Questions tagged [orbital-mechanics]

The application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft.

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Why are what end up being meteorites not in stable orbit as planets and large asteroids are?

We don't have to worry about Mars, etc. hitting Earth. Is it that being smaller, small asteroids have less inertia and so are more affected by, I guess, the gravity of various planets?
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What is the **actual** average distance of the Moon from Earth?

The Moon orbits Earth at a semi-major axis of 384400 km, with its periapsis being 363300 km and apoapsis being 405500 km. (All figures from this NASA fact sheet.) If the Moon orbited Earth at a ...
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Nbody problem solving on python with Leapfrog

I am relatively new to astronomical programming and I am trying to code a simulation of the solar system as simplified as possible on python. To do so, I am using numpy in order to have one array ...
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How time-symmetric is orbital mechanics?

Kepler's first two laws tell us that in a two body orbit in which one of the bodies is much more massive than the other, that: The smaller body orbiting the larger body has an orbital path that ...
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How to calculate the minimum number of satellites needed to maintain constant link between themselves? [closed]

Suppose we want to build a number of space stations, all orbiting Earth at the same altitude, equally distanced from one another, and with the same inclination. How many of those stations are needed ...
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Angular velocity of planets around Earth, and Sun

What are the values of angular velocity of planets around Earth, and Sun? I am looking for these two sets of values.
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6 votes
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What is pseudo-synchronisation when a planet is orbiting a host star?

I understand the term synchronous rotation - when the plant spin frequency is the same as the orbital frequency. However, I've seen the term pseudo-synchronization coming up in a few places and I'm ...
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1 answer
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If the Earth became tidally locked with the moon, would that last forever?

If the Earth and the moon became tidally locked, would this last theoretically forever (assuming no external gravitational force modifies their orbits, for example, ignoring the effects caused by the ...
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Is there a limit to how many objects can orbit eachother in a chain?

I was wondering if there is a theoretical limit to how long a chain of orbiting objects can be, for instance you can orbit the moon which orbits the earth which orbits the sun which orbits the galaxy, ...
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1 vote
1 answer
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How is a comet visible when far from the Sun

The latest news tells of a super large "mega" comet C/2014 UN271 (Bernardinelli–Bernstein) approaching the Solar System in about 9 years. It must be very far from the Sun, so how do we ...
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Which is closer to the Earth, Phobos, Deimos or Mars? [closed]

Which one is closer to the Earth, Phobos, Deimos or Mars? None of the answers that I find actually answer my question.
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3 votes
1 answer
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What is a Keplerian frequency, why do we specifically say Keplerian?

I am assuming that it means the frequency of a planet on its orbit. But why do we specifically say Keplerian? Is there some other kind of definition of frequency we use for astronomical bodies in ...
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Deriving the apparent angular speed of a star

The angular speed of stars in the sky is constant but the apparent angular speed is not, due to the star moving faster on the celestial equator and slower near the celestial pole. The apparent angular ...
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1 vote
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What is the relationship between true anomaly and solar longitude?

So, my ultimate objective is to map solar longitude values onto a pseudo-Gregorian calendar. I thought this would be simple, but it has turned out to be anything but. I have asked several questions on ...
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3 votes
2 answers
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With only seemingly two measurements 30 minutes apart, how were astronomers able to determine that asteroid 2022 EB5's trajectory intersected Earth?

Earthsky.org's Asteroid discovered hours before Earth impact begins Hungarian astronomer Krisztián Sárneczky at the Piszkésteto Mountain Station – part of Konkoly Observatory near Budapest – ...
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Discrepancy in Horizons planet ephemerides for equivalent times in TT and UTC in dates during 1969

I have recently been experimenting with JPL Horizons planet ephemerides web App, and found a puzzling discrepancy. Horizons allows to specify the time at which the planet ephemerides should be ...
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In a multi-planet system, what mechanism can cause the innermost planet's semi-major axis to increase?

I've been toying around with n-body simulations (using research-grade software) and I've noticed a particular effect in many of my simulations: In many arbitrary multi-planet systems I simulate, there ...
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Meteroids escaping the system

So the sun or any star has a certain gravitational pull. Technically the gravity extends infinitely only it will just become really small. If there is a meteroid around a star how do I calculate when ...
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Non-stable vs non-linear orbits

In orbital dynamics there are often two 'classes'- stable and non-stable, or periodic and non-periodic. Is this just a specific class of linear and non-linear harmonics? Would Klemperer's rosette ...
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1 answer
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Why circularization of an orbit has longer time scale than tidal locking?

