I think some lights are going on somewhere

[Guest]

On 08/11/2017 at 10:40 PM, GoSlash27 said:

Starchaser,

 You have noticed something important: Higher Isp won't necessarily pay off against the weight penalty if the DV required for the mission isn't high enough.

 Next step, see if you can strip out all the dead weight. Carrying excess fuel that you never use is dead weight. Generally, when you eliminate the unnecessary fuel, you can use a lighter engine, which strips out even more dead weight, and even more fuel. Likewise, using a bigger engine than necessary is dead weight. On paper, higher t/w saves DV, but in practice, lower t/w can save mass and money.

 Finally, be sure to account for aerodynamics during the atmospheric boost stage as KSP models it. A design may "look" clean by real world standards, but be exceptionally draggy in KSP.

 I know from experience that you can deliver this same payload to Minmus orbit with a *much* smaller and cheaper vehicle.

For example:

[IMAGE]

I have used this model to not only collect science from Minmus orbit, but actually return it to Kerbin.

Good luck!
-Slashy

Given you stuck fins on it, could you use a solid lower stage to make it cheaper?

[GoSlash27]

1 minute ago, Rocket Witch said:

Given you stuck fins on it, could you use a solid lower stage to make it cheaper?

Rocket Witch,
 Absolutely, so long as the SRB is a BACC or larger. However, it will invariably be heavier.

Objectively, the "best" stage is the one that does the job with the least mass and/ or cost, but there are practical considerations that may override that. In the case of this rocket, having a solid first stage would've been cheaper, but would put me over the pad mass limit and would've led to stability and heating issues because it's not throttleable.

Best,
-Slashy

 

[Rocket In My Pocket]

17 hours ago, Zeiss Ikon said:

One question -- when did stock get a central monopropellant engine?  I just opened the one I have on this computer (1.2.2) and don't see anything like that.  The only monoprop engine I have that answers throttle (instead of RCS controls) is the Puff.  I do have 1.3.0 on my laptop, but it's a little precarious trying to use it at my desk (limited space) -- and I don't recall any added engines in that version.

Are you talking about my screenshot? That is the stock Puff. I just rotated and moved it to the center so it would look nicer.

13 hours ago, Starchaser said:

As for talking it personally, up to a point I was not. I enjoy debate and math. But one response seems to boil down to "you're practically cheating"...it's starting to feel personal.

You can't really claim monoprop is useful when you are using a mod added engine to make it so. As a blanket statement for the average KSP user: monoprop is the worst, least effective fuel in the game and should never be used for anything but translation during docking. If you are going to claim that monoprop is useful as a propellant based on a mod..then you are sort-of "cheating."

To clarify no one has a problem with you using and employing whatever mod you wish in your game, we all do the same. You just can't make a big point about monoprop being better than everyone thinks when that doesn't apply in the majority of peoples games. Perhaps we could have avoided some of this confusion if you had mentioned in your OP (or at any point really) that it was a monoprop engine added by a mod.

Edited November 10, 2017 by Rocket In My Pocket

[Urses]

If i have to be honest, i did build thuch rockets by my self... but if they are like here with first stage for almost orbit i would go a step farther and add the fairing below the first decoupler and cover the complete upperstage inside. It would be a little higher in buck factor but i evade the radius changes this way and have a slick design... but its only me.

And as said as long you reach your mission parameters ... you win

Edited November 10, 2017 by Urses

[GoSlash27]

29 minutes ago, Urses said:

as long you reach your mission parameters ... you win

Urses,
 I agree with this. Improvements are always something to celebrate. My point is just that there is room for even more improvement in Starchaser's program, and that improvement can come from a change in design philosophy.

 If the objective is to produce lighter and cheaper rockets, then candidate stages must be evaluated in those terms, with everything else being equal. You define the job to be accomplished by that stage; The payload mass to be accelerated, the minimum acceptable t/w, and the DV it needs to impart. When you have defined the problem, you create candidate stages that fulfill the mission requirement. These stages are then compared by mass and cost, and the "best" stage is the lightest and /or cheapest, with the caveat that the designer may choose a non- optimal design for other reasons.
 If you compare 2 stages that do the job, then the one with higher t/w isn't "best". The one with the most DV isn't "best". The one with a higher payload capacity isn't "best". These requirements have already been defined, and "moar" is of no benefit. The considerations are simply "which is cheaper" and "which is lighter". That's how you create light and cheap lifters.

