CSEM Scientific and Technical Report 2008

Guidance Navigation and Control System Based on Lidar and Time-of-Flight Camera for
Safe Landing and Automatic Rendezvous
A. Pollini, V. Mitev
This paper presents a lidar (light detection and ranging) imaging altimeter, a device integrating a 3D camera developed by the Photonic division in a
lidar architecture realized by the Time and Frequency division. The resulting instrument offers unique characteristics matching requirements of
exploration space mission phases such as spacecraft safe landing on planets or asteroids and automatic spacecraft rendezvous.
3D Active Pixel Sensor (APS) cameras have not been
considered until recently by the European Space Agency
(ESA) in its effort to harmonize and coordinate Attitude Onboard
Control System (AOCS) and Guidance and Navigation
Control (GNC) sensors and actuators. Due to progresses in
APS technology, 3D vision detectors are now fully-fledged in
the diverse sensor families regarded by ESA for AOCS in
accordance with future space missions’ requirements [1] .
Time and Frequency division has anticipated this change and
is currently reporting to ESA an innovative sensing system for
autonomous vision-based navigation system. The related
work achieves the demonstration of the integration of a 3D
camera in the pseudorandom-continuous wave (prn-cw) lidar
architecture [ 2, 3] . The main challenge of this project was to
maintain the range resolution precision of the 3D sensor and
use the sensor at distances farther than its non-ambiguity
range, that is at distances further than the distance
corresponding to the first bin duration of the prn sequence (in
this case it is 7.5 m). The results confirm the potential of this
development as a competitive solution for space exploration
missions phases where distance (or altitude) and 3D imaging
are needed at the same time.
Figure 1: Range resolution of the instrument with a hard target
Figure 2: 3D image at 17 m (target: cross at 40 cm in front of a
backplane) – red/orange areas designate target parts at 17.2 m;
blue/cyan areas indicate target parts at 16.8 m
98
Target at
16.8 m
Cross in front,
at 16.8 m
Target at
17 m
Typical standard deviation = 3 cm
Backplane at 17.2 m
Backplane at 17.2 m
Target at
17.2 m
Distance m
Exploration missions include phases such as: approach,
descent, soft-landing, or flyby of planets, comets or asteroids,
terrain-relative navigation (rovers) with obstacle avoidance,
spacecraft rendezvous and docking. The summary of the
Mars Sample Return mission groups some of these phases
(Figure 3).
Figure 3: Mars Sample Return mission [4]
In the frame of this project, two novelty features coupling the
PRN lidar with detection based on 3D APS were obtained, as
compared to traditional prn-cw lidar: one is the vastly
improved range resolution within the lidar nominal range. As
Figure 1 shows, a resolution of a few centimeters (typical
standard deviation of 3 cm) is achieved. The second novelty is
the unique feature of taking - at the same time as the distance
is measured - 3D images at ranges exceeding the nonambiguity
range of the camera as shown in the Figure 2.
These unique characteristics come in addition to already
identified advantages of the prn-cw lidar architecture: high
power-efficiency, long life, robustness and compactness. With
a 3D APS camera, all those are grouped in one single
instrument.
This work is partly funded by ESA. CSEM thanks them for
their support.
[1] “European Space Technology Harmonisation”, AOCS Sensors
and Actuators Technical Dossier, issue 3, revision 0, November
2008, Ref. ESA/ESTEC/24.08
[2] V. Mitev, R. Matthey, M. Haldimann, CSEM Scientific Report
2007, page 104
[3] B. Büttgen, M’H.-A. El Mechat, F. Lustenberger, P. Seitz,
“Pseudonoise Optical Modulation for Real-Time 3-D Imaging
With Minimum Interference”, IEEE Transactions on circuits and
systems. Regular papers, vol. 54, no. 10, October 2007
[4] “Preliminary Planning for an International Mars Sample Return
Mission, Report of the International Mars Architecture for the
Return of Samples”, iMARS Working Group, June 2008