Possible Clues:

• Second American in space
• Astronaut Gus
• Gemini 3 commander
• First American to go into space twice
• GUS
• Gil ___, original lead role on 'CSI'
• Second American to fly in space
• William Petersen's role on 112-Down
• Is society sustained by good memory of Virgil, spatially?
• One of 39-Across