Iffy voltage: The plague of PC builders and Hubble space telescope controllers alike Good news, Hubble fans – NASA reckons it may have worked out what has upset the orbiting observatory: an iffy Power Control Unit (PCU). The agency is only saying the PCU is a "possible" cause of the Hubble's technical breakdown at this stage, but the theory is strong enough that engineers have been given the green light to …
I've seen this for years now - old computers from the 70's and 80's that have been running for years usually run into power supply problems - normally it's just capacitors that lose functionality or something in the PSU that has just been nice and warm for 30 years. I expect that a replacement will fix it.
It'd be interesting to know how they design PSUs for long term space missions. My guess would be that the electrolytic capacitors that are ubiquitous in Earthly gear would be about the last thing you'd want to use because they are sort of ephemeral. But what do you use instead for smoothing voltage flows -- inductors?
7805 plus loads of silver mica caps ;-) ?
It's power source is solar and batteries, so the PCU shouldn't need any big caps for taking low AC out. Most of the spike and noise caps will be local, rather than at the PCU.
Having said that, if it landed on my bench for repair then checking and replacing the caps would be top of the list if nothing else was obvious.
The PCU is apparently putting out a constant 5V, via it's regulator.
One assumes this is DC and is derived from the solar panels, which would be producing DC as well.
Electrolytic caps can be used to smooth out rectified DC voltages sourced from AC power supplies but I doubt they are needed in this case as decent quality, silicon voltage regulators have been available for many years.
However, I would also assume that there would be a high current output (to power many and various instruments and control systems), at 5 volts, and that alone can lead to time related issues, due to the possibility of effects such as dry joints, caused by heating/cooling cycles.
The vast majority of silicon regulators require both input and output capacitors.
The various types each have their own issues, but Sprague wet tantalums are likely to be in the mix somewhere given the years in which this was designed (Sprague is sadly no more). There could be any number of types (mylar was popular as it is dimensionally stable over temperature).
Without knowing the details, it seem this regulator is providing power to all the instruments and therefore as loads are switched in and out there will be thermal differentials. It is due to the load step response (along with loop stability) that output capacitors are required. I can't go into that any further without sending half the audience to sleep defining poles and zeros.
Note that electronic loads are not constant so there will be almost continuous output current variations; local capacitors should take care of that but anything within the loop bandwidth of the regulator should be taken care of by the regulator output capacitors.
Input capacitors are required under just about any circumstances I can imagine.
Given the time it was designed, it may well be a discrete design which means more components. More components = greater chance of failure.
Something else that can give issues is the internal reference voltage source - you cannot have an effective regulator without one.
Back in the day that would probably be a Zener (possibly a bandgap reference although they were not particularly common until about the late 80s) and such devices are just as susceptible to ageing as anything else electronic.
So there could be a number of different culprits.
Yesterday my wife's work laptop (about 8 months old) suddenly started popping and emitting smoke when she had the USB-C charger connected (manufacturer power supply - no cheap chinese knockoffs). She got about 2 more hours use from the battery but it can't be charged any more.
This was using the second USB-C port - the first one had already failed in exactly the same way a few months ago! But the company hasn't been able to get any new laptops (with their particular spec) from their supplier for months so they haven't been able to replace it. She is currently left using an old Microsoft Surface!
Apparently this is a known problem with this laptop model - the battery charging circuitry is known for blowing up the USB-C ports. It will get replaced under warranty, of course, but one wonders if the problem would have occurred with the old-style barrel connectors.
There was a component which would regulate voltage at a particular level. It was called a Zener diode. There would be a resistor in series for the voltage to drop across.
For power applications (such as here) you would probably use an integrated-circuit voltage follower feeding off the output of the Zener diode.
For space applications, you would need to shield against cosmic ray hits (which is why satellite installations use weirdly-shaped bits of tantalum).
For myself (now in retirement), I am looking forward to a future "On-Call" column.
Should we have a dinosaur icon?
https://www.kktv.com/2021/07/16/hubble-space-telescope-fixed-after-month-no-science/
56 minutes ago - 14:06:00 -03:00 GMT
Engineers successfully switched to the backup equipment Thursday, and the crucial payload computer kicked in. NASA said Friday that science observations should resume quickly, if everything goes well.
Kudos for these guys at NASA.
8^D !!!
O.
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