Finally landed on Laythe!

[Jebediah Kerman Jr.]

I've ascended back to Laythe orbit, and ejected back to Kerbin. I don't think I did anything wrong, but my Kerbin entry velocity was ~ 6000 m/s.

From Jool

I think everything was optimal, so what could I have done wrong?

I quickloaded back to Laythe orbit, of course.

Edited December 8, 2018 by Jebediah Kerman Jr.

[RealKerbal3x]

What kind of spacecraft are you using? Direct entry from Jool is never a good idea anyway. Try using your engines to brake into an elliptical Kerbin orbit, then aerobrake down from there.

[Jebediah Kerman Jr.]

I'm using a spaceplane. Single stage from Laythe's surface to Kerbin. Last time I visited Laythe with a spaceplane, I had to abort the landing. I used my engines to capture around Kerbin, but my initial velocity that time was more like 4500 M/S.

Also, my craft does not have a good thrust to weight ratio (one Nerv for 20ish tons of plane), and I probably don't have enough DV to capture, at least at 6000 m/s. I don't know what I'm doing wrong. I had a worse transfer last time, at least from what I could see.

Edited December 8, 2018 by Jebediah Kerman Jr.

[Gordon Fecyk]

27 minutes ago, Jebediah Kerman Jr. said:

I don't think I did anything wrong, but my Kerbin entry velocity was ~ 6000 m/s.

Your relative speed at Sun Periapsis / Kerbin Encounter is going to be absurdly high from way up there.

Have you looked at gravity assists yet? Passing close in front of Kerbin (daytime side) but not attempting aerocapture would lower your Sun Apoapsis and reduce your relative speed. Then you could repeat that as many times as needed until your relative speed is a lot more manageable. Of course this adds many, many days to your return trip.

Others have used Eve for this purpose as well, but at Eve's 1.5 degree inclination it might be harder to get an encounter. But Eve is heavier and moves faster, and can offer more of an assist. Just keep out of its atmosphere.

[Jebediah Kerman Jr.]

See, the main problem is that I need to get back to Kerbin in 8-9 years or less. I have a "science from surface of Laythe" contract, Ribfrod Kerman accidentally stepped on and broke the communications aerial, so I have to recover the data. Also, how can I do a Kerbin gravity assist anyways in minimal time, starting at a Jool-Kerbin transfer window?

[Gordon Fecyk]

@Jebediah Kerman Jr. Do you have your save file handy? Do you run a modded game? I wouldn't mind taking a look.

Actually getting back would take less time than 8-9 Kerbin years I believe, even with Kerbin or Eve gravity assists.

[Update] I tried a really rough return from Jool to Kerbin using a single Kerbin assist. Doing that brought my approach speed down a lot, to about 3500 to 4000 m/s, but the Mk1 lander can is still a terrible re-entry vessel. More importantly, it took 5y 150d game time to return and attempt re-entry, well within the 8y constraint.

The single assist brought me down to some place between the orbits of Duna and Dres. But my approach wasn't optimal and Kerbin wasn't at Sun Periapsis. Optimizing my departure time from Jool would have improved my chances of encountering Kerbin at the right time for a better assist, within the same time constraint, but I was also trying for a Tylo assist to leave Jool and I probably didn't need that. I might have done better by targeting Eve at first, maybe even burning at Eve PE if there was delta-v to spare.

Edited December 9, 2018 by Gordon Fecyk

[GRS]

Simple, keep your Kerbin periapsis in roughly 30 km, and avoid using radial burns too much, try waiting for a close counter, your TWR is roughly 0.15 in Kerbin, right ??? all i can say is that my Laythe lander return stage has over 0.64 Kerbolar TWR, try using gravity assists or spliting your burns, and wait for a good ecounter, you will have a top speed slightly above 5500 m/s if you do it properly, or wait for Jool to have a return window with Kerbin

Edited December 9, 2018 by GRS

[Jebediah Kerman Jr.]

Will my plane explode?

[GRS]

Depends on your velocity and Kerbin periapsis, do Eve or Kerbin assist for Spaceplanes, better safe than sorry, and give that Laythe a pair of eyes and some props to make it look interesting, my profile pic is a Tylo, with a pair of eyes, and a star shaped TTGL style sungglasses, how many delta v in Laythe orbit ? and do you mind giving a screenshot ? also, you need like 8 years in total if you want to get a good Eeloo counter, maybe after missing a shot, Jool transfers take no longer than 3 years, maybe you can use a crap amount of burn time and Mun assist, then send a rescue craft to get the Kerman back with all science, if that Spaceplane of yours run out of fuel

Edited December 9, 2018 by GRS

[Jebediah Kerman Jr.]

Well, the savefile I'm taking about is on my son's XBox (We got him KSP for his 11th birthday, and I decided to not bother buying it on my laptop, to save money), but I will modify my profile pic. Laythe, and by extension Jool, with its five very interesting moons, (save Bop maybe, since it's just a bigger Gilly, except for the kraken) is my favorite KSP planet. How would I add props to Laythe?

Don't know how much dv in orbit exactly, about 1300 needed to eject from Jool/Laythe, ~1200-1350 DV left after that. How's 2500-2650 for a rough estimate?

