To start both main and backup engine was standard procedure planned for Soviet lunar landing LK, at liftoff. If everything's fine, backup engine shuts down. "T

To start both main and backup engine was standard procedure planned for Soviet lunar landing LK, at liftoff. If everything's fine, backup engine shuts down. "The rocket company", https://en.wikipedia.org/wiki/The_Rocket_Company https://en.wikipedia.org/wiki/The_Rocket_Company , a great and quite realistic book, reminds about importance of knowing history; there, a company explicitly maintains a library of previous technical solutions to problems encountered.