Posted on 09/16/2002 7:21:12 PM PDT by Pokey78
WASHINGTON, Sept. 16 — Even in astronomy, there are some tough acts to follow. After parting a curtain to the universe with the Hubble Space Telescope and allowing millions to experience previously hidden wonders in space, what do you do for an encore?
The National Aeronautics and Space Administration last week revealed its choice for the next stage in expanding human vision into deep space. The agency announced that it would build the long-discussed Next Generation Space Telescope, selecting the design of a team led by TRW Inc., for a successor to Hubble to be launched in 2010.
The new observatory, while only half as big as the 24,000-pound Hubble, will have a primary, light-gathering mirror 20 feet in diameter compared with the existing telescope's 8-foot reflector. With a mirror that has a light gathering area six times as large as the Hubble's and a suite of more sensitive instruments, the new telescope should be able to detect objects a hundredth the brightness Hubble can see in visible light and one four-hundredth the brightness in the infrared part of the light spectrum.
Following recommendations from astronomers who suggested a bold new concept, NASA said it would build an observatory that would look back into time and space for some of the first light produced in the universe. Unlike Hubble, this telescope will be sent into orbit far from Earth and should be able to detect and analyze the faint, warm light produced when the first stars and galaxies formed a few hundred million years after the Big Bang, the theoretical beginning of the universe some 14 billion years ago, scientists say.
The observatory will also be used to study the formation of planets and to search for the hidden dark matter that is thought to make up most of the matter in the universe.
The new telescope will not be just a larger version of Hubble, a traditional telescope that mostly views objects in the visible light part of the electromagnetic spectrum that is seen by the human eye. The observatory will be optimized to see in the infrared, best for detecting faint light moving rapidly away from the observer that has shifted into the red, thermal part of the spectrum.
Dr. Alan Dressler, an astronomer with the Observatories of the Carnegie Institution in Pasadena, Calif., who took part in studies of what should follow Hubble, said scientists wanted more than just a bigger space telescope.
"The Hubble Space Telescope raised the ante," Dr. Dressler said. "The desire was to make a huge leap, to go for something bold that would really be a breakthrough. So the goal became to see the first light of stars and the emerging of galaxies. This is the birth of the modern universe we live in today."
Although the new telescope is optimized for infrared viewing, astronomers and NASA agreed that the observatory had to have the ability to produce visible light pictures at least as good as Hubble's, to assure public support. "NASA has tried for years to recapture the public imagination about space and, to everyone's surprise, the public got caught up in the images from Hubble," Dr. Dressler said. "We were conscious of this public perception in making our recommendations."
Dr. Marcia Rieke of the University of Arizona, the principal investigator for the observatory's primary instrument, a near-infrared camera, said pictures from the new telescope taken in the visible light range should be much better than Hubble's. "The telescope will be best in the infrared area, but it can extend into visible light and do just fine," she said.
Heartened by the success of Hubble, NASA readily embraced recommendations from the Association of Universities for Research in Astronomy and the National Academy of Sciences for the first-light telescope.
However, in a time of tightening budgets, the agency's challenge is to build and operate the new telescope for substantially less cost than Hubble. With its periodic hardware upgrades, the Hubble itself has cost more than $2 billion, not to mention operating costs of at least that much when the bill for space shuttle flights to the telescope for maintenance is included. Since its launching in 1990, NASA has sent four shuttle service missions to the observatory and a final upgrade and repair flight is scheduled for 2004.
TRW and its partners, including Bell Aerospace and Eastman Kodak, are to build, test and operate the new observatory for a year under an $824.8 million contract that does not include launching costs. NASA officials said the ultimate cost of the observatory, planned to last at least 5 years and perhaps 10, could be about $1.2 billion.
One way in which the new telescope will be cheaper to operate than Hubble is that it is not designed to be repaired or serviced once launched. Because of this, engineers are emphasizing high reliability and backup capabilities for all critical systems, said John C. Mather, the project scientist at the Goddard Space Flight Center in Greenbelt, Md.
