#### collinsmark

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"How hard can rocket science be anyway?"

Kerbal Space Program is a sandbox type computer game that leans heavily on concepts of physics (don't let that scare you though, you don't need a calculator nor a book of equations to play it. It's ultimately very intuitive).

Given the physics nature of the game, I figure there must be many PFers who play it. And being that the game is so open-ended, I would love to hear how others have fared in their Kerbal adventures. I figure this would be a good place to share your screen captures, success stories, failures, trials and tribulations with the game. (However, in an effort to be kind to Greg, if you have alot of images, preferably put them on the Internet somewhere first and then link to them here, rather than attach them directly to the post.)

(Btw, I noticed there was another PF thread with the same name and subject that got closed. I'm guessing it was closed because the thread was posted in the Aerospace Engineering subforum. I'm posting this in "Fun, Photo & Games" which I'm thinking fits the appropriate content.)

I don't know if it's because I used to build model rockets as a kid, or because I've been interested in physics and astronomy for most of my life, or because I play a lot of computer games -- and I do play a lot of computer games -- but less than two weeks ago, on a whim I bought the game on Steam, and I have to say that I have never been so captivated by video a game in decades, maybe ever, as I have with with Kerbal Space Program (KSP).

[Here's Jebediah Kerman along with Bill Kerman (or is it Bob Kerman. I can't always tell the two apart) gallivanting around on one of their more recent missions to "the Mun" (one of the two moons of the planet Kerbin).]
-------------------------------------

For those unfamiliar with KSP, it's an open-ended, sandbox type of computer game. By that I mean that there is no ultimate ending where you "win" the game. Instead, you are given things like rocket parts (and aeroplane parts), and you can put them together to build a rocket (or aircraft) as you see fit. What you do with it once you build it is completely your choice (assuming it doesn't crash or explode). You can try to visit other parts of Kerbin (Kerbal's home planet), try to get into orbit, try to go to a Kerbin moon or even another planet (or a moon of another planet). It's all left up to you, in any order (if at all). Whatever you'd prefer to do.

Typically though, one starts small, and gets a rocket to work. Then you'll probably strive to get something into orbit. Then you might want to push yourself to transfer that orbit to a Kerbin moon, eventually gaining the skill to land on that moon and return to Kerbin in one piece. A long term goal might be to visit other planets in the system.

And that's where KSP really shines: its implementation of orbital mechanics. It's difficult at first, but trust me, though trial and error you can easily gain an intuitive sense of things. Two weeks ago I barely knew terms like prograde, retrograde, inclination, ascending node, descending node, apoapsis and periapsis. But today, not only do I know the terms, I comprehend them intuitively. And I didn't even put any effort into it! After a few days playing KSP, it comes naturally! (I'm surprised by this as anyone else.) No mathematical calculations or equations are necessary. (Although you could use math and equations if you really wanted to -- the physics modeled by KSP is conceptually quite realistic).

Orbital Mechanics

[Source: Randall Munroe of XKCD, http://xkcd.com/1356/]

So is it a game for a layman?

Yes, I think so. A kid can play this game. Many kids do. There is a bit of a learning curve though. Don't expect to be an expert at everything right away. But don't worry, trial and error will take you far. This learning curve has its pros and cons:

• Con: You have to learn new things.

• Pro: You get to learn new things.

The neat thing about that is what one learns in KSP can apply to real life here on Earth. I've gained a new respect for programs like the Voyager and Apollo missions. Conceptually, from a high level, the things you do in KSP are the same sorts of things that are actually done by NASA (and space programs of other countries). There are some exaggerations, of course. It is just a game after all: The Kerbal's "stabilizer" technology is more advanced than anything humans have; the jet-packs on Kerbal space suits or more than an order of magnitude more powerful than those of NASA; the planets are smaller and denser, etc. Yes, there are these differences -- it is a game after all. But conceptually speaking, the intuition gained is priceless. That includes not just orbital mechanics, but the stuff in rocket design like thrust to weight ratios, specific impulse etc.

