Would this thing get me to the mun? Career Mode!

[Vane]

[Starstrider42]

Let's see if I've got this right...

1st stage: 4 LV T-30 engines and 1 LV-909 engine, backed by 25 FL-T400 fuel tanks.

2nd stage: 5 LV-909 engines, backed by 5 FL-T400 tanks and one FL-T200 tank.

Payload: 1 Mark I capsule

So for the 2nd stage, you have an I_sp of 390 s, a dry mass of 5*0.5 + 5*0.25 + 0.125 + 0.8 tons (plus a few extra bits), and a fuel mass of 5*2 + 1 tons. So that gives you a wet (i.e., fully fueled) mass of 15.675 tons and a delta-V of 4620 m/s. The total thrust from the five engines is 250 kN, for a thrust-to-weight ratio of 1.9-11.7. Definitely overkill.

For the first stage, you have an I_sp of a little over 320 (not sure how to average different engines together), a dry mass of 4*1.25 + 0.5 + 25*0.25 + 15.675 tons, and a fuel mass of 25*2 tons. That gives you a wet mass of 77.425 tons, and a delta-V of 3250 m/s. The total thrust is 4*215 + 50 = 910 kN, for a thrust-to-weight ratio of 1.2-3.4. Pretty reasonable for a first stage.

Delta-V for a round trip to Mun orbit is about 6000 m/s (http://forum.kerbalspaceprogram.com/threads/41652-A-more-accurate-delta-v-map), and you have a total of 7800 m/s. So you should be able to do a Mun trip with fuel to spare, but I suspect you could also doing by dropping some of the upper-stage engines and consolidating the fuel tanks.

EDIT: Oops, I didn't even notice the landing legs. So you want an extra 1700 m/s for a landing mission (the map I linked gives pretty optimistic numbers for landings), which means your rocket is barely able to do it. As Vanamonde said, you could probably save a lot of upper-stage weight by shifting some of the fuel to a lower stage.

Edited April 3, 2014 by Starstrider42
Found the stupid map

[robopilot99]

Your lander looks a little overkill. I think if you can get that part into orbit you will be fine. But seriously get Kerbal engineer. It will awnser all your questions and more

[Vanamonde]

Getting to Kerbin orbit is hard. Getting places from Kerbin orbit is relatively easy. Therefore, upper stages can be quite a bit smaller than that and still return from Mun. I'd suggest cutting your lander roughly by half, and shift those parts to the lower stages. This would keep about the same dV, but you'd discard a lot of empty tanks sooner, making the mission more efficient and easier to fly. As for the other stage, I second Starstrider32's suggestion that it could also be subdivided for similar reasons.

[Starstrider42]

Vane, could you explain to us your reasoning behind this particular design? That might help us give you more general advice.

[Vane]

Vane, could you explain to us your reasoning behind this particular design? That might help us give you more general advice.

Okay, My reason is because i really don't have much of a choice. I just started my carreer mode. So that means i've only done a few researches so not much parts to work with, If you can suggest a design i should try i'm all for it! And thanks for the tips!

[Starstrider42]

Okay, My reason is because i really don't have much of a choice. I just started my carreer mode. So that means i've only done a few researches so not much parts to work with, If you can suggest a design i should try i'm all for it! And thanks for the tips!

You misunderstood my question. We know you're early in career mode; we can tell that just from looking at the parts list on the left side of your screenshot. What I meant was "How did you decide which of the available parts to connect to which, and in what order?"

As for a design to try, my only suggestion without knowing more details is to have only a single LV-909 engine on your lander. You'll still have enough thrust for the job, and you'll save a lot of weight.

[Vane]

You misunderstood my question. We know you're early in career mode; we can tell that just from looking at the parts list on the left side of your screenshot. What I meant was "How did you decide which of the available parts to connect to which, and in what order?"

