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Questions tagged [jpl-horizons]

Questions relating to the JPL Horizons solar system data and ephemeris computation service

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32 votes
2 answers
5k views

Why does this plot show Starman's speed relative to the Sun fluctuating so often?

After the launch of Starman, during the inaugural flight of SpaceX's heavy lift vehicle, the Falcon Heavy, PearsonArtPhoto set up a website to track various stats about Starman and his Roadster. A ...
Edlothiad's user avatar
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18 votes
2 answers
2k views

How can I derive an mass/size estimate of an asteroid from JPL parameters?

I'm looking for a list of objects with a semi-major axis between 0.95 AU and 1.05 AU that are probably larger than 1 km in diameter. For this, the JPL Small-Body Database Search Engine seems to be ...
AlanSE's user avatar
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18 votes
2 answers
2k views

Is this what station keeping maneuvers look like, or just glitches in data? (SOHO via Horizons)

I've been enjoying the JPL Horizons web interface and after I discovered the incredibly extensive database associated with SOHO (Solar and Heliospheric Observatory, also see sohowww.nascom.nasa.gov) ...
uhoh's user avatar
  • 148k
15 votes
2 answers
1k views

Why is the sidereal period of the Earth 362.392667 days?

Using JPL's Horizons API I can look at the orbital elements for the EM Barycenter wrt the Solar System Barycenter at J2000. The output looks like this: Watch for the PR (Sidereal orbit period) ...
Daniel's user avatar
  • 293
15 votes
1 answer
3k views

Where to find the best values for standard gravitational parameters of solar system bodies?

Where can I find the best values to use for standard gravitational parameters of solar system bodies for numerical simulation experiments? Here are two sets I've put together. The first set is from ...
uhoh's user avatar
  • 148k
13 votes
1 answer
410 views

Different Earth-centered ICRF positions in GMAT and Skyfield/Spiceypy with DE421

I compared the Earth-centered positions from the Moon in the ICRF (i.e., in GCRF) using three different sources: SpiceyPy (https://pypi.org/project/spiceypy/) Skyfield (https://rhodesmill.org/...
Thibault's user avatar
  • 133
11 votes
3 answers
3k views

How to calculate the planets and moons beyond Newtons's gravitational force?

The question Calculating the planets and moons based on Newtons's gravitational force was pretty much answered with two items: Use a reasonable ODE solver; at least RK4 (the classic Runge-Kutta ...
uhoh's user avatar
  • 148k
11 votes
2 answers
620 views

Why do the LRO's orbital elements appear to constantly oscillate - except recently?

I plotted some of the orbital elements of the Lunar Reconnaissance Orbiter from JPL's Horizons database, and I see that there are constant oscillations. The period of the semi-major axis and ...
uhoh's user avatar
  • 148k
9 votes
3 answers
594 views

Are there any sources with high-confidence state vectors for GRAIL-A?

I have been experimenting with propagation of Moon-orbiting satellites. In particular, of GRAIL-A. In order to obtain state vectors to use as starting points for my propagation, and to compare the ...
Rafa's user avatar
  • 1,750
9 votes
3 answers
2k views

Getting state vectors from JPL Horizons ephemerides

I'm simulating the Sun-Earth-Moon system by numerical integration of equation of motion. I've confused a little bit in JPL Horizons ephemerides. Could anyone explain (if possible, on pictures), how ...
Tarlan Mammadzada's user avatar
8 votes
1 answer
734 views

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....
uhoh's user avatar
  • 148k
7 votes
2 answers
2k views

How do we track the exact location of the spacecraft which is millions or billions of miles away from us?

How do we track the exact location of the spacecraft which is millions or billions of miles away from us? What things do we study for tracking purpose? How exactly do we predict?
Pras4's user avatar
  • 335
7 votes
3 answers
4k views

Python API for JPL Horizons?

I found the python package HorizonJPL in the Python Package Index, but it looks like it's limited to activity in 2013. When I go to the linked documentation page https://docs.google.com/document/d/...
uhoh's user avatar
  • 148k
7 votes
1 answer
8k views

What is the difference between GCRS and J2000 frames?

What is the difference between GCRS and J2000 frames? Which is commonly used worldwide in satellite communications? I've read a statement here, that ...
Leeloo's user avatar
  • 733
7 votes
1 answer
639 views

Unravelling Cassini's "ball of yarn" orbit around Saturn, tabulation of propulsive maneuvers?

The cool GIF on the NASA JPL Cassini resources page All Orbits (2004-2017): The Ball of Yarn is quite beautiful to look at, but it also hints at some beautiful engineering and orbital mechanics as ...
uhoh's user avatar
  • 148k
6 votes
4 answers
918 views

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#/). ...
GuillaumeJ's user avatar
6 votes
0 answers
376 views

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 ...
uhoh's user avatar
  • 148k
5 votes
2 answers
1k views

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 $[-1,1]$...
Alexandru Lapusneanu's user avatar
5 votes
2 answers
699 views

Juno's original orbit around Jupiter - is this apsidal precession? If so, need expression

Below is a plot of Juno's originally planned orbit around Jupiter, extracted from JPL Horizons. It's shown in J2000 ecliptic coordinates, centered on the Jupiter barycenter. It turns out the orbit is ...
uhoh's user avatar
  • 148k
5 votes
2 answers
205 views

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, ...
Cornelis's user avatar
  • 7,535
5 votes
1 answer
485 views

Is Cassini's 183rd burn; some kind of engine record?

I've just read that when Cassini makes its first close pass of Saturn's F-ring on December 4, it will be the 183rd engine burn which sounds like a lot for orbital maneuvers using a spacecraft's main ...
uhoh's user avatar
  • 148k
5 votes
1 answer
446 views

Compatibility of osculating elements and cartesian vectors given by JPL Horizons?

I'm facing a problem I can't explain and I would like to know if someone has more information about it. I'm drawing a solar system and when I plot earth with the Horizon cartesian coordinates, it ...
DBCL's user avatar
  • 51
5 votes
0 answers
175 views

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 ...
Tony Macijauskas's user avatar
4 votes
2 answers
751 views

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, ...
Diego Suárez González's user avatar
4 votes
1 answer
310 views

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 ...
uhoh's user avatar
  • 148k
4 votes
1 answer
168 views

Does JPL's Horizons have better MU69 state vectors for the New Horizons flyby somewhere?

Today I downloaded the state vectors for New Horizons and MU69 Arrokoth and subtracted their positions. The two new get closer than about 596,000 kilometers. The New Horizons output header says: <...
uhoh's user avatar
  • 148k
4 votes
2 answers
188 views

How can I know if NASA Horizons output is measured, calculated, estimated or what-else?

This link allows downloading from NASA Horizons server data about the distance of a body (OSIRIS-REX spacecraft ) from the Sun (see link here): How can I know how the distance is obtained? Is it ...
jumpjack's user avatar
  • 3,043
4 votes
2 answers
249 views

How to calculate earth's precession using JPL Horizons System?

I'm new to JPL Horizons and understanding how to use the tool efficiently. I'm looking to extract earth's precession data and understand where we are in the current cycle. I understand we progress 1 ...
Alante Dancy's user avatar
4 votes
2 answers
136 views

How to show spacecraft position, heading etc relative to an asteroid

Given all the cool asteroid and comet missions out there (OSIRIS-REx, Hayabusa2, etc) I want to track the approach of the spacecraft to the asteroid. My favorite tool, JPL Horizons, can provide highly ...
nealmcb's user avatar
  • 761
4 votes
1 answer
302 views

What are the problems that need to be taken in consideration when trying to find planetary position by using jpl ephemerides?

I'm currently trying to determine the position of the sun and the moon from jpl ephemeris DE200 which is referred to the dynamical equator and equinox of 2000 and uses tdb time. I am using the j2000 ...
Alexandru Lapusneanu's user avatar
4 votes
2 answers
149 views

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 ...
uhoh's user avatar
  • 148k
4 votes
0 answers
78 views

What are exactly each of the coefficients in Modified Difference Arrays?

I am looking into the different types of SPK kernels. Type 1 are the so-called Modified Difference Arrays (MDA). The linked document mentions that its reference 163 contains a description of the ...
Rafa's user avatar
  • 1,750
4 votes
0 answers
64 views

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). ...
angst's user avatar
  • 143
4 votes
0 answers
702 views

Sources for SPICE Kernel (SPK) files for asteroids

Besides the official source for SPK files (ftp://ssd.jpl.nasa.gov/pub/eph ...) is there a place where people upload kernels for the smaller bodies in the solar system? I was looking for the Jupiter ...
Kaushik Ghose's user avatar
4 votes
0 answers
543 views

Ecliptic reference frame for satellite orbits in JPL Horizons

I'm trying to get orbital elements for natural satellites of all the plates with respect to their system's barycenters and I don't see how it is possible that using the ecliptic as a reference plane ...
Daniel's user avatar
  • 293
3 votes
2 answers
423 views

