Transcript Mars Sample Return In-Orbit Demonstration (MSR IOD

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The Ocean Surface Current Mission (OSCM)
Earth Observation for Ocean Atmosphere Interactions Science, ESRIN, Frascati, Italy
28th-31st of October 2014
Benjamin Dobke – Airbus Defence & Space, ESA OSCM Study
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Ocean Surface Current Mission (OSCM) Study
Outline
 Aim: to give an overview of some of the issues and options within and Ocean
Surface Current Mission (OSCM)
 Science Motivation
 Measurement Principle
 Key Mission Drivers
 Key Sensitivities
 Instrument Configuration Options
 Orbital Options and Regions-of-Interest
 Data Processing and Downlinking Options
 Estimated Performance
 Mass, Power and Launcher
 Summary
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prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design.
Ocean Surface Current Mission (OSCM) Study
Science Motivation
 Have known for centuries the large scale
ocean currents that traverse the world
 Have also known about smaller surface
currents (~1-100 km) called the mesoscale
and sub-meso scale.
 Unable to measure currents globally
 Eddies, jets, fronts and filaments are
ubiquitous and account for over 50% of the
oceans’ kinetic energy
 OSCM is a science mission, but could also
help inform multiple users, e.g. global
shipping routes.
Motivation
Measurement
Drivers
Sensitivities
Instrument
Orbit/Data
Performance
Launcher
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prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design.
Ocean Surface Current Mission (OSCM) Study
Measurement Principle
 The focus of the OSCM will be to attain Total Surface Current Velocites (TSCV)
 This is performed by measuring phase differences in via Along Track Interferometry (ATI)
 Area of ocean is illuminated with a radar swath at time t=0, and later at t=1.
 All else being constant, the phase difference between the two received signals will be due to ocean currents
T=0
Motivation
T=1
Measurement
Drivers
Sensitivities
Instrument
Orbit/Data
Performance
Launcher
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prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design.
Ocean Surface Current Mission (OSCM) Study
Key Mission Drivers
 Key mission drivers, or requirements, broadly fall into four catagories:
Measurement
•
•
Instrument
•
5 cm/s accuracy
Wind removal
•
•
Try to provide raw
data
200km swath
(split/non-split)
Ambiguity control
Orbital
•
•
System
2-10 day repeat
Global coverage
•
 A number of these requirements are being re-informed by the OSCM studies
Motivation
Measurement
Drivers
Sensitivities
Instrument
•
•
•
Orbit/Data
Performance
Launcher
VEGA class LV
Size, mass, power
Sufficient data
downlinking
Baseline control
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prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design.
Ocean Surface Current Mission (OSCM) Study
Key Sensitivites
 We measure the phase, which can be related to the baseline, the surface
current velocity, and the velocity of the satellite
 When measuring phase, the unknown position and lengths of the baseline
can introduce phase errors that dominate the signal you try to measure in
diffferent ways.
B’
dx
dβ
B
 Putting in representative numbers show that the across-track is negligable,
the alongtrack is important, but that the line-of-sight dominates.
Motivation
Measurement
Drivers
Sensitivities
Instrument
Orbit/Data
Performance
Launcher
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prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design.
Ocean Surface Current Mission (OSCM) Study
Instrument Configuration Options
 For the ESA OSCM study, we are focusing on single platform solutions.
 The focus is also exclusively on ATI rather than XTI (i.e. sea surface heights)
 Implies two high-level configuration restrictions.
1. A transmitter and receiver pair that must be separated by a significant distance (of the order of 10m)
2. A single, medium-sized platform
 Due to the VEGA class launcher, will most likely need a folding antenna to achieve acceptable performance
3.3m
boom
4.5m
antenna support
tapers in depth
0.7m
Motivation
antenna
Measurement
Drivers
Sensitivities
Instrument
Orbit/Data
Performance
Launcher
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prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design.