To isolate the telescope from infrared interference from the Earth and the Sun, the observatory will be launched on an expendable rocket on a three-month journey that will take it to an area 940,000 miles from Earth called L2 for Lagrange Point 2. At a spot like this, the gravity of the Earth and the Sun balance each other out and a spacecraft can keep a stable position with just a few rocket adjustments. The L2 spot is located on the side of the Earth in the direction away from the Sun, with the planet always positioned between the Lagrange point and the Sun.
The spacecraft, whose three main instruments consist of multiwavelength cameras and spectroscopic devices that break down light to be analyzed, also will have a multilayered sunshade the size of a tennis court to insulate it from light and heat produced by the Sun and Earth that could interfere with its observations. The shade and the remote location allow the observatory to cool to below minus 378 degrees Fahrenheit, allowing other cooling systems aboard to chill detectors even more for the best infrared readings.
For the 20-foot diameter mirror to fit into a rocket nose cone, it will be built as 36 hexagonal segments that are folded over into three panels at launch and unfurled into its circular shape once in space. These flexible panels will have multiple, computer-controlled actuators on their backsides that can alter the shape of the mirrors to make sure reflected light is perfectly focused on a collector.
To cut costs and reduce risk of technical problems, NASA has been supporting research into lightweight mirrors, star detectors and other relevant technologies. The telescope initially was planned to have a 26-foot-diameter mirror, but the size was reduced to 20 feet to cut costs by reducing complexity and fabrication time.
Mr. Mather said delays in developing the mirror technology increased cost estimates and pushed launch time from 2008 to 2010. "The mirror is the hardest problem," he said, "We saw that at the beginning so it's no surprise."
The Hubble's biggest problem was also the mirror: it was found to be defective after launching and later had to be corrected by installation of special lenses. NASA does not want a repeat of that embarrassment.
In a year, the agency must make the critical decision of what material to use for the new telescope's mirror. The candidates are a metal mirror made of beryllium or one made of some form of glass.
Mr. Mather said NASA would take its time selecting the best material and would thoroughly test the entire observatory as a unit before launching it.
"Some things you just can't rush," he said.
How can we then "see" the original light? Wouldn't it have gone "past" us and out into the empty void long, long, long ago?
That is not a dumb question. It is an excellent question.
There are two closely interrelated reasons, both from special relativity: time dilation and the relativity of simultaneity.
Let me preface my comments on relativity by saying that the earliest light we see is not from the instant of the Big Bang, but from a time about 300,000 years after the Big Bang. Before that, the universe was opaque, because it was composed of charged particles. Around that time, atoms began to form and the universe became transparent.
As another preface, let me emphasize the fact that because of the expansion of the universe, the farther away something is, the faster it is moving away from us. This is a very key point. Given the finite speed of light, Galileo would not have been surprised to hear that we can see objects in the early universe. If we're fleeing from a light emitting object at nearly the speed of light, then in the emitter's frame, it will take the light a very long time to catch up with us.
As you realize, however, life isn't so simple, because light is also moving at the same speed relative to us. If the object is close by when it emits its signal, it should reach us in a short time no matter how quickly the emitter is receding. How can these two seemingly conflicting pictures be resolved?
Time dilation: To an observer in an inertial frame, time passes more slowly in any other inertial frame that is moving relative to the observer. The objects that we see at a great distance are moving at relativistic speeds with respect to us, therefore, time is moving more slowly. Not only are we seeing them at an earlier time (owing to the time it has taken for the light to arrive), but time is elapsing at a slower rate there than here.
Relative simultaneity: Events that are simultaneous in one frame are not simultaneous in another frame. Because we are receding from these distant objects, events that occur in those distant locations simultaneously (in our inertial frame) with events here actually occur at a much earlier epoch of the universe than the events here. Our axis of simultaneity reaches into the past of receding frames, and the more distant the events, the farther back it reaches.
[Geek alert: why does distance matter, and not just relative velocity? Because the time of the event in the moving frame is the intercept along that frame's time axis. The relative velocity only determines the slope of our axis of simultaneity (i.e., our space axis). To find the intercept, you have to extrapolate that slope over the intervening distance, and the farther you extrapolate it, the farther back in time the intercept gets pushed.]
