Spin to Win! The momentum tether challenge

[Cunjo Carl]

Why?
Enchanted by tales of "reactionless propulsion", the folks at KSC have invented the momentum tether, an enormous device designed to spin and fling kerbals from one orbit to another. I'm certain it will be a safe and pleasant way to travel.

Rules
Create a device to spin+fling Kerbals from a low circular orbit around Ike (13km or as close as is convenient). Spin it up and fling your plucky astronaut to their destination! If you miss but are close, use a maneuver node to figure out how many delta V you were away from your trajectory. If you're within 10% of the listed deltaV for the trip, it's close enough! Kerbals have EVA packs, after all...

Additional Rules
0. Have another trip in mind? Fling it and I'll add it to the list!
1. Informational mods are ok, as well as any mods which won't effect this challenge. FAR is a-ok!
2. You can use cheats and hyperedit to get into low Ike orbit, but they're off limits for spinning up and flinging.
3. You can use rockets to spin your reactionless-propulsion tether. I like irony as much as the next fellow...
4. Rampant saving and reloading is expected!
5. Screen shots or videos are enjoyed but not required.

Kudos you can earn for your spot on the leader board
: D       Stuck the landing      
>:)        Bounced Kerbal off a surface at greater than 20m/s (physwarp helps)
(>'.')>   Hauled it out to Ike, legit.

Destinations (from Ike)
Duna reentry (130m/s)
Interplanetary resonant orbit for gravity assist (~250m/s resonance pending)
Vertical landing on Ike (340m/s). If your apoapsis is under 15km, use EVA propellant to arrest your vertical motion, set your navball to surface and have less than 34m/s horizontal surface speed.
Kerbin Reentry (500m/s)
Dres Flyby (~800m/s, but changes with the year)
Kerbol Escape (~2750m/s) added by @TheGuyNamedAlan

Have another trip in mind? Tell me the starting orbit and destination, and I'll add it to the list!

Silly Introductory Video

 

 

 

Leader Board


LKO to Mun
                @Baricus chose to go to the moon and do the other things not because they were easy, but because they were Kerbal! An epic fling and gravity assist sent Alan Kerman careening halfway to Moho.

LKO to Resonant Kerbin Orbit
                @Baricus lined up a fling-to and return-from interstellar space. The krakens were so bewildered and astonished, they apparently decided to KO Baricus' computer.

LIO to Duna
        >:)    @DoctorDavinci created the mythical staged tether to let Valentina headbutt Duna at a harrowing 180m/s. Both Valentina and Duna survived the encounter.
        : D    @DoctorDavinci followed the hallowed KSP tradition of MOAR by using a 3-stage tether to fling Jeb to a soft landing on Duna.

LIO to Resonant Duna Orbit

LIO to Ike
: D  (>'.')> @LaytheDragon with a heavy-duty mk3 tether landed the relieved Navy Kerman gently on Ike.
       : D     @Drone_Kerbal rocked it oldschool in v1.05, tossing Leaberta Kerman gently down to Ike. The same system should also be able to get her back to Kerbin!
 

LIO to Kerbin

LIO to Dres

LKO to Kerbin
      (>'.')>  @LaytheDragon spun 'till the tether exploded, flinging two kerbals safely back home.
                 @DoctorDavinci left an entire ring system around Kerbin with 4 stages of tether flinging Jeb to greater and greater heights. Reentry turned out to be a bit of a doozie, though.
 

 

Badge!

[Cunjo Carl]

Well. This is something I've wanted to do for a while, and now seems as good as ever. I guess it's time to be a bit gawdy!

 

 

To Valentina's extreme delight, she was flung from an orbiting station into a nearly vertical landing on Ike. The actual speed was about 4m/s, but I was slow to capture the shot!

[TheGuyNamedAlan]

boi thats gonna be hard D:

what if you fling out of the solar system??

[The Optimist]

17 hours ago, TheGuyNamedAlan said:

boi thats gonna be hard D:

what if you fling out of the solar system??

have you played the game

[TheGuyNamedAlan]

1 hour ago, The Optimist said:

have you played the game

yea i have. its just i like going crazy w/ it

but that's just crazier that i thought

[Cunjo Carl]

19 hours ago, TheGuyNamedAlan said:

boi thats gonna be hard D:

what if you fling out of the solar system??

