[aaeamdar]

As clearly outlined in the rules (highlighted in a recent update) nobody but the Human Players (or Payload Specialists, as they are called this year) can touch the game objects (moon rocks, empty cells, super cells).

I'm a little confused as to the responses in this thread - it seems the OP was asking "is it legal to do X" not "is it physically possible/adviseable to do X". Obviously it is physically possible for a non-physically impaired highschool student of moderate coordination to hold one ball in each hand and throw both balls - accuracy is a seperate question.

To directly answer my interpretation of the OP's original question: as far as I know (and I have read all the rules several times) there is no rule limiting the number of game pieces that the Payload Specialist can hold at a given time. Unfortunately, it's impossible/difficult to prove a negative (i.e. "there is no such rule..."), so I could be wrong. If someone can find such a rule, I will gladly retract my statement.

-Paul