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Exploited Aerospike

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Posted (edited)

I don't know if someone has done this before. How far can a craft go with only one aerospike engine? Rule are simple.

  1. Only one launch for this challenge. The craft should be launched from the KSC launch pad OR the KSC Runway on Kerbin. 
  2. The major and deciding source of thrust is a single stock aerospike engine. To justify this:
    1. There is only one engine on the craft. That is the Aerospike.
    2. RCS is allowed. However the maximum total amout of RCS thrusters is eight. Any "part" is counted as "one" thruster, including the multi-nozzle thrusters.
    3. The Aerospike engine cannot be dumped from the craft. This is to prevent using RCS to push a lightweight probe far away, which is a good design but spoils the fun.
    4. No other engines and/or Kraken Drive, bug exploits, are allowed for this challenge.
  3. Please keep it to stock parts. Aesthetics and/or Information mods are considered "Stock" (And some say they should be stock)
  4. Creative Staging / Lifting body / Gravity Assists / ... Any method to make full use of every tiny bit of ΔV is allowed and encouraged.
  5. (Optional)Go as far as you can. If you have (a) Kerbal(s) on the craft, it/they do(es)n't have to return for this challenge. The real challenge is to have as much ΔV as you can in LKO! Thanks to @Poppa Wheelie
  6. Refueling? Allowed!
    1. ISRU allowed. If you manage to bring an ISRU system to LKO... That's hard for me. If you manage to carry an ISRU system to the surface of a celestial body, refuel the craft and then go to orbit... That's extremely hard for me. You can fly or not fly the rest of the mission once you are refuel'd and launched into orbit. But there some exceptions. 
      1. Please do not refuel from an asteroid and/or a comet.
      2. Please do not land near your refueling base and then transfer fuel from you base.
    2. Docking with your orbital tug or space station and get refuel'd? No, thanks.
  7. By 2 and 6 I mean the craft should be able to fly independent of any other missions. Apollo-style rendezvous is OK, but I don't really see the point in doing that. Also commnet is not a problem: switch it off if you don't want to have a heavy antenna but want to go far.
  8. You know what to post for an entry. Some screenshots and description of your excellent mission so we all know!

An aerospike provides a maximum of 153.53kN thrust on sea level. Here are some of my personal trial-and-error suggestions:

Build a conventional SSTO rocket, and lift a maximum of 15.666t rocket off the pad. Stock fuel tanks have a wetmass-to-drymass ratio of 25 to 3. That means a maximum vacuum ΔV of 6021m/s without staging. With the probe core/Kerbal on board it will be less, but with empty tanks dumped it may be more. Just go to LKO, and you may find that an ascent with a low TWR is neither easy nor efficient. 

Build a SSTO spaceplane and launch it from the runway and try to bring more mass off the runway.  Sounds great, but the aerospike don't burn as long as a jet with the same amount of fuel. Drag losses and dead weight from wings may significantly reduce the final payload mass. I didn't make it to orbit. I didn't even make it above 12km on a horizontal launch.

I may make a badge for this challenge! if...


If you like this one! (Forgive me for that green-ish Kerbin. I did some recoloring.)


One is 200px, another is 400px. Direct links for 400, 200, 180, 100px also:

https://s1.ax1x.com/2022/05/13/OrMAyt.png (400)
https://s1.ax1x.com/2022/05/13/OrQ89H.png (200)

https://s1.ax1x.com/2022/05/13/Orl7FS.png (180)
https://s1.ax1x.com/2022/05/13/Orl5eP.png (100)


Honor Roll

  1. 4317m/s in LKO by @Ultimate Steve (using an amazing optimized spaceplane! This is definitely beyond what I could imagine!)
  2. 3087m/s in LKO by @Poppa Wheelie(by @swjr-swisusing a stock and optimized version of Poppa Wheelie's craft.)
  3. 2759m/s in LKO by @Poppa Wheelie(using a modded probe core; a minor problem with the rules.)
  4. 2642m/s in LKO by @Watermel00n(using a unique horizonatal launch!)
  5. 1575m/s in LKO by @zeta function (carries Jeb and was enough to go to minmus and back with a mun gravity assist on the way back!)
  6. 1110m/s in LKO by @AllenLi(using dumb heavy side tanks and heavy deadweight. poor design!)
  7. 1040m/s in LKO by @sevenperforce(rank 4 by ΔV, but got Jeb into LKO.)
Edited by CFYL
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Posted (edited)

