b'The Digital Twin | Engineer InnovationApollo 13 Mission Profile drawn to scale. Image Credit Andrew Buck. Digital twin to the rescue being modified to reflect the unusual NASA faced many problems that allspacecraft configuration, which needed to be solved in order to bringinvolved reprogramming the the crew safely home, several of themmainframes with information about the solved only with the extensive use ofnew spacecraft mass, center-of-gravity the simulator digital twins.and engine thrust. Working together with the lunar module manufacturer, One significant recurring problem wasNorthrop Grumman, the simulation that of maneuvering the spacecraft,team quickly worked out a new which was never designed to operateprocedure in which the ship could be using the lunar module with crippledstabilized using autopilot and deploying service and command modules attachedthe landing gear to get it out of the way for the whole return journey. With theof the descent engine. It worked and guidance computer powered down tothe crew were successfully able to save energy, the crew had to manuallyperform the free return burn, greatly align the spacecraft precisely to makeincreasing their confidence.three separate engine burns which required keeping the spacecraft on a freeA similar problem occurred two hours return trajectory to earth. In normalafter Apollo 13s closest approach to the operation these maneuvers weremoon (the so called aspericynthion or performed by the onboard computer, butPC for short), intended to speed up the in this unusual configuration much ofreturn voyage by 12 hours, and bring the work had to be performed manually.their return just within the lifetime of With limited fuel on board, any mistaketheir battery supplies. The problem this could have been terminal, and left thetime was that the lunar modules vessel on a wrong trajectory. guidance systems had been turned off to conserve power, forcing the The early signs were not promising, asastronauts to manually align the the crew struggled to control thespacecraft using only visual cues. spacecraft Why the hell are weOrdinarily the crew could have maneuvering like this, are we stillnavigated using the stars as a backup, venting exclaimed a frustrated Jimbut the large amount of debris Lovell at one stage.surrounding the crippled spacecraft made it impossible for the astronauts to Mission Control immediately dispatchedidentify any constellations. In the backup crew to practice thedesperation, NASA once again turned to maneuvers on the simulators that werethe simulators. After hours of trial and 15'