Save Kerbals Passing by Kerbin

[stewake1306]

So... I successsfully got some science from Eve and was able to get my ship back to Kerbin. However, the shuttle burns and explodes during re-entry! I also do not have enough fuel to circularize around Kerbin once I get into the sphere of influence.

I have my ship passing by, and I'd like to somehow transfer crew and data to another ship as it near periapsis around Kerbin. I tried to send a ship with a better module for re-entry to rendezvous, but this left me with another ship in solar orbit with no fuel to get back to kerbin.

Is there a better ay to "catch" the ship or crew as it's passing by? It is flying by at 4k m/s at about 150k altitude.

 

 

[DeadJohn]

Have you tried multiple-pass aerobraking?

Set your Kerbin periapsis low enough to get some drag, high enough to not burn up. When you reach periapsis burn the rest of your fuel to establish an elliptical orbit, then keep passing by Kerbin to lower the elliptical orbit, at which point you’ll hopefully be slow enough to survive recently.

What crew capsule did you use? If it’s a low temperature one it might still burn up.

[Superfluous J]

It's the exact same process as an asteroid capture (though you can set up the direction the "asteroid" is coming from when the "asteroid" is instead your own Kerbal - at least a little bit) so I present to you a video that tomorrow will be no less than 6 years old!

I pretty well describe exactly what I'm doing and why. My ship is obviously way OP for your needs but the mechanics are the same.

Those actual mechanics are spread through the video so no time stamps. Just skip through it. Or watch the whole thing I'm not your boss.

 

[king of nowhere]

8 hours ago, stewake1306 said:

So... I successsfully got some science from Eve and was able to get my ship back to Kerbin. However, the shuttle burns and explodes during re-entry! I also do not have enough fuel to circularize around Kerbin once I get into the sphere of influence.

I have my ship passing by, and I'd like to somehow transfer crew and data to another ship as it near periapsis around Kerbin. I tried to send a ship with a better module for re-entry to rendezvous, but this left me with another ship in solar orbit with no fuel to get back to kerbin.

Is there a better ay to "catch" the ship or crew as it's passing by? It is flying by at 4k m/s at about 150k altitude.

 

 

at that speed, you are too fast for aerobraking unless you have good thermal shielding, but you can send another ship to rendez-vous.

 

a few days before periapsis, send up a new ship with enough deltaV, and with high twr (because it will have to make large maneuvers fast). put it in an elliptic orbit so that its periapsis coincides with the eve mission periapsis. set your apoapsis so that it will pass at periapsis at the same time as the other ship. get a rendez-vous. transfer the crew on this new ship. then slow down

[stewake1306]

9 hours ago, king of nowhere said:

at that speed, you are too fast for aerobraking unless you have good thermal shielding, but you can send another ship to rendez-vous.

 

a few days before periapsis, send up a new ship with enough deltaV, and with high twr (because it will have to make large maneuvers fast). put it in an elliptic orbit so that its periapsis coincides with the eve mission periapsis. set your apoapsis so that it will pass at periapsis at the same time as the other ship. get a rendez-vous. transfer the crew on this new ship. then slow down

I didn't think of the higher TWR, I used nuclear engines and it took me til I was out of the sphere of influence to rende. 

How can I plan to get my periapsis to coincide with the other ship  at the right spot and right time? Trial and error?

[LHACK4142]

Just now, stewake1306 said:

I didn't think of the higher TWR, I used nuclear engines and it took me til I was out of the sphere of influence to rende. 

How can I plan to get my periapsis to coincide with the other ship  at the right spot and right time? Trial and error?

KSP has a pretty good rendezvous and docking tutorial, so I'd just do that. Maybe play it 2 or 3 times, but you don't strictly need to.

[king of nowhere]

1 hour ago, stewake1306 said:

I didn't think of the higher TWR, I used nuclear engines and it took me til I was out of the sphere of influence to rende.

you can arrange a rendez-vous with nuclear engines too, and with ions - I've done it - but it's a lot harder; you've got to plan in advance, pass several kilometers in front of the other vehicle so that your gradual slowing down will get you closer to rendez-vous.

but one step at the time; for now I'll teach you to do it with high thrust, low thrust later.

