Interplanetary crafts with huge dV

[seaces]

Hi,

So I have a few questions on how you guys manage crafts that need to have huge amounts of dV for interplanetary missions.  To put it bit in a context: I have a quite heavily moded instance of KSP with Beyond Home mod and I got sick of waiting optimal transfer windows for my probes (I play probes before kerbals + I have life support mod installed) so I decided to send relatively small probe, to planet called Gateway, which is around 1500kg heavy (with its own propulsion to hop around some moons once it gets there). The transfer window planner told me that I need around 3500m/s of dv to get there with insertion burn. However, as I dont want to wait for two years for optimal transfer window (I also dont wish to warp for that much as I dont want to miss other transfer windows and funs stuff to do) I picked a transfer that is around 6200m/s which is basically ASAP. Anyway, I managed to build a transfer/capture stage for the probe with required dV but bad TWR for most of the part. Now as for the research progress I dont have access to nukes, ions or other fancy propulsion, just good old LFO tech for now.

So to the questions:

1. I am interested to see how you guys build monsters that need huge dV? Just to get additional inspiration and ideas for future missions especially crafts with LFO engines only.
2. Perhaps I am wrong, but crafts with huge dV end up with low TWR always, well at least if you use space optimized engines (high vacuum ISP)? In my case that is mostly true then I need to split the ejection burns etc. In this case I ended up setting up a burn in solar orbit to get me to Gateway, which is fine but that will take me longer to get to Geteway. When I use a probe not much of a big deal, but in the future if I wish to send Kerbals then I am in pain as I use life support mod called Kerbalism. A craft to support few kerbals for a few years to go and get back would be even bigger with even more abysmal performance.
3. For any players here that are playing with some life support mods, how do you manage it when you go long distance for a few years? 

Feel free to reply even if you can cover some of the point or add any other points.

[18Watt]

I don’t play with mods, but here are some things I do to extend my range.

• Use ISRU refueling.  If you don’t have access to nukes yet, you probably don’t have access to the ISRU equipment, but that’s my go-to solution for extending range on larger ships.
• I like the Wolfhound engine.  It has a high Isp but also produces good thrust.
• Having multiple stages would also help.  
• You may need to assemble your ship in orbit, to get enough fuel.
• You said you don’t want to wait for optimal transfer opportunities, but that’s possibly the best way to extend your range.  Even using all the other tricks I still wait for efficient transfers.

As far as using nukes or ion engines with low TWRs, I only use those engines for special circumstances.  In real life those would be excellent solutions.  However, in KSP they take a lot of patience waiting for ridiculously long burns to complete.  I don’t have the patience, so if there’s any way to complete the mission with standard LFO engines, I use LFO engines.

[FleshJeb]

Efficient staging and/or orbital refueling is your only good answer.

One of the most efficient staging methods is called Asparagus, and has the benefit of a reasonably consistent TWR. You can also have multiple stacks of asparagus-staging, arranged in series, to suit the TWR and dV needs of that phase of the mission.

https://wiki.kerbalspaceprogram.com/wiki/Asparagus_staging

https://forum.kerbalspaceprogram.com/index.php?/topic/68532-staging-methods-overview/

If you really want to get into the weeds, a guide on optimizing multiple stages is on this page:

http://www.projectrho.com/public_html/rocket/multistage.php

I've built "serially asparagus-staged" LFO rockets that have in excess of 20000 m/s dV, and an average TWR > 1.0. Because when you're trying to circumnavigate the planet at faster than orbital velocity, you have to thrust straight down for extended periods.

[Vanamonde]

I used to build refuelable tractor ships and dock cargoes to them. Unfortunately the screenshots are on my old PC, but the tractor ship itself was just a probe core, lots of LV-N engines, and big fuel tanks. 

