in#co&opera+on#with# space-based polar remote sensing... slide 2 introduction value of...

www.strath.ac.uk/mae Slide 1

Space-Based Polar Remote Sensing

Malcolm Macdonald working with Pamela C Anderson, Carl Warren & Ben Dobke

12 October 2012 [email protected] www.strath.ac.uk/mae

in co-‐opera+on with

View of Earth at 1200hrs UTC, 12 October 2012


Introduction Value of space-based remote sensing is widely accepted,

–  yet polar remote sensing remains limited

•  Engineering concept to address polar remote sensing data deficit,

12 October 2012 [email protected] www.strath.ac.uk/mae Slide 2


An example, ECMWF quantified the value of space-based observations by comparing,

– Medium-range forecasts using conventional data only, &

– Medium-range forecasts including space-based observations

•  Found it necessary to add AMVs to ‘conventional-data’ to get a basic forecast…

12 October 2012 [email protected] www.strath.ac.uk/mae Slide 3


•  Spacecraft monitor the Earth from two basic orbital positions, –  near-polar LEOs of about 600 – 800 km altitude giving detail, –  GEOs at ~36 000 km above the Earth giving context

12 October 2012


GEO platforms Suffer rapidly decreasing horizontal resolution with increasing latitude; many products not available north of the central belt

12 October 2012 [email protected] www.strath.ac.uk/mae

Image Credit: E

UM

ETS

AT

Slide 5


Atmospheric Motion Vectors

Hourly AMVs generated using composite images •  A ‘ring’ of missing

observations exists –  from <50° to >70°

12 October 2012 [email protected]

GEO

LEO

GAP

Lazzara, M.A., et al., "High La+tude Atmospheric Mo+on Vectors: Applica+on of Antarc+c and Arc+c Composite Satellite Imagery", 10th Interna+onal Winds Workshop Tokyo, Japan, 22-‐26-‐February 2010


Mission Requirements •  GEO products break-down at ~55° latitude

–  at an observation zenith angle (OZA) of ~60°. Req.; Observation of all longitudes at latitudes 55 – 90°,

with OZA <60° •  To maximise analogy to GEO should avoid composite images,

–  also minimises data latency, •  And, Req.; Maintain apogee <45 000 km altitude



Молния Observations from a Molniya orbit are possible,

•  From GEO the ZOA at 55° latitude is 63°

•  On a Molniya orbit the minimum ZOA to all longitudes is 69°

–  i.e. A single platform cannot provide hemispheric-like observations

–  Polar observations would remain dependent on composite images

•  Three spacecraft required to provide continuous observation to all longitudes at latitudes 55 – 90°, with OZA <60° with composite images.

–  Requires three launches.



Molniya orbit inclination results from the shape of the Earth •  If Earth were a

different shape the critical inclination would be different…

•  So, lets change the shape of the Earth!


Image Credit: ESA

Image Credit: B

BC


Taranis Orbit Use low-thrust propulsion to modify the geopotential perturbations

–  i.e.how the spacecraft ‘feels’ the gravity of Earth

•  Thus re-define the critical inclination as a function of the thrust magnitude –  Molniya means lightning, while –  Taranis is the Celtic God

of Thunder


AcceleraBon required assuming conBnuous acceleraBon.


Molniya v’s Taranis Molniya Taranis Inclination 63.4° 90° Perigee Altitude 300 km 300 km Orbit period 12 hours 12 hours Minimum ZOA at 55° latitude at all longitudes 69° 50° Number of spacecraft required to image all longitudes from 55 – 90° latitude with OZA < 60° (composite coverage)

3 2

Number of launches required (composite coverage)

3 1

Number of spacecraft required to image all longitudes from 55 – 90° latitude with OZA < 60° (single platform coverage)

impossible 3

Number of launches required (single platform coverage) n/a 1



Mission Analysis Two 90° orbits consider, •  Quantifying impact of

mitigating space environment effects

•  ‘Soft’ orbit is, –  10000 x 41740 km (16-hr) –  & requires 4 spacecraft

•  ‘Hard’ orbit is, –  300 x 40170 km (12-hr) –  & requires 3 spacecraft

12 October 2012


Mission Analysis Two 90° orbits consider, •  Both require ‘space

qualified’ parts, –  with neither requiring

Rad-hard •  12-hr orbit is hence likely

to offer global minimum cost mission

But, •  accepting composite

images requires only 2 spacecraft on either orbit

12 October 2012


System Analysis Thrust arcs used to optimise design •  Significant reduction in required

thruster life-time •  No thruster on nadir face •  Thrusters ‘off’ when instruments ‘on’

–  Avoids contamination concerns

–  Provides power rich environment for instruments

•  Note, apogee coast length varies by architecture option


12-‐hr orbit shown


System-Level Mass Allocations •  Single platform coverage of target region

–  Assuming a Soyuz launch from CSG


16-hr 12-hr Estimated Soyuz Launch Mass Capability 2442 kg 2983 kg Available Launch Mass with 20 % margin 1954 kg 2386 kg Total Wet Mass Allocation per Spacecraft 488 kg 795 kg Thrust Magnitude per R & T direction (minimum BoL coast arc about apogee & no thrusting in shadow region)

5 mN 80.6 mN

Specific Impulse 3500 s 4600 s Electric Propulsion Input Power 0.6 kW 4.8 kW


Soyuz Payload Mass Allocation 16-hr; Single platform coverage •  Payload mass

–  5-yr = 130 – 215 kg –  7.5-yr = 125 – 210 kg

12-hr; Single platform coverage •  Payload mass

–  5-yr = 70 – 120 kg –  7.5-yr = 40 – 70 kg



System-Level Mass Allocations •  Composite coverage of target region

–  Assuming a Soyuz launch from CSG


16-hr 12-hr Estimated Soyuz Launch Mass Capability 2442 kg 2983 kg Available Launch Mass with 20 % margin 1954 kg 2386 kg Total Wet Mass Allocation per Spacecraft 977 kg 1193 kg Thrust Magnitude per R & T direction (minimum BoL coast arc about apogee & no thrusting in shadow region)

17.3 mN 162 mN

Specific Impulse 3500 s 4400 s Electric Propulsion Input Power 0.6 kW 10 kW


Soyuz Payload Mass Allocation 16-hr; Composite coverage •  Payload mass

–  5-yr = 270 – 455 kg –  7.5-yr = 265 – 445 kg

12-hr; Composite coverage •  Payload mass

–  5-yr = 65 – 110 kg –  7.5-yr = 20 – 35 kg



Soyuz Payload Mass Allocation Counterproductive to increasing spacecraft mass on 12-hr orbit •  Payload ≳100 kg drives

architecture to 16-hr orbit •  Payload ≳220 kg single

platform coverage in 16-hr orbit would require multiple launches –  Or a larger launch vehicle

•  Payload ≳450 kg single platform coverage in 16-hr orbit would require larger launch vehicle



Potential Payload Principle payload of a VIS & IR imager to monitor high latitude phenomena with sufficient temporal resolution related to, • winds, • clouds, • volcanic ash plumes, • sea ice,

• vegetation properties, • snow cover, etc… MSG’s main payload is SEVIRI

–  12 spectral channels; 4 visible/NIR & 8 IR

•  260 kg; 150 W; 3.26 Mbit/s & 7-yr nominal mission life Assuming a Soyuz launch is, •  aggressively compatible with single launch & platform coverage •  comfortably compatible with single launch composite coverage



Conclusions

3 (or 4) spacecraft can provide continuous single platform observation of all longitudes at latitudes 55 – 90°

– with OZA <60°

•  Only 2 spacecraft with composite images – 3 required on critical inclination orbits



Conclusions Payload mass traded against mission duration, launch vehicle selection and requirement for composite images •  Single platform coverage from single Soyuz launch limits payload

to ≲220 kg –  Challenging mass constraints for multispectral imager

•  Composite coverage from single Soyuz launch limits payload ≲ 450 kg –  More than sufficient mass for multispectral imager –  Single platform coverage with two Soyuz launches or single larger launcher

•  All technology appears to already at TRL 6 or above –  All major technology available within the UK and in areas of UK leadership


www.strath.ac.uk/mae Slide 23 12 October 2012 [email protected] Image Cred

it: SeeGlasgow

www.strath.ac.uk/mae

www.strath.ac.uk/mae Slide 24 12 October 2012 [email protected] Image Cred

it: SeeGlasgow

www.strath.ac.uk/mae


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