'Varia' class Science Dropship -- A multi-planet capable, fully reusable SSTO

[Tempestwrath]

Hi everybody! I've lurked here and made stuff for years, but I've finally decided to upload something for you fine folks. This is the Varia-class science dropship; Coram Technologies' workhorse and premier product. Designed as a multi-planetary landing craft, the Varia is capable of taking off from the Kerbal Space Center and making orbit with plenty of fuel to spare for orbital maneuvers, such as rendezvous and docking with a mothership. Additionally, when fueled in space, it's capable of landing on any point on Kerbin, and re-orbiting itself and re-docking with the orbital vessel. It's certified for usage on the Mun, Minmus, Duna, and Laythe with ease (provided it has a mothership transport it to a stable orbit above), and should be able to easily land and take off from any other moon with similar delta-v requirements. CORTEC does not warrant or guarantee the safety of individuals who wish to use the vessel outside of these parameters, such as on Eve, Tylo, or possibly Vall. Such actions void the warranty of the product and CORTEC waives all liability herein.

Additionally, it works just fine with NEAR, though I typically use stock aero due to it being a baseline for the community. In fact, it can reach orbit with NEAR with more spare fuel than it can with stock aero.

The uploaded version has an almost full scientific suite (minus the atmosphere cone thing, because there's no logical place to put one without clipping it, and I did some VAB acrobatics to ensure that nothing's clipped too badly in this, including the structural fuselage inside the primary fuel tank that anchors the engine pods). Science modules can be removed to provide access with less (sometimes considerably less) technology unlocked.

Ascent from Kerbin is easy, provided you follow these directions!

Engage SAS. Press [3] twice to retract the ladder. Engage engine by staging it, and as soon as thrust builds up enough to lift off the pad, press [G] to retract gear. Ascend to 10 kilometers at full throttle, and begin a gravity turn that puts your apoapsis at 22k~

At 22k and up, your nose should be pointed between 10 and 20 degrees above level. Over 23k it is strongly recommended that you engage RCS, as the vessel tends to veer when steering inputs are made above that altitude, or drift. The RCS adds sufficient control authority that lets you stay pointed forward (and thus keep the jets going) and is well worth the slight fuel cost. After 23.5k lower throttle to 60%. You'll want to gradually back it off to 50% as you keep ascending.

Your goal is at least 30k altitude at 1500 m/s before you switch over to rockets. If you can get this, you're golden for an ascent with roughly 1/3 the fuel left in your tank once you circularize at 75x75. Anything beyond this is definitely possible, but is just gravy. When you switch over to rockets (either manually by pressing [1] to close intakes or automatically via air starvation) switch off RCS, press [1] to close all intakes to minimize drag, and pitch up 10-15 degrees beyond your current heading. Gradually nose back down, once your apoapsis hits 60k until it hits about 80k, and drift to the apoapsis to circularize. I've found tilting up tends to get you through the remainder of the atmosphere quicker and leads to less delta-v loss than a shallower trajectory, but both will get you to orbit just fine.

Congratulations! You're in space. This was after a much less-than-perfect ascent, and I've still got more than enough fuel to do whatever I like in orbit.

On other planets, due to the egglike construction of the ship, descent and landing, and re-ascent is very similar to any other old planetary lander. When landing on Kerbin or Duna, a bit of thrust is required near at the moment of touchdown depending on the fuel remaining, moreso on Duna. It is recommended on planets with atmospheres to open up the intakes on descent to take advantage of additional drag. Additionally, on Kerbin or Laythe (other planets if you're really confident in your ability to re-orbit on whatever fuel you have left), you can forgo a traditional tail-end ballistic re-entry for a nose-in re-entry, using the RCS to keep the craft facing forward until you reach a sufficient altitude to re-engage the jet engines, allowing for some degree of inaccuracy when, say, returning to the Space Center. Just make sure to click on the engines and manually switch them over to airbreathing mode (and to re-open the intakes). It'll be a bit tricky until the craft is propelled primarily by the engines rather than its own inertia, but it definitely works well.

