How do you fly the navball?

[Hotel26]

Every time I have to fly a navball approach to a pinpoint target on an airless body[*] and I haven't done one for awhile, I have to re-teach myself.

Let O be the top of the blue section of the navball (that's the spot directly under my "vessel" (guys, you know what I am talking about))  If I have any horizontal mambo-jambo at all, that is NOT where I am going to be later today...

Let X be the target and let's assume it's on the surface of aforesaid air-forsaken body...

Let + be my navball Surface prograde marker; we has to fit it in somewhere.

And let V be my attitude (the which way I is pointed marker)...

If I get O X and + all aligned with X bracketed between O and +, I am looking fine.

+ is what is dragging my O (current position) toward X

I can use retrograde thrust against V to repel + from V and thus control its alignment with [OX+]  (Sadly, that's the only move I have got...)

Meanwhile, my Silent Foe, Gravity, is dragging + (line of flight) toward O -- which is kind of an Astronaut's Droop...  Not me, but I've heard on the grapevine...    So, you have to lead the target, X, somewhat.

Eventually, you want O, X, and + to arrive all together at the same time your altitude and velocity reach 0.

Except, when you do that -- and you certainly will do, if you follow the above -- you will have landed on top of, and possibly destroyed your target, so you had better detune this slightly when your AGL is close enough.  Just go for a soft, vertical landing right over wherever you are.

Reason I am posting this is that I don't really think I can explain it without a video.  (Which is maybe my next step.)  Can anybody explain this in a much more succinct fashion??  Kudos for doing so!

* not talking about my g/f

Edited January 14, 2018 by Hotel26

[invision]

radial out

it will push the craft upwards while continuing to go in the direction of the target, then you would retrograde while above the target to kill all velocity and come down for the landing.

im unsure if this is what you are asking it was a bit confusing to read, but its still solid advice

[AngrybobH]

I assume you are not using mechjeb or other landing mods. Even with mechjeb landing guidance, it sometimes tries to land on the target but, it does a braking burn to end up 500m above the target. Then it does a minor suicide burn just before the surface. When it tries to land on a base when I wanted to land beside it, I take control at the 500m above the ground point. I hold up with mechjeb and use RCS to steer while dropping slowly or hovering. So without mechjeb, I would line up for a collision course and kill all velocity just before impact. Then set SAS to hold and point the ship up(your position O) and use RCS thrusters to steer while hovering on the main engine. The problem with setting radial, or anything else other than hold, is that they change based on current velocity vector. If your RCS is well balanced you should be able to hold up and steer around quite easily. And, you know you are exactly vertical when the retrograde(when falling) marker is dead center of up(your O marker). Maybe that helps?

[Tyko]

The navball isn't very big...I'm sure it would fly great if you duct taped it to a booster

Kidding aside, coming to relative stop half a klick or so above the target and then using RCS to fine tune while you drop can give a lot of precision with a little loss in fuel because you're not doing an optimum suicide burn.

Edited January 16, 2018 by Tyko

[qzgy]

44 minutes ago, Tyko said:

RCS to fine tune while you drop can give a lot of precision

Assuming you even bothered to include RCS in the first place. For myself, careful throttle management with KER is the way to go.

[Tyko]

1 hour ago, qzgy said:

Assuming you even bothered to include RCS in the first place. For myself, careful throttle management with KER is the way to go.

yes...well almost any precision landing I've done has been to harvest fuel for a tanker or science for a lab...since those missions require docking back in space, the landers have RCS anyway. The only times I've done precision landings without docking were sending crews to heritage sites of early robotic landings for the fun of it. In those cases I didn't mind walking a half a kilometer or so.

Agreed that you can use your main engine and I've done that for fun to prove I could do it, but for repeatability RCS is a big help.

Edited January 16, 2018 by Tyko

[Corona688]

When I do docking-from-orbit I do it in several phases.

1. Rough intercept, just by eyeballing and nodes in map view.  I don't aim to land on the target, as much as do a low flyover directly overhead which intersects the surface some distance past it.  This can get you within 10km, surface-wise.
2. Deceleration, killing much (though not all) of my velocity near/overtop the target.  I burn at 45 degrees or so, so I don't end up too short.  This is also a good time to correct your course if your direction is off.  Straight-line distance should be less than 5km now.
3. Sustain, pointing straight up and applying enough thrust to keep the prograde marker a little above my target.  This can get me within a hundred meters.
4. Hover, killing all velocity and getting my engines to as close to 1.0 local-g as I can manage.
5. Docking, hovering on 1.0 local-g thrust and using RCS thrusters to move me around.  If the target isn't visible on navball you'll have to watch your RCS thusters in the live view and rough it in the right direction until it is.

