Multibody Probe Insertion

[Trann]

Now that the subject has caught your attention...

I'm having some uncharacteristic success going past Duna in my most recent simulation. All are probes but I'm happy with the delta-v calculations that got me there (mostly) comfortably.

Since I'm now at my first Jool mission, I'm looking for opinions from the collective Ground Control here on how to distribute my multiprobe ship efficiently.

The ship: each probe stack holds just over 5000 delta-v new (less 10% after circularizing)...

The Jool polar parking orbit is massive (1.xM Ap/Pe) and should let me make big changes for a small cost in delta-v...

The theory is that I split the ship and set up maneuver nodes to catch each moon when it passes my plane (like a transfer window)...

But before I do anything, I'm wondering if there's another approach I'm completely unaware of (for example, I just learned THIS WEEK about using the thrust limiter to better control and fine-tune my maneuvers... until then I was hitting power/kill, power/kill, flip, power/kill, repeat... like a n00b...)

Thanks.

Edited August 19, 2014 by Trann

[Aethon]

I would aerobrake the whole thing at Jool so that your apoapse crosses Tylo's orbit ( break for 69, 500,00 m or so).

http://alterbaron.github.io/ksp_aerocalc/

Raise your Jool PE at AP. Don't bother to circularize, and wait for a Tylo encounter. Dump a sat on it, and allow gravity assists to do all of the work for you. You can tour the whole system dumping sats wherever, and even return to Kerbin using little to no dv.

Seriously, the Jool system is like a Stargate. You can't miss it (huge SOI), and if time isn't a factor it'll take you anywhere.

[cantab]

That's an unusual parking orbit, but I think you've got the approach from there about right. Target the moon in question, and when you cross through the AN/DN, set up a combined retrograde and normal burn to put your orbit in the same plane and with low relatively inclination. For the inner moons I suggest making that retrograde burn down to low over Jool for an aerobrake to lower apoapsis, but watch out for the other moons interfering!

[Renegrade]

Just a note here - are those probes tested individually after deployment?

I've had some bad results with probes attached radially in that fashion (usually in RT2, in which probe clusters are quite handy), where the decoupler stays stuck to the other ones and throws off their balance..

That may have been with the Tier 3 radial decoupler though.

[TheScienceGuy120]

try getting near the jool system and set up a single maneuver node at that one sweet spot that will use the moon's gravitational pull to launch you to the next, andnd the next, and the next. the sweet spot will launch you through all of the moons without using any more fule, and is very hard to find.

[Kryxal]

A plane change is probably the most delta-v-intensive maneuver ... if you need to, use a slingshot around Tylo. In fact, I'd say that's worth doing in any case, see if you can get the orbits better aligned to the plane and maybe put your PE just outside Tylo's possible SoI when done. After all, the outer moons are easy to avoid, might take 1 m/s if you catch the possibility early.

Mind you, you probably have enough delta-v for the outer two in any case...

[Superfluous J]

After all the trouble I had with my Jool-5 mission I have one piece of advice for you:

Orbit Tylo.

Really, get the whole thing in orbit around Tylo and then launch each probe from there. For not much more than it takes to escape Tylo's SOI you can encounter Vall and from there slingshot yourself to any other moon.

[Trann]

I would aerobrake the whole thing at Jool so that your apoapse crosses Tylo's orbit ( break for 69, 500,00 m or so).

..

Seriously, the Jool system is like a Stargate. You can't miss it (huge SOI), and if time isn't a factor it'll take you anywhere.

Another thing I've never tried yet: aerobraking. (Love the Stargate analogy, BTW.)

That's an unusual parking orbit, but I think you've got the approach from there about right.

My Jool window wasn't a perfect one and I arrived well below its equator (probably >60deg inclination) so I caught the SOI, burned for 90deg at a distance, then circularized as big as possible, figuring a polar orbit wouldn't hurt and I'd save delta-v by not doing it over each moon.

I was thinking of separating things here and throwing each sat at each moon as they come by. Is it easier/cheaper to come in equatorially and then set up polar orbits over each body?

Just a note here - are those probes tested individually after deployment?

Nope (first multibody probe) and now I've developed flop sweat! Hopefully, any imbalance is easy to deal with using manual course corrections to keep the burn on track?

Really, get the whole thing in orbit around Tylo and then launch each probe from there. For not much more than it takes to escape Tylo's SOI you can encounter Vall and from there slingshot yourself to any other moon.

I'm guessing that implies an equatorial arrival?

I will definitely try coming in equatorially and trying some of these maneuvers with my first set of lander probe missions.

Thanks for all the wise advise.

Edited August 21, 2014 by Trann
tpyos

[Superfluous J]

I'm guessing that implies an equatorial arrival?

It does. I've found that once you get an encounter with Jool, fixing your normal at AN/DN in Solar orbit and at the same time burning a bit radially or pro/retrograde can get you encounters with several moons. Play with those encounters and you'll be surprised what you can do.

