Eve Reusable Launch System (REQUIRES MODS)

[Northstar1989]

Combine Extraplanetary Launchpads and KSP-Interstellar, and you've got the beginnings of a transport system. Eve has deuterium supplies in its "seas", so it's sustainable to run a fusion-powered lifter system from there (you'll need to mine Lithium to make Tritium as well, though- which is INCREDIBLY slow. Prepare to spam 20 or 30 ISRU refineries to get it at any decent pace). It also has reasonable supplies of Uranium and Thorium, so you can run fission reactors there (due to its lighter density and higher power, Thorium is a MUST on Eve to get much of anything done though...)

Your best bet for a transport system on Eve probably starts with building a launchpad on one of the tallest mountains (not an easy feat in itself). According to the Wiki:

"Eve's highest mountain range has a peak of 7526 m."

The Delta-V to orbit from an altitude of 7540m on Eve (the height of the CoM of a 20-30 m rocket atop a launchpad on the highest peak) is 7,968 m/s according to the Wiki. It's 11,282 m/s from sea-level according to the same table. So you save over 3,000 m/s Delta-V directly (and there might be some additional savings I'll discuss later...)

Building a mountain launch facility on Eve can definitely be done by helicopter. It doesn't require much mass either. Here's an example of the mountaintop launchpad facility I built on Kerbin- which weighs maybe 30 tons empty (most of that is in the large fuel tank)

The mass for that was lifted to a little under one scale-height on Kerbin: approximately the same relative height as the tallest mountains on Eve (Eve scale height is 7000 meters- but due to the thicker atmosphere the same helicopter can fly at a larger number of scale heights with the same payload, even taking higher gravity into account). The helicopter I used for that (the HELO had a theoretical maximum lifting capacity of at least 80 tons to that altitude: so you could definitely do it on Eve with something significantly smaller...

So, a basic mission-architecture to build an off-planet (this plan can easily be adapted to Duna) mountain launch site using an electric heavy-lift helicopter should look like this. Read it all the way first if you're going to try and use it:

(1) Transport approximately 42 tons of material to Eve orbit (18 for a minimal base, 24 for a helicopter capable of lifting it to Eve's tallest mountains with good safety margins). I suggest doing this using Orbital Construction RocketParts Modules, tied together with stock multi-couplers, or an Orbital Construction Medium Orbital Warehouse (the thing pictured at my Mountaintop Launchpad that looks like a Rockomax-32. It's less efficient storage than the RocketParts Modules, but holds a LOT more than 45 tons of material). MAKE SURE there are at least 2 KAS pipe end-points on the outside, or 6-8 in an attached KAS toolbox (I suggest looking at Scott Manley's "Interstellar Quest" videos to see how to use these parts). Extra (more than 2- but only even numbers help) pipe connectors can come in handy later if you miss your landing sites by a little, but aren't strictly necessary...

NOTE: Extraplanetary Launchpads also offers its own RocketParts storage containers, though they hold less than the Orbital Construction ones- so you can use those if you don't mind the higher part-count, and don't want an additional mod... There is also a mod somewhere out there that will let you procedurally-generate RocketParts containers, if you'd prefer that instead.

(2) Make a targeted (high-inclination) orbital "drop" of the RocketParts modules/warehouse aimed at a flat SEA LEVEL landing spot close to both the sea and a mountain range on Eve (the low altitude will give more time for atmospheric drag to slow you down, and parachutes will also work better there). Slow it down with PARACHUTES: this will save you MASSIVELY on descent fuel in Eve's extremely thick atmosphere... Alternatively, you can make this first drop untargeted (low-inclination, relying on aerocapture from an atmospheric periapsis), which will cost less fuel for de-orbit, and require fewer parachutes to slow down; but it might take a few "simulations" (F5/F9) to make sure it lands on dry land close to a mountain range, and at a sufficiently low altitude for the parachutes to prevent it breaking on impact with the ground...

NOTE: If you're feeling *especially* daring, you can try landing the RocketParts module as a glider dropped from orbit instead, to save greatly on part-count. Using Procedural Dynamics mod wings, you can easily get a great lift-mass ratio and land a payload *MANY* times heavier than 42 tons this way. No need to design a proper plane- it will never have to take off again once landed (a couple small rocket engines might help for control though- especially ones pointed downwards to help with pulling out of the initial steep re-entry dive just before hitting the ground...)

(3) Drop an Extraplanetary Launchpads launchpad at the same location via a targeted-drop. You should use the Mk2 (self-propelled) launchpad for this as its small amount of internal RocketParts storage will give you a lot more room for error (make sure the internal RocketParts storage is full before de-orbit). Its internal rocket engines will also be necessary to fine-tune the landing site to be as close as possible: it SHOULD land within 50 meters of the RocketParts module, and MUST be within a couple hundred meters (MechJeb will help a LOT with precision-landings like this, it could even land them literally on top of each other with enough fuel and engine power, it's that good...) Once again, rely mainly on PARACHUTES for the landing (you'll probably need to play with their deployment-altitude a little so they don't throw off your precision-landing).

If necessary, you can add extra rocket-engines/fuel for small "hops" to place the launchpad within a couple hundred meters of the RocketParts Module. Also, this is *VERY IMPORTANT*- make sure to include a command module or probe core of some sort on the launchpad, or you won't be able to control its descent, and you won't be able to operate the launchpad once it's on the ground. This will all add up to a rather high part-count between the two drops, but don't worry, you won't have to put up with it for long...

