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1991-01-16
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There's a Satellite in your Backyard!
=====================================
Tips & Techniques
for the
Novice Naked-Eye
Satellite Spotter
by Alan Bose
When the Space Age was young (and so was I), I can remember my father
taking us out in the backyard to watch the Echo satellite fly over.
It was a great event. It was even covered "live" on the radio. An
entire city looking for a point of light racing across the sky.
Today we take the marvels of space exploration for granted. We
forget that space is not something distant and remote. It's as close
as our own backyards.
A satellite is visible from the ground because the sun has recently
set and our sky is dark, but the satellite overhead is still in full
sunlight. On any clear night numerous satellites can be seen during
the hours after sunset if you just sit back and watch. Points of
light racing across the sky that suddenly disappear as they fly into
the earth's shadow. Not to be confused with high-flying aircraft,
satellites do not have visible navigation lights or strobes, nor do
they change direction, make noise, or leave contrails.
The "Satellite Spotters Guide" has become a recurring segment on the
Spike O'Dell radio program, afternoons on WGN-AM 720 in Chicago. The
satellite predictions announced on the air are usually the biggest,
brightest, easy-to-spot targets. For your viewing enjoyment, here
are some tips to successful satellite spotting.
Satellite Spotters Tip #1 -- Time
---------------------------------
Set your watch to the WGN time signal at the top of the hour, or use
some other accurate time standard. (Warning: some radio/TV time
signals are not all that accurate.) Since satellites in low-earth
orbit move across the sky quickly, a minute or two can make a big
difference.
Satellite Spotters Tip #2 -- Eyes
---------------------------------
Get outside a few minutes early and let your eyes become acclimated
to the dark, especially if you're coming out of a brightly lit house.
Choose the darkest location possible, shielded from bright light
sources such as street lights or nearby windows. Just turning off a
few lights in the house can darken your own backyard considerably.
In and near the city, "light pollution" overhead makes viewing
especially difficult by washing out all but the brightest objects.
Satellite Spotters Tip #3 -- Bearings
-------------------------------------
Get your bearings. Know which way is north. Know from which
direction the satellite will rise and in which direction it will set.
Satellite Spotters Tip #4 -- Zenith
-----------------------------------
Very important. Know where the satellite's zenith will be (its
highest point in the sky). It is not enough to know that it will
rise in the west and set in the east, without knowing if it will pass
to the north of you, to the south of you, or directly overhead. Yes,
I have stood in the backyard scanning the sky in vain to the south
while the bird I was looking for passed quickly and quietly behind my
head to the north!
Unfortunately, the zenith calculated for Chicago may or may not apply
for Rockford, Champaign or Milwaukee, depending on the satellite's
track. The satellite will certainly be visible, but it may be in a
totally different part of the sky from your vantage point! Knowing
the satellite's track may help you figure out the general area to
look.
Satellite Spotters Tip #5 -- Scan
---------------------------------
When waiting for the satellite to rise, don't stare at the horizon.
Even the brightest satellite won't be visible until it gets at least
20 degrees or so above the horizon -- above the atmospheric haze.
Instead, scan the entire path across the sky. The satellite could be
a few minutes early, and already at its zenith while you're staring
at the horizon. (I've done that too.)
Satellite Spotters Tip #6 -- Backlighting
-----------------------------------------
When a satellite rises in the west in the evening, the sun is below
our horizon, but it is still behind the satellite from our point of
view. In other words, as we look west we are looking at the unlit
side of the satellite. For this reason a satellite low on the west-
ern horizon in the evening (or low on the eastern horizon in the
morning) can be quite dim or impossible to see -- at least until it
climbs higher in the sky, where we can see some of its sunlit side.
Satellite Spotters Tip #7 -- Uncontrollables
--------------------------------------------
As timely & accurate as we try to be with these satellite visibility
forecasts, there are several variables that remain beyond our
control.
One is the orientation of the satellite itself. The Mir space
station, for example, is more than 100 feet long with a vast array of
solar panels. It is currently the brightest artificial object in the
sky. (Our Skylab was the brightest, I'm told.) What we see on the
ground is sunlight reflecting off this large surface area -- assuming
it is oriented properly. As an experiment, have a friend hold up a
pencil across a dimly-lit room. In most any orientation you will
have little trouble seeing the pencil. But if he holds it with only
the end facing you, it will be quite difficult to tell if he is
holding anything between his fingers or not. In the same manner, if
the station is end-on to either us or the sun, its apparent
brightness can vary considerably, and on occasion it can be almost
impossible to see.
