michal.don

Shuttle Challenge v5 - The STS thread [Stock and Mod Friendly]

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1 hour ago, 4x4cheesecake said:

. I have honestly no idea how the real shuttle did this trick

If I had to guess I'd think they balanced the thrust to make the vector be perfectly vertical at least, that way you're not wasting fuel on bad earo. The next trick is to balance the vectors on all your engines to get the roll to be balanced around the cot

With the real shuttle the flip isn't made until the boosters have been jettisoned, so the only vectors to account are those of the shuttle engines, while for the roll control in the first stage withe boosters they would only use the tail fin and block the vector control completely to avoid what you're describing altogether

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4 minutes ago, hoioh said:

With the real shuttle the flip isn't made until the boosters have been jettisoned

I actually thought about the roll right after the launch, to get into the right orbit:

(The video should start at 10:39, otherwise, skip there manually ;))

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2 hours ago, 4x4cheesecake said:

I actually thought about the roll right after the launch, to get into the right orbit:

(The video should start at 10:39, otherwise, skip there manually ;))

On close inspection it looks like they are using the wing mounted roll control flaps

Considering the amount of engineering that went into it, could it be possible that the center of mass is directly in line with the main wing at this stage?

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The thing about roll authority on initial ascent is - Space Shuttle actually had some thrust vectoring on the boosters. It's easy to see that those are actually the best positioned to provide roll authority with only minimal perturbations on other axis (and if there still is some yaw effect - with proper flight guidance it can be automatically cancelled by balanced yaw response of all the engines). While it's clear that SSMEs with their large gimbal range were the main source of pitch control, you clearly can't expect engines this close together to handle both roll and yaw while they aren't on the thrust axis

 

Also an advice from my experience: disable roll response on engines too close to CoM - those will likely produce more yaw than roll torque. Handling of my Energia replica greatly improved when I disabled roll on the 2 engines closest to Buran

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Thanks for the detailed explanation :)

I would have never expected that the booster were able to do this. While there are indeed in the best position to initiate the roll programm, they just don't seem to have any thrust vectoring capacities.

On my shuttles, I usually deactivate any roll authority on the engines and the elevons except the one on each side. In most cases, I don't need roll authority at all but you never know ;)

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I'm not 100% sure on technical details, but there were some moving parts in the nozzle to allow for a bit of thrust vectoring. Probably only a small authority, but you really don't need much for roll and yaw if you also have yaw deflection on SSMEs to compensate for any imbalance on that side

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On 2/15/2019 at 1:19 AM, Johnster_Space_Program said:

How does this look? (The CoL and Mass are in about the same place, is that good?)

Depends. I suggest you also try it without payload (most of the time you'll return empty); and I strongly suggest that you grab it by the root part, hold shift + WASD and see how CoM/CoL changes with AoA. Though IIRC the stock CoL overlay only considers wing pieces, while in flight you also get drag from other parts. Like, the fuselage.

If you enter at 40° AoA you may find getting airflow from below will make it pitch over backwards. Not sure if mods like CorrectCOL will help. In the end, I find that nothing can replace a proper test flight.

@michal.don Another video this time. Time lapse, I hope it makes it palatable. Two reentries are shown, the second one with a bad de-orbit so you can see how my script copes with inclinations, namely, not very deliberately. It should be easy to see how even this half-measures yield good results on a reasonably planned de-orbit. But if they don't, well, it just makes for the runway from wherever it finds itself after airspeed has dropped below a threshold. I had to circle on previous landings because I reserve a lot of altitude for getting to the space center. On that second return, this was finally good for something.

And what the hell, here's the script, cruft and all. If I first want to clean up the code, I'd never publish it at all...

It's written in Python -- if you're on Linux, it's just a question of installing krpc (available for 1.6), starting it in-game, and running "python /tmp/lander.py" from a shell. If on Windows, you probably first need to get Python, don't know how much hassle that is.

Chances are that you need to tweak control surfaces: the script doesn't like it if you have very much roll or yaw authority. My vessel only rolls with the outmost (smallest) elevons, and those are set to 20%.

 

Edited by Laie
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On 2/15/2019 at 7:09 AM, hoioh said:

If I had to guess I'd think they balanced the thrust to make the vector be perfectly vertical at least, that way you're not wasting fuel on bad earo. The next trick is to balance the vectors on all your engines to get the roll to be balanced around the cot

Then your guess would be wrong.  You can clearly see that at liftoff the shuttle is moving sideways and up, not straight up.  At T-7 seconds the main engines ignite, and the whole stack sways forward a bit, then back and when it is perfectly vertical, the boosters ignite.  You can clearly see it in this video:

 

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We already determined the boosters have a little gimbal range to do the rolling. Thinking about it now, it seems obvious that the com is not perfectly in the center, 1 weight of fuel pod and boosters, 2 the engines of the shuttle are positioned at an angle to accomodate for the com offset.

