Popular Astronomy January 1998
"Lunar rover of the imagination"
In the 1960s no fewer than 37 Soviet and United States spaceprobes flew by, crashlanded, softlanded, orbited, photographed, mapped, sniffed and sampled the Moon. Not since Galileo's lunar discoveries 350 years before had such a leap of lunar understanding been achieved. At this time more telescopes were pointed Moonwards than in the entire history of telescopic lunar observation, and through media coverage more people than ever before gained an insight into the nature of our satellite.
The first instance of mass participation in lunar exploration took place in March 1965 as Ranger 9's terminal plunge towards the Moon was followed by millions of Americans. More than 200 images of the rapidly nearing lunar surface were broadcast live on national television - the caption at the bottom of the TV screen read "Live from the Moon". The probe's final destination was the interior of the large crater Alphonsus. Just before it crashed a few kilometres northeast of the crater's central peak, the last image returned by the probe was taken from a height of just 530 metres and showed rocks as small as 25 cm.
The age-old dream of physical human contact with the Moon became a reality in 1969 when Neil Armstrong stepped off the lunar module Eagle and planted his size 11 boot into the lunar soil at Tranquillity Base. Hundreds of millions of people around the world followed the Apollo missions on their TV screens, sharing the thrills of lunar exploration as the astronauts walked, hopped and drove around their landing areas. More than 25 years have passed since the last Apollo Moonwalker, Gene Cernan, climbed back into the lunar module Challenger at Taurus- Littrow and blasted off back to Earth. Since then the Moon has only been visited by a few spaceprobes. In 1994 the Clementine lunar mapping mission seemed to revive the sense of excitement that was so tangible in the 1960s. With the arrival of the Lunar Prospector probe, the momentum in favour of returning to the Moon will be further enhanced.
Moon Rover
Some private companies see the Moon as an object capable of being tastefully commercialised. In 1999 a company called LunaCorp is planning to launch a pair of robotic Moon buggies atop a Russian rocket. The vehicles will land near Tranquillity Base and commence their travels around the lunar surface, controlled from the Earth. While only a lucky few will have the chance to actually drive the buggies, thousands will be able to fully share the thrills of being on board the rovers by viewing large 360 degree "sensurround" high-definition TV screens at theme parks around the world, or by donning virtual reality (VR) headsets linked to the live images. The rovers will journey northward to visit the Surveyor 5 softlander and then northeast to the wreckage of the Ranger 8 probe in Mare Tranquillitatis. Moving further north, the rovers will climb hilly terrain to visit the Apollo 17 landing site, and then through the wide mountain gap linking Mare Tranquillitatis to Serenitatis and across to the Soviet Lunakhod 2 rover (deposited by Luna 21) near le Monnier crater.
Lunar joyriding aside, scientific research will also be performed during the mission, and negotiations for science payloads are already in progress. A small experimental payload will cost $1.2 million per kilogramme - far cheaper than the cost of Apollo Moon rock. Researchers with a little spare funding may grab at the chance to pay a mere $7,000 an hour for research and operational time on the rover to perform astronomical observations, geological research or chemical analysis.
Endymion - Lunar Super Probe
Using our own VR capabilities - our imaginations - we've granted ourselves unlimited funding and recruited the world's best team of designers, technicians and engineers to construct a super lunar probe. The probe is named Endymion, after the legendary Greek shepherd boy whose beauty so enchanted the Moon goddess Selene that she lulled him into an eternal sleep to preserve his features. The travels of Endymion will be followed live by millions the world over on their PC screens and those fortunate to have VR headsets.
Endymion is a highly manoeuvrable six-wheeled rover with rocket engines which give it the ability to make several hops of up to 1,000 km over the lunar surface. It is shaped like a flattened cylinder, four metres long, with sprung alloy wheels. At the front of the vehicle is a pair of high resolution stereo TV cameras, a sampler arm to scoop up soil and secure small rocks, and a scientific bay into which samples may be deposited and analysed. The top of Endymion opens much like the Space Shuttle cargo bay, except that Endymion's bay doors are covered with highly efficient solar cells to augment the on-board nuclear power source. Inside the bay is the all-important communications equipment and antennae. A TV camera and powerful floodlight on a telescopic mast can be raised up to a height of 10 metres above the landscape, giving excellent panoramic views of the scene and revealing areas for potential exploration that might otherwise have been missed. The aft end of Endymion contains the fuel compartment, nuclear power source and fully steerable chemical rocket motors. There is also a bay containing a geological power tool kit consisting of mechanical drills, a high energy laser and powerful manipulator arm.
Our launch on Christmas Day, 2000, was a textbook operation. We blasted off from our rented launchpad at Baikonur in Kazakhstan atop an Energia booster; downwards-pointing cameras attached to the nosecone gave a live view of liftoff and insertion into Earth orbit. The trip to the Moon lasted four days, and as Endymion rounded the eastern hemisphere of the Moon its rocket engines were fired and it swung into a low lunar orbit. The prospective landing site on Mare Crisium was imaged at high resolution on the first orbit and soon the decision was made to burn the engines again for a lunar landing. In the same way as Mars Pathfinder probe landed some three and a half years previously, moments before impact a cluster of balloons inflated and shielded Endymion as it hit the Moon at breakneck speed. After several minutes of bouncing across the flat plains of eastern Mare Crisium, bubble- wrapped Endymion came to rest within sight of the small crater Fahrenheit.
