Puzzle of the Week 
 
You are the commander of the first manned base on the moon. You have a team of 5 scientists and 15 multipurpose robots. One day your whole team is busy preparing for the fast approaching sun-storm and you need to wisely allocate resources for the hundreds of the tasks that need to be completed. Otherwise, the very survival of the moon base will be in danger.

One of the tasks involves bringing back the precious equipment from a monitoring station in a crater that is 10 kilometers away. It is too dangerous for human scientists to venture out and this task will need to be performed by one of the robots. Unfortunately, each fully charged robot has enough energy only to go to the monitoring station but not for coming back. How will you accomplish this task using the minimum number of robots?

Notes:
  1.  All the robots are same in every respect.
  2.  Each robot can instantaneously transfer any part of its energy to another robot when they are in physical contact with each other.
  3. All the robots used in performing this task should safely return to the base immediately after completing the task. 
  4. The robots consume energy only when they are moving.
  5. The moon base station has enough energy to charge the robots as and when required. 
  6. Robots can be remotely controlled from the base station.
Provide detailed explanation with your answer.

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