We in the Space Sciences Laboratory at Marshall Space Flight Center receive many questions about the space sciences (and space flight and propulsion, and many other topics). This Q & A in Science page documents the questions and our responses. If you have a question that is not addressed here or on another of NASA's FAQ sites, please send email to our science communications team via our question form.
Other NASA FAQ sites:
NASA FAQ (Headquarters Public Affairs Office)
Comet
Hyakutake
Hubble
Space Telescope
Kuiper
Airborne Observatory
Live
from Other Worlds
Online
from Jupiter: Questions on the Solar
System's largest planet and the Galileo mission.
Spacelink: What's available on NASA's main online resource
for teachers.
TOPEX/POSEIDON: Questions on El Niño, oceanography and
the U.S.-French satellite.
Space Images
I would like to place a beautiful picture of the sun on my home page. Could you mail me a suite of pictures so that I can choose? I have visited your organizational site but I could find only an X-Ray image. I shall be grateful for your help.
Okay, we *do* have some pictures on line. Some solar images can be found at http://science.msfc.nasa.gov/ssl/pad/solar/mssta.htm, taken with our rocket-based X-ray telescope. Some of the colors look odd - they were chosen to reflect the temperature of the emission - and are not necessarily what the human eye would see.
Goddard Space Flight Center also has some nice pictures taken with SOHO, at http://sohowww.nascom.nasa.gov/synoptic/
Another location of full disk (and a sequence of images of the May 94 annular eclipse) can be gotten from our colleagues at National Oceanographic and Atmospheric Administration at: http://www.sel.noaa.gov/index.html (The Solar Environment Lab in Boulder Colorado).
Well, I couldn't find exactly what you describe, but I have a few interesting things for you to look at.
First, Marshall's mission operations team has a shuttle tracking program that shows you, using updated vectors, the shuttle's current position in orbit (if it's in orbit, that is). You can also select from a number of other satellites, and view their current positions. The program requires (at a minimum) a java-capable browser. You can try this program at http://liftoff.msfc.nasa.gov/RealTime/JTrack/. (The mission operations home page is also an interesting site to visit. It's at http://liftoff.msfc.nasa.gov/)
A search of the Johnson Space Center found some very interesting movies, although perhaps not exactly what you're looking for. Try http://shuttle.nasa.gov/sts-76/video/animate/ which has movies of the shuttle docking and undocking with Mir, and other events. These are either "mpeg" or "avi" movies from 1 to 4 Megabytes in size. If you need a viewer, go to http://browserwatch.internet.com/plug-in.html which will help you locate appropriate software for your system.
To locate all of Johnson Space Center's movies, go to http://shuttle.nasa.gov/ind_list.html, and enter "movie" and press the search button.
I would like permission to use some TV news footage of an Endeavour launch in a documentary programme for television on the subject of the Square Rigged Sailing Ship The HMS BARQUE ENDEAVOUR.
The usage would be incidental and visually support reference to her namesake spacecraft.
Can you please put me in touch with the appropriate department.
NASA has copyright on the use of its emblem, the "NASA meatball." However, NASA does not assert copyright on any public material produced by the Agency in support of the civilian space and scientific research effort. Proper credit for the source of re-used information is requested. For the official NASA position on reuse of material, go here.
Where can I download NASA images online?
NASA has an enormous photo archive, which is stored at various facilities. We are making a tremendous effort to put many of these photos online, and make them accessible from one area on the web - the NASA Image Exchange. As of December 1997, the reachable repository holds about 300,000 images. The NIX provides a search engine for finding what you want. Good luck!!
Astronomy
What is the Sun to a star ratio of luminosity from the reference point of Earth?
"Luminosity" is a term used to define the total energy outflow (power) from a star. This number is not dependent on distance from Earth - it's an absolute number.
Luminosity
Stars range in luminosity from utter black (no luminosity) to extraordinarily brilliant (massive blue-white stars) to unbelievable (quasars, if quasars are even stars, that is!). So any ratio is dependent on the star you pick to compare our Sun to. Our sun is a smallish star - a "dwarf" - burning hydrogen in the main phase of its life, called the "main sequence," and is classified as a G2 V star. According to my book (Astrophysical Quantities), it puts out energy on the order of 3.828x10e26 (that's 10 raised to the power of 26) watts - quite a light bulb!.
The brightest star, not including the Sun, is Sirius (in the constellation Canis Major). I picked Sirius to compare to because 1) it's bright as seen from Earth, and 2) it is a lot like our Sun, only more massive (approximately 6.3 times bigger than our Sun). The more massive a star, the hotter it burns. So Sirius (classification A1 V) , like the Sun, burns hydrogen on the main sequence, but burns hotter and hence puts out more total energy than our Sun - more than a thousand times more!
vs. Magnitude
If you want to talk about apparent magnitude (a measure of brightness of a star as viewed from Earth), it's pretty obvious the Sun's a lot brighter than any star, simply because it's close by. In numbers, the Sun's apparent magnitude (as seen from Earth) is -26.74. Compare this to Sirius, at -1.42. This is a logarithmic (base 2.5) scale, so the Sun is about 2x1011 (that's a 200,000,000,000 - two hundred trillion!) times brighter than Sirius, as seen from Earth. (Negative magnitudes are brighter; and a logarithmic scale means a single digit change in magnitude represents an approximate 2.5-fold change in brightness!)
