[newbie] Mothership burning issues

[GuyWithGlasses]

Hello everyone!

Yesterday I achieved to put in a LKO Orbit (100x85Km) my first mothership (more or less, 480Tn in one launch with a SSTO cargo-launcher), consisting in 1 Lander, 1 refueler, 1 toroidal orbital station, 4 sats and a interplanetary propulsion module. I want to make 4 contracts in Duna at the same time (in carreer mode, after the launch I realiced I have to do it again, as the refueler and one sat won't meet contract parameters) and is my first time kerbals go out the inner Kerbin system (kerbin-mun-mimmus).

 

The issue come with de interplanetary propulsion module, Its a "beast" made with 4100 m/s in dV (including the mass of the rest of the mothership) enough to go to Duna (and I think to other planets) and it has 4 LVNs engines, its my first time I use high-ISP-but-Low-Thurst engines.

I found a maneuver that intercepts Duna in around 197 days, but the burn maneuver takes 1h. If I start burning 25min before the node, as the mothership is in a LKO orbit, the mothership reduces its periapsis and fall into Kerbin XD

How can do a good maneoveur?  I think I need to go first in a higer orbit, but which? Shall Do I circularice in a higher orbit?  (for example 500x 500 Km)  Shall do I get into a higher orbit with excentricity (increasing the zone  of the node, for example)?

Another answer I have, Do I need to play myself the 50min-burn? I haven't unblocked in my tecnology tree  the "go-to-maneuver" Okto parts (my best part is OKTO2). I Don't want to add more LVNs, as they are expensive and will reduce the total delta-V of the mothersip.

I play with sotck parts only, and I have installed Kerbal Engineering Redux and Kerbal port aligment indicator as mods.

 

Thank you!

[Deddly]

Welcome to the forum, @GuyWithGlasses! Sounds like you're doing great! Those long burns can be a pain sometimes. The trick is to split the burn up into two or three shorter burns. So, for example, the first time, you burn for 20 minutes. You should still be in orbit of Kerbin, so come around again, burn for another 20 minutes and the third time you should be able to complete the burn. You can use 4x physics warp during the burn, so each of those burns should only take 5 minutes for you.

Have fun!

[BjM]

Hi! Sorry, newbie too, so newbie answer.

By what you say I can only think of 2 possible things;

1-because of your low orbit you need to start the burn so earlier that you're starting the burn towards Kerbin;

2-You are inverting your orbit;

I don't think 2 is the case. But if it was than at some point your orbit would go straight down kerbin and than start to circularize again.

But, to the more interesting, the 1. @Deddly is ponting a good solution. I would add that  I would look how much is my orbit time (sorry I'm not that into the correct terms) and divide the burn to something that made than start, guessing here, not more than 45º os so before the node. And not everyone the same time, like 3x20min. After every burn your orbit will becomes "larger" and you will get a greater window to burn. Even if it ends with a diferent result from the original node because the longer time to finish the burn it's really easy, and cheap, to do some adjustments on the middle of the travel to Duna.

Other solution is what you pointed, get a higher orbit. This way you will have more time "aligned" with your node, not burning towards Kerbin. 

I didn't do calcs, so others could point better what solution is less expensive.

Hope it helps!  

PS: while in orbit, rightAlt + > or < adjust the physics warp by default

[Spricigo]

 

7 hours ago, GuyWithGlasses said:

... in a LKO Orbit (100x85Km)...

...the burn maneuver takes 1h....

a small inconvenient : your orbital period is 32min

Imagine that you point at the maneuver marker and start your burn, At first you maneuver marker is pretty close to prograde and you raise your orbit (a painfuly slow rising).  But as you perform your burn those will deviate more and more, after 8min they are perpendicular, after 16min you are pointing retrograde. And that is your problem, half of the time you are lowering your orbit instead of raising it.

7 hours ago, GuyWithGlasses said:

How can do a good maneoveur?

