Sungrazer - To the very edge of the sun, and back again.

[Soralin]

Pushing delta-v and vehicle strength to the limits.

Your challenge: Using stock unmodded parts, approach the sun to within 10000 km, and return safely to Kerbin.

(hmm, one of the fuel tanks should be actually be showing as empty)

I've managed the first part, haven't quite got the second yet.

Oh, and when you're approaching the sun, I recommended keeping some timewarp on, getting that close moving that fast, calculations seem to get messed up, and it'll alter your orbit if you're on 1x speed.

If you're going straight up, taking off at sunset is also helpful.

And trying to wait for an alignment has shown me that timewarp could really use an extra notch higher on it.

[maltesh]

It should be noted that Kerbol has an invisible surface at about 4500km in v0.14-v0.16, so if you set your periapsis lower than that, you'll crash into it.

Also, a Bi-elliptic sundive cuts the delta-V required from LKO almost in half.

[Soralin]

Also, a Bi-elliptic sundive cuts the delta-V required from LKO almost in half.

Ooo, good idea, I'll try that.

Taking off at sunrise, for a bi-elliptic sundive. Our rocket of choice:

Wait, over 4 years travel time?

After a couple loops around the sun:

(Yes, this is a bit earlier in time, I did make use of some save/reload here)

Well, if I can take being closer than 10000 km to the sun, this doesn't seem so bad in comparison

End screen here doesn't have all the max speed/distance right, probably because of some re-loading done.

Well that was fun. I think I can get even a bit more delta-v out of my rocket if I take off the top layer of fuel tanks, and then use the mass saved to turn the upper stage into a smaller version of the lower stage.

There definitely needs to be a notch or two extra on the timewarp when it comes to inter-planetary maneuvering. Also it seems to be hard to control the direction of the ship when it's far away from Kerbin, and making a close pass of the sun alters your orbit in ways it shouldn't, from compounded calculation errors or such.

[simplemunrockets]

Uhh... Overkill much?

[NovaSilisko]

I think you've beaten your own challenge so hard that nobody else will have the courage to even try, Soralin.

[voleurinconnu]

Could use a few more boosters, maybe a stage or ten.

[Soralin]

Uhh... Overkill much?

Well it takes a lot of delta-v.

I think you've beaten your own challenge so hard that nobody else will have the courage to even try, Soralin.

Hehe.

Could use a few more boosters, maybe a stage or ten.

Well I tried making a version that had 17 of those large rocket towers (2 full hex-grids of them), that would drop them off in pairs as they got empty. But it always seemed to have something break off at some point during ascent. Also, I already had to adjust the positioning of the rocket so it wouldn't clip the launch tower on the way up. But I think I can basically replicate the bottom stage onto the upper stage in miniature, and that might get me some more delta-v.

[OdinYggd]

Lemme look, but I might actually be able to match you on this one. My Voyager rocket makes a very close approach to the sun, but it is a highly elliptical orbit that I put it in. It was launched with no intention of ever returning to Kerbin, and if I am not mistaken it's orbit actually goes from perhaps 100k of the sun all the way out past Minimus. Originally it was supposed to be a craft called the Kreutz that did this, but it didn't have enough Delta-V to get this close on the periapsis.

Edit:

AAHHHH WHY???!!!

My Voyager 1 had enough fuel remaining to lower it's periapsis to a mere 50k of the sun, while keeping a 20 billion meter apoapsis.

But now I see that there's something weird going on. Initially the periapsis started degrading further like some form of aerobraking, with the apoapsis degrading to only 9 billion meters.

On the next orbit around, the apoapsis and periapsis velocity is increasing exponentially, at this rate she's going to enter time warp or something.

I hope I didn't just break the game. Cause after only two orbits, my apoapsis is now -5.92 TeraMeters while my periapsis is 51Mm. Orbital period is now measured in years, my comet-like orbit just became a real comet's orbit.

That or Voyager 1 just boldly went where no Kerbin has gone before.

