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I was reading an article yesterday about circuits and IC's in deep space and how they need to be operable at high temperatures. A few questions popped up when I read this article. Today there are many and have been many missions/projects of surveillance ops in our outer universe Furthermore, NASA has put together missions involving asteroid research as well as JAXA. I realize there are numerous control variables that take a play aboard these specific systems. I have a few questions I thought someone could answer briefly or if to extensive could post a source where I could refer too for further information.

Does atmospheric pressure effect operating temperatures of circuits and/or IC's implemented on a system in space?

Does radiation/gases effect operating temperatures of a circuit and/or IC's in the same scenario above? If so, does the engineer have to take in precautionary measures in the construction of a circuit if the system might be exposed in low orbit of planetary systems?

What kind of precautionary measures are we talking about in GENERAL terms? Are there any good resources out there that explains how circuits can generate heat and tactics used to lower their levels of heat given off?

Thanks for any advice or information. Again, if information is to extensive please attach a source that I or anyone else could use for further information/research. Thanks again.

V/R Shane

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Atmospheric pressure, or the lack thereof, does affect electronic components. Components in low to near-zero pressure tend to outgas, and while ICs are relatively simple to condition for this, parts like electrolytic capacitors will fail. Hence, components specifically designated for zero-pressure are used instead.

Radiation affects ICs in two ways: Firstly, semiconductor behavior changes significantly under increased ionizing radiation, such as exists outside the earth's protective atmosphere, and in the highly ionized belts of the stratosphere. Hence, radiation-hardened parts are manufactured specifically for such purposes, and are used in space electronics.

Secondly, under normal operation (on the ground) the thermal output of any IC gets removed from the package by a combination of radiation and by being carried away passively by moving air... In low pressure or vacuum, only radiation of heat works, not passive air-borne cooling, thus changing thermal dissipation calculations for any component.

Thus non-traditional cooling mechanisms and considerably greater distribution of conductive cooling paths are required.

Regarding gas-related precautions for space electronics: Manned space vehicles have sometimes used oxygen enriched environments. This leads to a necessary rethinking of such circuit design elements as PCB spark gaps, which could lead to catastrophe.

Also, non-design sparking, such as due to motor / coil field collapse, metal contacts of switches, or just a loose connection, need to be eliminated entirely - much more critical than for normal earth atmosphere. Silicone-filled contact casings, like the classic oil-filled switches, are worth considering. Similarly, space-safe epoxy potting of practically all exposed metal including PCB traces, is a way to go.

Further, there is the whole thermal operation range to be considered, especially for unmanned craft: From very hot (due to solar exposure without atmospheric protection), to very cold (due to no "atmospheric" heat when facing away from the sun).

This cyclic heating and cooling causes potential metal fatigue, junction stress and fracture such as at solder joints, and loose contacts due to uneven mechanical expansion and contraction between different materials.

Finally, not all semiconductor components are specified for extremely low temperatures. While heat might be an obvious concern, cold is an equally big issue. Some parts are specifically manufactured, and tested, for extreme low temperature operation. For other parts, the component behavior changes need to be taken into design consideration. For instance, the simplest PTC resettable fuse is no longer a trivial circuit element in space electronics.

I hope this has given an insight into just some of the factors around your question. For the rest, a search engine is your best bet.

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    \$\begingroup\$ Voted up for good coverage while keeping things comprehensible to a layman. \$\endgroup\$ – Seemingly So Jan 28 '13 at 14:10
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Does atmospheric pressure effect operating temperatures of circuits and/or IC's implemented on a system in space?

It does effect the operating temperature of circuits and ICs implemented in space. It does this by changing the thermal dissipation mechanisms available to the ICs, as pjc50 noted in his answer. For regular applications, you rely almost exclusively on convective cooling cause by air flow. The thermal junction properties listed in power transistor and IC datasheets assume that the device is in air, and heat sink specifications assume the heat sink is in air. Thus the many fins in a regular heat sink - Increasing surface area increases the contact area with air and allows it to pull away more heat. This is completely absent in space (well, there's some air pressure if you're in low Earth Orbit, but the cooling effect drops to negligible levels even there). The problem is solved by using a combination of techniques to cool the circuitry and maintain the electronics within an allowed region. These are generally a combination of active and passive thermal control systems (including heating, not just cooling). Heat sinking is usually conductive, piping away heat to larger areas which can radiate effectively into the dark of space.

Additionally, there is rapid 'thermal cycling' if you're orbiting something between eclipse and non-eclipse periods, and also thermal gradients that are set up between the illuminated and dark sides of the satellites. These require better controlled fabrication processes and materials to avoid things cracking, breaking, and otherwise degrading.

Further, the vacuum itself causes a non temperature related problem in that the materials used may vaporize by a process known as degassing. This could cause wire insulation to fray, ICs to decapsulate, condensation of this vaporized material on optics, weakening of mechanical components, change of dielectric (and therefore RF) properties, change of thermal properties, etc.

Does radiation/gases effect operating temperatures of a circuit and/or IC's in the same scenario above? If so, does the engineer have to take in precautionary measures in the construction of a circuit if the system might be exposed in low orbit of planetary systems?

Radiation does. Gases, well, depends on which gasses. If its a highly ionizable gas, then it could spark easily.

