Multiple Launches or Bigger Probe Bus?

[Commander Zoom]

I have a working probe design with a single probe atop a transfer stage. I've also designed, and am in the process of testing, a "Double" (for bodies like Eve/Gilly, Duna/Ike, etc) and my most ambitious by far, the "Grand Slam" (five probes, for Jool and its moons). However, I'm starting to think that the last may be a little too ambitious. Iterating the original design after it failed, adding more tanks etc, has quickly brought me into the realm of diminishing returns; I'm starting to think I may need a whole new transfer stage / probe bus to carry them to, and then distribute them throughout, the Joolian subsystem. There's a part of me that dreads going back to the drawing board so much (especially as it'll probably require a larger lifter too, when I'm done) that I'm wondering if I should just throw up my hands on the multiple-probes-per-launch concept and just launch one rocket, with a proven payload, five times.

How do you all do it? Leaving aside for the moment big manned interplanetary voyages / craft, which often have room and delta-v to spare for lots of little limpets that pop off at the destination ... do your probe launches tend to be one per rocket, or what?

Edited November 12, 2013 by Commander Zoom

[Specialist290]

Might we see a screenshot? That might help us diagnose specific issues with your current design, if you're interested.

I haven't really done much with launching multiple probes to a single destination. However, I do often design my interplanetary probes to launch a separate orbiter and lander together.

[700NitroXpress]

I have the perfect solution for you. All you have to do is build a hive ship for the probes. Then attach it to an asparagus nuclear transfer stage and launch that sucker up into orbit with a super lifter.

Take this idea that I used for my Vall Challenge ship build, all you would have to do is replace the Mk1 pods with your probes, remove the lander that's shown on top, and launch it up with the super lifter in the second image. The Leviathan super max lifter can get payloads in excess of 200 tons into orbit with no problem.

If you build something that uses the same transfer stage design that I have shown on the Vall mothership, then you'll have no problem getting to Jool and back to Kerban, just add another round of those 360 fuel tanks to the asparagus and you're good to go.

You can download my Leviathan lifter here: https://drive.google.com/file/d/0B-vTRL2n8wvzQkEtUTBCNHpIMW8/edit?usp=sharing

Here's a video that shows you how it works:

[Geschosskopf]

If you use ion or similar exotic engines, you can do all Jool's moons with 1 probe that gets itself out there, and launch it with a tiny lifter like from the beginning of the tech tree.

[Commander Zoom]

For illustration, as requested:

(Interplanet) Janet, atop a Comet booster and "Single" transfer stage. The screenshots include Procedural Fairings, MechJeb, and the ISA Mapsat dish, but these have been omitted from the craft files below. MechJeb reports the total weight of the upper stage as 3.87 tons.

The "Double" - two Janets on a slightly extended transfer stage with its own probe brain. Not yet tested in its current form, as Jool is coming up first in the transfer windows. 5.73 tons.

The most recent attempt at a "Grand Slam" - note that I've added another transfer stage below the first, to be burned and discarded while still in Kerbin orbit. Doesn't seem to help as much as I'd hoped. A whopping 11.42 tons, which, again, if I were to continue, would probably mean switching from my home-grown Comet booster to the lightest of the Zenith family.

And here are the craft files, where I hope I've stripped everything non-stock out:

Janet - Janet Double - Janet Grand Slam

The current mission plan for all of these is for the transfer stage to deliver the probes to the planets in question, retroburning or aerobraking for capture as appropriate; the probe(s) will then cast off from the core and seek their own orbital encounters with their ion engines.

[Traches]

You seem to be perfectly competent at building rockets - go for the grand slam brother. You will probably need a bigger lifter, but once it's designed you can save it and use it for other things. Eventually you'll want to do a manned return mission somewhere, and you'll need some pretty serious payload for that!

It may be easier to stick a small engine and fuel tank on each of the probes, so the transfer stage doesn't have to travel to every single moon. For the bus, Asparagus fuel tanks with a single nuke engine in the middle is tough to beat for dV.

Speaking of dV-- Have you consulted a map, and compared mechjeb's reported stats?