As for a design to try, my only suggestion without knowing more details is to have only a single LV-909 engine on your lander. You'll still have enough thrust for the job, and you'll save a lot of weight.

Oh okay, Sorry for the misunderstanding.

I really didn't know how to do this, I don't know much about Delta-V and i'm not really a good math person so Yeah.

I can tell you from expirience i was messing around and that lander actually landed me on alot of trips, That was just by guesswork.

And i didn't want to test 500 times hehe.

So yeah from expirience i know that the 3 stages you need are the lifting one how you get off the landing pad, Then the burn one. And the lander.

I usually worked from that.

And i just used the bigger of the fuselages, I know that may sound stupid. But really i don't know how else i can explain.

I usually just think of bigger has more fuel and i also try to use other smaller ones.

I'm sorry if thats not what you need/meant. I'm just trying to explain how i can

Thanks for the tips too!

[Starstrider42]

I really didn't know how to do this, I don't know much about Delta-V and i'm not really a good math person so Yeah.

I can tell you from expirience i was messing around and that lander actually landed me on alot of trips, That was just by guesswork.

And i didn't want to test 500 times hehe.

So yeah from expirience i know that the 3 stages you need are the lifting one how you get off the landing pad, Then the burn one. And the lander.

I usually worked from that.

Ah, ok. Well, to design a rocket you need to either do some math, or have it done for you. Kerbal Engineer Redux and MechJeb both do thrust and delta-V calculations for you; unfortunately, they both have compatibility issues with 0.23.5 at the moment. I think there's a hotfix out for MechJeb, so you might try that one if you're in a hurry. Otherwise, Kerbal Engineer is more "lightweight" if all you want are rocket specs.

For each stage, from top to bottom, you need to answer two questions:

1. Does the ship have enough delta-V for the maneuvers you want it to do? For example, if you want something that can land on the Mun and make a direct trip back to Kerbin (with no orbiter), you need:
   
   • About 1000 m/s to go from Mun orbit to landing (personal experience)
     
   • About 700 m/s to launch into Mun orbit (personal experience)
     
   • About 310 m/s to escape the Mun (from the map I linked)
     
   • About 200 m/s to lower your periapsis into Kerbin's atmosphere (combination of personal experience, and fudging from the map).
     

for a minimum of 2200 m/s. You might want more if you want the same stage to take care of, for example, insertion into Mun orbit, but it's usually more efficient to make that a separate stage.

To maximize delta-V, you want to pick an engine with a high I_sp rating (the LV-909 is probably your best choice at this point), and you want to maximize fuel while minimizing other mass. Hence my advice to drop the other four engines; they weigh 0.5 tons each.

[*]Does the ship have enough thrust to fight against gravity for launches and landings? This is determined by the ratio of your engines' thrust to your rocket's weight, which goes up as you drain fuel. For launch the LV-T30 and LV-T45 are both good choices (the latter is less efficient, but may make your rocket easier to steer). The LV-909 is really too weak to use until you're already moving at, say, half of orbital speed, and no longer fighting gravity per se. The ideal thrust-to-weight ratio for a Kerbin launch stage is 1.2 when full -- any less, and you'll waste fuel almost-hovering; any more, and you'll have to throttle down your engine to keep it from wasting fuel against atmospheric drag. Again, use the minimum engine weight you can get away with -- lighter rockets fly farther for less fuel.

For landing on the Mun, theoretically the same rules apply, except that you want the thrust to the (Mun weight) ratio, which is 6 times higher. In practice, I like to have my landers capable of at least 5 m/s of acceleration (Kerbin TWR of 0.5, Mun TWR of 3), because otherwise you risk not giving yourself enough time to slow down. For a single LV-909 engine (50 kN of thrust) on the Mun (gravity of 1.63 m/s^2), you should be fine as long as your lander weighs 10 tons or less when you begin your descent.

