First of all, something I am very proud to announce, after a whopping total of six programs installed and two programs used online, excluding YouTube, I have found a way to record my screen and show it to you in a high quality form!
Observe in the form of a gif of a probe falling to Kerbin!
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| Needless to say I am very happy! |
Moving on, I have researched a lot since we last met and have applied it to the simulation. I have begun some planning for the Mun mission.
If we'll start on the research, I've mostly been researching the launch and flight related stuff, and have stopped for the most part on the orbital mechanics. Orbital mechanics are less important for the Mun seeing as how close the Mun is; no Hohmann Transfer Orbits needed here!
The two most important equations are the equations for Delta-v and the thrust-to-weight ratio (which is usually referred to as the TWR).
The thrust to weight ratio is rather straight forward, and is used to see if a rocket can lift off of the ground. If it is less than one, it will not lift off the ground. The equation goes as follows: Ft / m * g, where Ft represents the force of thrust, m represents the mass of the rocket, and g is the local gravitational pull.
For example, let's consider a rocket with engines that give 270 kilonewtons of thrust, has a total mass of 33, and is on Kerbin's surface, where the pull of gravity is 9.81 m/s squared.
The equation becomes 270 / 33 * 9.81.
This becomes 270 / 323.73.
The ratio is then less than one, and the rocket will be unable to lift off the ground. This is incredibly important so that I know if a rocket I thought would work can get a foot of the ground, let alone into space.
If none of that made any sense, NASA has a wonderful page describing it here. Try not to get too distracted by the plane; although it can also be applied there along with the lift-to-drag ratio, I will only be using it in terms of rockets.
The other equation is for delta-v; it is the most important equation in rocket science when it comes down to it. It is the rocket equivalent to saying that you have a gallon of fuel left and your car runs 40 mpg, so you'll make it 40 miles. The difference here being that since in space there is no friction, you could technically go an infinite amount of miles assuming nothing gets in the way.
For that reason scientists and engineers use delta-v to describe the capabilities of a rocket or space plane. It describes how much the vehicle can change its velocity; so, if a rocket had a delta-v of 100 m/s and was going at 0 m/s currently, it could change that so that it is going at 100 m/s.
The equation goes as follows: Isp * ln( mf / me ) * 9.81 m/s^2, where Isp is the specific impulse (basically the efficiency of the engine, how much thrust is produced per the flow rate), mf is the total mass of the craft, and me is the dry mass (the mass of the rocket without the mass of the fuel). 9.81 m/s^2 is to convert the delta-v to m/s, the desired unit, and ln is natural log.
NASA has a more comprehensive guide of it and the Ideal Rocket Equation it is based off of here. To be completely honest, though, I didn't understand what they were saying and just found a forum post that I felt explained it better; my description of it above is essentially what the forum posting said.
Moving away from the research, I have launched three Kerbals, the astronauts, into orbit and back using that research and the delta-v map below.
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| This map describes the approximate amount of delta-v required to reach certain bodies. |
calculating it again while in orbit I found I only had about 980 m/s of delta-v left.
If you are interested, I will hopefully be posting my notes on the rocket tomorrow or the day after. It is on graph paper, so I will have to transcribe it onto an excel sheet; I'll probably put it on a Google doc and post the link when I find the time.
Some more interesting things, about Time To Fly III, the rocket in question. Don't worry, no casualties involved in the other two!
Since some of the videos were too large for the in blogger program, here is a link to a playlist of them all. The first is 8 minutes long of making the orbit, the second is 45 seconds long of some space walking, and the third is of the reentry of Time To Fly III.
Since I couldn't show you them here directly, here is a screenshot of the dark side of Kerbin:
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| The dark side of Kerbin. Jebediah is loving it, but the others are quite afraid. |
I commented on these people's blogs:
Matt Autieri's (the fourth blog post)
Eric Lang's (the third blog post)
Nathan Leung's (the Cycle 2 blog post)
This is fascinating. I've been interested in space for a while, but I don't really have a passion for it. A lot of the concepts mentioned in your blog post were confusing to me, but you're good at explaining things, so it was easy enough for me to understand. I'm glad that you found a way to show us your progress. One suggestion might be to show a side-by-side comparison of the program you are using and an actual video or picture of a probe.
ReplyDeleteIt's good to know that I've done better at explaining some of the concepts. I'll be sure to detail some differences between the simulation and the real world in the next post; there are some size and density changes, among other things, in this simulation.
DeleteWow i can tell that you are extremely interested in space and your excitement is very clear. The simulator that you are using is very cool and the videos showing your probes and rockets are so life like. There seems to be alot of math involed to get one of these rockets to Mun or Kerbin, how long does it usually take you to complete each mission. Also what are Kerbin and Mun, are they moons or planets?Best of luck this topic is very intriguing.
ReplyDeleteIt usually doesn't take long; most of the equations are pretty easy. The hardest part thus far was wrapping my head around things like delta-v and specific impulse, but once you understand them they aren't too hard to calculate.
DeleteKerbin is the simulation's equivalent to the Earth; the Mun is the simulation's equivalent to the Moon.
Thanks for the luck!
This is about as far as I've gotten in KSP. After days of frustration upon not being able to make a Müner landing, I gave up and made rocket planes. Because why not?
ReplyDeleteAnyways, one thing you have to remember is that a rocket that usually has high ΔV usually has low thrust. A plasma rocket might have a high ΔV, for example, but it might not even be able to lift itself off the ground.
One other option if you don't want to do your boring old launches, is you could make a space plane! Seriously, you could you jet engines and wings as an efficient means to get to the upper atmosphere, drop those stages, and use a rocket for the rest of the way. They're much more difficult to design, though.
Also, there's a way to exchange rocket designs. Have you though of uploading them?
That high delta-v but low thrust was something that has been a problem; I think a solution might be to have the mid-stage engine have low thrust but high specific impulse. That should solve the problem, I think, but I'm going to have to research a bit more and maybe do a test or too.
DeleteI have been considering space planes since the start, because I think they're very cool, but I don't think I'll be doing that for this project since I haven't done too much research on lift and drag; I could use the website linked in the blog post for that if I desire.
I have but I don't think it saved the design. I'll try to find it and uploading it along with my calculations as soon as I can.
Thanks for your comments and suggestions, you've given me some stuff to think about!