LKO rescue plan

[MPDerksen]

Forgive me for not using the search feature.  With community help I’ve rescued the first of 3 Kerbals from LKO.  My hope is to get better each time. This time, I’m adding a few RCS “jets” for more precis control to get stable, since these are previews to learning to dock.  So, as I create my improved craft, I have a few questions BEFORE I end up in the wrong situation and have to spend hours correcting.

1). Running the current version, I think I can evaluate dV in the Assembly building, right?  How much monopropellent, oxidizer etc should I pack along?  Keep in mind I’m pretty new, so we should add about 20% for all the mistakes I’m about to make.

2).  My target has an Ap of 85K, and a Pe of 77K.  My mission plan is to launch ahead of him, ascend to a higher orbit, and let him catch up.  Any suggestion how I should set this up?  Circularize at 100K, then drop in on him?

3).  After picking up Vergas (nice to get a free engineer, right?), we left her derelict craft in orbit.  Is there a way to clear that out so I don’t end up with a bunch of junk in my orbit?

Thanks in advance,

MPD

Edited February 13, 2019 by MPDerksen
Forgot to ask #3

[bewing]

50 minutes ago, MPDerksen said:

1). Running the current version, I think I can evaluate dV in the Assembly building, right?

Right.

50 minutes ago, MPDerksen said:

How much monopropellent, oxidizer etc should I pack along?  Keep in mind I’m pretty new, so we should add about 20% for all the mistakes I’m about to make.

Use the same basic ship as last time, but add four of the 4-way RCS blocks, and 40 units of monoprop. When you become an expert, you will need less than 5, but 40 will give you a lot of practice. Or, if you want to add another challenge -- add another MK1 Crew Cabin, and try to rescue two kerbals with one mission. You may need a bit more Lf and Ox if you do that.

50 minutes ago, MPDerksen said:

2).  My target has an Ap of 85K, and a Pe of 77K.  My mission plan is to launch ahead of him, ascend to a higher orbit, and let him catch up.  Any suggestion how I should set this up?  Circularize at 100K, then drop in on him?

Thanks in advance,

MPD

I'd suggest an Ap of about 92 to 95k, and a Pe of about 80k. In general that will guarantee that you are higher, and that there are two orbit crossings. But the higher the difference between the orbits, the faster your intercept will happen. You don't want it to be all that fast yet. So, higher but not more than 10k higher, and the Pe at an altitude that guarantees crossings.

 

[Blaarkies]

1) Minimum 3500m/s dv to get to orbit, +200 m/s dv for orbital maneuvering
Adding 20% extra on top of this should be enough

2) Just match orbits with them first
- Burn prograde or retrograde at AP/PE to change the size of your orbit
- Burn "North"/"South" at the Descending/Ascending nodes to tilt your orbit (Remember to click the stranded ship and "Set as Target")

By only doing these, you can cheaply match orbit with the target.
Once matched, determine if you are leading the target.
- If you are leading, then wait until you see a new sunrise
- Burn prograde at this moment
- This will increase the size of your orbit (target will now catch up to you) AND your intercept will happen on the sunny side

Don't overdo any of these, just increase your orbit size by 20km max, and wait a few orbits to see the effects
With experience you will figure out how to do it quicker

3) Using the stranded kerbal, before exiting their wreck, try to Rename the vessel (Right-click on the capsule). Just choose the "Debris" icon.
- This is not possible with all wreckages though, but you can rename them in the Tracking Station. Select the vessel, change the name in the right-hand bottom corner of the screen...i think you have to double click on the vessel name

Edited February 13, 2019 by Blaarkies

[MPDerksen]

9 hours ago, bewing said:

I'd suggest an Ap of about 92 to 95k, and a Pe of about 80k. In general that will guarantee that you are higher, and that there are two orbit crossings. But the higher the difference between the orbits, the faster your intercept will happen. You don't want it to be all that fast yet. So, higher but not more than 10k higher, and the Pe at an altitude that guarantees crossings.

Last time, I worked really hard at matching the orbits, which seems to have been unnecessary.  When I got close, I would burn retro, the intersect point would move ahead of me, but slightly closer.  Rinse and repeat.  With the way you describe it, I get 1 shot at the intercept, and once I start burning towards the target, I'm committed, right?  

