Eeloo on SRB ∞ | KSP 1.11.2

so the channel has now reached over 100 000 subscribers to celebrate this occasion i thought it would be a cool idea to go back and remake one of my old videos with the knowledge i've gained over the years one of the oldest videos on the channel is this elu on srb's mission which i made a little over five years ago there is a lot of potential for improvement here so let's take a second go at it to make things a bit more challenging this time i'm gonna do this fully reusable as well that's right we're gonna recover everything back to kerbin with the challenge set here's what i came up with it has a mass of 69.7 tons on the pad and its first stage is powered by a single s2-17 thoroughbred solid rocket booster this is substantially smaller than my old design which had 81 kickback srbs in the first stage and had a launch mass of over 3000 tons to put that in relative terms the new design is only 2.3 percent the mass of the original one which i'd say is a pretty good improvement [Music] okay that's enough about the old design let's get this mission off the ground i'll explain the design of this as we go along [Music] first and foremost the biggest challenge of this mission is that we can't throttle solid rocket boosters as a result we need to be careful with each burn for the first stage it's easy to take a profile too steep because of the high thrust to weight ratio and end up with an apoapsis that's just too high to be efficient we want to get into a nice low circular curve in orbit so we need to tune our launch profile carefully to do that i angled the craft 15 degrees at launch and then switched the sis to pro grade once we've reached a specific velocity by doing this we can consistently get a good gravity turn since we're taking a shallow profile and we have a high thrust weight ratio we're also going to be taking a lot of aerodynamic heating especially at the end of the burn that's why i have this sideways heat shield on the front here ksp applies the most aerodynamic heating to the first part in the airstream and so this heat shield takes the high heat load instead of the nose cones or fairings which would explode otherwise as we leave the atmosphere we're going to open up the fairing in preparation for our circularization burn the fairing door here is made of a completely stock mechanism the nose cone has some rcs thrusters which are contained inside a housing of thermometers all inside the bearing you can see how this fits together here when we want to rotate the door we can just decouple the nose cone and then rotate the main craft to swing the door open [Music] one last note for this to keep everything aligned nicely i made a mechanism with these landing gear in here to lock the door in place before we grab it with the claw and re-dock it with the door open we just need to light up these small srbs to push ourselves into orbit i know this backwards setup looks strange but there is a good reason i'm doing it with this backwards orientation we can simply dump the payload out of the fairing once we reach a circular orbit the srb is still burning at this point so we can then flip the main craft around to do its deorbit burn all with just one stage of srbs we'll get to the payload in a moment but first let's recover the launch vehicle we're on a suborbital trajectory at this point so recovering this will be like any other space plane to land at the ksc we need to control our drag carefully this craft is fairly lightweight empty so drag slows it down pretty quickly with this in mind we want to keep it pointed pro-grade to minimize drag for most of the descent and then flare up to slow down and redirect our trajectory as we get closer and there's our first stage recovered let's head on back to the payload [Music] just looking at this you'll notice our payload is pretty small it's only 3.1 tons which is considerably smaller than my old design which was about 260 tons in low curb and orbit now that said with other propulsion methods such as ion engines this would be plenty of mass to get to elu and back but we're using srbs here and srbs are a lot less efficient there's only about 1.1 kilometers per second of delta v in the transfer stage here which is not enough to do a direct either transfer we need to get some help with this so we're gonna do some gravity assist to get all the way out to elu as with any good gravity assist route eve will be our first stop this is also why our inclination is so high we need this inclination to get a good encounter i'll talk more about how i figured this out later but as for right now we have exactly 1 111 meters per second in this transfer stage again we can't throttle this or shut them down so we need to be careful about how we spend this to give us the transfer we want i played with the timing and components of the maneuver node until i got a burn that gave an encounter while also expanding exactly 1 11 meters per second of delta v [Music] you can see that this burn got us pretty close it was within about 0.5 meters per second of the desired burn however if you've done gravity assist before you know this isn't good enough 0.5 meters per second can be the difference between getting a gravity assist chain and being completely off we certainly need to fine-tune this that's why for mid-course corrections i've added some separatrons with a small amount of fuel these burn through about 10 meters per second of delta v each we need to be extremely precise with these burns so i calculated how much delta v each separatron will give us exactly and then created maneuver nodes accordingly for example the first separatron burns 10.04 meters per second of delta v and you can see i've created a correction maneuver with 10.04 meters per second of delta v you can see this gets us very close to our desired periapsis we are within about 15 kilometers of the planned periapsis which is good enough to actually get a carbon encounter [Music] of course it's not quite there but it can be corrected as we get closer we're going to do the rest of the gravity assist like this as well as we go through this let's talk about how i planned this gravity-assist chain in the first place so unlike home and transfers gravity assists are not trivial to calculate due to the complexity of the problem this is not feasible to calculate by hand so we need a different method one way i've used in the past is just basically winging it i'd do a burn to reach eve then set up an encounter for curb and after that and then so on for the rest of the chain this works all right for a trip to jules since everything is mostly in circular orbits and the timing doesn't matter that much it's a different story for elu though it's in an inclined and elliptical orbit which means we need to encounter it at its apoapsis to be efficient to say the least taking the trial and error winging it approach would be a very time consuming task especially with the limited number of correction burns we have fortunately there is another way there are gravity assist calculators out there that can help us out with this in particular for this chain i used aerostar's trajectory optimization tool this tool can calculate gravity assist chains between a sequence of planets that said the results from this tool can be bad especially for