There are three known canonical designs for the impulse housing.Design One
Chapter 1, "The Enemy Within"
Elliptical housing.
Nine circular holes.
Pattern-two, two in gray rectangule, one in center, two in gray rectangule, and two.
Seen on USS Enterprise.
Design Two
Chapter 5, "The Enemy Within"
Elliptical housing.
Pattern-large black rectangule, upside down trapezoid, large black rectangule.
Seen on USS Enterprise and USS Exeter.
Replaced design one on USS Enterprise.
Design Three
"The Doomsday Machine"
Elliptical housing.
No features.
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takeoffs are optional; landings are mandatory