Economy of design

[Elukka]

Anyone know what the most efficient burn path is? I go straight up, full throttle, to around 430m/s, then tip sideways to get the horizontal. I've tried gaming the throttle but I haven't found a method that results in better final energies than full throttle all the way.

I don't know if it's the most efficient, but for me it worked to fly straight up to 5 km altitude, then start smoothly pitching over so that at 10 km my pitch angle is 20 degrees and at 20 kilometers 45 degrees. 90 degrees (horizontal) at about 35 km, and my upwards momentum still gets me to 45-50 km.

HarvesteR - Do you know what's up with the weird thing where a rocket with sufficient thrust can't lift off the pad until it has way more thrust than what it should need? If you put any module under the engine to lift the rocket up a little bit, it'll lift off provided that thrust > weight. Your rocket there doesn't really need those SRBs at all...

[HarvesteR]

HarvesteR - Do you know what's up with the weird thing where a rocket with sufficient thrust can't lift off the pad until it has way more thrust than what it should need? If you put any module under the engine to lift the rocket up a little bit, it'll lift off provided that thrust > weight. Your rocket there doesn't really need those SRBs at all...

I'm looking into that... sometimes the ship does seem to stick to the launchpad. I couldn't find what's causing it yet...

Cheers

[Elukka]

My initial slightly amusing theory was that as the atmosphere thickens exponentially the lower you go, it's really thick right on the ground. Not sure how likely that is since the pad is already a fair bit off the ground.

[DoctorEvo]

You people with your decouplers... and parachutes...

One Mk. 1 Command Module: 1600 credits.

Three FL-T500 liquid fuel tanks: 1650 credits.

One LV-T30 liquid rocket engine: 850 credits.

Achieving SSTO for just 4100 with enough propellant left over for a (marginal) powered landing: priceless.

[foamyesque]

Yeah, I eventually got to that design, but I couldn't find the thread again. I usually put a pair of winglets on; they make the landing much, much easier.

[DoctorEvo]

Yeah, I eventually got to that design, but I couldn't find the thread again. I usually put a pair of winglets on; they make the landing much, much easier.

Winglets? BAH! What a waste of money.

(No, but really, I like your style. A winged SSTO with 3x LFT and 1x LFE is an elegant minimalist design.)

[Yerbs]

What the real question is gonna be is when you have missions and payloads, whats the most economical way of getting those up, and in what quantity.

[foamyesque]

I have discovered that, with Kerbin now rotating, it is possible to put a pod, two tanks, and an LFE into orbit with the correct ascent profile. You can even deorbit it.

You just can\'t, you know, land.

Boost phase was done entirely @ 100% throttle.

[NovaSilisko]

Thank you for further proving my point that stock parts are unbalanced as fuck.

[UmbralRaptor]

I have discovered that, with Kerbin now rotating, it is possible to put a pod, two tanks, and an LFE into orbit with the correct ascent profile. You can even deorbit it.

You just can\'t, you know, land.

[images]

Boost phase was done entirely @ 100% throttle.

I\'m curious about why that throttle setting worked. In an attempt to minimize drag, I started at 80% (dropping to 60% at 1 tank before going exoatmospheric). My results have been frustratingly close.

Is this related to the way drag is broken? My issues with avoiding instabilities, or doing a gravity turn too late?

Thank you for further proving my point that stock parts are unbalanced as fuck.

It\'s a problem that should be reduced once we do more with actual payloads, can reuse parts, etc. If you\'re looking to make TSTO the standard, Isp values will have to be tweaked, also. (Even with 0 engine and decoupler mass, a second stage would be hardly worth the effort for LKO. Even less so, once the drag model is fixed.)

That said, having an enormous difference in size between the smallest rocket capable of something, and a more typical one is surprisingly realistic (the Pegasus has ~6% the liftoff mass of the Soyuz)

[Corona688]

This is efficient because empty liquid tanks weigh as much as marshmallows, giving ludicrous gees when running mostly-empty. They\'re so light that jettisoning empty tanks costs you thrust -- the mass of decouplers will negate any benefit. Empty liquid tanks should be heavier, or a lot more fragile IMHO -- how does something that light hold itself up? Unfortunately changing that will break tons of designs, but what else is new?

However: Throwing away a little mass saves a lot of fuel. They could have made the Saturn 1B much much smaller if they hadn\'t worried about getting the astronauts home; but it\'s not terribly realistic to throw away any chance at return.

