Subject: Tips for tracking Satellites with Autostar Sent: Sunday, January 13, 2008 08:03:38 From: Jerry Hailey (email@example.com) Tips for tracking Satellites with Autostar 1-Make sure to set the Time and Date of your Autostar correctly. I have an ETX-80BB with an internal time chip that loads the time automatically. However the first time I used the scope I found that the time was off about 25 minuets. Just go through the menu and set the time and date. Select Item- setup - date and then time. Get the time from www.time.gov 2 Program the Autostar for the satellites you want to track. I'll use the ISS for an example. You can get the TLE (two line element) data from www.heavens-above.com. Log on or enter as anonymous. Select your location. On the main menu select the 10-day predictions for the ISS. This will then predict when the next viewing of the satellite will be. Note that the lowest viewing will start at alt of 10. I set my scope to AOS of 10. Select Item - Setup - Telescope - Min Aos. This will start tracking at alt 10. You can change this back for viewing low stars later. At the top of the page, click on the orbit data. This will show the TLE for the satellite. Turn on the Autostar and navigate to the edit satellite data. Select Item - Object - satellite - edit Use the scroll down key to find the ISS. If you don't see ISS, then mode key back and select add instead of edit. The following steps are the same after selecting the satellite to edit or adding the name of a new satellite. 1-Epoch Year. Enter the year as found on the First line of the TLE. At the bottom of this document I have placed a sample of the ISS TLE data from www.heavens-above.com In this case the Epoch year is 2008 2-Epoch day. This is also from the first line of the TLE. This sample has an Epoch day of 012.57876630. You must round this number when you enter this into the Autostar to 012.5788. This rounding error will cause the Autostar to predict the satellite to rise a minute or so early or late. I always start the scope tracking a little early, then pause at a point that I feel I have the best shot of locating the satellite. For the ISS that is fairly low in the sky, but other satellites may not be in view until they get up around alt of 20 or so. 3-Inclination -This is the second number on the second line of the TLE. 051.6425. It is also listed by the nice folks at www.heavens-above.com 4-Ra Asc Node 103.9756 5-Eccentricity 0.0005880 6-Arg of Perigee 267.7348 7-Mean Anomaly 224.2797 8-Mean Motion 15.76898995 this is called Revolutions per Day on the web. You also have to round this number to 15.7690. Epoch year-2008 Epoch Day-012.57876630 1 25544U 98067A 08012.57876630 .00019493 00000-0 12163-3 0 6981 2 25544 051.6425 103.9756 0005880 267.7348 224.2797 15.76898995523813 Epoch (UTC): 1:53:25 PM, Saturday, January 12, 2008 Eccentricity: 0.0005880 Inclination: 051.6425 Perigee Height: 335 km Apogee Height: 343 km Right Ascension of Ascending Node: 103.9756 Argument of Perigee: 267.7348 Revolutions per Day: 15.76898995 Mean Anomaly at Epoch: 224.2797 Orbit Number at Epoch: 52381 Now just go out and align your scope normally with easy align. I usually view a few know stars to check that the go-to is going where it should. On your Autostar menu select object- satellite- select scroll to ISS and hit enter. Once a pass is located Autostar will tell you what time it rises. Cool! Now use the scroll down key to view the tracking data. The data should be close to the same as the data from the web. However! The exact time may be off due to the rounding error. This is where the challenge of tracking the satellite comes in. Now hit the Go To button on the Autostar. You will se a clock that counts down the time until the satellite is in the center of the scope. Well let's just say in theory. The reality is that the rounding errors make the next step part luck and part skill. I set my watch to the time from the web www.time.gov When my watch says the satellite will rise in two minutes , I hit the enter key. The Autostar countdown may be behind or ahead. I have found that the time predictions from heavens-above and Nasa are more accurate than the Autostar. Once the enter key is hit, the Autostar will star tracking. It is better to be ahead of the satellite than behind. You can hit the enter key again to pause the tracking. Once the satellite is in view, you can hit the enter key again to start tracking. Another tip- set your speed to Max. Satellites move very fast. I hope you find tracking satellites as fun and rewarding as I have.
