herrickd@uunet.UU.NET (daniel lance herrick) (01/22/91)
From: abvax!iccgcc.DNET!herrickd@uunet.UU.NET (daniel lance herrick) Dear Moderator - I found this on .ntp where it had been reposted from rec.ham.radio. It precisely fits your charter and is interesting to readers of sci.military. I wonder if Iraqi military were tracking this detail before the shooting began. dan herrick herrickd@iccgcc.decnet.ab.com X-News: iccgcc comp.protocols.time.ntp:104 From: milton@lion.ecn.purdue.edu (Milton D Miller) Subject:Re: 'time' for war Date: 17 Jan 91 19:06:54 GMT Message-ID:<1991Jan17.190654.15179@noose.ecn.purdue.edu> In article <9101170200.aa15102@louie.udel.edu> Shaw@udel.edu (Mark Shaw) writes: >Philisophically, scientifically, or just for a laugh ... >How is time effected by war? > In article <9101171132.aa10312@huey.udel.edu> Mills@udel.edu writes: >Colin, > >We will know the status of timekeeping in the Gulf more precisely >when we learn the fate of the LORAN-C station in Kuwait operated >by the previous government. > >Dave I found this article posted by Patty Winter for Phil Karn; it is not quite your question, but sort of the reverse: not how does war affect time, but how does time affect war. milton >From: winter@apple.com (Patty Winter) >Newsgroups: rec.ham-radio >Subject: Attack planning by celestial navigation? (P. Karn) >Message-ID: <48202@apple.Apple.COM> >Date: 17 Jan 91 07:38:19 GMT >Sender: winter@Apple.COM >Reply-To: karn@thumper.bellcore.com In article <48202@apple.Apple.COM> karn@thumper.bellcore.com writes: > > >[Phil's news server is acting up tonight so he asked me to post this >for him. His copy will probably show up on the net eventually. --pw] > > >Tuesday afternoon I read in Aviation Week that only 10 of the DoD's planned >18 Global Positioning System (GPS) block II satellites have been launched >and were operational. This means that the GPS navigation service is not yet >continuous world wide. > >It suddenly occurred to me that GPS coverage windows might be a factor in >the timing of the US attack on Iraq and Kuwait; especially at the beginning >of an nighttime air attack, precise and accurate navigation would be very >important. > >Since I have both the GPS operational status listing and a complete set of >GPS satellite orbital elements, I thought it might be interesting to run off >a set of GPS coverage windows for Baghdad. Unfortunately I didn't have time >to write the program until well after the attack had begun tonight, but I >think the results are still very interesting. > >A GPS receiver requires at least 4 satellites to be visible simultaneously >in order to produce an unambigous fix in latitude, longitude, altitude and >time. (Theoretically, you need only three satellites if you have an >accurate, i.e., atomic, clock in the receiver. But lots of civilian GPS >receivers have been shipped to Saudi Arabia, and these certainly don't have >atomic clocks.) > >Here are the results. > >Sunset in Baghdad occurred at about 1500 UTC on Wednesday the 16th (6pm >local time). At that time, there was four satellite coverage. This lasted >about two hours, when there was a 10 minute period in which only three >satellites were visible, and then four satellite coverage returned for >another hour. > >However, at that point, coverage got much poorer (at one point consisting of >only one satellite) until 2240 UTC when three satellites returned. Four >satellites returned at 0040 UTC. At least four satellites were then visible >until 0320 UTC. Four satellite coverage returned at 0600 UTC. > >The actual attack on Baghdad started at 0000 UTC on the 17th. It seems to >have lasted for several hours. And now a report on CNN right now (0612 UTC) >says that a second wave might be starting. > >Hmmm. Could it be...? > >The region does have good continuous Loran-C coverage from permanent sites >in Saudi Arabia, and of course inertial navigation is probably available in >every US military plane and missiles. On the other hand, GPS is the most >accurate navigation system ever built. Its availability might have been a >factor in planning, especially given the billions of dollars that the DoD >has invested in it so far... > >Phil
aardoom@donau.et.tudelft.nl (Eric Aardoom) (02/04/91)