This is my craft, I would call it "checker" because of the part variants I seleted. Launch TWR at 1.36. The R-12 'Doughnut' External Tank was offsetted to the position, because actually there is a Oscar-B Fuel Tank inside its central hole. Attachment works like probe core--OscarB--Doughnut--FLT200.


It has poor maneuverability, so it takes the very old "burn up and then burn right" profile.

Two side tanks detached. Still burning straight up to keep the craft stable. 

The "burn up" part stops when ap reaches 53km, and the "burn right" part begins when checker reaches 42km. (Now checker has long lost its dark tanks though)

All side tanks detached. Almost in orbit.

This one is possibly one of the lowest stable orbits I have ever reached, since I started playing KSP in 2020. 70.45×73.69 is not easy to reach, at least for me.

Then burn for a Mun encounter orbit.

The first Mun flyby sends checker to a higher orbit and also patches a second encounter.

Mun flyby with pe at 43km.

Then do a 4.2m/s correction burn near ap, and checker gets ejected out of the Kerbin system.

Second Mun flyby with a pe of more than 200km.

A screenshot of checker, just outside Kerbin's SOI.

This is the current situation of checker. Not much fuel left, but it has escaped Kerbin on an aerospike within 36 hours, or 15 minutes real time for flying and 5 minutes for designing the craft(and 20 minutes for making a post).

It is possible to send checker to a much further destination by planning small correction burns and multiple gravity assists from Kerbin and/or Mun. I've done the similar thing once--you can see it in my signature--but that took me some 15 hours in total. I don't really have the guts to do this again, so I will leave checker right here on Kerbol orbit.

This one is my own entry which sends my "checker" on a Kerbol orbit near Kerbin's. That quite near so you can absolutely go much farther than I do. BTW "far" and "near" are told by the typical ΔV needed for a standard trip from launchpad to the target orbit/position for this challenge. So I got to Kerbin Escape, which is 3400+950=4350m/s away.

4 hours ago, AllenLi said:

If I can make it beyond Kerbin's SOI lol

As I promised. Working on it already.

Edited by AllenLi
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Well my plan to get a mining rig to Minmus DEFINITELY is not going to work out. At least not with a vertical takeoff, anyway.

I got Jeb into LKO with 1040 m/s of vacuum dV which should be enough to get me gravity assists to anywhere but not enough for a landing.

I think if I had done more aero optimization I could have gotten there with more dV remaining.

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The real challenge is to get the most dV into LKO as possible.

@AllenLi got 1110m/s into LKO.  I think that's the standard to beat.

I got 2759m/s into LKO with this:


Full album (15 images):  https://imgur.com/a/7odzAhK





End of Stage 1


Passing 20km altitude


26 seconds to Ap


Drop empty tanks


LKO achieved with 2759m/s dV available


I didn't attempt to go anywhere from here.  With this dV we could wait for the opportune time and do all kinds of gravity assists to anywhere.  Or, if we didn't want to wait, we can still get a Jool encounter or get well beyond Eeloo's orbit


Jool encounter


Or well beyond Eeloo's orbit, with dV to spare.  I couldn't zoom out any further.



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I suspect the best way to go about this challenge will be to have a reusable core that launches multiple fuel tanks into orbit (or whatever other payload you may want). This approach is pretty standard for single engine missions - it's how I managed to do the Jool-5 on just a single engine.

Very nice challenge - I'll probably take a crack at it tonight when I get home.

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On 5/12/2022 at 10:13 PM, Poppa Wheelie said:

got 2759m/s into LKO with this:


Full album (15 images):  https://imgur.com/a/7odzAhK


Question: what is the part you used directly above the engine? Zooming in on some of the screenshots it looks like a very short shroud or fairing, and I imagine it's where you placed your probe core etc, but none of the stock (or DLC) ones are that short or flush with the tanks.


