Category: Space Exploration

Artist’s concept of humans set off to Mars. Image credit: NASA Click to enlarge
After reading this article, you might never look at trash bags the same way again.

We all use plastic trash bags; they’re so common that we hardly give them a second thought. So who would have guessed that a lowly trash bag might hold the key to sending humans to Mars?

Most household trash bags are made of a polymer called polyethylene. Variants of that molecule turn out to be excellent at shielding the most dangerous forms of space radiation. Scientists have long known this. The trouble has been trying to build a spaceship out of the flimsy stuff.

But now NASA scientists have invented a groundbreaking, polyethylene-based material called RXF1 that’s even stronger and lighter than aluminum. “This new material is a first in the sense that it combines superior structural properties with superior shielding properties,” says Nasser Barghouty, Project Scientist for NASA’s Space Radiation Shielding Project at the Marshall Space Flight Center.

To Mars in a plastic spaceship? As daft as it may sound, it could be the safest way to go.

Less is more

Protecting astronauts from deep-space radiation is a major unsolved problem. Consider a manned mission to Mars: The round-trip could last as long as 30 months, and would require leaving the protective bubble of Earth’s magnetic field. Some scientists believe that materials such as aluminum, which provide adequate shielding in Earth orbit or for short trips to the Moon, would be inadequate for the trip to Mars.

Barghouty is one of the skeptics: “Going to Mars now with an aluminum spaceship is undoable,” he believes.

Plastic is an appealing alternative: Compared to aluminum, polyethylene is 50% better at shielding solar flares and 15% better for cosmic rays.

The advantage of plastic-like materials is that they produce far less “secondary radiation” than heavier materials like aluminum or lead. Secondary radiation comes from the shielding material itself. When particles of space radiation smash into atoms within the shield, they trigger tiny nuclear reactions. Those reactions produce a shower of nuclear byproducts — neutrons and other particles — that enter the spacecraft. It’s a bit like trying to protect yourself from a flying bowling ball by erecting a wall of pins. You avoid the ball but get pelted by pins. “Secondaries” can be worse for astronauts’ health than the original space radiation!

Ironically, heavier elements like lead, which people often assume to be the best radiation shielding, produce much more secondary radiation than lighter elements like carbon and hydrogen. That’s why polyethylene makes good shielding: it is composed entirely of lightweight carbon and hydrogen atoms, which minimizes secondaries.

These lighter elements can’t completely stop space radiation. But they can fragment the incoming radiation particles, greatly reducing the harmful effects. Imagine hiding behind a chain-link fence to protect yourself in a snowball fight: You’ll still get some snow on you as tiny bits of snowball burst through the fence, but you won’t feel the sting of a direct hit from a hard-packed whopper. Polyethylene is like that chain link fence.

“That’s what we can do. Fragmenting — without producing a lot of secondary radiation — is actually where the battle is won or lost,” Barghouty says.

Made to order

Despite their shielding power, ordinary trash bags obviously won’t do for building a spaceship. So Barghouty and his colleagues have been trying to beef-up polyethylene for aerospace work.

That’s how Shielding Project researcher Raj Kaul, working together with Barghouty, came to invent RXF1. RXF1 is remarkably strong and light: it has 3 times the tensile strength of aluminum, yet is 2.6 times lighter — impressive even by aerospace standards.

“Since it is a ballistic shield, it also deflects micrometeorites,” says Kaul, who had previously worked with similar materials in developing helicopter armor. “Since it’s a fabric, it can be draped around molds and shaped into specific spacecraft components.” And because it’s derived from polyethylene, it’s an excellent radiation shield as well.

The specifics of how RXF1 is made are secret because a patent on the material is pending.

Strength is only one of the traits that the walls of a spaceship must have, Barghouty notes. Flammability and temperature tolerance are also important: It doesn’t matter how strong a spaceship’s walls are if they melt in direct sunlight or catch fire easily. Pure polyethylene is very flammable. More work is needed to customize RXF1 even further to make it flame and temperature resistant as well, Barghouty says.

The Bottom Line

The big question, of course, is the bottom line: Can RXF1 carry humans safely to Mars? At this point, no one knows for sure.

Some “galactic cosmic rays are so energetic that no reasonable amount of shielding can stop them,” cautions Frank Cucinotta, NASA’s Chief Radiation Health Officer. “All materials have this problem, including polyethylene.”

Cucinotta and colleagues have done computer simulations to compare the cancer risk of going to Mars in an aluminum ship vs. a polyethylene ship. Surprisingly, “there was no significant difference,” he says. This conclusion depends on a biological model which estimates how human tissue is affected by space radiation–and therein lies the rub. After decades of spaceflight, scientists still don’t fully understand how the human body reacts to cosmic rays. If their model is correct, however, there could be little practical benefit to the extra shielding polyethylene provides. This is a matter of ongoing research.

