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Subject
- Discovery and exploration312
- Legislative amendments201
- Oil and gas exploration147
- Claims134
- United States129
- Exploration108
- Oil and gas leases71
- Space exploration67
- Explorers61
- Astronautics52
- Commemorations45
- International cooperation45
- United States. National Aeronautics and Space Administration45
- Cost43
- United States. National Aeronautics and Space Administration (1958- )42
- Research41
- Petroleum industry and trade40
- Mineral Leasing Act37
- Petroleum37
- Public lands37