Author Topic: Atlantis STS-34 – Eppur si muove!  (Read 84710 times)

Offline Ares67

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #20 on: 10/16/2012 07:15 PM »
After a thorough review of the shuttle’s ascent-phase abort modes, NASA decided in June 1986 that carrying a Centaur with cryogenic hydrogen and oxygen would pose a severe risk for a shuttle attempting an emergency landing; joking about the dangers posed by 45,000 pounds of highly-volatile liquid propellant stowed away inside the orbiter’s payload bay, astronauts had nicknamed the Centaur “the Death Star.” So the Centaur was cancelled again – this time with no possibility of a reprieve. Unfortunately for Galileo, the three-stage IUS had long-since been cancelled, and the spacecraft had put on too much mass for the two-stage version to set it up for the EGA option.

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #21 on: 10/16/2012 07:17 PM »
With the straightforward EGA now insufficient, JPL’s interplanetary navigators set out to investigate multiple-encounter options. Even making a second Earth flyby would not provide sufficient energy to make up for the difference in capability between the IUS and the partially fuelled Centaur. The only option was to investigate the possibility of sending Galileo in the other direction, towards the Sun, and start the mission with a close pass by Venus. The Venus-Earth-Earth Gravity Assist (VEEGA) trajectory was “discovered” on August 1, 1986. Although this would allow an IUS to send Galileo-as-built to Jupiter, this would be at a terrible penalty in flight time – the spacecraft would now be dispatched in October 1989; a Venus flyby in February 1990 would ease its aphelion out beyond the Earth’s orbit; an Earth flyby in December 1990 would extend the aphelion out to the asteroid belt; and the second Earth encounter in December 1992 would sling it out to meet Jupiter in December 1995. The journey would take fully six years, and the spacecraft would arrive a decade later than originally planned! On the other hand, with opportunities for secondary scientific objectives at Venus and the Earth/Moon system, as well as 951 Gaspra and 243 Ida in the asteroid belt in October 1991 and August 1993 respectively, this circuitous route had its compensations.

With no other alternative, JPL set out to modify Galileo to endure increase thermal stress, because insolation is twice as intense at Venus as it is at the Earth’s distance from the Sun. The spacecraft had been designed to work at Jupiter, where the energy of sunlight is just four percent of that at the Earth. A change in procedure was also required: in previous circumstances, Galileo would have unfurled its umbrella-like high-gain antenna as soon as it was safely on its way, then orient itself to maintain its antenna facing the Earth. The antenna, however, was too delicate to be exposed to intense sunlight, so it would have to remain lightly furled around its axial tower until Galileo had performed its first pass by the Earth. The simplest way to protect the antenna was to mount a small disk-shaped sunshield on top of its tower, and then orient the spacecraft so that it maintained its axis towards the Sun. This meant that while it was in the inner part of the solar system the spacecraft would have to rely upon a rear-mounted low-gain antenna. A wide disk was mounted across the top of the main body of the spacecraft to shade its primary systems. With these decision made, a sense of stability returned to the project.

“We aren’t going to be resting for the six years in transit,” said Torrence Johnson, Galileo project scientist. “We have a number of opportunities given to us by this new trajectory, and we’re going to take use of them.” – “There’s something significant going on every year, with the exception of 1994,” project manager Richard Spehalski announced, starting with the Venus encounter. Galileo would be able to take different measurements of the planet than those being gained by the Pioneer Venus Orbiter, launched in 1978 and still operating, or Magellan, whose only instrument consisted of a radar mapper.

“We’ll be able to look for Venus lightning in the atmosphere,” Johnson said. “We have a number of instruments in the ultraviolet and visual spectral ranges that will allow us to understand more of the atmospheric structure, the distribution of water in Venus’ atmosphere, and cloud composition. It will be quite complementary to the information we have about Venus already.” No flood of “encounter day” pictures and information would flow from Galileo at Venus. With its high-gain antenna still folded the information was to be stored for later, slow playback as Galileo returned to Earth. “It will be a throwback to the old days of unmanned spaceflight when we had to wait for weeks to get the data back,” Johnson said. “So it will still be like waiting to open your Christmas presents late.”

