Astronomical Clocks

Astronomical clocks

In Western Europe the first mechanical clocks appeared during the first half of the fourteenth century. They were driven by a weight suspended from a drum, and controlled by a heavy bar, or “foliot”. Pivoted near its centre and pushed first one way and the other by a toothed wheel. The Chinese, however, had mechanical clocks long before this time. One particularly fine example, fully documented, was the 30-foot astronomical clock tower of Su Sung, built in 1080 A.D. In this case the motive power was provided by a turning water wheel, held in check by a weighbridge and trip levers.

A clock at 576 Sherbourne street. A modern clock at 576, Sherbourne street, Toronto. Photo: Elena

Most early mechanical clocks were designed to indicate the time by a hand or hands moving over a dial. But several had elaborate dials for showing astronomical events like the age and phases of the moon, and the position of the sun. Foremost among the latter was a remarkable clock designed by Giovanni de Dondi and made in 1364. This not only showed the time of day but also, through its complex system of gear wheels, the fixed and movable feast-days and the earth-centered motions and positions of the seven wanderers (the Greec definition of the sun, moon and five naked-eye planets).

By far, the most famous astronomical clock is the one in Strasbourg Cathedral, built between 1838 and 1842. It had two predecessors, the first completed in 1354, and the second in 1574.

TRW GROUP

TRW GROUP

In the early days of the Space exploration, TRW’s System Group was one of five operating units of TRW Inc. Along with its three sister groups – Automotive group, Equipment group, and Electronic group, plus industrial operations – it forms a large corporation that provided many different kinds of products and services to space, defense, aircraft, auto, electronics, and related industrial and commercial markets.

The larger whole of which TRW’s System Group formed a part was a giant international corporation – TRW Inc. Begun as a cap screw manufacturer in Cleveland, Ohio, at the turn of the XXth century, it employed 80, 000 people in the 1950s, maintained facilities in 13 countries, and had an annual sales volume well over $1 billion.

Nearly every engine manufactured in the US – from autos and jets to lawnmowers, – used TRW parts. Most color television receivers carried their electronic components. They manufactured grenade launchers and major subsystems for the MK 46 torpedo. Their cams, gears and bearings were used in a large proportion of automobiles and aircraft in the US and Western Europe.

Photo by Elena

TRW began in the early days of the ballistic missile crisis, providing systems engineering and technical direction on the Atlas, Thor, Titan, and Minuteman missiles. In addition to their headquarters facilities in Redondo Beach, the group had at that time major operations located at Houston, Washington D.C., and Cape Canaveral. They numbered some 16, 000 scientists, engineers, and support personnel, who applied advanced technology to some of the critical military, scientific, and socio-economic problems of our times.

Since the early days of its participation in the ballistic missile program, TRW designed and manufactured a variety of rocket engines for powering and controlling upper stage vehicles and spacecraft. One of their assignments included the design and manufacture of the Lunar Module Descent Engine, which safely landed Apollo astronauts on the surface of the Moon.

The TRW LM Descent Engine was assigned an extremely critical role: to launch an LM containing the two astronauts into a lunar transfer orbit (path which brought them directly to the lunar surface), then slowed their rate of descent from 3500 mph to zero at 200 feet above the lunar surface, and finally lowered them safely to a soft landing. To perform these tasks, it must be throttleable (capable of varying rates of thrust) – and, of course, it had to be very dependable. The LMDE was a pressure-fed, liquid be-propellant, gimballing (capable of swivelling so as to change the direction of thrust) rocket engine. It produced a maximum thrust of 10,000 pounds and was throttleable down to approximately 1050 pounds. The propellants, nitrogen tetroxide (N2O4) and a 50-50 blend of hydrazine and unsymmetrical dimethyl hydrazine, are hypergolic, – that is, they ignite upon contact with one another. Total weight of the engine without propellants was about 290 pounds.

