# Center of mass location on any popular rocket in any typical condition?

Where can I find the location of the center of gravity (CoG) of any rocket? I need any popular rocket, such as the Soyuz or Space Shuttle, in any typical condition, like fully fueled on the pad.

Since many assemblies are symmetrical, it will be enough to know CoG height from the ground.

• It would help you know why you're asking. The CG moves significantly during flight. Do you want wet or dry? How much precision are you looking for? Dec 20, 2014 at 18:52
• I want to calculate, how fast the rocket will change direction in the case it has no thrust control and no atmosphere and if the thrust vector is not directed into center of mass.
– Dims
Dec 20, 2014 at 20:32
• This is why I asked. For that calculation you need not just the center of mass of the vehicle, but assumptions about the thrust vector and a moment of inertia tensor. Plus all your calculations are going to depend on lots of assumptions based on when in the trajectory this happens. As a rule of thumb, without fins, you’ve got only a second or two before you lose control. Dec 21, 2014 at 19:04
• What are "fins", sorry, not native English...
– Dims
Dec 22, 2014 at 3:02
• Google "rocket fins" and look for photos. They are aerodynamic surfaces on rockets typically added to make the rockets stable during atmospheric fly out. The picture in the answer below of Apollo 11 shows find near the nozzles. Dec 24, 2014 at 19:14

Here is the Apollo 11 (Columbia and Eagle) graph of center of gravity during the AS-506 flight, taken from the APOLLO/SATURN V POSTFLIGHT TRAJECTORY - AS-506 (rather large scanned PDF):

I selected Apollo 11 flight for historical significance, but you could find many other postflight telemetry and flight analysis documents online for various launch vehicles, or approximate it yourself using e.g. such calculations (and technical data of specific launch vehicle configurations that can often be found online, say on Wikipedia):

Determining Center of Gravity - cg. Image source: NASA Rocket Fundamentals

Where weight $w= m \times g$ (mass times gravitational constant) and $d$ is distance from reference location.

Do note though that center of gravity does depend on individual vehicle's specific configuration, payload mass distribution, flight profile, that it will shift vertically during flight as stages consume propellants and during staging, and perhaps more significantly that this data is on its own only perhaps relevant to static stability of the launch vehicle. For anything else, i.e. dynamic / flight stability, you'll at the minimum also require values for center of pressure as a function of time.

Here's a graph showing movement of both along the long axis for the first 140 seconds of a Saturn V flight, taken from Description and Performance of the Saturn Launch Vehicle's Navigation, Guidance, and Control System, Walter Haeussermann, MSFC 1970 (PDF):

Variations of center of pressure and center of mass during flight.

You're right though that typically CG only moves along the long axis (vertically) and that the mass distribution of launch vehicles and their payloads are balanced to remain centered along this axis. For launch vehicles, mass distribution and center of gravity would most commonly be established during so-called boilerplate mass simulators, and for their payloads also during payload integration. Oftentimes, ballasts weights (or even secondary piggyback payloads - like e.g. OSCAR satellites) would be used to assure that launch vehicles and payloads are spin stable.

I don't know how commonly rocket CGs are published.

You can estimate it reasonably well from published weights and dimensions by modeling engines, fuel tank, and oxidizer tank as cylinders of uniform density, and computing weighted averages of the centers of those cylinders. If you don't know what order the fuel and oxidizer tanks are stacked in, assume the denser one is on top to keep the CG high; this will make more difference in hydrogen-fueled rockets with their very low fuel densities than in others.