Spin to Win! The momentum tether challenge

[Cunjo Carl]

@Baricus I must have missed part of your post (or maybe it was added later), because that's a ton of progress! The hardest part is totally aim, but the good news is you don't actually need to hit the Kerbin SOI, just get within 50m/s of it with a maneuver node. If your pod doesn't have any propulsion, it's probably easiest to ditch it and fly the manuever on jet packs. You can actually reenter from an interplanetary trajectory without space ships using an *ahem* unintended feature of KSP that I hold near and dear by telling anyone I think will get a kick out of it. Simply set your trajectory to be between 100-1000m over Kerbin's south pole, go to the tracking station and wait until just after periapse, fly the kerbal and wait a moment for them to slow down a bit. Quick save and quickload if ithe kerbal's trying to spaghettify, then go to 4x timewarp and hold shift+W to bounce off the ground or sploosh into the ocean with style. Boy, that's a longer explanation than I remember. Nice tether! I dig the use of cubic struts as mounting points for two-part struts. Your picture spinning up makes it look like a very stiff joint is created. The map-mode picture may not outwardly look impressive, but I see an eccentric orbit with the Ap/Pe pushed 90 degrees from your position- that takes a ton of impulse! Sweet pic. It just takes a couple dozen repetitions to get that magic shot. I hope you and Edlu find it amusing to give it another go at some point!

@DoctorDavinci I want to watch that movie so bad, but my Internet's on the fritz. Tomorrow I hope!

[Cunjo Carl]

@DoctorDavinci I finally made it back. I'm glad I finally got to see your 4-stager!

I guess I'm not the only one with the 'just one more stage' itch. The thing that amazes me most is that the intricate 3 stage tether balances and doesn't tear itself apart while being flung 'round the even-more-massive "mother tether" at a hundred m/s. That's some delicate wizardry- thanks for cranking things to 11 and then pushing it farther for the shear thrill.

[DoctorDavinci]

I think I reached the limit of momentum tether staging ... balancing is the first issue then positioning is the second ... After that it's struts, struts and more struts

The handymans secret weapon is Duct Tape (Red Green) ... Or in the case of Kerbals, struts

[Cunjo Carl]

Thread of the month? Hot diggity!

As a summary of this challenge, for anyone making their next trip with a momentum tether, I'll be happy to immortalize the journey. As a rule of thumb, any transfer with a deltaV in the few hundred m/s range is an ideal candidate. Good luck, and fling safe!

Speaking of which, an interesting ongoing question is how far you can fling using a momentum tether? Hundreds of m/s are a sure thing, but how about more?  When I get back to my computer next week, I'll start up a list of who's flung their Kerbals how far and with which buildling techniques. Hopefully we can build the technology to new, ludicrous horizons. The future is looking bright for Kerbals that can hold their lunch!

Finally, as a note for bulding, simple tethers fling farther. @DoctorDavinci has designed and demonstrated an exquisite multistage flinger (if you haven't seen it yet, it's beautiful- go take a look!), but the farthest flingers have been one and two stage designs; their simplicity allows them to rev up faster and launch further. That's good news, it means you can start it simple! Also, fortunately, reaction wheels can torque up your tether just as efficiently from anywhere on the craft, so you don't need to try fitting them all in the middle. I'm happy to show a graphic of why this is if anyone's curious, but the result is very pleasant for building. Rockets are still best used near the edges, of course. Both ways work great and make a lovely display! The real secret sauce technology is in that lever arm...

Cheers!

 

(KSP is totally Red Green rocket science btw!)

 

[Baricus]

Well, I tried to post this a few weeks ago and then the forums lost it all.  I've finally got the time to rewrite this though, so I guess here's my (hopefully first) entry to this challenge (finally).

 

After my failures with interplanetary travel, I decided to start with something a little smaller.  

I set a maneuver node for the Mun (after looking this appears to be a photo from when hyperedit glitched and I needed to reload.  The ship started at a 250km orbit, not suborbital as is shown here.  I sadly cannot find another picture until after I fired the first stage which is in the spoiler below).

Spoiler

This is after my first stage (rocket powered) was decoupled.  The second stage then boosted it to the final trajectory.  

 

Of course, I missed completely.  I mean, this thing is almost impossible to aim.  Yet somehow, when I looked at the map view. . .

I had gotten ridiculously lucky.  I have no clue how that happened; I still don't really believe it myself.  It seems this contraption has a lot more power than I thought.  Somehow I was able to send Allan to the Mun in:

Needless to say, Allan did not survive to witness the celebrations that took place upon his "successful" journey.  

