Meithan

4. Laythe Keeping up with the "most challenging first" strategy, my next target was Laythe. While the atmosphere makes landing almost free, it also conspires with the relatively high gravity to make takeoff quite expensive: about 3300 m/s is required to reach orbit from sea level. I went for a simple two-stage lander design, considerably lighter than the one used for Tylo. The first part was transferring to Laythe, with a 60 km orbit as target (just above the atmosphere). My original mission plan was to do a propulsive insertion, but in order to make up for overexpenses during the Tylo leg, I decided to take advantage of the atmosphere and perform an aerocapture. With this I ended up expending 467 m/s instead of the planned 700 m/s. During planning I pre-selected a landing site using Kerbal Maps. It had to be: At or very close to the equator Flat, with slopes not exceeding 10° in a wide area Around 1000 m ASL, in order to have a reasonable parachute descent speed while reducing takeoff drag losses After some scouting using Kerbal Maps, I selected a site on one of the larger islands (blue lines indicate the equator and the 0° longitude meridian): In the following slope map I indicated the target landing ellipse. The transfer and landing are documented in the following album. Note: you can also view the album directly on imgur. The ascent back to orbit was relatively easy. The lander still had 3951 m/s left, and about 3300 m/s are required. I started the "gravity turn" around 8 km, and flattened the ascent profile from there. I spent 3368 m/s on the ascent to a 60 km orbit. I'm sure it can be done more efficiently. After rendezvous with the Orbital Module, and deorbiting the ascent stage using the RCS tug, I waited for the planetary positions to be right and then transferred back to the Prometheus. The transfer was again more expensive than expected: 1064 m/s vs. the planned 700 m/s. By this time my overall delta-v deficit for the mission had risen to 624 m/s. See the ascent to orbit and rendezvous with the Prometheus in the following album. Note: you can also view the album directly on imgur.

3. Tylo Because the Prometheus remained in its parking orbit and only the Orbital Module and a lander transferred to the moons, there was really no forced order in which to do the landings. Still, I decided I'd do the hardest one first: Tylo. The Tylo Lander undocked from the Prometheus and was transferred to Tylo using the Orbital Module. Then, descent. With a gravity comparable to Kerbin's and no atmosphere, my estimates indicated I'd need at least 5000 m/s to land and return back to orbit. The Tylo lander has 6231 m/s, which gives me a large room for error. It was still a tough landing, requiring experience and good thrust management. Note: you can also view the album directly on imgur. It was now time to get back to orbit and rendezvous with the Orbital Module in its 30 km orbit. With no atmosphere, the strategy is pointing towards the horizon almost immediately after takeoff. Unfortunately I had some high mountains to the East and had to be careful to gain enough altitude to clear them. However, for some reason, during the second stage separation event the discarded fuel tanks exploded, possibly colliding with the central tank. While the ship survived, it imparted a serious kick that destabilized it. By the time I managed to recover a correct attitude I had been thrusting away from the intended direction for too long, and couldn't clear the mountains. On my second try I shut down the third stage engine just before second stage separation, but the problem occurred again exactly as before. This was weird, since I tried stage separation without problems on my multiple Kerbin tests before the mission. So I decided I'd have to live with it. On my third try I took off on a slightly more vertical trajectory and shut down the engine before staging. This gave me more time to recover orientation after the mishap. It worked. After rendezvous with the Orbital Module, I used the small RCS tug to deorbit the spent lander stage; no point in ferrying it back to the Prometheus. Finally, I rendezvous'd with the Prometheus in Jool orbit. However, I spent more fuel than planned on the return trip. By this point I was getting really worried. Pictures below. Note: you can also view the album directly on imgur.

2. Launch and Transfer The first part to be launched to orbit was the Lower Section, comprising the Propulsion Module as well as the Laythe and Mini landers. The launch vehicle took the payload all the way into a 120 km orbit, so that the Prometheus used none of its fuel, and then deorbited itself. Note: you can also view the album directly on imgur. Next, the Upper Section was launched. The small upper stage of the launch vehicle completed the orbital insertion and performed rendezvous with the first half of the ship already in orbit. Note: you can also view the album directly on imgur. I chose the Jool launch window occuring on Year 15 day 292, computed using alexmoon's fantastic Launch Window Planner: After checking all systems, the Prometheus departed on its way to Jool. More than two years later, it used Jool's atmosphere for aerocapture and circularized into a parking orbit between Tylo and Vall. Check the following album for the details. Note: you can also view the album directly on imgur.