Because of the many uncertainties, dose limits for astronauts on a Mars mission have not been set, notes Barghouty. But assuming that those dose limits are similar to limits set for Shuttle and Space Station flights, he believes RXF1 could hypothetically provide adequate shielding for a 30 month mission to Mars.

Today, to the dump. Tomorrow, to the stars? Polyethylene might take you farther than you ever imagined.

Original Source: NASA News Release

ISS photographed by STS crewmember. Image credit: NASA Click to enlarge
After saying goodbye to the Space Shuttle Discovery’s crew on Saturday, International Space Station (ISS) Commander Sergei Krikalev and NASA Science Officer John Phillips spent much of the week preparing for a spacewalk scheduled for next week.

The six-hour spacewalk begins at 2:55 p.m. EDT, Thursday. Live coverage on NASA TV starts at 1:30 p.m. EDT.

On the spacewalk, the crew will change out a Russian biological experiment, retrieve some radiation sensors, remove a Japanese materials science experiment, photograph a Russian materials experiment, install a TV camera and relocate a grapple fixture.

At 1:44 a.m. EDT, Tuesday, Krikalev’s time spent in space will surpass any other human. Cosmonaut Sergei Avdeyev set the previous record with 748 days in orbit. Krikalev is a veteran of two long-duration flights to the Soviet Union’s Space Station Mir; two flights on the Shuttle; and two flights to the ISS. Krikalev was aboard Mir when the Soviet Union disintegrated; was the first Russian to fly on the Shuttle in 1994; was a member of the Shuttle crew that began assembly of the ISS in 1998; and a member of the first crew to live on board the Station in 2000.

Krikalev and Phillips had an off-duty day on Sunday. On Monday they unpacked and prepared spacewalk tools and the Pirs docking compartment. They will use the Pirs for the spacewalk. During the week, they checked the Russian Orlan spacesuits they will wear and talked with spacewalk experts in the Russian Mission Control Center and in Houston.

On Thursday, the Russian Vozdukh carbon dioxide removal system shut down. The system is one of multiple systems used to scrub the Station cabin air. Flight controllers in Houston activated a U.S. Carbon Dioxide Removal Assembly to perform that function while the Vozdukh is not operating. Russian specialists are analyzing the problem.

Information about crew activities on board the Station, future launch dates, previous status reports and sighting ISS opportunities is available on the Web at: http://www.nasa.gov/station

For information about NASA and other agency programs on the Web, visit: http://www.nasa.gov/home/index.html

Original Source: NASA News Release

Artist’s concept of possible exploration programs. Image credit: NASA Click to enlarge
Have you ever walked across a wool carpet in leather-soled shoes on a dry winter day, and then reached out toward a doorknob? ZAP! A stinging spark leaps between your fingers and the metal knob.

That’s static discharge–lightning writ small.

Static discharge is merely annoying to anyone on Earth living where winters have exceptionally low humidity. But to astronauts on the Moon or on Mars, static discharge could be real trouble.

“On Mars, we think the soil is so dry and insulating that if an astronaut were out walking, once he or she returned to the habitat and reached out to open the airlock, a little lightning bolt might zap critical electronics,” explains Geoffrey A. Landis, a physicist with the Photovoltaics and Space Environmental Effects Branch at NASA Glenn Research Center in Cleveland, Ohio.

This phenomenon is called triboelectric charging.

The prefix “tribo” (pronounced TRY-bo) means “rubbing.” When certain pairs of unlike materials, such as wool and hard shoe-sole leather, rub together, one material gives up some of its electrons to the other material. The separation of charge can create a strong electric field.

Here on Earth, the air around us and the clothes we wear usually have enough humidity to be decent electrical conductors, so any charges separated by walking or rubbing have a ready path to ground. Electrons bleed off into the ground instead of accumulating on your body.

But when air and materials are extraordinarily dry, such as on a dry winter’s day, they are excellent insulators, so there is no ready pathway to ground. Your body can accumulate negative charges, possibly up to an amazing 20 thousand volts. If you touch a conductor, such as a metal doorknob, then–ZAP!–all the accumulated electrons discharge at once.

On the Moon and on Mars, conditions are ideal for triboelectric charging. The soil is drier than desert sand on Earth. That makes it an excellent electrical insulator. Moreover, the soil and most materials used in spacesuits and spacecraft (e.g., aluminized mylar, neoprene-coated nylon, Dacron, urethane-coated nylon, tricot, and stainless steel) are completely unlike each other. When astronauts walk or rovers roll across the ground, their boots or wheels gather electrons as they rub through the gravel and dust. Because the soil is insulating, providing no path to ground, a space suit or rover can build up tremendous triboelectric charge, whose magnitude is yet unknown. And when the astronaut or vehicle gets back to base and touches metal–ZAP! The lights in the base may go out, or worse.

