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Satellite communications
and the environment of space
Images: NASAV 1.1 Swiss Space Summer Camp 2016 1
Can you name these satellites ?
Sputnik
The Hubble Space Telescope The International Space Station
• The first man made satellite
• Launched in 1957 by The USSR
• Mass 84kg, diameter 53cm
Now there are hundreds of satellites in orbit around the Earth
while others are exploring the solar system.
You need an earth station …..
Source:
google/flickr/GoonhillyV 1.1 Swiss Space Summer Camp 2016 5
Satellite basics for building a
simple ground station
Swiss Space Summer Camp
2016
Contents
Satellite basics
Ground segment
Ground station
Hardware
Software
Project
Swiss Space Summer Camp 2016 7V 1.1
Satellites
Swiss Space Summer Camp 2016 8V 1.1
Erdfunkstelle Raisting
GPS Navstar
Range of applications for satellites
Earth observation satellites
meteorologic (weather) satellite
spy satellite
radar satellite
Communication satellites
for commercial purposes
e. g. Inmarsat, Iridium, Thuraia
mil-com satellites
for experimental tasks:
amateur radio satellites
Television satellites
Astra
Eutelsat
Astronomy satellites for scientific
purposes
Killer satellites to destroy hostile
satellites
Debris removal satellites
Research satellites, e. g. for
experiments in micro-gravity
Space Platforms for scientific
purposes
Navigation satellites (GNSS)
GPS (USA, seit 1995)
Glonass (Russland, seit 1993)
Galileo (EU, ab 2014)
Swiss Space Summer Camp 2016 9V 1.1
Different trajectories of satellites
Geostationary Earth Orbiter (GEO)
distance from earth: 36‘000 km
orbit directly above the Earth's equator
transmitter and receiver antennas can be permanently targeted.
Medium Earth Orbiter (MEO)
rotating around the earth
flying altitude between 10‘000 km and 15‘000 km.
Low Earth Orbiter (LEO)
rotating around the earth
flying altitude between 700 km und 1‘500 km
Swiss Space Summer Camp 2016 10V 1.1
Geostationary trajectories and footprint
Swiss Space Summer Camp 2016 11V 1.1
Geostationary trajectories and
footprintmit with three satellites
Swiss Space Summer Camp 2016 12V 1.1
Calculation of satellite trajectories
The three Kepler's laws of planetary
motion describe the movement of
satellites:
The orbit of a planet is an ellipse
with the host star at one of the
two foci.
A line segment joining a satellite
and the host star sweeps out
equal areas during equal
intervals of time.
The square of the orbital period
of a satellite is proportional to
the cube of the semi-major axis
of its orbit.
Swiss Space Summer Camp 2016 13V 1.1
Link Budget
Signal power is critical.
Satellites dispose of low power
Distances between space segment and
ground segment are very long.
(e. g. mobile phone <-> satellite)
Antennas are susceptible to failure
The Signal-to-Noise Ratio (SNR) has to
be big enough
The calculation of the SNR of the
complete round trip connection
(uplink/downlink) is called Link Budget:
Swiss Space Summer Camp 2016 14V 1.1
Cassegrain Antenne
Link Budget,
numerical example
of a commercial satellite
Swiss Space Summer Camp 2016 15V 1.1
Let's calculate a link Budget
of "our" satellite AO-73
Swiss Space Summer Camp 2016 16V 1.1
"Ideal" Downlink Budget
Swiss Space Summer Camp 2016 17V 1.1
Downlink Budget Analysis , f = 437 MHz, data rate = 9600 bps
Transmit Power PTx +30 dBm
Connector-, Cable- and Impedance-Loss (Lcon , Lcab , Limp) -2.0 dB
Antenna Gain GTx (ideal Monopole) +5.1 dBi
Friis Formula (RS = 1815 km, hOrbit = 550 km, δ = 10°) -150.4 dB
Atmospheric & Ionospheric Losses (Latm , Lion) [1] -0.2 dB
Antenna Gain GRx +24 dBi
Polarisation Loss (Lpol) -3 dB
Connector-, Cable- and Impedance-Loss (Lcon , Lcab , Limp) -5.0 dB
Power at Receiver PRx -101.5 dBm
Receiver Sensitivity (TS2000, S/N=16 dB) [2] -120.2 dBm
Link Margin +18.7 dB
Missing items in an "ideal" link budget
Swiss Space Summer Camp 2016 18V 1.1
a) UHF monopole antenna on a 1U
CubeSat is never ideal
b) Dynamic and static antenna
pointing errors (serious problem
for high gain GS antennas)
c) Signal fading due to multipath
(Atmosphere, Ionosphere,
Terrain Reflection and
Diffraction)
Channel Coding necessary
Even more error sources:
Offset between electrical and
mechanical antenna axis
Thermal deformation and wind
force disturbance
Gravity deformation
Gear backlash
Atmospheric refraction
Therefore Channel Coding:
moderate channel quality (Pb
approx. 10-4)
Link is available for 2 times of 10
minutes per day
Payload (PL) produces large
volume of compressed data
Signal fading due to scintillation,
especially by low elevation
angels
Swiss Space Summer Camp 2016 19V 1.1
Glossary
Zenith: point directly "above" a particular location
Nadir: point directly below a particular location
Apogee: point farthest away from the Earth
Perigee: point nearest to the earth
AOS Acquisition of Signal
TCA: Time of Closest Approach
LOS: Loss of Signal
Azimuth: the angle of horizontal deviation (from north) source: AMSAT
Elevation: the angle of vertical deviation (from horizon)
UTC: Coordinated Universal Time
Doppler: An increase (decrease) in the frequency waves as the
source and observer move towards (away from) each
other.