I would be ecstatic! Give it a go, I've added it to the list.

You'll probably need to build up to this goal, and that's one of the reasons I chose Ike. There's lots of things to hit with (relatively) large windows. Let's see what you can fling those Kerbals in to!

[TheGuyNamedAlan]

kk challenge accepted

1 minute ago, Cunjo Carl said:

I would be ecstatic! Give it a go, I've added it to the list.

You'll probably need to build up to this goal, and that's one of the reasons I chose Ike. There's lots of things to hit with (relatively) large windows. Let's see what you can fling those Kerbals in to!

 

can you make a badge 4 it??

 

<3 ur yt channel btw

[The Thyroid Man]

Bwahahahaha!!!

*jeb cowers nervously, even though that is totally out of character for him*

 

[Cunjo Carl]

On 6/23/2016 at 6:04 PM, TheGuyNamedAlan said:

can you make a badge 4 it??

Sure. I'll try to slap one up this weekend.

On 6/23/2016 at 6:04 PM, TheGuyNamedAlan said:

<3 ur yt channel btw

Thanks!

14 hours ago, The Thyroid Man said:

Bwahahahaha!!!

I definitely got my share of maniacal laughs out of this one, too! Happy mad sciencing.

[TheGuyNamedAlan]

mmm ok now i will do it. :DDD

[LaytheDragon]

I'm keeping my eye on this, and it shall be my next interplanetary mission (while I'm at it, I should send a Transport Trucker as a second payload to land on Ike). Can you do this with larger objects too? (say, could I eject from Kerbin a light "momentum tether" using a larger one that spins fast using Kerbodyne engines?)

[qzgy]

What about moons of Jool and Eeloo?

[Cunjo Carl]

22 minutes ago, LaytheDragon said:

Can you do this with larger objects too? (say, could I eject from Kerbin a light "momentum tether" using a larger one that spins fast using Kerbodyne engines?)

Flinging a momentum tether USING a momentum tether? That sounds intensely challenging design-wise and enormously entertaining to watch. Even if it doesn't pan out, send us the explosions, they're bound to be spectacular! Also, don't forget that you don't need to hit the Duna SOI, just get within 10% relative to the transfer deltaV. When you do the transfer, I'll add Kerbin -> Duna/Ike to the list and put an appropriate note next to your entry.

5 minutes ago, qzgy said:

What about moons of Jool and Eeloo?

You fling it, I'll add it to the list! Ike's just a nice proving ground, because Duna's so easy to hit.

[LaytheDragon]

Just now, Cunjo Carl said:

Flinging a momentum tether USING a momentum tether? That sounds intensely challenging design-wise and enormously entertaining to watch. Even if it doesn't pan out, send us the explosions, they're bound to be spectacular! Also, don't forget that you don't need to hit the Duna SOI, just get within 10% relative to the transfer deltaV. When you do the transfer, I'll add Kerbin -> Duna/Ike to the list and put an appropriate note next to your entry.

Well, I haven't done it yet, but I want to try. If around Kerbin is too hard, I'll do it in orbit of Minmus, but that is one possible entry I will attempt at the least,

[LaytheDragon]

Lots of pics, but I have done two things thus far:

 - Used a momentum tether to land on Kerbin from LKO (Low Kerbin Orbit)

 - Used a momentum tether to land on Ike from LIO (Low Ike Orbit)

Launch:

Spoiler

LKO Momentum Tether Flinging to Reenter and Land on Kerbin

Spoiler

Rather than ejecting the kerbals, I kept it spinning for the few more seconds using the engines, rcs. AND reaction wheels long enough for the reaction wheels at one end to start breaking off, and for the reaction wheel and battery that the decoupler and kerbals were attached to to also break off.

 

Leaving Kerbin

Spoiler

Arriving at Duna and Ike:

Spoiler

I didn't take many pictures here (though I can do it again if necessary), but Landed On Ike after using the momentum tether:

Spoiler

 

The Kerbal known as Navy Kerman was joyous to land with jetpack fuel rather than a head bonk as in the previous successful landing before quickloading.

