Large Payloads to Jool

[digger1213]

I am having trouble getting large payloads to Jool.

My payload is a 50 tonne base segment that I want to land on Vall. The payload is capable of landing itself from an orbit of Vall, but my problem is getting it there in the first place. With a 50 tonne payload, adding LV-N's on a stage below it usually results in an extra delta V of around 1000 maximum. Adding more can get that up to around 3000 Delta-V but by then I am lifting around 150 tonnes into LKO which I cannot seem to do even with the large Kerbodyne parts.

I've thought of some ideas, such as breaking it into multiple sections, brute-forcing it with loads of Kerbodyne engines, and Asparagus, but have not tried any out yet. I would like to keep the overall cost relatively low, anything under 1mil will be fine. I do have refuelling depots at Minmus and Duna, if those are of any help.

Any ideas on how I could get large payloads to far places like Vall?

Edited May 7, 2017 by digger1213

[Cpt Kerbalkrunch]

This is a base I sent to Bop, but Vall wouldn't be much different. Forgive the crazy look of it. I wanted to do something different this time (and fulfill a couple of contracts as well), so I made an all-in-one base instead of multiple modules to assemble on the ground like I usually do. Had to balance out the mass for a good launch, so it looks a bit goofy.

Note the abundance of boosters (they're cheap, and a good way to get off the ground). Also, everything has a cone to help with the launch (decouplers attached to dump them after leaving the atmosphere). A single module would be a lot lighter and cheaper, depending on what you wanna do. A bit cheaper (but more tedious) if you refuel at Minmus before heading out.

Just use Tylo or Laythe for the free capture, and you should have enough fuel to land on Vall.

 

 

Here's the base on the ground at Bop.

 

 

[Reusables]

You can get a 140t lifter with 3 Mammoths or a Mammoth and 4 Twin-boars. This is reusable TSTO version, but you can dispose of the first stage if you want.

And 110t interplanetary ship(including payload) with 6 nervs and 42t liquid fuselage gives 3.19km/s of dv with 0.33 TWR. The burn won't take too long with 4x physics warp. (About 3 minutes burn for 2km/s)

 

Gravity assists at Tylo/Laythe makes it easy to be captured at Jool and nearly match orbital velocity with Vall. Ideally, you can get into Vall orbit with 2.4km/s of dv.

Using ore mining on minmus, you can shave off extra 500~600m/s of dv. So 2km/s is sufficient in this case, which can be achieved with 90t interplanetary ship(including payload), 5 nervs and 25t liquid fuselage. The TWR is similarly 0.34.

[digger1213]

Thanks for the answers.

I have already been using Tylo for gravity assists every time I go to Jool, as I can see they are highly effective for slowing down. How much Delta V should I be aiming for to land on Vall, with some margin for error? I have looked at the Delta-V maps, but seeing how my numbers can vary quite a lot compared to the map, I am wondering how much I should be aiming for, Tylo assist included. I have managed to get the Delta-V up to 8k.

I am also dubious about using my Minmus depot for interplanetary usage. Last time I did that, the transfer to Jool from Minmus took more DV than it did from LKO. The refuel still resulted in a net gain, but it took me almost 2k DV from Minmus orbit to get to Jool.

Another question, is it worth using an Eve flyby as a gravity assist to get to Jool? I have messed around with it a little bit using my Eve probes, but considering it should only be a 500DV difference anyway I don't see much savings.

I won't be able to try anything till late tomorrow, so I won't be able to respond for at least another 24 hours. Thanks for your help.

[Reusables]

12 hours ago, digger1213 said:

How much Delta V should I be aiming for to land on Vall, with some margin for error? I have looked at the Delta-V maps, but seeing how my numbers can vary quite a lot compared to the map, I am wondering how much I should be aiming for, Tylo assist included

It highly depends on your TWR. If you have sufficient TWR(over 4 relative to the planet), you would get the dv written on the dv map. So what's your TWR?

I usually add 100m/s~200m/s or so for safety margin. This helps in case of accident.

12 hours ago, digger1213 said:

I am also dubious about using my Minmus depot for interplanetary usage. Last time I did that, the transfer to Jool from Minmus took more DV than it did from LKO. The refuel still resulted in a net gain, but it took me almost 2k DV from Minmus orbit to get to Jool.

