Do you think this can make it to Duna?

[UndyingWar]

I've spent ALL day getting this space station set up for my big duna mission. Do you guys think it can make it to Duna's orbit?

Here's a picture...

If it can't make it to Duna, I'll probably kill myself

[Snark]

What's the ship mass?  (Needed to be able to calculate dV.)  I see no reason why it shouldn't be able to, as long as it has enough dV.

Well, except for one potential thing:  do those LV-N's have enough lateral clearance so that their exhaust won't be hitting that hockey puck on the tail of the ship?

Also, depending on how long your burn is, you may need more radiators than that.

Edited February 15, 2016 by Snark

[Just Jim]

Looking at the pic... you have 6000 units of liquid fuel and 2 Nerv engines?  And your already at 200km above Kerbin?

Offhand, and this is just a guess on my part, I would say yes, although your burn time might be pretty long, so watch the Nerv's don't overheat.  You may need to do 2 or 3 shorter burns instead of 1 long one 

 

Edited February 15, 2016 by Just Jim

[UndyingWar]

Just now, Snark said:

What's the ship mass?  (Needed to be able to calculate dV.)  I see no reason why it shouldn't be able to, as long as it has enough dV.

Well, except for one potential thing:  do those LV-N's have enough lateral clearance so that their exhaust won't be hitting that hockey puck on the tail of the ship?

The hockey puck will be gone by the time the Atomic Engines fire. Also, I'm not sure what the mass is. I'll know when I get the crew up there. Without knowing the mass, if you had to guess, could it make it?

[Snark]

2 minutes ago, UndyingWar said:

The hockey puck will be gone by the time the Atomic Engines fire. Also, I'm not sure what the mass is. I'll know when I get the crew up there. Without knowing the mass, if you had to guess, could it make it?

The crew won't make any difference to the mass; KSP doesn't track that.

If you switch to the map screen and open the info panel for the ship, what mass does it say?

[UndyingWar]

1 minute ago, Snark said:

The crew won't make any difference to the mass; KSP doesn't track that.

If you switch to the map screen and open the info panel for the ship, what mass does it say?

Ohh, I didn't know that's how you look at it. I was just going to send an engineer up there, so a mod would pull up all of the info on the station. It's 86.98t.

[Snark]

15 minutes ago, UndyingWar said:

Ohh, I didn't know that's how you look at it. I was just going to send an engineer up there, so a mod would pull up all of the info on the station. It's 86.98t.

Okay, so looking at the resource numbers from your screenshot, it looks as though those nukes have around 30 tons of fuel available.

So, running the numbers:  800 * 9.81 * ln(87 / (87-30)) = 3300 m/s of dV.

So, you've got about 3.3 km/s of dV available.  That should be plenty to get to Duna, as long as you use a good transfer window.

Getting a good window is important, otherwise you waste a lot of dV.  I suggest using some sort of planner tool-- my favorite is http://ksp.olex.biz.

Note that I said "get to Duna", not "land on Duna" or "return from Duna".  But you've got a pretty good start on it.

Edited February 15, 2016 by Snark

[Nich]

Looks too flimsy I don't think your burns are going to go well might need to install KAS and put some struts on it.

[UndyingWar]

5 minutes ago, Snark said:

Okay, so looking at the resource numbers from your screenshot, it looks as though those nukes have around 30 tons of fuel available.

So, running the numbers:  800 * 9.81 * ln(87 / (87-30)) = 3300 m/s of dV.

So, you've got about 3.3 km/s of dV available.  That should be plenty to get to Duna, as long as you use a good transfer window.

Getting a good window is important, otherwise you waste a lot of dV.  I suggest using some sort of planner tool-- my favorite is http://ksp.olex.biz.

So, I just quickly set up a node to see how much dV it would cost and how long it would take it to get there. Do these numbers sound right? 1345m/s of dV, and I would arrive there in 152 days. Do both of these numbers sound reasonable to you?

 

Also, would it be possible for the space station to get back to Kerbin's orbit?

Edited February 15, 2016 by UndyingWar

[Snark]

3 minutes ago, UndyingWar said:

So, I just quickly set up a node to see how much dV it would cost and how long it would take it to get there. Do these numbers sound right? 1345m/s of dV, and I would arrive there in 152 days. Do both of these numbers sound reasonable to you?

Also, would it be possible for the space station to get back to Kerbin's orbit?

1345 m/s sounds a bit high, but not outrageous.  http://ksp.olex.biz/ puts it at 1043 m/s for a 100 km parking orbit.

The other thing to bear in mind is that you need to brake to orbit once you arrive at Duna.  If you follow an ideal transfer window, that not only reduces the amount of dV you need to expend to go there, but it also significantly reduces the speed with which you arrive.  If you pick a bad transfer, you could end up arriving at Duna with many thousands of m/s of velocity, and then you're toast.  Yes, aerobraking is feasible at Duna, but not if you've got a big, massive, unshielded space station going 4000 m/s or more.

