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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Why does the Sun-synchronous orbital plane rotate?

I've seen this movie: It shows Sun-synchronized orbit of a satellite. What causes this orbit to be Sun-synchronized? I mean, from what I know, it shouldn't rotate as ...
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Would a satellite in retrograde orbit have a different speed than it would in prograde?

I understand that more power is required to launch a satellite into retrograde orbit, but once it's up there how much does the orbit differ from the more usual West to East? Would you still use $v\...
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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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Why is the SOI of Jupiter less than that of Neptune?

Recently we had a question on gravitational SOI (Sphere of Influence) of planets but the image in answer has a plot showing that the SOI of Jupiter is less than that of Neptune. However, Jupiter's ...
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What's the name of this maneuver for unlimited delta-v?

Let's say you have magical unlimited delta-v, but very low thrust-to-weight ratio. You could travel by accelerating constantly for half the trip, then braking for the other half, until your arrival. ...
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Why do geosynchronous satellites appear to oscillate in North-Southward direction? How to I trace out their path on the surface of the earth?

During the course of a day, the geosynchronous satellite's position in the sky forms a 8-like figure. I'm having trouble visualizing the movement of geosynchronous satellite when viewed from the ...
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Balancing a mirror

A possible way of heating up Mars is to use mirrors to direct more sunlight towards the planet. I am not asking about the feasibility or cost of such a gigantic project, but I have a question ...
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The strange orbit of Ofeq 11 - how does it (actually) do this?

I assume the retrograde orbit ($\theta_{inc}=142°$) is a side-effect of geography - ocean overfly access only lies West of the secured launch site - this article in Spaceflight 101 makes several ...
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What is the first non-solar-system object Voyager 1 will run into?

I know that the farthest man-made object from Earth is Voyager 1, and was wondering if and when it will ever come relatively close to another star system, or some other object located outside the ...
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How to best think of the State Transition Matrix, and how to use it to find periodic Halo orbits?

I'll state my mathematical question about the state propagation and state transition matrices first, then show you a simple problem for which I would like to use these concepts to generate a densely ...
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How can you rendezvous with the ISS via the “Soyuz scheme” without a computer and out of ground contact?

Let's assume the flight rules don't prohibit you from going to the ISS in a malfunctioning craft and don't force you to land on next orbit, unlike the real life ones. Let's also assume you have an ...
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What will happen to Parker Solar Probe in the long term?

Will the probe be intentionally crashed anywhere? Or is keeping space decontaminated not an issue here since temperature and radiation will sterilize anything in that kind of orbit?
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Is it possible for moons to have their own moons?

I'm wondering, if it's possible for moons to have their own natural satellites, something big enough to be spherical? Stars have planets, planets have moons. Is it possible that moons have moons too?
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Could you stably orbit around a square (cubic) body? Would the orbit destabilize automatically if not corrected by input?

Given that the cubic body is of homogeneous mass (say Iron) and we want to start with the best possible orbit and input nothing afterwards, could something orbit this cubic body stably?
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Is it easier to land on Europa/Io than on Mars? What are the main considerations?

Europa orbits Jupiter at an average speed of 13.7 km/s. At the same time Jupiter orbits the Sun at a speed of 13.1 km/s. This means that Europa has an orbital speed relative to the Sun of 26.8 km/s ...
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What does the BackFlip lunar cycler do in its pass by Earth?

This paper describes an Earth-moon cycler orbit. In this concept, a 180 degree "BackFlip" is used to modify a more simple cycler orbit. However, I can't figure out what cycler orbit it modifies, and ...
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What sort of orbital elements are used to describe halo orbits?

For standard orbits we can use Keplerian elements, TLE, or other similar. These don't make much sense for Halo orbits, which are not around a central body, but around a Lagrangian point, and follow an ...
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Improvements to script for Finite Burn Trajectory Optimization with MATLAB

I've written a MATLAB script to use the bvp4c two point boundary equation solver to implement a Calculus of Variations trajectory optimization of the problem of a single finite burn with a free coast ...
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Are some Halo Orbits actually Stable?

UPDATE: I found another reference! While I always enjoy a good video starring Jimmy and Linda Carter, this one has Dennis Wingo describing ISEE-3's original Halo orbit. He describes Sun-Earth $L_1$ as ...
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Mars Orbit Upon Intercept

I'm running a numerical simulation that calculates an interplanetary trajectory from Earth to Mars, and I'm trying to get a spacecraft into an orbit about Mars upon intercept, but am having a little ...
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Are any precautions in place to prevent loss of the Rosetta Lander the way Hayabusa's MINERVA was?

Back in 2005, Hayabusa carried a mini-rover 'MINERVA'. MINERVA was a Solar Powered entity designed to hop around on Itokawa, and capture images. Unfortunately (perhaps due to the time-lag) MINERVA was ...
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What orbital mechanics toolkits available today are suitable for a real-time simulator?

I'm a software engineer and I've always loved Orbiter (also here). However I feel that it's growing a bit antiquated, and it would be nice to have a more modern, open source, or otherwise hackable ...
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Low Energy Transfer within Earth-Moon system

Practical aspects of a total low energy transfer to the Moon have been seen in missions like GENESIS, which uses Weak stability Boundary legs of Earth and Sun to reach ESL-2. This four body model ...
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Is there any reason to send space probes along the plane of our solar system instead of perpendicular to the plane of our solar system? [duplicate]

Is there any reason to send deep space probes (Pioneer and Voyager) along the plane of our solar system (maybe with a slight inclination) instead of perpendicular to the plane of our solar system? If ...
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Do planets further from the sun take longer to complete their orbit?

