Orbital and Technical Parameters

Reference Constellation Orbital and Technical Parameters

1: Reference date for the constellation is 2016-11-21 00:00:00 UTC⁶. The table shows a snapshot of the reference orbit at the given epoch. The reference orbit for a different epoch can be computed following the note. Occasionally the table might be consistently updated to a different epoch, for example when introducing new satellites. The reference orbit indicated corresponds to the final orbital slot within the constellation.

2: The above table provides values for the given UTC epoch. The reference RAAN, argument of perigee and Mean Anomaly are dynamic parameters, the other are static. To calculate the values for other epoch, users are advised to use a linear extrapolation for the RAAN, argument of perigee and the Mean Anomaly with the following temporal rates: 

Reference parameter rates	Nominal Galileo orbits	L3 Elliptical orbits
d(RAAN)/dt	-0.02764398 deg/day	-0.039867092 deg/day
d(Arg. peri)/dt	0.00000000 deg/day	0.034373586 deg/day
d(Mean Anomaly)/dt	613.72253566 deg/day	667.909221051 deg/day

Note that the average dynamic parameters values of auxiliary slots C14, B14 and B15 can be computed as per Nominal Galileo orbits.

 

3: True anomaly (υ) and mean anomaly (M) are related through the eccentric anomaly and the Kepler’s equation. The true anomaly can be also solved from the mean anomaly by using a series expansion approach of the so-called equation of the center. For reference orbit computation the series solution can be truncated in the following terms:

Note that for circular orbits (eccentricity =0) both mean and true anomalies are identical.

 

Source: ESA

 

4: ISO-8601 Date and time format

Parameters Definition

Coordinates System

The inertial reference frame is defined by the position of the vernal equinox ‘X’ at a certain epoch. The ‘Z’ axis is defined by the spin axis of the Earth (North Pole), and the ‘Y’ axis completes the orthogonal set of the right handed inertial reference frame.

Keplerian Elements

The next figure illustrates the geometric properties of the usual set of orbital elements used to describe the motion of a satellite in Earth orbit, well characterized by the Keplerian elements of an elliptical orbit.

   Click to enlarge

a: Semi-major axis of orbital ellipse is the semi-major axis of the ellipse defining the orbit.

e: Numerical eccentricity of the orbit is the eccentricity of the orbital ellipse. Eccentricity is a measure of how an orbit deviates from circular. A perfectly circular orbit has an eccentricity of zero; higher numbers indicate more elliptical orbits.

i: Inclination of orbital plane is the angle between the orbital plane and the equator.

Ω: Right ascension of Ascending Node (RAAN) defines the relative angular phasing between the orbital plane and the Vernal Equinox, which is the point of intersection between the Sun’s trajectory and the Earth’s equatorial plane. Due to the Oblateness of the Earth, the RAAN is decreasing about 10 degrees per year.

NOTE: the intersection of equatorial plane and orbital plane is called “Nodal Line”. Its intersection with the unit sphere defines two points: the “Ascending Node”, through which the satellite crosses to the region of the positive Z-axis, and the “Descending Node”. “Right Ascension” is counter-clockwise sense viewed from the positive Z-axis.

ω: Argument of perigee is the angle between the ascending node and perigee directions, measured along the orbital plane. The perigee is the point of closest approach of the satellite to the centre of mass of the earth. The most distant position is the Apogee. Both are in the orbital ellipse semi-major axis direction.

v: True anomaly  is the geocentric angle between perigee direction and satellite direction. The sum of the True Anomaly and the Argument of Perigee defines the “Argument of Latitude”. Notice that for a circular orbit (e = 0) the Argument of Perigee and the True Anomaly are undefined. The satellite position, however, can be specified by the Argument of Latitude.

u: Argument of latitude is the sum of argument of perigee and true anomaly. It is the angle measured from the equator to the satellite at a particular epoch. For the circular orbits the argument of perigee is not well defined, therefore it is more convenient to use the argument of latitude instead.  In the table, the argument of perigee has been set to zero, therefore the argument of latitude and the true anomaly are identical.

