Friday, August 13, 2010

SAFE AND EFFICIENT DE-ORBIT OF SPACE JUNK WITHOUT MAKING THE PROBLEM WORSE

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Global Aerospace Corporation (GAC) announced that Dr. Kristin L. Gates presented a paper on de-orbiting space junk at the August 2 Artificial and Natural Space Debris session of the AIAA Astrodynamics Specialists Conference in Toronto, Ontario, Canada. Dr. Gates described GAC's Gossamer Orbit Lowering Device (GOLD) for safe and efficient removal from Low Earth Orbit (LEO) of dangerous space objects. The patented GOLD system concept uses a very large ultra thin balloon envelope to increase the aerodynamic drag by a factor of several hundred. This will cause the space junk to enter the earth's atmosphere quickly and burn up. It will reduce the natural orbit decay of some objects from centuries to months.

The envelope material is thinner and lighter than sandwich bag material. It takes a very small amount of gas to inflate it in the almost perfect vacuum of space. The system will work even though it will get punctured many times by small debris objects and tiny meteoroids. Despite these small holes, the total leak rate will be very small. The pressurization system will very easily keep up with the leakage. In the very unlikely event that a large object hits the very thin envelope, it will not cause that large object to break up into new fragments. Therefore, the operation of GOLD itself cannot make the orbital debris environment worse as could be the case with some alternative approaches that others have suggested.

Although the ultra thin envelope could be the size of a sports field (100 m diameter) when inflated, it is so thin that it can be folded and stowed in a surprisingly small volume (a medium size suitcase). It is most economical to attach it to a spacecraft or rocket upper stage before launch and deployed after the end of mission. However, GOLD could be attached to existing large debris objects using an orbital robot. For large, dense objects that could pose a hazard to people or property on the ground during reentry, GOLD can be used to aim the reentry safely into an ocean.

Space debris is a growing problem in many orbital regimes despite international debris mitigation guidelines and policies. The recent collision of an operational Iridium satellite and a defunct Russian satellite underscores the need for an ability to safely de-orbit large objects from popular, congested orbital regions. Currently, there are many hundreds of old spacecraft and rocket bodies orbiting the Earth at the same altitudes as operating spacecraft. As these abandoned objects continue moving through space, collisions with other objects create a shotgun effect of new debris objects, each of which could kill an operating spacecraft. Orbital debris - or space junk - refers to all these large orbiting objects as well as the cloud of smaller objects due to explosions of these systems and collisions with other objects. Even if we do nothing, the problem will get worse for centuries to come. But it's a difficult problem to solve. People have suggested many approaches to de-orbiting space junk, such as using existing on-board chemical propulsions systems, electrodynamic tethers, gravity gradient-oriented drag tapes, boom-deployed drag sails or solar pressure sails. In many cases, while these de-orbit devices are operating there is an increased chance of having a collision with something else and creating new junk. With GOLD there is a negligible increase in the chance of creating new dangerous orbital debris and once the object is removed from orbit, that particular threat is gone forever.

Although the use of on-board propulsion systems do not increase the chance of creating new debris, many spacecraft do not have such propulsion systems, and for those that do, there is always the temptation to use the propulsion system to extend the mission, depleting the fuel that would be needed to bring the spacecraft down. The GOLD system actually weighs less than the propellant needed to do the same job and it is very inexpensive, and this means it is more cost-effective to add a GOLD system before launch than to carry the extra fuel.

We tend to think of space as being a complete vacuum, but there are enough molecules and atoms out to several hundred miles to produce a small but noticeable drag that slowly reduces the orbital altitude of spacecraft. GOLD takes advantage of this effect and increases it by a factor of several hundred. The air out at these altitudes has a very small density. Sun spot activity is known to follow an eleven-year cycle, with an associated cycle in the radiation coming from the sun. At "solar max", the extra radiation causes the Earth's atmosphere to bloom outward, increasing the average air density in LEO by a factor of three. When GOLD is attached to a spacecraft, it is usually beneficial to wait until solar max to use it because it then brings down that satellite three times faster than average.

There are three basic applications for GOLD. The first application is to attach GOLD to satellites and rocket stages that are planned for launch. GOLD is then inflated, de-orbiting the object at the end of its useful life. The second application is in an active debris removal program, which may be important if the orbital debris problem is ever to be reduced. Several GOLD devices could be carried to orbit by an orbital robot and placed on existing space junk like the defunct spacecraft that struck the Iridium satellite, permanently removing them from orbit and making the environment safer. GAC has found that that GOLD is very effective in the 750 to 900 km altitude, high inclination orbit regime, which is a highly used portion of space and where the Iridium satellite was located. In a third application, some large space objects require controlled, targeted de-orbit and reentry because too much material survives reentry and reaches the Earth's surface where it can jeopardize the safety of people or property. In this application, when GOLD has reduced the orbit to the point of imminent entry, the large envelope is allowed to deflate under natural conditions to reduce drag and defer reentry a few days. After making good orbit predictions and using careful timing, the envelope is fully inflated at the correct point in the orbit to achieve a substantial atmospheric drag sufficient for prompt and safe reentry into the ocean.

In summary, the operation of GOLD has a lower risk of disabling other operational satellites and a lower risk of creating large orbit debris objects than competing de-orbit concepts or the derelict satellite itself. In addition, GOLD does not require an operating satellite to provide attitude stabilization or power as with propulsive de-orbit. GOLD can be integrated onto the satellite prior to launch or attached to derelict satellites by robots. De-orbit from LEO can be reduced, in some cases, from many centuries to as little as a few months. Finally, GOLD can assist civilian, commercial and military space satellite operators in meeting their obligations to mitigate the growing space debris problem in a cost effective and low risk way.

