# Welcome

The aerospace sector currently lacks adequate security awareness, particularly concerning satellites and their communications. This website aims to bridge this gap by providing a comprehensive and freely accessible reference for testing and researching satellite security. 

This website provides access to both beginner and advanced topics in this field, aiming to spark collaboration among experts and enthusiasts to improve the general understanding of security in this space.

## Why?

Satellites are susceptible to cyber attacks just like any other computer-based system. Given their critical role in communication, navigation, weather monitoring, and other essential functions, any compromise in their security could have severe consequences.


# Satellites

First of all we need to understand what a satellite is? A satellite is an object which orbits a larger object in space. The term can refer to two different types of satellites, natural and artificial.

### Natural Satellites

Natural satellites are objects which naturally orbit a planet or star. An example of a natural satellite includes the moon orbiting the Earth. 

### Artificial Satellites

Artificial satellites are man-made objects that orbit a planet or star. An example of an artifical satellite includes the International Space Station orbiting Earth.

## Satellite Uses

Whether you realise it or not satellites are used constantly in our day-to-day lives. Some common use cases of satellites can be seen outlined below:

#### Navigation

Satellites are often used for navigation. One common exmaple of this is GPS - The Global Positioning System (GPS) utilises a constellation of satellites to calculate the position of client devies. 


# Further Resources

{% embed url="<http://hackasat.com>" %}

{% embed url="<https://www.amazon.co.uk/Cybersecurity-Space-Guide-Foundations-Challenges-dp-B0CXSM9FHW/dp/B0CXSM9FHW/ref=dp_ob_title_bk>" %}

{% embed url="<https://www.amazon.co.uk/Space-Mission-Engineering-New-Smad/dp/1881883159>" %}

{% embed url="<https://public.ccsds.org/default.aspx>" %}

{% embed url="<https://tools.g4lxy.space>" %}

{% embed url="<https://www.nasa.gov>" %}


# Apsides

Apsides refer to the two extreme points in the orbit of a celestial body around another body. These points represent the closest and farthest distances the orbiting object can attain from the central body. Apsides play a crucial role in comprehending the shape and dynamics of orbits.

Each apsis for an object orbiting the Earth is named “apogee” for the farthest point and “perigee” for the closest point.

<figure><img src="/files/xSYugnSlKPHMJX6SQd6b" alt=""><figcaption></figcaption></figure>


# Horizontal Coordinate System

The horizontal coordinate system is a celestial coordinate system that uses the observer's local horizon as the fundamental plane to define two angles, azimuth (az) and altitude (alt).

This system divides the sky into two hemispheres: The upper hemisphere and the lower hemisphere. The pole of the upper hemisphere is called the zenith. The pole of the lower hemisphere is called the nadir.

<figure><img src="/files/hJyrtP8Qi9kSMXM3clnk" alt="" width="375"><figcaption></figcaption></figure>

Azimuth and altitude/elevation can be useful to track satellites through space. An antenna could use these measurements to follow a satellite and constantly receive data.&#x20;

## Azimuth (az.)

The angle between North, measured **clockwise** around the observer's horizon, and a celestial body (e.g. moon, star).

## Altitude (alt.)

The angle between the object and the observer's local horizon. Also known as **elevation** (el.)

## Celestial Horizon

The great circle separating the upper and lower hemispheres of the celestial sphere. The plane is normal to the local gravity vector.


# Keplerian (Orbital) Elements

Orbital elements are the parameters required to uniquely identify a specific orbit and the position of a body along the orbit at a specific time (epoch).&#x20;

<figure><img src="/files/AscMiCKjmladVNxulHRS" alt="" width="290"><figcaption></figcaption></figure>

Keplerian elements are the six traditional orbital elements, as described below.

## Eccentricity

The eccentricity of an orbit defines the shape of the ellipse, describing how much it is elongated compared to a circle. An eccentricity of 0 means the orbit is a perfect circle.

## Semi-Major Axis

The sum of the periapsis and apoapsis distances divided by two. For classic two-body orbits, the semi-major axis is the distance between the centers of the bodies, not the distance of the bodies from the center of mass.

## Inclination

The inclination is the vertical tilt of the ellipse with respect to the reference plane, measured at the ascending node (a point where the orbit intersects the plane of reference) in degrees.

