Shuttle Parts Falling Off?
Published on Jun 13, 2008 at 12:07 pm.
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Filed under space debris, space shuttle.
A little while ago, I read a report that caught my attention. Apparently, astronauts aboard the Space Shuttle Discovery have reported something floating away from the orbiter. Not long afterwards, astronauts spotted what appeared to be a small protrusion from the aft end of the orbiter’s tail. The NASA image below shows the debris floating away from the shuttle.
The debris floated away from the shuttle after it test fired its thrusters and tested its atmospheric flight control surfaces. It is not uncommon for ice to form around the engine bells at the aft end of the shuttle. And, it is not uncommon for this ice to be dislodged when the Space Shuttle moves. Also, there have been plenty of times when something in the payload bay has not been secured properly and floated out when the shuttle moved. So, in the past when things floated away from the Space Shuttle, NASA officials took notice, but were not overly concerned. However, all that has changed. On its final mission into space, an object was detected moving away from the Columbia after it had reached orbit. Some NASA engineers were quite concerned, especially after ice had been observed striking the Columbia on launch. The people calling the shots, though, didn’t take the matter all that seriously, and the result was loss of the orbiter, along with all astronauts on board. So, now, whenever something floats off from the orbiter, everyone takes note.
However, I am not implying that this is really something to worry about. After all, lots of objects have floated off during previous shuttle missions without the orbiter ever being placed in any danger. So, all that NASA engineers need to do is to determine that this is yet another event of that sort. Then, we can rest easy. But, just what was it that floated off? A clue may be in the protrusion that astronauts saw on the tail.
According to a report from Space.com, the object is now believed to be a metal clip from the area around the orbiter’s speed brake. If that is indeed what the object is, then its loss poses no threat at all to the Space Shuttle. These clips have come off many times before on previous missions, always without any ill effect for the Shuttle. The clip helps to provide thermal protection to the back end of the orbiter’s tail during launch. For a short time on the launch pad as the engines are firing up, the back end of the shuttle is exposed to quite high temperatures. This clip is one of several devices used to protect against that heat. It does nothing of any importance during reentry or landing, so its loss is nothing to worry about. At present, losing the clip is only an issue because it means yet another piece of space debris is orbiting the Earth for a while.
So, what about that protrusion? Apparently, the protrusion is believed to be an artifact of the lighting and the camera rather than an actual protrusion. In that case, it isn’t really even there, so it is not an issue. Another thought had been that it may be a bit of thermal insulation sticking out. If so, it still would not have posed a threat. It may have produced a tiny bit of drag in the area once the shuttle has slowed to regular aircraft speeds, but nothing much to worry about. This is not an area of extreme heating during reentry.
So, in short, there is probably nothing to worry about.
-Astroprof
Images courtesy NASA TV
CoS 58
Published on Jun 13, 2008 at 11:31 am.
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Filed under blogging.
This week, the 58th Edition of the Carnival of Space is being hosted by Fraiser Cain over at Universe Today. Unlike many of the recent Carnivals of Space, where some big news story dominated everyone’s blogging, this week’s entries range all over the map. There are links to blog postings about suggestions for first telescopes, Jupiter’s moons, spacecraft, spacesuits, cosmology, model rocketry on Mars, the Aurora, and even some photographs taken years ago by Apollo 17 on the surface of the Moon. So, go on over to the Carnival and check out these various writings.
-Astroprof
Venera 4
Published on Jun 12, 2008 at 4:46 pm.
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Filed under history, space exploration.
41 years ago, on June 12, 1967, a modified R-7 rocket lifted off from deep within the Soviet Union carrying a spacecraft to another world. The spacecraft was Venera 4, and it was on its way to Venus. Venera 4 was not the first spacecraft to arrive at Venus. That honor goes to the American Mariner 2 spacecraft, launched in 1962. But, Mariner 2 just flew by Venus. Venera 4 was destined to actually enter the planet’s atmosphere.
As the name implies, Venera 4 was not the first spacecraft that the Soviet Union sent to Venus. However, it was the first one to work as expected. Contact with Veneras 1 and 2 was lost as they were en route. Venera 3 had arrived, but contact was lost before it entered the atmosphere, so it sent back no data from the most important part of its mission. Soviet scientists knew that these first spacecraft to Venus had no chance of landing, but the goal was to enter the atmosphere and send back as much data as possible before the spacecraft was destroyed.
