Matching Altitude and Speed

[rpedrosb]

Hello community,

I just started playing this awesome game yesterday. I am an aerospace engineering student so I find this game quite fascinating and with a good potential. 

Right now, I am at the initial missions where you have to test different equipment at different altitudes and speed. Is there any recommended procedure to do this? For example, if you have to be at altitude [27000,33000] m at a speed [1100,1300] m/s, is it just a trial and error thing or there could be some math behind? I guess I could do some calculations but I don't know how realistic the game is.

Thanks

[OhioBob]

The physics of the game is, for the most part, realistic.  So you could do calculations if you wanted to, though I think most people probably do it trial and error.  I haven't done many of the types of contracts that you're referring to, but for the ones I've done, I haven't found it especially hard to meet the conditions.  I think the contract parameters are generally set at values that you should be able to meet if you perform a normal launch, reentry, etc.

 

[Kryxal]

They're either reasonable for launching or landing, or they're not ... you're best off to pick and choose.  If you really want to do one of the high altitude, low speed ones, you're best off just using LFO engines with TWR above 1, and do it the hard way.

[maceemiller]

im not a clever guy so probably can't help much but heres my total KSP philosophy. ....

I build what I think might work then launch.....regardless of the outcome I repeat....then repeat....then repeat until I get it right.

not much help I know but it works for me..

 

[bewing]

I actually think it's a good idea to do a lot of those contracts. After you do a bunch, it gives you a really good feel for which SRB boosters can get how much payload how high and how fast.

Tweaking the thrust percentages on the boosters will fine tune your launch if you were going a little too fast the first time. And landing your rocket again will give you a good idea of how much mass a parachute or three can handle.

But as said above, if you want to get it done quickly then you need to use a liquid fuel engine that can be throttled. By steering and playing games with the throttle, you can usually complete a contract in a few tries. The important thing is to be flying almost horizontally in the target altitude range, so that you have a long time to match the proper speed. Also note that the speed requirement is always a surface speed -- which means you may need to change your navball mode.

 

[Mad Rocket Scientist]

You could also do the calculations, but there's a couple things to keep in mind:

KSP's aero model is not 100% realistic. I'm not entirely sure how it works, but I think it is pretty well documented. Just make sure your sources for it are up-to-date, it was majorly overhauled in 1.0.

Thrust and Isp vary with pressure, just like in real life. However, instead of being a function of nozzle shape, it is stored in the game as atmosphere curves. Again, I'm not entirely sure how to read these, but they are documented.

Aside from that, real world calculations apply exactly as expected.

If you want to avoid the worst of the calculus for burnout velocity in atmospheres, you can just approximate burn time (or use mods) and use some approximations to get gravity losses. Then just subtract that from rocket equation DV.

EDIT: some mods you might want to look into: 

 

Edited September 10, 2018 by Mad Rocket Scientist