Mun, Minmus or Duna?

[Squidiness]

^This is my new station thingy that was originally designed to go to the Mun or Minmus, but I'm not sure which moon to go to with this thing. Any suggestions?

[ottothesilent]

Duna's lots of fun, and if you go to Duna, you essentially get Ike, too, since it's so cheap in terms of Dv to get to once you're in orbit around Duna

[Squidiness]

On 1/8/2017 at 9:36 PM, ottothesilent said:

Duna's lots of fun, and if you go to Duna, you essentially get Ike, too, since it's so cheap in terms of Dv to get to once you're in orbit around Duna

Is it Duna-Capable though? Yes, it has an ISRU, but the second skipper stage is half empty/full

Edited January 9, 2017 by Squidiness
nacho business

[ottothesilent]

What's it got for Dv? Conservatively, you'd need somewhere around 3000 m/s, but you could theoretically get away with about 2500. Plus, you've got tons of RCS. If all else fails, you can do a complete refuel, since you're still in LKO.

[Squidiness]

On 1/8/2017 at 9:43 PM, ottothesilent said:

What's it got for Dv? Conservatively, you'd need somewhere around 3000 m/s, but you could theoretically get away with about 2500. Plus, you've got tons of RCS. If all else fails, you can do a complete refuel, since you're still in LKO.

It's 74.76 Tons, uses skippers and has 1,614 Units of fuel excluding the lander module, that's all I got for stats

[ottothesilent]

Assuming you just use the skippers, and 1614 is the number of liquid fuel and oxidizer, you'd have to use the lander's fuel as well, and even then it could be dicey. I'd refuel with a Klaw-equipped craft, and then it should be able to make it if you only use the higher-isp Skippers and you use a good launch window.

 

EDIT Or maybe I just did my math wrong. It's late, and I'm sleepy.

Edited January 9, 2017 by ottothesilent

[Squidiness]

On 1/8/2017 at 9:54 PM, ottothesilent said:

Assuming you just use the skippers, and 1614 is the number of liquid fuel and oxidizer, you'd have to use the lander's fuel as well, and even then it could be dicey. I'd refuel with a Klaw-equipped craft, and then it should be able to make it if you only use the higher-isp Skippers and you use a good launch window.

It sounds too risky, besides, it wasn't even designed for that kind of mission, so which moon do you suggest?

[ottothesilent]

I like the Mun, but only because I hate Minmus with a passion. Because you're not landing, it's actually cheaper to go to the Mun, by about 300 m/s. 

[Squidiness]

On 1/8/2017 at 9:58 PM, ottothesilent said:

I like the Mun, but only because I hate Minmus with a passion. Because you're not landing, it's actually cheaper to go to the Mun, by about 300 m/s. 

I am landing, as a matter of fact, the portion with the ISRU is the lander, and the portion with the lab is the orbiter; I'm doing it Apollo-Style, so the Mun? For me, the Mun is still mysterious, since my only trip to it was just a touch-down-on-the-Mun-and-go-home mission, and all I got back from it was an EVA Report and a surface sample. So what's the verdict?

Edited January 9, 2017 by Squidiness
nacho business

[Aegolius13]

I'd go Minmus.  It's overall the easiest and most productive place to start a mining / science grabbing program. 

You might not as much use out of a Duna station,  due to travel times and launch windows. I'd still go to Duna eventually,  but starting lunar makes sense. 

 

[Flamingo]

14 hours ago, Squidiness said:

 

^This is my new station thingy that was originally designed to go to the Mun or Minmus, but I'm not sure which moon to go to with this thing. Any suggestions?

I would go to either Minmus or Duna, Minmus because it is close and pretty easy, and its low gravity is fun to play around with. Furthermore its also great if you are planning to build a base. Duna is fun because it is bigger, it has an atmosphere and its further away. But it also so far away that trips take a WHOLE LOT longer, so not great if you are planning a lot of changes and new modules.
 

