Bay 12 Games Forum

We design an automated rescue craft. We stats, of course, with the part that will come back to Kerbin.


_{I briefly considered giving it wings and a jet engine before realizing that that was unneeded and that the wings wouldn't fit in the heat shield.}

Next is the stage which will go to Minmus and return.


_{If it wasn't for the poor TWR, it might be able to reach LKO.}

Next, we have the orbital workhorse.


_{It has less Δv than the Minmal stage, but a lot more thrust.}

Finally, some solid boosters...


_{These should provide enough thrust to let this behemoth reach orbit. I think.}

...and then odds and ends like more solar panels and struts, and we've got a rocket.
Note to self: Re-install KW Rocketry. Those ginormous SRBs and whatnot should help with these kinds of issues.

Anyways, we're exploiting the MechJeb unit's ability to act as a probe body to send the thing over there. Thanks to thrust limitation on the smaller SRBs, they all run out at about the same rate, and we can discard them at the same time (66 seconds in, 3800 meters up). Once we do so, we hear some kind of explosion.


_{Wait, aren't those the three Poodle units? ...I think we needed those...}

Well, we've still got a 1.33 TWR, so we'll still be rising, and we should have enough Δv, given how overbuilt the Rescue Stage was in that regard. I check, determine that the decouplers stayed on, and get rid of them. They're light, but no reason to drag 'em up, neh?
The gravity turn is executed. It is amended as the Time to Apoapsis is noted to be under 18 seconds and dropping. About two and a half minutes in, the upper half of the tanks run dry, and the three radial engines on it...keep running, keeping the thrust very high but the isp sub-optimal. Huh. We run out of fuel in that stage, and activate the Rescue stage...20,000 meters up, with a TWR just under 0.8. Still, as fuel was burned, the craft lightened...slowly...ever so slowly...eventually, we got the time to apoapsis to start increasing! (The TWR was still under 0.9, by the way. Weird, but yay!) It's a pretty steep ascent, though; this isn't a very efficient orbit. Hopefully, the lower stages gave enough velocity to us that our craft can get to orbit and still have enough fuel for its mission.
The mass drops to 30 tons and below. The TWR rises above 1. I shift the angle down a bit. The five-minute and 48-kilometer marks are passed, the former a bit after the latter. Fuel is around 60% at this point. Time to apoapsis: Almost 38 seconds, and rising. The craft is turned from 70 degrees from vertical to 40.
(I'm using MechJeb, so I can focus on non-attitude tasks. Like flying a spacecraft when three of its engines are knocked off and you need to burn the orbital insertion fuel to get to space.)
Much as I predicted, we continued to push that apoapsis up. I flatten more, wishing I had done so earlier. The apoapsis is pushed above 70 kilometers, and we're a bit above 65. Fuel: Just over 47%. No time for a manueuver node; I just start burning prograde and hope for the best, even as we begin to fall...


_{Fun fact: As I took this screenshot, the music stopped.}

Fuel drops. So do we. I notice that throttle is at 1/3 (when did this happen?), so I turn it up. I also turn the nose of the spacecraft up, even with the horizon; we're still falling. And we're entering the thick middle atmosphere.


<sub>Remember that bit where I said I installed Deadly Re-Entry?

Now you do.</sub>

Apparently, blasting through the air at over two kilometers per second is a bad idea. I try to turn the nose up, but...


<sub>Was that important?

MechJeb windows and control just vanished. That was definitely important.

And there go the engines.

This thing is just surrounded in an aura of fireballs.

Wait, I saw the Crew Hatch indicator for a second there--did the cockpits survive?

Yup, that's a cockpit. And another. Holy carp! Do I even need the heat shield? ...Well, the parachutes don't look so good.</sub>

Remarkably, the main fuel tank and the Kerbal Return Unit made it to Kerbin successfully.


<sub>It's flying pretty well, actually. Better than some of my planes.

The landing needs work, though.</sub>

According to the Flight Report, the solid boosters hit the Poodle tanks and knocked them off. This is an obvious thing to fix. Less obvious is adding a bit more fuel and a Poodle engine to the upper stage, giving it more Δv and more thrust. But the obvious thing is...a less obvious fix.


_{Do not adjust your monitors. Do not call the rocket scientists insane. We're not Junior, but we know what we're doing.}

The theory is that the small SRB will allow us to toss the other SRBs away from the rocket, stronger than a Seperatron. Also, we have a truss decoupler. Anyways, there was a staging mistake when fiddling with stuff, and so we have to adjust staging before launch.
Launch is a bit slower, and I think we might have lost some struts. Oh well.


_{Is it just me, or does that strut end in mid-air?}

The craft is spinning, more than even MechJeb's mastery can deal with. Still, we're pointing straight up, so for now it doesn't matter.
The fateful 66-second mark comes, and...


_{Stuff is exploding, but it isn't attached to us so we don't care!}

It's not pretty, but it works. Well, something works, dunno what. We start with a TWR around 1, but build up acceleration as the craft drops fuel. Good thing, too--we're under 40 m/s, and keep falling until after TWR exceeds 1.


_{Can exhauts hit fuel lines and slow us down?}

Something drops our throttle, and we begin losing speed. I bring it back up. Bad enough last time, potentially disastrous this time. We lose something like 10 m/s from that error. With full throttle and rising TWR, we manage to push our speed up past 50 m/s. Past 100. To 125 as we start the gravity turn. We get it to 200 right as we eject the three Poodle boosters.