Edited August 25, 2012 by OdinYggd

[Soralin]

Ahh, yeah, maybe I should have put the distance a bit further out, when you get really close to the sun, the calculations seem to get messed up and stuff like that happens. If you have timewarp on, you can seem to avoid the effects, probably because it isn't constantly recalculating your orbit.

[maltesh]

I think you've beaten your own challenge so hard that nobody else will have the courage to even try, Soralin.

Nah. If I hadn't been on my way to work when I'd first seen the post, I'd have flown this mission then.

There are two big benefits of the Bi-elliptic sunscraper path. The first, as I previously mentioned, is that it takes significantly less fuel than the direct Hohmann.

Almost every time I do a bi-elliptic sundive, I head for a 131Gm apoapsis. It's traditional. Anyway, 660 days later...

We slow. We sundive. And 1233 days into the mission, we're sunscraping.

Periapsis: 8971 km.

From there, we fly out to apoapsis again, and at Day 1804, burn to raise our periapsis to Kerbin's orbit.

And there, we hit the second benefit of the bi-elliptic return. At this distance, Kerbin will go around six times before we reach Periapsis. We know that Kerbin has a period of just under 106 days. And we know exactly how long it will take us to get to Periapsis. So we don't have to wait for a return window. We have a way of correcting our course with the instrumentation we have.

Use tab to center on Minmus (it's the least jittery object in the Kerbin SOI under high time accelleration), and run time ahead until Kerbin crosses your periapsis.

The timer uses 365-day years. So we'll get there in 656 days. Kerbin will next be there in 6*106 = 636 days. So we need to pull our periapsis 20 days backwards.

To do this, we burn a little retrograde, to slow us down, then burn a little radially outward, to raise our periapsis. At this distance, it's easy and cheap to do. Then we let Kerbin go around again, and re-check, comparing our time to periapsis against five revolutions of Kerbin.

If we need to push our periapsis forward in time, we burn a little prograde to go faster, and a little radially inward to pull our perapsis back down.

We check each time Kerbin goes around. Since we'll be moving faster than Kerbin at intercept, it's best if we err a little towards getting to periapsis later than Kerbin, instead of getting there before.

Typically, when I do this, I don't actually find an intercept until 106 days before periapsis. Whenever you do get an intercept, it's time to use the RCS system to feel around for the direction that lowers your Periapsis. Dump it in the low atmosphere for a good solid Aerobrake. Then go around again.

And, bam. 2448 days after launch, I now have a new record holder for "Longest trip I've made that has successfully returned to Kerbin." And this time, I knew what the heck I was doing.

For what it's worth: The stats screen.

Peaked at just under 178 km/s.

Edited August 25, 2012 by maltesh
Various periapsis/apoapsis issues.

[Soralin]

Woo, very nice.

Yeah, I just tried adjusting my orbit from near the sun, so that the apoapsis was near Kerbin, and then went around a few loops waiting for a timing that was close enough that I could intercept on. Adjusting it from the outer edge of the loop does seem like it would be easier to get the timing right. And save on fuel, considering how absurd my rocket there seems, compared to what you have there.

[Hremsfeld]

Ladies and Gentlemen, I present to you: The Really Big Rocket. I am not very good at creative names.

I made it so half the SRBs would go off at first, followed by the second half. During the time the second half took to deplete, I discovered that the first pair of liquid-fuel stack (Five FL-T400's each) had depleted. However, dropping them with burning SRBs is an idea only Jeb would do, and Bill was my lucky pilot. I should have combined the drop-SRB and drop-LFE stages, but I'd already taken the screenshot so I stuck with it, a few m/s of delta-v be damned. This was my second attempt with the same rocket design, my first ended in failure when I used all but 300L of fuel doing a Hohmann injection. A Bi-elliptic was therefore declared to be in order.

I don't know why Bill's so freaked out, he's going to be perfectly safe in his quest to smack into Kerbol. I waited until Kerbolrise so that I could just go straight out into a bi-elliptic orbit without worrying about any of that pesky "steering" stuff

Sitting on a stack of explosions really can't ever be something that doesn't freak you out.

Unless you're Jeb.