Venera 4 worked nearly flawlessly, making it the first spacecraft to perform in situ studies of another planet’s atmosphere. On October 18, 1967, after four months traveling through space from Earth to Venus, the Venera 4 atmospheric probe made its dive into the atmosphere. It deployed a parachute to slow its descent. It then used thermometers, a barometer, and gas analyzers to monitor the atmosphere as it descended. Contact was finally lost at an altitude of about 25 kilometer. The pressure and temperature on Venus are fatal to most spacecraft, and Venera 4 undoubtedly was crushed long before making it to the surface of the planet (though the first reports released by the Soviet Union had claimed that the craft had actually landed intact on the surface of the planet). Even if it had not been crushed, the heat would have destroyed the electronic circuitry of the craft.
Interestingly, Venera 4 wasn’t alone in its trip to Venus. Launched two days later, America’s Mariner 5 spacecraft also was on its way to Venus, flying by on October 19, one day after Venera 4 had arrived.
Today, with the amazing images coming back from Phoenix and the other successful space missions, we tend to overlook these important first steps in planetary exploration. But, without spacecraft like the early Venera series or the Mariners, we wouldn’t be where we are today in planetary exploration.
-Astroprof
Image Credit: NASA, NSSDC
Plutoids
Published on Jun 11, 2008 at 12:40 pm.
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Filed under planets, solar system.
We have yet another new word to describe some of the things out there beyond Neptune: Plutoids. As you may recall, a couple of years ago, the International Astronomical Union finally defined the word “planet.” It was something of a shock to many people in the public, but astronomers had never actually come up with a definition of “planet” in all these years. Originally, planet meant a “wandering star.” That would be a star that appeared to move from constellation to constellation. Five of them were known. The Sun and Moon also moved around in the sky, so they were often considered planets by the ancients. Eventually, astronomers realized that all of the planets and Earth moved about the Sun. Soon, it became apparent that Earth belonged in the group of bodies known as planets. Then, Uranus was discovered. Then, Ceres, Pallas, Vesta, and Juno were found. Neptune was discovered. All of these were called planets. But, then more and more planets were found between Mars and Jupiter. Eventually, astronomers realized that these bodies were far too small to fit it with the rest of the planets, so they were removed from the list. Then, Pluto was found. At first, astronomers mistakenly thought that it was far bigger than it really is, so it was placed on the list of planets. Eventually, we found that it is really quite small. Then, other bodies similar to Pluto in size and composition were found far beyond Neptune.
For some years, astronomers had expected to find icy things out there. Gerald Kuiper had proposed that there should be a large reservoir of these bodies beyond the farthest planet, much like an icy asteroid belt. These bodies, when their orbits are disrupted into highly elliptical orbits that bring them near the Sun would appear as comets. This is proposed to be a separate reservoir of icy comet nuclei than the Oort cloud. Kuiper’s hypothetical reservoir of comets became known as the Kuiper Belt. Finally, in the 1990s, the first of these Kuiper Belt objects was found. Then, more were found. Then, more. The first few were small, but then astronomers started finding larger ones. Some were nearly the size of Pluto, in similar orbits, and of nearly the same composition. This soon sparked a debate as to whether or not Pluto should be on the list of planets. After all, it was to these other bodies what Ceres was to the objects that became known as asteroids. Astronomers proposed several names for these bodies (including Pluto). Among the ones that I have heard have been: Kuiper Belt Objects (my preferred one), Centaurs (because the first few were named for centaurs), Plutinos (proposed by the team that found the first one past Pluto), Plutons, (a proposed category that never caught on), and Trans Neptunian Objects (the title of most of the AAS sessions on these bodies).
The whole matter came to a head, though, when an object larger than Pluto was discovered out there. That body, now known as Eris, triggered the International Astronomical Union (IAU), the professional organization of astronomers, to finally devise a new definition for the term planet. A committee for the IAU worked on a proposed definition for about a year. Unfortunately, that definition did little to clear things up. Bowing to popular opinion, the new definition was contrived to keep Pluto on the list, but it added Eris to the list and it put Ceres back on the list again. However, it also made Charon a planet. Charon had long been considered Pluto’s moon, but the two actually orbit a center of mass point that is between Pluto and Charon, so the new definition made Pluto and Charon a binary planet. But, the definition also left about a dozen “maybe” planets that needed more work to clear up their status. The IAU general assembly voted down this definition in favor of one that they hurriedly put together. The definition of planet that was accepted leaves Pluto off the list of planets, reducing the number to eight. It creates a new category called “dwarf planets” that includes Eris, Pluto, and Ceres.
