system
Given the following post, respond as if you're commenting on Reddit:
human
[Portal 2] How did Aperture Science get a hold of all those moon rocks?

They must have had hundreds of tons of the stuff, in order to be able to grind it up and coat so many walls in it (although I realize not all chambers are covered in moon dust). The test chambers never mention that there is a limited supply. So what gives? Did they make hundreds of rocket trips to the moon? Is that how they went bankrupt?
gpt
Moon rock is merely a good portal conductor, not the only one. Once they had a basic working model, they used the following method to collect moon rocks for testing:

1. Fire portal gun (orange mode) at moon
2. Reset portal device to close both ends of the portal, because you forgot that you had one end still set up next to your desk.
3. Fire portal gun (orange mode) at moon
4. Enter airlock chamber
5. Lock portal device in position
6. (Optional) Attach Aperture Science Personnel Retainment Harness
7. Fire portal gun (blue mode) at wall.
8. Hold Breath
9. Disregard previous instruction, exhale to avoid vacuum damage to lungs.
10. Use Aperture Science Moon Rock Collection Stick to slide several moon rocks into the airlock chamber against the air current. In most cases, lunar gravity will be downward, into the portal, assisting in this effort.
11. (Optional) wait for air pressure to equalize, as this will keep the moon rocks from blowing outward, but may lead to breathing difficulties.
12. Shut down portal device.
13. Wait 10-15 minutes for air lock chamber air pumps to normalize air pressure.

And there you go! All the moon rocks you need!