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That part is a "MK1 Drone Core", Manufacturer "Kerbal Standard".  I thought I was using a stock part, but I just searched through my save and see that this is actually from the Airplane Plus mod.  It has the following resources and capabilities which would have to be duplicated if using a stock probe core:

  • Mass:  0.1t
  • Electric Charge:  20.0
  • Pitch Torque:  10.0
  • Yaw and Roll Torque:  3.0
  • Requires:  Electric Charge, 0.4/sec
  • SAS:
    • Stability Assist
    • Prograde/Retrograde Hold
    • Radial, Normal Attitude Hold
    • Maneuver Hold
    • Target Tracking
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On 5/16/2022 at 10:17 PM, Poppa Wheelie said:

That part is a "MK1 Drone Core", Manufacturer "Kerbal Standard".  I thought I was using a stock part, but I just searched through my save and see that this is actually from the Airplane Plus mod.  It has the following resources and capabilities which would have to be duplicated if using a stock probe core:


To make up for compromising your entry, I redid your craft to meet the stock parts rule (octo 2 core, battery, and reaction wheel, stacked on the bottom node of the engine and clipped up into the tank), and improved a bit on it with a different tank size and staging strategy. The resulting craft now gets to orbit with 3087 m/s left in the tank.



00 - Redo of Poppa Wheelie's craft to replace the non-stock part so the craft can stay in the running. Includes some improvements on tank sizes and staging.


01 - On the launchpad. Tank PAWs open to know when to stage.


02 - Lift off. SAS Hold.


03 - Switching SAS to prograde at 120 m/s for a hands-off stock gravity turn.


04 - Staging off first set of side tanks. Note the asymmetric tank sizes, compared to the original.


05 - Staging off the smaller upper side tanks, continuing to burn for Ap.


06 - Engine cut-off at Ap > 70 km (bit late).


07 - Circularizing at low burn for a more accurate cut-off.


08 - Arrived to 70x72 km orbit with 3087 m/s left.


09 - Confirmation of orbit.


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8 hours ago, AllenLi said:

I‘ll count that as your entry:lol:

Thank you but no. All I did was a refactor to make the craft comply with the stock part rule. If you're gonna put it on the leaderboard do it under @Poppa Wheelie's name, please.

Maybe I'll make an entry of my own when I get time. Carry on.

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With 28.44 tonnes of spaceplane on a horizontal takeoff and some aggressively optimized staging, plus a Munar gravity assist, I was able to land Jeb on Minmus in a proper command pod with 858 m/s of dV remaining. Returning him to Kerbin was of course trivial.

Rethinking whether it would be possible to reach Minmus with a command chair and an ISRU unit. I didn't optimize aero entirely.

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  • 3 weeks later...

So I didn't take any pictures during the first bit of the flight, because it was just supposed to be a test and I didn't think I'd do well, but I did!



This is the Low 1, my take on some of the designs posted upthread, but with more staging - I think most of the gains come from the fact that the top fuel tank is ditched once in LKO.


This is what is clipped into the tank. Succeeded in reducing drag, but unfortunately I can't think of a good way to eliminate the drag from the drop tanks.


This is a picture most of the way through the ascent, the first one I took after I realized that I might actually do pretty well.




And, in orbit, with 3395m/s left! I did overshoot the apoapsis by a bit, so I would have had a tad more if I had carefully inserted into orbit instead of mashing Z and X like a madman.




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Posted (edited)

Here's my second attempt:



The core is exactly like the first one, but the drop tanks are now 4 stacks of 10 Oscar B fuel tanks ditched in pairs. From a mass standpoint, this is less efficient than my first attempt, due to only 3 staging events, and if the craft were the same mass, this one would probably have less Delta-V, but the cross sectional area has been reduced by a factor of 1/3, and every node, forward or rear facing, has a nose cone. For future attempts, I might try 6 or even 8 smaller drop tanks, as the greater mass efficiency might offset the higher drag.


