China's Space Program News Thread

[taxiya]

I worked on something like this way back in the day (surface coatings for solar panels). I didn't think siloxane coatings would be applicable to Mars which is a near water free environment.

I don't think or understand why "water free environment" is a concern. Siloxane is just a solvent in the process according to the paper. The final coating is kind of chemical mix of Fluorine and Silicon. It is baked in the oven for hours during the making, so there isn't any water left, nor experiencing any water loose reaction.

The English version is only an abstract which gives the impression by "The hybrid coating with MTMS/SiO2 mass ratio of 1.3:1". The detail of processing can be found in the Chinese version.

 

[FairAndUnbiased]

I don't think or understand why "water free environment" is a concern. Siloxane is just a solvent in the process according to the paper. The final coating is kind of chemical mix of Fluorine and Silicon. It is baked in the oven for hours during the making, so there isn't any water left, nor experiencing any water loose reaction.

The English version is only an abstract which gives the impression by "The hybrid coating with MTMS/SiO2 mass ratio of 1.3:1". The detail of processing can be found in the Chinese version.

I did not read the article outside the intro due to being on phone but in general a fluorinated siloxane coating is for reduction of chemical adhesion. This is because the fluorinated costing is both hydrophobic (no free hydrogen bonds) and oleophobic (very low induced dipole polarizability of C-F bonds).

Mars dust, to my knowledge, is adhesive due to electrostatic attraction generated by triboelectric and photoelectric charging of dust grains (see here):

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Otherwise Mars dust is fully oxidized, hard, mineral dust. It not likely to have chemical adhesion.

The other possibility is mechanical adhesion which this does solve through providing a hard, smooth, nonwearing surface.

Large scale electrostatic charging is only possible in very low water environments. on Earth in wet environments the water quickly neutralizes such static charges. Intuitively, this is why humidity cannot be too LOW in semiconductor fabs due to ESD risk.

I would have expected an anti-Mars dust system to focus on grounding and removal of electrostatic and mechanical adhesion.

 

[SanWenYu]

The anti-dust system on Zhurong appears to be working all right.

According to the designer of the solar power panels, "the rover's online monitoring data (up to one month ago) showed that Zhurong had lost just 2% to 3% of its electrical current, far less than the typical 6% to 9% loss to other rovers (of the US)."

中国航天科技集团八院(简称：八院)811所火星车太阳电池设计师王文强介绍，研制人员在火星车的太阳电池玻璃盖片表面做了特殊涂层，让太阳电池阵的表面不易沾染灰尘，即便沾染了灰尘，也可通过振动将其抖落。根据前期(1个月前)火星车在轨监测数据显示，使用该涂层后，“祝融号”的电流衰降率为2%至3%，远远低于国外火星车6%至9%的衰降率。

The rover is about to enter hibernation to withstand the upcoming winter of the northern Martian hemisphere.

在火星北半球进入深秋季节后，光照强度会持续减弱。此时，火星表面太阳辐照强度仅约为地球表面的30%，月球表面的20%，更别说寒冷的冬季。火星车能源获取将进入“告急状态”。

对此，研制人员的应对策略是：让火星车“冬眠”。八院811所深空探测专家金波透露，其“冬眠”将持续到第二年春季的到来。

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[FairAndUnbiased]

The anti-dust system on Zhurong appears to be working all right.

According to the designer of the solar power panels, "the rover's online monitoring data (up to one month ago) showed that Zhurong had lost just 2% to 3% of its electrical current, far less than the typical 6% to 9% loss to other rovers (of the US)."



The rover is about to enter hibernation to withstand the upcoming winter of the northern Martian hemisphere.

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The anti dust coating is something that I will definitely read about more later.

 

[FairAndUnbiased]

I don't think or understand why "water free environment" is a concern. Siloxane is just a solvent in the process according to the paper. The final coating is kind of chemical mix of Fluorine and Silicon. It is baked in the oven for hours during the making, so there isn't any water left, nor experiencing any water loose reaction.

The English version is only an abstract which gives the impression by "The hybrid coating with MTMS/SiO2 mass ratio of 1.3:1". The detail of processing can be found in the Chinese version.

so now I read the whole paper. It is not a fluorinated coating, it is just regular siloxane terminated with a Si-CH3 bond mixed with sol-gel silica nanoparticles. so it's essentially a hydrophobic glass formulation.

the theoretical basis for adhesion resistance is explored in pg. 319 - they propose that the nanoscale roughness of the silica nanoparticle-in-glass film (see Fig 3 for AFM images) prevents large area contact with microscale dust (reducing mechanical adhesion), the Si-CH3 surface bond prevents -OH surface bond on the metal oxide of dust from hydrogen bonding to what would otherwise be -OH terminations on glass (reducing chemical adhesion).

as I predicted without reading the paper, trace water in the Martian atmosphere was a key consideration (they note this in Scheme 2c); without the hydrophobic coating, a condensation layer of trace water, even nanometers thick, would cause chemical adhesion between the -OH surface bond on glass and -OH surface bond on dust.

what they did not address was how to reduce electrostatic adhesion like I mentioned, even though they themselves acknowledge it is a factor in the introduction. Maybe they don't think it was a major factor, and the experiments proved them correct.

 

[tiancai8888]

10M diameter connect ring

 

[Hyper]

It is also possible that the panels quickly accumulate dust since it is on Mars.

 

[Quickie]

so now I read the whole paper. It is not a fluorinated coating, it is just regular siloxane terminated with a Si-CH3 bond mixed with sol-gel silica nanoparticles. so it's essentially a hydrophobic glass formulation.

the theoretical basis for adhesion resistance is explored in pg. 319 - they propose that the nanoscale roughness of the silica nanoparticle-in-glass film (see Fig 3 for AFM images) prevents large area contact with microscale dust (reducing mechanical adhesion), the Si-CH3 surface bond prevents -OH surface bond on the metal oxide of dust from hydrogen bonding to what would otherwise be -OH terminations on glass (reducing chemical adhesion).

as I predicted without reading the paper, trace water in the Martian atmosphere was a key consideration (they note this in Scheme 2c); without the hydrophobic coating, a condensation layer of trace water, even nanometers thick, would cause chemical adhesion between the -OH surface bond on glass and -OH surface bond on dust.

what they did not address was how to reduce electrostatic adhesion like I mentioned, even though they themselves acknowledge it is a factor in the introduction. Maybe they don't think it was a major factor, and the experiments proved them correct.

".... what they did not address was how to reduce electrostatic adhesion like I mentioned, even though they themselves acknowledge it is a factor in the introduction. .... "

The ZhuRong Rover has metallic wheels and axles, so the grounding of the solar panels is probably quite straight forward. Hopefully lightning on Mars is none existent or very rare.

 

[FairAndUnbiased]

".... what they did not address was how to reduce electrostatic adhesion like I mentioned, even though they themselves acknowledge it is a factor in the introduction. .... "

The ZhuRong Rover has metallic wheels and axles, so the grounding of the solar panels is probably quite straight forward. Hopefully lightning on Mars is none existent or very rare.

Grounding is good but conditions on Mars can lead to localized charging. We see this when you bombard insulators with x-ray or elextron beams in vacuum, they charge because of electron loss or gain that can't be locally replenished fast enough.

 

[Quickie]

Grounding is good but conditions on Mars can lead to localized charging. We see this when you bombard insulators with x-ray or elextron beams in vacuum, they charge because of electron loss or gain that can't be locally replenished fast enough.

I wonder if the solar panels has been coated with a transparent material that is metallic-like and conductive (or some degree of it) and so prevent localized charging.