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Re: Space Shuttle - Development

Postby GinGin » Sat Aug 10, 2019 10:22 am

Indeed for the xml.
Like in real , I guess we can adjust the nominal one following the profile will fly , like a I load mission specific :)

I just changed the max to 109 ( 106 before ) and abort to 106 ( 109 ) before .
It was flipped .



For the performance issue , i have good documentation’s With propellant remaining , etc
Need to find it now :)

For me 6 pour-cent seems legit .
A ful’ Eastward with no payload .
Shuttle would have been able for polar orbit and heavy payload .
So I guess there was margin for a full earth relative speed assistance launching due east compared to what was forecasted for polar orbit.

I am wondering , because empty but with the 40000 pounds equipment was like fully loaded orbiter for your empty payload test .
Basically without payload and with that 40 kpounds , it was like if Shuttle was already full . So added to that a payload , it was a way overweight Shuttle .
So bad results on abort with full payload might be linked to that . An extra 40000 pounds outside of the envelop

I will test that . But removing like we said those 40000 pounds will give us much more realistic results to compared with real data’s.


As for the flight path . It is te gamma value , angle between local horizontal and velocity vector at meco.
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Re: Space Shuttle - Development

Postby eatdirt » Sun Aug 11, 2019 2:04 pm

, I'd appreciate if the people running the development branch could test whether the normal rendezvous stuff


Woo, fantastic features implemented. I am off from a real computer for a while, but I'll test asap. Thank you for the work Thorsten!
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Re: Space Shuttle - Development

Postby Thorsten » Sun Aug 11, 2019 2:07 pm

So bad results on abort with full payload might be linked to that . An extra 40000 pounds outside of the envelop


Actually the problems outside of contingency aborts had often to do with too much performance :(

***

So, over the last days, I've made the decision to start with a 'Scenario' concept. This will be a fairly general way to specify an xml file which can

a) place you at a specific state vector (e.g. for trying high or low energy entry)
b) spawn co-orbiting objects around you (for practicing capture, assembly or docking)
c) can cause specific failure modes
d) places the orbital target at a specific location to practice phasing/intercept

or a combination of all of them. Currently I have support for pre-defined scenarios, but I plan to also allow to pass a user-written scenario via the commandline. To avoid dumb outcomes, scenarios are linked to a specific mission phase, so unless you start with SpaceShuttle-entry you won't be able to access entry scenarios. In this way, this is complementary to what save/resume provides, in that you use save/resume for a complete mission, possibly over days, whereas scenarios give uou direct access to specific problems.

At least for me the advantage will be that testing some things (handover between near and far zone,...) will be faster.
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Re: Space Shuttle - Development

Postby GinGin » Sun Aug 11, 2019 8:22 pm

Actually the problems outside of contingency aborts had often to do with too much performance


Ah, alright :/

After a bit of readings, 1% of propellant was equal to 15000 pounds ( with the 6:1 LO2/LH2 ratio)
FPR ( Final Performance reserve) was around 4000 pounds to allow some margins, and usually at MECO , one % max was remaining in the ET plus the 5000 pounds into the feedlines/engines

Powered flight duration was around 500 s ( 8mn 30s), and Target Parameters at MECO for the closed loop stage 2 guidance was MECO altitude ( 52 Nm ), Flight Path Angle ( the gamma we talked about) and the Inertial velocity.

So, I will continue to dig as I am already closer to the real Nasa Ascent Path and try to see what is the Propellant left over to compare it to real datas.