Now, according to a press release from the IAU, the IAU’s Committee on Small Body Nomenclature is proposing to call these icy bodies in the outer Solar System Plutoids. The new designation is for bodies orbiting beyond Neptune that have sufficient mass to pull themselves into roughly spherical shapes, but not sufficient mass for them to dominate their portion of the Solar System, clearing their orbits of like bodies. Personally, I am not sure that this definition is really right. I think that rather than keying the definition to the location of the body, it should be keyed to the composition of the body. True, Pluto, Eris, and the handful of bodies that we suspect (but don’t know for sure) might fit the definition are all similar composition. But, what would happen if we found something out there that was more like Ceres in composition? It is not likely, but suppose it did happen. Would it be fair to lump it with Pluto rather than considering it to be an out-of-place body asteroid belt body? As I see things, we are still not coming up with really good definitions here.
And, of course the name itself, Plutoid, is an attempt to mollify those die-hard Pluto supporters. Typically, bodies are named for the largest member of similar objects. The inner, rocky planets, are called Terrestrial Planets because Earth (Terra) is the largest of these. The gas giants are often called Jovian planets because Jupiter is the largest. Of course, I have issues with that, because Jupiter and Saturn clearly go together, but they are quite different from Uranus and Neptune, which are both similar to one another. Eventually, we will need to come up with a better system of classifying these bodies.
-Astroprof
Image Credit: IAU, NASA/ESA Hubble Space Telescope, H. Weaver (JHU/APL), A. Stern (SwRI), the HST Pluto Companion Search Team and M. Brown
Clumpy Soil
Published on Jun 10, 2008 at 1:45 pm.
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Filed under Mars.
The Phoenix lander is now well into its mission to study Mars. The first steps, of course, are to look around with the cameras. But, while the pretty pictures are what excite the public the most, scientists are much more excited about the other instruments on board the craft. These instruments will tell us the composition of the Martian soil. Despite many press reports that state Phoenix is looking for life on Mars, what it is really doing is looking for the chemistry necessary for life. If you don’t have the chemicals, then you don’t have life as we know it. And, if it is not life as we know it, is it really life? Well, that’s a question left to a future blog entry.
The next step, though, beyond looking around the surface is to reach out with the robotic arm and push stuff around. Phoenix did that last week. This gives us an idea of the consistency of the regolith (soil). Next, Phoenix scoops up some soil to study a bit more carefully. Then, what we’ve all been waiting for, Phoenix dumps a scoop of soil into one of the instruments to study. The instrument chosen is one that studies volatile materials in the soil. Volatile materials are those with low vaporization temperatures. So, the soil is dumped into a small oven that is then sealed. The oven heats up to about 1000° C. The volatiles are baked out of the soil and are studied using a mass spectrometer. That tells us the composition of the volatiles. There are several ovens on board, so soil samples from several locations can be studied. The ovens don’t have a provision to be emptied, so they are used one time. By the way, this sort of study of Martian soil dates all the way back to the Viking days.
A number of spacecraft have landed on Mars. The Vikings landed in 1976. Pathfinder landed in 1997. The Mars Exploration Rovers Spirit and Opportunity landed in early 2004. We’ve learned a bit about Martian soil from those missions, we thought. The Martian soil is loose, with some small rocks in it. There is no liquid water on Mars, and the soil is dessicated. On Earth, it is water in the soil that tends to make it clumpy and hold together. That isn’t the situation on Mars. But, it is the soil that needs to go into the oven, not small rocks. And, the looser the soil, the better it works. So, on top of the intake to the oven is a small screen. The space probe’s robotic arm dumps a load of soil onto the screen. The screen then shakes and the small grains fall inside, leaving the rocks and large clumps outside. At least, that is how it is supposed to work.
