Editing Atmospheric entry (section)

===Biconic===
[[File:Delta Clipper DC-X first flight.jpg|thumb|right|upright|The [[McDonnell Douglas DC-X|DC-X]], shown during its first flight, was a prototype [[single-stage-to-orbit]] vehicle, and used a biconic shape similar to AMaRV.]]
The [[biconic]] is a sphere-cone with an additional frustum attached. The biconic offers a significantly improved L/D ratio. A biconic designed for Mars aerocapture typically has an L/D of approximately 1.0 compared to an L/D of 0.368 for the Apollo-CM. The higher L/D makes a biconic shape better suited for transporting people to Mars due to the lower peak deceleration. Arguably, the most significant biconic ever flown was the ''Advanced [[Maneuverable reentry vehicle|Maneuverable Reentry Vehicle]]'' (AMaRV). Four AMaRVs were made by the [[McDonnell Douglas]] Corp. and represented a significant leap in RV sophistication. Three AMaRVs were launched by [[LGM-30 Minuteman|Minuteman-1 ICBMs]] on 20 December 1979, 8 October 1980 and 4 October 1981. AMaRV had an entry mass of approximately 470&nbsp;kg, a nose radius of 2.34&nbsp;cm, a forward-frustum half-angle of 10.4°, an inter-frustum radius of 14.6&nbsp;cm, aft-frustum half-angle of 6°, and an axial length of 2.079 meters. No accurate diagram or picture of AMaRV has ever appeared in the open literature. However, a schematic sketch of an AMaRV-like vehicle along with trajectory plots showing hairpin turns has been published.<ref>Regan, Frank J. and Anadakrishnan, Satya M., "Dynamics of Atmospheric Re-Entry", AIAA Education Series, American Institute of Aeronautics and Astronautics, Inc., New York, {{ISBN|1-56347-048-9}}, {{doi|10.2514/4.861741}}, (1993).<!-- I think this refers to diagrams of simulations on pg. 268 & 269. Is there a way to note that? ([https://books.google.com/books?as_isbn=1563470489 Google Books]) --></ref>

AMaRV's attitude was controlled through a split body flap (also called a ''split-windward flap'') along with two yaw flaps mounted on the vehicle's sides. [[Hydraulic machinery|Hydraulic actuation]] was used for controlling the flaps. AMaRV was guided by a fully autonomous navigation system designed for evading [[anti-ballistic missile]] (ABM) interception. The [[McDonnell Douglas DC-X]] (also a biconic) was essentially a scaled-up version of AMaRV. AMaRV and the DC-X also served as the basis for an unsuccessful proposal for what eventually became the [[Lockheed Martin X-33]].