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6 votes

Access to Chebyshev coefficients from JPL ephemerides

Your question is slightly ambiguous, a file containing the Chebyshev coefficients wouldn't be an ephemeris, but it's something you could use to generate an ephemeris. Regardless, the article Format ...
Greg Miller's user avatar
6 votes
Accepted

Which SPICE kernels I have to load to calculate state vector of the outer planets

Insufficient ephemeris data has been loaded to compute the position of 699 (SATURN) relative to 0 (SOLAR SYSTEM BARYCENTER) at the ephemeris epoch 2023 NOV 06 19:16:53.612. That's because you are ...
David Hammen's user avatar
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6 votes

Why does Earth's North Pole RA flip by ~180 deg around AD2000 relative to SSB? (JPL Horizons data)

Is this an artifact to do with J2000 and ICRF? It's an artifact of choosing to use right ascension and declination to describe the Earth's orientation. Right ascension is undefined at a declination ...
David Hammen's user avatar
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5 votes

Change frame center definition of Chebyshev coefficients

I want to have all coefficients defined in the same frame center. That's not a good ask, for many reasons (see below). For example is it possible to have Chebyshev coefficients of the Earth w.r.t ...
David Hammen's user avatar
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5 votes
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How to get MARS2020/Perseverance EDL trajectory data from spice kernels?

This folder contains SPICE kernels for MARS2020: https://naif.jpl.nasa.gov/pub/naif/MARS2020/kernels/spk/ These SPK kernels contain planned EDL trajectory (prepared before actual landing): https://...
jumpjack's user avatar
  • 3,033
5 votes

How to obtain Chebyshev coefficients directly from the JPL Horizon's interface?

The best and most concise answer is here The "gold standard" is the SPICE toolkit. You can read more about using spice in this excellent answer. The JPL Development Ephemerides are lists of the ...
uhoh's user avatar
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4 votes
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SPICE toolkit occultation finder doesn't work with spacecraft

The error comes from bad formatted spk file. My application uses international unit system and spice uses km and km/s for state vector. When the occultation finder runs it see my spacecraft thousand ...
sl20's user avatar
  • 115
4 votes

Access to Chebyshev coefficients from JPL ephemerides

The best method I've found is to use Brandon Rhodes' Python "jplephem" from here, specifically using the _load() function of an SPK segment. You get a ...
ChrisR's user avatar
  • 6,180
4 votes
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How to convert a SPICE SPK kernel into human-readable data using SPICE toolkit and utilities

So I am using the following layout for my SPICE kernels (not essential but matches tutorial recommendations, adjust paths in the spm2oek input file as needed) ...
astrosnapper's user avatar
  • 2,506
4 votes

Horizons ephemeris - how did they calculate that “Keplerian GM” value?

Here's some info about that value of "Keplerian GM", $\mathrm{1.3289051881323761E+11 \, km^3/s^2}$, from https://ssd.jpl.nasa.gov/?horizons_news November 01, 2018: The mass-parameter used ...
PM 2Ring's user avatar
  • 2,612
3 votes

Access to Chebyshev coefficients from JPL ephemerides

Update : I have found a way to extract Chebyshev coefficients at a requested date for a particular body using CSPICE. Here the program that allows to do this : ...
GuillaumeJ's user avatar
3 votes
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Different Earth-centered ICRF positions in GMAT and Skyfield/Spiceypy with DE421

GMAT is wrong! Per their Jira they fail to consider the fact that J2000 and ICRF are the same in SPICE's eyes (as you mentioned), but then does a conversion to ICRF from that J2000 frame which causes ...
Dec M's user avatar
  • 301
3 votes

How to convert a SPICE SPK kernel into human-readable data using SPICE toolkit and utilities

Found another method/tool: "spy" from SPICE utilities, available for Windows (actually DOS), Unix and Mac. User manual: link Copy these data into a text file named "command.txt": <...
jumpjack's user avatar
  • 3,033
3 votes

How can I generate Chebyshev cofficients from SPICE for J2000 Inertial to Moon ME Frame?

