SP-06 Star Ranger
by XLjedi
uploaded 2017-06-24
(updated 2018-07-27)
stock spaceplane
#Star #Ranger #Interplanetary #Stock #SSTO

1.4.5 Craft File Update

• Auto-retract equipment on bay door closure
• Flight Tested and 1.4.5 Approved!

  • Type: SPH
  • Class: spaceplane
  • Part Count: 53
  • Pure Stock


The Untied Technologies SP-06 Star Ranger interplanetary space plane. Don’t forget to bring snacks! …you may be gone for a while.

A stock aircraft called SP-06 Star Ranger. Built with 53 of the finest parts, its root part is mk2Cockpit.Standard.

Built in the SPH in KSP version 1.4.5.

Demo Flight

Flight test in 1.4.1 using the basic documented ascension parameters as noted in the blueprint. Assume a 10° climb attitude (watch me point to the 10° line on the Nav Ball in the video) after takeoff, full throttle, and don’t touch anything til you run out of air.

Exhaustive Design Notes

Simple Design?

It actually took 3 weeks of agonizing over TWR, Delta-V, weight/balance, flight performance, etc… and no less than 27 design iterations, with at least 3 complete start-overs on wing design to finally arrive at this craft. Slide the rear landing gear forward or back even a fraction and your takeoff rotation speed changes dramatically! Right now, it’s exactly where it needs to be. Not too far back (preserving a takeoff rotation at 110 m/s) and not too far forward (preventing a ground strike on takeoff and potential loss of an engine). Every part was selected and positioned for a reason, if the part was deemed frivolous or served no purpose other than it looked cool, it was discarded. Throwing out nifty wing designs was a painful process, but the payoff in TWR and actual performance justified the omissions. …and now I finally hope to fly to planets beyond the moons of Kerbin!

The Star Ranger Project is my first design involving a Quad-RAPIER engine cluster. After transitioning from a rather nimble Dual-RAPIER Whiplash design (SP-04 Starlance) my expectation for doubling the RAPIER count was to trounce the prior performance benchmark. I wanted to see blistering performance as opposed to a space utility vehicle that has to be coerced into stable orbit with overly complicated ascension parameters. Designs that I scrapped along the way continually failed to meet this critical performance requirement. Thrust-to-Weight Ratios (TWR) of less than 0.9 at liftoff just did NOT feel like a high performance jet rocketing into the atmosphere. Several design iterations were just lacking in this respect and would experience a noticeable drop in acceleration during ascent which seems to (logically) kick-in near the Mach 1.0 barrier (330-350 m/s range). The final Star Ranger design, with a fully loaded Mission Bay, scores a very respectable TWR of 0.98 and the performance curve does not fall off during the sound barrier transition; it just powers right through it. I love the look of that laser straight exhaust trail while ascending!

The Naked Sport-Bike Variant
In an effort to further maximize performance by cutting weight, at one point I completely dropped the frivolous Mission Bay in favor of an open engine/equipment area. I also scrapped the twin vertical stabilizers as the Advanced Inline Stabilizer had more than enough torque to manage yaw and still does frankly. The shedding of weight did allow the Ranger to hit the 1.0 TWR target! …but in the 27th and final iteration, and after a fair amount of flight testing, I brought those two elements back. The stabilizers came back first because I did notice a more stable flight experience having them in place. Although, I opted for the fixed stabilizer fins as opposed to the heavier one’s with rudder control surfaces that really did not contribute to the flight dynamics. If you’re contemplating moving the fins, I can tell you it seems to fly better with them closer together as they are now. The Mission Bay came back for two reasons 1) improved airflow/drag at 1200-1400 m/s speeds during ascent and 2) it makes swapping out equipment for varied mission roles far easier. In both cases, the small 0.02 TWR tradeoff proved to be worth it!

Now reach for the stars! …err well, planets anyway, reach for those!

After reviewing several SSTA designs I set my Delta-V goal in the SPH for 14,000. The nuke engine also proved to be the only viable choice for interplanetary travel. I tinkered with the idea of a bank of Ionized Xenon gas engines at one point, but refueling the Xenon gas was an obstacle without a stock part solution. The final design scored an impressive 14,281 Delta-V which exceeded my expectations for a Mark 2 cockpit design carrying a hefty array of equipment. I have left Kerbin orbit with 1,300 liquid fuel, flown to Minmus, and landed the Star Ranger to refuel on an ore deposit with 500+ liquid fuel still in the tanks!

Orbital Delta-V

Depends on your frame of reference… After Kerbin ascent to 100km orbit and zero oxidizer, the remaining 1300 liquid fuel for the nuke drive should equate to about 2100-2200 Delta-V for the ride to Minmus. After refueling at Minmus you won’t burn too much fuel getting back into orbit so your Delta-V would be higher there. Additionally, if your mission did not require oxidizer you would see a modest Delta-V gain for leaving the Ox-tanks empty (lower mass for interplanetary travel). From a low Minmus orbit you should see 4100/4300 Delta-V for with and without oxidizer respectively.

Above we see refueling ops being carried out on Minmus! With a full tank here we can reach out to most (possibly all?) places in the Kerbol system. Takes a long time to drill and refine. Those fuel cells come in handy to keep the ops going 24/7 so you can time warp through it without too much pain and the heat radiator should keep the temps under control. Having an engineer on board for the efficiency boost doesn’t hurt either! Do not forget to TURN OFF THE FUEL CELLS when done refueling. They will eat your fuel in the time warps of interplanetary travel.

Mission Variant B as in Bigger

Although not quite as nimble, the slightly larger Star Ranger SP-06B model pictured above was also recently able to achieve a stable Kerbin orbit with 1,300 liquid fuel available for the nuke engine and may prove itself to be useful with time. Keeping all the equipment of the original and adding the extra weight of a crew cabin, docking port, RCS system, monopropellant and some additional liquid fuel storage, knocked the TWR down to 0.82 with Delta-V at 14,281. Notice the rear wings were widened for some additional lift area. Extra ailerons were added due to the extra width, and not pictured are a pair of Type 3 wing strakes on the underbelly that provide a couple hundred extra liquid fuel.

Thanks for downloading! Go try it out… and if you like the design, your up-votes do make me happy and are a great way to encourage posting another design. ;-D

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