Vertical launch...and big horizontal rovers?

[strider3]

I have yet to figure out how a person launches a large horizontally oriented rover...on a vertical rocket? Yes, I can hang some girders and wheels off the side of my rocket...and have done so. Two of these mining vessels are examples:

And they launched...fairly well. But, what I want is a Large horizontal tanker/rover on Minmus, to move the created fuel to a lander for transfer to a Minmus orbiting station. I've made one attempt (well, several attempts using the same theory), EPIC fail:

The problem is the change from vertical to horizontal. At the lower end of the Jumbo 64's I have a Mainsail (lots of bigger stuff under that but...whatever). That rig gets me to Minmus, gets my orbit "twisted" twice (Minmus from Kerbin + my mining operation is pretty far north on Minmus) and gets me retrograded to almost vertical over the mining site and slowed to 10 m/s at 2,000 meters. My "thought" was I could decouple the mainsail and all tanks except the rover's at about 2,000 meters, level this pig horizontally and use the 8 Twitches (which should be more than adequate) to softly drop this on the surface. Not so...not even close! The problem is control...nothing on the Navball works anywhere near as expected and every time I fire the Twitches the mule goes OFF.

So, Failure one. My REAL question is...how would you go about getting a Horizontal fuel tanker / rover onto a planet...horizontally?? 

Vic the Newbal

[Magzimum]

I posted an answer in an earlier thread. It may be relevant.

Executive Summary for the design below: I preferred fighting gravity than fighting the terrible drag, so gently on the throttle, no faster than 150 m/s until 14000m up, and keep it under 300 m/s until around 20 km up. Go straight up until at least 35 km. And bring some spare dV!! The one below had 5600 m/s dV to get to Minmus (one-way), which in retrospect was uncomfortably close to being insufficient. Add huge wings at the base of the rocket (note that I put 12 airplane wings on it). And empty the tanks of the rover if possible. The large white, and two orange tanks were all empty.

[edit] and LOTS OF STRUTS. The rocket above didn't even have the slightest wobble in it... due to at least 30 struts strutting everything down.

 

Edited September 5, 2016 by Magzimum
Moar struts!

[pincushionman]

You need to make sure your twitches are centered about the rover section's center of mass, specifically at the fuel level you expect to have at the time. It might help to open just the rover section in the SPH and  use the CoM and CoT markers to line those up. You might have to move some parts around to control your CoM, or it may be easier to just move your thrusters around to accomodate. Your setup looks pretty simple.

Also, put a docking port on the horizontal top, and when you go to flip the vessel sidways, right-click it and select "control from here." This will re-orient the navball so that instead of looking at the horizon like a rover, it's looking up like a lander can.

[Laie]

What pincushionman said. You should get close enough just loking at the CoM/CoT indicators; or if you want to get serious, RCS Build Aid is the go-to design aid for all your offset thrust assemblies.

Alternatively,

1. strap a poodle (or something) to the end of that rover
2. land it on it's tail
3. then let it tip over.

[Signo]

You can do it exactly like that, you just need to set the correct "command part" when decoupling the "rocket stage". 

I usually put a docking port on top of the rover's CoM to use as a command point for landing (and for "skycrane" type add ons later).

 

[pincushionman]

3 hours ago, Laie said:

Alternatively,

1. strap a poodle (or something) to the end of that rover
2. land it on it's tail
3. then let it tip over.

This too. You can get away with darn near anything on Minmus.

[magnemoe]

The thuds are pretty much perfect for landing huge rovers. The twitch works well enough for low gravity and lighter rovers. 
You will need to change your command from here, put an small docking port on top of rover and command from here then using the landing engines, switch to rover control then driving. 
With an fuel tank rover you would typical take it to say 1500 m/s and 40 km attitude before dropping core stage, now you change command from here to rover top change orientation and fire up engines, 
Make sure you have pretty similar dry mass on both side of rover, don't put an science lab or ISRU in front unless you balance it, worst case you can use an locked fuel tank for balance. 

 

[Plusck]

Like @Signo, I use docking ports to determine which way it's going - on top for landing and taking off, on the front for driving around and for docking to an orbital station.

