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Science / Space Race

[August 8, 1969] Two by Four (Mariners 6 and 7 go to Mars)

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photo of a man with glasses and curly, long, brown hair, and a beard and mustache
by Gideon Marcus

Into the Wild Black Yonder

Ten years ago, when we started our planetary series of articles, none of other worlds in our solar system had been explored.  Since then, five intrepid spacecraft have toured two planets.  Mariner 2 and Mariner 5 probed Venus, returning the revelation that the shrouded world is a seething cauldron.  Mariner 4 returned the first pictures of the Red Planet, shocking humanity with images of Moonlike craters and reports of a vanishingly thin atmosphere, dashing forever the vivid, science fictional conception of Mars as an inhabitable world.

Now, twin Mariners 6 and 7 have flown by Mars, dramatically increasing what we know about the fourth planet.  While we'll never get back that fantasy so elegantly woven by Edgar Rice Burroughs and Leigh Brackett, the new Mars is also not a blasted husk either.


Distant views of Mars, as seen by Mariner 7 as it approached the planet

The Next Generation

Despite the blow to morale given by Mariner 4, Mars still seemed like the most hospitable place for life to have arisen apart from Earth.  After all, are there not microorganisms living in the harsh environments of Antarctica and at the bottom of the sea?  Even though the Martian atmosphere is just 1% as thick as that of Earth, this is still plenty dense compared to, say, the Moon.  Moreover, Earth's atmosphere is just 1% that of Venus.  Who's to say when an atmosphere is "thick enough"?

So, just a few months after Mariner 4 flew past Mars, Mariners 6 and 7 were authorized.  At first glance, they look a lot like their predecessor, but the differences are profound—both internally and externally.


From top to bottom: Mariners 2, 4, 5, and 6/7 (note the family resemblance of the last three—Mariner 5 was actually a modified Mariner 3/4 backup!)

First, the insides: the new Mariners are the first spacecraft made only to examine their target planet.  All of the prior Mariners had experiments for monitoring the interplanetary environment—solar wind, magnetic fields, that sort of thing.  Mariners 6 and 7 carry two TV cameras (one narrow, one wide-angle), an infrared radiometer (to measure the temperature of Mars), and ultraviolet and infrared spectrometers (to determine the chemical makeup of the Martian atmosphere and surface).  That's it.

As for the outsides, since 1965, when Mariner 4 passed by the Red Planet, there has been a revolution in communications technology.  Not only do the new Mariners carry more powerful transmitters and antennas, but with the construction of the new 210 foot antenna at Goldstone, supplementing the old 85 footers, data can be transferred between the spacecraft and Earth at a rate more than 2000 times the 8.33 bits per second speed of Mariner 4.  It also helps that Mars is closer to Earth this time around, and that the rocket carrying Mariners 6 and 7 is the beefy new Atlas Centaur, which can loft more weight than the old Atlas Agena so the onboard electronics can be heftier and thus more capable.


The 210' "Mars Dish" at Goldstone, California

What this means for us on the ground is that instead of sending back just 22 images of Mars, the new Mariners could transmit hundreds of pictures, all while returning real-time spectrographic and radiometer data.  All of this aided by the installation of the first computer equipped on an interstellar probe, capable of remembering 128 "words" some 22 characters in length.  And that computer can be reprogrammed on the fly from Earth!

On their Way

Jet Propulsion Laboratory, the same folks who built the other Mariners, assembled four spacecraft for the mission.  The first was a stay-at-home test model, the second a source of spare parts.  The other two were redundant probes—an understandable precaution given the loss of Mariners 1 and 3.  However, the twin ships weren't entirely redundant; Mariner 6 was targeted to fly over the Martian North Pole while #7 was aimed over the South Pole.

Problems with the spacecraft began before liftoff.  Mariner 6's Atlas rocket, which maintains its structure through internal fuel pressure, sprung a leak and began to deflate like a balloon.  It had to be replaced with Mariner 7's rocket, and a new one ordered from Convair.  This did not delay the launch, however (which had to go at a set time to reach Mars with a minimum of fuel use), and Mariner 6 blasted off on February 24th.  Mariner 7 took off on March 27, but because of its course, was set to reach Mars just five days after its sister.


