Three Minute Challenge

[Raziaar]

My apologies if something like this has been done before.

In three minutes, how far out in space can you take your rocket using default components?

Here's my attempt.

EDIT: Made some slight modications removing the unneeded stage I had... And here's what I have.

EDIT: and beaten yet again.

[Monp]

Single stage, pure liquid.

[trydyingtolive]

Here is my run:

Edit: I also notice that this ship will orbit in about 2:30.

[Entroper]

197 868 m.

3x SRB

3x Radial Decoupler

3x LFE

6x LFT

Tricoupler

Pod

Going to try for higher with more SRBs. My first build with 9 SRBs kept kamikazeing, but I later discovered that it was because not all the engines were firing.

EDIT: Bizzare. With 9 SRBs, I got exactly the same result. I know that faster speeds are achievable.

EDIT: This is really difficult. I can't get a ship above 300 m/s in the lower atmosphere without it flipping end over end, even though it should be a tail-heavy design. I even add fins at the bottom, and it still wants to flip.

[semininja]

EDIT: This is really difficult. I can't get a ship above 300 m/s in the lower atmosphere without it flipping end over end, even though it should be a tail-heavy design. I even add fins at the bottom, and it still wants to flip.

It's because the thrust is at the bottom, so if the weight's off-center, it wants to fall over. The drag at the bottom helps some, but in order for it to actually make a difference, it would have to be below the engines.

[trifinity]

Here's my entry, I assumed 3 minute flight time so I delayed it to 0:05 to 3:05, quality on the video is a bit poor so I have a screenshot of the craft and at the pause. If people are really picky about time they can use the time remaining slider to see if I did 3 minutes or not.

Spacecraft - Tri-coupler with 2 liquid fuel and engine X3, 3 radial decouplers on each section holding a solid booster each.

End of flight - 197,909

video

[Entroper]

It's because the thrust is at the bottom, so if the weight's off-center, it wants to fall over. The drag at the bottom helps some, but in order for it to actually make a difference, it would have to be below the engines.

Yeah, even using the symmetry tool, there seems to be enough error present to throw the ship off balance under high drag loads. I may try again and just run partial throttle until the air thins out. Though I can't throttle down the SRBs.

Trifinity and I made exactly the same ship.

[trifinity]

Trifinity and I made exactly the same ship.

Yeah, well, that was after a bit of experimentation, it seems like no matter what edits I did, for this challenge that sort of craft is best, any less liquid fuel and it doesn't have enough of a burn to get past 170km in three minutes, any more and it accelerates too slowly. Also that seems to be the right amount of boosters as well, any more and it just gets too unstable while they're active. I JUST got an idea that might get me more altitude, however, we'll see.

The big issue with that craft is it wants to drift so much during flight, but again, SAS modules will weigh it down and reduce acceleration too much so you just need to be twitchy with the controls.

[Capt'n Skunky]

Yeah, even using the symmetry tool, there seems to be enough error present to throw the ship off balance under high drag loads. I may try again and just run partial throttle until the air thins out. Though I can't throttle down the SRBs.

Trifinity and I made exactly the same ship.

It's not the horizontal symmetry as much as the vertical. If your off by more than 2-3 pixels you can really get a curved flight path.

Arrr!

Capt'n Skunky

[Entroper]

It's not the horizontal symmetry as much as the vertical. If your off by more than 2-3 pixels you can really get a curved flight path.

Arrr!

Capt'n Skunky

Yeah, but the ships I was testing shouldn't have had any non-symmetry in any dimension, and were still flipping over. As soon as there was the slightest deviation from a perfectly straight flight path, it accumulated massively.

[semininja]

The problem isn't in the symmetry, it's that if the drag and thrust aren't both through the center of mass, the effect will amplify itself to destruction.

[Entroper]

Well, if the symmetry were perfect, then the net thrust and net drag would be through the center of mass.

Yeah, well, that was after a bit of experimentation, it seems like no matter what edits I did, for this challenge that sort of craft is best, any less liquid fuel and it doesn't have enough of a burn to get past 170km in three minutes, any more and it accelerates too slowly. Also that seems to be the right amount of boosters as well, any more and it just gets too unstable while they're active. I JUST got an idea that might get me more altitude, however, we'll see.

The big issue with that craft is it wants to drift so much during flight, but again, SAS modules will weigh it down and reduce acceleration too much so you just need to be twitchy with the controls.

I think if we spread the boosters out and activate them a few at a time, the ship will waste less energy to drag. Wish I could play during the day.

