| Photo | Name | NORAD | Int'l ID | Launch Country | Status |
|---|
OWNER).LAUNCH_DATE. Year of first object catalogued.| TLE (L1 / L2) | Satellite | NORAD | Country | Epoch (UTC) | Validity | Source |
|---|
A Two-Line Element set (TLE) is the standard
format NORAD uses to publish satellite orbital data. Every TLE
is two fixed-width 69-character lines. NAZAR feeds each one
through the SGP4 propagator
(satellite.js) in your browser to compute
lat / lon / altitude at any chosen moment.
Below is a typical TLE for the International Space Station (NORAD 25544) — every field is annotated with its character range, what it represents, and the example value.
1 25544U 98067A 26155.73640860 .00000690 00000+0 69294-3 0 9998
| Cols | Field | Example | Meaning |
|---|---|---|---|
| 1 | Line number | 1 | Always 1 for line 1. |
| 3–7 | Catalog number | 25544 | NORAD satellite ID. 25544 = ISS. |
| 8 | Classification | U | U = unclassified, C = classified, S = secret. |
| 10–17 | International designator | 98067A | Launch year + sequential number + piece. 98067A = 67th launch of 1998, piece A. |
| 19–32 | Epoch | 26155.73640860 | The instant this element set describes. Format: YYDDD.DDDDDDDD (year + day-of-year + fractional day). Decodes to 2026-06-04 17:40 UTC. |
| 34–43 | 1st derivative of mean motion | .00000690 | How fast the orbit is decaying, in revolutions per day². Positive = falling. |
| 45–52 | 2nd derivative of mean motion | 00000+0 | Acceleration of mean motion. Decimal point implied: 00000+0 = 0.00000 × 10⁰. Rarely non-zero in modern TLEs. |
| 54–61 | B* drag term | 69294-3 | Atmospheric drag coefficient. 69294-3 means 0.69294 × 10⁻³. Used by SGP4 to model atmospheric braking. |
| 63 | Ephemeris type | 0 | Always 0 in distributed TLEs (placeholder field). |
| 65–68 | Element set number | 999 | Version counter — increments each time NORAD re-issues a TLE for this object. |
| 69 | Checksum | 8 | Mod-10 sum of all numeric digits + minus-signs in the line. |
2 25544 51.6440 248.8311 0007020 113.7892 246.4063 15.49984836446432
| Cols | Field | Example | Meaning |
|---|---|---|---|
| 1 | Line number | 2 | Always 2 for line 2. |
| 3–7 | Catalog number | 25544 | Must match line 1. |
| 9–16 | Inclination | 51.6440 | Angle between the orbital plane and Earth's equator, in degrees. ISS at 51.6° is why it overflies most populated latitudes. |
| 18–25 | RAAN | 248.8311 | Right Ascension of Ascending Node — where the orbit crosses the equator northbound, measured from the vernal equinox in degrees. |
| 27–33 | Eccentricity | 0007020 | Leading 0. is implied: 0007020 means 0.0007020. Near-zero = near-circular orbit. |
| 35–42 | Argument of perigee | 113.7892 | Angle from the ascending node to the orbit's closest point (perigee), in degrees. |
| 44–51 | Mean anomaly | 246.4063 | Where in its orbit the satellite is at epoch, expressed as the angle (degrees) a circular reference body would have travelled. |
| 53–63 | Mean motion | 15.49984836 | Number of orbits per solar day. ISS at 15.5 orbits ~93 min each. Convert: period (min) = 1440 ÷ mean_motion. |
| 64–68 | Revolution number | 44643 | Orbit count since launch, at the epoch instant. |
| 69 | Checksum | 2 | Mod-10 sum check, same scheme as line 1. |
Together, those six Keplerian elements (inclination, RAAN, eccentricity, argument of perigee, mean anomaly, mean motion) plus the epoch and drag term fully describe the satellite's orbit. SGP4 takes them in, applies analytical perturbation models for Earth oblateness + atmospheric drag, and gives back a sub-point and altitude for any time you ask about — usually accurate to within a few kilometres for the first ~2 weeks after epoch, degrading thereafter.
| Name | NORAD / Int'l ID | Launch Country | Last seen | Remarks |
|---|
| TLE (L1 / L2) | Satellite | Alpha-5 | Decoded NORAD | Int'l ID | Epoch (UTC) | Validity |
|---|
A classic Two-Line Element set stores the NORAD
catalog number in just five columns (line 1,
characters 3–7), so it can only count up to 99999.
The real catalogue blew past that ceiling as tracked objects
multiplied — mega-constellations, rideshare cubesats and debris —
so a stop-gap extension called Alpha-5 was
adopted to keep the fixed-width, two-line layout every existing
tool already understands.
The trick: turn the first of those five columns
into a letter. Letters run A–Z
but skip I and O (too easily confused with 1 and
0), giving A=10, B=11, … Z=33.
The remaining four columns stay numeric. So the field now spans
A0000 = 100000 through
Z9999 = 339999 — roughly tripling
capacity without changing the line length at all.
E8493E8493 → E = 14 → 14 × 10000 + 8493 = 148493
Everything else in the two lines is unchanged, and
satellite.js decodes Alpha-5 designators natively —
NAZAR propagates these objects with SGP4 exactly like any other.
Alpha-5 is itself a bridge: the long-term successor is the
9-digit catalog number carried by the newer
OMM (Orbit Mean-Elements Message, distributed as
XML / JSON / KVN) rather than the fixed 69-character TLE.
| Photo | Name | NORAD | Int'l ID | Launch Country | Last seen | Remarks |
|---|