Duna Chronicles

[Radivis (Michael Hrenka)]

Part 1: Humble Beginnings

Kerbal Space Program is a game that allows you to build rather realistic rockets and do all kinds of space missions with them. The fun part of that is that so many things can go really wrong. And fixing all of them creates a rather interesting learning curve – and quite the feeling of accomplishment after a successful mission.

It took me about a month of watching people play the game on YouTube until I was motivated enough to try it out on my own. And it was worth it! A slightly humorous approach may explain why:

Orbital Mechanics

Also, building huge rockets and see them land on distant worlds, or explode catastrophically is really worth it!

As reasonable player I started the game with the tutorial. Which is where you can get many things wrong, but you can easily get them right, if you are paying sufficient attention. Afterwards I started the game properly in career mode. Meaning that I started out with almost no tech, cheap buildings with huge restrictions, and almost no money. I had to get money with randomly generated missions by contractors. Those could range from testing new experimental parts, over rescuing stranded astronauts from low orbit, to planting a flag (or whole base) on the Mun, the big moon of the home worlds of the Kerbals: Kerbin.

Getting into orbit

The first big challenge of every mission is getting a rocket into orbit. Don’t confuse that with getting into space (in this game above 70 km over sea level). Getting into space is rather easy in KSP. But without substantial additional effort your rocket will be likely to fall back down.

A tiny rocket like this will get you into space above Kerbin, but not much more. Also, it won’t get you back, because when falling down again, it will do so nose down first.

For an explanation why getting into orbit is rather hard, also see: Orbital Speed

Thankfully, the KSP tutorial does an ok job at explaining how to get a rocket into orbit. But for some reasons achieving orbit in the real game seems to be much harder. Probably due to the very serious restrictions on the size and complexity of rockets you can build at first.

It can take about an hour until you are able to get a rocket into orbit kinda reliably. Don’t get me wrong. Many rockets will still fail catastrophically, but sometimes you will succeed and get one into orbit.

Getting to the mun

After getting into orbit the next big challenge is getting something to the Mun. A rocket like the following can theoretically get the job done:

This is one of the more promising designs you can do with a quite low tech level. Unfortunately, it’s still crap. For many reasons:

• When the four side boosters detach they tend to collide with each other, or more problematically with the main engine in the middle.
• The main engine at the bottom is way too weak. It can hardly accelerate the tower of fuel above it.
• The eight tail fins make it rather stable, but make it very hard to steer while still being in the atmosphere!

Still, a rocket like that is good enough to get to the Mun, even to enter a nice orbit around it, and return safely to Kerbin.

If you want a bit more, you need a monster like this:

Theoretically this top heavy catastrophe bound to happen could land on the Mun and get back to Kerbin. If it had proper landing head, that is. But that’s a minor detail.

I don’t have sceenshots of my first Mun landings. Still, Mun landings aren’t too extremely difficult, since they are still covered by the tutorial.

Setting sight for Duna

After landing a couple of times on the Mun and Minmus, the second moon of Kerbin, I have collected enough science points to unlock the technology for building medium sized rockets. At first I really thought that a rocket like this was just sheer insanity:

But then I had really gone wild with my aspirations. I present to you the result of my hybris:

As you can see, I called this abomination the Icarus Test One. I called it Icarus, because it supposedly had enough power to fly into the sun. Test, because I wanted to see what a design like this could do. Well, one thing it could do easily, was to explode during ascent. Since all the 18 solid stage boosters are detached simultaneously, it’s really hard not to get them to hit the middle tanks or engines while falling or exploding. Especially since at that time I didn’t understand how strut connectors or any other kind of mechanical structural supports worked. So, the whole thing wobbled precariously while its boosters were firing.

Still, that didn’t stop me from trying to see how far such a rocket could get. Thus, I set out to get it to Duna, the planet most similar to Mars. So, it added a science return module and build the Icarus Test Two:

It even got a fancy faring that could be detached in space! Even better: the crew capsule had a docking port. But the engineers didn’t notice that they assembled it upside down! Well, thankfully never actually tried to use it anyway.

