Optimal Ascent Profile for this spacecraft

[PakledHostage]

Certainly everyone who\'s played KSP for a while has, at some time, wondered how efficiently they\'re reaching orbit. You too must have wondered: 'Could I use less fuel if I pitched over sooner or later than I normally do?', or 'What if I modulated my throttle on the way to orbit?'

And while the optimal ascent profile differs from rocket design to rocket design, I\'d like to propose an efficiency challenge where we compare apples to apples. Maybe we’ll all learn something? We certainly all learned a lot from Closette’s max Altitude with this supplied spacecraft challenge.

This is what I came up with:

Reach a 75.5 km (± 0.5 km) circular orbit with this spacecraft, using minimal fuel

Method

- Build a stock rocket using a MK-1 pod, ASAS, 3 liquid fuel tanks, 4 AV-R8 winglets and an LV-T30 liquid fuel engine.

- Launch into a 75.5 km altitude (± 0.5 km) circular orbit

- After reaching orbit, right-click on the lowest tank in the stack to bring up a window showing how much fuel you\'ve got left.

- Post a screenshot showing your craft in orbit, with the fuel quantity window showing.

Mods: None

Restrictions: We’ll need to have two categories – MechJeb assisted and pure stock.

Craft File: The .craft file is attached to this post.

Please describe your method of reaching orbit along with your entry.

LEADERBOARD (Unassisted)

1. jqhullekes - 89.5 kg remaining (Delta-V expended: ~4340 m/s)

2. tjoreilly - 89.4 kg remaining (Delta-V expended: ~4340 m/s)

3. Tarmenius - 88.7 kg remaining (Delta-V expended: ~4343 m/s)

4. PakledHostage - 84.2 kg remaining (Delta-V expended: ~4364 m/s)

5. Closette - 82.1 kg remaining (Delta-V expended: ~4374 m/s)

6.

7.

8.

9.

10.

LEADERBOARD (MechJeb Assited)¹

1. stucker - 87.3 kg remaining (Delta-V expended: ~4350 m/s)

2. Cryphonus - 85.5 kg remaining (Delta-V expended: ~4358 m/s)

3. Tarmenius - 85.1 kg remaining (Delta-V expended: ~4360 m/s)

4. Zephram Kerman - 84.7 kg remaining (Delta-V expended: ~4362 m/s)

5. Cruisix - 71.4 kg remaining (Delta-V expended: ~4424 m/s)

6.

7.

8.

9.

10.

¹ There is already a similar challenge to this one for pilots who prefer to use MechJeb, but I\'m including a category here in case anyone wants to submit an entry.

[infatuatedPP]

Definitively going to try this.

One question I have is why should we go to the quicksave.sfs when you can right click the fuel tank and the game will tell you how much fuel is left? People can post screens of this for proof.

[PakledHostage]

One question I have is why should we go to the quicksave.sfs when you can right click the fuel tank and the game will tell you how much fuel is left? People can post screens of this for proof.

Because I didn\'t know you could do that! Thanks for the heads up. I\'ll modify my post.

[closette]

I think there was a similar challenge last month for the smallest delta-v to orbit for a given spacecraft but I cannot find it - found it!

http://kerbalspaceprogram.com/forum/index.php?topic=11132.msg170932#msg170932

But the more of these the better!

Since there are no or few takers yet, might I humbly suggest using a spacecraft with an ASAS and some fins so that challengers can exercise smoother control over the flight? They could replace the parachute and stack decoupler. (Very humane - or kerbale - for you to include them, but not necessary). That way we are comparing strategy and not so much piloting skills.

Also, this set-up requires pretty much 100% throttle all the time for fuel efficiency (except when coasting), particularly for the vertical ascent. That should be OK though if it\'s just the pitch angle vs. time that you want to explore.

P.S. Mac users don\'t have a right-click button and the usual trick of pressing CTRL-click does not work - anyone know how to pull up tank fuel status on a Mac? (Mousing over the tank still highlights it).

