Re: [time-nuts] time sync by moonbounce
That’s it! And Author Mudgway turns out to be from Sonoma, a town in my county just a few miles east of me. I wonder if I can get him to sign my copy when it comes out? On Sat, May 23, 2020 at 3:52 PM Adam Kumiszcza wrote: > I think this is available here: > https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20020033033.pdf and > here: > > https://books.google.pl/books?id=vn5TMAAJ=frontcover=pl=gbs_ge_summary_r=0#v=onepage=false > > Best regards, > Adam Kumiszcza > > On Sat, May 23, 2020 at 5:20 PM Jeremy Nichols wrote: > > > Sufficiently interesting that I bought a paper copy through Abebooks. > Looks > > like a somewhat later version, author given as Douglas Mudgway, title > > “ Uplink-Downlink: > > A History of the Deep Space Network 1957-1997.” “Oversized,” 674 > > pages. Abebooks > > lists a couple dozen copies in both hardback and paperback at prices from > > reasonable to ridiculous, as is usual for bookstores. > > > > Jeremy > > > > > > On Sat, May 23, 2020 at 3:47 AM ew via time-nuts < > time-nuts@lists.febo.com > > > > > wrote: > > > > > This is a must read. Could not put it down, JPL, NASA, Eisenhowe,r did > > > learn a lot at the same time fascinating > > > Bert Kehren > > > In a message dated 5/22/2020 10:36:53 PM Eastern Standard Time, > > > jim...@earthlink.net writes: > > > > > > Apparently, they used moonbounce between DSN stations to synchronize > to 5 > > > microseconds in 1968. It was easier and cheaper than flying cesium > clocks > > > around. (And the Rb standards weren't good enough). > > > https://ntrs.nasa.gov/search.jsp?R=19770007245 > > > History of DSN - mostly about politics, history, transmitters and > > > receivers, but a whole section on timekeeping, phase measurements, etc. > > > starting around page 133 (The DSN Inherent accuracy project), and the > > > discovery during Mariner that UTC and UTI were different enough to > cause > > > nav errors. > > > ___time-nuts mailing list > -- > > > time-n...@lists.febo.comTo unsubscribe, go to > > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.comand > > follow > > > the instructions there. > > > ___ > > > time-nuts mailing list -- time-nuts@lists.febo.com > > > To unsubscribe, go to > > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > > and follow the instructions there. > > > > > -- > > Jeremy Nichols > > Sent from my iPad 6. > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > -- Jeremy Nichols Sent from my iPad 6. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] NYTimes: New geoid soon
In a similar vein I recommend “The Measure of All Things,” by Ken Alder, the story of Méchain and Delambre and the history of the meter. (Published by The Free Press in 2002.) On Sat, May 23, 2020 at 1:07 PM Steve Allen wrote: > On Sat 2020-05-23T12:21:17-0700 jimlux hath writ: > > > So fiendishly difficult that the first time the task was completed was > > > not until 1899 > > > > And how long did Mr. Schott and the team work on it? > > The reason that this report was in the Lick library is that the > observatory hosted one of the sites in 1888. google will reveal scans > of a lot of the preliminary reports for the traverse in parts farther > east. > > -- > Steve Allen WGS-84 (GPS) > UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat > +36.99855 > 1156 High Street Voice: +1 831 459 3046 Lng > -122.06015 > Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > -- Jeremy Nichols Sent from my iPad 6. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] time sync by moonbounce
I think this is available here: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20020033033.pdf and here: https://books.google.pl/books?id=vn5TMAAJ=frontcover=pl=gbs_ge_summary_r=0#v=onepage=false Best regards, Adam Kumiszcza On Sat, May 23, 2020 at 5:20 PM Jeremy Nichols wrote: > Sufficiently interesting that I bought a paper copy through Abebooks. Looks > like a somewhat later version, author given as Douglas Mudgway, title > “ Uplink-Downlink: > A History of the Deep Space Network 1957-1997.” “Oversized,” 674 > pages. Abebooks > lists a couple dozen copies in both hardback and paperback at prices from > reasonable to ridiculous, as is usual for bookstores. > > Jeremy > > > On Sat, May 23, 2020 at 3:47 AM ew via time-nuts > > wrote: > > > This is a must read. Could not put it down, JPL, NASA, Eisenhowe,r did > > learn a lot at the same time fascinating > > Bert Kehren > > In a message dated 5/22/2020 10:36:53 PM Eastern Standard Time, > > jim...@earthlink.net writes: > > > > Apparently, they used moonbounce between DSN stations to synchronize to 5 > > microseconds in 1968. It was easier and cheaper than flying cesium clocks > > around. (And the Rb standards weren't good enough). > > https://ntrs.nasa.gov/search.jsp?R=19770007245 > > History of DSN - mostly about politics, history, transmitters and > > receivers, but a whole section on timekeeping, phase measurements, etc. > > starting around page 133 (The DSN Inherent accuracy project), and the > > discovery during Mariner that UTC and UTI were different enough to cause > > nav errors. > > ___time-nuts mailing list -- > > time-n...@lists.febo.comTo unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.comand > follow > > the instructions there. > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > -- > Jeremy Nichols > Sent from my iPad 6. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] NYTimes: New geoid soon