Another uncontrollable is when a satellite's orbit changes. The Mir
is an active space station, and permanently manned, but each day it
looses a few meters of altitude. If not corrected it would
eventually re-enter the earth's atmosphere. To prevent this, it is
given a slight boost every couple months to kick it back up to the
desired orbit, but in the process it throws our orbital forecasts out
the window. Since the Russians don't announce the changes, we only
find out second hand, after the fact. If the changes aren't too
great it may only mean that the it shows up a couple minutes earlier
or later than planned. We strive to use only the most current
tracking data publicly available. Sometimes it is just not soon
enough. The best remedies are to go outside a few minutes early (Tip
#2) and to immediately scan the expected track (Tip #5).
Satellite Spotters Tip #8 -- Serendipity
----------------------------------------
How do you spot a hardy satellite spotter? He's the one who leaves
his reclining lawn chair out in the back yard all winter! (He also
sits there on summer evenings and "feeds the mosquitoes".) You'll be
amazed how many satellites you can spot just by sitting back and
looking up. Most are quite dim and only visible for a brief moment
directly overhead on clear nights. Some spent rocket boosters and
decommissioned satellites tumble slowly and appear to wink on and off
as they cross the sky (not to be confused with high-altitude aircraft
which can be identified by their navigation lights). Satellites in
polar orbit (north/south directions) tend to be spy satellites with
an occasional earth-resource satellite like the Landsats or Seasat.
Spy satellites are generally in low orbits so they can get better
detail in their pictures. But their low orbits also make them good
targets for satellite spotters.
A favorite challenge for satellite spotters is the Lacrosse, a top-
secret U.S. spy satellite deployed on a shuttle mission a few years
back. Its not hard to see - it's unusually big and bright for a
satellite in a near-polar orbit. It's just that you can't tell when
or where it will show up since current tracking data isn't made
public. On the other hand, a global network of amateur satellite
spotters often deduces the orbits of these 'secret' satellites from
as little as two or three accurate naked-eye observations.
Satellite Spotters Tip #9 -- 'Standard' Orbits
----------------------------------------------
Is the Space Shuttle visible? Yes, the Hubble Space Telescope and
the Space Shuttles are exceptionally bright objects -- if you live in
the southern tier of states from Los Angeles to Atlanta.
Unfortunately, most Shuttle missions do not venture as far north as
Chicago. The Kennedy Space Center is located at 28.4 degrees north
latitude. As such, the most energy efficient orbit (the greatest
payload in the highest orbit on the least fuel) is confined to 28.4
degrees north and south of the equator -- far from Chicago at 42
degrees north latitude. Most Shuttle missions pass just below our
horizon to the south. The Hubble Space Telescope follows the same
orbit, but at a higher altitude. The HST peeks above our southern
horizon briefly, though scarcely enough to be seen through the
atmospheric haze under the best conditions. The HST is in the
highest orbit attainable by the present Shuttle system.
Only large objects in low orbit stand a chance at being seen from the
ground with the naked eye. Higher orbits, such as the geosynchronous
orbits, are simply too high up for naked-eye observation. Numerous
satellites are in our sky constantly, but it is rare that we are
aware of them. Every once in a while we just need to sit still, look
up and watch!
Satellite Spotters Tip #10 -- How it's done. You can do it too!
----------------------------------------------------------------
The question that has been asked over and over is, "How does he do
that?" How is it possible for an average citizen like myself to
calculate and predict the passage of all these various satellites?
The personal computer, that's how. The average personal computer
sitting on your desk today has a couple hundred times the power of
the computers sent aboard the Voyager spacecraft in 1977 to explore
Jupiter, Saturn, Uranus, Neptune and beyond. It is this power that
can be applied to the serious number crunching required to predict
satellite movement and visibility. The second requirement is
accurate tracking data with periodic updates to feed to your
computer.
First, you need a personal computer. Either a Macintosh or an IBM-
compatible. Satellite computations are extremely math-intensive. A
computer with math co-processor is highly recommended. A lower
powered machine can do the computations just fine, as long as you're
willing to walk away and let it work. Overnight, if need be.
Tracking data is publicly available in a computer-readable file
called the "NASA Prediction Bulletin". Of course data on certain spy
satellites is withheld. The data is simply two lines of numbers for
each satellite (see Figure 1). The data is available for downloading
from a variety of public and private computer bulletin board
services, if you have a modem and suitable communications software
and are willing to make a 3-4 minute long-distance call. Bulletin
boards that cater to amateur astronomy and/or amateur radio generally
carry the files on a regular basis. The BBS systems listed here all
run 8 data bits, no parity, 1 stop bit. Each operates 24-hours a
day.
