HELP: Not 2.7k dV not enough to capture laythe?

[Leo-MathGuy]

I have a 300t craft (3 landers) in sun orbit, headed for laythe. I have a laythe intercept, but even If I use all my deltav at the SOI edge, including the landers, I will get 2800 dV, For some reason, it is not enough to even put a dent in the flyby trajectory. (Even though I went overkill and gave it 6.5k dV from lko) What can I do? I have recently left kerbin SOI so I have a early correction advantage. and have used the most optimal transfer (But it looks like I didn't get the Hohmann transfer correctly) from the calculator mod. Aerobraking is out of my possibilities. If there is no way to save it what can I express-send to fix the situation? And no I will not use hyperedit even though it is installed.

[18Watt]

Moved to Gameplay Questions and Tutorials for better visibility.

[Zacspace]

Your flyby trajectory is pretty extreme. The burn from low Kerbin orbit to make your Jool transfer should only cost you 1900-2100m/s. Ideally you want to come in ahead of Jool travelling almost the same direction and then get scooped up by it's gravity. As it is you're kind of almost smacking straight into the side of its SOI as it flies by.

As is, your options are to try and get a beneficial gravity assist off of Tylo, or try and line up an aerobrake in Laythe's upper atmosphere. I think it might take some combination of both.

As for what you should send, or anything else related to vessel construction, we'd need to see your ship. That said fuel is a good bet, or heat shields if you're going to go the aerobraking route. You might want to consider dropping your science equipment and using the landers as drop tanks. Better to send a rescue mission to Jool than to high solar orbit, even if you don't end up getting to do your planned mission.

Edit: You're trying to brake into Laythe orbit all in one go while descending straight into it. For starters, you'll want to make a course correction burn in solar orbit. If you play with the prograde/retrograde and normal/antinormal nodes you should be able to adjust the timing of your arrival so that your Laythe entry trajectory isn't so suicidal. This is also how you'd go about lining up a gravity assist off of Tylo. For best results at Laythe, meet it on the right side of Jool and enter the atmosphere on the right side of Laythe. That way you'll have the lowest relative velocity to Laythe, Aerobraking should be more survivable and your burn should be more reasonable.

Edited January 25, 2023 by Zacspace
Just noticed you're specifically trying to brake into laythe, also didn't see the picture of your ship.

[Streetwind]

Agreed with Zacspace, you are way outside the transfer window and forced the transfer by spending a massive amount of dV at Kerbin. Now you are traveling at a very high relative velocity to Jool.

When flying to other planets, the dV cost and quality of transfer depends strongly on when exactly you leave. Origin and destination must be in the correct alignment with each other. The game should provide you a list of upcoming transfer windows in its alarm clock tool.

[The Aziz]

So you're approaching a slowly orbiting moon at interplanetary speeds. Of course you'd be coming short. Your best bet right right now is to correct your approach so that you'll be crossing Tylo, the more parallel to its orbit the better, and hopefully with a minimal input at its Pe, you should get a well made equatorial orbit around Jool. From there, approaching Laythe is a piece of cake.

[jimmymcgoochie]

Gravity assists are your only option. Plonk down a quicksave first, then set up a node as close as possible to your vessel and tweak the trajectory so you get an encounter with Tylo; use the fine adjust tool in the bottom left corner to fine-tune the encounter so that Tylo’s gravity slows you down relative to Jool, possibly even into orbit, though with a fairly high-energy transfer like that it’s unlikely to be enough on its own. A retrograde burn at Tylo periapsis will be more effective than doing it around Jool and all you really need to do is capture into any orbit so you can come back down for future gravity assists from Tylo and/or Laythe to bring your apoapsis down so that Laythe capture is cheaper.

Done properly, a gravity assist can enable a Jool capture and a visit to any and all of the inner three moons without using any fuel at all:

 

(This is a slightly altered Jool system but the three main moons are all in the same places)

Edited January 25, 2023 by jimmymcgoochie

[Leganeski]

9 hours ago, Zacspace said:

For best results at Laythe, meet it on the right side of Jool

This is probably the most important part. Because Laythe orbits so quickly, it's really important to meet it in exactly the same direction as it is moving around Jool, effectively allowing you to subtract off Laythe's full orbital velocity (3223 m/s) from your velocity around Jool. As it is, you're meeting Laythe about 60 degrees too early, which is always going to waste at least 1500 - 2000 m/s.

12 hours ago, Leo-MathGuy said:

What can I do? I have recently left kerbin SOI so I have a early correction advantage.

Thankfully, the Laythe encounter problem isn't too hard to fix: you can make a correction maneuver halfway along the route to Jool which moves the entire Jool flyby about an additional two hours into the future. Keep adjusting it until the planned trajectory encounters Laythe just as it is about to reach its closest approach to Jool. This will save a lot of fuel when you reach Laythe, and 2800 m/s should probably be enough to complete the capture.

 

As others have stated, another relevant thing to get right is the transfer to Jool. Although your transfer isn't terrible, and is likely good enough considering how much extra fuel you packed, encountering Jool in the same direction that it is moving will save even more fuel. If you line up both encounters well, it costs less than 500 m/s to capture at Laythe.