 

Edited July 25, 2016 by LaytheDragon

[DoctorDavinci]

So I hyper-edited Valentina and a momentum tether with a second momentum tether attached into a 13km Ike orbit and managed to bounce the wee girl off the surface of Duna at just under 180m/s ... She survived too

 

[LaytheDragon]

Thanks, @Cunjo Carl . When I have more time, I'll try more with momentum tethers (I have a purposefully-self-given disadvantage of no hyperedit) when I have the time, with the one I have in orbit (after I quickload) or with a new one. I want to add the badge to my signature, but later, after I do more tether-testing. I also have a momentum-tethered momentum tether in the VAB I need to fine-tune and test.

Edited July 26, 2016 by LaytheDragon

[Cunjo Carl]

These were both fantastic submissions!

@LaytheDragon The mk3 structural elements were a fantastic design choice for launching the tether from Kerbin. I'm thinking about 'borrowing' the idea for a new design. I'm surprised your submission (the first one for this challenge) wound up hauling it out to Ike with real rockets rather than hyperedit! Kinda makes it a complete mission. The Kerbin landing was funny with the Kerbals just hanging out watching the shock layer burn past. Also, congrats on the gentle Ike landing, it has yet eluded me. Finally, your KSP looks super picturesque. That must have taken a lot of careful modding!

@DoctorDavinci, I can't believe you managed a staged tether! Your reaction-wheel-only design seemed very stable with the COM near the center of the ship. I think I might try 'borrowing' this idea, too! Good job setting up the lie-down reentry and the head bounce landing, and I'm happy you had good luck with the second (30m/s) bounce on her feet. I was surprised that Valentina didn't get any atmospheric entry effects, the lie down reentry must slow down Kerbals way more than I thought. Also, I like the eerie red lighting. It was a a nice touch.

 

[DoctorDavinci]

On 2016-07-26 at 7:11 PM, Cunjo Carl said:

@DoctorDavinci, I can't believe you managed a staged tether! Your reaction-wheel-only design seemed very stable with the COM near the center of the ship. I think I might try 'borrowing' this idea, too! Good job setting up the lie-down reentry and the head bounce landing, and I'm happy you had good luck with the second (30m/s) bounce on her feet. I was surprised that Valentina didn't get any atmospheric entry effects, the lie down reentry must slow down Kerbals way more than I thought. Also, I like the eerie red lighting. It was a a nice touch.

By the eye contracting ... I actually had the atmo effects set to lowest

Anyways, here's the Spun Out Mk2 ... I one upped myself and added another stage to my original design

It's Jebs turn this time ......

 

[moogoob]

Sorry to be pedantic (I swear I'll give this challenge a try, too!) but I don't think that tethers are reactionless. For every action there is an equal and opposite reaction, correct? By flinging the projectile (err.. payload) you impart an equal and opposite fling onto the rest of the tether assembly. So in this case the reaction mass would be the tether itself, correct? The only difference over a rocket burn is that the reaction mass is accelerated not by energy gained through a chemical reaction but by centrifugal (centripetal?) force.

Just sayin' these don't break the laws of physics. Unless you're thinking about the un-saturatable reaction wheels... those DO break physics.

Edited August 7, 2016 by moogoob
Pedantery

[Cunjo Carl]

15 hours ago, moogoob said:

Sorry to be pedantic (I swear I'll give this challenge a try, too!) but I don't think that tethers are reactionless. For every action there is an equal and opposite reaction, correct? By flinging the projectile (err.. payload) you impart an equal and opposite fling onto the rest of the tether assembly. So in this case the reaction mass would be the tether itself, correct? The only difference over a rocket burn is that the reaction mass is accelerated not by energy gained through a chemical reaction but by centrifugal (centripetal?) force.

Just sayin' these don't break the laws of physics. Unless you're thinking about the un-saturatable reaction wheels... those DO break physics.