My advice is to go back to the drawing board and redesign your entire mission. Rethink what is necessary to archieve the goals of the mission and what is just dead weight you can cut. Try to have just the necessary for each phase of the mission with a small safety margin. Particulary for engines, remenber to consider Thrust and Weight (Nervs have high Isp, but are heavy and weak). 

 

edit: for help with the redesign, please describe the mission objectives/requirements and provide a few images of what you had built so far.

 

Edited August 16, 2017 by Spricigo

[Shadowmage]

My solution to long ejection burns -- start from a much higher orbit.  You'll have a longer orbital period, and plenty of time to complete the burn.  I think for a 1hr burn, you might want to try a 1000km (1,000,000m) circular orbit.  I've had good luck with ~750km for 30-40m burns.

You lose a bit of effiency/oberth... but it is better than missing the x-fer window or massive post-ejection correction burns.

[Vanamonde]

I also like to fly large/low-G tractor ships hauling payloads, though mine tend to have 15-20 minute projected burn times. I simply launch from a higher orbit, knowing I will lose some efficiency due to sacrificing an Oberth boost. A long burn will take place over changing altitudes anyway, so I don't think the loss ends up being significant. Multiple burns on successive orbits is entirely practical as an alternative, but I find it not to be helpful since you have to worry about the moons of Kerbin interfering with your path as you cross their orbits during multiple passes. 

[DerekL1963]

6 hours ago, Shadowmage said:

My solution to long ejection burns -- start from a much higher orbit.  You'll have a longer orbital period, and plenty of time to complete the burn.  I think for a 1hr burn, you might want to try a 1000km (1,000,000m) circular orbit.  I've had good luck with ~750km for 30-40m burns.

This.  Messing about with node splitting complicates things and can require large correction burns. 

[Cpt Kerbalkrunch]

@GuyWithGlasses, you already have your ship built, and it sounds like you know what you want to do, but since you're asking for advice I'll just give my opinion. If I had to make just one suggestion, it would be this: ditch the Nervs. They have the lowest TWR in the game. They're heavy, expensive, and weak. I respect their capabilities, but I despise all their drawbacks and never use them. It's just a personal preference for me, but for you; you're only going to Duna. That's a big step early on (your first interplanetary mission is extremely exciting), but it's a pretty short trip from Kerbin. You can get there and back without building a large ship; even when using only chemical rockets. I'll assume you're planning to land on Duna and Ike while you're there as well; in which case, the higher TWR of chemical rockets will come in handy. Notice in the VAB that a Terrier has the same thrust as a Nerv at just 1/6th the weight, and about 1/25th the price.

[GuyWithGlasses]

Hehehe Thank you for all your comments! I'm stirred to see so much comments talking about kerbals things!

First of all, The problem is that  Spricigo says, I'm burning retrogade cause the ship has 30-40 minuts orbit in LKO.

As spricigo ask, I'll post the mission objetives;

First of all, boost the kerbalkind knowledge of the kerbol system and met the customers contracts in the cheapest way (cheers ).

Now, seriously, the mission objetives;

1.  Prepare the Duna's system to a full deploy of my agency; In my opinion it must have:

       1.1 Sats to prepare an efficient Relay network for unmmaned mission: avoiding as much as I can Duna/Ike/Kerbol/Kerbin/mun/Ike  eclipses  (or to land in a place of a planet that the own planet breaks the line of sight of Kerbin). I've had problemms with this in my unmmaned mission in Mimmus & mun (the mothersip has two specific sats for this).

       1.2 Ore Scan for Ike & Duna surface. Another two stats (with complement 1.1 as the already has a Relay antenna) that i'll deploy in polar orbit. I think the final result with 1.1 & 1.2 is to have two sats in each planet/moon in polar orbit with high excentricity each (I won't look for a synchronous orbit yet).

       1.3 An orbital station (with a torus, but without much H2 + O2, Its only have a tiny Poodle engine and little tank for orbit corrections). I've just added the toroidal life support cause its cool and I want to avoid the kraken gets angry x_D (but sincerely, Its about 10Tn waste compared with the stock Mk3 ).