I was actually very proud at this stage that I figured out how to get my experimental equipment back to Kerbin safely, after it has been to the Mun. The small science module just below the crew capsule usually exploded under the heat of reentry to Kerbin - even when a small heat shield was attached just below it! Attaching a larger head shield under it fixed that issue for good!

The Icarus Test Two Mission

This was of course a very experimental mission. A proof of concept, so to speak. That’s why the ship was called the “Icarus Test Two”. I never intended it to do a serious mission to Duna. My plan was to try flying there and then load the last saving point to see how I could improve the rocket.

That’s why I deemed to safe to send such an ill equipped experimental rocket to Duna. Heck, it didn’t even have any proper landing gear!

It still amazes me that back then with the limited understanding of the game, I managed to arrive at Duna…

Well, of course such an undignified landing was nearly inevitable due to the lack of landing gear. Also note that I landed in the northern polar region, which is really huge in Duna. The white of the ice mices nicely with the rust red of the soil to produce a joyful light pink. Time to plant a flag to spite the odds!

Valentina Kerman was so high on having survive that tripped that she climbed on the trippy flag.

The miracle of return

I quickly found out that landing on Duna provided lots of science points… given that I could get my stuff back to Kerbin in one piece. Having crash landed on Duna I figured out that I could try – just for fun – whether it’s possible to start a rocket from a horizontal position. After more than a dozen attempts I found out that it’s actually possible, although extremely hard. It requires an ungodly amount of luck.

With that brute forced luck I found myself back in Duna orbit and planned my way home. Leaving the gravity well of Duna wasn’t too hard, since it’s much less massive that that or Kerbin. The interplanetary travel from Duna to Kerbin was what too most of my remaining fuel. I actually managed to get back to the vicinity of Kerbin, but my fuel didn’t suffice to enter into an orbit of Kerbin. In other words, from my trip from Duna I had entered the gravity well of Kerbin so fast that I was just passing through.

The Kerbin escape orbit rescue mission

Having come so far, I wasn’t willing to admit defeat and to revert back to the start of the mission. Instead, I planned a rescue mission with a rocket that was planned to intercept what was left of the Icarus Test Two rocket. Given that it traveled at interplanetary speeds, that was a serious challenge!

After a couple of really crazy interception maneuvers I actually managed to approach the craft. The problem is that I forgot to add a docking port to my rescue rocket, so Valentina Kerman had to exit her crew capsule in her EVA suit and fly to the rescue rocket on her own. The whole scientific equipment with all the valuable data about Duna was lost.

In fact, I tried launching a second even crazier rescue mission to save the science equipment, but somehow I just managed to find burnt out rocket stages, rather than the science gear.

I was really proud about that rescue mission. However, I had licked blood and wanted to get science from Duna. My next months of playing KSP would revolve around getting back to the red planet. But this time, much better planned and prepared.

… to be continued …

[Radivis (Michael Hrenka)]

Part 2: Project Nezha

What my first tentative Duna mission has shown me is that getting to Duna is not that hard. It’s getting to Duna and getting back that’s hard. And for that I needed better rockets, or a better plan. Or both.

I started with an idea. Inspired by Elon Musk who wanted to land on Mars by launching two BFRs into orbit and refuel one with the other. Such a trick could surely get me to Duna and back. But, why just a use a space ship to refuel another space ship. Why not create orbital space stations that are usable as fuel depots for other missions?

Building space stations

I thought that was a nice idea, especially since some of the randomly generated missions required me to build space stations that had some fuel reserves anyway. The only problem was getting those space stations into orbit. My first approaches may have been a bit naive…

My idea here was to simply attach the space station to the side of the central rocket like a space shuttle. To make this a bit more stable I just added a regular fuel tank as counterweight on the opposite side of the rocket. The problem was that neither of them were mechanically soundly attached to the main rocket. Oops. Back to the drawing board…

I quickly realized my mistake and got the brilliant insight that it would work much better if the space station was simply the upper stage of the rocket:

That system worked much better … meaning that it worked at all!