 I'm advising against comparing 2 unequal designs and declaring one "better" merely because it imparts more DV. "More DV" is simply unburned fuel and tankage to hold it, which is dead weight. This philosophy winds up hindering your ability to create light cheap rockets.

 Best,
-Slashy

 
 

[Urses]

I agree with you Slashy. As i know in terms "most payload for lowest invest".... you need only to look in the challenges you are on the top places. The only thing where i would complain... KSP kills "debris", this way it prevents us to build "best" designs or follow other philosophies as "what i stage have to be cheap because it is scraped".

Other hand it would be plausible to build a SRB assisted lifter to bring a payload on a X-50 orbit where the upperstage circulacise on its own on Ap and the lifter comes back through aerobrake and shutes as near as possible at KSC.

I did this but i am not realy good pilot and landed over all of Kerbin.I am actualy on mode supported missuse. I build SSTO lifters, catch them up in Orbit with a tug and drain the fuel and disassemble them for materials needed for Stations.

Edited November 10, 2017 by Urses

[GoSlash27]

46 minutes ago, Urses said:

KSP kills "debris", this way it prevents us to build "best" designs or follow other philosophies as "what i stage have to be cheap because it is scraped".

Absolutely. The emphasis on "cheap" would be greatly reduced if the entire LV could be recovered. At that point, you run into fuel expenditure (or payload fraction) as the overriding economic concern, as we do in SSTO spaceplane design. You also run into a gamble with reliability, as you are betting that you will never lose a vehicle, which instantly erases the savings.

46 minutes ago, Urses said:

Other hand it would be plausible to build a SRB assisted lifter to bring a payload on a X-50 orbit where the upperstage circulacise on its own on Ap and the lifter comes back through aerobrake and shutes as near as possible at KSC.

 This is the basis of a counterpoint I was going to post in regards to a point raised upstream; "A stock monoprop design can never outperform a LF&O design".(Edit: A misunderstanding on my part. Nobody actually said this) One case this is not necessarily true: When the payload has monoprop tanks you weren't going to use and the DV budget is low. In this case, the monoprop engine has the advantage because the tankage is free. Even though the Isp is lower for the LF engine, there isn't enough burn time to make up for the mass of the fuel tank in fuel savings.
 On an even shorter scale, it may not be worth it to add the monoprop engine at all, as the reaction thruster itself is sufficient to provide the required DV. In this case, the monoprop engine would have to save more fuel than the engine itself weighs. On a short enough DV budget, there's not enough fuel expenditure to make this happen.

 Best,
-Slashy

Edited November 10, 2017 by GoSlash27

[Helmetman]

You load up a Minmus probe ship for a orbiting Minmus contract but you almost have the Delta V to land at the Mun and go back to Kerbin. Meanwhile your criteria is cost, not realizing you'd only need 4.3-4.6k to orbit Minmus.

For particular and direct help concerning the question where this thread started with the debate about LFO/RCS engine ISP and RCS/LFO tanks volume differences is moot although fun. Super duper moot in this case since the OP arguments so far are constructed on the basis of a mod, while the rocket in the OT wasn't even modded to begin with. At least I can't see any modded parts in the pic as per the pics that are shown. I don't want to derail that discussion, but I don't see how that discussion helps much tbh.

Anyway...

You do know you can put exterior parts as per the first pic on the OT into 1.25m service bays while meanwhile stop making draggier/weightier 2.5m rockets? 
Using a service bay reduces drag of all the batteries, solar panels and the other exterior science parts for which you apparently need a mushroom fairing.
Doing this reduces mass/cost considerably and you'd be better of. 

On the first design I see the top nosecone is lifted with a 0.625m part, but can't tell which one, I bet the small inline reaction wheels.
Attaching the end of a node with a different dimension creates a lot of drag. Any part under the nosecone can probably be put in the service bay also.

As for cost efficiency, only use SRB's for the first stage. Slashy mentioned this including the part of overheating, but you can reduce the thrust on solid rockets in the VAB and stop overheating below critical levels if your aiming for temperature limits.
Unless the rocket is covered with 1200 degrees Kelvin parts nothing should really explode on the way up. AFAIK tossing the science jr makes it so, which was your intention if I read correctly so no fuss there.

I see you used struts on the first iteration, but I just want to say that Struts produce drag. Less if the parent part of the strut is the most aerodynamic one but still. And honestly, I don't see why you would need struts at all. Is that joint really to weak? one strut will be enough, trust me. Put that one strut on the 90 degrees position facing the sea so it does a automatic gravity turn due to it's induced drag. I never do this, but if you desperately want the strut part it would work in your favor. Even better, why not use autostrut and forget all drag associated with them? Personally I'm not against a little bit of wiggling, as long as it reaches orbit.

Unless the first stage is powered by solids, I'm heavily against fins with control surface ability. So on your first design I can understand since it has SRB's. Meaning you want the fins attached to the SRB's, not on the center tank. No point hauling them further if the gimbal of the center engine does the rotation for you when activating it and dropping the srbs with the fins upon staging.
On your second design fins with control surfaces are not required. Just use normal fins or put pitch, roll and yaw off if you haven't already. Using the control surfaces of those fins and you will create quite a bit of aerodynamic drag when rotating during the gravity turn. At that point it is a gravity turn and aero turn/brake combo and this negates the pros of a gravity turn by a measurable margin if not completely. Added up drag loss due to control surface fins in operation is not much of a loss dv wise, but you don't really need control surfaces at the bottom, nor would you need fins if the rocket is aerodynamically stable without. A finless rocket is a design criteria I usually aim for anyway and perfectly achievable if you stop making mushroom fairings.

It's better to have a higher dry/wett mass ratio then the one you currently have when viewing the last two stages of your first design. Better spreading this will give you more Delta V for the mass your hauling. Engine isp and weight is just part of what's discussable. On the second last stage you have a wet mass of 8.2 tons, but a dry mass of just over 6.5 ton or thereabout. Basically your hauling the dry tank/engine mass for a small Delta V change which could be higher then tossing it for another stage. You would be more efficient packing more fuel in the last two stages then you have now.

Good change you end up with a two or perhaps 3 stage design if you apply all of the above. 

Edit: Oh blimey, did I write this much.

 

. 

 

Edited November 10, 2017 by Helmetman

[GoSlash27]

48 minutes ago, Helmetman said:

As for cost efficiency, only use SRB's for the first stage.

Helmetman,
 I was insisting on this same point a little over a year ago myself. I have since learned that this isn't quite correct. The cheapest disposable boosters are actually a quasi-asparagus arrangement of SRBs around a LF&O core.

Spoiler

 

An example of a quasi-asparagus hybrid design.

 

The cheapest solutions were in the $500 per tonne range, and about 150t payload.
 At the other end of the spectrum, the Flea and Hammer are not cost-effective when employed as first stages. LF&O designs will not only be lighter, but also cheaper.
 SRBs come into their own as first stages with the BACC and the Kickback, and can be very cheap... but it comes at the price of throttlability and steerability. Clustering boosters helps with the throttling issue, since the thrust can be tapered over the course of the flight. Unfortunately, by the time clusters come into play, you're getting into some pretty large payloads.

 All of that to say this: In the range of small rockets (such as the one I posted), SRBs aren't the best option. Too heavy, too expensive, and too temperamental. And since Starchaser's mission can be accomplished by a small rocket, SRBs are not viable in this case.
 

Best,
-Slashy

Edited November 10, 2017 by GoSlash27

[Urses]

We can go one step farther and misuse the abilitys given us woth actual fairings and use the interstages as structural Elements. The satelite core can be build on the fairing platform and all big elemenets like the antenas go in the interstages without decouplers as part of the structure. This way we have a slick strukture and linear and dont have any radii changes.

And for Slashys idea for a pure monoprop design. One of my beloved landers for small moons is a landable rover build of scince parts and have only RCS as engine for landings and to have stability on the ground. 2 command seats+sience container as option with own RCS and monotank with docking port and stackseparator to the main roverbody with science parts and you have a manned biomehopper with ability to gatger all science, reset all experiments and you have after personal recovery a perm station/rover for later missions. Switch the separator for a docking port and you can reuse this sweet little beast over and over again.

That is the part of KSP that will hold us in game.... you can try everething out and realy cant say it is impossible till no one trys it!

[Helmetman]

21 minutes ago, GoSlash27 said:

Helmetman,
 I was insisting on this same point a little over a year ago myself. I have since learned that this isn't quite correct. The cheapest disposable boosters are actually a quasi-asparagus arrangement of SRBs around a LF&O core.

  Hide contents

 

An example of a quasi-asparagus hybrid design.

 

The cheapest solutions were in the $500 per tonne range, and about 150t payload.
 At the other end of the spectrum, the Flea and Hammer are not cost-effective when employed as first stages. LF&O designs will not only be lighter, but also cheaper.
 SRBs come into their own as first stages with the BACC and the Kickback, and can be very cheap... but it comes at the price of throttlability and steerability. Clustering boosters helps with the throttling issue, since the thrust can be tapered over the course of the flight. Unfortunately, by the time clusters come into play, you're getting into some pretty large payloads.

 All of that to say this: In the range of small rockets (such as the one I posted), SRBs aren't the best option. Too heavy, too expensive, and too temperamental. And since Starchaser's mission can be accomplished by a small rocket, SRBs are not viable in this case.
 

Best,
-Slashy

That is really cheap indeed I'll see what I can do with what you call a quasi asparagus arrangement of srb's + lf/o center stage combo.   

Given your earlier posted designs your last argument holds true, definitely. Rather I was commenting on what could be done based on the pictures he posted. But going all the way for the best efficiency a complete re-design with a much lighter rocket is much better of course and I advice the same. 
But besides what you say is more efficient I don't see incredible differences in cost using 1st stage SRB's (Hammers, BACC or Kickback) compared to only LF/O 1st stages. SRB's are very temperamental indeed. A hammer with 3 basic fins is 575 funds to quikly get out of the atmosphere. A FL-T400 with a reliant as a second stage is 1600 Funds. On light rockets I usually use a hammer to get up to altitude so the second LF/O stage has higher ISP at higher altitude. I haven't really compared if a LF/O only design in this would be more cost effective, definitely by weight though. I Only know that the way I do it is very cost effective. But apparently not the most cost effective. 

I need to test this myself but I assume your right  

[regex]

16 hours ago, Starchaser said:

As for talking it personally, up to a point I was not. I enjoy debate and math. But one response seems to boil down to "you're practically cheating"...it's starting to feel personal.

It's because you're using a modded engine. Whether that's good or bad isn't really the issue, it's that monoprop engines aren't exactly the best thing in the stock game and most of these people are arguing from that frame of reference (using only stock parts). The isp of the modded engine you are using is 315 from the pictures I can see; monoprop in the stock game usually has an isp of 245 IIRC.

[regex]

4 hours ago, Rocket In My Pocket said:

AAs a blanket statement for the average KSP user: monoprop is the worst, least effective fuel in the game and should never be used for anything but translation during docking.

Incorrect. Monoprop engines and RCS should be used for whatever the player wants to use them for, within the confines of their effect within the game. That is, using RCS for any sort of velocity change is perfectly valid. Whether that meets your personal criteria doesn't matter, whether it meets the individual player's criteria of what is useful does matter. Blanket saying "this thing should never be used for any purpose other than this application" rules out many different creative designs and interrupts the learning process.

[Rocket In My Pocket]

16 minutes ago, regex said:

Incorrect. Monoprop engines and RCS should be used for whatever the player wants to use them for, within the confines of their effect within the game. That is, using RCS for any sort of velocity change is perfectly valid. Whether that meets your personal criteria doesn't matter, whether it meets the individual player's criteria of what is useful does matter. Blanket saying "this thing should never be used for any purpose other than this application" rules out many different creative designs and interrupts the learning process.

In the context of "just having fun" sure, use them for whatever you want!

Heck I make all sorts of designs that are impractical and goofy. That's half the game.

If we're talking about efficiency and practicality; which the OP was...that's a different story.

Edited November 10, 2017 by Rocket In My Pocket

[GoSlash27]

28 minutes ago, Helmetman said:

I don't see incredible differences in cost using 1st stage SRB's (Hammers, BACC or Kickback) compared to only LF/O 1st stages.