As you can see in this image, the soil is piled all over the intake. But, as things move, not much is sifting into the oven. A few days ago, I wrote about an image of the soil in the robotic arm’s scoop. I commented on the clumps in the soil at the time. But, the rather unexpected cohesiveness of the soil seems to be a problem. I didn’t realize that at the time, and apparently neither did the scientists on the Phoenix team.
You see, the soil is so clumpy that it is not sifting through the screen into the oven! If the soil can’t get into the oven, then it can’t be studied. Oops. We have not seen soil quite like this on Mars before. Close, perhaps, but not quite like this. So, this is a bit of a conundrum. Unfortunately, the screen does not appear to be retractable. Apparently, no one thought that such an option would be needed.
All is not lost, though. There are other ideas. Perhaps the scoop can be used to stir soil and crush the clumps before dumping onto the other intakes. Another option might be to sprinkle smaller amounts of material to try to get a handle on the situation. A far more drastic option might be to top the pile of material sitting on the screen with the arm, if it will reach (not recommended due to possible damage to either the arm or the craft itself). And, I am sure that they are thinking of all sorts of other options. Phoenix will be there for some months to come, so there is no real hurry to get everything done fast. It is best to take time, analyze the situation, and work out a solution. Then, of course, the solution can be tested out here on Earth with a mock-up before trying it for real on Mars.
Fortunately, this is the first real problem that Phoenix seems to have encountered. Sure, there have been a number of smaller problems, but you expect things to go wrong with any mission. The trick is to get past the problems and continue with a successful mission.
-Astroprof
Image courtesy NASA, JPL, UA
GLAST: T minus 4 days
Published on Jun 7, 2008 at 2:06 pm.
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Filed under astronomy, space telescopes.
About 3 months ago I wrote about the GLAST (Gamma-ray Large Area Space Telescope) and the search for a new name for the mission. The satellite was supposed to launch this weekend, but it has now been delayed until at least June 11. 
If all goes according to the plan, GLAST will lift off some time around noon on that date aboard a Delta rocket from Pad 17B at the Cape Canaveral Air Force Station.
GLAST is designed to study gamma rays. These are an extremely energetic form of light, and thus gamma rays are typically produced in very energetic events. Visible light is only a tiny portion of the electromagnetic spectrum. Light that is somewhat shorter wavelength (and somewhat higher energy) than visual light is ultraviolet light. Light that is somewhat longer wavelength (and somewhat lower energy) than visual light is infrared light. Radio waves, X-rays, and gamma rays are also forms of electromagnetic radiation. When I was in elementary school, some of the books that I read also listed something called “cosmic rays” as shorter wavelength, and higher energy, than gamma rays. The modern way of thinking, tough, is that that wavelength regime is really just extra energetic gamma rays. Once in a while, though, I get a student my age or somewhat older who remembers the old charts of the electromagnetic spectrum showing cosmic rays at one end. But, the term cosmic rays has an entirely different meaning for us today.
Among the sorts of things that GLAST will study are supernova remnants, neutron stars, and black holes (including the supermassive black holes in active galactic nuclei). High energy physicists are excited about GLAST, too, because these astrophysical bodies are able to accelerate particles to far higher speeds than can be attained with Earth-bound particle accelerators. So, GLAST promises to perhaps give some insight into high energy physics, too.
GLAST is not the first gamma ray telescope put into orbit. It is merely the latest, and possibly best. So, why do we want to go to all the expense of putting a gamma ray telescope into orbit? After all, when you first begin to learn about nuclear radiation, you are taught that there are three types of radiation: alpha rays, beta rays, and gamma rays. The gamma rays are the most penetrating of them all. It is the toughest to shield against. Alpha rays can be shielded with just heavy cloth, paper, or plastic. Beta rays can be shielded with a thin layer of lead, or a thicker layer of plastic. Gamma rays, though, require many inches, or sometimes even feet of lead to shield against. So, why bother putting a gamma ray telescope into orbit? Well, the reason is that while alpha rays and beta rays are fairly easy to shield against, so are gamma rays. Yes, they are penetrating, and it takes a lot of lead or concrete to block them. But, air also blocks them. Huh? If lead has trouble with gamma rays, how can air block them? Well, air blocks gamma rays the same way that the lead does. The electrons in the air molecules absorb the gamma rays. But, air is thin. So, it takes a whale of a lot of air to block gamma rays. What lead can block in a few inches takes dozens of feet of air to block. And what takes many inches of lead to block may take hundreds of feet of air to block. But, there are dozens of miles of air between the ground and space. So, gamma rays from space are effectively blocked from reaching the ground by the air over our heads. Even mountains have too much air above them for gamma ray telescopes to be of any use. So, you need to get the gamma ray telescopes above the air. That means putting them on satellites that are in Earth orbit. That is what GLAST is doing. And, if everything goes well in four days, we will have another gamma ray telescope in orbit to study high energy astrophysical phenomena.