Subject: Re: Satellites Sent: Wednesday, March 21, 2001 22:32:21 From: firstname.lastname@example.org (richard seymour) Mike Hadey (email@example.com) wrote: > I've been trying to get everything to work in Polar Mode first. > I'll need to set up in Alt/Az to try satellites. Whereas i ran for a year before building my polar wedgie. Plop'n'go. > Any suggestions on a good satellite to start with? All of them. Practice, practice, practice. Just as with all aspects of the astronomic/telescopic sport, the more you do, the better it seems to work out. Expect less than stunningly good results the first few times... you and it will get better. > I presume you go to the heavens-above web site and load in the > latest TLEs before you go out. You presume fairly correctly. > I've read some of your pointers on Mike's site but would be > interested in any special tricks. Did i mention practice? Let's take tonight: On a quiet day in the dim past, i visited www.heavens-above.com and told it where i live. It produces a page with links to tonight's satellite passes, cut off at various brightness levels. STOP: Bookmark this page! I choose the < 4.0 (less, i.e. brighter, than 4.oh) link. I click and go there. You're now facing a page of tonight's passes. STOP. Bookmark/Favoritize this page too. *this* is the first page you should visit every evening. From tonight's list I choose sats separated by at least 5 minutes. It's well-nigh impossible (i.e. even -more- frustrating) to try and pack more in. I choose a mix of brightnesses, knowing (practice) that dimmer than 3.5 are difficult to see in my finder/sky conditions. They're also usually far dimmer as they're first coming up, too. I choose ones which will have pleasing or interesting pass altitudes. Ones which pass -directly- overhead are difficult.. the ETX has to spin 180 in Az as the satellite goes merrily past... with practice you'll be able to manually catch up after that, and continue tracking down. But they're worthwhile for honing techniques of starting the pass and finding them at all. Then i visit each pass' chart, shuffle the Big Square view to show me the area i'll first be seeing the sat rise. I'll center on about 25 degrees elevation, since that'll cover the range of AOS points the Autostar shall offer. I'll either take good notes, or print that page. Then i click on the [orbit] link at the top right of that page. That brings me to the TLE-bearing page. I tend to highlight the two-line parameter set (below the globes, above the labelled numbers). Here's the set for tonight's Lacrosse 3 pass: 1 25017U 97064A 01078.08554567 0.00000900 00000-0 15504-3 0 07 2 25017 57.0100 89.2234 0007000 158.2663 201.7337 14.68206719 03 These i copy/paste into a Notepad (Mac: TypeText, BBedit) edit page, which i use to accumulate the sets i'll want tonight. (on -good- days, i do this the afternoon, or night before ("Next PM" link on tonight's passes page)). Now let's key a set into the Autostar. From the above, the 01078.08554567 (top line, sorta middle entry) breaks into : Epoch Year: 2001 (the "01") Epoch Day: 078.08554567 The Autostar only accepts 078.0855 ..since the next digit is below 5 i don't round it up. Now drop to the second line. The first item of interest here is the 57.0100 That's the inclination, and will be the next thing the Autostar wants. The rest of the line: 89.2234 0007000 158.2663 201.7337 14.68206719 are in the order the Autostar wants them. Two notes: the eccentricy 0007000 gets a leading "0." when keyed into the Autostar, so it becomes 0.0007 Second note: the Mean Motion (orbits per day) 14.68206719 -does- round up to 14.6821, since the next digit is a 6. OK... on -really- well prepared nights, i might pre-test a pass: fire up the scope, and fake the time to a few minutes before the prediction. H-A shows the 10-degree alt point. The Autostar will pick AOS's in the 15 to 38 degree altitude range. IF you don't like an Autostar AOS, just [mode] and re-select the satellite... it may take two or three spins of the dice, but it'll (randomly?) choose other altitudes along the same path. When yo're happy with one, press [goto] and the ETX will first go to the LOS point, then swing back to the AOS point. (it does that to avoid hitting the hard stops -during- the pass). In the heat (cold?0 of the actual pass, you can abort the to-LOS slew after it starts by a short tap on the [mode] key... the ETX will then go to the AOS point. The Autostar starts counting down to the predicted AOS time. I now press the 7 key to pre-set the manual slew speed thusly. Now... -really- good nights i'll remember to bring along binoculars. Failing that (usually) i'll just glue my eye to the finder as we get within 60 seconds of AOS. No need to watch the Autostar... it'll beep as we pass zero seconds. If i see the satellite in the finder prior to the AOS beep, i'll judge if it'll hit the center, or if i need to do a pre-slew fudge. If so, i'll do that -before- pressing enter. When the satellite hits the crosshairs (yeah, sure...)