Radiation effects the operation in a way other than in temperature. Radiation directly attacks the ICs and causes faulty operation and even failure of the device. This is also a problem on the Earth, by the way, and high performance computing clusters with thousands of nodes see data corruption and even node failure often enough to make it a serious problem. It would happen with desktops too, except that since you'd only be looking at a single node in isolation the failure rate seems incredibly low and mostly goes unnoticed.

The two principle ways in which radiation effects electronics is by latch-up and SEUs. Latch ups occur when a charged particle gets lodged in a gate. This effectively shorts the gate and causes a high current to flow through it. The fact that the gate is charged to begin with attracts the particles in the first place, and the current keeps it lodged in. If the situation persists, the gate would degrade and in the worst case condition cause the IC itself to fail. The way this is fixed is to cause the power to cycle, which is done by intelligent watchdog and power systems, which is usually enough to dislodge the particle. The second, more common kind, is a single event upset (SEU), where a single bit of memory is flipped because of a passing charged particle. This can cause data corruption, and depending on where the bit is (program counter, for instance), more serious system failure. This is overcome using a method known as triple majority redundancy (TMR), where each bit is stored in three places and is periodically checked (or checked at the time of use). The assumption is that the bit that is damages is unlikely to be damaged in all three copies, since this is a fundamentally random event.

The smaller your feature size (IC fabrication process), the larger the chance of one of these happening. The hotter the IC, the higher the chance of one these happening (although by a small factor).

Radiation hardening is done in the hardware and often IC level by building TMR into the IC itself. In fact, there are space grade processors which even have 3 cores operating in parallel, doing exactly the same thing. At a higher level, redundancy is maintained at a board or package level, and is used in some cases as a fallback and in others in a TMR kind of fashion. The chips are themselves ruggedized, to tolerate more heat, dissipate more heat by radiation, much better controlled processes so there are less 'outliers' which can make radiation's job easier, and often have embedded plates for shielding using a radiation opaque material. This depends on what sort of radiation you're worried about, but usually a plate of tantalum works in low earth orbit.

What kind of precautionary measures are we talking about in GENERAL terms? Are there any good resources out there that explains how circuits can generate heat and tactics used to lower their levels of heat given off?

There are general things that are done which are common even for regular electonics. FMEA / FMECA can help prioritize potential problem areas. Careful design and failure analysis can help identify and eliminate all sources of single point failure (where a single problem can cause catastrophic failure). Additionally, there are other measures taken such as careful selection of material for behaviour in vacuum, radiation, and thermal excursion. The NASA System Engineering handbook had some fairly good explanations, if I remember correctly. Off hand, I can't remember any specific, non-classified source which has the details collected in a single place.

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    \$\begingroup\$ I really don't mind if you upvote the answer or not. That's your prerogative. Personally, I think there's enough scope for a properly technical answer for a serious question (and this, by the way, wasn't a proper technical answer), and I disagree with your contention on principle. Also, while 'buzzwords' may seem distasteful, they are what are going to help the OP search for more details if he wants to. You call them buzz words, I call them technical terms unique enough for fruitful search. Finally, I'm curious to know which terms were too far out of reach in the answer. \$\endgroup\$ – Chintalagiri Shashank Jan 28 '13 at 14:27
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    \$\begingroup\$ @SeeminglySo industry standard terms != buzzwords. If the terms weren't defined you might have legitimate grounds for complaint; but they are and you don't. \$\endgroup\$ – Dan Neely Jan 28 '13 at 15:07
  • \$\begingroup\$ He wanted to know how radiation effected things and how people get around the problem. I don't know how any answer that addressed that would not introduce that concept. Excursion i'll give you. It was me being lazy and using two words instead of a one sentence definition of it, since the principle was primed in the answer earlier. \$\endgroup\$ – Chintalagiri Shashank Jan 28 '13 at 15:15
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    \$\begingroup\$ @ChintalagiriShashank Let it go: Rare visitor with strong views. I agree "why tantalum was specially mentioned not just radiation shielding plate" but. \$\endgroup\$ – ExcitingProjects Jan 28 '13 at 15:18
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    \$\begingroup\$ A suggestion: This debate might be better in a StackExchange private chat room, it has little value for future readers. No offence meant to any of the parties. \$\endgroup\$ – Anindo Ghosh Jan 28 '13 at 15:24
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Pressure and gases don't directly affect the operating temperature, but they do affect the normal passive air cooling that is possible with circuits on earth. You can't rely on air cooling in a vaccum. Usually the circuit will be cooled by thermal conduction through its ground planes off towards the casing and then emittted into space.

Conversely, there is also a risk of the circuit being too cold. The sunward side of a spacecraft will heat up and the dark side will cool, heading off asymptotically towards 3 kelvin. Hence careful insulation.

Generally, all energy used in an electronic system ends up as heat (obvious exception: radio emissions). The general approach is exactly like PCs on earth: reduced voltage and frequency reduces power consumption and thus overheating.

Radiation may present serious problems for spacecraft, especially when operating outside the Van Allen belts (which deflect charged particles away from the earth). I'm not sure exactly how "radiation hardening" works.

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  • \$\begingroup\$ Nice and to the point. Voted up. \$\endgroup\$ – Seemingly So Jan 28 '13 at 14:09

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