Mr Shifty

I just wrote a tutorial for this using alexmun's web app calcualtor: http://forum.kerbalspaceprogram.com/showthread.php/33547-Tutorial-Non-Hohmann-Interplanetary-Transfers Let me know if you can't figure it out using that.

Cosmic radiation is different than any of the radiation we're familiar with working around in Earth-based facilities. I've worked around nuclear facilities (both fission and fusion) for 12 years and am well aware of the risks and mitigation strategies we currently employ for these systems. Two radiation sources we worry about are alpha particles -- helium nuclei consisting of two protons and two neutrons with a +2e charge -- and neutrons, which have no charge. Charged massive particles like alphas on earth are easy to mitigate against; they're typically not super high energy, because it is hard to accelerate them, and shielding can be done easily with, for instance, your skin. They pose a hazard to mucous membranes like your eyes, and they can damage your stomach and lungs if breathed or swallowed, but generally aren't a worry externally. Neutrons, on the other hand, because they have no charge and thus are hard to stop, are difficult to shield against. Materials with many hydrogen atoms in them, like plastics and water (and humans!) tend to be pretty good neutron shields because the hydrogen atom nuclei have close to the same mass as a neutron and are able to deflect it. But, it takes, for instance, about 2 feet thick of water shielding to mitigate neutron radiation by 1/10. Cosmic radiation consists mostly of protons, i.e. particles with the mass of neutrons but also with charge like alphas. However, cosmic radiation particles have on the order of 1000 times more energy (GeV instead of MeV) than terrestrial radiation sources, which means they can penetrate metal, water, anything. The fact that they have charge means that as they pass through you, they'll do more damage. It's sort of like a neutron is a bullet that passes right through you, with a small exit wound. Potentially deadly, but survivable if it doesn't hit anything vital. Alphas are like a shotgun blast from far away. You might have a few small penetrating wounds, but it's unlikely to be fatal. Cosmic radiation is like a shotgun blast at point blank range. The mitigating factor is that cosmic radiation is pretty low background, except that during a solar flare, they can increase to 10-3000 times normal flux (July 11-13, 1982 had a 10MeV flux of 2900 pfu; the current 10MeV flux is 0.18pfu), which would kill astronauts in hours. The problem isn't trivial. The effects of cosmic radiation on biology haven't been well studied (because how would you?) Passive shielding is going to be heavy and not very effective. Active shielding (using electric or magnetic fields to repel or deflect the proton flux) is complicated, heavy, untested, and has unknown effects on humans. Add to this the complications that proton (and neutron) radiation has on electronics. (Neutron radiation is a major headache in my job as an electrical engineer at a fusion research facility.) Neutrons are just the right size to cause random bit errors in memories and cause latch-up and outright failure in microprocessors and other smart electronics (FPGA's, etc.) Space vehicle electronics (and nuclear facility electronics) typically look like they're 30 years out of date because we use large, simple components that are less likely to fail and can be easily replaced when they do.

Great updates! I notice that the 180 degree gradients are gone on the mid-course plane change graph (and thus on the optimal solution.) I presume this is because you've made the plane change for those Hohmann-like transfers much more efficient by moving it to mid-course. - Regarding the 90 degree point: I could easily be mis-understanding the mechanics, but shouldn't the course-correction point be a 90 (or 270) degree true anomaly on the transfer ellipse to ensure that the radius to target doesn't change. You're currently calculating it by determining the true anomaly at the destination and subtracting 90 degrees (with a fallback to ballistic if the transfer angle is less than 90 degrees.) But that doesn't result in a 90 or 270 degree true anomaly at course change unless the transfer is Hohmann. - Some of the solutions have a negative periapsis. What does that mean physically? I understand a negative apoapsis represents a hyperbolic orbit (and does this calculator work for such orbital transfers?), but what does a negative periapsis mean?

Damn, I did a search prior to posting this, but it missed the thread a few below this one. Please delete, moderators.

My workhorse is 5 Mainsails with 2 orange tanks on each, clustered in two asparagus pairs around a center tank, with locked outside gimbals and fins all around. Then above that I stack my transfer vehicle: two LV-Ns with FL-800's. Payload goes on top. Total delta-V is in the neighborhood of 11km/s. (And I end up adding a bunch of RCS and tanks to the center rocket because the whole thing is so long it won't pitch or yaw in vacuum without help.) The Mainsails get me into orbit with enough left in the center tank for another 1200-1300m/s. Would it be better if I used clustered engines instead of the Mainsails?

Tutorial is here.