From: aardoom@donau.et.tudelft.nl (Eric Aardoom) A collegue of mine showed me a message (Hi, patrick!), which he picked up from sci.military, about the availability of GPS for military navigation in the Gulf. I would like to add some comments to this message. Also I included a shar file, which contains a bar chart of the number of visible satellites and predictions of GPS accuracy (DOP values) in the area around the Gulf during 24 hours, as well as an almanac, containing satellite orbital parameters. The DOP file is pretty large, so I compressed and uuencoded it. The predictions can be used for longer periods of time if a correction of approx. 4 minutes time shift per day forward is added. [mod.note: Due to the excessive size, I have deleted this shar file. I would presume it would be available upon request from the author. - Bill ] Currently there are 11 block II satellites available, but let's not ignore the fact that there are also 5 block I satellites, which can still be used. Consequently, the number of available satellites totals 16, not 10! I suspect the launching schedule of GPS has been given special priority. I have noticed that since my latest almanac update (about a month ago) SV 23 was added to the constellation of active satellites, although there weren't supposed to be any launches until the end of february '91 (please correct me if I'm wrong). Anyway, I have just downloaded a new almanac from SV 13 with our experimental GPS receiver, and I would like to share it with the readers. Included below are the results in my own almanac format (does anybody know of a data interchange standard for GPS data?). Though it is not (yet) a complete almanac, it should be enough to make an estimate of GPS coverage. Note that the block I satellites SV 3, 6, 9, 11, 12, and 13 are still alive and well. Also note that the anti-spoofing capability of the block II satellites is turned off! (or could this be a bug in my decoding program?) The almanac contains mainly the truncated Keplerian orbital parameters of the satellites and the time of almanac (TOA). It should be sufficient to predict satellite visibility and GDOP values anywhere on earth. I am still working on a new prediction program, which I am willing to make available when it is finished, if the war isn't over by then. Just let me know. As I said, also included are a bar graph of the number of visible satellites during 24 hours and a listing of Dilution Of Position (DOP) values. There is almost full 24 hour 4 satellite coverage at this moment. However, visibility does not garantee accuracy. Most important DOP values for airplanes are PDOP and GDOP. Large values result in low inaccuracy position fixes. GDOP values < 6 can be considered reasonably good values, GDOPs < 3 are excellent. For those who are not going to have a peek at the tables in the shar file I would still like to make one observation. Latest SV launched, no.23, is visible only during nighttime, presently from 23:40 until 7:00 (UTC). Adding this satellite to the constellation has significantly improved accuracy and continuous availability during nighttime (guess why). For those of you who do not have the tools to unpack this, I can also make this information available through anonymous ftp. I hope this information will be useful.
budden@trout.nosc.mil (Rex A. Buddenberg) (02/06/91)
From: budden@trout.nosc.mil (Rex A. Buddenberg) There is a bit more usefulness to GPS. The conventional solution is a four-dimensional one (Lat, Long, Alt, time) which requires four satellites in view. However....two dimensional service is quite useful in many cases (ships, for instance have little practical use for the altitude figure) and if you have another source of stable time (a cesium, for instance), then you get get effective two dimensional coverage with only two GPS satellites. While few vendors are building integrated Loran/GPS receivers, but there is a highly effective ability to use the two systems in a complementary fashion. Roughly, two Loran stations = one GPS satellite. A line of position is a line of position whether it is a Loran rho-rho range, a Loran time delay hyperbola or a GPS pseudorange. To put this into perspective, there is a Loran chain in central Saudi Arabia designed to provide service over the Arabian Gulf (currently, the Kuwait station is off air...). A second chain in western Saudi Arabia provides Red Sea coverage. b