WanderingKid

High dV rockets without Nuke/Ion and limited tech ideas

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So, I've been building a series of different whip probes, and was wondering what kind of results other folks get from this style.  This probe's purpose is to leave at bad transfer times, "Whip" around another SOI for a flyby contract (without orbiting), then get itself shot home ASAP.   To do this, I'm aiming for triple, if not quadruple, the standard dV necessary for the transfer, and I want solid TWR (0.4+)so that the burns can be made with reasonable accuracy and not having to 'wind up' an orbit.

The best I've been able to fit into my 140 ton limit (255 parts, but I don't even get near that) has been between 11,500 - 11,800 m/s d/V at launch if I want decent takeoff TWR.  Here's one variant with some of the staging a bit off (I've been goofing around since then):

EDIT: Due to some confusion as to the purpose of my original image, this is one that has its staging correct and works as an example instead of a stripped down version showing most of the parts in play.  It runs at 12,909 d/v on the pad and hits orbit with about 9,700 d/v left after ditching the mainsail and finishing its burn on the Terriers.  There's an entire array of Oscars, Ants, science gear, antenna, and other stuff inside the fairing.

f9COzN8.png

Now, I realize Nukes change the landscape completely, but I was wondering who else had come up with purposely over-engineered vessels like this with limited tech so we can compare notes.

Edited by WanderingKid
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How to get more delta-v in three simple steps

1. Add more fuel tanks!

2. Then add more engines!

3. Enjoy! (Actually I don't really understand what you want, but at least I tried!)

Edited by Hypercosmic
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^ that gets him over the 140 ton limit. Also, that doesn't work. 2 orange tanks with 2 mainsails have the same dV as 1 orange tank and 1 mainsail. Adding more fuel tanks,adding more stages(done properly), using higher Isp engines, that gets you more dV.

To the OP, you're going to have to specify your tech level better. Do you have poodles? I see that you have fuel lines. 0.625m parts?

Your lower stages look like they could use a lot of work. You admitted the staging was off, but having a heavy mainsail as your core stage seems inefficient. As shown, stage 7 has a 1.0 TWR, I assume with staging fixed, it fires along with the mainsail of stage 6... that TWR would be well over 2:1. 

3 skippers firing would be better. Or go asymmetric ( a bit harder to make work), and have a single mainsail and a single skipper. Or ditch the cross feed, a signle mainsail should get you a starting TWR of about 1.5- that single stack would be enough. Above the mainsail, put a poodle, and the fuel tanks for those skippers above that. The mainsail should get you high and fast enough to circularize with a poodle, at excellent Isp and less mass than 2 skippers- certainly better than circularizing with a mainsail

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Have you checked if your stuffs are already efficient or not. I have a bad feeling about asparagus stage on the second stage.

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Do you have much in the way of 0.625m parts? You can get crazy dVs from tiny amounts of fuel with those things.

2Jglysh.jpg

Otherwise, shave your payload. You've got a service bay and a structural nosecone there; those are a bit luxurious for an ultralight probe. You've also got at least three more SAS units than you need (really, you shouldn't need any for a ship this size).

Edited by Wanderfound
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I managed to get 12,663 m/s with this contraption. Which, considering there aren't yet any science experiments loaded, isn't really much more than yours. The annoying thing is, I could have easily gotten over 13 km/s, but I ran up against the height limitation of the tier 2 launchpad. Height, of all things, not weight? That's a first! :P I had to skip on adapters to even make this thing work. Has ~9,250 m/s left once in an 80x80 km orbit.

w9lxaXU.jpg

Edited by Streetwind

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6 hours ago, WanderingKid said:

Here's one variant with some of the staging a bit off (I've been goofing around since then):

One thing I can't tell from your screenshot (especially since you mention that you've tinkered with the staging since the screenshot), but just to confirm:  Have you got the fuel crossfeed and flow priority set up asparagus-style?

That is, for example, do you lift off the pad using both Skippers and the Mainsail, with the fuel flow set up so that the Mainsail is draining the Skippers' tanks rather than the big orange one?

That way, you as soon as the Skippers run dry, you drop 'em and the Mainsail can continue with a full tank to start.