The launch of Mariner 7

Both rockets performed beautifully, requiring only minor mid-course corrections early in the flight to ensure they zoomed close by the fourth planet.  There were some minor technical problems: The radio on Mariner 6, used to determine range from Earth, kept locking on its own signal rather than Earth's, making it useless.  It fixed itself later in the flight, however.

Similarly, the star tracker designed to keep Mariner positioned properly lost sight of Canopus.  After weeks of engineers scrambling to find an alternative guiding star (they even tried the Large Magellanic Cloud, but the galaxy was too diffuse to be useful), that system fixed itself, too.  Finally, the onboard solar sensors that told how much sunlight was hitting Mariner 6's power panels, began reading too low.  Was the Sun going out?  No.  The sensors had just drifted out of calibration.

Mariner 7's only issue was a radio receiver that dropped to about 20% of its sensitivity, apparently due to cold.  Ground controllers switched it to high power, which warmed the thing up and fixed it.

Thus, its vexing teething pains dealt with, NASA now had, for the first time, two fully operating probes with which to explore Mars.

The Great Galactic Ghoul

On July 29, even as Mariner 6 was finishing the transmission of 33 low-resolution approach images, Mariner 7 suddenly began spinning wildly, all of its scientific data telemetry channels scrambled.  Had an asteroid hit the spacecraft?  Had there been an instrument explosion or some kind of short circuit?  Was there some kind of Great Galactic Ghoul guarding the Red Planet?  No answer was quickly forthcoming.


Collage of Mariner 6 images as it approached Mars

Nevertheless, engineers raced to salvage the mission—with Mariner 7 arriving shortly after its sister, and from a more favorable angle, the JPL science team wanted the spacecraft's experiments all in working order. 

Cautiously, computer engineers went over every bit of code and methodically tested all of Mariner 7's instruments.  They were in working order, but because of the accident, uncalibrated and useless.  How to get real data points to use to base the radiometer and spectrometer data against?


Engineers at the Mariner control center at JPL

As it turned out, the two TV cameras on board were in good order and unaffected.  By pointing them at Martian targets and using the data they returned, it was possible to calibrate the other experiments.  And so, just in the nick of time, Mariner 7 was ready, come close encounter time, to do some real science.

Exploring Barsoom

So what did the two probes find as they whizzed past Mars, almost grazing it from a scant few thousand miles away?

Well, at first they seemed to confirm Mariner 4's findings.  There were all the craters in stark detail.  There was no evidence that there had ever been widespread water—absent was the erosion one would expect from oceans or even rivers.


A lunar landscape, courtesy of Mariner 7

On the other hand, if Mars wasn't Earth's twin, neither was it sister to the Moon.  As each Mariner went behind the planet, beaming radio signals through the Martian atmosphere, it was confirmed that surface pressure was around 7 millibar—a refinement rather than a revelation.  But they did determine that carbon dioxide makes up a greater percentage of the air than even on Venus.  Nitrogen was completely absent, which was a surprise.  So was ozone, which means that the surface is fairly baked by ultraviolet—again, a strike against life on the planet.

The Red Planet is not quite geologically moribund, however.  The vast Hellas region, smooth of craters, and a region of convoluted terrain akin to the American Badlands, suggests some kind of volcanic activity in comparatively recent times.

Unlike the Moon, clouds scud across the Martian sky, mostly composed of dry ice.  While it may not rain on the planet, it does frost, and maybe even snow ice and carbon dioxide.  The climate changes with the seasons, with polar (dry?) ice caps spreading and receding.  The tropical highs soar to a balmy 60 degrees, but the polar lows plunge to 240 degrees below zero.


A view of the Martian North Pole, snapped by Mariner 6—note the ice cap

Thus, Mars is an inhospitable place…but it if it lacks biological life, it is nevertheless an interesting living, breathing planet in its own right.

What's next?

Mariners 6 and 7 are still functioning, and their onboard systems should work until at least 1971.  Not only might they return pictures of any asteroids or comets that drift by, they will also constitute an experiment in and of themselves.  As they drift through the solar system, terrestrial scientists will measure variations in the timing of their telemetry signals and use them to prove General Relativity—something that requires great distances to detect subtle theoretical variations.

As for successors, a Martian orbiter is already in the works for the 1971 alignment, and in 1973, a probe will use the gravity of Venus to enable a probe to fly by and then visit, for the first time, Mercury, the closest planet to the Sun.

And also in 1973, the Viking orbiter/lander combo, successor to the overlarge Voyager project, will give Mars a real look.


The 1971 Mars Orbiter

If the 1960s were the dawn of interplanetary science, the 1970s will see its maturity.  I find this as momentous an achievement as footprints on the Moon.

I can't wait to rewrite all of the articles in our solar system series!




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Science / Space Race

[July 20, 1965] No War of the Worlds After All? (Mariner IV reaches Mars)

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by Kaye Dee

Just a few days ago, on July 15, NASA’s Mariner IV space probe made history by being the first spacecraft to successfully reach the planet Mars, capturing images of its surface. These are the first close-up views of another planet in our solar system and the initial pictures suggest that, despite what science fiction would have us believe, Earth won’t have to fear an invasion from Mars any time soon!

The first close-up image ever taken of Mars, showing the limb of the planet and a haze-like feature that might be clouds. The smallest features in this image are roughly 3 miles across, but there's no sign of Martian canals!

The Canals of Mars

Mars has been an object of intense scientific and popular fascination since the last century, when telescope observations first suggested that the planet was potentially Earthlike, since it showed polar caps and surface changes that appeared to represent seasonal variations due to the growth and die-back of vegetation. Then, in 1877, the Italian astronomer Schiaparelli observed what he called “canali” on Mars. He apparently meant grooves or channels on the Martian surface, but his work was translated into English as “canals” and some astronomers took this literally to mean that he had observed structures that were the work of intelligent beings.

A section of one of Percival Lowell’s maps of Mars, published in his 1895 book Mars. The complete map depicted 184 named canals marked on it using numbers.

By the end of the 19th Century, the idea that there is intelligent life on Mars had taken hold, thanks particularly to the writings of American astronomer Percival Lowell (the same Percival Lowell who is also associated with the discovery of the Planet Pluto!) He believed in a Martian civilisation that had constructed vast networks of canals to bring water from the planet’s poles and wrote several books and innumerable newspaper articles detailing his observations of canal systems on the Red Planet. Science fiction stories like H.G. Well’s War of the Worlds, first published in 1897, and Edgar Rice Burroughs' "Barsoom" series further encouraged popular belief that there was intelligent life on Mars and generated something of a ‘Mars mania’ that has grown across the 20th Century.

Cover of the August 1927 issue of Amazing depicting the iconic Martian machines from Wells' War of the Worlds. This powerful story has been re-interpreted on radio and film and has had a tremendous influence in shaping popular perceptions of life on Mars.

The Mars Race

Most scientists have accepted for a decade or more now that modern telescope observations indicate that it is unlikely that higher forms of life will be found on Mars after all. Yet the fascination with Mars has been so strong that it’s not surprising the planet became an early target for space exploration, after the Moon. The Soviet Union started the race to Mars in October 1960, with “Marsnik” 1 and 2. We don’t know much about these probes, but it seems they both failed even to reach orbit. The USSR’s Mars 1 flew past Mars in June 1963, but it had stopped sending back data in March. Sputnik 22 and Sputnik 24, both launched around the same time as Mars 1, are also believed to be elements of a failed Mars mission. Zond 2, launched just 2 days after Mariner IV, is also assumed to be an attempted Mars mission, though it, too, ceased transmitting en route. Clearly, getting to Mars is hard. Mariner IV was meant to be a twin mission with Mariner III, but that mission also failed at launch.

Even though Mars 1 ceased transmitting long before it reached Mars, the USSR still celebrated it as an achievement on its 1964 Cosmonauts Day stamp.

