Questions tagged [two-line-elements]

Set of values carefully prepared to be used together with a simplified perturbations model (most often SGP4) to predict satellite positions with a moderate level of accuracy for times near the epoch contained within the TLE.

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15
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3answers
12k views

How can I plot a satellite's orbit in 3D from a TLE using Python and Skyfield?

I have obtained a Two Line Element (TLE) of a satellite in Earth orbit from Celestrak at https://www.celestrak.com/NORAD/elements/ and I would like to use it to calculate an orbit. How can I ...
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1answer
8k views

How to get semi-major axis from TLE?

This should be fairly straightforward, but, how do I get the semi-major axis (a) from at TLE. For example if I have the TLE: ...
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2answers
2k views

How (the heck) are military satellites with (apparently) classified TLEs still showing up on sat map websites?

As I first noted in this comment I couldn't get TLEs for the recently launched OFEQ-11 spy satellites from space-track.com. When I looked at Search Resuls: OFEQ 11 Satellite details 2016-056A NORAD ...
9
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1answer
404 views

How does the ISS Transit Finder website get the position of the ISS so accurately?

The recent Petapixel article How to Shoot the ISS Flying Across the Face of the Moon gives a lot of detailed, helpful advice for photographing transits of the ISS across the disk of the Moon. For ...
9
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1answer
509 views

Which two satellites had a 44% probability of collision at 2017-01-07 21:53 UTC?

I saw this message on space-track.org: The JSpOC has identified a close approach between two non-maneuverable satellites in a sun-synchronous orbit (approximately 800km altitude) with a time of ...
9
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1answer
736 views

Covariance matrix of a satellite position

In order to estimate the probability of collision with space debris, the covariance matrix of the primary and secondary objects should be calculated (JSPoC paper). I'm going to calculate the matrix ...
9
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1answer
376 views

Why did the frequency of TLEs for the Hubble Space Telescope drop by a factor of 3 in 2009?

I noticed that the TLEs for the Hubble Space Telescope (HST) are posted almost twice a day. Then I looked back in time and saw that this rate varies quite a lot! The plot shows the time interval ...
8
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2answers
713 views

What was the first proper Two Line Element to be generated?

In this question I describe looking for a TLE for Mercury-Atlas 6, the spacecraft piloted by John Glenn on February 20, 1962. I'll post here the relevant information: While the TLE catalog available ...
8
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1answer
394 views

Has NORAD ever experienced a catastrophic event and “lost track of” a bunch of objects?

NORAD tracks satellites for several very important reasons. From time to time an object might become temporarily mis-identified or otherwise confused with another object, these things usually get ...
8
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1answer
640 views

How does the SpaceBEEs' experimental passive radar reflector work?

My Question: What is the nature of the "experimental passive radar reflector developed by the U.S. Navy’s Space and Naval Warfare Systems Command"? How does it work, and why does it work for ...
8
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2answers
891 views

Where to look for historical or reconstructed orbit data for early NASA missions - Mercury-Atlas 6 for example

After reading this answer I decided that for my own use I'd like to plot the orbit of Mercury-Atlas 6, the spacecraft piloted by John Glenn on February 20, 1962. This thorough answer lists fourteen (...
8
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3answers
670 views

Why is the NORAD Catalog number of SpaceX's Starlink's “Darksat” both 71130 and 44972?

@BowlOfRed's answer to Which of the recently launched Starlink satellites is the coated one? links to Celestrak's supplemental table for Starlink. https://celestrak.com/NORAD/elements/supplemental/...
7
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1answer
355 views

What is “OBJECT BS”?

I checked 2018-099 in Celestrak's satcat again for the question Where can I find the TLE of ExseedSat 1, India's first ever private LEO satellite? and noticed that ...
6
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3answers
152 views

How do cubesat owners first find out their cubesat's initial trajectory? How do they point antennas at it before official TLEs start to appear?

When cubesats are first deployed it can sometimes take several days before they start appearing in official TLE distributions, and even then if many were deployed it may take a lot more work to decide ...
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2answers
915 views

Is SGP4 propagation necessarily more accurate near the epoch chosen for TLE generation?

This interesting answer includes a quote from Space-Track: From Space-Track.Org FAQ TLEs can contain future epochs. About 20 satellites are categorized as "multi-day objects" ...
6
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2answers
3k views

Obtain archived TLE data

Now I'm achieving the up-to-date TLE from the celestrak.com and tle.info However, for some analysis in the past, I need old TLE files, to make my calculations more accurate. Is there a way to obtain ...
6
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1answer
247 views

Is TESS really lost? What does Celestrak mean exactly?