These two different aspects of special relativity are really two ways of saying the same thing: that as viewed from our inertial frame, much less time has elapsed over there since the Big Bang than has elapsed here. We are only seeing their relic light now, because we had a big head start. (To them, of course, we are the retarded ones; our neck of the woods is the one that sent off its relic light way late.)
L2 is an unstable point, meaning that if you perturb the orbit of something there, the object will drift away from that point. Thus, nothing will collect there.
Stuff does congregate at L4 and L5, which are stable points.
With precise targeting it is possible to place an object "in orbit" about L2, which is basically what will be happening here.
FYI, here are the locations of the Earth-sun LaGrange points:
The basic geometry is the same for any two-mass system.
The system shown is a sun/earth type system. But what about for a three-mass system like sun/earth/moon? How does that complicate the LaGrange points? (both near field and far field)
Regards,
Boot
a how how how how
Yes, at L4 and L5, which are stable. L1, L2, and L3 are also zero points, but unstable. Things placed there can be kept there with minimal effort, but without such effort, they will drift away, first slowly and then faster and faster.
I'll have to think on it to understand more.
But thanks; at least I did get the notion that the reason we see light from "way back then" is because the time elapse is NOT a constant.
I really appreciate your taking time to explain something that has been bugging me for a very long time (er, "relatively" speaking of course!)
I'd say that's about 90% of it, rather than half.
Illbay,
If it was like a flash from a camera, yes it would but stars, galaxies and quasars are 'on' for millions to billions of years. Based on the distance, you're loking back in time. If you see an object 100 million lights years away you're seeing the light that shined from that object when it was towards the end of the Cretaceous period (Age of Dinosaurs) ... it's just been travelling all that time. In the meantime, the star could have gone supernova 50 million years ago. Because it's so far away the light from that explosion wouldn't reach us 50 million years from now.
On a smaller scale, the Sun could explode or go dark and we wouldn't know it for 8 minutes.
I think I understand a little better, now.
The objects that we see at a great distance are moving at relativistic speeds with respect to us, therefore, time is moving more slowly. Not only are we seeing them at an earlier time (owing to the time it has taken for the light to arrive), but time is elapsing at a slower rate there than here.Fine. Understood. But the last time I saw figures on this, the redshift from the most distant objects indicated a velocity of about 70% of lightspeed. That's fast, but not enough for a really significant time dilation factor. Gamma is only 1.4, and time is passing there (out at the farthest objects) at about 71% of our local time. Is this sufficient to account for our still seeing that old light? Or is more involved?
Just another mystery of the universe. I'm glad to see I'm not the only ZZ Top fan on this board.
Well, no, the highest redshift objects that have been found have a z of around 6.3, which is better than 96% of lightspeed. Furthermore, these objects are seen well after the decoupling time (that is, the time when atoms formed and the universe became transparent), so there's a considerable temporal "lever arm" (as I describe in my "geek alert" above). An object at the decoupling time (the physical limit of how far back we can see) would have a z of around 1000.
Now you're starting to get into the unsolveable problems (the unrestricted three-body problem being one of them).
However, in the particular case you're mentioning, the Earth and Moon are close together, and from a distance "seem like" a single mass. Thus, the sun is one of the masses, and the Earth-moon system is the other mass.
The LaGrange points would be measured with respect to the center of mass (barycenter) of the Earth and moon.
The complications introduced by the presence of other gravitational bodies are generally not that great, as the relative magnitude of the gravitational acceleration is small as compared to the two large masses. As such, those bodies can be treated as perturbations that can be corrected by station-keeping burns.
r9etb says: "The LaGrange points would be measured with respect to the center of mass (barycenter) of the Earth and moon."
So all I have to do to determine the size and shape of the resulting perturbations of the earth/sun L2 point is calculate each earth/sun L2 point, based upon the earth/moon barycenter and combined mass, for all positions of the moon's orbit about the earth? That I can do (with the help of MathCad and some data from my handy dandy Observer's Handbook) plus it should prove to be fun! But it will have to wait until tomorrow because I've been up all night and I'm too dingy to even type anymore.
Thanks for the intriguing reply.
Regards,
Boot Hill
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