For thousands of years explorers used the stars to navigate across the globe. Around 6,000 stars are visible to the naked eye under the best possible conditions (the sort you might get hundreds of miles out at sea for example) and mariners have typically used one or more of 58 navigational stars to chart a course on the open ocean.
Today’s explorers are pioneering new technologies and ideas in a completely different environment. Instead of mighty wooden ships they’re seeking new horizons with small satellites that can be just centimetres in length.
The technologies that combine in the build, launch and operation of these smallsats are some of the most advanced that humanity has ever created. But incredibly, these highly technical systems can still use the same approach that sailors have employed for centuries as part of their navigation - through the use of simple components called star trackers.
In this post we take a look at this fascinating piece of space equipment, discuss what to think about when selecting a star tracker for your satellite, and give an overview of some of the products available on the global marketplace for space.
If you’d like to skip the primer information and go straight to the product list, please click here.
Please note that this article is for information only and is not purporting to be an assessment of any of the products listed. If you need more information at any time, please don’t hesitate to contact us. In addition, while we try to be as comprehensive as possible new star trackers are coming to the market regularly and we will keep this article updated with new models and suppliers over time - so please check back often or consider bookmarking this page.
How star trackers work
In essence a star tracker is a simple navigational tool that can determine the orientation of its host satellite relative to certain stars.
It scans the starscape to pick out known stars and constellations contained in its catalogue and uses these to determine the satellite’s attitude.
The stars are located using cameras or photocells and onboard processing systems identify the images and process the measured position in the reference frame of the spacecraft.
Around 50-60 main navigational stars are primarily used to determine the satellite’s position, although for larger and more complex missions and spacecraft entire star field databases can be referenced in order to determine orientation.
What makes a good star tracker?
In order to work effectively a star tracker needs to be able to record accurate measurements of star positions during the satellite’s orbit. It needs to account for interference effects of light reflecting from the satellite’s surfaces or exhaust plumes during propulsion sequences.
The sensitive sensing components also need to be adequately protected from high radiation levels to continue working effectively and should also consume as little as power as possible.
As with most smallsat equipment, mass is obviously a factor. In addition, with many satellites incorporating a wider range of commercial-off-the-shelf (COTS) and bespoke sub-systems, interoperability and assembly options are also important when selecting a star tracker.
Star trackers available on the global marketplace
In the article section below we have included a selection of the star tracker products currently available on the market.
Please note that this list will be updated when new products are added to the global marketplace for space - so please check back for more or sign up for our mailing list at the end of the post for updates.
The ST200 and ST400 co-developed by Hyperion Technologies and Berlin Space Technologies
Hyperion Technologies and Berlin Space Technologies offer two star tracker models designed for varying mission demands and satellite sizes:
The ST200 - one of the world’s smallest and lightest fully autonomous, low power star trackers, aimed at applications in pico- and nano-satellite platforms. With an accuracy of 30 arcseconds and an extremely small physical footprint, the ST200 can be used in practically every platform that requires attitude determination.
The ST400 - with doubled attitude determination accuracy and improved radiation tolerance compared to the ST200, the ST400 is suitable for use in microsatellites and in more demanding missions. The ST400 is prepared to accept very narrow sun-exclusion angle baffles, which Hyperion Technologies can supply on demand. The dedicated RS422/RS485 interface allows networking of multiple ST400s which, combined with narrow sun-exclusion angle baffles, enables star trackin configurations to be found for even highly complex satellite and orbit geometries, there will always be a configuration that works.
The ST400 has been qualified for man-rated missions since October 2013 and has flight heritage since Q4 2015.
The NewSpace Systems (NSS) star mapper is used for accurate 3-axis attitude information in real-time and is optimized for small satellites. The star mapper uses a sensitive matrix CMOS sensor to ensure detection of enough stars above the limiting visible magnitude, and within the field of view, for 99% all-sky availability.
The NSS star mapper design is a low cost, mass, volume and power system featuring a built-in field-upgradeable star catalogue and star matching algorithm to allow the star mapper to initialise and refresh a fast tracking mode for fully autonomous operation.