From this answer to the question What artificial satellite has the farthest orbit around the Earth?: I found the following "far out" spacecraft: TESS (Transiting Exoplanet Survey Satellite)...
6
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3answers
148 views

How do two-line element sets handle rev numbers > 99,999?

In a two-line element set (TLE), five characters in line 2 -- columns 64-68 -- are for the rev number. (https://en.wikipedia.org/wiki/Two-line_element_set) But some satellites have been around the ...
6
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1answer
522 views

Are SpaceBEEs actually hard to track?

The IEEE News article FCC Accuses Stealthy Startup of Launching Rogue Satellites focuses mostly on the intrigue addressed in the question What checks are supposed to be carried out to prevent illegal ...
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183 views

How can I plot satellite's trajectory from three different TLEs to detect any deviation on path with time?

I have obtained TLE information of a satellite from space-track.org for three different times. I am trying to study any deviation of the satellite trajectory from its usual path. Here I am comparing ...
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98 views

What happens when the 3-letter suffix space of a SATCAT ID gets exhausted?

The ISS' SATCAT ID is 1998-067A. The CubeSats and other objects released from the space station are considered its sub-units, thus using different suffixes: 1998-067C, etc. The same principle applies ...
5
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3answers
538 views

Will the new “TLE format” be orbitally-mechanically better than traditional TLEs?

Celetrak's A New Way to Obtain GP Data (aka TLEs) by Dr. T.S. Kelso 2020 May 27 explains the arrival a new infoblob format that in several ways is "better" than the ancient TLE, and contains ...
5
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3answers
2k views

Determine orbit type from TLE

I was wondering if, and how, one can tell from the values in a TLE whether an orbit is LEO, MEO, HEO, or GEO. I'd like to do this in code eventually, so any formulas or threshold values would be much ...
5
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1answer
212 views

Why the PRN obtained from Android is different from calculated by TLE

I want to use TLE data to calculate the azimuth and elevation of every GPS satellites at user's location. In order to verify the correctness of TLE calculation, I wrote an Android app that can be ...
5
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1answer
1k views

Differences between SGP8 and the standard SGP4? Is it ever used in practice?

The Wikipedia article Two Line Element Set says: The SGP4 model was later extended with corrections for deep space objects, creating SDP4, which used the same TLE input data. Over the years a ...
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2answers
423 views

Why are Keplerian elements used in TLEs instead of Cartesian state vectors?

Propagating a state vector seems easier, you just account for the gravity, change the velocity and update the position. It also allows to easily apply perturbations, etc. Additionally, the ...
5
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1answer
323 views

ISRO's PSLV-C37 with 104 satellites - after 56 hours only six TLEs, which factor is greatest challenge?

It's been 24 hours 56 hours since ISRO's PSLV-C37 launched from Satish Dhawan Space Centre (SRI) at 09:28 local time (03:58 UTC). I see satcat numbers and object names for 105 total objects; ...
4
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1answer
233 views

Get dates when a satellite has performed maneuver from historical TLE data (python)?

I have been recently acquainted with orbital mechanics and am trying to do some analysis on the subject. Since I don't have subject matter expertise, I am at a crossroads with trying to decide that ...
4
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1answer
549 views

What would be a “big picture” understanding of how the orbits of Earth satellites are monitored?

In preparation for another question, I typed "keeping track of satellites in orbit" into a search engine, and found a website called keeptrack.space which has a ...
4
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2answers
332 views

What does it mean to ask for a date beyond epoch time?

I am fairly new to this industry. As I am playing around with a library on Python, ephem, I have encountered an error saying that: ...
4
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1answer
255 views

What does a steep change in mean anomaly indicate?

I'm following the slot swaps of the Iridium satellites in plane 6 and cannot make sense of the following: The TLEs of three of the old satellites very often show a marked difference in the mean ...
4
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1answer
257 views

How to construct $B^*$ drag term in TLE?

Is it possible to calculate $B^*$ term in TLE data using only a few or more velocity and position vectors for a satellite?
4
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2answers
202 views

What caused so many objects in Earth orbit to “go NEA”? (no elements availabe)

T. S. Kelso tweeted the following, is this a case of lost and found? How can so many substantial objects become lost like this? The list of 23 objects "formerly known as Prince NEA" all seem ...
4
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1answer
192 views

Why does 2018-099 (SpaceX, December 2018) still have a dozen unidentified payloads?