       1.4 One Refueler (with 3 seats for people, a pilot, an engineer and a scientist) with ISRU, to allow do extra missions in the future (and achieve a contract). I want it can land in Duna & Ike.

       1.5 One Lander  (with 3 seats for people, a pilot, an engineer and a scientist) for Duna & Ike. This lander is the ship that has the scientific staff, I want to unblock the lastest things in the tech tree.

       1.6 The cargo launcher. My first ship with (4) LVNs, It'll bring the ship to LKO to Duna, and will help the stats in the plane change. In adition, it has a mk3 module to transport kerbals back to kerbin/ another planet or to use it as a "tourist bus".

 

2. Achieve the contracts I have already accepted.

      2.1 Orbit around Duna (easy).

      2.2 Put a sat in a Kolinya Orbit (1 of the relay sats have modificed to meet the contract specifications).

      2.3 Harvest 2700 minerals from Duna and move it to Ike's orbit (I counted bad last time, and my refueler has only capacity for 2400 ore, I'm redesigning it).

      2.4 Test "Twitch engine" on the surface of Dune (I've installed it in the lander).

3. Other goals.

      3.1 As I'll travel across Kerbol SOI to met Duna, I've already added another sat with a SENTINEL telescope to discover asteroids.

      3.2 Practice/build the interplanetary transfer / mothership. With about 4100 dV (with the rest of the modules installed in it) I think  I could use this setup (with few changes in the refueler-lander) to meet moho - dres - jools moons.

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Comments.

Cpt Kerbalkrunch, I don't like low thrust engines either, but LVN dobles ISP respect poodles engines (the best ISP engine in VAC), and as the cargo-ship will be only in space, I think Its safe.  Am I wrong?

-----------

Rest. I'll try the splitted-3-burn-way, if there is consensus its the best way to do the maneuver.

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I'll try to take some screenshots of all the elements / parameters when I return at home this afternoon, to complete the post ( I think the key in this mission is the refueler, I'd modified it yesterday, but I'm not sure it has an optimal configuration).

 

But the thing I'm more afraid of about all this things i've written is I'll wont be able to launch it until I'll come back from my holidays (in two days i'll be out of the country). ¡one week thinking my mothership is waiting for me! LOL.

 

Thanks!

 

 

Edited August 17, 2017 by GuyWithGlasses
I havent finished the post, already. Orthographic corrections

[Cpt Kerbalkrunch]

2 hours ago, GuyWithGlasses said:

 

Cpt Kerbalkrunch, I don't like low thrust engines either, but LVN dobles ISP respect poodles engines (the best ISP engine in VAC), and as the cargo-ship will be only in space, I think Its safe.  Am I wrong?

-----------

Rest. I'll try the splitted-3-burn-way, if there is consensus its the best way to do the maneuver.

-----------

I'll try to take some screenshots of all the elements / parameters when I return at home this afternoon, to complete the post ( I think the key in this mission is the refueler, I'd modified it yesterday, but I'm not sure it has an optimal configuration.

No, you're not wrong at all. That's exactly what the Nerv is made for. It's just a personal preference. I can't stand those 30 minute burns. When I wanna make a plane-change or a transfer, I want it to happen quickly.

I like the mission profile you've set up. I'm a fan of stacking contracts myself. I try to make every flight as profitable as possible. I would agree that it sounds like the ISRU is going to be pretty important. Haven't seen your setup, but as long as you have thermal controls and a good engineer, you should be fine. Hope all goes well.

[Spricigo]

3 hours ago, GuyWithGlasses said:

I don't like low thrust engines either, but LVN dobles ISP respect poodles engines (the best ISP engine in VAC), and as the cargo-ship will be only in space, I think Its safe.  Am I wrong?

There is more to consider than just Isp.

A engine with better TWR would allow you to complete the burn in a much shorter time. It allow you to make more of oberth effect (no need to go to higher obit) or make your mission simpler (no need to divide the burn). IMHO more relevant, it free player time to use with other things in the game instead of an hour long burn.