NOTE: If you opted for a glider design instead, to land your RocketParts on Eve's surface, you *might* find it easier to land the launchpad first, and the RocketParts second- depending on how good you are at glider-landings. I suggested landing the RocketParts first because they should lack sufficient means of propulsion to make a precision landing withing a couple hundred meters of a launchpad if you took my advice and relied mainly on a "dumb" drop with parachutes. The Mk2 Launchpad, on the other hand, has sufficient fuel and TWR built into it to adjust its landing site on the way down- if not enough to hover in Eve's strong gravity without additional fuel and engines..

(4) Deploy the launchpad, and design (or have already designed earlier- but it might help to see the area around the launchpad where it will need to drive first...) a very small rover for use on Eve, with a KAS winch attached to the rear for dragging tiny things (you might need to drag probe-sized fuel tanks) as well as a KAS radial connector port somewhere else on the vehicle that is accessible. It will also need a "Recycling Bin" attached to the front-side. Give it a couple OX-STAT panels, but know it won't need to drive far... You can build the rover now (from the Mk2's internal RocketParts buffer), and drive it around a bit to test it out; or save constructing it for when you will actually need it (or have hooked up your RocketParts module, if you're using the Mk1 launchpad).

I suggest an unmanned rover variant (you might need to drive it out to retrieve your Kerbal- who you'll be landing next...) with a reaction wheel- as the recycling bin and dragging things will somewhat mess up the balance. Also, unless you're a fan of *VERY* long rover drives on Eve's surface (as in, the distance from your current landing site to the peaks of the target mountain range, including the long contour-paths necessary to traverse such steep slopes), I suggest placing a KAS connector port directly over the rover's Center of Mass, so you can eventually airlift it with your electric heavy-lift copter (the rover should be relatively lightweight- so lifting it into the mountains with a chopper designed to lift entire launchpads should be absolutely trivial...)

NOTE: *IF* you experience bugs/problems with the dock-recycle method I describe later using this rover, with the game not recognizing the docket RocketParts storage as being part of the same vessel, you might need to build an empty RocketParts storage module into the rover itself to allow it to recycle other vessels. Adjust your mission-architecture accordingly.

(5) Land *ONE* Kerbal near the launchpad site. Once again, you should rely *HEAVILY* on PARACHUTES for the drop. Make NO PROVISIONS for his return to orbit at this point- don't worry, you'll be taking care of that later...

(6) When the Kerbal is safely at the sea-level launchpad site, have him connect the RocketParts module to the Extraplanetary Launchpad using the KAS pipe end-points- giving you access to a much larger RocketParts pool to build things out of. The KAS pipes have a maximum length of about 50 meters, but can be re-attached by hand to connect anywhere along the surface of each "vessel"... If you didn't manage to land the two sites within 50 meters, build on the launchpad (from the Mk2's internal buffer) and drag TINY (probe-sized) empty stock fuel tanks to between the two using your rover (otherwise, you can hold off building the rover), and connect the vessels in a sort of "relay" using the fuel tanks as nodes every 50 or so meters (you will need extra pipe connectors for this) using any extra pipe-connectors you brought along earlier (if you didn't bring any extras, and missed making your earlier landings within single-pipe range, you will need to build additional ones from the Mk2 launchpad's internal RocketParts buffer. If you're using the Mk1 launchpad, you will need to land a small additional lander nearby, containing pipe-connectors, detachable fuel tanks to use as "nodes", and a small rover for dragging the nodes into place...)

(7) Build your heavy-lift electric helicopter on the launchpad, take off, and land it on the ground nearby (KSP-I fission reactors/generators help IMMENSELY for powering this- though it can also be done with NearFuture reactors...) Once again, my HELO B works well as a guideline if you're trying to figure out how to design it- but keep in mind you don't need something that over-engineered... Remember to test the helicopter design extensively on Kerbin before even *THINKING* of building it on Eve...

The HELO B weighs approximately 32 tons; has 22 paired opposing rotors (opposed to prevent unwanted spin) ; and has two KAS winches located equidistant from the Center of Mass on the bottom, protected inside cargo bays (which can easily be switched out for decouplers for internal cargoes- though this is less useful off-world unless you plan on recycling and rebuilding your chopper each time...) You will NEED two or more KAS winches to prevent pendulum-effects of having a heavy object suspended below the chopper by only one attachment point- trust me on this (the greater the angle between the two winch cables the better- this can be achieved either by placing the winches further apart, or by retracting both the cables so the cargo is held closer to the body of the chopper...)

Other than that, the more rotors the chopper has, the higher its theoretical lifting capacity; but the more balanced the chopper is, the more SAS force it has, and the heavier the helicopter is, the heavier the cargo it can ACTUALLY reasonably lift without spinning out of control... 24 tons is a bit on the light side for something that will need to be able to *STABLY* (the real challenge is in stability- not lifting power) lift at least 6, and preferably 12 or more tons of external cargo (a 5-ton Mk1 or 10-ton Mk2 launchpad won't fit inside a cargo bay, or be stable on most decouplers...) like this- but in *CAN* be done with careful design... (the HELO challenge requires airlifting 40 tons to the island runway on Kerbin- and after *MANY* attempts I finally did manage to do it as an external cargo with KAS winches using the HELO B- but ended up bringing my cargo down too quickly on the island, causing it to explode, and decided not to attempt it again as an external cargo after that experience- opting instead for a *much* stabler 40 ton internal cargo, which was a comparative cake-walk to airlift...)

