# Tag Info

24

Blockchain is a very poor solution to a specific problem: achieving ledger consensus among a large number of agents when there is substantial incentive to corrupt the record, and the entries in the ledger are directly related to one another. This is not a good fit to a satellite ephemeris. A relatively small number of agents add records to the system at a ...

17

SGP4 is the standard procedure that TLEs are intended to work with. All of the following are extremely helpful, but the most important point would be use a standard, recent SGP4 package that is recommended, do not try to use the elements in a TLE yourself. This is becuase the TLE and the SGP4 package are built for each other. Documentation webpage TLE ...

12

There is an international network of observers of classified satellites, organized around the Seesat-L mailing list: http://www.satobs.org/seesat/seesatindex.html They typically look for satellite passes using binoculars and a stopwatch, or using a camera. Then they fit TLEs to those observation, to be able to find the satellite on a later pass. You can get ...

11

The TLE gives mean motion ($n$) in $\frac{rev}{day}$. This needs to be converted to $\frac{rad}{s}$ which can be accomplished by multiplying the $n$ TLE value by $\frac{2\pi}{86400}$. Therefore, to go directly from $n$ in TLE to the semi-major axis $a$. We can use the following formula: $a=\frac{\mu^{1/3}}{\frac{2n\pi}{86400}^{2/3}}$. For \$n=15.5918272 \,\, \...

11

Yes, during the geomagnetic storm of March 1989, NORAD lost track of thousands of objects: During the great geomagnetic storm of 13-14 March 1989, tracking of thousands of space objects was lost and it took North American Defense Command (NORAD) many days to reacquire them in their new, lower, faster orbits. One LEO satellite lost over 30 kilometers of ...

9

This is more of a really-long comment than an answer, sorry, as it just narrows it down a bit. But I wanted to include links and quotes, so I put it in Answer form. First, it's not clear that what we call "two-line elements" today are the first two-line-thing-that-describes an orbit. The current two-line elements are based on the SGP4/SDP4 orbital model. ...

9

The original 4 satellites were 0.25U cubesats (as shown in the picture in the question) while the newer ones are 1U (cubical). The larger size of the newer sats provides space for Van Atta reflectors on four of the cube's faces1. Here's my understanding2 of how the reflectors work: In their most basic form, Van Atta reflectors are fully passive phased-...

9

It's somewhat an issue of the cart driving the horse -- TLEs are generated explicitly for the purpose of being an input into the SGP4 propagator. The data used to generate them often comes from propagators or observations far more precise than SGP4. SGP4 loses accuracy far away from the epoch because it is only an approximation of the full physical ...

9

In space bandwidth is a premium commodity. The blockchain technology treats bandwidth worse than dirt. EVERYONE receives a complete copy of the entire blockchain whether they need it or not - and satellites are only rarely in contact with each other. They are in contact with ground stations and these stations are expensive to operate. You're not gonna ...

8

According to Wikipedia, field 8 of TLE line 2 is the "mean motion in revolutions per day"; you can determine the orbital period from this. For geosynchronous orbit, you should expect 1.0 revolutions per day (in fact, due to complexity in the definition of "day", they're very close to 1.0027 as a rule). LEO defined as < 2000 km altitude should get ...

7

There are a few ways. Visual tracking Tracking of it's RF emissions Radar tracking. I suspect it's the first two. If you know about where something is, you can see it visually, and track it's RF emissions to boot. People make a hobby of such things. There are a number of web sites that track this information. https://www.prismnet.com/~mmccants/tles/ is ...

7

A typical TLE for a maintained satellite (as opposed to debris tracked via ground assets) has an error of only around 1 km at epoch (Vallado, et al, Appendix B), which grows at a rate of around 1-3 km per day. Worst case, a 1 km cross-track deviation from a distance of 400 km (approximate distance to ISS for a zenith pass) gives a deviation of only 0.143 ...

7

You're right; these objects aren't lost. However, Space-Track doesn't actually track a lot of higher-orbiting objects. They just don't seem particularly interested in anything with a multi-day orbit; I don't know why. Of the four objects you mention, TESS and IBEX are tracked by the people operating those missions. I know of no public data for IBEX, ...

6

Satellites are routinely monitored by the likes of US, Russia and China. China for example is known to blind American spy satellites with lasers. The goal is to track the approx 23000 (sources vary from 10 to 25000) objects, which could be anything from a satellite, debris from launches and even lost items from EVAs. US monitoring systems radar USSSN - US ...

6

First of all, it was a miss. Whew! The close approach predicted at 21:53:00 UTC on 7 Jan 2017 has passed without incident. The JSpOC has confirmed that both satellites are being tracked as single objects, indicating that no collision has occurred. A few tidbits that might help narrow it down: The percentage is very high, which means the objects must be ...

