Akatsuki Operational Plan Draft
Executive summary. Akatsuki must be treated as two different trajectory designs: the
original nominal mission and the recovered mission after the 2010 VOI failure. The
recovery campaign worked because heliocentric perihelion maneuvers lowered the later
Venus arrival energy enough to allow RCS-only capture in 2015.
1. Mission phases and trajectory logic
Akatsuki’s trajectory has to be read in two different ways: the nominal mission design and
the recovered mission design after the 2010 failure. This distinction is essential, because
the original target was a 30 h quasi-equatorial retrograde Venus orbit optimized for
tracking atmospheric super-rotation, while the recovered mission ended up in a much
higher and more weakly bound Venus orbit, chosen because only the RCS was available for
the second insertion attempt.
From the mission timeline, the operational phases can be divided into:
• Cruise phase from launch on 20 May 2010 to the first Venus encounter.
• Sun-orbiting phase after the failed VOI on 7 December 2010.
• Primary science phase starting with the successful VOI-R1 on 7 December 2015.
• Then extended science phases.
Functionally, the trajectory logic is:
Nominal design
• Direct Earth-to-Venus transfer.
• One critical VOI burn with the OME.
• Injection into a 30 h retrograde, near-equatorial science orbit.
After failure
• The spacecraft missed capture because only about 18–20% of the planned deceleration
was achieved.
• It escaped Venus and entered a heliocentric orbit with period about 203 days, perihelion
about 0.61 AU, and aphelion about 0.74 AU.
• The next natural return would have been only in early 2017, too late and with a high
reinsertion cost.
• JAXA therefore redesigned the transfer using perihelion maneuvers and a non-tangent V-
Infinity Leveraging Transfer, so as to anticipate the Venus re-encounter to late 2015 and
reduce the required capture energy.
This is also why the recovery design is operationally more robust than the original VOI
architecture: the perihelion correction can be split into several burns over days, whereas
VOI must be completed within minutes during a single critical event.