(it does!) i press [enter] and the game's afoot! Assuming hit-the-center, i switch to the eyepiece, ready to "help" the tracking with short burps (or long pans) of the slew keys. I do NOT try to keep it -centered-... i let it drift around in the eyepiece, and burp to overcorrect, so it'll drift past again. This -really- gets the old "which way do i press to move the satellite -in-?" reflexes trained (ready? Practice). As the stars stream by in the background, i make mental notes of "oh, -that's- pretty!" for visiting later, or perhaps even aborting the sat pass to visit -now-. Priorities, ya know. Well... that's it... keep burping along until it gets irretrievably off-aim, or until it drops below the LOS point (at which point -you're- the tracking engine), or drops behind something opaque. (i've GOT to remove that chimney...)] Catching up with over-the-top passes also develops aiming techniques which improve normal starwatching, too. Then consult your "tonight's" list, and set up for the next one. Continue until exhausted. I think it took -six- evenings before i even got a satellite -into- my eyepiece for 5 seconds. Now i can get 4 to 6 satellites held within my 13mm eyepiece in an evening. But i sweat a lot doing it... (That's a very recent accomplishment. Practice) (no, not the sweating) But wait! There's more! (or: swiss cheese memory strikes again) A footnote to all of the above: When looking at the H-A TLE page, note the satellite's altitude range. If it's above 400 km or so, then the orbital elements will "last longer" than something low, or frequently adjusted, like the ISS. Three nights ago i had a relatively successful pass with two month old TLEs for a 580/600 km satellite. "Rockets" (the leftover upper stages of the launch systems) also tend to have "longer lasting" TLEs, since they're not adjusted for orbital position, whereas many satellites are frequently nudged to keep on station (or to go somewhere else). There are two bugs in v21eK which can fight you when sat tracking: (1) if you press [enter] to "pause" during a track, the system will -not- resume properly thereafter. Rather than pick up with the speed and direction changes appropriate for the spot in the track, they restart the motion list from the beginning. Yes, i've told them. (2) If you have an electric focuser, do NOT press the Zero key to engage it during a track... the main Alt/Az axes stand a very good chance of taking off in a rapid slew. All that said, it really isn't as hard as it sounds... for the last three nights running i've ripped myself from the computer screen, dashed outside, plopped down the scope and have been tracking a satellite 8 minutes after powering up the Autostar. It can be done in fewer than 3 (more frantic, more sweat). Subtle secrets which help rapid setup (this is how i stargaze, too): Have a level, flat surface available. Have a due-north landmark which the "home" position can see. Park the scope the previous powerup. Why? The level, flat surface (and a tripod provides one) is always needed. The landmark allows point-with-finder-before-powerup alignment to within a degree or two of due north. This matches the PARK status. Parking skips the Alignment step on the next powerup. The scope will power up aligned as per the previous usage, corrected for current time and date. For satellites, that's quite adequate. Super secret: Even if you're at a new location, simply power up the scope, answer the time and date, [mode] to escape the Align step. Tell it the new location. Fake an Align (i.e. just hit [enter] when it asks). Park. The next time you power up, the alignment will match whatever the scope would do if its initial guesses were perfect. And that's probably good enough for satellites. (pretty good for off-the-cuff observing, too) --dick (who left in the midst of typing this to -track- that sat.)
End of 22 March 2001 update
Subject: re: entering TLEs for Satellites Sent: Thursday, December 21, 2000 13:33:07 From: firstname.lastname@example.org (Richard Seymour) To: email@example.com Hi... I saw your note on Mike's site. >I am having great difficultly loading an Elset for ISS using the >AutoStar update. I can not get the eccentricity value to change. The Autostar Updater program (on the PC) is buggy in the Satellite, Comet and Asteroid handling and loading areas. For entering a single satellite, i --strongly-- recommend doing it by hand on the Autostar itself. Object>Satellite>Add (or Edit) If you look in the (roughly) 56kb README file which came with the Updater, it has a long list of patches. At the very bottom of that list is the true version number of your copy of the updater. The last one known as "A2.1" shows as 2.0022. If it is below 2.0025, it will load satellites incorrectly. It byte-swaps some of the values (Intels use one way, Motorola (like the Autostar) uses the other) If it is below 2.0030, it will load comets and asteroids incorrectly. My experience with versions above 2.0025 is that, if i try to -edit- the list in the Updater, it will download trash to my Autostar, requiring a Flash Load to recover. >There are no instructions in the AutoStar manual for this so I have been >flying by the seat of my pants. I have even upgraded to firmware 2.1EK >in hopes that this would fix the problem. It made it worse and I >reverted back to 2.0h. Any suggestions? (a) don't use the updater for entering satellites. (b) you're not alone... i don't know of -anyone- who fully likes the Updater, most of us have managed to wrestle it to a draw, but occasionally it slips in a kicker... > I also noticed that my scope hesitates when slewing in azimuth. I hear > the servos kick in but the scope does not move for a few moments. It is > especially noticeable when slewing clockwise. I realize that the > pointing accuracy is not wonderful on a $1000.00 scope but I would > expect better. The pointing accuracy -can- be wonderful, but getting there is fraught with taking care. First off: v21ek does a much better job of pointing than v2.0anything. Second: Calibrate and Train your system. That tells the Autostar how much of a kick to deliver to overcome the mechanical slop in the system. Third: with v21ek, under Setup>Telescope>AzPercent (and AltPercent) try differing values (users report the range of 35% to 50% helping lots). That "tunes" the amount of kick delivered when you reverse your motors. The ETX/Autostar combination is trying to compensate for low-priced mechanicals with a "smart" controller. The "smart" controller is still taking a bit of a shortcut in the control algorithms, but they're working on it. It is also quite possible that your Az axis is excessively loose or sloppy. I'm not sure what "excessive" means with the ETX... my own ETX90's is within a degree (it used to be almost impreceptible... i've put a lot of miles on it). My Alt axis exceeds 3 degrees of slop. And it's hard for the Autostar's "avereage slop" compensation to counteract that cleanly. But after a half-hour of careful landmark training, it's now with 10 arcminutes of repeatable pointing. And that's without the workaround of "cheating" during training. good luck it'll get there... --dick
End of 23 December 2000 update
Subject: Satellite tracking with the ETX-EC & Autostar Sent: Monday, July 26, 1999 14:59:00 From: firstname.lastname@example.org (Ade) As promised in an earlier posting about my experiences of tracking the Russian space station Mir with the ETX-90EC/Autostar platform, here's how to interpret two-line or Keplerian elements from the web into a format that the Autostar can use. Apologies to those that already know about what follows, but I hope some will be new to all! Firstly, for those not familiar with such data, what are satellite elements and why do we need them? Artificial satellites in low orbit such as Mir or the International Space Station (ISS) are subject to atmospheric drag from the tenuous upper atmosphere of the Earth and the gravitational tugs of the Moon, so their orbits are continually changing. In order to keep track of these objects we regularly need to update our records as to the parameters that define the size, shape and orientation of their orbits: these figures are the orbital elements. For several years now astronomers and satellite trackers have been given access to the information stored with government and military agencies such as NORAD and thses figures have conventionally been distributed in a format that is not paricularly easy to read since they are intended for computer programs that do the hard work of orbital computation for you. So, where can you get hold of these so-called 'two-line' or 'Keplerian' elements and what do they look like? A first port of call should be Dr TS Kelso's Celestial WWW site at http://celestrak.com where all you ever need in terms of fresh elements for a whole host of satellites can be found. Links to other places can be easily found. A recent 'tle' for the space station Mir looked like the following: MIR 1 16609U 86017A 99200.17693748 .00007184 00000-0 55620-4 0 7001 2 16609 51.6605 180.0498 0005939 323.8279 36.2320 15.73139607766442 What at first looks like a meaning list of numbers can soon be broken down into groups of figures that correspond to the various parameters of the satellite's orbit. Fortunately, you don't have to be a rocket scientist to use these figures, nor do you strictly need to know that they mean, just as long as you can separate them into meaningful numbers. To update the Autostar's database, all you need to to is press the MODE key a few times until the "Select Item: Object" menu appears. Then hit ENTER and scroll down until "Object: Satellite" comes up. Hit ENTER again and scroll down until "Satellite: Edit" comes into view. ENTER again and "Select Satellite" appears; scroll down the list until MIR (or any other desired satellite) comes up. Yes, hit ENTER again to select it. Now the Autostar presents you with "Name MIR" where ENTER should be pressed. Next the Autostar will ask you in turn for the following (which I'll decipher later):- Epoch Year, Epoch Day, Inclination, RA Asc. Node, Eccentricity, Arg. of Perigee, Mean Motion & Mean Motion (... come back, it's not that bad!) Let's look at our (old) 'tle' for Mir again: MIR 1 16609U 86017A 99200.17693748 .00007184 00000-0 55620-4 0 7001 2 16609 51.6605 180.0498 0005939 323.8279 36.2320 15.73139607766442 We can disregard most of the data on the first line save for the bit that starts at character 19: 99200.17693748; take off the first two digits and you have the 'Epoch Year' (1999). The following 12 characters (200.17693748) is the 'Epoch Day'. All that's subsequently required is on line two. Starting at character 10, we find the 'Inclination' (51.6605). The 'RA Asc. Node' starts at character 18 (180.0498). The 'Eccentricity' starts at character 27, but we have to add a '0.' at the beginning, making '0.0005939'. Next comes the 'Arg. of Perigee' at character 35 (323.8279), followed by the 'Mean Anomaly' at character 44 ( 36.2320). Lastly, (phew!) the 'Mean Motion' comes in at character 53 (15.731396). To summarise, the data to be entered into the Autostar would be as follows:- Epoch day = 200.17693748 Orb. Inclination = 51.6605 R.A asc. node = 180.0498 Eccentricity = 0.0005939 Arg. perigee = 323.8279 Mean anomaly = 36.2320 Mean motion = 15.731396 Once that has been entered, you return to the 'Satellite: Edit' menu. Scroll down to 'Satellite: select' [ENTER], the pick Mir or any other object from the list that follows. Assuming that you've previously aligned your 'scope and accurately entered the date/time/location, the Autostar will slew to the point where the satellite will appear in the sky and give you a 'countdown' to the start of appearance. Obviously, it makes sense to have used one of the web predictors (or software on your PC or Mac) to find out when a pass is due to save unnecessary waiting around! I hope all this helps. It's huge fun locking onto and following these high fliers - try it! Clear skies, Ade
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