System requirements (spacecraft system)
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Spacecraft systems are normally developed under the responsibility of space agencies as NASA, 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 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 are sent out requesting proposals from industry.
Technical systems requirement
The technical system requirements documented in the System Specification stay on mission level:
- System functions and performances
- Launch vehicle
whereas the non-technical system (task) requirements
- Cost and progress reporting
- Documentation maintenance
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."
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 for a spacecraft has the following structure (e.g. Columbus Design Spec (COL-RIBRE-SPE-0028, iss.10/F, 06.25.2004):
- 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.
- 5.1 System interfaces
- 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).
The spacecraft system specification defines also the subsystems of the spacecraft e.g.:
- Data management subsystem incl. software
- Electrical Power
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 showing all specifications and their linkage as well as the issue / date of each specification.
- 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.
- Requirements analysis
- Requirements engineering
- Requirements management
- Specification tree
- Verification of system requirements
- Verification (spaceflight)
- Clarus Concept of Operations. Archived 2009-07-05 at the Wayback Machine. Publication No. FHWA-JPO-05-072, Federal Highway Administration (FHWA), 2005
- Systems Engineering Fundamentals. Archived 2006-02-11 at the Wayback Machine. Defense Acquisition University Press, 2001
- David Michael Harland, Ralph Lorenz (2005), Space Systems Failures: Disasters and Rescues of Satellites, Rockets, Springer, p.178.
- NASA Completes Milestone Review Of Next Human Spacecraft System Nasa article 1999.
- Example of a SYSTEM REQUIREMENTS sheet for a spacecraft
-  Columbus System Specification COL-RIBRE-SPE-0028 for phase C/D