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8 hours ago, Hypercosmic said:

How to get more delta-v in three simple steps

1. Add more fuel tanks!

2. Then add more engines!

3. Enjoy! (Actually I don't really understand what you want, but at least I tried!)

You should skip step 2.

There are really only four strategies to increase delta-V:

  1. Add more propellant mass.
  2. Reduce dry mass.
  3. Use higher Isp engines.
  4. Use staging to shed dry mass that is no longer needed.
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Apologies, many of you are treating this as a "fix my ship" discussion... which wasn't my intent.  I simply showed the ship as an example of what I was talking about.

@KerikBalm and @Wanderfound, Anything in the tier 2 (Level 7 and down) that isn't a nuke is considered fair game for this discussion.  It's more a "What have you played with via career" kind of thing.

@Snark  Yes I do.

@Streetwind How did you squeak out the extra 800 d/v?  I know I'm running a tad top-heavy to keep my stuff from having issues during re-entry as well as I wanted extra SaS for orbital maneuvers (moves like a drunken elephant otherwise), but even stripping those was only getting me 200-300 d/v. Is it the toroidal tanks that seems to have done it?

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1 hour ago, WanderingKid said:

@Streetwind How did you squeak out the extra 800 d/v?  I know I'm running a tad top-heavy to keep my stuff from having issues during re-entry as well as I wanted extra SaS for orbital maneuvers (moves like a drunken elephant otherwise), but even stripping those was only getting me 200-300 d/v. Is it the toroidal tanks that seems to have done it?

Here's a closeup of that upper stage. It has just over 3130 m/s dV, and will be firing for the final part of the return journey, where the service bay with the science equipment has already been dumped. One HECS core, three toroidal tanks and one oscar-B tank, three Spider engines, two solar panels and an antenna. Up on top there's a size 0 decoupler for separating the science container with its parachute. The thing has such a low ballistic coefficient that it can aerocapture and reenter without a heatshield if carefully managed (and perhas keeping some fuel for propulsive braking too).

And honestly, if you hadn't specified a need for a minimum of ~0.4 TWR? I personally would have gone with just a single Ant engine. That ends up with just 0.13 TWR, but also 3,562 m/s instead of 3,133 m/s through a combination of better Isp and less dry mass. The lower stages would also have slightly more dV due to having to push slightly less mass, and I'd have dropped the two Sparks in the second stage as well for even more gains. With those changes, I'd be up to 13,222 m/s. :wink:

DOH9vAl.jpg

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I send rockets up using their transfer engines to circularize, then refuel in space. Nice happy medium between trying to launch everything in one go and doing some kind of complicated orbital construction. My Moho probe, based entirely on chemical rockets, worked this way.

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8 hours ago, Red Iron Crown said:

You should skip step 2.

There are really only four strategies to increase delta-V:

  1. Add more propellant mass.
  2. Reduce dry mass.
  3. Use higher Isp engines.
  4. Use staging to shed dry mass that is no longer needed.

TWR is significant because this is the launch vehicle. Currently this rocket cannot even lift itself from the groupd because the TWR is exactly 1.00.

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9 hours ago, Hypercosmic said:

TWR is significant because this is the launch vehicle. Currently this rocket cannot even lift itself from the groupd because the TWR is exactly 1.00.

Thread is not about launch vehicles, near as I can tell.

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5 minutes ago, Red Iron Crown said:

Thread is not about launch vehicles, near as I can tell.

It is. Look closely at the bottom of the Kerbal Engineer box. See? TWR = 1, means weight = lifting force. With that, it won't go anywhere.

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34 minutes ago, Hypercosmic said:

It is. Look closely at the bottom of the Kerbal Engineer box. See? TWR = 1, means weight = lifting force. With that, it won't go anywhere.

If you're referring to the screenshot in the OP - that's just because the staging is wrong (as noted in the OP). It has only the two Skippers firing first, with the center Mainsail not activating. It should be set to activate all three, which would deliver plenty of TWR.

Edited by Streetwind
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22 minutes ago, Streetwind said:

If you're referring to the screenshot in the OP - that's just because the staging is wrong (as noted in the OP). It has only the two Skippers firing first, with the center Mainsail not activating. It should be set to activate all three, which would deliver plenty of TWR.