Each of the two Mariner’ 60 spacecraft incorporated a TRW-built propulsion subsystem. The Mariner 6 engine was fired in February of 1969 at 750,000 miles from Earth, the Mariner 7 in April at 2 ½ million miles, precisely adjusting the trajectories of both spacecraft for accurate flights past Mars in July and August of 1969. The weight of Mariner 69 engine was of 45 pounds including propellant. It stood slightly over 3 feet high and was capable of two starts and fired at 50 pounds of constant thrust.

The TRW identity as System group was perhaps best indicated by a 16 x 31-feet mural called “The Quadrisciences” which was displayed in the administration building at Space Park. The mural symbolically depicted four areas of man’s quest for knowledge: the earth, the sea, near space, and deep space. The TRW’s goal at System group was to acquire and apply scientific knowledge in those four environments.

From space craft design and manufacturing to anti-submarine warfare, from building mid-course correction engines for the Mariner Mars spacecraft to evaluating methods of high-speed ground transportation, from designing electronic warfare devices to developing plans for solving such pressing social problems as water and air pollution, overcrowded medical facilities, and ineffective community services – in short, in all for environments of Quadrisciences – the TRW expanded the frontiers of basic research in order to build a better world.

One example of electrical propulsion research at TRW: They developed an engine, a colloid microthruster, under contract to the Air Force. During the first 500-hour firing it produced 32 micro-pounds of thrust and 1SP of 1200 seconds. Engines like this, which have ISPs in the range of 800-1500 seconds and operational life expectancies of thousands of hours, are useful for such tasks as stationkeeping (keeping a spacecraft in the correct orbit), and attitude control (keeping a spacecraft pointed in the right direction). That engine weighs only 8-3/4 pounds together with a 5-watt electrical power unit.

Planetariums

Planetariums

A historical survey

Clocklike Gearing

Strictly speaking, a planetarium, as the name suggests, is a device that can be used to demonstrate the motions of the seven Greek “planetes” or “wanderers”, namely, the sun, moon and five naked-eye planets. A device of this kind involves the use of clocklike gearing, or at least, a system of pulleys, but it need not rely on some form of optical projection.

If we accept this definition it is a fairly easy matter to trace the development of the planetarium. We can, for example, include all models of solar system, consider astronomical clocks, and in fact, identify the origin of the planetarium with that of mechanical clock. The latter, as Derek Price and other historians have pointed out, grew out of the use of toothed wheels to transmit power, and not. As is commonly supposed, from sundials, sand-clocks and water-clocks.

Ancient Toronto Planetarium.

Archimedes’ Planetarium

An early example of the use of gears to provide power transmission and at the same time give special ratios of angular movement, is the planetarium said to be constructed by Archimedes in the third century B.C. The device was described by Cicero and several later authors, but unfortunately the accounts contain no technical information. As far as we can tell it took the form of a hollow metal globe presumably of a lattice construction , with a small model earth at its center.

According to Cicero, who got his information from C. Sulpicius Gallus, “a very learned man”, the globe could be rotated, so that the seven wanderers went through “various and divergent movements with their different rates of speed.” Ovid described it as a “miniature representation of the vast vault of heaven”.

Astrolabes

The planetarium of Archimedes could have been similar to an armillary sphere or spherical astrolabe, an instrument introduced by ancient Greeks for determining the positions of the seven wanderers relative to the stars. At first it consisted of a few graduated, concentric, and intersecting rings which represented the horizon, meridian, celestial equator, and ecliptic, but after the fifteenth century it became more elaborate. One development was to add further reference circles and to fix a model earth in the middle. Another was to add moving models of the seven wanderers, so that the whole affair illustrated the earth-centered or Aristotelian conception of the universe. Yet another was to turn it into a flat of planispheric astrolabe, in which form it was widely used by the Muslims as an aid to navigation. Many of these flat astrolabes are now preserved in museums. They are beautifully constructed and often bear exquisite designs. The men who made them were not only technicians and craftsmen but also great artists.

