satellite communications and the environment of...

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


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)


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


Geostationary trajectories and footprint


Geostationary trajectories and

footprintmit with three satellites


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.


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:


Cassegrain Antenne

Link Budget,

numerical example

of a commercial satellite


Let's calculate a link Budget

of "our" satellite AO-73


"Ideal" Downlink Budget


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


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


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


System structure: SEGMENTS

Space segment

Ground segment, Ground Station

Control segment

User segment


Space-/Ground-/User Segment


We focus on the

Ground Segment (GS)


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


Source: Surrey Space Technology Limited (SSTL)

@Bletchley Park

Awaiting next pass in Horw


Mission tracking @HSLU


Your project's radio receiver front-end


Inside your project's radio receiver front-end


Converts a radio signal from the antenna to baseband,

i. e. makes it processible (easy to handle) by software.


Inside your project's radio receiver front-end,

much more detailed

Software Defined Radio (SDR) Software


Source: GeraldYoungblood, AC5OG, K5SDR

All signal processing is done in software.

this is how a SDR looks like


Satellite Tracking Software:

example: ISS real time tracking


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


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

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Block diagram

of a simple ground station

satellite communications and the environment of...

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