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For example, let's say that you have the rail set to 5 degrees, and with your expected wind the
altitude at ignition is 1200' at 4.0 seconds. You've chosen a fast-lighting motor, so the ignition will
happen at maybe 3.0 seconds, and the simulation says that it will happen at 800' going at about 400
ft/sec. Take another ¼ second off the time, so you're looking at 2.75 secs, the rocket was at 700'
going just above 400 ft/sec (it's not doing to slow down much in ¼ second...). Take 85% of the
700' that you expect the ignition to be triggered at, so that's 595 feet. We'll use 600' as the
qualification. Similarly, if you want to use velocity rather than altitude, take 85% of the 400 ft/sec,
that's 340 ft/sec, so we'll use 350 ft/sec as the value. You will want to set the qualification so that it
is effective "@Timer", i.e. it does the check when the timer expires.
Remember how we told you earlier not to use high-thrust motors for two-stage builds? This is
another reason why. When you get near Mach 1, the pressure buildup drops the perceived altitude
(and also the perceived velocity) so the Proton "thinks" that it's going lower and slower than it
actually is. You're more likely to have a failure to trigger due to a failed qualification with high-
thrust motors, one more reason to avoid them.
Now, if your motor isn't quite so high-thrust but burns long enough that your rocket may hit mach
on the booster before the motor burns out, you probably don't need to use the qualifications. It's
pretty hard to get too far off-axis when you're going that fast, and if you go unstable you'll never get
that fast. However, it is still possible to use the qualifications as long as the timer starts at LDA (and
almost all motors will). To do that, you'll use the "Anytime" qualification option, and use the
velocity qualification, setting it to a lower value than you might expect to see at your expected
ignition altitude, typically something around 700 ft/sec. What this means is that if the rocket
achieves this velocity ANYTIME between the start of the flight and the ignition, it will assume that
you're going fast enough to be vertical. That's a pretty good assumption if you KNOW that your
booster motor is going to get you near Mach 1.
Another good reason to use the altitude/velocity qualification is if you're going for the absolute
maximum altitude you can get out of a given set of motors. Contrary to intuition, that's not achieved
by firing the sustainer right after the booster; it's achieved by waiting until the rocket has slowed for
some time. We've done some simulations and seen some maximum altitudes with the sustainer
firing when the velocity was under 200 ft/sec... that's a lot of slowing from the 800 ft/sec that the
booster got it up to. Obviously, if you wait a long time to light your sustainer the chance of it going
off-axis due to wind effects goes up, so an altitude or velocity qualification is a really good idea.
This brings up the issue of whether it is better to separate early or coast with the booster still on if
you're going to coast for awhile after burnout. In general, if your booster is the same diameter as
your sustainer, you should hang onto it because the extra mass will reduce the deceleration after
burnout without causing a significantly higher drag penalty. If you booster is larger (i.e.
RW/Madcow Double Shot, 4" booster and 54mm sustainer), the sooner you ditch it the better,
because that booster will be a big drag on the sustainer. Again, doing a good simulation with Open
Rocket or Rocsim is your best bet, but you'll probably find these guidelines to be pretty accurate.
The Deviation Qualification
One unique feature of the Proton is the Barometric:Acceleration Deviation qualification. During
flight both the filtered barometric altitude and filtered acceleration-integrated distance are computed.
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