Antikithera Machine. Fragments of the Antikythera Machine. An early form of planetarium instrument

Some astrolabes had a built-in system of gear wheels and served as elaborate astronomical computers. They may have an early representative in certain corroded pieces of bronze gear-wheels salvaged in 1901 from the wreck of an old ship found off the island of Antikythera, between Greece and Crete. The parts, believed to date from about 65 B.C., were accompanied by traces of what may have been a wooden case. They also carry partly legible inscriptions, and these, along with the partial reconstruction of the gears, indicate that the machine was in early form of astronomical computer.

Rebirth of America’s Manned Space Program

Rebirth of America’s Manned Space Program

The Beginning of a New Era

The rebirth of America’s manned space program happened in March, 1981. The space shuttle Columbia, carrying astronauts John Young and Robert Crippen, began its maiden voyage on April 12, 1981, twenty years to the day after Soviet cosmonaut Yuri Gagarin became the first human to fly in space.

Columbia’s fifty-four-hour mission was the first manned American space flight since the US/USSR Apollo-Soyuz mission six years earlier. The flight produced one of the most enduring images of the entire shuttle program: an almost giddy John Young pacing beneath Columbia after guiding it to perfect landing in California, smiling and gesturing like a schoolboy on the first day of summer.

Supernova Remnant Cassiopeia A. Source of the image: http://gallery.spitzer.caltech.edu/Imagegallery/image.php?image_name=ssc2005-14c. Authors: Oliver Krause (Steward Observatory) George H. Rieke (Steward Observatory) Stephan M. Birkmann (Max-Planck-Institut fur Astronomie) Emeric Le Floc’h (Steward Observatory) Karl D. Gordon (Steward Observatory) Eiichi Egami (Steward Observatory) John Bieging (Steward Observatory) John P. Hughes (Rutgers University) Erick Young (Steward Observatory) Joannah L. Hinz (Steward Observatory) Sascha P. Quanz (Max-Planck-Institut fur Astronomie) Dean C. Hines (Space Science Institute)

In the decade since Columbia’s inaugural flight, the shuttle fleet has played a major role in the space science. In April 1984, for example, shuttle astronauts repaired the crippled Solar Maximum Mission satellite. By replacing some of the electronics onboard the large satellite, astronauts brought Solar Max back to life, allowing it to collect important data on the Sun until it tumbled to Earth in 1989.

Telescopes carried into orbit by the shuttle have studied the Sun, examined objects that emit much of their energy in the infrared and ultraviolet regions of the electromagnetic spectrum, and scanned suspected black holes. In 1990, the shuttle-launched Hubble Space Telescope opened an entire new window on the universe.

Shuttle orbiters also have served as launch platforms for two planetary space craft. Magellan, which is using a high resolution radar to map the surface of Venus, was deployed in May 1989. The Jupiter-bound Galileo spacecraft was launched five months after Magellan, and arrived at the giant planet in 1995.

A Space Odyssey to Mars in 1986

A Space Odyssey to Mars in 1986

As seen in 1972

It is April 1986, one year since the giant spacecraft blasted out of the orbit around Earth and headed into deep space, propelled by powerful nuclear engines. The Earth is now so far away that it looks no bigger than a bright star. On board, the crew is too busy for sentimental homeward glances. In a few minutes, three astronauts will enter a smaller spacecraft and cast off from the mother ship to start the final lap of a momentous journey. Their little craft will carry the space travelers to man’s first landing on the surface of Mars.

Though the scenario has the ring of fiction, it could become fact – in the unlikely event that the US Congress has a change of heart and next year appropriates funds for a manned trip to Mars – a minimum of $30 billion to $40 billion, to be spent over a twelve-year period. If that approval were given, NASA’s dreamer planners would not be unprepared. They have already spelled out in detail a daring program that could land Americans on the Red Planet by the mid-1980s.

Mars, the Gothic. Illustration by Elena

The Mars expedition would make a twelve-day lunar landing mission like a Sunday excursion. If all could be in readiness by 1985, for example, the Mars astronauts would be blasted out of orbit on April 5, when the Earth, Venus and Mars will be in ideal positions for the mission. Their craft would swing by Venus on September 10, 1985, getting a valuable gravitational boost that would speed it to Mars by April 10, 1986. The expedition would depart from Mars on May 20 and arrive back in Earth orbit on November 15, 1986, 590 days after leaving.

The ambitious mission, as planned, will require two command ships, each carrying a crew of six. If one craft becomes disabled, the other can safely return all of the astronauts to Earth. Unlike lunar missions, the journey will not begin directly from Earth; that would require boosters too huge to be practical. Instead, the two cylindrical ships will be lofted piecemeal into earth orbit by Saturn type boosters. There, the separate parts will be latched together. Finally, a space shuttle will bring up the astronauts as well as their fuel and supplies.

Propulsion for the Mars craft will come from an engine not yet developed, perhaps the proposed NERVA (for Nuclear Engine for Rocket Vehicle Applications). It consists of a small nuclear reactor that heats liquid hydrogen until it is expelled as a jet of white-hot gas. To kick out of earth orbit, which requires much less thrust than the earth launch, the 270-feet-long ships will fire – and then discard – the two outboard NERVAs strapped to their sides’ the main booster, at the center of the engine cluster, will be retained. Then, as the two ships pull away from Earth orbit, they will be docked end to end to form a single unit within which the crews can pass back and forth through airlocks.

Some bottled oxygen will be taken along (so that it can be used, among other things, to repressurize the cabin in the event of a meteorite hit), but most of the oxygen will be produced by the electrolysis of water. Although the ships will also carry a supply of fresh water, a large portion of the water consumed by the astronauts will be produced by passing exhaled carbon dioxide through a reactor that separates oxygen from CO2 and combines it with hydrogen. Other water will come from recycled urine and wash water. Earlier plans to grow algae on board to supplement the food supply have now been shelved. “Algae cookies taste pretty horrible,” explains NASAs Robert Lohman. Instead, the food supply will consist largely of frozen and freeze-dried food.

To counteract the possibly damaging effects of weightlessness on such a long voyage, the joined spaceships will have a shielded compartment in which crew members can sit out dangerous barrages of radiation during solar storms. There will also be exercising facilities, games, a library and other diversions to while away the hours. One problem has not been resolved: what to do about the crew members’ sexual drives. NASA psychologists agree that pornography, which suffices as an escape mechanism for nuclear submarine crews on 60-days missions, may not be enough. With an all-male Mars crew, they believe, homosexual activity is inevitable. Including women in the crew poses other problems. As one psychologist puts it: “Sex will be more of a public relations problem than a medical problem for NASA.”

When the linked-up ships finally approach Mars, they will separate, fire their main engines to enter an orbit around the planet, and reunite. Before any manned landing takes place, the expedition will send down several small unmanned probes to scout landing sites and scoop up soil before returning to the mother ship.

When sites have been selected, three astronauts will descend in a lander which will contain a Mars rover, scientific gear and supplies for a month’s stay. The surface activities – televised up to the mother ship and relayed to Earth – will resemble the familiar rock gathering and experimenting of lunar exploration. The astronauts will wear oxygen packs to survive in the thin carbon dioxide atmosphere, and space suits to weather Martian temperatures, from 75 degrees F at the equator at noon, to – 180 degrees F in the Polar region. But there will be significant differences. Since Martian gravity is one third’s of the Earth’s (compared with the Moon one-sixth G), the astronauts will walk with a more normal gait. They may be buffeted by the high winds of Martian dust storms which often exceed hurricane force. They will also be on the lookout for things that do not exist on the Moon: water and primitive life forms.

During this stay, several expeditions will be sent to the surface. Finally, after 40 days in orbit, the twin ships will separate, fire their engines to boost them away from Mars, and redock for the long voyage home. After shipping back into Earth orbit 186 days later, the astronauts will transfer to a waiting space shuttle for the descent to Earth. Above them in orbit will be the empty Mars ships, awaiting the next crew of interplanetary travelers.

(Time, December 11, 1972)