Celestial BBS, Fairborn, Ohio Canadian Space Soc. BBS, Toronto
513/427-0674 - 1200/2400 baud 416/458-5907 - 1200/2400 baud
Good, but very, very busy Specialty: spy satellites
CocoLoco BBS, Houston, Texas RPV BBS, Rancho Palos Verdes, CA
713/923-6809 - 1200 baud only 213/541-7299 - 1200/2400 baud
Type "KEP" at the first prompt
Next you need a satellite tracking program that will take that data
from the Prediction Bulletin file and calculate where each satellite
is (or will be) at any particular time. There are two excellent
programs that I use regularly: MacSat written by Bill Bard for the
Macintosh, and TRAKSAT written by Paul Taufler for DOS compatibles.
MacSat $10 (disc & manual) TRAKSAT $10 (disc w/ docs)
Bill Bard $20 (disc & manual)
BEK Developers Paul E. Traufler
1732 74th Circle NE 111 Emerald Drive
St. Petersburg, FL 33702 Harvest, AL 35749
Both programs are well documented. You will need to know your
location, in terms of latitude and longitude. For anyone in the
Chicago area 42 degrees north latitude and 88 degrees west longitude
will work fine. TRAKSAT comes with a long list of cites already
entered. For other areas, just stop by your nearest airport. Any
private pilot will be happy to tell you your latitude and longitude.
Since satellites are visible over a wide, wide area you don't need to
calculate the latitude and longitude for your own backyard! Close
(within 10-20 miles) will do fine.
However, accurate satellite forecasts do depend on supplying your
program with the most current tracking data available. If a
satellite doesn't show up as predicted, it might be that your
tracking data is old. If your data is more than a month old, you
might want to call in again for fresh data. If you're a regular
satellite spotter, updating your data every other week should
generate forecasts that are quite reliable.
Both programs will calculate when a satellite will be above your
horizon (Figure 3). They will also calculate when it might be
visible. They can both draw you a real-time map of the planet and
show you where a satellite is located, just like the big map you see
on the wall at Mission Control in Houston. Other than minor
differences, both programs work very well and do everything needed
for successful satellite spotting.
Careful, both programs use time in 24-hour format. 0700 is 7:00am.
Twelve hours later, 7:00pm is 1900 (7+12=19). TRAKSAT is a bit
trickier still in that it uses UTC (what used to be called Greenwich
Mean Time) which is 6 hours ahead of Central Standard, or 5 hours
ahead of Central Daylight. 1900 Sunday Central Standard Time in
Chicago is 0100 Monday UTC (1:00am of the following day in London).
It can be a little confusing if you're not careful.
So, now that you can calculate where these satellites will be, can
you really see them? Well, there are only a few excellent targets.
The Russian Mir, the American Hubble Space Telescope, or any of the
Space Shuttle flights are all easy naked-eye targets. Unfortunately,
the HST and most Shuttle missions don't come far enough north (see
Tip #9). But don't give up. There are plenty of sights to see. You
just have to look a little more carefully.
For viewing around the Chicago area, you should select satellites
that have and inclination of at least 40 degrees, and have a mean
motion of 14.5 or more (which is the same as a period of 99 minutes
or less, depending on how your program displays its data). This
simply means that the orbit is tilted at least 40 degrees with
respect to earth's equator, and as such will pass over points as far
north as 40 degrees north latitude and points as far south as 40
degrees south latitude. The mean motion is simply the number of
orbits per day a satellite makes. Period is how long one orbit
takes. The lower the orbit, the more orbits per day, and the shorter
the period.
Even then, the satellite you've selected might only be the size of a
beach ball. Trying to see a beach ball 300 kilometers overhead with
the unaided eye just won't work. Binoculars and dark skies will help
spot dimmer targets, but the smallest birds will still fly over
unseen. A few you might want to try are:
COBE - variable, spins once every 10 seconds. Occasionally bright.
Cosmos 604 & Cosmos 1689 - dim, but quite visible directly overhead.
Cosmos 1689 r - rocket booster for Cosmos 1689, slow 90-second
tumble. Bright for 5 seconds of the 90, but
otherwise dark & invisible.
ERBS - Earth Radiation Budget Satellite. Dim.
Landsat 4 - tumbling every 15 seconds. Visible, but mainly dark.
Pegsat - pretty good target.
Be patient and trust your prediction program. Someone told me that
for satellite spotting, patience isn't a virtue, it's a requirement!
The times may be off slightly, but the path across the sky is usually
right on.