EDIT: Note that this tutorial actually does not work. Specifically, the non-Hohmann transfers do not necessarily require you to exit the origin planet's SOI parallel to its sun-centric trajectory. I'll update and remove this notice at some point. I'm loving alexmun's amazing Launch Window Planning web-app. It gives fantastic results, but it's not immediately obvious how to use them; this guide provides a step-by-step. To provide an example, I thought I'd plan a trip (my first) to Jool from Kerbin. Here are the constraints for my example problem: - My persistent game was about at 1yr:200d. - I have a launch vehicle plus transfer vehicle with a total delta-V of about 11km/s. With at least 4.5km/s to get into LKO, I have about 6.5km/s for the transfer. The ultimate goal of the trip is to put a survey satellite in orbit around Laythe, so wanting to reserve some m/s for that, I wanted to limit the total transfer delta-V to less than 5km/s. - My Kerbals have an election coming up in 2 Kerbin years (~106 Earth days) and need Jool intercept as a campaign booster. So, we need to make it there in less than 212 days. To reiterate: Start after day 200 and with a transfer delta-V of less than 5km/s achieve orbit prior to day 412. Step 1: Use alexmun's calculator to discover a transfer characteristic with your desired parameters. Here's what I got when I entered the parameters above. (I use a 500km parking orbit so I can use 10,000x warp.) Note my total delta-V is just under 5,000m/s. I've boxed the four important parameters in red. Step 2: Establish your orbit and warp to about 2 hours prior to your launch window. - Kerbal Alarm Clock is very handy for this. Step 3: Rotate your display in map view so that you're looking directly down (south) onto your orbit. Step 4: Zoom out until you can see Kerbin's procession around the sun, then orient your view so that Kerbin's prograde direction is pointing directly up to the top of the screen. - Make sure you do this near in time to your launch window, since Kerbin's prograde direction changes as it rotates around the sun. - Note that Kerbin, like all the planets, rotates counter-clockwise around the sun, so prograde means the sun is 90 degrees to the left of Kerbin when looking directly south. - You can zoom in and Kerbin's orbit should look like a vertical straight line from top to bottom of the screen. Unfortunately it fades after a second or so, so you'll probably have to zoom in and out a few times to make sure it's right. Step 5: Determine approximately where the ejection angle intercepts your orbit. This is the ejection point. - If you're moving to a higher orbit (e.g. from Kerbin to Jool), the ejection angle will be to prograde. If you're moving to a lower orbit, the ejection angle will be to retrograde. Here's the approximate position of the 101 degree ejection angle for my Jool transfer. (If you're clever, you'll notice that prograde is not actually at the top of this image. Please just pretend it is.) Step 6: Advance your orbit until you're just past the ejection point, with one rotation to go until your launch window. - Most LKO orbits run from 30-60 minutes. Add the times to and from apoapsis and periapsis to determine your orbital period, or just use MechJeb or Engineer Redux. - You probably won't be able to hit your launch window exactly. You should be able to get within 1/2 of an orbital period. Step 7: Add a maneuvering node at the ejection point, then add prograde delta-V until it equals delta-Vejection*cosine(inclinationejection). - The cosine function lets you determine how much of the escape trajectory is in the prograde direction. Step 8: Drag and rotate the maneuvering node around your orbit until the escape vector is parallel to the prograde or retrograde direction. - The point of the ejection burn is to put your ship onto an escape trajectory that parallels Kerbin's orbit around the sun. That way you make maximum use of your ship's orbital velocity around Kerbin to either speed you up or slow you down for your transfer. Here is my initial escape trajectory. Now nicely paralleled. Step 9: Adjust your maneuvering node for the ejection inclination. - Add north (for positive inclinations) or south (for negative inclinations) until the total delta-V equals the total ejection delta-V. Step 10: Zoom out and see how close you've gotten. - You may need to tweak the maneuvering node slightly to get an intercept. The launch window and angle imprecision could cause minor adjustments to be necessary. MechJab's maneuvering node editor is very useful for this. Note that my final trajectory passes much further from Jool than planned, is about 30 days shorter, and uses an extra 100 m/s or so of m/s. Step 11: Perform the burn. - These are typically long burns, 1-2km/s, so as with any burn, try to center the burn around the maneuvering node time. - Watch the orbit in map view as you get to the end of the burn to ensure you make intercept. - If you don't make intercept, then a very small (<100m/s) burn should get you there. Play with maneuvering nodes to find it. During my Jool transfer, I made a 67 m/s burn 6 days out that pulled my Jool periapsis all the way into its atomosphere. Now just coast to intercept and burn to achieve orbit. You're done! Here's my hyperbolic approach to Jool. Achieving orbit took less than 500m/s because I was able to aerobrake that hyperbola into a fairly small ellipse (semi-major axis of ~400km). I estimate my total delta-V for the transfer was well under 3500m/s. Plenty of energy left for a transfer from Jool to Laythe. Happy trails!

If you don't mind, I think I'm going to make a guide based on those steps.