Btw you can use f1 to take screenshots they will be in KSP/Screenshots. Just remember that you will also have to press fn so you don't just lower your brightness.
I can see that you are on mac so you can also use cmd-shift-4 for screenshots.

[Squidiness]

On 1/9/2017 at 11:52 AM, Flamingo said:

I would go to either Minmus or Duna, Minmus because it is close and pretty easy, and its low gravity is fun to play around with. Furthermore its also great if you are planning to build a base. Duna is fun because it is bigger, it has an atmosphere and its further away. But it also so far away that trips take a WHOLE LOT longer, so not great if you are planning a lot of changes and new modules.
 

Btw you can use f1 to take screenshots they will be in KSP/Screenshots. Just remember that you will also have to press fn so you don't just lower your brightness.
I can see that you are on mac so you can also use cmd-shift-4 for screenshots.

Thanks for the advice! I know now that this vessel is incapable of achieving a Duna round-trip, even with its ISRU, so I'll go to Minmus.

[LameLefty]

Minmus is a much better option for a long-term ISRU operation - in my humble opinion - than the Mun for two reasons. First, it's got very low gravity, so once you've got your miner(s) and converter unit(s) there and operating, you use much less of the resources you harvest landing and returning to orbit. Second, it's closer to the edge of Kerbin's SOI, which means that if you stage your planetary missions out to your Minmus base, your total dV cost to wherever you're going elsewhere in the system will be lower; basically you spent that energy getting out to Minmus and you don't need to spend it again to leave the system entirely.

 

[Snark]

On 1/8/2017 at 6:47 PM, Squidiness said:

It's 74.76 Tons, uses skippers and has 1,614 Units of fuel excluding the lander module, that's all I got for stats

"1614 units of fuel" is a little vague:  is that 1614 units if liquid fuel (not counting oxidizer), or do you mean you have a total of 1614 units of liquid fuel plus oxidizer?

From your screenshot, I think you probably mean liquid fuel itself (because if you only had 1614 units of LF+O, that would be just 8 tons of fuel, and your fuel gauges would show lower than that).

So, I'll assume you have 1614 units of fuel, plus an appropriate matching amount of oxidizer.  That makes 1614/90 = 17.93 tons of propellant.

If your ship is 74.76 tons, and you're using Skippers at Isp 320, your available dV is:  320 * 9.81 * ln(74.76 / (74.76-17.93)) = 861 m/s.  (Note that this assumes that you turn off those Thuds and use a Skipper only, since the Skippers have a higher Isp than the Thuds do.)

That's not enough to go anywhere.  Not to the Mun, not to Minmus, not to Duna.  From LKO, it takes ~850 m/s just to get to a low-Pe flyby of the Mun; that's not counting the extra couple of hundred m/s you'd need to circularize.

On the other hand... if you refuel your ship in LKO (by docking a fuel tanker to it), then you have lots of options.  If both of those big Skipper tanks were full in LKO, you'd have 32 tons of fuel to play with instead of 17.93.  Your dV would go up to 1400 m/s, and that is enough to get to Mun or Minmus orbit.

Duna would also be doable; you'd need to hit a good transfer window, plus use aerobraking on arrival.  It takes ~1050 m/s to get a Duna intercept from LKO, which would leave you with a little maneuvering reserve upon arrival, assuming you aerobrake.  You wouldn't have the fuel to get home again, but presumably that's what the ISRU-equipped lander is for. 

 

[TopHeavy11]

KAS, refuel, ANYWHERE.

[Freshmeat]

3 hours ago, LameLefty said:

Minmus is a much better option for a long-term ISRU operation - in my humble opinion - than the Mun for two reasons. First, it's got very low gravity, so once you've got your miner(s) and converter unit(s) there and operating, you use much less of the resources you harvest landing and returning to orbit. Second, it's closer to the edge of Kerbin's SOI, which means that if you stage your planetary missions out to your Minmus base, your total dV cost to wherever you're going elsewhere in the system will be lower; basically you spent that energy getting out to Minmus and you don't need to spend it again to leave the system entirely.

 

Actually, the second part is not true. The Oberth effect more than makes up for having to go up the gravity well, to the scale a couple of hundred m/s if you are going to Jool. I recently ran the numbers when I wanted to plan a low TWR trip. When you go from a higher orbit, you obviously can let your engine burn for a longer time, but it will cost you in extra fuel. 

Further, the siderial period of Minmus is 49 days. This mean you could easily miss a transfer window completely, especially is heading for Moho. Real careful planning might enable you to pull off a stunt not entirely unlike periapsis kicking, but personally I would consider that somewhat out of my comfort zone. Hmm... this will need some number crunching and experimenting.

[LameLefty]

5 minutes ago, Freshmeat said:

Actually, the second part is not true. The Oberth effect more than makes up for having to go up the gravity well, to the scale a couple of hundred m/s if you are going to Jool. I recently ran the numbers when I wanted to plan a low TWR trip. When you go from a higher orbit, you obviously can let your engine burn for a longer time, but it will cost you in extra fuel. 

Further, the siderial period of Minmus is 49 days. This mean you could easily miss a transfer window completely, especially is heading for Moho. Real careful planning might enable you to pull off a stunt not entirely unlike periapsis kicking, but personally I would consider that somewhat out of my comfort zone. Hmm... this will need some number crunching and experimenting.

I've never had a problem with the "careful planning" part, especially with KAC helping keep track of deadlines and transfer windows, but I've also come to realize that not everyone plays the way I do - I tend to not hyper-optimize my designs. Once I have something that works, I'd rather brute-force it to some extent because I enjoy the flying and operational part and do not enjoy trying to get the most dV out of every single mission design. But that's me. *shrug*

[Freshmeat]

@LameLefty Hey man, it is your game. Everyone get to play it their way

The planning problem I see is getting your craft to hit a periapsis at the correct angle to prograde. This means you have to leave Minmus at the correct time so your orbit is correctly oriented in space. Then the orbit need to have a period of a length that lets you hit periapsis during a transfer window, so you might need to adjust your apoapsis accordingly. Incidentally, I do have a sheet in my Excel workbook devoted to this kind of calculations, because I enjoy the planning as much as the actual flying. I suck at making good crafts, so I plan around getting by with as little dV as possible.

[Squidiness]

On 1/10/2017 at 9:44 AM, Snark said:

"1614 units of fuel" is a little vague:  is that 1614 units if liquid fuel (not counting oxidizer), or do you mean you have a total of 1614 units of liquid fuel plus oxidizer?

From your screenshot, I think you probably mean liquid fuel itself (because if you only had 1614 units of LF+O, that would be just 8 tons of fuel, and your fuel gauges would show lower than that).

So, I'll assume you have 1614 units of fuel, plus an appropriate matching amount of oxidizer.  That makes 1614/90 = 17.93 tons of propellant.

If your ship is 74.76 tons, and you're using Skippers at Isp 320, your available dV is:  320 * 9.81 * ln(74.76 / (74.76-17.93)) = 861 m/s.  (Note that this assumes that you turn off those Thuds and use a Skipper only, since the Skippers have a higher Isp than the Thuds do.)

That's not enough to go anywhere.  Not to the Mun, not to Minmus, not to Duna.  From LKO, it takes ~850 m/s just to get to a low-Pe flyby of the Mun; that's not counting the extra couple of hundred m/s you'd need to circularize.

On the other hand... if you refuel your ship in LKO (by docking a fuel tanker to it), then you have lots of options.  If both of those big Skipper tanks were full in LKO, you'd have 32 tons of fuel to play with instead of 17.93.  Your dV would go up to 1400 m/s, and that is enough to get to Mun or Minmus orbit.

