Open Rocket Error

I've been fooling around with a 3 stage rocket in Open Rocket, and everything was going great until I messed with the fins a bit, and started getting some big errors. In the quick simulation I am getting a bunch of N/As rather than estimates, and when I try to run the simmulation, I get this:


It seems to be somewhat related to fin size, or possibly velocity, because when I decrease the bottom stage fins enough to destabilize the rocket, it will give me an estimate based on unstable flight, and if I add about 30lb of nose weight, it will start giving me estimates again.

Any ideas?

View attachment Space Rocket 3 Stage decreasing.ork

Ah ha! I think I found the issue. Or at least I found a workaround. The trick is to reduce the time steps. It seems there was some acceleration or something like that that was too great for the simulation to handle, so I cut down the time step from .05 to .01 and it works!

edit: Ok, now another really odd question. I know OR isn't so great above the speed of sound, but that really shouldn't matter too much if you are launching at 100,000' (this is to be launched from a balloon.)

That being said, when I went to look at the printout of the data, it had motor burnout at 17 sec, at an altitude of 63,000' (relative to the launch altitude), and traveling at Mach 6.77. I really don't think it would make it anywhere close to that speed, but I could be wrong. Then it continues to coast up to an apogee of 887922' at t=243 seconds. Something has to be seriously wrong here. Any idea what?

If it's not a top secret project you could always post the .ork file and we could have a look?

you also gotta think of what motor's you're using. mach 6.77 is theoretically possible, but at that altitude, with anything less than a 200000 N motor shoving you, you'll be dead in the water, even worse, everything will probably melt off.

that and after running a sim, i realized a boosted dart from 54mm to 24mm was impossible if staging was at booster burnout (24mm rocket at mach 2.2 has ~700N drag, impossible to stage off that).

i think if you shared the file we could gauge this a little better.

Woops. Sorry I let this thread slip. Because of how I was saving my files, they were waaaay to large to post on the forum. Here is the current .ork. It is a L2300 staged to a J825.

The key behind this project is the initial launch conditions. The rocket is being launched from 100,000', where the atmosphere is 1% as dense. If everything scaled linearly, which I know it doesn't, then I wouldn't be running into melting problems till approximately mach 300.
If you look at the data printout from the flight, you'll see that after burnout, the rocket has a pretty consistent deceleration of ~40ft/s/s which is approximately the acceleration due to gravity. I don't expect air resistance plays much of a role in the launch of a rocket at this altitude, so I don't think those calculations will cause much error.

edwinshap1 said:

mach 6.77 is theoretically possible, but at that altitude, with anything less than a 200000 N motor shoving you, you'll be dead in the water

Click to expand...

I'm not really sure what you mean here. The higher the altitude, the lower the atmospheric pressure, so the less thrust you need to keep going.

Check out the flight profile and you will see what I am talking about. The 2nd stage provides a similar acceleration the the first. That is the rational of the 4:1 staging ratios, that seem to have proven themselves over time some how.


I appreciate all your comments!

View attachment Space Rocket 2 Stage decreasing.ork