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I read this post about finding the propellant mass needed to reach a specific altitude: How do you find the propellant mass needed to reach an inputted altitude?(altitude at end of burn plus altitude during coast). It has an amazing answer, but one part they say we have to do is compute the burn-time after computing the delta v. Basically, my conditions are exactly the same as the person who asked the question. I can't just straight up test it, so all my information on the propellant is based on what can be found online. So my question is how can I find the burn-time to be able to complete the calculations given in the answer?

Edit: A very probable solution is to use the burn-rate. The formula being:$$r=aP_c^n$$ In this equation $r$ is the burn-rate, $a$ and $n$ are both constants based on the propellant, and $P_c$ is chamber pressure. Something very annoying to note is that $a$ and $n$ are only valid for a specific range of chamber pressures which is extremely annoying. If anyone knows a solution to that, please tell. However, more importantly is the chamber pressure. How would I be able to calculate this? The solid motor I am using and am going to be using in the future will simply use a cylindrical propellant grain with a cylindrical hole down the center.

Rocket Man
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  • That's in the answer too: "Of course you don't know your burn time without knowing your propellant mass, etc. So making use of this correlation would best be done with some iteration (i.e. assume burn time/launch mass, compute delta V, compute vehicle mass, compute burn time, repeat)." A given solid propellant would have a known burn-rate, but that doesn't help unless you know how much there is. – Organic Marble Sep 07 '23 at 17:29
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    Burn-rate is dependent on chamber pressure, but how do you find chamber pressure? How do you find the chamber pressure based on simply stuff you can find online and the shape of your rocket motor design. Mine is simply a cylinder with a bunch of propellant packed in it. It also has a circular hole down the middle. – Rocket Man Sep 07 '23 at 17:51
  • You may find this thread helpful. https://space.stackexchange.com/questions/59522/chamber-pressure-and-burn-rate-equations – A McKelvy Sep 07 '23 at 19:56

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