 Yeah, they're not necessarily a night and day difference. In some payload ranges, pure SRB first stage is the cheapest. In others, the LF&O is cheapest. In all cases, however, LF&O is lighter and easier to fly. In the case of "lighter", a pad limit or part count restriction may dictate chucking SRBs (such as in my example). In the case of "easier", the designer may opt for a more friendly LF&O design, particularly when the prices are close.

 Best,
-Slashy

[regex]

34 minutes ago, Rocket In My Pocket said:

If we're talking about efficiency and practicality; which the OP was...that's a different story.

It's not, though. Practicality is a loaded word and highly subjective; I find it eminently practical to use RCS thrusters for correction burns because they offer unparalleled precision and will often use nothing but on a mission if they can also do a braking burn, for simplicity. For efficiency and cost, sure, an Ant engine is generally better than RCS (which are abnormally expensive for some reason). The point, though, is that any such judgments are for the player themselves to make and there are no hard and fast rules in a sandbox game. Efficiency is not the end-all, be-all qualifier in terms of gameplay, even in career mode and what works for some doesn't make sense for others.

[Zeiss Ikon]

20 minutes ago, regex said:

For efficiency and cost, sure, an Ant engine is generally better than RCS (which are abnormally expensive for some reason).

Presuming RCS to be either catalyzed hydrazine or catalyzed high test peroxide (the only monopropellants with significant representation in the real world -- and hydrazine is winning by about a factor of twenty), the catalyst packs are expensive to manufacture.  Hydrazine uses, IIRC, nickel catalyst, which is at least cheaper than the silver or noble metals used to catalyze peroxide -- but pure nickel, manufactured in a form with a large reactive area, isn't cheap, even by rocket engine standards.

Edited November 10, 2017 by Zeiss Ikon

[Rocket In My Pocket]

43 minutes ago, regex said:

It's not, though. Practicality is a loaded word and highly subjective; I find it eminently practical to use RCS thrusters for correction burns because they offer unparalleled precision and will often use nothing but on a mission if they can also do a braking burn, for simplicity. For efficiency and cost, sure, an Ant engine is generally better than RCS (which are abnormally expensive for some reason). The point, though, is that any such judgments are for the player themselves to make and there are no hard and fast rules in a sandbox game. Efficiency is not the end-all, be-all qualifier in terms of gameplay, even in career mode and what works for some doesn't make sense for others.

I'm not sure they offer more precision than just limiting your engine thrust to 1% (Lowering your overall throttle increment sensitivity in the game options helps too) but then again I don't really use monoprop for that, you could be right.

In my opinion, if monoprop is always less efficient than other fuel, than anytime you take it you are hurting your overall Dv so, assuming you are trying to achieve game play goals in an efficient manner; you should never take monoprop unless you need it for translation; we don't need translation unless we are docking. (Even then...I guess you don't NEED it. But it's really the only valid use.) In the stock game you can say definitively that monoprop powered engines are an inferior choice for main craft thrust. I'm not saying that should dictate your designs, but it is a fact.

That said; I'm not a minimalist, efficient guy. I have a Space Shuttle design that carries it's wing into orbit vertically on it's back and then redocks with it horizontally to re-enter. I have a stock tilt wing VTOL, I fly planes around Kerbin for an hour instead of sending rockets, I have piles and piles of ridiculous, useless, impractical crafts. I love out there designs that try different things, and creativity in general. However if we're having a discussion and literally comparing numbers about what's more efficient, then that's what I'm going to discuss. Everyone should however, design in a way that suits them and play the game however brings them the most fun; efficiency be damned!

Edited November 10, 2017 by Rocket In My Pocket

[Starchaser]

1 hour ago, Rocket In My Pocket said:

However if we're having a discussion and literally comparing numbers about what's more efficient, then that's what I'm going to discuss.

Ok.

I'm backing up this truck and parking it.

The original intent of the post had nothing to do with efficiency. My reference to 'lights coming on' in the title is a reference to the fact that I'm beginning to understand game concepts and how to manipulate them instead of doing things brute force and with the first idea that comes to my head. The efficiency discussion came about because people asked why used a monoprop. I posted numbers to back up my decision, and was told I was wrong. I posted further numbers. It was a rabbit hole I didn't really want to delve in, but got sucked in because I can't seem to help but debate a topic when presented with the opportunity.

