Sky & Telescope - November 2020 - 23

FIELDS
SWEAP
dynamic and bumpy, too.
"It's not just plus or minus
a mile," Korreck explains.
Thermal
"It's plus or minus a solar
protection
radius."
system
A primary goal for the
Parker Solar Probe is to
slip inside this boundary,
something no spacecraft
has ever done. Within the
Alfvén radius, Parker will
swim in the hot corona as
it's being heated and taste
the nascent solar wind as
its particles are being accelerated.

Electric field antennas (4)

Solar Probe Cup
Solar array
cooling system

IS IS
Low- and high-energy
particle sensors

High gain antenna

SWEAP
SPAN-B

FIELDS
WISPR
WI

Magnetometers (3)

Cor
Coronal
whiteligh
light imager
Solar array
wings (2)

Taking the Heat
Before Parker can do any of that, though, it must first survive
its close approaches to the stellar furnace. The good news is
that the environment doesn't feel as hot as one might think.
While the temperature of the corona is more than a million
degrees, that number describes the motions of the plasma's
particles, and they're too sparse to transfer heat to Parker.
The heat the probe does feel comes from the sunlight itself.
The difference is like sticking your hand in a hot oven rather
than in a glass of hot water.
Still, radiational heat at closest approach is 500 times what
we receive at Earth. Unshielded, Parker would reach temperatures approaching 1,400°C (2,500°F) - hotter than any lava
on Earth. Most of the instruments therefore take their measurements from behind the shelter of a heat shield, a masterpiece of thermal engineering that took more than a decade
to create. Two thin layers of a graphite-like carbon material
sandwich a thick slice of carbon foam that's so lightweight
it's 97% empty. An ultra-white aluminum oxide coating on
the shield's sunward-facing side reflects most of the light and

SWEAP
SPAN-A+

p ALL ABOARD These views show the instruments aboard the
Parker Solar Probe. The view at right shows the side of the spacecraft
that faces the direction of motion.

q STANDING TALL The Parker Solar Probe looks small inside one
half of the 19.1-meter-tall (62.7-foot-tall) fairing. Although the probe
was small compared to what a Delta IV Heavy usually carries, the
rocket provided the necessary lift to bring Parker close to the Sun.

PA RK ER INSTRU MEN TS: N ASA / JOHNS HOPK INS A PL (2); HE AT SHIELD: N ASA
/ JOHNS HOPK INS A PL / ED WHIT M A N; PA RK ER IN ROCK E T FAIRING: N ASA /
JOHNS HOPK INS A PL / ED WHIT M A N

q PARKER'S SUNSCREEN The heat shield consists of two main
components: a light carbon foam that's mostly space and a bright white
coating of aluminum oxide. A thin tungsten layer separates the two so
that they don't interact.

sk yandtelescope.org * NOVEMBER 2 02 0

23



http://skyandtelescope.org

Sky & Telescope - November 2020

Table of Contents for the Digital Edition of Sky & Telescope - November 2020

Contents
Sky & Telescope - November 2020 - Cover1
Sky & Telescope - November 2020 - Cover2
Sky & Telescope - November 2020 - 1
Sky & Telescope - November 2020 - Contents
Sky & Telescope - November 2020 - 3
Sky & Telescope - November 2020 - 4
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