Going to The Mun

[NewtSoup]

I am designing my first Mun Lander.  I am using Kerbal Engineer Redux and I've had a look at the dV chart.

I've decided on a 3 stage 2 Kerbal mission.

1) The lifter - Carries the two other stages to LKO ~ 3500dv

2) The transfer / return stage - Carries 2 Kerbals Lander will be docked with this. ~1500 dv

3) The Lander - Carries 1 Kerbal - has a materials bay, goo, temp, barometer, and seismograph. 1400dV (600 dv land 600dv up and 200 spare for orbit maneuver and docking )

If I'm understanding this correctly then I need about 600dV to reach land on the Mun from LMO and presumably the same to get back up plus a safety margin for docking?
And I use KER set to Mun to calculate my total dV?

[michal.don]

13 minutes ago, NewtSoup said:

If I'm understanding this correctly then I need about 600dV to reach land on the Mun from LMO and presumably the same to get back up plus a safety margin for docking?
And I use KER set to Mun to calculate my total dV?

Yes, you understand that correctly - 600m/s for landing, and 600m/s for going to orbit again. The numbers may differ a bit because of low/high TWR.

To calculate your total dV, it's not necessary to switch KER to the Mun, the dV is the same. But what differs is the TWR - you should definitely check the "local" TWR of both your descent and ascent stage of the LM.

And just a small tip for your launch vehicle - I don't think it's very practical to design the first stage of 3500m/s and the second of 1500m/s - I'd suggest to design it the other way around, or at least 2000/3000 m/s. You don't need all the thrust all the way to orbit. After the first stage engines do the heavy-lifting job, you should switch to the more efficient, even if not so powerful second stage engines. Your spaceship will end up much smaller, lighter, and probably cheaper

Hope this helps,

Michal.don

[Harry Rhodan]

26 minutes ago, NewtSoup said:

600dV to reach land on the Mun

And I use KER set to Mun to calculate my total dV?

If this is your first landing ever you probably need at least 50% more.

And you use KER set to mun mainly to see if your TWR is sufficient. The vacuum dV should be the same as anywhere else.

[NewtSoup]

I'm discovering this now.. I have no external fuel lines and my most powerful engine at the moment is a LT-30 Reliant.  The payload I want to get into orbit is 4.5 tons and it's proving "interesting " getting a TWR to even get off the launch pad

[michal.don]

38 minutes ago, NewtSoup said:

getting a TWR to even get off the launch pad

If the only issue is the TWR on the pad, the classic solution of "moar boosters" should do

[bewing]

That may be your most powerful liquid engine -- but you've heard of the phrase "moar boosters"?

[Snark]

So, @NewtSoup, if I'm reading between the lines correctly, you're playing in fairly early career or science mode so your tech is limited, yes?  (e.g. you mentioned "no fuel ducts", which I assume means you haven't unlocked them yet.)

One question I have is, what's your actual goal.  Is it just "I want to land on the Mun however I can", and you've picked the current design as the best way to do that?  Or are you more interested in the actual design of your ship, i.e. "I want to go to the Mun this way, 'coz I designed it and it's cool"?  Reason I ask:  if it's the former, you may want to consider some simpler/smaller designs, whereas if it's the latter, alternate design suggestions may not be relevant. 

In particular:  you could have a considerably smaller/simpler design, if you were so inclined, by making it a one-kerbal mission rather than two, and eliminating "transfer and return" stage as a thing as a thing.  There's just one single pod for one kerbal, and the lander is the return stage.  It has enough dV to head all the way home from the Mun's surface, and reenter and land on Kerbin.  That way, you only need to provide cabin space for one kerbal instead of three (since your current design has space for three kerbals, two in the transfer vehicle and one in the lander).  One-third of the cabin space = one third of the payload, so your overall rocket can be a third the size.  A small lander with, say, just a single Mk1 pod, a Terrier, and a 2-ton LFO tank (plus science paraphernalia) has lots of dV, plenty enough to get down to munar surface from LMO and then go all the way home to Kerbin.  And it's a tidily small package that means you can have lighter-weight lower stages for getting it to LMO.

