On 7/23/2020 3:18 PM, xxxxxx@gmail.com wrote:
> You know, I had just been thinking one could do that in Mathematica. I have
> several electrical engineer friends who swear by it for a wide range of tasks.
> Not something I'd have in my pocket though.... if I recall, licenses are not
> cheap....
>
> Is there a better way to generate dynamically stable systems? Would one have to
> start from some alternative aspect of system layout? It seems like stable
> systems evolve, but there might be some sort of way (knowing the constraints
> that apply to stable systems that make them stable) to work towards a way to
> generate stable (or at least mostly stable) systems.... ?
>

https://github.com/makhidkarun/accrete2

	This may work to generate stable systems. It's an old idea, and does not really
work with dice.

	The real problem ends up being using a fixed set of orbits without regards to
the size of the worlds or the ones to the next orbits in and out.

	I know the GT:First In and GURPS Space 4th rules use a system that gives some
variations to the layout, but still no modification for planet size, and may not
be any more stable.

>
>
> On Thu, Jul 23, 2020 at 11:15 AM Vareck Bostrom <xxxxxx@gmail.com
> <mailto:xxxxxx@gmail.com>> wrote:
>
>     This is all in Mathematica, using a bunch of methods I wrote. I have used it
>     in the Traveller context as well: https://i.imgur.com/VCGz5If.png ,
>     https://i.imgur.com/4yuGdAg.png ,
>     and https://i.imgur.com/kgMTsC3.png for examples.
>
>     The problem is that Traveller system generation very frequently (almost
>     always) generates dynamically unstable systems so physically simulating the
>     planetary or moon system results in planets and moons that are ejected from
>     their systems and makes flight planning difficult:
>     https://i.imgur.com/2fePnjX.png from https://i.imgur.com/3Na7hz3.png but I
>     do still try to use it to describe astronomical events (such as eclipses:
>     https://i.imgur.com/s6SohMa.png ). All versions of Regina that I have seen
>     published, book 6 and Traveller 5 and one or two variations of those, are
>     dynamically unstable as systems.
>
>     Ballistic or aerodynamic reentry is simulated: https://i.imgur.com/4WVVahX.png
>
>     On Thu, Jul 23, 2020 at 4:43 AM <xxxxxx@gmail.com
>     <mailto:xxxxxx@gmail.com>> wrote:
>
>         What is the software you use for this?
>         Would it only be usable with Sol system data? (vs. usable by entering
>         orbits and masses of various bodies in a fictional system?)
>
>         On Wed, Jul 22, 2020 at 6:01 PM Vareck Bostrom <xxxxxx@gmail.com
>         <mailto:xxxxxx@gmail.com>> wrote:
>
>             I did a free-return trajectory (TLI from earth-orbit as of this
>             afternoon) too: https://i.imgur.com/7539NS6.gifv
>
>             Spacecraft comes within 40km of the lunar surface:
>             https://i.imgur.com/tmSuEZY.png
>
>
>
>             On Mon, Jul 20, 2020 at 10:35 AM Jeffrey Schwartz
>             <xxxxxx@gmail.com <mailto:xxxxxx@gmail.com>> wrote:
>
>                 This reply just smacked me in the face with how the world has
>                 changed
>                 Back in the day, NASA would have spent hundreds of man hours
>                 grinding
>                 the math to do what he did in a few hours.
>                 And not had pretty pictures.
