System requirements in spacecraft systems are the specific system requirements

System requirements

To be used efficiently, all computer software needs certain hardware components or other software resources to be present on a computer. These pre-requisites are known as system requirements and are often used as a guideline as opposed to an absolute rule. Most software defines two sets of system...

 needed to design and operate a spacecraft

Spacecraft

A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

 or a spacecraft subsystem.

Overview

Spacecraft systems are normally developed under the responsibility of space agencies as NASA

NASA

The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

, ESA etc. In the space area standardized terms and processes have been introduced to allow for unambiguous communication between all partners and efficient usage of all documents. For instance the life cycle

Systems Development Life Cycle

The systems development life cycle , or software development life cycle in systems engineering, information systems and software engineering, is a process of creating or altering information systems, and the models and methodologies that people use to develop these systems.In software engineering...

 of space systems is divided in phases:

• Phase A: Feasibility Study
• Phase B: Requirements Definition
• Phase C/D: Design / Manufacturing / Verification
• Phase E: Operational usage.

At the end of phase B the system requirements together with a statement of work

Statement of work

A statement of work is a formal document that captures and defines the work activities, deliverables and timeline a vendor will execute against in performance of specified work for a client...

 are sent out requesting proposals from industry.

Technical systems requirement

The tomer technical system requirements documented in the System Specification stay on mission level:

• System functions and performances
• Orbit
• Launch vehicle
• etc.

whereas the non-technical system (task) requirements

• Cost and progress reporting
• Documentation maintenance
• etc.

are contained in the statement of work.

The customer (requirements) specification is answered by the contractor by a design-to specification.

For example the requirement "Columbus shall be launched by the Space Shuttle." is detailed in the contractor system specification "Columbus shall be a cylindrical pressurized module with max. length of 6.9 meters and 4.5 meters diameter as agreed in the Shuttle/Columbus ICD."

Operations environment

The spacecraft's systems specification, according to David Michael Harland (2005), usually also defines the operation environment of the spacecraft. It mostly is defined "as a model - often provide by the scientific community from available data - in the form of a set of curves, numerical tables, or software, usually with a nominal expectation and the minimal and maximum profiles which the environment is not expected to exceed".

System specification structure

A typical industry generated system specification

Specification (technical standard)

A specification is an explicit set of requirements to be satisfied by a material, product, or service. Should a material, product or service fail to meet one or more of the applicable specifications, it may be referred to as being out of specification;the abbreviation OOS may also be used...

 for a spacecraft has the following structure:

• Document change record
• 1. Scope
  • 1.1 Purpose
  • 1.2 Summary description
  • 1.3 Classification
  • 1.4 Applicability
• 2. Related documents
  • 2.1 Applicable documents (incl. order of precedence)
  • 2.2 Reference documents
• 3. Functional /Performance Requirements
• 4. Support requirements
  • 4.1 Product assurance
  • 4.2 Electro-magnetic compatibility
  • 4.3 Contamination
  • 4.4 etc.
• 5. Interface requirements
  • 5.1 System interfaces
    • 5.1.1 Launcher
    • 5.1.2 Ground stations
    • 5.1.3 etc.
  • 5.2 Subsystem interfaces
    • 5.2.1 Electrical power
    • 5.2.2 Data
    • 5.2.3 etc.
• 6. Implementation requirements
  • 6.1 Configuration
  • 6.2 Budget Allocations
    • 6.2.1 Mass
    • 6.2.2 Electrical power
    • 6.2.3 etc.
• 7. Preparation for delivery
• Attachments (Abbreviation list etc.)

Each requirement paragraph consists of the requirement to be fulfilled by the product to be delivered and the verification requirement (Review of design, analysis, test, inspection).

Specification tree

The spacecraft system specification defines also the subsystems of the spacecraft e.g.:

• Structure
• Data management subsystem incl. software
• Electrical Power
• etc.

For each subsystem a subsystem specification is prepared by the Prime Contractor with the same specification structure shown above including references to the parent paragraph in the system specification. In the same way the subsystem contractor prepares an assembly or unit specification. All these specifications are listed in a so-called specification tree

Specification tree

A specification tree shows all specifications of a technical system under development in a hierarchical order.For a spacecraft system it has the following levels:* System specification - generated by customer...

 showing all specifications and their linkage as well as the issue / date of each specification.

Literature

• 2005, David Michael Harland, Ralph Lorenz, Space Systems Failures: Disasters and Rescues of Satellites, Rockets, Springer, p. 178.
• 2003, Peter W. Fortescue, Graham Swinerd, Spacecraft Systems Engineering, John Wiley and Sons, 704 pp.
• 2001, DoD - Systems Management College, Systems Engineering Fundamentals. Defense Acquisition University Press, January 2001.
• Columbus System Specification (COL-ESA-RQ-001, iss.4/B, 15.01.2004)
• Columbus Design Spec (COL-RIBRE-SPE-0028, iss.10/F, 25.06.2004)

See also

• Requirements
• Requirements analysis
  Requirements analysis
  Requirements analysis in systems engineering and software engineering, encompasses those tasks that go into determining the needs or conditions to meet for a new or altered product, taking account of the possibly conflicting requirements of the various stakeholders, such as beneficiaries or users...
  
  
• Requirements engineering
  Requirements engineering
  Requirements engineering is a systems and software engineering process which covers all of the activities involved in discovering, documenting and maintaining a set of requirements for a computer-based system...
  
  
• Requirements management
  Requirements management
  Requirements management is the process of documenting, analyzing, tracing, prioritizing and agreeing on requirements and then controlling change and communicating to relevant stakeholders. It is a continuous process throughout a project...
  
  
• Spacecraft
  Spacecraft
  A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
  
  
• Specification tree
• Verification of system requirements
• Verification (spaceflight)
  Verification (spaceflight)
  Verification in the field of space systems engineering covers two verification processes: Qualification and Acceptance- Overview :In the field of spaceflight verification standards are developed NASA and the ECSS, and to specify requirements for the verification of a space system product, such as:*...
  
  

External links

• NASA Completes Milestone Review Of Next Human Spacecraft System Nasa article 1999.
• Example of a SYSTEM REQUIREMENTS sheet for a spacecraft