Notice that doing the maneuver along a curved trajectory have an inherent inefficiency. Either because of the  variable angle between the Thrust and a Velocity or because part of the early burn is canceled out by part of the later burn. A low thrust maneuver will sweep a larger angle thus suffereing more from this effect. It will be more or less relevant depending on what you do to deal with it (higher orbits, divided burn...) and how much of a 'safety margin' you have available.

 

 

[Kryxal]

16 hours ago, Vanamonde said:

I also like to fly large/low-G tractor ships hauling payloads, though mine tend to have 15-20 minute projected burn times. I simply launch from a higher orbit, knowing I will lose some efficiency due to sacrificing an Oberth boost. A long burn will take place over changing altitudes anyway, so I don't think the loss ends up being significant. Multiple burns on successive orbits is entirely practical as an alternative, but I find it not to be helpful since you have to worry about the moons of Kerbin interfering with your path as you cross their orbits during multiple passes. 

In this case, I don't think multiple burns (the "periapsis kick") will be effective.  I think the best thing to do is going to be locking on to prograde and moving to a MUCH higher orbit.  Given that the destination is Duna, delta-v is about 1 km/s, and for that to take an hour-long burn, TWR must be around .03 for the ship.  For a redesign, I'd suggest tripling the number of engines at least, but now, leaving from a high orbit's the practical way.

[Deddly]

Trust me. Splitting the burn into two (or maybe three) will make a big difference.

[GuyWithGlasses]

 

Here we go!

I never have used imgur, I hope this work!

The refueler.

http://imgur.com/7AE6CRN

Comments.

Yesterday I decided to equip it with a Vector engine intead the old one (skipper) to get more thrust (casue now it can carry 3000 of ore instead 2400).

The screenshoot is taken with the ore tanks full and simulating 14Km in the kerbin atmosfere using ker (I read its equivalent that landed in Duna). With respect the mum-mimmus refueler one, I just added 4 radial chutes & 4 normal chutes and reduced de converotron 250 to the smaller 125 (to reduce weight). The result, TWR is around 1 that I hope would increase in Duna (different G and stuff). I just realized I need to add I more seat  (only 2 avaliable in the lander can), i'll get lower TWR,  f*c# xD  

..and I must confess the temperature control system (1 big radiator + 8 little temperature control system) is not even thinked at all, Lol

 

The lander

http://imgur.com/EIYPWYu

I think its just correct (and a bit ugly)

 

The mothership

http://imgur.com/rAUrF4p
http://imgur.com/Dvfe08w
 

------

1 hour ago, Kryxal said:

In this case, I don't think multiple burns (the "periapsis kick") will be effective.  I think the best thing to do is going to be locking on to prograde and moving to a MUCH higher orbit.  Given that the destination is Duna, delta-v is about 1 km/s, and for that to take an hour-long burn, TWR must be around .03 for the ship.  For a redesign, I'd suggest tripling the number of engines at least, but now, leaving from a high orbit's the practical way.

 

I think there will be a war:  the greedy in me (you talk about raising 80k funds of the cost of the mission!) against the bored me !!! LOL.

Pd: I really apreciate all your comments, they are very interesting! thx!

 

[DerekL1963]

6 hours ago, Spricigo said:

Notice that doing the maneuver along a curved trajectory have an inherent inefficiency.

That's why you go high rather than splitting down low - you minimize that inefficiency by minimizing the swept angle.  (My rule of thumb is "orbital period <= 1/8 burn time".  I've never had to make a larger than normal mid course correction burn using this method.  (As compared to the burns made down low with a higher t/w engine.)

 

6 hours ago, Spricigo said:

A engine with better TWR would allow you to complete the burn in a much shorter time. It allow you to make more of oberth effect (no need to go to higher obit) or make your mission simpler (no need to divide the burn).

Except at the smallest sizes, a high TWR engine also considerably increases the weight of your vehicle, significantly reducing the total TWR of the vehicle.
 

6 hours ago, Spricigo said:

IMHO more relevant, it free player time to use with other things in the game instead of an hour long burn.

