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Reach for orbit with an ion glider!

zarakon
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O-Doc

O-Doc

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The question: Is it now possible to reach Kerbin orbit using the ion engine alone?

The answer: TWR on runway must the over 0.35

I see gamerpuppy has made it into orbit too and with a similar set of parts as myself. That's pretty obvious as there are very few parts combinations that are viable with a single ion engine. Every fraction of a ton matters. The experience was very different to an air-breathing SSTO which loses TWR as you climb. This one does the opposite!

JM43emJ.jpg

Download the craft.

OK, reading the rules again, I could have done the insertion burn earlier if I wanted to be competitive. The 50min is going to look pretty standard unless you go for a battery hog. I would have ranked on remaining delta-V myself.

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Ziv

Ziv

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after a lot of experiments finally I made it to orbit! :)

I used some "tricks", mentioned in the image description. I'm not fully glad with the result because I used droppable fuel tanks and so this is not a true SSTO and also the in-line Ion Engines made it feel cheaty a little bit.

Also, the front-back facing solar panels doesn't give you a good aerodynamical performance (in reality, but in KSP it's okay :D) and the front part of the ship is "levitating" because the big ASAS doesn't have visible parts there... I was thinking about making it somewhat more real but it would cost too much weight, which is crucial.

Anyway, I managed to get into orbit with ion engines only so it's not so bad for the first time! :cool:

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zarakon

zarakon

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Really cool, especially the idea of turning while ascending to extend your sun time

But there seems to be an odd disconnect in your photos. At one point you're under 40km with less than 50 xenon left, then in the next photo you have over 150 xenon left at 75km and ~450m/s higher speed. Did you accidentally include some images from a failed run?

I'll try to get around to updating the leaderboard tonight or tomorrow

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Nedal

Nedal

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after a lot of experiments finally I made it to orbit! :)

Very very nice.

Some sweet designs overall in that first image. I can only imagine the painstaking placement of all those panels on the canard version. lol

Trying in FAR. So far i can make it to about mach2 at around 28km. arg. Starting to feel its impossible in FAR.

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Ziv

Ziv

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Really cool, especially the idea of turning while ascending to extend your sun time

But there seems to be an odd disconnect in your photos. At one point you're under 40km with less than 50 xenon left, then in the next photo you have over 150 xenon left at 75km and ~450m/s higher speed. Did you accidentally include some images from a failed run?

I'll try to get around to updating the leaderboard tonight or tomorrow

Yeah, you're right, I mixed up the pictures with a failed run, thanks for noticing it! I changed those two pictures to the right ones. :)

Thank you for the challenge, I really enjoy this one! I might give it an other, more clean shot. :)

May I give you an advice to link the number of the post to the names on the leaderboard? That would make it easy to see the entries to this challenge and would make it worth more. :) Also, you are invited to my Jool-5 challenge... if you have a lot of free time. :D

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donfede

donfede

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The question: Is it now possible to reach Kerbin orbit using the ion engine alone?

The answer: TWR on runway must the over 0.35

...

Can you share any math on how you came to that number O-Doc?

Thank you for posting your craft file.

EDIT: with craft analysis

Reviewing your craft, I get a TWR of 0.29 (mass of 0.702t [not including landing gear, which are mass-less in game]).

Nedal's craft appears to have 0.26 TWR (mass of 0.782t).

EDIT2: updated craft analysis

So OX-S and cubic octagonal struts are mass-less in the game, at least up to a gross. The Z-100 batteries also appear to be mass-less, which is what I expect ihtoit was referring to.

I now get 0.38 TWR on your craft, and 0.33 on Nedal's.

EDIT3: ksp wiki docs on massless parts

I was directed by xZise to the ksp wiki docs/page on massless parts. There are even more than I had expected (and I'm glad as this saves me doing more oscarb/ant tests).

http://wiki.kerbalspaceprogram.com/wiki/Massless_part

Edited by donfede
updated ksp wiki link
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Nedal

Nedal

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Ha ha ha never would have even thought a solar eclipse would be a problem XD

lol ikr?

Just flyin along for like 10damn minutes. then all of a sudden im falling out the sky.. wtf? Click pannel, 0.0 power "Blocked by mun", look up. oh good lord...

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O-Doc

O-Doc

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Can you share any math on how you came to that number O-Doc?

Thank you for posting your craft file.

EDIT: with craft analysis

Reviewing your craft, I get a TWR of 0.29 (mass of 0.702t [not including landing gear, which are mass-less in game]).

Nedal's craft appears to have 0.26 TWR (mass of 0.782t).

EDIT2: updated craft analysis

So OX-S and cubic octagonal struts are mass-less in the game, at least up to a gross. The Z-100 batteries also appear to be mass-less, which is what I expect ihtoit was referring to.

I now get 0.38 TWR on your craft, and 0.33 on Nedal's.

Dammit donfede, I'm programmer not an engineer! I don't do maths. In fact I hate maths. :D

My craft is 0.54T on the runway with 2kN of thrust. That's 0.37TWR. #@$^&! Now I'm doing maths! :sticktongue:

My approach is always SCIENCE! Test and test again. So, I used the bare minimum parts to get stable flyer into the air and see how far I could go. I took 5 tries to get the combination right.

  • Attempt 1: I used single PB-X150 and ran out of fuel at about 35km and 1.5km/s
  • Attempt 2: I added another PB-X150 but fell out of the sky after about 30min from aerodiemanic issues
  • Attempt 3: I re-organised the plane with the same fuel, did some inflight fuel re-balancing but, ran out of sunlight with a about a quarter fuel remaining but was well, well off the performance of the first run in terms of speed and altitude for fuel burnt. I think I was less than half the efficiency
  • Attempt 4: I half emptied the second fuel tank and still couldn't come close to matching the performance of the first flight. Those tanks are heavy
  • Attempt 5: I swapped out the half full PB-X150 for the PB-X50R, swapped out the OKTO prode core I was using for the OKTO2 and, with touch of inflight fuel re-balancing at the halfway point, I comfortably made it to orbit.

So, based on those tests concluding in a successful result I can pretty accurately state that a TWR of less than 0.35 is going to result in two problems.

  1. Lack of sunlight because your ascent is too shallow
  2. Heavy empty fuel tanks you have to haul upward

Anything higher the a TWR of 0.4 is probably going to mean that you won't have enough fuel to get to orbit. As you can see on my craft, I used only what was absolutely essential. I don't even trust the weightless batteries enough to not even use them. I took off at just before noon a flew east flavouring climbing over speed until 30km altitude. I would say that I may be able to go back and use the PB-X150 with the OKTO2 and make and attempt at a Munshot with return. I wouldn't count that out but, you will have to get pretty tricky with your flight. One idea would be to fly north and hang the panels in a sail arrangement like you do with interplanetary probes. But, I never really thought that plan through as the amount of daylight flying east should always be enough based on issue two of the underpowered craft design.

Here's an afterthought. I'm seeing a lot of designs with big-ass wings getting close but never quite getting there even though they have a lot of fuel left. The problem with wings at altitude is drag which means that you don't get a good high speed high altitude run at the top of your ascent. That means that you get caught out trying to reach orbital speed with the sun sliding past the horizon. It's best to only take just enough lift that you need and not more. Hey, just like everything else in the design!

EDIT: Is Nedal using droptanks? I was describing an SSTO. Any dropable parts are going to allow you to get away with a lower TWR on the runway.

Edited by O-Doc
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Nedal

Nedal

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Nope. 4 radial xenons placed directly on the center of mass, so there's never a balance issue. I took off way in the morning and ascended somewhat slowly. But I ended with around 200 or so xenon left, as the drive wasn't always fully powered.

Like you said. Twr increases as you burn fuel.

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gamerpuppy

gamerpuppy

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Nope. 4 radial xenons placed directly on the center of mass, so there's never a balance issue. I took off way in the morning and ascended somewhat slowly. But I ended with around 200 or so xenon left, as the drive wasn't always fully powered.

Like you said. Twr increases as you burn fuel.

Anyone know the weight of the empty ion tanks?

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Nedal

Nedal

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not specifically. I remember placing an empty on the pad and seeing that it was pretty low, and then deciding it was probably pretty even trade off hauling a decoupler vs just holding onto the tank.

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cantab

cantab

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Anyone know the weight of the empty ion tanks?
Wiki lists the inline as having a dry mass of 50 kg, and the radial a dry mass of 30 kg. You could check this in-game with the tweakables. The masses mean the radial tank has a slightly inferior mass ratio.
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Spica

Spica

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Ive just gone to orbit in an ion plane, SSTO as well.

I really hope infiniglide wasn't helping me along the way, as i used 3 small control surfaces, and two delta winglets, the control surfaces were for the tail and canards.

Sorry though, I only have pics of it in orbit.

However, if pics of the entire flight are needed, I should be able to have those up by tomorrow.

http://cloud-3.steampowered.com/ugc/3281180233999001047/2794938175B22B442A78F0A4F3D75592B9E2AEC2/

http://cloud-4.steampowered.com/ugc/3281180233999088932/35CCD28F88D443BBBD47E67A6696DD9BECA50C99/

http://cloud-4.steampowered.com/ugc/3281180233999103110/F540A3CAE951F2A2823E1AAAD6EADCA339A59774/

Fun challenge

Spica

Edited by Spica
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O-Doc

O-Doc

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O-Doc, I loaded your craft. How to fly that? I reach 40000 m and 1500 m/s.

Make sure SAS is engaged. Take-off at 10-15 degrees and keep adjusting your pitch upwards as long as you have 10+m/s vertical. Find the angles that give you the best vertical speed. At about 15km you should be at 30 degrees and your vertical will start increasing. At about 20km you are going to have to re-balance the craft by taking the remaining gas in the X50 and moving it to the X150 to keep you nose up. You want to get to a target vertical of at least 50m/s but 100m/s is better. At about 25km you are going to start losing lift from your wings and so start pitching down gradually making sure your vertical speed is not too high that you will start losing lift. This maneuver will continue to 35km whereby you should be over 1.5km/s and getting to space is trivial at that point.

I should point out that even at late morning you have to balance your AoA precisely because too shallow and you waste energy on horizontal drag. Too steep and you lose sunlight and power. That was part of the fun for me. Most of my flights had the power bar either growing or shrinking at all times! You could throw some more solar panels on it to have a more forgiving ascent corridor. There's definitely a good case to be made for putting panels on its rear end.

I'm a bit of an SSTO veteran so, flying an optimal ascend is second nature to me. You're almost there, try it again just before lunch and focus on vertical speed over horizontal drag. ;)

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zarakon

zarakon

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Alright, I finally managed to reach orbit myself!

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Not an SSTO since it's got one drop-tank. I went for a very high TWR of 0.47 at takeoff, 0.61 max with 2 engines. Designed so that the CoM doesn't really move and is lined up with the CoL

Made orbit in just 31:04 and was able to land it back at KSC

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