lateral velocity

[Steampunked]

Hello again folks.

So I\'ve managed to land several rockets on the Mun- however, every single one of them falls over as soon as I touch down. This is because I still have just a handful of m/s lateral velocity. How should I go about killing this lateral movement? I\'m hesitant to simply flip my ship to direct the torch sideways. Would RCS solve this?

~ash

[vexx32]

Yes, RCS can solve this to some extent. However, if you find yourself with a large lateral velocity as you head towards the Mun, I suggest you click on the velocity display to change it to surface, then burn on the horizon in the direction of your retrograde in order to kill the majority of the lateral velocity whilst you\'re still high-up. Then, when you get closer to the ground, make corrections using RCS translation keys -- J,L,I,K or left, right, forward, back respectively and H/N for up/down. It is easiest if your rocket is oriented vertically when you\'re doing RCS corrections, as it\'s easier to predict what\'ll happen.

[ferram4]

vexx32 is correct, that does help a bit. You may want to try making your landing vehicle wider and squatter to help make it more resistant to tipping in the first place.

[BillWiskins]

I think it\'s worth mentioning that for best results, remember to position the RCS thrusters on the ship so that their effect is balanced - for example, don\'t group them all at the top, or when you thrust sideways you\'ll give yourself a rotation force. But you knew that.

[sal_vager]

If you find RCS isn\'t working for you, you can try my preferred method of using the main landing engine to control your lateral movement.

After the deorbit burn, point straight up and engage ASAS (if you have it), use WASD to tilt very slightly in the direction of the green direction marker on the navball, you will reduce speed in that direction and the marker will move towards the center, indicating that you are descending directly downwards.

If you fly without ASAS you will need to use capslock to engage fine control, and take a lot more care.

I personally find RCS is not powerful enough, and I only use it for changing my angle in orbit and for orbital rendezvous.

[Ydoow]

RCS may help, but I generally just use a thruster to touch down.

You can use the NavBall and watch your retrograde point. During a slow descent, it will be pushed opposite of your lateral velocity.

So if you tip your rocket on, or towards your retrograde point during the slow descent (or while hovering), you will chip away at that lateral velocity.

When the retrograde point is directly at the top of the NavBall is when you have near 0 lateral velocity.

[maltesh]

I\'m a keyboard player, and tend to rely heavily on RCS for killing lateral velocity on the vertical stage of final descent.

My manual landers invariably have an ASAS module, but I find that sufficient to cancel the rotation imparted by a single ring of RCS jets (either three or four of them, depending on whim or design), placed high on the lander.

Basically, I usually put my landers + last pre-lander stage into an orbit around the Mun with an altitude of about 10 km. I then make sure that the speed indicator on the navball is showing Surface Velocity rather than orbital Velocity(and click it if necessary to switch it over. The difference at the Munar equator is over 9 m/s of horizontal velocity, enough to tip many lander designs if you\'re reading the wrong value)

I then use the fuel remaining in the last-pre-lander stage to get as close to zero surface velocity as I can on the remaining engine.

I then flip vertical and begin the vertical descent. At about 5 km, I\'ll detatch the last-pre-lander stage and ignite the lander engine.From there, I try to keep a descent speed of about 1% of my altitude in meters, while using RCS to shove the velocity vertical. I watch the last pre-lander stage smack into the Mun below me, and that gives an idea of what the surface altitude of the landing zone is.

Crunch time occurs at about 1000-500 meters above the expected surface. From there on down, I try to find a setting on the throttle that will have my spacecraft descend at landing speed, < 9 m/s. RCS becomes very important there, both for shoving my velocity vector vertical, and fine-tuning descent speed. I usually don\'t touch the throttle until surface contact happens. Since I\'m usually pushing the craft downward with RCS at that point thanks to the craft lightening from fuel expenditure, touchdown is typically very gentle.

That\'s what works for me, anyway.

[Steampunked]

thanks for the reply guys 8)

[foamyesque]

I just chase the retrograde indicator until it\'s within the 5 degree ring at less than 6m/s. Easily done with precision control.

[Crimson_Pride14]

I just chase the retrograde indicator until it\'s within the 5 degree ring at less than 6m/s. Easily done with precision control.

This. If you stay on that indicator it\'ll kill your horizontal velocity component along with your vertical velocity component. It\'s the easiest way I\'ve found.

[hubbazoot]

The vertical ascent gauge at the top of your screen will give you your vertical height. Remember that it\'s on a logarithmic scale: Each 'notch' accounts for more units as the gauge moves further and further in either direction.