1. Mission Design Inspired by successful mission reports posted on these forums, my design was a one-kerbal (Jeb, of course) mission using three separate landers and a two-part mothership, comprising a propulsion module for the voyage to and from Jool, and a a smaller detachable module for transfers between the moons of the Joolian system. The whole ship was christened the Prometheus: More details are given in the following image gallery of the mission hardware: Note: if the album doesn't display properly here, you can view it directly on imgur. This mission requires a lot of planning because of the large delta-v expenditures and the fact that each leg depends on the successful completion of the previous ones with a limited margin of error -- which means that fuel has to be very carefully rationed. I decided I needed proper planning for this one, so I wrote a small Python program to pre-compute a flight plan for the entire mission, including all orbit changes and landings (using some conservative delta-v values to have some room for error): The resulting flight plan was dumped into a spreadsheet, which I used to closely keep track of my fuel consumption along the way. I also uploaded the full version of the spreadsheet as it was at the end of the mission (in Google Drive converted form; the original ODS file is also available). Finally, here are the full specs of the various ships, in case anyone's interested:

Well, I finally finished the mission report for my Jool 5 Challenge attempt. I took a lot of screenshots (many more than I show here), so I'll use imgur albums to keep it tidy. I also split the report in multiple posts. Meithan's Jool 5 Mission Table of Contents 1. Mission Design 2. Launch & Transfer 3. Tylo 4. Laythe 5. Vall 6. Bop 7. Pol 8. Return Objective To land a kerbal on all five moons of Jool in a single mission. Mission Overview Single kerbal lands on all moons Modular lander design using the same command capsule Three-stage Tylo lander Two-stage Laythe lander (parachute descent) Reusable single-stage mini lander for Vall, Bop and Pol Large propulsion module for Kerbin <-> Jool transfer Propulsion module stays in 50,000 km Jool orbit Orbital transfer ship takes landers to/from the moons Delta-v Breakdown I've collected a detailed list of actual delta-v expenditures incurred during the mission, in case it's useful to anyone. Mods used Here's the list of mods I used for this mission: MechJeb 2 (only info screens, no autopilots) Kerbal Alarm Clock Environmental Visual Enhancements + Astronomer's Pack Docking Port Alignment Indicator HotRockets! Toolbar Texture Replacer + Rareden's Real 8k Skybox (at end of mission only) Publicity shot:

To add to rdfox's informative answer about the Apollo deorbit & landing profile, you can directly browse a version of the original Apollo 11 Mission Report. On page 30 (of the document, page 42 of the PDF) you can see a diagram of the first type of LM separation and deorbit program rdfox was talking about. The next page has nice diagrams of LM attitude vs. distance to landing site. On page 39 (51 of the PDF) there's a more detailed graph of pitch attitude vs. time. That report contains a wealth of information about all aspects of the mission, by the way. I'm very glad NASA has made it publicly available. As you can see their landing profile was quite conservative, probably far from optimal for safety reasons. The Apollo descent engine had an available delta-v budget of 2500 m/s, and the mission plan was to use 2063 m/s during landing (so they had 21% more than needed). However, Apollo 11 used more fuel since Armstrong had to fly longer to avoid rough terrain, but I couldn't find exactly how much extra delta-v they used. It was pretty close, though. For reference, the ascent back to orbit required about 1850 m/s of delta-v, and the ascent stage had something like 2200 m/s total.

Yep, that is usually a problem, and the practical solution is to spend a bit more delta-v in order to have better control of your landing site. The more vertical your trajectory, the easier it is to pinpoint the landing spot. So try a compromise between the two methods (efficient "horizontal" landing vs. precise "vertical" landing). Streetwind's and Wanderfound's suggestions are good. I've done precision landings a few times (landing about 100 m from my target on the Mun) and trust me, they were nowhere near optimal in terms of spent delta-v. So my main suggestion would be: make sure your craft has a lot of delta-v to spare.