(Also it should be noted that the orbital modeling is in the form of conic patches, rather than true, n-body mechanics. But hey, it is just a game, and it doesn't need a extra beefy computer, but that leaves out Lagrangian orbits of course. But it's still good enough for government work.)

The game is presently in its "alpha" release. In other words, it's not near its official release yet. But it's available for sale anyway in a early release version.

Being that it's in its alpha phase, it is somewhat lacking in its in-game tutorials (there are some, but they are scant at best). That brings up another part of the learning curve: Early on, it's difficult to know what the game is even capable of doing. This has its own set of pros and cons.

• Con: Sometimes you might struggle doing things the hard way, only to find out later that the game offers you many other ways to meet your goal, some of which are easy.

• Pro: There seems to be no end to the game's joy of discovery.
Case in point: For the first three or four days of playing the game, I had no idea that Kerbals had jet-packs on their space suits. Once while in orbit, one of the Kerbals got separated from his ship and drifted away. I created a new, special rocket with all sorts of ladders and stuff attached to it, that would make it easy to grab. I sent that rocket on a rescue mission to retrieve the lost Kerbal. Little did I know, I could have just switched over to the Kerbal and had him use his jet-pack to get back to the original ship. Doh!

[Don't do this! It turns out Kerbals have jet-packs. If they get separated from the original ship, switch to the Kerbal (using the '[' or ']' keys), and press 'r' to activate his jet-pack.]

For this part of the learning curve (and the previous part, for that matter), the Internet is your friend. Just type in "Kerbal Space Program" with quotes, followed by whatever question you have, and you're bound to find a plethora of Wiki pages, blogs and YouTube videos answering your questions. If you find a hit of a YouTube video by Scott Manley, go for that; his videos are comparatively well edited and he gets to the point quickly and stays on point.

----------------------------------------------------

I'll get things started. Here are a few images after I restarted the game in "career" mode.

[Here's Jeb on Minmus (the smaller of Kerbin's two moons). This is the first Kerbal on a moon (for me in "career" mode anyway).]

[The rocket I've been using for most of the Mun and Minmus missions (on the launch pad). The first stage (orange part) is in what's called an "asparagus" configuration. By that, all the first stage engines (on the bottom) fire at once (all 17 of them). The outer four fuel tanks feed all the inner (13) fuel tanks until fuel is depleted in them (in the outer four). At that time, the empty, outer four tanks (including engines) are separated to reduce dead-weight, but now all the inner (13) tanks are completely full. Then there is a new set of outer four tanks that feed the inner (9) tanks, and the process repeats once again. (If you've played KSP before and wondering why I didn't use the heavy lifting engines, I'm playing in "career" mode and haven't unlocked them yet). After that, there is a second and third stage that are of the more conventional configuration. All except the fourth, very upper stage (consisting of the command module and lander module) are just to get into orbit around Kerbin.]

[Laying in a course for the Mun]

Here is the command module separating from the lander module.

[Jeb and Bill/Bob doing sciency stuff.]

[Jeb and Bill/Bob doing more sciency stuff.]

[Lander docked with command module. Ready to return home with all the science goodness.]

[On the way back to Kerbin.]

[Once entering Kerbin's atmosphere, I separate the fuel-tanks and engines. Why did I carry that all the way back to Kerbin? Space junk. KSP keeps track of space debris, and I'd rather not have a bunch of space junk orbiting around if I can avoid it. This way it gets destroyed on descent, and I don't have to worry about it.]

[Reentry. As of this writing, the game does not implement atmospheric reentry effects, besides drag, and the "showy" flames. I'm led to believe that the developers plan on introducing more realistic reentry effects in a future release of the game.]

[It's good to be home. (This is actually from an earlier mission than the one's above).]