Duna would also be doable; you'd need to hit a good transfer window, plus use aerobraking on arrival.  It takes ~1050 m/s to get a Duna intercept from LKO, which would leave you with a little maneuvering reserve upon arrival, assuming you aerobrake.  You wouldn't have the fuel to get home again, but presumably that's what the ISRU-equipped lander is for. 

 

Yesterday, I had to make the choice between the Mun or Minmus, and I wanted to go to Minmus, since the choice seemed clear, since everyone was telling me it was cheaper to get to and it had more potential science, so I went to Minmus. Unfortunately, I didn't make it with the (relatively) microscopic fuel supply I had aboard the vessel, so I went for the Mun instead, got an intercept, (barely) reached a stable orbit, (barely) landed, squeezed all the science out of the Mun I could, lifted off, docked to the orbiter (I got a <1km intercept without even reaching orbit yet or anything close to it, that's about how lucky I was), and got back on a suborbital trajectory with monoprop alone. Then, for about ten minutes, I loaded my 5-Kerbal crew onto the return module (the middle portion, which is docked to the top of the lander and looks like it is disconnected from the lab module), got Danuki Kerman to load up all the remaining science experiments into his capsule, and they were headed home. The Processing Lab of the Lab module and the capsule of the lander (with some extra science on it) both survived on re-entry too, and not only were they uncontrollable pieces of debris, but they had no parachutes or any other kind of thing that would provide a soft landing, which was nothing short of impressive, considering they were coming in at over 3000m/s (6710.808mps)

On 1/10/2017 at 9:44 AM, Snark said:

"If your ship is 74.76 tons, and you're using Skippers at Isp 320, your available dV is:  320 * 9.81 * ln(74.76 / (74.76-17.93)) = 861 m/s.  (Note that this assumes that you turn off those Thuds and use a Skipper only, since the Skippers have a higher Isp than the Thuds do.)

Now THAT made me feel dumb 

Edited January 11, 2017 by Squidiness
nacho business

[suicidejunkie]

16 hours ago, Squidiness said:

so I went for the Mun instead, got an intercept, (barely) reached a stable orbit, (barely)

At this point, you've spent enough dV to go to Minmus, get a surface sample, and return to Kerbin, so your craft is definitely capable of Minmus!  Sounds like your trouble may be lining up the transfer.

 

While you're in LKO, start a maneuver node about 90 degrees away from Minmus, and boost prograde until your AP matches Minmus' orbit.  Be sure to go by the numbers and/or swing the camera around to be sure, because the inclination will throw you off.  DO NOT BURN THIS.

Then add a second maneuver node half to 2/3rds of the way to Minmus.  Pull only the purple normal/antinormal directions and push your path to make it cross Minmus' orbital plane at AP.

If you have an intercept already, bonus.  Otherwise go back to the first node and tweak the timing or make SMALL tweaks to the prograde burn to get your closest approach to turn into an encounter.

Your encounter with Minmus should be 7-9 days away.  If it is less than that, you're doing a high energy transfer at the cost of fuel, and if it is longer than that, you need to improve the launch timing because you're missing it on the way up.

 

Now you can make the two burns and get a nice flyby of Minmus.  Making orbit is cheap from there, and landing is only 150m/s.  if you're careful about the burns, you can land and return to the ship with surface samples using the EVA pack.  (Key thing is to click-drag to tilt your kerbal.  If you burn up and backward simultaneously, the sine losses may kill you.  Instead tilt your head down a little and keep burning retrograde with only the S key, and you'll have excess fuel)

[sardia]

The joys of stock KSP. It's been a while since people manually calculated Delta very or eyeball manuvers. 

[Guest]

2 hours ago, sardia said:

It's been a while since people manually calculated Delta very or eyeball manuvers. 

[citation needed]

I do it all the time playing stock/vanilla. It's much easier nowadays with the VAB/SPH engineering report widget. Even ditched the mod I wrote because eyeballing the ejection angle for a maneuver and then tweaking the burn time results in better transfers.

Edited January 11, 2017 by regex