Good books about the moon landings hoax?

[ka9q]

We don't have to send a spacecraft up to verify how orbits work. Or how gravity works, or how vacuum works. It took a while for the engineering -- the power sources, the control strategies -- to get there, but the orbital principles were known by Kepler.

To a first order, yes. The actual practice must deal with some important second-order orbital mechanics. Several perturbing forces act on a geostationary satellite. The moon and sun tend to slowly change the inclination, causing the satellite to describe a north-south figure-8 pattern. The earth's equator is not a perfect circle, so the uneven distribution of mass tends to move geostationary satellites in an east or west direction toward a couple of stable longitudes.

The first (north-south) effect is the much bigger one, but both require periodic stationkeeping maneuvers to keep them in their assigned locations. When the fuel for these maneuvers runs out, the spacecraft usually has to be retired and replaced but sometimes alternate uses can be found for them that do not require them to be absolutely stationary. These include mobile communications (since the users need tracking antennas anyway) and communications with the poles which are not visible at all from a true geostationary orbit. The older TDRSS satellites are heavily used for communications with Scott-Amundsen Base at the south pole.

I don't think Clarke addressed these issues; in fact, he assumed the electronics would use vacuum tubes and be so unreliable that the relay stations would need crews to maintain them. He probably didn't foresee that space electronics would become so reliable that fuel exhaustion would be the major reason for mission termination.

[nomuse]

Heh.  Nicely put. I haven't had time to read his paper, but I suspected strongly -- if for no other reason than the audience -- he wasn't going to mention how the orbit wasn't quite as simple and perfect as that first approximation!

[ka9q]

He said "Cooky, we need to re-point the telescope. Some Chilean astronomers have discovered a supernova in the LMC."

Neat! How long after the actual explosion (earth received time) did you begin observing?

Given your location in the southern hemisphere and the absence of other large bodies of land (i.e., observatories) at your longitude, I suspect that at least some of your light curve data was collected by no one else.

[ka9q]

+420320.00 -0924513.21 19790822 230000-06

[...]
 You'd be a steely-eyed missile man if you could decipher what the data format is and what it means.

Okay, I'll bite.

The first token is a latitude, 42 deg 03' 20.00" N. The second is a longitude, 92 deg 45' 13.21" W. (This is northeast of DeMoines IA in what appears to be a plowed field. A good observing site away from light pollution?)

The third is probably a date, August 22, 1979 (a Wednesday).

Only the last one doesn't ring a bell. An object or catalog number? You did imply later that it was an ephemeris program of some sort.

Oh, wait. It could be a local time: 23:00:00, 6 hours behind UTC (which is the offset for the central time zone, including Iowa, although being summer they would be only 5 hours behind UTC).

[ka9q]

Heh.  Nicely put. I haven't had time to read his paper, but I suspected strongly -- if for no other reason than the audience -- he wasn't going to mention how the orbit wasn't quite as simple and perfect as that first approximation!

Right. Even nominally-geostationary satellites (the ones actively kept on station) are not precisely stationary. They're kept within a tolerance box to avoid wasting propellant on excessive precision. Typically it's only small enough to ensure that the satellite remains within the beams of the (usually non-steerable) antennas pointed at that orbital location, and that they don't drift into the beams of antennas pointed at some other location.

This is why east-west stationkeeping is usually more important than north-south stationkeeping; also, east-west stationkeeping uses much less fuel so satellites with a relaxed inclination tolerance (e.g., for mobile communications) can have much longer service lives. The non-zero inclination of the Inmarsat satellite over the Indian Ocean through which Malaysian Airlines 370 was transmitting is what allowed analysts to determine that it most likely went in a southerly direction.

In the mid 1970s I spent college summers as an engineering intern at the Baltimore PBS TV station. This was shortly before PBS started using geostationary satellites for program distribution, starting with Westar IV, I think. When I returned for a visit, they were uplinking a program and that gave me an idea. I punched up the satellite downlink on a vectorscope (a special-purpose oscilloscope that showed the NTSC color signal in a polar vector format) and selected house subcarrier (which was being used for the uplink). This would show me the relative phase between the uplink and downlink. Sure enough, the color burst was rotating very slowly, indicating that the range to the satellite was slowly changing. The NTSC color subcarrier is about 3.58 MHz, which has a wavelength of about 84 meters, so each complete 360 degree rotation corresponded to a change in range of 42 meters.

I don't remember the actual rotation rate, but it was quite slow so the actual range-rate was only a fraction of a meter per second. In these days long before GPS I thought it was totally cool that I could measure the relative velocity of something that far away so precisely using equipment that wasn't even designed for the purpose.

Apollo used the same two-way Doppler technique to measure range-rate, but they did it at the RF carrier frequency of about 2280 MHz so their measurements were considerably more precise than mine. The same technique is still widely used today.

[smartcooky]

+420320.00 -0924513.21 19790822 230000-06

[...]
 You'd be a steely-eyed missile man if you could decipher what the data format is and what it means.

Okay, I'll bite.

The first token is a latitude, 42 deg 03' 20.00" N. The second is a longitude, 92 deg 45' 13.21" W. (This is northeast of DeMoines IA in what appears to be a plowed field. A good observing site away from light pollution?)

The third is probably a date, August 22, 1979 (a Wednesday).

Only the last one doesn't ring a bell. An object or catalog number? You did imply later that it was an ephemeris program of some sort.

