APA (7th ed.) Citation

Engelbrektson, S., & Greenleaf, P. (1969). Let's explore outer space: Elementary research problems in space science. Sentinel Book Publishers.

Chicago Style (17th ed.) Citation

Engelbrektson, Sune, and P. Greenleaf. Let's Explore Outer Space: Elementary Research Problems in Space Science. New York: Sentinel Book Publishers, 1969.

MLA (9th ed.) Citation

Engelbrektson, Sune, and P. Greenleaf. Let's Explore Outer Space: Elementary Research Problems in Space Science. Sentinel Book Publishers, 1969.