juzeris

Thanks! Coming back to our crew, part 2 of the journey is complete, and the spacebird is now landed at Laythe. Currently the crew is starting to drill, thinking where to go next (probably Bop), and calculating how much oxidizer to load up on. Things learned during this part: -The performance of this craft depends a lot on how much oxidizer is loaded: less oxidizer - more delta-v, less burn-time of the high TWR Rapiers. -MechJeb delta-V calculations seem to fail to find the fuel in the wings, so it can happen that firing the engines increases the calculated available delta-V. -Kerbals can climb back in without a ladder (though they mostly need a boost with RCS). -Also, quicksaves are good, but we knew that already.

Well, I've made it as far as Minmus, and the ship is fully refueled, ready to continue the trip. Next stop - Laythe. The lessons of the day include: -Ore for mining is not everywhere, and the button to turn on the overlay is a well-kept secret. (Yes, this is my first mission actually using ISRU ) At least I thought to survey the resource beforehand. -Just because a jet engine does not flame-out, does not mean it's running at full power. I've had my top engine (which is drawing air from the shock cone, surface area 0.9) at almost 50% more thrust than the other ones (which are drawing air from the nacelles, surface area 0.5). Not all the time, though. I'm not set on the order in which to visit the planets yet, but I guess it will be one of the small ones for easy refueling after Laythe, and then Tylo. Don't want to postpone the scary one too much in case I fail.

It all started as an ambitious attempt at the fabled Jool-5 mission by the Kerbal Space Center crew. Complete with huge motherships, landers, heroic docking and maybe rovers. However, misunderstandings, misprocurements and misdesigns quickly snowballed, and, as of this moment, astronauts are boarding a single stage monster which is... still supposed to complete the Jool-5. Simulations (hyperedit) show it should be possible, but the safety margins are very narrow. So the engineering department decided to document the trip just to have evidence in future strategy meetings what happens when the interns are reviewing the designs, and nobody knows who made them in the first place. Bob is saying he saw the KSC cat spend way too much time at the location, but nothing could be conclusively proven. (The mission will probably be presented mainly as a series of accelerated videos, I'm still trying to figure out how to present everything nicely.) As an introduction, we are presenting our craft: Parental advisory: minor clipping, engines firing from within a cargo bay, floating parts (I realize these might disqualify me from the formal challenge, but, eh, this is too much fun not to try it , the only clipping I'm aware of, though, is the partially clipped in landing gear, and the slight clipping of the rapier engines. It is done for the purpose of nicely fitting into a cargo bay however.) She weighs 60 tonnes dry, 127 fully loaded. The launch weight is 111 tonnes, because getting through the Mach barrier has proven challenging with her fully laden. She has an integrated ISRU system, magnetically suspended nacelles which double as vertical landing gear, 6 rapiers, one nuke, a nose lift system and 8 big wings which make her look a bit like a centipede. Fun fact - she is made from exactly 100 parts (because I forgot the probe core). 20 of these parts are the monoprop nose lift system, 19 are SAS units. 36% of her launch cost comes from the 4 RTGs which power her. Those RTGs are the only thing providing electricity, except for the nuke engine when it's firing. Mods: I use MechJeb heavily, however it should not affect the viability of the craft, just compensate a bit for my piloting. I also have Hyperedit installed, which was used for testing but not the actual mission, and Throttle Controlled Avionics, which I am not expecting to use, but, well, the option is there. As of this posting, I have successfully reached Minmus, so no guarantees how it will turn out. Video of the first part coming up sometime today.

Well, the claw is used simply as a docking port, because radially attached parts create disproportionate amounts of drag, so I didn't want a docking port or two on the missile. The procedure doesn't change as compared to docking ports - the missile comes to the claw, the placeholder station doesn't even have engines or RCS, just reaction wheels. Though, arguably, the ability of the claw to attach anywhere makes it even easier. Or, yes, you could have a small tanker with RCS, if you can be bothered, as maccollo suggested.

Oxfam Missile, somewhat unsurprisingly, submitted for the Oxfam level. I honestly don't know if it's a spaceplane or a rocket, but it's fully reusable, and on the test flight delivered 820 units of fuel (9:11 LF+O mix) to 75x75 LKO. It costs 13 742 at launch, 12 917 dry, and I recovered 6 funds worth of fuel, so total flight cost is 819. So for all practical purposes delivered funds to LKO for 1 fund per unit of fuel including the cost of said fuel. For non-practical purposes, that's 0.99878 funds per unit. Craft file included for those interested: http://kerbalx.com/juzeris/Oxfam-Missile.craft

I'd like to submit my long range spaceplane - the Krau 6 - for consideration for the K Prize. It's a clunky thing with no fuel lines (lots of manual fuel transferring and eyeballing the delta-v) and 150% more parts stacked in the cargo bay than it should be able to hold (still it contains only about 15% of all the fuel carried). It can get you as far as Laythe and back in return for all the hassle, though. In case all that is acceptable, I'm adding some photos from the flight.

