  On-orbit manual attitude control of manned spacecraft is accomplished using
external visual references and some method of three axis attitude control. All
past, present, and developmental spacecraft feature the capability to manually
control attitude for deorbit. National Aeronautics and Space Administration
(NASA) spacecraft permit an aircraft windshield type front view, wherein an arc
of the Earths horizon is visible to the crew in deorbit attitude. Russian and
Chinese spacecraft permit the crew a bottom view wherein the entire circular
Earth horizon disk is visible to the crew in deorbit attitude. Our study
compared these two types of external views for efficiency in achievement of
deorbit attitude. We used a Unity Virtual Reality (VR) spacecraft simulator
that we built in house. The task was to accurately achieve deorbit attitude
while in a 400 km circular orbit. Six military test pilots and six civilians
with gaming experience flew the task using two methods of visual reference.
Comparison was based on time taken, fuel consumed, cognitive workload
assessment and user preference. We used ocular parameters, EEG, NASA TLX and
IBM SUS to quantify our results. Our study found that the bottom view was
easier to operate for manual deorbit task. Additionally, we realized that a VR
based system can work as a training simulator for manual on-orbit flight path
control tasks by pilots and non pilots. Results from our study can be used for
design of manual on orbit attitude control of present and future spacecrafts.