The flybys of the “earth system” would provide science benefits, too. On the first flyby, coming six months after Venus, Galileo would gain the opportunity to observe the Moon – in effect becoming the U.S.’s first lunar probe in nearly 18 years. Galileo would pass by the Moon’s far side from observing angles never seen before. “IT#s very exciting to be able to use our Galileo spacecraft to improve our knowledge of the Moon,” Johnson said. “We will be flying by the Moon with experiments which never have been used on the Moon before. Specifically, our charged-couple-device camera allows us to see into the infrared, and we have a near-infrared mapping spectrometer system called MIMS which is basically like a Landsat system but with 300 spectral channels extending out to the five micron region in the infrared. The Moon has never been studied with devices like this, particularly the far side. – We expect both to be able to extend much of the information we got from the Apollo samples on the front side and perhaps lay the ground work for a further set of studies at the Moon, possibly with an observer-class spacecraft supporting the agency’s pledge to get back to the Moon.”

The second pass through the Earth/Moon system would see Galileo passing over the north pole of the Moon. The spacecraft’s array of instruments would study this little-investigated area, a place where some scientists theorize water ice could exist in permanently-shaded areas of craters. In between the two Earth encounters, Galileo would have the opportunity to conduct the first mission to an asteroid. Fuel reserves permitting, it was to be targeted to fly by the asteroid Gaspra, about 10 miles wide, on October 29, 1991, during a nearly year-long pass through the asteroid belt. The spacecraft, passing within 620 miles of Gaspra, would attempt to determine the size, shape mass, composition and surface geology of the asteroid. A second asteroid could be observed as the spacecraft would again pass through the asteroid belt on its final trajectory from Earth to Jupiter. The asteroid Ida, about 20 miles wide, could be encountered on August 29, 1993. Scientists expected to be able to relate studies of both asteroids to meteorites found on Earth believed to have come from the asteroid belts. Galileo would spend a total of fifteen months flying through the asteroid belt, which isn’t as dangerous as it might seem. For one thing, the asteroids serve to sweep up small dust particles which could cause damage. The dust concentration is actually heavier at Jupiter, whose large gravity field tends to trap the particles. (David M. Harland: “Jupiter Odyssey,” Springer/Praxis 2000, and Countdown, October 1989 – edited)
« Last Edit: 10/16/2012 07:19 PM by Ares67 »

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #22 on: 10/16/2012 07:19 PM »
And then the real fun will start

Finally the main goal of Galileo looms ahead –Jupiter, which holds 70 percent of the mass of all the combined planets. “It is itself more like the central body of a planetary system than a planet as we normally think of one,” project scientist Torrence Johnson says. “Jupiter is a little bit more like a star.”

The planet, mainly consisting of hydrogen and helium, possesses no solid surface. As pressures and temperatures mount the deeper into the Jovian atmosphere, the hydrogen shifts into a liquid state – not a cold liquid as used on Earth to power the shuttle’s main engines, for example, but a hot liquid due to the crushing conditions. As those temperatures and pressures continue to mount, the hydrogen is squeezed into a strange metallic state. “It’s probably the region of the planet that the magnetic field originates, because metallic hydrogen forms a good conductor,” Johnson says. Somewhere unseen under the seas of atmosphere, a small rocky core exists, but still the planet is entitled to the name “The Gas Giant.”

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #23 on: 10/16/2012 07:22 PM »
Galileo will explore the Gas Giant in two ways – remotely with an orbiter and directly with a small atmospheric probe. The conical, 744-pound probe will be released from the base of the orbiter in July 1995, 150 days before reaching Jupiter. The separation maneuver needs to be precise. The probe carries no propulsion system and will follow a ballistic trajectory towards Jupiter like a rifle bullet. Before release, the orbiter will aim the probe and then spins it up to give it gyroscopic stability. After release, the orbiter will maneuver to a trajectory to miss Jupiter, flying parallel to the probe.

