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 Dec 9 asked What would have been required to boost Mir into a stable orbit? Sep 11 awarded Notable Question Jul 2 awarded Curious Apr 23 awarded Notable Question Apr 22 comment How to calculate the velocity needed for a rocket to get to a L1 point (escape a body without orbiting)? If launched from earth's equator, that would give 459 m/s of angular velocity. The moon rotates with 1024 m/s of velocity, so yes the rocket would need to 'add' 566 m/s in the rotational direction of the moon to simply 'Fall In'. However, I'm looking for the rest of the component, and I suspect that one would not need all 566 m/s if some fancy maneuvers were added. Apr 21 revised Rocket propelled by a giant monochromatic laser Edited to mark incorrectness Mar 27 comment How to calculate the velocity needed for a rocket to get to a L1 point (escape a body without orbiting)? And, (finalish question) - if I got a small rocket precisely to L1 and used the surface rotation timing, how much velocity/energy would it take for lunar capture? Or would it just speed past the moon unless slowed down significantly? Would it need to get much closer to the moon than L1 to actually be captured with the KE from earth's rotation? Mar 27 accepted How to calculate the velocity needed for a rocket to get to a L1 point (escape a body without orbiting)? Mar 27 comment How to calculate the velocity needed for a rocket to get to a L1 point (escape a body without orbiting)? Also, one of the things I'm confused about is atmospheric orbital speed: if the balloon setup sat at 100km altitude for long enough to synchronize with the atmosphere at that height (what little of it there is); would it speed up to the orbital rotation at that height (I.E. track the same geostationary location once settled), or slow down, or ? Mar 27 comment How to calculate the velocity needed for a rocket to get to a L1 point (escape a body without orbiting)? Nailed it. Would this be correct for solar gravity inclusion: $V_e = −Gm(\frac {M_e} {r_e} + \frac {M_l} {LD−r_e} + \frac {M_s} {SD-r_e})$ and $V_{L1} = −Gm(\frac {M_e} {d_{L1}} + \frac {M_l} {LD−d_{L1}} + \frac {M_s} {SD-d_{L1}})$ ? Mar 25 comment Can relativistic momentum (photons) be used as propulsion for 'free' after the initial generation? But the mass of the mirror is not infinite, and so with enough photons, you could move the mirror (as the other SO question alludes to), correct? Mar 24 comment Can relativistic momentum (photons) be used as propulsion for 'free' after the initial generation? So light bouncing off a mirror selectively transfers energy only if they aren't attached? Mar 24 comment Can relativistic momentum (photons) be used as propulsion for 'free' after the initial generation? I see, so energy would need to be added to keep the thrust constant. Does a laser get redshifted every time it bounces off something? I.E. if you pointed a green laser between two calibrated mirrors it would eventually be red? Mar 24 comment Rocket propelled by a giant monochromatic laser Mar 24 asked Can relativistic momentum (photons) be used as propulsion for 'free' after the initial generation? Mar 23 comment How to calculate the velocity needed for a rocket to get to a L1 point (escape a body without orbiting)? Sure - in theory, I get that. However, that 'fast enough' is orders of magnitude more energy than it takes to just get to an orbital height; indeed this article reports that in getting to LEO, 93% is spent increasing the horizontal speed, and 7% is raising the altitude. Since I don't even have very good odds to get the 7% it will take to get to the altitude, let alone the 93% it would take just to fall at the same rate that the surface of the earth does, then it seems that any thrust in the horizontal direction will be wasted. permanent.com/space-transportation-earth-moon.html Mar 20 comment How to calculate the velocity needed for a rocket to get to a L1 point (escape a body without orbiting)? Rockets usually take up their own oxidizer; for example Black Powder in model rockets and Liquid Oxygen in full scale ones, so they don't need 'air' to operate. I'm still confused as to how, say, a rocket engine is changing any of the horizontal kinetic energy from the 1 rev/day orbit, or utilizing it to move in the vertical direction. Mar 20 comment How to calculate the velocity needed for a rocket to get to a L1 point (escape a body without orbiting)? Can you explain the process by which horizontal kinetic energy is converted to vertical potential energy, without a ramp or some similar structure? I don't think $KE_{horizontal}$ or lack thereof has any effect on the height an object will reach, unless we're leaving Earth's rotating reference frame or something. Mar 20 comment Rocket propelled by a giant monochromatic laser If photons have non-zero effective mass, then why wouldn't a mirror on the rocket and on earth give perpetual free momentum as the photons bounce back and forth? Mar 20 comment How to calculate the velocity needed for a rocket to get to a L1 point (escape a body without orbiting)? Simplified for only the normal vector, and just reaching the Earth-Moon L1 from rest on earth's surface: $PE_{i} + KE_{i} + E_{rocket} = PE_{L1} + KE_{L1}$, so $0 + 0 + E_{rocket engine} = PE_{L1} + 0$, or $E_{required} = PE_{L1}$. I'm lost on how to calculate the Potential Energy at L1, since $PE = mgh$ doesn't really work (g = 0?). Your equation above doesn't seem to care about the mass of the object, a 100kg object surely has more PE at L1 than a 1kg object. Can you elaborate?