_{Is it just me, or does the Minmus Rescuer look a lot like some starship now?}

We keep going up, but time to apoapsis is staying at a constant 14.7 seconds, so we increase our angle for now. Not much--60 to 70 degrees--but it means less horizontal momentum, which means a less efficient orbital burn.


_{Yeah, that's definitely an awesome starship-looking thing.}

As TWR increases and time to apoapsis nears 40 seconds, I begin to flatten out the angle of attack. (Is it still called that when you don't have wings?) We discard the lower stage around 40,000 meters.


_{This part looks less like an awesome starship.}

Apoapsis is up to 71km by 60, but we're over a minute out so I can set up a crude maneuver node. The estimated burn time is about two minutes and I get back with about 20 seconds until the node, still just in the atmosphere. Whee.


<sub>Looks starshippier from the front or, to an extent, behind than it does from the front.

Vanity isn't a sin for rockets.</sub>

When we end the burn, we have an orbit just above 84-by-70*. We have a bit over three km/s of Δv left, more than enough to get to Minmus and back. "More than enough" is generally called for.

*How I think of an orbit with an apoapsis of 84 and a periapsis of 70. Well, 84.3 and 70.3, but eh.

Anyways, we do a bit of a plane-change maneuver, bringing the orbital difference from 6.0 degrees to 0.4. For some reason, I can't get it lower than that. I prepare to actually burn, and KAC (Kerbal Alarm Clock) helpfully reminds me about the manuever node. (I really appreciate all you do and will let me do, KAC, but you're annoying sometimes.) By a quirk of timing, I start burning just as the sun rises over the horizon.


_{A beautiful quirk of timing, even if it comes close to making me miss the end of the burn.}

We quickly and easily get a very, very good encounter with Minmus.


<sub>That's 24,000 meters, not kilometers? I'm...I'm not messing with that.

Okay, it looks a little like a starship. Or at least a clunkier Firefly-class transport.</sub>

So, we warp to the node, then burn.
The burn was estimated at 6 seconds, but turned out to be about a minute. What the hell, burn time estimator? Now we won't get that lovely encounter, we'll probably be lucky to encounter at all. Why did you screw up so much, any--


_{...In my defense, when I set up those fuel lines I thought that the main tank would hold up until like the very end.}

Ah. With only the 300 kN of thrust from the LV-909's, we couldn't accelerate fast enough. Phooey. And we've got under 1900 m/s of Δv left.

Well, I was right about one thing...


_Damn.

A few hours later, though, a retrograde burn brings us to a similar encounter to the one we lost.


_{Is this a cool-looking spaceship, or is it just cool-looking because it's a spaceship?}

I panic when I see the KAC timer tick down below the three-minute mark it's supposed to warn me at, only to realize after I've slowed to 1x time that that's the time until it warns me. Oops. I guess I just don't trust my new toy yet.


_{Still no reason not to trust space to look awesome, though.}

I don't burn perfectly, but a 63-km encounter is still pretty good, methinks.
Alright. The rocket has been in space four days, twenty minutes, almost exactly. We're twelve megameters from Kerbin. How long until we enter Minmal influence?


_{Good thing kerbals can go without nutrients for extended periods of time.}

I take a breather before accelerating through those days, and notice something neat about my currently-projected orbit.


<sub>Of course, the Minmus encounter will toss that periapsis way up, but it's still a neat ratio. Eccentricity 0.973; I wonder what 0.98 or 0.99 would look like.

And here we are, way above Kerbin, eight days (and change) out, fifteen minutes from Minmus.</sub>

I set up a capture maneuver.


<sub>Good, crcular-ish orbit.

Wha...? Must have clicked on Eve. Not today, Gilly, maybe later.</sub>

As I zoom in to prepare for the burn, I notice a fatal flaw of the redesign.


_{Can you spot it? If so, you're cleverer than old-me was. Or you just have fewer rocket bits in the way and have hindsight powers.}

Well...I guess it's a good thing the Poodle's out of fuel, so some hardware-assisted lithobraking won't cripple the vessel. Unless it makes a devastating explosion, but empty fuel tanks shouldn't explode...right?


_{We distract ourselves by looking at pretty pictures of Minmus.}

Yet again, the predictor gives me a burn time way, way lower than the actual; yet again, I fail to expect it.
Well, the craft's been journeying nearly nine days, so you know what time it is?


_{Time to bring that up to just over nine days, then burn to start coming down!}

As it happens, I didn't end up picking that point, on the opposite side of the orbit. I picked a spot 90 degrees past the originally-chosen point!
I do a little math. With our current mass and thrust, our acceleration will be about 13.4 m/s² to start. The burn will be 91.8 m/s, so we'll need almost seven seconds to do it. Hence, I should start about four seconds out. Better than the one-second guesstimate provided by the game.

The estimated and actual trajectories were both much further from the target than anticipated. Whoops. I prepare another node, 68.5 m/s, so about five seconds. I screw up, distracted by the modded-in solar panels which seem to not have an Extend option (but I added other ones so it's fine), but my trajectory looks fine.


_{Much steeper than it looked from above, though.}

---

And it's getting late, so I should probably end this one on a cliffhanger.