Crank-Driven Seismic Source Assembly for Low-Power Spacecraft
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Solution Overview
Problem
There is a need for a compact, lightweight, and low-power seismic source for interplanetary landing spacecraft to characterize lunar and planetary geology, as natural seismic events are unpredictable and terrestrial analogs are heavy and require large power, which is not feasible for spacecraft with limited resources.
Innovation Solution
An assembly comprising a motor, drive shaft, crank, one-way bearing, strike plate, hammer, and linkage arm, which converts rotational motion into linear motion to generate seismic waves with controlled impact energy, using a gearmotor and one-way bearing to minimize power consumption and prevent rebound.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If terrestrial analogs are used for seismic sources, then seismic signal content is reliable, but weight and power consumption become excessive for spacecraft
Solution Approach 1:
The seismic source is divided into distinct functional segments: a motor for power input, a crank mechanism for motion conversion, a hammer for impact generation, and a strike plate for seismic wave initiation. This segmentation allows each component to be optimized independently for minimal mass while maintaining reliable seismic signal generation.
Solution Approach 2:
The system employs dynamic motion conversion where the motor rotates the crank, which through the linkage arm dynamically positions the hammer to strike the strike plate. This dynamic mechanism replaces static terrestrial analogs with a lightweight, movable system that generates consistent seismic signals through controlled impact motion.
2Reliability
If terrestrial analogs are used for seismic sources, then seismic signal content is reliable, but power consumption becomes excessive for spacecraft
Solution Approach 1:
The motor operates in periodic cycles, rotating the crank to periodically position and release the hammer for impact on the strike plate. This periodic action allows the motor to consume power only during brief acceleration phases rather than continuous operation, dramatically reducing average power consumption compared to terrestrial analogs.
Solution Approach 2:
The biasing element stores potential energy during the hammer's retraction phase and automatically releases it during the strike phase, providing self-service energy contribution that reduces the motor's power burden. The one-way bearing also serves itself by automatically permitting rotation in the power-input direction while inhibiting reverse rotation, eliminating the need for complex braking or holding mechanisms.
3Weight of moving object
If a compact design is implemented for spacecraft, then mass is reduced, but device complexity increases
Solution Approach 1:
Multiple functions are merged into single components: the crank serves both as a motion converter and a positional controller for the hammer; the linkage arm combines guidance and force transmission functions; the strike plate integrates both the impact target and the seismic wave initiator. This merging reduces the number of separate parts and overall system complexity.
Solution Approach 2:
The motor serves multiple purposes: it provides power for hammer acceleration, controls the timing of impacts through crank rotation, and can be used to reset the mechanism after each strike. The crank mechanism universally converts rotational motion to linear hammer motion while also controlling strike position and force. This multi-functionality eliminates the need for separate components for each function.
4Measurement precision
If impact energy is increased for effective seismic characterization, then signal quality improves, but power consumption and force requirements increase
Solution Approach 1:
The biasing element performs preliminary action by storing potential energy during the hammer's retraction phase before impact. This pre-stored energy is released during the strike to amplify the impact force, allowing high impact energy without requiring proportionally high motor power or force during the actual strike moment.
Solution Approach 2:
The system controls impact parameters (energy, force, timing) by adjusting the crank rotation speed, hammer mass, and biasing element pre-compression. By changing these parameters, the system can optimize impact energy for different geological conditions without requiring a complete redesign, maintaining measurement precision while managing force requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The assembly provides a reliable, autonomous, and chatter-free seismic source suitable for spacecraft, with impact energies between 5 to 100 joules, low power consumption (11.2 W avg., 22.4 W peak), and a mass under 5 kg, enabling effective characterization of planetary surfaces.
Implementation Method 1
A one-way bearing can permit rotation of the crank relative to the drive shaft in the first rotational direction and inhibit rotation of the crank relative to the drive shaft in an opposed, second rotational direction
Implementation Method 2
The linkage arm can be configured to translate rotational movement of the crank to linear movement of the hammer
Implementation Method 3
A biasing element can be configured to bias the hammer toward the strike plate
Implementation Method 4
The motor can be configured to impart rotation of the crank in a first rotational direction
Data Source
AI summary
An assembly for providing an active seismic source includes a motor and a drive shaft coupled to the motor. A crank is coupled to the drive shaft. The motor is configured to impart rotation of the crank in a first rotational direction. A one-way bearing permits rotation of the crank relative to the drive shaft in the first rotational direction and inhibits rotation of the crank relative to the drive shaft in an opposed second rotational direction. The assembly also includes a strike plate, a track, and a hammer that is movable along the track along an axis that extends toward and away from the strike plate. The hammer contacts the strike plate. A biasing element biases the hammer toward the strike plate. A linkage arm couples the hammer to the crank and translates rotational movement of the crank to linear movement of the hammer.