undefined | Better HN

0 pointsmadengr7y ago0 comments

Where are you getting that temp range? The last payload electronics I designed (an RF PA) only had to handle -20 to 70 C, and the actual temp swing is less. Of course this is inside a bus.

Military electronics are just as bad, as they have to operate from the Antarctic to the desert, and be thrown from the back of a helicopter onto concrete.

0 comments

asteli7y ago

Tangential, but designing devices to handle shock is surprisingly hard as well. I was once tasked with building 900MHz GPS transponders that would allow us to see the shape of a tether being pulled behind an airplane. The device was about the size and shape of a soda can. Occasionally they would get dropped, impacting at terminal velocity.

One early prototype had a li-ion pouch cell (yes, I'd do things differently now). After an impact, I pulled it apart and found that the battery, via plastic deformation, had perfectly fitted itself to the contour of the inside of the enclosure. IIRC it was still working when I pulled it apart.

pocketstar7y ago

NASA’s box requirement is 70C. That means the ICs in the box are much hotter, parent is probably refering to IC temp, not unit.

geomark7y ago

There were some non-NASA boxes that had long periods powered off on the shaded side of the bus and had to operate at powerup at initially very low temperature. And then operate on the sun side for extended periods at an elevated temperature. Depending on the configuration of the bus there were sometimes challenging heat transfer issues. The plate temp wasn't 125 C (I don't remember the exact number) but there was assumed a significant temperature rise from the plate to the electronics. And then additional margin added on to that in case something wasn't quite up to spec in the thermal path. So we had to perform worst case analysis assuming junction temperatures of 125 C. It was pretty awful.

madengrOP7y ago

Ok, makes sense. The 70C for my unit was the temperature of the plate to which the PA was mounted.

j / k navigate · click thread line to collapse