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #24 on: 10/16/2012 07:24 PM »



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Re: Atlantis STS-34 – Eppur si muove!
« Reply #25 on: 10/16/2012 07:33 PM »
The orbiter begins gathering scientific data on the Jupiter system sixty days before reaching the planet on December 7, 1995. A study of the dynamic weather patterns of The Gas Giant, which has a complex system of cloud belts. Winds of up to 250 mph are found in areas between the belts. Cyclone storm systems ride through the cloud belts, spinning off colorful eddies. The storms can last centuries. The Great Red Spot, the largest of them all, has been observed from Earth for 300 years. It is the size of three Earths, measuring 16,000 miles in length.

About four hours before the probe hits the turbulent atmosphere, the orbiter will make a close flyby of the volcanic moon Io, the innermost of the four planet-like Galilean satellites. Heat generated by the tidal forces have turned and churned Io into the most volcanic body in the solar system. Voyager spotted eight active volcanoes spewing sulfur dioxide a s high as 175 miles above the surface in huge plumes as large as 620 miles across. Galileo will photograph what changes have occurred in the volcanic activity, which is constantly resurfacing the satellite with sulfur and silicates. The passage, only 600 miles above the pizza-like surface, will mark the only close flyby of Io. Because of the intense radiation fields that close to Jupiter, Galileo will orbit farther out for the remainder of the mission. The flyby of Io will serve a second purpose. What a planet can give to a spacecraft in a gravity assist, it can take away. Galileo will give to Io some of the energy it robbed from Earth – meaning it will use Io’s gravity to help slow down, thereby reducing the amount of fuel needed to brake into orbit.

The Galileo orbiter has another task to perform before the braking maneuver. “The orbiter, for a brief period, becomes a radio relay station,” Johnson says. The tiny transmitter aboard the probe cannot reach Earth. The orbiter will relay the signal to Earth. The probe, which must rely on a lithium-sulfur battery for power, remains dormant until just before it reaches the upper atmosphere of The Gas Giant. Project manager Richard Spehalski describes the probe’s world at the moment of atmospheric entry as “very traumatic.”

“The probe spacecraft enters the atmosphere at roughly 110,000 mph and decelerates to less than 1,000 mph in a matter of a minute. The deceleration forces are very high on it – 250 Earth Gs,” he says. “The heating on the peak of the aeroshield is roughly 450 million watts per square meter.”

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #26 on: 10/16/2012 07:38 PM »
After two minutes, the probe will drop its heat shield and deploy a parachute. The probe’s prime mission will last for 48 minutes as it drops through the upper layers of the atmosphere. It could last as long as 75 minutes, passing through pressures increasing from one-tenth of that on Earth’s surface to about 25 times Earth’s surface pressure. It will only penetrate the upper reaches of the atmosphere where the hydrogen and helium still exist in form of normal gasses. “But we expect to be sampling an atmosphere that effectively gives us a sample of the original material from which all the planets formed,” Johnson says. “Jupiter’s gravity is so huge that few, if any, of these elements have escaped even over the 4.5 billion years since the beginning of the solar system. We’re actually going back in time by going into this atmosphere,” he says.

The probe should pass through three cloud layers – the lower of which, coming 48 minutes into descent, will be at conditions at which water clouds could form. The probe is equipped with no cameras, but its sensor systems can detect the presence of clouds and the chemistry of the atmosphere. The probe will be listening for lightning, which was detected at Jupiter by Voyager. It will “listen for radio static from lightning very similar to what you hear on your car radio when there are thunderstorms,” Johnson says. “We expect to be able to hear evidence of lightning over thousands of kilometers.”

After passing through the layer of water clouds, the probe will enter what Johnson terms “the well-mixed part of the Jovian atmosphere where all the elements and condensable molecular species are present.” After 75 minutes the last possibility of contact should be lost as the probe’s batteries run down, the orbiter gradually moves out of relay range and the heat build-up begins. Eventually the dead probe will be crushed and vaporized.
« Last Edit: 10/19/2012 12:24 PM by Ares67 »

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #27 on: 10/16/2012 07:40 PM »
Meanwhile the orbiter’s mission is just beginning. The primary mission will last 22 months, during which the orbiter will make ten encounters with the outer three Galilean satellites. The first orbit will travel a long ellipse, taking eight months to trace. At the farthest point, the main engine on the orbiter will fire one last time to raise the low point of the orbit. Then another round of gravity assists will begin as Galileo uses the gravity of one moon to sling to the next. Johnson terms the show a “10-cushion billiards shot.” Because of the long first orbit, a majority of the encounters will occur later, averaging an encounter per month during the last year of the prime mission. “It should be pretty exciting for everybody,” Johnson says. “And I haven’t noticed the timeline saying that the project scientist has any time to sleep during that period!”

