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Questions tagged [orbital-mechanics]

Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft.

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How did the Apollo guidance computer handle the Earth-Moon system's rotation around the Sun?

In this comment I just wrote: "...but at all other times it is just doing math to calculate its trajectory." The math needed a stable clock Timing accuracy of the Apollo Guidance Computer? (also 2, ...
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Compute heliocentric ecliptic coordinates from Kepler's laws

I'm writing a program to compute the heliocentric ecliptic position of planets and asteroids. I want to output rectangular coordinates oriented according to the ecliptic: positive X in the direction ...
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Apollo Missions - Travel time to moon [duplicate]

I must be missing something - escape velocity is about 25,000mph. The distance to the moon about 240,000 miles. That computes to about a 9 hour flight. Why did it take 3 days for Apollo missions to ...
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Why is Angular Momentum of Satellite Rotating in ECI Frame?

Summary: The angular momentum per unit mass of satellite is rotating in ECI x-y plane and I can't understand why. I'm very new to orbital mechanics. What I'm doing: I'm taking the cross product of ...
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Ratio of low-thrust slow spiral to Hohmann transfer $\Delta V$?

Going from one circular orbit to another, there are tables out there and equations that give the total $\Delta V$ needed for a two or three impulse maneuver scenario. For a very low thrust propulsion ...
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How to calculate the kilowatt hours (kW-h) needed for a solar-electric engine to produce a given delta-v?

A spacecraft is in LEO and I would like to reach a certain point in space; let's say Mars. If I look at the diagram in this answer I see that the delta-v from low Earth orbit to low Mars orbit is ...
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Does a change in the rotational speed of something on its own axis (rpm) affect its orbit?

For example: if a satellite in orbit around earth had its prograde rotational speed increased from 60 rpm to 600 rpm, would its orbit be affected? Another example would be if earth’s rotational speed ...
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Moon Polar Days And Night

Moon's rotation axis from the orbit plane of earth is about 1.54° tilted. Just like earth because of tilt, do polar regions experience 6 months day and 6 months night? If so, aren't these places ...
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How do we know that an exoplanet is tidally locked to the parent star? [migrated]

Often in discussing exoplanets we hear that they are close to the parent star (usually a red dwarf) but then there's a caveat that the planet is tidally locked to that star and that that fact severely ...
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Two 1000 kg gold spheres orbit their CM in near-contact, great way to measure G or limited by spaceflight issues?

The hypothetical, non-existent crowdfunding site go-launch-me is so confident, they are offering a two-for-one special. For a limited time, if your project is funded they will foot the bill for a 2nd ...
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Use of thrusters for Collision Avoidance Maneuver

I'm building an orbit propagator that gives the position of two satellites at time T. The position are expressed in ECI and after that are being transformed in LVLH frame (as mentioned ECI to LVLH ...
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ECI to LVLH conversion

I want to transform the position and velocity of two satellites from ECI mean of date mean of equinox to LVLH(Local Vertical Local Horizontal). The problem is that there is little documentation that I ...
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How to get true anomaly using subsatellite point (latitude)?

I am working on an application which is using an orbit propagator. I have a satellite which sets its latitude using this orbit propagator. I want to change the latitude of the satellite by a new value,...
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How much does a swing-by change the orbit of the planet?

A friend of mine told me that one Voyager swing-by moved the orbit of Jupiter a foot closer to the sun. I understand that Jupiter was slowed by the gravity assist, but I figured it would be minuscule ...
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Help with my tensor tension; how to derive and calculate this rigid body gravity gradient torque?

Tensors make me tense. Imagine a long thin rod in a circular orbit. The gravity gradient will produce a net torque on the rod whenever it is not oriented parallel, or perpendicular to the radius ...
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What are the effects of orbital reflectors and advertising on scientific observation?

There's a couple of startups and initiatives which are proposing "space billboards" which have been getting a lot of bad press recently. Most of the proposals involve a bunch of cubesats with large ...
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Computing the local orbital frame vector directions and angles of gyroscope direction in the satellite

In the context of the study of a cubesat (little satellite), I am asked to define the local orbital frame and compute the local orbital frame vector directions as a function of time (...
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Would any manned orbital launches to date have been possible (but lower) if they were launched retrograde instead of prograde?

Manned launches have always been launched prograde to take advantage of the Earth's rotation velocity boost, and often in order to match the prograde orbit of another spacecraft for rendez-vous. I ...
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Time dilation between Mars and Earth due to different mass

I am not sure I understand the Time dilation correctly but if mass has dirrect impact on time...than lets consider cosmological event - one orbit of planet Earth around Sun. This event will person on ...
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Rotating in orbit?

Reading this question (Is the cupola, on the inside of the ISS, cold or warm to the touch?) prompted me to wonder about an object in orbit's orientation as it orbits its host object. For example, ...
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NAIF and SpiceyPy returning seemingly inaccurate results

I am yet another amateur astrophysics enthusiast creating a solar system simulator. I began by hard-coding planetary bodies and their satellite orbiting characteristics via JPL data tables such as ...
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How will JWST maintain its elliptical orbit around L2?

I understand that JWST will have a vertical elliptical orbit around L2, but what I don't understand is how the telescope will actually maintain an orbit if there is no body in L2 to actually orbit ...
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Why would the orbit of a satellite in GEO climb by 21 km in altitude over six months by itself?

This answer mentions several effects that tend to move geostationary satellites out of their "box" over time, but one really surprised me. According to the plot below (from there, but uncredited) the ...
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Which point in an orbiting body most closely follows its Keplerian trajectory?

Keplerian orbits can describe the motion of a negligible mass around a massive fixed central body, but they can also describe the motion of two bodies around their center of motion... with some ...
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Understanding shape of DSN's 'kinky uplink protocol' keeping frequency in coherent transponder's optimum bandpass?