## Longitude of The Ascending Node

Horizontally orients the ascending node of the ellipse (a point where the orbit intersects the plane of reference) with respect to the reference direction.

## Argument of Periapsis

Defines the orientation of the ellipse in the orbital plane, as an angle measured from the ascending node to the periapsis (the closest point the satellite object comes to the primary object around which it orbits).

## True Anomaly

The true anomaly defines the position of the orbiting body along the ellipse at a specific time (the "epoch").

## Further Reading

{% embed url="<https://en.wikipedia.org/wiki/Orbital_elements>" %}


# Obit Types


# Geostationary (GEO)

Geostationary satellites are a type of satellite that orbits the Earth at the same rotational speed as the Earth's rotation, allowing them to remain fixed relative to a specific location on the planet's surface. These satellites are positioned at an altitude of approximately 35,786 kilometres (22,236 miles) above the Earth's equator, providing valuable communication, broadcasting, and weather monitoring services.

## Characteristics and Advantages

Geostationary satellites have several key characteristics and advantages:

1. **Fixed Position**: Geostationary satellites maintain a fixed position relative to the Earth's surface. This characteristic makes them ideal for applications that require continuous coverage of a specific area, such as broadcasting, telecommunications, and weather monitoring.
2. **Global Coverage**: Due to their high altitude and fixed position, geostationary satellites can provide coverage over a large portion of the Earth's surface. This global coverage enables them to serve as a backbone for international communication networks and support services that require worldwide connectivity.
3. **Persistent Observation**: The fixed position of geostationary satellites allows them to continuously observe a specific region of the Earth, making them valuable for weather monitoring and Earth observation purposes. These satellites can capture images and collect data over extended periods, enabling scientists and meteorologists to track weather patterns, monitor climate changes, and study natural phenomena.
4. **Communication Services**: Geostationary satellites play a crucial role in global telecommunications and broadcasting. They facilitate long-distance communication, including telephone calls, internet connectivity, television broadcasting, and satellite radio. These satellites enable reliable and widespread communication, connecting people and facilitating the exchange of information across the globe.
5. **Navigation and GPS**: Some geostationary satellites are used for navigation and global positioning system (GPS) services. These satellites provide accurate positioning information that is utilised in various applications, including aviation, maritime navigation, and location-based services on mobile devices.

## How?

Geostationary satellites operate by following the Earth's rotation and remaining fixed relative to a specific point on the Earth's surface. They are placed in a geostationary orbit, which is a circular orbit above the equator with an inclination of zero degrees.

The orbital period of a geo-stationary satellite matches the Earth's rotational period, approximately 24 hours. To achieve this, the satellite is positioned at an altitude where its orbital speed matches the Earth's rotational speed, resulting in the satellite remaining stationary relative to the Earth's surface.

Communication with geostationary satellites is established through ground-based antennas, known as earth stations. These earth stations transmit signals to the satellites, which receive and retransmit the signals back to Earth. This communication process allows for two-way communication and enables the delivery of various services, including voice, data, and multimedia transmissions.

## Applications of Geostationary Satellites

Geostationary satellites have a wide range of applications, including:

1. **Telecommunications**: Geostationary satellites serve as critical infrastructure for global telecommunications networks. They enable long-distance communication, connecting people across continents through telephone calls, internet services, and video conferencing.
2. **Broadcasting**: Television and radio broadcasting heavily rely on geostationary satellites for signal distribution. These satellites facilitate the transmission of television programs, radio broadcasts, and multimedia content to a widespread audience.
3. **Weather Monitoring**: Geostationary satellites play a vital role in weather monitoring and forecasting. By capturing images and collecting data of the Earth's atmosphere, these satellites enable meteorologists to track weather patterns, monitor storms, and predict weather conditions with greater accuracy.
4. **Earth Observation**: The fixed position of geostationary satellites allows for continuous monitoring of the Earth's surface. This capability is valuable for observing environmental changes, tracking natural disasters, and studying the Earth's climate.
5. **Navigation and GPS**: Certain geostationary satellites contribute to global navigation and GPS services. They provide precise positioning and timing information that is utilised in navigation systems, aviation, maritime applications, and location-based services.