(Photo: Global Aerospace Corporation)

Global Aerospace Corporation

1 HIGH-FAT DIET, 2 DIFFERENT OUTCOMES: THE PATH TO OBESITY BECOMES CLEARER

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Why is it that two people can consume the same high fat, high-calorie Western diet and one becomes obese and prone to diabetes while the other maintains a slim frame? This question has long baffled scientists, but a study by Yale School of Medicine researchers provides a simple explanation: weight is set before birth in the developing brain.

The results are reported online in the Proceedings of the National Academy of Sciences.

Led by Tamas Horvath, chair and professor of comparative medicine and professor of neurobiology and obstetrics & gynecology at Yale School of Medicine, the research team analyzed the same question in specific groups of rats. These animals have been bred so that their vulnerability to diet-induced obesity is known before they would be put on high-fat, high-calorie diet diets.

Horvath said animals that become obese already had a significant difference in the feeding center of the brain. Neurons that are supposed to signal when you've eaten enough and when to burn calories, are much more sluggish in these animals because they are inhibited by other cells. In animals resistant to obesity, these satiety signaling neurons are much more active and ready to signal to the rest of the brain and peripheral tissues when enough food has been consumed.

"It appears that this base wiring of the brain is a determinant of one's vulnerability to develop obesity," said Horvath, who is also co-director of the Yale Program in Integrative Cell Signaling and Neurobiology of Metabolism. "These observations add to the argument that it is less about personal will that makes a difference in becoming obese, and, it is more related to the connections that emerge in our brain during development."

Horvath points to other unwanted consequences of these brain mechanisms. "Those who are vulnerable to diet-induced obesity also develop a brain inflammation, while those who are resistant, do not," he said. "This emerging inflammatory response in the brain may also explain why those who once developed obesity have a harder time losing weight."

Diet-induced obesity has become one of the most critical medical problems in the United States. In particular, the incidence of childhood obesity has reached unprecedented levels. Since genetics alone cannot explain the surge of obesity in society, investigators have been trying to determine the primary underpinnings of the vulnerability to develop obesity on a Western diet.

"What genetic, epigenetic and environmental factor determines this base wiring in the brain is a very important issue to address," said Horvath. "Specifically, the emerging view is that besides genetics, maternal impact on the developing brain is likely to be critical to imprint these feeding circuits thereby determining one's vulnerability or resistance to obesity."

(Photo: Yale U.)

Yale University

OXYGEN FUELS THE FIRES OF TIME

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Variations in the Earth's atmospheric oxygen levels are thought to be closely linked to the evolution of life, with strong feedbacks between uni- and multicellular life and oxygen. Over the past 400 million years the level of oxygen has varied considerably from the 21% value we have today. Scientists from The Field Museum in Chicago and Royal Holloway University of London publishing their results this week in the journal Nature Geoscience have shown that the amount of charcoal preserved in ancient peat bogs, now coal, gives a measure of how much oxygen there was in the past.

Until now scientists have relied on geochemical models to estimate atmospheric oxygen concentrations. However, a number of competing models exist, each with significant discrepancies and no clear way to resolve an answer. All models agree that around 300 million years ago in the Late Paleozoic atmospheric oxygen levels were much higher than today. These elevated concentrations have been linked to gigantism in some animal groups, in particular insects, the dragonfly Meganeura monyi with a wingspan of over two feet epitomizing this. Some scientists think these higher concentrations of atmospheric oxygen may also have allowed vertebrates to colonize the land.

These higher levels of oxygen were a direct consequence of the colonization of land by plants. When plants photosynthesize they evolve oxygen. However, when the carbon stored in plant tissues decays atmospheric oxygen is used up. To produce a net increase in atmospheric oxygen over time organic matter must be buried. The colonization of land by plants not only led to new plant growth but also a dramatic increase in the burial of carbon. This burial was particularly high during the Late Paleozoic when huge coal deposits accumulated.

Dr. Ian J. Glasspool from the Department of Geology at the Field Museum explained that: "Atmospheric oxygen concentration is strongly related to flammability. At levels below 15% wildfires could not have spread. However, at levels significantly above 25% even wet plants could have burned, while at levels around 30 to 35%, as have been proposed for the Late Paleozoic, wildfires would have been frequent and catastrophic".

The researchers, including Professor Andrew C. Scott from the Royal Holloway University of London, have shown that charcoal found in coal has remained at concentrations of around 4-8% over the past 50 million years indicating near to present levels of atmospheric oxygen. However, there were periods in Earth History when the charcoal percentage in the coals was as high as 70%. This indicates very high levels of atmospheric oxygen that would have promoted many frequent, large, and extremely hot fires. These intervals include the Carboniferous and Permian Periods from 320-250 million years ago and the Middle Cretaceous Period approximately 100 million years ago.

"It is interesting", Professor Scott points out, "that these were times of major change in the evolution of vegetation on land with the evolution and spread of new plant groups, the conifers in the late Carboniferous and flowering plants in the Cretaceous". These periods of high fire resulting from elevated atmospheric oxygen concentration might have been self-perpetuating with more fire meaning greater plant mortality, and in turn more erosion and therefore greater burial of organic carbon which would have then promoted elevated atmospheric oxygen concentrations. "The mystery to us", Scott states, "is why oxygen levels appear to have more or less stabilized about 50 million years ago".

Field Museum

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