Editing MESSENGER (section)

===Proposals for the mission===
In 1998, a study detailed a proposed mission to send an orbiting spacecraft to Mercury, as the planet was at that point the least-explored of the inner planets. In the years following the Mariner 10 mission, subsequent mission proposals to revisit Mercury had appeared too costly, requiring large quantities of propellant and a [[heavy lift launch vehicle]]. Moreover, inserting a spacecraft into orbit around Mercury is difficult, because a probe approaching on a direct path from Earth would be accelerated by the [[Sun]]'s gravity and pass Mercury far too quickly to orbit it. However, using a trajectory designed by Chen-wan Yen<ref>{{cite web|title=Finally! NASA Prepares to Orbit Mercury|url=https://science.nasa.gov/science-news/science-at-nasa/2011/15mar_messenger|website=Science NASA|publisher=NASA|access-date=March 26, 2018|archive-date=March 25, 2023|archive-url=https://web.archive.org/web/20230325052032/https://science.nasa.gov/science-news/science-at-nasa/2011/15mar_messenger/|url-status=dead}}</ref> in 1985, the study showed it was possible to execute a [[Discovery Program|Discovery-class]] mission by using multiple, consecutive gravity assist, 'swingby' maneuvers around Venus and Mercury, in combination with minor propulsive trajectory corrections, to gradually slow the spacecraft and thereby minimize propellant needs.<ref name="1998Design">{{Cite journal | first = J. V. | last = McAdams | author2 = J. L. Horsewood | author3 = C. L. Yen | title = Discovery-class Mercury orbiter trajectory design for the 2005 launch opportunity | journal = 1998 Astrodynamics Specialist Conference | publisher = American Institute of Aeronautics and Astronautics/American Astronautical Society | place = Boston, MA | pages = 109–115 | date = August 10–12, 1998 | id = AIAA-98-4283 | url = http://messenger.jhuapl.edu/the_mission/publications/McAdams.et.al.1998.pdf | url-status = dead | archive-url = https://web.archive.org/web/20130513075815/http://messenger.jhuapl.edu/the_mission/publications/McAdams.et.al.1998.pdf | archive-date = May 13, 2013 }}</ref>