I've never seen the problem here.  With MJ automating the burn, I just go do other things during long burns.  I either swap to my browser and cruise the web, or sit on the couch and watch anime, or go into the kitchen and start dinner...  once I even went to the grocery store.

[Spricigo]

2 hours ago, DerekL1963 said:

That's why you go high rather than splitting down low - you minimize that inefficiency by minimizing the swept angle.  (My rule of thumb is "orbital period <= 1/8 burn time".  I've never had to make a larger than normal mid course correction burn using this method.  (As compared to the burns made down low with a higher t/w engine.)

The fact there are ways to deal with it don't mean is not a issue. Chose your approaching and deal with the consequences. Going higher means forfeiting some Oberth Effect, spliting the burn means increasing complexity, more engines add to the dry mass... 

Quote

Except at the smallest sizes, a high TWR engine also considerably increases the weight of your vehicle, significantly reducing the total TWR of the vehicle.

No necessarily, it depends on how much more fuel (and tanks) is necessary for the vessel with those engines need to have the same deltaV. If 12t of nervs are not powerfuyll enough, maybe one should consider 3.5t of Poodles or 9t of Rhinos.

Quote

I've never seen the problem here.  With MJ automating the burn, I just go do other things during long burns.  I either swap to my browser and cruise the web, or sit on the couch and watch anime, or go into the kitchen and start dinner...  once I even went to the grocery store.

well, I prefer to fully avoid game parts that are less fun than grocery.

[DerekL1963]

2 hours ago, Spricigo said:

No necessarily, it depends on how much more fuel (and tanks) is necessary for the vessel with those engines need to have the same deltaV. If 12t of nervs are not powerfuyll enough, maybe one should consider 3.5t of Poodles or 9t of Rhinos.

Yes necessarily.  Except at the smallest size (where the weight of the engine dominates), if you want the same d/v as a NERV a conventionally powered vehicle end up heavier.  That's a mathematical and unavoidable consequence of the drastically lower ISP of those engines.  (Or to put it another way, your quoted comparison of the weight of the engines is dramatically and grossly incorrect and misleading because you leave out the weight of the fuel.)

Here's a simple comparison:

A NERV (vacuum ISP of 800) producing 5k d/v:



A Poodle (vacuum ISP of 350) producing 5k d/v:



A Rhino (vacuum ISP of 340) producing 5k d/v:



(Even though the Rhino's ISP is only slightly lower than Poodle's, it requires much more fuel because it weighs five times as much.)

The math doesn't lie.  The math never lies.  Except at the very smallest scale, where the weight of the engine dominates, a NERV will always have a dramatically higher d/v for the same weight due to it's dramatically higher ISP.  Always.

[wumpus]

On 8/16/2017 at 6:53 PM, Vanamonde said:

I also like to fly large/low-G tractor ships hauling payloads, though mine tend to have 15-20 minute projected burn times. I simply launch from a higher orbit, knowing I will lose some efficiency due to sacrificing an Oberth boost. A long burn will take place over changing altitudes anyway, so I don't think the loss ends up being significant. Multiple burns on successive orbits is entirely practical as an alternative, but I find it not to be helpful since you have to worry about the moons of Kerbin interfering with your path as you cross their orbits during multiple passes. 

Before embarking on this course I would suggest saving, jumping to a higher via hyperedit and checking how much delta-v it takes from an orbit that allows a ~50 minute burn.  Add the delta-v needed to get that orbit and make sure you have the required fuel (if you built the spacecraft based on the "subway map" numbers, you might be in for a bit of a shock).

In any event, you are almost certainly going to need multiple burns simply to get up to the orbit needed for a final burn.  A burn of 1-2 minutes on each side of periapsis (and/or the initial "burn here" mark) will quickly raise you up to a longer orbit (don't make it too long, you don't want to significantly change your trip to Duna) [hopefully you can deal with 2x physics acceleration.  Be careful, big motherships don't like much physics acceleration].  Once you are ready for a final burn, [save game] raise your PE (to allow for a longer, more accurate burn, if a less efficient one) and create another maneuver node. [Check your fuel reserves and be ready to reload with a lower orbit].  Hopefully it will be much less than 50 minutes, but you should be able to now handle even that much if needed.

