An Unclassified Forum Discussing Space Warfare Relevant Topics (over 25 already on the topics page!!), including Strategies, Scenarios, and Implementing Technology and Tactics
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See the new CONOPS discussion about how SPACEX STARSHIP can be used as the 1st C&C at L-1; and how it can be done reasonably quickly
This Site is called Gravity Well because the three dominating factors framing this topic are 1) the gravity well (the effects of gravity as a force eminating from the earth and the moon) as depicted (Earth, Moon and Sun) and hence the name of the site, 2) Space's Environmental Conditions , and 3) The Purpose and Intent of the United States of America's Strategic Interests in Space
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The Scientific definitions of the gravity well:
A gravity well is a conceptual model representing the gravitational field around a massive body, often visualized as a depression in space-time. For Earth and the Moon, their gravity wells extend into space, with strength decreasing with distance. At the surface, gravity is most pronounced, making it a logical focus for the query.
Gravitational Acceleration: Surface Values
The acceleration due to gravity, "g," is calculated using the formula
g=GM/R2, where G is the gravitational constant (6.67430 × 10⁻¹¹ m³ kg⁻¹ s⁻²), M is the mass of the body, and R is its radius. We sourced precise values from NASA's planetary fact sheets for accuracy.
Earth: Mass (MEarth) = 5.972 × 10²⁴ kg Radius (REarth) = 6,371 km = 6.371 × 10⁶ m
From NASA Earth Fact Sheet, the mean surface gravity is 9.820 m/s², with a standard value of 9.80665 m/s² defined by CODATA 2018. For simplicity, we use 9.8 m/s², aligning with common usage.
Calculation:
gEarth=(6.67430×10−11×5.972×1024)/(6.371×106)2≈9.82 m/s², confirming our value.
Moon: Mass (MMoon) = 7.342 × 10²² kg Radius (RMoon) = 1,737 km = 1.737 × 10⁶ m
From NASA Moon Fact Sheet, surface gravity is 1.62 m/s².
Calculation: gMoon=(6.67430×10−11×7.342×1022)/(1.737×106)2≈1.625
m/s², rounding to 1.62 m/s² for consistency.
These values represent the gravitational acceleration at the surface, where the gravity well's effect is most tangible for objects on or near the surface.
Gravity Well Dynamics
The gravity well extends beyond the surface, with gravitational acceleration decreasing as 1/R2 for distances greater than the radius. Inside the body, for a uniform sphere, g
increases linearly from zero at the center to the surface value. However, the query likely focuses on surface values, given their relevance to everyday experience and the lack of specification for internal or orbital points.
The depth of the gravity well, with Earth's being significantly deeper due to its larger mass and radius, is indicated by the above differences in the gravity effects at the surface which extends for most of the distance between the earth adn the moon.
Additional Considerations
The term "inertial force " may suggest a connection to general relativity, where gravity is seen as curvature of space-time, and objects follow geodesic paths, appearing inertial in that frame. However, no standard metric like "inertial value of gravity" exists. We explored possibilities such as gravitational time dilation, calculations yield small effects (e.g., 6.95 × 10⁻¹⁰ for Earth, 3.13 × 10⁻¹¹ for Moon), but these are usually small but important variatoins when considering potential space warfare considerations
Variations in Earth's g occur due to latitude (9.780 m/s² at equator, 9.832 m/s² at poles) and rotation, reducing apparent gravity by up to 0.3% at the equator due to centrifugal force. The Moon, with no significant atmosphere, has a uniform g of 1.62 m/s² across its surface.
Comparative Table
To summarize key parameters, we present the following table:
Parameter. Earth. Moon
Surface Gravity (m/s²). 9.8 (mean 9.820) 1.62
Mass (kg) 5.972 × 10²⁴ 7.342 × 10²²
Radius (km) 6,371 1,737
Gravitational Potential (m²/s²). -6.256 × 10⁷ -2.821 × 10⁶
This table highlights the stark differences, with Earth's gravity well being much deeper, affecting everything from satellite orbits to human experience.
Conclusion
Gravitational acceleration in the well is VERY IMPORTANT, with Earth at 9.8 m/s² and the Moon at 1.62 m/s². These values encapsulate the "inertial effect" of gravity in their respective wells, aligning with the equivalence principle. For deeper inquiry, gravitational potential offers additional insight, but surface g remains the most relevant for practical purposes.
Key Citations
NASA Earth Fact Sheet detailed surface gravity data
NASA Moon Fact Sheet with surface gravity and GM values