[jimmymcgoochie]

There are a few tricks that can increase your delta-V:

• Simplify, then add lightness. Do you really need that part? If not, get rid of it and save some weight. Is it really practical to do such a complex mission right now, or can you get away with a simple orbit of Gateway with the occasional coincidental flyby of a moon when the orbits align?
• Can you get a gravity-assisted capture or aerobrake when you arrive? Try to find an encounter with the biggest moon you can so that its gravity will slow you down relative to Gateway itself and so will help you brake into orbit. The alternative is going for a really low periapsis and using Gateway’s atmosphere to aerobrake, but this is a high risk strategy as you could a) burn up, b) overdo it and fall into the planet or c) get wrecked by radiation, assuming Beyond Home has magnetosphere configs for Kerbalism and you’re using the radiation system.
• Orbital assembly will allow you to build something larger and heavier than your biggest launch rocket can handle in one flight. You can also launch partly fuelled tanks and then send up a tanker to fill them up later.

Trying to cut the corners on transfers doesn’t work very well or very often. Stick to the proper transfer windows and you’ll save a lot of delta-V which means you can build a smaller, lighter mission.

Doing long voyages with Kerbalism is hard, but still feasible- here’s a ship I made to attempt a Grand Tour of the stock system, landing on every planet and moon (except Jool, obviously) in one trip:

It was huge, slow, laggy, weighed thousands of tons once complete, it didn’t even make it to Moho and I had to skip the Mun and Minmus on the way home too, but it got everywhere else and had decades of supplies for its crew of two. It’s all stock parts too, with the exception of the life support bits that Kerbalism itself provides.

There’s no need to build something quite so gigantic for a simple interplanetary mission, but you do need to keep an eye on the life support and also on the crew stress as stressed-out Kerbals have a tendency to accidentally dump food/water/oxygen overboard. Keep the crew happy with a spacious, fully pressurised ship and tick enough of the boxes to avoid stress buildup and you can run missions that last for years- add in the active radiation shield and radiation detox unit that you unlock late in the tech tree and you can run missions that last decades, just as long as you pack enough supplies.

[king of nowhere]

18 hours ago, seaces said:

Hi,

So I have a few questions on how you guys manage crafts that need to have huge amounts of dV for interplanetary missions.  To put it bit in a context: I have a quite heavily moded instance of KSP with Beyond Home mod and I got sick of waiting optimal transfer windows for my probes (I play probes before kerbals + I have life support mod installed) so I decided to send relatively small probe, to planet called Gateway, which is around 1500kg heavy (with its own propulsion to hop around some moons once it gets there). The transfer window planner told me that I need around 3500m/s of dv to get there with insertion burn. However, as I dont want to wait for two years for optimal transfer window (I also dont wish to warp for that much as I dont want to miss other transfer windows and funs stuff to do) I picked a transfer that is around 6200m/s which is basically ASAP. Anyway, I managed to build a transfer/capture stage for the probe with required dV but bad TWR for most of the part. Now as for the research progress I dont have access to nukes, ions or other fancy propulsion, just good old LFO tech for now.

So to the questions:

1. I am interested to see how you guys build monsters that need huge dV? Just to get additional inspiration and ideas for future missions especially crafts with LFO engines only.
2. Perhaps I am wrong, but crafts with huge dV end up with low TWR always, well at least if you use space optimized engines (high vacuum ISP)? In my case that is mostly true then I need to split the ejection burns etc. In this case I ended up setting up a burn in solar orbit to get me to Gateway, which is fine but that will take me longer to get to Geteway. When I use a probe not much of a big deal, but in the future if I wish to send Kerbals then I am in pain as I use life support mod called Kerbalism. A craft to support few kerbals for a few years to go and get back would be even bigger with even more abysmal performance.
3. For any players here that are playing with some life support mods, how do you manage it when you go long distance for a few years? 

Feel free to reply even if you can cover some of the point or add any other points.

1) i don't. I use transfer windows and gravity assists to reduce deltaV cost as much as possible.

If I still need lots of deltaV, I use ions. If ions are not an option, I use nuclear. All things you won't do.

So, if you want to build ships with lots of deltaV with only LFO, the only thing you can do is build a huge ship with multiple stages. No other way.

