Moho

[AlamoVampire]

Okay... Moho... Small planet. I think to myself, self: Moho is a tiny little rock, lets visit it. How hard could it possibly be to get there? I mean heck, I managed to get a probe into orbit around the sun, which is further into the the solar system, and that was easy enough. Now, most of you who have done the Moho thing just shuddered and called me naive. I agree. I WAS naive at the LEAST. Holy heck this was a hard hard mission!! Took a MONTH in KERBIN ORBIT, then another 48 days in transit AND to LAND. WOWSA!! I will never EVER assume this to be easy again! BUT, oh so rewarding! I have yet to eva Bob or Bill, only Jeb is out side right now on the ground. Even landed DAY side too!

[SoldierHair]

Why do you have so many nuclear engines?Make your mind, you want trust or efficiency?You don't have either when you spam nuclear engines.

[Guest]

Congrats!

I like to have at least 5,500m/s delta-V for a one-way trip, and that's cutting it close. 6km/s is probably better for safety margin and corrections. That, in and of itself, makes it tough.

The great thing about Moho is that there are so many launch windows you can leave pretty much every pay period (probably not accurate, but sure feels like it).

[AlamoVampire]

Why do you have so many nuclear engines?Make your mind, you want trust or efficiency?You don't have either when you spam nuclear engines.

why so many? Simple. My trip to Jool showed me something scary. 4 Nukes + 1 Rocko Max Poodle was BARELY enough to do Jool. SO, I figured that if 4 + 1 handled Jool, multiply it up by 3 on the nukes! I am currently scratching my head on the return trip, not sure how to pull it off, but, I figure, get into space and THEN try to at hit something manageable like Duna or Eve, atleast then IF thats all that ship can pull off, a rescue is easier, but hoping for a safe return XD

[Scotius]

I think your problems around Jool had more to do with amount of dV, and not the number of engines. More engines mean shorter burns, but also less deltaV, because huge fraction of the payload are engines. Anyways yes, Moho is hard to reach, harder to return and you were naive :-P Now you know better

[AlamoVampire]

I can always dump the outter 8 engines, they are on detachable pylons

[stupid_chris]

Moving this to mission reports.

Also, they are right, if you want to go further and get a better safety margin, add more fuel, not more engines. With more fuel you will get further, while with more engines, you won't go as far, but you'll get there faster.

[SoldierHair]

I was pushing >100 ton transfer stages with one nuclear engine.It takes a lot of time to do burns, but it is effective.Usually i put a big tank in the middle, a nuclear engine under it, put some smaller tanks on 2 times symmetry on the other tank with smaller and smaller tanks on ton of them, i copy them and put them again on 2 times symmetry between the other 2 tanks so i don't have to trow them away at the same time.If my rockets don't have atleast 8km Delta V i am not sending them in interplanetary missions, even if i am going to trow away most of the fuel.

Like this:

[ZenithRising]

Congrats on touching down on Moho! But, you seem to be confusing the utility of a few different things: thrust, efficiency (or specific impulse, Isp), and delta-v.

Thrust is how hard your engines fire. This is what you gain by adding more (or bigger) engines. Thrust is essentially useless once you get into the vacuum of space. Without friction to fight against, one of those little ant engines could (eventually) get any size payload anywhere. Once you are in orbit, all you really need to consider thrust-wise is how quickly you'll need to execute burns in order avoid messing up your timing or spoiling your patience.

Efficiency (Isp) is going to be far more important once you're in space, because the more efficient, the more you can do with less fuel. More engines does not improve your Isp, but you will instead have (more or less) an average efficiency of the different engines you are using.

Delta-v is the key concept to consider. It literally means change in velocity. It is a measurement of the actual amount of work you have to do to get some place. Consider that regex said it takes about 6,000 m/s of delta-v to get to Moho. So any craft needs to change its initial velocity by 6,000 m/s. The more mass that craft has, the more work it will take in order to get that change in velocity. So, the best possible design to get to Moho would have the lightest engines possible (to cut mass), the most efficient engines possible (so you need less fuel, which means less mass), and exactly the amount of fuel you need with no extra.

So adding all those nuclear engines may have increased your thrust, but that didn't help you get to Moho any easier. In fact, it made it harder because those engines add mass, and the nuclear engines in particular add a lot of mass.

[Guest]

Delta-v is the key concept to consider. It literally means change in velocity. It is a measurement of the actual amount of work you have to do to get some place. Consider that regex said it takes about 6,000 m/s of delta-v to get to Moho. So any craft needs to change its initial velocity by 6,000 m/s.

It's worth noting that my numbers aren't set in stone. You can get launch windows that are slightly less than 5km/s, or even less (there's a window on Day 234 of Year 1 that takes 4,426m/s), but I over-engineer and prefer to be able to launch whenever there's a semi-decent window. So when you make the transfer is fairly important when determining your delta-V budget and should be considered when building the craft.

[ZenithRising]

Yeah, I was just using your number as an example regex. I haven't been to Moho yet myself, so 6km/s seemed like a reasonable enough example to me.

But yeah, The delta-v you need can vary a lot depending on a number of factors, and you should probably pack some extra fuel.

[AlamoVampire]

Just thought you guys would like a pair of pictures from Moho Mission.

Bill, Jeb and Bob on Moho! Because Jeb is Jeb and is cool, he posed on the flag!

Jebs looking over at Bob during re-entry at Kerbin thinking: CHILL man, we are almost home!

[Scotius]

Congratulations on Moho landing And even bigger congratulations for returning home - it's not an easy task to climb all the way up from the bottom of Kerbol's gravity well.

[AlamoVampire]

Ty ty was fun but not eager to do it again

[UberFuber]

So, the best possible design to get to Moho would have the lightest engines possible (to cut mass), the most efficient engines possible (so you need less fuel, which means less mass), and exactly the amount of fuel you need with no extra.

So adding all those nuclear engines may have increased your thrust, but that didn't help you get to Moho any easier. In fact, it made it harder because those engines add mass, and the nuclear engines in particular add a lot of mass.

Another factor to consider is whether you're landing. If you're landing on a Celestial body, you'll need enough thrust to get yourself off it (and enough thrust to get yourself off it fast so you don't waste to much fuel fighting against gravity, or if there's an atmosphere, fighting against drag).

Another factor to also consider is your patience. Yes, 1 nuclear engine is probably most efficient if you don't want to pay for the electrical cost, but if you're craft weights a couple dozen tons, you're going to spend a LONG time accelerating to go anywhere.

[Superfluous J]

I don't go to Moho (or Eeloo or Dres) at transfer windows. I go when Kerbin and Moho (or Eeloo or Dres) are at each other's AN/DN. You can't aerobrake so you want to do the tilt correcting burn to be as far from Sun as possible (or during your encounter) which for Moho will then be right as you leave Kerbin, or for Eeloo and Dres will be when you arrive at their orbit. Then you can burn to get an intercept. Takes longer to get there but seems to really save on fuel.

Though Moho STILL takes a TON of fuel