The Cosmic RAy Telescope for theEffects 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

SEP’s

GCR’s

•Energetic particles can be, electrons, protons and heavier ions such as oxygen, carbon, and iron.

•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.

Solar Energetic ParticlesSEP’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(eV stands for electron volt)

Solar Flare that accelerates charged particles to near light speeds

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 events happen more frequently during solar maximum

• But…..• GCR’s are deflected more by

the Suns magnetic field during solar maximum

SEP’s

GCR’sYearly Average Sunspot Number

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1970 1975 1980 1985 1990 1995

Year

Averag

e S

un

sp

ot

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Protection on Earth

Quebec, CanadaAug. 19, 2009

http://www.spaceweather.com/

Atmosphere Absorbs High Energy Particles

Earth’s Magnetic Field Traps Charged Particles

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)

Step 1: Electrons freed from atoms by incident radiation

Step 2: Electrons collected and measured. More electrons = more energy deposited

Electric Field Electric Field

CRaTER Electronics

Incident C

osmic

Ray

How much energy is deposited?•Not all the particles energy is deposited

•Low energy particles leave more energy then high energy particles

Measuring Cosmic Rays with CRaTERDetectors

1 & 2Detector

3 & 4Detectors

5 & 6

Particles from Deep Space

TEP TEP

Particles from the Moon

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

PrototypeSame electronics as we would use in flight, but easy to

use (they plug into the wall!)

Protype TestingNeed a source similar to the one we will measure, e.g. Brookhaven National Lab, where they can accelerate ions to very high energies

Image taken with Iron nuclei at Brookhaven National Lab

Shadow of CRaTER

prototype detector

Power:Payload: 98 Watts CRaTER:

6 Watts

The Rest of LRO: 690 Watts

The Rest of LRO: 2092 lbs

Fuel: 1774 lbs

Payload: 190 lbs

CRaTER: 13 lbs

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?$ Mass = Launch Costs: $

Data Rate:

Engineering Model TestingNeed sources similar to the one we will measure in space

Radioactive SourcesCobalt-60

Source (gamma

rays)

Engineering Model TestingParticle 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

• 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 Science Goals

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 detectorcreating smaller ions

Flight Data

Why we do the experiment: Because this is what is really out there!

Two Detector Histograms

Detectors 1 & 2

Detector 3 & 4

Detectors 5 & 6

Particles from Deep Space

TEP TEP

Comparing Energy transfer to different detectors

•Particles deposit energy as they travel through material•Lower energy particles leave more energy

•Each ion species leaves its owncharacteristic plot.

Keeping Track of CRaTERhttp://crater.bu.edu/monitor/

Time of Upload

Instrument Power Usage

Counts for Each Detector

Instrument Temperature

Dosimeter Reading

Total Counts

- no data is available when the spacecraft is out of communication

- CRaTER runs on the same power as 6 mini-Christmas lights

- 3 pairs of detectors separated by Tissue Equivalent Plastic (TEP)

- some detector counts are deemed noise by the instrument electronics.

- instrument is warmed by the Sun but cools off in the Moon’s shadow; using electric current warms circuitry

- reading of medical dosimeter on board the instrument