You can set up a maneuvering node to help. This worked for me to catch Eve from Kerbal. I came really close to ejection delta-V and transit time estimations. I did end up pretty far from Eve (~50,000km periapsis) so the injection burn was really long, but with some tweaking, it should be possible to get much closer. 1. Rotate the camera in map view until you're looking directly down (south) onto the origin body 2. Zoom out until you can see the path of the origin body around its primary (e.g. the sun for planets) 3. Rotate the camera until the prograde procession around the primary is pointing up. 4. Locate the approximate escape angle and put a maneuvering node there. 5. Add prograde to the maneuvering node until it matches the prograde component of the ejection delta-V (should be delta-V*cosine(ejection-inclination.) 6. Zoom out until you can see the escape path for your ship. 7. Pull the manuevering node around your orbital path until the escape path is parallel to the prograde direction if you're moving to a higher orbit or to the retrograde if lower. It should be pretty close to start with since you put it at the approximate angle to prograde in step 4. 8.Zoom out and adjust the north/south on the manuevering node until you see intercept with the target. Total delta-V should match the ejection delta-V. I used dual LV-N's for transfer so the ejection burn runs about 3 minutes/1,000m/s. Like you said, centering the timespan on the burn point seems to work pretty well. You could add the prograde/retrograde and north/south components of the ejection delta-V to the calculator, but it's not hard to calculate cosines.

How are you burning at the correct ejection inclination? It's easy enough to start my burn at the correct angle to prograde using Engineer Redux, but adjusting inclination using just the navball seems... imprecise, and just a tenth of a degree can mean your approach is way north or south of the target. I suppose you could adjust your orbit around the origin body so that it's inclined at the proper angle, with either the ascending or descending node at the ejection angle as appropriate. You'd have to do it pretty near in time to your launch so that the origin's prograde direction doesn't change appreciably. Then you could just burn prograde when your launch window shows up.

It should; it solves for an orbital path that lies in the plane defined by your initial position vector in 3-space and the final position vector at intercept.

Is the gradient at a transfer angle of 180 real or an artifact of the discontinuity in the solution to the vector problem there? Seems like if the transfer angle is 180, you could just do a regular Hohmann transfer at any inclination, which my (probably faulty) intuition tells me would be a minimum delta-V solution.

Thanks for the speculation. I, in fact, e-mailed this question to Mr. Munroe simultaneously with posting on this forum when it occurred to me last week. It did seem like a perfect what-if for him.

That. Is. Awesome. It would be cool to be able to toggle the contour plot to show ejection/insertion/total delta-V's. And totally easy to update when new celestial bodies arrive. This tool needs a sticky somewhere. And let me just say that your code is very clean and elegant and easy to read. You are my new hero.

Good tip. In this case, I had designs on using RCS to soft-land the lander away from the transfer engines, and in fact it was necessary, since I still had about 2 m/s of lateral velocity when I hit Minmas, which broke apart the LV-N engines (as you can see.) I was able to separate the lander and bring it down softly away from the engine debris with RCS. Obviously this only worked because of Minmas's low gravity.

Thanks much! I will try that this evening.

I used a similar 4-symmetric stage to launch my first successful Minmas landing last night, but it was kind of a fiasco. I was having trouble controlling the final long rocket stage (it would not turn around the long axis to, literally, save itself). I eventually stuck 4 radial engines on long struts sticking out from the side. Trying to keep the thing pointed along my orbital route while at 50km up ended up whipping the Mainsail and lower orange fuel tank off the end of the rocket. Luckily, the radial engines were suspended off the side of the upper orange tank and got me the rest of the way into orbit. (And the payload was a lander with a couple LV-N's on the back for Kerbin to Minmas transport.) I'm just wondering how you make that last long rocket stage controllable.

I found this: http://www.daviddarling.info/encyclopedia/M/microwavefusion.html And this tokamak based one, which suggests 1.3Ms of Isp and 90MN of thrust, relying on some very unrealistic assumptions. http://energyphysics.wikispaces.com/Tokamak+Thrust+Engine (Disclaimer, I work at DIII-D, an experimental tokamak, which since I'm an engineer, not a physicist, gives me zero insight into the likelihood of this. I do know that working fusion reactors, even experimental ones, are still decades away.)

Electrical Engineer. I design, build and maintain diagnostic systems in a physics research facility investigating how to make fusion power a reality.

Hey, thanks Nova! And now I have a new sci-fi novel in the to-be-read stack.

In other words, what if the Earth spun fast enough that the velocity of objects on the Earth's surface at sea level was equal to the orbital velocity at that point? Could we all fly, or at least hover above the ground? Throwing a baseball would put it into orbit? I'm not sure about all the implications. Is this even possible? Has it been done in sci-fi?