>
>                 On Mon, Jul 20, 2020 at 12:42 PM Vareck Bostrom
>                 <xxxxxx@gmail.com <mailto:xxxxxx@gmail.com>> wrote:
>                  >
>                  > I inserted into a solar system n-body simulation a CSM in
>                 orbit of the moon at 50000 feet altitude at an inclination and
>                 ascending node to match the moon's orbit around the earth and
>                 then a 1000 m/s TEI burn when angled appropriately for Earth
>                 return. This was the result:
>                  > Fight path departing Lunar Orbit:
>                  > https://i.imgur.com/vSprVbG.png
>                  >
>                  > Moon-Earth return flight path: (positions of the Earth and
>                 Moon and shadows of those objects as of 10 minutes past the TLE
>                 burn):
>                  > https://i.imgur.com/tW4aBcq.png
>                  >
>                  > Velocity of the Apollo 11 CSM relative to the center of the
>                 Earth:
>                  > https://i.imgur.com/GQYsNmT.png
>                  >
>                  > As you can see, most of the velocity gain is at the end of
>                 the flight. Peak velocity is just before entry to the atmosphere
>                 and is 10712 meters/second (23963 miles/hour). That was my
>                 "winging it" TEI burn and CSM orbit position and orientation and
>                 would have resulted in a return to Earth, but I didn't
>                 particularly care where around Earth it reentered so my flight
>                 "plan" will be a bit off from the official one, but completely
>                 coincidentally would have reentered Earth's atmosphere
>                 south-west of Hawaii: https://i.imgur.com/kr6qKNi.png
>                  >
>                  >
>                  > On Mon, Jul 20, 2020 at 7:13 AM <xxxxxx@gmail.com
>                 <mailto:xxxxxx@gmail.com>> wrote:
>                  >>
>                  >> Those are more like the G-loads I'd have expected... yet....
>                  >>
>                  >> "On their way back from a lap around the Moon in 1969, the
>                 astronauts’ capsule hit a peak of 24,790mph (39,897km/h)
>                 relative to planet Earth."
>                  >>
>                  >> 39,897 km/h -> 39,897 m in 3600 seconds -> 11.0825 m/s
>                  >>
>                  >> So if this is their top speed relative to earth (that may be
>                 the issue as it is a fast moving target), that is not 1000 m/s.
>                  >>
>                  >> So if both your figures from the linked doc and the BBC's
>                 figures are accurate, there has to be something to tie them
>                 together... but I can't get there.
>                  >>
>                  >> Was the Earth receding at 990 m/s?
>                  >>
>                  >> And the other question I had was whether the figures you
>                 quoted included any portion of the velocity of their orbit (I'm
>                 guessing some of that is preserved if you break orbit right...)?
>                  >>
>                  >> ======
>                  >>
>                  >> Aside: Your 6.7 m/s should be m/s^2 (a minor thing).
>                  >>
>                  >> ======
>                  >>
>                  >> All that said, a 0.25 to 1.0 G acceleration (for some time)
>                 would be more what I'd have expected.
>                  >>
>                  >> If you were using some kind of nuclear turbine or some other
>                 sort of engine that ejected reaction mass, I wonder practically
>                 what speed you could get moving on the way to mars if you
>                 planned to stop there, do some stuff and come back (and not
>                 arrive back so fast you crashed into Earth or bounced off)?
>                  >>
>                  >> I'm guessing with some higher G capabilities, you could do
>                 0.5 gees or more continuously or spike up over 1G for short
>                 periods several times a day to build up speed. You could orient
>                 the vessels floors perpendicular to the main drive when moving
>                 at 1 G or less, you could just walk around (maybe up to 1.25 G
>                 or something), but anything higher for an acceleration burn,
>                 would be sit in our chair, rotate it so your back is to the
>                 floor, and the chair would maybe inflate or have gel that would
>                 help cushion you. Then you might be able to do limited 1.5 or 2G
>                 or more burns for short periods.
>                  >>
>                  >> The record, I understand, for Gs was a fellow who tried out
>                 the original 'rocket sled' (rocket on rails) at a momentary
>                 acceleration of 82.6 Gs. (Yes, I said that...) He passed out,
>                 but because of the very short duration and his good general
>                 conditioning, he recovered fully.
>                  >>
>                  >> On Mon, Jul 20, 2020 at 8:43 AM Jeffrey Schwartz
>                 <xxxxxx@gmail.com <mailto:xxxxxx@gmail.com>>
>                 wrote:
>                  >>>
>                  >>> I think this is what you're wanting.