If the two stars were equally distant, however, Sirius would beat out the sun in brightness by (can you guess?) about a thousand! (absolute magnitude of Sun: +4.83 vs absolute magnitude of Sirius: +1.45)
Part of the answer to your question is at
http://science.msfc.nasa.gov/newhome/help/glossary.htm
search for "electromagnetic spectrum." Be aware that there are no hard cut-offs that differentiate one band of radiation from another. For instance, "soft" gamma rays are often referred to as "hard" X rays.
The answer to the last two questions may take a little research - production of various types of radiation is accomplished a myriad of ways. You could look up stellar evolution - at various periods in a star's life (especially a massive one), a star produces lots of radiation covering much of the EM spectrum. The processes that produce various forms of radiation coming from a star should be documented in a good text on stellar evolution. You can also read some of the previous stories we've posted on the web. They are archived at http://www.ssl.msfc.nasa.gov/newhome/pad/padheadlines.htm. There are a number of stories dealing with the radiative effects of astronomical processes.
Production of the gamut of (primarily lower-energy) radiation on Earth is done lots of ways - from light bulbs to radio transmitters to microwave ovens to x-ray machines to atomic bombs to natural decay of unstable elements in the Earth's crust. You should have fun discovering the many ways to produce different radiation bands on Earth.
By the way, if you figure out what causes gamma-ray bursts (the kind our scientists see coming from the edge of our universe) let us know. That's one of the mysteries of the cosmos - and we're *very* interested. (check out http://www.ssl.msfc.nasa.gov/newhome/pad/cosmos_today.htm)
I live in Caracas, Venezuela. In recent days I went to the movies to see Contact, and I fell in love with the space and stars. Now I'm looking for a guide, or a map, I don't know which, in order to recognize the stars and constellations. I figure there are some maps on the Internet but I can't find them. If you can help, I'll be very grateful.
Sincerely
For an excellent monthly magazine showing a skymap, try subscribing to Sky and Telescope. Their web site is http://www.skypub.com/ They do not publish their sky maps on the web, which show the constellations. They do maintain a text description of interesting sky phenomena each month. Their subscription information is at http://www.skypub.com/s_t/s_tsubs.html.
An on-line sky map drawing program is available from the Osservatorio Astrofisico, Istituto di Astonomia, Catania, Italy. It will allow you to select your location and time for viewing the sky and will draw a sky map for you. The program draws an "altazimuth" view, or altitude and azimuth. The azimuth is the angle from the viewer's northern point of the horizon eastward, and altitude is the elevation above the viewer's horizon (90 degrees is straight up). It's at http://www.ct.astro.it/planetario/skyformori.html.
Next, there's a site that sells skymap drawing software: http://www.skymap.com/ . A shareware version of software for drawing skymaps can be obtained from http://www.gamesdomain.com/tigger/pc/skymap.html. You can download a 30-day trial version.
Off-line, I'm sure there are a multitude of books at your library that you can borrow that will show you sky maps and the constellations for Caracas that will get you started. If you have a pair of binoculars, they are really great to help you start looking up!
There is also an online list of world-wide planetariums, maintained by the International Planetarium Society, at http://sunsite.unc.edu/ips/planetariums.html. (But Venezuela apparently has no members in this society!)
Planets never exactly line up, but even if they did, the consequences for Earth are virtually nil. Planetary alignments have occurred in the past (most recently a 5 planet "alignment" in the 1980s) and will occur in the future. The sun and moon exert a much greater gravitational force on Earth than all the planets together, even in a "perfect" planetary alignment.
For additional information, you can read the following: http://www.earthsky.com/1996/es960708.html, which is an excellent Earth&Sky presentation on planetary alignments and what they mean.
Some other interesting reading, both from the Jet Propulsion Laboratory:
http://www2.jpl.nasa.gov/files/releases/chinacal.txt on the origin of the Chinese calendar
http://pdc.jpl.nasa.gov/Mariner10/ch1.html inner planet orbital geometry
I was just wondering what the angular speed of our galaxy is. I am aware that not all of the stars have the same speed around the galaxy's axis. It would suffice me to know just about our sun's speed around the galaxy.
Since the Galaxy is not a rigid object (like a record on a record player), the angular velocity varies from the center of the galaxy out. In the Solar neighborhood (i.e. our Solar System), the rotational velocity about the center of the Milky Way Galaxy is about 250km/sec (Allen/Astrophysical Quantities).
What is an Aurora? What causes them?
The Aurora is the more scientific name for what we usually call the "Northern Lights." There are actually two aurora, one in the northern hemisphere, or the "aurora borealis," and one in the southern hemisphere, called the "aurora australis."
The aurora is an interaction between charged particles like electrons and the Earth's upper atmosphere. These high-energy charged particles strike the atmosphere and cause it to glow. Generally you can only see the northern lights from very extreme northern latitudes, such as Canada, Alaska, Scandinavia, or in northern Russia. The Earth's magnetic field is the mechanism that causes aurora to be confined to the north and south regions of the globe. Charged particles like electrons are guided along the Earth's magnetic field, just as your compass is guided to point north by the magnetic field. At the poles, these particles become concentrated and collide with the atmosphere and each other, creating the beautiful light display that we can see from the ground.
Occasionally you can see this phenomena from much further south. These rare occurrences happen when large "storms" or increases in the intensity of the solar wind causes many more particles than normal, and a larger distribution of energies, to strike the Earth's magnetic field. The general result is a disturbance that creates a larger and more dynamic light show that can be seen from lower latitudes, like Chicago, Seattle, Cleveland, and so-forth.