On a recent mission I've tried my luck with getting a rover to the Mun.

[Rover attached to the lander. On the other side is a fuel tank acting as a counterweight. It's not going to waste though, the fuel is to be transferred to the lander's main fuel tanks, once the rover is released.]

[Jeb and Bill seem quite happy with the new rover. Unfortunately for them, I did a piss-poor job on its design. The rover tumbled out of control and crashed soon after this image was taken. Jeb and Bill barely escaped with their lives. Well, back to the drawing board.]

[Jebediah Kerman on Minmus, looking home, musing over the existential angst of being.]

Full Series
Part 1: Introduction and Basics
Part 2: Efficient Launch Into Orbit
Part 3: Rocket Design Basics
Part 4: Rocket Design and Orbital Mechanics
Part 5: Getting to the Mun
Part 6: Getting to the Mun P2
Part 7: Preparing to Land on the Mun
Part 8: Mun Touchdown
Part 9: Staying on the Mun
Part 10: Preparing to Leave the Lander
Part 11: Walking on the Mun
Part 12: Leaving the Mun
Part 13: Rendezvous and Docking
Part 15: Preparing for Docking
Part 16: Docking and Lander Reunion
Part 18: Entering Earth's Orbit
Part 19: Landing Back on Earth
Part 20: Launch for Duna
Part 21: Duna Probe Launch
Part 22: Duna Rocket Launch
Part 23: Duna Burn and Periapsis
Part 24: Duna Oberth Effect
Part 25: Duna Mid-course Corrections
Part 26: Using Gravity to Orbit Duna
Part 27: Landing on Duna
Part 28: Exploring Duna
Part 29: Launching Off Duna
Part 30: Fast Return Path From Duna
Part 31: Advanced Duna Flight Math
Part 32: Burn 2 Escape Duna
Part 33: Returning to Earth From Duna

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#### Greg Bernhardt

I am going to think about getting this. I was initially scared off when a friend told me it can be rather complex. Thanks for making a tutorial for this game. It should be very useful!

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#### Borek

Mentor
New Wolfenstein is definitely easier.

Gold Member
Why is this so slow? The research center(the land) is slow as a snail. I don't know why. Is is very fast for you?

#### collinsmark

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Why is this so slow? The research center(the land) is slow as a snail. I don't know why. Is is very fast for you?
Just to be thorough, let me say that if you are playing in "sandbox" mode, the research center is not available. You need to play in "career" mode for the research center to open (the research center is where one uses science points to unlock technology).

The present implementation of the game does seem to have some pretty significant load times when you go from one building to another. It might just be the present version isn't optimized yet, particularly for things like loading times.

For me, it might take several seconds to load up the research center (or any other building), but once there everything is pretty responsive.

There's only been a few times when building a rocket in the vehicle assembly building (VAB), where things slowed down to a crawl. I'm not sure why. I guess I did something it didn't like. The problem eventually fixed itself somehow though. I don't know why or how. It doesn't happen often.

#### Greg Bernhardt

Kerbal Space Program is now 40% off on Steam. Go download it!

#### collinsmark

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Kerbal Space Program (KSP) version 0.24 is now available!

And [STRIKE]it's[/STRIKE] KSP is 40% off presently on Steam, but the deal ends in less than a day as of this writing. [Edit: Btw, after initially purchasing KSP, you automatically get access to all future updates. I did not intend to imply that new KSP versions require repurchasing.]

The main addition to this version is contracts. When playing in career mode, you can now take on contracts to build funds and reputation.

(I've been meaning to post again with a shorter story introducing the Oberth effect, but I've been distracted playing the new version of KSP. With any luck I'll post it by next weekend.)

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#### beamthegreat

Sorry if I'm interrupting your thread. I've been playing KSP for almost a year now and I'm proud to say that I have learnt a lot of physics and orbital mechanics from this game. However, there's one thing I don't quite seem to understand and I would appreciate it if you could help enlighten me.

Whenever I approach a planet, I would always set my periapsis as close to the planet as possible to reduce the amount of delta-v needed to circularize the orbit. This is because the closer you are to the planet, the higher the orbital velocity gets.

However, if I were to circularize my orbit at a very high altitude, I would have to spend more delta-v to achieve a stable orbit around the planet.

Whats surprising about this is that if I wanted to re-circularize my orbit to a lower altitude (to rendezvous with a space station), I would have to perform a Hohmann transfer by burning retrograde and, cruise to my new periapsis and burn prograde. This wastes a HUGE amount of delta-v compared to circularizing once at the same altitude. This is especially true if you install the real solar system mod where the orbital speed is 7.7km/s. Your delta-v will totally be devoured by Kerbin!

Why is this so? Shouldn't the law of conservation of energy come into play? Why does circularizing at a higher altitude cost so much delta-v?

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#### collinsmark

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Not at all!

If anything, I've been monopolizing the thread. Feel free to post!

I've been playing KSP for almost a year now and I'm proud to say that I have learnt a lot of physics and orbital mechanics from this game. However, there's one thing I don't quite seem to understand and I would appreciate it if you could help enlighten me.

Whenever I approach a planet, I would always set my periapsis as close to the planet as possible to reduce the amount of delta-v needed to circularize the orbit. This is because the closer you are to the planet, the higher the orbital velocity gets.
Yes, that's often a good idea, shooting for a low periapsis when performing an orbital insertion at a planet.

If the planet/moon has an atmosphere, this allows you to areo-brake which essentially provides thrust for free.

And even if there isn't an atmosphere, you still get the most Oberth effect gains by performing insertion at a low periapsis.

If you intend to land your ship on the moon/planet, you should continue your retrograde burn at low periapsis all the way down to a low, circular orbit. Don't circularize your orbit as a higher orbit, merely as an intermediate step.

On the other hand, if you are parking a heavy space station (which you do not intend to land on the moon/planet), and you plan to use this space station to hold fuel as an intermediate step before escaping the moon/planet, things can get a little more complicated.

In the latter case, the optimal, orbital height of the space station is not the lowest orbit possible, and depends on the intended escape speed.

Let me give you an example. Suppose you want a big, heavy refueling station around Duna. And you want to use this refeuling station as a means to get back to Kerbin. If you use Hohmann transfer orbits to go to/from Duna and Kerbin, your vfs speed at the Duna system is roughly somewhere around 750 m/s. That means you should park the space station at an orbital speed of vor = (750 m/s)/(√2) = 530 m/s, roughly.

Invoking

$$h = \frac{GM_{\mathrm{Duna}}}{v_{or}^2} - r_{\mathrm{Duna}}$$

gives an orbital height of around 750,000 m. That's about 1/3 of the way out to Ike.

Your small ships might burn a little extra fuel getting up to the space station, but, will require less fuel when directly escaping the Duna system (and back to Kerbin) than at any other orbital height.

If you wish to park the heavy space station at even higher orbits, you can do so and save the most fuel, but you will need to leverage the fancy-schmancy escape, when escaping the Duna system. You should also use the fancy-schmancy when the space station arrives at the system.

However, if I were to circularize my orbit at a very high altitude, I would have to spend more delta-v to achieve a stable orbit around the planet.
If you go straight for a high orbit upon entering the SOI of the planet, you will burn a lot of fuel: a lot more than is necessary.

If you instead shoot for a very low periapsis, burn retrograde until the orbit is highly eccentric (very elliptical) and then circularize to a very high oribt upon reaching the new apoapsis, you can save some fuel that way. Of course, now you are stuck in a very high orbit, which might be good for a refueling station, but bad for a ship that wants to land on the planet.