I'm trying to understand the basic physics of orbital evolution. I know that in a two-body system (a planet orbiting a sun for example), eccentric orbits become circular, and the spin of the planet ...
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1 vote
2 answers
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Planet's distance data from JPL Horizons - Mars Curiosity mission

I am looking for distance measurement in AU between planets and Earth. E.g. For Mars, Current distance, or distance of Mars from Earth at any given datetime, along with minimum (closest approach), ...
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Is it possible that Planet 9 was thrown out of the Solar System? [duplicate]

Is it possible that this planet changed other planet orbits (from which we assume that it exists) but then was thrown out of the Solar System in past when Sun was close to some other star? And it ...
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How does the gravitational interaction between dark a matter bulge and an ordinary matter disk affects stability over time?

From Cosmology it is known that a spherical bulge of Dark Matter, that only interacts gravitationally, surrounds the nucleus of each galaxy, that has a spinning disc component of ordinary matter. How (...
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1 answer
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Why is the L1 point (Lagrange) almost 1 million miles from Earth? Shouldn't it be closer to us?

Try to follow my simple logic: The Sun is almost exactly 333,000 times as massive as Earth, and gravitational strength increases linearly with mass, so the Sun's gravity is about 333,000 times ours. ...
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4 votes
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Discrepancy between my calculated planet JPL ephemerides and those by Horizons online app

I'm currently using JPL DE440 ephemerides. Following the documentation here, verified with the header file (specially the records in GROUP 1050) for the DE440 ephemerides (file header.440 available ...
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26 votes
4 answers
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Can a planet with no atmosphere be orbited at extremely low altitudes?

Can a planet that has absolutely no atmosphere be orbited by a spacecraft at extremely low "altitudes" (if you'd even call it altitude at such a low orbit. For instance, if this planet's ...
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1 answer
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What is the difference between inclination and obliquity?

I'm trying to understand the differences between obliquity and inclination when it comes to a system of a planet orbiting a star. From what I understand, obliquity is the angle between the orbital ...
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6 votes
2 answers
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What is the maximum latitude from which a satellite in a geostationary orbit around Saturn would be visible to an observer on the planet?

This question is part astronomy and part mathematics. I'm aware it involves “basic” trigonometry, but my brain is short-circuiting. From my calculations, the distance from the center of Saturn where a ...
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2 votes
1 answer
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How can I reconcile the JWST journey time of thirty days to Lagrange L2 with simple orbital mechanics?

I am an electrical engineer and not an astrophysicist so excuse my simple question. NASA says that the journey time for the JWST to L2 will be about thirty days. However assuming the orbit dynamics ...
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6 votes
1 answer
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What's the difference between the Roche lobe and Roche sphere?

I am just beginning to look into this topic, so apologies if there are any striking misconceptions in the following. From Wikipedia, the Roche lobe is "the region around a star in a binary system ...
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Would a system consisting of Earth and Venus orbiting around a common center be stable in the long-term?

Earth and Venus and very close to each other in mass and would both orbit around a point in space positioned almost perfectly in between the two. Assume that this system is 1 AU from the Sun and the ...
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8 votes
1 answer
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Post-Keplerian orbital parameters; is there a generally accepted set with definitions?

Strong-Field Gravity Tests with the Double Pulsar is a pretty big deal! 16 years of precision timing including "timing parallax" via VLBI has provided a dataset for which analysis requires (...
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2 votes
1 answer
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Does the .43 arc-second per year deviation of Mercury's orbit from Newtonian predictions mean that its position is 'off' by 75 miles per year?

If I divide the elliptical circumference of Mercury's orbit by .43 arcseconds, I get an answer of almost exactly 75 miles.... BUT, it is the precession of the periapses that is off, not 'just' its ...
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2 votes
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Why are triple conjunctions in a resonance forbidden?

I was reading the Wikipedia article about orbital resonance and noticed that Laplace resonances forbid triple conjunctions. This seems to be supported by the Io-Europa-Ganymede system and the Nyx-Styx-...
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1 vote
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Relative orientation in a 1:1 resonance of a planet and a satellite

To my understanding, in a two-body problem of a planet and a satellite, a 1:1 resonance means that the orbital period of the satellite is the same as its angular frequency (maybe not, so please ...
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6 votes
1 answer
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Is there a reason Tethys and Dione are the only moons known to have trojans?