In a sense, the station I launched into the orbit of Minmus (the second moon of Kerbin) was a rocket in its own right. Unfortunately, as a space station it wasn’t very good. Even worse: It was a profound failure! It had only one docking port. And that docking port was blocked by the stage separator used the detach the crew return module.

The stage separation worked very nicely, but trying to dock a subsequent Minmus lander with the Minmus station proved to be impossible!

In the meantime I had figured out how to do the really cool Apollo-style landing missions in which you detach a landing module from the rocket and then dock it again with the carrier rocket, after the lander had landed on the celestial body and ascended from it again. On the left side you see the landing module docked with the carrier rocket. I wanted to refuel both at Minmus station, but despite my best attempts, the part of the stage separator that stuck to Minmus station prevented any kind of successful docking. Subsequently I evacuated the station and flew back with the fuel I had left in the carrier rocket. Thankfully, that turned out to be sufficient!

Here’s a proof that this rather top-heavy lander can actually land on a moon. After all, being a bit top-heavy is still slightly better than being way too tall.

Radial docking ports to the rescue!

Of course, I learned from my mistake and from now on added more docking ports to my space stations, so that even if one of them failed, I would have alternatives. One of the first of my new space stations was Space Zero in low Kerbin orbit:

Apart from being bigger, more advanced, and better designed than Minmus Station, Space Zero had a reaction wheel and reaction control thrusters (RCTs) that could quickly stop the station from spinning, if something bad happened. Minmus Station only had a single main engine and couldn’t really do that!

Space Station maturity

Eventually I got quite good at launching stations into the orbits of Kerbin and its moons. Just look at the rocket used to launch the Mun Gateway station into orbit of the Mun:

The outer boosters are of the really big kind. Meanwhile, after countless science missions to the moon of Kerbin I had acquired the technology to build really wide and big rockets. And in fact, I had long since acquired nuclear drives!

The nuclear option

Nuclear drives are much more fuel efficient than regular engines, but can’t start from Kerbin directly, because they aren’t sufficiently powerful for that. So, my thought was to build an interplanetary spaceship that should transport my landers form Kerbin to Duna and back. I would launch the interplanetary spaceship and the lander separately, dock them in orbit, and then off they would go.

So far, so theoretically plausible. This cool idea needed a cool name. After discarding “Project Hermes” and “Project Pegasus” for something more exotic, I settled for “project Nezha”, after the figure from Chinese mythology that probably most closely resembles Hermes. Check out the following video about this endearing mischievous boy:

The Most Powerful Boy in Chinese Legend

And here’s my first model of the Nezha spaceship:

Apart from being a bit weak, the main problem of this design was that the fairing turned out to kinda overlap with the external RCT tanks resulting in a spectacular explosion when I detached the fairing in space. Ok, back to the drawing board…

After having realized that fairings could be very dangerous, I decided that fairings were for pussies and tried launching this prototype into orbit. I also used a larger central tank emptied of oxidizer that isn’t needed by nuclear rockets after all. That also allowed my to switch from six boosters to eight. This increased the performance of this prototype quite dramatically.

In the end, I settled for an even bigger and powerful interplanetary Nezha that I launched successfully into orbit:

The Duna Lab mission

With this powerful spaceship in orbit I became very certain of final success and attempted a very ambitious mission to Duna. The plan was to send not only one lander to Duna, but two. One of them should land on Duna, and one of them would land on the Duna moon Ike. Additionally, I also wanted to drop a small space station around Duna. The whole package was constructed as vertical package on a rocket sufficient to launch the whole assembly to Kerbin orbit:

Getting that Duna Lab into Kerbin orbit wasn’t a big challenge.

From left to right: Duna Lab space station, two staged Duna lander, single stage Ike lander

Docking this sausage to Nezha was a bit harder, but still a manageable challenge.