Followed almost immediately by

Note within the first minute and a half I've gone through two six-groups of big SRBs and 20 400-capacity fuel tanks. I could probably make it more efficient by replacing the inner gimballing engines with aerospikes, but I know this way doesn't end with engines staying on the launch pad. One minute and 38km later, the second stack is emptied

I've now used the outer half of my booster stages, and it's barely getting me out of the atmosphere.

Each stack is lasting progressively longer, as you'd expect with two fewer engines each time.

Another quarter of my initial booster fuel later, I've added almost exactly 1.5Mm to my apoapsis. This final booster stack will get me almost to my target height.

Plus or minus a few dozen m/s, I didn't see the exact point it happened

Current fuel load on final booster stack:

Got me pretty far out. My final initial-stage engine can easily get me to my target apoapsis

I figured an AU sounded like a good distance. Unsurprisingly, it didn't take much fuel to get there.

http://i.imgur.com/skrSc.png

Passing the Mun:

Minmus:

Kerbin SOI:

At the point I exited Kerbin's SOI, something odd happened.

A few moments after exiting Kerbin's SOI, I re-entered it, and nearly instantly re-exited.

I was then going to very quickly re-enter and re-re-exit. My next destination was...not exactly where I expected. I'd reloaded the save I made when I had just pushed to an AU before I thought of screencapping my surprise periapsis, but it was roughly 100,000km, and thus too far out for the purposes of this challenge.

The "No MechJeb" part of the RBR's name is, you guessed it, because I was going to make a similar version using MechJeb, but hadn't tested it before I saw this challenge.

As it happened, Kerbin briefly re-captured an earlier sundiver, which was out of fuel and thus switching to it didn't let me re-enter the atmosphere.

Quite a while later, I reach my apoapsis.

Strangely enough, he isn't. Must've been a long 791 days.

I am clearly a genius and intentionally didn't include any RCS on this beautiful monstrosity. Spinning around therefore takes a considerable amount of time, but hey, I've got plenty of it.

Actually, no, that's too close, I'll crash into it and die. And that's bad. One long turn-around later,

It's gonna take an extra hour to be 1.5Mm farther from the sun. Yay, orbital mechanics!

Almost there...

Edited August 30, 2012 by Hremsfeld
Forgot the Spoiler tags don't like punctuation, see Bill loving life.

[maltesh]

Yeah, the Oberth effect makes little wiggles on your pod magnify into drastic differences in orbit at apoapsis.

As a result, when I did the challenge, I never dropped below 5x time acceleration near Kerbol. On rails, ship jitters don't mess with your orbit.

[Jason Patterson]

Yeah, the Oberth effect makes little wiggles on your pod magnify into drastic differences in orbit at apoapsis.

As a result, when I did the challenge, I never dropped below 5x time acceleration near Kerbol. On rails, ship jitters don't mess with your orbit.

In my case, the little jiggles completely tore the ship apart. I wanted to see how fast perihelion actually looked, switched to 1x warp and almost instantly was destroyed by wild spinning. I'm using a much much smaller ship, not entirely sure I can make it back to Kerbin as is. I also should probably put a parachute on the thing... Pictures forthcoming if I succeed.

[Hremsfeld]

Yeah, the Oberth effect makes little wiggles on your pod magnify into drastic differences in orbit at apoapsis.

As a result, when I did the challenge, I never dropped below 5x time acceleration near Kerbol. On rails, ship jitters don't mess with your orbit.

If I could have stayed above 5x time accel, I would have, but I kept getting a message informing me that I couldn't warp faster because I was accelerating. I blame the gravitational pull of Kerbol, but I can't prove that, because my Kerbol Orbital Observation Location hasn't been sending the information when we asked. You'd think having a Kerbal in there would mean you could be sure of getting a response, but no...

[OdinYggd]

That's the same phenomena my Voyager 1 experienced. The first pass it had a sharp drop in apoapsis, as though I had hit some kind of atmosphere and got aerobraked by it.

Second pass, the apoapsis rose to infinity, and my Voyager 1- which was supposed to obey a comet's path, ended up living up to it's namesake after all and leaving the Kerbin system entirely.