Hint: I'll never aerobrake at Jool again. Well maybe not never, but it'll be a last resort.

[Trann]

Since I have this thread anyway...

After Renegrade brought the decouplers to my attention, I went back to the VAB to take a look at the center of mass for the radial probes and how they were attached to the probe core relative to the decouplers. A definite offset.

If my visualizations are correct, staging this would kick out the top of the radial probe faster than the bottom, probably causing the radial engine bell to hit the center fuel tank. Without the word of warning, I probably would have decoupled without thinking about it. Instead, I decided to apply a little thrust in the hopes that the center probe moves out of danger while the radial probes kick out and away.

...

*whew* Just barely, I think

The probe core is as expected...

...but I never had to deal with a decoupled part before. I'll soon find out how the radial probes will perform with their decoupler remnants are once I put them under thrust.

[Jett_Quasar]

It takes a lot of dV to re-orient your orbit from polar to equatorial. Your probes might deal with it OK because of how their designed but it's probably not the most efficient method - it's best to come in on an equatorial orbit that way you use less dV and your path crosses the orbits of most of the moons.

And I think somebody covered this already but areobraking is also extremely helpful, but I read somewhere that you should do it at Laythe not Jool... I'll see if I can find the link.

JR

[Kasuha]

High polar parking orbit is a bad idea if you want to deploy your probes at individual moons. Not only it costs more dv to brake into it, it will cost a lot more dv to perform inclination change for each moon. If you're not there yet and just planning, bring your periapsis as low as possible and either aerobrake in Jool's atmosphere, or just perform powered braking near its surface. For comparison, I sent two similar probe carriers to the system. Braking in high orbit cost me 2000 m/s dv, braking just above Jool's atmosphere cost me 700 m/s dv. You can save even more dv if you brake by Laythe or using gravity slingshot off Tylo (then you may only need to spend some fuel on corrections, no actual braking needed).

If you're already there, fix your inclination to equatorial while you're still in high orbit. It costs less dv than doing it near each moon.

After that, I believe the easiest thing to do is a Hohmann transfer to each moon individually. Just make sure you don't get accidental Laythe or Tylo encounters.

Edited August 21, 2014 by Kasuha

[Trann]

This was an unplanned arrival well below the equator and it seemed I should circularize first. Having never done Jool, I haven't made any mistakes to learn from (yet). In hindsight, there really was no reason to make a polar orbit, either: I could have left it at >60deg inclination and brought the orbit down to intersect a moon just as easily. I'll probably set up a maneuver node and see what the price of rolling this orbit down to equatorial would cost. After all, each probe has 5k dv at this point.

That said, with this orbit there's no extra cost to "make" polar orbit at each moon and I have two "windows" to capture any moon below my current orbit when our paths intersect so I'm betting this will work. It's not efficient, but I'm thinking it's not all that terrible either.

[Kasuha]

This was an unplanned arrival well below the equator

It's always good idea to check your intercept within the SOI (now possible with stock settings by focusing on the target system) and perform course corrections to come on the best trajectory possible. It is usually not possible to come exactly in equatorial plane, but it is always possible to correct for low periapsis above the central body's equator.

That said, with this orbit there's no extra cost to "make" polar orbit at each moon

That is not true. You're going to need way more dv to circularize around that moon. For example Tylo's orbital speed around Jool is about 2000 m/s. So tylo will be going 2000 m/s horizontally and you'll be coming at (say) 3000 m/s vertically (faster than Tylo as you're at periapsis of elliptical orbit). Resulting relative speed is about 3600 m/s. If you came along Tylo's motion, your relative speed would be only 1000 m/s. And notice this relative velocity will rise as you'll be falling down the Tylo's gravity well within its SOI.

Definitely fix your inclination first, while you're in high orbit and it only costs a little dv. If your probes are completely separate and holding equal amounts of fuel each, then best is probably to separate them now and fix inclination of each probe to its moon separately. You can save even more fuel if you merge this inclination fix with braking maneuver to cross the moon's orbit.

Edited August 21, 2014 by Kasuha

[Trann]

I can't ignore so much solid advice and math telling me to come out of this polar orbit. A maneuver node shows I'm only spending about 700 delta-v (out of 5k) to fix the inclination and, once there, it's pretty easy to catch a moon intercept. Thanks for setting me straight. I'm strapping in now...

[Trann]

For the sake of closure...

I immediately threw the orbits of each probe into an inclination matching their target bodies.

And it was trivial to hook up with each moon from there.

Every probe had 1500-2500 (or more) d-v remaining so I certainly over-engineered this mission.

A probe elsewhere had mistaged and wasn't going to make orbit anyway so I decided to test my theory and everyone was right: although the intercept was possible, the d-v required to make that capture when their approach vectors were (more or less) perpendicular was massive. Thank you, Ground Control, for making my first Jool-5 mission a success.

Oh, and I won't be using these decouplers for controllable vehicles anymore...

They required constant slewing to maintain a heading during burns. Annoying and ugly.

Edited August 26, 2014 by Trann