I assume you're familiar with this list of documentation?: https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/req/index.html Here's a section on PCK files with Chebyshev polynomials: https://naif.jpl....
CourageousPotato's user avatar
2 votes
Accepted

Rotation matrix from J2000 to ITRF2008

Such a rotation matrix does not exist. In Vallado's book I found the following: "Because these stations [used to derive ITRF] are affected by plate tectonic motion ... conversions between ITRF ...
Carlos N's user avatar
  • 4,474
2 votes

How to obtain Chebyshev coefficients directly from the JPL Horizon's interface?

You don't get those from HORIZONS. You download them from here. They are best accessed with the SPICE toolkit, or you can roll your own to extract the Чебышёв coefficients from the SPK files.
Mark Adler's user avatar
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2 votes
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How does one use SPICE to compute the Greenwich sidereal time as an angle?

First things first: If the planet of interest is the Earth, I strongly suggest you consider using the Standards of Fundamental Astronomy library rather than SPICE. That said, hour angle is a measure ...
David Hammen's user avatar
  • 74.9k
2 votes
Accepted

Does SPICE function gftfov account for occultations?

Does SPICE function gftfov account for occultations? Almost certainly not. The documentation does not indicate that gftfov does this. The documentation instead ...
David Hammen's user avatar
  • 74.9k
2 votes
Accepted

SPICE defining a topocentric frame on the Moon

I believe what you'll want to do is create an SPK kernel for the ephemeris of the point on the surface of the moon and then whatever ID you give that point should be the center of the topocentric ...
Alfonso Gonzalez's user avatar
2 votes
Accepted

What does w.r.t. mean? I've found it in the summary of jup365.bsp

"w.r.t." or just "wrt" is a common abbreviation for "with respect to" or "with regard to". It's not a special astronomy jargon term or anything.
Darth Pseudonym's user avatar
2 votes

Computing viewing geometry of Solar System targets from ground-based observatories using SPICE kernels

We need to use PINPOINT utility program (only x86 not ARM). It is available on the utilities NAIF page. naif.jpl.nasa.gov/naif/utilities.html With this software, you can create SPK and FK kernels, and ...
Juan Luis Rizos's user avatar
2 votes

TT-TDB with SPICE from ephemerides kernels as 'de440t.bsp'

The data to compute the TDT-TT value is stored in the leap seconds file. The latest version as of now is naif00012.tls. The description should help in that computation but I must admit never having ...
ChrisR's user avatar
  • 6,180
1 vote

TT-TDB with SPICE from ephemerides kernels as 'de440t.bsp'

I know that the TT-TDB difference can be obtained with the SPICELIB DELTET function: https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/spicelib/deltet.html But the goal would be to read it ...
pgonibe's user avatar
  • 21
1 vote

SPICE toolkit occultation finder doesn't work with spacecraft

As in your comments, plugging in: sma = 7480km, e = 0.09, i = 5.5 deg, RAAN = 0.2 deg, AOP = 5.95 deg, true anomaly = 6.26 (I used true anomaly because its close since e is small and I don't remember ...
Alfonso Gonzalez's user avatar
1 vote

Should coordinate transformations from J2000 to ITRF93 in quaternions be cyclic?

I am looking at the result and I'm not sure that it's reasonable since there are a lot of cyclic fluctuations in the quaternion values. 1689593 seconds is about 19.6 sidereal days. The graph shows 19 ...
David Hammen's user avatar
  • 74.9k
1 vote
Accepted

Was the famous SPICE package of programs, utilities and data kernels named after "Melange" found on the planet Arrakis?

According to this, SPICE stands for Spacecraft ephemeris Planet (plus moon, comet, asteroid) ephemerides Instruments (geometric information such as field-of-view, shape, orientation) C-matrix (...
Bob Werner's user avatar
  • 1,124
1 vote

How to retrieve MSL EDL trajectory using Javascript and webgeocalc API?

After dozens of test, I found the way. Payload to be sent over POST query: ...
jumpjack's user avatar
  • 3,033

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