Wanted: Tugboat

[zapman987]

Trying to build a space station, and I launched a few different compoents, but some didnt have either RCS (oops), or enough fuel to rendezvous.

Figured ok, I can make a tugboat of out 2 ships docking. Bad idea. Blew up 2 ships completely.

So, is there a way to move a ship around while docked to another ship safely?

[boomerdog2000]

What docking ports do the components have? Clampotron Sr.s would be the most stable but you can generally get away with normal clampotrons as long as you don't accelerate too fast. Also how did the ships explode completely? That sounds fairly difficult to do.

[zapman987]

I think this connection was a set of standards. Ok so trick is acceleration. Thats probably why.

Explode after they crashed into each other in unintended ways with half full fuel tanks. With engines firing. Probably not too hard. I do it all the time trying to get my first stages separated and igniting second stages.

[Specialist290]

Yeah, once you close to less than 200m or so, it's best not to rely on your main engines unless you have some major velocity differences you still need to kill (in which case you probably messed things up somewhere earlier as well). For the most part, you want to rely on fine-tuning your approach with your RCS system as you close the distance, gradually slowing yourself down as you approach until your docking ports start pulling on one another.

EDIT: And yes, docking ports tend to compress under acceleration. They don't handle high accelerations very well, for the most part.

[HeadHunter67]

Tugs really aren't meant for maneuvering using engines. If you're that far away, a payload assist module (like the MOMS OAM) is a better choice - though that's not a bad example of what a tug could be.

A better tug for short-range work (such as maneuvering station components into place) could be better built with an RCS fuel tank, a probe core or RGU, the most powerful reaction wheels for that size, a battery and some means of power generation, and then place a balanced set of RCS thrusters out on girders for extra moment.

[Frederf]

One thing you can do is put multiple sets of RCS thrusters for different loadings and switch between them in various situations. RCS Build Aid and a sample X ton weight can be used to mimic typical tug loads.

[Seret]

A better tug for short-range work (such as maneuvering station components into place) could be better built with an RCS fuel tank, a probe core or RGU, the most powerful reaction wheels for that size, a battery and some means of power generation, and then place a balanced set of RCS thrusters out on girders for extra moment.

This works for small components, but for handling larger sections like you might get on a space station I find it's difficult to get balanced if the component you're moving doesn't have RCS thrusters too (which would somewhat defeat the purpose of the tug). The problem is the mass of the section you're moving is so much more than the tug, so RCS impulse tends to cause it to rotate instead of translate. For handling bigger lumps of metal a larger more massive tug can actually require less work from the RCS system to move a given distance, as it isn't continually compensating for unwanted rotation.

I tend to use a machine about this size:

...for all my orbital handling. I tried smaller RCS-only tugs for station assembly, but they actually ended up chewing through more RCS fuel than these bigger ones do. That might also be because I'm fairly crap at docking, of course.

[HeadHunter67]

for handling larger sections like you might get on a space station I find it's difficult to get balanced if the component you're moving doesn't have RCS thrusters too (which would somewhat defeat the purpose of the tug). The problem is the mass of the section you're moving is so much more than the tug, so RCS impulse tends to cause it to rotate instead of translate.

That is why, instead of mounting the RCS flush against the hull, you put them out on girders. This increases how much torque you have available. It doesn't improve translation per se, but it should reduce the rotation. Likewise the need for a powerful reaction wheel on the tug. But I do agree that really large work may require a larger tug.

Next time I load up the game, I'll try to cobble together something that shows what I mean.

[zapman987]

Ok so got an answer I didnt expect but very helpful! Hadnt goten much into space station construction (this is the first) so hadnt even thought of moving stuff around later.

[Seret]

Next time I load up the game, I'll try to cobble together something that shows what I mean.

No, I get what you mean. It's a bit of a bodge, but if you knew the size and mass of the objects you'd be handling I agree it would work ok. I tend to make sure I haven't got anything forward of the docking port, especially if I'm going to be docking with a station that's likely to have all manner of sticky outy bits. I've collected solar arrays before, but luckily never had a big smash.

Edited November 11, 2013 by Seret