Closer approaches to the moons than Voyager made, coupled with Galileo’s superior TV cameras will yield dramatic results. Voyager viewed the moons from distances varying from about 31,000 miles to nearly two-thirds of a million miles, producing photographs with the resolution of looking at Earth’s Moon through a small backyard telescope. “So they are, if you will, our pre-space age versions of the pictures of the satellites of Jupiter,” Johnson says. “We expect to go from this type of resolution to one similar to Landsat or Spot resource satellites imaging of the Earth… anywhere from 20 to a thousand times higher resolution than Voyager.”

Each moon is a planet in its own right, with the outer two, Ganymede and Callisto, actually being slightly larger than the planet Mercury. Like human beings, no two moons are the same. Io represents just one face of a diverse Jupiter system. Outermost Callisto presents an ancient battered profile, its ice surface peppered with craters that date back to the early bombardment in the solar system over four billion years ago. Ganymede, slightly larger than Callisto, checks in as the largest satellite in the solar system, with a diameter of 3,278 miles. Like Callisto, it is an ice world composed of half ice and half rock. Parts of it look like Callisto, yet other areas are grooved, appearing to have undergone a glacial version of the plate tectonics which causes the continents to drift on Earth. “We really don’t know why Ganymede and Callisto are different from one another, why one planet took one track and one took another. It’s one of the things we hope to investigate further with Galileo,” Johnson says.

Voyager was able to view Europa, another puzzle, the least well. Europa, about the size of Earth’s Moon, displays a smooth ice surface etched with lines and cracks, yet it is primarily composed of rock. “We don’t know how thick the ice is or whether there is any liquid water still in existence underneath it. We could be looking at the top of a frozen-over ocean, or we could be looking at a relatively-modest ice cap covering the entire planet,” Johnson says.

Galileo will have much more to investigate than even these fantastic works. Voyager discovered a thin, wispy ring around Jupiter. The ring appears composed of fine dust coming from two tiny moons near its outer edge. And, of course, the spacecraft will keep its eyes and sensors focused on Jupiter itself, building on the data gained from the probe’s short life. “Part of the mission of the orbiter is to provide global measurements of Jupiter using spectroscopic techniques and radio occultation techniques so that we can extend the information we have at the probe site to the rest on the planet,” Johnson says.

One prime target for study by Galileo, the vast magnetic field generated by Jupiter, cannot be seen, but certainly will be felt by the spacecraft. The vast size of the powerful field defies the imagination. If somehow magically lit up, the magnetic envelop around the planet would appear from Earth the same size as our Moon. Voyager provided a snapshot of the magnetic field’s area, called the magnetosphere, revealing its teardrop-shaped structure. But its quick passage could not reveal how the complex pieces of the field interact. “One of the things we don’t understand very well is the details of the dynamics interacting with the magnetosphere – how charged particles are injected into it, how they are accelerated to the very high energies we see and what their ultimate fate is. By spending two years in the system, continuously orbiting the planet and studying the magnetic field in all positions around Jupiter, we hope to gain a much better understanding of some of the basic physics that drives this type of system,” Johnson says.

In the end, it may be the intense radiation trapped by the magnetic filed that does Galileo in. By the completion of the 22-month prime mission, the radiation should have begun knocking out electronic systems. How much longer Galileo might last into an extended mission depends on luck. No one can predict which systems will be damaged first in this radiation-belt Russian roulette. In addition, maneuvering fuel and electric power will begin to run out. However, based on the JPL’s amazing success keeping Voyager alive, Galileo could take on more duties observing Jupiter or trying for more satellite encounters to follow up on any discoveries that were made in the prime mission. “My guess is we’ll have a lot of discoveries that Galileo will have made by that point,” Torrence Johnson predicts. (Countdown, October 1989 - edited)

« Last Edit: 10/19/2012 12:26 PM by Ares67 »

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #28 on: 10/16/2012 07:43 PM »
Oh, Chute!

