SSTL-Precision

Quick facts

Overview

Summary

Mission Capabilities

SSTL’s Precision imager consists of a novel architecture supporting rapid-tasking and high spatio-temporal resolution applications; built by SSTL for ESA’s inCubed programme. The Precision imager is capable of acquiring both Panchromatic (PAN) and MS imagery. 

Performance Specifications

The Precision imager has a ground sample distance (GSD) of 0.6 m for PAN, and 1.2 m for MS, which includes blue, green, red, and near infrared (NIR) spectral bands. Sub-metre resolutions are achievable with half-pixel shifting and a novel CMOS-in-CCD architecture. The imager also features a 9.5 km swath width, daily coverage of 130,000 km2, and a throughput of 1.5 TB per day. Multiple imaging modes are available, including along and across track stereo, mosaic mode, strip, spot, and inclined strip mode.
SSTL-Precision will have a revisit time of between 1-5 days, depending on target latitude, and can be enhanced when operated in a constellation. The satellite will operate in a 500 km Sun-synchronous orbit.

Space and Hardware Components

SSTL-Precision’s platform provides low-cost satellites ideal for constellation deployment with easy rideshare facilitation. Six SSTL SSW-100 reaction wheels support high agility and rapid tasking of high priority imagery, with its ability to acquire imagery separated by 60° in only 60 seconds. Two SSTL XTx-800 transmitters are used onboard Precision, supporting approximately 2400 Mbps over-the-air transmission rates.
The satellite has a seven year design life with a ten year target, and an approximate mass of 280 kg.
 

Overview

Surrey Satellite Technology Ltd. (SSTL)’s Precision satellite is a very high resolution (VHR) optical satellite that will provide high quality imagery in support of pan-sharpened colour mapping and surveillance applications. 1)

SSTL-Precision has government applications that concern high priority and private tasking of imagery, and commercial applications in data analytics and numerous low cost value-added services. The multispectral (MS) imagery of the spacecraft can support mapping, surveillance, infrastructure and asset monitoring, disaster monitoring, and insurance and loss adjustment.

The mission will achieve sub-metric imaging capability through careful sensor technology selection and designing for a low orbital altitude, whilst maintaining customer convenience. The spacecraft is designed for rideshare opportunities and constellation deployment, enabling high temporal resolution at the cost of a single high resolution satellite. 7) 8)

The mission has an emphasis on maximising its performance-to-cost ratio by resolving more information from a smaller aperture sensor hosted in a small, low-cost spacecraft. The spacecraft design is optimised for low-cost manufacture without compromising on stability and performance. 6)

Spacecraft

SSTL-Precision is designed for compactness in order to support affordable operations as a single unit or within constellations providing higher temporal resolution. Based on the SSTL-300 / SSTL-mini satellite platform, the Precision spacecraft is larger than the Carbonite high resolution imaging spacecraft, and provides a greater data return at higher resolution. 1)

The spacecraft supports wide launcher compatibility including 3-4 satellites onboard Vega, PSLV, and Soyuz launchers, an approximate launch mass of 280 kg and a seven year design life with 10 year target life, supported by redundant avionics onboard. Precision also supports high agility, capable of ±45° roll/pitch with 60 seconds between successive images separated by 60°. The platform’s propulsion capabilities facilitate orbit maintenance and correction, as well as end-of-life disposal. Precision’s payload employs a passive athermal approach which prevents excess thermoelastic stress in the mirrors and minimises bowing of the detector during operation. 6)

Precision is based on the SSTL-Mini platform, the latest iteration of the SSTL-300 platform, which has extensive flight heritage and is subject to many upgrades and enhancements. Through SSTL’s proven low-cost techniques, paired with high agility and data throughput, Precision provides unprecedented ‘bang for your buck’ to customers. 6)

SSTL addresses the demand for low-cost batches of satellites for use in constellations through investigated, qualified and implementation of a new satellite platform production process paired with a new set of avionics. The process makes use of automated manufacture and testing, which generates significant savings in production and schedule costs. 7)

The SSTL-developed XTx-800 transmitter has been selected for SSTL-Precision, building on SSTL’s X-band transmitter heritage for increased throughput. XTx-800 can support up to ~1200 Mbps over-the-air transmission with advanced modulation protocols, and Precision will be equipped with two of these transmitters in conjunction, effectively doubling its data transmission rate. This improvement allows Precision to maximise its output of high resolution imagery gathered over its lifetime. 8)