FWIW, 1) my total delta-v is what it is, because I had the idea with this rocket to start building comm constellations after fulfilling the initial orbit matching. Which is also why there are antennae on the craft that won't fit inside a 2.5m wide fairing, or a 1.25m service bay, which was also suggested. 2) The mod and the engine. I played KSP for maybe 3 weeks 2 years ago, and quit on it when I couldn't get landing and docking, and a different game I had been waiting for came out. I picked it up again about a month ago. I find it disingenuous to expect me to know what parts are stock and which are not when I've opened a node I haven't seen before, while on the other hand, you've played for at least 2 years and can't identify a part as non-stock when given it's name. That's not intended as an attack, but merely holding a mirror up from what you expected of me. 3) I do listen to what I'm told, even when it seems I'm being stubborn and pigheaded (my most endearing traits!) I've tried a few of the ideas presented here in the few rockets I've designed since this topic started and have altered my design plans for others. (I currently have 13 active flights. I often have to wait for gaps in the schedule to design and launch new rockets)

Edited November 10, 2017 by Starchaser
Hit submit before I was ready

[Rocket In My Pocket]

36 minutes ago, Starchaser said:

I find it disingenuous to expect me to know what parts are stock and which are not when I've opened a node I haven't seen before, while on the other hand, you've played for at least 2 years and can't identify a part as non-stock when given it's name. That's not intended as an attack, but merely holding a mirror up from what you expected of me.

Well to be fair, yeah; I do sort of expect you to know which mods you have installed; you installed them after all.

Also, you called it a "monoprop engine" in your OP, once you specified later on which engine in particular I realized it was not a stock option.

Perhaps we got off on the wrong foot here; I'm not judging you for using a mod; I use plenty of them. I was just trying to clarify why there were so many people questioning you about the monoprop engine design. I apologize if it came off like I was attacking you, certainly not my intent.

[Starchaser]

57 minutes ago, Rocket In My Pocket said:

Well to be fair, yeah; I do sort of expect you to know which mods you have installed; you installed them after all.

Heh. Yes, I know what mods I have installed.

I don't necessarily know what parts near future intersperses in existing nodes.

58 minutes ago, Rocket In My Pocket said:

Perhaps we got off on the wrong foot here; I'm not judging you for using a mod; I use plenty of them. I was just trying to clarify why there were so many people questioning you about the monoprop engine design. I apologize if it came off like I was attacking you, certainly not my intent.

Fair enough. I was most likely too defensive. My apologies also.

[Starchaser]

Stuff I learned about efficiency from this thread:

 

 

Note that 9000 of the cost is a required science part, to complete the scan contract. And I haven't thrust limited the SRB. It's on my to-do list!

[GoSlash27]

Very nice!

V1: $33,700/ 62.5t
V2: $26,500/ 47.0t
V3: $19,000/ 7.37t

That's some serious savings!

-Slashy

Edited November 11, 2017 by GoSlash27

[Atkara]

Good one.

I think you may want to check (if you haven't done so already) if your solar panels deploy properly. If not, I would consider moving them back a bit. And if I wasn't planning on retracting them (which is often the case in probes) I'd use a simpler (and slightly lighter) model, like the OX-4L.

[Starchaser]

1 hour ago, GoSlash27 said:

V1: $33,700/ 62.5t
V2: $26,500/ 47.0t
V3: $19,000/ 7.37t

That's some serious savings!

It's only fair to point out, Slashy, that V1 is designed for minmus orbit, v2 to take a payload to minmus, then become part of a duna comm constellation, and possibly fulfill a future scanning contract in the duna system, and v3 is only to do a scanning contract orbiting kerbin. I'd have given v3 less delta V but I am not terribly good at launching to a precise  inclination that isn't 0 yet. It had a couple hundred delta-v left when I got it on the designated orbit. On the other hand, I launched right to a 450 ish km orbit and my circularization burn was 36 delta V

 

1 hour ago, Atkara said:

I think you may want to check (if you haven't done so already) if your solar panels deploy properly. If not, I would consider moving them back a bit. And if I wasn't planning on retracting them (which is often the case in probes) I'd use a simpler (and slightly lighter) model, like the OX-4L.

The panels opened fine. I usually do use the 1 use panels on probes, but it was really late when I put this thing together and I missed that detail. Heh. Now I wanna look at my original pics and make sure I didn't use the retractable panels there too.