Status Report

Naked-Eye Mir Visibility Data From Selected Cities December 5 – 14, 2000

By SpaceRef Editor
December 6, 2000
Filed under ,

Naked-Eye Mir Visibility Data

From Selected Cities

December 5 – 14, 2000

The OSF Orbital Visibility schedules at present cover 3,406 locations
worldwide. To determine if your data for your city is available click on the
“List of Cities Served” link below and scroll through the list (alphabetized
by city name). If you do not find your city/location on the list, for the
time being, we ask that you to select the nearest listed entry.

Please note that the times reported in the U.S. Cities tables
are in the a.m./p.m. format familiar to most people in the United States. The
times reported in the Non-U.S. Cities tables are in 24-hour format most commonly
in use elsewhere.

U. S.

City Initials:


City Initials:

List of Cities Served

Click on the appropriate line below if your browser is unable to display HTML3 Tables:

NOTES: Included are only major cities currently in the range
of visibility, with maximum spacecraft elevations over the horizon larger
than 10 degrees. The data are also valid for suburban regions around these
cities, with slight changes in Direction of Movement and Max. Elevation.


Mir Altitude Update

There are two altitude charts provided below. The first chart shows the
altitude history in 7-day increments for the most recent 525 days. The second
chart displays the altitude history in 14-day increments and spans the entire
time period beginning with Day 1.


Mir Altitude History — 7-day Increments

ApogeeMean Altitude


Mir Altitude History — 14-day Increments

ApogeeMean Altitude

Two-Line Keplerian Orbital Elements

Jesco von Puttkamer

The "Two-Line Elements" (or TLE) format generally
used by PC-based satellite tracking programs contain all necessary numerical
data describing the orbit (position, flightpath and motion) of a satellite
such as Mir or the coming ISS, as well as its exact position along that
orbit at a specific reference time (the "epoch"). This format
dates back to the days when NORAD (North American Aerospace Defense Command,
today US Space Command) still used IBM punched cards on its computers. Thus,
because each card could only carry one line, today’s Two-Line Elements were
"Two-Card Elements" back then. TLE files are always in ASCII format,
and when they are copied or moved around with "Clip and Paste"
commands, non-proportional fonts (like Courier) must be used to preserve
the exact positions of the digits and their spacings.

To completely describe not only the size and shape of an orbit but also
its orientation around its central body (for Mir, that would be the Earth,
of course), only five independent quantities called "orbital elements"
are required. The object in question can be anywhere on that closed path
as long as its position at a specified time is not given. Thus, a sixth
element is required to pinpoint the satellite’s position. From this position,
the satellite tracking program then calculates "forward", in effect
predicting the object’s locations at any desired future time. The real world
is not ideal, however, and therefore all orbits are influenced by various
disturbances called "orbital perturbations"; in the case of Mir
and the Space Shuttle, such "perturbations" might include applications
of thrust from the craftsí maneuvering jets as well as naturally-occurring

To fully include these perturbations in the predictions would be impractical
for PC-based calculation routines. Thus, with time, their influences pile
up, causing increasingly noticeable deviations of the real orbital path
from the predicted one. To take care of that, predictions need to be "refreshed"
periodically with up-to-date TLEs based on the most recent radar tracking
measurements of the responsible organizations such as US Space Command.

The element data used by our TLE’s to describe the orbit size and shape
are: the Mean Motion (2nd line position 53-63) and the Eccentricity
(2nd line pos. 27-33). Mean Motion is used because, according to Kepler,
an object in an elliptical orbit moves at periodically varying speed, depending
on its distance from the mass center at its focal point. From the Mean Motion
(in degrees per second) we can calculate the orbital period and, with the
Earth’s gravitational constant, the semi-major axis of the elliptic orbit
(which could, in rare cases, reduce to a perfect circular orbit). With the
Eccentricity, the apogee (farthest point) and perigee (closest
point) of the ellipse can be determined and, with the known Earth’s radius,
their altitudes above Earth and also the mean altitude. (When not referring
specifically to Earth, we are using "apoapsis" and "periapsis",
or "apofocus" and "perifocus" for these characteristic
points of an elliptic orbit).

