Transcript CRaTER Instrument

The Cosmic RAy Telescope for the
Effects of Radiation
Presentation Goals
• Sources and Effects of Radiation in Space
• Designing and Testing a of a
Space Craft Instrument
• Initial Results and Expected Goals of this Work
Energetic Particles in Space
•Energetic particles can
be, electrons, protons and
heavier ions such as
oxygen, carbon, and iron.
SEP’s
•The particles are charged
and have enough energy
to break chemical bonds
such as those that hold
together DNA.
•Damage to DNA is a
major source of medical
problems due to radiation
exposure.
GCR’s
Solar Energetic Particles
SEP’s
• SEP’s are mainly protons.
• Some SEP’s are accelerated
during a solar flare.
• Others are created as a result
interactions in the solar wind.
• SEP’s come in short bursts.
• Particle energies can vary
from KeV to MeV
Solar Flare that accelerates charged
particles to near light speeds
(eV stands for electron volt)
Flare Movie: http://sohowww.nascom.nasa.gov/gallery/Movies/flares.html
Webcam Movie: http://www.youtube.com/watch?v=vCFQZqSxWns
Galactic Cosmic Rays (GCR’s)
• Sources outside of the solar system
•Supernovas can accelerate
heavy ions particles to very
high energies.
•GCR’s are a mix of electrons
and protons along with heavier
elements.
•GCR’s come from many
different sources and so are
constantly raining in from
outside the solar system.
Particle energies can vary from 10’s of MeV to GeV’s and higher
SEP’s and GCR’s are tied to the
solar cycle
SEP’s
• SEP events happen more
frequently during solar
maximum
• But…..
• GCR’s are deflected more by
the Suns magnetic field
during solar maximum
GCR’s
Yearly Average Sunspot Number
Average Sunspot Numbrer
180
160
140
120
100
80
60
40
20
0
1970
1975
1980
1985
Year
1990
1995
Protection on Earth
Atmosphere Absorbs High
Energy Particles
Earth’s Magnetic Field
Traps Charged Particles
Quebec, Canada http://www.spaceweather.com/
Aug. 19, 2009
http://radbelts.gsfc.nasa.gov/outreach/outreach.html
Effects of Ionizing Radiation
• Ionizing radiation can cause cell damage
• The damage is particularly harmful if DNA is
broken apart
• Top:
• Images of cellular nuclei that have been
bombarded by ionizing radiation
• Green spots are places where DNA was split
• Bottom:
• Visualization of DNA strand breaks from an
x-ray and a cosmic ray
Image Credits: A. Cucinotta / NASA,JSC,SRAG
Measuring Cosmic Rays
• This ionization effect is used by
instruments to measure the
particles
• Radiation ionizes atoms in our
detector
• Electric field accelerates electrons
into our electronics
• We measure the amount of energy
deposited by each particle (LET)
How much energy is deposited?
•Not all the particles energy is deposited
•Low energy particles leave
more energy then high energy particles
Electric Field
Electric Field
CRaTER
Electronics
Step 1: Electrons
freed from atoms
by incident
radiation
Step 2: Electrons collected
and measured. More
electrons = more energy
deposited
Measuring Cosmic Rays with CRaTER
Detectors
1&2
Detector
3&4
Detectors
5&6
Particles
from Deep
Space
TEP
Particles
from the
Moon
TEP
Warning: The animator’s creative license has LRO pointing the
wrong way. Don’t worry though…the spacecraft operators
know which way to point it!
Spacecraft Animation
Prototype
Same electronics as we would use in flight, but easy to
use (they plug into the wall!)
Protype Testing
Need a source similar to the one we will measure, e.g.
Brookhaven National Lab, where they can accelerate ions
to very high energies
Shadow of
CRaTER
prototype
detector
Image taken with Iron
nuclei at Brookhaven
National Lab
Data Rate:
Entire Satellite: 100 Mbps :
about the same as a wireless
router…not bad!
CRaTER: ~90 kbps (~0.1% of LRO rate!):
better than dial-up connection, but not
much!
But what’s the real limitation?
Power:
$
Payload: 98 Watts
CRaTER:
6 Watts
The Rest of
LRO: 690 Watts
Mass = Launch Costs:
Payload:
190 lbs
Fuel:
1774 lbs
$
CRaTER:
13 lbs
The Rest of
LRO: 2092 lbs
Engineering Model Testing
Need sources similar to the one we will measure in space
Radioactive Sources
Cobalt-60
Source
(gamma
rays)
Engineering Model Testing
Particle accelerators, e.g. Brookhaven National Lab
Flight Model
Flight Model Calibration
Flight Model Environmental Testing
Make sure that instrument can survive in space environment
Thermal – Large temperature gradients in space
Vibration – Huge vibrations during launch
Acoustic – Launch causes large sound waves
Integration with LRO
Who are those masked men??
Testing of Entire Satellite
Launch!
http://www.nasa.gov/mission_pages/LRO/launch/index.html
CRaTER Science Goals
• Originally driven by exploration goals (measure
energy deposited at different depths in the
human body)
• Exploration Enables Science!
• High-data-rate and uniquely capable galactic
cosmic ray (GCR) and solar energetic proton (SEP)
science instrument
CRaTER Sees the Moon!
When spacecraft is closer to the Moon, the moon
shields more cosmic rays coming from deep space
Altitude above the Moon
CRaTER Count Rates
Periodic Table as Seen by CRaTER
•Iron Ion Beam at Brookhaven
National Labs
•Iron factures in material
placed in front of the detector
creating smaller ions
Flight Data
Why we do the experiment:
Because this is what is really out there!
Two Detector Histograms
Comparing Energy transfer to different detectors
•Particles deposit energy as
they travel through material
•Lower energy particles
leave more energy
Detectors
1&2
Detector
3&4
Detectors
5&6
Particles from
Deep Space
TEP
TEP
•Each ion species leaves its own
characteristic plot.
Keeping Track of CRaTER
http://crater.bu.edu/monitor/
Time of Upload
- no data is available when the
spacecraft is out of communication
Instrument Power Usage - CRaTER runs on the same
power as 6 mini-Christmas lights
Counts for Each Detector
- 3 pairs of detectors separated by
Tissue Equivalent Plastic (TEP)
Total Counts
- some detector counts are deemed
noise by the instrument electronics.
Instrument Temperature
- instrument is warmed by the Sun but cools off in the
Moon’s shadow; using electric current warms circuitry
Dosimeter Reading
- reading of medical dosimeter on board the instrument