The rocket equation states that deltaV=ln(M_w/M_d)*V_ex: that is, the deltaV is equal to the logaritm of the ration between the wet mass (M_w) and the dry mass (M_d) of your ship, times the velocity of your exhaust gases (V_ex) - which is equal to Isp*g.

So, to increase deltaV, there are only two things you can do: increase Isp, or increase the Mw/Md ratio. You don't want to increase Isp, so you've got to increase the Mw/Md. Which goes threefold:

a) reduce the weight of the payload. self-explaining

b) increase the amount of fuel. again, self-explaining

c) use multiple stages. As the amount of fuel you bring increases, the mass of dry fuel tanks increases too. And of course, to lift all that stuff, you need a big heavy engine. So after you burned most of your fuel, you want to ditch all those empty, useless, heavy spent fuel tanks. And you want to ditch that big powerful engine that's no longer needed, and use something smaller and lighter instead. Drop tanks are also an option.

Still, you can't prevent the mass from skyrocketing fast as you increase deltaV. Say your probe weights 1 ton, and you want 2 ton of fuel to give it 3 km/s. then if you want to add 3 more km/s, you need to make another stage with the same 3:1 ratio between dry and wet mass, so you need 9 tons. An additional 3 km/s will again require three times more mass than before, so 27 tons. Three more km/3, to bring the total to 12 km/s, and you're at 81 tons. And then 240, and so on. Past a certain size, rockets become hugely impractical. Which is why people prefer to use orbital mechanics to reduce deltaV requirememnts as much as possible, and to use more efficient engines.

 

This game lets you "cheat" by mining new fuel everywhere cheaply. that also reduces the deltaV required. of course, if you're using kerbalism, then you're not supposed to use that - or you're supposed to use the kerbalism isru functionalities, which make refueling less practical than the alternatives.

 

2) it's not exactly required that high deltaV=low thrust; the rocket equation has nothing on thrust. However, there are two practical factors that link high deltaV to low thrust:

a) to maximize deltaV you want an engine optimized for efficiency. those tend to have lower thrust

b) to reduce your dry mass you want a smaller engine. and of course this means less thrust than with a bigger engine.

So, nothing to do there. you want to maximize your deltaV, you can do it by sacrificing thrust.

Regarding your concerns with kerbalism, yes, it requires a lot of additional life support resources, but not too much. in the end, the mass of the food and water and oxygen is still a pittance compared to that of the living space. My suggestion there is that it's still a lot more convenient to add more supplies for a longer trip, than it is to add more fuel to travel faster. One kerbal can live one year with less than 100 kg of resources. To shorten the trip by one year, you could easily need to double the mass of your ship. Put three redundant units for everything essential, and you'll be fine regarding malfunctions, too. you can easily last 20+ years that way if your ship is well made. Again, it's a lot cheaper than making a ship three times bigger to have a shorter trip.

 

3) you can take a look at my kerbalism grand tours linked in my signature; but the short answer is, with a BIG ship. Of course, a smaller crew would allow a much smaller ship either, and I like to put additional functionalities.

the one that most closely resembles your mission parameters is Bolt, from my second mission; a relatively small ship, only 4 crew members. Only living space was 4 hitchhicker containers, a lab some cupolas (all stuff that reduces stress). the living space itself was about 50 tons, and with roughly 10 tons of supplies I could have lasted almost 30 years. Still, to avoid isru and make a grand tour, I needed a good 20 km/s on the main ship. Which I got by a multiple drop tank design, and it raised the total mass up to 5000 tons. even using nuclears.

[seaces]

OMG, this is why I love this forum. You get to discuss stuff and exchange ideas and you guys gave plenty of ideas. Anyway here is my reply, sorry if I missed someone to quote:

@FleshJeb

17 hours ago, FleshJeb said:

Efficient staging and/or orbital refueling is your only good answer.