Yep, the reactionless here refers to our charmingly reactionless reaction wheels, as you say. The rest is also along the right vein, and it's a wonderful thought exercise to map out exactly how the forces work out for the system. You probably already understand the following, but here's an interesting way to look at it: The reason it's a bit hard to discuss is that the fling actually happens when the force stops. The payload goes exactly how fast it was going the instant before release, and so does the tether. The action/reaction pair is only there while it's still spinning and held together, which is funny, right? Regardless, 'equal and opposite fling' is correct and a nice way to look at it, too! Another aspect, the spinning must be started up by torquing against something, which typically means a rocket in real life (though there are some fun exceptions). Once a tether is already spinning, most people have in mind that the tether will catch as many incoming ships as it launches off, so it'll keep transferring without needing any additional fuel. Sounds scary to me, but there you go.

If you happen to be interested in the math, I'd be happy to sketch through it with you! It can be a fun way to see how pieces relate. In any case, glad it got you thinkin'!

[Baricus]

When I saw this, I knew I had to try it.  I immediately booted up KSP and created a momentum tether which, after some testing with hacked gravity and no drag, seems to be able to impart a little over 500 m/s onto the flung Kerbal.  Unfortunately, I haven't been able to launch an actual mission with it yet, as I wanted to go bigger with multiple stages and I think I went to big for my computer.  I'm pretty sure that its mainly due to a fairing I created over the entire original tether, which ended up being almost as many parts as the original craft.  Once I can get it up and running again, I will have an entry for your challenge, possibly a return to Kerbin if I can squeeze a little more momentum out of it.

----------------------------------------

I fixed my issues with my computer refusing to load the machine  and I figured I might as well upload the results from my latest test, which got about 850 m/s onto the "capsule" (no Kerbal was inside at the time) even though the launcher snapped which prevented the use of the main source of acceleration.  Please note this was done with hacked gravity and no drag to simulate space as I learned quickly it was a pain to launch this thing.  I hope to launch an actual mission with this soon.

Spoiler

Here's the final result.  There is a seat inside for a Kerbal to hitch a ride, but I only have a probe core in there at the moment.  In an actual mission a Kerbal would be present.

This is the original craft, before any explosive decoupling.  The SRB at the bottom is to give it an upward push so it won't hit the terrain.  It will be removed before I attempt a mission with this.  The engine and fuel tanks to the left are the first stage, and decouple from the rows of reaction wheels after it has spun to full power.  The reaction wheels then spin the original design up even faster than before and then releases the "capsule" from the end of the line of girders.  Unfortunately, in this trial, I over-spun the first stage and it ripped off the entire second stage, which meant that I was not able to spin the craft faster after separation to impart more velocity to the "capsule".  I am fairly certain that if both stages work as intended (much harder than it sounds) it can propel the "capsule" much faster.  

Edited August 9, 2016 by Baricus
typo's

[Cunjo Carl]

@Baricus Welcome to the forums! Even without staging those are some impressive results. I believe the bar for deltaV is currently in the high 300m/s-ish so your 850m/s is more than enough to make a splash. Thanks for posting your WIP, my favorite part of the challenge forums is seeing how peoples' designs improve over time.

    850m/s is a ton of deltaV by the way! Were you getting any whipping effects that were helping out, or was it just spinning bloody fast? Even a single stage with ~850m/s should be plenty for many different trips like LKO to Mun or Ike to Kerbin. Just like with rockets, staging adds to your deltaV, but often less than you might expect. At present, its primary role is for style points (though for me there is no greater calling). Also, if launching is being a pain in your side, I can recommend Hyperedit as a simple, convenient way to put your tether in space.The ability to launch a space tether is an engineering challenge all its own! They truly live up to the name "Wet noodle rocket". In any case, good luck!

 

 

 

[Baricus]

I'm now on my fifth design, but I was rather surprised to realize that it performed so differently.  I don't really know why I have a lot more deltaV though.  It could be whipping affects, but I'm not entirely sure what you mean by that.  Is it the same reason a whip's tip goes supersonic?  My ship doesn't spin up fast enough for anything but a slight buckle during the start (its agonizingly slow sometimes).  I think the main design difference that I've seen is that I have an offset tether while it appears everyone else has a symmetrical one.  I think that while that design may provide a few benefits in the max RPM achievable, the extra deltaV might just be because mine is about 200 tons and as long as the SPH.  I'm not really sure though, it could be either.  This might help to explain it. . .