Landis and colleagues at NASA Glenn first noticed this problem in the late 1990s before Mars Pathfinder was launched. “When we ran a prototype wheel of the Sojourner rover over simulated Martian dust in a simulated Martian atmosphere, we found it charged up to hundreds of volts,” he recalls.

That discovery so concerned the scientists that they modified Pathfinder’s rover design, adding needles half an inch long, made of ultrathin (0.0001-inch diameter) tungsten wire sharpened to a point, at the base of antennas. The needles would allow any electric charge that built up on the rover to bleed off into the thin Martian atmosphere, “like a miniature lightning rod operating in reverse,” explains Carlos Calle, lead scientist at NASA’s Electrostatics and Surface Physics Laboratory at Kennedy Space Center, Florida. Similar protective needles were also installed on the Spirit and Opportunity rovers.

On the Moon, “Apollo astronauts never reported being zapped by electrostatic discharges,” notes Calle. “However, future lunar missions using large excavation equipment to move lots of dry dirt and dust could produce electrostatic fields. Because there’s no atmosphere on the Moon, the fields could grow quite strong. Eventually, discharges could occur in vacuum.”

“On Mars,” he continues, “discharges can happen at no more than a few hundred volts. It’s likely that these will take the form of coronal glows rather than lightning bolts. As such, they may not be life threatening for the astronauts, but they could be harmful to electronic equipment.”

So what’s the solution to this problem?

Here on Earth, it’s simple: we minimize static discharge by grounding electrical systems. Grounding them means literally connecting them to Earth–pounding copper rods deep into the ground. Ground rods work well in most places on Earth because several feet deep the soil is damp, and is thus a good conductor. The Earth itself provides a “sea of electrons,” which neutralizes everything connected to it, explains Calle.

There’s no moisture, though, in the soil of the Moon or Mars. Even the ice believed to permeate Martian soil wouldn’t help, as “frozen water is not a terribly good conductor,” says Landis. So ground rods would be ineffective in establishing a neutral “common ground” for a lunar or Martian colony.

On Mars, the best ground might be, ironically, the air. A tiny radioactive source “such as that used in smoke detectors,” could be attached to each spacesuit and to the habitat, suggests Landis. Low-energy alpha particles would fly off into the rarefied atmosphere, hitting molecules and ionizing them (removing electrons). Thus, the atmosphere right around the habitat or astronaut would become conductive, neutralizing any excess charge.

Achieving a common ground on the Moon would be trickier, where there’s not even a rarefied atmosphere to help bleed off the charge. Instead, a common ground might be provided by burying a huge sheet of foil or mesh of fine wires, possibly made of aluminum (which is highly conductive and could be extracted from lunar soil), underneath the entire work area. Then all the habitat’s walls and apparatus would be electrically connected to the aluminum.

Research is still preliminary. So ideas differ amongst the physicists who are seeking, well, some common ground.

Original Source: NASA News Release

Artist’s conception of a bio-nanorobot. Image credit: NASA. Click to enlarge
When it comes to taking the next “giant leap” in space exploration, NASA is thinking small — really small.

In laboratories around the country, NASA is supporting the burgeoning science of nanotechnology. The basic idea is to learn to deal with matter at the atomic scale — to be able to control individual atoms and molecules well enough to design molecule-size machines, advanced electronics and “smart” materials.

If visionaries are right, nanotechnology could lead to robots you can hold on your fingertip, self-healing spacesuits, space elevators and other fantastic devices. Some of these things may take 20+ years to fully develop; others are taking shape in the laboratory today.

Simply making things smaller has its advantages. Imagine, for example, if the Mars rovers Spirit and Opportunity could have been made as small as a beetle, and could scurry over rocks and gravel as a beetle can, sampling minerals and searching for clues to the history of water on Mars. Hundreds or thousands of these diminutive robots could have been sent in the same capsules that carried the two desk-size rovers, enabling scientists to explore much more of the planet’s surface — and increasing the odds of stumbling across a fossilized Martian bacterium!

But nanotech is about more than just shrinking things. When scientists can deliberately order and structure matter at the molecular level, amazing new properties sometimes emerge.

An excellent example is that darling of the nanotech world, the carbon nanotube. Carbon occurs naturally as graphite — the soft, black material often used in pencil leads — and as diamond. The only difference between the two is the arrangement of the carbon atoms. When scientists arrange the same carbon atoms into a “chicken wire” pattern and roll them up into miniscule tubes only 10 atoms across, the resulting “nanotubes” acquire some rather extraordinary traits. Nanotubes:

– have 100 times the tensile strength of steel, but only 1/6 the weight;
– are 40 times stronger than graphite fibers;
– conduct electricity better than copper;
– can be either conductors or semiconductors (like computer chips), depending on the arrangement of atoms;
– and are excellent conductors of heat.

