Need help on Ideas to build a Tug

[jbdenney]

I am trying to build a Tug to move Asteroids. The core section will stay in space once it is build and hauled into orbit so it can be used several times and can be refueled in space. It is a Cupola with a docking port on the nose (Refueling and Crew Transfer) a singel large fuel tank with 4 smaller fuel tanks attached radially with a Mk-55 Thud attached.

I understand that when moving larger Asteroids that it is better to pull the body instead of pushing it. My problem is that this requires a grabber attached backwards on the central tank so I can back up to the asteroid and grab it and then pull it. The issue is that with a grabber on the bottom I cannot attach a stage to the bottom of the core since there is no nodes on the grabber to hook a decouple to.

I need ideas on how to attach a lifting body on my core (83 tons) to get it into orbit. 

 

Bruce

[OHara]

You can push, placing your thrusters as close as you can to the carried mass.  

The advantage of pulling is that the asteroid tends to pull the joint at the grabber straight when you apply thrust, where the force of a pusher can bend bend the joint.  Then the thrust stays in line with the massive load.
If, on a pusher system, your asteroid load swings so that its center of mass goes to the side,
so far that the gimbal on the pusher cannot aim the thrust at the center of mass,
then you lose control. 
So if you want to push you should place the thruster close to the load, so the gimbal can more likely aim at the center of mass even after it wobbles a bit.

For pullers, you would probably want to put the grabber in an 'interstage' fairing; attach the lower stages to an 'interstage node' of the fairing and then close the fairing shell around the grabber to extend down to the lower stage.  For pullers, remember to make the thrusters clear the asteroid, because KSP coarsely simulates the force of the rocket exhaust if it hits the asteroid.  (You can avoid this by moving the thrusters far away from the asteroid to fool KSP into failing to notice that the exhaust hits the asteroid.)

[Rhomphaia]

Flip it upside down and attach the launch vehicle to the docking port on the nose?

[bewing]

Are you familiar with fairings? Do you have Advanced Tweakables turned on? Do you know what an interstage fairing is, and what happens when you show the nodes in a fairing?

[jbdenney]

Ok - looks like the faring should work - thanks.

[Klapaucius]

6 hours ago, jbdenney said:

I am trying to build a Tug to move Asteroids. The core section will stay in space once it is build and hauled into orbit so it can be used several times and can be refueled in space. It is a Cupola with a docking port on the nose (Refueling and Crew Transfer) a singel large fuel tank with 4 smaller fuel tanks attached radially with a Mk-55 Thud attached.

I understand that when moving larger Asteroids that it is better to pull the body instead of pushing it. My problem is that this requires a grabber attached backwards on the central tank so I can back up to the asteroid and grab it and then pull it. The issue is that with a grabber on the bottom I cannot attach a stage to the bottom of the core since there is no nodes on the grabber to hook a decouple to.

I need ideas on how to attach a lifting body on my core (83 tons) to get it into orbit. 

 

Bruce

A simple quick fix as well is to mount two engines on nacelles the side of the tank facing the other direction.  Attach a decoupler to each engine and put on a nose cone on each for launch which you can then dispose of once out of the atmosphere.   You can then simply attach to the asteroid, shut down the rear engine and fire up the other two and start pulling.  There are pluses and minuses to this solution, but it passes the Keep It Simple test.

Edited May 17, 2020 by Klapaucius

[jbdenney]

The solution I found is to mount Thuds on the sides of fuel tanks that are mounted radial on a central fuel tank. No other engines are on the tug. I have the grabber mounted upside down on the rear of the central tank. I had no issues backing up to the Asteroid grabbing and then be able to pull hte asteroid. The only issue I had was to get it through my head that prograde and retrograde were now backward on the NAV BALL.

My major issue is getting enough fuel on the Tug after it is in orbit. I can refuel the tug in orbit but even with that, once I grabbed the Class C rock my mass went up so much I did not have enough available Delta V to get the rock back into Kerbin orbit (not to mention into orbit around Munmus)

I need a tug with enough DeltaV that I can grab a class E and pull it back into orbit. I don't need  the tug to re-enter with it as my plan is to leave it in orbit, refuel it and then go get the next rock (saving money). The only issue I have is having to match INC on an incoming rock which means I may need to to a big inclination change and then refuel again before I go chasing the rock. Unfortunately I have not been able to make CARGO/FUEL hauler SSTOs work. I watch the tutorials and make the same build I am shown and try to follow step by step launch and I just cannot get a Heavy SSTO into orbit so I have to use expendable fuel haulers so they have to be cheap. Even at that my Tug just does not carry enough fuel.

BTW - I am only using stock parts including Making History and Breaking Ground. I knwo there are heavy lifting mods out there but I dont want to get into the "MORE MODS" addiction.

