Download Week 20 Satellites and Probes

JH WEEKLIES ISSUE #20
2012-2013
Science—Satellites and Probes
Since the 1950s, the human race has launched satellites and space probes that to this day are very
important sources of scientific data about our planet, those of our solar system, and other stars
and their systems. Here, we will discuss several of the more recent space probes and satellites.
Voyager 1
Launched:
Primary Mission:
Estimated Velocity1:
September 5, 1977
Exploration of Jupiter, Saturn
17.1 kilometers per second (~38,000 mph)
The Voyager 1 space probe was initially planned as part of the Mariner probe program, but as its
mission parameters and design developed, the probe was split off into a separate program
supervised by NASA’s Jet Propulsion Laboratory (JPL) with its sister craft Voyager 2. Despite
its name as “1,” it was launched sixteen days after its sister craft “2” for optimal positioning for
the gravitational slingshots needed for its primary mission.
Voyager 1’s primary mission was the imaging and
exploration of the Jovian and Saturnian systems,
which it accomplished with flying colors.
Voyager 1 revealed Jupiter’s ring system,
analyzed its radiation belt, and discovered
volcanic activity on the Jovian moon Io. In its
encounter with Saturn, Voyager 1 performed a
flyby of the Saturnian moon Titan to perform
observations on its peculiarly thick atmosphere.
1
With respect to the Sun
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Voyager 1 took a series of images at the request of astronomer Carl Sagan that were stitched
together into the solar system’s “family portrait.” The images include the—now incredibly
famous—image of Earth from 6 billion kilometers (~3.7 billion miles) that has been termed the
“Pale Blue Dot” photo (in which Earth appears as a 0.12 pixel pale blue dot amidst image
artifacts).
Still operating 35 years after its launch due to the stability of
its radioisotope thermoelectric generators, Voyager 1 is
currently the furthest man-made object from Earth.
Information requires approximately 16.5 hours to travel
from the probe to Earth at the speed of light. Voyager 1 is
exploring the heliosheath2 on its way to interstellar space.
Voyager 1 carries a gold-plated copper record containing
soundbytes of Earth, greetings in 55 different languages,
and several pieces of music, as well as diagrams of humans
and of our solar system. This record, along with the one
carried on Voyager 2, is known as a Voyager Golden
Record.
Voyager 2
Launched:
Primary Mission:
Estimated Velocity:
August 20, 1977
Exploration of Jupiter, Saturn, Uranus, Neptune
15.4 kilometers per second (~35,000 mph)
The Voyager 2 space probe, identical in form, instrumentation, and payload to the Voyager 1
spacecraft, was launched 16 days before its sister craft with a lower initial velocity and similar
mission. Voyager 2’s primary mission—the exploration of the four gas giants—was completed
in full with a number of interesting discoveries.
Studies in the Jovian system included analysis of the Great Red Spot (found to be a massive,
rotating storm) and the (as yet unexplained in full) peculiar surface of the moon Europa.
In its Saturn encounter, the spacecraft probed the atmosphere of the giant with radio waves and
found the internal temperature ranges from -203°C to -130°C. It also imaged the peculiar
hexagonal vortices on the north pole of the planet (again yet unexplained).
Voyager 2 is the only spacecraft yet to explore the Uranian and Neptunian systems. In its
analysis of the Uranian system, the probe found that the magnetic field generated by the
retrograde rotation of the planet produces a peculiar (and as-of-yet not fully explained)
corkscrew as the planet moves in orbit. Voyager 2 discovered the Great Dark Spot (great storm)
of Neptune and found that the Neptunian atmosphere consists of hydrogen, methane, and helium.
Like Voyager 1, Voyager 2 is currently in the heliosheath on its way out of the solar system.
2
Suspected boundary between our solar system and interstellar space created by solar wind
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Dawn
Launched:
Primary Mission:
Estimated Velocity:
September 27, 2007
Exploration of Vesta, Ceres
Accelerating at Time of Writing
The Dawn space probe was launched to explore the
asteroids Vesta and Ceres3 over an approximate nineyear mission. Designed with an ion propulsion drive4
that would enable it to reach multiple targets and
change orbital velocity and altitude, Dawn
experienced orbital insertion at Vesta in 2011 and as
of September 2012 is en route to Ceres and is
scheduled to arrive in 2015.
The electric power required to run the scientific
instruments and the ion drive is provided by Dawn’s
solar array, a design decision made possible because
Dawn is expected to remain in the inner solar system.
Dawn’s primary mission was selected
because Vesta (right, image from
Dawn) and Ceres (left) are two of the
remaining protoplanetary remnants5
accessible in the inner solar system6;
they were not swept from the solar
system as a result of Jupiter’s gravity
well. Thus, the two protoplanetary
asteroids
present
an
excellent
opportunity to study the early solar
system and formation of terrestrial
planets—namely Mercury, Venus, Earth, and Mars.
Dawn’s analysis of Vesta indicates that the remnant appears to have been formed through
protoplanetary collision and cohesion—which supports theories of terrestrial planet formation7.
Dawn carries a microchip that contains the names of approximately 360,000 followers of the
NASA community.
3
Officially recognized as both a dwarf planet (only dwarf planet inside Jupiter’s orbit) and the largest asteroid
Electromagnetic acceleration of xenon gas; Dawn is NASA’s first exploration craft with such a drive.
5
Collections of rock and dust that formed in the early solar system but did not gain sufficient mass or mineralization
to be classified as planets
6
Other remnants may be in orbit in the theoretical Oort Cloud or in the Kuiper Belt.
7
The theories being that terrestrial planets formed through collision of smaller rocky bodies that then stuck together;
once sufficient masses were reached, gravitation slowly shaped the bodies into spheres.
4
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New Horizons
Launched:
Primary Mission:
Estimated Velocity:
January 19, 2006
Exploration of Pluto, Kuiper Belt Objects
15.2 kilometers per second (~34,000 mph)
When the New Horizons space craft was
launched, it was given the greatest escape
velocity ever achieved from the surface of the
Earth8 (without gravity assists) for its mission
towards the (then) planet Pluto9 and associated
Kuiper Belt Objects (KBOs). These targets
were chosen because they are suspected
protoplanetary
remnants—and
because
observation of the icy bodies is extremely
difficult from Earth due to the enormous
distances involved10.
New Horizons is scheduled to arrive in the Pluto
system in 2015 where it will undergo a flyby
with six months of observation time before
continuing into the Kuiper Belt to observe any
KBOs that may be within the flight path of the
space probe.
As of the time of this writing (September 2012),
New Horizons has yet to make extensive
observations of Pluto (though several images have
been returned). To date, New Horizon’s key
contributions to astrophysics have been its
observations of the Jovian system where it observed
the Little Red Spot and made measurements of
Jupiter’s magnetosphere. Also, New Horizons made
observations on the
Galilean moons that
illustrate
extreme
surface changes on Io (above) as well as the development of
massive—and peculiar—new volcanic plumes on Io’s north pole
(image on right).
8
16.26 km/s
Pluto was “demoted” to dwarf planet status by the IAU in September of 2006.
10
For comparison, trying to observe Pluto from Earth is like trying to observe a 1cm marble located in London, UK
from Boston, US (ignoring spherical distortion, using heliocentric distance averages).
9
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Hubble Space Telescope
Launched:
Primary Mission:
Estimated Velocity:
April 25, 1990
Observation of the Cosmos
7.5 kilometers per second (~16,800 mph)
The Hubble Space Telescope (HST) is one of the
most important astronomical tools ever developed.
Launched in 1990 via the Space Shuttle Discovery
to a geosynchronous orbit11, the HST originally
returned images with severe aberration due to a
miniscule flaw in the primary mirror. Thankfully,
the telescope was designed to be serviceable while
in orbit. The mirror was replaced and the HST
began an extraordinary career in observation.
