Understanding Space Weather Effects
with Distributed Sensor Systems
Richard Welle
Space Science Applications Laboratory
3 April, 2017
© The Aerospace Corporation 2017
Terrestrial Weather
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Terrestrial weather environment:
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Temperature
Pressure
Moisture content
Precipitation
Cloud cover
Fog
Wind
AeroCube-4 image
Terrestrial Weather is any time-variation in the environment
– Driven by a combination of uneven solar heating and the rotation of Earth
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Space Weather
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Space environment includes
– Electric and magnetic fields
– Energetic particles
(electrons, ions, neutrons)
– Energetic photons
NASA image: /www.nasa.gov/content/goddard/during-first-year-van-allen-probes-find-third-belt
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Van Allen Belts
– Existence postulated prior to space age
– Existence confirmed by Explorer 1 and Explorer 3 in 1958
– Detailed structure still being mapped
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Space Weather is any time-variation in the space environment
– Typically driven by solar variations (predominantly EUV, X-ray, and
solar wind), with a contribution due to the rotation of the Earth
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Comparison of Space and Terrestrial Weather
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Space weather takes place
primarily in the Van Allen belts
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– Van Allen belts extend up to about
eight Earth radii and have about
50,000 times the volume of the
troposphere
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Space weather has very limited (or
no) effect on day-to-day activities
for most people
– Routine space weather does affect
design and routine operations of
spacecraft
– Rare extreme events can have much
more extensive impact – in space
and on the ground
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Space weather is monitored by
limited set of satellite-based and
ground-based sensors
– Stationary in-situ space weather
sensors are impossible except in
geosynchronous orbit
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Essentially all terrestrial weather
takes place within troposphere
– Troposphere extends up to about 20
km above the surface (less at high
latitudes)
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Terrestrial weather has limited
effect on day-to-day activities
except for extreme events
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Terrestrial weather is monitored by
dense network of stationary and
moving in-situ and remote sensors
Space-Weather Sensors
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Targets:
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Charged particle number densities
Charged particle composition
Charged particle energy spectra
Electric fields
Magnetic fields
In-situ sensors
– Point observations at the location of the sensor
– Volume mapping by recording data as sensor moves in orbit
• Complicated by time variations in environment that are short compared to
single-satellite revisit time
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Remote sensors
– Line-of-sight measurements on electromagnetic radiation propagating through
environment
– GPS-Radio Occultation measures refraction of GPS signals to infer total electron
content along path
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Sensor Deployment Options
Dedicated SpaceWeather Satellite
Hosted Payload
Free-Flying
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Pros
– Available satellite
infrastructure
– Cost
– Robust
– Multiple sensor suite
– Orbit selection
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Cons
– Cost
– Flight frequency
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Pros
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Cons
– Volume, mass, and
power limits
– Communication limits
– Orbit selection
Pros
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Flight frequency
Rapid design iteration
Volume manufacture
Cost
Cons
Volume, mass, and
power limits
Communication limits
AeroCube 6
Two similar spacecraft, flying experimental dosimeters
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Launched as a 1-U CubeSat – split into two 0.5U CubeSats
Sun-pointing for power (anti-sun pointing for instruments)
Three dosimeters measure ionizing radiation from energetic
particles, from <50 keV up to 100 MeV
– Increase TRL for micro-dosimeters
– Fly new class of micro-dosimeters
– Space weather experiment
Combined 1U
Dosimeter Evolution
Historical
Current
Experimental
Separating into two
0.5U spacecraft
1.5 x 1 x 0.5 cm
3.5 x 2.5 x 0.5 cm
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18 x 25 x 25 cm
A
Payload/Science Mission Design
B
• Two nearly identical 0.5U CubeSats
• Four different energy level dosimeters
• Three are new (unflown)
• One standard control
• Fly in proximity to each other
• Testbed for a larger constellation
of space weather stations
• Correlate observations and study
small-scale radiation belt structure
• Resolves major unknown (spatial scale
sizes) in requirements for in situ space
weather monitoring
Dosimeter Variant
A
Baseline Dosimeter
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High LET
X
Two 0.5U flying in tandem
S/C
Dosimeter
Measures
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Standard Teledyne
>1 MeV electrons &
>10 MeV protons
A
Thin Window Low LET Variant
>50 keV electrons &
>600 keV protons
A
Thin Window High LET Variant
>600 keV protons
B
High LET Variant
>10 MeV protons
Thin Window Low LET
X
X
B
Thin Window Low LET Variant
>50 keV electrons &
>600 keV protons
Thin Window High LET
X
X
B
Thin Window High LET Variant
>600 keV protons
LET = Linear Energy Transfer
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B
Dosimeter Payload Board
Features of AeroCube-6 Bus
• One Radio (915 MHz, 1 W)
• Crosslink via radio >800 km
• GPS receiver with 20m accuracy
• Magnetic torque rods
• Magnetometers / Earth / Sun sensors
• Two 18650 batteries (16 W-hrs.)