Precision features an attitude and orbit control system (AOCS) improved from DMC-3 heritage, which includes six SSTL SSW-100 reaction wheels over the four used on the DMC-3 mission. More reaction wheels facilitates improved acceleration and retargeting rates, even in the event of a reaction wheel failure. A field of regard of 45° in pitch and roll is achieved, and paired with its high agility enables a range of novel imaging modes. High resolution imagery paired with these acquisition modes provides Precision with applications in disaster monitoring, risk assessment, reconnaissance, and urban planning. 8)

Launch

Orbit

SSTL-Precision will operate in a 500 km Sun-Synchronous (SSO) orbit with 10:30 local time of ascending node (LTAN). Precision will have a revisit time of between 1-5 days, with the 5-day estimate representing the worst-case revisit time for a target at 0° latitude.

Sensor Complement

Precision Imager

The Precision imager is a novel very high resolution (VHR) optical imager capable of acquiring both Panchromatic (PAN) and four-band Multispectral (MS) imagery. The imager can achieve a spatial resolution of less than 0.5 m with half-pixel shifting. Precision’s detector is a novel CMOS-in-CCD architecture that achieves low power consumption, read-noise, time delay, and high integration capability. The TDI CMOS sensor is provided by Teledyne e2V. The Precision Imager is built by SSTL as part of ESA’s InCubed programme. 1) 2) 8)

The imager supports imaging modes in along-track and across track stereo, 2x2 mosaic mode, and strip/spot/inclined strip modes. To improve the spatial sampling of the satellite operating in pushbroom (along-track) mode, additional overlapping samples of the same object can be collected at close time intervals and processed together. This removes the view that sampling is dictated by the sensor pixel size on the ground (GSD). 6)

The half-pixel offset incorporated by the sensor reduces aliasing in pushbroom imagery, and has proven flight heritage on the French SPOT-5 mission. The Precision imager features a 420 mm clear aperture primary mirror, a 4200 mm focal length, and four banks of offset pixels which achieve double the sampling of a conventional sensor. Each pixel is offset to one another by half, which are used to obtain additional samples.

References  

1) “SSTL-Precision,” Surrey Satellite Technology Ltd., URL:  https://www.sstl.co.uk/getmedia/e7a0554d-ca08-41d2-9ade-ec7f68fbbc20/SSTL-PRECISION.pdf

2) “Precision Multispectral Imager,” Surrey Satellite Technology Ltd., Missions in Build 2023, URL: https://www.sstl.co.uk/space-portfolio/missions-in-build/2023

3) “Earth Observation Spacecraft,” Surrey Satellite Technology Ltd., URL: https://www.sstl.co.uk/what-we-do/earth-observation-spacecraft

4) “Innovations,” Surrey Satellite Technology Ltd., Space Portfolio, URL: https://www.sstl.co.uk/space-portfolio/innovations

5) Andrew Haslehurst, “Precision an ultra-high resolution satellite,” Surrey Satellite Technology Ltd., URL: https://ceoi.ac.uk/wp-content/uploads/2021/09/Precision-an-ultra-high-resolution-satellite_Haslehurst_reduced_part1.pdf

6) H. Law, A. Haslehurst, S. Knox, V. Irwin and M. Sweeting, "Bang for Your Buck: Extracting Sub-50cm Performance from a Small Satellite Mission," IGARSS 2023 - 2023 IEEE International Geoscience and Remote Sensing Symposium, Pasadena, CA, USA, 2023, pp. 4594-4597, doi: 10.1109/IGARSS52108.2023.10283423.

7) da Silva Curiel, Alex, Andrew Cawthorne, and Martin Sweeting. "A low cost video and still imaging constellation for high temporal coverage," Surrey Satellite Technology Ltd, URL: https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=2ac864adaf082a724026618d1954660aeb9dea59

8) Law, Hamilton, et al. "Breaking the Smallsat Barriers to Sub-50cm Imaging," Surrey Satellite Technology Ltd, 2023, URL: https://digitalcommons.usu.edu/smallsat/2023/all2023/174/