Questions tagged [eci]

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Are ECI and ECEF Frames, and Do They Belong to the Geocentric Equatorial Coordinate Systems?

I'm completely confused about the difference between geocentric equatorial coordinate systems, ECI, and ECEF. David Vallado, in his book 'Fundamentals of Astrodynamics and Applications,' mentions that ...
83 views

ECI position and velocity from angular velocity

I need help with an orbital mechanics issue that I cannot figure out. I have the initial ECI position and velocity ($r_{vec},v_{vec}$) of a certain satellite. Through them, the angular velocity, the ...
1 vote
210 views

Perifocal to ECI using Argument of Latitude

Suppose a satellite is orbiting Earth in a circular orbit. I know the following orbital elements: Inclination i, RAAN (Ω), Semi-major axis a (or orbit radius given that it is a circular orbit) ...
516 views

Calculate velocity vector of elliptical orbit given the position vector at that point, the instantaneous speed, the true anomaly, and the inclination?

Sorry if this is obvious, but I am an amateur at orbital mechanics and trigonometry was never my strong suit. I would like to calculate the velocity vector at a point in an orbit given: position ...
172 views

(In ECI) How can I compute the RAAN of an orbit given the eccentricity vector, the declination of the orbiter at apoapsis, and the inclination?

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 ...
1 vote
66 views

Why ECEF does not coincide with ECI on January 1, 2000 at 12.00? [duplicate]

I assumed that ECEF frame coincides with ECI frame on January 1, 2000 at 12.00. To see that, on MATLAB, I used the dcmeci2ecef() function as: ...
927 views

Transformation ECI to ECEF acceleration and forces

I know that for velocity conversions between ECI and ECEF there is an $\omega \times r_{ECI}$ term, such that the overall transformation is $v_{ECEF}=v_{ECI}-\omega \times r_{ECI}$. In my belief ...
6k views

Are ECI and ECEF both frames and/or coordinate systems? Is there a difference?

I don't know really know the difference between a frame and a coordinate system. I'd proposed ECEF and ECI tags, do we need them? Frames seems to be the standard in meta but there is concern so any ...
750 views

How to solve the two-body problem in the ECI frame through numerical integration?

I need to know how to solve two-body problem by solving a system of first order equation derived from the equation below. $$\ddot{\mathbf{r}} = -\frac{\mu}{r^3}\mathbf{r}$$ How do I go about this, and ...
819 views

In which direction does the x axis of the ECI at 1.1.2000 at 12:00 (J2000) go and where is the 0 deg meridian?

I am currently getting a bit lost in reference frames and coordinate systems. From my point of view, I am currently in the ICRS frame. I know that the ECI from my point is only moving but not rotating,...
1 vote
44 views

Calculating angular deviation from LEO magnetic field

The situation I need to calculate pointing errors for a satellite that points along Earth's magnetic field. The satellite's position and orientation are given to me w.r.t ECI J2000. The orientation is ...
2k views

How to find ECI coordinates for a circular orbit

Suppose a satellite is orbiting Earth in a circular orbit, of which I know the inclination $i$, the right ascension of the ascending node $\Omega$, the semi-major axis $a$ (or orbit radius given that ...
2k views

Is this commonly attributed ECI (Earth-Centered Inertial) to ECEF (Earth-Centered Earth-Fixed) transformation accurate?

As noted in this previous Stack Exchange question, and many others like it, the transformation from ECI to ECEF (or vice versa) is not a simple process, requiring several steps and considerations (...
362 views

J2000 to current ECI transformation matrix

I want to find the transformation matrix that converts an ECI frame at some time 't' (lets say t = 1st January 2020) to J2000 ECI frame (that is ECI frame at noon of 1st January 2000). From what I ...
3k views

C/Fortran library for ECI to ECEF conversion

Does anyone know of a good C or fortran library which constructs the rotation matrix to convert from ECI to ECEF components?