Much of current nanotechnology research worldwide focuses on these nanotubes. Scientists have proposed using them for a wide range of applications: in the high-strength, low-weight cable needed for a space elevator; as molecular wires for nano-scale electronics; embedded in microprocessors to help siphon off heat; and as tiny rods and gears in nano-scale machines, just to name a few.

Nanotubes figure prominently in research being done at the NASA Ames Center for Nanotechnology (CNT). The center was established in 1997 and now employs about 50 full-time researchers.

“[We] try to focus on technologies that could yield useable products within a few years to a decade,” says CNT director Meyya Meyyappan. “For example, we’re looking at how nano-materials could be used for advanced life support, DNA sequencers, ultra-powerful computers, and tiny sensors for chemicals or even sensors for cancer.”

A chemical sensor they developed using nanotubes is scheduled to fly a demonstration mission into space aboard a Navy rocket next year. This tiny sensor can detect as little as a few parts per billion of specific chemicals–like toxic gases–making it useful for both space exploration and homeland defense. CNT has also developed a way to use nanotubes to cool the microprocessors in personal computers, a major challenge as CPUs get more and more powerful. This cooling technology has been licensed to a Santa Clara, California, start-up called Nanoconduction, and Intel has even expressed interest, Meyyappan says.

If these near-term uses of nanotechnology seem impressive, the long-term possibilities are truly mind-boggling.

The NASA Institute for Advanced Concepts (NIAC), an independent, NASA-funded organization located in Atlanta, Georgia, was created to promote forward-looking research on radical space technologies that will take 10 to 40 years to come to fruition.

For example, one recent NIAC grant funded a feasibility study of nanoscale manufacturing–in other words, using vast numbers of microscopic molecular machines to produce any desired object by assembling it atom by atom!

That NIAC grant was awarded to Chris Phoenix of the Center for Responsible Nanotechnology.

In his 112 page report, Phoenix explains that such a “nanofactory” could produce, say, spacecraft parts with atomic precision, meaning that every atom within the object is placed exactly where it belongs. The resulting part would be extremely strong, and its shape could be within a single atom’s width of the ideal design. Ultra-smooth surfaces would need no polishing or lubrication, and would suffer virtually no “wear and tear” over time. Such high precision and reliability of spacecraft parts are paramount when the lives of astronauts are at stake.

Although Phoenix sketched out some design ideas for a desktop nanofactory in his report, he acknowledges that — short of a big-budget “Nanhatten Project,” as he calls it — a working nanofactory is at least a decade away, and possibly much longer.

Taking a cue from biology, Constantinos Mavroidis, director of the Computational Bionanorobotics Laboratory at Northeastern University in Boston, is exploring an alternative approach to nanotech:

Rather than starting from scratch, the concepts in Mavroidis’s NIAC-funded study employ pre-existing, functional molecular “machines” that can be found in all living cells: DNA molecules, proteins, enzymes, etc.

Shaped by evolution over millions of years, these biological molecules are already very adept at manipulating matter at the molecular scale — which is why a plant can combine air, water, and dirt and produce a juicy red strawberry, and a person’s body can convert last night’s potato dinner into today’s new red blood cells. The rearranging of atoms that makes these feats possible is performed by hundreds of specialized enzymes and proteins, and DNA stores the code for making them.

Making use of these “pre-made” molecular machines — or using them as starting points for new designs — is a popular approach to nanotechnology called “bio-nanotech.”

“Why reinvent the wheel?” Mavroidis says. “Nature has given us all this great, highly refined nanotechnology inside of living things, so why not use it — and try to learn something from it?”

The specific uses of bio-nanotech that Mavroidis proposes in his study are very futuristic. One idea involves draping a kind of “spider’s web” of hair-thin tubes packed with bio-nanotech sensors across dozens of miles of terrain, as a way to map the environment of some alien planet in great detail. Another concept he proposes is a “second skin” for astronauts to wear under their spacesuits that would use bio-nanotech to sense and respond to radiation penetrating the suit, and to quickly seal over any cuts or punctures.

Futuristic? Certainly. Possible? Maybe. Mavroidis admits that such technologies are probably decades away, and that technology so far in the future will probably be very different from what we imagine now. Still, he says he believes it’s important to start thinking now about what nanotechnology might make possible many years down the road.

Considering that life itself is, in a sense, the ultimate example of nanotech, the possibilities are exciting indeed.

Original Source: NASA News Release

A magnified view of muscle fibres. Image credit: UM. Click to enlarge.
Experiments for NASA space missions have shown that small amounts of edible meat can be created in a lab. But the technology that could grow chicken nuggets without the chicken, on a large scale, may not be just a science fiction fantasy.