Anyway, just a thought.  If you prefer to stick with adjusting your current design, that's fine too ... in which case, above suggestion cheerfully withdrawn.  (Or you could have it both ways, if you want-- send an initial, small, 1-kerbal vehicle to gather some science, which will unlock a bunch of stuff and make it easier to build the bigger 2-kerbal follow-on mission that you like.)

1 hour ago, NewtSoup said:

my most powerful engine at the moment is a LT-30 Reliant.

As other folks have suggested, "moar boosters" can be your friend.    Also, if you use, say, SRBs to get off the pad (they're big, they're high TWR, it's what they're for), such that you don't need to turn on your liquid-fuel stage until you get at least a few kilometers up, then you may want to consider using the Swivel instead of the Reliant.  It has better Isp at low pressures, which means it's more fuel-efficient and you get more bang for the buck.  And if you turn it on when the SRB's have already brought you to the point in your gravity turn where you're already more than 45 degrees from the vertical, TWR is considerably less of an issue, so the fact that it has a somewhat lower power than the Reliant doesn't matter as much.

[NewtSoup]

Yes.. it's not helping though.. I have enough dV and I have enough TWR but the whole caboodle is mighty unstable in flight.. tried moar fins too.. doesn't help  - Adding a fairing has helped  I'm now in orbit on pretty much just the lifter

 

[Invader Jim]

5 minutes ago, NewtSoup said:

Yes.. it's not helping though.. I have enough dV and I have enough TWR but the whole caboodle is mighty unstable in flight.. tried moar fins too.. doesn't help  - Adding a fairing has helped  I'm now in orbit on pretty much just the lifter

 

Post a pic please.

[NewtSoup]

@Snark,  It's pretty much the second.. I knew it was making life difficult for myself and I could have followed any number of designs on youtube.  I fancied doing the 2 Kerbal mission just to see if I could.   I switched from 2 capsules and 1 lander can.. 1 kerbal would move to the lander can and then undock, land, do science, re-dock etc. The other kerbal would remain in space and control the return stage if need be. However that was 4.5 tons and I couldn't get it to lift from the pad no matter how many engines I added.. though I suppose a LOTMOAR boosters might have done it. Now I've switched to 2 berth passenger cabin and an OKTO instead of the second capsule.  The means it's only the OKTO controling the return stage while it's in orbit and the second kerbal is now redundant ( except for getting experience. ).  But hey it's in orbit. I have a total of 2600dv left and I'm hoping that will be enough to get in to LKO do my stuff and return.

You're suggestions have not been ignored though and I will do those too.

This is what's going to the moon though

[Kerbal101]

If caboodle is caused by center of mass behind or off-center (asymmetry and such) from center of lift when in atmosphere. And when outside of atmosphere, its same thing but between center of mass and center of lift. Fins and gyroscopes to the rescue

Edit: and autostrut behind head, tail and heavy parts helps cure the bend-o-med.

[Snark]

1 hour ago, NewtSoup said:

the whole caboodle is mighty unstable in flight

Did you set up your fuel-flow options?

Here's what I mean:  Instability in atmospheric flight is generally because your CoM isn't far forward enough.  The screenshot you posted shows that your main booster stack has five fuel tanks stacked one atop the other.  If that's all you did-- just stacked them without tweaking any settings-- then what will happen is that they all have equal fuel flow priority, which means they all drain together.  Which doesn't help your CoM much.

What you can do is, in the VAB, twiddle the flow priorities of those fuel tanks.  Give the bottom-most tank the highest flow priority, then the one above it the second-highest, and so forth.  Doing this means that the bottom tank will drain first, which will rapidly move your ship's CoM upwards as it accelerates.  This will significantly improve your aerodynamic stability.

1 hour ago, NewtSoup said:

However that was 4.5 tons and I couldn't get it to lift from the pad no matter how many engines I added.. though I suppose a LOTMOAR boosters might have done it.