-Astroprof
Images courtesy of NASA
An even smaller super-earth
Published on Jun 6, 2008 at 2:33 pm.
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Filed under extrasolar planets.
A few days ago, I wrote about a possible record setting small super-earth. Now, I have read about an even smaller super-earth discovered by a team of astronomers led by David Bennett of Notre Dame.
This newly announced planet is designated MOA-2007-BLG-192L b. Actually, everything in that string of letters and numbers refers to the star except for the letter “b” at the end. That is the planet. This planet may be only about 3 times Earth’s mass (the one that I talked about a few days ago was 4 times Earth’s mass). Doing the sort of back-of-the-envelope calculations that I did before, if this planet has similar composition to terrestrial planets in the Solar System, that puts its surface gravity at less than 50% greater than Earth’s gravity. Once again, that is a figure that raises interesting questions. Humans could move about under that sort of gravity. In fact, over time, I would imagine that Earth species could adapt to such gravity.
Interestingly, this planet was discovered using a microlensing technique. As the planet passes in front of a background star, its gravity slightly bends the light from the star, acting rather like a lens. Carefully monitoring of the light intensity from the star can detect this effect.
Another interesting bit of information from this system is that the host star is nothing like our own Sun. It is tiny. When extrasolar planets were first discovered, most were found around stars more or less like our own. This led to speculation that perhaps very massive stars form too quickly to permit planets to form, and that stars that are too small take so long to form that the planets simply spiral into the star like the rest of the material in its accretion disk. There is some indication that some stars do have planetary debris in their atmospheres. But, in recent years, several low mass stars have been found to have planets. This is the lowest mass star to date to be found with a planetary system. In fact, this star’s mass is so low that it is very near the cutoff point where a body can sustain nuclear fusion. The initial estimates for the mass are indeed that it is about 0.06 times the mass of the Sun. The cutoff is 0.08 solar masses. Objects with less mass than this cannot sustain nuclear fusion, and so they are not proper stars. We call them brown dwarfs. But, the mass estimate for this new object is very uncertain, so it may or may not be a brown dwarf. Though the initial estimate is 0.06 solar masses, it could well be just barely big enough to sustain fusion, and thus be a minimal star. At any rate, it is tiny, and it is cool.
If it is a minimal star, it will stay cool for just about forever. In fact, it would be able to sustain itself at that level of temperature and brightness for many times the current age of the universe. If it is a brown dwarf, though, then it can only produce energy through the gravitational compression of its gases. That doesn’t last as long, and it will eventually cool off. But, even in the former case, where the object is a star, the planet is still nothing that we would call habitable. The host star (or brown dwarf) is so cold that the planet itself is probably as cold as the objects in the Sun’s Kuiper belt. It may be a bit larger than Earth, but if it has any atmosphere, it is probably largely frozen solid on the surface. The surface might be warmed as much from heat working its way out from the interior of the planet than from light from the star.
What makes these findings of small super-earths exciting is that it suggests that planets like Earth may not be all that uncommon. The technology has not existed until recently to find planets this small. Now the technology is here, and we are finding planets. But, it also raises a question as the just how small something can be and still be called a super-earth. The term, itself, is not official. It is just a term that has come about from common use among astronomers. It does not have an official definition. But, I am thinking that a body only that only two or three times Earth’s mass is probably a bit on the small side to be calling a super-earth. Of course, we don’t really know anything about these bodies other than their possible masses. They may be nothing at all like Earth in composition. In fact, if this new body formed where it did around this small star, then a major component of it may be water, as is the case in planets and other bodies in our outer Solar System. So, that might make it more of a super-duper-pluto rather than a super-earth.
-Astroprof
Image courtesy NASA
