Delta-V needed for orbit?

[Affan]

Hey, I just learnt the math of basic orbiting and I wanted to ask how much delta-v would be needed to take 1 unit of mass (kg or tonne) to a height of 100km above Kerbin's surface. I am unable to calculate the effects of gravity and drag on my craft. If I can find that out then I can calculate how much delta-v is needed to put a ship into oribt around kerbin.

If you could post the figure in m/s needed for 1kg or 1000kg to rise straight up to 100km above ground.

Thanks

[toadicus]

In the stock game, a clean ascent is about 4500 m/s. If you use Ferram Aerospace Research, it's more like 3600 m/s.

[EtherDragon]

Toadicus has it right, but here is some additional context:

The amount of delta-V required to get 1kg of mass into orbit is the same as what it takes to get 1000kg into orbit. The amount of dV required to reach orbit doesn't really change based on mass.

In fact, if you look at the Rocket Equation:

Source: http://en.wikipedia.org/wiki/Rocket_equation

You can see that this equation doesn't rely on how much mass your ship has, but the ratio of it's full to empty mass.

What you are trying to solve is how much Propellant is required to get a 1kg mass into orbit - so, in your case you want to solve the Rocket Equation for M0, given a known dV, M1, and Isp.

[arq]

To get 4500m/s of dV with an asparagus lifter usually yields a payload fraction of 14-16%. This means that your launcher should be 5-6 times heavier than your payload, assuming you've tuned your TWR appropriately.

EDIT: When I say 'asparagus,' I mean 'efficient'. Some non-asparagus rockets can be 'efficient,' but this becomes increasingly difficult as the rocket gets larger.

Edited November 3, 2013 by arq

[capi3101]

Expounding on arq's post, a typical single-stage to orbit rocket usually has (my observation) a payload fraction of only about 4%; your booster needs to be 24 times as heavy as your payload. You also will need to adjust your throttle as you go with that kind of design (all that thrust you had at launch isn't necessary when you're further up and if you keep it at full throttle you'll pancake your stack). It's about as inefficient as you can get. The advantage is that construction is much simpler, but that's about it.