Stability issues

There was just one problem with the Duna Lab mission:

Trying to move the spaceship Nezha anywhere caused the whole assembly to pivot around the moderate sized docking port connecting Nezha with the Duna Lab! This eventually turned out to be an irreparable flaw of the Duna Lab mission. I couldn’t get the assembly from breaking around the docking port when attempting any serious maneuvers.

Nezha Duna Lander mission

So, I thought maybe I need to limit my ambitions and size down to a single lander…

While at first sight, this assembly looked much more stable, in mid flight to Duna it started to act up and produce the vibrations of the kind that only get worse and end up in catastrophic disassembly. Interestingly, the breaking part turned out not to be the breaking port itself, but the stage separator right below the crew module of the lander.

Still, this hardly avoidable failure doomed Project Nezha to be put onto hold.

… to be continued …

[Radivis (Michael Hrenka)]

Part 3: The Brute Force Option

Fed up with the stability problems with Project Nezha, I decided to go back to the good old chemical rockets. After all, they work, and no docking assembly is required. But I still had to grapple with general stability problems.

Seeking Stability

I figured out that very long rockets are inherently unstable – at least with conventional designs. The center of thrust is too far away from the center of mass. Any small vibration will cause the thrust to be misaligned with the tip of the rocket. This creates a torque that further increases any initial vibration. In contrast, you hardly get any initial vibration within the rocket in the first place, so there isn’t much of a problem.

It does seem to help a bit to make the upper stages smaller than the lower stages, but not by much.

The MaxV is a very powerful rocket that’s sufficiently stable. The problem is that its payload is very tiny. Getting on an escape trajectory from the Kerbol system or flying into the sun are easily achievable, though.

When building tall rockets is the problem, there’s obviously the option to build wide rockets. I tested that idea with a concept rocket called “Snowflayke”:

This may look a bit ridiculous initially, but this rocket was extremely stable. The only problem was not getting the outer stages to crash into the inner stages at stage separation. It turned out to be necessary to fly very straight upwards at first.

The Duna Lander Mission

With this experience, I started planning my Duna mission. Instead of multiple landers, I would be content with a single one. The Duna Lander would land with 3 Kerbals on Duna, and its upper stage would launch from Duna to dock with the return rocket. The return rocket would then fly from Duna orbit into an orbit around Kerbin. Atmospheric braking would then get the Duna Lander back on the surface of Kerbin.

Now, I needed an interplanetary transfer rocket that got both the Duna Lander and the return rocket to Duna. And then I would need more rockets to get the whole assembly into Kerbin orbit in the first place. So, the big Duna rocket had four major stages:

1. Kerbin orbit stage
2. Interplanetary transfer stage
3. Return stage
4. Duna Lander

And here’s my first attempt:

The outer two stages were the Kerbin orbit stage. The orange rockets were the interplanetary transfer stage. The inner tower was the return stage at the bottom, and the Duna Lander on top. I thought this construction was overpowered enough. After all, I used 12 mammoth engines to get this Leviathan into Kerbin orbit! Surprisingly, that turned out to be not enough!

What to do in such a case? The single most important sentence in Kerbal Space Probject applies here: Add more boosters!

Now this was the proper rocket that I used to start my travel to Duna. Overengineered? Certainly! Expensive? Absolutely! Awesome? Hell yeah!

With this baby there weren’t too many surprises. In fact, I made sure that there wouldn’t be too many surprises. I tried to conserve as much fuel as possible. I started with a gravity assist maneuver around the Mun to get the rocket into interplanetary space. Then I used the large orange stage to get to Duna and then enter into a circular orbit around that small planet.

After detaching the Duna Lander from the rocket, I decided to head for a large canyon on Duna, because that was an interesting landing spot. To preserve more fuel, I used atmospheric braking. With the thin atmosphere on Duna that was not very easy, though. So, I used two sets of parachutes of the Duna Lander to slow my descent. First, I used 64 (!) small drogue parachutes that got me down from 600 m/s to about 100 m/s in an experienced blink of the eye. I had no idea whether than plan would work out, but it turned out to unfold perfectly. Then, the next stage of 8 regular sized parachutes slowed me down from 100 m/s to about 20 m/s. Landing such a rocket on relatively plane terrain turned out to be surprisingly simple!