How did you perform the transfer burn? Did you get the periapsis down to Kerbin?

12 hours ago, digger1213 said:

Another question, is it worth using an Eve flyby as a gravity assist to get to Jool? I have messed around with it a little bit using my Eve probes, but considering it should only be a 500DV difference anyway I don't see much savings.

After reaching Eve, you can get to Jool with several gravity assists. I think this approach will get you to Jool in 1.2km/s of dv with several gravity assist, which should save good amount of fuel. (Also chemical engines take over nukes with the dv)

There is one disadvantage with this approach: takes too much time, both in-game one and real one.

[Cpt Kerbalkrunch]

12 hours ago, digger1213 said:

Thanks for the answers.

I have already been using Tylo for gravity assists every time I go to Jool, as I can see they are highly effective for slowing down. How much Delta V should I be aiming for to land on Vall, with some margin for error? I have looked at the Delta-V maps, but seeing how my numbers can vary quite a lot compared to the map, I am wondering how much I should be aiming for, Tylo assist included. I have managed to get the Delta-V up to 8k.

I am also dubious about using my Minmus depot for interplanetary usage. Last time I did that, the transfer to Jool from Minmus took more DV than it did from LKO. The refuel still resulted in a net gain, but it took me almost 2k DV from Minmus orbit to get to Jool.

Another question, is it worth using an Eve flyby as a gravity assist to get to Jool? I have messed around with it a little bit using my Eve probes, but considering it should only be a 500DV difference anyway I don't see much savings.

I won't be able to try anything till late tomorrow, so I won't be able to respond for at least another 24 hours. Thanks for your help.

I used to refuel at Minmus all the time. It's actually worth refueling there, but you have to ask yourself if it's worth the real time it's going to take you. If you do, when the Jool window is near, wait 'til Minmus is almost directly between Kerbin and the sun. Then, burn retrograde to Minmus' orbit to drop back down to Kerbin. It only costs about 150 m/s, I think. Been a while. Aim for a Pe of 70km to 75km. It seems like you're going backwards, but the Oberth gained is worth it. Place your maneuver node at Pe and plot your maneuver. You'll see that as soon as you spin your mouse wheel on the prograde node, you'll have already left Kerbin's SOI. Your orbit will rise very quickly. Even if you just stopped at that moment, you'll see that you left Kerbin's SOI with full tanks. So you saved whatever it would cost to leave Kerbin's SOI from LKO, minus the 150m/s or whatever you needed to drop down. So the savings are worth the trip but, again, only you can decide if it's worth your time.

[Aegolius13]

13 hours ago, digger1213 said:

Thanks for the answers.

I have already been using Tylo for gravity assists every time I go to Jool, as I can see they are highly effective for slowing down. 

I've found that those Jool system gravity assists can be a little deceptive.  They definitely look like they slow you down a ton, since you can easily go from an escape trajectory to a tight little orbit around Jool.  However, if that post-assist orbit ends up hitting your target at an angle that's not close to the optimum Hohmann-type tangent, you can end up spending a lot of fuel to capture.  If you do nail the assist, you can definitely save a lot of delta-V,  though.  I've recently taken to doing the first assist so it just barely captures me around Jool orbit.  Then, when my apo is way out at the edge of the SOI and maneuvers are cheap, I plan a second assist that will line me up nicely for my target.  

 

16 hours ago, digger1213 said:

Adding more can get that up to around 3000 Delta-V but by then I am lifting around 150 tonnes into LKO which I cannot seem to do even with the large Kerbodyne parts.

Hey, finally MOAR BOOSTERS might actually be the correct advice.  Asparagus staged Mammoths and/or TwinBoars mounted out radially can help you lift a lot of weight.  I also like Kickbacks bolted to my outermost stage (no decoupler), with thrust tweaked so they burn out the same time as that stage.  Strut and/or Autostrut liberally, though.  

Here's an example of a Jool 5 rig I did a while ago.  Not the most economical design, but I got 250+ tons to LKO with for under 700,000 funds.  This was pre-autostrut days, so a lot of those struts could be auto'd.

 

16 hours ago, digger1213 said:

I do have refuelling depots at Minmus and Duna, if those are of any help.

