I have no specific knowledge of NRO or anything else spooky. However, from watching TV shows, etc., it is well known that "spy" satellites operate in low Earth orbit (LEO) or maybe medium Earth orbit (MEO). These orbits are polar, allowing the satellites to be tasked wherever imaging, etc., is desired. Think "Clear and Present Danger".
It's cool to talk with a Rush fan on here. (I'm sure there are plenty, but it's cool just the same to hear what you have to say.)
You're right about the metalhead reaction to synths and stuff. Oh, well; their loss I think. Of course, they're getting what they want again these days--Vapor Trails has some hard guitar work in it. And if you bought the EP, well, that's got a lot of rockin' in it for most anyone.
I wonder if you're 100% right in saying they refuse to play some songs because they might be "simple" or "embarassing". I'm not trying to argue with you, mind you, but I'm just wondering if that is, indeed, their thinking. I've gathered from my reading, etc., that it's more of a feel thing. For instance, I heard they struggled quite a bit coming up with the set list for the 30th anniversary tour, but settled on what they went with as a best combination. I heard that some songs were thrown out just because they weren't getting a good vibe playing them, for whatever reason. And, as you know, getting into a song is totally where it's at to produce a good live experience.
I do think it's interesting that they did the same set list for all the shows on that tour. Vapor Trails wasn't that way, of course. I was happy that the Manchester show, which I flew cross-country to go see and which was their last show in North America before heading to Brazil, included "Closer To The Heart"; this was the only stop in NA that had that song and it's a real crowd pleaser. I felt treated that night.
BTW, I sure wish I could hear "Camera Eye" live. I have just recently "discovered" that song for myself ("buried as it were on the not often played second side of Moving Pictures") and I think it's great. I sure don't think it's simple or embarassing. That one probably gets thrown out on account of length.:-)
Oh, yeah, I forgot to make my point w.r.t. SW and George Lucas vs. the Rush analogy. The big difference to me is that, aside from remastering their existing albums in the 1990's to take advantage of improvements in A/D technology, etc., Rush doesn't go back and change their work. They are content to let it rest on its merits, warts and all. And it rests just fine that way.
You know, it's funny, because I was thinking of drawing an analogy with Rush in my post. Rush is my favorite group, so I am aware of criticisms, etc.
Many people dismiss everything after Moving Pictures. (Some people dismiss everything other than Moving Pictures!) These folks seem to want more and more Moving Pictures-type songs from the band, as though that is what Rush should ever be about.
Now, I have no problem with people liking Moving Pictures, or even thinking it's their fav Rush album. But the fact is that Rush has been around for thirty years now, making new music almost the entire time. And another fact is that there is a lot of good music in their more recent offerings. In part, this is because they have evolved in life and their music has evolved with them. For us listeners that have evolved, too, the gems are there.
I know I've never enjoyed concerts more than 2002's Vapor Trails tour (Manchester, NH) or this year's 30th anniversery tour (Hollywood Bowl, CA, and Irvine Meadows, CA).
I think the difference is that, despite what we think of the latest movies, (I believe) George Lucas really cares about the movies he's making. I think they are exactly what he wants, exactly how he envisions them (as opposed to, apparently, the original three). He is putting a tremendous amount of effort into these projects to realize his vision and probably is getting burned out in the process.
It's just too bad for us that his "imperfect" versions of the stories from the 1977-1983 timeframe are the ones we really like.
Thank you. Well, I work for Boeing Satellite Systems (nee Hughes), where I've worked since college graduation (17 years now!).
But on to your questions....
Yes, space is a pretty hard vacuum. There is a little dust, etc., but it's a vacuum. It is also quite cold, in general. As another poster below explains, there are several modes of heat transmission, including conduction and radiation. You are correct in asserting that conduction is not where it's at in space since there's no conducting medium. However, radiation is where it's at.
The sun radiates thermal energy; that's one of the things that keeps us all alive.:-) This radiated energy impinges on the satellite, heating its surfaces just as it heats the Earth's surface. The effect of solar heating can be easily seen when monitoring spacecraft temperature telemetry during eclipse. As the satellite transits the penumbral and umbral regions, temperatures drop since the Earth shadows the satellite from the sun's radiation. When the satellite emerges from eclipse and reenters the sun's light, temperatures rise again. (Incidentally, these cooling and heating transients can induce localized deformations as the satellite's structure expands and contracts with the heat. These deformations can even create attitude disturbances, which can be seen via satellite gyro telemetry.)
