# 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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### What is the frame of reference for orbital speed?

Don't treat this question lightly. It's a thing that's been biting me for a pretty long time, and while it's "intuitively obvious", if you get into finer details, it gets quite convoluted. So, a ...
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### What is a “Sailboat Island of Stability”?

The New Horizon's team, in response to an announcement of a press conference from the Hubble team, posted some speculations as to what the press conference might be about. On the list includes "Small ...
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### What target is the most difficult to reach in the solar system?

"Most difficult", as in the minimum $\Delta v$ required, the objective being capture into an orbit around the object. Looking through some Delta-v maps, I would suspect the answer to be some inner ...
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### What is the ISS drag?

ISS constantly loses altitude to air drag and other forces (tidal, electromagnetic). While finding that rate in the sources isn't that hard, with orbital mechanics of altitude loss actually increasing ...
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### Calculating solar system escape and and sun-dive delta V from lower Earth orbit

According to http://en.wikipedia.org/wiki/Escape_velocity at the Earth/Moon distance from the sun, the escape velocity is 42.1 km/s. According to http://en.wikipedia.org/wiki/Earth the average ...
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### How do spacecraft rendezvous in orbit?

Given two spacecraft (let's say, the ISS and an unmanned resupply capsule), how do the two spacecraft rendezvous with each other in space? If they're moving at the same speed in space, they'll never ...
1answer
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### Is the Flyby Anomaly still a thing?

The Flyby Anomaly is a name given to an unexplained, unexpected difference between the best theoretical calculation of a change in several different spacecraft's velocities due to flyby (Gravity ...
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### Why is momentum transferred to the moon?

The moon whizzes around the Earth, dragging water after it and producing tides. In a comment on this question, I asserted this would sap the momentum of the moon causing it to fall to Earth. This was ...
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### Will Rosetta have to adjust its orbit around Chury due to the comet's coma and tails?

ESA's Rosetta spacecraft is scheduled to orbit 67P/ChuryumovāGerasimenko after it reaches the comet by mid-2014: Rosetta's main objective is to rendezvous with, and enter orbit around, comet 67P/...
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### Do we sufficiently understand mechanics of Lagrange point stationkeeping for EML2 rendezvous and assembly?

I've been watching some recorded videos from the April 22 - 24, 2014 Humans2Mars conference (videos and live streams, when available, are on the National Institute of Aerospace channel on Livestream), ...
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### Earth Moon Pork chop plot

Does pork-chop plots exist for Earth-Moon System? I could only find pork-chop plots for Earth-planet systems.Could someone please shed some light on this topic?
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### Orbital mechanics: trying to understand counterintuitive behavior (braking to overtake)

If one spacecraft wants to overtake another (e.g. for a rendezvous), it has to (counterintuitively) brake, go into a lower orbit and use the higher angular velocity of that orbit/shorter orbital ...
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### Multiple aerobraking

I have spent a lot of hours with Kerbal Space Program recently and I am curious about one thing. I got into orbit around the Moon and then I was able to get back to an orbit of "Kerbin" (the home ...
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### Tiangong-1 reentry impact place probabilities

Following all the news concerning Tiangong-1, I have seen the following plot made by the Aerospace Corporation where Blue area: null probability of impact Yellow area: high probability of impact ...
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### How can I plot a satellite's orbit in 3D from a TLE using Python and Skyfield?

I have obtained a Two Line Element (TLE) of a satellite in Earth orbit from Celestrak at https://www.celestrak.com/NORAD/elements/ and I would like to use it to calculate an orbit. How can I ...
3answers
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### Can someone give me a 'trajectory optimisation for dummies' answer?

So, I am currently doing a project on trajectory optimisation. I get the principle of it, minimise fuel cost for a journey, or try to maximise the spacecraft weight at target destination, and that ...
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### How to tell a satellite is tumbling and out of control?

I've just read North Koreaās āsuccessfulā satellite in orbit, but tumbling and useless. How can we tell a satellite is tumbling or not? It's so far away!
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### How much delta-v can we squeeze out of a gravitational slingshot and what factors limit it?

A lot of space probes use gravity assists from various space objects to boost their speed and save on propellant requirements. On what factors does the increase of delta-v depend? My guesses are: ...
1answer
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### How does the gravity of a massive non-spherical object act on things around it?

Firstly, not sure if this question ought to be in the physics SE site. Please let me know if it should. Secondly, I don't know a whole lot about physics (I'm just inquisitive). So please try to keep ...
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### Are there any remaining spacecraft that can retrieve objects from Earth orbit?

Now that the Space Shuttle has been retired, are there any spacecraft available that can retrieve an object from orbit and return it safely to Earth? What would be the maximum size of such an object?
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### How is a Russian satellite's behavior “very abnormal”?

The BBC has a news article saying: "Mystery Russian satellite's behaviour raises alarm in US". But the article doesn't say how or why the behavior is "abnormal". And the linked transcript of Remarks ...
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### Online Porkchop Plotter

Is there an online tool available to calculate porkchop plots at arbitrary resolutions? Real world only please -- I am aware of the tools available to do this for, say, KSP.
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### How accurate is the patched conic approximation when performing a Hohmann interplanetary transfer?

I've been making a Mathematica script whereby a spacecraft is transferred from Earth to Mars using a Hohmann interplanetary transfer by means of a patched conic approximation. As far as I can tell ...
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### Apollo 10: Where's Snoopy?

During the Apollo program, we launched a total of 9 Lunar Modules (LM's). The Ascent module from Apollo 10, or "Snoopy," is unique in that it was neither deliberately crashed into the Moon (Apollo 11, ...
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### If we could send an orbiter to the Pluto-Charon system, could we put it in a stable orbit?