As a general rule of thumb, I_sp and saving mass gets more and more important as you go to later and later stages -- any excess mass in a stage will hurt the performance of that stage and ALL earlier stages, but have no effect on later stages. So make your lander as light as you can, and work backward from there.

[Taki117]

Unless I am sorely mistaken and they have seriously upgraded the joint connections the tops of your first stage are going to flop around like you wouldn't believe. Also, if you're not playing with far you can drop the nosecones as they don't really help much. With the LV-909 in the center of your first stage it will burn longer, meaning you could add a radial decoupler between the girder segment and ditch your boosters when they run dry. Alternatively, if your TWR is high enough (Which it should be) you could put the 909 in it's own stage and get even more total dV out of it.

Judging from the amount of parts I'd say this is your second, maybe third launch, meaning you probably haven't even been to the Mun yet. So a better idea is to build a ship that can take you into a Munar orbit and do EVA reports (Don't forget to pack Goo cans!) that will get you several more tiers of science so you can build a proper rocket (One that includes struts!)

[kurja]

I see radial decouplers on your parts list but none on the rocket; you'd want to drop those ascent stage boosters when they run out of gas, since you'll still have fuel left in the center stack when that happens. That 909 engine isn't going to be able to really move the center stack though... it'll just fall down at that point.

[MalfunctionM1Ke]

I can only affiliate with my fellow Rocketeers that you might consider downloading Kerbal Engineer.

It is giving you all the Data you Need in the Vehicle Assembly Building or Spaceplane Hangar PLUS all the telemetric Intelligence you would want while flying your ships.

In fact it is a Little part without weight or drag that you add to your ship if you want to. So it only Shows up if you want/Need it.

Attach it, check your dV and TWR and remove it again. You can also Switch from Kerbin refferenceto any other Celestial Body.

Edited April 3, 2014 by MalfunctionM1Ke

[SRV Ron]

I see radial decouplers on your parts list but none on the rocket; you'd want to drop those ascent stage boosters when they run out of gas, since you'll still have fuel left in the center stack when that happens. That 909 engine isn't going to be able to really move the center stack though... it'll just fall down at that point.

Go for a fly by, then orbital mission of Mun and Minmus before building a lander. This early Career design will do both.

Fly by free trajectory return.

A simple ship that did the mission.

Edit; Current basic Career Mun orbiter and next tier Mun orbiter.

Edited April 3, 2014 by SRV Ron

[Kasuha]

Best way to figure out if it will take you to Mun is to try it.

Also, it's possible to get pretty far in tech tree using Kerbin science only. There are 6-8 biomes just next door from KSC (launchpad, KSC, waters, shores, grasslands, highlands, mountains, even tiny strips of tundra) plus you can reach all levels of atmosphere easily. And all of that can be visited and measured within one Kerbin day. When you get to flying beyond Kerbin orbit, you could be able to build asparagus staged rockets already.

[Taki117]

Best way to figure out if it will take you to Mun is to try it.

Also, it's possible to get pretty far in tech tree using Kerbin science only. There are 6-8 biomes just next door from KSC (launchpad, KSC, waters, shores, grasslands, highlands, mountains, even tiny strips of tundra) plus you can reach all levels of atmosphere easily. And all of that can be visited and measured within one Kerbin day. When you get to flying beyond Kerbin orbit, you could be able to build asparagus staged rockets already.

Don't forget Runway! (Yes, it's it's own Biome)

[magnemoe]

I see radial decouplers on your parts list but none on the rocket; you'd want to drop those ascent stage boosters when they run out of gas, since you'll still have fuel left in the center stack when that happens. That 909 engine isn't going to be able to really move the center stack though... it'll just fall down at that point.

This. fire the four boosters first, then decouple and fire the center engine, I would put an T-30 in center too. You lander is good, however add decoplers on the side boosters here too, then they run dry you drop them, it they run dry during landing unless just over the ground drop them and abort.

I always go Mun flyby with free return after suborbital flights then straight to Minmus, usualy two missions here, first is to gain science to unlock all the science parts, then a second mission to fill it out.