[Cavscout74]

11 minutes ago, jbdenney said:

My major issue is getting enough fuel on the Tug after it is in orbit. I can refuel the tug in orbit but even with that, once I grabbed the Class C rock my mass went up so much I did not have enough available Delta V to get the rock back into Kerbin orbit (not to mention into orbit around Munmus)

I need a tug with enough DeltaV that I can grab a class E and pull it back into orbit. I don't need  the tug to re-enter with it as my plan is to leave it in orbit, refuel it and then go get the next rock (saving money). The only issue I have is having to match INC on an incoming rock which means I may need to to a big inclination change and then refuel again before I go chasing the rock. Unfortunately I have not been able to make CARGO/FUEL hauler SSTOs work. I watch the tutorials and make the same build I am shown and try to follow step by step launch and I just cannot get a Heavy SSTO into orbit so I have to use expendable fuel haulers so they have to be cheap. Even at that my Tug just does not carry enough fuel.

I've usually found it easiest - especially for class E's - to just include an ISRU setup on my asteroid tug so it can self-fuel.  With the built-in ISRU, I can make a small maneuver, let it refuel for a few days, make another small maneuver, etc.   Yes, you lose some of the asteroid resources but much easier than launching multiple refueling missions.  Also, despite the low thrust, NERV's work well for me - or multiple NERVs for an asteroid tug.  I figured I'm not going to get good acceleration on a class E no matter what I use for thrust, so I might as well go for higher efficiency. 

[jbdenney]

IRSU - good idea - but new skill I have to learn.

[Laie]

4 hours ago, Cavscout74 said:

With the built-in ISRU, I can make a small maneuver, let it refuel for a few days, make another small maneuver, etc.

4 hours ago, jbdenney said:

IRSU - good idea - but new skill I have to learn.

Asteroid mining is fast -- if you bring along an Engineer,  you can refill even a large vessel in a matter of a few hours. A single drill will provide lots and lots of ore, the bottleneck is refining it to fuel. If you have sufficient power, you can run the Lf+Ox, Lf and Ox converters in parallel.

With a 5-Star engineer, this will provide enough fuel to run one Terrier indefinitely. Or if you have a Rhino to feed, you will need about 30 minutes of refining to run it for a minute. A Two star-engineer will be about half as fast, but still 13x faster than no engineer at all. Check the Wiki for details.

 

 

[jbdenney]

OK - frustration has set in.

I got the tug built with two Drill-O-Matic' Mining Excavator, two Convert-O-Tron 250, two Radiator Panel (large), and eight Radial Holding Tank. I have a pilot, an engineer, and a Scientist.

I got the Class C asteroid grabbed and proceeded to refuel the ship with the Ore and the Convert-0-trons. No problems. I then used up my fuel moving the Asteroid. Still need to move more. Did more mining and and moving On the 3rd mining and refueling cycle suddenly the Drill-o-matic stopped running the Asteroid harvest and once the Convert-o-tron drained the Holding tanks fuel production stopped. At that point I figured that the spot I grabbed had run out of ore so I detached and re-attached at a different spot. No luck. I tried a third spot. Still no luck.

Can a single asteroid produce only a certain amount of ore?

If that is the case  I nave no idea how I am supposed to move a class C or larger asteroid where needed with out having to get a un-affordable amount of fuel to the rock ( I am running career mode).

Am I missing something? I have plenty of power. No sign that the equipment has over headed or broken. Is there something  I can/have to do  generate several cycles of re-fulling so I can get the blasted thing into an orbit?

[Laie]

20 minutes ago, jbdenney said:

Can a single asteroid produce only a certain amount of ore?

Yes.

Right-Click the asteroid and you will see data about it's mass and ore percentage.

Moving the drills to a new location won't help: as long as the drills make contact with the asteroid, they will mine the asteroid. It's just one single ball of resources and it doesn't matter where you tap into it.

[AHHans]

8 hours ago, jbdenney said:

Am I missing something?

Probably. But I don't know exactly what, it might be this (quoted from the Flying Rock Challenge):

Quote

In version 1.9.x there is a bug that affects the mass of small asteroids: #24855 on the bugtracker. Affected asteroids get a mass of 150 t assigned to them instead of the correct value. In the bug report on the bugtracker there is an explanation of a patch that fixes this issue.

Some more general tips:
One thing you did right: never use the  Convert-O-Tron 125 unless you know what you are doing. That thing wastes 90% of the ore you feed into it.
You don't usually need two Convert-O-Tron 250s on spaceships. If one doesn't cut it, then the other one is unlikely to help you more than the increased dry mass costs you.
When moving asteroids you don't have unlimited dV (as you found out). The easiest way to get one into orbit of Kerbin is to grab one that enters Kerbin's SOI anyhow, so that you "only" need to slow it down into an orbit, instead of moving it around to get into Kerbin's SOI in the first place.

 

[jbdenney]

I used 2 Convert-O-Trons 250s to balance the ship. I have 4 radial fuel tanks with thuds in the front. The Conver-o-Trons are mounted on two of the opposite tanks with the drills. I figured if nothing else it would speed up my processing.