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Page 16 of 35 Kulkarni et al. Soft Sci. 2025, 5, 12 https://dx.doi.org/10.20517/ss.2023.51

Soft sensors used in space environments
Soft sensors can be used for monitoring equipment, environmental conditions, or feedback sensing on soft
robots. IPMCs can be used as sensors for space equipment as they can conform to the structure of the
equipment to provide more detection area on these structures . Equipment damage or defects are sensed
[201]
through changes in IPMC bending and resulting voltage differentials. IPMCs can also be used for vibration
monitoring in satellites. Satellite vibration can affect orbiting trajectories, disrupting the aim of instruments
attached to the satellite. It is proposed that IPMC sensors be placed on the structure to record vibration data
for vibration modeling to monitor the health of the spacecraft. These models can help determine the
impacts on the structure, trajectories, and instrument tasks based on vibration .
[201]

Flexible sensors have been proposed for soft space robots and astronaut health monitoring devices. These
applications require high accuracy, adaptable geometry, and efficient energy systems . Fu et al. developed
[202]
flexible pressure sensors composed of ceramic nanofibers which provide high-temperature resistivity as they
can withstand temperatures up to 370 °C. These ceramic sensors have quick response speeds of less than
-1
16 ms and sensitivities of ~4.4 kPa that may facilitate monitoring physiological signals of humans in space
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environments [Figure 8A]. Textile sensors that conduct physiological monitoring can be easily and
comfortably worn by astronauts. Fan et al. propose a triboelectric textile sensor array to detect aerial pulse
waves and respiratory signals. This sensor can be easily worn as a wristband, fingerstall, around the neck, or
integrated into a sock [Figure 8B]. Given the unique challenges and variable climates present in space,
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research is needed to leverage new materials and hybrid structures to effectively meet the needs of this
environment.

SOFT ROBOTS FOR SEARCH, RESCUE, AND CONFINED SPACES
Natural and man-made environments often create conditions that are unsafe for humans to enter during
search and rescue operations . Confined spaces that are fully enclosed or have limited entryways include
[108]
pipes, mines, tanks, and pits . These spaces may contain toxic gases, fumes, and dust, potentially causing
[204]
[204]
negative health impacts to humans . Thus, robots have been developed to conduct search, rescue, and
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inspection operations in these environments . They must be able to navigate through narrow areas and
obstructions such as rubble, debris, dust, darkness, and collapsed structures . Soft robots can minimize
[93]
friction for gripping, moving, and sensing operations to prevent further damage to the search and rescue
site . Thus, they offer new design solutions for increased mobility on rough and obstructed surfaces and
[93]
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enclosed spaces through their distinct actuation mechanisms , thereby reducing health and safety risks in
these critical rescue operations.
Soft actuators used for search, rescue, and confined space applications
To navigate confined spaces and rough obstructed terrains, robots must be able to conform elastically to
avoid surface wear, absorb energy, and bear impact loads on collision. Additionally, these devices must be
compact and able to travel in narrow spaces. Some soft robot designs proposed for search and rescue are
growing-type robots that can grow axially with directional control to steer the robot . The growing
[206]
mechanism of these robots can be achieved by continuous additive manufacturing or pneumatic
actuation . However, buckling can cause growing robots to move in unexpected directions as they can
[108]
retract, resulting in disturbances to the environment. Vine-like robots are another class of growing robots
that only undergo internal friction and can also feed cables through the center of the actuator . El-
[108]
Hussieny et al. propose a soft vine robot built from a polyethylene tube that extends from the tip once air
pressure is applied [Figure 9, Vine robot] . The robot can be steered by applying air pressure to serial
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PAM oriented around the structure’s circumference. These robots can conform to the surrounding
environment without impacting obstructions and preventing further destruction.