For $30 a pair of binoculars will help you find many dimmer
satellites. A small 7x35 pair will do fine, though for $80-$100 a
pair of 7x50s will collect even more light. (For dim objects it is
light gathering power (the second number), not magnification, that is
the desired feature.) A telescope is far too cumbersome. A scope's
high power and narrow field of view make it almost impossible to zero
in on a fast moving satellite. And you're not going to see antennas
hanging out. It's just too small and too far away for that.
Binoculars are ideal.
Get everything you need from CompuServe.
----------------------------------------
Everything you need to get started with satellite spotting is
available in one place. It was on the CompuServe Information Service
that I found, and downloaded these programs that got me started. I
also found other satellite spotters all around the globe. If you
already subscribe to similar services like Delphi, GEnie, America
Online, or others, check around for an astronomy or ham radio area
with files available for downloading. Prodigy is not suitable since
they do not allow you to download programs and datafiles for use
offline.
I've worked out a method using CompuServe that will let you: 1) get
all the programs and data files at little or no cost, and 2) ask
questions via electronic mail (my CompuServe ID is 76703,3044.
MacSat author Bill Bard is at 75366,2557). You'll also have the
opportunity to meet a wide variety of amateur and professional
astronomers and space enthusiasts.
The only thing you'll need in addition to your computer and modem is
a CompuServe User ID to get access to the system. Call CompuServe
Customer Service toll-free at 1-800-848-8199. Ask for Operator 176.
They will send you a free Starter Kit that includes a User ID and
password, and comes with $15 of free connect time. If you also need
communications software for your computer, they will offer the
CompuServe Information Manager for $25 (this also includes $25 of
connect time, so your cost is a wash). When you get your kit, it
will include your User ID, password, and a directory of telephone
access numbers across the country.
When you log on, you will want to make your way to the Astronomy
Forum. Depending on your software you'll probably type GO
ASTROFORUM. If you're using the CompuServe Information Manager, use
the GO option under the Services menu and type ASTROFORUM.
Each forum maintains up to 18 libraries loaded with files available
for downloading.
In this case we are interested in:
Library 7 "Astrocomputing"
and the files MACSAT.DOC and MACSAT.SIT (for Macintosh users)
or the files TRKSAT.DOC and TRKSAT.EXE (for DOS users)
Library 17 "New Uploads"
for datafiles KEPELE.NAS or SATLOW.DAT for all users.
(Updated frequently.)
The file TRKSAT.EXE is the largest file at 329,000 bytes, and will
take about 48 minutes to download with a 1200 baud modem, or 24
minutes with a 2400 baud modem. MACSAT.SIT is only 105,000 bytes
long (approx 14 minutes at 1200 baud, 7 minutes at 2400).
So, now you know how the Satellite Spotters Guide is created. You
can do it yourself anytime at all. While I can't answer all
questions about every program on every machine, I do run both
Macintoshes and DOS clones. Feel free to drop me a note via E-Mail
on CompuServe at 76703,3044.
+--------------------------------------------------------------------+
Mir
1 16609U 86 17 A 90183.89213145 .00020188 00000-0 22865-3 0 7711
2 16609 51.6127 251.5145 0010974 101.2360 258.9979 15.62331916250556
+--------------------------------------------------------------------+
Figure 1. The Keplerian elements (named after Johannes Kepler who first
worked out the orbit of Mars and proved Copernican theory of the solar
system correct) are a set of numbers that describe the path and motion of
an object in orbit. The data files you download are in "NASA 2-line format"
shown here. These numbers describe the exact position and motion of a
satellite at a given time. With this information we can calculate its
current (or future) position and motion.
+-------------------------------------------------------------------------+
| |
| Satellite Mir NORAD Number 16609 |
| Int'l Designation 1986 017A Epoch 90 183.89213145 |
| Inclination 51.6127 Deg RAAN 251.5145 Deg |
| Eccentricity 0.00109740 Argument of Perigee 101.2360 Deg |
| Mean Anomaly 258.9979 Deg Mean Motion 15.62331916 Rev/Day |
| Epoch Revolution 25055 |
| |
| Semimajor Axis 6759.0 Km Period 92.17 Min |
| Apogee 388.27 Km Perigee 373.44 Km |
| |
+-------------------------------------------------------------------------+
Figure 2. The NASA 2-line format is decoded showing Mir's orbit
inclined to the earth's equator at an angle of 51.6 degrees. This
means it will pass directly over points as far as 51.6 degrees
latitude north and south of the equator. (Chicago is 42 degrees
north.) It's mean motion of 15.6 means it is low enough to be a
candidate for visual observation. MacSat allows you choose
satellites by inclination or mean motion and display the data as
shown here. On DOS machines a separate program called EDSAT is
needed. EDSAT is available in the CompuServe libraries, but is not
required to generate satellite forecasts.