For determining the orientation of the orbit about the Earth, the TLE
also contains the Inclination (2nd line pos. 09-16) of the orbit
plane in degrees measured from the Earth’s equatorial plane, the Right
Ascension of the Ascending Node
(RAAN, 2nd line pos.18-25), and the
Argument of Perigee (2nd line pos. 35-42). The ascending node is
the point where Mir crosses the Earth’s equatorial plane in the northerly
direction. (The opposite point is the descending node, and the line connecting
both points is called the Line of Nodes). RAAN, measured in degrees, is
the angular distance of the ascending node from the line pointing to the
Vernal Equinox on the ecliptic (the point where the Sun crosses the celestial
equator in spring around March 21). Argument of Perigee defines the orientation
of the elliptical orbit’s semi-major axis: measured in Mir’s orbit plane
in the direction of motion, it is the angle between its ascending node and
its perigee.

The sixth element is the Mean Anomaly (2nd line pos. 44-51), which
is used for calculating the satellite’s exact position at a particular time
("epoch") from perigee.

The first line of the TLE file, under the name, contains the US Space
Command-assigned Catalog Number of the object (often called the "NORAD
Number"), the Epoch Year and Epoch Date (pos. 19-32) and other identifiers
of interest. In line 2, pos. 64-86 are reserved for the number of revolutions
accumulated at epoch.

The two-line elements are not the only factors necessary to predict the
orbit of the Mir Space Station for the purposes of these visibility tables.
Many additional factors must be taken into account
to ensure the reasonable precision of these predictions over the dates covered
by the tables.

Following are the Two-Line Elements and Translated Orbital Data for the
Mir Space Station as of 12/6/00 10:58am EST:

1 16609U 86017A 00341.66537881 .00077270 00000-0 36390-3 0 2873
2 16609 51.6469 94.0602 0016402 84.6020 11.5398 15.82215301846293

NORAD ID#…………………………16609
Epoch Year………………………..00
Epoch Da………………………….341.6654 12/6/00 10:58am EST
Mean Altitude (km)…………………324.130
Period (min)………………………91.01
Apogee (km)……………………….335.123
Perigee (km)………………………313.137
Inclination (degrees)………………51.6469
Right Ascension of Ascending
Node (RAAN, degrees)……………..94.0602
Argument of Perigee (degrees)……….84.602
Mean Anomaly (degrees)……………..11.5398
Mean Motion (revs. per day)…………15.82215
Decay Rate………………………..0.0007727
Epoch Revolution…………………..84629
Element Set#………………………287
Visible up to Latitude (degrees)…….69.5
12/6/00 1:13 PM EST

NOTES: Included are only major cities currently in the
range of visibility, with maximum spacecraft elevations over the horizon
larger than 10 degrees. The data are also valid for suburban regions around
these cities, with slight changes in Direction of Movement and Max. Elevation.

Pickup Time: The local time of day that the spacecraft becomes
visible on the horizon.

Direction of Movement: The spacecraft will appear in the first
direction and travel across the sky, rising to the "Maximum Elevation"
and disappearing at the horizon in the second direction shown. These compass
directions are understood to embrace an angular field of 22.5 degrees each,
with their symbols defined as follows:

N: North NW: Northwest NNW: North-Northwest SSE: South-Southeast
E: East SW: Southwest WNW: West-Northwest ESE: East-Southeast
S: South NE: Northeast WSW: West-Southwest ENE: East-Northeast
W: West SE: Southeast SSW: South-Southwest NNE: North-Northeast

Responsible NASA Official:

Jesco von Puttkamer


SAIC Information Services

SpaceRef staff editor.