QUESTION: A Moho Lander. Will ant engines be good enough to land, or should I use more powerful engines?

[yarknark]

So this is my lander for Moho. I'm certain it'll be able to land, but there's no harm in making more certain: Will the ant engines be enough to land? I have 3 of them. After adding the panels and batteries, we have about 770 DeltaV. Looking at the subway style cheat sheet thing, I need about 840. So, if I boost it up to about 870 DeltaV, will the ants still have enough power to land?
Thanks to anyone, cheers.

[Gargamel]

Moved to gameplay questions. 

[Streetwind]

In the editor, set your performanc calculation app (the one with the dV symbol on it in the toolbar) to Moho.

Then, click on the stage with the lander's engine in the list on the righthand side of the screen to make it pop out and show advanced info, like thrust to weight ratio. You can configure what info is shown exactly in the app.

Remove two thirds of all fuel from the lander. At this point, you want a TWR of at least 2.5, or it will be difficult to land. Not impossible; you can land just fine even with a terminal TWR of below 2. But the lower it gets, the more piloting skill is required to not add a new crater to your destination.

[king of nowhere]

14 hours ago, yarknark said:

So this is my lander for Moho. I'm certain it'll be able to land, but there's no harm in making more certain: Will the ant engines be enough to land? I have 3 of them. After adding the panels and batteries, we have about 770 DeltaV. Looking at the subway style cheat sheet thing, I need about 840. So, if I boost it up to about 870 DeltaV, will the ants still have enough power to land?
Thanks to anyone, cheers.

it's not even clear how many ants are there, and we can only grossly estimate the mass, so it's hard to tell.

But by personal experience - and by that I mean, I almost lost a big mission because my moho lander was inadequate - I would tell you to have at least 950 m/s to land, for safety, and a twr (moho) of 2 with your tanks full. You can get by with a bit less, but it's better to play it safe. I assume you don't want to return to orbit after landing, by the way.

A couple more tips: first, you don't need landing legs. You can just land on your engines, and you save 75 kg, which on such a small probe are not insignificant.

Second, you don't need batteries; the hecs2 probe core already has lots of battery capacity.

 

[swjr-swis]

I would advise you to run a few simulations/trials, in a separate sandbox save if need be. You need to get a feel for how long it takes to slow down enough for a controlled landing, how long ahead of the intended landing spot you need to start your burn.

On a low orbit around Moho, you'll be going  around 800 m/s. That's horizontal speed you need to kill with the burn. You will also gain some vertical speed purely from gravity alone, which also needs to be countered - the longer you 'hover', the more you need to burn. Don't underestimate this: on three Ants this is likely to take a burn of 2-3 mins (!). That whole time you'll be falling, so don't start from too low an orbit or gravity will have you before you even had the chance to kill your orbital speed.

Doing this with 840-870 m/s would require picking a flat area and executing a near to perfect suicide burn with a high TWR craft. I would not recommend it if you've never done it before; even the 950 m/s suggested is likely on the low side. I can't stress enough my first recommendation above - try it out a few times and you'll get a better idea of how much you may need.

 

3 hours ago, king of nowhere said:

A couple more tips: first, you don't need landing legs. You can just land on your engines, and you save 75 kg, which on such a small probe are not insignificant.

Second, you don't need batteries; the hecs2 probe core already has lots of battery capacity.

I would keep the landing legs; it's only 45 kg for the three, and they up your safety margin a good bit compared to landing on the engines. I do agree with not needing batteries. In fact, you can do without that 0.625m reaction wheel too - the HECS2 includes a strong reaction wheel as well.

You will however need a good antenna, or a strong relay in high polar position to keep line of sight with both your probe and Kerbin, or you risk losing control at the wrong moment (assuming you play with CommNet and requiring connection for control).