Expanse MCRN torpedo project

I had some inspiration, being an "The Expanse" cable show fan, and decided to try building an MCRN (Martian Congressional Navy) torpedo. I used Rocksim for the first time, and this is what I am going to try and build...

Original picture from the show:


Rocksim rendering:

Length is 25.25" long, loaded weight is 5.807 oz. Stability margin while loaded is 1.72.

Suggestions for improvements welcomed, as this is my first Rocksim project. The actual nosecone will have the tip removed to make it more flat, but I could not figure out how to show that in Rocksim.

I had initially thought to use clear plastic fins, but after researching the difficulties in a) finding the correct polycarbonate, and b) attaching the fins with epoxy, decided to stick with the more familiar balsa fins. I am rationalizing that while the torpedo is intended for space use (which is all we see in the show anyways), that it has small pop-up fins for use against upper atmospheric targets.

What motor(s) are you planning on using in it?

I was planning on using D engines in it; Rocksim notes that a D12-5 should yield an altitute of about 715 feet, though I expect a bit less. I don't have an altimeter though, so I can't verify altitute anyways.

I looked at using an E engine, and while it should go about 1100 feet, the optimum delay is about 4.9 seconds, and I'm not sure whether it would be better to choose a 4 second or 6 second delay. The acceleration looks to be a bit sluggish as well, with it barely moving 39.5 ft/sec off the launch rail vs 45.9 with the D engine. In any event, because the launch area I have access to is a little smallish, I would be reluctant to use an E engine anyways.

I was able to shave a about .3oz off the rocket by switching to a narrower and lighter rear body tube (I mistakenly chose a LT275, which is thicker walled vs the Bt80 I ended up switching to).

I think I have the design finalized for now, so I now have to write up the parts list and order parts.

Bill S said:

I looked at using an E engine,

Click to expand...

E9 or E12?

E9. Rocksim only came with E9s in the database, and I haven't been able to find where I can edit the engine database (I can find other databases like nose cones, body, engine blocks, etc).

I just looked at the Estes catalog, and they aren't even selling E9s anymore. If I can figure out how to edit the engine database, I'll remove the E9s and add the E12s.

***edit. Apparently with the demo version of Rocksim, you can't add engines. I do plan to purchase it, so at some point I will add them.

I found an Apogee newsletter that covers how to do that.

I'd recommend you try Openrocket (its free!). There's a sticky in the software forum that shows how to install it, and adding motors isn't difficult either.

I did try it first, but you can't do the rocket I designed in Open Rocket (can't do pods). I also plan to fool around with tailcones, which it apparently doesn't do either.

Bill S said:

E9. Rocksim only came with E9s in the database, and I haven't been able to find where I can edit the engine database (I can find other databases like nose cones, body, engine blocks, etc).

Click to expand...

To add motors in Rocksim, click "File", "Reload engine data...", select the "Download engine data"

Type in the description in the "Common name:" field (like E12), then hit "Start search". Click on the file you want to download, click "Download selected engine data...". Save it to the default location (in Data).

Then go back to the "Engine data files", and select your newly downloaded file under "Available engine files", and then click the "Add ===>" button to add it to the database. Click "Ok" and you're done.

Sometimes the naming is a bit different, for example a Cessaroni motor may show up under CTI or Cessaroni, depending on the file.

mbeels said:

To add motors in Rocksim, click "File", "Reload engine data...", select the "Download engine data"

Type in the description in the "Common name:" field (like E12), then hit "Start search". Click on the file you want to download, click "Download selected engine data...". Save it to the default location (in Data).

Then go back to the "Engine data files", and select your newly downloaded file under "Available engine files", and then click the "Add ===>" button to add it to the database. Click "Ok" and you're done.

Sometimes the naming is a bit different, for example a Cessaroni motor may show up under CTI or Cessaroni, depending on the file.

Click to expand...

Wow, that worked, though it is a bit clunky to update it. Thanks.

Here are some preliminary drawings as to how the rocket is to look. The blue fins will be 1/16" polycarbonate after all.
I may have some custom decals made, and maybe use some automobile pinstriping if I can find some that will work.