Questions tagged [orbital-elements]

Orbital elements are a set of parameters that uniquely identify a specific orbit.

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34
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3answers
48k views

How to programmatically calculate orbital elements using position/velocity vectors?

I would like to build some orbital mechanical software from scratch. I feel that this would be a great way to learn the steps required to calculate different Kepler orbital elements of an object, plot ...
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What is the accuracy / uncertainty of Two Line Elements (TLEs)?

I use TLE sets supplied on this website to find the future position of satellites (well usually just the ISS) using the SGP4 propagation method implemented in C++. My question is: What is the ...
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Nuances of the terms (mean / osculating / Keplerian / orbital) elements

I've been assuming that osculating, Keplerian, and orbital elements are all synonyms, with mean orbital elements just being these averaged over some time. However occasional comments make me suspect ...
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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) ...
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Converting Orbital Elements to Cartesian State Vectors

Updated 2016-12-12 I'm writing an orbital mechanics program in Unity. I convert an orbiting object's position and velocity into orbital elements, then converting the orbital elements back into ...
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4answers
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How to obtain UTC of the epoch time in a satellite TLE (two line element)?

I want to convert the epoch time of a TLE to UTC. At this moment I am less interested in explanations and history - I just want to know quantitatively, with certainty, how to convert. I'm confused ...
13
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2answers
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Can the Right Ascension and Argument of Perigee of a spacecraft's orbit keep varying by themselves with time?

I came across the orbital data for a low Earth orbit spacecraft and one thing which I am not able to understand is why does its Right Ascension of ascending node and Argument of Perigee keep changing ...
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Lowest possible lunar orbit and has any spacecraft achieved it?

Because the Moon has no atmosphere a spacecraft can theoretically cruise at a very low orbit. What is the lowest possible lunar orbit and which spacecraft achieved it? Was it the Lunar Module of ...
11
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1answer
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How to get semi-major axis from TLE?

This should be fairly straightforward, but, how do I get the semi-major axis (a) from at TLE. For example if I have the TLE: ...
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How (the heck) are military satellites with (apparently) classified TLEs still showing up on sat map websites?

As I first noted in this comment I couldn't get TLEs for the recently launched OFEQ-11 spy satellites from space-track.com. When I looked at Search Resuls: OFEQ 11 Satellite details 2016-056A NORAD ...
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1answer
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At which point would two GSO/GEO satellites with similar orbital elements be closest to each other?

While I was answering another question on How closely spaced are satellites at GEO I came to realize I can't really word it with much conviction how two close proximity satellites in GEO/GSO orbits ...
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Where to look for historical or reconstructed orbit data for early NASA missions - Mercury-Atlas 6 for example

After reading this answer to How many earth stations had astronauts on-site during John Glenn's orbit in Friendship-7? I decided that for my own use I'd like to plot the orbit of Mercury-Atlas 6, the ...
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1answer
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How to calculate the time to apoapsis & periapsis, given the orbital elements?

I have the 6 orbital elements (excluding Time of Periapsis Passage, obviously), 2 state vectors, and a lot of other parameters like orbital period. I am looking to use them to calculate the time to ...
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How much delta-v does it take to go from one arbitrary orbit to another?

This is, in theory, very basic rocket science. I can't seem to find a solution on here though, so I'm asking in the hopes you'll enlighten me and my amateurish ways. I've got a set of Keplerian ...
8
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1answer
300 views

Deviation of semi-major axis

If I calculate the semi-major axis of Molniya-1T with $a = \sqrt[3]{\dfrac{GM}{n^2}}$ with $n=3.18683728\text{ }d^{-1}$, I get another apoapsis ($a=19505.7$ km) as noted at Heavens Above: apogee ...
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2answers
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What is hyperbolic eccentric anomaly F?

I have no idea what this is and have been searching on the net but all I get is eccentric anomaly. The equation that relates hyperbolic eccentric anomaly F to its true anomaly $\theta$ is exactly the ...
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2answers
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Is an orbital epoch merely a timestamp?

Just what the title states please. This site writes to say Orbit epoch is the time at which the established orbital elements are true The site goes on to mention sub-elements - Start Day The ...
8
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Are 3 points on an orbit enough to determine the shape of it in practice?

In a question about determining orbital elements from two points on an orbit, some discussion arouse regarding how many points are actually necessary, since two is not sufficient. Determining a conic ...
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1answer
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How Local time of a sun synchronous orbit is related to Right ascension of ascending node?

My question may sound naive and hence would like to apologise if this question is already answered in same or other form in this forum. How does ...
7
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3answers
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Differences between numerical propagators

I am a trainee who is working on a numeric orbital propagator developed in the company. I can't show you the code but I can tell you that the propagator was developed to work in Simulink. My job was ...
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3answers
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Is it possible to achieve a perfectly circular orbit?

Is it possible for a spacecraft to achieve an orbit around a celestial body that has no orbital eccentricity at all? The smallest orbital eccentricity of a natural satellite is that of Triton's orbit ...
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1answer
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Is there a low Earth orbit with a 24-hour day night cycle?

Are there any possible low-Earth orbits that use precession to match Earth's day/night cycle? So like SSO, but specifically aimed to achieve a 24hr day/night in LEO. If so, what would its parameters ...
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1answer
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Calculate True Anomaly at future point in time with hyperbolic orbits

Given: Semi Major Axis (negative) Eccentricity (>1) Argument of Periapsis Inclination Longitude of Ascending Node Current True Anomaly Mass of Central Body How can one calculate the true anomaly at ...
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Tracking of Mir space station backwards in time?

Is there a site with the tracking information for the old space station Mir? Or some place with the data location tracking information still available? Maybe even a site with orbital mechanics ...
7
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1answer
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LEO metric to determine the ground track of a satellite

I'm trying to correlate a behavior on LEO satellites with the position it is over the Earth. The behavior takes place over a period of time. I'm trying to come up with a metric that will identify ...
7
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1answer
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How to calculate the complete true anomaly motion in an elliptical orbit?

The true anomaly motion as I understand, is not constant in an elliptical orbit. The rate of change of true anomaly is not constant as in the case of circular orbits, in which case the true anomaly is ...
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Will crewed vehicles ever follow multi-flyby trajectories?

A while ago, I asked a similar question here, but I think it was confusing, so nobody answered. Two questions: This one is a bit subjective: Do you think that lengthy (+5y) multi-flyby trajectories ...
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How to get true anomaly from time?

An exercise that was left unsolved from last year's class gives me this equation : $$ t-t_{p} = \sqrt{\frac{a^3}{\mu}}*(\arcsin(X) - e*X) $$ where : $$ X = \frac{\sqrt{1-e^2}*\sin(v)}{1+e*\cos(v)}. $$...
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What is the highest inclination orbit ever attained from a Cape Canaveral launch?

The launch facilities at Cape Canaveral, FL are located at a latitude of about 28.5° N, so that puts a hard lower bound on inclinations from that site. I assume there are well-defined azimuth limits ...
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3answers
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Determine orbit type from TLE

I was wondering if, and how, one can tell from the values in a TLE whether an orbit is LEO, MEO, HEO, or GEO. I'd like to do this in code eventually, so any formulas or threshold values would be much ...
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2answers
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What's a Brouwer-Lyddane mean semi major axis, or any other, for an orbit in a lumpy gravity field?

The really nicely written question Brouwer-Lyddane mean semi major axis bias describes the use of the software GMAT (General Mission Analysis Tool) (website, YouTube, giant PDF for TESS) for ...
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Obtaining orbital state vectors given two position vectors and an eccentricity

I was looking into the dynamics of basic 2-system orbits, and I came across a PDF (attached below) showing how to calculate orbital elements given a position and velocity vector. This led me to the ...
6
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Is it possible to plot the ground track of a satellite with just azimuth & elevation angles without range?