So, over the last days, I've made the decision to start with a 'Scenario' concept. This will be a fairly general way to specify an xml file which can


Very nice and very useful, Thanks!
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Re: Space Shuttle - Development

Postby amalahama » Thu Aug 15, 2019 10:45 pm

Thorsten wrote in Sun Aug 11, 2019 2:07 pm:
So, over the last days, I've made the decision to start with a 'Scenario' concept. This will be a fairly general way to specify an xml file which can

a) place you at a specific state vector (e.g. for trying high or low energy entry)
b) spawn co-orbiting objects around you (for practicing capture, assembly or docking)
c) can cause specific failure modes
d) places the orbital target at a specific location to practice phasing/intercept

or a combination of all of them. Currently I have support for pre-defined scenarios, but I plan to also allow to pass a user-written scenario via the commandline. To avoid dumb outcomes, scenarios are linked to a specific mission phase, so unless you start with SpaceShuttle-entry you won't be able to access entry scenarios. In this way, this is complementary to what save/resume provides, in that you use save/resume for a complete mission, possibly over days, whereas scenarios give uou direct access to specific problems.

At least for me the advantage will be that testing some things (handover between near and far zone,...) will be faster.


That actually sounds very cool! You might consider to extend the scenario framework to support some sort of scripting engine, so people can set interactive missions based on real data, with MCC messaging, or interactive tutorials. LUA seems to be a quite popular scripting language, although I don't know if there is an API implemented in FG so it can read/write internal variables.
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Re: Space Shuttle - Development

Postby Thorsten » Fri Aug 16, 2019 4:17 am

We have a scripting language in FG, it's called 'Nasal', and if you can code in it, you can read data files, do interactive scenarios, play messages via text to speech or interface with the Shuttle systems. That kind of thing is enabled without any effort in FG - effort is to structure things to look unscripted for the end user such that he can use an xml file :mrgreen:
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Re: Space Shuttle - Development

Postby amalahama » Fri Aug 16, 2019 11:50 pm

Oh I see. So something that could be quite useful to consider in further iterations is the "trigger" concept - so several hard-coded events such as mission steps complete, distance to target, successful docking, orbital parameters, mission time etc can invoke custom-made effects - text messages, system failures, AI reactions (chase aircraft?) etc, in a way that can be customized easily through XML files or similar. That addition would pretty much open the door to simulating real (and hypothetical) missions in a richer and more stimulating environment.
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Re: Space Shuttle - Development

Postby Thorsten » Sat Aug 17, 2019 4:52 am

something that could be quite useful to consider in further iterations is the "trigger" concept - so several hard-coded events such as mission steps complete, distance to target, successful docking, orbital parameters, mission time etc can invoke custom-made effects - text messages, system failures, AI reactions (chase aircraft?) etc, in a way that can be customized easily through XML files or similar.


I don't think you realize how flexible FG is right out of the box in that department - if you consider scripting scenarios, you have access to the whole property tree, i.e. you can simply set a listener to anything and use that as trigger.

Likewise, you can interact with the whole property tree.

Once you consider xml, it's just rather complicated conceptually to define an 'event' - the tutorial system is there and tries to do that, but it's been expressed by several people who used it to code scenarios that sometimes it just doesn't get the obvious and persists in doing wrong things (you have no power in the cockpit because of an electric failure, but it advises you to switch on more an more avionics).

Which is why I don't use it, because scripting is more flexible.
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Re: Space Shuttle - Development

Postby GinGin » Tue Aug 20, 2019 3:57 pm

I tested the last dev version.
A lot of useful new stuff, thanks :)

I love the Auto Countdown launch sequence.

I tested a quick rendez vous to ISS, it works like before.
I will try a complete one to Hubble tomorrow to see if there are some discrepancies like you requested

I found some interesting old ascent cue card showing the much more lofted trajectory chosen at the beggining ( with less margin for dual engine failures and more black zone)

This one, from a sim sessiosn I guess ( dated from end of year 1980)
Max altitude of 72 Nm and MECO at 63 Nm ( compared to 52 Nm for the last sts decade mission)


Image



And that one from STS 3, less lofted

Image
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Re: Space Shuttle - Development

Postby GinGin » Tue Aug 20, 2019 4:09 pm

I forgot a point about propellant remaining.
I made a lot of tests with different payload, ascent path,MECO time, inclination etc