[PakledHostage]

I think there was a similar challenge last month for the smallest delta-v to orbit for a given spacecraft but I cannot find it - found it!

I obviously missed that one... But it seems to be a MechJeb only challenge.

I\'ll leave this challenge up for a bit though in case someone wants to take it on.

I think testing this configuration has value because it seeks insight into the Ascent paths discussion currently going on over in the general discussion area. Presumably it isolates the variable of pitchover altitude, but I could turn out to be wrong.

If anyone wants to suggest an alternate test configuration, please feel free.

[closette]

Well it\'s a slow day - happy Father\'s Day in the USA - but I think this is a great challenge.

In fact 'crowd sourcing' might be one of the better ways to find an optimum ascent path. ESA tried this once a few years ago for one of their proposed interplanetary missions (using a weak stability boundary transfer).

I feel I\'m being presumptious since it\'s your challenge, but I propose we use the spacecraft attached, which consists of a pod, ASAS, 3 tanks, 4 AV R-8 winglets:

- 0.13.3 compatible so more people can use it (I think - someone please test this)

- an ASAS module and 4 AV R-8 winglets for stability and control. I tried using 3 winglets, but that caused 'adverse roll' when pitching over at 90^o.

- no decoupler or parachute, sorry guys!

I gave this craft a whirl (and ended up in a way-too-high orbit) but a nice feature is that 100% throttle results in -close-to-optimal vertical ascent below 12 km, so the challenge should be more about pitchover strategy not throttle control.

If you like it, you could copy the .craft file to the first post in the thread for others to use.

[PakledHostage]

I feel I\'m being presumptious since it\'s your challenge, but I propose we use the spacecraft attached, which consists of a pod, ASAS, 3 tanks, 4 AV R-8 winglets:

No problem. Let\'s sacrifice some Kerbals for science!

I\'ve updated the challenge above to use your design and I\'ve flown one attempt myself. That effort reached a 75.3 km x 75.7 km orbit with 84.2 kg of fuel remaining. It did not use MechJeb.

I\'m interested to see what can be done with this configuration, both with and without MechJeb!

Prior to launch, I switched to “orbital speed mode†on the navball by clicking on the speed readout. The prograde reticle then showed the orbital velocity vector rather than the “surface†velocity vector.

After launching, I climbed vertically at 100% throttle until the prograde reticle was centred on the navball’s 60 degrees latitude line. I then pitched over and performed a gravity turn, still buring at 100% throttle.

MECO1 occurred when my apoapsis reached 75 km in the map view.

Orbit insertion burn was completed at close to 100% throttle, but a few trim manoeuvres were also required to circularise my orbit.

[closette]

Will try myself later tonight, but you\'ve set a good standard. Thanks for updating the challenge with my design, let\'s hope you get more takers in the coming week.

[jqhullekes]

My best attempt so far (75.4kg) - no MechJeb

[closette]

My best attempt: 77.07128 kg remaining after a 77 x 78 km altitude orbit. I don\'t know how to pull up the fuel tank state on a Mac (no right-click) so cannot prove it, unfortunately! (I got the data from the quicksave file, however anyone could edit that so it\'s not good proof).

http://i50.tinypic.com/3583mki.jpg]

Strategy (all at 100% thrust): vertical ascent to about 12 km altitude, switched the Navball to 'orbit' mode, then pitched over to match the velocity and heading vectors. Kept pitching over in a gravity turn until apoapsis reached about 75 km, then MECO, followed by coast to just before apoapsis, and a final prograde boost to circularize.

[jqhullekes]

My new personal record: 81.2kg - no MechJeb

75.4 x 75.3 km

What I did: I went straight up (with SAS on) until reaching 110 m/s. Then I turned off the SAS and hit the D key very shortly and when my heading 'hit' the right side of the yellow circle, I turned on SAS again (this all happens in like less than a second). Waited until I was in the middle of the yellow circle again, and turned off SAS. So just a tiny turn.