So through the magic of quick-loading, I altered his trajectory using his jetpack.  

After a close Mun flyby, he exited the Kerbin system to find himself on a final orbit of about 13 billion m by 8 billion m, which crosses Eve's orbit.  

Unfortunately, it seems it will take a very long time for anything interesting to happen for Allan.  I looked ahead for a while, but he didn't end up encountering anything.  

 

The design hasn't changed much, the earlier photos are still accurate.  If anyone's interested, i can put some more photo's up of the actual launch process, but it is pretty much identical to my earlier posts.  I can't wait to see what some other people will come up with for this challenge.  I have a few ideas floating around in the back of my head, but they all seem rather outlandish.  I think @Cunjo Carl summed it up perfectly,  faster = farther.  

 

PS:  when I looked at the picture again, it seems this thing was able to impart somewhere over 1000 m/s onto Allan.  I don't really know the exact numbers, but that looks like it should be plenty for an interplanetary transfer.  Maybe its time to head back to Ike.  

 

Edited September 4, 2016 by Baricus
Typos, typos and more typos

[TheGuyNamedAlan]

well done, thread of the month 

[Drone_Kerbal]

Congrats on thread of the month!

Looked fun and easy, but aiming it proved to be quite hard...

My Attempt

WIP:

I started of with a massive(ly impractical) design with ore tanks as counterweight with Vectors for spinning up. The victim willing volunteer kerbal would have to EVA to get flung. I quickly discovered that the whole design was flawed. The Vectors, at full power, would create too much torque for the craft to handle and it would snap. Also, there is a slight delay between the kerbal getting out and falling off the ladder. I shortened the girder and replaced the Vectors with Darts, ditched the obscenely heavy ore in favour of a simple fuel tank and thought that accounting for the lag would be quite easy. This gave me this beauty abomination:
Turns out, dealing with the lag wasn't that easy.

Eventually, I got to this: a pod with a decoupler and three darts.

The submission:

Using the design above, I got from LIO to 30 m/s surface velocity - a shade under 10% off perfect.

Got out of the pod and EVA'd down to a bouncy landing.

View the full album, in no particular order and with all failures included here.

I probably could get to Kerbin with this design as this picture shows, but looking ahead I couldn't find a good intercept. I don't know if that qualifies as going to Kerbin.

Looking forward to hearing from you and getting a verdict on the Kerbin intercept.

Note:
This was done in 1.0.5 as I find 1.1.x slightly buggy. If this disqualifies me, I completely understand.
Also, hyperedit was used to get the craft to a 12km Ike Orbit.
Thanks for reading!

Edited September 7, 2016 by Drone_Kerbal
Details

[Cunjo Carl]

Congrats to both @Baricus and @Drone_Kerbal on their recent journeys! I'm totally impressed that you've both managed missions so deep into interplanetary space. I've updated the main list, and look forward to posting more complete comments soon. The only hanging question I saw was from @Drone_Kerbal, and yes v1.05 is just fine. It took me a long while to adapt to the new bugs of v1.1.x, too! The earlier version should give a fair advantage in joint stiffness, so I'll just note the version in the records.

[Drone_Kerbal]

@Cunjo Carl, thanks for adding me to the leaderboard! Also, does this mean I can have the badge now?

[Cunjo Carl]

Just now, Drone_Kerbal said:

@Cunjo Carl, thanks for adding me to the leaderboard! Also, does this mean I can have the badge now?

For sure!

 

[Cunjo Carl]

@Baricus, I'm glad you took your design back to basics and got such fantastic results from it. Also, sorry the forums ate your first post- I lost one of mine recently, too. In general, this forum's pretty awesome at saving progress.... except when it's not .

  That gravity assist was a thing of beauty! You can judge how much energy you gained from the assist by the curvature of the path (the change in velocity), and that is a huge curvature for a Mun assist... and it launched you straight retrograde Kerbin's orbit- so cool! I should mention that this launch set you tantalizingly close to the 3:2 Kerbin orbital resonance, which is actually why you weren't seeing any Kerbin encounters in the near future. The closer you are to a resonance, the longer it takes for things to realign... phases and all. Long story short, if you happen to have a save and drop your sun periapsis to ~142 days during the Mun flyby, then go around the sun 2.5 times, you'll be in perfect position to set up a Kerbin encounter. If KSP doesn't project your trajectory out far enough to see what you're doing, just put a 0m/s manuever node in every SOI your trajectory travels through until it does. Just if you want to of course, I just saw the 144 days and can't help but thinking.... it's so close!