Calculating spacecraft thrust manoeuvres with JPL data

I've recently programmed an animated simulation of the main elements (core planets and Sun) of our solar system: by using the initial coordinates from the JPL (Jet Propulsion Laboratory - NASA) ...
Tarius's user avatar
  • 163
3 votes
1 answer
120 views

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 ...
angst's user avatar
  • 143
3 votes
1 answer
511 views

Discrepancy between HORIZONS and SPICE

I am trying to reproduce the output of the HORIZONS system using the SPICE toolkit from NASA, but I am not getting exactly the same results. I am using this script to compute the position and velocity ...
user avatar
3 votes
1 answer
297 views

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

I’ve been playing with the NAIF’s SPICE library for some time (CSPICE in particular). In order to obtain the state vector of an asteroid from its osculating elements, I’m calling the “conics_c” ...
Georgi Vidinski's user avatar
3 votes
1 answer
138 views

Why aren't there any trajectories for the Viking missions in JPL Horizons' database?

Horizons has calculated trajectories for deep space spacecraft, including six objects related to Apollo 8 through 12. See an (old) list in the currently unanswered question What was Chang'e-2'...
uhoh's user avatar
  • 148k
3 votes
1 answer
492 views

Why are JPL using this expression to emulate Schwarzschild orbits?

From the documentation ”Formulation for Observed and Computed Values of Deep Space Network Data Types for Navigation ” expression 4-61 on page 4-42 it can be seen that JPL uses the following ...
Agerhell's user avatar
  • 231
3 votes
1 answer
565 views

JPL Horizons original reference orbit data for Juno - how to retrieve now that it's been updated?

Because of the slow helium valve responses, Juno was not instructed to execute the large delta-v maneuver to drop from the ~53 day orbit to the ~14 day orbit originally scheduled for 2016-Oct-19. I'd ...
uhoh's user avatar
  • 148k
3 votes
2 answers
181 views

Generating JPL HORIZONS parameters for use with JPL HORIZONS itself

I want to be able to calculate RA/Dec for a given body with JPL HORIZONS, using a heliocentric specification of the orbital elements for a small solar system body (say, Apophis), but instead of using ...
juandesant's user avatar
3 votes
1 answer
394 views

What was Chang'e-2's 3D orbit in space? (since it's not in Horizons)

edit: A simple web search in Chinese may turn up something, but I don't know anyone personally who is both both fluent and interested in space exploration. This is a pretty cool orbit - there must be ...
uhoh's user avatar
  • 148k
3 votes
1 answer
282 views

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

I used SPICE's pxform at an interval of epochs to determine the transformation from J2000 (inertial) to ITRF93 (Earth body-fixed) frame. Then, I converted these rotation matrices to quaternions with ...
Shen's user avatar
  • 63
3 votes
1 answer
297 views

Determining the spacecraft position vector with respect to ICRF frame for Venus flyby

For an interplanetary mission design to Saturn, I have considered doing multiple gravity assists starting with Venus. I am using the JPL Horizons ephemeris and ESA Lambert Solver. I have the velocity ...
Suraj's user avatar
  • 147
3 votes
1 answer
695 views

How exactly to use astroquery.jplhorizons to get the state vectors of Mercury and the Parker Solar Probe?

In the question Is the Parker Solar Probe's semimajor axis being so close to that of Mercury's just coincidence? Does it help somehow? I used a Python script to plot the heliocentric orbit of the ...
uhoh's user avatar
  • 148k
2 votes
2 answers
233 views

Why hasn't DSCOVR's trajectory determination been updated in JPL's Horizons after 2015-Aug-4?

I tried to download orbital positions for the DSCOVR spacecraft in its Lissajous orbit around Sun-Earth L1 from JPL's Horizons web page but I was surprised to see the following! No ephemeris for ...
uhoh's user avatar
  • 148k
2 votes
2 answers
445 views

What does "coord@10" mean exactly as a target for JPL's Horizons? How to access it?

According to this answer, using "coord@10" as a target code for JPL's Horizons represents the motion of a hypothetical location on the Sun's surface; presumably as a way to represent the rotation of ...
uhoh's user avatar
  • 148k
2 votes
2 answers
942 views

Is it posible to convert JPL Horizons Vectors to ECEF?

I'm needing to accurately find the sun and moon position in ECEF and I'm wanting to make use of JPL's Horisons VECTORS to do this. What data should I export from the web interface and how should I ...
complistic's user avatar