I personally like using the Mun as an interplanetary waypoint.  Compared to Minmus, the better Oberth effect should pretty much cancel out the lower position in Kerbin's gravity well.  The Mun's big advantage is that since the Mun's orbital period is much shorter that Minmus', it's easier to depart near your ideal launch window.  As a bonus, the non-inclined orbit makes your manuevers a little easier.  Yeah, it's less efficient to bring fuel up from the surface than with Minmus, but both are quite doable.  

[digger1213]

Well, that wasn't 24 hours but oh well, I meant 12. xD

Using these tips I was able to land my base on Vall... with about 50DV spare. Probably will give myself a little extra next time. I am now focusing on expanding said base for full expansion of the Jool system. Also discovered the parking orbit of an elliptical orbit that is resonant with all 3 low moons, which was quite fun to set up.

Anyways, I'll answer any questions that were here anyway.

4 hours ago, Abastro said:

It highly depends on your TWR. If you have sufficient TWR(over 4 relative to the planet), you would get the dv written on the dv map. So what's your TWR?

I usually add 100m/s~200m/s or so for safety margin. This helps in case of accident.

My Vall landing section has a TWR of just over 2. Is higher better when landing? The extra weight would probably make it even more difficult with lower DV for the rest of the rocket, or so I think.

4 hours ago, Abastro said:

After reaching Eve, you can get to Jool with several gravity assists. I think this approach will get you to Jool in 1.2km/s of dv with several gravity assist, which should save good amount of fuel. (Also chemical engines take over nukes with the dv)

There is one disadvantage with this approach: takes too much time, both in-game one and real one.

This is what I thought. Even if it only takes 1.2km/s of DV, it would still only save 300 DV or so, and the real-time and game-time isn't worth it. My game clock is already up to year 40, and Jeb has been stuck in a refueling depot he hitched a ride with for about 36 of those.

 

4 hours ago, Cpt Kerbalkrunch said:

I used to refuel at Minmus all the time. It's actually worth refueling there, but you have to ask yourself if it's worth the real time it's going to take you. If you do, when the Jool window is near, wait 'til Minmus is almost directly between Kerbin and the sun. Then, burn retrograde to Minmus' orbit to drop back down to Kerbin. It only costs about 150 m/s, I think. Been a while. Aim for a Pe of 70km to 75km. It seems like you're going backwards, but the Oberth gained is worth it. Place your maneuver node at Pe and plot your maneuver. You'll see that as soon as you spin your mouse wheel on the prograde node, you'll have already left Kerbin's SOI. Your orbit will rise very quickly. Even if you just stopped at that moment, you'll see that you left Kerbin's SOI with full tanks. So you saved whatever it would cost to leave Kerbin's SOI from LKO, minus the 150m/s or whatever you needed to drop down. So the savings are worth the trip but, again, only you can decide if it's worth your time.

The months/days that would take is tiny compared to the years the Jool transfer takes anyway. I have seen other people mentioning this tactic, but I always wondered how I would line it up, and how long it would take for Minmus to get in position, as its orbital period is many days.

3 hours ago, Aegolius13 said:

I've found that those Jool system gravity assists can be a little deceptive.  They definitely look like they slow you down a ton, since you can easily go from an escape trajectory to a tight little orbit around Jool.  However, if that post-assist orbit ends up hitting your target at an angle that's not close to the optimum Hohmann-type tangent, you can end up spending a lot of fuel to capture.  If you do nail the assist, you can definitely save a lot of delta-V,  though.

Yeah, I have started to wonder about those as I have had some high DV slowdown costs. However, I believe it is still more efficient to do a bad gravity assist than to spend over a thousand DV to slow down from interplanetary speeds. I'd rather a 1k DV slowdown around Vall than a 1.5k DV slowdown around Jool + transfer to Vall.

 

3 hours ago, Aegolius13 said:

Hey, finally MOAR BOOSTERS might actually be the correct advice.  Asparagus staged Mammoths and/or TwinBoars mounted out radially can help you lift a lot of weight.  I also like Kickbacks bolted to my outermost stage (no decoupler), with thrust tweaked so they burn out the same time as that stage.

