Stockton Astronomical Society
Valley Skies - July 2005 Issue
Rosemary and I are back from our three week trip, visiting friends and family in Oregon, Washington and British Columbia, and touring the Canadian Rockies in Alberta and BC.
In Washington we spent a couple of nights with Jeff and Glenda Baldwin in their new log home. Although we had seen pictures during construction, we had no idea how big this house is. When we walked through the front door our jaws dropped. The living room is huge, with a cathedral ceiling about 35 feet high.
So now we have a better understanding of why they were so frustrated at having to return to Stockton last year, and why they ultimately decided to bite the bullet and go back to their home-in-the-woods.
When we left, Jeff and Glenda extended an invitation to any SAS members who get up to their neck of the woods...north of Forks on the Olympic Peninsula…to "Come on by!" They'll be pleased to have you visit.
Why Deep Impact?
Out beyond the orbits of the planets on the outer fringes of the solar system, a swarming belt of billions of dormant comets circles the Sun. Frozen balls of ice, rocks and dust, they are the undercooked leftovers that remained after a sprawling cloud of gas and dust condensed to form the Sun and planets about 4.6 billion years ago. From time to time, the gravitational pull of other comets or the giant outer planets will nudge some of them out of their orbits, plunging them into the inner solar system, where they erupt with sparkling tails as they loop around the Sun.
One of these nomadic frozen ice balls is the target for NASA's Deep Impact mission. On July 4, 2005, Deep Impact will produce a crater on the surface of comet Tempel 1 that could range in size from a two-bedroom house to the Roman Coliseum. The impact is expected to eject ice and dust from the surface of the crater and reveal untouched, primordial material beneath. While this is happening, the spacecraft's cameras will radio images to Earth of the comet's approach, impact and aftermath.
Data returned from the Deep Impact spacecraft could provide opportunities for significant breakthroughs in our knowledge of how the solar system formed, the makeup of cometary interiors, and the role that cometary impacts may have played with Earth's early history and the beginning of life.
...from NASA/JPL Press Kit
The Science Directorate at NASA's Marshall Space Flight Center sponsors the Science@NASA web sites. The mission of Science@NASA is to help the public understand how exciting NASA research is and to help NASA scientists fulfill their outreach responsibilities.
A Force Field for Astronauts?
by Patrick L. Barry
Researchers are reviving an old but wild idea to protect astronauts from space radiation.
June 24, 2005: 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.
Supernovas produce dangerous radiation.
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?
Artist's concept of an electrostatic radiation shield, consisting of positively charged inner spheres and negatively charged outer spheres. The screen net is connected to ground. Image courtesy ASRC Aerospace.
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.
How the voltage would vary above a lunar base for the sphere configuration shown above.
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.
One scenario for how an electrostatic radiation shield could be deployed for mobile lunar exploration vehicles. Inverted green cones denote regions of partial radiation protection. Image courtesy ASRC Aerospace.
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.
Moving a Mountain of a Dish
By Patrick L. Barry
Your first reaction: "That's impossible!"
Giant Deep Space Network antenna in Madrid is moved using four 12-axle, 24-wheel crawlers.
How on earth could someone simply pick up one of NASA's giant Deep Space Network (DSN) antennas-a colossal steel dish 12 stories high and 112 feet across that weighs more than 800,000 pounds-move it about 80 yards, and delicately set it down again?
Yet that's exactly what NASA engineers recently did.
One of the DSN dishes near Madrid, Spain, needed to be moved to a new pad. And it had to be done gingerly; the dish is a sensitive scientific instrument full of delicate electronics. Banging it around would not do.
"It was a heck of a challenge," says Benjamin Saldua, the structural engineer at JPL who was in charge of the move. "But thanks to some very careful planning, we pulled it off without a problem!"
The Deep Space Network enables NASA to communicate with probes exploring the solar system. Because Earth is constantly rotating, a single antenna on the ground can communicate with a probe for only part of the day, when the probe is overhead. By placing large dishes at three locations around the planet-Madrid, California, and Australia-NASA can maintain contact with spacecraft around the clock.
To move the Madrid dish, NASA called in a company from the Netherlands named Mammoet, which specializes in moving massive objects. (Mammoet is the Dutch word for "mammoth.")