>                  >>> https://www.hq.nasa.gov/alsj/a11/a11fltpln_final_reformat.pdf
>                  >>>
>                  >>> Go to page 1-8 (page 30 in the file)
>                  >>> It's got time, duration of burn, and delta-v in feet per second
>                  >>>
>                  >>> TransLunarInjection (breaking Earth Orbit and heading for
>                 the moon) is
>                  >>> a 5:20 minute burn  (320 seconds) for 10,451 fps.
>                  >>> I call that about 3185 m/s over 320sec , or right about 1g
>                  >>> Note this is the last of the fuel in the last stage of the
>                 Saturn
>                  >>> launch vehicle, and they dump it after this.
>                  >>>
>                  >>> Lunar Orbit Injection is just shy of 6 minutes (5:58.9 or
>                 358.9sec) for 888m/s
>                  >>> I make that 2.47 m/s^2 , or about  1/4g
>                  >>>
>                  >>> TransEarthInjection (breaking lunar orbit) is 2:29.4 (149.4
>                 sec) for
>                  >>> 3292.7 fps or about 1000m/s
>                  >>> I make that as 6.7m/s, or about 2/3g
>                  >>> (Note the performance increase from not pushing the LM any
>                 more)
>                  >>>
>                  >>> There's a lot of really neat stuff in that document...
>                  >>> If I had a bunch of free time, it'd be tempting to rewrite
>                 it as an
>                  >>> IISS "Mission Planning Workbook", with fill-in-the-blank
>                 sections.
>                  >>>
>                  >>> On Mon, Jul 20, 2020 at 1:02 AM <xxxxxx@gmail.com
>                 <mailto:xxxxxx@gmail.com>> wrote:
>                  >>> >
>                  >>> >
>                  >>> > So this article
>                 https://www.bbc.com/future/article/20150809-how-fast-could-humans-travel-safely-through-space
>                 got me thinking....
>                  >>> >
>                  >>> > The Apollo 11 capsule was doing around 40K km/h at top
>                 speed coming back. The distance to the moon was 377,349km at
>                 that time.
>                  >>> >
>                  >>> > Now, I've seen some discussion of the S shaped curve to
>                 enter a retrograde orbit around the moon as well, but it was
>                 lacking in some of the information I wanted (I did find out
>                 about 600 m/s was the velocity you need to enter said orbit).
>                  >>> >
>                  >>> > So if they left the moon starting with 600 m/s and
>                 accelerated half way back, flipped, and decelerated, and they
>                 were doing 40K km/h at flip over, if I get my math right, they
>                 would have reached 40 K km/hr  minus 600 m/s in half the
>                 distance of 377K km.
>                  >>> >
>                  >>> > Close to 250 minutes at the flip.
>                  >>> >
>                  >>> > Now, I don't think they did constant acceleration nor
>                 constant deceleration nor did they need to get intercept
>                 velocity to zero (the atmo helps here on the return).
>                  >>> >
>                  >>> > Punching in:
>                  >>> > V(0) = 600 m/s (orbital velocity of the moon)
>                  >>> > V(final at th flip) = 40,000,000 m/s
>                  >>> > Time = 250 mins
>                  >>> >
>                  >>> > Acceleration then looks to be 42 m/s^2.
>                  >>> >
>                  >>> > That looks like 4 gees for nearly 5 hours accel then flip
>                 and decel at the same, so that's about 10 hours of 4 gees...
>                 that seems pretty hard on the astronauts.
>                  >>> >
>                  >>> > Am I off in space with my numbers? The G load would be
>                 worse if you accelerated like mad for some minutes and then cut
>                 off for the rest of the trip to the mid-point.
>                  >>> >
>                  >>> > I'm trying to figure out what sorts of acceleration you
>                 could reasonably sustain during system travel without grav
>                 plates if the journey took more than a short window (say 10
>                 minutes or so)...
>                  >>> >
>                  >>> > Would system ships in these settings then boost at a
>                 maximum of about 1.25 gees for a long haul? Or would they burst
>                 at 2-3Gs or more for up to 15 or 30 minutes, then come down,
>                 then have another heavy accel again if needed every (insert
>                 period of hours)?
>                  >>> >
>                  >>> > Thoughts?