This is my "perfected" fuel carrier from 1.0.5. I use three tanks rather than one big orange to make it easier to build symmetrically, and also to make it easier to get the right ratio of LF and Ox when keeping a minimal load of fuel for the return to the surface. I tested on Kerbin using KER to get the thrust perfectly centred.

Spoiler

In 1.0.5, the landing legs actually served a purpose in cushioning the landing and getting the docking port to the exact right height to fit the mining craft. I haven't tried in 1.1.3 yet but I doubt they will be useful...

[foamyesque]

Landing a large rover, you say.

 

Use your main engine to kill your horizontal velocity (a node helps here with timing and orientation), then go nose-level-to-horizon (SAS stability mode helps here) and land the rest of the way on RCS controls. I used vernors because I was landing something heavy and monoprop tanks all look ugly, but for smaller things linear RCS or even quads will do just fine on Minmus. It's pretty forgiving.

 

[strider3]

Thanks, as always. The one thing most mentioned was the addition of a small docking port on top, at CoM, for control when going horizontal (in the famous words of Homer Simpson..."Doh!" ). I also thought about Laie's suggestion of landing vertically and letting it tip over...maybe a pair of tiny thrusters at the "top / front", to ease the fall to horizontal? So I added the small docking port on top and redistributed the twitches to align the CoT. I don't have a port on the front...I'm guessing here but, since I remapped my rover wheels to the "8, 5, 4, 6" number keys I should be fine? I use the KAS small ports with pipes for material transfer, which does mean I have to carry an engineer along (he's got a small platform at the front under the nosecone, with a KIS container, that he can ride on).

Plusck, I have KER but have not even scratched it's surface, I mostly use it for flight info, rendezvous, radar altitude, etc. Can you explain how you used KER for testing in this situation?

Thank yous!

Edited September 6, 2016 by strider3

[Plusck]

10 hours ago, Victor3 said:

 

Plusck, I have KER but have not even scratched it's surface, I mostly use it for flight info, rendezvous, radar altitude, etc. Can you explain how you used KER for testing in this situation?

KER's "flight engineer" window gives "thrust offset angle" and "thrust torque" (basically another way of saying the same thing for most designs). Unfortunately it isn't available in the VAB/SPH, so you have to build the ship, launch it on the runway to check the angle, go back and move things about (I put empty fuel tanks on the ends so that I can shift fuel about to see exactly how much weight needs shifting), rinse and repeat.

It's a bit of a slow method. I should probably take a look at the build aid mod (or whatever it's called).

This is what I mean:

Spoiler

0.1° thrust offset - good enough for me now, but still...

Spoiler

By shifting 2.4 units fuel towards the "front" end it gives 0°. I should probably move the most central solar panels a few pixels forward.

However, checking with nearly-empty tanks shows that the thrust offset is 0.1° towards the back when empty. That means the engines themselves aren't centred. Since I'm sure to mess it up if I tried moving them, I'll stick with that... the torque wheels can easily cope with such a small offset anyway, so I can save fuel by locking engine gimbal.

Edited September 7, 2016 by Plusck

[Plusck]

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Edited September 7, 2016 by Plusck
double post please delete...

[foamyesque]

@Plusck: KER actually does provide the torque numbers, though not the angle, in the build windows. You can use that to zero out your offsets.

[Plusck]

49 minutes ago, foamyesque said:

@Plusck: KER actually does provide the torque numbers, though not the angle, in the build windows. You can use that to zero out your offsets.

I'm constantly discovering features of KER. Maybe there should be a manual. Maybe there is a manual that I haven't discovered yet...

[strider3]

Success! I had to make some changes...added the docking port, a large reaction wheel to make the rover more stable, got rid of the Twitches...they were...twitchy? (see what I did there?). instead I went with all RCS for the final descent, added RCS tanks (which I needed anyway, in hindsight), 8 thruster blocks for directional control and 7 Place Anywhere 7 linear thrusters along the bottom, for descent control. Balanced everything out and moved the girder/rover wheel assemblies forward and aft for extra stability. Landed it sweet as you please.