The barycenter of Pluto and Charon is in space between the two bodies, close to Pluto. It is the center point of the animation below. The image is roughly to scale. Note that the two bodies are ...
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### Spacecraft Maneuvers as Intellectual Property? Wow!

In the past I had encountered a few mentions of orbits being patented (or at least applications filed) but didn't take much notice. Then I did a simple search and was blown away by the sheer volume of ...
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### Why did the rendezvous attempt fail on Gemini 4?

It is said in Wikipedia, that On the first orbit, McDivitt attempted to rendezvous with the spent Titan second stage. This was unsuccessful for a number of reasons: NASA engineers had not ...
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### Why do so few satellites pass over the poles, and why do so many focus on the equator?

The following screenshots from the website Stuff in Space, which tracks satellites and man-made debris orbiting the earth show us a few things: Very few satellites (or pieces of debris) pass over the ...
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### Ordering of the Lagrange points

Is there any basis for the ordering of the L-points? Specifically, is there any particular reason for choosing L1 as the first L-point?
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### Are patched conics (and by induction, KSP) “useless” for simulating ion propulsion?

My previous KSP question What can the KSP game actually teach about spaceflight and orbital mechanics, and what are its limitations? resulted in some really productive discussions and under-the-hood ...
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### Why would Sun-synchronous orbits be impossible around perfectly spherical bodies?

This is a special case follow-up to Are sun-synchronous orbits possible around any body? Reading Wikipedia on Sun-synchronous orbit a few days ago when trying to refresh my memory on orbital mechanics ...
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### What's the reasonable “window” in days for a Mars-Earth Hohmann transfer?

As any popular science reader knows, when traveling between Earth and Mars, there's a Hohmann transfer opportunity about every two years (I believe it's every 26 months, specifically). What I've ...
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### How stable are satellites in a graveyard orbit

How stable are graveyard orbits? How big of an issue is orbital decay? As the wikipedia article states, the graveyard orbit is higher than the synchronos orbit from which the satellites are disposed ...
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### A spacecraft is travelling at X units per hour. But relative to what exactly? Does it depend on orbit? How?

If I am walking, the ground is stationary, and I move X units/hour relative to the ground. If I am in low-earth orbit, then I am still moving X units/hour relative to the ground, only its a much ...
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### How frequently do asteroids collide with each other?

Space is empty ... lots of empty. Apparently so empty that the risk of collision between a spacecraft of our times, and an asteroid in the asteroid belt is said to be infinitesimal. Running a search ...
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### If something “falls off” the L2 or L1 point, where will it go?

The L1 and L2 points are thought to be unstable "saddle" points, meaning that there is stability in two directions of movement, but not in the other. That raises an obvious question - when a ...
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### Are sun-synchronous orbits possible around any body?

Sun-synchronous orbits are popular around Earth, and the Mars Reconnaisance Orbiter uses one as well (so I think Wikipedias definition as a geocentric orbit is wrong). Considering that probably any ...
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### Where to find the best values for standard gravitational parameters of solar system bodies?

Where can I find the best values to use for standard gravitational parameters of solar system bodies for numerical simulation experiments? Here are two sets I've put together. The first set is from ...
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### Could JWST stay at L2 “forever”?

Using only reaction wheels powered by solar panel and the sunshield as a sail (in continuous active attitude control) to generate thrust from solar photon pressure in the desired direction, could JWST ...
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### What is the maximum mass of a satellite that can be placed in GEO?

What is the maximum mass of a satellite that can be placed in GEO? Or can satellites of any mass be placed in GEO?
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### How large a body could a probe with ion engines land on and launch from?

Researching small asteroids up close by use of robotic probes seems like an appealing near-future mission. One option is a sample return mission that goes to one large body, another is a mission where ...
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### Docking in orbit

What systems are used for range, speed and alignment when docking in orbit? Whether automatic, human controlled arm, or Apollo style human controlled ship to ship? Playing Kerbal Space Program, I ...
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### Why does Starman/Roadster have radial acceleration?

Discussion in chat pointed out that the SpaceX Roadster or Starman has a Marsden A1 coefficient. From solution 10 in Horizons: ...
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### What is a near rectilinear halo orbit?

A proposed option for the lunar orbit of a Lunar Orbital Platform-Gateway (formerly known as Deep Space Gateway) is a near rectilinear halo orbit, or NRHO. This excellent answer discusses the ...
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### 2D Orbital Path from State Vectors

Given a planet of mass $M$ at the origin, and the state vectors $\textbf{r}$ (in meters) and $\textbf{v}$ (in $m/s$) at time $t = 0$ for a satellite, what are are the equations for: Distance $d(t)$ ...
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### Transfer between elliptical orbits

For circular orbits the most efficient transfer is achieved with a hohmann transfer or a bi-elliptic transfer. But what is the most efficient way to transfer between elliptical orbits? I assume in ...
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### Can a satellite work like a radiometer?

Like a Crookes Radiometer, could a satellite have a stiff vain to maneuver? With a white side to let light pass and the black side capture light radiation be enough provide radiation pressure to keep ...
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### What kind of mission objective would make a parabolic escape trajectory desirable?

As far as I can tell, a trajectory with zero excess velocity would place it (essentially) in nearly the same orbit around the sun as earth (assuming it even departs far away enough for the sunās ...
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### Why are there no LEO satellites in the earth's equatorial plane?

From my elementary school understanding of Satellite orbits, I know that GEO satellites are placed in equatorial plane, MEO satellites are placed in an smaller degree inclined plane while LEO ...
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### Land a cubesat on the moon with ion engine

Say I have a 3U cubesat with a BIT-3 ion thruster, an iodine tank and landing legs. Can it land on the Moon with just an ion thruster?

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