What exactly is a space tug

[Mike0190]

So I'm pretty good at the game I just don't know a lot of the lingo and what everything is exactly and it's purpose so I've been reading and watching videos because I want to build a space station around Kerbin and I've read a lot of people mentioning that space tugs are either a necessity or extremely helpful.. I'm just curious as to exactly what it is and its function,

Thanks in advance for the assistance.

[Red Iron Crown]

It's a reusable propulsion system, sometimes with tanks built in, sometimes not. The classic example is using nuclear rocket engines, which are both very efficient and very expensive, so you want to reuse them. A nuclear tug lets you use the same engines over and over to move multiple payloads around.

[Mike0190]

Ahh I see so let me see if I have this idea correct. Say you have a nuclear tug in low Kerbin orbit and your space station is in a higher orbit.. You would launch x part for your space station, dock with the tug and then let the tug take it to the space station?

[Feradose]

Yes, thats how its used.

[Lord_Demon]

You could also make a tug vessel. Small plane with fuel efficient engines (nukes?) and docking port. Get parts into the orbit, dock with tug, and move to final location. You can also equip your tug with the grapple, and use that to move parts and junk that does not have docking ports, but that is harder.

[capi3101]

You can also use it as a re-usable transfer stage for certain destinations. Back in 0.21 or thereabouts, I used a system of nuclear tugs (the Thunderbolt 7 series) that would take landers launched from Kerbin and carry them on to places like Duna, Ike and Gilly. You do have to dock refueling missions to the tugs, but the price of a tank of gas or two is usually far less than that of such a system - especially if you can set things up to where you can deliver the fuel to the tug via an SSTO spaceplane (the fuel delivery in that case just costs you the fuel involved, provided you can land the plane back at KSC safely).

The key thing with tugs - you have to be able to comfortable with the procedures of rendezvous and docking, and you have to make sure that the connection between the tug and the paywad is secure (otherwise it has a tendency to wobble). There are several mods that would help with both; off the top of my head, Docking Port Alignment Indicator is extremely useful. I think you can use Quantum Struts to make strut connections on the fly - I don't use that one myself - or perhaps KIS/KAS, which I do use (but haven't tried to use to make a strut connection). There's also the old multiple-docking-ports-at-once trick, with which DPAI is also useful.

[ajburges]

You can also use it as a re-usable transfer stage for certain destinations. Back in 0.21 or thereabouts, I used a system of nuclear tugs (the Thunderbolt 7 series) that would take landers launched from Kerbin and carry them on to places like Duna, Ike and Gilly. You do have to dock refueling missions to the tugs, but the price of a tank of gas or two is usually far less than that of such a system - especially if you can set things up to where you can deliver the fuel to the tug via an SSTO spaceplane (the fuel delivery in that case just costs you the fuel involved, provided you can land the plane back at KSC safely).

The key thing with tugs - you have to be able to comfortable with the procedures of rendezvous and docking, and you have to make sure that the connection between the tug and the paywad is secure (otherwise it has a tendency to wobble). There are several mods that would help with both; off the top of my head, Docking Port Alignment Indicator is extremely useful. I think you can use Quantum Struts to make strut connections on the fly - I don't use that one myself - or perhaps KIS/KAS, which I do use (but haven't tried to use to make a strut connection). There's also the old multiple-docking-ports-at-once trick, with which DPAI is also useful.

I planned to take it further with a reusable staged interplanetary tug. Then 1.0 came.

Two tugs. After the ejection burn, one is nearly emptied, detaches, and burns retrograde to cancel its ejection. The second tug handles insertion burn at target and the return trip. Connections by docking port so it can be reassembled and refueled on return.

With 1.0 I'll probably salvage the ejection tug idea, but mining will necessitate a rethink of the 2nd stage. It will likely stop being for general use and instead for ferries with refuel planned. My career game is still over 100 days from Duna window and I think I may have ISRU unlocked in time for even that mission. (Without the MPL)

[cybersol]

The other common type of tug besides a nuclear tug is an RCS tug. These just have a decent amount of RCS and control wheels and are most often used to assemble a space station from individual modules. You can make them fairly small, and you can even use a pair of them to get better thrust balance while towing and docking the modules.

[Snark]

Back to the OP's question: Generally speaking, a tug is a ship that's optimized for moving payloads in space. Typical characteristics:

1. Is designed never to land

2. Has the highest Isp possible

3. Usually is low thrust to save on engine mass (since if you're not landing or taking off, you can do long slow burns)

[magnemoe]

One tricks I use in 1.02 is to have an LV-N tug and an base with ISRU and science lab. Tug takes the base all the way to target and where act as an local tug, first mission is to move and handle an small science lander. Later on it will handle follow up payloads

[Captain H@dock]

These are space tug:

(middle ship. chemical = not so efficient)

Nuclear = more efficient. (these are mock-up, they lack electricity and RCS)

[Red Iron Crown]

Oooh, sharing tug pics? Here's my 1.0 4xLV-N nuclear tug design, all LF tanks with enough fuel to push a full orange tank from LKO to low Mun orbit and return it to LKO without refueling: