Preparing for first manned interplanetary trip, including return, and need some help.

[vildar87]

So I am planning on visiting Moho for my first manned interplanetary trip, and have part of it planned, and could use some help figuring out the rest. I have planned on assembling a ship in Kerbin orbit of the various parts that I will need for the trip, so far I have figured I will need these modules;

1) Return Craft - For returning from Moho's orbit with crew and science on board.

2) Moho Lander - to detach from the craft in Moho's Orbit, land on Moho, then return to the craft

3) Science Lab - self explanatory really

4) Fuel ring - to hold the main fuel tanks for the trip.

For engines, I was planning on just using the engines on the lander and return craft, instead of adding more to get to Moho.

so I currently have these questions;

1) is there a tutorial for the most delta-v efficient way to transfer to other planets

2) While the individual sections have enough Delta-V for their tasks, I have no idea how to figure out the Delta-V for the entire craft in orbit. So just trying to figure out how to figure out the Delta-V for the entire craft to make sure it can complete its Mission.

any other help would be greatly appreciated

[federicoaa]

Use Sr. clamps between stages to avoid wobbling. Also, don't make the whole ship to thin and tall or it will wobble a lot.

Moho is quite hard to reach, why don't you try Duna first?

I recommend having 2 stages:

1) Command pod with the science lab and lander. Ditch the lab and science parts once you lift

2) Fuel tanks with LV-N for interplanetary lander. Leave this stage in orbit before landing and dock again to leave home

Now, answering your questions:

1) Figure out the launch window and burn from LKO to maximize efficiency (oberth effect)

2) The rocket equation! delta V = ISP*g*ln(total mass / dry mass)

Edited January 9, 2014 by federicoaa

[Speeding Mullet]

I second federicoaa, Duna may be a better option for a first interplanetary foray.

Here is a handy delta-V map which will allow you to plan your staged delta-V in your various parts.

If you fancy adding a little more complexity you could make your lander surface mobile so you can check out the scenery a little before leaving.

[federicoaa]

I second federicoaa, Duna may be a better option for a first interplanetary foray.

Here is a handy delta-V map which will allow you to plan your staged delta-V in your various parts.

If you fancy adding a little more complexity you could make your lander surface mobile so you can check out the scenery a little before leaving.

Yep, also wheels are better than landing struts for landing, as they have higher impact tolerance and can be repaired if broken

[Speeding Mullet]

Yep, also wheels are better than landing struts for landing, as they have higher impact tolerance and can be repaired if broken

Ah, I was talking about the powered rover wheels which are far weaker. I think the aircraft wheels are stronger, but you can't go for a drive.

[celem]

You got your head around the basic logistics of this trip. Your checklist of modules looks good. I guess the lab is there to clean material bays/goo pods since you stated a desire to return the science. Fair enough, i use throwaway multiples of the experiments, but whichever works.

As other folks have said, Moho is not the easiest first time target. Of all the landing sites in the system that one is top 5 for difficulty. The lander itself isnt too tricky, but braking into moho parking orbit, and then braking in kerbin return orbit are both highly expensive. A big transfer stage with enough fuel to do the trip, pushing a lander needs more than 1 nuke or your orbit burn at moho will become 25 minutes in a 20min SoI very easily. Watch your TWR!

When returning science we have the awesome new 0.23 feature whereby we can move the experiment results on an EVA and stash them in a pod. Remember however that surface sample still cant be moved like this, so the pod that makes the landing is probably the one you want to re-enter into Kerbin. Bear this in mind during design. A decoupler right below the lander pod lets you ditch the lander deadweight to push the pod home. This also means it wants chutes even if it doesnt need them for moho (unless you deorbit it at kerbin with a 'chuted' module to help it down.)

[theend3r]

Just like federicoaaUse said, use LV-N so you don't have to worry about dv, I usually horribly overbuild (http://i.imgur.com/7len15h.png), ending up with a ship that could bring the whole VAB to Eeloo and back, but better safe than sorry

[federicoaa]

Just like federicoaaUse said, use LV-N so you don't have to worry about dv, I usually horribly overbuild (http://i.imgur.com/7len15h.png), ending up with a ship that could bring the whole VAB to Eeloo and back, but better safe than sorry

How did you put that thing in space?!

[Traches]

Celem's right-- moho is hard to get to, especially as a first time target. You've got a hefty plane change to deal with, no atmosphere to aerobrake in, and a huge dV requirement to get there. Try going to duna first! Then, go to dres to learn how do deal with differing inclinations. You'll have an easier time with Moho after that.

[theend3r]

How did you put that thing in space?!

The upper tanks were empty and refuelled in orbit. Asparagus did the rest.

[stevism]

I have a lot of experience doing interplanetary, and almost every mission has gone off without a hitch. I've been (landed and returned where applicable) from a lot of places, just haven't hit any of Jool's moons except Laythe.

I tried Moho last night and wow, I miscalculated. I wouldn't recommend it as a first interplanetary trip, not at all.

I know have 3 brave kerbals stuck in a highly ellipitcal orbit around moho...their main engines are gone, their landing engines are depleted and dumped, and the final orbit maneuvers was accomplished via RCS.

sooo I'll let you know how the rescue mission goes.

[LethalDose]

Finding an alternate destination is the best advice: Moho has the highest dV requirement of any planet in the Kerbol system (It's absolutely greater than Duna, Eve, Dres, and even Jool, I haven't done the numbers for Eeloo). Duna has the lowest, and Eve is about twice Duna's IIRC. Moho's is 3-4x's greater than Eve's, again, IIRC.

As for your specific questions:

1.

by Scott Manley should help. You can also read up on Hohmann transfer orbits on wikipedia.

2. If all the individual pieces have sufficient dV, you're probably okay.

Hope that helps

[vildar87]

wow, surprised at all the support, compared to posting to Reddit for help, lol. So yeah, I will try Duna instead, only chose moho since it was the next transfer window.

federicoa; I remember reading up on the Delta-V formula before, and what confused me was how to figure ISP and such when you have multiple engines, and different types of engines as well.

Celem; I knew you could transfer science between command pods and such, and I thought that surface samples were included in that?

as for using rover wheels, well i am not against the idea, will need to figure which are best

[Tokay Gris]

Not sure if anybody told you yet.

But Moho is a PAIN to get to and return.

First: It is a smaller orbit around Kerbol. Sounds like no big deal but amounts to a big injection burn right there. 2000/m/s upwards. I haven't managed to get below 3500 m/s so far. SOI is really small....

Second: Inclination. Mohos orbit is a paint to get to.

I would say, it is just as easy to get to Eeloo than to get to Moho. And Eeloo is easier to land on. Just takes longer.

Heck, the joolian moons are simple. You get the "auto brake" of Jool. Moho is a pain.

My first orbiter for Moho ended up in a wild trajectory that a long time later reached Kerbin again and never established Moho orbit. Just couldn't do 4000 m/s to get caught by Moho.

So, to cut it short: Why not try Duna first? Or one of the joolian moons? Or Eve's moon? Why start with one of the three hardest things there are? (Eve ascent, Tylo and Moho)

[Dangerous_Beans]

federicoa; I remember reading up on the Delta-V formula before, and what confused me was how to figure ISP and such when you have multiple engines, and different types of engines as well.

from memory, and i could be way off here, ISP for a craft with multiple different engines firing at the same time is: ([iSP engine 1]*[engine 1 thrust] + [iSP engine 2]*[engine 2 thrust] + ect) / total thrust.

good luck with Moho!

[maltesh]

wow, surprised at all the support, compared to posting to Reddit for help, lol. So yeah, I will try Duna instead, only chose moho since it was the next transfer window.

Don't worry, Moho's transfer windows come around every 35 days or so. When you decide you're ready for the beast that is Moho, there'll be a window within five weeks.

[vildar87]

okay, so i have switched my target from Moho to Duna. right now though I am trying to figure out the Delta V and fuel required for the trip.

Math never has been my strong point, so sorry for being basic, but...

Looking at the formula, it is; delta V = ISP*g*ln(total mass / dry mass)

I first want to make sure I understand each part of the formula;

1) from my research into other threads, G is often used as 9.8, which is the surface gravity of Kerbin as on the wiki. so that changes depending on what planet your launching from. just want to make sure i am correct about that in case I want to play with that later...

2) ln(total mass / dry mass) is the total mass of the ship, minus the liquid fuel of the ship, multiplied by some math magics called Natural logarithm. I assume that the liquid mass subtracted is only liquid fuel and oxidizer, and not monopropellant and such.

3)ISP....well, its simple if its just one engine...but i have multiple engines, and two different type of engines....so...makes my brain hurt. I have 4 LV-909 and 4 areospikes. I would like to understand how to to calculate the ISP for delta V, when using multiple engines like this. I know one of you guys could just tell me, but I would appreciate it more if someone could explain how to figure it out so i could do it myself later. I have looked it up, and all the different terms and such just confuse me, so if you could explain any terms and such used.

the main reason I want to know this is because I figure that once I understand how to calculate the delta v, I can swap the equation around to figure out the fuel needed in order to get the delta v i need in order to make the trip.

if this makes any sense, please let me know

[TheDarkStar]

okay, so i have switched my target from Moho to Duna. right now though I am trying to figure out the Delta V and fuel required for the trip.

Math never has been my strong point, so sorry for being basic, but...

Looking at the formula, it is; delta V = ISP*g*ln(total mass / dry mass)

I first want to make sure I understand each part of the formula;

1) from my research into other threads, G is often used as 9.8, which is the surface gravity of Kerbin as on the wiki. so that changes depending on what planet your launching from. just want to make sure i am correct about that in case I want to play with that later...

2) ln(total mass / dry mass) is the total mass of the ship, minus the liquid fuel of the ship, multiplied by some math magics called Natural logarithm. I assume that the liquid mass subtracted is only liquid fuel and oxidizer, and not monopropellant and such.

3)ISP....well, its simple if its just one engine...but i have multiple engines, and two different type of engines....so...makes my brain hurt. I have 4 LV-909 and 4 areospikes. I would like to understand how to to calculate the ISP for delta V, when using multiple engines like this. I know one of you guys could just tell me, but I would appreciate it more if someone could explain how to figure it out so i could do it myself later. I have looked it up, and all the different terms and such just confuse me, so if you could explain any terms and such used.

the main reason I want to know this is because I figure that once I understand how to calculate the delta v, I can swap the equation around to figure out the fuel needed in order to get the delta v i need in order to make the trip.

if this makes any sense, please let me know

1) G is a constant that is there that is simply there because of varying unit systems used. It doesn't matter where you are; G is the constant that you use because you are using metric.

2) Total mass is of course total mass, but dry mass is simply the mass without the fuel that you have used for this particular stage (you have to work out the dV seperately for each stage). If you use no RCS fuel on that stage, you don't count it. If you do, then count it. Also, here's how to think of what ln means. ln is the same as log_e, which means that for ln_e x = y, e^y = x. Basically, it gives you the exponent when you know the base and what the base raised to the exponent is.

3) First, it's usually best to limit the number of engines you use. Burns take longer, but it is much more efficient (because of less dry mass). Second, they average exactly 390, since that is what they all have. However, if you have different engines with different I_sp, it is sum(thrusts of all the engines) / sum(thrust / I_sp of each engine).

For example: 2x Aerospike + 1x Rockomax:

(175 + 175 + 1500) / ([175/390] + [175/390] + [1500/330]) = 1850 / 5.4429 = 339.892 s. Thus, the I_sp of all the engines combined is 339.892.

[Captain Sierra]

That math makes my brain hurt, so I tend to use a dV chart and this calculator, which is simpler than the first one linked in this thread.

http://ksp.olex.biz/

I cannot remember what dV it takes to re-orbit from Duna, but I know and unpowered descent is almost possible. You typically need to thrust a bit at the very last minute as Duna's thin atmosphere means chutes don't produce quite enough drag for safe landings. The tip about wheels earlier is partially invalidated by .23 as landing legs can now be repaired too.

Also, it takes roughly <1500dV to get to Duna as you can aerobrake into a nice orbit. 12-13km periapsis will capture you into a stable orbit. The lower, near 12 side can almost circularize you but you have to be careful, too much and you get eaten. I advise quicksaving before attempting the aerocapture maneuver.

Also, IIRC, it's <1000dV to return to Kerbin (assuming you are going for a direct landing, and still, aerocapture is possible with a periapsis <40-45km). Overall, I'd say you need about 3500-4000dV on your transfer stage to be safe. That leaves a sizable margin for error and less than perfect lineups and maneuvers, which is good for any first mission. For your lander, I suggest an LV-909 engine. Duna's atmosphere is thin so engines you typically reserve for vacuum use can work quite well there (save for nukes, then again, I roleplay and avoid irradiating my landing site). I can orbit a orange tank (~36 tons) with 8 LV-909 engines and another orange tank's worth of fuel. It makes quite an effective tanker lander. Again, I do not recall the ascent dV, my apologies.

[vildar87]

1) okay, so just keep it as 9.8 no matter what

2) hmm all right, I understand what you mean by stages and that, just not sure how to apply it specifically to my ship, but i can get to that later.

3)All right, I followed along with that, and assuming I understood it correctly;

4 LV 909 and 4 Aero spikes;

([175*4]+[50*4]) / ([(175/390)*4] +[(50/390)*4]) = 900 / 2.3077 = 390? huh.....all the engines have the same ISP....so.....if all the engines have the same ISP, is the ISP for the entire craft the same regardless the thrust, as in this case? or was that just a fluke with these ones?

and Sierra; yeah I know there are delta v calculators and maps and such, but I want to be able to do this so I can figure out the delta V my ship has once its assembled in orbit, and from that, figure out other things, such as how much fuel I will need.

[theend3r]

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