Rapideye - an Earth Observation Smallsat Constellation for Daily Agricultural Monitoring

SSC03-VIII-6

RAPIDEYE - AN EARTH OBSERVATION SMALLSAT CONSTELLATION FOR DAILY AGRICULTURAL MONITORING

Dr. George Tyc, Keith Ruthman MacDonald Dettwiler & Associates 13800 Commerce Parkway, Richmond B.C., V6V 2J3, Canada Tel: 604 278 3411 Fax: 604 231 2127 Email: [email protected]

Paul Stephens, Alex Wicks, Tim Butlin, Dr. Manfred Krischke, Michael Oxfort Prof. Sir Martin Sweeting RapidEye AG Surrey Satellite Technology Ltd. Wolfratshauser Str. 48 Surrey Space Centre , University of Surrey 81379 München Guildford, Surrey GU2 7XH, UK Tel: +49 89 72495 455 Tel: (44) 1483 689278 Fax: (44) 1483 689503 Fax: +49 89 72495 291 Email [email protected] Email: [email protected]

ABSTRACT The RapidEye mission is a commercial remote sensing mission by the German company Rapi- dEye AG. The RapidEye mission will deliver information products for various customers in the agricultural insurance market, large producers, international institutions and cartography. The mission that generates these information products consists of a constellation of five identical small satellites and a sophisticated ground infrastructure based on proven systems. The five satellites will be placed in a single sun-synchronous orbit of approximately 620 kilome- ters, with the satellites equally spaced over the orbit. The satellites will each carry a 5 band multi-spectral optical imager with a ground sampling distance of 6.5 meters at nadir and a swath width of 80 km. The RapidEye system has the unique ability to image any area on earth once per day and can also provide large area coverage within 5 days. This capability along with the processing throughput of the ground segment allows the system to deliver the information products needed by the customers reliably and in a time frame that meets their specific needs.

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Introduction prehensive information for these purposes. The RapidEye Mission is a commercial undertaking by the German company • Cartography: The need for current RapidEye AG who intend to offer a land maps is significant given that much of information service to a variety of custom- the current data is out of date. Rapi- ers. These information service products are dEye will be the first company to based on the data that is generated by a provide regular updates at a scale of constellation of Earth Observation satel- 1:25,000. Commercial sales to the lites. Macdonald Dettwiler & Associates military will be a major opportunity in (MDA) is the prime contractor for the mis- this segment. sion responsible for the implementation of the entire system, including the develop- ment of the space and ground segments, Key Mission Requirements launch and in-orbit commissioning and To meet RapidEye’s business needs, the calibration of the spacecraft constellation, mission design must have the following and establishing the mission operations key characteristics: infrastructure. • Multi-spectral Optical Imager: High quality ortho-rectified imagery is required in 5 spectral bands that provides RapidEye Key Market Segments a ground sampling distance (GSD) be- The information products that RapidEye tween 5–10 m. will be offering are focused on the follow- • Global Daily Revisit: Rapid turn- ing four key market segments: around from a customer’s request for • Agricultural Insurance: RapidEye information products to delivery is a will offer regularly updated field maps key requirement for RapidEye’s mar- to help insurers in the insurance con- ket segments. Hence, it is required that tract assessment and will support the the satellites have daily revisit capabil- loss adjustment process by providing ity anywhere on the Earth. quick and reliable information about • Rapid Area Coverage: To allow moni- damaged areas. toring large areas of interest and • Agricultural Producers: The informa- provide frequent information updates tion generated by the RapidEye system to customers, the system must have the will support the precision farming sys- capability to provide large area cover- tem substantially by regularly age in less than 6 days for the primary providing crop condition information. regions of interest. • International Institutions: Interna- • Large Data Capacity: A significant tional agencies and institutions require ortho-image data capacity is required knowledge of the levels of expected to allow building up and maintaining crop harvests, monitor the usage of an extensive database of information subsidies and provide emergency relief for large areas of interest. in disaster situations. RapidEye will be able to provide up-to-date and com-