Here's a shot in the SPH, just ignore the engines at the front as those were from my foray into launching through hacked gravity.  I forgot the center of mass indicator, which would explain this a little better, but at the end of the long line of girders is the payload (the first stages treats that and the set of reaction wheels as the payload).  All the stuff to spin it is on the other end, with the center of mass always as close to whatever is doing the spinning as possible which is why there is a ridiculous amount of fuel for the first stage.  This, if I understand the physics right, acts almost like a lever, and propels the payload further for a lower overall RPM.  However, since I made it so long, this quickly became a battle of structural integrity.  Almost all of my major design upgrades involved struts or positioning pieces to be able to withstand the most possible centripital force.

As you can see, this resulted in over 600 parts (KSP does not like it in the slightest) and most of them struts.  I have a hunch that this is letting me spin a lot faster, which is probably what is giving me the majority of the extra deltaV.  Currently the only limitation that I've found when revving up my second stage (the first will still break off if spun up to gaps between the tanks of about 1 inch on my screen) is this:

Normally the kerbal is supposed to be inside of that service bay and the docking ports should be touching (the capsule in the other photo is just to get the kerbal there).  This is just slightly under the limit of the seconds stage's max speed (no physics warp was used).  I don't really have a way to track the g forces or RPM (the in game accelerometer surprisingly works from the center of mass of the craft), but I'm pretty sure this would not be pleasant.  Even with the large quantities of struts, the girders still separate, its just that the payload now snaps before they do (before the second round of struts the reaction control wheels would snap off first and then the kraken would be summoned and/or kerbin's graphics would break).  Needless to say, it does give me quite a lot of power to work with.

 

In terms of actual missions I think I may have shot to high.  I attempted to send Edlu Kerman back to kerbin, but I found that aim is the hardest part of this challenge.  After wasting almost all 1,000 M/S of my deltaV by firing in the wrong direction I think I need a mod for slowing down time (assuming that is allowed).  I was able to easily escape Duna's sphere of influence though, so I guess I'll take that as a consolation prize.  I hope that I'll actually end up somewhere next time.  The pictures of my spin at this are in the spoiler below.

Spoiler

After a brief attempt to fly this there using hacked gravity, I gave in and installed hyperedit to place this monstrosity in a 15km by 15km orbit around Ike.  

While this is from my first attempt, which was stopped due to a queer glitch with hyperedit, it shows how the first stage works.  The single vector engine quickly (within three to five minutes. . .) spins the entire craft up to speed.  The massive amount of fuel there isn't needed to fire the engine, but is needed to adjust the center of mass to be past the decoupler, to take advantage of leverage.

This is a close-up of the first stage just before separation.  I really just have to guess to see how long it will let me spin it up faster.  Sometimes that means that it snaps off, like in the test from my earlier post.  

while it is hard to see here, this is the first stage being dropped.  This leaves the second stage already partially spinning, but I couldn't use that in this run as I time warped between firing the stages.

I realized I didn't get any good pictures of the trajectory after the first stage fired, but this is the end result after I left Duna.  I was still aiming for Kerbin and thought I might just be able to hit it if I lowered my orbit enough from the apoapsis.

I spun up for much longer than I had thought it would take (I had never spun the second stage up from a complete stop before,  It took around 10 minutes).  This was as fast as it went, which actually seems a little bit less then it could have gone from looking at some of my earlier tests.  

I, sadly, completely missed when I fired though, so instead of slowing myself down, I launched radially and only altered my orbit, instead of slowing it down much.  

Edlu didn't seem to mind that much, though his pushing isn't going to get him home any time soon.  

 

Overall, I think this craft can return a kerbal to Kerbin, but the main issue is just lining him up.  Hopefully i'll hit one soon on one of these tries.  If not I'll see if I can slow down time for better aim.

I will have to try again to see if I hit anything interesting.  Its rather odd just how fun it is to spin these things up, I am constantly trying to guess if I can throw on a little more speed without it snapping in two.  Its surprising addictive.

Edited August 10, 2016 by Baricus
Typo's again

[DoctorDavinci]

@Cunjo Carl - Sorry, The Kraken compelled me ......