Did almost nothing after that steering wise (this is key I think): Newton at the steering wheel... just made sure I kept right in the middle of the yellow circle (which it does naturally with the fins attached in atmoshpere).

When looking at the Map view, I stopped the engines (with X) at the moment my apogee hit 75km. Then did a burn just before apogee until had a mostly circular orbit.

PS. actually I had 82.6kg, but I overshot and had to do a small retrograde burn.

PPS. I do use the normal surface speed indicator in the beginning

[PakledHostage]

My new personal record: 81.2kg - no MechJeb

75.4 x 75.3 km

Nice job! I\'ll update the leader board. I guess that means you started your pitchover manoeuvre at about 1500-2000 m?

I started mine at what works out to about 11000 m. I also tried pitching over to start a gravity turn at relatively low altitude (~5000 m) and pitching over very high (~30000 m). The 5000 m test got me close to your result while the 30000m test failed to even reach orbit.

There\'s an optimal pitchover altitude/angle between those extremes; I suspect we can get close to it by experimenting.

[jqhullekes]

New personal best 82.8kg - no MechJeb

76.1 x 76.3 km

I also think that it is not the height that really matters at which point you do you initial turn, but much more the rate at which you turn. And I think it\'s best to start turning as soon as you can, but at exactly the right rate. This is tricky: the lower you are the harder it is to make the exact right turn.

I found that if I am at 80 degrees (I mean the white circles in the blue ball) I should be at around 200 m/s and at 70 degrees I should be at around 300 m/s (surface speed that is). This is close to the right rate, but this is the part I am experimenting with. Tricky, since you can\'t really reliably set your rate. And you shouldn\'t adjust it too much later on, because that doesn\'t really work, and costs fuel.

So I think the question is: at what angle are you at what (surface) speed?

I also want to try the oribital indicator in the beginning, maybe that will help a bit.

[closette]

I just did a 75 x 79km orbit with 78.07175 kg remaining, slightly better than I could do before.

For me, the I let the 'pitchover rate' be determined by the gravity turn, chasing the yellow ball from it\'s 'orbit' position. So I have been trying to optimize the start altitude of the gravity turn, and I\'m finding it\'s somewhere between 11 km and 15 km.

A close-to-optimal ascent 'feels' different from the ones which don\'t work out well, hard to explain. Even though (unlike real world rockets) we are not constrained to small angles between heading and velocity, it seems to make sense that lining up both of them will maximize the conversion of delta-v into kinetic energy.

However, the few times I have used MechJeb I was surprised to learn how small the 'steering losses' are when compared to gravity and drag. Therefore a pure gravity turn may not be optimal in this case.

*EDIT* Sorry guys I\'m an idiot - I read the challenge as requiring a 75 +/- 5 km orbit, not +/- 0.5km as clearly stated. So I would have spent a little more fuel in a circularization burn. I guess I was just happy to reach any kind of decent orbit!

[Tarmenius]

I decided to give this a shot merely as a learning exercise for myself, but was fairly surprised at the result I ended up with. I put the ship in a 75.3km x 77.7km orbit with 81.2kg of fuel remaining (no mech-jeb). I started pitching over to +80deg at about 8000m, hit +45deg around 20000m and +30deg at 30000. At MECO, I was heading at +20deg with an Ap of about 76km, so as I coasted through the rest of upper atmosphere, my Ap settled to the target altitude. Then I circularized as normal, reducing thrust to keep my Ap just in front of the ship. I use this process for almost every rocket I fly, but I never bothered to test how efficient it actually is. Thanks for putting up this challenge, PackledHostage.

[Edit]: Second attempt with the same profile yielded almost identical results (go figure). Seems to be a pretty easily repeatable profile in case anyone else wants to use it.