I ended up using the MOAR BOOSTERS advice, and my rocket in the end had 5 TwinBoars mounted on the outside for my liftoff + orbit stage, in an Onion staging configuration. My transfer consisted of the medium sized Rockomax tank with oxidizer removed and 8 liquid fuel fuselages + 8 Nervs. I know that is inefficient, but I couldn't be bothered with low TWR.

Thanks for the help, everyone!

[Spricigo]

7 hours ago, Cpt Kerbalkrunch said:

It seems like you're going backwards, but the Oberth gained is worth it. 

Unfortunately,  you are really going backwards. If you go below the gate orbit Oberth it's not worth. 

 

[Cpt Kerbalkrunch]

3 hours ago, Spricigo said:

Unfortunately,  you are really going backwards. If you go below the gate orbit Oberth it's not worth. 

 

Yeah, I've read that thread before. I used to refuel anything going beyond Duna at Minmus before heading out. As the OP said, it didn't seem to be helping me as much as I thought it would. But then I started dropping down to LKO before my burn and it changed everything. Now, it made total sense because the burn was much easier.

In the Oberth thread, the argument seemed to be that burning from a slighter higher orbit resulted in less loss to gravity. I don't know the numbers for these things (I really do love the to just wing it), but through trial and error it seemed that dropping lower worked better.

I couldn't figure out why I was coming up with something different than a guy like OhioBob (who's obviously really smart and know's what he's talking about). I remember now the answer I came up with (that seemed like it might be the right one). In his example, OhioBob shows the effects on a five minute burn. That was when I realized that his example might not apply to what I was doing. I wouldn't have such a long burn when leaving Kerbin. It's usually about a minute and a half to Jool. Anything over two minutes I would consider a long burn. Reason being is that I never use nukes, so I'm using a more powerful (though obviously less efficient) rocket. It seemed that getting down lower and building as much speed as possible, and then taking advantage of that speed with a quick burn at Pe was working better.

It's been a while since I refueled on the way out, though. I tried a bunch of different things, so I really don't remember them all. If others say that something else works better, I certainly won't dispute it.

Edited May 8, 2017 by Cpt Kerbalkrunch

[Spricigo]

@Cpt Kerbalkrunch I re-read what you said. And seems that indeed in your case Pe just outside atmosphere is the way to go. As often is the case when the physics guys talk about something, looks like @OhioBob did some assumptions  and his results are for circular orbits. If you are coming from  Ap around Minmus you will have much more speed at Pe. (or maybe I misunderstood his post, if that is the case I hope he show up to correct me).

Of course we are ignoring the DeltaV necessary to reach Minmus. I Just have a question: what do you do to get the correct ejection angle? Minmus will often be in a bad position when the transfer window show up.

 

 

[Cpt Kerbalkrunch]

4 hours ago, Spricigo said:

@Cpt Kerbalkrunch I re-read what you said. And seems that indeed in your case Pe just outside atmosphere is the way to go. As often is the case when the physics guys talk about something, looks like @OhioBob did some assumptions  and his results are for circular orbits. If you are coming from  Ap around Minmus you will have much more speed at Pe. (or maybe I misunderstood his post, if that is the case I hope he show up to correct me).

Of course we are ignoring the DeltaV necessary to reach Minmus. I Just have a question: what do you do to get the correct ejection angle? Minmus will often be in a bad position when the transfer window show up.

 

 

I find that Minmus is pretty much never in the right position, sadly. I see it as leaving two options. Either go early (when in the correct position but before the window opens), or go late (ditto but after the window). I prefer to go late. Jool is such a huge target, it's pretty forgiving.

If I've only missed the window by a week or so, I don't really change much. I just catch Jool on the "back" side, so to speak. With Ap set slightly beyond the planet, dropping down on top of it. It has one benefit of making a Tylo-assisted free capture extremely easy, since you're passing in front of Jool's orbit as you fall down into it.

If I've missed the window by a few weeks, I just compensate by using the radial-out dial as well as prograde when plotting my maneuver. Also, at that speed, moving the maneuver node even the slightest bit has a dramatic effect on your orbital path. Basically, I just play around with it 'til I get an encounter I'm happy with. I probably lose a bit of delta-v, but I feel it's trivial compared to the savings.

Certainly not the most scientific approach, but nothing I do ever really is.