I am using the NASA NEO object data:
Given the information in this JSON data, is it possible to calculate the position of the NEO in relation to Earth? It doesn't seem to offer any positional information that I can see.
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$\begingroup$ The "orbital data" section should be sufficient to determine it's elliptical orbit, including position at any given time, assuming the orbital data is in reference to a known plane (I'm guessing it's the plane of the ecliptic, but it might be the Earth's equator, so doublecheck). You can also use HORIZONS to check your results. Just enter the neo_reference_id (3726710 in your example) for "target body". Correction: data appears to be for the asteroid's solar orbit, not geocentric orbit. $\endgroup$– user7073Commented Oct 30, 2017 at 12:48
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$\begingroup$ This is great but I am looking for an example of how to calculate this information? $\endgroup$– Marc CCommented Oct 30, 2017 at 13:27
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$\begingroup$ Same way you would with any planetary orbit-- there should be resources online to do that and perhaps even here or on astronomy.SE $\endgroup$– user7073Commented Oct 30, 2017 at 14:32
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If you would like Horizons to calculate it for you, I've found the following setup the most useful. Instead of using those orbital parameters, a pre-calculated trajectory can usually be found that is made by direct numerical integration, which is more accurate than using static parameters. It's nice to see the eccentricity and semi-major axis on the screen, but for calculating the orbit into the future and past, it's better to stick with state vectors.
You can type several different names or designators and Horizons will make a guess for you. Usually it does a good job, but double check! Here I chose the ID number 3727181 from the file in your link, and it seems to have found the right object, also called Asteroid (2015 RC).
I choose the state vector with both x, y, z and vx, vy, vz. Most of the time I don't use the velocities, but sometimes they come in handy, so I save them at the same time. I choose km and km/sec for units since they directly compatible with off-line numerical integration.
Ecliptic plane (rather than J2000.0 cartesian plane) is the default, and is usually what looks the nicest when plotting, and the CSV format is easy to read in to another program.
The actual table of numbers begins after the line with $$SOE and ends before the line with $$EOE. I assume those are Start Of Ephemeris and End Of Ephemeris.
- HTML format will generate text on your screen that you can copy/paste while keeping the menu options.
- plain text format creates a window in your browser with plain text you can save as a text file or copy/paste.
- download/save opens a dialog box and allows you to save the text file directly to your hard drive
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$\begingroup$ This is a great answer @uhoh thank you, I am really looking to see how to calculate it myself as I wish to great a visualisation that will generate these on a time line that is interactive. This is a good way for me to check the output is the same, I just need to look at how to get to the answer! $\endgroup$– Marc CCommented Oct 31, 2017 at 9:52
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$\begingroup$ Oh if this is not the answer you really want, then you should un-accept it, which will then increase the chances you get what you are looking for. You could also see the six links (1 through 6) I've included in this answer or try out some of the math in this answer. As long as they are good, there's no limit to the number of questions you can ask. $\endgroup$– uhohCommented Oct 31, 2017 at 10:44
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1$\begingroup$ No its led me onto being able to research the answer a little further myself so I accept it as its got me over the block I had, thanks again $\endgroup$– Marc CCommented Oct 31, 2017 at 15:04