>                  >>> >
>                  >>> > (I'm also thinking about, for say a trip to mars with a
>                 conventional rocket, how much would be coasting and what sort of
>                 Gs would be applied to get you moving? I'm assuming you couldn't
>                 burn all the way due to fuel weight...)
>                  >>> >
>                  >>> > (Also curious if some form of maglev launch from the moon
>                 (lower escape velocity) might get you some of your initial
>                 velocity for a trip out to mars ...)
>                  >>> >
>                  >>> > (Also curious - having trouble figuring out (via
>                 research) how fast one could 'fly' with a good push off inside a
>                 station in zero-G - I'm not sure what sort of velocity a
>                 straight jump from a surface using strong leg muscles could
>                 produce...)
>                  >>> >
>                  >>> > Tom B
>                  >>> >
>                  >>> >
>                  >>> >
>                  >>> >
>                  >>> >
>                  >>> >
>                  >>> > --
>                  >>> > “The only stable state is the one in which all men are
>                 equal before the law.” ― Aristotle
>                  >>> >
>                  >>> > -----
>                  >>> > The Traveller Mailing List
>                  >>> > Archives at http://archives.simplelists.com/tml
>                  >>> > Report problems to xxxxxx@simplelists.com
>                 <mailto:xxxxxx@simplelists.com>
>                  >>> > To unsubscribe from this list please go to
>                  >>> > http://archives.simplelists.com
>                  >>> -----
>                  >>> The Traveller Mailing List
>                  >>> Archives at http://archives.simplelists.com/tml
>                  >>> Report problems to xxxxxx@simplelists.com
>                 <mailto:xxxxxx@simplelists.com>
>                  >>> To unsubscribe from this list please go to
>                  >>> http://archives.simplelists.com
>                  >>
>                  >> -----
>                  >> The Traveller Mailing List
>                  >> Archives at http://archives.simplelists.com/tml
>                  >> Report problems to xxxxxx@simplelists.com
>                 <mailto:xxxxxx@simplelists.com>
>                  >> To unsubscribe from this list please go to
>                  >> http://archives.simplelists.com
>                  >
>                  > -----
>                  > The Traveller Mailing List
>                  > Archives at http://archives.simplelists.com/tml
>                  > Report problems to xxxxxx@simplelists.com
>                 <mailto:xxxxxx@simplelists.com>
>                  > To unsubscribe from this list please go to
>                  > http://archives.simplelists.com
>                 -----
>                 The Traveller Mailing List
>                 Archives at http://archives.simplelists.com/tml
>                 Report problems to xxxxxx@simplelists.com
>                 <mailto:xxxxxx@simplelists.com>
>                 To unsubscribe from this list please go to
>                 http://archives.simplelists.com
>
>             -----
>             The Traveller Mailing List
>             Archives at http://archives.simplelists.com/tml
>             Report problems to xxxxxx@simplelists.com
>             <mailto:xxxxxx@simplelists.com>
>             To unsubscribe from this list please go to
>             http://archives.simplelists.com
>
>         -----
>         The Traveller Mailing List
>         Archives at http://archives.simplelists.com/tml
>         Report problems to xxxxxx@simplelists.com
>         <mailto:xxxxxx@simplelists.com>
>         To unsubscribe from this list please go to
>         http://archives.simplelists.com
>
>     -----
>     The Traveller Mailing List
>     Archives at http://archives.simplelists.com/tml
>     Report problems to xxxxxx@simplelists.com
>     <mailto:xxxxxx@simplelists.com>
>     To unsubscribe from this list please go to
>     http://archives.simplelists.com
>
> -----
> The Traveller Mailing List
> Archives at http://archives.simplelists.com/tml
> Report problems to xxxxxx@simplelists.com
> To unsubscribe from this list please go to
> http://www.simplelists.com/confirm.php?u=QWmJ5KKpHa3MBU63jjs3knG6o9jLMkSu
>

--
         Thomas Jones-Low
Work:	xxxxxx@softstart.com
Home:   xxxxxx@gmail.com