[Leo-MathGuy]

Quote

Thankfully, the Laythe encounter problem isn't too hard to fix: you can make a correction maneuver halfway along the route to Jool which moves the entire Jool flyby about an additional two hours into the future. Keep adjusting it until the planned trajectory encounters Laythe just as it is about to reach its closest approach to Jool. This will save a lot of fuel when you reach Laythe, and 2800 m/s should probably be enough to complete the capture.

Lol I missed that

Quote

Although your transfer isn't terrible, and is likely good enough considering how much extra fuel you packed, encountering Jool in the same direction that it is moving will save even more fuel. If you line up both encounters well, it costs less than 500 m/s to capture at Laythe.

 

Yea I went overkill

Quote

Agreed with Zacspace, you are way outside the transfer window and forced the transfer by spending a massive amount of dV at Kerbin. Now you are traveling at a very high relative velocity to Jool.

When flying to other planets, the dV cost and quality of transfer depends strongly on when exactly you leave. Origin and destination must be in the correct alignment with each other. The game should provide you a list of upcoming transfer windows in its alarm clock tool.

I have been playing ksp for a long time, and I knew it is not the most efficient transfer, so I went overkill in the fuel, and this was partly like this because a very funny thing happened

I forgot to put my antennas, so I modified the trajectory a bit so I can dock an antenna module to the ship.

 

Also as I look at it it does look really forced rather than a Hohmann transfer.

 

I will try to fix the attack angle and see what happens. If things go bad I will try to get tylo assist. Thanks for the help!

Edited January 26, 2023 by Leo-MathGuy

[Leo-MathGuy]

Got a jool orbit with a 150dv maneuver

 

EDIT: After that with 70dV maneuver I can intercept laythe

EDIT 2: Also I am in sandbox

EDIT 3: After accidentally deleting the node, I got an even better assist to jool orbit with just a 7m/s correction

EDIT 4: After that I can do a 10m/s correction to get another tylo assist and get the perfect laythe capture orbit

Thanks for all the help!

Edited January 26, 2023 by Leo-MathGuy
edits

[Leo-MathGuy]

I now have done 2 gravity assists, used 25 dV (this was so fine I just used rcs) to get a laythe encounter that is in line with the thing I'm trying to deliver the landers to orbit

 

I love the jool system now

 

Also its unmanned

Edited January 26, 2023 by Leo-MathGuy

[Leo-MathGuy]

I need your help again.  Yup I didnt burn up it shaved off 150m/s yay

 

This is my craft, captured into a 200k-1mil orbit. Is 45km a good aerobeaking altitude? I will stow away the antennas and solar panels. I can go multiple times if i need

EDIT: Laythe orbit

 

Edited January 26, 2023 by Leo-MathGuy

[Leo-MathGuy]

Somehow, the top right engine tank in the picture got disabled, I had literally 4.5k dV in there. I feel like (Cast Away spoilers) 

Spoiler

It was like the package in Cast Away he did not open. It had a sattelite phone, water filter, fishing rod, bacically irony

 

But thanks to this mistake and you all I learned the joys when the gravity assist works out for you! Thanks!!

Edited January 26, 2023 by Leo-MathGuy

[king of nowhere]

On 1/25/2023 at 5:14 AM, Leo-MathGuy said:

I have a 300t craft (3 landers) in sun orbit, headed for laythe. I have a laythe intercept, but even If I use all my deltav at the SOI edge, including the landers, I will get 2800 dV, For some reason, it is not enough to even put a dent in the flyby trajectory. (Even though I went overkill and gave it 6.5k dV from lko) What can I do? I have recently left kerbin SOI so I have a early correction advantage. and have used the most optimal transfer (But it looks like I didn't get the Hohmann transfer correctly) from the calculator mod. Aerobraking is out of my possibilities. If there is no way to save it what can I express-send to fix the situation? And no I will not use hyperedit even though it is installed.

Your laythe intercept is horrible.

You are crossing the planet orbit. using the screen as a reference, laythe is moving to the bottom, while your ship will intercept laythe moving towards the top of the screen. of course the intercept speed will be huge.

here's a few screenshoots on how you should approach a moon - they are taken for another moon named wal, but it's the same principle

see, this is the proper way to inject on a moon. you touch the orbit while the moon is moving in the same exact direction as your ship. This way, the speed of the moon is subtracted from your incoming speed. in this case, it results in 300 m/s intercept speed

here you can see an intercept like you are doing, and it's much more expensive, at 450 m/s. It's the same principle for which hitting a car in front of you while going in the same direction will result in less damage than a lateral crash.

But you may say, the difference between 300 and 450 m/s is not much. Yes, because Wal moves slowly, and so subtracting or adding its speed to the intercept matters little. Laythe moves at more than 3 km/s, so subtracting its speed means a lot. Salvaging your mission is very easy: you can get a cheap intercept (I'd wager less than 500 m/s) just by moving your intercept properly like I showed in the figure. Use a combination of normal and radial burn, 1 m/s should suffice.

 

Also, you must not use your deltaV at the SoI edge, but at periapsis; you save deltaV by Oberth effect.