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Leaving Earth: Outer Planets» Forums » Rules

Subject: Ion Thrusters at Difficulty 9 & 10 rss

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Niko
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Is there a reason why on the player aid cards ion thrusters only start at 4 years for difficulties 9 and 10?
At difficulty 10 they can carry 1/2 over 3 years and 2/3 at difficulty 9 in the same time.
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Will H.
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I'm not understanding your question. Can you give an example of a spacecraft at one location trying to move to another?

Like: Ion Thruster x2 + Probe at Earth Orbit attempting to move to Inner Planets Transfer.

Maybe then I can try to answer...
 
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Will H.
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Going to take a shot anyway...

So a single Ion Thruster has a mass of 1 and provides 5 thrust. Sending a single Ion Thruster somewhere is probably not very useful, so lets assume your spacecraft has one other component (which does not provide any thrust--maybe a sample). The lightest mass that component can have is 1, so combined with your Ion Thruster, your spacecraft now has a mass of 2.

If you are attempting a maneuver that is difficulty 9, that is 9 x 2 = 18 thrust required. 18 / 5 (the thrust provided by the Ion Thruster) = 3.6, rounded up to 4 years.

So it's not really possible for a single Ion Thruster to do anything useful in less than 4 years on a difficulty 9 maneuver.
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Larry L
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Many tables provide for fractional payloads. So my answer is "I don't know if there is a reason. Maybe it was an oversight?"
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skipper 2206
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RingelTree wrote:
"I don't know if there is a reason. Maybe it was an oversight?"


No.. with fractional you can easily multiply to see how much of this type of rocket you need to perform this manoeuver..
 
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Larry L
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skipper2206 wrote:
RingelTree wrote:
"I don't know if there is a reason. Maybe it was an oversight?"


No.. with fractional you can easily multiply to see how much of this type of rocket you need to perform this manoeuver..


I don't think you understood what I said.
 
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Jakub Glazik
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Larry is right, indeed there are missing the values 9diff-2time, 9d-3t, 10d-3t. You can compare with my "reverse engineered" table: https://docs.google.com/spreadsheets/d/1S17qQDsGTwZCXequcGPn...

My guess is such high difficult maneuver describes situation when the very first burn is made in periapsis (closest approach to planet) to inject into initial very eccentric orbit with long period and next maneuvers sequentially lower apoapsis. Maybe that's why the cut were made in the table to mark more time needed.

Or just to balance pretty powerful ion engines.

Or both. :-)
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Niko
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The reason I noticed this was the Jupiter Orbit/Flyby manoeuvre, difficulty ten.
When looking at the ion thruster player aid from outer planets there are no entries in the difficulty 10 row for less than four years. That would indicate that even with multiple ion thrusters there is no way to move any load in less than four years for that manoeuvre. However, doing the full calculations this is not the case:
Two ion thrusters and something else with mass one create a mass three space craft. The two ion thrusters will create 30 thrust in three years, enough to complete the manoeuvre.
Therefore there should be an entry in the difficulty ten row at three years indicating 1/2 mass. Similarly the difficulty nine row needs more entries.

Will: You are of course right that one ion thruster won't be useful for a manoeuvre of that difficult, but the player aid gives loads of less than one all the time so it should be given here too.

Jakub: I don't think that the lack of an entry should be read as a rule change. The chart is just a shortcut for the calculation of mass times difficulty equals minimum thrust.

Larry: Seems no one else has an obvious reason, so I'm now leaning towards it being an oversight as well.
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Jakub Glazik
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Ze_German_Guy wrote:
Jakub: I don't think that the lack of an entry should be read as a rule change. The chart is just a shortcut for the calculation of mass times difficulty equals minimum thrust.
You are right of course, I use only tgese tables and I forgot while "normal" thrust calculation there will be duch maneuver. Anyway, I have also no answer.
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Joe Fatula
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Looks like it was probably an oversight on my part. I'll take a look at the tables and see about changing it for the next printing.
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