General Question What if I wanted to recreate a launch vehicle?

[Pipcard]

If you have orthographic schematics and information (e.g. masses, specific impulse of each stage, etc.), then the first part is easy.

The second part is hard, though. It's about the launch profile of the rocket. Do you have to learn a lot of C++ to make a launch autopilot?

If you have to do a manual launch, how do you know at what times/altitudes to pitch down (specifically)? (That information is hard to find if you research)

 

[Izack]

Take a look at Multistage 2 (by the author of Spacecraft 3) or Velcro Rockets.

 

[Urwumpe]

start with multistage or velcro, they already solve many problems for you.

A C++ module for a launcher is not much C++ (less than 4000 lines of code with autopilot), but requires some basic knowledge about launcher theory: what are physical and logical stages? What is a gravity turn? Also it helps knowing some computer science stuff, like what state charts are and how you optimize state charts.

 

[Pipcard]

Take a look at Multistage 2 (by the author of Spacecraft 3) or Velcro Rockets.

Yes, but does that help you calculate the proper launch profile? Not just a vague, "get out of the atmosphere, then accelerate horizontally," but the proper pitching maneuvers?

 

[Spacethingy]

LaunchMFD is open source, code included in the download - that has a generic autopilot, dunno if that helps.

 

[Pipcard]

LaunchMFD is open source, code included in the download - that has a generic autopilot, dunno if that helps.

That's only for SSTOs, not rockets with multiple stages.

 

[Urwumpe]

Yes, but does that help you calculate the proper launch profile? Not just a vague, "get out of the atmosphere, then accelerate horizontally," but the proper pitching maneuvers?

The proper pitching maneuvers are the result of many hours of simulation and updated for every flight. You can of course simulate them in Orbiter...

 

[PhantomCruiser]

For manual launches there was a rule-of-thumb I read somewhere here on the forum. The post (and I can't remember who it was, sorry) said to aim for 40 degrees pitch angle at 20 K altitude, 30 at 30, and 20 degrees at 40 K. Hold 20 degrees pitch while watching the vertical speed and adjust as needed.

It may not be ideal, but it works.

I've since started to watch LoadMFD to see what the g-load during the flight is doing. This helps me to adjust the guidance program for multistage, I generally take note during a manual launch, so I can get the guidance file to work like I want (or close anyway).

I've spent hours with Orbiter working on guidance files.

 

[Pipcard]

Does Multistage2 or Velcro allow you to set a ground offset? (for example, your rocket starts 10 meters off the ground)

 

[Urwumpe]

Does Multistage2 or Velcro allow you to set a ground offset? (for example, your rocket starts 10 meters off the ground)

AFAIK yes, but don't ask me how. I start at C++ code because I am too lazy to learn Multistage2. :lol:

 

[PhantomCruiser]

Yes, both allow an offset from the ground.

 

[garyw]

Both allow offsets from the ground. Both cover this in their respective manuals which I would suggest reading and then testing in orbiter.

 

[Notebook]

Does Multistage2 or Velcro allow you to set a ground offset? (for example, your rocket starts 10 meters off the ground)

Shameless plug:

My Blue Streak F2 addon uses Sputnicks Velcro system, and has an offset launch position, and a simple pitch profile. It does try to follow the original, vertical for 20 seconds, then pitch down at .7 degree/second till 20 degrees and hold that.
[ame="http://www.orbithangar.com/searchid.php?ID=4232"]Blue Streak F1(Velcro).[/ame]

Its a bit of a dogs dinner, some folk had problems with it, and you need my Woomera 6A base. But the velcro .cfg file might be useful.

N.

 

[RGClark]

That's only for SSTOs, not rockets with multiple stages.

Has it ever been used for that purpose?

Bob Clark

 

[PhantomCruiser]

LaunchMFD? Yes, OFSS 1, 2 and 3 have all used it AFAIR. But more as a timer, I've not given the AP a spin. But I often use Artlav's UAP.

 

[RGClark]

LaunchMFD? Yes, OFSS 1, 2 and 3 have all used it AFAIR. But more as a timer, I've not given the AP a spin. But I often use Artlav's UAP.

LaunchMFD used for a SSTO was that for a partial scramjet propulsion vehicle or all rocket?
BTW, for getting a realistic trajectory you might try following the space shuttle trajectory to orbit, approximated mathematically here:

Space Shuttle Launch Trajectory - I.
spacemath.gsfc.nasa.gov/weekly/5Page40.pdf


Bob Clark