Trojans have been found at the L4 and L5 points of most planets. However Tethys and Dione, both moons of Saturn, are the only known moons in the Solar System to have trojans of their own. Is this just ...
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1 vote
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Orbital mean motion expression derivation

I'm reading an article about tidal forces, and the expression for the mean motion is given by: $$ n = \sqrt{ \frac{G(M + M^*)}{a^3}}$$ Where $G$ is the gravitational constant, $M$ is the mass of the ...
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0 votes
1 answer
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Why do planets' orbital velocities drop off by less than a third when twice as distant from the sun, rather than three-quarters? If gravity is $1/4$?

Looking at the speeds of the planets in our solar system when traveling around the sun and their distances from it (or, using Kepler's third law,), it seems that when a planets distance is doubled, it'...
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2 votes
1 answer
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predicting angular seperation between planetary objects and earth satellites

I am struggling to calculate the angular separation between a satellite in earth orbit and a planetary object using the Skyfield library. It's equivalent to calculating the angular separation between ...
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23 votes
10 answers
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Is the closest planet to another planet always the innermost planet?

In our Solar system Mercury is not only the closest planet to Earth on average but also, for the same reason, the closest planet on average to all other planets (Jupiter, Neptune, etc...). Does that ...
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2 votes
1 answer
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When will Alpha Centauri A and B overtake Proxima Centauri as the closest stars to us?

There are 3 stars in the Alpha Centauri system: 2 large stars orbting around each other (A & B) and a distant Proxima Centauri (C) orbiting around both. Right now it just happens that Proxima ...
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0 votes
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How to predict future position of body in solar system (without Kepler's equations, N-body problem)?

I have a solar system where each body interacts with each other by force $F = \frac{Gm_1m_2}{R^2}$ Is it possible to predict future position of some random body after t seconds since bodies velocity ...
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If a satelite is in orbit around a two body system what is it's shape?

For example if something was orbiting the sun only slightly further out than the earth, it would risk capture by the earth when the earth caught up to it in it's orbit. If it was orbiting at a great ...
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11 votes
5 answers
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If a satellite is put into the same orbit of the Sun as Earth, how does it avoid hitting Earth?

If a spacecraft follows literally the exact orbit of Earth at a different speed to Earth then why doesn't it hit Earth at some point? I'm specifically thinking about this in relation to these ...
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1 answer
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Where can I build my house on Mercury so that I can see double sunsets (and sunrises)? Can I do it near the poles where it's cooler?

CNN'S Mercury mission flies by closest planet to the sun for the first time says at the end: Mercury's unusual rotation and oval-shaped orbit around the sun (sic) means our star seems to quickly rise,...
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1 answer
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Could the Moon placed near the Sun-Earth L1 point remain in a heliocentric 1:1 resonant orbit with Earth? If Earth were at 1 AU, where's the Moon?

This answer to How much mass can be put in an L4 or L5 and it still maintain reasonable stability? has left me with the gedankenexperiment of the Earth in a circular orbit around the Sun, and the Moon ...
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2 votes
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How to calculate orbital velocity of binary star?

I am trying to simulate the Alpha Centauri AB System. I built the simulation, it works flawlessly when trying to simulate our solar system, and I am now trying to simulate the AB System. I found all ...
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3 votes
2 answers
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Why doesn't Triton orbit over Neptune's equator?

In this answer, I wrote (on another account) why most moons orbit over their planet's equator. Any rotating planet has an equatorial bulge that shifts its moons' orbits around its equator over long ...
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5 votes
1 answer
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Confused on how you are supposed to calculate eccentricity without apsides

I'm kinda confused on how to calculate either the apsides or the eccentricity without knowing one or the other. Let's say you have an object in orbit around another. If you know the current distance, ...
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1 vote
1 answer
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What is the maximum speed in which a human jumping away from Deimos and towards Mars would actually fall back down rather than enter Mars' gravity?

Imagine a universe in which Deimos and a human are the only objects in the universe. It doesn't matter if the human jumped even 1 nanometer per second slower than escape velocity, they would still ...
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