Long-term Laythe - Part 24.5

Tweaking Tugs

Here's a short episode on the upgrading of the Nuclear Tugs that are used by the Laythe expedition. As mentioned before, there are some things I'd like to see incorporated into Kerbal Space Program because they would make the game more fun. One of those things is giving kerbals the ability to do some limited construction in space by being able to add struts to a ship, or cut loose parts of a ship. Yes, I understand that the KAS mod apparently allows this, but I try to run with a few mods as possible (for various reasons, such as ease of upgrading over version changes, fewer bugs, working from a more common and understood baseline of parts, etc.). But I still mention things I'd like to see included in KSP just in case SQUAD is paying attention and might be persuaded to do so.

So here's a little imaginary mission of space construction showing what I'd like to be able to do. Below, Jebediah Kerman lifts off on a Reusable Rocket in the capsule of the Tug Refurbisher payload.

The Tug Refurbisher mainly consists of two Rockomax X200-32 fuel tanks (one of which will become part of the finished Tug) to refuel the Tug. I also figured that allowing the kerbals to attach struts should probably require that there be raw materials available. Lacking a Standard Strut Parts Pack part, I've represented the raw materials by struts that I have attached to the Refurbisher -- several attached to small cubic octagonal struts on the top tank, and several attached to small cubic octagonal struts attached to the inside of the radiation shields (those 2x2 plates) at the back of the Refurbisher.

The mass of the Tug Refurbisher is such that the Reusable Rocket can get it into a 110 km orbit (where Nuclear Tug 8 awaits) and still have enough fuel in the sustainer (about 220 units of fuel) to allow the sustainer to return to KSC and land on its engine flame.

Below, Nuclear Tug 8 moves in to dock with the bottom end of the Refurbisher (both are equipped with standard docking ports there). I had the Nuclear Tug perform the rendezvous and docking because it is much lighter (no need to waste fuel moving all that heavy fuel around; the Tug's tanks are mostly empty after its return from Laythe).

Once the Refurbisher was docked, I decoupled the rear tank and then turned the Tug around so that the remainder of the Refurbisher could dock to the forward end of the Tug (everything is upside-down by the third part of the image below). Again, two regular docking ports are docking at this point.

Next, Jebediah got out and EVA'd over to connect struts between the main tank of the Tug and the new Senior docking port there. The 2x2 structural plates represent radiation shielding. Remember, those LV-N nuclear engines have previously been used to take this Tug to Jool and back to Kerbin, so they will be 'hot'...and I wanted Jeb to be happy working near them. These shields were attached to the tank using cubic octagonal struts, and we'll have Jeb remove them at the end of the procedure. You can see Jeb getting a strut from the bunch mounted on the inside of the radiation shield.

We see that Jeb has a new strut in place (isn't Photoshop wonderful?).

Below, Jeb finished all the struts between the two tanks (well, between the main tank and the new Senior docking port there). He then moveed up (I've flipped the ship over to point the other direction now) and got to work on the forward structure. (What I've done here is cheat a new version of the ship into place...since although I don't have the ability to install struts, I DO have HyperEdit to help me tell my story).

Next, Jeb installed the struts between the main tank and the new Senior docking port that became the new front port of the Tug. Struts for that operation were attached to the sides of the Refurbisher's main tank.

While Jeb was working on those forward struts, I also imagined him using his cutting torch to chop through most of the cubic octagonal strut legs that were holding the stacks of probe cores in place (but not yet completely detaching them). You may recall that I added all these probe cores to my standard Tug design a couple versions back when pointing our ships using RCS was very wasteful of monopropellant. These 18 probe cores were added to provide torque to help point the Tug so the RCS fuel could be saved for doing translation-only maneuvers. The need for this technique was rendered unnecessary when SQUAD finally gave us non-capsule/probe parts that produced torque. There is an ASAS unit in the middle of all those probe cores that will nowadays provide this Tug with all the torque it needs. Sometimes I do get what I wish for.

Once all the struts were in place, it was time to dump the garbage. So Jeb did a couple burns to raise the apoapsis of the Tug, and lower its periapsis a little way down into the atmosphere of Kerbin.

Then Jeb hopped out and quickly cut loose the cubic octagonal struts that were holding the stacks of probe cores and the radiation shielding plates to the Tug. He was working against the clock here, because after a couple aerobraking passes, the ship would reenter Kerbin's atmosphere. But after the parts were quickly cut loose, Jeb returned to his capsule and went through the first aerobraking pass (which lowered the apoapsis back to 110 km), and then did a maneuver to circularize the orbit. All the discarded parts should, of course, eventually enter Kerbin's atmosphere and burn up (so I deleted them).

With the refurbishment completed, Jeb transferred all but about 20 units of fuel from the remaining tank of the Refurbisher into the Tug's forward tank, and then separated the remainder of the Refurbisher. The Tug now has stronly-strutted Senior docking ports at both ends, and is almost fully fueled.

Jeb then used the remaining fuel in the Refurbisher (assisted by RCS...there was plenty of RCS fuel left) to deorbit the Refurbisher and target it for a landing at KSC.

Other Option

The advantage of the procedure above is that it involves fun space construction, and has better continuity of storyline (I like the idea of having Tugs that have made the trip to Jool and back again multiple times). The disadvantage, or course, is that I don't have the tools in vanilla KSP to do this, and that the Tug is somewhat clunkier with a couple extra docking ports in its structure.

The alternative, of course, is to just deorbit the Tug and return it to KSC for refurbishment, and then claim that a new Tug I launch is that refurbished Tug. All of the used Laythe Tugs I have in Kerbin orbit (except for the oldest, Laythe Tug #3) include parachutes on their nuclear engine nacelles (in case of the need to recover the reactors during a launch failure). These parachutes are sufficient for recovering the whole Tug if one is careful. It starts with a deorbiting burn (below).

The potential problem is that the shock of the parachutes opening can be strong enough that a nuclear engine could snap loose from the ship and crash onto the surface of Kerbin. If the Tug had enough fuel, engine firings could be used to decrease the shock of the parachute deployments...but these Tugs don't have that much excess fuel. I originally worked up a procedure for deploying the chutes in opposing pairs so that the ship needed to survive the shock of only two chutes opening at once.

But now that we have tweakable parachutes, I have one opposing pair set to fully deploy at 600 meters, and the other two set to deploy fully at 500 meters. So, just wait until the Tug gets slowed to below 400 m/s after entry, then pop all four chutes. That way all four chutes get to help slow down the ship when they are reefed, and then first one set fully opens, and then the other set. This prevents any environmental embarrassment.

So for now, I'll land my obsolete Nuclear Tugs west of the KSC where they can be picked up and refurbished for re-launch. Not as much fun as construction in space, but maybe I'll get that some day in vanilla KSP.