Probing the Heavens

[Geschosskopf]

OK, with the obligatory noob haphazard Minmus and Mun landings out of the way, it's time for the my Kerbals to try interplanetary missions. But these are serious undertakings so I want to know what I'm getting into and maybe land at an Easter Egg or 2. Thus, before Kerbals themselves leave home, I'll learn how to get them there and find good landing spots with an opening salvo of ISA MapSats. But even this has to start small so my first efforts so far have only been in the Kerbin system, although I have 2 more probes parked in LKO waiting on upcoming launch windows for Moho and Duna.

Because this is a sort of mass-production batch of probes, I've developed a standard MapSat design and some standard rocket combinations to sit it on. The core of the program is the MapSat 3000, so named because it's got 3000dV on the probe itself and just an INSANE TWR. Because of this, the MapSat can reach and achieve a good, high polar orbit at Mun, Minmus, Eve, Duna, Ike, and Dres, all by itself once a reasonably small booster lifts it into LKO. It only needs a bit more juice to get to Eeloo, but Moho and Jool required a substantial transfer stage, which in turn requires a monstrous ascent stage.

Here's the probe naked and faired. Note the info displayed by Kerbal Engineer without the fairing.

The probe consists of:

Probodobodyne QBE core

ISA MapSat dish

2x OX-4W 2x3 solar panels (just for show--dish doesn't use power)

KW Rocketry SA-1 fuel tank

4x Rockomax 24-77 engines, only 2 of which are actually needed most of the time (disable the others with right-click).

The fairing is KW Rocketry 1.25m parts, below which is a stack of 4x FL-R25 RCS tanks and 8x KW Rocketry RCS clusters. Note the stitching struts between various pieces don't line up vertically with any other stitches--it's stronger this way. The fairing and the stitching are because I use Farram Aerospace, which likes long, tall rockets. This gives them a huge moment of inertia, which means you require RCS to point them in the right direction before you pass the circularizing maneuver node on the way up where the tailfins no longer function. I lawndarted quite a few rockets figuring this part out . And all this means there's a lot of sideways force applied to the skinniest part of the whole rig, so it needs all the stitching and sometimes some diagonal bracing to the side boosters as well to keep the payload from snapping off.

This is the standard ascent stage under the standard payload, capable of reaching all the aforementioned destinations. It's just the stock adaptor (KWR's don't seem to work for me) with 2 of the KWR big fuel tanks and the 4-barreled KWR engine under it, and 4x stitching at all joints. With a carefully flown ascent trajectory tailored to FAR's atmosphere, this rig will reach 80km LKO with about 500-600 delta-v to spare which can be applied to the ejection burn. I prefer to eject from 80km because the lower you are, the faster you're moving, which helps with the ejections.

NOTE: If you look closely, you can see there are only 4x RCS clusters on this one. This was actually the prototype and it worked, but just barely, so I gave it more RCS and it worked better.

The prototype in 80km LKO with enough juice in the big rocket for most of the ejection burn to Mun.

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OK, enough about hardware, on to the action. The MapSat 3000 is a real sportscar. Its TWR is so high that the calculated burn times are always less than 5 seconds. That's 5 seconds at full throttle, but I've never found the need to open the throttle more than 2 or 3 taps on the shift key because it accelerates too fast to control if you do more. That's with all 4 engines working, which is why I usually disable 2 of them for even finer control. So, while Kerbal Engineer says it only has 41 seconds of burn time, in practice with the engines just idling and 3000 delta-V in the tank, you've got a LOT of maneuvering you can do. Especially if you're smart about when you burn, which minimizes the delta-V needed.

For example, polar orbits are extremely easy to achieve around other bodies (different story at Kerbin). When you're about 1/2way to the target where you've already got an encounter, do a burn up or down so when you go by the target, you're as close to polar as you can get. Just a few m/s is usually all you need for this, as opposed to maybe a few hundred if you wait until you arrive. Like in the pic below, going to Mun, the burn to switch from a 0^ inclination approach to instead make me come up from the south pole at about a 65-75^ inclination cost me all of 2 delta-V. Even counting what I burned during ejection, I've still got over 3000 delta-V in hand and the final orbit is already well on the way to being established, even with a decent periapsis of about 250km.