The satellite height is characterized by the orbit’s semimajor axis ‘a’, the variation in the radial distance due to the ellipticity of the orbit (the eccentricity ‘e’), and the angular distance ‘v’ (the true anomaly) from the point of closest approach in the orbit (called the Perigee).

Slot: The Galileo reference constellation has a total of 30 Medium Earth Orbit (MEO) satellites, including 6 auxiliary satellites, in a so called Walker 24/3/1 constellation. This particular Walker configuration implies that the Galileo constellation consists of 24 satellites homogenously distributed in three different orbital planes (A, B and C) separated in the equatorial plane by 120 degrees.

Click to enlarge

Satellite Launch Information

Launch ID & Date (UTC)	Satellite		Nickname1	Launch site	Carrier rocket
L1 2011-10-21 10:30	IOV PFM	GSAT0101	Thijs	Guiana Space Center (Kourou, French Guiana)	Soyuz /Fregat
	IOV FM02	GSAT0102	Natalia
L2 2012-10-12 18:15	IOV FM03	GSAT0103	David	Guiana Space Center (Kourou, French Guiana)	Soyuz /Fregat
	IOV FM04	GSAT0104	Sif
L3 2014-08-22 12:27	FOC FM01	GSAT0201	Doresa	Guiana Space Center (Kourou, French Guiana)	Soyuz /Fregat
	FOC FM02	GSAT0202	Milena
L4 2015-03-27 21:46	FOC FM03	GSAT0203	Adam	Guiana Space Center (Kourou, French Guiana)	Soyuz /Fregat
	FOC FM04	GSAT0204	Anastasia
L5 2015-09-11 02:08	FOC FM05	GSAT0205	Alba	Guiana Space Center (Kourou, French Guiana)	Soyuz /Fregat
	FOC FM06	GSAT0206	Oriana
L6 2015-12-17 11:51	FOC FM08	GSAT0208	Andriana	Guiana Space Center (Kourou, French Guiana)	Soyuz /Fregat
	FOC FM09	GSAT0209	Liene
L7 2016-05-24 08:48	FOC FM10	GSAT0210	Danielė	Guiana Space Center (Kourou, French Guiana)	Soyuz /Fregat
	FOC FM11	GSAT0211	Alizée
L8 2016-11-17 13:06	FOC FM07	GSAT0207	Antonianna	Guiana Space Center (Kourou, French Guiana)	Ariane 5
	FOC FM12	GSAT0212	Lisa
	FOC FM13	GSAT0213	Kimberley
	FOC FM14	GSAT0214	Tijmen
L9 2017-12-12 18:36	FOC FM15	GSAT0215	Nicole	Guiana Space Center (Kourou, French Guiana)	Ariane 5
	FOC FM16	GSAT0216	Zofia
	FOC FM17	GSAT0217	Alexandre
	FOC FM18	GSAT0218	Irina
L10 2018-07-25 11:25	FOC FM19	GSAT0219	Tara	Guiana Space Center (Kourou, French Guiana)	Ariane 5
	FOC FM20	GSAT0220	Samuel
	FOC FM21	GSAT0221	Anna
	FOC FM22	GSAT0222	Ellen
L11 2021-12-05 00:19	FOC FM23	GSAT0223	Nikolina	Guiana Space Center (Kourou, French Guiana)	Soyuz /Fregat
	FOC FM24	GSAT0224	Shriya
L12 2024-04-28 00:34	FOC FM25	GSAT0225		Kennedy Space Center (Florida, USA)	Falcon 9
	FOC FM27	GSAT0227
L13 2024-09-17 22:50	FOC FM26	GSAT0226		Kennedy Space Center (Florida, USA)	Falcon 9
	FOC FM32	GSAT0232

¹ The satellite nickname corresponds with the name of the child who was the winner of the “Galileo Children's Drawing Competition” on each European Member State.