Optimizing Mun Trips With Science Collection

[Baker]

Hi everyone I'm a while into KSP and just started using MechJeb. I'm really struggling building a spacecraft that would allow me to collect a lot of science from the Mun in trip. I've shared below my tech tree, my mun lander, my return craft, and the lander+return+booster craft I launch from Kerbal. Specific questions/observations I'm hoping you can help me with:

1. This craft has more fuel than needed. Where can I optimize?
2. My lander is pretty big. Mainly because I struggled to build something that (a) has a science jr for materials studies and (b) carries two Kerbals for piloting and science jr reset. Can I get this down to a smaller design and hop all over the Mun for many samples?
3. The lander+return is modeled after Apollo 11. But I'm unsure if KSP actually needs this design. Is there a design that will hit many points in the Mun and have fuel to return to Kerbal? A design that allows for a Science Jr. that can be reset by a scientist.
4. With the lander+return design, what Mun altitude is optimally fuel efficient? I usually prefer very low Mun orbit (<10k) but in playing around with the lander's return to the return ship it appears a higher orbit is more fuel efficient. Is it?

Thank you for any help!

Mun return ship: 

 

Mun lander: 

 

Lander+return+boosters: 

 

Tech tree: 

 

[James Kerman]

Welcome to the forum @Baker.

I have moved your thread to gameplay questions.

[Flibble]

Your booster stage has a lot of thrust - you have over 1.8 TWR on the pad, which is far more than needed. You should be able to reduce your engines to give ~1.3 TWR on the pad. Try swapping down to mainsails which are lighter, cheaper and more efficient.

Mun hopping isn't that easy because of the gravity, it's about 600 m/s for a landing, so to do two hops is 1200 m/s just for the landings, plus take off fuel. You could try using 4 terriers arranged around the central tank / science jr to get a bit more efficiency (and lower weight I think).

Return ship also has an absolute stack of fuel, you could always run the tanks half empty to reduce weight.

[Kryxal]

I'd actually transfer out of the return ship to a point, but that can be unsafe in a way.

[Zhetaan]

5 hours ago, Baker said:

1. This craft has more fuel than needed. Where can I optimize?

You don't need that much booster to go to the Mun.  Keep a Twin Boar for the centre (they are actually the best general lifting engine for cost versus a lot of parameters) but you can probably do with a lot less rocket on the sides.

Alternatively, you can shift some fuel load to the upper stage and use it in drop tanks for your hopping issue.

5 hours ago, Baker said:

2. My lander is pretty big. Mainly because I struggled to build something that (a) has a science jr for materials studies and (b) carries two Kerbals for piloting and science jr reset. Can I get this down to a smaller design and hop all over the Mun for many samples?

If you're willing to accept a taller-but-narrower lander, you can use a Mk. I pod on top of a Mk. I lander can.  A lot of my early designs use a set of three FL-T200 tanks arranged radially around a Science Jr. under an FL-T100 tank with a decoupler and usually a set of Spiders.  The landing legs, lights, and perhaps other experiments are on the outer tanks, and when I take off for the last time, I stage away those outer tanks and the Science Jr.  If I really want to avoid a tall lander, I use angle snap and replace one of the 200 tanks with the Science Jr., though that makes getting the landing legs correct a bit tricky.  On the other hand, three legs guarantees zero wobble, so I don't need to get them exactly correct.

However, the Mun has enough gravity that biome hopping is almost not worth it.  It can be done, but you may want to consider a rover.

5 hours ago, Baker said:

3. The lander+return is modeled after Apollo 11. But I'm unsure if KSP actually needs this design. Is there a design that will hit many points in the Mun and have fuel to return to Kerbal? A design that allows for a Science Jr. that can be reset by a scientist.

KSP does not need that design; I once accidentally tried a Mun landing with a rocket modelled after Apollo 8.  Think about that for a second.

It worked, though I don't recommend it.  (The accidental part was that I forgot the lander; I landed deliberately because I didn't want to reload if I didn't need to do so.)

While I don't like taking unnecessary parts home with me (they were purchased before the mission and I wouldn't do the mission if it didn't make money; I don't need to bring them home), I have been seen putting a Science Jr. on the bottom of a one-seat pod or on the top of a three-seat pod.  If you get rid of the Mk. II lander can and Poodle engine, you can have a combined lander/return rocket that has the fuel of both stages at the cost of a bit more parasitic mass.

You may also consider taking a one-seat pod for a scientist and using a probe core for a pilot.

5 hours ago, Baker said:

4. With the lander+return design, what Mun altitude is optimally fuel efficient? I usually prefer very low Mun orbit (<10k) but in playing around with the lander's return to the return ship it appears a higher orbit is more fuel efficient. Is it?

Not exactly, but it is easier.  It will always cost more fuel to go to a higher orbit.  However, rendezvous tends to be more forgiving at higher altitudes because it costs less to match planes and the orbits themselves are slower, so a slight mismatch does not result in so drastic a difference in relative velocity.  I usually don't have a problem with rendezvous, so I find fifteen kilometres to be a good all-round parking orbit altitude for my missions to the Mun, but I will vary between ten and twenty-five, depending on what I'm doing.

6 hours ago, Baker said:

Thank you for any help!

Additionally, for the love of aerodynamics, get rid of that sudden wasp-waist constriction in the middle of your rocket.  Put the Science Jr. into a service bay, or a fairing, or else neck down your rocket and put it there.

Otherwise, welcome to the forum, and please enjoy your stay!

 

[Mikenike]

6 hours ago, Baker said:

Hi everyone I'm a while into KSP and just started using MechJeb. I'm really struggling building a spacecraft that would allow me to collect a lot of science from the Mun in trip. I've shared below my tech tree, my mun lander, my return craft, and the lander+return+booster craft I launch from Kerbal. Specific questions/observations I'm hoping you can help me with:

1. This craft has more fuel than needed. Where can I optimize?
2. My lander is pretty big. Mainly because I struggled to build something that (a) has a science jr for materials studies and (b) carries two Kerbals for piloting and science jr reset. Can I get this down to a smaller design and hop all over the Mun for many samples?
3. The lander+return is modeled after Apollo 11. But I'm unsure if KSP actually needs this design. Is there a design that will hit many points in the Mun and have fuel to return to Kerbal? A design that allows for a Science Jr. that can be reset by a scientist.
4. With the lander+return design, what Mun altitude is optimally fuel efficient? I usually prefer very low Mun orbit (<10k) but in playing around with the lander's return to the return ship it appears a higher orbit is more fuel efficient. Is it?

Thank you for any help!

Mun return ship: 

 

Mun lander: 

 

Lander+return+boosters: 

 

Tech tree: 

 

What is the top part on the lander for? Also try to add rhinos or mastodons instead of having the twin boars.

[Baker]

On 5/15/2019 at 12:20 AM, Zhetaan said:

If you're willing to accept a taller-but-narrower lander, you can use a Mk. I pod on top of a Mk. I lander can.  A lot of my early designs use a set of three FL-T200 tanks arranged radially around a Science Jr. under an FL-T100 tank with a decoupler and usually a set of Spiders.  The landing legs, lights, and perhaps other experiments are on the outer tanks, and when I take off for the last time, I stage away those outer tanks and the Science Jr.  If I really want to avoid a tall lander, I use angle snap and replace one of the 200 tanks with the Science Jr., though that makes getting the landing legs correct a bit tricky.  On the other hand, three legs guarantees zero wobble, so I don't need to get them exactly correct.

Remember I wanted my mun hopper to be able to reset the science jr for multiple materials studies. That means I needed scientist. And of course a pilot. So I needed capacity for two. I recently tried going with only a scientist and a Probodobodyne OKTO but haven't confirmed this works.

In my first attempts at mun landing I had a tall lander with inline fuel, Mk 1, science jr. It was really tough to land and stay stable. So I'm afraid of that still.

 

On 5/15/2019 at 12:20 AM, Zhetaan said:

However, the Mun has enough gravity that biome hopping is almost not worth it.  It can be done, but you may want to consider a rover.

I've not yet tried a rover because I don't have the tech for the rovemate. I'm not exactly sure how to land with a rover and something that will allow that kerbal to return home. Also it seems that rovers move so slowly. I doubt that I could get them to many biomes for my materials measurements.

On 5/15/2019 at 12:20 AM, Zhetaan said:

Additionally, for the love of aerodynamics, get rid of that sudden wasp-waist constriction in the middle of your rocket.  Put the Science Jr. into a service bay, or a fairing, or else neck down your rocket and put it there.

 

LOL yeah you're right.

Thank you for all the help!

On 5/15/2019 at 12:35 AM, Mikenike said:

What is the top part on the lander for? Also try to add rhinos or mastodons instead of having the twin boars.

Nothing. That's just where it attached to my return ship on the journey from Kerbal to the Mun. Do you have an idea of something I could/should have up there?

[Mikenike]

No, I don't have any recommendations, I barely can get an orbit done, was just wondering. Hey you could add a klaw or docking port instead. It would lower your total mass.

Edited May 15, 2019 by Mikenike
Because I thought of something

[StrandedonEarth]

You could consider leaving a fuel depot with a scientist in Mun polar orbit. Land, collect, launch, dock, reset, rinse, refuel, and repeat.

[Snark]

A question, @Baker.  Do you have Making History, or not?  If you do, it has some "engine plate" parts that could would be helpful here.

First of all, your return craft:

...that's got way, way, way too much engine on it.  So you can make this part of the ship considerably lighter by slimming down a few things:

• Make sure you've zeroed out the command pod's monopropellant, if you haven't already done that.  Saves 120 kg.
• Reduce the ablator on the heat shield, if you haven't already done so.   You really don't need much for a Mun return.  Reduce it down to, say, 10%.  Saves 720 kg.
• Replace the Poodle with a pair of Twitch engines.  Saves 1.59 tons
• Alternatively, if you have Making History, you can replace the Poodle with a 2.5m engine plate, and then mount a single Spark under it. The engine plate then lets you attach a 2.5m component directly to it, which is nice.

So, overall, you can reduce the mass of this component by over 2.4 tons, which should help your dV bottom line by quite a bit.  (I also note that it's got more fuel than it really needs, too-- it's got more than double the dV it needs to get home from Mun orbit, even before saving 2.4 tons as suggested above.  So you could save another couple of tons by cutting the fuel amount in half.  2 tons of fuel is plenty to get home on.

Next, let's look at your lunar lander:

That's got way, way overkill in several aspects.

• First of all, it's got far too much engine. Remember that munar surface gravity is only 1.63 m/s².  You don't really need more than a local TWR of 3, meaning that a lander this size needs under 60 kN of thrust.  Whereas you've got four times that.
• Second, you don't need the big legs, unless you just like them for looks.  The medium legs should work just fine.
• Make sure you've zeroed out the lander's monopropellant supply, if you haven't already.

So, for example.  Get rid of the can's monoprop, that saves 160 kg.  Replace the large legs with medium legs, that saves 200 kg.  Replace the 8-ton LFO tank with a 4-ton LFO tank, saves 4.5 tons.  Replace the pair of Thuds with a pair of Twitch engines.  Result:  you get a craft that has about the same dV but only half the mass.

(And it's worth noting that even that is way more dV than you need.  Getting from low Mun orbit to the surface and back takes 1200 m/s plus a bit of safety margin.  You're packing over double that.  So unless you're planning on doing a bunch of biome hopping before returning to orbit, you could cut your fule considerably to save even more mass.)

Now, the 1.25m Science Jr does present a problem, since you've got a 2.5m stack.  One convenient way to solve that is with an engine plate (a Making History part), which would let you mount a Science Jr. there but still mount the 2.5m stack below directly to the lander without breaking up the radius.  If you don't have Making History, you could instead put a 2.5m service bay on the craft, and stick the Science Jr. inside of that.

 

Finally:  your lifting and transfer stages:  Note that doing the simple things described above can cut the mass of both your return ship and your Mun lander approximately in half, without losing any functionality.  So since that stuff weighs half as much now, that means you only need half as much booster to get it launched.  So you can do a lot of slimming down there, too.