Space exploration crossword

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Across
  1. 2. Something that scientists have observed as always behaving in the same way (3 letters)
  2. 5. A person who travels in space (9 letters)
  3. 9. Puzzle:
  4. 11. A section of a rocket or spacecraft that has its own engine (5 letters)
  5. 12. Units of measurement for determining energy (6 letters)
Down
  1. 1. Thread of a particular substance that are combined to form materials (7 letters)
  2. 3. The height of an object above Earth's surface or sea level (8 letters)
  3. 4. The loads carried by spacecraft, such as passengers, cargo, or satellites (8 letters)
  4. 6. The amount of matter that an object contains (4 letters)
  5. 7. An invisible force that pulls two objects towards each other (7 letters)
  6. 8. A machine used to travel in space (6 letters)
  7. 10. The programs that run on a computer, telling it how to complete certain tasks (8 letters)