On Sat 2020-05-23T12:21:17-0700 jimlux hath writ: > > So fiendishly difficult that the first time the task was completed was > > not until 1899 > > And how long did Mr. Schott and the team work on it? The reason that this report was in the Lick library is that the observatory hosted one of the sites in 1888. google will reveal scans of a lot of the preliminary reports for the traverse in parts farther east. -- Steve Allen WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] time sync by moonbounce
On 5/23/20 8:19 AM, Jeremy Nichols wrote: Sufficiently interesting that I bought a paper copy through Abebooks. Looks like a somewhat later version, author given as Douglas Mudgway, title “ Uplink-Downlink: A History of the Deep Space Network 1957-1997.” “Oversized,” 674 pages. Abebooks lists a couple dozen copies in both hardback and paperback at prices from reasonable to ridiculous, as is usual for bookstores. Jeremy A good read (there's a morning for you)... Not much technical detail in the book (it's a history, not a textbook), but there are good references. An interesting comment in the early part about why there's not a good set of documents to refer to. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] NYTimes: New geoid soon
On 5/23/20 11:52 AM, Steve Allen wrote: On Fri 2020-05-22T23:16:49-0700 Hal Murray hath writ: It is a fiendishly difficult math and physics task that, once completed, will have taken a decade and a half to accomplish. So fiendishly difficult that the first time the task was completed was not until 1899 And how long did Mr. Schott and the team work on it? What about the Clarke 1866 spheroid? A book about the Indian subcontinent measuring: "The Great Arc" by John Keay is also good. These days, in the US, making similar measurements we don't have to worry too much about being eaten by tigers. The Transcontinental Triangulation and the American Arc of the Parallel Assistant CHAS. A. SCHOTT, Chief of the Computing Division, USC ftp://ftp.library.noaa.gov/docs.lib/htdocs/rescue/cgs_specpubs/QB275U35no41900.pdf -- Steve Allen WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] NYTimes: New geoid soon
On Fri 2020-05-22T23:16:49-0700 Hal Murray hath writ: > It is a fiendishly difficult > math and physics task that, once completed, will have taken a decade and a > half to accomplish. So fiendishly difficult that the first time the task was completed was not until 1899 The Transcontinental Triangulation and the American Arc of the Parallel Assistant CHAS. A. SCHOTT, Chief of the Computing Division, USC ftp://ftp.library.noaa.gov/docs.lib/htdocs/rescue/cgs_specpubs/QB275U35no41900.pdf -- Steve Allen WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] time nuttery in Space Communications
Some of the stories of deep space communication are really interesting. Round-trip light times measured in hours, data rates measured in bits per minute, remote transmitters with only a few watts. The knowledge is limited to just a handful of people, I suppose. On Sat, May 23, 2020 at 10:44 AM jimlux wrote: > One thing in all these DSN histories is that they don't make very much > of the essential thing that separates Deep Space radio links from Near > Earth radio links, and that's the timing: specifically the coherent link > between the received signal and transmitted signal. I suspect that's > just because it's an "of course it's coherent" for everyone who does > deep space comm, so it's of no great notice. > > > One thing I find in folks building and using ground stations (and > spacecraft) for LEO (vs beyond GEO) is that they essentially treat the > communications path to the spacecraft (telecommand, in the lingo) as > entirely separate from the communications path from the spacecraft > (telemetry, in the lingo). > > This is also found in textbooks on communications systems at whatever > level - you have a sender, you have a propagation path, you have a > receiver. > If there's a "connection" between the two directions, it's usually > handled as a "network" thing (in the sense of ARQ or ACK/NAK, perhaps). > > Things like Doppler and oscillator stability are "nuisances to be > compensated for" so that the receiver can be tuned to the right frequency. > > More than one ground station system for Earth orbit has no idea how long > it takes for the signals to propagate through the chain - it doesn't > matter - I put bits in at one end, and not too long (milliseconds, maybe > seconds) the bits come out the other end. > > > However, for those of us using the radio signals to track and navigate, > or to do science, that "round trip light time" or "phase difference > between receiving the signal at two different stations" is really, > really important. > > And, a bit of codger, "get off my grass" sense (and I'm a relative > newbie, having only done this for 20 years) - all those folks who are > excited about going to the Moon are having to learn this all again. > There's no GPS to give you your position, an omni antenna won't close > the link, etc. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > -- Jeremy Nichols Sent from my iPad 6. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] time nuttery in Space Communications