[bewing]

Yup.

Well, you get one shot every 5 days or something. It takes a long time for the ships to come back around for another close approach if you end up timewarping through your intercept (as a theoretical example, but this has never happened to me *coff*).

 

Edited February 13, 2019 by bewing

[MPDerksen]

So above is my target.  I would love to be able to intercept in the daylight.  Notice one of the 3 craft orbiting is the leftover Vergas Derelict I left behind when I picked her up.  Maybe I create a mission at some point to bump them out of orbit, but that's another thread.  Option #2, if I can't get a daylight encounter, should I put a few lights on my craft?

Here is the top part of my rescue design.  Each of those pods have 20 mono in them, so 4 is over-kill?  Is it a problem to have the jets below that over-hang like that?  I also added a few places to grab on, since last time it was tricky to get her around to the hatch.

Finally, here is the staging for my full rocket.  I have 4 LF boosters around a central one.  Each is made up of 2 x T800 tanks.  I have no issue getting into my orbit of choice with this.  Once I'm close, I was using the terrier 909 with a T400 to handle the changes to get me close.  Am I reading correctly that the 4x2 tanks provide 2045m/s, the 2x2 in the middle give 1613ms and the little T400 gives 366m/s?  Does it calculate this based on the reduced weight I've dumped when I decouple?  

Lots of details here, but I'm learning a TON.

[bewing]

6 hours ago, MPDerksen said:

I would love to be able to intercept in the daylight.

Once you intercept, if you reduce your relative velocity to exactly zero and then wait 15 minutes, you are guaranteed to be in the sunlight again.

6 hours ago, MPDerksen said:

Notice one of the 3 craft orbiting is the leftover Vergas Derelict I left behind when I picked her up.  Maybe I create a mission at some point to bump them out of orbit, but that's another thread.

It's easier just to terminate them in your tracking station.

6 hours ago, MPDerksen said:

should I put a few lights on my craft?

They have some built-in lights. It's enough to provide you something to aim for, which is all that you really need -- when combined with the Kerbal's helmet lights. But if it helps your role-playing then go ahead and stick them on. But they add mass, drag, and cost -- which can cripple your craft if you do it wrong.

6 hours ago, MPDerksen said:

Each of those pods have 20 mono in them, so 4 is over-kill?

Actually, one has 10 and the other has 15. But if you fill them up, that should give you lots of good practice time.

6 hours ago, MPDerksen said:

Is it a problem to have the jets below that over-hang like that?

No, RCS jets can't be obstructed by other parts of your craft like engines can. You can clip them completely inside and they will still work. You can build a box around them and they will still work. But understand that is not true for engines.

6 hours ago, MPDerksen said:

I also added a few places to grab on, since last time it was tricky to get her around to the hatch.

We all do that at one time or another. But keep in mind that you can only board a craft at the hatch. So your ladders have to lead to the hatch, or else you will still have to let go again and fly around from the ladder to the hatch.

6 hours ago, MPDerksen said:

Am I reading correctly that the 4x2 tanks provide 2045m/s, the 2x2 in the middle give 1613ms and the little T400 gives 366m/s?  Does it calculate this based on the reduced weight I've dumped when I decouple?  

The default numbers are for when you are flying around in the atmosphere. Which you almost never are. You can change the deltaV display to show "vacuum" numbers instead, which is more informative.

And yes, it calculates that number based on how much mass is remaining in the craft after you've staged away all the rest.

 

Edited February 14, 2019 by bewing

[MPDerksen]

So here we are, in orbit, with an intersect coming up.  I already tried this once, and failed to create a 0m/s situation (well, I did, but it wasn't stable, and it quickly got away from me).  I have my AN and DN at 0.0, so I'm good there.  What kind of maneuver node should I place to get the 25.9km down to <2km?  I suspect I'm trying to do my retrograde burn while I'm still really far away from my target.

[bewing]

Your target is behind you. So you need an orbit that takes longer than your target's orbit, so your target can catch up to you. Which means it has to be bigger than your target's orbit.

So, just after you pass the intercept point, you want to burn prograde in orbital mode, to make your orbit bigger. Do it gently, and watch the intersect numbers while you burn. They will tick down to something under 1km, because you are coplanar.