Observations from the HST (including the now
famous Hubble Ultra Deep Field, see below right)
have granted astrophysicists and astronomers access
to billions of years of the past in form of distant
galaxies and star formation. Further, observations of distant
stars have revealed the presence of exoplanets as well as
evidence that the universe is expanding—a peculiar effect
that, as of September 2012, is attributed to Dark Energy12.
The HST has also taken some incredibly iconic images such
as the “Pillars of Creation” in the Eagle Nebula (below left).
As of 2012, the last servicing mission to the HST was in
2009 to replace and repair several aspects of the instrument
that will permit
functionality until
at least 2014.
Degradation of the
telescope due to
moving parts and
degradation of the orbit due to atmospheric drag will
eventually force a deorbit of the telescope; it is unsure
exactly how long the HST will be usable. The spiritual
successor to the telescope is the James Webb Space
Telescope (see next page).
11
12
Orbits at the same rate as the Earth’s rotation so as to be “fixed” above the Earth’s surface
An as-yet-unexplained force, energy, or object driving the accelerating expansion of the universe.
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James Webb Space Telescope
Launched:
Primary Mission:
Estimated Velocity:
Planned 2018
Observation of the Cosmos
Not yet in Orbit
The James Webb Space Telescope (JWST) is
considered to be the spiritual successor to the
HST even though it will be observing primarily in
infrared (whereas HST observed in both infrared
and visible [primarily visible]). The JWST was
nearly canceled by Congress and NASA multiple
times over its development due to managerial
snafus causing extreme budget overruns, but it is
now fairly well entrenched in NASA’s budget.
JWST will orbit at one of the Lagrangian Points13
between the Earth and the Sun with its massive
Sun shield oriented towards the star. This will
permit JWST to make high-quality observations
in relative darkness on infrared wavelengths of extremely far-away galaxies and formations.
The JWST primary mirror consists of 18 gold-coated beryllium panels that act together as a
single objective mirror with approximately five times the surface area of the HST primary
mirror.
Mars Curiosity Rover
Launched:
Landed:
Primary Mission:
November 26, 2011
August 6, 2012
Exploration of Mars Environment, Biological
The Mars Curiosity rover landed via an elaborate “sky
crane” system on the surface of Mars on the sixth of
August, 2012. Curiosity is the largest rover ever to
reach Mars (larger than Spirit, Opportunity, and
Pathfinder) and carries an enormous scientific
payload with which it will analyze composition of
rocks in a search for biological specimens and
evaluate the habitability of the Martian surface. The
rover can take images in high definition color as well
as in stereo black and white. In terms of on-site
scientific analysis, the rover can conduct full x-ray diffraction and laser-aided chemical
decomposition.
ALL IMAGES IN THIS PACKET ARE COURTESY OF NASA
13
Point in a gravitational system where the net gravitational attraction from certain bodies is null; occurs in orbital
resonances between massive bodies
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GLOSSARY
Asteroid Belt
The asteroid belt is a large band of rocky-metal objects that orbit
the Sun between the orbits of Mars and Jupiter. The asteroids are
protoplanetary remnants left over from the formation of the planets
in the early solar system’s planetary nebula. Roughly half of the
total mass of the asteroid belt is contained in the four largest
asteroids (of which Vesta and Ceres are two).
A commonly-held misconception is that the asteroids are close
together as to necessitate “dodging” as in the Star Wars films.
Whereas this may be true for certain stars as recent 2012
observations indicate, it is not true for our solar system—asteroids
are scattered across wide regions leaving enormous gaps.
Dark Energy
Observations made using the HST and terrestrial telescopes have
revealed that the universe is expanding non-linearly—that is to say
that the expansion of the universe is accelerating. The known laws
of physics require some force or energy to cause the acceleration,
but no force is immediately evident on observation. Cosmologists
have termed the mysterious force or energy “dark energy.”
Current theories on the nature of dark energy span from the
Cosmological Constant used by Einstein to modify his General
Theory of Relativity (in the form of a universally-distributed
vacuum energy) to multidimensional irregular scalar energy fields.