Mariner IV was launched on an Atlas Agena rocket from Cape Canaveral at 12:22 GMT on November 28, last year. It has an octagonal magnesium frame, 50 inches across the diagonal and 18 inches high, which houses the electronic equipment, propulsion system and attitude control gas supplies and regulators. Four solar panels, containing a total of 28,224 solar cells, are attached to the top of the frame. They are able to generate 310 watts of power at the distance of Mars from the Sun. Mariner also has two antennae for transmitting data back to Earth: An elliptical high-gain parabolic antenna and an omnidirectional low-gain antenna, mounted on a seven-foot, four-inch-tall mast next to the high-gain antenna.

Mariner IV is an incredibly sophisticated space probe for its size, packed with scientific instruments, plus its television camera system. Its design is a radical departure from the conical design used for the Ranger Moon probes and NASA's successful Mariner II mission to Venus.

Deep Space Laboratory

For its relatively small size, Mariner IV is a spacegoing scientific laboratory, designed to measure the conditions in deep space between Mars and the Earth and in the vicinity of Mars itself. Its scientific instruments include a helium magnetometer to measure the characteristics of the interplanetary and planetary magnetic fields; an ionization chamber/Geiger counter, to measure the charged-particle intensity and distribution in interplanetary space and in the vicinity of Mars; a cosmic ray telescope, to measure the direction and energy spectrum of protons and alpha particles; a solar plasma probe, to measure the very low energy charged particle flux from the Sun, and a cosmic dust detector, to measure the momentum, distribution, density, and direction of cosmic dust. Although the Geiger counter failed in February and the plasma probe's performance is degraded, the other instruments are all working well.

Mariner IV's 'endless loop' magnetic tape recorder. Its 330ft of tape has a storage capacity of 5.24 million bits – right at the cutting-edge of recording technology!

Probably the most important instrument on Mariner IV, and certainly the one of the most interest to the public, is its television camera, designed to obtain close-up images of the Martian surface. The camera is mounted on a scan platform at the bottom centre of the spacecraft and consists of 4 parts: a Cassegrain telescope with a 1.05° by 1.05° field of view; a shutter and red/green filter assembly with 0.08s and 0.20s exposure times; a slow scan vidicon tube which translates the optical image into an electrical video signal, and the electronic systems required to convert the analogue signal into a digital signal for transmission. During the fly-by of Mars, all the television images and the data gathered by the scientific instruments were stored on an ‘endless loop’ four-track magnetic tape recorder for later transmission back to Earth. 

First Pictures from Another World

On July 15 Mariner 4 passed within 6117 miles of Mars, spending just 25 minutes doing visual observations of the planet’s surface. During that brief time, its television camera captured 21 full pictures and part of a 22nd, the first ever close-up images of the surface of another planet. Each photo covers an area of about 77 square miles. It takes about 10 hours to transmit each image back to Earth and each picture is being transmitted twice to ensure that all the data is correctly received.

The second Mariner IV image released by NASA shows the border of Elysium Planitia and Amazonis Planitia. Taken from around 9,940 miles, the picture is about 310 miles across and 560 miles from top to bottom because the surface is curving away. North is up and the sun is illuminating the area from the southeast.

Only three of the Mariner Mars images have so far been released, but already they have disappointed scientists and the public alike by putting an end to any hope of finding intelligent life on the Red Planet. What they have so far revealed is a world that looks more like the Moon than the Earth, with no signs of water, vegetation or animal life. When this is coupled with the findings of the scientific instruments, which show that Mars has an atmosphere of carbon dioxide with only a very low atmospheric pressure (only a fraction of that found on Earth, which was quite a surprise to scientists), a daytime temperature of -148 degrees F and no magnetic field (meaning that the surface of the planet is bombarded by the solar wind and cosmic radiation), it means that the prospects for any kind of life on Mars are very small indeed. However, Mariner’s images only cover just 1% of the Martian surface, so perhaps we should not entirely give up hope that future missions will find Mars more exciting and scientifically interesting than it seems right now. After all, the pictures have not yet revealed the cause of the apparent seasonal changes observed from Earth….

The third image we have seen so far shows the Orcus Patera region in western Amazonis Planitia. It was taken with the sun only 13 degrees from vertical, so the topography is hard to make out, although some raised areas can be seen at upper left. The image is 202 miles across and 319 miles from top to bottom. The resolution is about 1.9 miles and north is up.

