RockSim and SpaceCAD

Having been (and still am) a RockSim user, I thought I might check out the competition, i.e., the SpaceCAD software. And, as you might guess, the comparison is illuminating:

Areas where RockSim version 7 has the edge:

1) Stability calcs - SpaceCAD apparently only does Barrowman, whereas RockSim gives you choice of 3 techniques (Barrowman, RockSim, and cardboard cutout).

2) CD calculation - SpaceCAD requires entry of the rocket CD - default is 0.75. RockSim can calculate it at simulation time.

3) Variable launch conditions - Change wind, etc. in RockSim. Can't do it in SpaceCAD. SpaceCAD does allow you to vary launch guilde length, but you have to estimate amount of friction (in newtons).

4) More extensive parts database - RockSim's dwarfs SpaceCAD's. Also, I tried the "RockSim database import" tool provided with SpaceCAD (after deinstalling RockSim 7, and installing the RockSim demo, as per the SpaceCAD instructions). As far as I can tell, it imported nada. Somewhat peeved, I scrapped the RockSim demo, and reinstalled RockSim 7.

5) Greater flexibility in design - RockSim allows you to design exotic fin shapes, and clusters are handled better. Plus, Bruce Levison and others have figured out how to handle tube fins and side pods.

This flexibility came in handy in designing my entry for the EMRR "Longnecks" competition. I could do fins with 7+ corners in RockSim - couldn't figure out a way with SpaceCAD, which seemed to force me to only four corners.

6) Recovery devices, especially streamers, are handled in a more realistic manner. In SpaceCAD, streamers are entered as mass objects.

7) Extensive libraries of rocket designs.

Areas where SpaceCAD version 3 has the edge:

1) Cost - 2/3 that of RockSim

2) Much better plots of the flight profile (thrust, acceleration, etc).

3) Better printouts of part lists, fin patterns and alignment guides, and transitions. RockSim's ain't bad, but SpaceCAD's are better.

4) Ability to export rocket information to html, which is not insignificant if you would like to post your rocket designs on the web.

I guess the short of it is that SpaceCAD is prettier, whereas RockSim sports greater design flexibility with better realism. I must confess that I am annoyed at the failure of the SpaceCAD tool to import RockSim databases, as the ones with SpaceCAD are pretty lean. Sure, I could sit down with a bunch of rocket catalogs and input the stuff, but I could also use these with pencil and paper to do my designs. So why spend 60 bucks for a tool that I will have to spend a fair amount of time entering parts into a database? Moral of this story is don't believe everything the ads tell you - I bought into the import database one, and it doesn't work.

I'm sure I will use SpaceCAD in future rocket work - after all, I paid money for it. You can bet that I am darn well going to use it to create information for my rocket web site when I get it up and going. However, for anything except simple designs, RockSim remains the tool of choice.

Is RockSim worth the extra money? You betcha!

And will someone please tell me how to get parts data into SpaceCAD without having to enter a bunch of catalog info?

RockSim rules!

I use both RockSim and SpaceCAD.

When I have problems with SpaceCAD, I contact Andreas directly at https://www.spacecad.com/contact.html . Andreas has always been responsive to my messages.

I do prefer RockSim over SpaceCAD.

My ONLY RockSim complaint:

Altitude prediction is much higher than actual performance. According to RockSim, my Level 3 BIG Thor should have gone to 8500' AGL, but actually only reached 6451' AGL.

When I specified the CD of .60 it was only a few hundred feet difference.

Understand, I have not discussed this with Tim, so there may be something I am not doing correctly. There is probably an easy solution.

Originally posted by bsdrocketry
When I have problems with SpaceCAD, I contact Andreas directly at https://www.spacecad.com/contact.html . Andreas has always been responsive to my messages.

Click to expand...

I did email Andreas with the following:

Hello,

I have the demo version of Rocksim installed on my computer, but I cannot seem to import the databases into SpaceCAD using the import tool.

Can you help please?

His prompt reply was:

Dear Bill,

SpaceCAD can import the database by running the "rocksim database import" utility in your application / SpaceCAD folder on the start menu.

Best regards,
Andreas
spacecad.com

which is exactly what I have been doing... I think there may be a language obstacle to overcome, so I shall put a little more thought as to how to convey my situation in the next email message.

BTW, installed the RockSIM 5 demo on my laptop, and then installed SpaceCAD. Ran the import tool, which still did not work. Two computers, two strikes.

As far as altitude prediction, I created identical 2 stage rockets in both programs, making sure the weight, the location of the CG, etc. agreed. SpaceCAD had the rocket traveling 276 feet higher than RockSim, using the default SpaceCAD CD of 0.75. Do you tweak this to achieve more realistic values?

As far as altitude prediction, I created identical 2 stage rockets in both programs, making sure the weight, the location of the CG, etc. agreed. SpaceCAD had the rocket traveling 276 feet higher than RockSim, using the default SpaceCAD CD of 0.75. Do you tweak this to achieve more realistic values?

Click to expand...

In RockSim, uncheck "calculate Cd at simulation time" and manually input a Cd=0.75. Rocksim and SpaceCad should, in theory, now agree. I know RockSim solves the differential equations correctly. I never used SpaceCad, but I assume it does too.

RockSim has a Cd vs. velocity estimator based on Estes TR-11 and Hoerner with some Mach adjustments. You can override this estimator with the fixed Cd for the sustainer and the boosters. I think this feature will be enhanced even more in v8.

Tweak the fixed Cd with SMARTSim.

Ken

Another thing. By default, RockSim has launch conditions set with some level of variable wind and thermals. If you want to compare RockSim results with other software that does not have variable weather, then make sure to zero out the wind and such in RockSim before the simulation.

Ken

Just one other note of difference for those that don't know about either product:

Its much faster to create a design within the SpaceCad environment, BUT this ease comes at the price that it doesn't have the flexibility and detail that Rocksim has.

Yes, I'm the first to admit that I still don't know all that Rocksim has to offer, BUT a huge turn-off for me is the amount of steps necessary to simulate pods - as just one example. It shouldn't be like that, BUT theres no use complaining about it. lol

Apples to apples comparison...

Rocksim can be as complex as a Senior level Trig test, while Spacecad is a 5th Grade extrance exam. Having said that, I think both products do a good job at fullfilling their "niche" within the rocketry design software category.

If you don't need all the flexibility then go with SpaceCad.
If you want to save about 50 bucks, go with SpaceCad.
If you want to get your feet wet with simplistic designs that are functional and give you the proper output - i.e. my new rocket design would be stable, and thats all I need to know...go with SpaceCad.

IF you want detail go with Rocksim
If you need all types of base input - for launch conditions etc., go with Rocksim.
If you don't mind spending 95 bucks for a complete software package, go with Rocksim.

If however you want a platform that has the industry standard - that being the .rkt format, then I'd tell you to purchase Rocksim...period. More people use Rocksim to share their designs of fictional rockets and more real world designs than any other package out there. All thanks in large part to Rocksim's ability to open previous .rkt version with the newest version of the software. (i.e. version 5 rkt files can be opened in version 7).

Cheers,