In a paper in the June 29 issue of Tissue Engineering, a team of scientists, including University of Maryland doctoral student Jason Matheny, propose two new techniques of tissue engineering that may one day lead to affordable production of in vitro – lab grown — meat for human consumption. It is the first peer-reviewed discussion of the prospects for industrial production of cultured meat.

“There would be a lot of benefits from cultured meat,” says Matheny, who studies agricultural economics and public health. “For one thing, you could control the nutrients. For example, most meats are high in the fatty acid Omega 6, which can cause high cholesterol and other health problems. With in vitro meat, you could replace that with Omega 3, which is a healthy fat.

“Cultured meat could also reduce the pollution that results from raising livestock, and you wouldn’t need the drugs that are used on animals raised for meat.”

Prime Without the Rib
The idea of culturing meat is to create an edible product that tastes like cuts of beef, poultry, pork, lamb or fish and has the nutrients and texture of meat.

Scientists know that a single muscle cell from a cow or chicken can be isolated and divided into thousands of new muscle cells. Experiments with fish tissue have created small amounts of in vitro meat in NASA experiments researching potential food products for long-term space travel, where storage is a problem.

“But that was a single experiment and was geared toward a special situation – space travel,” says Matheny. “We need a different approach for large scale production.”

Matheny’s team developed ideas for two techniques that have potential for large scale meat production. One is to grow the cells in large flat sheets on thin membranes. The sheets of meat would be grown and stretched, then removed from the membranes and stacked on top of one another to increase thickness.

The other method would be to grow the muscle cells on small three-dimensional beads that stretch with small changes in temperature. The mature cells could then be harvested and turned into a processed meat, like nuggets or hamburgers.

Treadmill Meat
To grow meat on a large scale, cells from several different kinds of tissue, including muscle and fat, would be needed to give the meat the texture to appeal to the human palate.

“The challenge is getting the texture right,” says Matheny. “We have to figure out how to ‘exercise’ the muscle cells. For the right texture, you have to stretch the tissue, like a live animal would.”

Where’s the Beef?
And, the authors agree, it might take work to convince consumers to eat cultured muscle meat, a product not yet associated with being produced artificially.

“On the other hand, cultured meat could appeal to people concerned about food safety, the environment, and animal welfare, and people who want to tailor food to their individual tastes,” says Matheny. The paper even suggests that meat makers may one day sit next to bread makers on the kitchen counter.

“The benefits could be enormous,” Matheny says. “The demand for meat is increasing world wide — China ‘s meat demand is doubling every ten years. Poultry consumption in India has doubled in the last five years.

“With a single cell, you could theoretically produce the world’s annual meat supply. And you could do it in a way that’s better for the environment and human health. In the long term, this is a very feasible idea.”

Matheny saw so many advantages in the idea that he joined several other scientists in starting a nonprofit, New Harvest, to advance the technology. One of these scientists, Henk Haagsman, Professor of Meat Science at Utrecht University, received a grant from the Dutch government to produce cultured meat, as part of a national initiative to reduce the environmental impact of food production.

Other authors of the paper are Pieter Edelman of Wageningen University , Netherlands ; Douglas McFarland, South Dakota State University ; and Vladimir Mironov, Medical University of South Carolina.

Original Source: UM News Release

Computer illustration of a potential antimatter drive. Image credit: Positronics Research LLC. Click to enlarge.
We all played the game as children – “leapfrog” involved one child squatting on all fours while a second placed their hands on the first’s shoulders. Braced against the pull of gravity, the standing child bends at the legs deeply then thrusts up and over the top of the first. The result? The second child now squats and the another froglike leap follows in turn. Not the most efficient way to get to the swing set – but a lot of fun in the right company!

Leapfrogging however is not the same as ‘bootstrapping’. While bootstrapping, a single player bends and grabs the leather loops on the outside of both boots. The player then makes a tremendous exertion upward with the arms. Leapfrogging works – bootstrapping doesn’t, it just can’t be done without hopping – an entirely different thing altogether.

The NASA Institute for Advanced Concepts (NIAC) believes in leapfrogging – no not on the playground but in aerospace. From the institutes own website: “NIAC encourages proposers to think decades into the future in pursuit of concepts that will “leapfrog” the evolution of current aerospace systems.” NIAC is looking for a few good ideas and is willing to support them with six-month-long seed grants to test feasibility before serious research and development funds – available from NASA and elsewhere – are allocated. Hopefully such seeds are allowed to germinate and future investment grows them to maturity.

NIAC wants to separate out leapfrogging from bootstrapping, however. One works and the other makes no sense whatsoever. According to NIAC, the positron drive could lead to a giant leap forward in the way we travel throughout the solar system and beyond. There’s probably no bootstrapping about it.

Consider the positron – mirror twin of the electron – like human twins, a very rare thing. Unlike human twins, a positron is unlikely to survive the birth process. Why? Because positrons and their siblings – electrons – find each other irresistible and quickly annihilate in a burst of soft gamma rays. But that burst, under controlled circumstances, can be converted into any form of ‘work’ you might want to do.

Need light? Mix a positron and an electron then irradiate a gas to incandescence. Need electricity? Mix another pair and irradiate a metal strip. Need thrust? Shoot those gamma rays into a propellant, heat it to outlandishly high temperatures and push the propellant out the back of the rocket. Or, shoot those gamma rays into tungsten plates in a stream of air, heat that air and jettison it out the back of an aircraft.

Imagine having a supply of positrons – what could you do with them? According to Gerald A. Smith, Principle Investigator for Positronics Research, LLC of Sante Fe, New Mexico you could go just about anywhere, “the energy density of antimatter is ten orders of magnitude greater than chemical and three orders of magnitude greater than nuclear fission or fusion energy.”

And what does this mean in terms of propulsion? “Less weight, far, far, far less weight.”

Using chemically based propulsion systems, 55 percent of the weight associated with the Huygens-Cassini probe sent to explore Saturn was found in the probe’s fuel and oxidizer tanks. Meanwhile to hurl the probes 5650 kg of weight beyond the Earth required a launch vehicle weighing some 180 times that of fully-fueled Cassini-Huygens itself (1,032,350 kgs).

Using Dr. Smith’s numbers alone – and only considering the maneuvering thrust required for Cassini-Huygens using positron-electron annihilation, the 3100 kgs of chemical propellant burdening the original 1997 probe could be reduced to a mere 310 micrograms of electrons and positrons – less matter than that found in a single atomized drop of morning mist. And with this reduction in mass the total launch weight from Canaveral to Saturn could easily be reduced by a factor of two.

But positron-electron annihilation is like having plenty of air but absolutely no gasoline ? your car won?t get far on oxygen alone. Electrons are everywhere, while positrons are not naturally available on Earth. In fact where they do occur – near black hole event horizons or for short periods of time after high energy particles enter the Earth’s atmosphere – they soon find one of those ubiquitous electrons and go photonic. For this reason you have to make your own.

Enter the particle accelerator
Companies such as Positronics Research, headed up by Dr. Smith, are working on technologies inherent in the use of particle accelerators – like the Stanford Linear Accelerator (SLAC) located in Menlo Park, California. Particle accelerators create positrons using electron-positron pair-production techniques. This is done by smashing a relativistically accelerated electron beam into a dense tungsten target. The electron beam is then converted into high energy photons which move through the tungsten and turn into matched sets of electrons and positrons. The problem before Dr. Smith and others creating positrons is easier than trapping, storing, transporting, and using them effectively.

Meanwhile during pair-production, all you’ve really done is packed a whole lot of earth-bound energy into extremely small amounts of highly volatile – but extremely light-weight – fuel. That process itself is extremely inefficient and introduces major technical challenges related to accumulating enough anti-particles to power a spacecraft capable of journeying into the Great Beyond at velocities making large space probe – and human spacetravel – possible. How is all this likely to play out?

According to Dr. Smith, “for many years physicists have squeezed positrons out of the tungsten targets by colliding the positrons with matter, slowing them down by a thousand or so to use in high resolution microscopes. This process is horribly inefficient; only one millionth of the positrons survive. For space travel we need to increase the slowing down efficiency by at least a factor of one thousand. After four years of hard work with electromagnetic traps in our labs, we are preparing to capture and cool five trillion positrons per second in the next few years. Our long-range goals are five quad-trillion positrons per second. At this rate we could fuel up for our first positron-fueled flight into space in a matter of hours.”

While it is true that a positron-annihilation engine also requires propellent (typically in the form of compressed hydrogen gas), the amount of propellant itself is reduced to almost 10 percent of that required by a conventional rocket – since no oxidizer is needed to react with the fuel. Meanwhile, future craft may actually be able to scoop propellant up from the solar wind and interstellar medium. This should also lead to a significant reduction in the launch weight of such spacecraft.

Written by Jeff Barbour

Artist illustration of an electromagnetic shield that could protect astronauts. Image credit: Hubble. Click to enlarge.
Opposite charges attract. Like charges repel. It’s the first lesson of electromagnetism and, someday, it could save the lives of astronauts.

NASA’s Vision for Space Exploration calls for a return to the Moon as preparation for even longer journeys to Mars and beyond. But there’s a potential showstopper: radiation.

Space beyond low-Earth orbit is awash with intense radiation from the Sun and from deep galactic sources such as supernovas. Astronauts en route to the Moon and Mars are going to be exposed to this radiation, increasing their risk of getting cancer and other maladies. Finding a good shield is important.