There are other sources of heat on the satellite,of course. Most prominent are any high-power amplifiers, especially TWTAs (travelling wave tube amplifiers, the primary technology used for high-power amplification), but all electronics boxes generate heat to one extent or another.
Another dimension is that the satellite is not uniformly lit by the sun; for instance, the "backside," i.e., the side facing away from the sun, is in shadow. These areas do not get the benefit of solar heating and would be quite cold if not for active heater control.
So, you have to manage heat and cold, making cold areas sufficiently warm for electronics (and mechanisms) to operate and keeping hot areas from getting too hot. This is where the various technologies and tricks I mentioned come into play.
Radiation is a big part of this strategy. Remember that, unlike conduction, radiation does not require a medium to work. Thus, radiators on the satellite can, in fact, radiate excess heat to space.
Hopefully, this sheds a little light on the subject.:-)
Years ago, I processed reports from an organization known as the IFRB, which I seem to remember as the International Frequency Registration Board, or something like that. This organization received, circulated, and arbitrated RFCs for frequency bands made by the various satellite providers/manufacturers around the world. The purpose was to avoid interference between new systems and existing systems.
Many techniques exist for reducing or eliminating interference, not just frequency separation. Polarization schemes are a big part of the solution, but there are others (spatial isolation, of course, and coding schemes with digital systems).
If your data transmission is at all on the radar, so to speak, I think it'd be safe to say people are designing new systems to be compatible. Or so we think.:-)
Solar cells are small. They are arrayed to create solar arrays, or solar panels. These can be quite large, depending on the power requirements of the satellite.
Nominal power ratings for satellites assume sun-normal orientation of the solar arrays, which is actively maintained by the satellite. The satellite receives 100% illumination by the sun during most of the year, the exceptions being the spring and fall eclipse seasons, when the satellite transits the Earth's penumbral and umbral regions for up to a couple of hours per day. During these events, solar array power is augmented with battery power. Bus voltage drops and current draws increase, but transmitted powers generally stay the same. Yes, over the life of the satellite (10-15+ years) batteries degrade somewhat, though battery reconditioning techniques are employed to mitigate this. With today's designs, running out of fuel is usually what limits mission life.
The reason terrestrial radio stations require the power levels they do is that they typically transmit more or less omni-directionally (or at least toroidally), as opposed to how geo satellites use highly-directional (high gain) antennas for CONUS (or whatever) coverage. The effect of the differences between these two antenna types (tens of dB in gain) far outweighs the 20 dB power difference you mention (1 kW vs. 100 kW). The high gain antennas for DBS allow multiple channels of high bandwidth at reduced power vs. their terrestrial brethren. They're really two totally different kettles of fish.
Finally, thermal management is an important part of modern satellite design. Heat pipes, thermal radiators (mirrors), finishes, and other techniques are all used to collect, distribute, and reject heat. The effectiveness of these techniques can limit a design, and how capable a company is at dealing with thermal problems can determine the capabilities of its offerings relative to those of its competitors.
BTW, the current commercial satellite models offered by Boeing are based on the 702 bus, which supercedes the 601. Both of these designs were the product of Hughes Space and Communications Co. (part of the old Hughes Aircraft Company), now Boeing Satellite Systems (Boeing bought HSC in 2000).
The power levels seen at the Earth's surface are exceedingly low, hence the need for highly sensitive low-noise amplifiers to retrieve the signals. Not a cause for concern.
C band hardware doesn't have a problem with rain fade because the dish is over a meter wide.
Actually, the primary reason for C band's superior performance w.r.t. rain fade is the reduced atmospheric attenuation associated with lower frequencies, in general, and, in particular, with C band's frequencies vs. K band's frequencies. The atmosphere has different effects at different frequencies. The reduced attenuation at C band allows for greater link margin and, therefore, greater link robustness vs. rain.
The gains of a 1.8m dish at C band and a DirecTV dish at K band are similar. (Higher frequencies require smaller dishes for the same gain.)
If you aimed a 1.8m dish at one of the DTV birds, you wouldn't have a problem with rain fade either. (you'd have a bigger problem keeping it properly aimed, btw.)
Very true. Of course, the dish (antenna, in general) would have to be designed to operate at K band frequencies. It's not a given that you can just swap reflectors around. Antenna design at microwave frequencies is complex.
