Wednesday, March 29, 2023

3936 - NEW SATELLITE - in a new atmosphere?

 

-   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.

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-   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.

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-    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.

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-    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.

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-    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.

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-    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.

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-   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.

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-    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.

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-    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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