+------------------------------------------------------------------------+
| Time CDT Az El Range Height North West RA Decl |
| MM DD YY HHMM:SS Deg Deg Km Km Lat Long Hr Min Deg Min |
| |
| 07 10 90 2238:30 238 22 893 379.7 37.84 95.62 13 33.4 -6 38.1 |
| 07 10 90 2239:00 239 31 706 379.4 39.04 93.77 13 52.7 0 32.7 |
| 07 10 90 2239:30 241 44 540 379.2 40.19 91.85 14 23.5 11 55.8 |
| 07 10 90 2240:00 248 66 421 378.9 41.31 89.86 15 21.3 30 9.8 |
| 07 10 90 2240:30 23 80 394 378.7 42.39 87.79 17 27.6 51 3.3 |
| 07 10 90 2241:00 48 54 475 378.4 43.43 85.66 20 35.1 56 29.2 |
| 07 10 90 2241:30 51 36 623 378.2 44.42 83.44 22 26.2 50 23.3 |
| 07 10 90 2242:00 53 26 801 378.0 45.36 81.15 23 17.5 44 8.6 |
+------------------------------------------------------------------------+
Figure 3. Using the Keplerian elements, MacSat and TRAKSAT can then
calculate when a satellite will be above your horizon, if it is
illuminated by the sun at the time, and if the sun is below your
horizon, making a visual sighting theoretically possible. Here we
show a passage that begins with the satellite to our southwest
(azimuth 238 degrees) at 10:38pm (2238) low in the sky (elevation 20
degrees). It reaches its highest point in the sky at 10:40pm (2240)
to the northeast (azimuth 23 degrees) almost directly overhead
(elevation 80 degrees).
Azimuth refers to the direction to look, measured in degrees from
north. 0/360 = north. 90 = east. 180 = south. 270 = west.
Elevation is the angle above the horizon. 0 degrees is the horizon,
90 degrees is directly overhead. The North Star is 42 degrees above
our northern horizon, which corresponds to Chicago's latitude of 42
degrees.
Today's students are tomorrow's explorers. The "Satellite Spotters
Guide" is dedicated to the proposition that the United States has the
will, the determination and the resources to remain a leader in
future space exploration.
Please pardon the fact that this is a simple ASCII version of a
typeset flyer complete with illustrations. Recently we sent hundreds
of flyers to interested Chicagoans who regularly catch the "Satellite
Spotters Guide" on WGN-AM 720.
If you must have the finished, typeset, illustrated, printed version
(for your astronomy club or school?) please by send $1 plus a
stamped, self-addressed, #10 (business size) envelope to:
Satellite Spotters Guide, P.O. Box 366, Itasca IL 60143.
Please mention which BBS or service you found this file on.
Yes, it does look a whole lot nicer.
My special thanks to John Williams [73615,1407] of the Dallas Remote
Imaging Group for all of his help and suggestions in preparing this
paper. My thanks also to T.S. Kelso of the Celestial BBS; Ted
Molczan of the Canadian Space Society; Conrad Kirksey [71575,1677] of
the CocoLoco BBS; and David Ransom of the RPV Astronomy BBS. These
guys are the *real* satellite trackers and observers. And finally my
thanks to Bill Bard [75366,2557] and Paul Traufler for their well
written programs that make it all seem so easy.
Alan Bose is Manager of Information Services at a large commercial
printer in the northwest suburbs of Chicago. He is also a speaker
and author on the use of computers and barcodes in the printing and
paper industries. He is a graduate of the Institute of Design at the
Illinois Institute of Technology. His interest in computers,
astronomy, aviation and space exploration dates back to the heady
days during our race to the moon. As a private pilot he has written
computer software for aircraft navigation and flown the North
Atlantic in a light plane. Over the past ten years he has been one
of the system operators on AVSIG - the Aviation Forum on CompuServe.
As an amateur astronomer, he is a member of the Northwest Suburban
Astronomers, and has been doing naked-eye satellite spotting since
1989, and stirring up interest in Chicago by forecasting brighter
objects on WGN Radio since July 1990. Skiing, Cub Scouts and
classical music consume any remaining time.
(c) Copyright 1991 Alan Bose
All rights reserved.
For quantity/educational reprints, please write:
Satellite Spotters Guide, P.O. Box 366, Itasca IL 60143