4 ms·

Do you have a link with an elementary explanation of this type of numbers? I'm not doubting what you say, I'd just like to learn more about the topic.

vkou 10y ago
Here's a breakdown of reaching orbital speeds, vs doing a vertical sub-orbital hop. [1] Here are some specs for an ICBM. It has a range of 6,000 miles, and has to reach ~7 km/s (Mach 23) to do so. [2] The mathematical reason for why suborbital flights that take you somewhere require so much velocity is because all ballistic trajectories are actually elliptic orbits. When you throw a baseball into the air, it is in an elliptic orbit - a very small orbit, with most of it passing through the space occupied by the earth. The Earth's center is one of the two centers of the ellipse. This means that in order to send a ballistic rocket to the other side of the world, you need to 'almost get into orbit'. At this point, it takes very little energy to turn your orbit into a circle... But it also means that you had to expend orbital-levels of energy to get to the point that your suborbital hop takes you somewhere. [3] Knowing that sub-orbital ballistic trajectories are ellipses, with one of their centers at the center of the Earth, you can calculate the velocity requirements yourself by using Kepler's second law. [1] http://www.orbspace.com/Background-Information/Suborbital-vs-Orbital.html http://www.orbspace.com/Background-Information/Suborbital-vs... [2] https://fas.org/nuke/guide/usa/icbm/lgm-30_3.htm https://fas.org/nuke/guide/usa/icbm/lgm-30_3.htm [3] http://lh3.ggpht.com/_1wtadqGaaPs/TF0zyBaNisI/AAAAAAAANLc/uU0kJHSubOQ/tmp438_thumb_thumb.jpg?imgmax=800 http://lh3.ggpht.com/_1wtadqGaaPs/TF0zyBaNisI/AAAAAAAANLc/uU...
- credit_guy 10y ago
  Great explanation, thank you. From the links you provided (all very good), I started browsing and ended up with the book "Orbital Mechanics: Theory and Applications" by Tom Logsdon [1], which appears quite good. [1] https://www.amazon.com/Orbital-Mechanics-Applications-Tom-Logsdon/dp/0471146366/ref=sr_1_1?s=books&ie=UTF8&qid=1486922811&sr=1-1&keywords=9780471146360 https://www.amazon.com/Orbital-Mechanics-Applications-Tom-Lo...

vkou 10y ago

Here's a breakdown of reaching orbital speeds, vs doing a vertical sub-orbital hop. [1] Here are some specs for an ICBM. It has a range of 6,000 miles, and has to reach ~7 km/s (Mach 23) to do so. [2] The mathematical reason for why suborbital flights that take you somewhere require so much velocity is because all ballistic trajectories are actually elliptic orbits. When you throw a baseball into the air, it is in an elliptic orbit - a very small orbit, with most of it passing through the space occupied by the earth. The Earth's center is one of the two centers of the ellipse. This means that in order to send a ballistic rocket to the other side of the world, you need to 'almost get into orbit'. At this point, it takes very little energy to turn your orbit into a circle... But it also means that you had to expend orbital-levels of energy to get to the point that your suborbital hop takes you somewhere. [3] Knowing that sub-orbital ballistic trajectories are ellipses, with one of their centers at the center of the Earth, you can calculate the velocity requirements yourself by using Kepler's second law. [1] http://www.orbspace.com/Background-Information/Suborbital-vs-Orbital.html http://www.orbspace.com/Background-Information/Suborbital-vs... [2] https://fas.org/nuke/guide/usa/icbm/lgm-30_3.htm https://fas.org/nuke/guide/usa/icbm/lgm-30_3.htm [3] http://lh3.ggpht.com/_1wtadqGaaPs/TF0zyBaNisI/AAAAAAAANLc/uU0kJHSubOQ/tmp438_thumb_thumb.jpg?imgmax=800 http://lh3.ggpht.com/_1wtadqGaaPs/TF0zyBaNisI/AAAAAAAANLc/uU...

credit_guy 10y ago
Great explanation, thank you. From the links you provided (all very good), I started browsing and ended up with the book "Orbital Mechanics: Theory and Applications" by Tom Logsdon [1], which appears quite good. [1] https://www.amazon.com/Orbital-Mechanics-Applications-Tom-Logsdon/dp/0471146366/ref=sr_1_1?s=books&ie=UTF8&qid=1486922811&sr=1-1&keywords=9780471146360 https://www.amazon.com/Orbital-Mechanics-Applications-Tom-Lo...