One of the most efficient staging methods is called Asparagus, and has the benefit of a reasonably consistent TWR. You can also have multiple stacks of asparagus-staging, arranged in series, to suit the TWR and dV needs of that phase of the mission.

https://wiki.kerbalspaceprogram.com/wiki/Asparagus_staging

https://forum.kerbalspaceprogram.com/index.php?/topic/68532-staging-methods-overview/

If you really want to get into the weeds, a guide on optimizing multiple stages is on this page:

http://www.projectrho.com/public_html/rocket/multistage.php

I've built "serially asparagus-staged" LFO rockets that have in excess of 20000 m/s dV, and an average TWR > 1.0. Because when you're trying to circumnavigate the planet at faster than orbital velocity, you have to thrust straight down for extended periods.

Thank you for the links provided. When I was building my craft I was aware that my mission payload as well as dry weight of the stage that is supposed to get me to Gateway needs to be light I tried to cut down on dry weight as much as possible. I arrived at idea of multiple smaller tanks connected with fuel lines that I keep dropping in space as I go. Per you link provided I think I made something called "Breadcrumb" staging. Stage pushed by two Terrier engines and FLT-T400 tanks (I think) that I drop. Initial TWR is around 0.5 and it grows as I burn till 1.1.

@jimmymcgoochie

6 hours ago, jimmymcgoochie said:

There are a few tricks that can increase your delta-V:

• Simplify, then add lightness. Do you really need that part? If not, get rid of it and save some weight. Is it really practical to do such a complex mission right now, or can you get away with a simple orbit of Gateway with the occasional coincidental flyby of a moon when the orbits align?
• Can you get a gravity-assisted capture or aerobrake when you arrive? Try to find an encounter with the biggest moon you can so that its gravity will slow you down relative to Gateway itself and so will help you brake into orbit. The alternative is going for a really low periapsis and using Gateway’s atmosphere to aerobrake, but this is a high risk strategy as you could a) burn up, b) overdo it and fall into the planet or c) get wrecked by radiation, assuming Beyond Home has magnetosphere configs for Kerbalism and you’re using the radiation system.
• Orbital assembly will allow you to build something larger and heavier than your biggest launch rocket can handle in one flight. You can also launch partly fuelled tanks and then send up a tanker to fill them up later.

Trying to cut the corners on transfers doesn’t work very well or very often. Stick to the proper transfer windows and you’ll save a lot of delta-V which means you can build a smaller, lighter mission.

Doing long voyages with Kerbalism is hard, but still feasible- here’s a ship I made to attempt a Grand Tour of the stock system, landing on every planet and moon (except Jool, obviously) in one trip:

It was huge, slow, laggy, weighed thousands of tons once complete, it didn’t even make it to Moho and I had to skip the Mun and Minmus on the way home too, but it got everywhere else and had decades of supplies for its crew of two. It’s all stock parts too, with the exception of the life support bits that Kerbalism itself provides.

There’s no need to build something quite so gigantic for a simple interplanetary mission, but you do need to keep an eye on the life support and also on the crew stress as stressed-out Kerbals have a tendency to accidentally dump food/water/oxygen overboard. Keep the crew happy with a spacious, fully pressurised ship and tick enough of the boxes to avoid stress buildup and you can run missions that last for years- add in the active radiation shield and radiation detox unit that you unlock late in the tech tree and you can run missions that last decades, just as long as you pack enough supplies.

The moons around Gateway some of them are inclined so I struggle to get encounter with them. So what I will do (no idea if this will help) make insertion burn by going retrograde in relation to the Gateway, going against its spin if you know what I mean. My biggest issue with kerbalism is habitation/stress management. To get 20m3 per Kerbal I need loads of hitchikers. I almost sent Kerbals to another planet but aborted mission as I could not provision them with habitat for 3+ year mission (mostly due waiting the transfer window to get back home) as craft was to heavy for the engines that I had unlocked at that moment. Now I am aiming to unlock a tech node where I get that gravity ring part (I think it comes with kerbalism) has almost 100m3 of habitation and provides loads of habitation bonuses. That and radiation management, this time I play with radiation resets whenever they land home, I tried once with lifetime radiation but I was roasting them way to fast even with full shielding going to the Mum/Minmus in stock solar system. In no time I would get 25% of lifetime radiation and if I send them like that interplanetary they are very close to dying from radiation poisoning by the time I get them back. Note I play on Hard.

