Related Clues:

• Complicated stuff, so to speak
• Stephenson's cutting edge?
• Great technical skill
• Something said to require great intelligence (usually referred to in the negative)
• Something very difficult to understand (involving gravity?)
• Space technology
• It¿s not that hard perhaps getting one to moon
• Proverbial activity requiring greater intelligence?
• (Not) an intellectual demand (slang)
• Informal expression for complex and intellectually demanding activity
• Something intellectually challenging that goes beyond blue-sky thinking?
• Brain surgery that's required by astronaut?
• Complicated material, metaphorically
• Branch of aerospace engineering (it's not!)
• Scenic eco-trek (anag) — complex subject for boffins?