As soon as I entered Mun's SOI and not a moment later, when I could see better what I was doing but was still as far away as possible, I did the final inclination tuning, getting just a hair shy of 90^. Then all that was needed was to circularize the orbit and voila:

That's Jeb's abandoned roving lander still orbiting Mun there. Anyway, the MapSat still has about 2850 delta-V in the tank so once it gets done mapping Mun, I'll see if I can move it over to Minmus. But while it's very cheap in delta-V to get INTO a polar orbit when arriving at another body, you might have to pay a lot to leave it. We'll see. That's a low-priority mission. Right now, the focus is the other planets.

As it happened, the 1st launch window to open up once I started this project was for Moho. You really need to stand on the brakes coming into there, which means the MapSat 3000 needs a transfer stage. And the weight of this means a MUCH bigger ascent stage. But I had 20-odd days to get the thing into orbit to wait for the window, which gave me ample time to have numerous spectacular launch failures . Sadly, I don't have any pictures of those, but I do have a pic of the finished product, my biggest rocket to date that's flown successfully. So I call it "Got my Moho Workin'". It weighs in at 217 tons on the launchpad. But for all that, it's just a big ascent stage. All that leaves Kerbin is the standard payload with a nuke engine and small tank under it.

Sadly, despite a flawless launch, I totally bungled the ejection. By the time KSP adds an Oort Cloud to the Kerbin system, this probe will be out there to map it . But that's why I'm sending probes, not Kerbals, for my 1st interplanetary missions. Anyway, the replacement is already in orbit ready for another try in 29 days, but next on the schedule is a Duna window. But that uses the small, boring standard launch vehicle you've already seen so I'll cut to the chase on that one when it's time comes.

As a side note, the 1st planet I mapped was Kerbin, which was an adventure in itself. Being an ignorant noob, I didn't realize it took a LOT more than the standard 4500m/s to do this, so I littered Kerbin's northern hemisphere with the fragments of failed rockets. I must have had 10-15 epic fails from all causes: total instability, inability to turn in the right direction in a vacuum, weak structure, overheating, etc., all before I even realized I didn't have near enough delta-V, and then I had another 5-6 fails before one finally succeeded. But all this was before I developed the MapSat 3000, with 3000 delta-V in just 1.75 tons. No, the Kerbin probe weighed about twice as much and only had enough juice for minor orbit tweaks, so all its thrust had to come from stages, which made for some rather large rockets. Here's the successful version on its way:

It was this experience that led me to rethink my whole probe design and come up with the much more effective MapSat 3000. MUCH less rocket needed with this thing. Give it a try if you don't already have something similar.

[Geschosskopf]

I was expecting to have half the Kerbol system mapped by now but I kept running into a problem. I'd get a MapSat in Kerbin orbit and it would just drop dead on me just as I was about to do the ejection burn. I had no idea why and this kept happening over and over. Finally, after asking around, I discovered I was running out of electricity, so I added an RTG to the MapSat 3000 and this time is worked (stupidly forgetting I could have shed the fairing and opened the solar panels). So here's about my 8th try to burn for Duna finally leaving Kerbin:

Because of all the ejection failures, the window was closing rapidly so by the time I finally got this figured out, the window was closing rapidly so the burn took more delta-V on both ends, plus I wasted some with unnecessary mid-course maneuvering. Thus, it was going to be a question of whether I could actually get into Duna orbit. But in the meantime, I did get my polar orbit set up relatively cheaply while still a long ways out.

Then it was time for the do-or-die capture burn. Rather less fuel than I was expecting to have by this point in the trip.... I suppose I could have aerobraked but the original plan was to have way more delta-V than I needed so I wasn't going to bother with that. Now I wished I'd taken the time to read up on how to do it but it was too late now. All I could do was cross my fingers and hope for the best.

Fortunately, the Kods were smiling on me and I made it with just 107m/s to spare. I was shooting for a 231km orbit and I got 230x235 so I'm happy. Already got a full-coverage map .

Planning for a crewed mission with lander and rover is now in progress, now that I know where I might want to go. But until the next Duna window, I'll send out a few more probes to refine my interplanetary techniques.