Where is radiation detox unit and how I can operate that one?

@king of nowhere

2 hours ago, king of nowhere said:

1) i don't. I use transfer windows and gravity assists to reduce deltaV cost as much as possible.

If I still need lots of deltaV, I use ions. If ions are not an option, I use nuclear. All things you won't do.

So, if you want to build ships with lots of deltaV with only LFO, the only thing you can do is build a huge ship with multiple stages. No other way.

The rocket equation states that deltaV=ln(M_w/M_d)*V_ex: that is, the deltaV is equal to the logaritm of the ration between the wet mass (M_w) and the dry mass (M_d) of your ship, times the velocity of your exhaust gases (V_ex) - which is equal to Isp*g.

So, to increase deltaV, there are only two things you can do: increase Isp, or increase the Mw/Md ratio. You don't want to increase Isp, so you've got to increase the Mw/Md. Which goes threefold:

a) reduce the weight of the payload. self-explaining

b) increase the amount of fuel. again, self-explaining

c) use multiple stages. As the amount of fuel you bring increases, the mass of dry fuel tanks increases too. And of course, to lift all that stuff, you need a big heavy engine. So after you burned most of your fuel, you want to ditch all those empty, useless, heavy spent fuel tanks. And you want to ditch that big powerful engine that's no longer needed, and use something smaller and lighter instead. Drop tanks are also an option.

Still, you can't prevent the mass from skyrocketing fast as you increase deltaV. Say your probe weights 1 ton, and you want 2 ton of fuel to give it 3 km/s. then if you want to add 3 more km/s, you need to make another stage with the same 3:1 ratio between dry and wet mass, so you need 9 tons. An additional 3 km/s will again require three times more mass than before, so 27 tons. Three more km/3, to bring the total to 12 km/s, and you're at 81 tons. And then 240, and so on. Past a certain size, rockets become hugely impractical. Which is why people prefer to use orbital mechanics to reduce deltaV requirememnts as much as possible, and to use more efficient engines.

 

This game lets you "cheat" by mining new fuel everywhere cheaply. that also reduces the deltaV required. of course, if you're using kerbalism, then you're not supposed to use that - or you're supposed to use the kerbalism isru functionalities, which make refueling less practical than the alternatives.

 

2) it's not exactly required that high deltaV=low thrust; the rocket equation has nothing on thrust. However, there are two practical factors that link high deltaV to low thrust:

a) to maximize deltaV you want an engine optimized for efficiency. those tend to have lower thrust

b) to reduce your dry mass you want a smaller engine. and of course this means less thrust than with a bigger engine.

So, nothing to do there. you want to maximize your deltaV, you can do it by sacrificing thrust.

Regarding your concerns with kerbalism, yes, it requires a lot of additional life support resources, but not too much. in the end, the mass of the food and water and oxygen is still a pittance compared to that of the living space. My suggestion there is that it's still a lot more convenient to add more supplies for a longer trip, than it is to add more fuel to travel faster. One kerbal can live one year with less than 100 kg of resources. To shorten the trip by one year, you could easily need to double the mass of your ship. Put three redundant units for everything essential, and you'll be fine regarding malfunctions, too. you can easily last 20+ years that way if your ship is well made. Again, it's a lot cheaper than making a ship three times bigger to have a shorter trip.

 

3) you can take a look at my kerbalism grand tours linked in my signature; but the short answer is, with a BIG ship. Of course, a smaller crew would allow a much smaller ship either, and I like to put additional functionalities.

the one that most closely resembles your mission parameters is Bolt, from my second mission; a relatively small ship, only 4 crew members. Only living space was 4 hitchhicker containers, a lab some cupolas (all stuff that reduces stress). the living space itself was about 50 tons, and with roughly 10 tons of supplies I could have lasted almost 30 years. Still, to avoid isru and make a grand tour, I needed a good 20 km/s on the main ship. Which I got by a multiple drop tank design, and it raised the total mass up to 5000 tons. even using nuclears.

