Calculating distance to stop

Bugbear
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Calculating distance to stop

Post by Bugbear » Sun Apr 23, 2017 3:52 am

This question is probably for ecraven but I'll put it here in case others have the answer.

@ecraven, legend has it that you've written some code that will calculate the distance to stop given the current speed. Has this made it into the main build yet? If so, how do I access these calculations?

Cheers

nozmajner
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Re: Calculating distance to stop

Post by nozmajner » Sun Apr 23, 2017 8:25 am

Don't know, if ecraven monitors this forume actively, so I answer. It's in his imgui-hud branch / Imgui reticule PR which should be merged in a day or so. Which means it should be in the next build also.
But you could check his brannch already.

Bugbear
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Re: Calculating distance to stop

Post by Bugbear » Sun Apr 23, 2017 9:42 am

Thanks. I'll check it out and give it a spin..

impaktor
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Re: Calculating distance to stop

Post by impaktor » Mon Apr 24, 2017 12:36 pm

It's been merged to master now, so either compile from source, or wait until next build.

Bugbear
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Re: Calculating distance to stop

Post by Bugbear » Thu Apr 27, 2017 2:50 pm

Just finished a fresh build of master (I've been having hassles for the past month or so where I haven't been able to successfully compile - evidently, there's something different in this version that plays nicely with my aging laptop).

I'm liking the new HUD. Ecraven, you've done a great job! It will take a bit of practice to get used to the numbers but distance to stop is in a really logical place (just a shame I still managed to crash into the suburbs of Tranquility Base on my maiden flight :-) ).

The only thing that would make my life complete would be to have two distance to stop calculations - one using the main thrusters, and one using the reverse thrusters, but I can have a go at that.

impaktor
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Re: Calculating distance to stop

Post by impaktor » Thu Apr 27, 2017 3:08 pm

I think idea is that spinning the ship around is such a cheap operation compared to trying to use inferior non-main thrusters.

Make sure to check out the wiki on all the features, and add as need be.
https://pioneerwiki.com/wiki/Flight_UI

Bugbear
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Re: Calculating distance to stop

Post by Bugbear » Thu Apr 27, 2017 3:27 pm

Oh yes, I totally agree. Spinning the ship is definitely the logical solution. I just like to have the ship pointing in the direction of travel as much as possible.

I had done quite a few trips using my hacky mod and found that by using the retro thrusters, it was possible to always traverse across a system and arrive at my destination with a minimum of over/undershooting (usually zero over/undershooting). It's difficult to explain in words. I'll have to put a video together (not this weekend - already committed...).

I'll have a go anyway. I think the Sinonatrix has a total delta-V of about 9000km/s. Meaning you can theoretically accelerate to 4500km/s, coast in-system, then decelerate to wipe off that 4500km/s. Time this to perfection (impossible) and you arrive at the doorstep of your destination.

It's prudent to reserve some delta-V for course corrections (say 1000km/s), so that brings your coasting maximum speed down to 4000km/s.

So I jump to a new system and find myself 10.0AU from my target starport. The main thruster takes about 1.0AU to accelerate to 4000km/s, the reverse thruster takes about 2.5AU to decelerate from 4000km/s, therefore I begin braking at 2.5AU from my destination.

There's always going to be errors introduced by planetary movement, and gravitational pull of the main star (it's not much but it all adds up). There's probably some floating point errors due to the big numbers we're playing with (but don't quote me on that). Bottom line, it may take more or less than 2.5AU to decelerate using the reverse thrusters, but that's a good thing because you always have your main thrusters to introduce any corrections to bring your braking distance back in line with the distance to your destination.

So in spite of my desire to keep the ship pointing in the direction of travel, I do need to spin about from time to time - I'll call that a small price to pay for never having to carry an autopilot. (I have a bee in my bonnet with the autopilot manufacturers - they recently put in some code that constantly phones home reporting 'telemetry'. My courier customers demand discretion and the last thing I need is some two-bit junk think box screaming my position to all and sundry....mutter..rant..mutter..)

One of these days I'll do enough courier runs to pick up a new ship that has more balanced main / non-main thrusters.

nozmajner
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Location: Budapest HU

Re: Calculating distance to stop

Post by nozmajner » Thu Apr 27, 2017 5:03 pm

Bugbear: don't forget to install gimballed seats to your ship, or you will feel like you are hanging from the ceiling during that long deceleration burn :D

Bugbear
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Re: Calculating distance to stop

Post by Bugbear » Sat Apr 29, 2017 2:00 pm

Oh didn't you know? I'm a vampire. Hanging from ceilings is how it's done, and it's always night-time in space :-)

Bugbear
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Re: Calculating distance to stop

Post by Bugbear » Sat Apr 29, 2017 2:18 pm

On a more serious note, I finally R'd TFM and I'm having some difficulty with the delta-V calculations when using the non-main thrusters. It appears that the reverse thrusters are using 5x the delta-V that is actually imparted to the ship. Has something changed with the flight model?

As an example, I've got the starter ship, the Sinonatrix, in open space after jumping to a new system (so as to minimise gravitational effects). I then zero my velocity relative to the frame of reference.

Current delta-v = 9957 km/s
Accelerate to 10 km/s using main thrusters, delta-v = 9947 km/s
Decelerate to 0 km/s using reverse thrusters, delta-v = 9901 km/s

In other words, using the retro thrusters takes 46 km/s delta-v to wipe off 10 km/s.

I'll log this as a bug but could someone else confirm / deny my observations?

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