This tweet by deep space SDR enthusiast and amateur radio operator Edgar Kaiser @df2mz shows a squiggly tone from MRO. Mars Reconnaiscance Orbiter (MRO) X-band downlink. The signal shows this ...
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Could the $C_L$ of the X-15 be calculated from the flight data near the Kármán line altitude?

The "lift coefficient" $C_L$ can be very different for one specific aircraft at different speeds. According to this article from NASA about the lift coefficient: So it is completely incorrect to ...
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Did the astronauts of Gemini 4 have any realistic rendezvous simulator training of orbital mechanic effects?

Gemini 4 was launched on June 3, 1965. It mission included the first attempt of a rendezvous manoeuvrer in space. The rendezvous test failed. Two years earlier, in June 1963, the Rendezvous Docking ...
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Why did rendezvous on Gemini 4 fail so badly?

I can't for the life of me understand why commander Jim McDivitt thought he could eyeball a rendezvous - point the nose and thrust . The futility of that technique is one of the first things even ...
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Does an airplane in orbit near the Kármán line altitude, with the air providing lift, ever reach orbital velocity? [duplicate]

The equation for an airplane in orbit with the air providing lift would be: $$\frac{GM_Em}{(R+h)^2} - \frac{\rho(h) v^2 S C_L}{2} = \frac{mv^2}{R+h} $$ $GM_E$ is Earth's standard gravitational ...
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How do long range space probes adjust trajectory?

More specifically, after the main launch adjustments have been made using the primary boosters and temporary adjusting propellants how might even the slightest trajectory and orientation corrections ...
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Puzzler: Precisely what maximum distance from the Earth did the Apollo 13 astronauts achieve?

tl;dr: Both this answer and this answer quote Wikipedia to state that the Apollo 13 astronauts reached 404,171 km from Earth. I'm not able to reproduce that value. According to JPL's Horizons the ...
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Quantitatively, how deep are the stable equilibrium points in GEO? How much delta-v to move from one to the other?

This answer discusses a spacecraft in GEO using a two-impulse (circular → elliptical → circular) raise & lower maneuver to move (phase) itself by 180 degrees in longitude then return to synchrony. ...
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Calculating a de-orbit burn, is this problem written correctly?

I'm having trouble finding the velocity and acceleration and therefore the time in seconds it takes, and I find the way the problem is written confusing, especially Determination of $\Delta V$: ...
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Delta-v to move from GEO to GEO

To move a satellite in geostationary orbit, 166°55′E, to the antipode, 13° 4' 3.2" W, what delta-V would be needed for this to be accomplished? As for time constraints, I do not know what are the ...
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Algorithmic methods or techniques to find conjunctions in large ensembles of state vectors?

Suppose I wanted to answer the question Will Starman/Roadster pass particularly close to any asteroids in the next few years? or try to predict satellite conjunctions around Earth (e.g. Celestrak's ...
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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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How much delta-v is expended to get <out of the atmosphere>

How much delta-v it's spent in getting up to avoid the air drag once in orbit?
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Is the equation showed below the right one for an airplane flying at the Kármán line altitude?

$$\frac{GM_Em}{(R + h)^2} - \frac{ \rho v^2 S C_L}{2} = \frac{mv^2}{R + h}$$ $GM_E$ is Earth's standard gravitational parameter , $R$ is Earth's radius and $h$ the altitude of the airplane above the ...
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Does a credible Kármán plane reach escape velocity within 1 minute or does it follow the curvature of the Earth? [duplicate]

Edit: This question is no duplicate because here the dropping of the atmospheric density together with the horizontal line, play an important role. Furthermore none of the answers and question ...
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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 ...
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Where does the definition of the Kármán line on Wikipedia come from?

According to Wikipedia's article about the Kármán line: The Kármán line is the altitude where the speed necessary to aerodynamically support the airplane's full weight equals orbital velocity ( ...
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Is it correct to use the vis-viva equation when there are two forces acting on the orbiting body? [closed]

Edit: Although this question seems similar to the question "Is it correct to apply the vis-viva equation to an airplane that flies in a straight line", it is different because there the airplane flies ...
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Are 2 satellites joined better than 2 apart?

Could new satellites be designed to intercept other older functioning artificial satellites or space junk already in orbit to add weight to the new satellite in order to last longer in orbit?
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Is it correct to apply the vis-viva equation to an airplane that flies in a straight line at the Kármán line?

The vis-viva equation models the motion of an orbiting body and it applies when the only force acting on the body is it's own weight. So is it correct to apply this equation to an airplane that ...
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Artificial ring around the Earth?

What pros and cons would a orbiting ring have for Earth? Is there enough satellites in orbit to form a joined ring?
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What are the practical uses of a state transition matrix?

I am studying different dynamical models of relative motion of satellites. In my work, I've always just used a numerical integrator like RK78 to integrate the cartesian system of equations: $\dot{r}=...
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Diagram of Hayabusa 2 in “Hill Coordinate System”; what is that exactly? How to convert it to inertial?

These JAXA's Hayabusa-2's two Tweets: 1 2 show a diagram of the spacecraft's motion relative to Ruygu in what they call a Hill Coordinate System, This is a diagram of the trajectory during solar ...
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How much does the tidal effect affect satellites in a retrograde orbit?

How much more unstable are satellites in retrograde then a pro-grade orbit? Does the stability of a retrograde orbit increase with altitude? This answer said this orbit is unstable and made me think,...
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How would propagation differ between a GEO and a Retrograde GEO?

A Binary Equatorial Synchronous Retrograde Orbit is an orbit that would travel in the opposite direction of GEO and would pass over the same point on Earth twice per day at the same altitude of GEO. ...