Action Groups:

[1] Toggle intakes

[2] Toggle engines on and off

[3] Toggle ladder

[4] Toggle solar panels

Here are a few pictures of it docked to some ships of mine. These were built, in fact, in tandem with the Varia Project and the vessels' capabilities are designed to compliment one another. I might upload them in the future if there's sufficient interest.

Docked to the Astraeon science cruiser, with a Standard Fuel Pod attached to the back for interplanetary operations.

Docked to the smaller Relias, a simplified science cruiser that lacks the modularity and expandability of the Astraeon for economical use within the Kerbin system.

.craft file for the Varia is available here.

Update :: I have repositioned the Vernors after a lot of tweaking for more efficient usage, while retaining a pleasing (in my opinion, more pleasing) aesthetic. Additionally, I have updated the action groups so that [1] toggles intakes, [2] toggles engine modes and [3] toggles engines, with the ladder moved to Action Group [5]. That file is available here.

Edited August 28, 2014 by Tempestwrath

[Rune]

Awesome aesthetics! I love the curved exterior with the inline intakes. But, because I have built stuff very similar... wouldn't three RAPIERs be enough and get you more delta-v? And in that vein... the kerbals can exit the spacecraft without clipping into the intakes, then get back in in kerbin-like gravity? Seems a bit close on that one. And Vernors, those are totally OP for the size, aren't they?

Rune. I also have to show you my Klaw pods some time, you'll like them.

[FleshJeb]

That's beautiful work. LOVE the aesthetics.

[Tempestwrath]

I tried a version with just three RAPIERs and the TWR was inadequate in Kerbin's lower atmosphere. The current configuration is perfectly balanced to hit 200 m/s precisely when you hit 10k altitude. My three-engine version also had issues maintaining level flight near horizontal when building speed. Remember, this thing has no inherent lift characteristics.

Three was more viable despite the drawbacks in. 23, but with the RAPIER's newly reduced weight, four feels like a sweet spot.

I imagine with a smaller fuel tank configuration, it might work, but I have taken pains to ensure I only have one large primary fuel tank for simplicity of operation. (It does have four smaller tanks in the intakes that help dramatically with balancing the atmospheric and orbital fuel loads, but I have a thing against craft that are overly "fiddly" to operate and re-fuel)

Also, Kerbals can enter and exit easily under all circumstances. I have tested it quite thouroughly. In fact, with the intakes the tiniest bit higher, they cannot.

Vernors for two reasons. The first is I can save space/weight by having my maneuvering thrusters use a single fuel source with my main engines, which did increase delta-v compared to older versions that used monoprop. Additionally, that extra power dramatically increases stability in the upper atmosphere, and that power is quite necessary when attempting to keep the craft oriented forward for a powered re-entry. The older versions got far more squirrely than this one.

I've also used the thing as an orbital tug, and Vernors help there too!

Edited August 27, 2014 by Tempestwrath

[Rune]

I tried a version with just three RAPIERs and the TWR was inadequate in Kerbin's lower atmosphere. The current configuration is perfectly balanced to hit 200 m/s precisely when you hit 10k altitude. My three-engine version also had issues maintaining level flight near horizontal when building speed. Remember, this thing has no inherent lift characteristics. I imagine with a smaller fuel tank configuration, it might work, but I have taken pains to ensure I only have on large primary fuel tank for simplicity of operation. (It does have four smaller tanks in the intakes that help dramatically with balancing the atmospheric and orbital fuel loads, but I have a thing against craft that are overly "fiddly" to operate and re-fuel)

Also, Kerbals can enter and exit easily under all circumstances. I have tested it quite thouroughly. In fact, with the intakes the tiniest bit higher, they cannot.

Vernors for two reasons. The first is I can save space/weight by having my maneuvering thrusters use a single fuel source with my main engines, which did increase delta-v compared to older versions that used monoprop. Additionally, that extra power dramatically increases stability in the upper atmosphere, and that power is quite necessary when attempting to keep the craft oriented forward for a powered re-entry. The older versions got far more squirrely than this one.

