GoSlash27

Alshain, There's no wrong way to play this game, and far be it from me to tell you how to run your railroad. But for me *personally* I have no problem getting SRBs to behave just as well as LFBs. They're *definitely* not "painful to fly" and I have no problems getting efficient gravity turns out of them. Best, -Slashy

Ahh... that's the source of the confusion; we're talking about 2 different things. You're talking about using SRBs to add DV to a parallel stack. *I'm* talking about using SRBs as the first stage in a series stack. Best, -Slashy

Snark, This is absolutely true... *if* you're landing on a very smooth body and if you aren't particular about where exactly you want to touch down. If you have to avoid terrain and/ or want to land precisely, you will have to intentionally take those losses. DV expenditure goes up as a result. Best, -Slashy

Alshain, I use SRBs exclusively as a first stage, and for a completely different reason: SRBs are *cheap!* Without stage recovery, the booster stage is disposable. No recovery value. Therefore you want to provide that first 1,800 m/sec DV as cheaply as possible. Nothing provides that DV as cheaply as a trash can fulla boom. If I'm using a recoverable upper stage, I may intentionally reduce or even eliminate the SRBs in order to minimize launch expense (and thus maximize recovered value), but if I just want a cheap disposable launch, I use SRBs for the first stage. Best, -Slashy

Starhawk, No harm, no foul A reverse hohmann transfer can come very close to the minimum calculated DV, but we usually have a very specific touchdown point in mind. This precision costs a good amount of DV to achieve. Plus translating around in the landing zone, gravity losses from low t/w, pilot error, and safety margin... a good approach can get well- over the minimum calculated DV. A bad approach can exceed twice the calculated value. For safety's sake, I like to err to the side of caution for airless body landings. I'm not saying that all approaches should expect twice the listed DV expenditure, only that it *can* happen and it's best to plan for it so you don't end up short. For example, see davidpsummers' example. If he designs his lander from the outset with 2x the DV budget for landing, he's safe even if he's never shot the approach before. Best, -Slashy

BoilingOil, You've got the formula for the kerbosynchronous orbit, which my spreadsheet says is an altitude of 2,868,723m. The next step is to figure out how much DV you need to place an object there. The vis-viva will tell you how much additional DV is required to execute a Hohmann transfer from LKO to KSO. There's an excellent write-up of the procedure here: http://www.braeunig.us/space/orbmech.htm ^ Bookmark or download a copy of this! for a Hohmann transfer from an altitude of 101,305m to LKO, the first burn will be 650 m/sec and the circularization burn will be 424 m/sec; a total budget of 1,074 m/sec. Why such an odd LKO altitude? well... Where it really gets fun is figuring out the longitude your vehicle needs to be at in order to place the sat over a specific longitude on the globe in KSO. In order to do this, you need to look back at your transfer orbit from the previous problem. You need to convert it's SMA into an orbital period (also in the guide I linked) and then divide by 2. This is how much time it will take you to go from Pe to Ap; 5,033 seconds. You need to know this because Kerbin is going to rotate during the transfer and you need to lead it so that you will arrive overhead the target. Kerbin has a rotation period of 6 hours (21,600 seconds), so it will rotate (5,033/21,600) *360° = 83.88° in that time. Since your Pe must be on the opposite side of the planet, you would start the transfer when the vehicle's longitude is 180°-83.9°= 96.1° west of the target longitude. And before you can make use of that, you have to answer a more fundamental problem: How do you know your vehicle's longitude at any given moment? On a bone-stock installation, there's no direct readout of the vehicle's longitude. This requires some inventiveness to work around and this is how I solve it: The reason I chose such an oddball LKO altitude is because it has an orbital period that orbits Kerbin exactly 11 times per day. Since Kerbin rotates once per day, that means that it passes over KSC 10 times per day, or once every 36 minutes. By placing a seeker pointed up on KSC grounds and tracking it, I can mark the time of it's passage over KSC down to the second. Since it passes over KSC once every 36 minutes, it covers 10° per minute and 1° every 6 seconds. I therefore know what it's longitude is simply by the time of day. It's then a simple matter to calculate a transfer window from the time it passes over KSC. If I wanted to place a sat directly over KSC, I would fire at 360°-96.1°= 263.9° after passage. That's 26 minutes, 23.4 seconds. For ultimate accuracy, I would want to know how long my transfer burn will take so I can split the difference. Orbital mechanics is fun math once you get the hang of it, and it opens up all sorts of interesting possibilities. Good luck! -Slashy

