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. For the movements of celestial bodies, see [celestial-mechanics].

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NASA GMAT: Any good tutorials or methods to learn how to use patch points and control points to come up with viable and optimal trajectories?

I'm a beginner to trajectory design, and have to use NASA's GMAT software. It's been a few weeks now, and I have done the first four tutorials and managed to create a (very unrealistic and sub-optimal)...
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Is this JWST Halo orbit plot fouled up somehow?

After looking at this plot and many others I've come to the conclusion that this plot does not represent current JWST halo orbit. If the plot is supposed to be of JWST halo... it disagrees with many ...
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How can I find the x, y position of apogee and perigee, if I only have the value of distance vector (position) and velocity vector?

I am currently working on a 2D space simulator where I have two bodies; one is still and other is an orbiting object, which I can also control like a rocket. I'm using the Newton's gravity: $F = \...
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How did India get to the Mars?

A few years back ISRO sent their orbiter to the Mars, It is known to be the biggest feat achieved by Indian Space Research Organization over the years. It special because ISRO manage to pull this out ...
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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 ...
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With independent control of attitude and thrust direction, could JWST be kept pointing in a “safe” direction during "towing"?

Context: JWST is considered un-repairable in its current L2 location for a number of reasons: Diagnosis is difficult since JWSR has no “selfie” capability. This makes planning for any repair mission (...
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Is the inter-manifold transfer of JWST between Sun-Earth L2 and Earth-Moon L1 within the capability of existing propulsion systems?

Context: JWST is considered un-repairable in its current L2 location for a number of reasons: Diagnosis is difficult since JWSR has no “selfie” capability. This makes planning for any repair mission (...
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Question: Does JWST have hardware that could be used as a docking fixture by repair spacecraft?

Context: JWST is considered un-repairable in its current L2 location for a number of reasons: Diagnosis is difficult since JWSR has no “selfie” capability. This makes planning for any repair mission (...
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Why do we use Chebyshev polynomials to predict positions of solar system bodies?

I've seen information for how to use the Chebyshev coefficients that JPL publishes, but nothing that explains why. Why isn't a simpler mathematical model used? I'm also surprised that JPL uses a ...
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Is it (theoretically) correct to apply an equation that is derived from a hyperbolic trajectory, to an elliptic transfer orbit?

The equation in question is this one: $$v^2 = v_e^2 + v_{\infty}^2$$ and it is showed in this answer. The Escape velocity page on Wikipedia mentions a link (num. 4) to the book "Fundamentals of ...
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Halo Orbits for Dummies: Can the tilt orientation of an L2 halo orbit be modelled on Coriolis Effect?

L2 Halo orbits are often portrayed as a pair of “North” and “South” orbits. Could the difference in “tilt” around the Y axis be explained by the direction of rotation and the Coriolis Effect? https://...
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How to make an algorithm that finds time to a true anomaly at epoch?

I am having trouble creating a function that finds the time for an inputed true anomaly when I know my current eccentric and mean anomaly (my equations are in vector form). Note that I only intend to ...
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Starting refueled in LEO, how much payload could a heat-protected Starship softly land on Mercury after a gravity assist from Venus?

This question may be a crucial follow-up to this one because in this answer it is calculated that the payload to Mercury without a gravity assist would probably be minimal, so if already a moderate ...
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If one Starship can transport 100 people to Mars, how many could it safely land near Mercury's north pole after one Hohmann-like transfer?

Personally, I would rather live near Mercury's north pole than anywhere on Mars mainly because: The permanently shadowed craters harbor abundant water ice and other frozen volatile materials Mercury ...
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Are Interplanetary mission trajectory computations based entirely on Newtonian mechanics?

I am wondering if the application of General Relativity is ever needed(?) I assume that Newtonian mechanics is sufficient with some trajectory corrections applied as needed on route. I also assume ...
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James Webb orbit insertion

Webb will issue a final course correction burn to insert it into the orbit around L2. It arrives from earth so the approach velocity should be higher than the desired orbit velocity and the vector ...
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Why “super” for supersynchronous orbits? Why not “trans”?

I was just getting used to “cis” and “trans” for orbits inside and outside the Lunar orbit. “Trans” is a Latin word root meaning “across, beyond, or through”(Meriam Webster). “Trans” seems like a ...
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Are there uses for these 'quasi iso-propic' supersynchronous transfer orbits?

In my answer to What are the benefits of supersynchronous transfer orbits? I stumbled upon an interesting outcome when considering the total $\Delta V$ cost from an inclined low altitude parking orbit ...
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When is the supersynchronous orbit more efficient than a typical Hohmann transfer where inclination change and circularization are simultaneous?

The title essentially explains it all. Some GEO launch vehicles like Proton, which launches from Baikonur at a latitude of 46 degrees, launch into a supersynchronous orbit. So at what point is the ...
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What are the benefits of supersynchronous transfer orbits?

Some satellites are injected into higher apogee than standard GTO apogee of 35 786 km. Next the satellite then has to increase its perigee ( usually 250 km ) to GEO altitude. Then the apogee has to be ...
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Why is NASA choosing such a large “halo” orbit at L2 for JWST?

According to “https://webb.nasa.gov/content/about/orbit.html”, NASA plans to exploit a quarter million mile radius “halo” orbit at L2. And Webb will orbit around L2, not sit stationary precisely at ...
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JWST Halo Orbits for Dummies: can halo orbits be usefully approximated by Simple Harmonic Motion?

Halo Orbits for Dummies: can halo orbits be usefully approximated by Simple Harmonic Motion? I am an undergraduate in the Kerbal Academy of Astrodynamics. Patched conics have given me an intuitive ...
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How does gravity change beyond L2?