Whats surprising about this is that if I wanted to re-circularize my orbit to a lower altitude (to rendezvous with a space station), I would have to perform a Hohmann transfer by burning retrograde and, cruise to my new periapsis and burn prograde. This wastes a HUGE amount of delta-v compared to circularizing once at the same altitude. This is especially true if you install the real solar system mod where the orbital speed is 7.7km/s. Your delta-v will totally be devoured by Kerbin!
Yes, this is true. If you plan to land your ship on Kerbin, then I'd shoot straight for a low orbit. If you don't plan to land the ship on Kerbin, but instead plan on docking with a space station around Kerbin, don't put the space station in such a low orbit.

If you plan on having a space station for refueling trips to Duna, for example, and you use Hohmann transfer orbits to get to Duna, you'll find (similar math to above) that a space station near the Mun's orbit is a pretty good place. For destinations farther out than Duna, you'll want somewhat lower orbits (lower than the Mun) for direct escapes.

Why is this so? Shouldn't the law of conservation of energy come into play? Why does circularizing at a higher altitude cost so much delta-v?
Conservation of energy does come into play, but only if you also consider the energy of the ship's exhaust.

Simply put, higher orbits have less Oberth effect gains for direct arrivals and escapes, meaning more fuel. (Unless you are prepared to do the fancy-schmancy.) Extremely low orbits can also use more fuel than necessary, if you are not landing on the moon/planet, because the orbital velocity is higher. There is a local minimum in the Direct Escape equation (Figure 103). Higher orbits than this local minimum will use more fuel, and lower orbits than this local minimum will also use more fuel.

#### collinsmark

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By the way, we can find that minimum Δv in the direct escape equation, and find the vor that requires the minimum fuel for escape.

Direct escape equation:

$$\Delta v = \sqrt{v_{fs}^2 + 2 v_{or}^2} - v_{or}$$

And we can find the minimum by taking the derivative and setting it equal to zero.

$$0 = \frac{d}{dv_{or}} \left\{ \sqrt{v_{fs}^2 + 2 v_{or}^2} - v_{or} \right\}$$
$$= \frac{1}{2} \left( v_{fs}^2 + 2 v_{or}^2 \right)^{- \frac{1}{2}}(4)v_{or} - 1$$
$$1 = \frac{2 v_{or}}{\sqrt{v_{fs}^2 + 2 v_{or}^2}}$$
$$v_{fs}^2 + 2 v_{or}^2 = 4 v_{or}^2$$
$$v_{or} = \frac{v_{fs}}{\sqrt{2}}$$

Plugging $v_{fs} = \sqrt{2} v_{or}$ back into our original equation, we find

$$\Delta v_{min} = v_{or} = \frac{v_{fs}}{\sqrt{2}}$$

(The above applies to direct arrivals and escapes only, not the fancy-schmancy varieties.)

#### Monsterboy

This game looks too interesting , if I start playing I might get addicted and spend too much time on it . If only I could get an aerospace degree for playing this game and reaching some level in it I would gladly choose this over a regular college course. Your technical discussions are bit scary but I like them.

#### Lsos

This game looks too interesting , if I start playing I might get addicted and spend too much time on it . If only I could get an aerospace degree for playing this game and reaching some level in it I would gladly choose this over a regular college course. Your technical discussions are bit scary but I like them.
Unfortunately, you WILL get addicted. I have started playing a year ago and I can't stop. No other game has drawn me in like that, and keeps me hooked.

On the other hand, I have reached a point where at least I can stop for a while and take a rest. And I HAVE learned a lot. Sure, going to college you can learn the same amount and more, but I doubt you would understand it so intuitively.

I guess best thing to do is play the game and then take the college course. That way you can just breeze right through it, and get the credit :)

#### Delta31415

k i will try this game

#### Greg Bernhardt

KSP is 40% off on Steam this week!

#### Delta31415

cool i will see if i can buy it

#### collinsmark

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KSP is 25% off on Steam, for Steam's holiday sale!