Once the air bags had deflated, the first images to be transmitted live from the Moon's surface since Luna 24 in August 1976 were received on Earth. It was early morning, and the Sun had risen to an altitude of 25 degrees in the east. The gibbous Earth loomed large and motionless, low in the western sky. The panoramic view was somewhat monotonous - flat grey plains dotted here and there with shallow dimple craters. During the systems check the camera zoomed in upon a brilliant glint near the eastern horizon - it was none other than Luna 24! It was decided to pay a visit to the last lunar softlander (a successful soil sample return mission) and at the same time put the rover through its paces.
The wheels gave a good grip in the one-sixth Earth gravity environment as several sharp low speed turns were executed. The suspension was excellent, and the ride wasn't too bouncy, even at speeds up to 30 km/h. To appease the public's sense of "being there" viewers had the option of added sound effects - to hear the simulated crunch of lunar soil under the rover's wheels and the revving of its engines as it changed speed. Of course, most people knew that sound cannot be transmitted through the vacuum of the lunar environment, but this added audio dimension made the experience more enjoyable, especially to those listening and viewing in stereo wearing the full VR headsets.
Within minutes the squat descent stage of the 24 year old probe was approached and found to be covered with a thin layer of dust. The once vivid red colour of the flag of the old Soviet Union flying above one of the propellant tanks had been bleached pale pink by the harsh Sun. On close inspection a couple of small puncture holes were found in the tanks - undoubtedly meteoritic impacts. What if one of these meteorites could be recovered intact? Endymion squared up to Luna 24 and slowly extended a flexible endoscope into the hole. Incredibly, several tiny fragments were spotted at the base of the tank, and one of them was grabbed and retrieved. On-board analysis showed the piece to be a rare stony-iron meteorite - such objects comprise only one percent of all known meteorites, and it was quite a catch.
Endymion trundled 100 metres clear of Luna 24 and pointed towards the southwest - the next destination was the twin crater Messier in Mare Fecunditatis, more than 500 km distant. It was a tense moment as the clock counted down to the main engine's ignition. At blast off, a cloud of dust temporarily obscured the scene, but within moments the onboard cameras gave spectacular views of the lunar landscape, both in front of and behind Endymion as it climbed to a height of over a hundred kilometres above the mountain border between Maria Crisium and Fecunditatis. Later enhancement of the pictures revealed the scattered wreckage of the Luna 15 probe that crashed in southern Mare Crisium in July 1969 - a probe that had hoped to out-do Apollo 11 and return the first lunar soil sample back to Earth.
Retrorockets slowed Endymion as it approached the Messier pair, and the craft touched down some distance west of Messier A within one of the bright rays that emanate from the craters. The Messier duo have enthralled Moon watchers for centuries. Messier is the smaller of the pair, an elliptical crater measuring 9 x 11 km. Messier A is an odd 13 x 11 km peanut shaped crater, from which flows a remarkable double linear ray which travels west across Mare Fecunditatis for over 100 km. The crater and its rays look like the nucleus and bright gas jets of a Halley-sized comet. As Endymion approached the flanks of Messier A, samples of the ray system were taken. Closer to Messier A the route became tougher to negotiate, with great numbers of large rocks and boulders amid large dust dunes. It appeared as though a great explosion had torn apart the Moon's rocky crust at this site. Perhaps Messier had been formed by a the impact of a large meteoroid at a shallow-angle, mechanically excavating the crater into its elongated shape - the impactor might then have exploded beneath the lunar crust, blasting out Messier A and producing the ray system to the west.
Next, Endymion made another long flight between maria, as it hopped across to Mare Tranquillitatis and the landing site of Apollo 11. Care was taken not to disturb the historic traces of mankind's first contact with another world. Endymion approached the site to within 100 metres and made a televisual survey. Armstrong and Aldrin's footsteps were still clearly visible in the Moondust, as if they were made yesterday. The US flag still hung from its mast, although the mast itself was at a rather precarious angle, having been knocked askew by the exhaust blast of Eagle as it left the Moon. It was strange to see the descent stage of the lunar module sitting there, surrounded by the dead Apollo experimental packages - like a giant spider in the centre of an insect-laden web. Endymion remained at the site until the early hours of 1 January 2001 - the first day of the new millennium.
Having reminisced and celebrated, it was time to move on. Endymion drove due north to the wrinkle ridges of the Lamont formation, 50 km away. Lamont is a unique feature on the Moon. It is roughly circular in outline, 75 km in diameter, with a complicated system of low rounded ridges and wrinkles that radiate up to 100 km away from it across the lunar sea. Is it an impact crater that was covered with lava? Or is it a volcanic crater that failed to develop fully? Was Lamont formed as a result of the cooling and contraction of the lavas of Mare Tranquillitatis, like the wrinkles that appear as porridge gets cold? Are the wrinkles ancient lava flows?
