Miniature Optical Systems for CubeSat Applications

Key Takeaways

• Miniaturized optics are revolutionizing CubeSats by providing high-resolution imaging, agile beam steering, and real-time spectrum analysis on a much smaller scale
• Innovations like folded telescopes, MEMS mirrors, and compact spectrometers allow advanced performance in tight 1U-6U payloads
• Optical engineers use techniques like additive manufacturing, athermal designs, and hermetic sealing to overcome challenges such as vibration, thermal shifts, and radiation
• Small but powerful optical devices make space missions more flexible, cost-effective, and data-rich than ever before

Led by CubeSats, the small satellite (small sats) revolution has broken down traditional barriers to space exploration and Earth observation.

From capturing stunning photographs of distant galaxies to providing real-time surveillance of the planet, these compact spacecraft are accomplishing feats that were previously impossible on such a small scale. Miniature optics has been a key player in enabling this transformation.

This article explores the interesting world of miniature optical systems intended for CubeSats, which include cutting-edge telescopes, MEMS mirrors, and spectrometers.

Looking at their technical specifications, this article will demonstrate the innovative design advantages they provide, the manufacturing challenges they face, and compelling real-world examples that illustrate the engineering brilliance behind these compact, high-performance payloads.

CubeSat telescopes. Image Credit: Avantier Inc.

Compatible Telescopes: Big Vision, Small Package

Technical Information:

CubeSat telescopes, available in 3U to 6U platforms, use folded optical systems to optimize focal length despite limited space. Key configurations include

• Richey-Chrétien or off-axis reflective designs eliminate color distortion and provide sharper images
• The apertures range from 60-100 mm, resulting in effective focal lengths of 300-1000 mm
• Innovative usable optics and custom baffles minimize stray light and allow for wider apertures after their launch

RC Telescope. Image Credit: Avantier Inc. 

Advantages:

CubeSat telescopes offer numerous advantages. These include:

• Outstanding ground resolutions of 5-10 meters per pixel from a 500-kilometer orbit
• Impressively compact payload volume of 1U-3U
• Compatible with both off-the-shelf and customized CMOS/CCD detectors

Manufacturing Challenges:

These high-performance systems can be difficult to manufacture. Key issues include:

• Reducing weight without sacrificing structural strength
• Developing dependable small actuator systems for critical activities such as focusing and deployment
• Maintaining exact optical alignment during launch vibrations and high orbital temperature variations

Innovative Solutions:

Avantier's design team consistently leads the manufacturing industry, finding creative solutions to these problems.

Some examples are:

• Using diamond turning and optical polishing on lightweight aluminum mirrors
• Incorporating athermalized designs to adapt to thermal changes
• Using additive manufacturing with high-performance materials like titanium or carbon-reinforced plastics for precision mounting

MEMS Mirrors: Agile Beam Steering in a Tiny Footprint

Technical Information:

MEMS (Micro-Electro-Mechanical Systems) mirrors are extremely fast-acting, tiltable devices used for precision beam steering in CubeSat payloads.

• Tip/tilt actuation from ±5 ° to ±30 °
• Response times in the sub-millisecond range for bandwidths greater than one kHz
• Silicon-based platforms are commonly coated with silver (Ag) for enhanced reflectivity in VIS-NIR wavelengths

Advantages:

MEMS mirrors have several advantages, including:

• Compact size (usually less than 10 mm²)
• No mechanical links, improving dependability and reducing power consumption
• Providing dynamic target tracking, accurate jitter correction, and fast raster scanning for LIDAR and imaging applications

Manufacturing Challenges:

Production of these high-performance mirrors has particularly unique challenges:

• Maintaining surface flatness and homogeneous coating to avoid optical distortion.
• Reducing vulnerability to extreme vacuum conditions and harmful radiation exposure.
• Providing durable vacuum packaging and hermetic sealing for long-term orbital operation.

Ingenious Solutions:

Avantier's optical engineers are constantly looking for new ways to enhance their designs. Their solutions involve:

• Advanced fabrication techniques like Silicon-on-Insulator (SOI) wafer processing and deep reactive ion etching (DRIE).
• Protective SiO₂ overcoats.
• Hermetically sealed packaging with glass frit bonding or anodic bonding.

Compact Spectrometers: Unlocking Spectral Intelligence from Orbit

Technical Information:

CubeSat-ready spectrometers are transforming in-orbit chemical and environmental analyses. The key technologies include:

• Diffraction grating-based slit spectrometers (transmissive and reflecting).
• Compact size, typically less than 1U.
• Lightweight, usually around 500 grams.
• FPIs provide extremely selective and customizable bandpass filtering.
• Hyperspectral imagers provide high spectral resolution (10-20 nm) for visible and shortwave infrared (VNIR/SWIR) bands.
• Low power consumption, often under 5 watts.

Advantages:

A small spectrometer offers various advantages to miniature spacecraft. For example:

• Real-time gas analysis, mineral mapping, and vegetation health monitoring.
• High compatibility with sophisticated CMOS and InGaAs detector arrays.
• Enabling robust deployment through monolithic or semi-monolithic integration.

Manufacturing Challenges:

Manufacturing challenges for miniature spectrometers include:

• Maintaining high grating replication precision and constant groove quality.
• Maintaining accurate co-registration and steady calibration in the challenging orbital environment.
• Minimizing stray light and maximizing throughput in compact designs. 

Innovative Solutions:

To address these issues, consider:

• Using nanoimprint lithography to replicate gratings precisely on glass or polymer surfaces.
• Direct bonding optical elements to stable silicon bench structures.
• Integrated micro-optic collimators with thermoelectric stabilization.

System-Level Integration: A Holistic Approach

Integrating compact optics into the larger satellite bus necessitates careful consideration of various linked variables.

Source: Avantier Inc. 

Miniaturized Optics for Small Satellites and CubeSats

Miniaturized optics for Small Sats and CubeSats have significantly altered the capabilities of CubeSats and the larger nano satellite scene.

From sophisticated telescope designs that enable groundbreaking astronomical observations to agile beam steering for dynamic applications and real-time spectroscopy that provides invaluable environmental insights, the convergence of photonics, micromechanics, and systems engineering is encouraging remarkable progress.

Engineers continue to design and create compact optical systems that meet, if not surpass, the performance norms set by much bigger spacecraft. Their designs successfully address major manufacturing issues, including alignment stability, thermal performance, and flawless component integration.

As the demand for timely and cost-effective space-based data grows, micro-optics will remain a key component in developing scalable and intelligent space missions for many years to come.

Breakthroughs in optical engineering will likely unlock even more possibilities from these small but powerful systems in the future.

This information has been sourced, reviewed, and adapted from materials provided by Avantier Inc.

For more information on this source, please visit Avantier Inc.