I realize I'm being pedantic here but, for the benefit of those who might not know, the term "odds-on" refers to odds that are better than even or 1:1. None of the events I saw cited had "odds-on" odds.
Thanks for your reply, AC. I would definitely fall under the n00b classification relative to PVR. The Tivo unit I'm considering is the Pioneer Elite DVR-57H, which has a built-in DVD recorder that supposedly makes archiving recorded shows pretty simple. That said, I'm not sure how much archiving I really would want to do; I think I'm more of a simple time-shifter.
Based on all of that, it sounds to me like you'd endorse the Tivo path. Thanks again for your input, whoever you are.:-)
Thanks for the excellent answer; I now feel as though I have a better idea about Tivo. Additionally, you have piqued my curiosity on ReplayTV. Can you provide any additional commentary on why you decided to go with ReplayTV and how you like it? Maybe this would be a better way for me to go.
Thank you for your reply. I'm curious as to how long you think Tivo has in your scenario. Years? Months? Also, if one rolls one's own hard disk recording setup, is there some sort of OSS equivalent to the downloadable program guide, or is it strictly manual programming only?
I apologize if this is semi-OT, and this might not be the best place to ask, but I value intelligent Slashdot readers's views so I would like to ask your advice. I am considering purchasing a Tivo hard disk recorder (my first) and I am wondering: Is this wise or am I going to find myself the proud owner of a device which might soon be rendered inert by DMCA-related stuff.
I am largely ignorant of the details, and maybe even the broad strokes, so please be gentle.:-)
I've read through quite a few posts and have a couple of thoughts. I think a lot of the sensitivity does surround the devfs/udev issue, since that was a key item in the article and has been advertised in the past. My experience with devfs, in the context of Gentoo Linux, has been positive, though I am looking forward to trying udev. We've all known devfs was not much longer for this world; I think we're just a little surprised that it's being yanked out of 2.6.
Beyond that, my reaction to this article is mixed. Like many who have posted, I am hopeful that the Linux developers, in concert with those distribution developers who contribute actively to kernel development, will keep the process on the right track. Perhaps this is just a paradigm shift, with its attendant acceptance resistance, or maybe it's even just an official statement of the de facto way of doing things that has been in place for a while. (I'm no expert on this, so I can't tell myself.) Regardless, I can't help but consider it on the heels of the kernel headers decision and glibc's altered (i.e., non) release strategy as being a potentially dangerous direction to pursue. But we must allow for change and give folks the benefit of the doubt. As a few have pointed out, it is their project first and foremost; we are but the beneficiaries of their work.
A whisker doesn't have to survive conducting enough current to let the smoke out of the power supply - in it's incandescent passing, if the ghost of it's exisistance is a sliver of plasma, a very substaintial, if evanescent, conductor is created, literally, out of thin air.
Thanks for this, gessel. In the aerospace industry, where I work, tin whiskers are the problem. In a vacuum (test or on-orbit), a shorting whisker can result in a plasma condition that will arc, allowing literally hundreds of amperes of current to flow for durations on the order of tens of seconds. This has been the cause of loss of many units and even entire systems. Of course, this is in a vacuum; in a non-vacuum situation, though, it is still possible to create localized low-pressure areas that might enable this phenomenon.
Whether or not this relates to the computer room problems of this article is not strictly relevant to the point I want to make. My point is: Many things happen in ways you wouldn't expect; intuition is not always your best guide to determining cause-effect.
I'm curious as to why you think the usefulness of a moon-based telescope would be restricted to only two weeks per month. Can you explain?
I'm assuming that no matter where it is located (near side or far side), a telescope that can be gimballed can be useful 24/7, so long as sun and Earth intrusion in the field of view is eliminated. Am I missing something?
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I live in Torrance, CA (Los Angeles area). But I was born and lived my first 13 years in Vancouver, Canada. You know, the Great White North.
Good day, eh.
Actually, I just included that to help the less technically inclined relate to what I was saying. Lighten up, man.
I agree this was greatly worded. The effluvium of post-mortem porcine matter is priceless.
Think "Clear and Present Danger".
Oops, I meant "Patriot Games".