[jqhullekes]

New record 86.0kg - no MechJeb

75.8 x 75.6 km

I did almost the same: at 110 m/s I did a small turn, left it flying without SAS. But now I switched to 'orbit speed mode indication' and with several presses on \'D\' (every few seconds) I moved my direction closer to the yellow circle until I was in the middle of it. Then stopped the enigines when apo reached 75 km, and circularized my orbit just before reaching apo. Had to retro burn a tiny bit, but it cost almost no fuel.

[jqhullekes]

I really wonder now: will anyone try this with MechJeb to see how it does against our humans (who really want to be Kerbals anyway)...

[Phoenix Aerospace]

I don\'t know how to pull up the fuel tank state on a Mac (no right-click) so cannot prove it, unfortunately!

The Magic Mouse has support for right-clicking, but if you\'re not using one, press Ctrl/Command + Click.

[Tarmenius]

jqhullekes, I was wondering the same thing. I was so curious that I decided to get MechJeb for the first time and try it out. I simply slapped on the case, keeping the stock ASAS since I don\'t know if MechJeb has any mass (1E-05 could mean anything to me), and programmed the Auto Ascent for 75.5km. If any one else is curious as well, here\'s the profile it used:

Initial pitch-over to 60deg at 10000m. It held there until about 18000m when it began to pitch again to 50 deg by 20000m. From there it was a steady, incremental series of pitch changes passing 45deg at 23000m, 40deg at 25000m. Then it paused for a moment before a major pitch change to 20deg at 30000m followed by another set of incremental changes to 20deg by 33000m and finally 15deg by 35000m. After that, it coasted to Apoapsis then circularized. When all was said and done, the remaining fuel was 81.8kg.

Pretty interesting though jqhullekes and PackledHostage proved that it isn\'t quite the most efficient path.

[jqhullekes]

jqhullekes, I was wondering the same thing. I was so curious that I decided to get MechJeb for the first time and try it out. I simply slapped on the case, keeping the stock ASAS since I don\'t know if MechJeb has any mass (1E-05 could mean anything to me), and programmed the Auto Ascent for 75.5km. If any one else is curious as well, here\'s the profile it used:

Initial pitch-over to 60deg at 10000m. It held there until about 18000m when it began to pitch again to 50 deg by 20000m. From there it was a steady, incremental series of pitch changes passing 45deg at 23000m, 40deg at 25000m. Then it paused for a moment before a major pitch change to 20deg at 30000m followed by another set of incremental changes to 20deg by 33000m and finally 15deg by 35000m. After that, it coasted to Apoapsis then circularized. When all was said and done, the remaining fuel was 81.8kg.

Pretty interesting though jqhullekes and PackledHostage proved that it isn\'t quite the most efficient path.

Very interesting indeed. Have you tried other profiles?

[Tarmenius]

Yes, I tried a couple others. I used the same pitch angles (80, 60, 45, 30, 20), but reached them at different altitudes. I tried 6km, 10km, 15km, 20km, 30km respectively for a more shallow ascent ending up with around 45kg remaining fuel. Then I tried higher altitudes. When I hit them at 13km, 20km, 30km, 35km, I had to leave out the 20deg pitch mark because my Ap had already reached 75km. That produced better results than the shallow ascent, but with 77kg remaining fuel it still wasn\'t as efficient.

My next trial will use my original profile with MechJeb along for the Ascent Stats so I can see how much I lose to the various competing forces. I suspect I\'ll lose less turning late than I would fighting atmosphere early, but the real trick will be finding out where each are minimized then aiming for something in the middle to get the best net reduction. If I remember correctly, you and PackledHostage both pitched to 80deg early on and made a slow turn later; is that right? If so, it\'s a profile I\'ll have to try out and see if I can come up with similar results.

[Zephram Kerman]

Here\'s my entry: 83.1 kg (dV=4369 m/s), using MechJeb to do a shallow gravity turn starting at 12 km.