Then you have a choice: you can either just accept the intercept you already have -- wait until you are under 1km separation, and burn to a 0m/s stop in target mode.

Or, you wait most of one orbit. Then, in target mode, you use your retrograde-marker-pushing technique that you learned to get even closer than what the intercept was showing. And then come to a stop.

And yes, after you come to a stop, you will slowly start to drift apart again. But it takes a long time to build up speed, and you can always come to a stop again.

 

[MPDerksen]

7 hours ago, bewing said:

Your target is behind you. So you need an orbit that takes longer than your target's orbit, so your target can catch up to you. Which means it has to be bigger than your target's orbit.

So, just after you pass the intercept point, you want to burn prograde in orbital mode, to make your orbit bigger. Do it gently, and watch the intersect numbers while you burn. They will tick down to something under 1km, because you are coplanar.

Then you have a choice: you can either just accept the intercept you already have -- wait until you are under 1km separation, and burn to a 0m/s stop in target mode.

Or, you wait most of one orbit. Then, in target mode, you use your retrograde-marker-pushing technique that you learned to get even closer than what the intercept was showing. And then come to a stop.

And yes, after you come to a stop, you will slowly start to drift apart again. But it takes a long time to build up speed, and you can always come to a stop again.

 

So if BOTH my Ap and Pe are greater than my target, I won’t cross paths, and there is a danger that the closest I will ever get is the distance between orbits?  But since you had me put my Pe below the Ap, and there is no appreciable inclination, I should be able to actually cross paths and get really close.  Is that the idea?

I’ll try this tonight and come up with new issues to be frustrated by  

[Kryxal]

If your AP is above the PE of the other orbit, or your PE is below the AP of the other orbit, you MAY cross it ... if your AP is above the other AP and your PE is below the other PE you MUST cross it.  Really, it's best to just keep an eye on the orbital tracks and be sensible.  By the way, if you go straight to the higher AP and only do enough circularizing to set up crossing paths, you save fuel and later modifications are easy enough.

[bewing]

5 hours ago, MPDerksen said:

and there is a danger that the closest I will ever get is the distance between orbits?

More like a certainty.

[MPDerksen]

I'd love an explanation of what just happened.  I did like you said, and thrusted (slowly) in prograde to my target at the intersection point.  I watched the distance of the next intersect slowly drop to about 5Km.  I waited until I got to that one, and repeated.  I was able to get that one down to 0.5Km!!!  Now, using small words and concepts, can you explain why this was the case?

When I reached the 500m intersection point, I burned retrograde to drop my relative speed from 14.6m/s down to 0.0m/s.  It only stayed that way for a few seconds before becoming 0.1m/s and climbing.  Slowly, but still.  I switched to the stranded Kerbal, and tried (and failed) to EVA.  I'll try again, but think I should thrust TOWARDS my target to close the gap from 500m to much closer.  Is the proper method to burn retrograde to get 0.0m/s, then burn towards the target, then get back to 0 once I'm as close as I want?

I do need EVA practice, and I think I'll nail this one after a few more tries.  But given that docking is even MORE delicate, I really need a longer window to work with than I'm getting.

[bewing]

2 hours ago, MPDerksen said:

I did like you said, and thrusted (slowly) in prograde to my target at the intersection point.

Did I say "target"? Hmmmm, I think I said "orbital".

2 hours ago, MPDerksen said:

Now, using small words and concepts, can you explain why this was the case?

If you thrust directly toward your target with some residual velocity in your craft, that will get you closer until you are a couple hundred meters apart. But no matter how hard you try after that, you will just go around in circles a couple hundred meters from your target. However, you said you thrusted prograde. Your prograde vector in target mode is pretty much just random. If you thrust prograde and get closer to your target, you just got lucky.

If you come to a dead stop, then thrust directly toward your target, then you will get a lot closer than you started from. If you start at 500m, then you will probably get within about 20 meters when you pass by. If you are within 30 meters, and you come to a dead stop, point at the target, and thrust again, you will hit it.

2 hours ago, MPDerksen said:

It only stayed that way for a few seconds before becoming 0.1m/s and climbing.