I have no specific knowledge of NRO or anything else spooky. However, from watching TV shows, etc., it is well known that "spy" satellites operate in low Earth orbit (LEO) or maybe medium Earth orbit (MEO). These orbits are polar, allowing the satellites to be tasked wherever imaging, etc., is desired. Think "Clear and Present Danger".
It's cool to talk with a Rush fan on here. (I'm sure there are plenty, but it's cool just the same to hear what you have to say.)
:-)
You're right about the metalhead reaction to synths and stuff. Oh, well; their loss I think. Of course, they're getting what they want again these days--Vapor Trails has some hard guitar work in it. And if you bought the EP, well, that's got a lot of rockin' in it for most anyone.
I wonder if you're 100% right in saying they refuse to play some songs because they might be "simple" or "embarassing". I'm not trying to argue with you, mind you, but I'm just wondering if that is, indeed, their thinking. I've gathered from my reading, etc., that it's more of a feel thing. For instance, I heard they struggled quite a bit coming up with the set list for the 30th anniversary tour, but settled on what they went with as a best combination. I heard that some songs were thrown out just because they weren't getting a good vibe playing them, for whatever reason. And, as you know, getting into a song is totally where it's at to produce a good live experience.
I do think it's interesting that they did the same set list for all the shows on that tour. Vapor Trails wasn't that way, of course. I was happy that the Manchester show, which I flew cross-country to go see and which was their last show in North America before heading to Brazil, included "Closer To The Heart"; this was the only stop in NA that had that song and it's a real crowd pleaser. I felt treated that night.
BTW, I sure wish I could hear "Camera Eye" live. I have just recently "discovered" that song for myself ("buried as it were on the not often played second side of Moving Pictures") and I think it's great. I sure don't think it's simple or embarassing. That one probably gets thrown out on account of length.
Take it easy, dude.
Oh, yeah, I forgot to make my point w.r.t. SW and George Lucas vs. the Rush analogy. The big difference to me is that, aside from remastering their existing albums in the 1990's to take advantage of improvements in A/D technology, etc., Rush doesn't go back and change their work. They are content to let it rest on its merits, warts and all. And it rests just fine that way.
I think this is a key difference.
You know, it's funny, because I was thinking of drawing an analogy with Rush in my post. Rush is my favorite group, so I am aware of criticisms, etc.
Many people dismiss everything after Moving Pictures. (Some people dismiss everything other than Moving Pictures!) These folks seem to want more and more Moving Pictures-type songs from the band, as though that is what Rush should ever be about.
Now, I have no problem with people liking Moving Pictures, or even thinking it's their fav Rush album. But the fact is that Rush has been around for thirty years now, making new music almost the entire time. And another fact is that there is a lot of good music in their more recent offerings. In part, this is because they have evolved in life and their music has evolved with them. For us listeners that have evolved, too, the gems are there.
I know I've never enjoyed concerts more than 2002's Vapor Trails tour (Manchester, NH) or this year's 30th anniversery tour (Hollywood Bowl, CA, and Irvine Meadows, CA).
Rock on!
I think the difference is that, despite what we think of the latest movies, (I believe) George Lucas really cares about the movies he's making. I think they are exactly what he wants, exactly how he envisions them (as opposed to, apparently, the original three). He is putting a tremendous amount of effort into these projects to realize his vision and probably is getting burned out in the process.
It's just too bad for us that his "imperfect" versions of the stories from the 1977-1983 timeframe are the ones we really like.
You seem to know what you are talking about.
:-) This radiated energy impinges on the satellite, heating its surfaces just as it heats the Earth's surface. The effect of solar heating can be easily seen when monitoring spacecraft temperature telemetry during eclipse. As the satellite transits the penumbral and umbral regions, temperatures drop since the Earth shadows the satellite from the sun's radiation. When the satellite emerges from eclipse and reenters the sun's light, temperatures rise again. (Incidentally, these cooling and heating transients can induce localized deformations as the satellite's structure expands and contracts with the heat. These deformations can even create attitude disturbances, which can be seen via satellite gyro telemetry.)
:-)
Thank you. Well, I work for Boeing Satellite Systems (nee Hughes), where I've worked since college graduation (17 years now!).
But on to your questions....
Yes, space is a pretty hard vacuum. There is a little dust, etc., but it's a vacuum. It is also quite cold, in general. As another poster below explains, there are several modes of heat transmission, including conduction and radiation. You are correct in asserting that conduction is not where it's at in space since there's no conducting medium. However, radiation is where it's at.
