[DUNA MISSION FAILURE] Ship issues... again.

[KerbMav]

.

I meant radial docked tanks for the transfer ship that could be dropped to safe mass/fuel for the return trip, not the lander, you might want to use that one again later!

And if you brought fuel for landing on Ike and Duna but only one lander capable of doing both, you would safe even more on the whole trip.

I second this. 'Man up and just sit through the burn on physwarp'.

It is still mean for larger ships that double or quadruple the real time though!

[Starwhip]

Did the DV calcs again. It's got 400 Isp from the Aerospikes, and 68 tons of fuel from... wait. Crud. Forgot the arm tanks.

Okay, it's got 3203.85 m/s^2 of Delta V. That's not half bad. And the TWR is...

Weight = 136.287 tons

Thrust = 700 kn

TWR (Kerbin) = 0.523.

TWR (Duna) = 1.747. Woah. It could land on Duna. Impressive.

Got the crew transferred, refueled it, now just got to wait until Duna window in, oh, 125 days or so.

Crud.

Bye-bye, old DTV!

(I got Jeb and what's-his-face off of it first, though )

[KerbMav]

You are using many docking ports? You might want to make sure they are only cross-fuel enabled if you want them to be, to get reliable dV readouts and do not use up fuel intended for landing operations!

[Vindelle_Sunveam]

As you might be used to notice, maneuver nodes make the "burn towards" marker like the burn is going to be instantaneous.

As I set my maneuver node for long burns headed for interplanetary transfers, I tend to keep my ship burning not towards the burn marker, but prograde, adjusting my ships' attitude to keep it aligned with the vector for the whole burn. This implies good empirical guesswork, but it is quite comfy.

Still, I prefer to inform you that I do my interplanetany transfers with Skipper engines, so it might not work for you.

[Rickenbacker]

Hmm, why do you need two landers? The Duna lander can easily land on Ike as well.

[G'th]

You know, considering its just Duna you don't necessarily need nuclear engines. Especially when you don't plan on going anywhere else other than home.

[KvickFlygarn87]

Here's just a quick tip: Delta V is speed, not accelleration. Drop that square part

[Starwhip]

Here's just a quick tip: Delta V is speed, not accelleration. Drop that square part

Delta V literally means "Change in Acceleration". In meters per second per second. Yes, two "per second"s. Thus, m/s^2 or m/(s*s)

Well, the mission failed. Horribly. I think I have to restart from the Duna Aerobrake, because at the moment, nothing is coming back home right now. Need some redesigning.

I think I'm going to change out the Ike lander for a fuel tank or two, and just refuel the Duna lander and use it for Ike.

[Red Iron Crown]

No, delta-V is literally "Change in Velocity", and is measured in m/s.

Edit to be more helpful: Delta-V is the amount of velocity change, acceleration is the rate of velocity change.

Edited May 22, 2014 by Red Iron Crown

[Decent Weasel]

Holy lord, you build your ships more substantially than I do.

I was reflecting last night that I sucked at landing on Duna, as I could never design a lander powerful but stable enough to do the job.

however, on a more pragmatic note, cut mass anywhere you can:

-Like other folks say, use one lander. Refuel from the main ship, if need be. Carrying two means you carry extra ship for two landings, when all that's needed is extra fuel.

-Omit the cupola. The hitchhiker is a good idea, since it's weight efficient, but if you only plan to carry one or two kerbals down to the surface, consider having a single habitat module that rides up and down with the lander.

-Use docking ports to join it to the transfer and descent stages, and attach the lander's parachutes to it if you think you can survive descent without the ship popping apart. That way, you can dump the extra weight of the descent module and engines once you've emptied it of fuel, and just carry the hab module home.

-Join the radial engines by means of radially-mounted fuel tanks with feed pipes. Omit the fuselage elements and four-way junction and replace them with fuel tankage. If you're add structure, carry fuel with that structure.

-Replace the large solar panels with ox-stat single panels mounted all over the craft. Four should do it, radially arranged around the tank.

You should be able to shave off a substantial amount of mass this way, which will allow you to get a better TWR, which will allow you to use LV-Ns since they're so much more efficient, which will allow you to carry less fuel, which will give you a better TWR.

A virtuous cycle, if you will.

[Tortoise]

Physics warp and cut the burn time to 4-ish mins

[Starwhip]

Okay, I'm seeing some good ideas. But I want to keep the Cupolas; I find them I iconic. I think that what I'll do is get rid of the Ike lander, and give the Duna lander enough capacity to go to, land, and return from Ike. Or have drop-tanks. I'll figure it out... I hope.

I got some really nice screenshots, anyway.

