Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Thu, 15 Nov 1990 03:01:26 -0500 (EST) Message-ID: Precedence: junk Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Thu, 15 Nov 1990 03:00:54 -0500 (EST) Subject: SPACE Digest V12 #556 SPACE Digest Volume 12 : Issue 556 Today's Topics: STS 38 Observation Guide (Long) Administrivia: Submissions to the SPACE Digest/sci.space should be mailed to space+@andrew.cmu.edu. Other mail, esp. [un]subscription notices, should be sent to space-request+@andrew.cmu.edu, or, if urgent, to tm2b+@andrew.cmu.edu ---------------------------------------------------------------------- Return-path: X-Andrew-Authenticated-as: 0;andrew.cmu.edu;Network-Mail Date: 13 Nov 90 13:12:28 GMT From: ubc-cs!news-server.csri.toronto.edu!utgpu!molczan@beaver.cs.washington.edu (Ted Molczan) Organization: UTCS Public Access Subject: STS 38 Observation Guide (Long) Sender: space-request@andrew.cmu.edu To: space@andrew.cmu.edu STS 38 Visual Observation Guide ------------------------------- by T.J. Molczan, Toronto, Canada 12 Nov 1990 This report is intended to assist those who wish to make visual observations of STS 38. This is a DoD mission, and therefore, most aspects of the mission have been classified, including the orbit. However, it is possible to make an accurate estimate of the orbital elements using the information that is in the public domain. Use has been made of basic orbital mechanics and some leaked information made available by various news media. Highlights: ----------- Section 2 provides a simple step by step procedure to produce an estimate of the orbital elements in the standard NORAD "2-line" format. Section 3 has tables that tell you whether or not the shuttle will be visible at your latitude. Section 5 includes information on obtaining free software for making orbital predictions and how to make and share observations. 1.0 STS 38 Mission Synopsis ----------------------- 1.1 AV WEEK Report -------------- According to AVIATION WEEK and SPACE TECHNOLOGY, STS 38 will launch a digital imaging reconnaissance satellite, with a mass of about 10,000 kg. The shuttle will enter a 217 km orbit at an inclination of 28.45 deg to the equator. It will later raise its altitude to at least 241 km. The satellite will be deployed during the latter part of flight day two, and eventually will manoeuvre to a 741 km altitude. The launch has been scheduled for the night of 15/16 November. The announced 4 h launch period begins at 23:30 UTC on 15 Nov. It has been widely reported that the actual launch window begins at 23:46 UTC on 15 Nov., and ends at 01:12 UTC on 16 Nov. The duration of the mission is expected to be four days. AV WEEK believes that the payload was originally planned to be placed in a geo-stationary orbit, but was retargetted to provide support for Operation Desert Shield, in the Persian Gulf. 1.2 (Informed?) Speculation ----------------------- Some of my friends in the media who cover shuttle missions have expressed doubts about the AV WEEK story. Their main concern is with the claim that an imaging reconsat would be placed in a low inclination orbit. There is also concern about the claim that the payload was originally intended to go into a geostationary orbit. There are also concerns about the mission being changed in response to Desert Shield. Here are my views. 1.2.1 Why the Low Inclination Orbit? ------------------------------ At first thought it appears absurd that a U.S. imaging reconsat would be placed in a low inclination orbit. However, a case can be made for doing so. In the past, the U.S.S.R. and China were the primary reconnaissance targets, which necessitated the use of high inclination orbits. Early U.S. reconsats used 70 deg to 80 deg inclination orbits. Eventually, sun-synchronous orbits, which have inclinations between about 96 deg and 100 deg (the required inclination is a function of semi-major axis and eccentricity) became the standard because they offer near constant sunlight angles from one day to the next. The U.S. has three KH-11 (Keyhole) satellites in sun-synchronous orbit: Int'l NORAD INC PER APO Name Launch Desig # deg km km USA 6 KH-11-6 84122A 15423 97.8 335 758 USA 27 KH-11-7 87090A 18441 97.9 291 975 USA 33 KH-11-8 88099A 19625 97.9 292 983 (The orbits of these objects are known through the efforts of amateur astronomers, who track them.) USA 27 and USA 33 appear to be fully operational. They use their propulsion systems to maintain their approximately 300 km by 1000 km orbits. USA 6 was originally in the same orbit as USA 33, which replaced it. In a break from past practice, USA 6 was not de-orbited. Since the launch of USA 33, it has been allowed to slowly decay from orbit, with the exception of a single manoeuvre in July 1989, which raised its perigee about 50 km, apparently to reduce drag and prolong the life of the orbit. This suggests that this satellite may be at least partially operational. In addition to the KH-11's there are two other satellites which are strongly believed to be imagers: USA 34 Lacrosse 88106B 19671 57.0 669 687 USA 53 KH-12 ? 