Bare Minimum: M2245 to 50,000 feet

[FredA]

Rocket Apogee is the highest point in the flight.
If your rocket took off and turned into a horizontal land shark, then the point of the turn is likely to be the rocket's actual apogee OR the onboard flight computer may interpret the transition from "fast-up" to "no-up" as being apogee.

 

[kjhambrick]

Rocket Apogee is the highest point in the flight.
If your rocket took off and turned into a horizontal land shark, then the point of the turn is likely to be the rocket's actual apogee OR the onboard flight computer may interpret the transition from "fast-up" to "no-up" as being apogee.

I understand the apogee part but I can't imagine how one would write code for a flight computer that could differentiate unexpected events like sudden, violent turns at burnout from the peaks of nice, smooth parabolic arcs that we know and love and try to shoot for

And then there are @JimJarvis50's flights where he programs amazing profiles into his VOS ... check out the latest posts in TRF > I could use just a little guidance ... existing flight computers work in his rockets because there are velocity rules baked into the apogee detect algorithms in the flight computers that we fly.

I am thinking that Bare Minimum's flight profile violated several apogee detect rules when and if it lost the nose before it broke up ( or did it break up and then lose the nose ? )

-- kjh

 

[boatgeek]

The Blue Raven votes 2 of three sensors for apogee detection, between accel, gyro, and baro, and it would be hard to spoof more than the baro sensor.

If a flight failure happens on this type of flight, causing the rocket to go sideways and/or tumble, how do the accelerometer/gyro sensors feed into deployment logic? For example, does the Blue Raven try to figure out what the vertical acceleration is as the rocket tumbles? That seems like you'd max out either the accelerometers or gyros pretty quickly with a failure at high speed. Alternatively, if the rocket hits apogee while tumbling, the baro would show apogee and then falling altitude. Does the apogee charge then fire as soon as either the accel-calculated velocity goes negative or the gyro shows the rocket horizontal?

 

[FredA]

Typical high-level code is something like this:
- Wait for baro to show negative pressure change for X amount of time to indicate launch.
- Wait for baro to stop going negative and perhaps a little positive to indicate apogee.

Now there is usually a bit more to it than that, especially to ignore Mach transitions, but once the baro flattens out and goes positive, you're on the way down.

 

[Adrian A]

If a flight failure happens on this type of flight, causing the rocket to go sideways and/or tumble, how do the accelerometer/gyro sensors feed into deployment logic? For example, does the Blue Raven try to figure out what the vertical acceleration is as the rocket tumbles? That seems like you'd max out either the accelerometers or gyros pretty quickly with a failure at high speed. Alternatively, if the rocket hits apogee while tumbling, the baro would show apogee and then falling altitude. Does the apogee charge then fire as soon as either the accel-calculated velocity goes negative or the gyro shows the rocket horizontal?The Blue Raven's fault-tolerant apogee detection starts at motor burnout and has three criteria, with apogee detection after the first 2 of them are true:

The apogee detection logic starts running at motor burnout, and detects apogee when the first 2 of the following three criteria are true:

1. Tilt computed by gyros is > 90 degrees
2. Baro sensor (with an aggressive low-pass filter that rejects even very large transients) detects increasing pressure
3. Accelerometer-based upward velocity estimate < 0

If a rocket takes a big turn and starts tumbling, the sensed tilt will be > 90, and the apogee will be detected once the baro pressure starts persistently rising when the rocket is falling, even if the accelerometer-only velocity estimate is spoofed by a 180 degree turn where drag looks like thrust.

The puff that was seen 5 seconds after the rocket turn was probably the Blue Raven firing a charge at actual apogee, seconds after the failure occurred.