NASA SR-71 testing a linear aerospike, a type of rocket engine that maintains its aerodynamic efficiency across a wide range of altitudes.
https://diqn32j8nouaz.cloudfront.net..._aerospike.jpg
Previously:
https://www.homemadetools.net/forum/...979#post144904
https://www.homemadetools.net/forum/...or-photo-77778
https://www.homemadetools.net/forum/...367#post150701