It depends on the mass of your ship and the number of LV-909s, as well as the balance between engine Isp and mass. It's complicated. The bottomline is that it's all a matter of thrust-to-weight ratio: the higher it is, the closer you can get to the optimal landing trajectory (in terms of delta-v). While it's possible to land with a TWR less than one, it becomes rather expensive. Weird, they work fine on my browser. Here are direct links to the graphs: Delta-v cost for "vertical drop" landing strategy Delta-v cost for "lower periapsis" landing strategy Exactly. The most efficient landing strategy is the same as the most efficient takeoff strategy, just in reverse: always try to burn as horizontal as possible. Doing that minimizes delta-v lost to fighting gravity ("gravity losses"). You're in luck: some time ago Kosmo-not posted a very nice video showing how to land using a "constant-altitude trajectory": As you can see, it's not a vertical suicide burn. It's rather much like a "horizontal takeoff" in reverse. The fundamental idea is to control your vertical speed by pitching your spacecraft. At the start you'll need very little pitch to keep your descent speed low and thus will be thrusting almost horizontally, which means your thrust is used almost entirely to decelerate instead of fighting gravity. It's indeed hard to control your landing site since the landing trajectory is long and it's difficulty to predict exactly when to start the landing burn. So in practice one usually trades off a bit of efficiency for more control over the landing spot (by doing a slightly more "vertical" landing profile). What I normally do is lower the periapsis so it's close to the surface and past my intended landing site. I figure out approximately how much time I need to burn to kill my orbital velocity and use that to determine when to start burning. When I'm close to the landing site, I then use pitch to fine tune where I will touch down. It's a matter of practice, and one can get fairly close to the figures quoted in delta-v maps.

I think I can see why you'd think that: what's independent of the landing strategy is the required change in orbital energy. You start in orbit with an energy E0, and after landing your energy will be E1, and the difference E0-E1 is completely independent of the landing trajectory (since gravity is a conservative force). But a difference in orbital energy is not directly equivalent to a difference in velocity (a delta-v)! The Oberth effect is a great example of this non-equivalence: by burning deeper in a gravitational field, you produce a larger change in orbital energy with the same delta-v. Said plainly: while the required change in orbital energy is indeed independent of landing strategy, the delta-v used isn't, and delta-v is directly related to fuel usage so that's the quantity that matters. Technically, both strategies assume velocity changes are exactly instantaneous, which means they assume infinite TWR. In practice, how large a TWR can effectively be considered "large enough" for purposes of these calculations will depend on the specifics of the landing profile and so it's hard to tell. One thing that can be said though is that the impact of low TWR will be worse for the "vertical drop", since you'll be thrusting vertically (which is inefficient, since part of your thrust is used to fight gravity instead of decreasing your speed). Weird. Did you click on the "Spoiler" links? Sure, with perfect flying landing and takeoff costs are identical, but I'm not talking about takeoff here, just the landing part.

Z-Man had the right hunch: the extremum you found is actually a maximum. Here's a graph for KSP's Mun (R=200 km, μ=6.5138e10 m^3/s^2). The black curve is the total delta-v spent with this landing strategy. It peaks at 400 km (2R, as you correctly found). Here's the corresponding graph for the better landing strategy which has been mentioned in this thread: first lower the periapsis to the surface, coast to the surface (i.e., periapsis) and then kill all your velocity. Note that both landing strategies assume that TWR is large enough that velocity changes are nearly instantaneous. If this isn't true, expect landing costs to be higher than those calculated here. Doing a "vertical drop" from high altitude is a bad idea since the higher you start the more gravity accelerates you on your way down, which is extra speed you have to kill to land. And for small altitudes the vertical drop is still not the best idea because it's more efficient to kill your orbital speed (which you have to do at some point either way) when you're as low as possible in the gravitational field (yes, the good ol' Oberth effect).