PS: thanks to the difference in escape velocity vs. hohmann transfer, you shouldn't have much of a problem doing this Kerbin->Duna.  You can start with up to 900m/s on Kerbin (don't go that high or your orbits take so long they throw off your window calculations) and only need ~200 m/s for the final kick to Duna.  Going to Jul means an extra ~1000m/s from Kerbin (according to the subway map, which assumes a burn from LKO.  Don't expect to be able to burn 1000m/s efficiently from there), so the final kick needs as much delta-v as all previous kicks combined.

[Spricigo]

10 hours ago, DerekL1963 said:

Yes necessarily.  Except at the smallest size (where the weight of the engine dominates), if you want the same d/v as a NERV a conventionally powered vehicle end up heavier.  That's a mathematical and unavoidable consequence of the drastically lower ISP of those engines. 

Take a look at the rocket equation:  

So are you arguing that  800X will always be greater than 350Y, no matter the value of X and Y.  You didn't checked if the math backed up your assumptions  and it cleary don't.

Quote

Or to put it another way, your quoted comparison of the weight of the engines is dramatically and grossly incorrect

The OP had 4 nervs engines, that is 12t. He stated that the low power of those (240kN) is a issue for him. I just presented more powerful chemical options, namely a pair of Poodles (500kN, 3,5t) or a single Rhino (2000kN, 9t) something the OP may explore instead of more (heavy and weak) nervs.

And that was never intended as a comparision of the engines TWR  because the nerv is pitfull in that regard. Terrier, poodle and rhino not only have better TWR, they have better TWR at sea level than the nerv at vacuum.

Quote

 misleading because you leave out the weight of the fuel.

No, I didnt left it out. Exactly the opposite, as  I said, that is the variable to consider. And make all the sense to keep it as a variable. What would be misleading is to assume a incorrect value.

 

Quote

Here's a simple comparison.

Simple and totaly irrelevant. 1. I never said that cases where nervs are superior don't exist (or even are incommon) and you just picked cases where it happens. It just 'proves' the incontested obvious. 2. The TWR of the vessels with Poodle and Rhino are bigger by a lot.* make a comparison of vessel with similar TWR and see how the nerv fares.

Well your idea of a fair comparison is Okto2, fuel tank, engine, let me try it with tiny tanks:

nerv+Mk0Fuselage+50LF+OKTO2=556m/s; 

Rhino+OscarB+18LF+22Ox+OKTO2=72m/s; 

Poodle+OscarB+18LF+22Ox+OKTO2=352m/s;

Ok, seems that nerv is superior, however the Poodle variant is more powerfull and ligther, lets try with poodle with an extra OscarB:

 Poodle+(2x(OscarB+18LF+22Ox))+OKTO2 =675m/s   

still more powerful and light than the nerv let use a FL-T200:

Poodle+FLT200+90LF+110Ox+OKTO2+smallReactionWheel+HG55+2solarpanels+ScienceInstruments=1300m/s, it can flyby Duna or Eve to collect some science. 

*Intersting that you previouly tried to imply that the weight of those more powerful engines would shift the TWR advantage in favour of the nervs and your example show quite the opposite.

**You probably guessed that terrier, spark and ant are even more efficienty in this  envelope.

Quote

The math doesn't lie.  The math never lies.

So stop to ignore the math. Design a reasonable vessel for the Kerbin-Duna transfer with nervs and similar one with poodle and see what MJ says about it. if the one with nervs is better for you fine, but dont just assume the poodle can't compete because the only stat you cared to look at is Isp.

Quote

Except at the very smallest scale, where the weight of the engine dominates, a NERV will always have a dramatically higher d/v for the same weight due to it's dramatically higher ISP.  Always.

False. just some point to you consider:

1st: 4km/s to a transfer to Duna is not an advantage but a hindrance. More than half of this is just dead weight and will not be used unless a murderous inefficient trajectory is chosen.