Thank you for mathematically explaining what is happening. Kinda goes in line what I noticed by trail and error, except that I suck at math big time  (I play this game by trial and error and some feel) but anyway I got what you are trying to say. I am just now going through your Boly/Nail (very cool stuff) I might have some few questions around that one specifically. For now how radiation detox works where I can find it and activate it?

Also I am still new to deep interplanetary voyages with kerbalism, but is it worth to take greenhouse for food? Is there any breaking point where it becomes better to have greenhouse then ready to consume supplies to sustain kerbals? 

I must admit that I was playing KSP on and off for years but never went past Duna or Moho in stock let alone used ISRU in stock. What is the pain in using ISRU with kerbalism?

 

[magnemoe]

Here is one of my designs, the lander / base is around 30 ton dry mass. It uses mods but no mods for the rocket itself. 

From the left we have an space plane for use on Laythe, the Laythe base who has an small part manufacturing capability, nuclear reactor, research lab and an greenhouse. 
Then an heavy tug using 2.25 long fuel tanks. Then an disposable LV-N stage who is cross feed to the tug, finally an chemical stage at the bottom. 
Trick here was to launch the base, fly the plane up and dock refuel in lko, fly to Minmus to fuel up.  Then launch the bottom part as in from the tug to the chemical stage to orbit, refuel and its to off to Minmus. It could not land but stayed in Minmus orbit getting refueled. This had above 4 km/s, I then put it in an high orbit around Kerbin drop Pe down to there I want my burn to be, timing here require some adjustment but the benefit is an free 8-900 m/s from the oberth effect. This is also there the chemical stage is nice. 
Minmus was an busy place during the Jool launch preparation. 

Did all other sort of stuff like using the fuel tanks in the plane to store fuel fro the tug and bringing ore to make fuel underway. 
Jool in one year with an overbuild Switch army knife of an base. 

Use Minmus, an larger chemical stage would probably be easier, make it capable of landing on Minmus and fill it up well ahead. 

For pure dV you have this thing.

This was to rescue an kerbal in retrograde orbit close to Dress orbit. Unfortunately I added too little life support so I had to do an burn who passed Kerbin in a year. 
So it would come in very fast, this was the second of these ships, this did not go to Minmus as it was no need, just launch it, think this was a circulation / intercept burn, then I had to match its velocity, catch the capsule and brake down to orbital velocity, made it with 

[king of nowhere]

33 minutes ago, seaces said:

Where is radiation detox unit and how I can operate that one?

@king of nowhere

Thank you for mathematically explaining what is happening. Kinda goes in line what I noticed by trail and error, except that I suck at math big time  (I play this game by trial and error and some feel) but anyway I got what you are trying to say. I am just now going through your Boly/Nail (very cool stuff) I might have some few questions around that one specifically. For now how radiation detox works where I can find it and activate it?

Also I am still new to deep interplanetary voyages with kerbalism, but is it worth to take greenhouse for food? Is there any breaking point where it becomes better to have greenhouse then ready to consume supplies to sustain kerbals? 

I must admit that I was playing KSP on and off for years but never went past Duna or Moho in stock let alone used ISRU in stock. What is the pain in using ISRU with kerbalism?

 

- radiation detox is in the hitchhicker container. it requires some additional technology first, so you may not have access to it. anyway, once you do have the hitchhicker and the tech required, you put the kerbonaut inside the container, you right click on the container, and there will be an option "RDU: heal [name]". You activate it, and it will heal the kerbonaut by about 1% every 4 days. it consumes some additional oxygen, though.