(8) Build an Extraplanetary Launchpad (Mk1 or 2- the Mk2 will be more useful, due to its flatter surface that you can actually drive rovers off of- but far more difficult to airlift due to its much greater weight) and airlift it with your chopper a short distance off the original launchpad using your electric helicopter. I find adding structural panels to the bottom gives it a wider base, and thus helps *greatly* in preventing it from tipping over on the ground (the mountain you'll eventually be moving the launchpad to will probably be far from flat, though you should search for the flattest location possible- expect to build your mountaintop launch base on at least a gentle slope...)

(9) Build a command module with a sufficiently wide base it won't roll or slide off a mountaintop (the stock Mk2 lander can should work fairly well for this- or a smaller command module with structural panels attached to its base, parallel to the ground.) You'll need it to operate your mountaintop launchpad facility. Note that something as simple as a structural panel with a lawnchair strapped on top, and KAS ports to airlift it and to connect it to the other modules should work for this...

(10) Build another RocketParts container of some kind. This one could be extremely large and heavy even when empty, if your helicopter is powerful enough- or it could be about the same mass as the launchpad. I would suggest one of two strategies at this point: either building a moderately-sized pair of RocketParts modules you think your helicopter can easily transport to your mountain base site completely full- and use to build a much larger, empty module at the site; or transporting a really big, but empty RocketParts module to your mountaintop landing site. Personally, I prefer the first strategy: as I find it's much easier to airlift a pair of smaller, denser objects that I can retract and lock (KAS winches can lock into place at close range- preventing any unwanted rotation) into a pair of internal cargo bays on each side of the Center of Mass; than it is to sling a larger object below the 'copter, between two CoM-equidistant KAS winches...

Either way, you want the final size of the large and empty RocketParts Module to be great enough to hold at least a mass in RocketParts equivalent to the dry mass of *EVERYTHING* you've built or landed on Eve up until this point (that includes the chopper, the lawnchair-lander, and even any boosters or abandoned probes that were on Eve before this mission even began), minus the dry mass of the rover, the command module, and the launchpad you're going to be landing on the mountaintop... You might also want to build a large enough container to hold the RocketParts for really large launch-platforms now too, so you won't have to build a larger container later... If you need to build multiple, smaller, full RocketParts modules; and hook them all up to the mountaintop launchpad you'll be deploying to build a sufficiently large RocketParts storage unit on-site, after lifting them there in multiple airlifts, then do it- and adjust the mission-architecture accordingly...

Also, I said "dry mass" because fuel doesn't count- while you'll be recycling every helicopter, booster, and probe you can find on Eve back into RocketParts; you'll need to build separate fuel tanks to hold any fuel you already have on Eve's surface at this point (if you followed my dumb-drop approach, it shouldn't be much yet...) as well as the very large amount of fuel you'll eventually be wanting to be producing on-planet (even with the launch systems I'm going to describe later, you'll still want an EXTREMELY large amount of fuel storage- I suggest using StretchyTanks to build enormous fuel tank cylinders with very wide bases, so they won't tip over on uneven ground...) By the way, you can also subtract the dry mass of the fuel tanks from the RocketParts mass you'll need to be able to store in the final mountain RocketParts module- as you can build the fuel tanks at some point before you completely fill up the mountain RocketParts storage...

(11) Build a moderately-sized, full RocketParts module (or pair of modules, if you will be carrying them locked to two KAS winches equidistant from the helicopter's Center of Mass- most useful if your KAs winches are inside cargo bays like on my HELO B, as it makes landing much easier when you don't have to worry about detaching cargo dangling below your copter first...) You will need this/these module(s) to transport RocketParts from your RocketParts module near Eve sea-level to the larger, empty RocketParts module you will be deploying/building in the mountains... Stick a couple KAS pipe-connectors on the outside of this to make your life easier later on... (you can grab these from the launchpad and sea-level RocketParts storage before step 12 if you'd like) Once again, make sure it won't roll off the mountaintop when landed... Also, as always, bigger is better- I recommend building the largest full RocketParts module you think you can safely and easily transport with your heavy-lift chopper, to minimize the number of airlifts you have to perform, and allow you not to waste RocketParts when you recycle the empty sea-level RocketParts module later...

(12) To reduce lag at this point (with at least your chopper, launchpad + connected RocketParts module, an additional launchpad for mountain deployment, an additional RocketParts module for the mountain, and a small lawnchair-lander nearby that got your Kerbal here, plus the possible addition of your rover; your lag should be through the roof by now considering the number of parachutes required to land something as heavy as the RocketParts module safely...) build your recycling-rover, detach the KAS radial port by hand using your Kerbal and attach it to the *RocketParts Module* portion of the launchpad base, connect up the rover to the KAS port via winch in *DOCKED* move, and detach the launchpad from the RocketParts Module (or the RocektParts module from the closest relay node to itself, if using nodes).

Then, extend the winch cable to maximum length (you will need some slack), "Activate" the recycling bin, and drive the rover into the original launchpad (the one you dropped with tons of parachutes attached, or as a glider). This will instantly destroy the launchpad, and convert it into an equivalent mass of RocketParts- which should now be stored inside the RocketParts Module if you remembered to attach the winch in "docked" mode. Do the same with the lawnchair-lander, if you rover can reach it while still attached to the RocketParts module by winch-cable (or deploy a chain of nodes like before, to extend the rover's range, deploying and using the mountain launchpad to build the nodes this time- don't worry, you can pack the launchpad back up afterwards...) This will all help with lag a bit.

