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INTERVIEW
WITH FLORENCE TAN
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Hi, my name is Florence Tan. I’m an electrical
engineer at Goddard Space Flight Center. I have
built and am building electronics for mass spectrometers
flying in space. I have built electronics on
mass spectrometers that are flying on the Cassini Mission. One
(the mission) now orbiting Saturn.
I’m here to talk about the sun’s affects
on spacecraft flight instrumentation. The sun
provides a headache for me in terms of design for space. I
have to mitigate for the affects of the sun when I
design for space. The affects are radiation and
heat. The radiation can be particles or ionizing
radiation. These particles and radiation vary
with the conditions of the sun. If you have an
active sun you have an active environment for charged
particles and radiation goes up. Higher energy
radiation such as x-rays and gamma rays can damage
packaged and integrated circuits, crew and internal
parts, similarly with the particles.
We all use a radiation unit called a rad to measure
the affects of radiation. For example on Cassini
I used parts that can withstand 100,000 rads, 100 kilo
rads. For comparison medical fluoroscopy or x-rays
have .4-4 rads. 200 rads causes a person to be
sick and 600 rads is fatal in 90% of the cases in 1-2
weeks and 10,000 rads is instant death.
So, what does radiation and particles do to the material? The
radiation and particles can cause things called “latch
out” which physically damages the integrated
circuit to the point that it’s stuck on zero
or one bit. It damages the structure which damages
the structure of the electrons. Another thing
it does is it can change a zero to one and one to zero
and that also causes problems because the program has
changed.
In addition charged particles can cause a phenomena
called spacecraft charging. This is when the
spacecraft environment is charged in a geomagnetic
storm where the spacecraft
Is charged and what you’ll have is differential
charging from one part of the spacecraft to the other. Eventually
electrical charges can arc across spacecraft components
in harming and possibly disabling them. All of
these are radiation and particle effects
There are many ways to mitigate this. One way
to mitigate is to use shielding with a denser material
like aluminum or lead. And the other thing we’ve
done is to use parts that are naturally immune to these
affects called single event affects.
Now, about heat. The heat of the sun causes the
atmosphere around the earth to expand up to 1000 kilometers. So,
what happens to a spacecraft orbiting the sun is that
the sun… When it expands it cause drag on
the spacecraft and the spacecraft will have to continually
boost its orbit. That happened to Skylab and we
have premature mission death or end of the mission. The
other thing with thermal cycling is when you have fatigue
to the materials. So careful thermal design is
extremely important when you design for space. So,
in conclusion we have radiation and particles thermal
affects that we have to design for. If you’d
like to learn more about this subject please visit the
website and have fun. Thank you.
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