I've also used the thing as an orbital tug, and Vernors help there too!

K, don't take his as criticism, because I am going to start debating merits of different design choices, and those are like coffee: a gazillion ways to take them, everyone has its own flavour. First, the comment about T/W in lower atmosphere: while it makes getting to orbit more tedious, there is no need to hit some arbitrary speed number at some arbitrary height. As long as you can get to 20kms to start airhogging, with the airbreathing effective isp, you end up saving weight. Just consider the hover time you could get out of taking one of those RAPIERS out and substituting it with 1.75mT of aviation fuel. But I'll be the first to admit sometimes you just want to lift off faster, so YMMV. The same, of course, is very much not true for standard rocket engines and their "poor" isp, there gravity losses matter a lot.

About the intakes, yeah, I had a hunch it would be close, but it doesn't surprise me that you got them right, you can tell at a glance this thing has a lot of work behind. And the common fuel for vernors and main engines... yeah, I could see that, but then again mine made do with the capsule's 30 monoprop units, and just 4 physics-less, massless, RCS thruster blocks. I have a hunch that is also efficient in weight Also, I took oxi out of the main tank to get the atmospheric juice, which makes it even lighter. But being slightly more serious, take into account that those vernors run through fuel very fast, and that the way you have them placed, most of the thrust is wasted on forwards-backwards translation, and a significant percentage in other translation axis. With 4-way RCS thruster well placed, the wasted thrust to cosine losses is less, and the isp is the same.

Rune. But that's all nitpicking, because I like it. Good job!

[Tempestwrath]

I would like to mention that according to the wiki, the Vernor are also physicsless and massless as well, one of my considerations for use. I kind of rely on the forward angle of those on the front to give a slight push when docking, but in general I only need minor amounts of translation thrust when docking (in space,I set fine controls on and set the engine thrust limiters to 10%)--I need moderate amounts in brief bursts for atmospheric flight, so the apparent inefficiency of the design is something that was engineered into it with testing, if that makes any sense.

I do appreciate the input though. I would like to try a three-thruster variant at some point, but if my previous development is any indication, that would require a clean-slate re-engineering of the chassis. If I did that, I'm sure I could get it to work.

Edited August 27, 2014 by Tempestwrath

[Tempestwrath]

Just to kind of demonstrate the issues I've found in the three-engined version that I kind of figured initially would be the better choice as well, along with the problems I had with traditional monopropellent RCS, I've designed a variant, the Entia-class dropship, which is more or less a straight conversion of the initial chassis, with the changes we talked about included.

It has two problems, currently, both of which I came across in the Varia during its development.

1) The short, round fuselage makes rotation occur very easily past 23k, and the SAS with pod torque and thrust vectoring alone doesn't have enough initial force when you change your course to correct for yawing. Any deviation of the nose past 15 degrees to either side starves off the RAPIER engines, causing a premature switch over to closed loop mode. Monopropellent isn't strong enough to compensate. Solveable with wings, but, well, not having them was kind of the point.

2) Three engines, while theoretically sufficient, with the current amount of intakes cannot supply enough power in the upper atmosphere before closed loop engages if they're throttled down to compensate for low amounts of air available. Solvable with more intakes, but there really isn't a spot to logically add more.

The second issue would likely be solved by solving the first, because one would be able to gain more velocity pre-changeover if the ship was simply better at loitering up there for long periods. It -is- good with loitering when Vernors are added, for whatever reason, and the fuel cost is really minor, but you suggested getting away from that.

Here is the in-development version. To be honest, I'd like to make it work, as the Varia kind of hit a sweet spot where any improvements one can make are marginal at best. I've actually spent lots of time debating stuff like the aesthetic and 'realism' value of the shielded docking port versus the lighter weight of the regular Clamp-o-Tron among other things, but those are negligible gains at best.. I always love to iterate and actually make it better at its job while remaining somewhat true to its concept, so I was kind of excited at the prospect of a new direction with some outside input. Also, the three-engine version looks pretty cool. Feel free to mess around with it and see where it gets you!

