The Sands of Duna
Part 2: Ship construction
Okay! Let's construct the ship. Like before, when designing a rocket, trace the mission from the end, backwards to the beginning.
This mission will rely on the Kerbals performing extra vehicular activities (EVAs) to collect science, and bring it back into the command pod. So we don't need to bring the actual science pods (and their weight/mass) back with us. So the part of the ship that needs to make it back home is quite small. We'll start there.
[Figure 1: Command module, based around the Mk1-2 command pod.]
The parachutes on this command module section are not only used for a safe descent back to Kerbin, but will also be used for descent on Duna. They serve a double purpose and will be used twice.
The "Mk25 High Altitude Parachute" has Duna written all over it. Duna has a very thin atmosphere, and we are going to rely on parachutes to do most of the braking on the descent to Duna. Duna has a very thin atmosphere, yet we want to utilize atmospheric drag as much as possible during the descent. "Mk25 High Altitude Parachute" does not have as much drag when fully deployed as standard parachutes do, but it has greater drag when not fully deployed and at higher altitudes and lower pressure (compared to standard parachutes that are not fully deployed). This is ideal for our planned descent to Duna, getting everything we can from the thin atmosphere for braking.
Because all these parachutes will be used twice, I have also configured their deployment using "Action Groups." I have set the key '0' to trigger the deployment of the "Mk25 High Altitude Parachute" and the key '9' to trigger the deployment of all the rest of the standard parachutes.
If I was designing this in KSP version 0.24 or later, I might have chosen to bring more back to the surface. You get extra "funds" for the recovered parts in version 0.24 or later, so the more you successfully bring back, the more funds you can recover. There wasn't any funds in version 0.23.5, which is why the returning portion of the craft is so minimal.
[Figure 2: Docking port orientation. Don't put it on backwards!]
Notice the docking port orientation. Again, once you have installed it on your ship, if you see a yellow triangle, you have it on backwards. (Recall that I once had to de-orbit an entire space station because I put all the docking ports on backwards.)
By the way, in my imagination, the docking port is also functioning as a heat shield. In present versions of KSP (at the time of this writing [0.24.2]), reentry heating effects are still not implemented. So that's just my imagination there.
[Figure 3: Auxiliary Service Module: Lander section to at least from Duna atmosphere back up to dock with the main, Service Module (and maybe a touch more)]
The Aux module (Figure 3) is just to get the command module from high Duna's atmosphere into a low orbit, and then to a higher orbit to dock with the Service Module. It's fate is undetermined at this point. It contains the necessary equipment for de-orbit around Duna (remote guidance unit, solar, battery, RCS and monopropellant), or if there is enough fuel, we can take it back to Kerbin and use the extra fuel.
[Figure 4: Complete, Duna lander module]
Note that the science bays (Figure 4) are attached to the lander with the radial decouplers. Once we take off from Duna, they will be ejected to reduce mass/weight.
What's not pointed out in Figure 4 are the extendable ladders. The extendable ladders are the rectangular things on the Aux Service Module, another on the lander's main fuel tank, and then one on each of the three science bays (you can see one on the science bay to the right).
The goal is for the Kerbals to do EVA on Duna and collect all the science available, and bring the science data back up to the command pod.
Like before I used the "Action Groups" for conveniently toggling all ladders using a single key. In my case I used the '5' key.
In more recent versions of KSP (0.24 or later), I might have considered bringing all the science back to Kerbin, not only for the science, but also for the increased funds. But this time, all the science and most of the lander will ultimately be left behind on Duna.
The lander's main fuel tank must contain enough fuel to land on Duna (fortunately that will be assisted
a little by the parachutes), and enough fuel left to
almost reach a low Duna orbit. Upon leaving Duna, the plan is to separate from the main fuel tank just before reaching a stable Duna orbit, to reduce space junk.
[Figure 5: Main, upper stage fuel tanks.]
Figure 5 shows the main, upper stage fuel tanks. This section contains the fuel needed to get from Kerbin orbit to at least a low Duna orbit.
Note there are some Rokomax 24-77 engines. These engines are small and light, and will be used when transitioning from high, Duna orbit to a low, Duna orbit, and hopefully will have enough fuel to aid in the Duna descent. (Note that there are no capabilities of remote de-orbiting, so by gosh I hope there's enough fuel left for at least a little aid in the descent.)
The Rokomax 24-77 engines were chosen because they are light, thrusty, and are radially mounted. At this point it's unsure how much they will get used. It's all a matter of how much fuel is left in the main, upper stage tanks when we arrive at Duna.
[Figure 6: Service module]
Figure 6 shows the service module. It's powered by the LV-N Atomic Rocket Motor. The LV-N Atomic Rocket Motor will be used to get everything from Kerbin orbit all the way to a high, Duna orbit, where it will be parked for the return trip. Upon re-docking, the service module will bring the command module back to Kerbin.
The service module must contain enough fuel for the return trip, but not the trip there -- the main, second stage fuel tanks carry the necessary fuel for the trip from Kerbin to Duna.
Note that there is only a single, LV-N Atomic Rocket Motor. The LV-N has very low thrust. But that's okay, since once in space, high-thrust is not necessary. Sure, it might be convenient, but it's not usually necessary.
The LV-N Atomic Rocket Motor is also very heavy. It's as heavy as all get out. ("Heavy as all get out" is American vernacular for "Ah, yes. Very heavy indeed. Jolly good.") Be careful when doubling up or tripling up on LV-N Atomic Rocket Motors. They can add a lot of weight to the overall rocket.
One of the goals of this mission is to demonstrate how to use an underpowered, low-thrust stage of the rocket. So only a single LV-N is used here. More on this in future posts.
[Figure 7: Main lifter vehicle (1/2)]
Figure 7 shows the main lifter vehicle. Note that it has all the hardware for remote de-orbiting of the center stack. Had I designed this with KSP ver. 0.24 or later, I might have included some parachutes for center-stack recovery. The combination of parachutes and a touch of leftover fuel can be used for safe recovery, and thus extra funds, in ver. 0.24 or later (the asparagus boosters and SRBs would still be unrecoverable though).
Also, if I was designing this wit 0.24 or later, I might have used the new Vernor engines in addition to the RCS thrustors. The new Vernor engines are linked to the RCS controls, but use regular rocket fuel and are more powerful -- great for steering assistance and stability with large rockets.
[Figure 8: Main lifter vehicle (2/2)]
Note the use of the Sepratrons in Figures 7 and 8. These things are awesome at getting separated asparagus stages quickly away from the rest of the rocket when separating. Since I've started using them, and found out how cool they are, I never leave home without them.
The SRBs, and SRB sepratrons, are staged using "Action Groups," since I don't know when I'll need to separate from them relative to the main, asparagus stages.
[Figure 9: Rocket on the launch pad. Well, this is actually in the future. We're not quite ready to launch yet.]
Figure 9, shows what the rocket will look like on the launch pad. But unlike a trip to the Mun or Minmus, we can't just take off whenever we want, all willy-nilly. Careful timing is important. So long before we launch, we need to do some waiting and planning.
To be continued ...
Full Series
Part 1: Introduction and Basics
Part 2: Efficient Launch Into Orbit
Part 3: Rocket Design Basics
https://www.physicsforums.com/threads/kerbal-space-program-rocket-design-and-orbital-mechanics.970334/
https://www.physicsforums.com/threads/kerbal-space-program-getting-to-the-mun.970335/
https://www.physicsforums.com/threads/kerbal-space-program-getting-to-the-mun-part-2.970336/
https://www.physicsforums.com/threads/kerbal-space-program-preparing-to-land-on-the-mun.970337/
https://www.physicsforums.com/threads/kerbal-space-program-mun-touchdown.970338/
https://www.physicsforums.com/threads/kerbal-space-program-staying-on-the-moon.970339/
https://www.physicsforums.com/threads/kerbal-space-program-preparing-to-leave-lander.970340/
https://www.physicsforums.com/threads/kerbal-space-program-walking-on-the-mun.970341/
https://www.physicsforums.com/threads/kerbal-space-program-leaving-the-mun.970342/
https://www.physicsforums.com/threads/kerbal-space-program-rendezvous-and-docking.970343/
https://www.physicsforums.com/threads/kerbal-space-program-prograde-retrograde-and-approach.970344/
https://www.physicsforums.com/threads/kerbal-space-program-prepare-for-docking.970345/
https://www.physicsforums.com/threads/kerbal-space-program-docking-and-lander-reunion.970346/
https://www.physicsforums.com/threads/kerbal-space-program-heading-home.970347/
https://www.physicsforums.com/threads/kerbal-space-program-entering-Earth's-orbit.970348/
Part 19: Landing Back on Earth
Part 20: Launch for Duna
https://www.physicsforums.com/threads/kerbal-space-program-duna-probe-launch.970351/
Part 22: Duna Rocket Launch
https://www.physicsforums.com/threads/kerbal-space-program-duna-burn-and-periapsis.970354/
https://www.physicsforums.com/threads/kerbal-space-program-duna-oberth-effect.970355/
https://www.physicsforums.com/threads/kerbal-space-program-duna-mid-course-corrections.970356/
https://www.physicsforums.com/threads/kerbal-space-program-using-gravity-to-orbit-duna.970357/
https://www.physicsforums.com/threads/kerbal-space-program-landing-on-duna.970358/
https://www.physicsforums.com/threads/kerbal-space-program-exploring-duna.970359/
https://www.physicsforums.com/threads/kerbal-space-program-launching-off-duna.970360/
https://www.physicsforums.com/threads/kerbal-space-program-fast-return-path-from-duna.970361/
Part 31: Advanced Duna Flight Math
https://www.physicsforums.com/threads/kerbal-space-program-burn-2-to-escape-duna.970363/
Part 33: Returning to Earth From Duna