Launch Efficiency Exercise [Updated for 0.21.1]

[Nabukadnezar]

what's the new .craft file for 0.21? what time should we get?

[tavert]

The inline SAS/ASAS parts are unusably heavy now, so here's a proposal. Tarmenius, let me know what you think. How about an Avionics Package and 4 OX-STAT solar panels (or 2 panels and 2 small batteries), that should have the same mass as the old ASAS.

Using the Nao-jectory and not touching the settings, I got 10.46 fuel remaining in 0.21, so seems consistent enough to me.

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I am curious what Nao's real-time adjustments were to get another tenth though.

[Nao]

The inline SAS/ASAS parts are unusably heavy now, so here's a proposal. Tarmenius, let me know what you think. How about an Avionics Package and 4 OX-STAT solar panels (or 2 panels and 2 small batteries), that should have the same mass as the old ASAS.

Using the Nao-jectory and not touching the settings, I got 10.46 fuel remaining in 0.21, so seems consistent enough to me.

-img snip-

I am curious what Nao's real-time adjustments were to get another tenth though.

It was changing the "final flight path angle" after gravity turn (from around 35deg attitude) to better match velocity vector (VV). I don't remember this flight in particular but it was mostly increasing the angle (up to 15deg) to burn ~10deg off VV at first and then no more than ~5deg below VV for the final path.)

Also man this new update, the loading times and bugs are killing me (especially in the fixed 0.21.1 version... i think i'll revert to 0.21.0) The rest is awesome thou I'll be finally able to create proper racing challenge around KSC YAY.

[Raptor831]

Looks like I'll have to retry the launch with the new craft for .21. I need to try and get a few more drops of fuel out of it anyway!

[Nabukadnezar]

OK... I guess FAR shouldn't have been used.

1. Is there anything we could read in order to understand perfectly the options from mechjeb's Ascent Guidance and Ascent Path Editor and learn how to optimize them?

2. When piloting manually I was using Flight Engineer in order to watch the terminal velocity and make sure my speed doesn't go past it. When using only mechjeb, in order to do the same thing do I have to make sure current acceleration doesn't get bigger than maximum acceleration (from Vessel Info)?

[numerobis]

"Current acceleration" is just max acceleration times the throttle, so it'll never get to be more than max acceleration.

Using the custom window editor you can add a readout of the terminal velocity; no need to guess at it.

The only thing to read to understand exactly how MechJeb works is the code; look at ModuleAscentSomthinorother.cs and ModuleThrustController.cs

[tavert]

I don't think terminal velocity can be calculated properly by MJ when you're using FAR. The scoring in this challenge is strictly for stock aerodynamics, though it is interesting to see how the same craft and ascent profiles do with FAR.

[Tarmenius]

How about an Avionics Package and 4 OX-STAT solar panels (or 2 panels and 2 small batteries), that should have the same mass as the old ASAS.

Sounds like a great idea. I hadn't played around with the new version enough to realize the mass difference between the old and new parts, so I'll go experiment and come back with the new craft file. So that's a tentative "yes." I'll be back in a few then.

[Tarmenius]

Ok, it turns out that the Inline Advanced Stabilizer (0.05t) with an Inline Reaction Wheel (0.03t) have the same mass as the old ASAS (0.08t). I think this will be the better configuration, as the Avionics Package + 4x OX-SAT Panels will impart greater drag and mass (0.08 + 4(0.005)).

Unfortunately, I haven't managed a successful orbit in the four attempts I've made so far. I think my throttle control is suffering from having to pay far more attention to managing the non-locking SAS behavior during my gravity turns. I'm sure I'll get it, though.

[tavert]

Ok, it turns out that the Inline Advanced Stabilizer (0.05t) with an Inline Reaction Wheel (0.03t) have the same mass as the old ASAS (0.08t). I think this will be the better configuration, as the Avionics Package + 4x OX-SAT Panels will impart greater drag and mass (0.08 + 4(0.005)).

That's odd. In 0.20.2, ASAS mass was 0.1t for me. And in 0.21.1, the Inline Advanced Stabilizer (former ASAS) is 0.5t, Inline Reaction Wheel (former SAS) is 0.3t.

One possible downside to 4x solar panels is it's slightly harder to verify from screenshots. If we required 4x batteries, then at least the electric charge capacity is verifiable from the resources panel.

[Tarmenius]

You're absolutely right, my mistake I suppose that explains my difficulty in achieving orbit with the extra 0.7t.

So let's go with your suggestion of the Avionics Package with 4x Z-100 batteries.

[Nao]

Gais why not Zoidb... why not use two Z-1k batteries (the 1m circular ones)? Each one have half mass of old ASAS. So the rocket looks almost the same, have the same mass and drag. And command pod is already SAS-equipped, so there is no need for the cone i think.

Using the same profile as previous record, just little different late ascent corrections (keeping it a little more close to velocity vector this time).