KerikBalm feels exactly like I do regarding this. I understand what you're saying Brotoro, and you're right. But no matter how complicated the transfer to GEO ends up being, the point is that the moment in time chosen to start the whole affair shouldn't matter because the relative configuration between the Earth, the launch site, and the target spot in GEO never changes. There's complete time symmetry in this respect. Launching at any other time would make the whole deal look exactly the same, except rotated with respect to Earth's inertial frame -- but the point is that the target spot also rotated in that time in the exact same amount, so the whole series of maneuvers, as complicated as they are, would end up reaching the same longitude in GEO. I'm pretty convinced by now that the reason for there being a launch window has nothing to do with the actual trajectory with respect to the Earth. Something else is involved here, and my only guess so far is that it has to do with the position of the Sun (which completes a revolution relative to the Earth in almost 24 hours -- that would explain why the launch windows repeat almost exactly every 24 hours, like in the SpaceX SES 8 mission example). And I found this in the Google Books preview of the Handbook of Geostationary Orbits by E.M. Soop: Could this be it ???

By the way, it seems i'm not the first person bothered by this question: r/askscience: Why is there a launch window for a geosynchronous orbit. But none of the answers given there strike me as solving the issue either. The basic argument remains: relative position of the target spot being constant with respect to the launch site. I don't see how any of the answers provided so far explain this point.

But my point is that there's no timing involved because the target spot in the geostationary orbit is motionless relative to the Earth's surface and, hence, launch site. If they waited 5 minutes, 30 minutes, 2 hours, 6 hours, 1000 hours more to launch, it'd be still in the same place relative to the launch site. So why does it matter *when* they decide to launch? Indeed, launching directly into an equatorial orbit is impossible if the launch site is not on the equator, so midcourse corrections are necessary to deliver a satellite to GEO. But I don't see why you assert it's only possible twice a day, Could you elaborate?

If the window repeats daily, such as in the SpaceX example, then this is definitely something related to Earth's rotation (such as waiting for the launch site to pass through some orbital plane or for the phase angle to a target to be correct -- but none of these seem to apply for a launch to GEO). Speeds in LEO and GTO sure, but not speeds in GEO, that's my point: things in GEO rotate at the same rate as the Earth. You can picture a launch to GEO with a specific target longitude as a rendezvous with an empty spot in space that's in GEO orbit. But since GEO has a 24 h period, that "rendezvous target" is always in the same place relative to the Earth: it doesn't seem to orbit (relative to Earth's surface), it's just motionless with respect to the launch site. So why would launching at a different time make any difference?

Uhm, I'm not convinced. 15 minutes sounds too short compared to Earth's rotation period. Besides, as it climbs towards GEO altitude, a spacecraft will quickly exit the Earth's shadow, no matter when it was launched. In fact it's not particular of this launch. A recent SpaceX launch to GEO (SES-8) also had a shortish ~1 hour window that repeated daily: SpaceX SES-8 launch attempts What orbital mechanics detail am I missing here? Well the point is that a spot in geostationary orbit is stationary with respect to the surface of the Earth, so it holds a constant relation to the launch site. Thus, no matter when you launch, your target orbital position is always in the same spot relative to the launch site. So I don't see why there is a launch window at all.

Perhaps. But 15 minutes sounds like an awfully short window. If the crux is that the transfer orbit to GEO occurs in sunlight, I'm sure the window would be considerably larger (a few hours, at least?). No, this short window makes me think that the reason has to do with orbital mechanics, but I just don't see it. Wouldn't this make for a short "don't launch" window, instead of a short "do launch" window?

Yesterday I watched India launch another of their navigational satellites into orbit. The satellite is intended to operate in geostationary orbit, and the launch rocket put it on a transfer orbit, as usual. What got me thinking is that they said the launch window was 15 minute long, and I got thinking that I don't quite understand why this is so. If the intended orbital position is geostationary, it means it does not move relative to the Earth's surface. So I don't see why it matters when the satellite is launched. You can launch at any time and the target orbital spot will always be at the same place relative to the launch site. Other than things like solar illumination, I don't see why there's a launch window at all. Anyone?

Considering Kerbin's density is around 58 g/cm^3 (as opposed to something like 5.5 for Earth), I'm willing to accept they're liters even if that'd make fuels too dense compared to real life (and tanks not properly scaled for the volume they hold). As has been said, knowing what the game's units for propellant volume are is not important anyway. As long as you know the mass of a unit, you can call them whatever. Propellant volume units do not interact with anything directly.