- greenhouses are not convenient except in extreme cases. you need 2 greenhouses (total weight, almost 10 tons) to feed one kerbal. if, instead of putting in 2 greenhouses weighting 10 tons, you give the kerbal 10 tons of food, he'll eat for over a century. furthermore, growing food consumes water. by weight alone, it takes more water and nitrogen and carbon to grow food, than you get in food and oxygen. even after you account for recycling organic waste.

greenhouses can only be convenient if you plan a trip lasting over a century, and you have access to outside resources. i did put them to good use in my A'Tuin mission, which was a 327-years-long grand tour with outer planet mod, and I could get new water and nitrogen for the greenhouses when I landed. but that's an extremely corner case.

aside from that, though, there are a few additional advantages to bringing a greenhouse instead of its own weight in food: it's cool, it looks cool and it makes you feel good about colonizing space, it provides some additional living space to the crew (stress reduction), and it's required for a couple of experiments. In theory, plants should also give a bonus to happyness, but they don't, probably a bug.

- isru in the stock game just requires you to find "ore", which you find more or less everywhere, have a drill and convert-o-tron, and you're good to go. with one electricity per second, you can make somewhere around a ton of fuel per day. You bring in 6 tons of machinery, including a couple of gigantors solar panels, and you can refuel a large (tens of tons) ship in a few weeks.

In kerbalism, you need to use water and carbon dioxide to make fuel. Water is rare, a lot of planets don't have it, others only have it in one or two biomes. Carbon dioxide can be extracted cheaply by the atmosphere of Duna, or by that of Eve (but Eve has no water, so you can't do anything with it). Otherwise you need to extract it from ore, which is a process so energy intensive that I needed 500 tons of concert-o-trons and 20000 electricity/second to produce no more than 1 ton of fuel/day. I had to get nuclear power plants from near future to get enough energy, and that added the additional requirement that the landing zone would also have uranium. If you look at my A'Tuin mission, subchapter 0.2, you see a more detailed explanation of trying to do ISRU under kerbalism.

[FleshJeb]

1 hour ago, seaces said:

Thank you for the links provided. When I was building my craft I was aware that my mission payload as well as dry weight of the stage that is supposed to get me to Gateway needs to be light I tried to cut down on dry weight as much as possible. I arrived at idea of multiple smaller tanks connected with fuel lines that I keep dropping in space as I go. Per you link provided I think I made something called "Breadcrumb" staging. Stage pushed by two Terrier engines and FLT-T400 tanks (I think) that I drop. Initial TWR is around 0.5 and it grows as I burn till 1.1.

Breadcrumb is a fantastic method. Be aware that all those decouplers and fuel lines (and struts) add dry mass, so it may make sense to use fewer, larger/longer tanks, especially as you get down to the smaller diameters. FLT-T400s are pretty small. Structural complexity/part count can be an issue too.

There's also a rule of thumb for mass-efficiency that says for engines with roughly the same efficiency, each stage should have the same amount of dV. This is somewhat broken by the non-serial staging methods, but it's a good guide. You may be best off having your probe stage sitting on top of:

• A long 1.25m stage with one Terrier (capture)
• A 2.5m stage with a Poodle, or a Wolfhound if you've got it. (capture)
• A 3.75m stage with a Rhino. (transfer)
• Surrounded by 3.75m stacks with Mammoths, Asparagus-ed into the Rhino core. The Rhino and Mammoths all start at launch. You'll probably have a couple of Mammoths +Rhino left in orbit to start the transfer.
• Add SRBs to fill launch TWR needs, if any.

This is the gravity brake that Jimmy mentioned. From the BH dV map, it looks like you want to use Kohm, as I'm guessing it's the biggest moon at Gateway:

https://wiki.kerbalspaceprogram.com/wiki/Tutorial:_Gravity_Assist#Gravity_brake

https://forum.kerbalspaceprogram.com/index.php?/topic/186643-how-to-plan-a-tylo-gravity-assist/

[seaces]

Thank you all for your suggestions and tips. All very useful on how manage large ship going interplanetary with loads of dV. Hard to pick best answer as they are actually useful to me so I will pick one random to mark this question as answered.