(collinsmark is not affiliated with Squad or Kerbal Space Program)

KSP version 0.9 was just released! It is now officially in Beta (as opposed to Alpha). A few highlights on recent developments:
• New parts!
• Contracts that make sense, such as put satellites in orbit, build and transport outposts and space stations, capture asteroids, perform surveys, etc.
• Upgradable "buildings": Rather than start career mode with a complete, fully functional space program in place, you need to gradually build it out. This fits in very nicely with the funds and contracts. At the beginning, the space program capabilities are very modest. As you gradually upgrade your facilities and increase tech/funds/reputation, you gradually increase the space program's potential.
• Kerbal experience: Kerbals are actually important now, and individually gain skills and experience points. When I first started playing the game (several versions ago), kerbals were pretty much just along for the ride. And one kerbal was just like any other. But now they learn piloting, science and engineering skills, and can individually level up as they gain experience.
• Ship construction tools have been greatly enhanced (with newly added gizmos and filters).
• Other stuff.
I've already build a few prison outposts* and launched a space commune* into orbit around the sun.

*(I'm kidding, sort of. The game called them outposts and space stations, but I have an active imagination.)

#### Greg Bernhardt

Wow I didn't realize it was Alpha before. This game has a lot of potential! I hope they continue through to gold version.

#### DaveC426913

Gold Member
Must. Resist.
Resolve. Weakening.

#### collinsmark

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KSP version 1.0 is being released within the week! The announced date is this Monday, 27 April 1015.

The 1.0 version number means that it's the first official release: At that point KSP will be neither alpha nor beta, but an actual, commercial release.

Some new things that I know of so far,
• New, more realistic aerodynamics. This includes actual reentry effects. To go with this there are also heat shield parts.
• Many other new parts.
• Some existing parts are overhauled or even re-purposed.
• Fairings! (Fairings are essentially aerodynamic shells that are removed once the rocket leaves the atmosphere. On the aesthetic side, they'll make your rocket actually look like a rocket at launch.)
• Female kerbals. (And here this whole time I thought there already were female kerbals, just indistinguishable from the males. Huh. Well, now males and females will look different I guess.
• Kerbals can clambor/climb. This should help those situations where you want a kerbal to climb up onto a ledge, but didn't place the ladder just right.
• Revamped science tree.
• Some aspects of science have changed, such how the mobile lab part is used: the lab now produces a slow, but continuous source of science (up to a point for a given amount of experiments) rather than merely give a transmit bonus (however it needs to be manned with kerbals for this to happen).
• A bunch of new tutorials.
I've also read of something that hints at gathering resources in situ. But I don't know much about that, so I won't comment on it yet.

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#### Lsos

Resources are indeed confirmed. This means you scan a planet/ asteroid for resources and can mine it to create fuel.

#### collinsmark

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Here's Scott Manley's preview of the new changes for KSP version 1.0.

It's most useful for those who have already played KSP before, since it focuses on the changes from the previous version.

Two days before release! Counting down.

#### collinsmark

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Here's another preview that touches on several things that didn't make it into Scott Manley's preview. This one is by "EnterElysium"

#### collinsmark

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Some of the reviews of Kerbal Space Program have started to come out. Here's one from PC GAMER, which scored it a 96 out of 100.

"A perfect blend of science and slapstick, and a robust and compelling sandbox of possibility. Simply outstanding."​

[...]

"Through its basis in real world scientific principles, KSP's challenge is merely a bar it expects you to match. It's not arrogant, vindictive or malicious. It just is. Design a top-heavy rocket with more fuel tanks than stability, and it will fall over and explode. You're not judged for this failure, you're just left to discover it. This is physics, the game is saying. What did you expect? Its logic is grounded and real, and thus consistent and always fair."
collinsmark is not affiliated with Squad or Kerbal Space Program.

Hi Collins

#### Emmy wealth

I love to be a good engineer too