By the way: The strange contraption on top of the rocket were science containers. After all, I needed lots of storage space for all the science I would collect on Duna!

In fact, this landing just outside of the large canyon was so efficient that I still had 60% of the fuel of the lower stage left! So, I choose another interesting landing spot (the mountain ridge of the large canyon) and flew the rocket there and landed again. This time that turned out to be more difficult, because finding a flat landing spot on the more interesting area turned out to be challenging.

But first, time for a group photo:

Note the dark sky even though I landed on the day side of Duna! With the thin atmosphere even the brightest parts of the sky appear as dark grey.

I did lots of experiments at both sites and then stored all the data in the science storage boxes at the top of the lander.

There was a third interesting landing spot: The deeper parts of the canyon itself. Unfortunately, it turned out that the lower stage of the lander didn’t have enough fuel to fly it to the canyon and actually land there. I considered landing with the upper stage of the lander, but it was never intended to land anywhere, so I didn’t add any landing gear for that stage! Landing a rocket without landing struts is not impossible, but you need very plane terrain for that. The inside of the canyon wasn’t sufficiently plane for that.

So, I reverted to my last save and reverted to the situation at my second landing spot. Then I started my ascent with the lower stage and then continued my ascent with the upper stage. Getting that into orbit around Duna was quite easy. It was also relatively easy to dock the upper stage of the Duna Lander with my main rocket:

Now, the Duna Lander was at the bottom of the interplanetary transfer stage. That wasn’t fully intentional. I assumed that the orange stage would be nearly empty after entering into a low Duna orbit. But no, I still had plenty of fuel left in the orange stage, so I planned on using that.

Anyway, I opted for a flyby with the Duna moon Ike. At least I would be able to get some science from flying closely above the surface of Ike. Landing was out of the question with the upper stage of the Duna Lander.

Note how tiny the upper stage of the Duna Lander appears in contrast to the orange interplanetary transfer stage. Also note that I passed 3 km above Ike’s surface at very high speed. An unfortunate mountain could have ended the mission quickly! Yet, the Kerbals were happy as ever!

After the Ike flyby (which also doubled as gravity assist maneuver, I was on my way back to Kerbin. I still had enough fuel in the interplanetary transfer stage for the whole trip towards the gravity well of Kerbin!

This only looked dangerous. The flames of the rockets were illuminating the Duna Lander nicely, but didn’t manage to burn any part of it down, luckily.

This time I did the ecologically sound thing and entered into a straight collision course with Kerbin. Then I detached the orange stage and let it crash into the planet, so that it wouldn’t clutter the space around it. I still had plenty of fuel left in the return rocket to enter a nice circular low orbit around Kerbin. In fact, I had so much fuel left that I considered using that stage as fuel depot in Kerbin orbit. Unfortunately, this possibility didn’t even enter my consideration at planning stage remotely, so I didn’t add any docking ports…

Therefore … what the heck, just enter the Kerbin atmosphere with the whole thing!

In the end, of course, it didn’t turn out to be viable to land with such a huge rocket. So, I did the sensible thing and detached the Duna Lander from it and landed it … regularly?

Honestly, the parachutes were only designed to land the crew capsule and the data storage boxes safely. I never really intended to land the whole upper stage of the Duna Lander completely!

Ah, a perfect landing! Wait, something seems to be missing! Hmm, shouldn’t there be an engine at the bottom of the lander? Oh well, it seems to have collapsed during impact. Thankfully everything else was pretty much unharmed!

Mission successful! I brought back lots of ground samples and sensor data back from Duna!

2870 science in one mission was more than 5 times as much as I’ve gotten from any other mission before!

Also, my crew leveled up and became planetary heroes!

… to be continued?