The outputs of the NSS star mapper matches between the measured and catalogue vector pairs to an ADCS processor, where the data can be blended with other attitude and rate sensors in a full state Kalman filter. Additionally, the star mapper can also output an attitude quaternion referenced to J2000 inertial coordinates.
The STAR-T3 is a compact and autonomous star tracker that provides high accuracy determination. Precise results are provided based on an advanced star-tracking algorithm for micro and nano-satellite missions with a mission lifetime up to 5 years (minimum).
The STAR-T3 has been jointly developed by Terma A/S and Space Inventor ApS based on a scaled-down version of the Terma’s T1 star-tracker with a smaller optical system and computer processing unit based on high reliable COTS components.
The compact optics of the camera provide a 20° circular field of view and enough signal to track across the entire celestial vault. The standard baffle provides a Sun exclusion half-angle as low as 40° and the newly designed Optical Head features very few components, for high reliability and low recurrent cost.
The processing unit houses the star catalogue and the software algorithms for initial attitude determination and continuing attitude update, while also providing power to the camera.
The star tracker portfolio of Sodern S.A.
Sodern S. A. is a subsidiary of ArianeGroup with over 50 years’ experience in optronics and neutron technology. Sodern specialises in star tracker manufacture and has contributed to several cutting-edge projects including ESA’s Jupiter Icy Moon Explorer (JUICE) mission, NASA’s InSight and Europa Clipper missions, France’s MegaJoule Laser and the CNES’ PHARAO atomic clocks. Sodern manufactures an array of star tracker models to meet various mission requirements:
AURIGA-SA - a low-cost, plug-and-play star tracker for small satellites. Delivering at least 7 years’ guaranteed operation in low earth orbit and capable of supporting up to 2 optical heads connected to their own electronic unit. Thanks to algorithms inherited from HYDRA, the AURIGA-SA also offers excellent robustness, particularly at End-Of-Life and for high detector temperature conditions in both acquisition and tracking modes.
Auriga-CP - an innovative, low-cost, low-weight star tracker for small satellites. AURIGA-CP offers fast acquisition and arcsec tracking for 7+ years of guaranteed lifetime in LEO. Thanks to algorithms inherited from HYDRA, the AURIGA-CP also offers excellent robustness, particularly at End-Of-Life and for high detector temperature conditions in both acquisition and tracking modes.
HYDRA - a multiple head star tracker with separate optical heads and electronic units. HYDRA is versatile, robust, accurate and flight proven. HYDRA incorporates extensive autonomy, offering significant potential for AOCS simplification.
HYDRA-CP - a star tracker that is directly linked to the spacecraft’s processor. HYDRA-CP has a guaranteed lifetime of 18 years in GEO. HYDRA-CP autonomously manages any situation and the sensor always delivers accurate attitude data in operating domains with selectable update rates up to 16Hz.
HYDRA-M - a two-head star tracker with separate optical heads and electronic units, suitable for microsats, at moderate cost. HYDRA-M is intended for use on a temperature regulated base plate. Hydra-M is a small deviation from Sodern’s flight proven HYDRA Baseline Active Pixel Sensor (CMOS) star tracker.
SED26 - an autonomous CCD Star Tracker that operates in worst case Space environments, including maximum solar flares and 18 year cumulated dose in GEO. First flown in April 2005 to support the attitude control of a 15 year GEO spacecraft, the compact and low-weight SED26 provides all the features of a modern autonomous star tracker.
The CubeSat Pointing star tracker offers arc second range pointing accuracy for CubeSats. The custom algorithms are optimised for accuracy, robustness and low computational cost. The star tracker has a built-in baffle to reduce the effect of stray light and the system is compact and easy to interface in CubeSats and large satellites.
Antrix’s Star Sensor system provides attitude information for spacecraft pointing and control. The Mark-3 Star Sensor consists of optics, detector, embedded processor-based processing electronics, memory, and power circuitry. A baffle is used to eliminate unwanted stay-light entering the optics.