KerikBalm, Ah, but this is only true for vertical flight and ignores Mach effects on drag. As you turn prograde and fly more horizontally, the optimal acceleration falls below 2 Gs in proportion to the sine of the pitch angle. As a practical matter you'll never reach terminal velocity in the vertical boost phase. And as I said earlier, minimal DV expenditure isn't a useful design criteria anyway. It's really about minimal cash/ fuel/ and stage mass. Best, -Slashy

Snark's got it covered. The real cost of high t/w isn't so much the drag penalty as the mass and cost of the engines. There's also a penalty in additional control systems (fins/ reaction wheels/ batteries/ etc) to keep a high t/w launcher pointed the right way. A high t/w stage can get the job done with minimal DV expenditure, but this doesn't necessarily translate to the lightest, cheapest, or most fuel- efficient way to go about it. Generally, the important criteria for a booster stage is bucks per tonne and for an upper stage is mass. Neither is optimized by seeking minimum DV expenditure through high acceleration. I design my boosters to have an initial t/w of 1.4. This tends to maximize the payload fraction. SRBs will go even lower in order to keep the t/w in check throughout the flight (they can't be actively throttled). Best, -Slashy

I'd say humans are genetically predisposed to wandering around in search of food, but not so much just wandering around for the sheer heck of it. We do like to explore and learn new things, but I don't think that extends to space travel unless there's a compelling reason for it. Best, -Slashy

tatonf, DV to orbit is empirical for atmospheric bodies. Everything else is calculated and rounded to the nearest 10 m/sec. For airless bodies it's the orbital velocity at sea level plus the DV required to Hohmann transfer to the specified low orbit altitude. Best, -Slashy

radonek, A lot of people use a "stop 'n' drop" technique to land at a specific location. I've seen instances of this going upwards of 200% minimum. See kerikbalm's analysis above. My favorite technique for pinpoint landings exceeds 150% minimum. It's not "doing something wrong", it's simply a tradeoff. If you want to land in a precise location, it's gonna cost you. Best, -Slashy

egogo, You've got it figured out. The map you're using is accurate. DV to orbit is a rough estimate for atmospheric bodies and calculated fairly precisely for airless bodies. Having said that... You will actually need more than 580m/sec DV to land on the Mun safely. Perhaps as much as twice that depending on your technique. Landings are highly- inefficient processes. Best, -Slashy

Van Disaster, The wing loading and incidence is independent of overall spaceplane mass. I don't know if that holds true for FAR ( I run strictly stock), but to my way of thinking anything that's too underpowered to get off the runway is going to be too underpowered to break Mach 1. Best, -Slashy

Right, The mass is a pretty minor concern. Spaceplanes aren't particularly sensitive to that. As for the area, again... it depends on what you're doing with it. If it's a small crew taxi (which is what I use Mk2 for) you're going to be hard- pressed to build a Mk. 1 that will do the same job as cleanly. *Edit* Yeah, the drag gets bad when you pitch it. That's why I don't consider body lift to be an advantage and I design my spaceplanes to fly with zero incidence from Mach .9 on. Aye, I'm talking about the side flow numbers. A long section has the same side flow as a short section. I'll kick you a copy of my "Brawndo" Mk.3 tanker to play with. *edit* http://wikisend.com/download/714318/BrawndoIV.craft Best, -Slashy

