The speed of light in a vacuum cannot change, by current definition. The meter is currently defined as 1/299,792,458 of the distance light travels in a vacuum in one second. Of course that hasn't always been the definition: the basis for the meter has been, in historical order:
(1) The quadrant of the Earth.
(2) The length of a particular metal bar.
(3) The wavelength of a particular atomic spectral line.
(4) The speed of light and the frequency of an atomic clock.
Each change improved the reproducibility of the best length measurements, given the technology at the time the change was made.
The observations that suggest alpha varies are based on comparing wavelengths of light from different atomic oscillations, potential distance standards similar to (3) above. They appear to vary relative to each other. If you want to attribute this to varying c, which one is the reference yardstick?
For our present technology the most reproducible clocks and yardsticks are atomic oscillations. If these lack relative constancy and you choose the frequency of one as your time standard and the wavelength of another as your length standard, you will apparently observe a changing value of c. However, the direction and magnitude of the change will depend on which pair you choose. If we had really independent distance and time standards (and it was clear which was which) it would make sense to consider c an experimental quantity. Since we don't we have just chosen one standard (a particular oscillation of cesium), and c is a defined constant.
Similarly, the electromagnetic quantities "epsilon nought" and "mu nought" were once experimental quantities, but are now by definition exactly {10^7/(4 Pi c^2)} and {4 10^-7 Pi} respectively. This means that the coulomb is no longer defined electrochemically: it is a derived unit, not a fundamental one in the SI system.
The HETE batteries *are* Energizers! The cells are cordless screwdriver size (2/3 C) rapid charge NiCd cells, 23 cells to a battery. There are six batteries in three *aluminum* cases.
HETE is a low cost mission. The HETE spacecraft were built mostly from off the shelf commercial parts, not high cost aerospace parts. The commercial NiCd cells have actually proved very robust and reliable in space: the batteries on HETE-2 have gone through about 8000 discharge cycles so far and are still holding a charge just fine. The HETE-1 batteries could not be charged after the rocket's failure to fire its pyros left HETE-1 in the dark inside the DPAF can. Can't charge batteries without energy.
The press release is a bit confused: I believe the stainless steel batteries must be in SAC-B. There is very little stainless steel in HETE: there are no large refractory parts at all.
One very difficult property of radio is the inverse square law: when you're 100 times closer to the transmitter than the intended receiver, you receive 10000 times more power than the intended receiver. This makes channel separation a very important issue. The promoters of broadband radio schemes gloss over this problem.
The separation of channels by frequency has two special properties that help with this problem:
1. There are no common physical processes that change frequency much between the transmitter and receiver (Doppler and changing refraction effects are generally small).
2. It is possible to get very large channel separation with frequency-selective filters.
You give up these special properties with broadband schemes. Time-division and code-division separation of channels are particularly sensitive to multipath propagation, a ubiquitous property of radio. While multipath can produce fading and distortion in narrowband transmission, it cannot cause one channel to spill into others.
Yeah and it's too bad the people on the team have fried some of the coating on their detector.
The soft x-ray cameras have lost their primary optical/micrometeorite blocking filters. The secondary filters that cover half of the detectors are still intact, and those detectors still work when the moon is out of the aperture.
You imply this was an operational error, but it was not. The filters were eroded by atomic oxygen. The available literature on atomic oxygen in HETE's orbit at the time the cameras were designed suggested that this was not a worry. A slight change in the filter design could have prevented this problem, but it was unanticipated.
This is in part what small missions are for: to try new technologies (the SXC modules are by far the highest resolution coded aperture cameras ever flown) and to scope out their capabilities and hazards. Nobody would have dared fly an SXC on a high cost mission. It still works, just not as well as intended. The next mission that needs something like this will reap the benefits.
Take that and add an gamma/ x-ray detector and lookin the ecliptic at Sco X-1, the freaking brightest x-ray source in the whole damned sky and you aren't going to detect anything because you're busy frying your detector.
Sco X-1 is far from the field of view right now. It's primarily an issue in the month of May. It doesn't damage the detectors, but when it is in the field of view the detectors are less sensitive to the fainter gamma ray bursts. Last May, it was very useful for calibration. Now that it's not needed for that, and routine operations have become routine, the ops team may be able to arrange an attitude dance that will avoid it next year.
Never mind additional months from Jan to July/Aug of this year where they had to write and upload new software because what they had didn't work.
HETE launched with very few software bugs compared to other scientific missions with similar software complexity. The trouble was that the ops team was too small to give priority to 24/7 operations and still find time to fix the bugs.
The satellite is good- the execution of the science is crap! This is why satellites like this should not be run by people at Goddard!
The team that built the satellite and continues to operate it is centered at MIT. Goddard's operational involvement is the final steps in disseminating the burst data. It's just a very hard problem to capture, reduce, and disseminate an astrometric result in a few seconds, expecially when the operations budget has been cut below its modest minimum requirement.
The design of a satellite such as ENVISAT takes years. It is true that today, one would probably design things differently. Ah, how easy it would be to know 5 years in advance how a system should be designed.
The standard official excuse. There's some truth here, of course, but it fails to address the real issue. The technology in the Apollo moon missions was genuinely advanced for its time, but space technology has fallen steadily behind other technical endeavors ever since. I think the main reason is that Apollo had a powerful informal support system behind it: a tremendously vital program that included balloons, rockets, and spacecraft on a wide variety of scales. Experience gained in low cost missions was rapidly incorporated into the big missions.
We've largely destroyed this system. The result is that space exploration is no longer truly a high tech endeavor.
Must I add that it was fun to work on such a project?
Big projects are organized around the emotional needs of managers and the technical capabilities of specialists. For generalists and inventors, small projects are more fun. Neither is better, both kinds are needed for progess in space.
The only thing is that they had initially hoped to have found rather more than one by now!
Some of their problems have been related to the fact that their team is very small. So, it is possible to make things too cheap.
HETE's operations team is indeed too small. HETE-2 was ready for launch in January, 2000 (it was integrated with the rocket!), but after the Mars lander failure NASA got cold feet and ordered it shipped back to MIT for additional testing. HETE-2's operations were also funded below the HETE project's minimum estimate of operations costs. Since people without long term support need to find new jobs, this combination meant that several people left for new employment either before launch (having already lined up new jobs before the delay) or shortly afterward. While a reduction in the team's size post launch was intended, what happened was too drastic.
This definitely made it harder.
It would have been fine if they had no time constraints, but it seems that spending most of the first year essentially in a kind of engineering mode is a bad thing.
Part of the trouble is that HETE needed to be well calibrated before it could generate useful results. A mission like Chandra could do a lot
of interesting stuff (especially pretty pictures) before its calibration was finished. Astrometric calibration takes time, however.
In any case, this extra time has not added much to the overall mission cost.
Is there anyway that the community (esp. NASA) could have helped bring things on line sooner?
A launch in January 2000, when HETE was ready, would have helped. Adequate funding of the operations phase would have helped.
Patience also would have helped, I think. The HETE team, NASA, and the community were all impatient for results. This meant that there was an emphasis on working through the inevitable operational problems rather than taking the time to fix them. A team that is too small cannot do both in parallel. Once some of the more time consuming problems had been fixed, positive feedback set in: operations became less labor intensive which meant more time was available to fix problems.
Yes, lasers follow the inverse square law.
In the "far field" or "Fraunhofer" region, diffraction cause the beam to spread, and the intensity follows the inverse square law. This is conventionally considered to start at a distance 2*D^2/Lambda from the source, where D is the aperture diameter, and Lambda is the wavelength. For your laser pointer example, D is 2 mm, Lambda is 700 nm, and the far field begins about 10 m from the pointer.
Perhaps not regularly, but...
A couple of months ago my son came into my basement office with a question about his chemistry homework. After he'd gotten the concept straight, he asked if he could sit down at my (LinuxPPC) desktop machine and do the calculations. OK, fine. His next question was "Can you check my work?". He's now at my desktop, my laptop and my HP-42S are upstairs in my backpack, but I'm prepared for just such an emergency: my K+E Deci-Lon (1968 model) is on the shelf above the computer!
These low power numbers are perfectly within the reach of conventional technology. These are relatively low data rates over relatively short distances. One can go farther: I have conventional CPFSK 300 BPS links that carry data 100 meters for 1 *nanowatt* of RF power. These are test links for spacecraft communications that use 400 million times that power to get 20 thousand times that range (isn't the inverse square law wonderful?:-(
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(1) The quadrant of the Earth.
(2) The length of a particular metal bar.
(3) The wavelength of a particular atomic spectral line.
(4) The speed of light and the frequency of an atomic clock.
Each change improved the reproducibility of the best length measurements, given the technology at the time the change was made.
The observations that suggest alpha varies are based on comparing wavelengths of light from different atomic oscillations, potential distance standards similar to (3) above. They appear to vary relative to each other. If you want to attribute this to varying c, which one is the reference yardstick?
For our present technology the most reproducible clocks and yardsticks are atomic oscillations. If these lack relative constancy and you choose the frequency of one as your time standard and the wavelength of another as your length standard, you will apparently observe a changing value of c. However, the direction and magnitude of the change will depend on which pair you choose. If we had really independent distance and time standards (and it was clear which was which) it would make sense to consider c an experimental quantity. Since we don't we have just chosen one standard (a particular oscillation of cesium), and c is a defined constant.
Similarly, the electromagnetic quantities "epsilon nought" and "mu nought" were once experimental quantities, but are now by definition exactly {10^7/(4 Pi c^2)} and {4 10^-7 Pi} respectively. This means that the coulomb is no longer defined electrochemically: it is a derived unit, not a fundamental one in the SI system.
The HETE batteries *are* Energizers! The cells are cordless screwdriver size (2/3 C) rapid charge NiCd cells, 23 cells to a battery. There are six batteries in three *aluminum* cases.
HETE is a low cost mission. The HETE spacecraft were built mostly from off the shelf commercial parts, not high cost aerospace parts. The commercial NiCd cells have actually proved very robust and reliable in space: the batteries on HETE-2 have gone through about 8000 discharge cycles so far and are still holding a charge just fine. The HETE-1 batteries could not be charged after the rocket's failure to fire its pyros left HETE-1 in the dark inside the DPAF can. Can't charge batteries without energy.
The press release is a bit confused: I believe the stainless steel batteries must be in SAC-B. There is very little stainless steel in HETE: there are no large refractory parts at all.
The separation of channels by frequency has two special properties that help with this problem:
1. There are no common physical processes that change frequency much between the transmitter and receiver (Doppler and changing refraction effects are generally small).
2. It is possible to get very large channel separation with frequency-selective filters.
You give up these special properties with broadband schemes. Time-division and code-division separation of channels are particularly sensitive to multipath propagation, a ubiquitous property of radio. While multipath can produce fading and distortion in narrowband transmission, it cannot cause one channel to spill into others.
The soft x-ray cameras have lost their primary optical/micrometeorite blocking filters. The secondary filters that cover half of the detectors are still intact, and those detectors still work when the moon is out of the aperture.
You imply this was an operational error, but it was not. The filters were eroded by atomic oxygen. The available literature on atomic oxygen in HETE's orbit at the time the cameras were designed suggested that this was not a worry. A slight change in the filter design could have prevented this problem, but it was unanticipated.
This is in part what small missions are for: to try new technologies (the SXC modules are by far the highest resolution coded aperture cameras ever flown) and to scope out their capabilities and hazards. Nobody would have dared fly an SXC on a high cost mission. It still works, just not as well as intended. The next mission that needs something like this will reap the benefits.
Take that and add an gamma/ x-ray detector and lookin the ecliptic at Sco X-1, the freaking brightest x-ray source in the whole damned sky and you aren't going to detect anything because you're busy frying your detector.
Sco X-1 is far from the field of view right now. It's primarily an issue in the month of May. It doesn't damage the detectors, but when it is in the field of view the detectors are less sensitive to the fainter gamma ray bursts. Last May, it was very useful for calibration. Now that it's not needed for that, and routine operations have become routine, the ops team may be able to arrange an attitude dance that will avoid it next year.
Never mind additional months from Jan to July/Aug of this year where they had to write and upload new software because what they had didn't work.
HETE launched with very few software bugs compared to other scientific missions with similar software complexity. The trouble was that the ops team was too small to give priority to 24/7 operations and still find time to fix the bugs.
The satellite is good- the execution of the science is crap! This is why satellites like this should not be run by people at Goddard!
The team that built the satellite and continues to operate it is centered at MIT. Goddard's operational involvement is the final steps in disseminating the burst data. It's just a very hard problem to capture, reduce, and disseminate an astrometric result in a few seconds, expecially when the operations budget has been cut below its modest minimum requirement.
The standard official excuse. There's some truth here, of course, but it fails to address the real issue. The technology in the Apollo moon missions was genuinely advanced for its time, but space technology has fallen steadily behind other technical endeavors ever since. I think the main reason is that Apollo had a powerful informal support system behind it: a tremendously vital program that included balloons, rockets, and spacecraft on a wide variety of scales. Experience gained in low cost missions was rapidly incorporated into the big missions.
We've largely destroyed this system. The result is that space exploration is no longer truly a high tech endeavor.
Must I add that it was fun to work on such a project?
Big projects are organized around the emotional needs of managers and the technical capabilities of specialists. For generalists and inventors, small projects are more fun. Neither is better, both kinds are needed for progess in space.
Some of their problems have been related to the fact that their team is very small. So, it is possible to make things too cheap.
HETE's operations team is indeed too small. HETE-2 was ready for launch in January, 2000 (it was integrated with the rocket!), but after the Mars lander failure NASA got cold feet and ordered it shipped back to MIT for additional testing. HETE-2's operations were also funded below the HETE project's minimum estimate of operations costs. Since people without long term support need to find new jobs, this combination meant that several people left for new employment either before launch (having already lined up new jobs before the delay) or shortly afterward. While a reduction in the team's size post launch was intended, what happened was too drastic. This definitely made it harder.
It would have been fine if they had no time constraints, but it seems that spending most of the first year essentially in a kind of engineering mode is a bad thing.
Part of the trouble is that HETE needed to be well calibrated before it could generate useful results. A mission like Chandra could do a lot of interesting stuff (especially pretty pictures) before its calibration was finished. Astrometric calibration takes time, however.
In any case, this extra time has not added much to the overall mission cost.
Is there anyway that the community (esp. NASA) could have helped bring things on line sooner?
A launch in January 2000, when HETE was ready, would have helped. Adequate funding of the operations phase would have helped.
Patience also would have helped, I think. The HETE team, NASA, and the community were all impatient for results. This meant that there was an emphasis on working through the inevitable operational problems rather than taking the time to fix them. A team that is too small cannot do both in parallel. Once some of the more time consuming problems had been fixed, positive feedback set in: operations became less labor intensive which meant more time was available to fix problems.
Yes, lasers follow the inverse square law. In the "far field" or "Fraunhofer" region, diffraction cause the beam to spread, and the intensity follows the inverse square law. This is conventionally considered to start at a distance 2*D^2/Lambda from the source, where D is the aperture diameter, and Lambda is the wavelength. For your laser pointer example, D is 2 mm, Lambda is 700 nm, and the far field begins about 10 m from the pointer.
Perhaps not regularly, but... A couple of months ago my son came into my basement office with a question about his chemistry homework. After he'd gotten the concept straight, he asked if he could sit down at my (LinuxPPC) desktop machine and do the calculations. OK, fine. His next question was "Can you check my work?". He's now at my desktop, my laptop and my HP-42S are upstairs in my backpack, but I'm prepared for just such an emergency: my K+E Deci-Lon (1968 model) is on the shelf above the computer!
These low power numbers are perfectly within the reach of conventional technology. These are relatively low data rates over relatively short distances. One can go farther: I have conventional CPFSK 300 BPS links that carry data 100 meters for 1 *nanowatt* of RF power. These are test links for spacecraft communications that use 400 million times that power to get 20 thousand times that range (isn't the inverse square law wonderful? :-(