Jump to content

Docking and RCS and Monoprop to Weight ratio


Recommended Posts

Currently doing setup and prep work on a large tourist rocket. Main purpose once done will be to transfer tourists plus fuel to a station where the mun lander flights will depart from. However i've got a bit of an issue, i'm not exactly sure how much monoprop i should have on the rocket. I've done docking in older versions of KSP, but allways with much smaller rockets, this is currently running in at 114 tons of rocket, a bit more if i need more monoprop. The problem is i'm not sure how much monoprop is enough for somthing this size.

Link to comment
Share on other sites

It depends on your docking skills. I used to barely use over a few units to dock things weighing a couple dozens of tons in LKO (used to since I now play RSS and have lost the habit of dealing with the stupidly strong LKO drift).

Though if you want to dock something over 100t you might want to consider using Verniers: they have more thrust and you don't have to worry about monoprop.

Link to comment
Share on other sites

Quote

Though if you want to dock something over 100t you might want to consider using Verniers: they have more thrust and you don't have to worry about monoprop.

I was under the impression they where single thrust direction only? 

Still a few dozen units to dock a few dozen tons sounds like i don't need that much monoprop I've got 780 feeding 40 RCS quads, but no idea how quickly i'd go through that or how adequate the thrust is. 

Link to comment
Share on other sites

1 hour ago, Carl said:

 I was under the impression they where single thrust direction only? 

Verniers are single thrust direction, but that means you only need six if they're clustered around your CG.   They are also twelve times more powerful than quads and have 10% better ISP,  for just 50% more weight per thruster.  If you struggle with the "clustering around CoM" thing, RCS Build Aid mod helps to sanity check your design.

I don't have much experience of large rockets but two of them can VTOL a spaceplane like so..

@Gordon Fecyk also borrowed my nuclear "Stearwing" and performed the same trick -

 

Link to comment
Share on other sites

Furthermore, you can turn off individual control directions for each port. Now I always turn off all 3 rotation inputs (only keep translations on) for all my RCS ports, place them just roughly at CoM (I now rarely use RCS build aid to match CoM exactly) - and let reaction wheel to handle the induced little rotation. Works like a charm. I always had hoped I could turn off RCS rotation since early versions, and I was so glad when it was finally introduced.

Link to comment
Share on other sites

6 hours ago, Carl said:

I was under the impression they where single thrust direction only? 

Still a few dozen units to dock a few dozen tons sounds like i don't need that much monoprop I've got 780 feeding 40 RCS quads, but no idea how quickly i'd go through that or how adequate the thrust is. 

When you get pretty good at docking, you'll probably find that you only need 3 thrusters per ship, total. L/R and reverse. You want very low thrust, because the lower the thrust, the more accuracy you can achieve, and docking is all about accuracy. If you want to thrust in other directions, you do it by rolling your ship. Even huge ships roll pretty well. Many players use gigantic ships through their whole career, but small ships are easy to flip end-for-end -- which enables you to use the main engines for doing all your docking maneuvers, and then you don't need RCS at all.

Link to comment
Share on other sites

I wouldn't want to try using a mainsail to dock with, even on a 114 ton craft. Also all the quads is just so the thrust is well balanced along the length of the rocket whilst giving enough thrust . I'm likely as with most things to use mechjeb to handle it all, (i've done upto and including mun missions without it, (well with the info panel and ASAS, but this was way back when the mainsail was new). But i vastly prefer letting an autopilot do it, it needs smaller rockets as it's better than me and i just don't enjoy flying them that much, now designing them, different story). From sounds of it Verniers to hand forward backward translations sounds better, more thrust and LOX and KR i can spare, the upper stage has 3 Jumbo tanks, that should be enough to hand rendezvous burns plus fueling the lander with enough to spare, with the RCS for the other two axes, (because it's going to be emptying it's fuel, then boosting the payload back to kerbin ground it's going to have to undock with very different CoM).

Edited by Carl
Link to comment
Share on other sites

9 hours ago, FancyMouse said:

Furthermore, you can turn off individual control directions for each port. Now I always turn off all 3 rotation inputs (only keep translations on) for all my RCS ports, place them just roughly at CoM (I now rarely use RCS build aid to match CoM exactly) - and let reaction wheel to handle the induced little rotation. Works like a charm. I always had hoped I could turn off RCS rotation since early versions, and I was so glad when it was finally introduced.

^ This, it was an absolute godsend when they added this feature.  I'd been wanting it for ages.  :)  Then just add a little snippet of ModuleManager config so that pitch/roll/yaw are off by default (so I don't have to remember to turn them off every single time I build a ship with RCS), and it's just perfect for me.

11 hours ago, Gaarst said:

It depends on your docking skills.

Very much this.  Use main engines to kill your relative velocity down to zero (I mean, zero, as in, "enough less than 0.1 m/s that it shows as zero on the velocity gauge").  Orient the two ships so that their docking ports are pointing at each other.  Then use RCS to complete the docking.  You never need to nudge faster than 0.2 m/s (or, indeed, 0.1, if you're patient).  It takes a vanishingly small amount of monoprop to impart 0.2 m/s of dV, even if you're moving a hundred-ton ship.

If the ship is long and skinny, I generally put a ring of RCS thrusters around each end, that way I can just hit caps lock to turn on fine-control mode so that the RCS thrusters will automagically configure their thrust to compensate for thruster placement that's not perfectly centered around the CoM.  I try to get the placement approximately right, but it's never perfect (the CoM tends to move around as fuel gets consumed, for one thing), and using this helpful, magical tool conserves monoprop by not wasting it in creating unwanted ship rotation.

Personally, I never use Vernor engines-- they're simply way too huge and powerful for, well, pretty much anything I've ever docked, up to hundreds of tons.  The only place I've ever used Vernors was on the underbelly of a spaceplane that needs to land somewhere with a super-thin atmosphere, to allow slowing to reasonable speed before landing.  Not VTOL, just an assisted landing.

Link to comment
Share on other sites

On 1/2/2017 at 8:07 AM, FancyMouse said:

Furthermore, you can turn off individual control directions for each port. Now I always turn off all 3 rotation inputs (only keep translations on) for all my RCS ports, place them just roughly at CoM (I now rarely use RCS build aid to match CoM exactly) - and let reaction wheel to handle the induced little rotation. Works like a charm. I always had hoped I could turn off RCS rotation since early versions, and I was so glad when it was finally introduced.

OMG we can finally force craft to use RCS for translation ONLY,and use reaction wheels for all our rotation needs?  HUZZAH!  I had no idea!  I learned something new today!

Link to comment
Share on other sites

Here's the MM script that will disable yaw/pitch/roll. Just make a new text file, paste in the text below and save it as a .cfg file (just give it a name and append .cfg to the end of the name). Drop that text file into your GameData folder and you're good to go. You do need Module Manager installed, but if you're using mods, you likely have that already.

Spoiler

// Make all RCS thrusters have yaw / pitch / roll disabled by default.
// Author: Community

@PART[*]:HAS[@MODULE[ModuleRCS]]
{
    @MODULE[ModuleRCS]
    {
        %enableYaw = false
        %enablePitch = false
        %enableRoll = false
    }
}

@PART[*]:HAS[@MODULE[ModuleRCSFX]]
{
    @MODULE[ModuleRCSFX]
    {
        %enableYaw = false
        %enablePitch = false
        %enableRoll = false
    }
}

 

Edited by Tyko
Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...