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Apotheosist

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Posts posted by Apotheosist

    Efficient atmospheric launches: More staging or less drag?

    in KSP1 Gameplay Questions and Tutorials

    Posted · Edited by Apotheosist

    The drag values for the parts to not add up if you use more parts. The drag values shown are relative to the mass of the part. This is especially shown when you notice that both the big and small parachutes have the same drag values. However, the large parachute has three times the mass of the small one, and so it has three times the drag.

    What is your most fuel efficient machines? to the mun / minmus and back

    in KSP1 Discussion

    Posted · Edited by Apotheosist
    correction

    For the lightest category, this I'd say is close to the lightest. http://imgur.com/tsST3 I use mechjeb to help me control that jet engine and those SRB's though, it's very difficult to control them by hand. It of course does not use the fuel bug. I managed it to the mun and back with a slightly lighter rocket, by taking the decoupler and fuel line away to have a lander with one and a half tanks, and adding three landing legs, but it was had a very tight delta-v budget and I found it difficult to repeat the mission.

    I dont usually use RCS or ASAS, but I occasionally make and test rockets with them. Here's one I like: http://imgur.com/j3L5d It has about 7700m/s delta-v, more than enough for a Mun mission. It also has the RCS attached to the command module, so if you get into trouble you could still return home. It does not have many parts, if you take away the ladders. It is very easy to fly.

    Lowest start weight challenge (optimal construction)

    in KSP1 Challenges & Mission ideas

    Posted · Edited by Apotheosist
    Craft file

    I made it with the design I posted a picture of above.

    Nomination: Command Pod Mk1

    Ship name: Minimun 16 IV

    Start mass: 9.8

    Screenshots: http://imgur.com/a/wIvg0 I forgot to upload pictures of the whole rocket here, but it is the one I posted above, 2 SRB's, 1 jet engine.

    Craft file: http://www./?kd62ywilic1n3z5

    Thanks to Nao and adammada for design ideas on this one.

    Im still going to try to fly something a teeny bit lighter...

    Lowest start weight challenge (optimal construction)

    in KSP1 Challenges & Mission ideas

    Posted

    Recently mechjeb gives me strange results. I order him to end at 3 or 20 km periapsis over mun, but he ends with -199 (hit the mun).

    I assume, that circularizing orbit, not direct descent, cost less fuel?

    I also think that Nao's lander could be quite usefull. Bigger tank would go on top and could would be decoupled after emptying. I just don't know how he managed to connect those tanks.

    I dont use mechjeb to do everything, only to keep me pointed in the right direction. I control the amount and timing of thrust. When I do the trans Mun injection, I use smart A.S.S to keep me pointed prograde, and I just wait for the Mun to appear over the horizon. Mechjeb is not very accurate, it does give starnge results. It can still be useful though, you just need to have a mix of useing mechjeb and your own control.

    Yes, I think it's more efficient to retro burn at about 3km and circularise orbit before landing.

    I think the way Nao connected the tanks was by connecting one fuel line to the decoupler, then from the decoupler to the lower tank. Like in this picture, which I am trying right now: http://imgur.com/tsST3

    I tried the one you showed with one jet engine, but I didn't quite make it. I do think that it would be possible if I flew it more efficiently. But using Nao's tank seperation with bigger tank might be better. We will see.

    Lowest start weight challenge (optimal construction)

    in KSP1 Challenges & Mission ideas

    Posted · Edited by Apotheosist

    So I decided to see what I could do with jet engines. Here is the result:

    Nomination: Command Pod Mk1

    Ship name: Minimun 16 III

    Start mass: 11 tons

    Screenshots: http://imgur.com/a/qa4mA

    Craft file: http://www./?al19s36r421091j

    Complete with parachute and landing legs! :D

    As you can see it is quite heavily based on adammada's design, and what he said about almost making it without the aerospike stage. Thanks adammada!

    Lowest start weight challenge (optimal construction)

    in KSP1 Challenges & Mission ideas

    Posted

    Nomination: Command Pod MK1

    Ship name: Nowy

    Start mass: 15.4 Tons

    stages: 4

    KSP: 0.16

    Screenshots: http://imgur.com/a/loIWm

    I'm aware that this design can be beaten - for example hard landing without parachute, cause there is lots of fuel left. I also created once ship without aerospike stage, and I almost returned (but ship didn't had parachute and i wasted too much fuel on retrograde, so he hit Kerbin too hard), but it needs really good piloting skills to use.

    So i'm proud of this - it has less weight than Apotheosist's and it forgives mistakes :).

    Bravo adammada! :D You managed to beat my design by quite a bit. Something I often tell myself is, no matter how well you do something, there will almost always be someone who can improve on it :P

    On that note, I'm going to try to see what I can do using jet engines like you have.