Do yourself a favor and practice this on Minmus, where you can hover for tens of minutes at very little cost.

Edited January 17, 2018 by Corona688

[Corona688]

P.S.  When I say "point straight up", I mean STRAIGHT UP.  Any slight angle off becomes a slow drift that will become unstoppable if you let it accumulate long enough,  That's what's happening when you steamroller straight past your target sideways - you've gradually accumulated a sideways 4m/s drift and can't possibly stop in time.  You'll end up fighting it with RCS most of the way.

The higher the gravity, the worse this drift is.  Anywhere but Minmus, you'll need more RCS punch than you would in space.

Edited January 17, 2018 by Corona688

[Corona688]

Stop the presses!

7 hours ago, Hotel26 said:

@Corona688: "you cannot aim PERFECTLY upwards on a probe's navball,"  Well, done!! first of all.  I use Surface:Radial Out on the SAS setting...

Radial Out is the "hover" setting.  Radial Out is the "hover" setting.  Why didn't anyone tell us this!?

And just yesterday I was thinking "Ugh, centering it would be easier if this stupid purple mark wasn't always there".

Edited January 17, 2018 by Corona688

[Hotel26]

> How do you fly the navball?

Yes, sorry.  I was being rhetorical.  "How do YOU fly the navball?".  Then I outlined how I do it, or think of it.  But I need to make a video demonstration.

In the very early days of KSP, I saw a video of a guy in a rocket launching from KSC to intercept a target that had just passed over the tip of the desert to the West.  And he simply FLEW THE NAVBALL the whole way to rendez-vous.  It's one of the most amazing things I've ever seen in Kerbal space history.  (I'll see if I can find that video...)

I've used three techniques for pin-point landing (by which I mean the fuel truck does NOT have to pick its way through rocks and across craters to cover 5 km to you):

1. Asymptotic method: in which I basically come asymptotically to a stop over the target and then shoot a vertical approach.  Arriving at 5 degrees before the target,  I want to be down to 500m/s (using the Mun as reference here).  400 m/s by T-4d, 300 m/s by T-3d, etc.  (90 degrees before the target, I'll have made a very slight inclination burn to try to align the flight path over the top of the target.)  This whole technique is wasteful of fuel!!  Biggest problem is that you have to a) start a horizontal correction maneuver and then b) cancel it out when you arrive.  Possibly one for lon and one for lat.  Lot of work just because the whole approach is so primitive.

2. Suicide burn.  On a body without atmosphere, the way to ascend to orbit most efficiently is jump 100m into the air and then turn almost horizontal and burn, baby, burn until you have just over 10km apoapsis.  (This is Newton shooting a baseball at sufficient speed from a sufficiently high mountain such that it never comes back to earth, but continues orbiting.  (He'd better take oxygen if the mountain is that high!)

The most efficient way down is the reverse: T-270deg, I make a small inclination change to align the flight path over the top of the target.  At T-180, I lower my periapsis (which now becomes directly over the target) to as low as litho-obstructions (mountains) and my nerve (chicken) will allow, e.g. 6km.  Then I put my speed v and max decel  rate (MechJeb for instrumentation!!) into s = v  / (2 * a).  (This comes from s = 1/2 a.t^2 and v = a.t)  A number like 11.3km will come out.  When the target marked closes in to 11.3km, I burn on my initial Orbit retrograde direction (Set Orbit mode; set Retrograde; set Hold (to ignore changes)).  You became a flaming hockey stick streaking toward the target.  Don't kill all velocity but get down to about 50m/s or a little more.  Then go Surface Retrograde as base alignment (this is your big tool for landing with only mm/s horizontal "wander") and then jiggle it down however you like to do it.

3. Just Fly The Navball the whole way!  For greater fuel efficiency, you can do the suicide burn and transit to Navball over the target.  But that requires a mental transition.  Flying the navball from the start keeps you in control of the ball the whole way.

