# Luanch angle to put a satellite in an orbit?

1. Feb 15, 2010

### smhni

I have a Question:

suppose we have a satellite (m=400kg, V0=40m/s) and we want to put it in a 1000km orbit (r=1000km)...what should be the launch angle?

P.S: is this question complete?(For Lack Of A Better Word) .. I mean do we have a formula which relates these parameters.. or perhaps a couple of formulas that relates them...

thx for you help...

2. Feb 15, 2010

### rcgldr

The main goal is to increase speed, so the best path would be nearly horizontal, except that atmospheric drag is much less at higher altitudes, so there needs to be a significant veritcal component during the early part of the path until the atmosphere gets thinner, reducing drag force (along with heat) on the rocket as it's speed increases. Once past the atmosphere, then something similar to a Hohmann transfer orbital path is used, depending on the weight of the target object:

http://en.wikipedia.org/wiki/Hohmann_transfer_orbit

3. Feb 15, 2010

### D H

Staff Emeritus
The question is not complete, and not by a long shot. The ideal launch angle is neither vertical nor horizontal. A horizontal launch won't gain the altitude needed to clear the atmosphere. A vertical launch isn't aligned to gain the requisite horizontal velocity. For the Space Shuttle, the ideal launch angle would be about 78º rather the the 90º vertical alignment.

The Shuttle is not launched at a 78º pitch angle for the simple reason that the vehicle is too danged heavy to be launched at any angle but vertical. It would fall over before it could ever be launched were it oriented at 78º. Vertically-launched vehicles such as the Shuttle have to pitch down to the desired angle soon after launch. Once in this desired attitude, the vehicle maintains a zero angle of attack and follows a gravity turn (google this phrase). The gravity turn lets gravity and aerodynamics turn the vehicle so that by the time the vehicle leaves the atmosphere it is oriented nearly horizontally and has attained orbital velocity.

Vehicles are not launch directly into a 1000 km orbit. The launch vehicle takes the spacecraft to a very low Earth orbit. From that point, upper stages transfer the spacecraft from this insertion orbit to the desired orbit. This is typically done in multiple steps so as to insure that not only is the vehicle in the desired orbit but is also in the right place on that orbit.

4. Feb 19, 2010