Editing Talk:681: Gravity Wells
Please sign your posts with ~~~~ |
Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.
The edit can be undone.
Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.
Latest revision | Your text | ||
Line 19: | Line 19: | ||
:::I solved for the wells on Earth, Moon and Mars using the equation Randall gave and masses and equatorial radii from NASA, getting 6371 km, 287 km and 1286 km, respectively. [[User:Fewmet|Fewmet]] ([[User talk:Fewmet|talk]]) 23:07, 5 July 2014 (UTC) | :::I solved for the wells on Earth, Moon and Mars using the equation Randall gave and masses and equatorial radii from NASA, getting 6371 km, 287 km and 1286 km, respectively. [[User:Fewmet|Fewmet]] ([[User talk:Fewmet|talk]]) 23:07, 5 July 2014 (UTC) | ||
The Oberth Effect mentioned in the title text is [//www.askamathematician.com/2013/01/q-how-does-the-oberth-effect-work-and-where-does-the-extra-energy-come-from-why-is-it-better-for-a-rocket-to-fire-at-the-lowest-point-in-its-orbit/ well-explained here] (assuming you are not intimidated by the algebra in squaring a binomial). The gist of it is that using a bit of fuel in a rocket thrust will increase the rocket’s kinetic energy . The higher the kinetic energy at the time of the thrust, the greater the increase in kinetic energy. It works because the energy of the fuel goes into increasing the kinetic energy of the ship and the kinetic energy of the spent fuel. The faster you go, the greater the portion of the energy the ship gets. | The Oberth Effect mentioned in the title text is [//www.askamathematician.com/2013/01/q-how-does-the-oberth-effect-work-and-where-does-the-extra-energy-come-from-why-is-it-better-for-a-rocket-to-fire-at-the-lowest-point-in-its-orbit/ well-explained here] (assuming you are not intimidated by the algebra in squaring a binomial). The gist of it is that using a bit of fuel in a rocket thrust will increase the rocket’s kinetic energy . The higher the kinetic energy at the time of the thrust, the greater the increase in kinetic energy. It works because the energy of the fuel goes into increasing the kinetic energy of the ship and the kinetic energy of the spent fuel. The faster you go, the greater the portion of the energy the ship gets. | ||
− | |||
− | |||
The “gravity assist” is also known as the slingshot effect. The [//en.wikipedia.org/wiki/Gravity_assist#Explanation Wikipedia explanation] is good, especially with its diagram. In it a spaceship (or other body) accelerates toward a planet (or moon, star, etc.) in the same direction that body was going. The ship picks up a little of the body’s momentum and so goes faster, although only according to an external reference frame. An observer at rest with respect to that other body would actually see the ship approach and depart with the same speed. | The “gravity assist” is also known as the slingshot effect. The [//en.wikipedia.org/wiki/Gravity_assist#Explanation Wikipedia explanation] is good, especially with its diagram. In it a spaceship (or other body) accelerates toward a planet (or moon, star, etc.) in the same direction that body was going. The ship picks up a little of the body’s momentum and so goes faster, although only according to an external reference frame. An observer at rest with respect to that other body would actually see the ship approach and depart with the same speed. | ||
Line 40: | Line 38: | ||
In the XKCD strip, the artist states above Earth in the lower right popout that the geosynchronous altitude is well below top of Earth's gravity well. While the rest of his strip is a wonderful representation of the science behind gravity wells, this one bit is not accurate. A geosynchronous altitude for Earth is nearly 36,000 km, not under 6000 km. Kudos for the rest of the strip, though. | In the XKCD strip, the artist states above Earth in the lower right popout that the geosynchronous altitude is well below top of Earth's gravity well. While the rest of his strip is a wonderful representation of the science behind gravity wells, this one bit is not accurate. A geosynchronous altitude for Earth is nearly 36,000 km, not under 6000 km. Kudos for the rest of the strip, though. | ||
: The strip scales the heights of the corresponding wells based on the assumption of constant Earth surface gravity; in other words, it takes the same amount of energy to climb such a well as it does to escape the real gravity well. By contrast, as one ascends from the Earth's surface, gravity decreases, so it requires less energy to climb to an orbital altitude than it does to reach the same height in the hypothetical well. The amount of energy required to put a geostationary satellite in orbit, for example, is equivalent to that used in raising it 5413 km in Earth surface gravity, and thus it is located 5413 km from the bottom of the well. [[User:Arcorann|Arcorann]] ([[User talk:Arcorann|talk]]) 03:42, 8 February 2019 (UTC) | : The strip scales the heights of the corresponding wells based on the assumption of constant Earth surface gravity; in other words, it takes the same amount of energy to climb such a well as it does to escape the real gravity well. By contrast, as one ascends from the Earth's surface, gravity decreases, so it requires less energy to climb to an orbital altitude than it does to reach the same height in the hypothetical well. The amount of energy required to put a geostationary satellite in orbit, for example, is equivalent to that used in raising it 5413 km in Earth surface gravity, and thus it is located 5413 km from the bottom of the well. [[User:Arcorann|Arcorann]] ([[User talk:Arcorann|talk]]) 03:42, 8 February 2019 (UTC) | ||
− | |||
− | |||
− | == | + | == How much of the gravity well can be overcome by launching from a high mountain? == |
− | How much of the gravity well can be overcome by launching from a high mountain? | ||
If we constructed a spaceport on a mountaintop that was, say, 14,505 ft (Mt. Whitney, CA), or even 20,310 ft (Denali, Alaska), or slightly less after clearing a flat surface, would it significantly reduce the amount of the gravity well a rocket had to climb, and hence the amount of fuel needed to reach LEO? Would thinner air reduce drag and increase efficiency significantly as well? | If we constructed a spaceport on a mountaintop that was, say, 14,505 ft (Mt. Whitney, CA), or even 20,310 ft (Denali, Alaska), or slightly less after clearing a flat surface, would it significantly reduce the amount of the gravity well a rocket had to climb, and hence the amount of fuel needed to reach LEO? Would thinner air reduce drag and increase efficiency significantly as well? | ||
Line 54: | Line 49: | ||
:What killed it was the issue of what happens when one malfunctions or crashes on launch. You've got Space Shuttle & parts raining down on the Denver metro area; not good. | :What killed it was the issue of what happens when one malfunctions or crashes on launch. You've got Space Shuttle & parts raining down on the Denver metro area; not good. | ||
− | + | Source: My dad worked on the project for the Air Force back in the 70s or thereabouts. [[User:Flug|Flug]] ([[User talk:Flug|talk]]) 21:52, 22 September 2019 (UTC) |