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Lunar Caves Exploration with the DAEDALUS Spherical Robot
D. Borrmann1, A. N ¨uchter1, A. Bredenbeck1, J. Zevering1, F. Arzberger1, C. A. Reyes Mantilla1, A. P. Rossi2, F.
Maurelli2, V. Unnithan2, H. Dreger2, K. Mathewos2, N. Pradhan2, R. Pozzobon3, M. Massironi3, S. Ferrari3, C.
Pernechele4, L. Paoletti4, E. Simioni4, M. Pajola4, and T. Santagata5.
1University of W¨urzburg, Germany, 2Jacobs University Bremen, Germany, 3University of Padova, Italy, 4INAF
Padova, Italy, 5VIGEA – Virtual Geographic Agency, Italy
Introduction: During the past few years crewed and
robotic exploration of the Moon has regained focus in
the activities of the scientific community and space agen-
cies. Following this trend, ESA placed a call for ideas
on its Open Space Innovation Platform for a SysNova
LunarCaves system study to explore lava tubes through
skylights. Part of this effort is the DAEDALUS (De-
scent and Exploration in Deep Autonomy of Lava Un-
derground Structures) mission design concept that aims
at exploring and characterising the entrance of Lunar
lava tubes within a compact, tightly integrated spherical
robotic device, with a complementary payload set and
autonomous capabilities. The mission concept specifi-
cally addresses the identification and characterisation of
potential resources for future ESA exploration, the local
environment of the subsurface and its geologic and com-
positional structure using laser scanners, cameras and an-
cillary payloads. A sphere is ideally suited to protect sen-
sors and scientific equipment in rough, uneven environ-
ments. When lowering the sphere into the skylight via a
crane, it explores the entrance shaft, associated caverns
and conduits. A moving mass enables motion on the bot-
tom of the pit. To improve the locomotion capabilities, to
increase stability for data collection and to prevent fail-
ures extendable pods complete the actuator scheme.
Mission Summary: The DAEDALUS mission is
planned within the Marius Hills region where a lunar
skylight with underlying void has been discovered in the
past decade [1] and consists of four mission phases to im-
prove the science return. Approaching the pit is not part
of this mission. Nevertheless, a characterisation of the
landing site was carried out as part of the DAEDALUS
study to ensure feasibility of landing, approach to the pit
and deployment of the sphere [2]. During the first three
phases the sphere is lowered into the pit by a crane allow-
ing for both tethered communication and power supply.
Only in the last phase the sphere is detached and operates
autonomously.
I) Skylight approach and descender deployment: The
DAEDALUS sphere is deployed and lowered into the
pit using a crane system mounted on a dedicated rover.
Since the Marius Hill skylight has a sloping area before
the void, the spherical shape of the robot and the extend-
able pod subsystem help to overcome issues arising when
the sphere cannot be suspended directly into the pit due
to a shortness of the crane.
II) Skylight descent and mapping: While descending
the laser scanner and the panoramic cameras are used to
create a 3D point cloud of the shaft. An encoder measur-
ing the tether length gives an inital depth estimate. Re-
dundancy is achieved by performing robotic SLAM (Si-
multaneous Localization and Mapping) on the laser data
and stereo vision as well as SfM (Structure from Motion)
on the camera data. Besides context 360 imagery, VIS
dual hemispheric cameras provide also stereo imaging
of illuminated overlapping areas as well as close-range
imaging, useful for textural characterization of the lava
layers of the shaft walls. In the meantime, thermal, ra-
diation and dust sensors will provide information about
the thermal gradient as well as the environment condition
within the pit enabling the generation of vertical radia-
tion and temperature profiles during descent.
III) enter the main void and mapping from the de-
scender tether the main cave environment: When pass-
ing the cave ceiling, the lidar system acquires the first
3D point cloud from within the cave taking advantage
of the larger range from an elevated view point and al-
lowing for a structural analysis of the cave. The cameras
capture a full view of the main void using natural or ar-
tificial illuminations, if required. Thermal/radiation/dust
sensors acquire define horizontal radiation and tempera-
ture profiles. Before touchdown, the objective of close
characterization of the ground with multi-band LIDAR
and cameras will be achieved.
IV) Initial navigation and tunnel mapping: Once
touching the ground the sphere detaches from the tether
and navigates through the cave autonomously using the
3D data from phase III for initial navigation planning.