90019B 20516 65.0 806 813 (Our knowledge of these orbits is also due to the efforts of the amateur astronomers.) USA 34 was reported by AV WEEK to use a powerful synthetic aperture radar to enable it to resolve objects to a resolution of about 2 m. It was launched aboard Atlantis on STS 27. USA 53 was reported by AV WEEK to be a digital imager. It was launched on Atlantis on February 28, 1990, and deployed the following day. The Soviets spotted four large pieces of debris in the payload's orbit on 7 March, and reported that the satellite had probably "been blown up by its owners". In October, amateur astronomers found the satellite (by chance) in the orbit given above. One feature of USA 53's orbit which tends to support the claim that it is an imager, is its 9 day (127 rev) repeating groundtrack. Repeating groundtracks are a common feature of Earth imagers, civilian as well as military. With four (possibly five) operational imagers in high inclination orbits, and the greatly improved relations between East and West, it is possible that a decision was made to place the next digital imager in a low inclination orbit, to permit better coverage of the Middle East and the drug trade regions. One argument against this, might be that a high inclination orbit can see everything that can be seen by a low inclination orbit, so why sacrifice the high latitudes? Although it is true that a high inclination orbit also crosses the equatorial region, the spacing between adjacent groundtracks is farther apart than at the higher latitudes, creating some short term gaps in coverage. This problem could be reduced through the use of a higher altitude orbit, at the cost of some loss of resolution, or through the use of a lower inclination orbit, at the cost of high latitude coverage. 1.2.2 Was the Original Orbit Geosynchronous? -------------------------------------- It seems highly unlikely that a payload designed for GEO (geosynchronous orbit), could operate successfully in LEO (low Earth orbit), or vice versa. For example, a satellite in GEO would use a different system to point its instruments at targets than one in LEO. Also, there would be a vast difference in instrument resolution between GEO and LEO. It is possible that the AV WEEK story confused the terms geosynchronous and sunsynchronous. Prior to the Challenger accident, the plan was to launch imaging reconsats into sunsynchronous orbits from the Vandenberg AFB launch facility. With the post Challenger decision not to launch from Vandenberg, satellites such as Lacrosse and USA 53 have had to be launched into lower inclination "compromise" orbits. 1.2.3 Was the Mission Retargetted for Desert Shield? ---------------------------------------------- Planning a shuttle mission requires about 18 months. The planned orbit has a significant effect on the details of the mission plan. It seems unlikely that the orbit of this mission could have been changed in less than the three months between the Iraqi invasion of Kuwait and the publication of the AV WEEK story. A more likely explanation is that a decision was made one or two years ago, to launch this payload into a low inclination orbit, for the reasons given in Section 1.2.1, contingent upon the success of the USA 53 payload. 1.3 Payload May be Similar to USA 53 -------------------------------- There are some similarities between the STS 36 and STS 38 missions which may be an indication that the same type of payload is involved in both missions. Shuttle Atlantis was used for STS 36, and STS 38 will be its first mission since then. Both missions involve the use of a much lower than normal orbit. The STS 36 payload, USA 53, repeats its groundtrack every 127 revs (about 9 days). The STS 38 payload's groundtrack will repeat every 128 revs (about 8.8 days). 2.0 Orbital Elements ---------------- The following is a simplified procedure to estimate the orbital elements of STS 38 and represent them in a pseudo NORAD "2-line" format. 2.1 Inclination ----------- It is assumed that the inclination will be 28.45 deg as reported by AV WEEK. 2.2 Mean Motion and Rate of Decay ----------------------------- The 241 km orbit would result in a mean motion of 16.147 revs/day. In case the orbit turns out to be a little higher or lower, it is recommended that several mean motions between about 15.9 and 16.3 be used. Orbital decay can be set to zero because of the uncertainty in the mean motion. 