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Pds314

Equatorial Orbit [From The Poles]

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Posted (edited)

Very simple challenge, go to an equatorial LKO (inclination under 2 degrees in the advanced info on the maneuver tab), starting at 90 or -90 degrees latitude using set position in the 1.9 alt-f12 menu. Final Apokee and Perikee must be between 70 and 150 km.

After reaching orbit, don't reenter the atmosphere. No aerobraking.

 

No jet engines,  nukes, ions, or props, no ISRU. Only chemical rockets. Try to do it with as good a payload fraction as possible.

Entries:

1. Laie: 6.00% payload in a Wolfhound and Vector design with 20 T to orbit in a 334 T vehicle using a direct burnAs they have deemed Wolfhound "pay to win," I will accept competitors to this entry with CFG editing similar-sized engines to match the publicly available specs of a Wolfhound. But it must match all aspects. Mass, thrust, ISP at sea level. ISP in a vacuum, etc.

2. EveMaster: 3.36% payload. Flew down to the equator on rocket thrust and used wings to turn the trajectory. 19.2 tonnes to orbit on a 571 tonne vehicle.

 

Edited by Pds314

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Posted (edited)

Can we get a definition of what counts as LKO, please? Specifically, what's the highest allowed apoapsis?

I ask because I'm pretty sure the way to do this with minimal delta-v is either with a bi-elliptic transfer or a gravity assist off the Mun or Minmus — both of which will first put you into a highly eccentric equatorial orbit that you then need to circularize with a retrograde burn at periapsis, and the shorter that burn can be, the less delta-v you'll need.

(Also, is using 1.8 + HyperEdit / VesselMover allowed?)

Edited by vyznev

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48 minutes ago, vyznev said:

Can we get a definition of what counts as LKO, please? Specifically, what's the highest allowed apoapsis?

I ask because I'm pretty sure the way to do this with minimal delta-v is either with a bi-elliptic transfer or a gravity assist off the Mun or Minmus — both of which will first put you into a highly eccentric equatorial orbit that you then need to circularize with a retrograde burn at periapsis, and the shorter that burn can be, the less delta-v you'll need.

You can aerobrake to circularize at your leisure with negligible dV. @Pds314 might want to specify that you cannot re-enter the atmosphere after leaving it.

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27 minutes ago, sevenperforce said:

You can aerobrake to circularize at your leisure with negligible dV. @Pds314 might want to specify that you cannot re-enter the atmosphere after leaving it.

Good point. I'm more used to doing these kinds of maneuvers around airless moons, where that's more difficult. :D

Anyway, whether aerobraking is allowed or not, I'd still like to see an altitude limit of some kind. I guess something like "periapsis > 70 km, apoapsis < 250 km" (which matches the in-game definition of "in space low over Kerbin") would make a reasonable default if you don't want to be stricter.

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Posted (edited)

Right.

Aerobraking will not be allowed.

Both Apoapsis and Periapsis will be limited to 70km <Ap/Pe< 150 km.

 

Edit: decided there's no balanced way to allow aerobraking.

Edited by Pds314

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Can we use Mun or Minmus for gravity assists? Can we leave Kerbin's SOI?

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While we are clarifying rules, forgive me if there is a standard convention for this as I've never done a payload challenge, but what exactly counts as payload? Can any of the following parts be counted as payload if they assist in getting to orbit: engines, fuel tanks, command modules, SAS, fairings? Does the payload have to separate?

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On 5/23/2020 at 2:16 PM, Pds314 said:

After reaching orbit, don't reenter the atmosphere. No aerobraking.

Technically, I could do a bielliptic plane change followed by aerobraking without ever raising my periapsis above 70 km. But I guess the second part rules that out. :wink:

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On 5/23/2020 at 5:50 PM, Superfluous J said:

Can we use Mun or Minmus for gravity assists? Can we leave Kerbin's SOI?

Yes you can, and yes you can. I don't entirely see what that gets you though, considering if you're doing bi-elliptic at the edge of Kerbin's SOI it costs almost nothing to do the actual plane change.

I will make one more rule though. Please don't use ISRU xD.

Edited by Pds314

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45 minutes ago, Pds314 said:

Yes you can, and yes you can. I don't entirely see what that gets you though, considering if you're doing bi-elliptic at the edge of Kerbin's SOI it costs almost nothing to do the actual plane change.

I agree with you about leaving Kerbin's SOI, but I figured I'd cover all bases while I was thinking of using Mun to get the plane change for free without going up to the far edge of Kerbin's SOI.

I don't think it'll save a lot, and may require more fuel than it saves. But I want to try it :D

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On 5/24/2020 at 4:03 AM, bayesian_acolyte said:

While we are clarifying rules, forgive me if there is a standard convention for this as I've never done a payload challenge, but what exactly counts as payload? Can any of the following parts be counted as payload if they assist in getting to orbit: engines, fuel tanks, command modules, SAS, fairings? Does the payload have to separate?

Payload is considered separated and not a functional part of the rocket. You may however have reaction wheel torque from cockpits or probe cores, electricity generation, and control systems in your payload, as any practical stock payload would likely have these. A big pile of dedicated reaction wheels is not payload though. In general, if I couldn't substitute your payload for one that's the same shape, size, and mass, but functionally very different, that's not really payload.

Edited by Pds314

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I managed to get a payload fraction of 3.36%. Total launch mass 570.626tons, payload 19.2t.

My craft has just one Mammoth engine and 4 SRB for increased TWR at takeoff.

I stay in the atmosphere until close to the equator and then use aerodynamical lift to turn 90 degrees.

My flying was far from perfect. I slowed down considerably when doing the turn. But I had just enough fuel left to speed up again and reach a low equatorial orbit.

Spoiler

XGo29K8.jpg

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jBS7aUC.jpg

 

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4 hours ago, EveMaster said:

I managed to get a payload fraction of 3.36%. Total launch mass 570.626tons, payload 19.2t.

My craft has just one Mammoth engine and 4 SRB for increased TWR at takeoff.

I stay in the atmosphere until close to the equator and then use aerodynamical lift to turn 90 degrees.

My flying was far from perfect. I slowed down considerably when doing the turn. But I had just enough fuel left to speed up again and reach a low equatorial orbit.

  Hide contents

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ucLgyLr.jpg

8leG8Kk.jpg

jBS7aUC.jpg

 

Very interesting approach. Basically the world's longest dogleg maneuver! 3.36% Payload is basically real life numbers.

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I'm not too happy about that "payload fraction" thing: once more we have a challenge that favors Vectors and Wolfhounds, the latter being pay-to-win. But anyway, here's my approach:

pole2eq1-140.jpgpole2eq1-144.jpg

pole2eq1-147.jpgpole2eq1-148.jpg

pole2eq1-150.jpgpole2eq1-152.jpg

Launched into a rather high, lopsided orbit, not caring too much about the details as long as it seems that it will take me well over the equator. Then I turned left, 55° NE on the compass, and just kept going. A bit of pitch was added as necessary to keep the climb (or rather, descent) rate within acceptable limits. PE was below the surface to begin with and dropped further at first, I didn't reach an workable orbit until I was well past the equator. At that point I still had a 16° inclination, that was trivially fixed with a normal maneuver.

pole2eq1-154.jpgpole2eq1-155.jpg

Decoupled payload of exactly 20t, final orbit shows 0.0° inclination. With a takeoff mass a little shy of 333t, that resolves to a payload fraction of slightly more than 6%.

 

 

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1 hour ago, Laie said:

I'm not too happy about that "payload fraction" thing: once more we have a challenge that favors Vectors and Wolfhounds, the latter being pay-to-win. But anyway, here's my approach:

pole2eq1-140.jpgpole2eq1-144.jpg

pole2eq1-147.jpgpole2eq1-148.jpg

pole2eq1-150.jpgpole2eq1-152.jpg

Launched into a rather high, lopsided orbit, not caring too much about the details as long as it seems that it will take me well over the equator. Then I turned left, 55° NE on the compass, and just kept going. A bit of pitch was added as necessary to keep the climb (or rather, descent) rate within acceptable limits. PE was below the surface to begin with and dropped further at first, I didn't reach an workable orbit until I was well past the equator. At that point I still had a 16° inclination, that was trivially fixed with a normal maneuver.

pole2eq1-154.jpgpole2eq1-155.jpg

Decoupled payload of exactly 20t, final orbit shows 0.0° inclination. With a takeoff mass a little shy of 333t, that resolves to a payload fraction of slightly more than 6%.

 

 

Wow. And it's a direct approach too.

 

If someone wants to CFG edit something to match the exact specs of a Wolfhound because they don't have DLC, and that thing is similar in size to a Wolfhound (i.e. a 1.25m nozzle), I will let them do so, that way it's less pay to win.

Edited by Pds314

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Is it allowed to temporarily go above 150km?

I tried to to into a low polar orbit, then raise the apoapsis to 10000km turn the orbit by 90 degrees and lower the apoapsis back to 150km using rocket thrust (no aerobraking). Using this maneuver left me with 12tons of spare fuel. So it was much more efficient than the approach I posted with turning within the atmosphere.

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15 hours ago, EveMaster said:

Is it allowed to temporarily go above 150km?

I tried to to into a low polar orbit, then raise the apoapsis to 10000km turn the orbit by 90 degrees and lower the apoapsis back to 150km using rocket thrust (no aerobraking). Using this maneuver left me with 12tons of spare fuel. So it was much more efficient than the approach I posted with turning within the atmosphere.

Yes you can definitely go past 150 km. Your final orbit needs to be inside 150 km.

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I optimized my launcher and managed to achieve a payload fraction of just above 10.00%. Total mass: 519.485 tons. Payload: 51.950 tons. No turning inside the atmosphere this time, but multiple mun assists. The mun assists were necessary, otherwise about 200m/s would have been missing. Engines used are one mammoth engine, a poodle engine and 4 long, sleek SRBS.

VEVc5p6.jpg

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Gallery with mission decription: https://imgur.com/gallery/1DFwaAi

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All right, here we go.

screenshot171.png

276.1 tonnes on the pad. Rhino and asparagus-staged Vectors for the first stage. All biprop liquid fuel.

Here we are at our launch point:

screenshot117.pngscreenshot116.png
 

Spoiler

screenshot118.png

Liftoff

screenshot119.png

Almost an immediate gravity turn. Very high TWR at liftoff. Perhaps too high, but oh well.

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First parallel stages dropped.

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Supersonic less than two minutes into flight.

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Second set of parallel stages dropped.

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Surface heating, nosing over, approaching third staging event.

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Goodbye Vectors. By now the Rhino is burning at nearly full Isp.

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A little inefficiency here as I have to nose below prograde to keep the trajectory depressed.

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Approaching Rhino burnout.

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Several things happening at once here. We have separation of the Rhino stage and explosive deployment of the fairing in six pieces. Note the extra tank tucked inside the fairing. Six Terriers ignite around a single Wolfhound. The Terriers are there to nudge up the TWR so I can do this properly.

screenshot136.png

All the decouplers from this point on are set to crossfeed so the Wolfhound is drawing from the lower tanks.

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We are not actually that close to orbit, all things considered.

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The Terriers are out of fuel so they are staged off, dropping TWR extremely low.

screenshot140.png

The Wolfhound is going to do the rest of the work. At this point we have a suborbital trajectory, but one suitable for our first burn to bi-elliptic transfer.

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Here's that burn setup. 

screenshot144.png

Burn started. One of the trick with using the Wolfhound in a challenge like this is to give it enough of a payload to actually utilize. If you are using a payload of 10-15 tonnes then you are better off using a Spark or Terrier or something as your final stage despite the Wolfhound's impressive specific impulse.

screenshot145.png

Still burning to transfer.

screenshot147.png

Performing this burn at just 60 km gave me a bit more efficiency than I otherwise would have gotten. 

I toyed with the idea of doing the entire mission with a suborbital periapsis and claiming that since I had "never entered orbit" that I was justified in aerobraking, but I am not a jerk.

screenshot149.png

Staging off the toroidal tank.

screenshot150.png

You can now see three pairs of drop tanks tucked between the Wolfhound and the base of the main tank.

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First drop tanks away.

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Transfer burn complete and we are jettisoning our second set of tanks.

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Plotting the second burn.

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Closer view of the drop tanks.

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Burn completed!

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Now we just have to circularize.

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Final tanks dropped.

screenshot164.png

At this point I've actually lowered my periapsis rather dangerously, so I'm going to warp around and raise it.

screenshot165.png

Preparing to raise periapsis. Nearly bingo on fuel.

AAAAAAND here we have it:

screenshot166.png
screenshot167.png
 

 

Final payload separation:

screenshot168.pngscreenshot169.png

33.41 tonnes to an equatorial Kerbin orbit with a 276.1-tonne launcher for a payload fraction of 12.1% with no gravity assists.

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2 hours ago, sevenperforce said:

33.41 tonnes to an equatorial Kerbin orbit with a 276.1-tonne launcher for a payload fraction of 12.1% with no gravity assists.

Impressive! I did not know that a fairing could be part of your payload. But even if I did and if I counted my spare fuel as a payload I might have reached 10.3%, still quite some difference to your submission.

What ascent profile and inclination correction maneuvers did you use?

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3 hours ago, EveMaster said:

Impressive! I did not know that a fairing could be part of your payload. But even if I did and if I counted my spare fuel as a payload I might have reached 10.3%, still quite some difference to your submission.

What ascent profile and inclination correction maneuvers did you use?

I could have blown the fairing on ascent, which would have decreased my payload mass but also decreased my propellant usage; I would have to just go back and design with less propellant. Figured it didn't hurt anything to keep it.

As far as ascent profile -- I wanted to use the Wolfhound for as much as I could, which meant I needed to get suborbital as quickly as possible. So I was very, very  thrusty off the ground...well over two gees, I think. Like I said above, the Wolfhound is quite heavy, which means it needs a large payload or it's a waste of the dry mass. It's also not very thrusty. I also wanted to do my first transfer burn as low as possible since I was planning on going all the way to the edge of Kerbin's SOI. This meant I needed to nose over almost immediately. I actually reached an in-atmo orbit (periapsis and apoapsis both greater than 0) on ascent.

I used the Mun as a target to figure out where to put my node for the first transfer burn. It took four burns. My ascent gave me an apoapsis just outside of the atmosphere and right above the equator. The second burn was a transfer to the edge of the SOI. The third was the plane change, which was just 56 m/s at that altitude. The fourth was a retrograde burn at periapsis to bring my apoapsis all the way back down under 150 km. I did have to do a small correction to bring my periapsis up at one point.

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