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Spacecraft Control Centre

Figure 1 The RapidEye System

RapidEye Mission Overview (FOV) can be oriented across track by rolling the spacecraft up to +/-25 degrees To achieve the key business requirements, to provide the necessary coverage capabil- RapidEye system consists of five identical ity. The RapidEye mission ground small satellites and a ground infrastructure infrastructure includes: a dedicated Space- as shown in . craft Control Centre to control the spacecraft constellation; a ground segment Rapideye Constellation that provides the data processing, archiv- The five satellites will be launched to- ing facilities and the customer interface; gether on a single launch vehicle into a commercial data downlink sites; and the sun-synchronous orbit at an altitude of RapidEye value-added product processing approximately 620km. The satellites will facility that uses the ortho-rectified image be in a single orbit plane, equally spaced data from the ground segment to generate around the orbit. As a result, the satellites the information products needed by the follow each other approximately 19 min- customers. The key mission parameters are utes apart. Each satellite, weighing given below in Table 1. approximately 150 kg, carries a push broom optical imager that provides a swath width on the ground of approximately 80 km. The imager’s field-of-view

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Table 1 Key Mission Parameters. design is based on a flight proven microsat platform requiring very little new devel- Parameter Value opment. The small spacecraft size allows Orbit 600-620 km, all 5 spacecraft to be launched on one sun-synch launch vehicle providing significant cost Number of Satellites 5 savings to the program. Also, the identical Spacecraft Mass 150 kg design for all five spacecraft enable the Image Data Downlink > 60 Mbps advantages of scale and efficient assembly (in X-band) and integration. To address the high reli- Onboard Data Storage > 1500 km of im- ability, two redundancy levels have been age data designed into the mission. First the space- Max Spacecraft Roll Angle 25 deg craft has internal redundancy for mission critical components and graceful failure Payload Type Push broom scanner modes (i.e., providing reduced perform- (no moving parts) ance in the event of a failure) so that they are at least one failure tolerant. Second, all No. of Optical Bands 5 the RapidEye business requirements can (400–850 nm) be met by a constellation of only four sat- Detector 12 K pixel linear ellites, allowing for a total failure of one CCD per band satellite. This comprehensive set of redun- Nadir Pixel GSD 6.5 m dancy is considered a key requirement for investors in the RapidEye business.

Swath Width 80 km The Rapideye Spacecraft

Global Revisit Time < 1 day The RapidEye Spacecraft is shown in Fig- ure 2. The overall spacecraft mass is approximately 150 kg, which includes Average Coverage Repeat < 5 days about 35 kg for the Payload. Period (Europe & North America) Spacecraft Bus DEM Generation Capabil- Yes ity The spacecraft bus will be developed by Surrey Satellite Technology Ltd (SSTL) Mission Lifetime 7 years and will be based heavily on a flight proven design. The general spacecraft lay- out has the spacecraft divided into two Mission Implementation separate functional volumes. At the base To meet the business objectives, the Rapi- of the spacecraft is the core bus hardware dEye mission implementation must be including the launch vehicle separation highly cost effective while providing a system, which is baselined as a 4 point high degree of reliability. To achieve the release system with integral deployment cost and reliability goals of the program, springs. At the top end of the spacecraft is the spacecraft hardware is based, to the the payload which is comprised of a Multi- maximum extent possible, on heritage de- spectral Imager (MSI) and a Payload Elec- signs. For example, the spacecraft bus tronics Unit (PEU) as shown in Figure 2.

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Three body mounted GaAs solar panels The compact spacecraft configuration is are located on the +X (velocity direction), required to allow launching 5 spacecraft -Z (zenith), and –X faces of the spacecraft. together on a single launch vehicle.

Star Camera Multi-Spectral Imager

Payload Electronics Unit

GaAs Solar Arrays (3 sides)

720 mm

X Z (velocity vector) (nadir) 865 mm 750 mm

Figure 2 The RapidEye Spacecraft

The architecture of the spacecraft is shown NiCd battery packs providing a total ca- in Figure 3. Redundant spacecraft onboard pacity of 8 A-hrs. The Battery Charge computers (OBC’s) are used to perform all Regulators (BCR’s) are based on a Peak bus housekeeping functions. A dual re- Power Tracking approach. Six individual dundant CAN bus architecture provides BCR’s are used (2 per solar panel) which communication between the OBC’s and also provides some graceful failure modes the other spacecraft subsystems including should a failure occur. the Payload. This provides a reliable The attitude control system relies on 4 means for controlling the spacecraft sub- reaction wheels for 3-axis control with systems and managing the onboard redundant magnetic torques for momen- redundant systems. tum management. Redundant sun sensors The power system consists of the three and magnetometers provide the coarse GaAs solar panels which provide about attitude knowledge with a star camera pro- 100 W of power generation capability viding the high accuracy attitude when in the sun. The battery uses two information. To minimize alignment atti-

