# ecef2eci

Position and velocity vectors in Earth-centered inertial mean-equator mean-equinox

*Since R2019a*

## Syntax

## Description

`[`

calculates the position vector in the Earth-centered inertial (ECI) coordinate system for a
given position vector in the Earth-centered Earth-fixed (ECEF) coordinate system at a
specific Coordinated Universal Time (UTC). For more information on the Earth-centered
Earth-fixed coordinate system, see Algorithms.`r_eci`

] = ecef2eci(`utc`

,`r_ecef`

)

`[`

calculates the position and velocity vectors for given position and velocity vectors. `r_eci`

,`v_eci`

] = ecef2eci(___,`v_ecef`

)

`[`

calculates the position, velocity, acceleration vectors for given position, velocity, and
acceleration vectors. `r_eci`

,`v_eci`

,`a_eci`

] = ecef2eci(___,`a_ecef`

)

`[`

calculates the position, velocity, and acceleration vectors at a higher precision using
Earth orientation parameters. If Earth orientation parameters are not specified, the
function sets them to `r_eci`

,`v_eci`

,`a_eci`

] = ecef2eci(___,`Name,Value`

)`0`

.

## Examples

## Input Arguments

## Output Arguments

## Algorithms

The `ecef2eci`

function uses these Earth-centric coordinate
systems:

Earth Centered Inertial Frame (ECI) — The inertial frame used is the International Celestial Reference Frame (ICRF). This frame can be treated as equal to the ECI coordinate system realized at J2000 (Jan 1 2000 12:00:00 TT). For more information, see ECI Coordinates.

Earth-centered Earth-fixed Frame (ECEF) — The fixed-frame used is the International Terrestrial Reference Frame (ITRF). This reference frame is realized by the IAU2000/2006 reduction from the ICRF coordinate system. For more information, see ECEF Coordinates.

## References

[1] Vallado, D. A.
*Fundamentals of Astrodynamics and Applications*. alg. 4. New York:
McGraw-Hill, 1997.

[2] Gottlieb, R. G., "Fast Gravity, Gravity Partials, Normalized Gravity, Gravity Gradient Torque and Magnetic Field: Derivation, Code and Data," Technical Report NASA Contractor Report 188243, NASA Lyndon B. Johnson Space Center, Houston, Texas, February 1993.

[3] Konopliv, A. S., S. W. Asmar, E. Carranza, W. L. Sjogen, D. N. Yuan., "Recent Gravity Models as a Result of the Lunar Prospector Mission, Icarus", Vol. 150, no. 1, pp 1–18, 2001.

[4] Lemoine, F. G., D. E. Smith, D.D. Rowlands, M.T. Zuber, G. A. Neumann, and D. S. Chinn, "An improved solution of the gravity field of Mars (GMM-2B) from Mars Global Surveyor", Journal Of Geophysical Research, Vol. 106, No. E10, pp 23359-23376, October 25, 2001.

[5] Seidelmann, P.K., Archinal, B.A.,
A’hearn, M.F. et al. "Report of the IAU/IAG Working Group on cartographic coordinates and
rotational elements: 2006." *Celestial Mech Dyn Astr* 98, 155–180
(2007).

## Version History

**Introduced in R2019a**

## See Also

`eci2ecef`

| `dcmeci2ecef`

| `aeroReadIERSData`

| `deltaCIP`

| `polarMotion`

| `deltaUT1`

| `siderealTime`

| `datetime`

| CubeSat Vehicle (Aerospace Blockset)