NASA launched the Mars Climate Orbiter and Mars Polar Lander in the late 1990s. Both missions failed because of critical yet preventable errors in testing and communication. The MCO was lost due to a unit conversion error between metric and imperial measurements, while the MPL likely failed because of an early engine shutdown caused by incorrect signals. This study looks at why these missions failed and how much they cost by reviewing NASA's investigation reports, financial documentation, and other related writings. The findings reveal systemic flaws, including inadequate software verification, incomplete end-to-end testing, and miscommunication between engineering teams. Financially, the combined direct losses from both missions exceeded $492.6 million, with additional opportunity costs in delayed scientific progress. These results underscore the necessity of rigorous testing, standardized protocols, and cross-team communication to enhance mission success and mitigate future risks.