2008 Annual Report - NASA Airborne Science Program
2008 Annual Report - NASA Airborne Science Program
2008 Annual Report - NASA Airborne Science Program
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
UAVSAR<br />
Trajectory<br />
Control<br />
A<br />
Platform Precision Autopilot<br />
(PPA) has been developed to<br />
enable an aircraft to repeatedly<br />
fly nearly the same trajectory<br />
hours, days, or weeks later. This<br />
capability allows accurate earth deformation<br />
measurements through precise repeatpass<br />
interferometry, a key element for the<br />
success of the <strong>NASA</strong> Unmanned Aerial<br />
Vehicle Synthetic Aperture Radar (UAVSAR)<br />
program. The PPA uses a novel approach to<br />
interface with the <strong>NASA</strong> Gulfstream III by<br />
imitating the output of an Instrument Landing<br />
System (ILS) approach. This technique<br />
minimizes, as much as possible, modifications<br />
to the baseline GIII. In addition, the safety<br />
features of the aircraft’s autopilot are<br />
retained. The PPA finished all phases of flight<br />
testing in early <strong>2008</strong>.<br />
Objective<br />
The objective of the PPA is to enable repeat<br />
pass flights within a five meter radius tube<br />
over a 200 kilometer course in conditions of<br />
calm to light turbulence for over 90 percent<br />
of the time. In order for JPL’s synthetic<br />
aperture radar to generate the best images,<br />
it is important to operate on a steady<br />
platform. Hence, as a secondary goal, the<br />
PPA has to minimize motion of the GIII<br />
during data collection runs. The end product<br />
is a “care-free, user-friendly” autopilot suitable<br />
for deployment and operation by the flight<br />
operations engineer.<br />
Approach<br />
The PPA uses a Kalman filter to generate a<br />
real-time navigation solution with information<br />
from the GIII systems and a differential GPS<br />
unit located in the UAVSAR pod. The realtime<br />
position solution is used to compute<br />
commands (Guidance and Control modules)<br />
which in turn drive two modified ILS testers.<br />
The ILS tester units produce modulated RF<br />
signals fed to the onboard navigation receiver.<br />
These correction signals then allow the GIII<br />
autopilot to fly a simulated, constant-altitude<br />
ILS approach to meet the PPA requirements<br />
for UAVSAR operations.<br />
83