If anyone else uses the navball technique and can give a comprehensible explanation for everyone (mine is kinda incomprehensible, even to me!), please do so.  But I will make a video, too, since I think that is the best demonstration.

 

NOTE: NO hovering and NO jiggering was used in grouping the above.  Slowed down to land softly with the landing spot already dialed in on the ball.

Edited January 18, 2018 by Hotel26

[Hotel26]

1 hour ago, Hotel26 said:

NOTE: NO hovering and NO jiggering was used in grouping the above.  Slowed down to land softly with the landing spot already dialed in on the ball.

Here's how that works.  IF you fly the navball ALL the way to the target you WILL land on top of the TARGET and cause EMBARRASSMENT all round. 

After the umpteenth time getting chewed out for this back at the Academy, I learned that you pick an altitude, like e.g. 300m, and you fly the NAVBALL to that altitude and then just go into a stop-the-hztl-motion/land-on-the-point-below mode.

The higher you are when you let go of the ball, the greater the final, maximum, surface distance from the target can range within.  But yes, you can still get unlucky and land ON TOP.  So by then, you've had to have gone fully visual and are ready to haul off, if necessary.

Edited January 18, 2018 by Hotel26

[Atkara]

17 hours ago, Corona688 said:

Radial Out is the "hover" setting.  Radial Out is the "hover" setting.  Why didn't anyone tell us this!?

Up until I saw Hotel26's post and browsed upwards to see what was going on, I assumed people were generally aware of this. I mean, if I stumbled upon it by just playing (I'm a relative late-comer in KSP forums) they must have too, right?

In retrospect, I suppose the "jump around till you hit your mark" is so popular, that it's -most propably- assumed to be the only way to do it and the subject isn't being brought up often.

[Hotel26]

56 minutes ago, Atkara said:

I assumed people were generally aware of this

The great thing about KSP is that it is so rich [so much to learn] and the great thing about the forum is that there is such a distribution of knowledge that it is an incredible place to learn.

I played KSP 3 years without using the forum much.  The kindest way to judge myself is that "I had no idea what I didn't know".  This forum is an incredible trove of skill, experience and insight.  We're all pooling know-how.  Best to just stay open-minded and pay attention at all times and don't make too many assumptions about how much you know!

Edited January 18, 2018 by Hotel26

[Atkara]

17 minutes ago, Hotel26 said:

I played KSP 3 years without using the forum much. The kindest way to judge myself is that "I had no idea what I didn't know".  This forum is an incredible trove of skill, experience and insight.  Best to stay open-minded and pay attention at all times!

I wasn't using the forums much either (let alone posting), which was like re-inventing the wheel on my own at times.

I wasn't trying to downplay or devalue the forums in any way -God no! I was simply surprised and nothing more than that. The part about jumping around comes from videos and streams I've watched, where players were doing just that and I had decided I would do no such thing, even if it was the only way

[Hotel26]

6 minutes ago, Atkara said:

and I had decided I would do no such thing, even if it was the only way

Amen, brother.  I'm with you.  Unless one is in a rotary wing...  fugeddaboutit!! 

But the same thing goes for designing stuff in which you dock pieces on the ground together from above.  Kudos to those who attempt it but too much trouble for me.

At the moment, I've gotten re-interested in surface mining set-ups.  I'm about to load what I have to KerbalX and start surveying how other people do it...  In summary, I have 3 mining rigs, one with ISRU, a fuel truck and a lander (and an ion-powered "flitter" that all have a standard docking system.)  It's the best I could do and I think it has some advantages, but I'm pretty sure I could learn heaps from the "state of the art" in this community!

Edited January 18, 2018 by Hotel26

[Atkara]

34 minutes ago, Hotel26 said:

But the same thing goes for designing stuff in which you dock pieces on the ground together from above.  Kudos to those who attempt it but too much trouble for me.

Yeah, that's something I'd rather not do -especially with the tendency of surface bases to spaz out to oblivion, after each KSP update. As much as I love modular bases (and stations) my go-to solution is still the all-up, rigid and compact type.

I've described it more extensively in another thread, but my "system" is based on orbital refineries, supplied (for the most part) by ISRU equipped surface miners, capable of bringing 3.3k units of ore in orbit around the majority of planets & moons. For Tylo & Laythe, whenever I get to deploy installations and crew, I'm going for an ISRU+Claw equipped surface miner, on wheels.

