Typical energy ratios to get into orbit? (height, friction, velocity)

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Discussion Overview

The discussion revolves around the energy ratios involved in launching a craft into orbit, focusing on the contributions of potential energy, kinetic energy, and overcoming atmospheric friction. Participants explore the complexities of these energy distributions in relation to different orbital heights and the characteristics of the craft.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that the energy ratios depend on various factors, including the altitude of the desired orbit, the craft's size and weight, and the atmospheric conditions.
  • Another participant suggests that most of the energy is allocated to the kinetic energy of the rocket, with a smaller fraction (approximately 10%) going towards potential energy, while atmospheric drag is considered a minor contribution.
  • A later reply acknowledges that drag is indeed a small portion of the energy expenditure, given that most of the ascent occurs through thin air, although high velocities can still result in significant drag forces.
  • Participants discuss the challenges of using balloons for telescopes, citing issues with weight and stability, as well as the potential for obstructed views.

Areas of Agreement / Disagreement

Participants generally agree that kinetic energy is a significant hurdle in reaching orbit and that atmospheric drag is relatively minor. However, there is no consensus on the exact ratios of energy distribution or the feasibility of alternative launch methods like balloons.

Contextual Notes

Participants mention the complexity of calculating energy contributions due to changing atmospheric conditions, Reynolds numbers, and varying fuel mass and speed, indicating that these factors may complicate straightforward assessments.

Who May Find This Useful

This discussion may be of interest to those studying aerospace engineering, physics of flight, or anyone curious about the mechanics of launching objects into orbit.

Stargazer19385
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I realize the answer depends how where in the atmosphere speed is increased more, and whether a higher orbit or lower orbit is desired, and the shape size and weight of the craft. But I'm just curious about typical ratios.

About what fraction of the fuel goes to lifting the weight of the craft? The weight of the fuel? (giving them potential energy)
What fraction goes to giving the craft the kinetic energy (final speed)?
What fraction goes to just overcoming friction through the atmosphere?

Thanks. lots of math with the atmosphere thinning and the reynolds numbers changing and fuel mass and speed changing.
 
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Most of the energy goes into the velocity and heat of the fuel, most of the interesting energy goes into the kinetic energy of the rocket (for low Earth orbits), and some smaller fraction (I think it was something like 10% compared to the kinetic energy) into potential energy.
For higher orbits or even escape routes, the initial part is the same. Gravity exchanges kinetic energy for potential energy afterwards.

For a given rocket, it is easy to calculate the final potential and kinetic energy of the rocket. Atmospheric drag is hard to evaluate, but it is a small contribution.
 
That all makes perfect sense. I kind of should have known drag would be a small portion, since it only goes 400 miles up, and most of that is through very thin air. Only about 3-5 miles of the air is remotely thick. However, high velocity through thin air could still mean high drag.

So kinetic energy is the hurdle...

I guess the reason we don't have large telescopes hanging from balloons instead of in orbit is the telescopes are too heavy and would need a very big balloon. The balloon blocking the view could be solved by suspending the telescope well below the balloon so it is angularly small at that distance.
 
So kinetic energy is the hurdle...
Right.

Balloons are also unstable.
For small telescopes, the atmosphere is not so problematic, and large telescopes are really heavy.
 

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