One thing in all these DSN histories is that they don't make very much of the essential thing that separates Deep Space radio links from Near Earth radio links, and that's the timing: specifically the coherent link between the received signal and transmitted signal. I suspect that's just because it's an "of course it's coherent" for everyone who does deep space comm, so it's of no great notice. One thing I find in folks building and using ground stations (and spacecraft) for LEO (vs beyond GEO) is that they essentially treat the communications path to the spacecraft (telecommand, in the lingo) as entirely separate from the communications path from the spacecraft (telemetry, in the lingo). This is also found in textbooks on communications systems at whatever level - you have a sender, you have a propagation path, you have a receiver. If there's a "connection" between the two directions, it's usually handled as a "network" thing (in the sense of ARQ or ACK/NAK, perhaps). Things like Doppler and oscillator stability are "nuisances to be compensated for" so that the receiver can be tuned to the right frequency. More than one ground station system for Earth orbit has no idea how long it takes for the signals to propagate through the chain - it doesn't matter - I put bits in at one end, and not too long (milliseconds, maybe seconds) the bits come out the other end. However, for those of us using the radio signals to track and navigate, or to do science, that "round trip light time" or "phase difference between receiving the signal at two different stations" is really, really important. And, a bit of codger, "get off my grass" sense (and I'm a relative newbie, having only done this for 20 years) - all those folks who are excited about going to the Moon are having to learn this all again. There's no GPS to give you your position, an omni antenna won't close the link, etc. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] time sync by moonbounce
On 5/23/20 9:18 AM, Mike Millen wrote: Probably a good idea... there are two page 19s and no page 20 in the pdf. :-( That's the page where the aliens came and told us how to build the DSN, then the story resumes with 26m antenna design and operation. (If anyone's interested, I can probably ask the librarians to find it at JPL - correcting the pdf/microfilm is probably beyond scope) Mike - M0MLM On 23/05/2020 17:12, Wes wrote: You talked me in to it. Wes N7WS On 5/23/2020 8:19 AM, Jeremy Nichols wrote: Sufficiently interesting that I bought a paper copy through Abebooks. Looks like a somewhat later version, author given as Douglas Mudgway, title “ Uplink-Downlink: A History of the Deep Space Network 1957-1997.” “Oversized,” 674 pages. Abebooks lists a couple dozen copies in both hardback and paperback at prices from reasonable to ridiculous, as is usual for bookstores. Jeremy ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] time sync by moonbounce
On 5/23/20 8:19 AM, Jeremy Nichols wrote: Sufficiently interesting that I bought a paper copy through Abebooks. Looks like a somewhat later version, author given as Douglas Mudgway, title “ Uplink-Downlink: A History of the Deep Space Network 1957-1997.” “Oversized,” 674 pages. Abebooks lists a couple dozen copies in both hardback and paperback at prices from reasonable to ridiculous, as is usual for bookstores. Different author (The report I pointed to is by William Corliss), but perhaps the same source material, (at least up to 1975) it's available as a downloadable pdf, theoretically (although the link is to the cover page only) - I'll talk to the site owner and get that fixed. https://descanso.jpl.nasa.gov/history/dsnHistory.html (there's a version here: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20020033033.pdf) The second link on the dsnhistory page, to a list of references, is something you might find interesting. There's a set of books published by JPL at https://descanso.jpl.nasa.gov/ Various series.. Some are not particularly time-nutty, but some are - I'd look for things on radiometric tracking and nav. Here's a whole series on it: https://descanso.jpl.nasa.gov/evolution/evolution.html - not much technical detail in the paper, more a history of what was done when, but the papers in the references might be useful. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] time sync by moonbounce
Probably a good idea... there are two page 19s and no page 20 in the pdf. :-( Mike - M0MLM On 23/05/2020 17:12, Wes wrote: You talked me in to it. Wes N7WS On 5/23/2020 8:19 AM, Jeremy Nichols wrote: Sufficiently interesting that I bought a paper copy through Abebooks. Looks like a somewhat later version, author given as Douglas Mudgway, title “ Uplink-Downlink: A History of the Deep Space Network 1957-1997.” “Oversized,” 674 pages. Abebooks lists a couple dozen copies in both hardback and paperback at prices from reasonable to ridiculous, as is usual for bookstores. Jeremy ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] time sync by moonbounce