Uplink/Downlink: transmission from earth to space and vice versa
Swiss Space Summer Camp 2016 20V 1.1
System structure: SEGMENTS
Space segment
Ground segment, Ground Station
Control segment
User segment
Swiss Space Summer Camp 2016 21V 1.1
Space-/Ground-/User Segment
Swiss Space Summer Camp 2016 22V 1.1
We focus on the
Ground Segment (GS)
Swiss Space Summer Camp 2016 23V 1.1
Source: Surrey Space Technology Limited (SSTL)
Use a Software Defined Radio (SDR) and a
SW telemetry decoder
Build a simple omni-directional antenna
Use a Software Defined Radio (SDR) Front-End
GS impressions
Swiss Space Summer Camp 2016 24V 1.1
Source: Surrey Space Technology Limited (SSTL)
@Bletchley Park
Awaiting next pass in Horw
Swiss Space Summer Camp 2016 25V 1.1
Mission tracking @HSLU
Swiss Space Summer Camp 2016 26V 1.1
Your project's radio receiver front-end
Swiss Space Summer Camp 2016 27V 1.1
Inside your project's radio receiver front-end
Swiss Space Summer Camp 2016 28V 1.1
Converts a radio signal from the antenna to baseband,
i. e. makes it processible (easy to handle) by software.
Swiss Space Summer Camp 2016 29V 1.1
Inside your project's radio receiver front-end,
much more detailed
Software Defined Radio (SDR) Software
Swiss Space Summer Camp 2016 31V 1.1
Source: GeraldYoungblood, AC5OG, K5SDR
All signal processing is done in software.
this is how a SDR looks like
Swiss Space Summer Camp 2016 32V 1.1
Satellite Tracking Software:
example: ISS real time tracking
Swiss Space Summer Camp 2016 33V 1.1
Ground track. The orbit data is extracted from the following two-line orbital elements
1 25544U 98067A 16244.94384549 .00002647 00000-0 46831-4 0 9998
2 25544 51.6449 40.0209 0002636 269.9580 224.1034 15.54358481 16773
Epoch (UTC): 31 August 2016 22:39:08
Eccentricity: 0.0002636
inclination: 51.6449°
perigee height: 402 km
apogee height: 406 km
right ascension of ascending node: 40.0209°
argument of perigee: 269.9580°
revolutions per day: 15.54358481
mean anomaly at epoch: 224.1034°
orbit number at epoch: 1677
http://www.heavens-above.com/
Practical example:
ISS real time tracking
Swiss Space Summer Camp 2016 34V 1.1
Ground track. The orbit data is extracted from the following two-line orbital elements
1 25544U 98067A 16244.94384549 .00002647 00000-0 46831-4 0 9998
2 25544 51.6449 40.0209 0002636 269.9580 224.1034 15.54358481 16773
Epoch (UTC): 31 August 2016 22:39:08 Time of snapshot of orbital Elements
Eccentricity e: 0.0002636 Shape of the ellipsis (e = 0 for a circle)
Inclination i: 51.6449° Angle between planes of equator and ellipsis
Perigee height: 402 km Distance from closest point to earth
Apogee height: 406 km Distance from farthest point to earth
Right Ascension of ascending node: 40.0209° Point, where the satellite crosses the equator
from south to north. Defines together with
inclination i the orbital plane
Argument of perigee: 269.9580° Angle of the point closest to earth
Revolutions per day: 15.54358481 i. e. 92.64 minutes for one revolution
Mean anomaly at epoch: 224.1034°
Orbit number at epoch: 1677 Total number of revolutions up till now
Drag Not appropriate (Why?)
Swiss Space Summer Camp 2016 35V 1.1
Block diagram
of a simple ground station