Jump to content

How far is the initial pitch maneuver usually?


Spaced Out

Recommended Posts

It depends on your launch vehicle's thrust-to-weight ratio. As a good rule of thumb, I typically try to pitch over gradually enough that my heading always stays inside the prograde marker, but rapidly enough that I hit 45 degrees (halfway over) at around 500 m/s. That's for KSP, obviously; pitchover for real-world launch vehicles is going to be different.

A vehicle with very high TWR can execute the pitchover much lower in the atmosphere than a vehicle with a lower TWR, but the curve of airspeed vs pitch angle is going to be pretty similar across the board.

Edited by sevenperforce
Link to comment
Share on other sites

Not only for different rockets but also for different ascent paths (orbit aimed for), twr's (payload), mass distribution, velocities, atmosphere, ....

Example for calculation

Edit: more, with references

If you mean it game related then yeah, twr is the main figure since the rest isn't modeled that thoroughly. Also a slight variation in profile in the game doesn't matter that much in terms of dV (a few hundred m/s) as long as you just do a gravity turn. In ksp you must force the rocket "around the curve" a bit as the kerbin has too high a curvature. Once you have your ascent vehicle designs (i used to stick to 3 or 4 basic launcher designs) and a little experience it's no problem.

Edited by Green Baron
Link to comment
Share on other sites

5 degrees at latest 100m/s (with a TWR of 1.3 usually). Optimize staging to not need to throttle and maximum stage burn out TWR's of 2.5 where after the TWR drops to around ~ 1 again. I can keep my hands off and follow prograde switching the navball to orbit mode at 25km up. One continuous burn to orbit in stock scale is Satisfying. 

 

You dont want to keep 45 degrees until apoapsis, be level at a point in your ascent :? 

Link to comment
Share on other sites

2 minutes ago, Theysen said:

5 degrees at latest 100m/s (with a TWR of 1.3 usually). Optimize staging to not need to throttle and maximum stage burn out TWR's of 2.5 where after the TWR drops to around ~ 1 again. I can keep my hands off and follow prograde switching the navball to orbit mode at 25km up. One continuous burn to orbit in stock scale is Satisfying.

Basically exactly this. If you can manage it, it's not just efficient but makes you feel like a BadS.

Link to comment
Share on other sites

39 minutes ago, thekspbegginer said:

And I keep it at 45 degrees until circularization.

That is not a gravity turn. Assuming you head for an 80km orbit and an initial twr of 1.5 (which is too much for some), you want to turn continually right from the start and be relatively flat (burn a few degrees over the horizon) already at 40/50km altitude, gaining mainly horizontal speed. A single burn to orbit is ideal, but a few hundred m/s circularisation are no shame. Also, in my eyes, i was never ashamed to throttle down in the lower parts of the atmosphere, like the real world rockets do. Saturn 5 first stage switched off the center engine at a point to avoid structural overload.

Try it out, it'll save you several hundred dV in comparison to 45° all the way up and then 1000-1500m/s for circularisation ...

Initial pitch can be 5°, can even be 20° for massive rockets with high inertia, can be right after clearing, can be at 100m/s. Depends.

Much has been written in this forum on this, just search a bit around :-)

Edit: long exposure, rocket launch trajectory

Edited by Green Baron
Link to comment
Share on other sites

I can't believe that nobody has mentioned this (being the science and spaceflight tab), but real life launches pitch over as soon as possible (not sure if this applies to crewed flight).  Not for flight optimization purposes, but so the rocket doesn't crash back on the pad during a failure like the Anatares recently did.

In KSP my initial pitch usually depends on how much control authority I have.  If I need control winglets, I can typically wait.  If I have a lot of TWR, I need to pitch early (I will lose control soon enough).  If I am relying on the capsule (or worse, octo) for all my control authority (and have a relatively large rocket), I need to pitch as soon as possible to get the thing to move at all.

Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...