Galilean Moons
The four largest moons of Jupiter (Ganymede, Callisto, Io, Europa)
are called the Galilean moons because they were first observed and
described by Galileo Galilei in the 17th century. The moons are of
particular interest to astrophysicists and other scientists due to their
varied composition and other peculiarities.
Europa’s surface is covered with peculiar expansion and
contraction lines; Io is highly volcanic and undergoes major
surface changes in short periods of time; Ganymede is huge (2
times the mass of our Moon), is suspected to contain a saltwater
ocean, has a magnetosphere, and an oxygen atmosphere; Callisto
has an extremely old surface covered in odd craters. Further,
Ganymede, Europa, and Io are locked in orbital resonance.
Gas Giants
The gas giants are planets shrouded by immense layers of gaseous
elements and compounds. The four gas giants in our solar system
are Jupiter, Saturn, Uranus, and Neptune.
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GLOSSARY CONTINUED
Gravity Assist
A gravity assist is when a space probe is “slingshot” around a large
planet, entering partially into its gravity well and being ejected at a
higher speed and in a different direction than when it entered.
Gravity assists have been used on nearly every probe entering the
outer solar system. The two favorite subjects for gravity assists
from Earth are Mars (due to its proximity to Earth and position
between Earth and the other solar system) and Jupiter (due to its
immense size).
Great Dark Spot
The Great Dark Spot was an atmospheric feature observed and
photographed by the Voyager 2 space probe in the atmosphere of
Neptune. It was a storm similar to the Great Red Spot though may
have been more of a “hole” in the methane atmosphere due to
reduced cloud cover in the storm region, and contained the
strongest winds ever observed in the solar system (2,400 km/hr
[~1,500 mph]). Further, it was short-lived—on observations a few
years following the Voyager 2 space probe, the Great Dark Spot
was gone and another smaller storm had developed in a different
hemisphere.
Great Red Spot
The Great Red Spot is a massive rotating storm (an anticyclone) in
the atmosphere of Jupiter that has been raging for at least the last
400 years (when Earth telescopic observations began). It is oval in
shape, though it is steadily losing length on its major axis and may
become circular within the next fifty years. It is unknown exactly
what causes the storm or how long it will last.
Heliosheath
The heliosheath is a “bubble” of stellar particles emitted from the
sun that surrounds and protects our solar system from interstellar
cosmic radiation. Because the sun is in orbital motion around the
Milky Way’s galactic center, the bubble (which is composed of
solar wind) is stretched and elongated like a golf ball’s
atmospheric wake. The two Voyager spacecraft are currently in
the heliosheath on their way into interstellar space.
Kuiper Belt Objects
Outside of the orbit of Neptune, there is a large collection of small
rock and ice bodies that form a belt similar to the asteroid belt—
though much larger in diameter and with a different composition.
This belt is called the Kuiper belt (after Gerard Kuiper who
proposed its existence) and the objects that it contains are called
Kuiper Belt Objects (KBOs).
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GLOSSARY CONTINUED
Little Red Spot
First observed on Jupiter in the year 2000, Oval BA was the result
of a merger between three small white storms. The storm
increased in intensity and began turning red in 2005, which
resulted in its nicknames of the “Little Red Spot” and “Red Spot,
Jr.” It is undetermined how long the little red spot will persist in
Jupiter’s atmosphere.
Protoplanetary Remnant
A protoplanetary remnant is a collection of rock and dust that
formed in the early solar system but did not gain sufficient mass or
mineralization to be classified as a planet and partially broke apart.
Few of these bodies remain in the inner solar system—taking the
role of the larger asteroids (namely Ceres and Vesta)—while the
rest were either consumed by the terrestrial planets or cleared from
the inner solar system due to Jupiter’s gravitational field.
Protoplanets and their remnants formed from planetesimals, which
may remain as shattered asteroids.
Terrestrial Planet
The terrestrial planets are rocky, mineralized planets that are
typically the smaller planets in a solar system. In our solar system,
the four terrestrial planets are Mercury, Venus, Earth, and Mars.
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