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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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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! ...
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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) ...
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CSpOC’s identical TLEs

Identical TLEs are often published by CSpOC at https://www.space-track.org/. For example, here’s the first line of the three newest TLEs for IRNSS-1H: ...
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Who released pre-launch TLE data for the Space Shuttle?

The question Pre-launch TLEs for NASA launches asks: I was curious if the United States is on the verge of launching maned flights to the ISS, will anyone release Pre-Launch TLE data like was done ...
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Pre-launch TLEs for NASA launches

I was curious if the United States is on the verge of launching maned flights to the ISS, will anyone release Pre-Launch TLE data like was done back when the shuttle was flying.
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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 ...
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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: ...
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192 views

How to correctly make a fake, counter-propagating TLE?

In this answer I have said: Do not make FAKE TLEs! I would now like to make a fake TLE. Specifically I'd like to generate a counter-propagating "twin" of an orbit by flipping inclination by 180° ...
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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 ...
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How would blockchain be integrated into spaceflight? Have any methods been proposed yet?

Blockchain offers a way of keeping track of information such that its authenticity can be verified and it can not easily be falsified. In a space environment with an increasing number of both active ...
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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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Can the deactivated satellites also be tracked through TLE?

TLE is used to track whether the satellites are in orbit or not. However, is it possible that a particular satellite is deactivated, decommissioned or deorbited yet its TLE is being updated regularly?
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TLE/SGP4 state vector accuracy assessment

I’m using the Planet Labs state vectors downloadable from http://ephemerides.planet-labs.com/planet.states or http://ephemerides.planet-labs.com/planet_YYYYMMDD.states to assess the TLEs/SGP4 accuracy ...
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Why Celestrak has Archived TLEs for most space stations from Russia and the US, but not Tiangong-1, Tiangong-2 or Skylab?

Thinking about this question, I wanted to look at historical data. Then I noticed that while Celestrak does provide Archived TLE data for Salyut 7, Mir, Kvant-1, Kvant-2, Kristallm, Spektr, Priroda, ...
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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 ...
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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" ...
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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 ...
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Are there publicly-available non-amateur sources of TLEs other than Space-Track?

As an amateur satellite tracker, and sometime reentry analyst, I am always anxious to get the newest tracking data for low-orbiting spacecraft. I have had to rely exclusively on Space-Track for the ...
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Converting TLEs into the input data for SGP4

At face value this seems like a trivial question the TLE's are the input to SGP4, but my question is a little more specific. Given a TLE, the values are in specific units (eg. argument of perigee is ...
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321 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 ...
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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 ...
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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 ...
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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 only a ...
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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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How can I plot a precessing orbital plane of an artificial satellite on a polar plot from a TLE in Python?

How can I plot the orbital plane of an artificial satellite on a polar plot from a TLE in Python? Very new to all of this. As I understand it I need to extract TLE's from Space-track.org. Then use ...
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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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It's been over two weeks now, will the real Humanity Star please stand up?

edit: This must be some kind of record! (cf. ISRO's PSLV-C37 with 104 satellites - after 56 hours only six TLEs, which factor is greatest challenge? This time its only six total!) At the end of ...
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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 ...
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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 ...
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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 ...
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“Deep space” corrections in SGP4; how does it 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 ...
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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 ...
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761 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 ...
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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 ...
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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 ...
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Calculate ground track from CCSDS OEM

Are there open source solutions (preferable Python) to calculate the ground track of a spacecraft (i.e. in latitute/longitude) from CCSDS OEM (orbit ephemeris message) format (which is a dataset of ...
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344 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 ...
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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 ...
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Elevation and Azimuth of satellite in different location

I know the Elevation and Azimuth of the a specific GPS satellite (I have the RINEX files of the station in a specific Location 4.4801,-73.3433; in order to calculate this), but I want to know the ...
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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 ...
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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 ...
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PRN number in TLE files are the same in RINEX files? (in GPS constellation)

I want to compare the position calculated with Pyephem and TLE files, with RINEX files and GPSTK library in a specific date and time, but I have not the certainly if the name of the satellite "PRN ##" ...
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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 ...
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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; ...
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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 ...
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379 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 ...
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558 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 (...
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How 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 ...
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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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Regarding the vernal equinox and calculate a TLE code

I am utterly confused as to how the ecliptic co ordinate system works. My understanding is that the vernal equinox is comparable to greenwich for longitude here on earth. But how do we know where the ...