Upon arrival at Duna, you'll need to spend fuel to achieve orbit there.  Hopefully not too much, if you can do aerobraking effectively and if you've picked a good window to go there.  With a well-chosen window, you'll arrive at Duna going a bit over 1500 m/s, which should be straightforward to aerobrake.

Coming back, you'll need a burn of a bit over 600 m/s of dV (again, got this from http://ksp.olex.biz/, it's your friend), and you'll arrive back at Kerbin going something over 3000 m/s, which will be a killer for your ship-- there's no way for that ship to aerobrake like that at Kerbin, it'd get fried.  So you'll need to spend dV to slow down.

So, your total dV budget for "go to Duna, make circular orbit, come back to Kerbin, make circular orbit" will look something like this in the best case where you pick a good transfer window:

• Leave LKO:  1050 m/s
• Arrive Duna:  Aerobrake.  Assume you'll need to spend some fuel to circularize, let's say 200 m/s.
• Leave Duna:  650 m/s
• Arrive Kerbin:  1050 m/s to brake to circular orbit.

That's a total budget of 3000ish m/s, which is getting very close to your available dV for the station-- it's doable, but there's very little margin for error, and if you're new to all this you definitely want more margin than that.

If I may offer a suggestion:  It's really wasteful to shove big massive things back and forth.  Consider sending the station to Duna and just leaving it there in orbit, where it will be waiting for you the next time you return.  Your kerbals can come back to Kerbin in a lightweight return vehicle, rather than trying to drag the whole shebang back home.

[UndyingWar]

3 minutes ago, Snark said:

1345 m/s sounds a bit high, but not outrageous.  http://ksp.olex.biz/ puts it at 1043 m/s for a 100 km parking orbit.

The other thing to bear in mind is that you need to brake to orbit once you arrive at Duna.  If you follow an ideal transfer window, that not only reduces the amount of dV you need to expend to go there, but it also significantly reduces the speed with which you arrive.  If you pick a bad transfer, you could end up arriving at Duna with many thousands of m/s of velocity, and then you're toast.  Yes, aerobraking is feasible at Duna, but not if you've got a big, massive, unshielded space station going 4000 m/s or more.

Upon arrival at Duna, you'll need to spend fuel to achieve orbit there.  Hopefully not too much, if you can do aerobraking effectively and if you've picked a good window to go there.  With a well-chosen window, you'll arrive at Duna going a bit over 1500 m/s, which should be straightforward to aerobrake.

Coming back, you'll need a burn of a bit over 600 m/s of dV (again, got this from http://ksp.olex.biz/, it's your friend), and you'll arrive back at Kerbin going something over 3000 m/s, which will be a killer for your ship-- there's no way for that ship to aerobrake like that at Kerbin, it'd get fried.  So you'll need to spend dV to slow down.

So, your total dV budget for "go to Duna, make circular orbit, come back to Kerbin, make circular orbit" will look something like this in the best case where you pick a good transfer window:

• Leave LKO:  1050 m/s
• Arrive Duna:  Aerobrake.  Assume you'll need to spend some fuel to circularize, let's say 200 m/s.
• Leave Duna:  650 m/s
• Arrive Kerbin:  1050 m/s to brake to circular orbit.

That's a total budget of 3000ish m/s, which is getting very close to your available dV for the station-- it's doable, but there's very little margin for error, and if you're new to all this you definitely want more margin than that.

If I may offer a suggestion:  It's really wasteful to shove big massive things back and forth.  Consider sending the station to Duna and just leaving it there in orbit, where it will be waiting for you the next time you return.  Your kerbals can come back to Kerbin in a lightweight return vehicle, rather than trying to drag the whole shebang back home.

That's not a bad idea, I'll probably do that. Thanks for all of the help. You're right about the whole margin of error thing. I don't even know if my drop pod can land two kerbals safely on Duna, then launch them back up to rendezvous with the space station. This whole thing is exciting and stressful at the same time. I'm guessing there's gonna be about a 70% chance something goes wrong, and I'll need to send a rescue mission. Wish me luck!  

[Snark]

3 minutes ago, UndyingWar said:

That's not a bad idea, I'll probably do that. Thanks for all of the help. You're right about the whole margin of error thing. I don't even know if my drop pod can land two kerbals safely on Duna, then launch them back up to rendezvous with the space station. This whole thing is exciting and stressful at the same time. I'm guessing there's gonna be about a 70% chance something goes wrong, and I'll need to send a rescue mission. Wish me luck!  

Good luck! 

The nice thing about coming home in a lightweight return vehicle is that not only is it much cheaper to move (since it's so much lighter), but it can use a heatshield for reentry at Kerbin, so you don't have to spend a lot of fuel slowing down.

For your drop pod:  your best bet to land on Duna is to put a couple of little drogue chutes to slow down from 500 m/s to 250ish, then a small "regular" chute to slow you down to a few dozen m/s.  Then use a brief burst of retro-thrust from the engines to slow down to survivable speed just before impact.  Don't try to pack on enough parachutes for a safe landing-- the air is so thin that you'd need way too many chutes, and the mass would be prohibitive.  Cheaper to spend one little blip of fuel on landing.