Quote

How can I plan to get my periapsis to coincide with the other ship  at the right spot and right time? Trial and error?

the thing about a high apoapsis is that a small push at periapsis will change your orbital time by a lot. You can use that.

1) get your circular orbit with the same inclination of that of the target vehicle, and with the same height.

2) make your orbit elliptical, with periapsis in the rendez-vous point. You must do this several days in advance, to have time to set up the next step

3) for your next passage at periapsis, plan a prograde burn. The idea is to change your orbital time so that your next passage at periapsis will be timed exactly with that of the target vehicle.

For example, target vehicle will pass there in 2 days 3 hours 15 minutes? Then you must burn so that your next orbit will have a time exactly of 2 days 3 hours 15 minutes.

You don't need to make calculations, because once you are close enough the game will show you the close approach.

 

Unfortunately I don't have a good picture to show this exact process - it's been a while since I needed to use it. But I can show a similar picture, only difference is that in this case I was coming from a higher orbit.

so, the vehicle to be rescued was traveling along the light green line. the rescue vehicle is labeled as "Eve mission + comet catcher". It's in high orbit around Minmus.

First thing I planned the yellow maneuver. It raised my apoapsis, and that was made to change the orbital time.

Then the purple maneuver. Ok, there are two of them, the one on the left for 8.2 m/s. That's a plane change, because I had yet to fix inclination.

Finally the purple maneuver on top (17.8 m/s) to lower periapsis so that it touches the trajectory of the stranded vehicle. and you se, it says intersection at a distance of 0.2 km. That happened because my first burn prolonged my orbital time just enough that I'd fall down to periapsis with the proper timing.

this was actually more difficult than the maneuver I'm suggesting you, because the time depended on two different maneuvers and not only on one.

54 minutes ago, LHACK4142 said:

KSP has a pretty good rendezvous and docking tutorial, so I'd just do that. Maybe play it 2 or 3 times, but you don't strictly need to.

the rendez-vous tutorial is good for a vehicle in orbit. but it doesn't help with a vehicle on a hyperbolic trajectory.

Edited October 6, 2022 by king of nowhere

[magnemoe]

On 10/6/2022 at 12:23 PM, king of nowhere said:

at that speed, you are too fast for aerobraking unless you have good thermal shielding, but you can send another ship to rendez-vous.

 

a few days before periapsis, send up a new ship with enough deltaV, and with high twr (because it will have to make large maneuvers fast). put it in an elliptic orbit so that its periapsis coincides with the eve mission periapsis. set your apoapsis so that it will pass at periapsis at the same time as the other ship. get a rendez-vous. transfer the crew on this new ship. then slow down

The easiest is just to have your Ap intercept target Pe, once target enter Kerbin SOI you can set up an intercept raising Pe so you get an intercept. Note you will need twice the dV you would need to get target into Kerbin orbit, yes you can keep Ap high and aerobrake but it saves less than 1 km/s and you will accelerate not braking at target Pe.

An cheaper but harder way is to try to intercept early as in well outside of Mun orbit as the target speeds up a lot getting close to Kerbin, this also set you up for an more efficient braking burn. 
If you set up an 0 m/s node for target inside Kerbin SOI you can target it, try to catch as far out as near Minmus orbit or then falling back to kerbin. 

I once got an rescue contract, rescue an kerbal in retrograde solar orbit outside of Dress. 
I build this: 

3.75 meter first stage who was refueled in LKO then 1+8 nuclear asparagus and an 2.3 km/s upper stage to do the deep space intercept, the very expensive intercept and then turn the orbit the other way to get Kerbin intercept. 
One problem, that was an +2 year mission, I found I only had life support for 100 days. So I needed to intercept Kerbin in less than 100 days. That was doable if I not only dropped Pe well inside Moho orbit but also burn to reach Kerbin faster. 
Downside of this plan that I would need 8 km/s to circulate and was left with 300 m/s 

Solution is an second of the high dV interceptors or the one you see in screenshot waiting for initial intercept burn outside Minmus orbit. Accelerate to intercept then enter orbit again.