It takes 1800 m/s to land and take off on Mun, less than 400 on Minmus. Jumping around suborbital is also cheap on Minmus. 100-200 m/s

[kurja]

This. fire the four boosters first, then decouple and fire the center engine, I would put an T-30 in center too. You lander is good, however add decoplers on the side boosters here too, then they run dry you drop them, it they run dry during landing unless just over the ground drop them and abort.

I always go Mun flyby with free return after suborbital flights then straight to Minmus, usualy two missions here, first is to gain science to unlock all the science parts, then a second mission to fill it out.

It takes 1800 m/s to land and take off on Mun, less than 400 on Minmus. Jumping around suborbital is also cheap on Minmus. 100-200 m/s

Having 11 fuel tanks + 5*909 engine + capsule to carry, I'm pretty sure a T-30 won't lift that ship either. It's just too heavy. Here's what I'd do: lose at least 2 engines and ~1/3 of fuel on last stage, add a short stage between current stages, and on the bottom stage, make the center stack a lot shorter, as short as is needed that a T30 can still lift it, and fire that only after the radial boosters have been dropped. Or, completely redesign Rockets a lot smaller than that have made it to Mun and back!

[sdj64]

Don't forget batteries! I wouldn't do a mun landing mission without at least the basic battery, so you have enough charge to transmit crew reports and to make sure you don't run out when you're trying to land. LV909 doesn't generate electricity. Also, your side stages are probably too wobbly.

[kurja]

Well I made a suggestion so I had to try it... =D worked out ok, I was already down to last stage on ascent from kerbin but those two 909's served well and got me to landed on mun and back to kerbin with about a hundred units of fuel left.

[cantab]

The stability of the outer stacks is a concern. You can only attach them in one place since you don't have struts, and towards the bottom is the place to do it, but those girders will add flexibility and weight. If you want to drop the outer stacks, use the radial decouplers. If you don't, just attach the lowest fuel tank to the central stack directly. (Whether to drop them or not mainly depends on whether they have enough thrust for the launch themselves, in which case you drop them then ignite the centre engine, or if you need all the engines burning from the start in which case you just drop them all together.)

I'd also shorten them to three FL-T400s or three FL-T400s and an FL-T200 each. 5 FL-T400s is probably too long to be stable. If you're left without enough fuel, make it six outer stacks instead of four.

If you want an easy extra few hundred m/s of delta-v, slap stack decouplers under each first stage engine and an SRB under that.

[kurja]

Having tried it out, wobble wasn't a problem really, lack of control made ascent a bit iffy but if you don't have rcs, reaction wheels or those -45 engines yet, there's not much you can do about it apart from trying to make the rocket smaller.

[Kryxal]

Actually, gimbals may be a fair reason to use that one LV-909, though I don't know if it has the sort of power you'll need ... possibly ignite the two side LV-909s after dropping the LV-30s and transfer fuel to replace what you use up top...

[kurja]

Actually, gimbals may be a fair reason to use that one LV-909, though I don't know if it has the sort of power you'll need

It does not, look at the picture I posted - I tried adding just one more tank in the center stack and twr went <1 even with the T-30, which is over 4 times as powerful as a 909.

[KSK]

With a bit of practice, SRV-Ron's TriMun Orbiter would probably just about double up as a TriMun Lander. It might need three detachable RT-10s on the first stage though.

[SRV Ron]

With a bit of practice, SRV-Ron's TriMun Orbiter would probably just about double up as a TriMun Lander. It might need three detachable RT-10s on the first stage though.

A set of SRBs will give you the extra push to attempt a lander. Suggest Minmus first due to its low gravity and flat surface.

Once you get fuel lines, this Demo Ship, use the bigger SRB in place of the twin cans, makes Mun with lots of fuel for landing and return.

You should be able to pack Goo canisters and a science bay.