4.5 tons is quite a modest payload, doesn't seem like it ought to be much of a problem.  For example:  If you had a quartet of radially attached Thumper SRBs, around that central core, they'd develop 1000 kN on the pad, which would be enough to give you a TWR of 2 (i.e. puh-lenty) right off the pad, for a total ship mass of up to 51 tons.  The Thumpers themselves mass 7.65 tons each, which would leave a bit over 20 tons for the rest of the ship.

So, basically, if you can keep your total ship mass without SRBs to no more than 20 tons, then four Thumpers will be enough to give you a nice big hard shove off the pad, taking off using the SRBs alone.  By the time your initial liquid-fuel booster kicks in, you'll already be at an altitude of several kilometers going hundreds of meters per second-- well on your way to orbit.

[NewtSoup]

I will post picture of the whole launcher later.  In the mean time here's a mission update.
Yeah I landed on a bit of a slope but I managed a gentle touch down of 3.8 m/s and I most certainly didn't explode four times before managing it.  Those flashes you saw from The Mun?  Marsh gas and weather balloons!

Edited July 7, 2017 by NewtSoup

[NewtSoup]

Unfortunately I just quick saved instead of quick loaded after a cockup on docking.  Mission has been reverted to a save before lauch and I'll go back to it later with perhaps a better design.

Here's the whole thing.  It does have enough dv to get off the moon and dock with the return vehicle again but you have to be a better/luckier pilot than I.

[Spricigo]

4 hours ago, NewtSoup said:

I knew it was making life difficult for myself and I could have followed any number of designs on youtube.  I fancied doing the 2 Kerbal mission just to see if I could.

Kudos for you for playing how you want instead of how people think you should.

Now about the difficulties you are finding:

• A craft will in atmospheric flight will tend to go heavy side first, drag side last. You need Center of Drag behind Center of Mass*.  Keep in mind that CoM will shift as you burn fuel (and ditch stages) and CoD will shift depending on angle relative to airflow.
• Landing is just the reverse of lift-off. The problem is that you need be much more precise in your timing.

*Necessary but not sufficient enough for stability.

[NewtSoup]

This is what finally got me there and back and 745 science off one trip which is the really important thing! I DID SCIENCE.  I know it's gross overkill on the DV and I had 2000dV still at takeoff on the Mun but I don't care.  I just went back into LMO transferred to Kerbin.  Went in to LKO just to use up the fuel and because I could   Jettisoning the lander stage was interesting though.  because the tanks come up alongside the materials bay we didn't actually part company.  The solution was to turn spin rapidly until centripetal force ensured the LFO tripus released its suckery grip on me.  I suspect it will scamper off into the depths of space and grow into a full blown kraken.

[NewtSoup]

Also I discovered that landing is so so so much easier when you have a pilot that can "hold retrograde"

[Spricigo]

Congratulations. It really don't matter if you were "inefficient" this time,  remember that  not reaching the Mun would be 100% inefficient.  

[Snark]

3 hours ago, NewtSoup said:

Also I discovered that landing is so so so much easier when you have a pilot that can "hold retrograde"

Yeah, it really is.  That, or a HECS-or-better probe core (in case you're flying with a non-pilot, such as a scientist).

The most efficient landing is the so-called "suicide burn", meaning that you plummet towards the surface and turn on the engine at the last possible moment so that you slow to a stop right at the surface.  The tricky part, of course, is judging when that "last possible moment" is.  Misjudge it and start the burn just a little too late, and you find out how the maneuver got its name.    So the safe thing is to just build a bit of extra dV into the craft, so you have the luxury of being a bit inefficient and slowing down somewhat earlier to be on the safe side.

Most efficient takeoff is a lot easier (and considerably less hair-raising)-- basically just crank it over to nearly horizontal immediately on takeoff, with just a few degrees above the horizon so you don't scrape your toes.  Then just keep burning until you get Ap up to something high enough that you don't have to worry about smacking into any mountains.