2.3 Eccentricity, Argument of Perigee and Mean Anomaly -------------------------------------------------- Shuttle orbits are usually close enough to circular that a zero eccentricity and argument of perigee can be assumed. The mean anomaly will be zero because the argument of perigee is zero and the epoch will be chosen to coincide with an ascending node. 2.4 Epoch ----- The epoch is chosen to be the time of the ascending node (north bound equator crossing) of the first full revolution of the Earth. For a 28.45 deg inclination mission, this occurs about 1 h 13 m after liftoff. The launch time and date must be expressed in UTC (Universal Time). If the shuttle is launched as expected on 15 Nov at 18:46 EST, then this would be 15 Nov 23:46 UTC. The time of day of the epoch would be : 23:46 UTC + 01:13 ----- = 24:59 UTC 15 Nov = 00:59 UTC 16 Nov The day of the year is also part of the epoch and is commonly combined with the time of day of the epoch as follows : EPOCH = YYDDD.dddddd where: YY = last 2 digits of year i.e. 90 for 1990 DDD = day of year, i.e. 16 Nov 1990 is day 320 .dddddd = fraction of day, i.e. 00:59 UTC = (0 + 59 / 60) / 24 = 0.040972 Putting the above pieces together yields: EPOCH = 90320.040972 2.5 Right Ascension of the Ascending Node (RAAN) -------------------------------------------- The RAAN is a function of the longitude and the time and date of the ascending node. For the above EPOCH, which corresponds with the ascending node of the first revolution of a 28.45 deg orbit, the longitude of the ascending node is -173.2 deg W. The first step is to calculate the Greenwich mean sidereal time at the epoch. An accurate formula for 1990 is: GMST = (6.6265 + 0.06571 * DDD + 24.06571 * 0.dddddd) mod 24 where DDD and 0.dddddd are as defined above For the epoch calculated earlier the, GMST is : GMST = (6.6265 + 0.06571 * 320 + 24.06571 * 0.040972) mod 24 = 4.63972 h The final step is to calculate RAAN : RAAN = (15 * GMST - WEST LONGITUDE) mod 360 = (15 * 4.63972 - (-173.2)) mod 360 = 242.8 deg 2.6 Summary ------- The above estimates are summarized below in a pseudo NORAD "2-line" format : 90320.040972 .00000000 00000+00 00000+00 28.4500 242.8000 0000000 000.0000 000.0000 16.147 The first line contains the epoch (Section 2.4) and the three NORAD drag related quantities, set to zero per Section 2.2. The second line contains inclination (Section 2.1), RAAN (Section 2.5), eccentricity, argument of perigee set to zero per Section 2.3, and mean motion (Section 2.2). Remember to bracket the mean motion between about 15.9 and 16.3. 3.0 Visibility Window Analysis -------------------------- The tables below show the visibility windows (range of dates of visibility) of the shuttle during the upcoming mission. There are individual tables for evening and morning. Visibility windows are a function of time/date of launch and observer's latitude. The windows have been computed for the start and end of the expected launch window of 15 Nov 23:46 UTC to 16 Nov 01:12 UTC. In many cases the windows begin several days prior to the launch date. This merely indicates when the window would have begun, had the orbit pre-existed the launch date. The windows were based on a 241 km, 28.45 deg inclination orbit, as reported by AV WEEK. If the shuttle goes higher (it can't go much lower), then the windows generally will be wider. For this project, a window was defined as passes which culminate at least 5 deg above the horizon, and which are illuminated for at least half of the pass. The visibility windows will not be greatly affected by a delay in the date of launch, as long as the launch window does not change greatly. In case there is a delay, add the number of days of the delay to the start and end of each visibility window. If your latitude is not in the table, then there will be no window. If an entry for your latitude is blank, then there is no window corresponding to that launch time. EVENING VISIBILTY WINDOWS ---------------------------- LAUNCH (UTC) LAUNCH (UTC) --- ------------- ------------- LAT 15 Nov 23:46 16 Nov 01:12 --- ------------- ------------- 40N 14/11 - 18/11 35N 11/11 - 21/11 13/11 - 24/11 30N 09/11 - 23/11 12/11 - 25/11 25N 08/11 - 24/11 10/11 - 26/11 20N 06/11 - 25/11 09/11 - 27/11 15N 18/11 - 26/11 08/11 - 16/11 MORNING VISIBILTY WINDOWS ---------------------------- LAUNCH (UTC) LAUNCH (UTC) --- ------------- ------------- LAT 15 Nov 23:46 16 Nov 01:12 --- ------------- ------------- 10S 10/11 - 16/11 15S 09/11 - 16/11 12/11 - 19/11 20S 10/11 - 27/11 13/11 - 30/11 25S 12/11 - 26/11 14/11 - 29/11 30S 14/11 - 25/11 16/11 - 28/11 35S 16/11 - 24/11 18/11 - 26/11 4.0 Observation Tips ---------------- The shuttle is easy to spot with the naked eye. When favourably illuminated, nearly overhead and in a dark sky, it has a