[AR] FPGAs and history (was Re: LEO radiation shielding)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 21 Dec 2019 12:14:14 -0500 (EST)
On Sat, 21 Dec 2019, Craig Fink wrote:
...When I was school, the University had an Analog Computer for control
systems development of Flight Control systems, have these Analog
Algorithms made it into the FPGA?
Well, FPGA = Field Programmable Gate Array, i.e. it's fundamentally a
digital device.
There are now some mixed-signal chips that also have analog sections, but
it's a tricky thing to do well -- the chip processes that produce dense,
low-power FPGAs are considerably different from the ones that do good
linear analog components.
...One of the problems these first few flights was in attitude control,
the gains were wrong resulting in excessive fuel usage. Essentially,
banging back an forth from positive limit to negative limit, hosing out
propellant. Things haven't changed much in 40 years with Starliner as
the NASA administrator is talking about the problem... Forty years and
no progress...
Some branches of engineering pay a lot of attention to the lessons of past
failures. Space engineering unfortunately tends to forget its past rather
than recording it and learning from it, so each new generation of
engineers tends to repeat the same mistakes. The guys who did Starliner
probably never studied Shuttle development history, never mind Apollo or
Gemini (just like the guys who did ISS paid no attention to Skylab and not
much to Shuttle-Mir).
That said, this is what flight tests are for -- finding the mistakes that
are hard to spot on the ground. We have to resist the idea that anything
going wrong in a flight test is a sign of criminal negligence. One reason
why aviation delivers better reliability than spaceflight at lower cost is
that they do much more intensive flight testing, and expect (and design
for, and plan for) doing some of their debugging in flight. Insisting
that everything must be perfect the first time gets very expensive, and
worse, it doesn't actually work very well.
Henry
Other related posts: