Hi Lillian,
Yes you have to "walk the walk" past the ufo
Well lillie you solved it faster than I could make the spoiler, but now its here for others that might need it!
***SPOILER AHEAD***
When you stand at the red cross, keeping an eye on the ufo, when it starts moving left you run to the blue cross, wait until the ufo is just about to move into the field just above you, then run to the red arrow. If you do this just right the ufo won't shot.
When you have dont this, all you have to do

, is get out the same way you got in, turn the reflector around and put it on the yellow X, then the ufo will shot it self.
BTW, the grass above the cyan line is the model my wonderfull wife made.
DKgiz

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