Update :: I spent the evening messing around with this, trying everything I could think of outside of restarting from scratch to get it to be stable enough in the upper atmosphere to really take advantage of its theoretically higher exoatmospheric delta-v, but the one time I successfully managed a Kerbin ascent, it still had less delta-v available than the four-engined Varia on a bad ascent. The three engine configuration tends to suffer from quite a bit less stability than its cousin, and the design doesn't particularly lend itself well to a balanced RCS layout. While Vernors helped on this particular unit, the inability to place them in a configuration that let them really do their work without wasting tons of fuel, as well as the fact that they simply had to do more work, didn't really justify their use.

However, from the experimentation I have managed to dramatically improve the Vernor layout on the original Varia (No more awkwardly angled thrust due to the shape of the pod, and proper reverse thrusters!), so at least that issue has been solved.

Edited August 28, 2014 by Tempestwrath

[Rune]

Ohhh, now I get it. Your problem is a drag problem. See, at this point I have to show you mine:

Obviously much less beautiful than yours (mine screams "no frills functionality" all over), but look at that intake arrangement and CoM. And the CoM moves slightly forwards as the flight progresses, too. The hard part is keeping it controlled on reentry without the chutes, actually. See, even though you don't have an indicator for it, there is also a "Center of Drag". That "CoD" basically depends on where the intakes are with respect to the CoM , and it will tend to place itself behind it in respect to the direction of movement. Remember, while most KSP parts have the same drag coefficient and will therefore fall at the same rate, some parts, notably nosecones and intakes, have different drag values (nosecones lower, intakes higher) and therefore create aerodynamic forces within the ship. Which means your design with most of the intakes before the CoM wants to fly backwards, basically. I imagine it is very stable in reentry, right?

Also, note how I take more fuel and empty mass (that electric drive system is anything but light), and still use just the three engines, but with a 4-1 intake ratio and with the intakes at the CoM.

Rune. Hope that helps!

Edited August 28, 2014 by Rune

[Rune]

BTW, just so you get a glimpse of what you sparked, here's the VSSTO MkIX (I don't add to the VSSTO line even a third as often as to the SSTO line). I like the "coca-cola bottle" fuselage style a lot:

Rune. Prettiest one in the line, and it can go cismunar!

Edited August 28, 2014 by Rune

[Tempestwrath]

That is indeed very pretty!

After doing some research, I've narrowed down the issue with the yawing-at-altitude not to drag, as we previously suspected, but to this issue. I've improved the atmospheric performance of the Varia somewhat by using the techniques described there, and greatly reduced the need for Vernors to correct for the yawing. With the Entia, the issue is reduced but still present, but I'm still working on that front.

In other news, the Varia has undergone a weight cutting regimen and I've managed to reduce its tonnage by a whole ton without sacrificing much (The drogue chute, which was necessary in earlier versions with the much weaker part connections, smaller solar panels, etc). It's a cleaner, sleeker craft, and due to the tonnage decrease the delta-v has been increased by roughly 50 m/s.

The previous Varia (albiet, a version not here, but almost identical to the last posted) had 1655.67 m/s of delta-v with all tanks full and 1738.79 m/s with no fuel in the nacelles--a great trick to squeeze a bit more out in space for a landing. With my weight reduction, it's gone up to 1695.15 m/s with 1782.48 m/s without any in the outside tanks. It's a minor increase, but it allows for a bit more slack when doing a Duna landing, for instance.

The Entia (the three-engined version of the Varia) in comparison has 1889.83 m/s and 1970.95 m/s respectively--a pretty sizeable increase, but even if I sort out its issues, I'm not sure if its worth it since the higher TWR of the Varia does a fine job of brute-forcing its way through the atmospheric drag before it becomes a delta-v robbing issue; Also, the TWR is simply a bit too low when back-throttling at high altitudes to postpone RAPIER switchover to actually gain any appreciable velocity while not losing altitude. Again, I might have to work on a different flight profile or more tweaking.