Designing a parachute for a space probe is more art than science. Over the decades, parachute design work has been mostly the result of trial and error, with spectacular successes and failures, rather than orderly application of engineering rules. It takes the talents of aerodynamic experts, working with supercomputers to tackle the problems of how air and fabric interact during a plunge to a planet’s surface. Roles for parachutes in the space business now include lowering products churned out by space factories safely back to Earth, as well as slowing probes as they speed through the atmospheres of distant planets.

Take, for instance, the high-tech parachute needed for the Galileo spacecraft, now en route for a rendezvous with Jupiter in December 1995. “We used a lot of data gathered from the Voyager space probes for the design and construction of the parachute that will slow the decent of Galileo’s probe in Jupiter’s upper atmosphere,” says William Everett, head of engineering at the Pioneer Aerospace Corporation in South Windsor, Connecticut. Everett’s firm made the Galileo probe’s 12.5-foot parachute that will lower the 760-pound, instrument-packed device into Jupiter’s tumultuous atmosphere. The probe will relay measurements as it descends before being crushed by intense atmospheric pressures.

The parachute design was based on assumptions made from Earth’s atmosphere, as the upper density of Jupiter’s atmosphere is similar to Earth’s high altitude atmosphere, Everett says. In designing the parachute for the mini-probe, Everett and his team found that Dacron and Kevlar were the choice materials to construct the probe’s parachute. Kevlar is a light synthetic fiber with a tensile strength ten times greater than stainless steel. Its lightness means more parachute can be packed into a smaller space, providing stopping power superior to common, all-nylon parachutes. “The selection of Dacron and Kevlar for the Galileo’ probe’s parachute was also the best choice for sterilization,” Everett says. “Dacron and Kevlar also get rid of outgassing better than other parachute materials.” If the probe’s parachute were to experience outgassing during its descent in Jupiter’s atmosphere, it would affect the probe’s descent, possibly causing mission failure, Everett explains. (Final Frontier, September / October 1994 - edited)

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #29 on: 10/16/2012 07:47 PM »
The real Galileo - a heavyweight, nuclear-powered exploring machine

Will the real Galileo please stand up? Galileo – the name implies a single spacecraft, but it actually is two, a probe and an orbiter. And the sophisticated orbiter is actually a hybrid fusion of the spin-stabilized Pioneer and non-spinning Voyager designs. Galileo’s name encompasses an international effort to explore Jupiter. Yet for some anti-nuclear protesters, the name Galileo strikes fear of plutonium contamination. They see Galileo as causing cancer rather than cruising by new worlds. What is the real Galileo?

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #30 on: 10/16/2012 07:49 PM »
In simple numbers, the orbiter stands about 20 feet tall, weighs 5,230 pounds and carries ten scientific instruments weighing 227 pounds, with the radio system serving as an eleventh. The spacecraft is topped by a gold-mesh high-gain antenna, 16 feet in diameter. Very similar to the antennas of the TDRS communications relay satellites used by the shuttle, the antenna is folded at launch. It can transmit science data in the X-band communications range at a maximum rate of 134,000 bits per second. The high-gain antenna is attached to – and is considered part of – the spun section of the spacecraft. During most of the mission, this section, containing the main electronics compartment, “bus,” is revolving at 3 rpm. It can be spun up as high as 10 rpm. Instruments to measure magnetic fields and particles are mounted on a 36-foot boom to escape interference from the spacecraft. The spin benefits the instruments, giving them a full spherical coverage of space.

