Questions tagged [orbital-mechanics]

Orbital mechanics (also called astrodynamics) is the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft on an orbital or escape trajectory. For the movements of celestial bodies, use [celestial-mechanics], not this.

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Dimorphos natural orbit variability vs DART impact

As we know, DART spacecraft have impacted Dimorphos, a satellite of Didymos. The impact will change the orbital period. Depending on the properties of Dimorphos (mass, porosity, cohesion), the period ...
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Roughly, how much of our Moon's apparent libration amplitude seen from the Geocenter is due to different effects?

My understanding is that when tidal locking of a body first happens it transitions from a state where the average rotation period is faster than the orbital period to a state where they are the same ...
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For the mathematical relationship between J2 (km^5/s^2) and dimensionless J2 - which one is derived from the other?

The term $J_2$ seen in discussions of nodal precession of orbits (e.g. sun-synchronous) appears to come in two flavors. For example, in the Wikipedia article Geopotential model it has a value of $1....
uhoh's user avatar
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What is the rationale behind NORAD's use of TEME?

The most popular catalog of Earth-orbiting objects is NORAD’s. The catalog provides the so-called « two-line elements » (TLE) which essentially are computed orbital parameters of a catalogued object, ...
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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 ...
Samuel Low's user avatar
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How long does the SYLDA fairing stay in orbit after deploying?

For dual-manifest missions, Ariane 5 often uses the Système de Lancement Double or SYLDA system to encapsulate the lower of two stacked satellites. It can be seen in the following image encapsulating ...
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Is there a general relativistic relativistic rocket equation?

I am not to familiar with rocket equations but I know that if you combine special relativity with classical mechanics you get "c" as a speed limit. Basically the closer you get to "c" the more you ...
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Understanding formula for geocentric position of Moon

I am trying to understand a basic formula in a Celestial Mechanics reference. The formula is for the position of the Moon in a geocentric frame. The reference claims in line (981) that this should be ...
viktor79's user avatar
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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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Were the Apollo lunar ALSEP transmitter signals ever analyzed or used after the experiments were shut down?

This answer to the question Why were the “perfectly functioning” seismometers placed by Apollo 12, 14, 15 and 16 astronauts all shut off in 1977? links to a NASA News Release No: 77-47 dated September ...
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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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Did Rosetta improve on models of non-gravitational effects on comet 67P's orbit?

Question: Since the presence of the Rosetta spacecraft near comet 67P allowed for a detailed mass measurement, extremely precise position and velocity determinations, and physcal measurement and ...
uhoh's user avatar
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Could a “solar gravitational synchrotron ” use solar thermal rockets to "powerslide" spacecraft out of the solar system?

Could a “solar gravitational synchrotron ” use solar thermal steam rockets to launch spacecraft out of the solar system? Solar thermal steam rockets https://en.wikipedia.org/wiki/Steam_rocket have ...
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Are L1 and L2 orbital periods always half the orbital period of the massive bodies?

Are L1 and L2 libration point orbital periods always half the orbital period of the massive bodies? The halo orbital period of JWST is a half a year. https://webb.nasa.gov/content/about/orbit.html The ...
Woody's user avatar
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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 ...
Tony Macijauskas's user avatar
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Is JWST actually in a Lissajous orbit? What will it look like? Implications for station-keeping?

Note: for lots of great background related to this question, see lagrangian points - The design of the halo orbit of the James Webb Space Telescope - Space Exploration Stack Exchange There are ...
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What is the benefit of an inverted rocket stage?

For example the Chinese rocket Jielong 1 has an inverted 4th (final) stage. So the payload sits between 3rd and 4th stage. When 3rd stage separates it has to do a 180 degree turn before igniting the ...
user16734390's user avatar
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How to perform a Hohmann-like transfer to mercury on GMAT

I am trying to simulate a Hohmann-like transfer from Earth to Mercury and establish an orbit there on GMAT. I have the following values already: launch velocity (22.25 km/s) Launch burn (-7.53 km/s) ...
Andrew Blair's user avatar
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When was Lucy's mission first scripted in Excel and why is that what Lockheed Martin chose to do it with?

CNBC's NASA spacecraft launches toward Jupiter asteroids on an intricate path charted by Excel Years before Lucy took off, Lockheed Martin mission architect Brian Sutter used Excel to chart the ...
uhoh's user avatar
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Who invented the sun-synchronous orbit?

I was explaining sun-synchronous orbits to a co-worker and he asked me who invented it and when. I could not find an answer on wikipedia or a quick google search, so I thought about asking here.
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What is the sign of Earth's J₂?

From Wikipedia's Geopotential model; The deviations of Earth's gravitational field from that of a homogeneous sphere and the question For the mathematical relationship between J2 (km^5/s^2) and ...
uhoh's user avatar
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Where can I find data on satellite orbits?

I'm an enthusiast who'd like access to satellite orbital data to simulate / plot trajectories of manmade satellites (of any kind) on my home computer. Where's the best place for me to find this kind ...
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Solar system galactic velocity vector relative to ecliptic plane

The Solar system moves through the Milky Way galaxy with velocity of 230 km/s. The ecliptic plane is located ~60 degrees with relation to the galaxy plane, according to this source. The page also ...
Sergiy Lenzion's user avatar
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Outlier detection algorithm for orbit determination, how do different ones compare?

I have been reading about outlier detection algorithm for improving determinations based on realistic data. Outlier exclusion is an important tool in any analysis of realistic noisy data. There are ...
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Small-bodies landing strategies

Looking at past landing missions on small bodies such as Eros, Itokawa and 67P I found different landing strategies Eros: NEAR Shoemaker probe performed 4 impulsive pre-planned open-loop maneuvers to ...
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Solutions to a "Lambert's problem in velocity"

Lambert's problem (also here and here): $$\mathbf{r_1}, \mathbf{r_2}, t \rightarrow \mathbf{v_1}, \mathbf{v_2}$$ was solved by Johann Heinrich Lambert via Lambert's Theorem (see references below). ...
Benoit Lebeaupin's user avatar
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How to calculate if a co-location intercept is possible in a ballistic counter-battery scenario

Let us presume that we have a scenario with ballistic objects. As an example, one object $m_1$ is launched at time $t_0$ from Earth Location $a$ towards Earth Location $b$, both of which are in the ...
Monty Wild's user avatar
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Would the Earth still precess if it were an ideal sphere?

I am trying (unsuccessfully) to acquire an intuitive understanding of planetary precession. Is Earth’s precession Torque-free Precession due to its asymmetry as per https://en.wikipedia.org/wiki/...
Woody's user avatar
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Can Tisserand's parameter be modified to correct for perturbing eccentricity?

Tisserand's parameter is an "almost" conserved quantity in the CR3BP, even after flybys (useful for identifying asteroids). $$T_P = \dfrac{a_p}{a}+2\sqrt{\dfrac{a}{a_p}(1-e^2)}\cos(i)$$ It ...
SE - stop firing the good guys's user avatar
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How would I or who/what could help me find the trajectory of an "Extended Grand Tour" spacecraft, without having to take a long course on the subject?

(As forewarning, the most integral details of this question are bolded.) For context, I have been writing an alternate history involving the accelerated development of spaceflight technology for over ...
Grant Hartlage's user avatar
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What are the specifications for electrical connectors that can be used for repeated mating in space?

We’re working on an interface between satellites that when docked has to transmit power and data. The interface needs to have a port for transmitting power and data. Majority of the connectors ...
Asher's user avatar
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Is there a known solution for optimal impulsive transfer between two arbitrary elliptical orbits?

If not, what optimization methods or tools do people use? (Code libraries?)
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How to find a vector's elevation angle with respect to a point on Earth?

tl;dr: Spacecraft's antenna should point to a ground station but there is a pointing error. I want to express the error as a vector rather than a simple angle that a dot product provides, so that I ...
Ceren's user avatar
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Just how much "dumb luck" was reaching the space age during the "Grand Tour" opportunity? Would we have been SOL 1050 or 2100 years before/after?

@OscarLanzi's answer to Why is the gas giant grand tour interval 175 years when the synodic period of Uranus and Neptune is 171 years? is an excellent answer describing a subtle situation; each pair ...
uhoh's user avatar
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How many burns does it take to reboost the ISS?