2nd: For the necessary deltaV, depending on the payload mass, the chemical transfer vehicle will be considerable lighter then the nuclear transfer vehicle

3rd: Not everyone like to fly gargantuan vessels that take ages for the slightest trajectory adjustment.

 

 

 

[DerekL1963]

18 minutes ago, Spricigo said:

2nd: For the necessary deltaV, depending on the payload mass, the chemical transfer vehicle will be considerable lighter then the nuclear transfer vehicle

I've already pointed that out, twice. ("Except at the smallest scale (where the weight of the drive dominates) the NERV will always be lighter".)

 

20 minutes ago, Spricigo said:

So stop to ignore the math. Design a reasonable vessel for the Kerbin-Duna transfer with nervs and similar one with poodle and see what MJ says about it. if the one with nervs is better for you fine, but dont just assume the poodle can't compete because the only stat you cared to look at is Isp.

I didn't say it couldn't compete, not even once.  I pointed out (twice) that (except at the smallest scale) a vehicle powered by Poodle's will be heavier than one powered by NERV.
 

22 minutes ago, Spricigo said:

Well your idea of a fair comparison is Okto2, fuel tank, engine, let me try it with tiny tanks:

Congratulations!  You've "proved" what I already admitted to and pointed out two times now - at small scales a NERV comes off far worse.
 

29 minutes ago, Spricigo said:

Not everyone like to fly gargantuan vessels that take ages for the slightest trajectory adjustment.

No offense, but do you even understand what this discussion is about?  Please scroll back up and read the OP's post.  This discussion is all about gargantuan vessels - vessels in a weight range where NERV's have a vast advantage.


 

[Spricigo]

3 minutes ago, DerekL1963 said:

I've already pointed that out, twice. ("Except at the smallest scale (where the weight of the drive dominates) the NERV will always be lighter".)

 

what the heck you are considering the smallest scale? Certainly not the same I consider a small scale: probes under 1t.

Lets recap:

-I pointed out that under some circumstances the nerv is not the better option. And I  pointed out some advantages of other engines with better TWR (anything but the down)

-You quoted the my comment about engine TWR and claimed I was wrong because: 1. except at the smallest size , no matter how much deltaV is required, the nerv is better.

-I pointed out that you cannot generalize that conclusion to any case. And again pointed out that under some circunstance the nerv is not the better option exemplifying with the case where someone start to use multiple nervs to have a better thrust.

-You insisted that the nerv is better, no matter deltaV, no matter thrust. you claimed that only Isp matter. And you added a demonstration.

-I pointed out that Isp not the only factor and that you demonstration just show a particular case. I give an example where your conclusion are incorrect.

-you are arguing that I'm misinterpreting you.

ok let tell you what I'm interpreting: I claimed that under some circumstances the Nerv is worse, under other is better; You said I'm wrong; I patiently tried to clarify my point, show what are the factor I'm considering and that I didn't claimed that the nerv is always worse but under some circumstances is. You keep avoiding any argument I present, keep ignoring my point and telling I'm wrong. Now you are claiming that I'm misinterpreting you? Really?!

You are claiming that I'm wrong., Show me some evidence that, no matter the required deltaV, no matter the required vessel TWR the nerv engine will be superior to the poodle. 

And what the heck are the engines in the smallest scale if the Poodle, a LARGE engine, is included in it?  

 

 

 

[Deddly]

I think the discussion has moved beyond what OP was asking for and is now in danger of getting out of hand with a disagreement. Please be careful, people. 

[GuyWithGlasses]

Hello everybody!

I came back from my holidays last week, soI have to update the space program advances!

First of all, I changed the interplanetary booster, the final configuration has 9 LVN, and the interplanetary burn is around 20 minutes. Thanks to all for your comments, modifying phisics warp has been a good learning for me!

In all the tests I have done, I usually do the tranfer burn in three times; two consisting around of 4-5 minutes burn and the last a longer burn (If the total burn time in the first two burns is more than 15minutes, more or less, the ship escapes from the kerbin orbit or has a time orbit of a lot of days).