Australia Plays Its Part

Australia has played a crucial role in the Mariner IV mission, with its first images being received at the Tidbinbilla tracking station outside Canberra. NASA’s second Deep Space Network station in Australia, Tidbinbilla became operational in December 1964 so that it could support the Mars mission. As the signal from Mars is very weak, the station asked the civil aviation authorities to divert any aircraft that might interfere with the reception of the signals from Mariner at the time of the fly-by. This resulted in an amusing incident: at the critical time, just when Mariner 4 had gone behind Mars, the direct phone from Canberra Airport rang and the station was asked if it was experiencing interference from a UFO! It now seems that the offending object was a weather balloon and not a Martian saucer come to check on what the Earthmen are up to.


Nestled in a secluded valley, for protection from radio interference from nearby Canberra, NASA's Tidbinbilla Deep Space Network Station received the first images of Mars from Mariner IV. Australia is host to a growing number of NASA tracking stations covering all its space tracking networks.

A Role for a Radio Telescope

Australia’s Parkes radio telescope, the largest fully steerable radio telescope in the world, also played a role in receiving Mariner IV’s Mars images. NASA is basing the design of its new 210 ft antennae for the Deep Space Network on that of the Parkes telescope. As a demonstration of its tracking capabilities, Parkes has also tracked Mariner IV and received some of its images from Mars. Its greater antenna size, and therefore better reception capabilities, mean that its images will be more detailed than those received by the 85 ft dishes at Tidnbinbilla and other NASA stations and they will enhance the overall quality of Mariner IV’s Mars pictures when the Parkes and Tidbinbilla images are combined. I hope that NASA will release the rest of the Mariner images soon: even if they have dashed almost a century of Martian fantasies, they are revealing a planet that is very different from what we have expected and I wonder what further surprises might be in store for us as we explore more of Mars and the rest of the Solar System….

The world-leading radio telescope developed by the Commonwealth Scientific and Industrial Research Organisation, Australia's national civil scientific research body. Located near Parkes, New South Wales, this astronomical instrument is also proving its value as a space tracking facility and I'm sure that NASA will call on it again in the future for further tracking support




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Science / Space Race

[December 1, 1964] Planet Four or Bust! (What we know about Mars)

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by Gideon Marcus

Mars or Bust

This week, humanity embarked on its most ambitious voyage to date.  Its destination: Mars.

I use the term "humanity" advisedly, for this effort is a global one.  On November 28, 1964, the United States launched Mariner 4 from Cape Kennedy.  And just yesterday, the Soviet Union's Zond hurtled into space.  Both are bound for the Red Planet, due to arrive next summer. 

That both missions commenced so close to each other was not a coincidence.  Every two years, Earth and Mars are situated in their orbits such that a minimum of energy can be used to get from one planet to the other.  This favorable positioning applies equally to democracies and communist states.

Mariner 4 and Zond are not the first Martian probes: identical Mariner 3 was lost a few weeks ago, and Zond's predecessor, Mars 1, failed a couple of months before it could reach its target.  Let us hope these new spacecraft have more luck.  So far so good!

It is possible that these two probes will revolutionize our understanding of Mars, just as Mariner 2 changed our view of Venus forever.  It is, therefore, appropriate that I summarize our knowledge of the planet on the eve of collecting this bonanza of new information.

Another Earth?

Mars has been known to us since ancient times.  Because it wanders through the constellations throughout the year, it was classified as a "planet" (literally Greek for wanderer).  When it is in the sky, it is one of the brightest objects in the sky, with a distinct reddish tinge, which is why it has been associated with the bloody enterprise of war.

Until the invention of the telescope, all we knew about the fourth planet from the Sun was its orbital parameters: its year is 687 days, its path around the sun very circular, and its average distance from the Sun is around 141,600,000 miles. 

Even under magnification, Mars can be a stubborn target; at its nearest, about 35 million mies away, the planet measures just 25 seconds of arc from limb to limb (compared to the Moon, which subtends 1860).  Still, early telescopes were good enough to resolve light red expanses, darker expanses (believed to be seas), and bright polar caps.  Said caps waxed and waned with the Martian seasons, brought on by the planet's very Earthlike tilt of 25 degrees.  Because the Martian surface was visible, unlike those of Venus or Mercury, the day was calculated to be just over 24 hours long.  Indeed, Mars appeared to be a world much like Earth.