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tude knowledge errors, the star camera is knowledge and also to provide timing syn- mounted directly to the payload optical chronization with the payload. bench. The propulsion system is based on The TT&C uplink and downlink utilizes a cold gas blow down system utilizing a redundant S-band transmitters and receiv- resistojet thruster with a single propellant ers, while the data downlink utilizes a tank and associated plumbing located in dedicated X-band transmitter providing a the middle section of the bus. On-board data rate > 60 Mbps. A fully redundant GPS is used to provide accurate orbit transmitter and antenna chain is provided as shown in Figure 3.

Comms Command and AODCS Data Handling AlRxSa0t Rx0 XYZ? XYZ? AlSat Rx0 2x SS--banbandd Prop.

CACANN SIL SIL SIL SIL SIL SIL Uo-12 Uo-12 Star Prop. MTR-10 MTR10 MTR-10 Uo-12 Uo-12 SS-1 SS-2 SS-3 Star MTR-10 MTR10 MTR-10 Mag 0 Mag 0 SS-1 SS-2 SS-3 Mapper MTQ-X MTQ-Y MTQ-Z Mag 0 Mag 0 Mapper AlAlRxSaSa1ttRRxx11 MTQ-X MTQ-Y MTQ-Z SS--banbandd PPrrooppuullssioionn CACANN CoContntrroolllleerr

CACANN

ALALSASATT--mimicrcroo SSttararMMaappppeerr ADADCSCS inintteerrffaaccee MMoodudulele SGSGRR--1100 PPS CAN CAN SSppacacehehabab CAN CAN AlAlTxSaSa0ttTTxx00 GPS GPGPSS SS--banbandd CACANN 38 kbps RW1 RW2 RW3 RW4 PPS CACANN UO-12 UoUo--1122 UO-12 OBC386 OBOBCC338866 OBC386 AlTxSa1t Tx1 AlSat Tx1 CAN CAN SS--bbanandd CAN CAN CAN CAN CAN CAN 38 kbps CAN CAN CAN CAN CACANN

Umbilical CAN 0 CAN 1

Power CACANN CACANN PPayaylloaodad X-band Tx >60 Mbps BCBCR(R(ss)) Power Control interface to bus PCMPCM PDPDMM PCPCMM BCBCR(R(ss)) X-band Battery BBCCR(R(ss)) Battery 28 V Tx (unregulated) >60 Mbps Power Control interface to bus Figure 3 Spacecraft Block Diagram and Architecture

Multi Spectral Imager Design The Rapideye Payload The MSI is a pushbroom style imager The RapidEye payload on each spacecraft which images the earth in 5 spectral bands is comprised of 2 separate units, a Multi over a 80 km swath at 6.5 m resolution (at Spectral Imager (MSI), and a Payload nadir). The collector optics image onto Electronics Unit (PEU) as shown in Fig- five parallel linear 12K pixel CCD detec- ures 2 and 4. tors. The collector optics utilizes a Three

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Mirror Anastigmat (TMA) design. The mable table of coefficients. This must be requirements for the optical camera are done prior to data compression to prevent well within what has already been demon- image defects from biasing the compressed strated for similar systems. The required data. CCD correction coefficients, derived aperture is approximately 150 mm. Filters, from imaging of ground calibration sites, placed in close proximity to each CCD, can be periodically uploaded from the separate the spectral imaging bands. The ground station. five spectral bands are as follows: The corrected image data can be processed Table 2 RapidEye Spectral Bands. in a variety of ways to reduce data volume prior to transmission. Pixel binning in 2x2 Channel Spectral Spectral or 3x3 sizes provides the most rudimentary Band Name Range (nm) data compression method (one axis is bin- 1 Blue 440 – 510 ned directly on the CCD to reduce readout 2 Green 520 – 590 noise). The PEU also supports both se- 3 Red 630 – 685 lectable lossless 2:1 compression and lossy 4 Red edge 690 – 730 (up to 10:1) compression ratios based upon 5 Near IR 760 – 850 direct cosine transform (DCT) or wavelet algorithms. The compressed data, together with space- Payload Electronics Unit Design craft GPS and attitude information, is stored in mass memory, which provides Each CCD produces 4 outputs, which are sufficient storage for a 5-band imaging synchronously clocked out by the detector swath length of up to 1500 km at 2.5 readout electronics at a rate of approxi- bits/pixel. The final stage of processing is mately 3.2 MHz, allowing for 12 bit performed by the data formatter, which digitisation with low readout noise. The encodes the data for error correction and raw pixel data, totalling nearly 765 Mbps, encryption and sends it directly to the is transferred to the PEU via a set of high spacecraft X-band transmitters. speed serial interfaces. The PEU provides overall control of the The PEU provides a separate processing imaging process. Each imaging segment chain for each CCD, with a redundant can be individually configured for differ- chain cross-strapped to the others. The ent compression schemes, allowing first step in the processing chain is to cor- multiple user data requirements to be met. rect CCD data, in real time, for gain and offset non-uniformities using a program-