According to today's Raw SATCAT Data from Celestrak, the launch designated 2018-099 (SpaceX, December 2018) still has twelve unidentified payload objects! ...
4
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1answer
374 views

TLE and RINEX gps differences

I have TLE and RINEX navigation file for GPS satellite PRN 20, for 01.04.17r. 19:56:56 and 20:00:00 respectively. See also The Receiver Independent Exchange Format Version 3.03. It seems that the ...
4
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1answer
212 views

What caused the ISS Two Line Element Day of Year problem beginning 12-24-2019?

Does anyone know happened at NORAD or NASA or wherever the published TLEs originate, that caused the ISS TLE wonkiness during the last week of 2019? It did not happen in 2018. What happened? The ...
4
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2answers
293 views

PSLV-C39/IRNSS-1H TLE accuracy

The TLEs accuracy for PSLV-C39/IRNSS-1H seems low when compared to that of the other LEO satellites (ISS, HST, Tiangong, Sfera 2, ...). Look, for example, at the following graph that shows the radius ...
4
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2answers
869 views

How do SDP4's “Deep space” corrections to SGP4 account for the Sun's and Moon's gravity?

The Simplified Perturbations model SGP4 is used to calculate Earth satellite state vectors (position and velocity) using standard ephemeris data encoded as TLEs (Two Line Elements). According to ...
4
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2answers
120 views

Has IBEX “gone dark”?

I'm having a difficult time finding information on the Interstellar Boundary Explorer's (IBEX) orbit. Unless I've made some kind of error, the TLE's have stopped at TLE epoch ...
4
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1answer
43 views

Textbook or scholarly discussion of equations used by the SDP4 part of SGP4 TLE propagators beyond Space Track Report #1?

(the famous) Space Tract Report #3 discussed at length in Dr. T.S. Kelso's Revisiting Spacetrack Report #3, AIAA 2006-6753 Describes the "deep space" corrections to the original SGP4 known ...
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112 views

Equinoctial Elements and Perturbative Effects

I have an Orbital model in Equinoctial Elements (paper). There is a perturbative acceleration term in the model. Can someone point me to some relevant papers showing how to include different ...
3
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2answers
221 views

What is/was legacy TLE ephemeris type 2? (TLE, line 1, column 63)

Wikipedia's Two-Line Element Set entry for line 1, column 63 (1.12) says: Ephemeris type (internal use only - always zero in distributed TLE data)13 13Celestrak Frequently Asked Questions: Two-Line ...
3
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2answers
5k views

How to generate TLE file?

Subsequently to this answer: What is the way of generation of TLE file for a satellite? How to deal with BSTAR drag term, mean orbital elements, etc.? The generated TLE will be used as the input for ...
3
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1answer
112 views

Does this electronics box, or any other non-spacecraft released by astronauts have a TLE?

According to Space.com's 02-Feb-2018 article Cosmonauts Break Russian Spacewalk Record During Space Station Antenna Repair: The cosmonauts spent the day replacing an electronics box for a high-gain ...
3
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1answer
731 views

Recreating the eccentricity value of TLE

I cannot confirm the eccentricity value of a TLE using corresponding position and velocity vectors. Let me go through an example, ISS, to explain the situation. Using this TLE for ISS, 1 25544U ...
3
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1answer
64 views

What is the “+” symbol for the drag term encoded in a TLE?

I have two TLE, the drag term for the first TLE is -26868-1, which I suppose equals to -0.026868. But on the second TLE, we have ...
3
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1answer
256 views

Why are there some NORAD catalog IDs larger than 80000 in space-track?

I was trying to find the international designator for the Starlink-2 constellation launch. Not finding anything in Celestrak I looked in Space-Track. The following space-track.org query builder setup ...
3
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1answer
661 views

Generating TLEs with STK Using SGP4 Propagator;

STK has two methods for generating TLEs; Trajectory Sampling method and Single Point method. I have read the differences both of them at http://help.agi.com/stk/index.htm#stk/tools-10.htm but I am ...
3
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2answers
631 views

Has a TLE ever been issued for a spacecraft trajectory not bound to Earth orbit?

This excellent answer to the question Why has no TLE been published for the DSCOVR satellite and the Falcon 9 R/B? suggests that to the best of the writer's knowledge TLEs are only issued for ...
3
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1answer
281 views

Are 1U cubesats sufficiently detectable to get at least minimally usefully predictive public TLEs, updated regularly?

Satellite radar cross-sections is a complex function of satellite structure, design, materials, instantaneous attitude, (radar) frequency, polarization, and if has moving parts, configuration, just to ...