Shorter booms extending from the spun section contain the Radioisotope Thermoelectric Generators, which provide power. A tubular low-gain antenna, used when the main one is folded, extends from one of the RTG booms. The retro-propulsion module is also attached to the spun section, below the main bus. The propulsion system, contributed by West Germany, was built by Messerschmitt-Bölkow-Blohm. It consists of twelve thrusters with 2.2 pounds thrust. The propulsion system uses monomethyl hydrazine fuel and nitrogen tetroxide oxidizer. David M. Harland in his book “Jupiter Odyssey” (2000): “(The axial 400-newton primary engine) represented a major achievement because it had to remain dormant in space for years, then start several times and perform flawlessly. (…) However, as the probe was to be tucked against the nozzle for carriage, the engine would not be able to be fired until the probe had been released, which was not scheduled to occur until Galileo approached Jupiter.”

The despun section is located below the retro-propulsion module. Electric motors can nullify the spin of the upper part of the spacecraft, yielding a stable platform for instruments such as the cameras. The cameras, using charged-couple devices much more advanced than Voyager’s vidicon tubes, will yield images up to a 1,000 times better than its predecessor. Voyager could take pictures to resolutions of two miles. Galileo will routinely be able to see objects the size of a football field, and at times can achieve resolutions five times beyond that. Voyager could take a picture every 48 seconds at the best. Galileo will be able to snap them every eight seconds – or even every 2.66 seconds. The cameras are mounted on a scan platform, which can combine its movements with those created by using the despun electric motors to aim the science instruments. Three other instruments are also mounted on the scan platform: The near-infrared mapping spectrometer to make multispectral images for atmosphere and surface chemical analysis; the ultraviolet spectrometer to study gases and ionized gases; and the photopolarimeter radiometer to measure radiant and reflected energy.

An antenna for receiving signals from the descending atmospheric probe, which are then relayed to Earth via the main antenna, is also attached to the despun section, as is the probe itself. The despun section must be spun up briefly to impart spin stabilization to the probe just prior to its release. The conical probe, weighing just 744 pounds including the heat shield, measures 34 inches tall. It will enter the Jovian atmosphere six degrees north of the equator. The spherical descent module, containing six science instruments weighing 66 pounds, will descend through the atmosphere on an eight-feet-diameter parachute. A transmitter operating at 128 bits per second will relay data to the orbiter, 120,000 miles overhead.

“The probe carries a rich complement of scientific instruments, very similar to the ones we’ve used in the atmospheres of Venus and Mars,” says Torrence Johnson, Galileo project scientist. “Most of the instruments tend to concentrate on the structure and composition of atmospheres – temperature and pressure as a function of depth in the atmosphere. These are the types of things any terrestrial meteorologist would like to know about a new atmosphere.” As the probe descends, a complex of instruments will measure temperature, pressure and deceleration. A nephelometer will determine the location of cloud layers and some of the characteristics of the particles that they are composed of. A net-flux radiometer will investigate the energy forces at work in the atmosphere by measuring changes in the energy being radiated inward and outward at each level. A lightning and radio-emission instrument will listen for static generated by lightning flashes.
« Last Edit: 10/19/2012 12:30 PM by Ares67 »

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #31 on: 10/16/2012 07:57 PM »

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #32 on: 10/16/2012 07:59 PM »
What could endanger Earth by such a scientifically rich mission? To some, the danger rests at the ends of the orbiter’s two power-supply booms. Jupiter receives only 1/25th the sunlight that Earth does, making use of solar-power panels impossible for a spacecraft of Galileo’s size. Instead, the spacecraft generates power with the RTGs, which convert the heat created by plutonium 238, a non-weapons grade of the radioactive material, into electricity. “The RTG is not a new device to the space business,” says Richard Spehalski, Galileo project manager. “Voyager used RTGs, three on each spacecraft. Viking used RTGs in the landers. The Pioneers that went to Jupiter and are now leaving the solar system used RTGs. Apollo used RTGs on the ALSEP devices the astronauts left on the Moon, and there have been other RTGs used on early weather satellites. So there is a relatively long history of use of RTGs.”