[Iskierka]

In terms of realism, the empty tank is massively heavy. The tank is only around a mass ratio of 8; 10 is considered low-ish for a real rocket. Yes, the weight of decouplers negates the benefit of jettisonning a tank, but that\'s because decouplers and engines are absurdly over-weight compared even to the empty tanks.

[foamyesque]

I was running some numbers and it\'s tantalizingly close. To execute a powered landing that will save the pod, assuming perfect control, requires two seconds of full thrust. Finding an ascent profile that will guarantee me that reserve after deorbit burn is tricky, but it won\'t take much in the way of improvement over my best results. SO CLOSE.

[witeken]

command pod

fuel

fuel

fuel

engine

[Warshawski]

Parachute

--

Pod

--

Fuel tank

Fuel tank

Fuel tank

Wings (2)

Control Surfaces (2)

---

Thrust-vectored engine.

[yaang]

command module

Fuel tank

Fuel tank

engine

can orbit and return back

parachute

command module

decoupler

fuel tank

fuel tank

fuel tank

engine

can orbit, return back and safely land the command module

[Selrahc4040]

Foamy, I haven\'t checked it yet, but couldyou use a single rcs block and tank to helb deorbit?

[UmbralRaptor]

Foamy, I haven\'t checked it yet, but couldyou use a single rcs block and tank to helb deorbit?

The payload capacity isn\'t there for an RCS tank. Or even a parachute.

[PakledHostage]

I was running some numbers and it\'s tantalizingly close. To execute a powered landing that will save the pod, assuming perfect control, requires two seconds of full thrust. Finding an ascent profile that will guarantee me that reserve after deorbit burn is tricky, but it won\'t take much in the way of improvement over my best results. SO CLOSE.

I just managed to get the boys up and safely back down again using only a pod, 2 LFTs and a LFE. I admit to having tried and failed at this mission about 3-4 times before I finally got it right, so I attribute the success in part to luck...

I used 100% throttle to 110 m/s then ~80% throttle through ~15000 m before advancing again to 100% throttle. I intentionally placed them into a decaying orbit with a ~63.5 km periapsis to save fuel both going up and coming home. They managed about 3 1/2 orbits before re-entry.

I\'d calculated that I should be able to get them slowed to survivable impact speed (i.e. less than 10 m/s) if I ramped up the throttle to 100% starting at about 200 m AGL. In the absence of a radar altimeter, I figured my best shot would be if they came down over the ocean. In the end, they came down over land. The engine and two tanks were destroyed in the impact but the pod survived.

Reentry after about 3-1/2 orbits

PH.

Edit: Removed attached screenshots and added links to screenshots on Imgur

[foamyesque]

Excellent work. I think that\'s the minimum-- I don\'t think anyone\'s going to manage 1 tank. =)

I wonder what the minimum for a Mun & return is? I\'ve seen a ship that got there and back on 7 LFTs and an RCS tank; I\'ve managed a landing on an RCS tank and 5 LFTs with a pair of boosters.

[sal_vager]

I managed a Munar landing and safe return with 8 tanks, 3 engines, 1 RCS tank and 3 thrusters (plus some wings to land on), my attempts with a 7 tank 2 engine ship could only get me to Munar orbit and back, just not enough juice for a landing as well.

Here\'s the ship: http://kerbalspaceprogram.com/forum/index.php?topic=7229.0

I didn\'t think of trying to land without a chute and I can\'t land on the Mun without wings, so maybe there\'s room for improvement.

[Samonite]

The smallest rocket that have landed on Mun (IIRC):

Command module

1 x Fuel tank

2 x side decouplers with Fuel tanks connected with fuel lines

1 x Engine

I have never tried that myself but I have seen it a few times here on the forums.

[hebdomad]

I can get into orbit and out of orbit (with crew survival)

Parachute

Command

Liquid tank

Big thruster

On the sides I have three decouplers holding three more tanks of fuel with pipes feeding the single thruster.

There might be even potential for saving the three tanks with Parachutes if it comes down to cost efficacy.

[cardgame]

Try this:

command pod

stock RCS tank

24x Forward RCS thrusters (C7 pack)

[sal_vager]

Is it enough to just have 'orbit' show on your navball though or should it only count when you get into a non decaying orbit?

I haven\'t really tried hard yet but I can get into a stable orbit with:

Chute

Capsule

Fueltank

2 Double stacked fueltanks on radial decouplers

3 Light engines

There seems to be a sweetspot of thrust to weight, something like 3 or 4 tanks per engine but I didn\'t want to wait that long.