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CDS / ADC AUTO SELECTION & CCD READOUT CORRECTION COMPRESSION

IMAGING CDS / ADC AUTO SELECTION & CCD INTERFACE OPTICS READOUT CORRECTION COMPRESSION MULTI-BANK DATA CONTROL SELECTABLE FORMATTER AND TELEMETRY MASS INPUT (REDUNDANT) CDS / ADC AUTO SELECTION & STORAGE CCD SELECTOR READOUT CORRECTION COMPRESSION

CDS / ADC AUTO SELECTION & CCD READOUT CORRECTION COMPRESSION

AUTO SELECTION & INPUT BAFFLE CORRECTION COMPRESSION

OPTICAL BENCH

INSTRUMENT COMMAND SUPPORT STRUCTURES CONTROLLER CONTROLLER & CONTROL AND THERMAL CONTROLS SOFTWARE (REDUNDANT)

POWER ELECTRONICS CONDITIONER CONDITIONED CHASSIS (REDUNDANT) POWER POWER

MULTI SPECTRAL IMAGER PAYLOAD ELECTRONICS UNIT Figure 4 Payload Block Diagram

Ground Segment Description • Satellite command and control to task The RapidEye Ground Segment features the constellation and maintain its Commercial-Off-The-Shelf (COTS) hard- health and safety. ware that has been selected for its • Image processing capability to convert performance, maintainability and expand- raw imagery into ortho-products. ability. The proposed architecture features • A capability to extract DEMs from high-performance technologies for the stereo imagery using an optimal mix of network, processors, output peripherals, automated processing and manual edit- archive, and workstations, which will be ing. installed at RapidEye’s operational facility • A calibration capability to ensure the in Germany. Figure 5 provides a block performance of the sensors and proc- diagram depicting the Ground Segment. essing system. Ground Segment Characteristics • An interface to the value added information product processing facility. The Ground Segment provides the follow- • A product catalogue and multi-tiered ing key functions: data archive for raw data, ortho- • A customer order interface capability. products, DEMs and information prod- • Satellite acquisition planning function ucts. that takes into account satellite con- • Support to other data providers to ob- straints, weather and cloud predictions, tain weather forecasts, cloud cover the underlying data acquisition plan, predictions, DEMs and other informa- and special image tasking requests for tion stereo data acquisitions and acquisition of specific targets.

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Customers

RapidEye Ground Segment

Satellite Acquisition Command and Order Taking Planning Control

RapidEye Orth-Tile and Information Satellite Calibration DEM Product Product Constellation Processing Processing

Satellite Reception facility and Mission Archive and Catalogue communications infrastructure

Figure 5 RapidEye Ground Segment

Conclusions by the customers reliably and in a time frame that meets their specific needs. The RapidEye mission is a unique com- The RapidEye mission will generate a mercial small satellite Earth Observation unique earth observation data set on which mission that is focussed entirely on deliv- exclusive information products can be ering an information service to the developed. The ability of the system to RapidEye customers. All system design monitor large areas with repeat periods in decisions are based on meeting the busi- the order of a few days and at the same ness plan requirements and have resulted time respond to specific requests within a in a highly cost effective and very capable single day offers a capability that is not constellation of five reliable small satel- available from current remote sensing sys- lites along with a proven ground tems. infrastructure. The system is capable of delivering the information products needed

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