The Star Tracker VST-68M and VST-41M by Vectronic Aerospace GmbH
Vectronic Aerospace is a Berlin-based firm that manufactures mechanic and electronic subsystems for small satellites, with a focus on attitude determination and control, power control and data handling. The portfolio consists of flight proven components such as star trackers, reaction wheels, and magnetorquers, which have shown their reliability in various space missions. Vectronic offers two star tracker models designed for small satellites:
The VST-41M is a high performance 3-axis star tracker for small satellite applications with the technical capabilities and radiation tolerance suitable for LEO, GEO and even for interplanetary missions. The sensor has been successfully used in several small satellite missions showing excellent in-orbit performance.
The VST-68M performs direct and autonomous measurement of the spacecraft attitude in the body fixed star tracker reference frame relative to the celestial reference system J2000.
Nano Star Trackers by Blue Canyon Technologies Inc.
Blue Canyon Technologies’ Nano Star Tracker (NST) range offers reliable, high-performance design compatible with a variety of CubeSat and Nanosat configurations and missions. The Star Trackers include an internal baffle and electronics, user-friendly interfaces and feature over 99% sky coverage and a 10x12 degrees field of view. They are also designed to operate for more than 5 years in low earth orbit (LEO). In addition, the products all feature star tracking down to 7.5 magnitude, an on-board star catalog featuring more than 20,000 stars and lost in-space star identification.
Three models are available:
The Standard NST - 0.35 kg (w/ baffle), volume of 10x5.5x5 cm and 45 degrees (half cone) sun keep out.
The Extended NST - 1.3 kg (w/ baffle), volume of 25x10x10 cm and 17.5 degrees (half cone) sun keep out.
The Thin Slice NST - 0.2 kg (w/ baffle), volume of 10x10x3 cm and 90 degrees sun keep out.
The Second Generation Star Tracker (ST-16RT2) and Laser Downlink plus Star Tracker by Sinclair Interplanetary
Sinclair Interplanetary builds high-performance star trackers and baffles for small spacecraft. There are currently 55 on-orbit.
The Second Generation Star Tracker (ST-16RT2) is a low-power (less than 0.5W) system weighing just 29.6 grams and featuring a lifetime of 13 years. The star tracker’s attitude knowledge error is 5 arcsec and it has a slew tolerance of less than 3 deg/s. In addition, the small footprint (62x56x38 mm) enables the ST-16RT2 to be easily integrated into a variety of satellite sizes.
The Laser Downlink plus Star Tracker features internal fine-pointing to ground station based on built-in star tracker and a passive ground receiver with a 0.55m diameter Newtonian telescope with silicon APD. The star tracker performance is; 5 arcsecond cross-boresight (RMS) and 55 arcsecond around boresight (RMS), and the product has a mass of 335g and a small physical volume of 79x68x68mm. The system also features a lifetime of 13 years in GEo or 9 years in GEO and a downlink data rate of 1 Gbits/s in 1000 km range at 250 Mbits/s at 2000 km range.
Autonomous Star Sensors by Jena-Optronik GmbH
Jena-Optronik GmbH manufactures autonomous star trackers for a wide range of LEO and GEO applications and has more than 20 years’ experience in star sensor development:
ASTRO 10 - a fully space-qualified autonomous sensor with an Electronic Box separated from the Optical Head for a flexible accommodation on the spacecraft, giving minimum impact on the S/C structure with respect to thermal and mechanical stress and therefore providing maximum pointing accuracy. The ASTRO 10 has a mission lifetime of more than 12 years.
ASTRO 15 - The ASTRO 15 combines a high degree of flexibility with outstanding features for lifetime, reliability and robustness. The sensor is a flight proven, autonomous star tracking system for long-term GEO and LEO missions on telecom, science and Earth observation satellites. More than 130 flight units of the ASTRO 15 sensor have been ordered for geostationary communication / Earth observation satellites. More than 50 Flight Models are operating successfully in orbit. The ASTRO 15 has been selected as the standard star sensor for Boeing’s 702 platform.
