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This article is missing some big details. Dust is a concern for sure, but it's way more complicated than that. Basically most satellites fall into three camps,
by edrxty 5y ago
This article is missing some big details. Dust is a concern for sure, but it's way more complicated than that.
Basically most satellites fall into three camps, communication, optical imaging, and radar imaging. The most sensitive of these are in the optical category. High performance optical satellites (think JWST, Hubble, Kepler, KH-x series, worldview, etc) are absurdly sensitive to contamination. The clean rooms exist in no small part to keep people from using or introducing substances and chemicals that will destroy mirrors, lenses and focal plane arrays (image sensors). By far the biggest threat is anything silicone related as in a vacuum environment, silicone will off-gas and coat optical surfaces fogging them. If this happens on the ground during thermal vacuum testing the satellite would need to be completely disassembled and decontaminated. If it happened on orbit it would effectively kill the satellite. As such volatile compounds that are likely to emit any vapor are carefully controlled during assembly.
The other side of the coin is electrical static discharge. Pretty much all satellites are extremely susceptible to this including the optical sats as the focal plane arrays are absurdly sensitive. The white suits you see in the cleanroom are not only to contain dust but also electrically conductive to ground any buildup of static charge. By maintaining a controlled environment with trained workers you can combat this much more easily along with humidity control to reduce buildup of charges. It's worth noting that the charge levels at work here are far lower than the ones you've experienced on doorknobs or are worried about assembling ie. a computer. As little as a few volts of buildup can destroy or degrade some parts and the normal human body can almost instantly build up hundreds of volts just moving around under normal circumstances.
Finally a big issue is large FOD (foreign object damage) and having a nice controlled environment is beneficial for keeping it under control. Stuff like hair and wire clippings would be common examples. You need to control that stuff as it can either short out circuits or be heated and vaporize to coat optics/controlled impedance circuits. Everything in space behaves like a giant vacuum plating chamber so the less stuff floating around the better.
- breput 5y agoYou're not wrong, especially about optical components. But there has been a general overreaction about ESD and milspec/spacespec components since, I don't know...maybe the mid-1970s budget cuts? And we have a lot more knowledge about cosmic rays and other bit flipping events now. It wasn't unusual to launch a Pioneer 10 and 11 or Voyager 1 and 2 back in the day both because the launch vehicle wasn't super reliable and also because the overall system and the environment it was going to wasn't fully known. Now we have Hubble, which initially a disaster but after multiple manned servicing missions, was turned into a glorious scientific instrument. But we also have a couple equivalents sitting around in a warehouse[0] that could have been launched (at least now) for much less money. I'm very concerned that JWST will be the next. [0] https://www.space.com/16000-spy-satellites-space-telescopes-nasa.html https://www.space.com/16000-spy-satellites-space-telescopes-...
- edrxty 5y agoI'm not sure what you mean. ESD is a big deal with sensors, namely optical FPAs and ADCs for radios. Their voltage tolerance is well established and the ESD generated by humans is easily measured. It's not that this stuff isn't necessary or we don't understand it so we overreact, it's a calculated risk decision that's currently changing with cheaper launch costs. Satellites are starting to get smaller as the components are being miniaturized much like most tech and launch costs are falling. Small-sats are frequently built in much less strict clean environments and instead of massive controlled transporters, are shipped in crates by Fedex. It just depends on the reliability profile of the mission and the type of instruments in use.
- breput 5y agoESD is a huge deal with passive component too, and honestly even with components that you never thought could fail in the past like resistors, lately. Obviously an instrument that is never going to be serviceable deserves the best components and handling, but they will fail eventually and you either have a redundant circuit or another fallback.
- breput 5y agoI guess my only point was that I've seen both approaches - you either over-spec the components and when it doesn't fail like you think the spec was the secret, or you design for unreliable parts and when they don't fail as expected, you look like a genius.
- Cadwhisker 5y agoIn addition to the above, the effects of ESD are cumulative. You may think you're getting away with not following correct ESD procedures until one day something stops working and you're left wondering why, because nothing you did has changed.
- bryananderson 5y agoOne of the “equivalents” will be launched in a few years as the Nancy Grace Roman Space Telescope (formerly WFIRST). It isn’t quite an equivalent: it was designed to image the Earth, not distant objects. It has a wider field of view than Hubble, but is less useful for imaging distant galaxies and exoplanets in detail. Unfortunately it also doesn’t deliver the expected cost savings, since the telescopes came without instruments or electronics. Different people at NASA made different estimates, but most showed the NRO telescope as being roughly a wash compared to the earlier WFIRST concept, and it has overrun its cost substantially since then.
- qqqwerty 5y agoI spent the better part of a summer internship scrubbing vacuum chambers with nasty solvents at SSL. They were in the process of retrofitting their testing chambers, but something in the new equipment was off-gassing. After a lot of trial and error (and scrubbing) we narrowed it down to the spacers on the new thermal equipment. Wasn't quite how I had hoped that summer would have went, but was interesting none the less.
- adwww 5y agoFOD... It would be pretty depressing to launch a multi million dollar optical imaging satellite, only to discover an 300 mile long eyelash obscures every photo.
- dharmab 5y agoIt wasn't contamination related, but something similar happened to Hubble in the 1990s. https://www.nasa.gov/mission_pages/hubble/servicing/index.html https://www.nasa.gov/mission_pages/hubble/servicing/index.ht...
- secondcoming 5y agoSince anti-satellite missiles could cause debris issues for everyone, would it be feasible for an adversary to launch a silicone payload at an enemy satellite, with the intention that any optics would be rendered unusable through some electro-static attraction between the satellite and the silicone?
- dharmab 5y agoThere are probably better methods, such as using electromagnetic weapons, or attempting to capture the satellite. https://en.wikipedia.org/wiki/Sokol_Eshelon https://en.wikipedia.org/wiki/Sokol_Eshelon https://www.esa.int/Safety_Security/Clean_Space/Setting_a_satellite_to_catch_a_satellite https://www.esa.int/Safety_Security/Clean_Space/Setting_a_sa...
- deleted 5y ago[deleted]
- edrxty 5y agoNot the worst idea really. There's far more worrisome stuff than silicone, like a small can of black spray-paint which would simultaneously obscure the optics and solar panels while also degrading thermals causing the sat to overheat itself if it still managed to function.
- dharmab 5y ago> You need to control that stuff as it can either short out circuits or be heated and vaporize to coat optics/controlled impedance circuits. You don't even need to be working on satellites to observe this. For example, car headlight bulbs have a much shorter life if you touch the glass bulb with bare, oily skin during the installation.
- drdeadringer 5y agoThis came to my mind as well. I've worked on satellites in clean rooms and have also had cause to change the bulbs in my car's headlights. The packaging on the bulbs made it clear that touching the glass was not good.