We track the Earth's aurora in real-time using our Ultraviolet Imaging instrument aboard the Polar spacecraft. These images detect the aurora on both the day and night side of the earth, and are located on the front of our WWW page, as you may have seen. By looking at the response of the aurora, we can better understand the physics of these particles, their interaction with the Earth, and how they help to create the "weather" in space.
If you are interested in talking directly to a scientist who studies these auroral images, I'd recommend Dr. Jim Spann from our laboratory here in Huntsville. He can be reached by e-mail at jim.spann@msfc.nasa.gov.
Astronauts and Life
Sciences
Because children or teenagers are not able to make legal "informed consent" decisions, NASA is unable to recruit minors, eager and capable as they are. Children are our best investment in the future and to consider using them (however willing they may be) for research is not possible.
At this time, NASA can only recruit adults for the space program. So keep your interest up! You'll be an adult before you know it!!
An excellent educational web resource for many branches of NASA research is Spacelink at http://spacelink.nasa.gov/
One of their links that may help you is in the "instructional materials" section, at:
http://spacelink.nasa.gov/Instructional.Materials/Curriculum.Support/Life.Science/ - although it depends on sunlight as its first-line energy source. Perhaps your students can dream up alternative energy sources if sunlight from our sun is not available. Your project is not only applicable to that time when our sun is extinguished (maybe 10 billion years from now or longer), but could apply to long-term interstellar space travel - the slower-than-light speed kind that doesn't depend on warp drive!
I would like to know how the astronauts were able to run for exercise in the spaceship. How were the effects of gravity countered so that this was possible?
They use resistance. For the full story, check out http://liftoff.msfc.nasa.gov/academy/astronauts/exercise.html
What is it like to be an astronaut? Do you have any journals online?
Great question! Only a few people each year get to experience the thrill of space travel; many go on to give talks, which audiences never tire to hear. As it happens, our own Dr. Fred Leslie flew on board STS-73 in October, 1995. Fred prepared a web story of all his experiences as an astronaut (full story), as well as a "frequently asked questions" section. Enjoy!
My son asked me what would happen to a human body if it were ejected into outer space from the shuttle? Would it explode, freeze or what? I've asked around and been to the library but can't find a resource. Can you help?
The basic answer to your question is that if someone (accidentally, I hope) is ejected into space without a suit, he develops the bends. That is, human blood will boil as nitrogen disassociates from the blood and creates bubbles in the bloodstream. It's exactly same problem deep-sea divers have if they surface too quickly.
There are lots of other effects: the lungs expel air; the body is, if in a shadow, cooled, or, if exposed directly to the sun, heated and irradiated with lots of radiation. It wouldn't explode, though. Johnson Space Center is the center for life sciences for NASA; try viewing their site (for kids) at http://lsda.jsc.nasa.gov/just_for_kids.html
A NASA fact sheet on space suits has
been prepared by Johnson Space Center at
http://www.jsc.nasa.gov/pao/factsheets/wardrobe.html
You can also find out what NASA is doing
about preparing to support human life in space, at
http://augusta.msfc.nasa.gov/ed61/papers/rp1324/rp1324.html
I was wondering where I could locate what the effects of a low/no gravity environment has on a human. And are there any plans to test fetal development in space of a living organism?
The effects of spaceflight on a human are widely varying, and only understood to similar varying degrees of detail. This is the primary reason why NASA is interested in pursuing aggressive research into the biological effects of spaceflight on humans.
In general, you'll find that if you fly in space, your body fluids are redistributed for the first few days, since your heart no longer has to pump against gravity. Many of the astronauts experience stuffiness in their head, plump faces, and "bird legs," due to the redistribution of fluid. After awhile, the body works itself out and things kind of get back to normal. However this comes at the cost of an overall loss of fluid to the body, and documented calcium loss, as well as effects on the blood and immune systems. Since I'm not a medical doctor, and have no first-hand spaceflight experience, I wouldn't want to get into too many physiological details. However I'd recommend that you send a message to the folks at Johnson Space Center, where all of our space life-sciences research is directed. They have an upcoming shuttle mission called Neurolab, which is designed to study the spaceflight effects on the neurovestibular system, and can answer your detailed questions about the development of a fetus in microgravity.
I do know that in the late 1960's or early 1970's, the Russians actually flew a pregnant woman cosmonaut onboard one of their early missions. She did a spacewalk, if memory serves me correctly, and the baby was born quite normal.
I am doing an essay about the effects of microgravity on the human body. I was wondering why red blood cell mass and red blood cell count are decreased inflight and post-flight and I also was wondering how T-cell function is affected in space.
Good questions, many of them are currently the subject of much research in the life sciences areas at NASA. Unfortunately you have reached an astronomer, but I'll answer these to the best of my ability and also offer you with a few leads.
The red blood cell (or erethrocyte) mass is indeed depleted, as previous space flight studies have shown consistent reductions in the circulating red cell mass and blood plasma volume of crew members. Scientists postulate that when microgravity causes fluid to move toward the head, the body perceives an increase in fluid and reduces body liquids such as blood plasma. This results in an increased proportion of solids, such as cells, to plasma in the blood. Thus, the body may try to reduce what it perceives as too many erythrocytes.