The most common way to deal with radiation is simply to physically block it, as the thick concrete around a nuclear reactor does. But making spaceships from concrete is not an option. (Interestingly, it might be possible to build a moonbase from a concrete mixture of moondust and water, if water can be found on the Moon, but that’s another story.) NASA scientists are investigating many radiation-blocking materials such as aluminum, advanced plastics and liquid hydrogen. Each has its own advantages and disadvantages.

Those are all physical solutions. There is another possibility, one with no physical substance but plenty of shielding power: a force field.

Most of the dangerous radiation in space consists of electrically charged particles: high-speed electrons and protons from the Sun, and massive, positively charged atomic nuclei from distant supernovas.

Like charges repel. So why not protect astronauts by surrounding them with a powerful electric field that has the same charge as the incoming radiation, thus deflecting the radiation away?

Many experts are skeptical that electric fields can be made to protect astronauts. But Charles Buhler and John Lane, both scientists with ASRC Aerospace Corporation at NASA’s Kennedy Space Center, believe it can be done. They’ve received support from the NASA Institute for Advanced Concepts, whose job is to fund studies of far-out ideas, to investigate the possibility of electric shields for lunar bases.

“Using electric fields to repel radiation was one of the first ideas back in the 1950s, when scientists started to look at the problem of protecting astronauts from radiation,” Buhler says. “They quickly dropped the idea, though, because it seemed like the high voltages needed and the awkward designs that they thought would be necessary (for example, putting the astronauts inside two concentric metal spheres) would make such an electric shield impractical.”

Buhler and Lane’s approach is different. In their concept, a lunar base would have a half dozen or so inflatable, conductive spheres about 5 meters across mounted above the base. The spheres would then be charged up to a very high static-electrical potential: 100 megavolts or more. This voltage is very large but because there would be very little current flowing (the charge would sit statically on the spheres), not much power would be needed to maintain the charge.

The spheres would be made of a thin, strong fabric (such as Vectran, which was used for the landing balloons that cushioned the impact for the Mars Exploration Rovers) and coated with a very thin layer of a conductor such as gold. The fabric spheres could be folded up for transport and then inflated by simply loading them with an electric charge; the like charges of the electrons in the gold layer repel each other and force the sphere to expand outward.

Placing the spheres far overhead would reduce the danger of astronauts touching them. By carefully choosing the arrangement of the spheres, scientists can maximize their effectiveness at repelling radiation while minimizing their impact on astronauts and equipment at the ground. In some designs, in fact, the net electric field at ground level is zero, thus alleviating any potential health risks from these strong electric fields.

Buhler and Lane are still searching for the best arrangement: Part of the challenge is that radiation comes as both positively and negatively charged particles. The spheres must be arranged so that the electric field is, say, negative far above the base (to repel negative particles) and positive closer to the ground (to repel the positive particles). “We’ve already simulated three geometries that might work,” says Buhler.

Portable designs might even be mounted onto “moon buggy” lunar rovers to offer protection for astronauts as they explore the surface, Buhler imagines.

It sounds wonderful, but there are many scientific and engineering problems yet to be solved. For example, skeptics note that an electrostatic shield on the Moon is susceptible to being short circuited by floating moondust, which is itself charged by solar ultraviolet radiation. Solar wind blowing across the shield can cause problems, too. Electrons and protons in the wind could become trapped by the maze of forces that make up the shield, leading to strong and unintended electrical currents right above the heads of the astronauts.

The research is still preliminary, Buhler stresses. Moondust, solar wind and other problems are still being investigated. It may be that a different kind of shield would work better, for instance, a superconducting magnetic field. These wild ideas have yet to sort themselves out.

But, who knows, perhaps one day astronauts on the Moon and Mars will work safely, protected by a simple principle of electromagnetism even a child can understand.

Original Source: Science@NASA

The European Space Agency’s Cebreros radio telescope in Spain. Image credit: ESA. Click to enlarge.
On 9 June, a powerful new 35-metre antenna, presently undergoing acceptance testing at Cebreros, Spain, successfully picked up signals and tracked Rosetta and SMART-1. It is ESA’s second deep-space ground station in its class and adds Ka-band reception capability and high pointing precision to the ESTRACK network.

Construction of the new ground station, located in the Spanish province of Avila, has proceeded in record time. Procurement activities started in February 2003, and in spring 2004, on-site work was initiated.

After successful assembly of the antenna structure in November 2004 and the acceptance testing of radio-frequency components, the system is now entering final on-site testing. All portions of the antenna’s infrastructure, including power systems, buildings and communications, are already complete and are ready to hand over for operations.

Tuned in to signals from distant space
Successful reception of signals from the two spacecraft demonstrates that the antenna is working well. Rosetta, Europe’s comet-chaser, is presently 46 million km from Earth while SMART-1 is orbiting the Moon.