But all of that advice is redundant now, of course, since you've already been and gone and done it.  Congratulations! 

[bewing]

5 hours ago, NewtSoup said:

I suspect it will scamper off into the depths of space and grow into a full blown kraken.

Only if there was a Mystery Goo container attached.

 

[NewtSoup]

With my new scientific riches I took - Miniaturisation, Fuel Systems ( yay asparagus staging ), Heavy Rocketry, Precision Engineering, Specialised construction ( for space station building ) and Actuators.

I am starting to build a collection of expensive debris in LKO.  I think I may send up actuator drones with loads of parachutes to try and recover the parts, just for fun, I realise I will probably spend as much if not more recovering debris as simply destroying it from tracking.

[Spricigo]

3 hours ago, NewtSoup said:

 Fuel Systems ( yay asparagus staging )

I think I used true asparagus just enough to convince me to not use it anymore. OTOH crossfeed enabled on radial decouplers that holds SRBs and fuel tanks on top of SRBs are standard design. 

[NewtSoup]

1 minute ago, Spricigo said:

I think I used true asparagus just enough to convince me to not use it anymore. OTOH crossfeed enabled on radial decouplers that holds SRBs and fuel tanks on top of SRBs are standard design. 

Yes, I just realised that I can simply enable cross freed on most if not all of the de-couplers which would have the same effect.

A while ago I accepted a contract to make a station to hold at least 13 kerbals and hten put it in orbit of the mun.  Station also needs 6000 liquid fuel and 7200 battery storage and a docking port.  At the time I only had a docking port junior so I put this to one side.   I'm guessing I'm going to have to make the whole thing modular and build it in space.  The contract specifies "lastly, put your station in orbit of The Mun".    Trying to decide if it's practical to build the station in LKO and then move the whole thing into a transfer orbit and then Munar Orbit.  It's going to be quite a large station... Well bigger than anything I have made so far ( I did make a 7 kerbal station with just a docking port junior).
 

Ahh have to stop playing now. Time for work

[Spricigo]

BTW if you landed on the Mun,  you also can land on Minmus.  

And deltaV and technology wise Duna, Ike and Gill are a step further. 

For this size of station I'd launch in one piece and refuel in space. But assembling in LKO  or Mun orbit also work.  (matter of  preference, I think) 

[WanderingKid]

3 hours ago, NewtSoup said:

The contract specifies "lastly, put your station in orbit of The Mun".    Trying to decide if it's practical to build the station in LKO and then move the whole thing into a transfer orbit and then Munar Orbit.  It's going to be quite a large station... Well bigger than anything I have made so far ( I did make a 7 kerbal station with just a docking port junior).

It most likely won't be practical to move it afterwards unless you're very careful in your design about where your Center of Mass for the station is... or you make it a giant noodle.  6,000 Liquid Fuel doesn't include oxidizer, it's just the LF component.  That's monstrous.  That's more than two of the orange tanks, the 2.5 meter long one.  On the bright side, you'll be able to operate Mun missions for ages with that for landers and tourists!  Battery storage isn't anywhere near as bad, thankfully, they're just heavy unless you want a lot of part count (you typically try to avoid huge part counts).

My recommendation would be to send up semi-empty tanks and other components to Mun, rendezvous there to assemble the station in a cool looking way, add in some extra ports on extended I-Beams so you can dock landers and refuelers easily, toss in some RCS storage for your landers, and then finally send refueler rockets to the station.  Also, you might want to check out the mod DPAI (Docking Port Alignment Indicator), I find it invaluable for those last docking maneuvers when the target ship doesn't rotate easily.

On a final note for that station, though, if you *do* design it in such a way you can assemble it in LKO then move it to Mun... you can then move it anywhere you want.  Once the contract completes it's still yours, so you could, for example, use it to feed your Mun landers... then transfer it to Minmus as a base, then perhaps send it off to Duna and Ike as a fuel ship.