Basic concepts of space missions
This chapter introduces the basic concepts of space missions and provides the foundational knowledge required for the following sections. Readers who already have experience or familiarity with space systems and mission architecture may choose to skip this chapter.
Space System Model
We will begin by introducing the concept of the Space System Model, defined by the ECSS as a way of representing a space system by decomposing it into elements and the activities associated with them. This concept aims to simplify the understanding of complex space systems by breaking them down into smaller and simpler subsystems. An analogy would be zooming in to observe and understand the individual parts of a larger system.1
The Space System Model is based on functional decomposition, where each category represents a group of physical elements within the mission architecture. A Space System is the highest level of organization in a space mission, encompassing all major elements required to achieve the mission objectives.
Space System
├─ Space Segment
│ ├─ Space Segment System
│ │ ├─ Space Segment Subsystem
│ │ │ ├─ Components/parts
├─ Ground Segment
│ ├─ Ground Segment System
│ │ ├─ Ground Segment Subsystem
│ │ │ ├─ Components/parts
├─ Launch Segment
│ ├─ ...
├─ Support Segment
│ ├─ ...
Example: The Apollo mission
Space System: Apollo Program
├─ Space Segment Spacecraft
│ ├─ Space Segment System: Lander Module, Command Module
│ │ ├─ Space Segment Subsystem: Data Handling
│ │ │ ├─ Components/parts: On-board Computer
│ │ │ | ├─ Sub-components: Processor
├─ Ground Segment
│ ├─ Ground Segment System: Operations Center
│ │ ├─ Ground Segment Subsystem: Telecommunications
│ │ │ ├─ Components/parts Antenna
Ground Segment
The Ground Segment (GS) reefers the the part of a space mission located on Earth that is responsible for communicating with, controlling, and supporting the spacecraft. It is
composed by the Ground Station infrastructure, including operation center buildings,
radio systems, antennas, processing units, software, etc.
The Space Segment must be within line of sight to establish communication with the Ground Segment. During this portion of the orbit, contact is established and the communication link is maintained.
Space Segment
The Space Segment is the part of a space mission that operates in space. It includes the spacecraft (such as satellites, rovers, probes, rockets), along with all onboard systems, instruments, and software required to perform the mission and communicate with Earth.
Note that the Space Segment can be compose oif several spacecrafts,
Spacecraft Bus
The term bus in the context of spacecrafts, refers to the basic structure of
the satellite and its subsystems, which house and support the payload.
The bus is composed by:
- Mechanical structure
- Electrical Power Subsystem (EPS)
- Communications Subsystem (COMS)
- Thermal Control Subsystem
- Attitude and Orientation Control (AOCS)
- Command and Data Handling (CDHS)
Note that the bus does not include the payload, his goal is to host and support the payload.
Payload
Space missions are developed to achieve specific objectives, such as taking images of the Earth or stars, measuring the characteristics of planets, or providing communication services. These objectives are accomplished through specialized instruments or technologies known as the payload.
This Payload is the primary reason for the mission and the satellite's existence.
Examples of payloads include radars, cameras, telescopes, and telecommunications equipment.
-
European Cooperation for Space Standardization. Space Engineering: Test and Operations Procedure Language. Technical Standard ECSS-E-ST-70-32C, European Cooperation for Space Standardization (ECSS), 2008. URL: https://ecss.nl/standard/ecss-e-st-70-32c-test-and-operations-procedure-language/. ↩