ASTRO APS - The ASTRO APS uses advanced radiation hard CMOS Active Pixel Sensor (APS) detector technology. With a single box design with minimized dimensions, low mass and low power consumption, while maximizing the ease of integration. The ASTRO APS shows high reliability and radiation hardness by careful selection of EEE Parts, reduced number of components and special software algorithms to cope with radiation events. Featuring attitude quaternion accuracy of <1arcsec (1sigma) and a new level of compactness compared to CCD-based star sensors for the GEO telecom market (>18 years life time, <25 years radiation robustness for GEO missions). The improvements in dimensions and performance are realized with the replacement of the CCD detector by the APS detector technology.
The A-STR , AA-STR and SPACESTAR by Leonardo Finmeccanica S.p.A
Leonardo Finmeccanica S.p.A is a Italy-based space business active in a number of sectors including; Earth observation, remote sensing for weather phenomena and ecosystems, communication and navigation, intelligence services, space exploration missions. Leonardo manufactures three star tracker models:
A-STR - a medium Field of View (FOV) star tracker integrated in a single assembly with a radiation hardened design. Featuring robust and accurate three-axis attitude determination with very low mass and power consumption for the class of instrument. The high performance of its CCD detector means that the A-STR can be used in extremely accurate pointing space telescopes and in agile (or spinning) satellites. This is achieved via the A-STR’s dedicated operative modes that can be entered via telecommand. More than 100 A-STR FMs have been sold for GEO, LEO and inter-planetary missions since 2001 and more than 90 years of successful operations in space have been accumulated to the date.
AA-STR - a medium Field of View (FOV) star tracker integrated in a single assembly with a radiation hardened design. The tracker features robust and accurate three axis attitude determination with very low mass and power consumption for the class of instrument. The AA-STR is a high TRL-9 next generation product. The AA-STR, while offering similar performance and improved radiation capabilities with respect to CCD based star trackers, incorporates all the advantages of miniaturization and reduced weight, power and cost.
SPACESTAR - SPACESTAR (Satellite Platform Avionics Computer Embedding Star Tracker Algorithms And Resources) is a novel star tracker architecture, originally developed for a high volume constellation program which, through an integrated configuration to Attitude Control System computers, enables significant size, weight, power and cost benefits. The results of these efficiencies provide the ability to utilize high performance star tracking systems on small satellites that were previously unable to accommodate the size, weight, and power of legacy architectures.
The Terma HE-5AS Star Tracker is a fully qualified design, offering a favorable combination of arc-second performance at an affordable price. Robust algorithms provide full autonomy in initial attitude acquisition and attitude update. Terma quality standards, documentation and component screening meet the requirements of discerning customers including the European Space Agency and the U.S. Department of Defense.
The Camera is separate to make it easier to accommodate on the satellite, and to minimize heat dissipation (<1.5W) near the sensor. The camera is a compact, weighing less than 1.0 kg. The optics provides a 22º field of view and – although compact – provides enough aperture to track across the entire celestial vault. A cable provides digital data-link (LVDS) and power supply from the processor unit. The Camera can be supplied with a thermo-mechanically stable bracket.
Custom or standard baffles are available providing a Sun exclusion half angle as low as to 30º. The processing unit houses the star catalogue and the software algorithms for initial attitude determination and continuing attitude update. Also, the unit provides power to the camera. The interface towards the spacecraft is redundant RS-422 or MIL-STD-1553, and a power supply voltage from +22 V to +34 V and dissipation is 5.5 W.
The MAI-SS Space Sextant is a low-cost Star Tracker intended for CubeSat and SmallSat missions. The unit is completely self-contained and features ‘Lost in Space’ star identification. Just apply power and begin receiving quaternions accurate to about 5.7 arcseconds.
The system has been extensively rate tested and shown to have 96.4% availability of solutions at rates in excess of 2°/sec. The electronics have been radiation tested to 75krad while an optional baffle provides 45° Sun rejection. The MAI-SS is available in either vertical or horizontal mounting. As this product was developed under NASA SBIR funding, U.S. Government customers may purchase this product on a non-competitive basis.
Amanogi provides the Star Tracker (STT) system for micro- and CubeSats. The product that can estimate the attitude in the star coordinate system by matching with the star coordinate catalog. Amanogi’s aim is to deliver at half the market price and development time, ensuring that you’re able to get your systems to the launchpad as quickly as possible.
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