I've been working to see if I could improve my time and break that 40 minute barrier, and I finally did it. After several crashes (Bob survived, and has proven he is not a pilot), Valentina did it in 39:58 (F3 screen). The craft is only an incremental upgrade over the old Dartagor, aptly named Dartagor 2 (download link). It is yaw-unstable at high speeds, but anything I'd put up to fix that kept exploding at the speeds it's going, so it ended up not fixed. Honestly, I'm not certain I can break 39 minutes with anything I'd be willing to assert is an 'aircraft'. Footage of the flight:

After running some tests and melting off some 20 canards, the pilots at Abstract Aerodynamics figured they can get a pretty fast "possibly maybe survivable" trajectory with the Puny Tim. It runs very red the whole way, and is risky, but with practice can be done. So here's the footage of our run to KSC2 in 11:15, for 59.36 fuel (F3 image). Not THE most economic, but still pretty good. Running the exact same Puny Tim as in the previous attempt without any modifications. The landing is a fluke, I just messed up, fell down, and survived, but came out pretty good. Also, yes, I did this just to mess with the scatterplot.

I had a go at the fuel economy thing too. The craft came out pretty well, the piloting could probably use some improvement. Getting there took a whole quarter of an hour (15:00), minus maybe a couple of seconds while I was trying to remain upright but already stationary, but managed it in 45.9 fuel (F3 image). The craft itself - Puny Tim (download link) - features just one wheel, on which it balances with the use of gyroscopes (SAS), and variable tilt wings (toggle with 3) for safe take-off and landing. It doesn't have any control surfaces, but with enough torque to unicycle across the KSC, who needs them. Also please enjoy our flight footage:

Please note all the below is just my opinion based on my probably flawed understanding of KSP physics. Yes, the precooler does have an emissive constant of 0.95, which is the same as wings, control surfaces and the shock cone intake, and only slightly higher than mk3 (0.87), mk2 (0.8) parts and engines (0.8, 0.83 for nukes). It's significantly higher than rocket parts (including mk1 LF tank), cockpits and sensitive equipment, but it's probably not gonna pull its weight on a rocket as a radiator, and the thermodynamics benefit is marginal on a spaceplane. To put it into numbers, given a constant conductive energy flux into the part and the formula above, a precooler emits heat as if its temperature is (0.8/0.95)^(1/4)=~4.4% higher than an engine of the same temperature. Compared to the usual part threshold of 2000, that's 1915, which is almost completely red on the temperature gauge. The actual benefit will be even smaller due to the fact that conduction is not immediate and it will be at a lower temperature than the heating part. I personally have exactly one plane which stabilizes in terms of temperature at above 1900 and it's engineered and flown to do specifically that, and scenarios where a part goes above 1900 but survives are rare in my life. It's either way too much heat or manageable heat. And these are the only times where it would make a difference. Also, for short term heating, a part with a high thermal mass (for example a full fuel tank) will probably absorb more heat which you can dissipate later than the precooler will radiate away due to the higher emissivity, though I don't have the numbers to back that up, just my intuition. Your mileage may vary.

Excellent heavyweight Falconer, inspired me to make another entry. Nowhere near as big as yours, but it has it's own charm, I'd think. Thus presenting to you the Spinoctyl, type J. Clocks in at 25.1t wet on the runway, turbojet and twin nuke powered, has plenty of mileage provided you can pump that fuel around... Yes, we have no idea how much delta V it has precisely. Also here's the photos from our demonstration flight, where Jeb took it to orbit, and then safely landed it.... well... somewhere. Is that even Kerbin? Engineer's note: I (personally) don't subscribe to the "precooler cools thing" belief, but it's an excellent intake which is completely sufficient to power one turbojet. And then you can mount a proper nose cone instead of having a blunt intake screaming through the air like a warhammer. And to embed albums from imgur, just type imgur in brackets, then the 5 symbol code from the url, and then close the tag, so, for example, if I'm embeding http://imgur.com/a/8YhVP, then it goes like this: [IMGUR]8YhVP[/imgUR]

Yay, thanks for the dishonorable mention. Regarding autopilot for a plane, the only thing it does better than a real pilot is maintain heading while cruising - if you fly stock without SAS and use trim to maintain pitch, you generally get roll drift, if you fly with SAS, you're constantly pitching up due to SAS not adjusting for the curvature of Kerbin. So you end up using the controls to constantly pitch down a bit (for my entry I couldn't leave it alone for more than 15 seconds or it'd start gaining altitude like crazy), which, at least for me, is the most fun thing to keep doing for 10 minutes. I don't think using smart a.s.s. from Mechjeb gives any other benefits, esp. when landing or climbing, I honestly haven't tried other autopilots though. Just my 2 cents. Oh, and, yes, I actually do have an entry! Flew the distance in 11:23 using 183.53 units of fuel (F3 image link). And here's the craft file as well (link). A couple of additional questions regarding what's an exploit in your book (didn't use any of that on this entry, so I'm perfectly fine with a 'no' ): -Would placing landing gear in the fairing be OK? -Is closing the air intake to spin up the jet dry on the runway an acceptable shenanigan? Thanks for the nice challenge!