See Topic. I know it is true for Sol, but in another solar System, is it possible that the mid or outer planets are completing one full orbit in a shorter amount of time than what a (smaller?) planet, ...
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What is the exact format of the JPL ephemeris files?

I'm attempting to do some basic planet position calculations using the JPL ephemeris data. The first step is to properly parse the files. Here's my understanding so far: The header file gives a ...
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If you throw a baseball from the space station, will it return to you in 90 minutes?

Something I've learned playing Kerbal Space Program is that if you make a change in your orbit with a single, short maneuver, your new orbit will intersect your old one at the point where you made the ...
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A spacecraft leaves Earth exactly with escape velocity V2 - what trajectory it will have in Solar System?

A textbook solution: if a spacecraft leaves the isolated Earth with escape velocity V2 (=11.2 km/s at Earth's surface) it will have parabolic escape trajectory. But Earth is in orbit around Sun. The ...
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Could the Hubble HST be saved by docking with the ISS?

I'm sure it cannot because I've never heard it suggested even on the pretty imaginative space flight communities on line. But the question is why, what makes it a bad idea. Some orbital data I find ...
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Pushing down a projectile from LEO

If I go for an Extra-Vehicular Activity on LEO and I drop a ball, I'm pretty sure nothing will happen in the short term. Both me and the ball are in a circular free fall around the earth CoG and ...
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What creative orbital maneuvers might I do to save fuel for a geosynchronous spacecraft?

I've heard that there might be some creative ways to get to Geosynchronous Orbit that could save a lot of fuel. How might I manage to make this happen?
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How to intuitively explain that reaching geostationary orbits consume more Delta V than escape orbits?

Studying again orbital maneuvers, I found the following plotting the cost of a Hohmman transfer between coplanar circular orbits (black line), in terms of $\Delta V$ against the orbit ratio $r_f/r_i$. ...
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Can a booster be designed to withstand 10,000 Gs?

In Could any existing gun reach the Karman Line?, Richard Graf's Kickstarter campaign for his Starfire space-gun is referenced & discussed. Setting aside my native skepticism for a project with ...
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Was the Apollo spacecraft always gravitationally bound to the Earth-Moon system?

When the Apollo spacecraft was en route to the Moon, was it an escape trajectory from the Earth-Moon system? If not for the burn(s) to enter lunar orbit, would it have continued in an independent ...
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How are gravity assists conceived?

So there are some very complex gravity assists out there. The Cassini mission, for instance, used a VVEJ (Venus Venus Earth Jupiter) gravity assist to make it to Saturn. Similar flybys have been done ...
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Is it possible to reach the Sun without expending any fuel/reaction mass?

Imagine that I'm designing a space probe, that will initially be placed into an Earth-like orbit around the Sun. My goal is to have the probe fly/fall into the Sun; it's allowed to take as much time ...
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Converting Orbital Elements to Cartesian State Vectors

Updated 2016-12-12 I'm writing an orbital mechanics program in Unity. I convert an orbiting object's position and velocity into orbital elements, then converting the orbital elements back into ...
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Why do rockets launching to the ISS from Florida point at 45 degrees to reach a 51.6 degree inclination?

In the Everyday Astronaut video about roll programs, it was mentioned in passing that in order to launch to a 51.6 degree inclination (to rendezvous with the ISS), the rocket must point at about 45 ...
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Oberth is confusing me. Apparent violation of conservation of energy

Let's say we have an elliptical orbit that goes from LEO periapsis to apoapsis near Earth's Hill Sphere. You can merely nudge your satellite at the apoapsis a bit higher (a tiny burn at periapsis), ...
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Why does in-flight mission abort often ends in ballistic high-g reentry?

I am seeing a lot of references to the “ballistic reentry” mode of the crew return vehicle in relation to the abort during the powered ascent stage. In partiulat, the recent crewed Soyuz MS-10 abort ...
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Deploying multiple satellites from one second stage

I’m just watching the Iridium-6/GRACE-FO launch from SpaceX. Before the launch they showed a video of the Iridium satellite network and in this mission they deployed 5 additional satellites into LEO. ...
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Why Earth flybys?

When playing around with the NASA trajectory browser, I noticed that practically every mission to the Jupiter system followed the mold (order of magnitude of $\Delta V$): Start in Earth Orbit (of ...
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Why is FORTRAN recommended for astrodynamics rather than MATLAB?

I understand that FORTRAN might be faster in terms of computation time, but I don't understand why it is always recommended by people in the field. Everyone tends to avoid MATLAB for astrodynamics; is ...
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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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How to get semi-major axis from TLE?

This should be fairly straightforward, but, how do I get the semi-major axis (a) from at TLE. For example if I have the TLE: ...
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Is “medihelion” a word?

"Medihelion" is what I call the two points on a solar elliptical orbit where distance from the sun is the same as the ellipse's semi-major axis. These two points also correspond to the end-points of ...
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Ephemeris data usage in interplanetary trajectory application

I'm trying to write a Mathematica application that allows users to choose their date of departure and time-of-flight for an interplanetary transfer mission (currently only working for Earth-Mars ...
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No need for gravity assist with Falcon Heavy?

Elon Musk is quoted to have said, after the launch of Falcon Heavy, that «it can launch things direct to Pluto or beyond, no stop needed, don’t even need gravity assist or anything». Now, I am not an ...
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How much “wobble” does a typical geostationary satellite experience?

Recall that geostationary satellites are placed into an orbit which is designed to stay above a fixed point on the Earth's surface. If the Earth and the satellite were both spherical cows in an ...
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Is a lunar Sun-synchronous orbit possible at the “frozen” inclination of 86°?

I have been considering if it would be possible to place a satellite in a Sun-synchronous orbit in one of the lunar frozen orbits at 86°. According to NASA scientists there are four inclinations for ...

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