I came across this question on StackOverflow about Satellite Trajectory plot. In the code mentioned in the question, the user takes only the Azimuth & Elevation angles (radians) & converts ...
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1answer
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Brouwer-Lyddane mean semi major axis bias

I'm using the software GMAT (General Mission Analysis Tool) (website, YouTube) for propagating spacecraft and calculating their Brouwer-Lyddane (BL) mean semi-major axis (SMA). I found out something ...
6
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1answer
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What is this algorithm to calculate orbital state vectors?

I came across the following algorithm to calculate the cartezian vectors from the orbital elements: First calculate some coefficients that will be used in determining the position: $$ r_x' = a (\cos ...
6
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1answer
678 views

Ascending node with zero inclination

Long time ago, I was wondering which orbital element should I use to differentiate between the blue and red orientation of an otherwise same elliptical orbit on this image (all the three orbits are in ...
6
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1answer
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J2 long-period perturbations in the inclination

As a continuation of my previous post regarding the use of the software GMAT (General Mission Analysis Tool) (website, YouTube) for propagating spacecraft, I have an additional question. This time I ...
6
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1answer
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Can I move the ISS for free?

Say I want to change the inclination of the ISS by one degree. The ISS orbits at 7660m/s so the manoeuvre will cost me 133.7m/s of $\Delta v$: From time to time, the station must be reboosted because ...
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0answers
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Locally optimal control for low thrust transfers with J2 and other Earth perturbations

Background As detailed in this answer low thrust optimization is subject of ongoing research. There are a few closed-loop control laws which allow to achieve a locally optimal (but close to globally ...
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2answers
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Required Orbital Components to Fully Define Orbit

As a follow-up to this question. I have this JSON coming back from the ESA's DISCOSweb API: ...
5
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2answers
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Why does NASA Horizons say that Earth inclination is not 0 at J2000 epoch?

I'm using NASA Horizons system to get Earth orbital elements with following settings: ...
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2answers
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Do I have enough info to find the true anomaly of an orbit?

For a personal coding project, I'm trying to model orbits of satellites around the Earth. I take in some values from a user and use them to determine the shape of the orbit. I want to model the ...
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2answers
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Perifocal coordinates and the orbit equation

Given the position $(p,q)$ and velocity $(v_p,v_q)$ of a satellite in perifocal coordinates $(\hat{p},\hat{q})$ where $\hat{p}$ is pointing toward periapsis, I can easily calculate the specific ...
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2answers
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How significant is orbit propagator choice/error when considering a year-long satellite coverage simulation, and which is the most appropriate?

I'm currently considering a project to simulate the (Earth-seeing) coverage of 1 or more satellites over the course of a year. The point would be to compare how different orbits result in different ...
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1answer
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TLE SGP4 Coordinate Transformations

I am working on developing a user friendly SGP4 orbit propagator in C on a PIC24. I have extensively read Revisiting Spacetrack Report #3 and celestrak - there are a few outstanding questions I have....
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3answers
980 views

Keplerian approximations for moons as well as planets

I'm writing code to simulate planetary and lunar orbits in a heliocentric reference plane. I'm using E.M. Standish's Keplerian Elements for Approximate Positions of the Major Planets as my reference ...
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1answer
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Why is argument of periapsis defined in terms of longitude of ascending node?

According to the Keplerian system of orbital elements, a reference direction is given; the longitude of the ascending node is an angle with respect to that direction, and the argument of periapsis, ...
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1answer
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How are Two Line Elements (TLEs) obtained?

This question is a follow up of another question I have asked recently. For the sake of experiment I propagated the ISS's position (using SGP4) from epoch of first TLE to the epoch of next released ...
5
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1answer
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Why does the eccentricity vector always point towards the periapsis of an orbit?

I hope you know that eccentricity can be derived from the position and velocity vectors of a spacecraft (only applies to a two body problem) through this formula : $$\textbf{e} = \frac{\dot{\textbf{r}}...
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How can I calculate the future position of a satellite orbiting a central body as a function of time using known orbital elements?

Given the position and velocity vectors at one point in an orbit, one can calculate the keplerian elements and thus graph the subsequent orbital path as a circle/ellipse/parabola/hyperbola depending ...