Ocean Surface Current Mission (OSCM) Study
Orbital Options and Regions of Interest
 There are specific highly dynamic regions that are of most interest to oceanographers.
 Raw data and fast, good area coverage should prioritise these areas.
 Open ocean can fill up remaining data allowance
 Sun-Synchronous orbit performs best for coverage, thermal, and power
 Fixed and drifting orbits at altitudes between 400-600km are being explored
Motivation
Measurement
Drivers
Sensitivities
Instrument
Orbit/Data
Performance
Launcher
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prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design.
Ocean Surface Current Mission (OSCM) Study
Data Processing and Downlinking Options
 Depending on the number of polarisations used, data from a single receiver is of the order of 1.4Gbit/s
 Depending on number of receivers and orbital duty cycle, total data per orbit can be ~5-10Tbits
 A few downlinking options:
 Relying solely on X-band implies that an OSCM would require fully compressed data.
 Raw SLC data can be provided with K-band / EDRS. Assuming a likely 1st generation K-band, ~3 minutes
of raw data could be provided per orbit in selected areas
 Lossless BAQ is also a help (factor of ~2), but could be is not ‘noiseless’ compression.
 An on-board data compression could reduce data rate to 30kbit/s allowing high level of coverage at X-band
Motivation
Measurement
Drivers
Sensitivities
Instrument
Orbit/Data
Performance
Launcher
Estimated Performance
 Starlab Ltd. and Airbus DS have tools to help estimate expected performance.
 Ongoing refininment in design understanding of the complexities of performance
Varience of Surface Velocity [cm/s]
200
 Error on the current retrieval can be considered as two
separate factors:
50
45
195
40
190
1. Bias errors: a fixed error dependant upon baseline and
spacecraft attitude errors. Can be measured and removed
by calibration although residual error will remain
2. Variance: error dependant upon instrument performance
and surface decorrelation time
 Working on making the performance
as compliant as possible
Motivation
Measurement
Drivers
Sensitivities
Swath Position in X [km]
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Ocean Surface Current Mission (OSCM) Study
35
185
180
Orbit/Data
25
20
175
15
170
10
165
160
Instrument
30
Performance
5
120
140
160
180
Swath Position in Y [km]
Launcher
200
220
0
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prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design.
Ocean Surface Current Mission (OSCM) Study
Mass, Power and Launcher
VEGA
 Mass, volume and power are other critical areas for the mission
PSLV
 Mass capacity reduces with altitude,
power increases with altitude for the
same SNR.
 But performance not necessarily better
at lower altitudes. Trade-off…
Motivation
Measurement
Drivers
Sensitivities
Instrument
Orbit/Data
Performance
Launcher
Summary
1) Strong science
motivation to measure
un-observed global
currents
5) Configuration will most
likely need folding antenna.
In an in-line ‘Sentinel-1’
style configuration
2) There are key
mission drivers that
influence mission
design
6) Data rates are
extremely large. X-band
only enabled through
compression, 1st Gen Kband offers minutes of raw
data
Measurement
Instrument
Orbital
System
3) Errors in the phase
are central to the
instrument design
issues and
performance. Arrise
due to baseline
knowledge.
7) Performance is
continually being refined.
Bias dominate but
calibration should be able
to remove most. Low wind
performance a challenge
4) Coverage will likely
focus on key dynamic
areas with open ocean
coverage secondary
8) Launch dictates mass
and size. Vega is prefered,
PSLV can provide a higher
mass alternative.
Varience of Surface Velocity [cm/s]
200
50
45
195
40
190
Swath Position in X [km]
© 2014 Airbus Defence and Space – All rights reserved. The reproduction, distribution and utilization of this document as well as the communication of its contents to others without express authorization is
prohibited. Offenders will be held liable for the payment of damages. All rights reserved in the event of the grant of a patent, utility model or design.
Ocean Surface Current Mission (OSCM) Study
35
185
30
180
25
20
175
15
170
10
165
160
5
120
140
160
180
Swath Position in Y [km]
200
220
0