The sun radiates thermal energy; that's one of the things that keeps us all alive.
There are other sources of heat on the satellite,of course. Most prominent are any high-power amplifiers, especially TWTAs (travelling wave tube amplifiers, the primary technology used for high-power amplification), but all electronics boxes generate heat to one extent or another.
Another dimension is that the satellite is not uniformly lit by the sun; for instance, the "backside," i.e., the side facing away from the sun, is in shadow. These areas do not get the benefit of solar heating and would be quite cold if not for active heater control.
So, you have to manage heat and cold, making cold areas sufficiently warm for electronics (and mechanisms) to operate and keeping hot areas from getting too hot. This is where the various technologies and tricks I mentioned come into play.
Radiation is a big part of this strategy. Remember that, unlike conduction, radiation does not require a medium to work. Thus, radiators on the satellite can, in fact, radiate excess heat to space.
Hopefully, this sheds a little light on the subject.
Years ago, I processed reports from an organization known as the IFRB, which I seem to remember as the International Frequency Registration Board, or something like that. This organization received, circulated, and arbitrated RFCs for frequency bands made by the various satellite providers/manufacturers around the world. The purpose was to avoid interference between new systems and existing systems.
:-)
Many techniques exist for reducing or eliminating interference, not just frequency separation. Polarization schemes are a big part of the solution, but there are others (spatial isolation, of course, and coding schemes with digital systems).
If your data transmission is at all on the radar, so to speak, I think it'd be safe to say people are designing new systems to be compatible. Or so we think.
Solar cells are small. They are arrayed to create solar arrays, or solar panels. These can be quite large, depending on the power requirements of the satellite.
Nominal power ratings for satellites assume sun-normal orientation of the solar arrays, which is actively maintained by the satellite. The satellite receives 100% illumination by the sun during most of the year, the exceptions being the spring and fall eclipse seasons, when the satellite transits the Earth's penumbral and umbral regions for up to a couple of hours per day. During these events, solar array power is augmented with battery power. Bus voltage drops and current draws increase, but transmitted powers generally stay the same. Yes, over the life of the satellite (10-15+ years) batteries degrade somewhat, though battery reconditioning techniques are employed to mitigate this. With today's designs, running out of fuel is usually what limits mission life.
The reason terrestrial radio stations require the power levels they do is that they typically transmit more or less omni-directionally (or at least toroidally), as opposed to how geo satellites use highly-directional (high gain) antennas for CONUS (or whatever) coverage. The effect of the differences between these two antenna types (tens of dB in gain) far outweighs the 20 dB power difference you mention (1 kW vs. 100 kW). The high gain antennas for DBS allow multiple channels of high bandwidth at reduced power vs. their terrestrial brethren. They're really two totally different kettles of fish.
Finally, thermal management is an important part of modern satellite design. Heat pipes, thermal radiators (mirrors), finishes, and other techniques are all used to collect, distribute, and reject heat. The effectiveness of these techniques can limit a design, and how capable a company is at dealing with thermal problems can determine the capabilities of its offerings relative to those of its competitors.
BTW, the current commercial satellite models offered by Boeing are based on the 702 bus, which supercedes the 601. Both of these designs were the product of Hughes Space and Communications Co. (part of the old Hughes Aircraft Company), now Boeing Satellite Systems (Boeing bought HSC in 2000).
The power levels seen at the Earth's surface are exceedingly low, hence the need for highly sensitive low-noise amplifiers to retrieve the signals. Not a cause for concern.
C band hardware doesn't have a problem with rain fade because the dish is over a meter wide.
Actually, the primary reason for C band's superior performance w.r.t. rain fade is the reduced atmospheric attenuation associated with lower frequencies, in general, and, in particular, with C band's frequencies vs. K band's frequencies. The atmosphere has different effects at different frequencies. The reduced attenuation at C band allows for greater link margin and, therefore, greater link robustness vs. rain.
The gains of a 1.8m dish at C band and a DirecTV dish at K band are similar. (Higher frequencies require smaller dishes for the same gain.)
If you aimed a 1.8m dish at one of the DTV birds, you wouldn't have a problem with rain fade either. (you'd have a bigger problem keeping it properly aimed, btw.)
Very true. Of course, the dish (antenna, in general) would have to be designed to operate at K band frequencies. It's not a given that you can just swap reflectors around. Antenna design at microwave frequencies is complex.
