The OSF Orbital Visibility schedules at present cover **3,409 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.

U. S.City Initials: |
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |

Non-U.S.City Initials: |
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |

** 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.

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.

*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 conditions.

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 3/8/01 9:17am EST:

MIR 1 16609U 86017A 01067.59524234 .00333173 63704-4 40049-3 0 6577 2 16609 51.6404 329.1783 0009514 105.4217 254.7773 16.07629756860947 Name...................................MIR NORAD ID#..............................16609 Epoch Year.............................1 Epoch Day..............................67.59525 3/8/01 9:17am EST Mean Altitude (km).....................253.306 Period (min)...........................89.57 Apogee (km)............................259.615 Perigee (km)...........................246.997 Inclination (degrees)..................51.6404 Right Ascension of Ascending Node (RAAN, degrees).................329.1783 Eccentricity...........................0.0009514 Argument of Perigee (degrees)..........105.4217 Mean Anomaly (degrees).................254.7773 Mean Motion (revs. per day)............16.0763 Decay Rate.............................0.00333173 Epoch Revolution.......................86094 Element Set#...........................657 Visible up to Latitude (degrees).......67.5 3/8/01 11:46 AM 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

**Curator:**

SAIC Information Services

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