You talked me in to it. Wes N7WS On 5/23/2020 8:19 AM, Jeremy Nichols wrote: Sufficiently interesting that I bought a paper copy through Abebooks. Looks like a somewhat later version, author given as Douglas Mudgway, title “ Uplink-Downlink: A History of the Deep Space Network 1957-1997.” “Oversized,” 674 pages. Abebooks lists a couple dozen copies in both hardback and paperback at prices from reasonable to ridiculous, as is usual for bookstores. Jeremy On Sat, May 23, 2020 at 3:47 AM ew via time-nuts wrote: This is a must read. Could not put it down, JPL, NASA, Eisenhowe,r did learn a lot at the same time fascinating Bert Kehren In a message dated 5/22/2020 10:36:53 PM Eastern Standard Time, jim...@earthlink.net writes: Apparently, they used moonbounce between DSN stations to synchronize to 5 microseconds in 1968. It was easier and cheaper than flying cesium clocks around. (And the Rb standards weren't good enough). https://ntrs.nasa.gov/search.jsp?R=19770007245 History of DSN - mostly about politics, history, transmitters and receivers, but a whole section on timekeeping, phase measurements, etc. starting around page 133 (The DSN Inherent accuracy project), and the discovery during Mariner that UTC and UTI were different enough to cause nav errors. ___time-nuts mailing list -- time-n...@lists.febo.comTo unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.comand follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] time sync by moonbounce
Sufficiently interesting that I bought a paper copy through Abebooks. Looks like a somewhat later version, author given as Douglas Mudgway, title “ Uplink-Downlink: A History of the Deep Space Network 1957-1997.” “Oversized,” 674 pages. Abebooks lists a couple dozen copies in both hardback and paperback at prices from reasonable to ridiculous, as is usual for bookstores. Jeremy On Sat, May 23, 2020 at 3:47 AM ew via time-nuts wrote: > This is a must read. Could not put it down, JPL, NASA, Eisenhowe,r did > learn a lot at the same time fascinating > Bert Kehren > In a message dated 5/22/2020 10:36:53 PM Eastern Standard Time, > jim...@earthlink.net writes: > > Apparently, they used moonbounce between DSN stations to synchronize to 5 > microseconds in 1968. It was easier and cheaper than flying cesium clocks > around. (And the Rb standards weren't good enough). > https://ntrs.nasa.gov/search.jsp?R=19770007245 > History of DSN - mostly about politics, history, transmitters and > receivers, but a whole section on timekeeping, phase measurements, etc. > starting around page 133 (The DSN Inherent accuracy project), and the > discovery during Mariner that UTC and UTI were different enough to cause > nav errors. > ___time-nuts mailing list -- > time-n...@lists.febo.comTo unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.comand follow > the instructions there. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > -- Jeremy Nichols Sent from my iPad 6. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] time sync by moonbounce
This is a must read. Could not put it down, JPL, NASA, Eisenhowe,r did learn a lot at the same time fascinating Bert Kehren In a message dated 5/22/2020 10:36:53 PM Eastern Standard Time, jim...@earthlink.net writes: Apparently, they used moonbounce between DSN stations to synchronize to 5 microseconds in 1968. It was easier and cheaper than flying cesium clocks around. (And the Rb standards weren't good enough). https://ntrs.nasa.gov/search.jsp?R=19770007245 History of DSN - mostly about politics, history, transmitters and receivers, but a whole section on timekeeping, phase measurements, etc. starting around page 133 (The DSN Inherent accuracy project), and the discovery during Mariner that UTC and UTI were different enough to cause nav errors. ___time-nuts mailing list -- time-n...@lists.febo.comTo unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.comand follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] NYTimes: New geoid soon
The US is tilted. Florida is about right. Seattle is a meter high. The U.S. Is Getting Shorter, as Mapmakers Race to Keep Up https://www.nytimes.com/2020/05/22/science/maps-elevation-geodetic-survey.html But across the United States, the heights of structures, landmarks, valleys, hills and just about everything else are about to change, at least with regard to average sea level. Most will get shorter. Parts of the Pacific Northwest will shrink by as much as five feet, and parts of Alaska by six-and-a-half, according to Juliana P. Blackwell, director of the National Geodetic Survey. Seattle will be 4.3 feet lower than it is now. That's because height is only height compared to a reference point -- and geodesists, who calculate the Earth's shape, size, gravitational field and orientation in space over time, are redefining the reference point, or vertical datum, from which height is derived. It is a fiendishly difficult math and physics task that, once completed, will have taken a decade and a half to accomplish. --- But making highly detailed measurements of the gravitational field, in order to factor them into heights captured by GPS, is no small task. In 2007, the National Geodetic Survey launched an ambitious mission -- GRAV-D, for Gravity for the Redefinition of the American Vertical Datum -- to accomplish just that. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