As Endymion approached one ridge a ten metre wide cavity was noticed, as if the ridge had been struck by a meteorite and had collapsed on itself. Because the sunlight made a narrow angle with the edge of the ridge the cavern was in deep shadow. It was essential to explore this feature, as nothing like it had been seen before. At the cavern entrance the rover's searchlight was switched on; the interior receded into blackness, giving the impression that this ridge was hollow throughout its length! This feature could have been formed when a river of fast-flowing molten lava cooled and solidified on the outer surface yet remained hot and fluid underneath. As the source of molten lava dried up a long tubular cavity was left behind. The interior walls appeared to be tightly striated. But no stalactites hung down from this cave, for such features are the result of thousands of years of fluid water depositing minerals, and the Moon is an entirely dry world.
The cavern floor was piled with sizeable blocks that had fallen from the ceiling, making it impossible to proceed any distance into the cavern. As an experiment the main lights were switched off and the ultraviolet (UV) light turned on. The cameras recorded signs of fluorescence as certain minerals in the rocks converted the UV light to visible light. When the UV light was switched off several mineral pockets continued to emit visible light - this is a rarer phenomenon known as phosphorescence. Many natural history museums (including those of London and Birmingham) have special mineral displays that show these fascinating phenomena. As the camera panned around in the darkness an amazing image was seen low down on a smooth section of the wall - it was a clear pinhole projection of the glorious blue gibbous Earth outside. Through a tiny crack in the roof, the cavern was acting as a natural camera obscura!
Over the next three days Endymion made its way north into Mare Serenitatis, paying a visit to the flooded crater le Monnier, the Luna 21 lander and the lunar rover Lunakhod 2 - a "bathtub on wheels" that explored the crater's floor in early 1973. The lava flows that filled the Serenitatis basin and le Monnier flowed around 3,500 million years ago. Since then, few large impacts have scarred the plains of Serenitatis. It is one of the least-cratered regions on the entire lunar surface, with only one decent sized crater - 16 km diameter Bessel - in the entire 300,000 square kilometres of the sea. One feature that is visible in small telescopes is the bright patch surrounding the tiny crater Linné, 2.4 km across. It was this feature that Endymion next visited.
Linné looks innocent enough, but it occupies an infamous place in the annals of lunar observational history. The crater was once cited as the best evidence that areas of the lunar surface can still occasionally undergo permanent change. Several highly respected names in 19th century lunar science (and a few in the 20th century, too) claimed that this now diminutive crater had once been far larger and readily discernible in small telescopes. Somehow, they claimed, the crater had shrunk by several kilometres! There is no doubt that these observers were mistaken because they relied upon comparing their views to older maps which were full of drawing errors and positional inaccuracies.
Endymion drove towards the sharp eastern rim of Linné across its bright collar. Samples indicated that Linné had been formed around 20 million years ago. The view from the ramparts showed a spectacular bowl-shaped pit 600 metres deep with steep sides - remarkably similar to the Barringer Crater in Arizona which is of comparable size. The meteoroidal impact that excavated Linné had created a geologist's paradise, for layer upon layer of ancient lava flows could be traced on illuminated inner walls, all the way down to the lunar bedrock.
Perched on Linné's rim, the main camera turned to the southwest and craned upwards to capture the Sun in its field of view. Filters cut down the solar glare to an acceptable minimum and viewers were assured that a slender crescent Earth lay just to the right of the Sun. The date was 9 January 2001, and within a few hours the Earth would move across the Sun's disk and totally eclipse it. Gradually, the surrounding moonscape turned grey, and then deep shades of red. The direct view of the Earth showed a black disk surrounded by brilliant coloured arcs as the Earth's atmosphere refracted sunlight like a lens.
At 20h 25m UT, just after mid-eclipse, the image being transmitted by Endymion began to shake slightly and was then lost. It seems that a strong Moonquake whose focus lay deep beneath the lunar Caucasus Mountains some 150 km distant shook the probe from its perch on Linné's rim. Mission controllers were unable to save the probe as it tumbled down into the crater. Hundreds of telescopic lunar eclipse observers in Europe, Asia and Africa saw a brilliant flash within Linné at this time - undoubtedly the explosion of Endymion's fuel tanks. It is unlikely that the eclipse caused the Moonquake, since the only detectable change is a drop in temperature on the Moon's surface from 130 degrees C to -170 degrees C as the Earth's shadow covers the lunar disk.
We never got the chance to explore Mare Imbrium, drive along the floor of the magnificent Alpine Valley, climb Mount Pico, view the wonders of Copernicus or peer down the volcanic vent of the Milichius Pi dome. Nor did we race up the scarp face of the Straight Wall fault or nose around Alphonsus, Gassendi and the Aristarchus region. Yet some time within the 21st century these magnificent locations will be explored, both by roving probes and by humans. This fictional account will certainly pale beside those future reports, live from the Moon.