I experimented with different profiles by clicking the \'edit path\' button and adjusting the \'turn start\' altitude and \'turn shape\' slider. Here\'s the data:

Fuel Remaining (kg) After Various Gravity Turns

[table]

[tr]

[td]

slider position (%)

25 (shallow)

50 (standard)

75 (steep)[/td]

[td]turn start (km)

8 10 12

65.6 kg 83.0 83.1

75.6 71.2 65.6

42.3 36.9 31.2

[/td]

[/tr]

[/table]

The results varied wildly! I should collect more data between these points to better spot the trend. But it\'s getting late for today. At the moment, my gut says we\'ll find the \'sweet spot\' where gravity drag and air drag are in balance. Perhaps we\'ll find out tomorrow.

[jqhullekes]

Here\'s my entry: 83.1 kg (dV=4369 m/s), using MechJeb to do a shallow gravity turn starting at 12 km.

I experimented with different profiles by clicking the \'edit path\' button and adjusting the \'turn start\' altitude and \'turn shape\' slider. Here\'s the data:

Fuel Remaining (kg) After Various Gravity Turns

[table]

[tr]

[td]

slider position (%)

25 (shallow)

50 (standard)

75 (steep)[/td]

[td]turn start (km)

8 10 12

65.6 kg 83.0 83.1

75.6 71.2 65.6

42.3 36.9 31.2

[/td]

[/tr]

[/table]

The results varied wildly! I should collect more data between these points to better spot the trend. But it\'s getting late for today. At the moment, my gut says we\'ll find the \'sweet spot\' where gravity drag and air drag are in balance. Perhaps we\'ll find out tomorrow.

I would be really interested in the 2,4 and 6 km turn start. Since this is what I do myself manually. And I think a steep profile would work best in such cases. Because going 12km straight up and then shallow is actually almost equivalent with a 2km straight up and then steep.

[Tarmenius]

So, I messed around with various profile configurations using MechJeb and the best I came up with had 85.1kg remaining fuel. That profile was damn close to my original one but with a sharper turn around 25km: 70deg @ 8km, 60deg @ 15km, 45deg @21km, 30deg @ 28km and 25deg @ 32km. Gravity Losses were 1426 m/s (32.7%); Drag Losses were 826 m/s (18.9%); and Steering Losses were 33 m/s (0.8%).

From there, I tweaked the Turn Start Altitude alone to see the effects it would have. Lowering the TSA resulted in greater Drag and Steering Losses with lesser Gravity Losses. Unfortunately, the lesser Gravity Losses were not enough to make up for the greater Drag and Steering Losses. Raising the TSA resulted in lesser Drag Losses, but greater Steering and Gravity Losses making another net increase in fuel consumption.

Then I tried mixing it up a bit. Lower the TSA, but make a steeper ascent profile. Raise the TSA, but make a more shallow profile. Nothing worked. The closest I got in those attempts had a remaining fuel level of 80.6 kg. For the most part though, I got similar results as Zephram Kerman did on his trials. At this point, I think I\'m at the limit of what I can accomplish with MechJeb\'s settings as they are now. If I could some how program various degrees in pitch to correspond to various altitudes, then I could probably engineer more definitive results. But with the slider not having values assigned to its position I feel like I\'m working in the dark. Of course, I could be just missing something as I haven\'t even had MechJeb for a whole day yet.

[Zephram Kerman]

Finally! Collected a bunch of data points, using two of MechJeb\'s ascent profile settings. Lots of data, so I made a graph.

Sorry jqhullekes, but it turns out the right side of the \'Turn Shape\' slider is toxic! (Basically, as the slider gets moved to the right, for steeper angles, the graph peaks move left towards ground level and below it.) On the other hand, if your manual curve shape works better than MechJeb\'s, it might be just fine.

The best shape for MechJeb seems to be around 1/3 from the left. With this setting, and a \'Turn Start\' altitude of 9 km, my best run was 84.7 kg fuel remaining.