If you can arrange your drop pod to have some lift, that'll help get slowed down enough that you can pop your drogues before faceplanting.

Getting from the surface of Duna back up into orbit takes somewhat more than 1000 m/s (I forget the exact number, seem to recall it was 1200ish?) so just make sure your craft has that much dV when it's sitting on the surface and you'll be fine.

[I_Killed_Jeb]

Install Kerbal Engineer Redux and never worry about it again!

[UndyingWar]

23 minutes ago, Snark said:

Good luck! 

The nice thing about coming home in a lightweight return vehicle is that not only is it much cheaper to move (since it's so much lighter), but it can use a heatshield for reentry at Kerbin, so you don't have to spend a lot of fuel slowing down.

For your drop pod:  your best bet to land on Duna is to put a couple of little drogue chutes to slow down from 500 m/s to 250ish, then a small "regular" chute to slow you down to a few dozen m/s.  Then use a brief burst of retro-thrust from the engines to slow down to survivable speed just before impact.  Don't try to pack on enough parachutes for a safe landing-- the air is so thin that you'd need way too many chutes, and the mass would be prohibitive.  Cheaper to spend one little blip of fuel on landing.

If you can arrange your drop pod to have some lift, that'll help get slowed down enough that you can pop your drogues before faceplanting.

Getting from the surface of Duna back up into orbit takes somewhat more than 1000 m/s (I forget the exact number, seem to recall it was 1200ish?) so just make sure your craft has that much dV when it's sitting on the surface and you'll be fine.

Okay... one last thing. Whenever I try to throttle up, the space station turns to the right, and I can't seem to stop it. Is there a way to fix this? Or am I screwed?

[Reactordrone]

5 minutes ago, UndyingWar said:

Okay... one last thing. Whenever I try to throttle up, the space station turns to the right, and I can't seem to stop it. Is there a way to fix this? Or am I screwed?

The side mounted pod probably has a higher mass than the solar panel array so your centre of gravity isn't along the centreline. The reaction control wheels can't correct for the offset thrust at full throttle but you might be able to get away with a reduced throttle setting.

[UndyingWar]

Just now, Reactordrone said:

The side mounted pod probably has a higher mass than the solar panel array so your centre of gravity isn't along the centreline. The reaction control wheels can't correct for the offset thrust at full throttle but you might be able to get away with a reduced throttle setting.

The most I can throttle up to is like 15%... Is that even worth it?

[Snark]

Well, can you rotate the nukes 90 degrees? Then you could lower the thrust limiter on one of them to compensate for the off-center mass.

[Reactordrone]

You might be better off sending up another module to counterweight the ship and install it under the solar panel array.

[UndyingWar]

19 minutes ago, Snark said:

Well, can you rotate the nukes 90 degrees? Then you could lower the thrust limiter on one of them to compensate for the off-center mass.

I could get my engineer to move the location of the engines, but the tricky part is that I need 3 kerbals to move the big atomic engine. I have 3 out there in eva right now, but they keep floating away slowly. Any way to keep the other two Kerbals still while my engineer works?

 

EDIT: So, through the great work of my engineer, the engines have been adjusted, and it's now flying much better. Quick question though... If the burn will take 30 minutes, when should I start the burn? When it tells me to? Or should I do it beforehand?

Edited February 15, 2016 by UndyingWar

[Snark]

Generally speaking, if you have a node at time X, you want to split the burn 50/50 across the node.  However, for very long burns (like 30 minutes) it's not that simple, and more technique is required. 

Gotta go offline now, sorry.

[FancyMouse]

9 hours ago, UndyingWar said:

Any way to keep the other two Kerbals still while my engineer works?

Ladders should work.

[Snark]

1 hour ago, FancyMouse said:

Ladders should work.

Actually, they won't.  If a kerbal is on a ladder, the game won't let you switch.  It's physically impossible to have two kerbals on a ladder at once.

[UndyingWar]

1 hour ago, Snark said:

Actually, they won't.  If a kerbal is on a ladder, the game won't let you switch.  It's physically impossible to have two kerbals on a ladder at once.

I added another module to balance the station, and it flies well now. Hopefully I can get this thing to Duna. Thanks for all of the help.

 

Also, is there no way to make kerbals stay still while controlling another kerbal on eva?

[Snark]

31 minutes ago, UndyingWar said:

Also, is there no way to make kerbals stay still while controlling another kerbal on eva?

Short of bolting a command chair to the ship and putting the kerbal in it... nope, there isn't.  At least, none that I'm aware of.

[Evanitis]

1 hour ago, UndyingWar said:

Also, is there no way to make kerbals stay still while controlling another kerbal on eva?

Cargobays work if you have one with a bit of space in it... well, until you try timewarping.