The RTGs produce 572 watts at the start of the flight, decaying to 435 watts at mission’s end. “It’s not a lot of power. It’s about one-third the power that you’d use in a regular home hair dryer,” Spehalski says. Galileo will carry the plutonium jacketed in metal pellets and surrounded by layers of graphite. Each of the two RTGs holds 21 pounds of plutonium. In addition, the spacecraft is carrying 131 one-watt heaters that use small pellets of plutonium, replacing electric heaters to keep portions of the spacecraft warm.

Hence, the worry – what if a launch accident occurs? Could radioactive plutonium be released? NASA says no – for nearly every conceivable accident scenario, no matter how remote. The graphite casks are designed to withstand blast damage and entry through the Earth’s atmosphere under most conditions (as occurred during the aborted Apollo 13). And even if one broke open, the plutonium would have to be pulverized into fine dust and then inhaled into the lungs to cause a direct fatality – another order in magnitude of improbability. “The safety features all are designed to withstand the types of environments that would result from accidents, ones that might be far more severe than the Challenger accident, for example,” says Johnson.

In addition to a launch accident, opponents of the RTGs worry about the chance that Galileo could enter the Earth’s atmosphere – either from being stranded in Earth orbit or due to a problem during its two flybys of Earth, which are needed to give gravity-assist boost to Jupiter. Galileo will pass 621 miles over Earth during its first flyby in December 1990, and will come within just 185 miles of Earth during its second pass in December 1992. Steps are being taken to minimize any hazard. If the IUS upper stage should fail to boost Galileo out of orbit, the spacecraft could use its own thrusters to boost it high enough to prevent reentry. During the Earth flybys, Galileo will maintain a course to miss Earth until just a week before the encounters, thus reducing the time when any problems could result in an Earth entry. In addition, the plutonium cases are designed to survive intact from many entry trajectories.

About $50 million has been spent in eight years of testing of the RTG design. “The tests have been large scale,” says John Casani, deputy assistant director of flight projects at JPL, describing just some of the testing. “They have involved full-size explosions – ten or twelve – that represent almost every conceivable accident. There have been a whole series of tests involving accidents and the kind of fragments that would result if an SRB were to fail. These involved actually taking pieces of the SRBs that were recovered from the ocean floor from the Challenger accident, accelerating them on rocket sleds into the RTGs. We have taken another whole series of tests where small fragments in the form of 50 caliber aluminum and titanium bullets were fired at the RTGs and fuel capsules. These tests were designed to simulate the effects of nuts and bolts – things like that – that might impact the RTGs in the event of an accident. There were tests where components of the RTGs were fired using high-pressure gas guns into sand, concrete and steel, simulating the response in the event of impact of an RTG into those surfaces. There were tests to simulate the effects of fire…”

Under extreme – and unlikely – conditions the fuel capsules can break open. “There were some tests where there was release, but in all cases it was very small. In any accident scenario we have examined, this magnitude of release would not represent a health hazard to the public,” Casani says- “We wouldn’t be doing this if we didn’t think it was safe. No mission is worth taking the deliberate risk of one person’s life, and we wouldn’t do that,” he says. “There are 50 or 60 JPL people who are attending the launch with their families. I’ll be down here at KSC with my family.”

Mission Commander Don Williams sums up the feeling of the STS-34 crew: “I’m convinced in my own mind, the crew is convinced in their minds, that it’s absolutely safe to fly these RTG power sources on the Galileo spacecraft. The return we’re going to get from this thing is so much more than the risk involved that it is worth doing. These guys have built a spacecraft that is absolutely an engineering and science masterpiece.”  (Countdown, October 1989 – edited)
« Last Edit: 10/19/2012 12:27 PM by Ares67 »

Offline Ares67

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #33 on: 10/16/2012 08:05 PM »

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #34 on: 10/16/2012 08:07 PM »

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #35 on: 10/16/2012 08:21 PM »
January 6, 1989: NASA: SHUTTLE'S PLUTONIUM LOW-RISK
NASA said today that there is little risk posed by radioactive plutonium aboard shuttle mission STS-34 later this year. Workers at Kennedy Space Center, according to an environmental study, face a one-in-500 million chance of an "early fatality" due to exposure to plutonium should there be an accident within the first two minutes after launch. In an environmental impact statement published Friday in the Federal Register, the space agency says health and environmental consequences of the "most probable" of accidents - a one-in-10 million chance - would be small. The electric generator, holding nearly 50 pounds of plutonium oxide, will be aboard the Galileo spacecraft scheduled for launch from Atlantis in October for a two-year study of the planet Jupiter. According to one estimate, if that amount of plutonium were released into the atmosphere, it would have about 10 times the radioactivity of the Soviet spy satellite that crashed into Canada in 1978. Plutonium is used in nuclear weapons as well as nuclear reactors.

