Microsatellite Constellation for Earth Observation in the Thermal Infrared Region Federico Bacci di Capaci Nicola Melega, Alessandro Tambini, Valentino Fabbri, Davide Cinarelli Observation
Index 1. Introduction 2. Requirements 3. Constellation Design Orbital Geometry Deployment Constellation Features 4. Platform System Design Drivers Subsystems Mass Budget 5. Conclusive Remarks 2
Introduction AS-50 Platform 3
Requirements Mission Statement: Design a microsatellite constellation for EO applications reducing the modifications to the current AS-50 platform and the overall mission cost Mission requirements: Innovative concept Commercial interest Single launch Adaptation of AS-50 platform Satellite mass < 100 kg (AS-50x2) Max size 440x440x820 mm 3 Operational life 4 years Mission definition: Multi-Sun-Synchronous Constellation Repetitive illumination conditions Best for mid-low latitudes Max 5 satellites in different orbital planes Thermal Infrared Remote Sensing: during day/night Possible use of uncooled detectors Several applications (water management, urban heat islands, evapotranspiration etc...) GSD around 60 m is the target value 4
Orbital Geometry (1) Multi-Sun-Synchronous Constellation Conditions: Satellites in circular periodic orbits: Same radius and inclination Equally spaced in RAAN Each satellite provides complete coverage of the equator in a repetitiveness period Each satellite observes the same area at the same local time after an integer number of repetitiveness cycles Different satellites observe the same area with periodic illumination conditions 5
Orbital Geometry (2) h=572 km i = 47.7 deg ΔΩ=72 deg 121 days illumination repetitiveness period 5x3=15 equally spaced passages over the same Ground Track 6
Constellation Features Example of observation capabilities: Forlì, Italy (44.2 N) 109 obs. in 121 days Widely spread observation times 7
Deployment Strategy Drifting Parking Orbit Maneuver: Same for all satellites Larger semi-major axis Slower nodal drift No out-of-plane maneuvers Trade-off: ΔV vs. Deployment time Analysis results: ΔV=237.3 m/s Complete deployment in 294 days Parking orbit altitude 1027.98 km 8
System Design Drivers (1) Operation ΔV [m/ s] Deployment 237.34 Drag compensation 11.96 Margin 20% 49.86 Residual 2% 5.98 TOTAL 305.14 ΔV Requirement Propulsion system: Monopropellant, non-toxic, low-cost Hydrogen Peroxide I sp ~120 s Required volume: 14.79 dm 3 Tank issue: A large spherical tank would not allow for proper structural design of the Payload Bay (~300x300x300 mm 3 ) Use of 4 COTS cylindrical tanks (ATK) Increase of platform size: 350x350x650 mm 3 400x400x730 mm 3 9
System Design Drivers (2) Power generation Nadir-pointing attitude profile (Nominal Mode) Variable solar vector position System simplicity Analogy with AS-50 platform Body-mounted configuration: AOP: 28.1 49.1 W (depending on LTAN) Battery Charging Mode (Sun-pointing) 10
System Design Drivers (3) Payload Sensor: Uncooled microbolometer 1024x768 px, 17µm pitch Optics: EFL=162 mm D = 118 mm Swath = 61.44 km Duty cycle: PL Power ~ 5.8 W Increases RF power Reduces batteries life Average Consumption: 43.64 W (with margins) 11
Subsystems (1) Telecommunications GS selection within Estrack network Perth (Australia) + Santiago (Chile) Access for 81% of orbits (10 deg elevation) Average access time 307.3 s RS data downlink in X-band 10 Mbps with 1.86 W RF (~15 W at the S/C) TMTC uplink/downlink in S-band Receiver: 4.3 W Transmitter (rms over an orbit): 0.15 W 12
Subsystems (2) AOCS Increased agility and accuracy Main sensors: Star Trackers GPS Receiver Main actuators: 3+1 RWs H 2 O 2 µthrusters EPS BM Solar Panels: 30 120x60 mm 2 Ga-As cells per panel Li-Ion Batteries: Same as current AS-50 6 packages, 6 batteries each Capacity 340 Wh 13
Mass Budget AOCS 44.44 TELECOMMUNICATIONS 4.38 Reaction Wheels 4 4.32 S-Band RTX 2 1.20 Star Trackers 2 0.84 S-band RTX Antenna 2 0.36 Magnetorquers 6 2.95 HPA 2 0.36 Magnetometers 2 0.34 LNA 2 0.12 GPS Receiver 1 0.28 X-band TX 1 0.60 GPS Antenna 1 0.17 X-band Antenna 1 0.18 Prop. System 1 5.22 X-band HPA 1 0.36 Prop. Electronics 1 0.32 Cabling - 0.72 Propellant Tanks 4 6.53 Propellant - 24.48 STRUCTURE 32.81 All values include 20% margin Bus Module 1 11.04 Payload Module 1 10.90 Lateral Panels 4 10.87 POWER 4.56 Battery Packs 6 3.31 PDU 1 0.50 PMB 1 0.74 OBDH 0.53 OBDH 2 0.53 PAYLOAD 3.96 Sensor 1 0.36 Baffle 1 1.50 Optics 1 1.50 Electronics 1 0.60 TOTAL MASS: 93.17 kg 14
Conclusive Remarks Mission requirements: Innovative concept Commercial interest Single launch Adaptation of AS-50 platform Satellite mass < 100 kg (AS-50x2) Max size 440x440x820 mm 3 Operational life 4 years Phase-A output: Proven feasibility Defined orbital geometry Initial system budgets Preliminary subsystem design Alternative solutions: Deployable SPs Electric Propulsion Use of TDI Read-Out mode THANK YOU FOR YOUR ATTENTION! 15
Contacts Federico Bacci di Capaci Mission Analyst federico.bacci@sitael.com SITAEL S.p.A. Premises Via Filippo Guarini, 13 47121 Forlì (FC) ITALY Tel: +39 0543 25280 Headquarters Via San Sabino, 21 70042 Mola di Bari (BA) ITALY Tel: +39 080 5321796 Fax: +39 080 5355048 www.sitael.com 16