• 4W solar cells (peak)
• Nominal operation is Sun-pointing
– Spin about Z-axis at ~30 deg/s
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AeroCube 6, June 19, 2014
Sample Dosimeter Results
AC6 is investigating spatial and temporal behavior of radiation environment.
A1: >50 keV e-, >600 keV H+
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South Atlantic Anomaly
A2: >600 keV H+
Seeking Fine Spatial Structure in LEO Radiation Belts
Having two spacecraft at a well-known in-track separation provides
information on the fine structure of the LEO radiation belts.
Temporal separation of data due to
in-track separation of spacecraft.
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Two spacecraft measuring the same
variability strongly suggests the existence
of fine spatial structure.
AeroCube-6 Formation Flying
Using variable drag to control satellite separation
In Track Separation (km)
800
In Track Separation
80.000
700
Semi‐Major Axis Difference
60.000
600
40.000
500
20.000
400
0.000
300
‐20.000
200
‐40.000
100
‐60.000
0
‐80.000
‐100
25 September
2013
Jun‐14 Sep‐14 Dec‐14 Mar‐15 Jun‐15 Sep‐15 Dec‐15 Mar‐16 Jun‐16 Sep‐16 Dec‐16
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‐100.000
SMA Difference (m)
100.000
900
CubeSat Paradigm
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Existence of the CubeSat ICD enables the CubeSat paradigm
– Simple launch interface
– Frequent and inexpensive rides
– “Containerized space launch”
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Elements of the CubeSat paradigm
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Short development cycle
Fly often
Learn by flying
High risk tolerance
Incremental improvements
Fly whether ready or not
Schedule flexibility (launch agnostic)
The CubeSat ICD allowed ejectors to be flight-qualified for
any launch vehicle only once as long as the CubeSats
within meet certain specifications.
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Images courtesy U.S. DOT
Putting experience to work
Develop
Build/test
Launch Integration
Fly
Time
Traditional Satellite Model
Program A
Simple CubeSat Model
Extended CubeSat Model
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Lessons
learned
Program B
Sequential Redundancy
• Any one satellite in a technology-development series can tolerate more risk
than can single-satellite missions
• If each satellite in a series has an 80% probability of success, the probability
of four sequential unrelated failures is well under 1%
• The success of the program is defined by the success of the nth satellite
in the series
• Sequential redundancy requires adequate (and reliable) on-board
diagnostics to understand any anomalies
• Sequential redundancy can support rapid development of satellites for
constellation missions
• Each successive flight can enhance capability and reliability
• Tolerance to risk must be understood at beginning of program
Time
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Avoiding Space Debris
GEO
Populating near-Earth space without
violating the 25-year rule
• Space debris must be removed within 25 years
GTO
• Natural orbital decay period is driven primarily by
perigee altitude
• Explorer flights:
Explorer 1
Explorer 3
Apogee (km)
2550
2799
Perigee (km)
358
186
lifetime (years)
12.2
0.25
• A satellite deployed in GTO can have a lifetime well
under 25 years with no active deorbit system, provided
the perigee is low enough
• A satellite deployed in an 800-km circular orbit cannot
meet the 25-year rule without an active deorbit
capability
Explorer Initial Orbit
800-km circular orbit
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Summary
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Space weather occurs in a volume many orders of magnitude larger than
the Earth’s atmosphere
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High-spatial-density in-situ sensing would utilize large numbers of satellites
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Orbital debris can be mitigated by using highly-elliptical orbits with low
perigees
AeroCube-6 provides example of “free-flying” space-weather in-situ sensor
The CubeSat paradigm offers an approach to developing increasingly
capable, low-cost, disposable network of free-flying sensors
Acknowledgements
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The Aerospace CubeSat program has received support from the following:
– SMC/AD
– NASA/STMD
– Aerospace Corporation IR&D
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