The environmental impact statement calls for public comment over the succeeding 45 days before a final statement is issued. "An intensive analysis of the proposed action indicates that the possible health and environmental consequences of launch or mission anomalies pose small risks," the statement says. "The accident estimated to be the most probable would pose very small health risks and very small probability of environmental contamination."

Dr. Michio Kaku, a theoretical physicist at City University of New York and a spokesman for Citizens to Stop Plutonium in Space, said, "I think they are wildly optimistic" about the safety of the plutonium power source. "They are living in a fool's paradise. The consequences of real natural disasters are much worse than in computer modeling. Basically, they are playing Russian roulette with the people of Cocoa Beach," he said. (Deseret News, The Orlando Sentinel and Florida Today, Jan. 6/7, 1989 - edited)


April 17: PART OF JUPITER PROBE ARRIVES AT KSC
Amid final preparations for the STS-30 Atlantis mission, part of another scientific mission - the Galileo space probe - arrived at Kennedy Space Center at 7:00 a.m. this morning, according to KSC spokesman George Diller. The rest of the probe is scheduled to arrive May 17. Galileo is scheduled for launch aboard Atlantis on Oct. 12. (Florida Today, April 18, 1989)


May 16: REST OF GALILEO PROBE ARRIVES AT KSC AFTER NINE-DAY-TRIP
The Galileo probe to Jupiter arrived at Kennedy Space Center today at 7 p.m. and was taken to a spacecraft assembly building at Cape Canaveral Air Force Station, where workers were to begin preparing the spacecraft for its Oct. 12 launch aboard Atlantis. It will remain in the spacecraft assembly building till July 24, when it will be moved to the Vertical Processing Facility for final launch preparations. Rollout to the launch pad is scheduled for Aug. 23. (Florida Today, May 17, 1989)

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #36 on: 10/16/2012 08:24 PM »
May 16: STS-34 EXTERNAL TANK ARRIVES AT KSC

Offline Ares67

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #37 on: 10/16/2012 08:25 PM »
June 10: TESTING GALILEO
The Galileo planetary probe to Jupiter was scheduled for a 13-hour test today to simulate electrical events that will take place from launch through separation from the probe's two-stage booster rocket. (Florida Today, June 11, 1989)


June 15: ATLANTIS BOOSTERS ASSEMBLED
The first segment of one of Atlantis' Solid Rocket Boosters has now been mounted on the Mobile Launch Platform in the Vehicle Assembly Building at Kennedy Space Center. Three other major segments will be added to the booster as they are inspected and cleared for flight during the next few weeks. The next mission of Atlantis, with the Galileo Jupiter probe aboard, is scheduled to launch Oct. 12. Two tanks inside the Galileo spacecraft have been filled with 1,300 pounds of nitrogen tetroxide and about 600 pounds of hydrazine will be loaded into Galileo next week. (Florida Today, June 16, 1989)


June 29: JUPITER PROBE ANTENNA INSTALLED
The Galileo planetary probe reached a processing milestone today when Kennedy Space Center workers installed the main umbrella-like antenna on the spacecraft. The antenna will enable the probe to communicate with NASA's Deep Space Network satellite dish system. The antenna is capable of both sending and receiving signals and is one of the last major spacecraft components to be assembled. On June 30 technicians will conduct electrical tests to assure the antenna works properly. (Florida Today, June 30, 1989)

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #38 on: 10/16/2012 08:33 PM »

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Re: Atlantis STS-34 – Eppur si muove!
« Reply #39 on: 10/16/2012 08:35 PM »

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