I'd like to submit an entry too - the Fierder 3 (download). It's a bit on the heavy side for single turbojet SSTOs, weighing 15.4 tonnes at launch, but it still has quite a bit of delta-V left once you get it up there (in the demo attempt I had 1351m/s left once in a 80x80 orbit). Watch those wings though, they get crispy real quick, especially when empty.

Well, to be fair, the turbojet was strictly better than the rapier before 1.0. Things change, however, and since it is actually not a very hard question, let's try to answer which is better and when. Starting from the simpler aspects: The Turbojet (1.8t) is slightly lighter than the Rapier (2.0t), but the difference is not very significant for atmospheric vessels, where drag dominates the speed equation and not mass. It might become more significant for a Nerva powered SSTO where the Rapier rocket mode is not used, not sure. The Turbojet has an alternator (it generates electricity), while the Rapier does not. The Rapier has a back stack mounting point, while the Turbojet does not. The uses are limited to shenanigans, because otherwise it would block the engine, but, personally, I often end up using it. The Rapier seems to generate slightly less drag (1.299081 0.9353406) than the Turbojet (1.275294 0.9736242), I haven't tested this though, the data comes from this post. The Turbojet has a better fuel efficiency (Isp 8000) than the Rapier (Isp 6400) for a given thrust level. I calculate that as using 80% of the fuel a Rapier would use. Both jets are still very fuel efficient however. (Credit to Red Iron Crown for correcting this ) The Turbojet uses a higher proportion of air to fuel (15:1 vs 12:1), this may or may not mean more intakes producing more drag for a given level of thrust, depending on your design. I cannot really comment with any authority on the thermodynamics of the engines, the parameters seem fairly similar and they both appear to produce a similar level of heat for a given thrust level. And, of course, most importantly, engine power - it is calculated as thrust*velocity coefficient*atmospheric coefficient, where thrust for the Turbojet is 180 and 140 for the Rapier. Of course, the coefficients are the interesting part. These are saved as curves in the .cfg files in your KSP directory, but for simplicity I've rendered them into graphs below. Let's start with the atmospheric coefficient. The graph below shows the relation between the coefficient and atmospheric pressure. The relation is logarithmic, however I could not figure out how to make my graph logarithmic, so apologies. According to the wiki converting between pressure and altitude is not as straightforward as it used to be, but it includes a handy table. From the graph we see the Turbojet has a better coefficient up until about 0.08, which, based on the table, is somewhere a bit below 15km altitude, and the Rapier stays significantly above the Turbojet the rest of the way. Turbojet is red, Rapier is green. Next up, the velocity coefficient. I've scaled the graph to adjust for the Turbojet's higher thrust, it's easier to look at that way. The speed is in Mach, and I believe the conversion to m/s varies with altitude, but a general assumption of about 300m/s per Mach at 20-25km should hold. Here we see the Rapier overtakes the Turbojet at somewhere a bit below Mach 2. Turbojet is... grey? Rapier is green. Conclusion/tl;dr: The Rapier appears to be strictly better in terms of performance when flying above 15km and over 600m/s, which should be most of the cases when you actually care about the engine type. The turbojet has the benefit of being more fuel efficient, but you'll probably make up for the efficiency to some extent by going higher and faster where you need less thrust and the journey is shorter (by time). Please let me know if I got something wrong somewhere. Sources and tools: game files, the KSP curve tool by MuMech, Gimp, and a calculator. You can find some intermediate graphs here, if you want them for some reason.

I'll bite . Since my first entry was just a bunch of parts crumpled together and tucked into a cargo bay, I figured I should do a proper circumnavigation anyway. Thus, Abstract Aerodynamics present to you the newest member of its hypersonic sportsjet line - the Dartagor (download link). This 13 ton beast sports a cozy cockpit certified for one Kerbal, a wingspan of 12.3 metres (perfect for any garage), an operating altitude of up to 30km (regulatory limit), sustained cruise speeds of up to 1640 m/s at 25km altitude and a bit higher top speed (we clocked it in at 1680 m/s) at lower altitudes for showing off, just don't keep the twinned powertrain running that hot for long. Our trademark engine housing also ensures a smooth experience by directing noise away from the cockpit and helps keep the engines below melting point in flight. While we won't say it is a simple construction, it is almost completely organic and contains only minimal part clipping. We also included a handy parachute for more convenient parking. Oh, and it also has global range, with full circumnavigation times as low as 41:44 To fly, the first tumbler switch toggles the engines, the third tumbler opens and closes the engine housing, and the tenth tumbler is for alternative parachute activation. As usual, we included extra tumblers for showing off, because nothing says 'pro' like flicking tumblers. EDIT: We also have an 'endurance' version of the Dartagor (download link), with significantly expanded fuel storage. Of course performance suffers slightly, the cruising speed is 10% lower, but Jeb just flew four times around the world in it in just 3:02:33. He even caught the whole event on his phone camera: I messed up my settings, so the video ended up cropped, and, of course, both the fuel screen and the delta-v screen are cropped off. You can still see the vehicle mass decreasing in the vehicle window, which proves I'm indeed using fuel. There is also a heading control (MechJeb smart a.s.s.) screen open in the cropped off area, I kept it at a 1.2 degrees angle of attack for most of the trip. The F4 screen is also added: