- Maximum acceleration time: 255 seconds (two drives of 180 + 75)
- Range without ballistic phase: 33.8 light-seconds (10.14 million km)
- Final velocity: 84176 km/s
I was in doubt from the text whether 84176 km/s was the final velocity after two stages or after just the first. The text says: "<pronoun> could inject a ballistic phase at 180 seconds, [...] but velocity at that point would only be 84,176 KPS."
Only one of two interpretations is physically possible. If that velocity is at 180s at the end of the first drive, the first drive accelerates at 84176 / 180 ≅ 467.6 km/s² or 47686 gravities, which is a decent acceleration for a missile. It would have crossed 7,575,840 km. But then if the missile does nothing and coasts for the next 75 seconds, it'll cover another 6,313,200 km. For it to cover only 2,564,160 km, it would need to have a negative acceleration.
The other interpretation is that the combined acceleration of both stages results in a speed of 84,176 km/s. This one results in a physically valid pair of acceleration numbers, but it's equally unlikely. 84,176 km/s is a decent Δv for a single stage; for two stages, it would mean that both stages are actually pretty poor, at around 30,000 gravities each.
I think the range here is the wrong number and I think I know where the math went wrong: David forgot to add the base velocity of the first stage when calculating the range. If instead we were to calculate the acceleration of the second stage from a standing start to cover the remaining 2.56 million km, it would have an acceleration of 911.7 km/s² or 93000 gravities. That's pretty much the acceleration of everyone's stage in high-power mode for 60 seconds. They've managed to extend it to 75 (though I expect the Manticoran Mk14 ERM can do 90).
If I'm right, the correct calculation would be that the missile covers nearly 8.9 million km during the second stage's powered phase, making the missile have a full range without ballistic phase of nearly 16.5 million km. Or 54.9 light-seconds.
Or did I get my math wrong somewhere? I've corrected myself already half a dozen times...