visual magnitude between -1 and -2, about as bright as Jupiter. The shuttle has been observed as early as 15 minutes after sunset or before sunrise, however that is probably too difficult for the inexperienced observer. The uncertainty in the mean motion makes the search for the shuttle a challenge, but far from impossible. The best search strategy is to produce several different orbital element sets covering the range of uncertainty in the mean motion, as recommended in Section 2.2. In this way the predictions will "bracket" the shuttle's actual time of passage and path across the sky. This procedure takes advantage of the fact that the orientation of the shuttle's orbital plane with respect to the Earth can be predicted with much greater accuracy than the position of the shuttle within its orbit. The idea is to "stare" at the imaginary ring in the sky which is the shuttle's orbit. As you wait for the shuttle to appear, the Earth rotates, which makes the orbit ring move across the sky. The shuttle must occupy each point along the orbit once per revolution, so eventually it must be seen. If the shuttle makes a near overhead pass, even the small uncertainty in the orientation of the plane can result in large errors in its predicted path across the sky, especially at maximum elevation. Therefore, take care to scan a wide section of the sky. It would be unfortunate to be looking for a 65 degree high pass in the south only to have the shuttle pass behind your back, 70 degrees high in the north. 5.0 Observation Network ------------------- During the STS 27, STS 28, STS 33 and STS 36 DoD missions there was an informal network of amateur observers who found the shuttle and shared their observations. This made it possible for more people to see the shuttle because we were able to quickly refine our orbital elements and pass on the information. The following sections discuss making orbital predictions, accurate observations and how to report your observations. 5.1 Making Predictions ------------------ You require an orbit prediction program to make use of the elements from Section 2. SEESAT, by Paul Hirose is a good public domain program for this purpose. It enables you to make accurate predictions for any location on Earth. Predicted positions are given in azimuth and elevation as well as right ascension and declination. The program was written in C and has been compiled for the IBM-PC. The source code has been included to enable use on non-IBM systems. You can download a copy from the Canadian Space Society BBS, at the number given in Section 5.3. The name of the file is SEESAT2X.ARC. If you are not into making predictions but wish to make observations, I will try to provide you with predictions. Contact me via one of the channels listed in Section 5.3, well in advance of the launch. 5.2 Making Accurate Observations ---------------------------- The best observations are positions related to the stars along with the time accurate to 1 second or better. For example, "passed between Castor and Pollux, 1/3 distance from Castor to Pollux, 08:34:21 UTC 22 Feb 1990" or "passed 3 degrees below Vega, 09:12:10 UTC 22 Feb 1990" In addition, estimates of visual magnitude and colour would be useful. If the magnitude is varying regularly, measure the period of variation. If two objects are seen, then state the separation between them. For example, "the brighter object led the fainter by 10 seconds of time", or "the red object was about 4 degrees behind the other at maximum elevation of 50 degrees" would be useful. Also, if possible, note the time and approximate position of shadow entry or exit. This can be very helpful in determining the orbital eccentricity and argument of perigee. Make certain to provide your latitude and longitude as accurately as possible. 5.3 Sharing Your Observations ------------------------- If you have information to share, use one of the following communications channels. I will attempt to respond in kind. If you make an observation on the first day of the mission, please if possible, phone it in to me. The initial observations are very important in determing an accurate orbit so that a maximum number of people will have an opportunity to observe later orbits. 1) Leave a message on the CSS (Canadian Space Society) BBS for Ted Molczan. This is a free, 24 h/d board, 2400 8N1, (416) 458-5907. This will be the primary communications channel. 2) Phone me at (416) 921-1564 3) Send e-mail message to molczan@gpu.utcs.utoronto.ca This is on NETNORTH, which is connected to BITNET and other academic/research networks. Please pass this on to other BBS's or interested individuals. * * * * -- Ted Molczan@gpu.utcs.utoronto.ca ------------------------------ End of SPACE Digest V12 #556 *******************