Edited December 9, 2018 by Jebediah Kerman Jr.

[Gordon Fecyk]

On 12/9/2018 at 8:00 AM, Jebediah Kerman Jr. said:

Well, the savefile I'm taking about is on my son's XBox (We got him KSP for his 11th birthday, and I decided to not bother buying it on my laptop, to save money), but I will modify my profile pic.

I wonder if it's even possible to copy saves from Console to PC. I didn't know that.

OK, I can try to reproduce my last attempt with the delta-v constraints you raised. Or at least try to minimize the dV spent and minimize the time. Eight years, about 2 km/second, low Laythe orbit, space plane. Maybe a stock Aeris 4A with an RTG added would serve in place of your craft.

Hey, this could be a forum challenge!

Is this a close enough approximation? Space plane, just over 1800 m/s delta-v, and eight years to return home safe. Here's the save. (20 KB ZIP)

[Update] Right, I know this can be done on 1800 m/s. On my last attempt I might have left too early and ended up being too aggressive on a correction burn after a Tylo gravity assist. The ejection from Laythe via Tylo only cost 650 m/s and Sun PE was down pretty close to Kerbin's orbit, but I attempted a correction that cost me over 900 m/s, but would have put Kerbin at Sun PE. The first assist got me an orbital period of two years, which was what I wanted so I could get a second Kerbin encounter, but a plane correction cost 100 m/s more than I had left.

Just to see what would happen, I cheated the last 100 m/s out of the game and then turned that cheat off. With a Kerbin PE of 40 km and a lot of spinning, I was barely able to capture from a 3.9 km/s approach speed. By the time I was flying within the air, the elapsed time was just three years, 338 days.

I'm pretty sure this can be done within eight years if:

• You wait for a good transfer window from Jool
• You use Tylo for an ejection gravity assist
• You encounter Kerbin at Sun PE
• You use Kerbin for a gravity assist and get a two-year solar orbit
• You re-encounter Kerbin at the new Sun PE
• You aerocapture on that pass at 40 km up

If your craft has more delta-V than 1800 m/s, you should have an easier time. If your craft is more heat tolerant, you should have an easier time.

Edited December 12, 2018 by Gordon Fecyk
Success

[bewing]

54 minutes ago, Gordon Fecyk said:

I wonder if it's even possible to copy saves from Console to PC.

No, savegames (or craft files) can't be transferred either to or from a console.

Edited December 9, 2018 by bewing

[Foxster]

If you are re-running the mission then put a mk1 capsule (with small 'chute), heatshield (with 20% ablator) and decoupler on the front of your craft to replace whatever cockpit you have there. Then dump the rest of the craft before hitting Kerbin's atmos. There is nowhere you can return from at any speed that this combo cannot survive Kerbin re-entry. 

Edited December 9, 2018 by Foxster

[GRS]

6 hours ago, Jebediah Kerman Jr. said:

Well, the savefile I'm taking about is on my son's XBox (We got him KSP for his 11th birthday, and I decided to not bother buying it on my laptop, to save money), but I will modify my profile pic. Laythe, and by extension Jool, with its five very interesting moons, (save Bop maybe, since it's just a bigger Gilly, except for the kraken) is my favorite KSP planet. How would I add props to Laythe?

Don't know how much dv in orbit exactly, about 1300 needed to eject from Jool/Laythe, ~1200-1350 DV left after that. How's 2500-2650 for a rough estimate?

Well, seems like its more than enough, but feel free to take that much delta v, try to ascend to a low Laythe orbit so the ascent wont be bothersome, about props on Laythe, use GIMP or Photoshop, google about how to use brush to get some simple eyes, maybe Paint to merge pics, kinda glad that KSP is in fact not for children only, you can just pass Kerbin in first counter, second orbit wont be too long, use aerobrake prediction mods for ease.

Edited December 9, 2018 by GRS

[Aegolius13]

It might help to post a screenshot of some of the maneuver nodes leading you from Jool to Kerbin.  But the short answer is yeah, you can probably reduce the 6,000 m/s with a different approach.  Assuming an optimal Hohmann transfer, it takes around 2,000 m/s to transfer from Kerbin to Jool.  The same is true in terms of the excess velocity you'll need to shed to capture around Kerbin off of an optimal Jool transfer -- meaning the lowest possible velocity at perikee is something like 4,200m/s.  So the extra ~1,800 your experiencing suggests there is something suboptimal about your approach - either your periapsis around the sun is inside Kerbin's orbit, or (more like) you're not coming in perfectly tangent to Kerbin.  [EDIT] Or you're coming in at a high inclination, retrograde, or something other than the optimal equatorial orbit.

One other thing to keep in mind - once you've captured around Kerbin, you can aerobrake at your leisure to get back to LKO, or capture and reenter.  So you really only need your velocity at perikee to be about 3,200 m/s.  If fuel is limited, it's most effectively to use it to help capture, then rely on aerobraking for the rest (but save a tiny bit of fuel to adjust your periapsis during aerobraking).  

 

Edited December 10, 2018 by Aegolius13