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Measurement storage schema
Bin measurements by rate
Highest frequency grouped into several measurements
24 bits requires us to define our own endianness, error-prone
Microsecond accuracy reasonable
Down-convert inertial measurements to 16 bit ints because that’s how they start
Fundamentally, 32 bits of precision is too many for 16 bits of information
Store only one of the several temperature readings
Events of interest
Everyone detects boost, because we can’t store all the high-frequency measurements
Everyone detects landing, to save power and have less garbage at the end
Grim and Potato need to capture before and after apogee, to get load measurements
Detection options
Detection choices
Final CONOPS
Backplane
Grim Reefer
POTATO
Boost
Acceleration
Not affected by venting or wind
Potentially affected by bumping, but powered on at the pad
Altitude
Less reliable than acceleration due to venting issues
May be overblown
Testable
RRC3s capable of live serial output
Reliable because of COTS
Adds complexity to code
Adds complexity to wiring harness
Choice:
For all, OR gated:
5 gees for 0.25s
Magnitude
Insensitive to orientation changes
Insensitive to programming errors
5 half (arb) of expected g
0.25s worked for SCRAP
Altitude reaches 500 ft above ground level in less than 3s
500ft common arming alititude for altimeters
3s double (arb) of simulated 1.6s
Pre-Apogee
Timer after boost
Timer after burnout
Slightly less simple
Altitude slowly changing
Choice, for Backplane:
After boost, <50 fps gives 2 (arb) seconds leading up
Choice, for Grim:
Not needed, enough data rate
Choice, for POTATO:
After boost, <50 fps gives 2 (arb) seconds leading up
OR backplane detecting pre-apogee
Apogee
Not specifically helpful during the flight
Main
Pure timer
Altitude on the way down
Choice, for Backplane:
Main + 500ft (arb)
Choice, for Grim:
Not needed, enough data rate
Landing
Timer
Acceleration
Altitude
Choice, for all:
Timer is the simplest, no loss to over-timing
Final CONOPS
Backplane
Stores a 3s rolling buffer
Detects boost OR gated measurements
5g 0.25s
>500ft <3s
Detects 3s before apogee
<50 fps vertical velocity
Detects 10s before main
500 ft above main
Detects landing by 400s timer
Grim Reefer
Stores a 3s rolling buffer
Detects boost OR gated measurements
5g 0.25s
>500ft <3s
Detect landing via 400s timer
POTATO
Stores a 3s rolling buffer
Detects boost OR gated measurements
Sensor module command
Own altimeter 500ft <3s
Detects 3s before apogee
Sensor module command
<50 fps vertical velocity
Detects 10s before main OR gated
Sensor module command
500 ft above main
Detects landing by 400s timer
To do
- Is LittleFS file-growing overhead a problem?
- How much data do the currently set thresholds eat up?
- What ranges in descent rate does this timing allow for?