NOTE: You can skip this step if you want to have a runway on Eve, at sea-level (the safest altitude for plane-landings by far). You'll just want to come back later and build an Extraplanetary Launchpads runway at the sea-level site using the launchpad. You can then recycle the launchpad, use the RocketParts at the runway to build a Command Module or probe-core, and another (stationary) RocketParts storage module without all the parachutes or wings attached, use the helicopter or a really big rover to drag each off the runway, and connect them all together via KAS pipe or winch...

(13) Now comes the *FUN* part- AIRLIFTS! I hope I don't need to tell you this, but it might be a good time to Quicksave before attempting this. In fact, to design an electric helicopter that can lift this much, you should have already made several test-airlifts of similar or heavier cargos on Kerbin to prove to yourself you can do it with your chopper design... (ideally, landing your modules on the mountains west of KSC to also prove you can safely make mountain airdrops, and your modules won't tip over and roll/slide away on the slope of a gentle mountain-shoulder... This is a MAJOR issue for mountain launch sites- I find, once again, that structural panels parallel to the ground help with this a lot...)

The things you will need to airlift to the mountains that should be nearby your landing-site:

- Your mountain launchpad, of course

- Your RocketParts storage modules (either large/empty, or small/full to build large/empty modules on-site)

- Your Command Module (for operating the mountain launchpad)

- Your Kerbal (he will be needed to make KAS connections between the launchpad and RocketParts storage modules)

The last two can easily be combined- if you lift the Command Module with the Kerbal inside/on-board it...

Once all of these have been safely landed at your planned mountain launch site on Eve, use your Kerbal to connect your RocketParts storage modules, your mountain launchpad, and your Command Module together via either KAS winches in "docking" mode or KAS pipes (the three can be connected in a string- they don't need to all connect directly). VOILA! You now have a functional mountain launch facility!

(14) While your mountain launch is now functional, it shouldn't yet have anything in the way of RocketParts in it... Go and pick up the full RocketParts module from step 11 with your helicopter, and airlift it to your mountain base. Unload the RocketParts from this to your mountain RocketParts storage using the KAS pipe connectors you slapped on earlier (perhaps recycled from your launchpad and sea-level RocketParts storage, or taken from the the toolbox full of pipe-connectors I suggested earlier...) Return this module to the sea-level RocketParts storage, load it up again, and bring its load of RocketParts back to the mountain again. Repeat this as many times as necessary until the sea-level RocketParts storage is completely empty... (You might leave some behind to build a runway, if you decided not to scrap the sea-level launchpad in step 12 in favor of building a runway there...)

(15) Airlift the empty RocketParts transport module back to the sea-level site one or two more times; re-attach the rover to it in "docked" mode instead of the sea-level storage module, via the KAS winch on the rover and the radial connector port on the sea-level storage you used to connect it to the rover, and recycle the sea-level storage as you did the launchpad before. Repeat this process with the lander you used to get your Kerbal to the surface earlier, if you haven't done so already...

Each time, airlift the RocketParts back to the mountain launch site before proceeding- as any dry mass you recycle without sufficient storage capacity in the vessel used to recycle it (the rover and the "docked" RocketParts transport module count as one vessel in this example) simply disappears into nothingness... (if your transport module is too small to hold the entire mass of the EMPTY sea-level RocketParts storage- which will be indicated by the transport module filling completely with Rocketparts, usually indicating the actuaal amount you could have obtained is greater than the capacity of the storage unit, and there was some overflow- then decide if you want to build a larger transport module and attempt to airlift it between the sites, possibly with a larger helicopter to airlift it if necessary...)

CLEANUP: When step 15 is complete, you're almost done constructing your mountain launchpad on Eve! All you need do now is airlift the rover itself back to the mountain launch site, use it to recycle the helicopter as you should have done to many other vessels by now in this process, and then decide what you want to do with the rover itself. (Perhaps you want to keep the rover for future recycling operations. Perhaps you want to build a stationary recycling bin into your mountain launch site, and attempt to drive or lift the recycling-rover itself into it to recycle its wheels and chassis for a few extra RocketParts... Perhaps you simply want to drive it off a cliff near your mountain launch site to its demise, as you're sick of recycling stuff by this point... ) Then again, maybe you want to keep the helicopter that has proven so capable as an airlift platform for future needs as well...

NEXT: I'm going to break it into a separate post, but I also have a lot to say about the vehicles for the reusable launch system you'll want to use on Eve. The mountain launch site, while saving you over 3000 m/s Delta-V on each launch from Eve, was only the beginning of such a system- and worthless without an actual sustainable way to get things into orbit and back...

Regards,

Northstar

P.S. Once again, this plan for putting a mountaintop launch site on Eve can easily be adapted to Duna- and in fact I plan to do so. The atmosphere on Duna is significantly thinner relative to gravity than on Kerbin or Eve, though, and the scale height is less though (only 3000 meters)- so I won't be able to build on top of one of Duna's highest peaks (the mountains on Duna reach as high as 8264 meters- almost three scale heights! The HELO B can't even fly that high on Kerbin unloaded- and in fact might not even be able to fly at 6000 meters on Duna unloaded...)

Edited February 28, 2014 by Northstar1989

[Northstar1989]

Now, as to the reusable launch system itself...

