As a fitting tribute, the Sea of Tranquility was chosen as the landing site for Googol to commemorate the first manned lunar landing of Apollo 11 in July 1969. The Sea of Tranquility is located at 0.67408°N latitude and 23.47297°E longitude. The Sea of Tranquility is aptly named for its relatively flat and non-hazardous terrain.

 

Landing Accuracy

It is assumed that the desired landing at the Apollo 11 site will be accurate to within 20 km due to the fact that Googol is not implementing a pinpoint terminal guidance algorithm. 10 km of error can be attributed to navigation state error and another 10 km can be attributed to errors such as thrust error, specific impulse error, etc. To calculate landing probability, a normally-distributed 20 km radius circular landing footprint at three standard deviations is assumed.

By integrating the above PDF from -20 to 20 and -1 to 1, one can calculate the probability of landing within 20 km and within 1 km. Performing this calculation, it is found that Googol has a 99.73% chance of landing within 20 km and a 11.94% chance of landing within 1 km of its target.

 

Landing Hazards

Although the Sea of Tranquility has relatively flat terrain, it was desired to calculate the density of landing hazards within the 20 km circular landing footprint. Using known distributions of rocks and craters in the vicinity of the landing site and assuming that rocks greater than 0.7-1.0 meters in diameter and craters greater than 2.0 meters in diameter could pose a landing hazard, it was determined that only 1.26% of the landing area is potentially hazardous. It was deemed that this is an acceptable risk and therefore the design team decided against budgeting additional fuel for hazard avoidance.