Suborbital Rendevous

[Human Person]

Hi all. I'm planning a mission to Eve.

Why does the ascent vehicle has to achieve orbit, when we could try to rescue them from Sub-orbit with a powerful orbiter?

First things first, let's start on Kerbin and see what it takes to do a suborbital rescue:

 

- Have a powerful rescue craft in Orbit of Kerbin

- Launch a manned craft on a suborbital trajectory

- Use the Orbiter to rendezvous with the craft, EVA the crew (better start with a crew of 1) over to the orbiter and get back to a stable orbit. 

 

The lower your apoapsis and the steeper the suborbital arc, the better. This is 100% safe, no risk at all, now sign this waver.

 

Have fun and share your experiences with this task.

 

1st entry @FungusForge He actually went through the atmosphere, on an escape trajectory in order to get to his kerbal.

Edited March 30, 2017 by Physics Student

[Human Person]

Ohh, new Idea: Why not catch their command pod with the claw? This should be faster than spacewalking them over (especially for more than 1 kerbal)

[Foxster]

Please have a look at the challenge setting rules

 

[Human Person]

8 minutes ago, Foxster said:

Please have a look at the challenge setting rules

What about the "and mission ideas"

Still this makes a fine challenge imho, what's wrong with it?

do you want a leaderboard?

everybody who achieves this is awesome, how would you determine the winner?

Edited March 30, 2017 by Physics Student

[FungusForge]

I'll give this a shot. I've not got much else to do right now anyway.

[wibou7]

This was proven possible in the past, but it is terribly unpracticable.

You have to time you ascent just right so you get within close range (probably within ~5km) of your orbiter.
It is possible to achieve on a manual ascent by sheer luck but you would most likely need some automation mods if you wish to reproduce the result.

Then your orbiter has to match speed (i.e. goes sub-orbital) as fast a possible, hook the pod and then get back into orbit. All this on a few minutes timerange (depends how high you are and how close to orbital velocity the pod is).
The orbiter would need substential TWR both before and after it grab the pod.

Then there is the delta-V requirements... If we assume you are missing X m/s to achieve orbit, then your orbit need at least 2*X m/s (1 time to match speed and 1 time to go back into orbit).
Achievable but it gets harder and harder the farther your pod is to orbit.
If it is very close to orbit it gets way easier to simply add the missing dV to the pod itself.
If it is very far from orbit, the dV + TWR requirements on the orbiter makes it a challenge on itself.

 

Soooo... in conclusion, this might seems like a good idea but it's just too terribly hard to be used on a real mission.
It might be good challenge material (that's challenging for sure!) but you might want to add some more meat then.

[Human Person]

12 minutes ago, wibou7 said:

you wish to reproduce the result.

That's exactly what I'm aiming for, but I do need help. It's possible to develop a technique. I start with bruth force, then try to do it smarter.

[Hypercosmic]

18 minutes ago, wibou7 said:

This was proven possible in the past, but it is terribly unpracticable.

You have to time you ascent just right so you get within close range (probably within ~5km) of your orbiter.
It is possible to achieve on a manual ascent by sheer luck but you would most likely need some automation mods if you wish to reproduce the result.

Then your orbiter has to match speed (i.e. goes sub-orbital) as fast a possible, hook the pod and then get back into orbit. All this on a few minutes timerange (depends how high you are and how close to orbital velocity the pod is).
The orbiter would need substential TWR both before and after it grab the pod.

Then there is the delta-V requirements... If we assume you are missing X m/s to achieve orbit, then your orbit need at least 2*X m/s (1 time to match speed and 1 time to go back into orbit).
Achievable but it gets harder and harder the farther your pod is to orbit.
If it is very close to orbit it gets way easier to simply add the missing dV to the pod itself.
If it is very far from orbit, the dV + TWR requirements on the orbiter makes it a challenge on itself.

 

Soooo... in conclusion, this might seems like a good idea but it's just too terribly hard to be used on a real mission.
It might be good challenge material (that's challenging for sure!) but you might want to add some more meat then.

On my average rescue mission in my current career, I just launch when the doomed ship is flying over the sea to the west of the KSC, then when I got a nice intercept, I cancel out the velocity. Works every single time for me.

[Human Person]

9 minutes ago, Hypercosmic said:

Works every single time for me.

The encounter must be really close (ideally wihin docking range) because time is extremely critical here. Can you do it that precise?

[wibou7]

39 minutes ago, Hypercosmic said:

On my average rescue mission in my current career, I just launch when the doomed ship is flying over the sea to the west of the KSC, then when I got a nice intercept, I cancel out the velocity. Works every single time for me.

That's your "average rescue mission"? Gosh, I'd hate to be part of your space program!

