Orbital Vagabond

How much Vacuum dV does your SSTO start with? It sounds like your profile is already pretty efficient.

The game actually is based on real science, specifically Newton's laws. Pretty much everything else gets derived from those three laws. By learning *how* those laws work in KSP, you can learn how the work in the real world. The only two truly important differences between KSP and real-life I can think of are: Specific numerical values (planetary radii, gravitational parameters, ISPs, etc) How atmospheres interact with vessels Beyond that, things work in KSP pretty much exactly they way they would in real life. In fact, I would argue (as an academic in a different field) that learning on a different system (i.e. the Kerbol and it's satellites) is more educational than learning on a familiar system (the Solar system) because you can't simply recycle what previous engineers and scientists have used before. Solutions need to be novel. I agree that there are still substantial shortcomings in KSP (no life-support, crappy heat management, etc), but I really can't see it as a 'missed opportunity' for tangential learning about spaceflight.

The trick is to find the "sweet spot" where the dV cost is the lowest. On the one hand, the closer you are to semilatus rectum (line through the focus of the orbit and perpendicular to the semi-major axis), changes along the normal vector are most effective at changing the elevation at the apoapsis. However, normal burns are pretty expensive at the semilatus rectum because you're still pretty low, and hence moving pretty fast. So you've got to balance the effectiveness of a normal burn, which goes down as you approach the Mun (in your example) and the cost of the burn, which is also going down as you approach the Mun. The good news is, it sounds like you've found a good spot near the transition. I'd bet you could save some dV by making the burn an hour or two before the Munar intercept. Making the inclination change when you're initiating the transfer for a fair to good hohmann transfer is a bad place to make the normal burn for two reasons: It's where you're moving fastest, and it won't lead to much elevation change at the target.

I also prefer multiple ships. Multiple vessels means lighter individual payloads, which makes it easier to engineer vessels to have good TWR, in turn allowing more precise transfer burns.

RoverDude, seriously love your work, but I can't get on board with this kind of point of view, especially after HarvestR's little "Speculation leads to disappointment" lecture a few months ago.

I'm sorry, but I really don't care for Squad's vague hints. I thought they would have learned by now that encouraging speculation is an irresponsible way to build up hype, but, oh well, the community just seems to keep eating it up. I still don't think we ever got told what HarvestR's "little last minute addition that KSP just wouldn't feel right without" was just before launch.

For the IRL details: The aircraft a modified 747-100 and was officially called the "Shuttle Carrier Aircraft". As mentioned above, it was used for glide testing the "Enterprise" orbiter (A STS prototype that never flew into orbit) and transporting shuttles from Edwards to Kennedy/Canaveral.

I fill like a possible solution to producing low thrust in an atmosphere would be to provide a stock electric propeller. You still get to use electricity to produce a small amount of thrust. You just need to provide a second means of propulsion to make it into orbit in the vacuum.

What kind of dishes? what are they aimed at? There's a lot of information that isn't here if you want help.

A bit of a necro, but I'd like to see this feature added to KSP.

I think this is the most likely explanation. The "skipping off the atmosphere" probably referred to how the capsule generated lift to modify it's trajectory and ease re-entry. In fact the pod is supposed to escape the atmosphere after it's initial re-entry, but at suborbital speeds, so that it re-enters again more slowly and at a steeper angle. If it was travelling in excess of escape velocity and didn't kill enough velocity on the first re-entry phase, then yeah, it would "skip" out into interplanetary space.

Is Kerbin's sidereal period still 6 hours? I thought they changed the synodic period to 6 hrs back in 0.24 or something.