Cheers!

edit: having Pe of 73,895 bothered me a little so i finished the flight properly and replaced the picture.

edit2: 16,86 litres to 74x74 orbit still within the rules What does Tarmenius will do about this, see in the next episode of the Game of ascents!

Edited July 29, 2013 by Nao

[numerobis]

Why aren't your liquid fuel and oxidizer balanced?

[tavert]

Why aren't your liquid fuel and oxidizer balanced?

I was wondering that same thing... just hit me. Nao must've burnt off about 19.6 units of oxidizer to save weight before he started. Disable liquid fuel on both tanks, enable engine, throttle up until you get rid of however much oxidizer you want. Sneaky.

Gais why not Zoidb... why not use two Z-1k batteries (the 1m circular ones)? Each one have half mass of old ASAS. So the rocket looks almost the same, have the same mass and drag. And command pod is already SAS-equipped, so there is no need for the cone i think.

Also d'oh, forgot that they changed the mass of the inline batteries, that does look better and I think you're right that the avionics package is useless now (haven't read through the thread with that title though, conclusions may differ there?).

Edited July 29, 2013 by tavert

[Tarmenius]

Hmm, I hadn't considered that the Avionics Package might now be useless with all pods having SAS built in. If the rocket flies fine manually without it, I'll switch to Nao's recommended configuration as it does look better and simpler.

Sneaky.

Quite sneaky indeed. Bravo, Nao!

[numerobis]

Could have saved another 5 kg by venting that last unit before liftoff!

[Nao]

Could have saved another 5 kg by venting that last unit before liftoff!

Yup, but here is the problem, the amount of launching to get "perfect" flight is much bigger if we allow burning oxidizer at launch. I'm personally ok with this but for people that just want to try their launch profile against others it creates unnecessary blur on performance based on how much gamble you will do with the oxidizer. So maybe another leaderboard for people who want (and have time) to minmax

Also a food for thought. At 10l of fuel this craft's 0,01 liters of fuel is worth 0,124m/s Dv and that is 73m difference in orbit height (for circular orbits), so if somebody got 74,3 x 74,4 , compared to 74x74 thats worth ~0,05 litres (which is around half of what currently separates top two spots).

edit: ARGH why does i find all mistakes after i post and not before >_< (cleared some math as i counted oxy and fuel together)

Edited July 30, 2013 by Nao

[tavert]

Yup, but here is the problem, the amount of launching to get "perfect" flight is much bigger if we allow burning oxidizer at launch. I'm personally ok with this but for people that just want to try their launch profile against others it creates unnecessary blur on performance based on how much gamble you will do with the oxidizer. So maybe another leaderboard for people who want (and have time) to minmax

Or just change the scoring to be based on fuel plus oxidizer, to avoid the unintentional loophole.

[Nao]

Oh yeah they weight the same per liter so this should be foul proof, good catch. Current scores can be easily converted too (multiplied by 2,2(2)).

[Tarmenius]

If there is going to be a new design and new scoring implemented with a new scoreboard (which I agree there should be, of course), it may warrant creating a whole new challenge. And, I've been thinking about how different the ascent profile would be for a more massive (yet still simple) craft, so this could be a good opportunity for that. Perhaps a two-stage rocket of some sort, or a single-stage using the larger tanks.

If that sounds interesting to anyone, I'd be glad to make a new challenge. This one has been pretty fun.

[PakledHostage]

If that sounds interesting to anyone, I'd be glad to make a new challenge. This one has been pretty fun.

Sounds like an interesting idea. Especially the idea of a two stage rocket. It would be fun to see how different the optimal ascent profile is, if at all.

[Tarmenius]

Well, it's a good thing I have tomorrow off. I'll be playing around with a couple designs to see if I can make something worth using in the potential new challenge. If anyone has a suggestion on that, I'm all ears

[numerobis]

A brief report on my mechjeb modding: I coded up the following set of rules:

- vertical at terminal velocity until 3 km

Then:

- net vertical thrust must be non-negative (taking into account engines, drag, gravity, and centrifugal effects)

- gravity loss must exceed drag loss

- maximize thrust

Unfortunately this is unstable: the rocket ping-pongs between going up and going sideways. As a result, according to MechJeb I have 150 m/s of steering loss and the rocket doesn't make orbit. Obviously, I'll need to work something smarter out.

Perhaps I should code up the Naojectory with "limit to terminal velocity" actually doing what it says, and see how well that does.

[Goozeman]

Here's my entry. Score is 9.05mt. I manually controlled the throttle and used the Smart A.S.S. to control orientation.

[Tarmenius]

Here's my entry. Score is 9.05mt.

Congratulations on completing the challenge! The score is 4.07, though since I didn't institute a new scoring system with the update to 0.21.

Once mid-terms are over (tomorrow!) and I can take a breather, there will be a new challenge with a new craft and method of scoring, so keep an eye out for that.