Right, The Cd and area nose-on is the bulk of the drag in spaceplanes. The Mk.2 has an advantage over Mk.1 in that respect due to the low Cd of the Mk.2 cockpit. As for the Mk.3, it's side drag doesn't increase with longer sections. I'm a big fan of Mk.2 for personnel transports and Mk.3 for tankers. I suppose it depends on what you're trying to do... Best, -Slashy

Van Disaster, Not so. I've built several extremely underpowered spaceplanes that could take off just fine without assistance. I agree with Hodo on this one. Best, -Slashy

The Mk2 parts also have the advantage of using the Mk2 cockpit, which has excellent drag characteristics. In spaceplanes, good drag properties often trump mass. Best, -Slashy

http://www.gi.alaska.edu/AuroraForecast/NorthAmerica http://www.gi.alaska.edu/AuroraForecast/Europe/20151102 This is the result of a large coronal hole that will be pointed at us tonight. This should yield a very energetic aurora display visible much farther south than usual. It may also cause some disruption in satellite comms and power grids. Best, -Slashy

Xennari, Correction to the earlier correction: g0 *used to be* approximated as 9.82 prior to 1.0. That has since been rectified. It is now 9.81 like it should be. Proof: Best, -Slashy - - - Updated - - - Aye, but the tank mass matters as a practical concern since you can't add fuel without adding tank mass to hold it. Since the LF&O tanks weigh 1/8 the fuel they contain, you will never be able to build a rocket with a Rwd higher than 9. This sets an absolute maximum DV of Isp*9.81* ln(9), or approx. 21.6*Isp. And this is with an infinite number of fuel tanks. Best, -Slashy

Fubarbrickdust, Congratulations! This just made my morning Best, -Slashy

zolotiyeruki, The easiest way to quantify wing drag is to take a peek at the physics.cfg file. Drag as a function of the sine of the AoA: AoA: Drag 0 (0°): 0.01 0.3420201 (20°): 0.06 0.5 (30°): 0.24 0.7071068 (45°): 1.7 1 (90°): 2.4 drag by Mach Mach: Drag 0: 0.35 0.15: 0.125 0.9: 0.275 1.1: 0.75 1.4: 0.4 1.6: 0.35 2: 0.3 5: 0.22 25: 0.3 Best, -Slashy

Fubarbrickdust, Not a problem and you're very welcome. People on this forum are nothing if not helpful. And don't sweat the design of your ship. Efficiency is something that will come with experience. Right now we just want something that we know will do the job and get Bob home safe. If this design is good enough to reach the Munar surface, then it's good enough to use for the rescue in orbit and that's all we really care about. Feel free to hit me up if you have problems with the rendezvous. You'll have all sorts of DV to play with. Best, -Slashy

I'll put in yet another "Whackjob for Jeb" vote and also second OhioBob's nomination for Wernher Von Kerman. Best, -Slashy

zolotiyeruki, I'm not sure which "wing type A" you're referring to; structural, swept, or connector. 2 wings with equal lift ratings will always exhibit the same drag at any given AoA, altitude, and airspeed in KSP. Trust NathanKell on this; he literally "wrote the book". Best, -Slashy

Fubarbrickdust, I would go ahead and orbit him now (make sure he's transferred the science to the pod). When the rescue ship arrives, you will be able to target him and rendezvous in a single orbit. 1) target him 2) set your closest point of approach to match his orbit 3) retroburn to orbit 4) continue to retroburn while watching his predicted position marker (red arrow pointed up) spin around his orbit. 5) the lower your Ap gets, the slower it will spin. Try to get the marker to line up with your closest point of approach while maintaining a reasonable Ap (still higher than his orbit). 6) if you miss the last encounter, just burn prograde to get it back. 7) orbit once and rendezvous on the next encounter. Do you know how to rendezvous? Best, -Slashy