# Low Earth (LEO)


# Sun-Synchronous (SSO)


# Satellite Identification & Tracking

{% embed url="<https://www.n2yo.com>" %}


# Satellite Telemetry


# Two-Line Element Sets (TLE)

A two-line element set (TLE/2LE) or three-line element set (3LE) are lists of [Keplerian (Orbital) Elements](/aerospace-fundamentals/keplerian-orbital-elements) for satellites orbiting the earth at a given point in time, the epoch.

The TLE, alongside a suitable prediction formula, can be utilised to calculate the position and velocity of a satellite at any point in the past or future.

## Format

Take the following two-line element set for the International Space Station (ISS):

```
ISS (ZARYA)
1 25544U 98067A   08264.51782528 -.00002182  00000-0 -11606-4 0  2927
2 25544  51.6416 247.4627 0006703 130.5360 325.0288 15.72125391563537
```

Considering the above example, the TLE can be broken down line-by-line. First, an optional title line is present, in our instance `ISS (ZARYA)`. Following this, the first line can be broken down as follows:

<table><thead><tr><th width="124">Column</th><th width="477">Description</th><th>Example Value</th></tr></thead><tbody><tr><td>01</td><td>Line number</td><td>1</td></tr><tr><td>03-07</td><td>Satellite number</td><td>25544</td></tr><tr><td>08</td><td>Classification (U=Unclassified, C=Classified, S=Secret)</td><td>U</td></tr><tr><td>10-11</td><td>International designator (Last two digits of launch year)</td><td>98</td></tr><tr><td>12-14</td><td>International designator (Launch number of the year)</td><td>067</td></tr><tr><td>15-17</td><td>International designator (Piece of the launch)</td><td>A</td></tr><tr><td>19-20</td><td>Epoch year (last two digits of year)</td><td>08</td></tr><tr><td>21-32</td><td>Epoch (Day of the year and fractional portion of the day)</td><td>264.51782528</td></tr><tr><td>34-43</td><td>First time derivative of the mean motion</td><td>-.00002182</td></tr><tr><td>45-52</td><td>Second time derivative of the mean motion</td><td>00000-0</td></tr><tr><td>54-61</td><td>BSTAR drag term</td><td>-11606-4</td></tr><tr><td>63</td><td>Ephemeris type</td><td>0</td></tr><tr><td>65-68</td><td>Element number</td><td>292</td></tr><tr><td>69</td><td>Checksum</td><td>7</td></tr></tbody></table>

Finally, the second line can be broken down to the following:

<table><thead><tr><th width="124">Column</th><th width="477">Description</th><th>Example Value</th></tr></thead><tbody><tr><td>01</td><td>Line number</td><td>2</td></tr><tr><td>03-07</td><td>Satellite number</td><td>25544</td></tr><tr><td>09-16</td><td>Inclination (Degrees)</td><td>51.6416</td></tr><tr><td>18-25</td><td>Right ascension of the ascending node (Degrees)</td><td>247.4627</td></tr><tr><td>27-33</td><td>Eccentricity</td><td>0006703</td></tr><tr><td>35-42</td><td>Argument of perigee (Degrees)</td><td>130.5360</td></tr><tr><td>44-51</td><td>Mean anomaly (Degrees)</td><td>325.0288</td></tr><tr><td>53-63</td><td>Mean motion (Revolutions per day)</td><td>15.72125391</td></tr><tr><td>64-68</td><td>Revolution number at epoch</td><td>56353</td></tr><tr><td>69</td><td>Checksum</td><td>7</td></tr></tbody></table>

## TLE Datasets

There are several websites which provide two-line element set data for free, updated daily.

* <https://www.space-track.org/>
* <https://celestrak.org/>

## Further Reading

{% embed url="<https://en.wikipedia.org/wiki/Two-line_element_set>" %}

{% embed url="<https://celestrak.org/NORAD/documentation/tle-fmt.php>" %}


# Orbit Mean-Elements Message (OMM)


# Orbital Predictions

Utilising information and telemetry data transmitted from satellites, in conjunction with mathematical models, it is possible to make reasonable estimates as to where a satellite may be positioned and its movement.&#x20;

This is used for a wide range of applications such as satellite-based image mapping, navigation systems, and satellite tracking systems.

## Visual Passes

A visual pass occurs when a satellite becomes visible to an observer on the ground as it traverses the sky. This happens when the satellite reflects sunlight while it passes overhead, usually during dawn or dusk when the sky is dark enough for the satellite to be visible, yet it is still illuminated by the Sun.

