- 3936 - NEW SATELLITE - in a new atmosphere? A new propulsion system could levitate vehicles in the Earth’s upper atmosphere. There is a novel type of propulsion using only light to collect data in the Earth’s challenging-to-explore mesosphere.
------------ 3936 - NEW SATELLITE - in a new atmosphere?
- The
“mesosphere” is the part of the atmosphere that ranges from 50 km to 80 km, and
it has several disadvantages for current exploration technologies. It’s too
high for balloons or typical aircraft to reach, making standard high-altitude
exploration technologies impractical.
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- It’s also too
low for satellites, as their orbit would degrade too quickly in its relatively
thick soup of molecules, making the other typical space-based sensing platform
impractical as well. The only way researchers have been able to explore it so
far is through research rockets that only traverse it for a few minutes before
falling back to Earth.
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- This new
technology takes advantage of a phenomenon known as “photophoretic levitation”
to float devices simply by hitting them with light.
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- That
propulsion technology might sound similar to that used on a solar sail, but the
delicate layers of foil used on solar sails would die a horrible death in the
Earth’s atmosphere.
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- The
photophoretic effect, which has been known for almost a century, uses the
heating of a solid compared to the ambient gas as a lifting force. The photophoretic force creates lift in
structures that absorb light on the bottom yet stay cool on the top.
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- Previous
attempts had all been on the micrometer scale, as the lifting force is
extraordinarily weak, making it difficult to exert any significant lifting
force on whatever payload it might be attached to.
-
- The lab’s
design relies heavily on the pressure its plates operate in, and it just so
happens that the mesosphere, which ranges in pressure from 1-100 pascals, hits
right in the sweet spot where the lifting action is most effective, creating
enough lift to hold a centimeter-scaled probe in the air, potentially
indefinitely.
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- Even with
only a few centimeters, there are plenty of miniaturized sensors that could be
packed onto that platform to relay data that had before been accessible only by
research rockets. Those microfliers
could potentially stay aloft indefinitely if the technology was modified to
utilize solar energy and have a day/night cycle where it would shift from ascending
in the day to descending in the night.
-
- The
technology could be modified slightly to enable horizontal thrust, allowing the
sensing platform to travel to any point in the mesosphere using only light as a
propulsion source.
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- Did you
know the Earth’s atmosphere extends beyond the orbit of the Moon? There aren’t strict boundaries between Earth
and space. Our atmosphere doesn’t just end at a certain altitude; it peters out
gradually. Our atmosphere extends out to 630,000 km into space.
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- This study
is all about what’s called the geocorona. It’s a vast cloud of hydrogen atoms
that’s situated where Earth’s atmosphere merges with space. SOHO has 12 science
instruments onboard, and one of them is called SWAN, (Solar Wind Anisotropies.)
SWAN was able to trace the hydrogen signal from the geocorona and detect its
outer boundaries more precisely than ever before.
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- A camera on
the Moon shows Earth’s geocorona glowing with Ultraviolet light. Apollo 16 astronauts actually took pictures
of the geocorona with the first camera on the lunar surface, in 1972. But at
the time, they didn’t know they were actually still inside Earth’s atmosphere.
-
- Lyman-alpha
light is a particular wavelength of ultraviolet that interacts with hydrogen
atoms. The atoms can both absorb and emit this light. The problem is that
inside Earth’s atmosphere, this light is absorbed. The only way to see the
extent of the corona is from space.
-
- SWAN’s
design allows it to measure the hydrogen atoms in the geocorona, and filter out
or discard the hydrogen atoms in space.
The scientists behind the new study found that sunlight compresses
hydrogen atoms on Earth’s dayside, and it also produces enhanced density on the
night side.
-
- However,
that density is only relative; the dayside dense region has only 70 atoms per
cubic centimeter at 60,000 km above Earth. At the distance of the Moon, there
are only about 0.2 atoms per cc.
-
- The Moon
flies through Earth’s atmosphere. Even
though the geocorona extends far enough to encompass the Moon, it doesn’t mean
it would help space exploration in any way. Though the hydrogen is an extension
of the atmosphere, the density of hydrogen atoms is still so low that it’s
pretty much a vacuum.
-
- On Earth we
would call it vacuum, so this extra source of hydrogen is not significant
enough to facilitate space exploration.
But it is significant when it comes to exoplanets. For planets with
hydrogen in their exospheres, water vapour is often seen closer to their
surface. That is the case for Earth, Mars and Venus. That fact could be helpful
when trying to determine which exoplanets might have water.
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- This is
especially interesting when looking for planets with potential reservoirs of
water beyond our Solar System,” explains Jean-Loup Bertaux, co-author and former
principal investigator of SWAN.
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- This
extended atmosphere and the ultraviolet in it don’t pose any danger to
astronauts on missions in this region of space. There is also ultraviolet
radiation associated to the geocorona, as the hydrogen atoms scatter sunlight
in all directions, but the impact on astronauts in lunar orbit would be
negligible compared to the main source of radiation – the Sun.
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- But it’s
possible that the geocorona could interfere with astronomical observations
performed near the Moon. This is something that any lunar telescope would have
to consider. Space telescopes observing
the sky in ultraviolet wavelengths to study the chemical composition of stars
and galaxies would need to take this into account.
-
- SOHO was launched
in 1995, and has been studying the Sun for over 20 years. It’s still up there
orbiting L1, even though it was designed for a two-year mission. Over its
lifetime so far it has a number of “firsts” under its belt.
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- SOHO’s SWAN
instrument observed Earth’s geocorona three times between 1996 and 1998. The
team decided to retrieve this data from the SOHO archives and to analyze it
further. This discovery makes us wonder what other discoveries are hidden in
its archives.
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March 28, 2023 NEW
SATELLITE - in a new atmosphere? 3936
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--- Wednesday, March 29, 2023 ---------------------------
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