(ORDO NEWS) — Space probes designed to study the sun are the last place you’d expect moisture problems.
However, a recent study found that the aluminum filters on two different satellites are deteriorating due to water eating away at their surfaces.
These filters help detect radiation in the extreme ultraviolet (EUV), so any haze will inevitably affect their effectiveness. While the problem has been obvious for a while, scientists now finally know what is causing it.
NASA‘s Solar Dynamics Observatory (SDO, launched 2010) and the NASA/European Space Agency Solar and Heliospheric Observatory (SOHO, launched 1995) both have the same problem.
In the first six months, the EUV SOHO solar monitor deteriorated by about 35 percent; in the next five years, it worsened by another 60 percent.
Solar probes aren’t exactly cheap, nor is the launch of annual recalibration missions to send new sensors into space. Finding out why filters fog up could make future solar probe missions more reliable.
In 2021, a team of scientists led by physicist Charles Tarrio of the National Institute of Standards and Technology (NIST) conducted experimental studies figured out what it wasn’t, which was carbon buildup causing fogging, which was long thought to be the culprit.
Now they figured out what it is, and it’s amazing: the oxidation of aluminum caused by the presence of water and induced by ultraviolet radiation.
As layers of oxidized metal build up, the filter fogs up, preventing it from passing through the light waves that the sensor is designed to track.
The surface of aluminum is usually naturally covered with an oxide surface layer, which occurs when oxygen atoms bind to atoms on the aluminum surface. UV light increases the rate of oxidation, causing additional oxide layers to form.
Normally, there isn’t much oxygen in space that could bond with aluminum, but the presence of water containing oxygen atoms could be a game changer.
To test the water hypothesis, the researchers used the National Institute of Standards and Technology’s Synchrotron Ultraviolet Radiation (SURF) facility to generate EUV radiation by shining it onto an aluminum filter in a vacuum chamber fed with water vapor. has been entered.
In their experiments, Tarrio and his team did find an oxide layer on the aluminum sample that was much thicker than conventional theory suggests, although not as thick as those seen with solar probes.
However, simulations have shown that with enough exposure – about 10 months – they would develop an oxide layer comparable to aluminum filters on space probes. -two hits.
“Impact number one physically showed that this chemical process involving water could cause something comparable to what we actually observe on satellites.
And hit number two says that once you create a theoretical model that takes into account all the factors, then the numbers quantitatively match what we see on satellites, ”explains physicist Robert Berg from NIST.
“Putting it all together, I am convinced. Water is responsible for filter degradation.”
The next question is: where did water come from on Earth? The team believed she must have somehow hitchhiked on the probes themselves.
“It had to be something that could continuously emit water for five years at a fairly constant rate,” says Tarrio. “That made Bobby [Berg] go looking for what the hell could it be? What would be a suitable source? And he found it.”
The answer, which will be detailed in a forthcoming paper, is a thermal blanket used to protect delicate probe instruments from extreme temperatures.
They consist of layers of a thin sheet of polyethylene terephthalate (PET) coated with a reflective metal that reflects most of the heat that hits the material.
However, PET is known for absorbing and retaining water from the atmosphere. So it goes into space with all this water retention, and then when the sun’s heat hits it, the water evaporates and slowly evaporates, getting into the spacecraft and causing the aluminum EUV filter to oxidize.
“It was difficult,” says Berg, “to come up with something else that holds that kind of water.”
Everything the Sun does is interesting, but solar flares and coronal mass ejections are of particular interest here on Earth.
If they are released in the direction of the Earth, the amount of matter flying towards us can cause geomagnetic storms that risk disrupting satellite and radio communications and even interfere with power grids.
This solar matter can take two hours. It takes six days to get to us, so instruments that can detect EUV telltale waves early are critical to early warning and predicting the strength of a coming geomagnetic storm.
In future work, the team hopes to explore ways to prevent this oxidation by working on protecting aluminum or developing a new filter that can operate in the required wavelength range.
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