Cebreros will be capable of receiving signals in the X and Ka bands. The X band (7-8 GHz) is used for routine telecommanding and to transmit high-volume data to Earth; the Ka band (32 GHz) offers enhanced data reception rates and will be used for future missions.

Additional measurements using radio-emitting stars gave good first results with respect to pointing accuracy and antenna performance, indicating that the station’s specifications will be met.

Full operational readiness of the antenna is anticipated for 30 September 2005, and Cebreros is subsequently scheduled to swing into operation to support the Venus Express mission, scheduled for launch on 26 October 2005.

With Cebreros, Spain, and New Norcia, Australia, ESA spacecraft operations will benefit from two 35-metre deep-space antennas. Future plans foresee the possible construction of a third 35-metre station at an American longitude to become ready by the end of 2009.

ESTRACK family grows
Cebreros is the latest station to join ESTRACK, ESA’s worldwide network of ground stations operated from the agency’s Space Operations Centre (ESOC) in Darmstadt, Germany. Ground stations are used for sending commands to spacecraft and receiving data from onboard instruments.

With Cebreros, there are 8 stations in ESTRACK, located in Europe, Africa, South America and Australia. Additional stations in Kenya, Chile and Norway are available when needed. The system is highly automated and most stations run with little or no manned intervention for routine operations, providing a significant cost benefit.

Original Source: ESA News Release

The Planetary Society’s solar sail prototype Cosmos 1 was launched from a Russian submarine yesterday, but it seems have gone missing. There are conflicting reports coming from Russian news sources that say that the Volna rocket booster failed 83 seconds after launch because of problems with the first stage of its three-stage rocket. This is different from a US team also working to track the solar sail who said they’ve detected it a few times in orbit (link to BBC article).

The Short Radius Centrifuge will test human’s ability to withstand gravity. Image credit: NASA. Click to enlarge.
NASA will use a new human centrifuge to explore artificial gravity as a way to counter the physiologic effects of extended weightlessness for future space exploration.

The new research will begin this summer at the University of Texas Medical Branch (UTMB) at Galveston, overseen by NASA’s Johnson Space Center (JSC) in Houston. A NASA-provided Short-Radius Centrifuge will attempt to protect normal human test subjects from deconditioning when confined to strict bed rest.

Bed rest can closely imitate some of the detrimental effects of weightlessness on the body. For the first time, researchers will systematically study how artificial gravity may serve as a countermeasure to prolonged simulated weightlessness.

“The Vision for Space Exploration includes destinations beyond the moon,” said Dr. Jeffrey Davis, director of JSC’s Space Life Sciences Directorate. “This artificial gravity research is an important step in determining if spacecraft design options should include artificial gravity. The collaboration between NASA, the National Institutes of Health (NIH), UTMB and Wyle Laboratories demonstrates the synergy of government, academic and industry partnerships,” he added.

For the initial study this summer, 32 test subjects will be placed in a six-degree, head-down, bed-rest position for 21 days to simulate the effects of microgravity on the body. Half that group will spin once a day on the centrifuge to determine how much protection it provides from the bed-rest deconditioning. The “treatment” subjects will be positioned supine in the centrifuge and spun up to a force equal to 2.5 times Earth’s gravity at their feet for an hour and then go back to bed.

“The studies may help us to develop appropriate prescriptions for using a centrifuge to protect crews and to understand the side effects of artificial gravity on people,” said Dr. Bill Paloski, NASA principal scientist in JSC’s Human Adaptation and Countermeasures Office and principal investigator for the project. “In the past, we have only been able to examine bits and pieces. We’ve looked at how artificial gravity might be used as a countermeasure for, say, cardiovascular changes or balance disorders. This will allow us to look at the effect of artificial gravity as a countermeasure for the entire body,” he added.

The research will take place in UTMB’s NIH-sponsored General Clinical Research Center. The study supports NASA’s Artificial Gravity Biomedical Research Project.

“Physicians and scientists from all over the world will travel to UTMB to study the stresses that spaceflight imposes on cardiovascular function, bone density, neurological activity and other physiological systems,” said Dr. Adrian Perachio, executive director of strategic research collaborations at UTMB. “This is an excellent example of collaboration among the academic, federal and private sectors in research that will benefit the health of both astronauts and those of us on Earth,” he added.

The centrifuge was built to NASA specifications by Wyle Laboratories in El Segundo, Calif. It was delivered to UTMB in August 2004 and will complete design verification testing, validation of operational procedures and verification of science data this spring. The centrifuge has two arms with a radius of 10 feet (3 meters) each. The centrifuge can accommodate one subject on each arm.

Paloski has assembled a team of 24 investigators who designed the study. The first integrated research program is expected to end in the fall of 2006.

Original Source: NASA News Release