Okay... I'm gonna preface this post with a few points. First, I really appreciate your website, it's a fantastic resource I use ton. I have tons of respect for you, and I know you know your stuff. I hope it's clear my posts are not intended to be condescending, belittling, etc. I have respect for you knowledge and understanding of the field. Second, I'm not looking for a fight on this; I've lurked on these forums for a long time, and I've seen things go really south really quick. Finally, I'm not even looking for a debate: I'm going to state my reasons for my opinion and leave it alone. That said, I think SI is vastly superior to the Imperial system because... 1) What the frak is a slug? I've never heard of the unit "slug". Now, on it's face that may not mean much, lots of people don't know lots of things. However, I have two doctorates, and while both are in the life sciences, I've still spent enough time in science to think that should qualify as kinda weird. This speaks to the fact that there are lots of cryptic, uncommon, and otherwise bizarre units in the Imperial system. This issue is so uncommon in SI I don't think it's hyperbole to state it doesn't exist. For mass, everything is a [x]gram; For length, everything is an [X]meter. Once you know the set of units, and the set of prefixes, you know it all. The closest this comes to being an issue is KSP is the "ton" unit. It's a metric ton, same as a Megagram. I can understand that unit of mass immediately. 2) Is it a ton or a ton? In the Imperial system, the nomenclature is a mess. You have to differentiate "short" tons from "long" tons, and that doesn't even touch metric tons, but that's SI... ish. Same issue for ounces: You've got fluid ounces mass/weight ounces, and troy ounces... Just... C'mon! 3) I've only got so much brain power In your post, you listed... *checks* 5 measures of mass? Slugs, pounds-mass, kips (?), tons, and ounces? To go directly between these, I'd need to memorize 15 separate conversions, many of which need a lot of digits for accuracy (3 or more). The option is to put everything into one unit, which is extremely inconvenient when nothing is given to you in that unit to start with. Conversions in SI mean moving a decimal point. That's it. I can remember that. 3A) So 9 ounces is 0.625 lbs? or 0.63 lbs? or 0.6 lbs? Precision in a decimal numerical system is way easier when [practically] all the units are related to each other on a base 10 scale. There simply is no round off error. The Imperial system almost never uses conversions that are multiples of 10, which can cause some serious issues with precision when you're applying multiple conversions in series. Avoidable(ish) with computers, but for mental math and estimation, its a needless source of error. This is really a subpoint of 3 and you mentioned it in the post, but it bears repeating. 4) Hybrid Units I'm out of clever titles. In the Imperial system, it's common to report quantities in two additive values, e.g. 5 lbs 6 oz. Yes, I know how to deal with it, but the point is I have to deal with it. This is never convention in SI/metric. I think that's it. You can chalk all this up to "poor training and habits", but those are very large and very real issues in the real world. The SI is simple and straight-forward because it was designed to be simple and straight forward, and is one of the few examples where a rational and intentional design produced such a system. I think it's a shame to not use it in place of the Imperial "system", which has, been cobbled together from a multitude of sources and disciplines, many of which are now obsolete. Again, just my opinion with supporting points for why I think it's quantitatively inaccurate to say Imperial is "just different names for the same things." The way in which I thought your response post supported my point was that you had to bring "oh, if you're doing it right" and "people need to be taught appropriately," and you did because the Imperial system is not as easy to use as the SI system. It takes more experience and training to use than the SI system, and offers no benefits to the SI system. IMO, it's hard to use the SI system wrong and I can't imagine having to write a post that starts with "if you're using the SI system correctly".

I feel like this whole post just made my point...

In theory, the "more thrust is better" is true, but in practice, TWR > 3 provides almost no dV savings.

Primarily, yes, you're exchanging KE for PE, but you are still losing some orbital energy to drag as you ascend up to 70 km alt. It's always most efficient to add energy into your orbit by thrusting directly prograde, regardless of what the prograde direction relative to the horizon, so you're correct in being concerned about thrusting off prograde (in this case, radial). This isn't so much an issue with the Oberth effect as it is that you're canceling out velocity with a non-parallel thrust (basically vector math). While thrust in your direction of travel is the most efficient way to add energy, it won't necessarily put you in the orbit that you want to be in. If you want a circular 70 km orbit, I would perform your orbital insertion right at 70 km thrusting mostly prograde, and slightly radial in (below the horizon). That way you won't go any higher than you need to, and will minimize losses due inefficient radial burning since your radial/vertical velocity vector will be lower (less vertical velocity to cancel). If the suborbital trajectory with a 100 km Ap is locked in stone, I think this is the most efficient method to get a 70 km x 70 km orbit. Hope that helps.

