Orbital and Technical Parameters

Reference Constellation Orbital and Technical Parameters 1

Satellite SV ID Slot Semi-Major Axis (Km) Eccentricity Inclination (deg) RAAN (deg)2 Arg. Perigee (deg)2 Mean Anomaly (deg)2,3
Nominal Slots
GSAT0101 E11 B05 29599.8 0.0 56.0 77.632 0.0 15.153
GSAT0102 E12 B06 29599.8 0.0 56.0 77.632 0.0 60.153
GSAT0103 E19 C04 29599.8 0.0 56.0 197.632 0.0 345.153
GSAT0104 E20 C05 29599.8 0.0 56.0 197.632 0.0 30.153
GSAT0203 E26 B08 29599.8 0.0 56.0 77.632 0.0 150.153
GSAT0204 E22 B03 29599.8 0.0 56.0 77.632 0.0 285.153
GSAT0205 E24 A08 29599.8 0.0 56.0 317.632 0.0 135.153
GSAT0206 E30 A05 29599.8 0.0 56.0 317.632 0.0 0.153
GSAT0208 E08 C07 29599.8 0.0 56.0 197.632 0.0 120.153
GSAT0209 E09 C02 29599.8 0.0 56.0 197.632 0.0 255.153
GSAT0210 E01 A02 29599.8 0.0 56.0 317.632 0.0 225.153
GSAT0211 E02 A06 29599.8 0.0 56.0 317.632 0.0 45.153
GSAT0207 E07 C06 29599.8 0.0 56.0 197.632 0.0 75.153
GSAT0212 E03 C08 29599.8 0.0 56.0 197.632 0.0 165.153
GSAT0213 E04 C03 29599.8 0.0 56.0 197.632 0.0 300.153
GSAT0214 E05 C01 29599.8 0.0 56.0 197.632 0.0 210.153
GSAT0215 E21 A03 29599.8 0.0 56.0 317.632 0.0 270.153
GSAT0216 E25 A07 29599.8 0.0 56.0 317.632 0.0 90.153
GSAT0217 E27 A04 29599.8 0.0 56.0 317.632 0.0 315.153
GSAT0218 E31 A01 29599.8 0.0 56.0 317.632 0.0 180.153
GSAT0219 E36 B04 29599.8 0.0 56.0 77.632 0.0 330.153
GSAT0220 E13 B01 29599.8 0.0 56.0 77.632 0.0 195.153
GSAT0221 E15 B02 29599.8 0.0 56.0 77.632 0.0 105.153
GSAT0222 E33 B07 29599.8 0.0 56.0 77.632 0.0 240.153
Extended Slots
GSAT0201 18 Ext01 27977.6 0.162 49.850 52.521 56.198 316.069
GSAT0202 14 Ext02 27977.6 0.162 49.850 52.521 56.198 136.069

1: Reference date for the constellation is 2016-11-21 00:00:00 UTC4. 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 2. 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 slots Extended slots
d(RAAN)/dt -0.02764398 deg/day -0.03986760 deg/day
d(Arg. peri)/dt 0.00000000 deg/day 0.03383184 deg/day
d(Mean Anomaly)/dt 613.72253566 deg/day 667.86467481 deg/day
 
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 spares, 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.

As observed in the graph below, in each orbital plane, each satellite is separated with an angular distance of 45 degrees. The relative phase shift factor between satellites in adjacent planes is 1, leading to an offset of 15 degrees between satellites in adjacent planes.
 

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

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.