6

I think the answer to this is basically no or at least not any harder than other 1U CubeSats. I base this answer on two lines of argument. Also your data above more or less proves what I am about to say. First, this quote from Swarm co-founder Sara Spangelo "All seven SpaceBEE satellites launched to date have been consistently tracked by both the Space ...

6

Celestrak For some selected groups of satellites, Celestrak has already-built group definitions of satellite archives at https://www.celestrak.com/NORAD/elements/ Space-Track Another option is to subscribe to Space-Track.org. You have to register using your name and e-mail address, then verify, but it is a straightforward process. Make sure to read all of ...

6

About fifteen years ago, I very carefully implemented SGP8 and SDP8 (and the 'original' SGP) into my software (see https://github.com/Bill-Gray/sat_code ). It is hard to prove a negative -- i.e., that the 8 versions never saw any use -- but I've since seen SDP4/SGP4 get an incredible amount of use, and have seen the 8 variants get absolutely zero use and ...

6

It seems that latitude and longitude can (or must?) be provided to PyEphem as a string, using the degrees:minutes format i.e. Longitude: 116:17.75718, Latitude: 40:3.00174 See rhodesmill.org/pyephem/quick.html#observers PyEphem also needs Universal Time (and not the time in the local Timezone) See rhodesmill.org/pyephem/quick.html#dates Given that 40 N, ...

6

For Python and TLE propagation using SGP4 one very handy option is https://rhodesmill.org/skyfield/ As you probably already know a TLE is a strange animal. It does not really contain proper orbital elements, but instead is engineered with one purpose; to be fed into SGP4 so that that will generate reasonable position information for at least a few days ...

6

Skimming CCSDS RECOMMENDED STANDARD FOR ORBIT DATA MESSAGES, it looks to me like three different message types are defined: Orbit Parameter Message (OPM), Orbit Mean Elements Message (OMM), and Orbit Ephemeris Message (OEM). OPM gives position and velocity and optionally "osculating Keplerian elements". It is "suited to exchanges that "do ...

5

Code updated for python3* def makecubelimits(axis, centers=None, hw=None): lims = ax.get_xlim(), ax.get_ylim(), ax.get_zlim() if centers == None: centers = [0.5*sum(pair) for pair in lims] if hw == None: widths = [pair[1] - pair[0] for pair in lims] hw = 0.5*max(widths) ax.set_xlim(centers[0]-hw, centers[0]+...

5

The earliest TLE in the public catalog, according to elset epoch is for catalog number 15, Explorer 6, with an epoch of 1959-01-11 01:49:23 1 00015U 59004 A 59011.07596599 .00141866 +00000-0 +00000-0 0 09660 2 00015 047.0999 025.2139 7504899 076.7382 327.1285 02.03707726003008 I'm not sure why MERCURY 6 doesn't have a TLE, but suspect it's due to the ...

5

Orbital values provided by TLEs are mean elements. They change through the orbit and propagation. Therefore, a direct calculation of eccentricity from position and velocity vectors would not produce the same eccentricity value, it gives the eccentricity of the satellite for one moment in orbit only. That is why calculated eccentricity and the TLE value are ...

5

Do not make FAKE TLEs! Step 1: Read this answer. Step 2: Review all of the links in the answer. I'll repeat them here: Documentation webpage TLE format PDF Spacetrack report #3 PDF Revisiting Spacetrack Report #3 webpage Revisiting Spacetrack Report #3 PDF Step 3: Decide that this is a Bad Idea for the following reasons: Making Fake TLEs is dangerous!!...

5

There are 330 objects with an international designation starting with 1998-067, the first of which is the ISS. All of these are associated with the ISS, either being intentional or unintentional satellites released, or other related objects. Many of these are called "ISS Deb". It can be difficult to trace exactly which one corresponds to a particular object, ...

5

Changing only the data wouldn't do much, if it were just fed to the same old SGP4 we've been using for decades. However, to my delighted surprise, at long last, the US government has provided a new propagator for public use! I haven't seen it announced anywhere, but if you go to https://www.space-track.org/documentation#/sgp4 and download the zip file, the ...

5

This has to do with ambiguities in the definitions used for certain terms, and software doing strange contortions to avoid breaking backwards compatibility. The USAF's family of Simplified General Perturbations propagators are based on mean element theories of orbital motion. However, there are multiple ways to define and compute mean motion, and ...

5

A cubesat without a propulsion system deployed from the second stage of the rocket using weak mechanical forces only just follows the trajectory of the second stage. Differences between the trajectories of the deployed cubesats and the second stage are very small. So the cubesat owners may use the latest trajectory information from the launcher as initial ...

4

From experience, I assume that Space Track is in fact tracking them all. The difficulty lies in making positive identifications of the names of all of them, which will happen soon. As the separate further, this identification will be made easier, but I'm confident that in the end, all such objects will be listed, and all of them are being tracked. FYI, this ...

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