[Hotel26]

24 minutes ago, Atkara said:

but my "system" is based on orbital refineries,

Me too.  I have an ISRU in space and I'd prefer to lift 15 tons or ore and turn it into 30 tons of fuel.  I don't recall why I had an ISRU on the ground too, but it might have just been lack of confidence!! 

The "claw" is how you dock to transfer fuel/ore?  I use two junior docks all recipients facing Up and the one on the fuel truck faces Down.  Easier to guarantee alignment even on uneven surfaces because the fuel truck has a couple of back legs to push the dock down in an arc if necessary.

I'd like to see your thread! and I'll let you know when I have these up in KerbalX...  (I've never used the "claw".)  If you put a claw on a fuel truck would it mean you could refuel aircraft that don't otherwise have docks??  This would be a big advantage because most airplane designers do not like putting draggy docks on their designs, no way/no how...

EDIT: Yay.  Looks like I put one of those Grabbing Units on my fuel truck and need nothing else. 

Edited January 18, 2018 by Hotel26

[XLjedi]

@Hotel26

Yep, I use a "Fuel Claw" on all of my fuel trucks...

https://kerbalx.com/XLjedi/RV-10A-Fuel-Truck

 

 

Edited January 18, 2018 by XLjedi

[Atkara]

4 hours ago, Hotel26 said:

The "claw" is how you dock to transfer fuel/ore?  I use two junior docks all recipients facing Up and the one on the fuel truck faces Down.  Easier to guarantee alignment even on uneven surfaces because the fuel truck has a couple of back legs to push the dock down in an arc if necessary.

So far, I haven't really felt the need to fuel up anything on the ground. Tylo & Laythe will change that. I could've gone for a solution like the one you described -heck, I had one in testing and it worked as expected. The claw however, offers simplicity in both the design and the process itself. In the end -how did I say it yesterday? Ah, yes. "I'll pretend there's a fuel plug where I'm grabbing" 

In orbit, I'll use normal/shielded docking ports.

[Hotel26]

15 hours ago, Atkara said:

haven't really felt the need to fuel up anything on the ground

As best I can remember, I ran missions with a tight enough budget that I couldn't be sure I could get a lander down twice (to deliver rig and truck), which is why I put an ISRU on the rig to operate on the surface.  I'd delete that now if I were reworking things (and it looks like I am).

In addition, I did it before asteroids and the claw (and have never been interested yet in asteroids) which is why I didn't contemplate the claw.

I actually prefer my docking solution to the claw, but the claw has the advantage I mentioned, at least for aircraft, that you don't need to put draggy docks on them.  (Unless of course you can fit in an inline dock or a cargo bay without simply paying for drag induced by extra weight...)

Edited January 19, 2018 by Hotel26

[Atkara]

2 hours ago, Hotel26 said:

In addition, I did it before asteroids and the claw (and have never been interested yet in asteroids) which is why I didn't contemplate the claw.

I played around with both the claw and asteroids a lot in 1.05, which is propably why I love Dres so much. Anyway, with most of my asteroid adventures involving Class E rocks and with no autostruts back then, I'd say I was taught a thing or two about maneuvering large & heavy things around

[Hotel26]

7 minutes ago, Atkara said:

asteroid

One of these days, I will go get me an asteroid and hog-tie that dogie real goood...  

[invision]

speaking of asteroids.

when i figured out how to grab an asteroid i was quite happy. so over the course of the next few weeks i would gather one when i played and put it in kerblin lower orbit. i started to notice the game played worse and worse. my pc was not impressed with me. i would launch and watch my fps tank to 10-15 fps when i got into low orbit. i ended up just starting over.

[XLjedi]

@invision if the looming threat of deep impact doesn't eventually wipe you out, the frame rate drop certainly will!  ;-D

[Hotel26]

7 minutes ago, invision said:

my fps tank to 10-15 fps 

the only thing I could think of to explain this would be: "extra sphere of influence [in close proximity to many orbiting vehicles]", an n^2 effect.  Do asteroids have this effect, I wonder?  I should think that even a Class E asteroid would have mass too low to garner a "sphere of influence" but it would just depend on what Squad decided...

(A bit "conspiracy", I admit...)

Edited January 19, 2018 by Hotel26