It is algorithmic, which, in my view, is primarily due to the step-wise method of dV calculation for staged rockets. It also depends on what value you're trying to optimize: launch mass, dV, cost, etc. I recall seeing a webpage (which I frustratingly can't find right nowon project rho here) that discussed having a hapless graduate student plug in various values to determine the optimal ration of fuel between two rocket stages to minimize total launch mass. In a two stage system the solution is relatively easy to find, but in a three stage system the solution becomes much more difficult to locate. If you're optimizing dV, in theory there wouldn't be a solution because larger stage attached below any described rocket, which can have another booster stage attached beneath it, etc etc. In my experience, it's simply easier and equally (if not more) effective to design rockets with stages for specific jobs, e.g. 1 or 2 stages to launch to LKO, a separate stage for a transfer, etc. You can optimize for each leg of the journey. Additionally, Wikipedia has some interesting information on optimizing rocket staging here and cites Curtis' Orbital Mechanics for Engineering Students. If there's an answer to you question, it'll probably be in there.

Yeah, but it's another step.

Not really, I grew up using Imperial units my whole life, strongly prefer SI because it's easier. Especially in astrodynamics/physics for no reason other than SI uses distinct units for force/weight (Newtons) and mass (kg), where as the lbs are used for both in imperial.

Is this bad time/place to point out that the "Gamer's edition" is $80 US/55£?

3-5 Kerbal days (6 hrs) or Earth days (24 hr days). If it's the former, it's gonna be tight. And if Remotetech is an issue, then send a manned mission.

escape velocity is also much lower from Minmus, and it may actually take less dV to transfer from cis-Minmus orbit to LKO than from a cis-Munar orbit to LKO. if it's more, it's not by much.

I think a 2-man command pod (be it Gemini or Soyuz inspired) would be a great addition to the game. I don't think any propulsion systems should be integrated, though, since that would somewhat defeat the purpose of the "lego" style design concept the devs have stated a preference for (basically, it's the reason we don't have procedural tanks of any kind).

Like most everyone else has mentioned, I would recommend KER to calculate the dV of your vessel. I would also recommend thinking of your vessel in two parts: The launch stage and mission playload. Figure out how much vacuum dV you need to get to orbit (vacuum dV is reported by default in the KER readout and is a convenient metric for figuring this out), and design your launch stage to supply that much dV. Then, separately, design your mission payload to have sufficient dV for your mission (more on that in a second). For example, lets say you tend to need 4,000 m/s of vacuum dV to get into orbit, and your mission will take about 2,000 km/s from LKO. You should design your total vessel to have about 6,000 m/s in total. To calculate your dV by hand, you need to familiarize yourself with Tsiolkovsky's rocket equation. Now, to calculate the dV you need for your mission, there are two option: dV maps and the ol' fashioned manual method. Using the dV maps that have been created by other players is pretty easy. The best one I've seen is Kowgan's revision of WAC's map (posted here). Just add up the values on the way to your destination. The manual method is substantially more complex. Do really do it well, having a year or so of high school/secondary level physics really helps. Basically, you need to calculate the desired velocity for your desired orbit at the location where you intend to burn, and subtract from that velocity at which you will be traveling at the location you intend to burn given your current orbit. Repeat this process for each maneuver you intend to make to reach your mission target. Since velocity is speed and direction, this REALLY is vector math, so being familiar with vectors is helpful as well. A good summary of the equations you'll use is available here. It's a great site that I've been using since I found it. I think it's maintained by someone on these forums. You'll start with the vis-viva equation, and work your way up. Hope the helps.

Holy Kerbol, here's why you can't mine Xe: It would be a massive career mode exploit for cash. 1 unit of Xe is weighs 0.1 kg and is worth 4 funds, that means that at 50% mass efficiency (I think that's ISRU refinery's base mass conversion efficiency), you could refine 1 ton of ore into 5,000 units of Xe worth 20,000 funds! Compare that to LF, 1 ton of ore becomes 100 units of LF (1,000 kg ore x 0.5 kgs LF/1 kg ore x 1 unit LF/5 kg LF), which is worth 80 funds. You'd be basically printing money. I personally think this feels like an exploit. Maybe some players feel that this should be included to represent some kind of orbital manufacturing, but omission of Ore -> Xe means that the current game isn't balanced around this alternate source of income, and this would lead to a LOT of income: 100 tons of ore -> 1 million funds if you can get 50 tons back to the KSC. And that's before engineer bonuses (Not quite sure how they work). That's my take on it, at least. - - - Updated - - - Then why does the vessel have 3 chutes on it? Sounds like that's going to the Kerbin's surface, not staying in orbit.