"A field attendant will be positioned behind the Tetra Loading Station, and will place a Tetra on the loading station each time one is removed by a Robot. Minor variations in the precise position and orientation of the Tetra on the Tetra Loading Station are to be expected, and are considered part of the challenge of the competition."
So from what i can interpret you can just keep going back on and off the loading area and keep collecting those terra's and i would expect you to be able to carry more than one at once since i'm looking through the rule and see nothing contrary to that