Why does gravity appear to increase again on the far side of L2 from earth as indicated on the gravitational contour diagram? One would expect gravity to continue to decrease as the distance from sun ...
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calculating satellite position and velocity from TLE

I'm trying to calculate satellite orbit from the TLE set at first, I used several libraries including SGP4, Skyfiled to get the initial position and velocity of the satellite at the epoch time I know ...
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When calculating the six Keplerian Orbital Parameters, why do we need both Eccentricity AND the Semi-Major Axis? Doesn't one tell you the other?

Perhaps I am misunderstanding elementary math, but.... How is it possible to know the eccentricity of an ellipse (e) but not the semimajor axis (a)?
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How will JWST come to rest at L2?

As L2 orbits the sun at more than 67,000 mph, JWST will approach that orbit asymptotically . In doing this, will L2 be behind JWST and catch up with the satellite or will it be ahead of JWST and JWST ...
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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 is the moon's orbital motion accounted for in determining the best observation platform/location for JWST at L2?

The moon's periodic motion would appear to impose a perturbation to the otherwise equilibrium state of the solar/earth L2 point.
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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 ...
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Trouble understanding the memorandum "Cartesian State Vectors → Keplerian Orbit Elements"

So, I was reading this memorandum to make some c# classes helping with keplerian/newtonian orbital simulations. Then, I found this weird piece for solving for $n$... $n = (0, 0, 1)^T × h = (−h_y, h_x, ...
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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 ...
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"Hohmann-Like" and Chemical / Electric Thrust Comparison

Part of the work I have to do for my degree is to perform a "Hohmann-like" transfer between Earth and Mercury, of which I believe I have accomplished. I have attempted numerous times to ...
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Why are Jupiter's trojans even remotely stable?

The spacecraft Lucy is en route to explore Jupiter's trojan asteroids. Lucy is so named because the trojan asteroids are believed to be fossil remnants from the formation of the solar sytem. ...
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What is the intuition behind crossing angular momentum to derive the eccentricity vector?

When deriving the eccentricity vector you first start of with the equation of motion for the two body problem (we are concerned about the motion of the smaller body around a much larger mass) the ...
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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 ...
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Are there any Earth orbits where the duration of eclipse increases with semi-major axis with all other parameters fixed?

This answer to Is there a low Earth orbit with a 24-hour day night cycle? suggests that: In fact, it's a rule of thumb that the higher you go the less time you spend in Earth's shadow: the shadow not ...
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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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Calculating time for several transfer orbits

I was watching a video that displayed how the time to get to Mars varied with the production of varying delta-v and was looking for the mathematics behind such a calculation. Here is the link to the ...
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Why did the last six TDRS satellites start at ~7° inclination on a downward trend that appears to be "repelled" by zero & bounce back w/o crossing?

The most recent six TDRS satellites (8 through 13) were inserted into moderate inclination orbits of roughly 7°, and in all cases their inclinations immediately decreased at rates of about +/-1 or +/-...
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Why can't you travel to Mars in a straight line?

I had two questions regarding choosing a path to Mars. Firstly: I wanted to have a look at the mathematics behind the reason as to why we choose Hohmann's transfer over a journey that is a straight ...
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How is delta-v calculated for an interstellar journey?

Just recently I have been learning about orbital mechanics and I came across the following article: https://blogs.scientificamerican.com/life-unbounded/why-chemical-rockets-and-interstellar-travel-...
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What is the equation that relates delta v of a rocket to time taken to complete an orbit?

I wanted to see how the delta-v produced by a rocket affects the time it takes to complete a certain orbit. So what is the equation that relates these two quantities?
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How much delta-v could be saved with a Hohmann-like transfer orbit to the aphelion of Mercury 's orbit instead of its perihelion?

I wrote "Hohmann-like" of course because Mercury's orbit is rather eccentric and has an inclination of 7 ⁰. From this factsheet I've learned that perihelion is at 46 million km and aphelion ...
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Software to estimate radiation dose for an orbit

I am searching for a software/method, possibly open-source or free, to estimate the radiation dose for an orbit around earth.
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Osculating oscillations! What makes Akatsuki's eccentricity and inclination about Venus vary periodically?

Watching this animated GIF of Akatsuky's orbit I noticed that it seems to "walk" around Venus. Some orbital elements oscillate ~3-4 times a year, others drift and then slowly "step up ...
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Why end-of-life GPS satellites given orbits that seemingly still intersect active satellite orbits but with a different period? Recipe for disaster?

This answer to Where are MEO satellites put at the end of their operational life? says (currently in full): This is an active area of research. As you noted, the main satellites that are in MEO are ...
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Why was Telstar 1 put in a 952 x 5933, 2.6 hour 44.8° MEO orbit?

Wikipedia says that Telstar 1 was put into a 952 x 5933, 2.6 hour 44.8° MEO orbit but doesn't really say exactly why this particular orbit was selected. Did it perhaps behave roughly like a Molniya ...
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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) ...
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Why does the moon’s transit appear so inclined in this STEREO-B video?

Question: Why does the moon’s transit appear so inclined in this STEREO-B video? This video of the Moon transiting the Sun on Feb 25 2007 is from STEREO-B during its solar orbital insertion. https://...
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Hohmann transfer using GMAT software

I am trying to plot an orbit using gmat. I fixed apogee(RadApo) and perigee(RadPer) for the inner orbit(green) and inserted an impulsive burn. I got the desired shape of the outer orbit but I am ...

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