  I'd love a photo of the two stage design, if you have one. Your previous post showed the primary stage, but I don't think I've seen the second one yet. Regardless, the prodigious use of struts (aka. "moar struts") on that primary tether arm seems to have worked a treat! As a final note, I'm super amused that your Kerbal shared a name with @TheGuyNamedAlan, a fellow KSP challenge enthusiast who's been keeping an eye on this thread. I'm sure he'd be bemused to hear of his namesake's far-flung adventures.

 

@Drone_Kerbal . I like the simple tether design- it looks really low lag for the deltaV. I agree about those ore tanks. For their weight, those ore tanks don't grip on to things very tightly and tend to break off of stuff unless they're strapped in really tight. The 3.5m fuel tank just winds up being convenient all around.  I was checking through your full album, and noticed something: How did you get Leaberta to stand on the flag like that? Can you just jump on top of it? I've never seen that before! For the shot out to Kerbin, don't forget you have ~80m/s of play you can use to arrange a Kerbin encounter from the solar periapsis if you want to try lining one up from interplanetary space. You're poised to get our first interplanetary encounter :D. If you do decide you want to, I can share a way to re-enter a Kerbal from interplanatary trajectory.

  Finally, your picture of the Ike-landing fling shows you moving at 30m/s relative to the surface, but the direction was almost straight up, so 25-ish seconds after you took that pic you were probably almost stationary relative to the surface. Total win!

[TheGuyNamedAlan]

On 10/09/2016 at 3:13 PM, Cunjo Carl said:

  I'd love a photo of the two stage design, if you have one. Your previous post showed the primary stage, but I don't think I've seen the second one yet. Regardless, the prodigious use of struts (aka. "moar struts") on that primary tether arm seems to have worked a treat! As a final note, I'm super amused that your Kerbal shared a name with @TheGuyNamedAlan, a fellow KSP challenge enthusiast who's been keeping an eye on this thread. I'm sure he'd be bemused to hear of his namesake's far-flung adventures.

aww thx

[Drone_Kerbal]

Quote

How did you get Leaberta to stand on the flag like that?

I don't know if it's different in later versions, but in 1.0.5 you just walk up to the flag and it will give you a prompt saying something like "Press [F] to climb" and you can get on top of it.

For the Kerbin encounter, I definitely could've made it but was a bit short on time and I couldn't really be bothered.

Quote

I like the simple tether design- it looks really low lag for the deltaV.

Thanks! The amount of deltaV did surprise me. For the Ike landing, I had to spin it exactly 5 times to get the right amount of throwage (for the lack of a better word) and it wouldn't break until past 10 spins, giving perhaps 700 deltaV maximum. As for the lag, I'm playing on a laptop so I couldn't overengineer it as much as I wanted to but it still turned out pretty good.

Sorry about the funny quotes, I'm in mobile and don't think it's possible to do it any other way.

[Baricus]

Sorry that it took so long for me to get back to you @Cunjo Carl, I tried out what you suggested (unfortunately no pictures yet), though I think that I messed up the resonance, because I forgot to account for time to escape.  Do you know what the altitude was for the resonance orbit?  The time to periphrasis has given me an intercept around 15 years into the future, but as I warped to the last maneuver my computer crashed.  Once I get the computer issues sorted out I'll try to get to an intercept one more time before transitioning over to 1.2.  Afterwards, I have a few ideas that might be able to make my design practical for actual use.  The lag my current design generates is killing it.  

 

Also, I looked back, and I'm pretty sure that the first stage is in some of the pictures.  Its a little hard to tell, because it very hard to put the whole contraption onscreen at once.  The part with the giant white fuel tanks is the first stage.  Afterwards it decouples and the reaction wheels next to it spins the tether faster for the second launch.  My first post showing the actual design has some pictures of the first stage.  The one in the VAB shows it and there are a few pictures in the spoiler near the end of the post.  I'm sorry that I can't upload more pictures to make it clearer.  Once my computer troubles get fixed I'll see if I can.  

[Cunjo Carl]

@Baricus  Crashy computers are the pits. Hey, if you got a projected encounter, that's all that's needed for a resonant orbit. Mission added! Also, I remember you mentioning now the first stage is similar to your initial design, which you took some nice shots of. I can see where the lag is coming into play with all the connector struts keeping it locked together- it definitely has given you the edge on spin speed though! I hope your computer troubles resolve nicely.

   As for 1.2, I hear it'll be coming with a hefty re-balance... I wonder what that'll do for momentum tethers?