Q: Have you ever achieved a stable orbit around Kerbin?(2 points) Yes. Q: Have you ever landed and returned from the Mun?(4 points) Yes. Q: Have you ever landed and returned from Minmus?(4 points) Yes. Q: On how many objects outside the Kerbin system(which includes Kerbin, the Mun and Minmus) have you landed on(doesn't have to be a return mission)(2 points per object, or 24 if you've landed on all) I've landed on all of them. Q: Have you ever successfully docked?(10 points) Yes, routinely now. Q: Have you ever intercepted an asteroid?(16 points) Yes, once just after the ARM update came out. Haven't tried ever since. Optional question 1(if you use mods): How many of the following difficulty enhancing mods: TAC life support, Remote Tech, Deadly Reentry, FAR, RSS; have you used at the same time in a save?(4 points per mod) I don't use any of these difficulty-enhancing mods. I only use aesthetics-enhancing mods as well as MechJeb (no autopilots though, just a lot of info screens), Kerbal Alarm Clock (must have!) and Docking Port Alignment Indicator (I learned to dock proficiently before installing it, but it's just so cool to use). Optional question 2(if you don't use mods): Do you rarely(in less than half of your career saves) use reverts/reloads? If only your revertless/reloadless worlds were counted, would the amount of 'yes' answers to the above questions be roughly the same?(+0.25 points for every 'yes' answer to the above questions that would remain the same, not including optional question 1) I do quicksave like a maniac and I've quickloaded quite a few times, but I think more than half of my landings / maneuvers were done on the first try (so it's mainly paranoia). Still, i'll take zero points here to be fair. I'll have to try a non-quickload save after 0.25 goes out, and see how well I fare. Q: On which of the following objects outside the Kerbin system have you done successful return missions: Duna(2.5 points), Ike(2.5 points), Dres(5 points), Moho(5 points), Gilly(5 points), Laythe(10 points), Vall(10 points), Bop(10 points), Pol(10 points), Tylo(15 points), Eeloo(15 points), Eve(30 points) All of them, including manned return missions to Moho, Tylo and Eve. Score : 2 + 4 + 4 + 24 + 10 + 16 + 0 + 0 + 2.5 + 2.5 + 5 + 5 + 5 +10 +10 + 10 + 10 + 15 + 15 + 30 = 180 Final Score : 180 / 20 = 9.0

WOW! Fantastic!

I was sort of away from the forums but I did keep up with the insertion. Congratulations to ISRO for this remarkable achievement!! Proud of your engineers and scientists, Tech Support. The following is about a point Tech Support touched (about space programs and poverty) and may be off-topic. Feel free to skip it. I think the poverty question is valid, and it can lead to an interesting debate. I can think of arguments for and against having a space program when there is so much poverty. By the way, I speak as a citizen of another country which has a lot of poverty: I'm Mexican. In reality this question goes so much beyond just space programs and specific countries. I'm an astronomer and I've often been asked how do we justify spending billions in building huge telescopes when there are, for instance, millions starving in Africa. Astronomy doesn't directly improve the quality of life of people around the world. So I think it's a valid moral question to raise, and I've seen it pop up in discussions many times. The most satisfying answer I've read is the following. There are two ways to make the world a better place: 1) reduce the suck; 2) increase the awesome. In other words, while it's important to improve the living conditions of those less privileged around the world, it's also important to promote human activities that are done out of passion and that give people things to dream about and provide sources of awe and admiration. These activities keep the human spirit going. What's the point of having well-fed, healthy, long-living individuals if they have nothing to dream about, no awe-inspiring things to give them a reason to work passionately? Space programs are one such thing, in my opinion. So are astronomy, poetry, pure mathematics, music, etc. If you allow me saying it, though, India does have to address the severe poverty problem it faces. But it doesn't have to be at the expense of its space program. Keeping it will inspire many future generations of scientists and engineers and give the general public a reason to dream on. And I'm sure there are many other budgetary items that can go before the space program.

Thank you, hadn't seen that PDF. It seems it'll use all but the last 50 kg of propellant (according to SpaceFlight101). They don't do like me and pack 20% more fuel than needed, then .

Nice. Any idea on what's the delta-v for MOM's Mars insertion? Should be around 1 km/s.

¡Saludos! Wow, desde la 0.13. Yo llegué en la 0.20. Me cuentan que el juego era mucho más difícil en aquellos tiempos.

One month to go! Marking it down in my calendar so I can follow news of the orbital insertion.