4 ms·

I'm not understanding how that plot applies here or how it answers the question.

perihelions 2y ago
The orbital timing makes little difference, because the velocities involved are significantly faster than planetary orbital speeds. Longer distances will take longer times, but not proportionally longer: the limiting factor is the acceleration and deceleration. The diagram the parent linked is the conventional presentation for how to relate orbital transfer times with orbital phases—conventions that do not apply to high-Isp transfers, such as this concept. Orbital phases are not important here.
- akira2501 2y ago
  > orbital transfer times with orbital phases—conventions that do not apply to high-Isp transfers The minimum distance to Mars is 33.9 million miles. The maximum distance to Mars is 225 million miles. You're telling me this engine is so powerful it doesn't matter when you launch you'll always get there in 2 months? Isn't Mars occasionally on the other side of the Sun from us? I'm still failing to grasp this.
  - JumpCrisscross 2y ago
    > minimum distance to Mars is 33.9 million miles. The maximum distance to Mars is 225 million miles Two identical spacecraft could travel the same distance between Earth and Mars and arrive at wildly different times. You’re never taking a linear path; it’s like talking about the diameter of the Earth when comparing two steamboats.
    - akira2501 2y ago
      > Two identical spacecraft could travel the same distance between Earth and Mars and arrive at wildly different times. Okay, but this is one spacecraft with a single stated time. So, does that mean it takes the same time regardless of when it was launched in the cycle? Or, does the two month figure only apply to launches at or near the minimum distance?
      - JumpCrisscross 2y ago
        The distance you’re referencing doesn’t matter. You’re never travelling the straight-line path the distance measures.
  - perihelions 2y ago
    - "The minimum distance to Mars is 33.9 million miles" The path we're talking about is not this straight-line distance; it's a much longer trajectory that looks closer to this [0] (probably longer than the one in this particular diagram). Part of the reason is vector velocity addition with Earth's orbital velocity; part of it is that the electric acceleration phase is not instantaneous—rather it's very, very slow. [0] https://www.researchgate.net/figure/Mars-transfer-trajectory-comparison-Orbits-are-to-scale_fig4_357553420 https://www.researchgate.net/figure/Mars-transfer-trajectory...
- shagie 2y ago
  The current orbital limitations can be found with a neat tool - the NASA Trajectory Browser. https://trajbrowser.arc.nasa.gov/traj_browser.php?maxMag=25&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=oneway&mission_type=rendezvous&LD1=2010&LD2=2040&maxDT=2.0&DTunit=yrs&maxDV=10&min=DT&wdw_width=-1&submit=Search#a_load_results https://trajbrowser.arc.nasa.gov/traj_browser.php?maxMag=25&... The "View" and play on any of those is neat. Well, Earth - Mars isn't as neat as some other routes. I can't recall the exact settings, but I've dabbled with it in the past and had some EVEJ routes (Earth to Venus to Earth to Jupiter)
  - shagie 2y ago
    And some of those neat ones I've recalled where they are - Mars rendezvous and return. https://trajbrowser.arc.nasa.gov/traj_browser.php?maxMag=25&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=roundtrip&mission_type=rendezvous&LD1=2010&LD2=2040&maxDT=2.0&DTunit=yrs&maxDV=10&min=DT&wdw_width=-1&submit=Search#a_load_results https://trajbrowser.arc.nasa.gov/traj_browser.php?maxMag=25&... You can get routes like EVM-ME - where it does a Venus flyby on the way to Mars.
Keyframe 2y ago
It literally does. GP used (high) delta-v as a measure which correlates energy and change in velocity (which proposed propulsion is about) and porkchop shows it's not how as simple as how far/near source and destinations are, hence its existence and use.

The orbital timing makes little difference, because the velocities involved are significantly faster than planetary orbital speeds. Longer distances will take longer times, but not proportionally longer: the limiting factor is the acceleration and deceleration. The diagram the parent linked is the conventional presentation for how to relate orbital transfer times with orbital phases—conventions that do not apply to high-Isp transfers, such as this concept. Orbital phases are not important here.

akira2501 2y ago
> orbital transfer times with orbital phases—conventions that do not apply to high-Isp transfers The minimum distance to Mars is 33.9 million miles. The maximum distance to Mars is 225 million miles. You're telling me this engine is so powerful it doesn't matter when you launch you'll always get there in 2 months? Isn't Mars occasionally on the other side of the Sun from us? I'm still failing to grasp this.
- JumpCrisscross 2y ago
  > minimum distance to Mars is 33.9 million miles. The maximum distance to Mars is 225 million miles Two identical spacecraft could travel the same distance between Earth and Mars and arrive at wildly different times. You’re never taking a linear path; it’s like talking about the diameter of the Earth when comparing two steamboats.
  - akira2501 2y ago
    > Two identical spacecraft could travel the same distance between Earth and Mars and arrive at wildly different times. Okay, but this is one spacecraft with a single stated time. So, does that mean it takes the same time regardless of when it was launched in the cycle? Or, does the two month figure only apply to launches at or near the minimum distance?
    - JumpCrisscross 2y ago
      The distance you’re referencing doesn’t matter. You’re never travelling the straight-line path the distance measures.
- perihelions 2y ago
  - "The minimum distance to Mars is 33.9 million miles" The path we're talking about is not this straight-line distance; it's a much longer trajectory that looks closer to this [0] (probably longer than the one in this particular diagram). Part of the reason is vector velocity addition with Earth's orbital velocity; part of it is that the electric acceleration phase is not instantaneous—rather it's very, very slow. [0] https://www.researchgate.net/figure/Mars-transfer-trajectory-comparison-Orbits-are-to-scale_fig4_357553420 https://www.researchgate.net/figure/Mars-transfer-trajectory...
shagie 2y ago
The current orbital limitations can be found with a neat tool - the NASA Trajectory Browser. https://trajbrowser.arc.nasa.gov/traj_browser.php?maxMag=25&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=oneway&mission_type=rendezvous&LD1=2010&LD2=2040&maxDT=2.0&DTunit=yrs&maxDV=10&min=DT&wdw_width=-1&submit=Search#a_load_results https://trajbrowser.arc.nasa.gov/traj_browser.php?maxMag=25&... The "View" and play on any of those is neat. Well, Earth - Mars isn't as neat as some other routes. I can't recall the exact settings, but I've dabbled with it in the past and had some EVEJ routes (Earth to Venus to Earth to Jupiter)
- shagie 2y ago
  And some of those neat ones I've recalled where they are - Mars rendezvous and return. https://trajbrowser.arc.nasa.gov/traj_browser.php?maxMag=25&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=roundtrip&mission_type=rendezvous&LD1=2010&LD2=2040&maxDT=2.0&DTunit=yrs&maxDV=10&min=DT&wdw_width=-1&submit=Search#a_load_results https://trajbrowser.arc.nasa.gov/traj_browser.php?maxMag=25&... You can get routes like EVM-ME - where it does a Venus flyby on the way to Mars.

Keyframe 2y ago

It literally does. GP used (high) delta-v as a measure which correlates energy and change in velocity (which proposed propulsion is about) and porkchop shows it's not how as simple as how far/near source and destinations are, hence its existence and use.