The number displayed over the nav ball is your absolute speed. So, for ballparking it.. your absolute speed minus your vertical speed will give you a rough idea of how much horizontal speed you have. (It\'s actually a square root sum, more complicated).

My method of landing is that I try to kill off as much 'horizontal' speed when I start my descent as soon as possible. If the x on the nav ball that shows the opposite of which direction I\'m going (i.e. when you\'re facing \'backwards\'. I\'ll call it the anti-path), I try to get that centered on 90 degrees (or as close to) as soon as possible. Once I have it just about there, I center my ship on the anti-path marker and decelerate. My general rule is speed=(Altitude-3000)/100 as you descend. So if you\'re between 10k and 9k, try to shoot for coming down no faster than 90m/s. This will leave you just about stopped when you get to the surface.

As you have more and more vertical speed killed off, the anti-path marker will start to 'drift' towards one side. I always burn at twice the angle it is away from the nav ball (sometimes more) to re-center it back on top of the ball. If the anti-path is at 80 deg, I\'ll do a deceleration burn at about 70 deg.

For the final little bit of the path, I tend to lock on my SAS unit and then 'helicopter' down; using the same method as above, I\'ll leave the SAS on but still try to point the ship towards twice the angle of my anti-path. I get the throttle adjusted to the point where my rockets are having me maintain speed, and then I\'ll increase or decrease throttle as needed to adjust my speed. The RCS units tend to come in handy for killing off any remaining horizontal speed when you get down into the >20m/s range.

When you get really good with the throttle control, you can get it adjusted so that the main engines are pushing just hard enough to maintain your current height. I\'ve gotten to the point that I usually do this, and then use the RCS thrusters to 'push' me down to the surface. Using this method, I\'ve managed to land on the surface of the mun at 0.1m/s.

Also, besides this, having LOTS of landing gear helps; they\'re pretty brittle. I tend to have about 3 per fuel tank. My munar lander uses only the small rockets as they\'re a good deal easier to control.

[Zephram Kerman]

All these techniques are winners. For what it\'s worth, my style is pretty close to Hubba\'s and Sal\'s. Sometimes I shun RCS entirely, since it tends to run out at very inconvenient times. Even with just keyboard controls, I can land safely (almost) every time now.

I prefer to use at least four lander legs. That way, if one breaks, it isn\'t a disaster. (I\'ll use more if the craft is heavy.) By the way, the legs can be reinforced with two struts to make them less brittle.

[hubbazoot]

Sometimes I shun RCS entirely, since it tends to run out at very inconvenient times.

By the way, the legs can be reinforced with two struts to make them less brittle.

1. My current lander has 5 cans of RCS, but that\'s because it\'s also designed to do a rendezvous.

2. Pics of the reinforced landing strut?

[Zephram Kerman]

Like this:

[hubbazoot]

Thanks for postage. That\'s awesome.

[Enture]

Ok, bringing this thread back to life with a few questions...

I get what the method to kill horizontal velocity is, however no matter how hard and carefully I try (with main engine or RCS), I always still end up with 4 to 6 m/s horizontal velocity upon landing, causing my lander to tip over. So how do you manage to kill that velocity entirely? Am I missing something?

Should I have my velocity display and pro-/retrograde markers on the "Orbit" position or "Surface"position to use them efficiently during this phase?

Thanks for your help!

[Bluejayek]

Hello Enture, I realize you are new to this forum, but it is generally seen as bad practise to "necro" a thread by posting in it months after it died.

That being said, I find a good way is to kill velocity completely while still 1000m up or so, and then descend perfectly vertically. Wastes fuel, but better success rate.

[Serratus]

The retrograde indicator should be perfectly on vertical point on the navball. Just achieve that ~5km above the surface, and You'll be fine, Your horizontal velocity will be 0.

[EndlessWaves]

Alternatively, build a more stable lander with a lower centre of gravity and/or more widely spaced landing legs.

[Enture]

Hello Enture, I realize you are new to this forum, but it is generally seen as bad practise to "necro" a thread by posting in it months after it died.

Oh. I'm a regular user from another forum, where it is bad practice not to search through older threads and using those if their topic is similar, to keep the number of threads as low as possible; that's why I acted that way. But OK, I'll change my habits on the KSP forums then... :-)

Thanks for your answers; I know my retrograde indicator should be on the vertical point, but should I use my Orbit-retrograde indicator, or my Surface-retrograde indicator?

[UNSC]

You could try a larger lander, and more legs there is no limit on number of legs. The most important part of the landing to me is the lateral speed. I have found that I can get away with some horizontal velocity if I am landing with < 5 m/s lateral velocity. I was even recently able to land on a semi-steep hill on minmus with some horizontal velocity going down hill.