Making Orbit Consistently for RSS and FAR

[HexYZAsh]

Hello,

I have been using FAR and Real Solar System and I have been getting into orbit okay, but there are a few things I would like to know.

1. How much vacuum dV do I need precisely? 9600 seems to be the number, but I am not sure. Also, how does t/w ratio affect that number?

2. What is the best ascent profile?

3. Where is the best place to launch for which missions?

4. Also, are there any numbers for Mars/Moon?

If there is anything else I need I will edit this post.

If anyone has any answers to these questions or any suggestions/tips, just reply!

Thanks!

Edited January 4, 2015 by HexYZAsh

[NathanKell]

Low earth orbit is ~7.7km/sec. That means: dV expended - gravity losses - drag losses - steering losses + rotational boost = 7.7km/sec. Thus you can see that the vacuum delta V will depend on how much of that delta V was expended in atmosphere, and the delta V expended will heavily depend on the gravity losses you incur, the site you launch from, and (to a lesser extent) the drag losses and steering losses you suffer. From the Cape, the nominal vacuum delta V is around 9300; with high-thrust lower stages I have been able to expend only 8800m/s getting to a 185x185km parking orbit, but with a low thrust first stage it may be up to 9400+, yes.

Higher TWR early on will drastically decrease gravity losses, but will (a) increase the mass and probably lower the payload fraction of your LV and ( may make your LV hard to control and © can make things dangerous due to high dynamic pressure.

Note that there is no single correct ascent profile or correct amount of delta V required; PhD theses are written on this subject, and years of CPU-time expended to calculate it for particular LVs with particular payloads let alone general cases (not least because there cannot be a general solution since the inputs differ). Here's some info from ferram that might help, however--good rules of thumb.

Note that, again, if you're optimizing for dV expended, you're not optimizing for mass of LV nor for cost of LV (and optimizing for one of the others means not optimizing for the other two...).

As for best place to launch from, that depends on the orbit you want to reach. Kourou (CSG) is best for equatorial orbits, and one of the high-latitude sites (like Kodiak) is best for polar. See here for how latitude affects things.

[HexYZAsh]

Thanks! I will need a bit of optimization then.