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Across 2. used as the propulsive gas in Hero's rocket 3. acronym for the U.S. space program 8. scientific foundations for modern rocketry were done by him 10. rocket-like device invented by Hero of Alexandria 11. created the flying pigeon in the 400 B.C. 12. opposition to weight 13. forces are generated by fins, body tube and this (2 words) 16. father of modern astronautics 18. weight force is due to this 19. forces that have both magnitude and direction 20. resistance felt by the rocket in the air 21. the number of laws for physical motion

Down 1. when the thrust of the engine is greater than the weight of the rocket 2. name of the Russian satellite in 1957 4. used in the Chinese fire arrows as propellant 5. magnitude of forces depends on shape, size and this 6. placed inside of the model rocket to help slow its fall time back to the ground 7. Chinese used these against the Mongols (2 words) 9. name of first living creature to go into space 14. U.S. satellite launched in 1958 15. first to conduct a successful flight with a liquid-propelled rocket 17. used to stabilize and control direction of flight