complicated gravity assists like this one to get around that i ran the tool a hundred times or so to increase the odds of finding a good chain and it did eventually deliver it gave me this pretty good one here now i'm not following its burns exactly i'm mostly just using the times from the tool to plan out the gravity assist for example it said that we need to encounter our second carbon assist at year 3 day 136 so i set up the assist to encounter it at roughly this time speaking of second curb and assist that's coming up now at this point the transfer stage is spent and is dead weight to us to recover it we're just going to dump it off as we fly by kerbin we just use a correction thruster to put it on track and then re-enter it there's a wing panel on the bottom of this which helps slow it down and absorb the re-entry heat this wing panel is the first part in the airstream again and so protects the other components from excessive heating even then you can see it gets pretty hot kerbal engineer shows that we get up to 98.5 percent of our max heat tolerance which is decently toasty through some dumb luck the ksc is in the path of our descent perfect opportunity to land this closer to the space center to save mass we don't have any landing gear or parachutes so we're just gonna land this in the water nearby and with that our transfer stage is safely home okay let's get back to jeb with the second carbon assist done we are approaching the most important gravity assist of this chain jewel this jewel assist is going to do two major things for us for one it's going to boost our apoapsis up to meet elu and secondly it's going to match our inclination with elu you can see why timing this was so important here as you can see there's only really two places in jewel's orbit where it can do this well fortunately for us the plan worked out as intended and it's in the right place to give us this assist [Music] so our final assist is done and our trajectory looks good we are now on the way to the furthest destination in the kerbal system just two more correction burns to get our flyby tuned we can see the results of our efforts paying off big here our insertion burn is only about 400 meters per second by contrast if we did a direct transfer from kerbin this would be 1.4 kilometers per second which is over three times higher overall this whole chain only cost about 1.6 kilometers per second including the correction burns the direct transfer on the other hand would have been 3.5 kilometers per second which is over two times higher and there we are after four long years of gravity assists we have finally made it to ilu orbit okay let's get this thing landed jeb i know you're eager to get out of that chair and stretch your legs first let's detach the lander the transfer stage will be left in orbit and the claw on board will be armed we'll need that for later for the landing again the fact we can't throttle or shut down srbs is a problem the challenge is we need to do the landing in one burn and come to a stop at the same time we run out of fuel the first step to do this is to be in a low orbit this will get us close to the ground when we start the burn and allow us to tune our landing better i've chosen these mountains over here as our landing site since we will fly less than a kilometer overhead next problem is the delta v we have more delta v than we need to land so if we just burn retrograde we'll end up burning too much and then flip around to fine tune the delta v i'm going to oscillate the craft to waist delta v and other directions so we have just enough for the landing the terrain is behaving a bit strangely but we are safely down let's get out and plant our flag [Music] our transfer window is another four years out so looks like we have some time to kill alright jeb you're dismissed you've got this planet to yourself go have some fun [Music] hello jeb welcome back it's been fun to stay around but our launch window is coming up and we should get going launch to orbit is more complicated than the landing we have to rendezvous and dock with the stage we left in orbit so we have to get everything timed right we launch when the transfer craft is about 15 kilometers behind us after lighting up the engines we then try to cancel out as much relative velocity as possible this first stage here gets us most of the way to orbit and gets us close to the target [Music] next we have two separate chance stages to get our approach these are slow burning stages so that we can carefully adjust our encounter you can see that this first separatron stage gets us an encounter within about a hundred meters so we're on our final approach now let's do this we're going to do the docking with just one stage now that sounds incredibly difficult if not impossible to pull off but it's not as bad as it sounds we can use a similar approach as what we did with the landing we can light up the srb and then control our approach by oscillating and doing flips by doing this we can hopefully arrive at our target with a low enough velocity to dock to make this whole thing easier i set the thrust limiter to 0.5 percent the lowest possible value that way we can have more time to react to changes and adjust our approach [Music] and after that graceful series of maneuvers we have docked the difficult part of the mission is now behind us let's go home we're going to be using a gravity assist chain to get home again but not the same route we can just use a dual gravity system no need to do any eve or kerbin assists [Music] okay i lied joule wasn't quite enough we'll need to get some extra help from tylo to get the rest of the way [Music] the re-entry will be about the same as for the transfer stage we have a wing panel to protect jeb and to help slow us down this time though i'm not relying on entirely dumb luck to get as close to the space center this time i've tuned the time of our re-entry with our final correction burn to actually put us on track for the space center now i didn't do any calculations for this i basically just set up an encounter blindly saw how far it was off and then moved the arrival time accordingly so my blind attempt put the craft 60 degrees east of the space center this is 1 6 of a rotation of carbon so i move the entry time 1 6 of a carbon day forward or 1 hour forward as you can see this got us very close we're right on target now which is good since this craft has the glide profile of a brick [Music] home at last we've gone to elu and back using only srbs and recovered all parts from the mission in the process i'd say this is a pretty good improvement over my last attempt right [Music] thank you all for watching and thank you all so much for a hundred thousand subscribers this was an incredible journey for me i've changed a lot as a person in these past five years in addition to becoming a better ksp player i'm very fortunate that this silly hobby of mine turned into this so thank you for stopping by well jeb i'm not gonna leave you in the ocean here i called in an old friend to take you home as for myself i'll be heading out see you all in the next one [Music] [Music] [Music] you

Channel: Stratzenblitz75

Views: 214,421

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Id: AyOwTYQVdmk

Length: 21min 51sec (1311 seconds)

Published: Thu Jun 24 2021