ShortSCOPE: Optical Short-Period Seismic Sensor Designed for Planetary Exploration

This article presents ShortSCOPE, a compact optical force-balanced seismometer designed for planetary missions.

Key points

• Purpose: Detect seismic activity and study planetary interiors on targets such as the Moon, Europa, asteroids, and other ocean worlds.
• Technology: Uses a suspended coil–magnet proof mass with an 850-nm laser interferometer to measure extremely small displacements. Feedback forces keep the proof mass near equilibrium.
• Performance:
  • Target noise: approximately (1\times10^{-9}\ \mathrm{m/s^2/\sqrt{Hz}}) at 10 Hz
  • Flat acceleration response from 0.0095 to 150 Hz
  • Extended response up to approximately 400 Hz
  • Shock tolerance: up to 500 g
  • Random vibration tolerance: 14.1 g RMS
  • Thermal-vacuum qualification from −55 °C to +70 °C
  • Survival at housing temperatures as low as −170 °C
• Size and resources:
  • Approximately (3.2 \times 4) cm
  • Mass: 115 g per sensor
  • Power: 40 mW per sensor
• Deployment advantages: It can tolerate at least ±30° of tilt in lunar or Europan gravity, reducing or eliminating the need for leveling mechanisms.
• Design improvements over the commercial SiA sensor:
  • Larger proof mass, up to roughly 30 g
  • Lower mechanical resonant frequency, about 15 Hz
  • Modified leaf springs
  • Reduced self-noise through improved suspension and operation in low-pressure or vacuum environments
• Mission relevance: The sensor reached Technology Readiness Level 6 and is intended for potential deployment through the Lunar Environment Monitoring Station (LEMS). It could provide long-duration seismic observations near the lunar south pole, particularly at frequencies above 20 Hz.
• Scientific significance: On Europa, such measurements could help constrain ice-shell thickness, ocean depth, internal layering, tectonic activity, and high-frequency icequakes.

In short, ShortSCOPE combines optical displacement sensitivity with low power, small size, ruggedness, and high tilt tolerance, making it well suited to planetary surface missions where conventional broadband seismometers may be difficult to deploy.