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Results for "eccentricity vector"
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7 votes
1 answer
1k views

Why does the eccentricity vector always point towards the periapsis of an orbit?

Double lines around a vector like this : $\mid\mid \textbf{v} \mid\mid$ represents the length or magnitude of a vector $\textbf{e}$ - Eccentricity vector $\textbf{r}$ - Position vector $\dot{\textbf{r} … }$ - Velocity vector $\mu$ - Standard gravitational parameter (mass of the earth multiplied by the gravitational constant G) This formula gives the eccentricity vector but to get eccentricity (which is …
John's user avatar
  • 113
3 votes
1 answer
621 views

Why is the eccentricity vector used to describe near-circular orbits?

$\omega$ are commonly replaced by the eccentricity vector. … vector. …
JuliusC's user avatar
  • 163
6 votes
1 answer
3k views

Why does the eccentricity vector equation always equal -1?

This is the eccentricity vector equation, $$e=\frac{1}{\mu}[(v^2-{\mu \over r})r-(r \cdot v)v]$$ $$e=|e|$$ Now this equation is written differently from many different sources but they essentially mean … I understand that the eccentricity of a parabola is 1 but this equation is for ellipses as well. So why is the answer always -1? Am I missing something? Thanks in advance. …
Star Man's user avatar
  • 5,986
2 votes
1 answer
183 views

Eccentricity Vector as a function of position only, as seen on Wikipedia?

It has a parameterization gamma, a normal vector N, and then eccentricity and semilatus rectum equations. … I'm trying to figure out how they managed to get an eccentricity vector with no velocity and no gravitational parameter. …
Michael Gunnarson's user avatar
3 votes
1 answer
150 views

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 equations … ^3}$$ Though I am not too sure why the author does this, it does say that now the equation can be integrated though I am not too sure why that is the case, like could this have been done with any old vector
John's user avatar
  • 113
2 votes
1 answer
204 views

(In ECI) How can I compute the RAAN of an orbit given the eccentricity vector, the declinati...

I am working on a personal project, and I want to write a program to obtain the RAAN given the angle of the eccentricity vector to the X-axis (ECI) along the XY plane, the declination (angle from XY plane …
John Doe's user avatar
2 votes
Accepted

(In ECI) How can I compute the RAAN of an orbit given the eccentricity vector, the declinati...

All you have is the eccentricity vector and the orbital inclination. … For any orbital inclination and chosen eccentricity vector direction (magnitude is irrelevant for these purposes) where the angle between the eccentricity vector and the reference plane is less than the …
notovny's user avatar
  • 5,565
5 votes
Accepted

How can I find the x, y position of apogee and perigee, if I only have the value of distance...

The eccentricity vector has a magnitude equivalent to the orbital eccentricity of the ellipse, and points along the line of apsides in the direction from the central body towards the periapsis. … of the eccentricity vector: $$e = \|\vec{e}\|$$ From that, you can get the perifocal unit vector $\hat{p}$ which points in the same direction as the eccentricity vector: $$\hat{p} = \frac{\vec{e}}{e}$ …
notovny's user avatar
  • 5,565
9 votes
Accepted

Why does the eccentricity vector equation always equal -1?

The expression on the right is meant to give the eccentricity vector but the vector notation has been lost. … You can see that the eccentricity vector x component is +0.8 and constant, and the y component is 0.0 That confirms that the eccentricity vector always points towards the direction of periapsis and it's …
uhoh's user avatar
  • 151k
3 votes

Eccentricity changes of an orbit during out-of-plane burns

An out of plane maneuver definitely changes where the eccentricity vector points. It might or might not change the magnitude of that vector. … This changes the $\hat r$ and $\hat z$ components of the eccentricity vector but leaves the $\hat \theta$ component unchanged: $$\Delta \vec e = \frac{-r v_r \Delta v\,\hat r + r\Delta v^2 \hat z}{\mu} …
David Hammen's user avatar
  • 77.4k
3 votes
1 answer
654 views

Calculate velocity vector of elliptical orbit given the position vector at that point, the i...

Other information which I could add to the script to find the velocity vector is eccentricity eccentricity vector semi-major axis periapsis radius declination of the orbiter at apoapsis With this info … The position vector and the eccentricity vector are in the ECI reference frame if that is important. …
John Doe's user avatar
4 votes
Accepted

Calculate velocity vector of elliptical orbit given the position vector at that point, the i...

for these calculations: Eccentricity Vector has a positive magnitude Eccentricity Vector is not parallel to Position Vector. … $\hat{p}$ points at the orbital periapsis, and is co-directional with the eccentricity vector. This calculation requires a non-zero eccentricity. …
notovny's user avatar
  • 5,565
2 votes

Solution to two-body problem in orbital mechanics for r(t) and theta(t), rather than r(theta)?

Why does the eccentricity vector always point towards the periapsis of an orbit? Why is the eccentricity vector used to describe near-circular orbits? … Let's start with this answer to Why does the eccentricity vector equation always equal -1?. …
uhoh's user avatar
  • 151k
2 votes

Eccentricity Vector as a function of position only, as seen on Wikipedia?

The eccentricity vector meanwhile, points from the central body to the periapsis, and has magnitude equal to the eccentricity. … With these in hand, calculating the eccentricity is basically the focal length / the semi major axis, which then completely nails down the eccentricity vector. …
dsdy120's user avatar
  • 121
1 vote

Given orbital parameters and position vector along that orbit, how can I determine the eccen...

$$ This vector is a constant of motion. … The eccentricity vector is thus useful for determining both the eccentricity and the argument of periapsis. …
David Hammen's user avatar
  • 77.4k

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