As you can see here, the largest source of drag remaining on the craft is probably the decouplers (there might be internal arrows we can't see). This might be fixed by attaching everything to the bottom node with a stack decoupler using part clipping and the offset tool.


And, in orbit (still overshot a bit, but less), we have 3498m/s remaining! So close to 3500...

I still have a few optimization ideas, but once this craft is reasonably optimized, I plan to construct a plane around it and transition to rocket flight later on.



Edited by Ultimate Steve
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And, my next attempt! 3606m/s, still with room for improvement.



This is Low 6, so as you can see, I've been messing around and didn't upload all of the other ones. The main changes are that the core tank has been segmented into 6 droppable sections, and the drop tanks have been expanded to 12 tanks (from 10) to make up for less fuel in the core. More drop tanks didn't end up being better, just comparable.


The optimal trajectory is a very low one.


Second separation of the side boosters.


Getting to orbit requires ditching the top core tank.

I overshot my apoapsis this time, but my periapsis was spot on. Just by piloting better (lower trajectory, not overshooting apoapsis), some improvement is possible.

In orbit with 3606m/s remaining! I'm probably done for the while, I've improved the best by 519m/s.



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Probably my last update for today, but it is a big one - 4317.



This is the Low P1, which is basically the Low 6 with a few modifications, with an airplane strapped to the outside. Unencumbered by the TWR>1 restriction, we have managed to add 4 FL-T800s worth of fuel to the craft.

Looking back on it, since the craft has little control authority and a TWR of exactly 1 upon wing jettison, removing one of the drop tank sets and spending more time as a plane may be the better move.


After the takeoff, a slow subsonic climb to 10 kilometers is made. This can probably be improved on to end up at higher speeds, higher altitudes, or both.


Just before jettison.


And just after jettison.


We actually ended up falling down and didn't end up recovering until after the first drop tank jettison. Might add 2 forward winglets to help with control.


Perfectly nailed the apoapsis this time.


And a reasonably circular orbit! 4,317m/s remaining in LKO!

Assuming I play with comms off and add a solar panel, that's enough to go quite far, indeed. At least 3.5 tons of useful payload to LEO if you replace the center fuel stack with something useful.  That is easily enough to get a minimal ISRU setup to Minmus with a kilometer per second worth of fuel to spare, but I'm probably going to leave that as an exercise for the people willing to put the time in.



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I have a mildly funny idea for this.

Just for clarification, there are the guidelines I'm following:

-Only one aerospike engine is allowed for propulsion
-The mission must be a single launch and must not interact with any other launch

Would any stock mission that satisfies these two constraints be allowed?

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On 6/10/2022 at 6:02 AM, camacju said:

Would any stock mission that satisfies these two constraints be allowed?

I would say yes. I'm not good at making myself understood in a few sentences... So my post is often a thick pile of sentences with poor logic:lol:

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Ok, great. My plan is to make a single giant launch with a small ssto, a bunch of modular fuel tanks, and a refueling vessel. Then launch the tanks one at a time into LKO, launch the ssto into LKO, and refuel it. I should get over 6K delta-v when I'm done

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  • 2 weeks later...
  • 2 weeks later...
On 6/12/2022 at 1:04 AM, camacju said:

Ok, great. My plan is to make a single giant launch with a small ssto, a bunch of modular fuel tanks, and a refueling vessel. Then launch the tanks one at a time into LKO, launch the ssto into LKO, and refuel it. I should get over 6K delta-v when I'm done

I built a HTOL SSTO which can trivially deliver 5.2 tonnes of payload to LKO and return to the KSC:


And it's got two long Mk2 cargo bays worth of volume, so it's not difficult (at all) to utilize all the payload capacity on each launch.

Construction of an ISRU single-stage-to-anywhere in 5.2-tonne modules will take a minute, but it's entirely doable. The Dart engine is also mounted on a docking port so it can be removed and transferred to the orbiter at the final stage of assembly.

However, I do not think it is possible to get off Eve with only a single Dart.


Turns out I had gravity set to 48% due to some earlier testing I had begun and then forgotten about, so this DEFINITELY is not nearly as powerful as I thought.

However I'm sure I can still manage.

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