilometers per second), slowing down until it impacted on the surface of Venus at 19:40 UT. It landed at 4.4 degrees north latitude and 304 degrees east longitude at a velocity of 20 miles per hour (32 kilometers per hour). Transmissions ceased at impact as expected.
The three Small Probes (2.5 feet or 76 centimeters in diameter) arrived in the atmosphere within minutes of the bigger one and descended rapidly without the benefit of parachutes.

They each opened their instrument doors at altitudes of about 43.5 miles (70 kilometers) and began to transmit information about the Venusian atmosphere immediately. Each probe took about 53 to 56 minutes to reach the surface. Amazingly, two of the three Small Probes survived the hard impact. The so-called Day Probe transmitted data from the surface for 67 minutes, 37 seconds, before succumbing to the high temperatures, pressures and power depletion. Information from its nephelometer indicated that dust raised from its impact took several minutes to settle back to the ground.

All three Small Probes suffered instrument failures, but not significant enough to jeopardise their main missions. Their landing coordinates were: 60 degrees north latitude and 4 degrees east longitude (North Probe); 32 degrees south latitude and 318 degrees east longitude (Day Probe); and 27 degrees south latitude and 56 degrees east longitude (Night Probe).

The main spacecraft, meanwhile, burned up in the atmosphere at an altitude of about 75 miles (120 kilometers);about 1.5 hours after the probes and provided key data on higher regions.

Data from the probes indicated that between about 6 and 31 miles (10 and 50 kilometers) there is almost no convection in the atmosphere of Venus. Below a haze layer at about 19 miles (30 kilometers), the atmosphere is relatively clear.

In addition, below an altitude of 31 miles (50 kilometers), the temperatures reported from the four probes indicated very few differences even though their entry sites were separated by thousands of miles (kilometers).

Mr Rea concluded saying that years ago he had a telescope and all he could see where the planets of the solar system at a distance looking very fuzzy and distant. He stated he believes he has been very fortunate that during his lifetime he has been privileged to see the planets of the Solar System up close and personal through these pioneering missions into outer space.