Try activating both three engines simultaneously. Transferred fuel should make it to some amount.

Edited by Hypercosmic

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20 hours ago, Red Iron Crown said:

You should skip step 2.

There are really only four strategies to increase delta-V:

  1. Add more propellant mass.
  2. Reduce dry mass.
  3. Use higher Isp engines.
  4. Use staging to shed dry mass that is no longer needed.

Somebody here a while ago had a C++ algorythm for this in their sig.   Haven't seen it in a while though. 

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8 hours ago, Hypercosmic said:

It is. Look closely at the bottom of the Kerbal Engineer box. See? TWR = 1, means weight = lifting force. With that, it won't go anywhere.

From the OP:

On 3/25/2017 at 6:26 AM, WanderingKid said:

To do this, I'm aiming for triple, if not quadruple, the standard dV necessary for the transfer, and I want solid TWR (0.4+)so that the burns can be made with reasonable accuracy and not having to 'wind up' an orbit.

Thanks for the tip about what TWR is and how to read KER, though. :D

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TL;DR: upper stages -- abuse Oscar-B tanks for droptankage, around an FL-N core.  For engines, abuse Terriers, Ants if you can handle the lower TWR.  Toss a Poodle in if you're really heavy, to take advantage of that best-non-nuclear-in-game Isp, but as mass goes up be prepared to augment it with sparks, terriers, more poodles, as needed.  If you've got the tech, Rhino works great when you're heavy enough for a couple of poodles.
For complete insanity, abuse ants and oscar-Bs, pushed by Terriers and FL-Ns coated in oscar-B droptanks, all pushed by a poodle with a short rockmax tank stack coated in FL-N droptanks coated in Oscar-B subtanks, pushed by a Rhino using a kerbodyne tank stack coated in more FL-N droptanks (but sans the oscar-B's at this point, as the ratio of decoupler mass tankage ratio improvment from staging gets sub-optimal here, also part count).

lower stages -- depending on tech, a skipper and a couple of thuds make a poor kerb's mainsail, and a couple of thuds on a bare 2.5m tank make for a poor kerb's skipper.  And of course, SRB's make any staged lifter cheaper and more fun.

The best trick to maximize dv for this kinda probe, though, is stage-lock (alt+L) -- to prevent km/s being lost to the void due to a rogue keystroke.

 

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On ‎3‎/‎27‎/‎2017 at 0:44 PM, Archgeek said:

TL;DR: upper stages -- abuse Oscar-B tanks for droptankage, around an FL-N core.  For engines, abuse Terriers, Ants if you can handle the lower TWR

I'll bite... What's an FL-N Core?  It's not a tank, an engine, or a probe that I can see.  I dug around a bit but can't seem to find one and Google-Fu dost fail me now.

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To gentle the "It won't launch" concerns, I'm going to update the first post with a different example with my staging correct.  That should kill the distractions.  :/  I hadn't been overly concerned about it at first... sorry this got a bit derailed there if anyone was enjoying this.

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@Streetwind  I like your idea of using the antenna and the solar panels in an array that balances each other off, that's pretty neat.  Unfortunately at tech two, you'd need two of the DTS-M1s unless you've got a relay sat network already set up.  I have managed to get a ship up to 12,909 d/v with this discussion, with my quality of life improvements installed (some extra SaS modules, enough antenna, etc...) so so far it's been a good conversation, at least for me.

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One thing I've found however, when trying to abuse second and third stage Fuel to Payload ratios is there's a point ~5 tons of fuel where you'll want to switch over to the 1.25m tanks, even if you're using a spark, just for part count and anti-wobble.  Have others found that to be the case, or has most of this conversation been theoretical and not practical for those involved?

Edited by WanderingKid

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3 hours ago, WanderingKid said:

I'll bite... What's an FL-N Core?  It's not a tank, an engine, or a probe that I can see.  I dug around a bit but can't seem to find one and Google-Fu dost fail me now.

