DeltaV savings from equatorial Mountain launch

[Nibb31]

I will ask though, How much does 200m/s DeltaV weigh ?

The 200 m/s number is what you gain when launching from an equatorial location to an equatorial orbit compared to a higher inclination location to a higher inclination orbit. I am not disputing that number, but it really depends on what you are launching and where you are putting the payload.

A launch site can only launch into an inclination that is higher than its latitude. For example, a launch site at 45° N can only launch into an orbital inclination from 90° (polar) to 45°. Only a site on the equator can launch directly into an equatorial orbit. If a launch site is above (or below) the equator and wants to launch into an equatorial orbit, then the launcher or spacecraft must perform a plane change, which costs a lot of dV, and this is where you can potentially gain much more when launching close to the equator.

Once you take into account the necessary dog-legging required to reach an equatorial orbit from a high inclination launch site, then the benefit is more like 500 m/s, and you might be right about a 30% increase in payload to GTO. I never disputed that, and it is put into practice by Ariane and Soyuz on every GTO launch they fly from Kourou, which is the closest permanent launch site to the equator.

Also, don't forget that launching from the equator to a high inclination orbit gets you less benefit, because in this case, the high inclination launch site doesn't have a dog-legging handicap. In practice, launches from Kourou to the ISS gain less from the equatorial boost than launches from Kourou to GTO. In this case, the gain will potentially be less than 200 m/s. Launches to a polar orbit gain nothing.

What I am disputing is your claim to a significant increase in payload from launching from a mountain top. In this case, the benefit in terms of altitude gains you less than 5 m/s, not 200 m/s. 8 km altitude is negligeable compared to a typical GTO apogee of 36000 km, and even though atmospheric pressure is too low for us to breath, the aerodynamic loads are pretty much the same as at sea level. If you are getting a 30% payload difference between launching from 8000m compared to launching from sea level, then there is something wrong with your simulation, and those 5 m/s are not worth the trouble of hauling your rockets to the top of a mountain, building fuel production factories up there, paying higher wages for extreme working conditions, and the risk of having your launch site confiscated by a foreign country.

Edited March 2, 2015 by Nibb31

[Bryce Ring]

The dog leg thing, am starting to understand. Would it be more efficient to aim for a Descending node across the Equator at exactly 45 degrees post Launch site then correct at the DN? (Wow, this is interesting, I will try to remember to test that stuff out later. I did notice a server constant correction requirement by mech jeb when launching from the Cape. I was thinking it was just due to some coriolis effect. I want to know more about this later.

I apologise for the Silly remark suggesting you made a few Silly assumptions. I am beginning to think it was me.

I was thinking more on the AoA for correction needed should I attempt to gain Horizontal speed faster than the Zero lift Gravity turn. Destruction may be inevitable if I don't adhere to its true beneficial name (zero hull busting, Side drag turn).

I do however think slightly that due to the rocket being higher by the time it is at pitch angle x , you may begin to be more aggressive with turn , IE get to more than 1deg from zero lift(Should you scale up the launch profile, such as, from sea level start turn at 1km have a Mech jeb percentage of about 33 or more and aim for 200km with the final orbit of 200km < just numbers I had been taught to use in KSP Stock. Scale that up by launch height from mountain to be start turn at 5.6km <Being 1km above my start height> same 33% and aim for 204.6km <Being 200km above launch height and finish turn at 204.6)

I was thinking so hard about the gravity turn I was beginning to think of the vectors in my head and wondering how TWR can allow you to use a different percentage of turn without the need for correction. I then began to think that maybe the turn shape % is more related to time required to achieve orbit, which is also related to TWR. HMMM I am so young to this rocket stuff.

Please Accept my Apology, whether I was right or wrong. And thank you for helping.

Bryce Ring.

Edited January 21, 2015 by Bryce Ring
Added my Google-ful Links as I self educate