On a clear day (bad weather might blow the dish over!), they began to slowly lift the dish. Hydraulic jacks at all four corners gradually raised the entire dish to a height of about 4.5 feet. Then Mammoet engineers positioned specialized crawlers under each corner. Each crawler looks like a mix between a flatbed trailer and a centipede: a flat, load-bearing surface supported by 24 wheels on 12 independently rotating axes, giving each crawler a maximum load of 194 tons!
One engineer took the master joystick and steered the whole package in its slow crawl to the new pad, never exceeding the glacial speed of 3 feet per minute. The four crawlers automatically stayed aligned with each other, and their independently suspended wheels compensated for unevenness in the ground.
Placement on the new pad had to be perfect, and the alignment was tested with a laser. To position the dish, believe it or not, Mammoet engineers simply followed a length of string tied to the pad's center pivot where the dish was gently lowered.
It worked. So much for "impossible."
Find out more about the DSN at http://deepspace.jpl.nasa.gov/dsn/ . Kids can learn about the amazing DSN antennas and make their own "Super Sound Cone" at The Space Place, http://spaceplace.nasa.gov/en/kids/tmodact.shtml.
This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
Night of the Deep Impact
This image shows how Deep Impact's impactor targeted comet Tempel 1 as the spacecraft made its final approach in the early morning hours of July 4, Eastern time. The autonomous navigation system on the probe was designed to make as many as three impactor targeting maneuvers, identified as ITMs in this picture, to correct its course to the comet.
The upper left dot indicates where the probe would have passed the comet's nucleus if no maneuvers were performed. The dot below the nucleus shows where the probe would have flown past the comet if only the first maneuver was made. The leftmost dot on the nucleus marks the spot where the probe would have crunched the comet if only the first two maneuvers had been performed. The lower dot on the nucleus indicates the vicinity where, once the third maneuver was performed, the probe met its final reward and collided with the comet.
This image was taken by the probe's impactor targeting sensor.
All Images Credit: NASA/JPL-Caltech/UMD
Images and captions courtesy of: http://www.nasa.gov/mission_pages/deepimpact/
Deep Impact Star Party
With great hopes we gathered at the Highway 4 site on July 3rd. Knowing the odds of seeing anything interesting were slim, we were buoyed by the notion that we've never attempted to smash into a comet before, so no one really knew what to expect.
James Schuknecht, well versed in all things skyward, was well-prepared and even came up the night before to clear some of the brush that had trespassed onto our tiny claim on Shirley Road. Pamela Mathers, delightful in her curiosity, and even more so as the foil to James when he got too serious, was there as well. Doug Christensen, a relatively new member who has already committed a good deal of time and effort (and name badges) to the SAS, drove up in his portable planetarium (otherwise known as a convertible). David Dow, and his mother, Raquel, attended as well. David has a telescope that many SAS members helped to make, including Lloyd Altamirano and Jeff Baldwin. We were also joined by Ray (I forgot his last name) from Modesto, who frequents the Shirley Road site. Roger Stark came out, after a long day at work, and a couple friends of mine from the running club, Arie and Bev Hope attended as well. Mary joined me, mostly to keep me company on the way home.
With all of that energy devoted to the introduction, you'd expect to find me reporting something exciting, but as comet hunters, we all proved to be quite inept. We couldn't find a trace of a comet-like object before the appointed time, or after. While searching in vain through the region near Spica, I had visions of all the people in their homes, watching the event on their televisions, with live, up-close images of the collision - while we were out here in the dark looking for some small speck of fuzz in the sky. I felt a bit like the Peanuts' character, Linus, dragging Sally out to the pumpkin patch on Halloween waiting to see the Great Pumpkin, while everyone else was collecting candy.
It was a beautiful, clear night, and we didn't waste it for lack of a comet. We got a good view of a fireworks display down in the valley. We got a glimpse of Mercury before it went down. We looked at a few of the many objects out on a great dark night, including a meteor that seemingly traveled through a 60-degree arc across the sky. Nevertheless, we packed it in around midnight, somewhat dissatisfied that the Deep Impact comet collision had eluded us.
I received an email from Chuck Marble in the early hours of the next morning. His group was also unable to find the comet with their telescopes. Where they outdid us, was that they had a live NASA TV feed on site. What they couldn't see in their scopes, they got to see up close on the monitor.
Oh the indignity of it all. Did I mention we saw a very cool meteor?
Copyright © 2005 by Stockton Astronomical Society
Last Updated: 7/12/2005