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One thing I've found however, when trying to abuse second and third stage Fuel to Payload ratios is there's a point ~5 tons of fuel where you'll want to switch over to the 1.25m tanks, even if you're using a spark, just for part count and anti-wobble.  Have others found that to be the case, or has most of this conversation been theoretical and not practical for those involved?

'Just me using variables again.  I meant the stock FL-800, 400, 200, and co. 1.25m fuel tanks.
Edit: well, well, I'd forgotten there was a 'T' in those.  I meant the stock FL-T(8|4|2|1(00)) tanks.

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Yup, hence the tomfoolery with attaching Oscar-B stacks around your first FL-2/4/8(00) or so.  Also of interest, research into insane delta-v shenanigans in stock with the ion engine led to math that indicated that optimal staging for a given amount of fuel (assuming constant mass ratio in the tankage) is found when each stage brings the same delta-v to the party, up to the point where the decouplers become too much (for xenon this doesn't even come up, due to the heavy tanks, but for the Oscar-B, things could be different and rocket tanks are about the same, with the tiny decoupler weighing in at less than half a single empty tank).
So depending on how that shakes out, your stages could go 1 tank, 1 again, 2, 3, 3 again, 4, 5, 6, 8, 10, 13, 16... until you wind up with enough fuel that you may as well use a bigger tank instead of several long Oscar-B stacks (20 Oscar-Bs is exactly as much fuel as the FL-T800, the largest 1.25m tank).  (If decoupler mass is too close to tank dry mass, you'd just have more tanks in the top stage and on down.)  The mass ratio gets worse at this point, so that point's slightly higher than one would think.
Of course, that's if you're not switching tankage earlier to reduce noodlage or for part count.  You'd technically still be better off dv-wise to stick with the tiny tanks all the way, but no one's going to do that, for obvious practical reasons.

Edit mk2: Well, nevermind that then -- it turns out every rocket tank has the same mass ratio of 9, even the toroidal one.  The tiny tanks just get you better resolution in trying match stage dv, plus the smaller decoupler if you're matching node sizes.  The main thing to abuse is that it lets you put side stacks of tiny droptanks around a 1.25m upper core, increasing fuel density per unit ship length.

Edited by Archgeek
I was very wrong about Oscar-B mass ratios!

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Another option that i don't see mentioned would be to launch your probe without fuel. This allow you to make the probe much larger and capable of holding much more fuel and still be able to launch it under the 140 ton 255 part limit. Once the probe core is in orbit simply start launching fuel missions until it is full. 

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On 3/29/2017 at 2:51 PM, Archgeek said:

Edit mk2: Well, nevermind that then -- it turns out every rocket tank has the same mass ratio of 9, even the toroidal one.  The tiny tanks just get you better resolution in trying match stage dv, plus the smaller decoupler if you're matching node sizes.  The main thing to abuse is that it lets you put side stacks of tiny droptanks around a 1.25m upper core, increasing fuel density per unit ship length.

It also gives you finer-grained control of ship width. Which is very important at times...

xN69GCe.jpg

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On 29.3.2017 at 5:51 AM, Archgeek said:

Edit mk2: Well, nevermind that then -- it turns out every rocket tank has the same mass ratio of 9, even the toroidal one.  The tiny tanks just get you better resolution in trying match stage dv, plus the smaller decoupler if you're matching node sizes.  The main thing to abuse is that it lets you put side stacks of tiny droptanks around a 1.25m upper core, increasing fuel density per unit ship length.

For what it's worth: the mk0 liquid fuel fuselage actually has a mass ratio of 10, higher than any other tank in the game. So technically, if you took a LV-N, you could to some "tiny tank abusing" with that :wink:

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47 minutes ago, Streetwind said:

For what it's worth: the mk0 liquid fuel fuselage actually has a mass ratio of 10, higher than any other tank in the game. So technically, if you took a LV-N, you could to some "tiny tank abusing" with that :wink:

Oh, indeed.  Those little tanks are just great -- beautiful droptanks for LV-N systems designed to use droptanks, amusing fuel density, and drained of fuel, the lightest structural part per unit length that isn't the cubic octag.  Great for the panel-mounting spine on ion ships or solar arrays on stations, with a nicer look than girders or I-beams, too.

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