[Northstar1989]

Okay, I'm seeing some good ideas. But I want to keep the Cupolas; I find them I iconic. I think that what I'll do is get rid of the Ike lander, and give the Duna lander enough capacity to go to, land, and return from Ike. Or have drop-tanks. I'll figure it out... I hope.

http://i57.tinypic.com/2vwsl0l.png

I got some really nice screenshots, anyway.

I assume that was from the failed mission? (it looks like it's not going to make it back to orbit) Even so, that was a nice screenshot...

Ways to increase mission viability/decrease mass:

(1) Consider if you can't get by with OX-STAT solar panels. They are the most efficient producers of ElectricCharge per ton when facing the sun, and it looks like you already have some radial extensions from the main body you could stick a few on to provide front/rear sun coverage...

(2) Make sure you can detach the extra fuel tanks you no longer need after the transfer burn to Duna, so you won't have to haul them back with you. A great place to dump them is just after your aerobrake- your periapsis should still be in the atmosphere of Duna, so if you load them up after you circularize, you can ensure they crash into the surface so you don't have to worry about orbital debris... Alternatively, you can design the extra fuel tanks as a detachable section with a docking port to leave in Duna orbit (after circularization) as structural elements and fuel storage for a future Duna space station...

(3) Winged lander for Duna! (works best if the Kerbals ride down on External Command Chairs) You can get away with a lower TWR if your lander ascends back to orbit as a spaceplane, instead of like a rocket. This will enable your lander to ascend to orbit more fuel-efficiently, and provide your lander with a lot more freedom to select its landing spot on Duna's surface (so you don't have problems coming down over a mountain). Just remember to ditch the wings after you exit Duna's atmosphere on the way back up, so you don't have to haul the wings to Ike when you use the lander there... (attach the wings to decouplers rather than directly to the body of the lander) This would also give you the opportunity to knock out the Flying Duna Challenge while you're carrying out your mission...

(4) Consider sending a fuel tanker AHEAD of the main mission. That way, you can build a heavier mission vehicle, with just enough Delta-V to get to Duna and rendezvous with the tanker, and have your return fuel already waiting for you before you return. It also means you don't need as much tankage on your main vehicle, because you can refill and re-use the same tanks that carried the fuel to get to Duna for the return trip... Obviously this doesn't work well if you drop empty tanks like in (2)

(5) Consider how much Monopropellent you really *NEED* for your mission- I saw you packed an awful lot. Many new players make the mistake of packing entire 2.5 meter tanks full of Monopropellent when all they REALLY need is a couple small radially-attached tanks of the stuff. Once you get REALLY good at docking, you might even find you can get by with just tiny bursts of thrust at low throttle from your main engines instead... (precisely match velocities with the vehicle your are rendezvousing with, and then have both vehicles point their docking ports at each other, and one give a tiny burst of thrust towards the other such that they approach each other at 0.3 or 0.4 m/s...)

Regards,

Northstar

Edited May 23, 2014 by Northstar1989

[Starwhip]

Ok, so, new plan:

1. Cut back on the payload. ONE lander is good enough.

2. Higher TWR. Although a NERVA is highly efficient, if you can burn closer to the node, you save Delta V. So, I'm thinking Kerlington.

3. Drop tanks. Let's not haul around all that extra fuel, everybody! I'll build the craft with a core stage that can make it back to Kerbin, which carries only the crew. It would have parachutes and legs to land back on Kerbin.

4. Less monopropellant. I'll use Reaction Wheels, on a stronger craft. Saves fuel.

5. Emergency Procedures. If I can't get back to Kerbin, the core stage will be Duna-landing capable. Unintentional bases, anyone?

Until these changes are implemented, please enjoy my new desktop background:

[Starwhip]

Issues again...

The new ship is designed with a 1-way transfer stage which will drop prior to the Kerbin return burn (KRB). The Habitat module will decouple the Cupola prior to KRB, saving weight. A "Poodle" engine is concealed directly under the Cupola, it will be used to execute the KRB.

My main issue?

Upon gravity turn at 9000 meters, the ship decides to spin out of control. The 3-wide RCS reaction ports are not enough to stabilize it. Tips? Perhaps detachable canards on the fuel tank? Would that help, or is there another alternative?

[Starwhip]

OOOH! I know what it is. The Cupola is generating so much drag that the darn thing is being rotated.

I fix it.

[Random Tank]

Upon gravity turn at 9000 meters, the ship decides to spin out of control. The 3-wide RCS reaction ports are not enough to stabilize it. Tips? Perhaps detachable canards on the fuel tank? Would that help, or is there another alternative?

Right, I was going to say about the cupola; just put a stack separator and the big nose cone on top. Though without FAR, this shouldn't be too much of an issue... I'd some canards on it though, they always help with stability!