Did you leave your RCS thrusters on your ship turned on? If you do, they will continue making little adjustments and throwing off your nice dead stoppage.

 

[MPDerksen]

1 hour ago, bewing said:

Did I say "target"? Hmmmm, I think I said "orbital".

If you thrust directly toward your target with some residual velocity in your craft, that will get you closer until you are a couple hundred meters apart. But no matter how hard you try after that, you will just go around in circles a couple hundred meters from your target. However, you said you thrusted prograde. Your prograde vector in target mode is pretty much just random. If you thrust prograde and get closer to your target, you just got lucky.

If you come to a dead stop, then thrust directly toward your target, then you will get a lot closer than you started from. If you start at 500m, then you will probably get within about 20 meters when you pass by. If you are within 30 meters, and you come to a dead stop, point at the target, and thrust again, you will hit it.

Did you leave your RCS thrusters on your ship turned on? If you do, they will continue making little adjustments and throwing off your nice dead stoppage.

 

Yes, you said Orbital, and that's what I did.  That was a typo.  I haven't turned on the RCS yet at all.  

[bewing]

Hmmmm. Then I'm not sure why your relative speed didn't stay zero for more than a few seconds.

[MPDerksen]

Rescued.  Needed 2 tries with the EVA part, but even that is starting to make a bit more sense.  I had about 1,400dV left over, so I inclined a ton, and tried to land in a new biosphere.  Ended up in the highlands, which wasn’t new after all.  1 more derelict in orbit to go get.  Then I think it’s time to attempt an actual docking.

[Xd the great]

2 hours ago, MPDerksen said:

Rescued.  Needed 2 tries with the EVA part, but even that is starting to make a bit more sense.  I had about 1,400dV left over, so I inclined a ton, and tried to land in a new biosphere.  Ended up in the highlands, which wasn’t new after all.  1 more derelict in orbit to go get.  Then I think it’s time to attempt an actual docking.

Do you have da klaw? Or are you planning to build 1?

I use these to practice my KKVs

Edited February 15, 2019 by Xd the great

[MPDerksen]

11 hours ago, Xd the great said:

Do you have da klaw? Or are you planning to build 1?

I use these to practice my KKVs

Is that a mod?  I have NO mods yet.  I'm still, obviously, very new here.

[GoatRider]

"Da Klaw" is better known as the Advanced Grabbing Unit. It's intended for grabbing asteroids and also can be used for grabbing wayward spacecraft, or docking to something without a docking port.

[Tallinu]

The Klaw is the (official!) nickname for the Advanced Grabbing Unit, in the Actuators (160) research node. It's capable of latching onto other vessels/parts without needing a docking port on the target (and can latch onto asteroids in order to stay attached while mining or moving them).

(Ninja'd!)

Edited February 15, 2019 by Tallinu

[MPDerksen]

3rd stranded Kerbal rescued on the first try, and a ton of left-over dV in the tanks.  Thanks for the help.

[MPDerksen]

Today I rescued 2 Kerbals from LKO in a single trip.  At one point, my control completely stopped.  Could fire the engines, but no way to maneuver.  I had full batteries, and my solar panels were facing Kerbal.  Plus, Jeb was piloting.  I relaunched that save and it worked great.  Second time that happened.  If I have a pilot, I don’t need solar, right?  I did take the Mono out of the capsule and the lander cans since I am not using any RCS.

Otherwise, I think my ability to do these missions is solid.

[Espatie]

You need Electricity to run Reaction Wheels.

[Xd the great]

8 hours ago, MPDerksen said:

Today I rescued 2 Kerbals from LKO in a single trip.  At one point, my control completely stopped.  Could fire the engines, but no way to maneuver.  I had full batteries, and my solar panels were facing Kerbal.  Plus, Jeb was piloting.  I relaunched that save and it worked great.  Second time that happened.  If I have a pilot, I don’t need solar, right?  I did take the Mono out of the capsule and the lander cans since I am not using any RCS.

Otherwise, I think my ability to do these missions is solid.

Always have solar, just in case jeb ejected in space.

Plus solar panels look nice.

I blieve the reqction wheels were too weak, sometimes RCS is really helpful in manouvering.