Indeed, it seems to have a 3- 4 % ish of propellant remaining in excess at MECO ( very hard to have solid data on that from real flight datas)
I remarked that I had a bit too much Vertical Speed before SRB sep ( 2500 ft/s vs 2000 ft/s ish normally with equivalent ascent path) and a quicker and higher srb sep than reality ( around 2 mn , 150 kfeet instead of 2 mn10 and 130 kfeet ish)
Maybe something like you say about less amtosphere effects during first stage than it should be, but I am highly not competent on that matter :)
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Re: Space Shuttle - Development

Postby GinGin » Fri Aug 30, 2019 11:02 am

Two very interesting articles about space rendez vous really well explained for an introduction to it

https://www.baen.com/rendezvous

https://www.baen.com/rendezvous-part2

I think I will do a post for intersting links/ books/documentations




I am testing phasing and catch up speed in the far zone, and compare them to real datas.
As usual, not a lot of surprise, really close to what we can expect from theory and from that kind of useful Rule of thumbs

13 Nm of difference between ( target sum of apogee plus perigee) and ( chaser sum of apogee plus perigee) give 1 ° per orbit of catch up rate
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Re: Space Shuttle - Development

Postby Johan G » Fri Aug 30, 2019 4:38 pm

Skimmed through the images and saved for later, but noted his background (found in small print near the bottom of those pages). :D
Low-level flying — It's all fun and games till someone looses an engine. (Paraphrased from a YouTube video)
Improving the Dassault Mirage F1 (Wiki, Forum, GitLab. Work in slow progress)
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Re: Space Shuttle - Development

Postby Thorsten » Tue Sep 03, 2019 3:02 pm

Maybe something like you say about less amtosphere effects during first stage than it should be, but I am highly not competent on that matter


I gave first stage aerodynamics and the 950 pages of wind tunnel data a good hard look and, well, it seems to do something.

Before I had SRBSep at 168.000 ft, with the improved table for the full stack we're down to 154.000 ft (likewise, upward speed is a bit lower) - Wikipedia says we separate at 146.000 ft, but my ascent pitch schedule may differ (?)

Anyway - while this may (or may not) require tuning a few values, I leave the correction in for the moment (there's also the possibility that I didn't fully understand the tabulated quantities... though generally their behavior looks plausible)
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Re: Space Shuttle - Development

Postby GinGin » Tue Sep 03, 2019 3:38 pm

Wow, that is already a huge difference.
Your pitch ascent differs indeed from latest sts flight

Is it closer to first sts lofted ascent ( like the one I putted in pictures above)
The autolaunch .nas I used In modding files is based on latest open loop stage 1 ascent with a shallower ascent path .

If you put the changes in the dev branch , I will try with that one as I already had a staging around 150 kfeet
So we might be good there
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Re: Space Shuttle - Development

Postby GinGin » Wed Sep 04, 2019 4:32 pm

After tests :

51 ° Inc, bucket between 30 and 60 s, 104 % of thrust and the modified ascent profile plus last correction on aerodynamic datas.



Nasa datas
1mn30: 84Kfeet // 1900 ft/s
1mn50: 125Kfeet// 2200ft/s
2mn: Staging 146Kfeet// 2400 ft/s



Before Update :


Max Q : Alpha= -2° and 795 psf
1mn30: 94Kfeet// 2200ft/s
1mn50: 140Kfeet// 2500 ft/s
1mn56: Staging 154 Kfeet// 2600 ft/s



After Update:

Max Q:

Image

1mn30: 87Kfeet// 2000ft/s
1mn50: 130Kfeet// 2300 ft/s
1mn56: Staging 148 Kfeet// 2400 ft/s

Image



So even better, especially for the Max Q
Almost on spot with real datas regarding the profile flown.

-4 degrees and 730 psf, like in the article "why wings stay on the Shuttle during Lift off"
So for me, A nice catch there.
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