[trydyingtolive]

Here is my one up:

-->204Km

[Entroper]

Here is my one up:

-->204Km

Gah! As soon as I get ready to post my 204 km run, someone beats me to it. Well done. This time our rockets are very different.

[trydyingtolive]

What will really get you going is I made a slight mod and reached 108k, but didn't record it.

[Entroper]

8)

[trydyingtolive]

Awe, man. There goes my night.

[trydyingtolive]

I did some modifications to my design with much improvement. It continues to coast, for the last 30 seconds, but this rocket is a 3 stage rather than a 2 stage. While the tricoupler is essentially dead weight the lighter final stage allows the previous stages to get just a little extra acceleration. By the time the rocket burn out it has already reached escape velocity.

-->218Km

[Entroper]

Well done! And you gave me an idea for my next version. ;D

EDIT: Minor tweak, even better! I know 250 km is possible. I didn't want to say it when we were still in the 190s.

[trydyingtolive]

This was very very hard. I did several runs where I would beat you in 3:01. I probably did 20 different redesigns. I didn't think that 130Km was possible, I still don't know if 150 will be. The left hand of the image has been removed to hide design secrets, but this is all stock parts. Final result --> 235.6Km

[Entroper]

Excellent! Now to see what I 'left out' of my 229 km design. I really want to have a final stage of just one SRB pushing the pod, but it blows itself up before it's halfway expended.

[trydyingtolive]

If you put a decoupler on top of a SBR it will run without blowing up... that is if you haven't built up any heat before hand. I've tried several iterations and I think that SBRs in the final stage are probably a dead end. I also tried out using a three liquid engine rocket as the final stage as it would have slightly better acceleration than a single liquid, but being heavier makes earlier acceleration troublesome.

Anyway here is a new run of 243.8Km. Again the left side is removed because I feel it displays too many secrets.

[DoctorEvo]

EDIT: This is really difficult. I can't get a ship above 300 m/s in the lower atmosphere without it flipping end over end, even though it should be a tail-heavy design.

It's because the thrust is at the bottom, so if the weight's off-center, it wants to fall over. The drag at the bottom helps some, but in order for it to actually make a difference, it would have to be below the engines.

Both of you (semininja especially) need to read this: http://en.wikipedia.org/wiki/Pendulum_rocket_fallacy

It doesn't matter WHERE along the thrustline the thrust is being applied, just so long as everything else balances around the thrustline. Furthermore, having a bottom-heavy rocket does NOT aid stability - in fact, it aggravates it when aerodynamic forces are taken into consideration. (ever wonder why darts are weighted in front?)

Alternatively, your rocket may be (and probably is, judging by the behavior of some of my high-thrust rocket designs) suffering structural issues; i.e. twisting or bending in a fashion that causes the CG to no-longer be lined-up with the thrustline. If you're running 0.9, I recommend trying out those struts; if not, look at rearranging your SRBs so that all loads and stresses are balanced-out (I was forced to run a star-shaped pattern on my 13-SRB cluster).

[semininja]

Allow me to rephrase what I think I meant to say. Having the thrust at the bottom means that the air resistance in-atmo is always trying to push the rocket over. if there is any flexibility in the stack, the top of the rocket will bend to one side or the other, and that will lead to a spin-out. If the thrust is at the top of the rocket, the drag from the rest of the rocket trailing behind will try to keep it on target. That's what I was talking about when I said this:

The drag at the bottom helps some, but in order for it to actually make a difference, it would have to be below the engines.

If there is drag from below the boosters, it will help, somewhat, to stabilize the rocket.

[foamyesque]

Both of you (semininja especially) need to read this: http://en.wikipedia.org/wiki/Pendulum_rocket_fallacy

It doesn't matter WHERE along the thrustline the thrust is being applied, just so long as everything else balances around the thrustline. Furthermore, having a bottom-heavy rocket does NOT aid stability - in fact, it aggravates it when aerodynamic forces are taken into consideration. (ever wonder why darts are weighted in front?)

Alternatively, your rocket may be (and probably is, judging by the behavior of some of my high-thrust rocket designs) suffering structural issues; i.e. twisting or bending in a fashion that causes the CG to no-longer be lined-up with the thrustline. If you're running 0.9, I recommend trying out those struts; if not, look at rearranging your SRBs so that all loads and stresses are balanced-out (I was forced to run a star-shaped pattern on my 13-SRB cluster).

If things aren't balanced, though, it does matter a great deal. Take a look at Sunday Punch's medium SRBs and how moving them along a radial coupler affects their flight characteristics-- or how you can make an L, and use that to build a spin-stabilised doom machine.