[Dangerous_Beans]

i tried doing a single launch and transfer, 5 probe Jool mission, and i was unable to get it to work. the mass wasn't too bad, the problem i was having was the symmetry bug and limited parts available to me at the time.

i would recommend designing a probe that will do the work, and then launching 6 of them. by doing 6 separate probes the launchers are simpler, you can go straight to the moon you are interested in, and if the space Kraken decides to eat one the entire mission isn't a write off (my first Eve probe got eaten by the Kraken, while if i had a two probes one would have gotten through).

only downside is 6 launches, followed by 6 interplanetary burns and 6 aero braking manoeuvres.

[Commander Zoom]

ah - now that you mention it, I hadn't considered using an LV-N for the Grand Slam core - the Single and Double are both light enough to get away (and be more efficient overall, I believe) with 909s.

And it's not like the nuke is going to wind up anywhere "environmentally delicate" ... possibly dumped into Jool itself.

*goes and noodles a bit*

EDIT: Yes, it looks like changing to an LV-N (and some other minor tweaks) might be enough to do the trick. I'll have to actually flight-test / sim it, see if it gets out to Jool, but...

I'll leave this topic up for a while before officially changing and closing it, so that others can weigh in, but it's looking good. Thanks.

Traches: If I'm reading the "subway" map right, it's about 1900 to get from Kerbin orbit to an intercept with Jool, yes? That would leave me, with the current 3k+ of my upper stage, another 1.0 - 1.5k for setting up the aerobraking and other miscellaneous maneuvers.

Edited November 11, 2013 by Commander Zoom

[Superfluous J]

I launch 5-thing probes all the time. In my current career mode I've launched 5-landers to Mun, Jool and Duna. The Mun landers were to land in craters and transmit back data of them (and also mark them so I knew which crater was which). The Jool one has 3 different lander designs - 2 big ones for Tylo and Vall, 2 little ones for Pol and Bop, and a parachuted one for Laythe. The Duna one has 4 chuted probes for Duna and one regular lander for Ike.

Why launch 5 individual ships when you can launch 1 (that is 5 times the size for 5 times the price)?

[Traches]

Traches: If I'm reading the "subway" map right, it's about 1900 to get from Kerbin orbit to an intercept with Jool, yes? That would leave me, with the current 3k+ of my upper stage, another 1.0 - 1.5k for setting up the aerobraking and other miscellaneous maneuvers.

Sounds about right! You might have a plane change to hit Jool to the tune of about 300 m/s, but Jool's SOI is a big easy target so it shouldn't give you too much trouble.

[Monkeh]

Remember to match the inclination on the big burn too. It looks like you'll be arriving in a similar plane but look closer and you'll see a gap.

If I don't correct for it I've had encounters that required 3000 m/s to slow enough to be captured by Jool. Get the inclination right and I've had burns of less than 500 m/s to be captured...yes, it can make that big of a difference.

[Commander Zoom]

Tried it tonight, and everything worked great... until I discovered that my second set of Procedural Fairings (one to get the whole thing out of atmo, the other to act as a heat shield during aerobrake) also did a fine job of getting between the Sun and the solar panels I'd put on the transfer stage, leaving me with dead batteries and a course that went through Jool. (I did get enough juice during the flaming tumble to jettison the fairings, which promptly ripped away everything delicate on the doomed craft, and to test the probe separation once the fire went out - which also worked just fine, resulting in five expensive paperweights falling to crush depth in a tight little group.)

And this is why we restore from backups "run test simulations". The one I "actually" launch will have a damn RTG embedded in it. (Before that, I considered putting more panels on the inner fairing - no worries if they fail during braking, what matters is keeping the batteries topped up until then - but decided to go for the sure thing rather than trying to be excessively clever.)

Monkeh: I didn't think of that before, and in any event, my habit is to match planes midcourse, at the AN/DN - which took, IIRC, almost exactly the 300 quoted by Traches, which is also in line with your figures. So, six of one, maybe?

Edited November 12, 2013 by Commander Zoom