When the International Space Station is given a reboost, how many burns are performed? Is it a Hohmann transfer orbit, with one perigee burn and one apogee burn? Or is it one burn at apogee just to ...
DrSheldon's user avatar
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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 ...
Brian V's user avatar
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How are B-Plane parameters actually determined for a planetary flyby?

Reading from this document, I am trying to simulate the New Horizons probe trajectory in GMAT and I am puzzled with how the authors of the original paper (by legendary mission designer Robert W. ...
the_parzival's user avatar
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81 views

What is the closest polar lunar orbit that can be sustained? What are the limiting factors on closest approach?

I'm wondering how close a lunar orbit can get at periapsis to the south pole. I want an orbit that is sustainable for at least ~20 orbits. I'm working on a small sat concept for studying the lunar ...
sgp45's user avatar
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How to get lunar L, B, C parameters from the Moon's 3x3 rotation matrix from the Python package Skyfield?

Answers to What are the “Moon L, B, C” angles shown in this solar eclipse simulation? explain that L and B (or "l" and "b") are the "selenographic coordinates of the Moon's apparent center" (latitude ...
uhoh's user avatar
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Good example of early and simple orbital mechanics?

I am doing a talk on Katherine Johnson at my school extremely soon and I was wondering if you could give a relatively quick example of a simplified calculation in any kind of orbital mechanics ...
Isky Mathews's user avatar
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Interplanetary Taxi Orbit

I would like to know the feasibility of an interplanetary "bus" or "taxi" which moves between, say, Earth-Mars or Earth-Venus without entering the orbit of either. The idea is that the taxi is large--...
Lawnmower Man's user avatar
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248 views

How do I calculate the change in the argument of periapsis after a plane change maneuver?

Let's say I have a spacecraft in an initial geocentric orbit with the following parameters: a = 7,960,000 m, e = 0.010, $\Omega$ = 180$^{\circ}$, i = 98$^{\circ}$, $\omega$ = 90$^{\circ}$, $\theta_0$ =...
ReluctantEarthling's user avatar
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Just how record-setting was the launch-to-docking time of the April-4-2019 Progress resupply mission?

Digital Trend's article 3-plus-hour supply trip from Earth to International Space Station breaks record mentions that this was even faster than the typical "fast-track" Russian launch-to-docking time ...
uhoh's user avatar
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Proper handling of terminal guidance of finite burn closed-loop execution for rendezvous conditions?

I'm writing some software which uses Optimal Control Theory / Calculus of Variations / Pontrayagin's Minimum Principle / Primer Vector Theory to do closed-loop execution of finite burns (in KSP). ...
lamont's user avatar
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How to specify constraints for launch windows

I'm trying to learn trajectory design and optimization, and I'm struggling to understand how one determines the launch window using trajectory design programs. I know that my satellite's initial ...
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Variation in Earth's aphelion and perihelion

I see from Astropixels.com that Earth's aphelion and perihelion each vary by a little over 29,000 km, while the earth-moon barycenter wobble is about 4,000 km. Is Astropixels.com correct? Are Jupiter ...
user16692's user avatar
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(How well) Did Juno provide any insight into the Flyby Anomaly?

I ran across an old BBC article titled Juno: The spacecraft putting sling theory to the test — Why a probe passing our planet on its way to Jupiter might end a decades-old mystery, and reveal ...
uhoh's user avatar
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197 views

Atmospheric Entry Simulation: Numerical Inaccuracy

I am trying to make an atmospheric entry/aero-assist simulation. For the propagator, I have used conventional equations of motions in planet fixed reference frame: where the scalar states are- ...
Kuldeep Barad's user avatar
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2k views

Differential Equations for Rocket Launch in Polar Coordinates

I'm trying to understand the equations of motion for a rocket launched from earth, through the atmosphere, and into LEO. I found a set of ordinary differential equations which describe the motion of ...
Paul's user avatar
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Resonances and the seven sisters recently discovered

In reference to the discovery of seven planets around Trappist-1, I'm just wondering if any of these planets are in an orbital resonance and if that is the case, what the implications for habitability ...
Happy Koala's user avatar

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