## Radio Passes

A radio pass refers to the specific time frame when a satellite is within the range of a ground station’s radio antenna, facilitating radio communication between the two entities. During this period, the satellite remains above the local horizon and is directly visible to the ground station, allowing for the transmission and reception of radio signals.<br>

## Simplified General Perturbations 4 (SGP4)

SGP4, a mathematical algorithm, calculates the state of an Earth-tracking satellite using its Time and Epoch Leap Second (TLE) sets. It accounts for various perturbations, such as gravitational fields from nearby celestial bodies, atmospheric drag, and the Earth’s oblateness, to predict the orbits of artificial satellites launched into space.

#### References

<https://systemweakness.com/satellite-osint-space-based-intelligence-in-cybersecurity-e87f9dca4d81>


# Space System

<figure><img src="/files/EvFciB48RK4QJTNeX6Iy" alt=""><figcaption></figcaption></figure>


# Satellite Subsystems

Given the complexity of a satellite, they are often split of multiple specialised subsystems. Each individual subsystem is designed to perform a specific set of functions that contribute to the overall mission of a satellite.&#x20;

## Attitude Determination & Orbit Control System (AOCS)

The attitude determination and orbit control system, or AOCS, is responsible for controlling the satellite's orientation (attitude) and orbit. Star trackers, gyroscopes, and magnetometers are used as sensors to determine the satellite's current attitudem while actuators like reaction wheels, gyroscopes, and magnetic torques are used to change it.&#x20;

## Payload

The payload subsystem houses mission-specific instuments and equiptment. For example, in Earth observation satellites, the payload might consist of high-resoultion cameras, spectrometers, and radar. In communication satellites, the payload usually consists of transponders that relay signals between ground stations.

## Command & Data Handling System (CDHS)

The command and data handling system, or CDHS, is the "control center" of the satellite. It includes a centeral computer, data storage devices, and a command decoder. This subsystem is able to interpret and execute commands received from ground control, manage task scheduling, and oversee data collection and storage.&#x20;

## Communications (COM)

The communications subsystem serves as the primary interface between the satellite and ground control (and sometimes other satellites). This system contains equipment such as antennas for transmission and reception, transmitters to send data to Earth, and receivers to collect incoming data from ground control. Signal processing units handle the modulation and demodulation of data, as well as the encoding and decoding of data.&#x20;

More advanced communication subsystems may employ adaptive modulation techniques, beamforming, and onboard data processing to improve reliability and data throughput.

## Telemetry Subsystem

The telemetry subsystem is crucial for monitoring the health and performace of the satellite. It collects data from sensors embedded in other subsystems and transmits this information back to ground control.

#### References

[https://newspaceeconomy.ca/2023/10/23/what-are-the-subsystems-of-a-satellite/](https://newspaceeconomy.ca/2023/10/23/what-are-the-subsystems-of-a-satellite/#:~:text=The%20payload%20subsystem%20houses%20the,relay%20signals%20between%20ground%20stations.)


# Communication Protocols


# Frequency Bands & EM Waves


# Intercepting Satellite Signals


# Uplink & Downlink


# Frameworks

* Mitre ATT\&CK
* SPARTA
* TREKS
* SpaceShield


# Spacecrafts


# Anti-Satellite Weapons


# Space Debris


# Software Vulnerabilities


# Denial of Service


# Communication Links


# Uplink/Downlink Jamming


# Replay Attacks


# Encryption


# Spoofing Attacks


# Ground Stations


# Network Attacks


# Physical Attacks


# Signal Jamming


# Pyephem


# Skyfield


# Examples

###


# Azimuth and Altitude

The following example uses the Skyfield library in python to calculate the azimuth and altitude of Mars above Boston (US) on the 1st March 1980.

```python
from skyfield.api import N,S,E,W, wgs84

# Altitude and azimuth in the sky of a specific geographic location

boston = earth + wgs84.latlon(42.3583 * N, 71.0603 * W, elevation_m=43)
astro = boston.at(ts.utc(1980, 3, 1)).observe(mars)
app = astro.apparent()

alt, az, distance = app.altaz()
print(alt.dstr())
print(az.dstr())
print(distance)

# OUTPUT
# 24deg 30' 27.2"
# 93deg 04' 29.5"
# 0.678874 au
```