 

My first try I wasn't able to put the ship in the interplanetary orbit, due to I had to do myself the control of the ship (Okto2 doenst have "follow manouveur"). So I purchased the science for the RC-001S and updated all the ships.

My second and third try I was able to put the ship in the interplanetary orbit, but it was a very bad orbit (around 84 days of trip, but the ship wasnt able to acomplish the insertion burn, too much cost of deltaV).

My fourth try I configured de interplanetary orbit for a 284 days trip (more or less, the standar). I could put the ship in a rasonable orbit around Duna, but wasting a lot of fuel (all indeed xD since the encounter distance was  20000Km, the ship orbited Duna in a near polar orbit that I had to change, etc...). Now,  I have to learn to fine-tune the distance of the encounter once I've done the three burn maneouveur . ¡But, I was able to do my first experiments with landers in Duna!

 

The results of the experiments were a bit bad:

- I think the lander had few deltaV (around 1400m/s before the landing burn), and few aerobraking parts (one or two of the times I tried to land, it was a crash xD).

- The refueler had few solar panels (4) and for this reason, worked bad (I couldnt power on at the same time the four drills and the converotron 125).

 

Now, I have redone the lander (around 1900m/s in the VAB at 20Km simulation of the atmosfere) and the refueler. Now I'm doing the interplanetary burn,  I hope this week I wiil be able to do the second Duna test of the landers!  but honestly, I think it will go bad, I think the modifications of the refueler has added too much weight, its about around 1400m/s of deltaV, but with 4000 units of ore in it (I can convert fuel during flight... we'll see).

 

I'll try to update the post with some screenshots later!

 

Best regards!

 

 

 

 

Edited September 5, 2017 by GuyWithGlasses
correct orthographics issues

[mk1980]

1 hour ago, GuyWithGlasses said:

My fourth try I configured de interplanetary orbit for a 284 days trip (more or less, the standar). I could put the ship in a rasonable orbit around Duna, but wasting a lot of fuel (all indeed xD since the encounter distance was  20000Km, the ship orbited Duna in a near polar orbit that I had to change, etc...). Now,  I have to learn to fine-tune the distance of the encounter once I've done the three burn maneouveur . ¡But, I was able to do my first experiments with landers in Duna!

consider doing a correction burn during the transfer (ie. while you're in solar orbit). it's much cheaper that way. i started a duna mission in my career yesterday. set course for duna, had an encounter at ~45,000 km. correcting that encounter via a burn at AN/DN during transfer is really cheap (see image) - the whole correction burn to turn that insane 45,000 km flyby trajectory into an almost perfectly lined up equatorial flyby at ~60km above the surface costs a whopping 15.8 m/s when you plot it far away from the target SOI. a similar set of correction burns within the SOI probably would cost a few hundred (or even thousands) of m/s

https://imgur.com/a/Gmv2A

[GuyWithGlasses]

1 hour ago, mk1980 said:

consider doing a correction burn during the transfer (ie. while you're in solar orbit). it's much cheaper that way. i started a duna mission in my career yesterday. set course for duna, had an encounter at ~45,000 km. correcting that encounter via a burn at AN/DN during transfer is really cheap (see image) - the whole correction burn to turn that insane 45,000 km flyby trajectory into an almost perfectly lined up equatorial flyby at ~60km above the surface costs a whopping 15.8 m/s when you plot it far away from the target SOI. a similar set of correction burns within the SOI probably would cost a few hundred (or even thousands) of m/s

https://imgur.com/a/Gmv2A

 

But... How? I suposse in Map Window, I'll nedd to add one node (with a time to node of minutes) , swtich the reference to Duna, and modify the burn-out characteristics of the node in the three axis (when I've tried to do the fine-tun2, the nearest encounter was 800Km, and I wasn't able to reduce it, pherhaps cause its dificult to set a very short burn with the node-editor ...) and execute it with RCS...

 

Best Regards!