Depending highly on the morphology and geometry of
the lava tube, exploration up to several hundred meters
is possible with the tether acting as a wifi hotspot and
charging station. Obstacle evaluation and terrain strength
data are to be acquired by passive seismometry with the
embedded accelerometers and extendable pods acting as
Schmidt hammer at touchdown. While terrain rough-
ness, obstacles, radiation and rock magnetism limit the
deployment and distance of travel, this mission phase is
highly dependent on the unpredictable cave configura-
tion.
Science Return Levels: The DAEDALUS mission is
designed to yield progressive scientific return in each of
the phases. The overall scientific objectives are:
2073.pdf52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548)
1. Exploration of the evolution of volcanism through
windows within the lava flow successions on lunar
maria;
2. Identification and characterization of potential
paleo-regolith layers and pyroclastic deposits;
3. Detection of fresher rocks and outcrops from
deeper locations less affected by space weathering;
4. Generatation of a 3D map based on LiDAR and
SfM data of pit walls and lunar caves;
5. Verification of the volatiles’ presence within the
cave;
6. Research of locally sourced resources that can be
integrated in crewed missions architecture;
7. Definition of subsurface environmental condi-
tions;
8. Generation of temperature and radiation profiles.
While the minimum viable scientific return is
achieved in phase I and the early stages of phase II by
analysing the lunar skylight entrance, the nominal mis-
sion science return is achieved during phase II and phase
III by analysing the entire pit and the cave floor at the
main void. The extended mission science return will be
achieved during the tunnel mapping in phase IV. Here
more information about the stability of the cave ceiling
as well as the trafficability of the cave is collected.
Robotic Sphere: The DAEDALUS sphere design con-
sists of two main structures (Figs. 1,2). The inner
structure comprises the imaging and controlling com-
ponents, namely two laser scanners, four multispectral
cameras with hemispheric lenses, two micro controllers,
two switches, one heater, and one rotatable battery. To
characterize the surface material the lidars operate in
two different wavelengths and the cameras are coupled
with narrowband filters for further analysis of the surface
composition using four identified spectral bands. In idle
position off-centered battery shifts the center of mass to-
wards the ground. The outer structure holds mainly the
pole mechanism, a light source, and the shell itself. One
of the outer poles is used as a physical connection , elec-
trical and data transfer when connected to the cable. Two
electrical motors connect the inner and the outer struc-
tures allowing them to rotate relatively to each other.
Figure 2depicts the four different operation modes.
In descending mode, while being lowered into the cave,
the sphere is coupled to the tether via one of the side
pods. The inner structure rotates to enable full coverage
of the surroundings by the optical sensors and LIDAR.
When on the ground, due to the low center of mass of the
inner structure caused by the battery, using the motors
triggers rotation of the outer structure leading to a rota-
tion of the entire sphere and therefore locomotion. Steer-
ing can be achieved by rotating the battery and therefore
center of mass to one side. The camera system has full
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Figure 1: Overall CAD sphere design without outer shell.
Figure 2: The different modes of the Sphere. Top-Left:
Desending Mode. Top-Right: Rolling Mode. Bottom-
Left: Scanning Mode. Bottom-Right: Obstacle Mode.
mono and partial stereo coverage. The lidar scans for-
ward and backward. To overcome this two limitations
in lidar, optical stereo coverage and to increase the data
resolution a special scanning mode is introduced, where
the poles lift up the sphere acting as a tripod. Activating
the motors will now lead to a rotation of the inner struc-
ture of the sphere and with it the optical payloads. In the
obstacle mode the poles are used to push the sphere over
obstacles, resolving the limitations of locomotion by ro-
tation .
References
[1] J. Haruyama, K. Hioki, M. Shirao, T. Morota, H. Hiesinger, C. H.
van der Bogert, H. Miyamoto, A. Iwasaki, Y. Yokota, M. Ohtake,
T. Matsunaga, S. Hara, S. Nakanotani, and C. M. Pieters. Possi-
ble lunar lava tube skylight observed by SELENE cameras. Geo-
physical Research Letters, 36(21), 2009. ISSN 1944-8007. doi:
https://doi.org/10.1029/2009GL040635.
[2] R. Pozzobon, A. P. Rossi, S. Ferrari, M. Massironi, M. Pajola, and
the DAEADALUS Team. Marius hills skylight characterization
as a possible landing site for subsurface exploration: hazard and
potential subsurface detections. In 52nd Lunar and Planetary Sci-
ence Conference (LPSC 2021), 2021.
2073.pdf52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548)