Ummm... I don't mean to cause offense, but isn't this whole mission a bit... over-engineered? That's quite a big interplanetary ship you're using, for a mission that only requires a bit more dV than a mission to the Mun (as Duna's atmosphere, though thin, cuts out any dV for slowing down and most/all for landing). I just think that setting your sights a bit smaller may get right of a lot of problems you are having, and generally make it easier to carry the mission out as a whole...

If you want to carry on building bigger, by all means, go ahead; i'm just suggesting that a smaller ship can be more beneficial, like my latest Duna lander:

And even that has too much dV...

[NecroBones]

Usually, if the stability is bad in the atmosphere, it's due to the center of lift being in front of the center of mass. Turn on those indicators with the buttons in the lower-left of the VAB, and make sure your center of lift/drag is behind the center of mass. Then, set all of the fuel tanks to be empty, and make sure it's still behind. It's possible that during flight, after some of the tanks have drained, your center of mass may have moved just enough to put you into an unstable aerodynamic situation (which even with KSP's terrible aerodynamics model, is still important to consider).

Adding canards can actually be counter-productive, if it moves the center of drag too far forward.

Edited May 23, 2014 by NecroBones

[Starwhip]

Refueling in progress. Need to give it a little bit more fuel, plus put some crew onboard.

@RandomTank: Over-engineered? I think I know what you mean. But I like over-engineering: This is literally my first manned Duna mission. It's a big milestone. This ship is literally the biggest thing I've ever put into orbit. Well, minus stations.

I can't see any images you're posting right now, as I'm at school, but eventually I'll figure them out.

Edited May 23, 2014 by Starwhip

[Starwhip]

So here we are at Duna. Got everything ready to go... except the aerobrake. What's the correct altitude? I need to get to Low Duna Orbit, something like 60,000 meters. 10,000 meters for the aerobrake is too low, 13,000 too high... it's frustrating.

[Random Tank]

But I like over-engineering: This is literally my first manned Duna mission. It's a big milestone. This ship is literally the biggest thing I've ever put into orbit.

I was merely suggesting using a smaller vessel to make it a bit easier on yourself; but if you want the bigger ship, go ahead, its your choice, just makse it more of a challenge!

So here we are at Duna. Got everything ready to go... except the aerobrake. What's the correct altitude? I need to get to Low Duna Orbit, something like 60,000 meters. 10,000 meters for the aerobrake is too low, 13,000 too high... it's frustrating.

It's dangerous to aerobrake alone! Take this.

[Northstar1989]

Upon gravity turn at 9000 meters, the ship decides to spin out of control. The 3-wide RCS reaction ports are not enough to stabilize it. Tips? Perhaps detachable canards on the fuel tank? Would that help, or is there another alternative?

Almost anything can be stable in a straight-up trajectory. Launch the thing straight up with MOAR AND BIGGER FUEL TANKS and MOAR BOOSTERS and start the gravity turn significantly later (perhaps even after you're already out of the atmosphere).

On top of that, where's the launch vehicle? All I see are some radially-attached SRB's (and some strange-looking fuel tanks connecting them like spokes). Need it not be said that you could lift a lot more to orbit with an SLS underneath?

You can ALWAYS use more Delta-V. If you have extra, more than you need for the mission, just use it to get a faster transfer to Duna- which is great for roleplaying purposes (wait a bit past the Hohmann window, so the distance is shorter, and then launch with a radial outward as well as prograde ejection angle relative to Kerbin's movement around the Sun... You can also launch an intercept orbit than would have an apoapsis further past Duna, but still intersects its SOI, for a faster transfer...)

Regards,

Northstar

EDIT: Oooo. Looks Like I posted too late to be helpful...

Edited May 24, 2014 by Northstar1989

[SSSPutnik]

I've done Kerbin SoI departures with TWR as low as 0.02 using multiple kicks from a higher orbit.

[Duxwing]

I agree with the previous weight-shaving ideas and further suggest:

1 - Keep your Kerbals in the lander can throughout the trip

2 - Connect the lander can to its lander with a pair of Clampotron Sr.'s

3 - When done exploring Ike, leave the lander in Low Ikean Orbit and dock the can to the transfer stage

4 - Remove the Cupola, Hitch-Hikers, Hubmax, and big RCS tank from your transfer stage.

5 - Make your transfer stage just a Clampotron Sr., fuel tanks, and engines.

6 - Move all life-support functions (e.g., solar panels) to the lander.

-Duxwing

[Red Iron Crown]

Sometimes it's not all about making the most efficient ship, but making one that you like for aesthetic or roleplay reasons. Starwhip's ship might be way overbuilt for a Duna trip, but it looks much more plausible than a high-efficiency 20-odd part minimalist ship.