Questions tagged [ephemeris]

An ephemeris provides a means for quickly estimating the positions, and sometimes orientations, of solar system bodies as a function of time.

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Meeus on the Positions of the Satellites of Jupiter

Ex. 44.a of Meeus Astronomical Algorithm, Second Edition, provide the position of the Galileans on December 16 1992 at 0h UT (p.311/488). Procedure 1: For Io, in terms of the Jupiter's equatorial ...
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Calculating the elevation and azimuth angles of satellites with location information obtained from sp3 ephemeris files

I'm trying to calculate elevation and azimuth angles of a satellite for a ground GPS receiver. I downloaded the SP3 file for the day '12-01-2015'. The ephemeris files are in the link below. https://...
-1 votes
1 answer
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Retrieving TLE file when offline

How does one retrieve the TLE file without any internet access? For instance, I am out in the open sea without an internet connection for a few days. Can I still get the latest TLE file by some other ...
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Distance between Sun and Earth using JPL horizons

Using the JPL Horizons app at https://ssd.jpl.nasa.gov/horizons/app.html#/ would someone help to calculate the distance between the Sun and the Earth say 1 May 2023 00:00 UT? I used the following for ...
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Using NASA Horizons with Celestrak Socrates's TLE CDMs?

Has anyone succeeded with getting a list of Collision Data Messages (CDMs) from nice sites like Celestrak in order to feed them into NASA Horizon's ephemeris computation service. These would include ...
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Positions of asteroids in heliocentric ecliptic (x,y,z) coordinates

I would like to make positions of asteroids in heliocentric ecliptic (x,y,z) coordinates plot for a given date, like in the image below (Matsuoka N. Ryo (CC-BY 4.0)). For that I need so-called state ...
6 votes
2 answers
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Is it possible to create an analytical ephemeris from raw position and velocity of a Body?

I would like to have an analytical ephemeris for various bodies of the solar system (planets, natural satellites and asteroid). I have at my disposition spice kernels from which i can extract position ...
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Why does Earth's North Pole RA flip by ~180 deg around AD2000 relative to SSB? (JPL Horizons data)

Using JPL's Horizons API I see that the Earth's North Pole RA flipped by ~180 degrees quite suddenly around AD 2000. It was pretty stable around 180deg for at least 1000 years prior, and then remains ...
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Where to get data for axis of rotation of solar system bodies?

Where can I get data for the axis of rotation of the (major) bodies of the solar system? For each solar system body, I want to get a unit vector of its axis of rotation (at a specified point in time). ...
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Why is there a 38.6 km Earth-Moon distance difference between Ephemeris types "Observer table" and "Vector table" on Horizons Web Application?

The image above is a screenshot from Horizons Web Application with the Ephemeris type: Observer Table. It shows the distance (delta) from the geocentric observer location to target Moon on April 15, ...
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Calculating positions of Moon's ascending and descending nodes from ephemeris files

I am trying to find the position of planets and moon at any specific date which I was able to find using the JPL ephemeris ASCII files. I am however stuck now at finding the positions of the moon's ...
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How to add an asteroid into GMAT (General Mission Analysis Tool). How to generate a reliable SPK file

I'm currently trying to use GMAT to represent a mission centered around the asteroid 523632 2009UX17. To represent the asteroid's orbit I've used the Horizons Online Ephemeris System: https://ssd.jpl....
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New to GMAT. Where do I start to build an orrery?

The goal would be an animated, variable-speed, 2-D view from celestial north of the Sun and planets. A stretch goal would be showing photorealistic rotations of CelestialBodys as a function of time. I ...
6 votes
4 answers
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Access to Chebyshev coefficients from JPL ephemerides

I want to generate an ephemeris file containing the Chebyshev coefficients, similar to how we can generate ephemeris file of positions with Horizon tool (https://ssd.jpl.nasa.gov/horizons/app.html#/). ...
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How to calculate Local Time of Ascending Node (LTAN)

I have a time series of satellite position, $\mathbf{r}(t_i) = (r_i,\theta_i,\phi_i)$ representing geocentric radius, colatitude and longtiude at universal times $t_i$. I want to compute the Local ...
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Do the proper ephemerides yet exist to calculate trajectories to Sedna?

While going through links mentioned in What software can be used to determine deep-space trajectories? and What are the choices today for orbital mechanics simulation software?, I find that a great ...
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Change frame center definition of Chebyshev coefficients

I am using SPICE to read and store Chebyshev coefficients to then compute position of Solar System bodies in my navigation software (see this post). The coefficients are defined with respect to the ...
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3 answers
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State vector conversion when changing central body

I have the following state vector of a spacecraft : [X, Y, Z, VX, VY, VZ]. The state vector is expressed in the inertial frame of the central body. I would like to convert this state vector when ...
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1 answer
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GMAT Sun Ephemeris Output

I need the sun's position vector for an analysis, conducted in Matlab. Thus, I let output the ephemeris files for the spacecrafts and additionally I would like to do the same with the sun. A Report ...
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How does JPL define the exact position of Lagrange points in the real solar system where (I thought that) they can't be defined?

My answer to Does the distance to L2 vary? is The correct answer is "No, they are only mathematically defined when the orbit is circular". but @DavidHammen's answer explains that they can ...
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How do you compute horizontal coordinates of a GPS satellite from its broadcast ephemeris?

I'm not an astronomer by any means, and am trying to extract the horizontal coordinates, azimuth and altitude, of a GPS satellite given its most recent broadcast ephemeris. Here is some example ...
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What is the inertial heliocentric reference system used by NASA JPL to calculate the ephemerides of Near Earth Objects?

I'm using the website of NASA JPL Horizon system at this link Small-Body Database Query to download a database of orbital elements for NEOs (asteroids and comets). Although I checked the Horizons ...
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Why do we use Chebyshev polynomials to predict positions of solar system bodies?

I've seen information for how to use the Chebyshev coefficients that JPL publishes, but nothing that explains why. Why isn't a simpler mathematical model used? I'm also surprised that JPL uses a ...
3 votes
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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 "...
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How does Curiosity know how to point and move it's high gain antenna in real time?

The Curiosity rover has a compact X-band high-gain antenna (HGA) that allows for low data rate communication directly with Earth, but is used though for higher data rates it usually uses UHF to ...
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Source of Satellite and Debris Ephemerides for Analysis

I'm working on some code that will fuse ephemeris data, the raw telescope and radar data used for locating and tracking active satellites and space debris. Most of this data is owned by the Air Force ...
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Setting up orbit propagation in Orekit

Please forgive my ignorance, I'm new to orbital dynamics. I am using Orekit [https://www.orekit.org/] for orbital propagation in order to determine rise and set times for a MEO satellite, and am ...
6 votes
2 answers
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How to convert a SPICE SPK kernel into human-readable data using SPICE toolkit and utilities

SPK2OEM is one of many of SPICE tools available here: https://naif.jpl.nasa.gov/naif/utilities_PC_Windows_32bit.html I am trying to extract ephemeris from one of the SPK files listed here: https://...
3 votes
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Looking for help in drawing diagrams to explain graphically NASA Horizons output

I searched a lot for a javascript library or a REST API to access full functionalities of powerful NASA Horizons tool, but with no luck, so I am trying to write my own interface, to replace the very ...
4 votes
2 answers
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How to calculate position of GPS Satellite with transmitted ephemeris data?

How can I calculate the position of a satellite using the ephemeris data transmitted by each satellite? I will then use positions generated from each GPS satellite's self-reported ephemeris to ...
12 votes
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What is the exact format of the JPL ephemeris files?

I'm attempting to do some basic planet position calculations using the JPL ephemeris data. The first step is to properly parse the files. Here's my understanding so far: The header file gives a ...
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How is the Chebyshev method used by JPL?

In the DE packages, NASA gives us a series of coefficients for the Chebyshev approximation. As I understand it, those approximations are given by a series of polynomials $T_n$ for the interval $[-1,1]$...
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Calculate Date of Spring Equinox, possibly using JPL's Horizons website?

I'm familiar with orbit ephemerides and the ways to use those to plot orbits and positions. However, in all the charts I find, I can't seem to find a way to determine when an equinox on another planet ...
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Interpolating precise ephemerides of GPS satellites

My objective is to obtain at least a sub-meter position accuracy by interpolation of the GPS ephemerides. There is conflicting research outside, where some authors state that a simple Lagrange or ...
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JPL ephemerides: effect of Saturn, Uranus and Neptune

According to the Folkner ( Folkner et al, 2014, The Planetary and Lunar Ephemerides DE430 and DE431, IPN Progress Report 42-196 • February 15, 2014), JPL ephemerides consider the following effects: ...
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The Moon's shadow could not possibly look like this — could it?

The NASA Goddard video Tracing the 2017 Solar Eclipse is a visualization of the calculated shape of the umbra during the upcoming August 2017 total solar eclipse, as it moves across North America. ...
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How to choose between Hermite and Chebyshev interpolation for spacecraft trajectory?

There's a related question, but it doesn't seem to apply to spacecraft trajectories. Suppose you want to send a non-thrusting spacecraft far from earth, and you have ground tracking of the spacecraft,...
4 votes
1 answer
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What format is a "TSA Ephemeris?"

I am working on software that needs to parse an ephemeris file for the ISS. However, I cannot find any documentation for the particular format I have. The only mention I found is in this ...
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How can I find orbital parameters for a sun-synchronous orbit?

I would like to compute ephemerides for a satellite on a sun-synchronous orbit, starting with only the following parameters1: altitude or inclination; local time of the ascending or descending node; ...
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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 ...
4 votes
2 answers
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How to obtain Chebyshev coefficients directly from the JPL Horizon's interface?

I'm from Spain and I'm currently finishing my degree in Aerospace Engineering. I am starting with all of this. My objective is to obtain the Chebyshev coefficients for the major planets position, ...
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JPL ephermeris table

For an interplanetary mission design problem, I am using the JPL Horizons Ephermeris to obtain the state vectors of Venus and Earth. I have selected the Coordinate origin as the body centre of the Sun....
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SPICE GFPOSC is returning incorrect sunrise (and sunset) times for topocentric frames

I cannot get SPICE to produce accurate sunrise times for topocentric frames I specify. I'm using spiceypy to interface with SPICE. As a first test, I set up topo coordinates for the MARE landing site,...
4 votes
1 answer
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What happened to time in 1962? (JPL Horizons changes displayed time from UT1 to UTC for dates starting in 1962)

I was viewing some observer output from JPL's Horizons while writing this answer and I saw this annotation. "Prior to 1962, times are UT1. Dates thereafter are UTC". Presumably users of JPL's ...
3 votes
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Orbit ephemeris or visualization for the BepiColombo mission?

Where is it possible to see the progress of the BepiColombo mission in terms of ephemeris and or graphical visualisation? I should add, I've checked JPL Horizons, though its not clear how to specify ...
8 votes
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I've almost learned to spell Chebyshev, why has JPL switched to Hermite interpolation for DE438?

According to @ChrisR's thorough answer One caveat however is that the interpolation in DE438 is a Hermite interpolation, and no longer a Chebychev interpolation, so you may need to update your code....
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Calculation of Sun-Satellite and Moon-Satellite distance

I have the coordinates of a satellite in the Earth Centered Inertial frame. I have calculated the Sun-Earth and Moon-Earth vectors using the JPLEphemeris package. Now I have to calculate the Sun-...
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1 answer
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Difficulty trying to use the SPK file ast343de430.bsp

I'm looking for a NAIF SPK file (these typically end in .bsp) for a bunch of asteroids in the J2000 reference frame. I found ...
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How does JPL calculate Epochs for generating ephemerides?

How exactly do epochs fit into the computational propogation of data of NASA's Jet Propulsion Laboratory and what methods do they use to calculate the properties of those epochs in the first place? ...
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How to get the coordinates from NASA JPL Ephemerides DE430 ( ECRS) to ECI?

I'm trying to make a software that determines the orbit of a satellite which is affected by the Sun and Moon. The coordinates [x y z] that I have for the satellite are in Eci. For the position of the ...