Not that I have anything against Mr. Garfinkel, but...
... SUCKS!"
:-)
"Simson Garfinkel
Those of you who watched an LSC show in 26-100 ~20 years ago will recognize what I am referring to. (Sorry for ending with a preposition
-- Adam Grenberg, MIT '87
I realize I'm being pedantic here but, for the benefit of those who might not know, the term "odds-on" refers to odds that are better than even or 1:1. None of the events I saw cited had "odds-on" odds.
Thanks for your reply, AC. I would definitely fall under the n00b classification relative to PVR. The Tivo unit I'm considering is the Pioneer Elite DVR-57H, which has a built-in DVD recorder that supposedly makes archiving recorded shows pretty simple. That said, I'm not sure how much archiving I really would want to do; I think I'm more of a simple time-shifter.
:-)
Based on all of that, it sounds to me like you'd endorse the Tivo path. Thanks again for your input, whoever you are.
Thanks for the excellent answer; I now feel as though I have a better idea about Tivo. Additionally, you have piqued my curiosity on ReplayTV. Can you provide any additional commentary on why you decided to go with ReplayTV and how you like it? Maybe this would be a better way for me to go.
Thank you for your reply. I'm curious as to how long you think Tivo has in your scenario. Years? Months? Also, if one rolls one's own hard disk recording setup, is there some sort of OSS equivalent to the downloadable program guide, or is it strictly manual programming only?
I apologize if this is semi-OT, and this might not be the best place to ask, but I value intelligent Slashdot readers's views so I would like to ask your advice. I am considering purchasing a Tivo hard disk recorder (my first) and I am wondering: Is this wise or am I going to find myself the proud owner of a device which might soon be rendered inert by DMCA-related stuff.
:-)
I am largely ignorant of the details, and maybe even the broad strokes, so please be gentle.
I've read through quite a few posts and have a couple of thoughts. I think a lot of the sensitivity does surround the devfs/udev issue, since that was a key item in the article and has been advertised in the past. My experience with devfs, in the context of Gentoo Linux, has been positive, though I am looking forward to trying udev. We've all known devfs was not much longer for this world; I think we're just a little surprised that it's being yanked out of 2.6.
Beyond that, my reaction to this article is mixed. Like many who have posted, I am hopeful that the Linux developers, in concert with those distribution developers who contribute actively to kernel development, will keep the process on the right track. Perhaps this is just a paradigm shift, with its attendant acceptance resistance, or maybe it's even just an official statement of the de facto way of doing things that has been in place for a while. (I'm no expert on this, so I can't tell myself.) Regardless, I can't help but consider it on the heels of the kernel headers decision and glibc's altered (i.e., non) release strategy as being a potentially dangerous direction to pursue. But we must allow for change and give folks the benefit of the doubt. As a few have pointed out, it is their project first and foremost; we are but the beneficiaries of their work.
Good answer. I have grown weary of the typical devfs bashing; it's nice to hear a coherent and non-inflammatory explanation for a change.
A whisker doesn't have to survive conducting enough current to let the smoke out of the power supply - in it's incandescent passing, if the ghost of it's exisistance is a sliver of plasma, a very substaintial, if evanescent, conductor is created, literally, out of thin air.
Thanks for this, gessel. In the aerospace industry, where I work, tin whiskers are the problem. In a vacuum (test or on-orbit), a shorting whisker can result in a plasma condition that will arc, allowing literally hundreds of amperes of current to flow for durations on the order of tens of seconds. This has been the cause of loss of many units and even entire systems. Of course, this is in a vacuum; in a non-vacuum situation, though, it is still possible to create localized low-pressure areas that might enable this phenomenon.
Whether or not this relates to the computer room problems of this article is not strictly relevant to the point I want to make. My point is: Many things happen in ways you wouldn't expect; intuition is not always your best guide to determining cause-effect.
To paraphrase...
:-)
"There are only two things I can't stand: People who are intolerant of other people's culture... and the Dutch!"
-- N. Powers
Toit since 1965
I'm curious as to why you think the usefulness of a moon-based telescope would be restricted to only two weeks per month. Can you explain?
I'm assuming that no matter where it is located (near side or far side), a telescope that can be gimballed can be useful 24/7, so long as sun and Earth intrusion in the field of view is eliminated. Am I missing something?