    I have also been thinking about what we might be able to do about how easy it is to fly these craft. Perhaps there could be a rule saying that the ship must have a certain amount of delta-v, or maybe categories for different ships with different delta-v, and maybe categories for use of certain components, like parachutes, or even an ASAS. This would make it easier for those who are less experienced at flying to find a small mun ship they are still able to fly.

    Lowest start weight challenge (optimal construction)

    in KSP1 Challenges & Mission ideas

    Posted

    I see that this still is more piloting thant construction challenge. I tried to use your construction and eneded with 6L of fuel when trying to break to land on Kerbin... So what is most efficient way?

    Which one of my ships did you use? And if you have some fuel left to brake on Kerbin, you're doing well. When braking to land on Kerbin, you need to thrust the engine right at the very last moment, but you only have to slow down to about 70 m/s. The engine and tank beneath you can usually absorb the impact from that speed and your capsule will survive intact. That only works if you land on solid ground, of course. Water landings tend to swallow the whole ship up even at relatively low speeds.

    As for the rest of the mission, my flight plan to orbit is very simple in both craft. Full power all the time, at 12km, pitch over 45 degrees. At 30km, pitch over 90 degrees. Circularise the orbit at about 70km. Then do the rest the usual way. When landing on th Mun, I try to be as efficient as possible, by doing my retro-burn as close as possible to the surface of the Mun, usually about 2500m, but 3000m is efficient enough sometimes. The same applies for when lifting off from the Mun. I try to pitch over fairly soon, and get into about a 3000m circular orbit. Then I wait for the right time to do my burn to send me back to kerbin. The time at which you do this burn affects the efficiency. I use Munar landmarks as visual guides to tell me when to start the burn. You want to try to time it so that after your trans-Kerbin burn, your apoapsis is as close as you can get it to 11,400km. 11,400km is the altitude the Mun orbits at. I found that I used least fuel when my apoapsis was at this altitude. Try to get your periapsis at 30km. Any lower and you're wasting fuel, any higher and you might not get caught by the atmosphere. So your return trajectory back to kerbin should be a 30km x 11400km elliptical orbit. Then the landing would be as I described previously.

    I have learnt most of my efficiency techniques from Kosmo-not, and specifically by watching his video: http://www.youtube.com/watch?v=GzEEcNnBxqM&feature=plcp

    I then replicated the mission using his craft and using his video as a guide. It isn't in version 0.16, but the principles and technique shown there could still be helpful.

    Other things I have learnt from guides and challenges on these forums, such as the optimal ascent (goddard problem) challenge, and optimal descent (to the Mun) challenge.

    Hi, amateur rocket scientist here with a question...

    in KSP1 Gameplay Questions and Tutorials

    Posted

    @Darkstorm406, specific impulse does not 'stack'. If four engines have a specific impulse of 320 each, then all of them together will still have a specific impulse of 320. As you know, specific impulse is related to the exhaust velocity. If you think about it, each rocket engine has it's own exhaust velocity, and putting more of the same rocket engines next to each other will not increase their exhaust velocity.

    It gets more complicated if you're using more than one engine with different specific impulse values. This thread explains how to calculate the average specific impulse: http://kerbalspaceprogram.com/forum/showthread.php/15796-A-Guide-to-Basic-Kerbal-Rocket-Design-Through-Rocket-Science

    Arospike engine efficiency in a vacuum

    in KSP1 Discussion

    Posted

    From memory of something I read a while ago, (or possibly complete rubbish I'm making up) I think aerospikes had about 90% the efficiency that a bell nozzle would have for a specific altitude. However, the aerospike kept it's efficiency through all altitudes, whereas a bell nozzle rocket would lose it's efficiency with changes in altitude. So, it's 90%. But don't quote me on that.

    Lowest start weight challenge (optimal construction)

    in KSP1 Challenges & Mission ideas

    Posted

    Great job!

    But i'm forgot about aerospikes. :-)

    At this time try build craft with this engines.

    PS: You use for travel about 300-400 m/s dV less then i. :-)

    Hehe, yep, aerospikes have a very good performance ;) Many people think they will get nerfed.

    After some practice, it's possible to fly much more efficiently than mechjeb can. I usually try aiming for a total delta-v for a Mun return mission of 7500m/s, but with my MK-1-2 command pod I managed to to do with 7242m/s :)

    So did you say aerospikes are not allowed? If so, maybe you should edit your post to say that. But I'd be very happy to go do the challenge again without aerospikes :D I just love designing rockets!

    Specific impulse?

    in KSP1 Gameplay Questions and Tutorials

    Posted

    Is one fuel unit in game equal to 1kg?

    How would you calculate actual usage then? Say for instance you were using a engine with a 390 ISP and 250 thrust. What would the fuel usage per second be?

    This is a bit tricky because in KSP fuel units do not correlate to mass in nice numbers. We want to know how many units of fuel we use per second. We can't do that directly, but we can work out the mass flow rate per second. There is a formula for this:

    m=F/Ve

    Where m is the mass flow rate of propellant, F is the thrust force produced by the engine, and Ve is the exhaust velocity of the rocket engine. Exhaust velocity can actually be found by multiplying specific impulse by the acceleration due to earth's (or kerbin's) gravity), which is about 9.81. So our exhaust velocity is

    390*9.81=3825.9m/s

    Now we can plug in all the numbers to find out the mass flow rate.

    m=250/3825.9=0.0653 (to four decimal places)

    So there is 0.0653 kerbal units of mass of propellant being used per second. This however still does not tell us how many units of fuel we use per second. Before we can do that we need to know the mass of one unit of fuel.

    So let's work out the mass of one unit of fuel. Choose any tank. I'll take the smallest one, the FLT-200. Take away the dry mass from the total mass to get the mass of the fuel.

    1.125-0.125=1

    So all the fuel in the tank weighs 1 kerbal unit of mass. The tank has a capacity of 200 units of fuel. We can find the mass of one unit by dividing the mass of the total fuel by the number of units.

    1/200=0.005

    Ok, now we know the mass of one unit of fuel and the mass flow per second, we can work out the fuel consumption per second. We can do this by dividing the mass flow per second by the mass of one unit of fuel.

    0.0653/0.005=13.068

    So there you have it, your engine (Toroidal Aerospike Rocket, I see) uses 13.068 units of fuel per second. That is to a certain degree of accuracy; I suppose this calculation could be made more precise. I hope this helped.

    Specific impulse?

    in KSP1 Gameplay Questions and Tutorials

    Posted

    Well I could try, But I'm not promising anything.

    The specific impulse for the rockets shows how efficient they are. The higher the specific impulse, the greater the efficiency. So basically a lower specific impulse means the rocket uses more fuel, but does not make more thrust.

    Most rockets have different specific impulse values at one atmosphere and in a vacuum. For example, an engine might have a specific impulse in one atmosphere of 320, and in vacuum of 370. Specific impulse depends on air pressure outside the engine. The air pressure outside the engine at sea level is called "one atmosphere" because you have one whole atmosphere above you pushing down and creating that pressure. As you go higher in the atmosphere, the air pressure gradually drops, until eventually there is no air at all, so it is called a vacuum. Your engines will be more efficient (use less fuel to produce the same thrust) in the vacuum of space than they are at sea level, where there is one atmosphere.

    However, the "Toroidal Aerospike Rocket" has a constant specific impulse, no matter how much atmosphere it's in.

    If this isn't detailed enough for you I could go further into the physics of it.

    The planetary lander delivery challenge

    in KSP1 Challenges & Mission ideas

    Posted

    @liorg1993, I have also tried modifying your Lander, and I'm quite pleased with the result. I called it "Heavy Lander Lite". I could have started from scratch, but I wanted to keep it as similar to your original lander as possible, while drastically reducing it's weight. The last stage is unchanged, but I have changed the stages before the last. Where you had two stages, I have replaced them with a single stage. This single stage consists of 6 FLT-400 fuel tanks, 6 parachutes, four landing legs and two aerospike engines. Your original lander had a mass of 41.43 tons, the redesigned version has a mass of 23.38 tons. Using only the aerospikes in this stage is more efficient because they have a higher ISP. Even using only the aerospikes this gives a thrust-to weight ratio on Kerbin of 2.18, which is easily powerful enough. I read somewhere else on the forum that the optimum thrust to weight for atmospheric flight is 2.

    The mass ratios of the Heavy Lander and the Lite version are almost exactly the same, I think less than 0.5% difference. This suggests that (ignoring any fuel bugs) they should have the same delta-v. However if you're only using aerospikes as I mentioned, it actually gives more delta-v.

    The Lite lander uses four large parachutes and two small parachutes for landing. This was to fine tune the descent speed as close to your original lander as possible. I measured the descent speed on the heavy lander to be 8.2m/s at touchdown, the lite version only 0.1m/s less at 8.1m/s.

    It should be considerably easier to build a delivery rocket for the lighter lander. However I would like to try out Nori's design.

    @Nori, I could check this myself, but do you know the mass of your redesigned lander?

    Ship: http://www./?bz4yia520osvxc9

    Pics: http://imgur.com/a/7WHOA

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