Oh, wait. It could be a local time: 23:00:00, 6 hours behind UTC (which is the offset for the central time zone, including Iowa, although being summer they would be only 5 hours behind UTC).

There was an annular solar eclipse on 22 August 1979, but I'm sure it wasn't visible in Iowa!!

[smartcooky]

He said "Cooky, we need to re-point the telescope. Some Chilean astronomers have discovered a supernova in the LMC."

Neat! How long after the actual explosion (earth received time) did you begin observing?

Given your location in the southern hemisphere and the absence of other large bodies of land (i.e., observatories) at your longitude, I suspect that at least some of your light curve data was collected by no one else.

SN1987a was detected at around 23:00 UTC on 24 February 1987. That is around 8pm in Chile, and around midday on the 25th in NZ (actually I must have the day wrong in my post because the 24th was a Tuesday and I would not have been at the observatory on a Tuesday night.)

So, we were observing it and recording data by about 11pm, roughly 12 hours after its discovery (the exact time of the explosion was no known).

It was also being observed by Merv Thomas and Stuart Ryder at the Beverly-Begg Observatory in Dunedin. We supplied all our data to the RASNZ, and they forwarded it to the relevant people (IAU I guess)

[Dr_Orpheus]

I don't think Clarke addressed these issues; in fact, he assumed the electronics would use vacuum tubes and be so unreliable that the relay stations would need crews to maintain them. He probably didn't foresee that space electronics would become so reliable that fuel exhaustion would be the major reason for mission termination.

In 1945, electronics which could remain reliable for decades with no human intervention would probably have seemed more fantastic than sending men to the moon.

[ka9q]

In 1945, electronics which could remain reliable for decades with no human intervention would probably have seemed more fantastic than sending men to the moon.

Indeed. And space exploration was one of the drivers for more compact and reliable electronics. Case in point: the Apollo Guidance Computer was the first computer built entirely from integrated circuits.

Interestingly there is one vacuum tube still used by many spacecraft: the traveling wave tube (TWT) RF power amplifier, though they are slowly giving way to solid-state power amplifiers. While TWTs do fail, they are well enough characterized that providing a few spares with a switching arrangement (N-for-M redundancy) is usually enough to get the spacecraft through its design life.

TWTs are so ubiquitous in space communications that their properties (wide bandwidth, a linear region with saturation) has driven the design of most of the modulation, error correction coding and multiple access schemes used in space communications.

Stationkeeping fuel is still the usual limit on communications satellite lifetime. Because thrust requirements are low, it's become a natural application for ion propulsion.

[Luke Pemberton]

In 1945, electronics which could remain reliable for decades with no human intervention would probably have seemed more fantastic than sending men to the moon.

I visited Bletchley Park about 8 months ago where the Heath Robinson code breaking machine was on display. It was a tortuous process to decipher the German codes using the machine. A young engineer (Tommy Flowers) from the Post Office Research Station was invited by Turing to assess whether he could automate the process.

Tommy suggested using valve technology. He could not convince the management at Bletchley Park because the technology was not trusted and prone to breaking down. He argued that the main problem with valves was switching them on and off, which caused them to break. If the valves were switched on and left on, and were operated in a stable environment, there ought not be too many problems. He was correct, and Colosus was born.

OK, time for a bit of chemical warfare with an annoying blue bottle.

[ka9q]

He was correct, and Colosus was born.

I saw that Colossus reconstruction at Bletchley way back in 2001 (shortly before 9/11 -- got home just in time) and I recall that they rarely fired up the tubes -- they were too precious, being no longer made, and probably burned a lot of power too. They just ran that tape loop reader to impress the tourists.

And now I routinely perform that same operation (digital correlation) purely in software on my laptop at far higher speeds than Colossus, though I do it for a different application than codebreaking (looking for noisy sync sequences in communication protocols). Come to think of it, every CDMA mobile phone and every GPS receiver does the same thing.

[JayUtah]

Okay, I'll bite.

Right on all counts.

[Philthy]

The first token is a latitude, 42 deg 03' 20.00" N. The second is a longitude, 92 deg 45' 13.21" W. (This is northeast of DeMoines IA in what appears to be a plowed field. A good observing site away from light pollution?)

This is about 135 miles east of me. Weird.

The third is probably a date, August 22, 1979 (a Wednesday).

My 26th birthday. Even weirder.

Phil

[nomuse]

In 1945, electronics which could remain reliable for decades with no human intervention would probably have seemed more fantastic than sending men to the moon.

I visited Bletchley Park about 8 months ago where the Heath Robinson code breaking machine was on display. It was a tortuous process to decipher the German codes using the machine. A young engineer (Tommy Flowers) from the Post Office Research Station was invited by Turing to assess whether he could automate the process.

Tommy suggested using valve technology. He could not convince the management at Bletchley Park because the technology was not trusted and prone to breaking down. He argued that the main problem with valves was switching them on and off, which caused them to break. If the valves were switched on and left on, and were operated in a stable environment, there ought not be too many problems. He was correct, and Colosus was born.

OK, time for a bit of chemical warfare with an annoying blue bottle.

You know we probably have the greatest concentration here of Americans who actually know what you meant by "Heath Robinson." Wait...they actually NAMED it Heath Robinson? That's so cool....

[Andromeda]

I think Jockndoris is giving us the silent treatment.