Joke aside, how sub-orbital is your doomed ship, in term of dV?
As stated, if you are a hundred or two dV short than orbital velocity, that's quite doable. But then it would be easier to simply add that to your launch vehicle (OP wants to catch an ascent vehicle, not the other way around).
 

[FungusForge]

Here's my entry. what @Hypercosmic said is more or less correct, however it does matter how you launch. If you go for a rather flat trajectory (which I did) you may find yourself a little behind the target. I myself ended up having to take a shortcut through the atmosphere and only caught the pod just before reentry. Had I left room in the rescue vessel's pod, a spacewalk probably would've been faster (and been easier).

[Human Person]

@Hypercosmic

@wibou7

doing it the other way around is actually a good start. It could help getting the encounter as close as possible.

7 minutes ago, FungusForge said:

I myself ended up having to take a shortcut through the atmosphere

Great work! Shortcut through atmosphere: noted. 

Keep the good work up, this is real rocket science right there!

[Foxster]

2 hours ago, Physics Student said:

What about the "and mission ideas"

Still this makes a fine challenge imho, what's wrong with it?

do you want a leaderboard?

everybody who achieves this is awesome, how would you determine the winner?

Umm, not sure it's exactly a mission. Sure sounds like a challenge...and a good one. You just might like to tighten up on a few things, like mod usage and such. Otherwise it is just too temping to "cheat", what with all the mod and cheat options that KSP provides. 

[Human Person]

51 minutes ago, Foxster said:

Otherwise it is just too temping to "cheat"

Go ahead and cheat if you feel like it. You'll still need to figure out how to do the maneuver.

if you use infinite fuel, it would be good to have mechjeb or something to keep record of the overall delta-v expended. 

[wibou7]

2 hours ago, FungusForge said:

Here's my entry. what @Hypercosmic said is more or less correct, however it does matter how you launch. If you go for a rather flat trajectory (which I did) you may find yourself a little behind the target. I myself ended up having to take a shortcut through the atmosphere and only caught the pod just before reentry. Had I left room in the rescue vessel's pod, a spacewalk probably would've been faster (and been easier).

Interesting attempt...

That said, on the picture 5, your ascent vehicle seems to be on an escape trajectory out of kerbin already (or maybe I don't get the picture right, but there is no orbit or sub-orbital trajectory there).

That vehicle would have easily made orbit by itself...
Maybe it's just me but I feel the spirit of the challenge would be to keep the ascent vehicle sub-orbital the whole time, which is quite hard due to time constraint on rendez-vous.
 

[Human Person]

I did it!

 

This was Overkill. Apoapsis of 280 km, Speed needed to Orbit: 900 m/s. I was so excited this worked out, I forgot to stage, didn't matter.

 

Doing the rendevouz prior to apoapsis seems like a good Idea. I'd also recommend putting a ton of RCS- Thrusters on your orbiter, because It's great for fine-tuning your closest approach.

 

improved Attempt (less btuth force) and more Brutal Attempt (going straight up) coming soon. I guess I'll try to make a video as well

Edited March 30, 2017 by Physics Student

[jonny]

45 minutes ago, wibou7 said:

That said, on the picture 5, your ascent vehicle seems to be on an escape trajectory out of kerbin already (or maybe I don't get the picture right, but there is no orbit or sub-orbital trajectory there).

I would say it is the capture vehicle which is on a escape trajectory:

3 hours ago, FungusForge said:

I myself ended up having to take a shortcut through the atmosphere

... in order to reach the target before reentry.

with some better timing this should be possible with way less dV.

[FungusForge]

12 hours ago, wibou7 said:

Interesting attempt...

That said, on the picture 5, your ascent vehicle seems to be on an escape trajectory out of kerbin already (or maybe I don't get the picture right, but there is no orbit or sub-orbital trajectory there).

That vehicle would have easily made orbit by itself...
Maybe it's just me but I feel the spirit of the challenge would be to keep the ascent vehicle sub-orbital the whole time, which is quite hard due to time constraint on rendez-vous.
 

Oh that's not the ascent vehicle, that's the capture vehicle. The ascent vehicle had a max apoapsis of 125km, although I was aiming for the capture vehicle's initial 96km orbit when I launched. I decide to roll with the not-so-optimal timing and plotted the most direct intercept course, which happened to take the capture vehicle through the atmosphere, and (I didn't notice until you pointed it out) apparently an escape trajectory.

[wibou7]

9 hours ago, FungusForge said:

Oh that's not the ascent vehicle, that's the capture vehicle. The ascent vehicle had a max apoapsis of 125km, although I was aiming for the capture vehicle's initial 96km orbit when I launched. I decide to roll with the not-so-optimal timing and plotted the most direct intercept course, which happened to take the capture vehicle through the atmosphere, and (I didn't notice until you pointed it out) apparently an escape trajectory.

Ah! Right, sorry about that. I've got to say, I'm surprised you got it that easily.

I guess the next step would be to try on Eve