Mars for the Martians

In 1877, our understanding of the planet broadened.  Astronomer Asaph Hall discovered two tiny moons, named Phobos and Deimos, and we were able to deduce the mass of Mars — about 10.7% that of Earth.  Combined with the planet's diameter of 4200 miles, that meant Mars' density was about four times that of water.  This is only two thirds that of the Earth, which suggests that the planet is poorer in heavy metals, and/or that, because the planet is less massive overall, its layers are not so tightly bound together with gravity.  From Mars' measured mass and diameter, we learned that the surface gravity is 38% that of Earth; sprinting and jumping should be much easier there.  Flying…well, more on that in a moment.

1877 was also the year that Mars came into our public consciousness in a huge way — all because of a silly mistranslation.  Giovanni Schiaparelli turned his 'scope to Mars and saws something remarkable: dozens of fine straight streaks crisscrossing the planet that seemed to link up the dark patches (which were, if not oceans, at least areas of vegetation suggesting the existence of water).  He called them canali, which is Italian for "channels".  But to English ears, it came out as "canals", which strongly connotes construction by intelligent beings.

Well, you can see what an uproar that would make.  Very soon, folks like Wells and Burroughs were writing tales of Martian aliens.  And not just aliens — civilizations beyond those found on Earth.  The thinking went that the planets' ages corresponded to their distance from the Sun.  Hence, Mercury was a primordial hunk of magma.  Venus, shrouded in clouds, was probably a steamy jungle planet on which Mesozoic monsters roamed.  And beyond the Earth, Mars was a cold, ancient world, its verdant plains dessicated to red deserts.  To avoid catastrophe, the Martians built planet-spanning canals to bring water to their cities.  Being so advanced, it was obvious that they had mastered space travel, and had either visited us or were on the verge of doing so.

Even the more practical-minded scientists were hungry for evidence of life, even primitive stuff, existing off of the Earth.  Mars seemed like the prime location for extraterrestrial creatures to be found.  For one thing, the planet clearly had an atmosphere, wrapping the planet's edges in a haze and producing a marked twilight. 

Originally thought to be a touch thinner than Earth's, more recent measurement of the polarization of Martian light (the vibration angles of light reflected off the atmosphere) suggested that the surface air pressure was about 8% that of Earth.  That was too thin for easy breathing, but not too thin for life.  If there was enough oxygen in the mix, perhaps a person could survive there. 

Mars Today

Such was our understanding of the planet perhaps a decade ago.  Recently, ground-based science has made some amazing discoveries, and it may well be that Mariner and Zond don't so much revolutionize as simply enhance our understanding of the planet.

I just read a paper that says the Martian atmosphere is about a quarter as dense at the surface that thought.  This isn't just bad for breathing — it means NASA scientists have to rethink all the gliders and parachutes they were planning for their Voyager missions scheduled for the next decade.  Observations by spectroscope have found no traces of oxygen and scarcely more water vapor.  The planet's thin atmosphere is mostly made up of nitrogen and carbon dioxide.  The ice in the polar caps may well be mostly "dry".

Because of the lack of water and the thin air, erosion is probably much less of a factor on Mars.  In a recent science article in Analog, George Harper says that the planet's surface may be riddled with meteorite craters that never got worn away.  Close up, Mars may end up looking more like the Moon than the Earth!

And those canals? Telescopic advances in the late 40s made it possible to examine Mars in closer detail than ever before. The weight of astronomical opinion now disfavors the existence of canals.

Still, old dreams die hard.  I imagine we will cling to our visions of Martian life and even civilizations long after such notions are proven unworkable.  To kill such fancies, it'll take a blow as serious as that delivered by Mariner 2, which told us that it's hot enough to melt lead on the surface of Venus.

We'll find out, one way or another, in July 1965!

[Come join us at Portal 55, Galactic Journey's real-time lounge! Talk about your favorite SFF, chat with the Traveler and co., relax, sit a spell…]




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