But that does not neccesarily mean that at the time of the final belly down roll the com may have moved towards the shuttle enough to roll using the flaps, but by then the air is too thin to gain anything by that

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On 2/15/2019 at 2:09 PM, hoioh said:

If I had to guess I'd think they balanced the thrust to make the vector be perfectly vertical at least, that way you're not wasting fuel on bad earo.

3 hours ago, linuxgurugamer said:

Then your guess would be wrong.  You can clearly see that at liftoff the shuttle is moving sideways and up, not straight up. 

To be fair, with most of the thrust being SRBs and most of the weight being ET+SRBs, the resulting thrust vector should still be quite close to being along the ship. But all of this also means the SRBs have to do most of the work on yaw and roll control

And to think of it, with such thrust vector, starting pitch program early on (pretty mush as soon as roll to the proper azimuth is complete) and with noticeable deflection from vertical gives a good option to actually pass maxQ with the Shuttle perfectly aligned with airspeed, while the offset thrust compensates for perpendicular to velocity gravity component.

2 hours ago, hoioh said:

But that does not neccesarily mean that at the time of the final belly down roll the com may have moved towards the shuttle enough to roll using the flaps, but by then the air is too thin to gain anything by that

Well, after booster separation SSMEs have to align their pitch axis deflection with CoM, at which point they have perfect control over all 3 axis of rotation. And while air may be too thin for control surfaces, isn't the point of the belly-down roll to have the lift turned up? Given the offset between thrust vector and the longitudinal axis at this point, lift should be a concern.

 

Of course, with the tools we are offered in stock KSP all of this typically boils down to "forget the efficiency optimization, just choose something SAS can handle without wobbling the shuttle apart steering with this gimbal range!"

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54 minutes ago, Alchemist said:

Well, after booster separation SSMEs have to align their pitch axis deflection with CoM, at which point they have perfect control over all 3 axis of rotation. And while air may be too thin for control surfaces, isn't the point of the belly-down roll to have the lift turned up? Given the offset between thrust vector and the longitudinal axis at this point, lift should be a concern.

Being upside down has nothing to do with lift.  It had two reasons:

1.  First, it was so the pilots had a view of the ground,  giving them a frame of reference

2.  In the event of an abort, they would do a simple flip to be able to get back to the space center

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53 minutes ago, linuxgurugamer said:

Being upside down has nothing to do with lift.  It had two reasons:

1.  First, it was so the pilots had a view of the ground,  giving them a frame of reference

2.  In the event of an abort, they would do a simple flip to be able to get back to the space center

The question of lift was about why it doesn't stay upside down, but rolls the other way around soon after SRB separation.

By the way, this maneuver is not a thing for Buran - it stays belly-up. Which clearly means the reasoning involves something about the configuration after booster separation - and here Shuttle and Energia-Buran have high thrust deflection in opposite directions

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37 minutes ago, Alchemist said:

The question of lift was about why it doesn't stay upside down, but rolls the other way around soon after SRB separation.

Again, nothing to do with lift.  It goes right-side up in order to be able to jettison the external tank into a decaying orbit, without running into it again.  The altitude is so high at that point, there is no lift

Edited by linuxgurugamer

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On 2/12/2019 at 5:13 AM, Alchemist said:

You can take any size and mass. However, be aware that even class A won't fit in the mk3 payload bay, and with densities they have in stock (styrofoam???), carrying a small asteroid is more about drag than weight.

Back when I was doing this mission there was a bug which made all the rocks spawn with 150t mass. Now that was a cool chance to drill it down to whatever mass you can carry while also picking something of a manageable size

I'm using a Mk2.5 shuttle for this

Going to be interesting

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On 2/15/2019 at 7:33 PM, Laie said:

Another video this time. Time lapse, I hope it makes it palatable. Two reentries are shown, the second one with a bad de-orbit so you can see how my script copes with inclinations, namely, not very deliberately.

Nice one again - I love the idea of an on-orbit attached docking port and the following assembly :) One issue I have with the bideo report though - could you please include liftoff and ascent next time? Or, at least, a few short clips of the significant parts of them? I won't make you re-fly this mission, but I'd like to see them the next one. Thanks!

And, regarding the reentry/descent - the script makes it look soooo easy :D Especially the second one, the map view shows really well how the script beutifully gets the shuttle home - I think this is approaching the Skunkworks territory quite fast - I am truly impressed :) 

Anyway, a badge for you and I am indeed looking forward for more!

qZ10w1g.jpg?1

Michal.don

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4 hours ago, michal.don said:

Nice one again - I love the idea of an on-orbit attached docking port and the following assembly :)

Anyway, a badge for you and I am indeed looking forward for more!

Thank you very much.

That docking port... I didn't want to play hide-and-seek with the satellite, and also wasn't willing install any more mods just for the sake of a robotic arm to hold it still. Seemed like an easy workaround, that's all.

I've skipped the ascent because I thought it was boring -- barely distinguishable from the last one I featured at length. I'll include it again next time. If there is a next time.... I'm sorry to say that I'm not that into Shuttle stuff, after all. I'll certainly skip STS-4. I'm also not that into station-building. Next entry will come if I can think of something I'd like to assemble and can make it fit into my shuttle. Currently I'm drawing a blank, but well... maybe.

I might take this thing to Duna just for the heck of it, but can't think of anything worthwhile to do there either. Unloading a ground installation from that shuttle will certainly be difficult: I can't just turn the bay to open at the bottom, as the wings are in the way.

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On 2/18/2019 at 7:46 PM, Laie said:

I'm sorry to say that I'm not that into Shuttle stuff, after all. I'll certainly skip STS-4. I'm also not that into station-building. Next entry will come if I can think of something I'd like to assemble and can make it fit into my shuttle. Currently I'm drawing a blank, but well... maybe.

I might take this thing to Duna just for the heck of it, but can't think of anything worthwhile to do there either. Unloading a ground installation from that shuttle will certainly be difficult: I can't just turn the bay to open at the bottom, as the wings are in the way.

I'm sorry to hear that, but I understand not everybody has fun doing this thing, and when your script works so well, it takes a bit of the fun from flying the missions. Nevertheless, if you do any more missions with your shuttle, even if they are not related to the challenge, let us know here - I'd love to see the script working in yet another circumstances ;) 

 

Michal.don

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I for one am still here. I'm alternating between trying to work out the problem with my wings breaking off of my new STS-9 potato grabber, and boring stuff like financial planning and chores and all that. I've also been cheating on KSP a little with Horizon Zero Dawn. But don't worry, that's just a fling.

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39 minutes ago, sturmhauke said:

wings breaking off of my new STS-9 potato grabber

Do they break during reentry or during the landing? In generall, moar struts are always a good idea ;) Do you have some heavy parts connected to the wings?

41 minutes ago, sturmhauke said:

I've also been cheating on KSP a little with Horizon Zero Dawn

Could be worse^^
Horizon Zero Dawn is a lot of fun :)

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47 minutes ago, 4x4cheesecake said:

Do they break during reentry or during the landing? In generall, moar struts are always a good idea ;) Do you have some heavy parts connected to the wings?

They break off during landing tests. Haven't tested reentry yet; I imagine they'd break off there too. I'm using Pwings just for the sake of something different, and to save on part count, but apparently they're known to have breaking problems at high loads. Something to do with when the joint strength is calculated vs. when the Pwing fully loads. I might have to switch back to Tweakscaled wing pieces, or even manual struts (ugh).

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8 minutes ago, sturmhauke said:

I'm using Pwings

What are Pwings? o_O

But if I understood you correctly, this is just a single wing part? Not sure how KSP deals with it but if you think about it: The more parts you have, the merrier joints can carry a part of the load. A single wing element will carry the full load on a single joint, so this might be actually an issue on your shuttle. More struts to increase the number of joints or more (upscaled) wing elements may help :)

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36 minutes ago, 4x4cheesecake said:

What are Pwings? o_O

But if I understood you correctly, this is just a single wing part? Not sure how KSP deals with it but if you think about it: The more parts you have, the merrier joints can carry a part of the load. A single wing element will carry the full load on a single joint, so this might be actually an issue on your shuttle. More struts to increase the number of joints or more (upscaled) wing elements may help :)

Procedural Wings, AKA Pwings for short:

I suppose I could try using a few smaller segments. Currently I have one giant segment per wing and stabilizer, plus some for control surfaces.

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I finished STS-9 last night, with a Class A asteroid.

Before I post my results, I'm trying to do it with a Class B asteroid, hopefully will get that done tonite

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Alright, so I've done STS-3, although due to my janky MMU and solar panel design, I managed to break one of the solar panels and I didn't have a quicksave, that means only one of the solar panels are on the telescope. I've recorded it and I did dock both of them with two separate kerbals/MMU's, so would my entry still count?

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12 minutes ago, JacobTheFoxx said:

Alright, so I've done STS-3, although due to my janky MMU and solar panel design, I managed to break one of the solar panels and I didn't have a quicksave, that means only one of the solar panels are on the telescope. I've recorded it and I did dock both of them with two separate kerbals/MMU's, so would my entry still count?

I would be inclined to say, launch a spare, or two and go make repairs, it will be very "hubble"

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