Editing Legacy system (section)

==NASA example==
Andreas M. Hein researched the use of legacy systems in space exploration at the Technical University of Munich.  According to Hein, legacy systems are attractive for reuse if an organization has the capabilities for verification, validation, testing, and operational history.<ref>{{Citation | author = A.M. Hein | title = How to Assess Heritage Systems in the Early Phases? | publisher = ESA | series = 6th International Systems & Concurrent Engineering for Space Applications Conference 2014  | year = 2014 |url=https://www.academia.edu/8441540 }}</ref><ref>{{Citation | author = A.M. Hein | title = Heritage Technologies in Space Programs - Assessment Methodology and Statistical Analysis | publisher = Technical University of Munich | series = PhD thesis Faculty of Mechanical Engineering  | year = 2016 |url=https://www.researchgate.net/publication/310478449 }}</ref> These capabilities must be integrated into various software life cycle phases such as development, implementation, usage, or maintenance. For software systems, the capability to use and maintain the system are crucial. Otherwise the system will become less and less understandable and maintainable.

According to Hein, verification, validation, testing, and operational history increases the confidence in a system's reliability and quality. However, accumulating this history is often expensive. NASA's now retired [[Space Shuttle]] program used a large amount of 1970s-era technology. Replacement was cost-prohibitive because of the expensive requirement for flight certification.  The original hardware completed the expensive integration and certification requirement for flight, but any new equipment would have had to go through that entire process again.  This long and detailed process required extensive tests of the new components in their new configurations before a single unit could be used in the Space Shuttle program. Thus any new system that started the certification process becomes a ''[[de facto]]'' legacy system by the time it is approved for flight.

Additionally, the entire Space Shuttle system, including ground and launch vehicle assets, was designed to work together as a closed system.  Since the specifications did not change, all of the certified systems and components performed well in the roles for which they were designed.<ref>{{Citation | author = A.M. Hein | title = How to Assess Heritage Systems in the Early Phases? | publisher = ESA | series = 6th International Systems & Concurrent Engineering for Space Applications Conference 2014 | year = 2014 |url=https://www.academia.edu/8441540| page =3 }}</ref>  Even before the Shuttle was scheduled to be retired in 2010, NASA found it advantageous to keep using many pieces of 1970s technology rather than to upgrade those systems and recertify the new components.