First of all, the requirements of any rocket can always be understood in terms of thrust, ISP, and payload fractions. In the case of Eve, that means at least 8400 m/s Delta-V even launching from a mountaintop launch site, especially considering you will have at least some steering losses. That's certainly nothing to sneeze at.

Half the solution to a problem like this is technology. You simply can't build a reusable launch vehicle like this with standard chemical rockets. It won't work with any kind of a reasonable payload fraction- ever.

The question is how futuristic you're willing to allow your technology to be then. In the case of a Duna colony, I generally limit myself to the technology of fission and ion engines that either currently exist (molten-sodium fission reactors) or will soon exist (such as the VASIMR engines from NearFuture pack, or KSP-I's plasmodynamic thrusters: both of which which are basically just upscaled standard ion engines that work slightly differently under the hood...)

On Eve, however, I'm willing to accept for myself up through upgraded fusion-power technology (the fusion reactors that become available with Antimatter Power) ; and the other parts, such as upgraded KSP-I fission reactors and hybrid thermal turbojets, that become available at the fusion-power tech node (the upgraded reactors utilize plasma cores instead of solid cores- a fission power technology that is still some ways off as of the current moment.)

NOTE: The design I discuss below will also work with antimatter reactors- although the very rapid rate at which they consume antimatter as reactor fuel, as well as their lack of dependence on sea-mining for reactor fuel will make a mountaintop launchpad even more useful...

The other half of making a system like this work is design. You want to design a launch system that works *WITH* the peculiarities of the celestial body you are launching from, rather than against them. On Kerbin or Laythe, this means using the readily-available oxygen supplies in the atmosphere to build oxygen-breathing launch platforms wherever possible. On Duna, this making use of the fact that orbital velocity is very low- and velocity curves are absolute (it doesn't matter if orbital velocity is 850 m/s or 2300 m/s, if an engine loses half its thrust at 1000 m/s, it loses half its thrust at 1000 m/s), and building thermal turbojet-powered spaceplanes, which can easily reach orbital velocity *INSIDE* Duna's atmosphere, due to their velocity curves only losing about half their thrust by 1000 m/s (Duna's orbital velocity is about 850 m/s). On Eve...

Well, aside from thermal turbojet spaceplanes- which don't work as well on Eve as on Kerbin or, say, Duna- as velocity and atmospheric curves are absolute, and unrelated to the scale height of the atmosphere (which is greater on Eve- so you have more atmosphere still above you at maximum cruising altitude with a spaceplane's atmospheric engines) or low-altitude orbital velocity (which is much higher on Eve- meaning you can't reach as high a fraction of orbital velocity in the atmosphere using thermal turbojets... The much lower orbital velocity of Duna, by contrast, allows spaceplanes to reach and exceed orbital velocity while still in the atmosphere...) what DOES work on Eve are rockets- even if they normally have to be incredibly large...

Specifically, the first key technology for a reusable launch system is an AIR-BREATHING rocket engine. Not to be confused with an oxygen-breathing rocket, as no combustion occurs (Eve's atmosphere contains little to no Oxygen to support combustion), but rather thermal turbojets utilized as rocket boosters. This eliminates much of the need for massive quantities of fuel to reach orbit on Eve, and is better adapted to the planet's characteristics- instead of trying to shove massive quantities of rocket fuel through miles of dense atmosphere, you rely on the very long scale-height of Eve's atmosphere (the fact that atmospheric pressure essentially falls off very slowly as you ascend) to derive much of your propellant from the atmosphere itself- which is abundant until you reach rather extreme heights. You essentially get "free" propulsion for your rocket until you reach an altitude where thermal turbojets no longer are capable of producing a Thrust-Weight Ratio greater than one...

Of course, nothing is ever entirely free- and propulsion least of all. In order to get decent performance from such a system on Eve, you need to make use of 2.5 meter hybrid thermal turbojets (I'll get into the reason for the "hybrid" part later) coupled to 2.5 meter KSP-Interstellar fusion reactors (the larger-diameter reactors achieve higher power-density, at the expense of more rapid fuel consumption).

These will give you great raw lifting power at low altitudes on Eve- but as stated, eventually you will reach an altitude where the TWR of the system falls below 1 (this actually occurs when the air intakes Thermal Turbojets require can no longer bring in enough IntakeAtm, the resource utilized by Thermal Turbojet's and present even where there is no oxygen- as they engage in no combustion- to produce thrust great enough to lift the reactor's mass. You can delay this until higher altitude with a higher intake:engine ratio, but eventually you will reach this point well before exiting Eve's atmosphere unless you do something exploitative like attach 56 intakes for each engine...)

Further, fusion reactors make use of the extremely rare resource Tritium, as well as the still somewhat difficult-to-get resource Deuterium. Both of these resources can theoretically be obtained on Eve- the Deuterium from centrifuging the "sea water", the Tritium from breeding Lithium (centrifuged from sea water) in a fission reactor (fissile fuels are also locally available on Eve), but only VERY slowly- requiring a MASSIVE number of ISRU refineries and fission reactors breeding tritium to produce it at any decent rate...

Finally, fusion reactors require a continuous supply of electricity to operate. While they can more than provide enough power to keep themselves running once activated; they require an external power source to start them up. As such, I *HIGHLY* recommend installing a large fission reactor (or a fusion one you will always keep running) at your mountaintop launchpad that can be connected to the rocket via KAS winch to jump-start its fusion reactors before liftoff (you can detach the winch, and remove the KAS connector port from the rocket if desired, once the reactors have been jump-started shortly before liftoff...) You'll also need to install generators on your rocket to keep the fusion reactions self-sustaining after the reactors are active (you won't need a generator attached to every single reactor, however- but the number/size of generators you WILL need increases with the total number of fusion reactors you'll be running on the rocket...)

The rarity of fusion reactor fuels is one reason you want to launch your reusable rockets from a mountaintop launchpad- the higher the launch site, the less time it will take to escape the atmosphere (you spend the greatest amount of time in the lowermost atmosphere, where drag causes you to ascend more slowly. Though an almost completely negligible effect, gravity is also *slightly* weaker at higher altitudes...) You will be able to deactivate the reactors once the launch stage is safely back on the ground a little sooner- so a high-altitude launch will save some Deuterium/Tritium mix- and with the rather anemic Tritium supplies you will likely be able to produce on Eve, you will want to save every bit of Tritium you can...

The other, more important reason you *NEED* to utilize a mountaintop launch site is because thick atmosphere "chokes" thermal turbojets. They have an ideal atmospheric pressure at which they produce their maximum thrust (it is the equivalent of about 4000-5000 meters above Kerbin Sea Level), and at higher pressures than that, the dense atmosphere "chokes" the turbojets, leading to reduced thrust output. Even given everything else I will be describing below, this reusable rocket design is *VERY* marginal, and still only capable of carrying relatively small payloads to orbit (the model version I present is basically only capable of carrying a roughly 8 ton payload to orbit on Eve, for instance- even though it utilizes UPGRADED fusion reactors...) If you make use of a sea-level launchpad on Eve, you'll need to make use of disposable boosters of some sort to get it up to optimal altitude, or accept a lower maximum payload fraction for the same launch vehicle.

You will want to make use of a 2.5 meter hybrid thermal turbojet in the "core" of the rocket, but you will also want to strap on 3-6 1.25 meter hybrid thermal turbojet "boosters" to your 2.5 meter core (depending on desired lifting capacity), or even 2-3 2.5 meter boosters (essentially clones of the 2.5m core- 2.5 meter reactor/TTJ combinations get higher TWR than the core- although they will require a greater number of intakes to keep them supplied with air...) These "boosters" SHOULD NOT BE DETACHABLE- they will be part of the reusable launch stage, and are present mainly for the additional thrust they provide.

Although your thermal turbojets will be providing all of the thrust during your early ascent, you will want to switch the 3 hybrid TTJ boosters to internal fuel mode to provide additional thrust when your TTJ thrust starts to taper off due to limited availability of IntakeAtm (increasing your airspeed- and thus the intake mass of your air intakes) later in your ascent, when your TWR on TTJ power alone starts to approach 1... (MechJeb's "Vessel Info" window can be very helpful for showing you when this point is approaching...) This will enable you to get by mostly on TTJ power a little longer- by raising the altitude at which your TWR falls below 1...

Thermal Rocket Nozzles are another technology introduced by KSP-Interstellar, and they are actually the technology that real-life NERVA designs utilized (the LV-N engines from stock actually look and function more like high-ISP rocket motors than actual NERVA engines... For one, they don't require a separate nuclear reactor. Additionally, they rely solely on LFO mix- whereas the real-life thermal rocket designs can make use of virtually any liquid propellant, including liquid hydrogen, liquified hydrazine, or purified water; as they rely on the heat of the nuclear reactor, rather than the heat from combustion, to generate the rocket's thrust...) They produce significantly less thrust that Thermal Turbojets, but have higher ISP (although they rely on expelling internal propellant you have to lift in the rocket- and TTJ's rely on expelling atmosphere), and when you make use of fusion reactors for these boosters will still produce enough thrust to significantly prolong the useful life of the core Thermal Tubojet during ascent.

The Thermal Tubojet, as I mentioned, should be a "hybrid" Thermal Turbojet (this technology becomes available with the Fusion Power tech node in KSP-Interstellar). The advantage of the hybrid TTJ, over a conventional TTJ, is that it will be able to switch "internal propellant modes" later in the ascent, and essentially start to act like a thermal rocket. You will eventually want to switch all of your hybrid TTJ's over to internal propellant mode once you climb too high for the TTJ's to continue to provide a useful amount of thrust to lift your rocket...

Fusion-powered or not, thermal rockets don't provide an awful lot of thrust (the fission-powered 2.5 meter variant only ties with the LV-N in terms of TWR and ISP, when powered by Thorium), and with the relatively large amount of fuel you'll need to stack on top of your engines just to get a moderate-sized payload to orbit, you'll be lucky just to be getting a TWR a little over 1 for your rocket at this point... You'll want to package LFO-mix as fuel for your TTJ's, as LFO mix yields the highest thrust of any thermal rocket propellant, at the expense of ISP (fusion-powered Thermal Rockets still get *GREAT* ISP with LFO-mix though: over 3000 with the 1.25 meter reactors, and over 4,000 with the 2.5 meter reactors- which have a higher core temperature).

Drag might cause you to actually start slowing down- although to minimize this effect, you should try and slap on as many stack and radial air intakes as you feel comfortable placing on your rocket to keep the TTJ running as long as possible... (Remember, it's an air-breathing ROCKET that shoots superheated air out the back, not a combustion-powered plane: its design could reasonably accommodate a much higher intake:engine ratio than most real-life fuel-burning jet plane designs...)

The thermal rocket stage won't be able to efficiently carry your payload to orbit due to its extremely low TWR- and besides, you'll need to re-use this launch stage to carry future payloads to orbit. So, once your apoapsis is a *CONSIDERABLE* distance beyond the atmosphere, and you are nearing the atmosphere's edge (you should be following a highly VERTICAL ascent trajectory up until this point. No gravity-turn here: you'll need as much vertical velocity as possible in order to re-use your lower stage, and additionally your TWR will dip so low as you approach maximum altitude for the TTJ and then switch to the thermal rockets that you'll need to be pointed more or less straight up in order to continue to build vertical velocity...) you will need to decouple this lower stage from your rocket (which should contain the four fusion reactors; the attached electric generators you will actually need for the fusion reaction to self-sustain; a probe core, a small amount of leftover LFO-mix, drogue parachutes, and reaction wheels for re-entry and landing; inline heat radiators to disperse excess reactor WasteHeat, and a considerably-sized nearly-empty 2.5 meter LFO tank as you will be firing your thermal rockets in LFO mode for quite a while before you come close to exiting the atmosphere...)

The next stage should be a high TWR upper stage. You will need either the unbeatable TWR that chemical rockets provide (only exceeded by a few specialized nuclear propulsion systems, such as the Orion and DT-Vista, which destroy anything in a several-kilometer sphere directly beneath them- making their use in a reusable launch platform completely unsustainable- unless you want to airlift a DT-Vista several kilometers from your Eve colony; and plasma thrusters with VERY HIGH amounts of available beamed microwave power, on the order of hundreds of Megawatts...), or a powerful NERVA engine like the stock LV-N's or the (slightly better) NearFuture inline fusion-powered NERVA engines with a correspondingly reduced fuel-load (although the engine itself has lower TWR, it is actually possible to achieve a higher initial extra-atmospheric TWR for the vessel as a whole with stock-like NERVA's than with chemical rockets if you compensate for the reduced thrust but more than doubled ISP by cutting the size of the fuel tanks in half) to circularize your orbit enough to raise your periapsis above the majority of the atmosphere (a little dipping a few thousand meters in should be acceptable) before your launch stage comes crashing back down into Eve's atmosphere and disappears due to being unloaded... The higher your apoapsis, the more time you will have to accomplish this- but under Eve's gravity it probably won't be very long at all, which is why you need a chemical rocket...

Note that I don't recommend utilizing KSP-Interstellar fusion reactors for the upper stage, even though they out-perform stock-like NERVA's both in terms of TWR and ISP (this is realistic and to be expected, as you are comparing fission and fusion technology when you compare LV-N's and KSP-I fusion reactors. NearFuture fusion-NERVA engines, on the other hand, barely outperform fission NERVA's, but might be thought of as lower-tech fusion reactors more in line with today's technology rather than KSP-I's slightly more futuristic fusion reactors... NearFuture fusion-NERVA engines also become available at a much earlier tech node than KSP-I fusion reactors...) This is as KSP-Interstellar fusion reactors are much HEAVIER than the corresponding stock-like NERVA's of the same radius. A 2.5 meter reactor is too heavy for the upper stage, and a 1.25 meter reactor is going to create structural problems if the rest of the stage is of a 2.5 meter radius... (as it should be- you would need to make a *VERY* long 1.25 meter upper stage to carry enough fuel to get your payload to orbit- and any upper stage that long would have serious issues with the re-entry/landing necessary to re-use the upper stage as well... Though, go ahead with and use a 1.25 meter KSP-I fusion thermal rocket if you think you can keep a rocket with an upper stage that long or with a thinner engine than the stage on top of it stable ascending through the the atmosphere, and plan on leaving your upper stage in orbit...)

Once you've accomplished the relatively mundane task of circularizing your orbit; that nonetheless should require a rather significantly-sized upper stage, due to the high orbital velocities around Eve, and your lack of large amounts of horizontal velocity from your lower stage; you will need to switch back to your lower stage *ASAP*. This is the *FUN* part- you will need to target its re-entry so that it lands at a sea-level site near the base of the mountain range where you built your mountain launchpad (if you kept a runway at the initial landing site from before, this is the single best place to target your landing, regardless of its distance from the mountains...) Once again, you will need the following components in the lower stage to safely land it back on Eve:

A probe core- for guidance

Reaction Wheels- for control

Drogue Chutes- to reduce your velocity

A small amount of leftover LFO-mix (to adjust your re-entry and landing trajectory)

What you will basically do is target your landing (if you *LISTENED* before, and did not perform much or any of a gravity turn with your lower stage active, your trajectory should be largely vertical- which should make this relatively easy) so that it comes down directly over your sea-level runway base or a flat recovery zone, and let drag and the drogue chutes slow your lower stage down. When it gets close to the ground, you will need to perform a suicide-burn using your Thermal Turbojets (which should be at full thrust again by this altitude- and have a bit of Thermal Power left) and thermal rockets to kill the last part of your vertical velocity: which should be relatively small due to the parachutes.

Once your lower stage has touched down, you should *IMMEDIATELY* shut down its fusion reactors to save fuel. You then need to reach it with some sort of vehicle (preferably a helicopter or VTOL aircraft, although rovers can also work- depending on the distance from your nearest base/outpost) once its fusion reactors are completely cooled down, and drain the remaining fusion and chemical fuels from them. Then, you can recycle your lower stage for an equivalent mass of RocketParts, exactly as I discussed before with the mountaintop launchpad set-up, and re-build it at your mountaintop launchpad upon transporting the RocketParts there (this is a much better alternative than hauling the lower stage there and literally rebuilding it by re-attaching it via a docking port used to attach it to its upper stage in the first place...)

As for the upper stage- you can de-orbit it and re-use it in a similar manner if desired, or you can recycle it utilizing an orbital Scrapper Ship (see the picture below) and utilize it to build something else useful in Eve orbit (like a Microwave Power Transmission Station, or a fuel depot)

Regards,

Northstar

P.S. Here is an album showing images of an example craft for this type of system in use on Kerbin. Note that the rocket was designed so as to be capable of operation on Eve, even though it is being used here on Kerbin (its TWR is sufficient for operation on Eve, as are the fuel loads...)

Javascript is disabled. View full album

Obviously, this rocket could use some optimization (such as a significant reduction in the lower-stage fuel load, and a corresponding increase in the upper-stage fuel load), and I haven't bothered to show re-entry of the upper stage as well (assume it would be used in this example as a transfer stage for an interplanetary transfer of the upper stage, or its fuel drained into a depot and mass recycled for RocketParts to help build an Orbital Microwave Power Transmission Station...) Note also that, although I utilized LFO to perform a suicide burn close to the ground, this could equally well be accomplished through use of standard parachutes instead of drogue chutes, or through use of the thermal turbojets in atmospheric mode...

Edited February 28, 2014 by Northstar1989

[wasmic]

For Eve asceends, Hooligan Labs balloons. 'Nuff said. But your tips on how to set up a launch site will sure come in handy.

[Northstar1989]

For Eve asceends, Hooligan Labs balloons. 'Nuff said. But your tips on how to set up a launch site will sure come in handy.

Please don't make comments like that. They're not at all helpful.

Balloons wouldn't be useful for reusable rocket designs like this, anyways. It would be *EXTREMELY* difficult to stably attach a rocket this large to a balloon, for starters. Second, this rocket design needs some time in denser atmosphere to build up some vertical velocity before its TWR falls below 1. Its ideal launch altitude (about 5,000 meters below where thrust would hit a maximum) would be about 12,000-14,000 meters on Eve (unfortunately, Eve has no mountains that high), so a balloon wouldn't even be that great of a help if you could get one to stably hold the rocket...

Re-loading the rocket onto the balloon wouldn't be a trivial matter either (and would likely require recycling the entire balloon and rebuilding the rocket on it each time...)

Besides, don't Hooligan Labs balloons have problems with losing all buoyancy (and dropping like a rock) as soon as they exit physics loading range? For obvious reasons, a balloon that went crashing into the ground and exploded shortly after rocket liftoff wouldn't be of any use for a 100% reusable launch system...

Regards,

Northstar

[undercoveryankee]

I seem to recall one of Manley's Eve or Bust series showing a Hooligan Labs envelope retracting into a bay in the vehicle. If you can get the weight to work out, you could recover the balloon by retracting it and taking it with you.

[wasmic]

Please don't make comments like that. They're not at all helpful.

Balloons wouldn't be useful for reusable rocket designs like this, anyways. It would be *EXTREMELY* difficult to stably attach a rocket this large to a balloon, for starters. Second, this rocket design needs some time in denser atmosphere to build up some vertical velocity before its TWR falls below 1. Its ideal launch altitude (about 5,000 meters below where thrust would hit a maximum) would be about 12,000-14,000 meters on Eve (unfortunately, Eve has no mountains that high), so a balloon wouldn't even be that great of a help if you could get one to stably hold the rocket...

Re-loading the rocket onto the balloon wouldn't be a trivial matter either (and would likely require recycling the entire balloon and rebuilding the rocket on it each time...)

Besides, don't Hooligan Labs balloons have problems with losing all buoyancy (and dropping like a rock) as soon as they exit physics loading range? For obvious reasons, a balloon that went crashing into the ground and exploded shortly after rocket liftoff wouldn't be of any use for a 100% reusable launch system...

Regards,

Northstar

Seems that I missed some of the points in your post. My goal was not to write an in-dept critique of your tutorial, but rather to say how I would do it, and to say thank you for the tips on setting up a launch site.

EDIT: I just noticed that this post could seem a little snarky. It's not intentional.

[Northstar1989]

I seem to recall one of Manley's Eve or Bust series showing a Hooligan Labs envelope retracting into a bay in the vehicle. If you can get the weight to work out, you could recover the balloon by retracting it and taking it with you.

That doesn't sound like a bad idea. Maybe I'll give it a try- if my computer's memory doesn't implode from the extra mod (I might have to find a way to reduce the existing memory usage further). How much do the Hooligan Labs balloon envelopes weigh.

And more importantly, how much mass can one hold up at 12,000 meters on Eve? Remember, my reusable rocket can only *maybe* lift 8 tons on Eve, even with its upgraded fusion reactors, and some further optimization (I realized after my last payload test on Kerbin, which was calculated from maximum payload with a TWR >2.7- as Eve's gravity is 1.7 times Kerbin's; that payload capacity would actually be quite a bit less on Eve thanks to the thick atmosphere choking the thermal turbojet at 7000 meters there- where the air is still much thicker than at the KSC Launchpad...)

Regards,

Northstar

Edited March 2, 2014 by Northstar1989