A decrease in red blood cells may impair a crew member's ability to function with full efficiency upon return to Earth. While red blood cell loss has been clinically insignificant, doctors consider it a potentially adverse response that may require control during inflight illness or injury, repeated space flights, and long- duration missions. If the body adjusts to microgravity and produces a normal quantity of blood cells, there may be no problem created by lengthy stays in space; however, if the reduction grows more severe with longer space trips, investigators will have to determine why.
I'm not terribly sure of the specifics on the behavior of T-Cells, however in the area of the immune system in general, analyses of lymphocytes from crew members on the first 12 Shuttle flights revealed decreases in the number of circulating lymphocytes; postflight results showed that the lymphocytes were not as effective in responding to challenges. However, astronauts have shown no increased susceptibility to disease, and white blood cell counts return to normal a few weeks after landing. Still, these changes in the immune system must be understood and controlled because they could have undesirable consequences on longer missions. Space flight may reduce white blood cell counts and effectiveness either because microgravity causes a decrease in lymphocyte production or because the stress of space flight alters cell counts or function. (Studies on Earth strongly suggest that the body's lymphocyte count is lower during periods of increased stress.) Researchers have conducted most previous immunology studies pre- and postflight, but it has been difficult to separate the direct effects of microgravity from the indirect effects resulting from the stress of postflight recovery. An experiment flown on Spacelab 1 contributed substantially to understanding the immune system's operation in space.
For more detailed information, I would recommend contacting the folks at Johnson Space Center regarding their life-sciences investigations. You'll also find a wealth of information on NASA's Spacelink service, which can be accessed at http://spacelink.nasa.gov. Simply type in the topic your interested in, and you'll get much more information than you probably need!
We do very little life-sciences research here at NASA/Marshall. Most of the NASA life-science activity is handled by the Johnson Space Center in Houston, Texas, since that's where all the astronauts are based. I did, however, find a few contacts for you to whom your questions may be directed.
The ENTIRE Life Sciences Data Archive is on-line at JSC, just type in the URL
and you should be able to find what you are looking for in this resource. However, should you not be able to find something in there, they have a feedback page for e-mail, and, the director of the life sciences research laboratory may be reached by telephone at:
Director, Life Sciences Research Laboratories, code SD3, (281) 483-4401.
Physics and Space
- spacecraft
During the Apollo missions, did the Apollo spacecraft receive an assist in terms of energy by orbiting the earth before making translunar insertion; i.e.: would it have taken more fuel to go directly from launch to translunar insertion without orbiting the earth? Is this an example of the much ballyhooed sci-fi term "sling shot effect?"
This is a great question, and a tough one to answer. First, we'll talk about Apollo, and then, some of the interplanetary probes, which are given a boost using the "sling-shot" effect. (NASA engineers actually call it a "gravity assist" - but we know what it really is!!)
Apollo
(An orbit is defined as the path of a celestial body or man-made one as it revolves around another body.)
Objects orbiting Earth do not receive extra energy by merely orbiting. However, all Earth objects do have a certain amount of energy from earth's rotation itself. Most spacecraft are launched in the direction of the Earth's rotation (west to east). Although we can launch and orbit spacecraft in the other direction (called a retrograde orbit), it takes more energy, and isn't done except for very specific reasons.
If you consider the energy the Earth's rotation gives a spacecraft to get to orbit as a constant, then it makes it easier just to consider the extra energy required to get it to the moon. The rockets themselves (Saturn V from ground to earth orbit; Saturn 1B, for translunar insertion) supplied this extra required energy to achieve (Earth) escape velocity and propel the spacecraft toward the Moon.
The primary reason the Earth-Moon shots were not all done at once is, to put it ungracefully, slop. The physics of calculating and achieving an Earth-Moon trajectory is reasonably straightforward, but the practice of making man-made objects behave perfectly the first (and only chance) is not. The word slop doesn't do this complicated maneuver justice! To be sure the spacecraft and astronauts made it safely, the Apollo spacecraft were put into a parking orbit around Earth for final systems checkout and navigational calculations before translunar insertion. If any systems appeared to be failing, a near-Earth abort of the mission would have been much easier. (Too bad the imminent failure of the oxygen tank on Apollo 13 was not detected from the parking orbit!!)
From a pure physics point of view, it takes slightly less fuel to launch a direct earth-moon shot as it does to do it in stages, even if the staged orbital burns are done along the path of least required energy. The reason is that orbits of objects directly after launch are elliptical, and must be circularized before translunar insertion. (Circularization permits the needed slop, making check-out of systems easier and giving greater latitude in performing the calculations for translunar insertion.)
Interplanetary Probes
(In physics, the term velocity specifically refers to the speed and direction an object is travelling. And the measurement of velocity is relative to the observer. If we treat the solar system as the observer's "frame of reference," it makes sense to look at interplanetary spacecraft motion from the point of view of the Sun, which is the center of the solar system.)
And the answer is... yes! The "sling-shot" effect has been used to change velocity of interplanetary probes!! The gravity of the nearby planet is used to change both elements of the velocity of the spacecraft - direction and speed. The spacecraft actually gains momentum by the encounter! How? Well...
During the gravitational encounter with a planet, the probe is dragged along the planetary orbit (around the sun) for a bit before effectively passing beyond the planet's gravitational reach. This would tend to speed up the probe if the approach is from behind the orbit. Approach from the "front" of the orbit would tend to slow the probe down (remember to view this from the point of view of the Sun!). Interestingly, (and strictly according to Sir Isaac Newton) the planet is slowed down by the encounter by a microscopic amount (inversely proportional to its mass) - but the probe is significantly sped up - since it's so much smaller than the planet - you notice it! Depending on where the probe enters the planet's effective gravity field, and where it exits, the probe's direction can be changed, too.
This effect not only saves on fuel, it probably made all of the interplanetary missions feasible, since the orbits were calculated so as not to require gobs of on board fuel to make the journey. Voyager was the first to make use of this effect - it was first thought of in the 1960s!
Finally, JPL has an interesting site related to Galileo's use of gravity assists to get to Jupiter, and you can find it here: http://www.jpl.nasa.gov/galileo/trajstuff.html.
If you're in a space vehicle traveling at a meager 1000 Km/hr and you immediately do a "U-turn", what kind of forces would the spacecraft and the pilot feel?
It depends how fast the U-turn is. The number of "g's" felt is equal to the change in velocity divided by the how long you take to do the turn. And that's true whether you're in space or on the ground.
If you turn instantaneously, i.e. in 0 seconds, the acceleration would be infinite - not a pretty sight. The shorter time you take to make the turn, the greater the "g's".
Let's use numbers. Let's say you're going 1000Km per hour and you want to turn completely around and go minus 1000Km per hour, and you want to make the turn in 1 second. The acceleration due to the change in velocity over time is 2000Km/hr (divided by) 1 sec, or, 556m/sec/sec. 1 gravity (or 1 "g") at sea level is 32feet/sec/sec (or, converting units, 9.75m/sec/sec). Dividing 556 by 9.75 gives you approximately 57 g's. That is, for one second, you'd feel more than 57 times heavier than usual. Still not a pretty sight.
Both the spacecraft (or vehicle, or whatever) and the pilot would "feel" the same acceleration - 57 g's.
Aside: The "force" on an object is actually the acceleration (number of g's) multiplied by the "mass" of the object. So there would be a greater total force acting on the vehicle - unless it's made of aerogel. However, I think people have a more intuitive feel for what it would really "feel" like if you just talk about "g's".
The answer to both your questions is yes. For example, the Long Duration Exposure Facility, a free-flyer launched by the shuttle Challenger in April 1984, and picked up and brought back to Earth several years later, was struck by numerous micrometeors. A technical analysis of many of those impacts can be found in the paper
ELEMENTAL ANALYSES OF
HYPERVELOCITY MICROPARTICLE
IMPACT SITES ON INTERPLANETARY DUST
EXPERIMENT SENSOR SURFACES
which is on the web at NASA's Langley Research Center:
http://dbdev.larc.nasa.gov/ldef/IDE/REFERENC/CGSLD2CH/CGSLD2CH.HTM
A "hypervelocity microparticle" is a tiny piece of space dust travelling very fast with respect to what it hits. Most people would call such a particle a "micrometeor" or "micrometeoroid." The paper above states that they have thoroughly analysed 79 such hits from the LDEF, and further analysis of their locations on the LDEF show bursts of hits which were related to LDEF passing through orbital dust clouds (which are often left by passing comets). Even more interestingly, they found there were lots of hits they could not ascribe to astronomical sources of micrometeorites. Chemical analysis from the tiny craters showed most of the hits were actually residue from manmade debris!
None of the micrometeorites which hit LDEF were bigger than about 50 micrometers (.000050 meters or less than .002 inches) in diameter. Numbers: Out of 79 carefully analysed impacts, 57 were caused by micrometeors of less than 3 micrometers in size, 18 were less than 20 micrometers, and only three were between 30-50 micrometers). The LDEF was in low-Earth orbit for at least four years, so you get an idea that larger impacts would be few and far between.
So yes, spacecraft are struck by meteors pretty regularly. The larger the meteor, the greater the danger. Fortunately, most of them are small, and do not have enough energy to penetrate the hulls of spacecraft. And none (that I know of!) as yet has penetrated an Astronaut's space suit.
NORAD also keeps track of thousands of larger space debris items (e.g. abandoned satellites, pieces of stuff that were lost from previous flights, etc.) The ones that can be tracked from the ground indeed present a danger, and shuttle orbit planning takes into account the orbits of such space debris.
Can you tell me where I can find information on the effect of weightlessness on Gyros? Also, do you know why a spinning gyro resists having its axis moved? If so, can you explain why in relatively simple way?
A spinning top is like a gyroscope in that it tends to keep spinning in the same orientation the spin started. On the ground, precession of the top is caused because gravity is pulling the top toward the center of the Earth. Any imperfection in the spin (which always happens, because something will cause the top to wiggle - like friction between the point of the top and the ground, or imperfections in the balance of the top, or a breath of wind. If nothing else, on Earth, friction will always cause a top to fall away from a perfect spin. (A "perfect" spin is where the orientation of the spin axis is is exactly parallel to the force on the top from gravity.)
Once a top begins to fall away from parallel, it will wobble about the spin axis. This is called precession.
See http://www.projmath.caltech.edu/mu120.htm for a concise explanation of a precessing top and a diagram.
In free-fall orbit, where one has nullified the effects of Earth gravity, a top (or other spinning object) will still probably precess if any perturbations to the spinning occur. In a perfect environment - no drag, no apparent external forces (like the ones used to re-orient a spacecraft in orbit), a perfect instrument and a perfect spin, the top, or gyro, will spin forever with virtually no precession - according to classical, Newtonian mechanics. But nothing is ever perfect - not even Newtonian physics!!
Our story on the relativistic effect of "frame-dragging," at http://science.msfc.nasa.gov/newhome/headlines/ast06nov97_1.htm, scientists at MIT and Marshall determined that space and time near a black hole were indeed being distorted by the rotation of the black hole.
The heart of Gravity-probe B, a spacecraft to be launched into orbit (next year, I believe) is a very sensitive gyroscope which will be used to carry out "laboratory" experiments to directly observe and better understand Einstein's frame dragging effects. The idea is that even if you have as near a perfect spinning environment for your top (or gyro), effects predicted by Albert Einstein will be observable and measurable - the gyro will still wobble!!! (but very slowly)
Check out Spacelink's http://www.spacelink.nasa.gov/NASA.Projects/Space.Observatories/Gravity.Probe.B for more information on this mission.
You can also go to search engines and search on Gravity-Probe B.
As for what makes a gyro "resist" having its axis move - good question! The answer is not exactly intuitive - rotating objects are just not so easy to understand as other moving objects.
The short answer is inertia. It's the
very same thing that makes a car want to keep moving in the same
direction and at the same speed. You have to apply force to either
speed it up, slow it down, or - more pertinent to your question
- turn! Inertia is a basic property of matter, and it's due to
an object's mass. If you feel comfortable with the idea that you
have to apply force to turn a car toward a new direction, then
maybe the picture I drew will make some sense. Take a look, at
http://science.msfc.nasa.gov/publish/topinertia.gif.
Whether you have a spinning object on Earth or one in free-fall orbit - the effect is the same. There is no difference in this behavior on the ground or in space - except friction is a lot harder to avoid on the ground!
Aerogel
NASA is using aerogel to insulate a number of spacecraft and satellites over the next decade, including the recent Mars Rover and forthcoming Comet Return mission.
Commercially available aerogel can be ordered via FAX from MarkeTech International. (This link from NASA does not imply endorsement of this firm or any other! - ed)
Marketech International
4750 Magnolia Street
Port Townsend, WA 98368 Phone: (360) 379-6707
Fax: (360) 379-6907
Email: mkt@olympus.net
Thanks for your email. Aerogel would
make an excellent filler for a fiberglass case, but will lack
the strength and water-repellent aspects required for shaping
a board. There are two kinds, silica and carbon-based, so the
properties can be tuned between different profiles for strength
and resiliency. If you really want to try to play around with
some small pieces of aerogel, I suggest you contact Aspen Systems,
since they are industrial sellers. If you want to try to make
some yourself,
there are a number of candidates which begin as a gel (agarose,
carrageenan, even ordinary gelatin) from which you can air dry
a much denser product called a xerogel. If you are really desperate
for the real silica xerogel, a local pharmacy will probably sell
some sodium silicate gel (used as lubricants, <$5) which can
be gelled and air dried to various products. These will not have
either transparency or be that much lighter than what you are
probably using now.
See also the aerogel home page at http://aerogel.msfc.nasa.gov/ for technical specs and other online information.
The aerogel pore size is nanometer length and typically smaller than the mean free path of various gases. Slow diffusion is possible but the cell structure is definitely open-cell, thereby available for gas passage over time.
The current market for low emissivity (low E) coated triple pane window glass (4 x 6 feet) costs on the order of $500-600 or approximately $20-25 per sq. feet. For transparent aerogel, the cost of manufacture is $3/ sq. foot., thus the addition of aerogel between window panes represents less than 10-15% of total product cost. The thermal performance of the transparent product would be about three times better than current low E triple pane windows, thus defining a cost-effective, high-performance product for existing markets.
Thanks for your science fair inquiry about aerogel. In a high school lab, it is rather difficult to make aerogel since it requires a high pressure vessel and is not particularly user-friendly. There are a number of easier experiments with what is called xerogel, which are silica gels that are air-dried rather than dried at high pressure. While xerogels tend to be much denser than aerogel, they do provide some of the same high temperature insulation and, in the case of future applications, may have as much promise as aerogel for new materials, particularly in the computer chip industry.
The simplest way to make a xerogel is to form a variety of gels and simply leave them out in air to dry. Ordinary gelatin can be an interesting model system and the project can record volume, weight and density variations with time. If you want to venture into silica xerogels, you can buy a jar of sodium silicate gel forming liquid at a local pharmacy for <$5. This is used as a lubricant and is simple to gel as silica. There are also a number of gelling materials supplied by the major chemical companies, with catalogs for Sigma and Aldrich having silica, agar, carageenan, polyacrilamide and other kinds of precursors which could be compared for drying characteristics and various thermal, mechanical properties.
If you are truly desperate for a piece of aerogel, check out MarkeTech International.
Low-Gravity Science
What, exactly, is the definition of "microgravity"?
On the microgravity overview page we define the term Microgravity as:
"Microgravity is a term used by scientists to mean "very little gravity." The effects of gravity aboard an orbiting spacecraft like the space shuttle are reduced significantly compared to what one experiences on the ground..." "...The "gravity" part of the word "microgravity" is fairly obvious. The "micro" part comes from the Greek word "mikros," meaning "small." Commonly it is used in science to mean "one millionth," however a "microgravity environment" is defined as one in which the apparent weight of a system is small compared to its actual weight on Earth. This effect is easily acheived in orbiting laboratories."
The interesting part of this question is that the gravity environment aboard the shuttle is actually constantly changing, as pumps turn on, fan motors whirr, the crew moves around, thrusters fire, and lots of other things happen. So, strictly speaking, one cannot say the gravity environment aboard the shuttle is `x' and leave it at that. Indeed that's why scientists are so interested in measuring the level of gravity and forces on their experiments at all times. Dave Dooling wrote a short piece on this aspect of the mission
On average, the total environment comes out to be around 1/1,000,000 of the gravitational force on Earth, sometimes a bit more, so we use the term "microgravity" to describe it.
How does Microgravity work? How does spinning make fake gravity?
There's really no magic to making a low gravity environment, you simply need to create a condition where an object is in free-fall, just like the shuttle is in it's orbit around the earth. So any time you find yourself in free-fall, such as when you go off the high-dive at your local pool, maybe, you are actually experiencing a low gravity environment. Of course it doesn't last very long, eventually you hit the water and stop your free-fall. You can test this next summer with a tennis ball. After you spring off the board, let go of the ball (don't impart any extra force), and you'll see that it basically stays put relative to your body - it goes up and then down into the water just as you do. Both you and the ball are falling at the same rate, just as Newton predicted, and experiencing low-gravity. If you further imagine that you and the ball are both inside the shuttle, and falling for 16 days (a really high diving board!!!), then you'll get a feel for what the environment in orbit might be like. As you've probably guessed, microgravity is not created by "switching off" gravity like a light switch, but instead by putting one's environment (whether it's the shuttle, or you and the tennis ball) into a free-fall condition, where the effects of gravity can be removed - at least temporarily.
Time is one of the principal obstacles in creating a microgravity environment. On the ground, you can drop things from towers, but even that only lasts a few seconds...and you have to figure a way to make a "soft" landing so that your experiment isn't smashed into a thousand pieces when it hits the ground. In aircraft, we can fly what are called "parabolic trajectories," which basically means that the aircraft pulls up its nose and flies a big arc, similar to the arc your body goes through after leaving the diving board, but on a much larger scale. This will obtain about 30 seconds of low-gravity, because the airplane eventually has to pull out of the dive!!! That's why we like to fly microgravity experiments on the shuttle, to give us nearly two weeks of a free-fall environment that is even better than we can get on the ground. And with MIR and space station, we can go even longer.
As far as spinning things to make "artificial
gravity", gravity is a force, just like any other force you
normally feel, such as when you pull away from a stop sign in
an automobile, taxi down the runway at takeoff in an airplane,
or go up in an elevator. So you can simulate gravity by putting
something in a spinning environment, like a merry-go-round or
centrifuge, where the centrifugal force acts upon the object,
and the object feels the force or "weight" due to the
rotation.
I was just looking at the NASA homepage shuttle web, that's what brought me here. One of the topics is "Why zero-G", it goes on to explain about scientists doing experiments in zero gravity. But in fact isn't there gravity in space? After all, gravity is what is holding the moon in its orbit. Wouldn't it be better to say weightless? The space shuttle and the satellites are in a continual free fall toward the earth, but keep missing the earth, which would appear like zero gravity. In fact, you'd be hard pressed to find any place in the universe which would be a zero gravity situation, right?
You are absolutely correct in your understanding of the nature of gravity in space. The misconception that somehow one goes 100 miles up in the air and gravity disappears is a common one, and something that we try to steer people away from through things like the free-fall tutorial, etc. The result of satellites continually falling yet missing the earth, as you indicated, is an effective or apparent zero gravity environment, not the total absence of gravity as the name "zero-gravity" might imply. If you have any suggestions about the pages and how we might minimize any inadvertent propagation of such a misconception, I'd be interested to hear them and implement them on the science.msfc.nasa.gov pages.
Does hot air rise because it is less dense than cold air and if so, what would a match burning in zero gravity look like, i.e. - what is the effect of gravity on fire?
You're right on when you say that hot air rises because it is less dense than cold air, and indeed a flame in low gravity looks very different than the familiar teardrop shape that we see on birthday candles or on a match. In fact in microgravity, the flame is actually round, as there is no convection to distort its shape. Oxygen has to get to the flame by diffusion, and if the diffusion is not fast enough, the flame may actually go out. A great deal of combustion/burning research was done this summer aboard the MSL-1 mission flown in July, and we actually have many pictures on the MSL site related to combustion. You can find these images and much more information at the following URL:
http://science.msfc.nasa.gov/msl1/
Could you tell me if there is a Journal of Protein Crystal Growth?
Several Jounals are available which publish science articles concerning Protein Crystal Growth:
Many common polymer materials have very different reactions to gamma exposure. Favorable strengthening of polymers can be achieved for example in nylon 6,6 in the MRad range because of polymer cross-linking and free-radical reaction. Degradation can also occur at high doses or if free-radical damage or ozone production becomes too great. I believe the more rigid polymers are less amenable to gamma exposure and seem to recall that polyacrilimides are examples of degrading polymers. There are a number of industry sources for information, but the best place to start is probably government and defense department studies on radiation hardening of plastics.
The original citation was in NASA Tech Briefs,
MFS-28921, April 1995 (paper copies available on request).
Subsequent articles appear in:
"New Toxicity Testing System," High Tech Breakthroughs,
Bottom Line/Business, Nov. 1996 p. 14
There is a discussion of this article with pictures in December 1995 issue of Organic Gardening magazine, p8
I am doing a report on how the USA economy will be affected by a technological revolution that will enhance space technology. What are some of the cutting-edge science discoveries being made today and how will they affect the future?
I would refer you to the web pages at the address below first.
You could classify next generation breakthroughs and their ripple effects in the economy into a couple of classes. Satellite technology for communications, imaging of natural resources, weather forecasting and navigation (GPS) are well-established economic builders. The next generation internet may require as many as 800 satellite launches to truly link the global network across sparsely populated areas. The increase in mobile communications and reconnaissance also may depend on the outcome of the next decade of space technology, somewhat surprisingly with an emphasis on less-developed economies where a single satellite in many cases can be less expensive than the ground infrastructure to support telephone coverage. Increasingly, it is mobile communications that are growing in the Third World because of the infrastructure issue.
Materials science is considered very important to a number of technological bottlenecks, particularly for next generation computer chips, sensors and detectors for medical application and high performance metals and alloys. The National Research Council prioritized materials' science as one of the most serious weaknesses in the current US research emphasis which directly bears on economic growth and competitiveness. Here space research is attempting to use the low-gravity environment in orbit to fashion entirely new materials or to better understand the processes on earth that limit improvements currently. An example here is the making of bulk infrared detecting crystals of sufficient size and purity to image, for example, blood clots or temperature differences in heart disease.
The most substantive breakthroughs may come from biotechnology, as many consider the 1990's and beyond as the biological age. Two areas in life sciences, namely the growth of protein crystals in space for better drug design methods and the study of fundamental human responses to low-gravity, may bear on such issues as osteoporesis, heart disease, AIDS and cancer. There are several references on the web page to specific aspects of these research programs. A bottom line figure has been put together from a number of studies, ranging from several billion dollars in return to numbers as high as $30 billion per year depending on the assumptiosn and growth projections. NASA is currently emphasizing much international cooperation in its research, so the collaboration of many countries is a factor added to this transfer and commercialization of fundamental research in the marketplace. Good luck!
Engineering
Johnson Space Center has responsibility for design of the space shuttle orbiter fuel cells. To search all publically available JSC pages, go to http://shuttle.nasa.gov/find/, and enter your search string. The string "fuel cell" will bring up about 100 links to more information, such as
I also went to Alta Vista (http://altavista.digital.com) and entered a simple search for
and came up with the following (non-JSC) URLs which look appropriate.
NASA:
non-NASA:
There were lots more URLs which looked like they might contain information you are seeking.
I am interested in description of the differences between LCD and LED displays. I would also like to know how many other kinds of displays are available and if color is separate from LCD and LED or if a display can be both color and LCD or LED at the same time. I am speaking in reference to cell phone displays.
The following web sites describe LCD displays and how they work:
http://www.cyberg8t.com/chomp/bytesApr96/Laptop.html
http://plc.cwru.edu/turorial/enhanced/files/lcdindx.htm
The following web site is a web site that reports on Display Technologies in Japan. Included in this site is some information on electroluminescent displays.
http://itri.loyola.edu/dsply_jp/toc.htm
Liquid Crystal Displays (LCD) and Light Emitting Diodes (LED) are used in many fashions for displaying data. The LCD can be black and white or color. The following web site is a manufacturer of an Active Matrix Liquid Crystal Display (AMLCD) which has a miniaturized Liquid Crystal Display.
http://www.kopin.com/index.html
The LED is color only, since the diode emits a particular frequency of light. The early LED’s were red only, but recent times have brought about the development of green and blue LED’s. For displays the multi color LED’s can be placed next to each other much like the RGB dots of a television tube. There is a new technology known as Organic Light Emitting Diode (OLED). This new type of device can allow the different color light emitting diodes to be stacked on top of each other. Thus, instead of having three different color diodes next two each other (like your TV set) they can be literally at the same place. This can lead to higher image resolution. Currently the Universal Display Corporation in partnership with Princeton University, the University of Southern California, and Hughes Electronics are working on developing this technology. This technology is described in the trade journal Advanced Imaging, May 1997 issue.
Miscellaneous Questions
I am a high school student and I am gong to enter the Space Student Involvement Program contest for NASA internships. I am going to enter the Space Transportation field of the contest which concerns the Marshall Space Flight Center. Could you give me more info if you have any or could you give me some help.
Information on SSIP can be accessed through
the Spacelink homepage
then click through the following sequence:
Library
Educational Services
Elementary and Secondary
Programs for Students
Science Student Involvement Program
(Here's a shorcut to all that.)
which is the SSIP that you're looking for. It gives another site that requires a .pdf reader for the announcement and info from the National Science Teachers Assn.
Why is a nautical mile the length it is(6000+)? I have a theory it is based on the distance between longitude lines - any help would be appreciated.
You are right, and a nautical mile is defined as the distance travelled to move one arc minute (1/60 of a degree) on the great circle. In rough longitude, the Earth is about 25,000 miles around at the equator, divided by 360, and then again by 60, you get 1.157 statute miles, or about 6100 feet. Interestingly enough, (or perhaps not!) when the meter was first defined by the French as one ten-millionth of the distance from the north pole to the equator on the meridian passing through Paris, they inadvertently developed an easy conversion between the metric meter and the nautical mile. Since 60 nautical miles equals a degree, there are 5400 nautical miles to the distance between the pole and the equator (on a spherical earth), or by definition therefore 5,400 nautical miles is exactly 10,000 km.
Two current contacts for property disposal at Marshall Space Flight Center are:
205-544-8811
Carolyn A. Landry
Property Disposal Officer
205-544-0846; fax 544-1151
Curator: Linda Porter
NASA Official: Gregory
S. Wilson
