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Hotel26

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Posts posted by Hotel26

  1. 9 hours ago, Snark said:

    bit of an error because of the mass loss

    I measured the practical effect of this and it is negligible on the practical outcome.  You'd need to integrate an inverse to handle this mathematically, which -- as a fuel truck orbiter guy -- is way above my pay grade [I found a nice paper on this].  I used KER to read the max decel rate at start and end of burns.  I used an average (still not mathematically exact) and it made no practical difference to the objective of getting the vehicle low and slow in the approach cone [think ILS].

    Meanwhile, the big picture is how to use the efficiency of a suicide burn -- do all the work close to the surface to minimize time in flight -- to get close enough to the surface to spot land.  Without helicoptering.

    I'm taking the mining view company perspective and the shift-worker pilot's perspective  to think that 10m arrival is a world of difference to 150m-distant touch-down.  It might be the difference between a 1-man operation and 2-man.

    Assuming it isn't all automated (0-man), in which case they are integrating that inverse and landing at 9.8m from the truck, each time, every time.

    The maneuver-node trick is valid and useful in combination with flying the nav-ball at the end for the spot landing.  It's a great technique to know.  But note that I landed 6m from the pin without maneuver nodes using only what is inside the cockpit [interior view].

    The nav-ball rocks!

  2. One more footnote to the above.  The whole point of a fuel-efficient approach via the ball is to keep the descent going to a precise landing without helicoptering.

    Both landings pictured above were continuous descents shepherded to landing with the following proviso:

    in every landing, close to the surface, I deliberately reduce speed momentarily to 0 because it's a sure way to kill horizontal motion which could otherwise topple your landing.  Once this is done, you are committing to land straight down, with no further tuning of horizontal distance to target.  So it's done very close to the surface.  It has to be done with alacrity.  So it's usual for me (and happened on both approaches) that the SFC retrograde/prograde direction markers momentarily interchange, then revert, indicating an unintentional, positive "float" [throttle overshoot].  Apart from that, the approaches were continuously downward with direction to the target also being tuned continuously.

  3. It's Easter, I have a deadline but I'm fooling around, procrastinating, playing, to avoid real work.

    I resurrected an old 1.2.1 world that I had been setting up as a potential challenge but that I had abandoned.

    Precision instrument landings.

    Goal is to de-orbit and land ("under the hood') between the flags with as much fuel remaining on-board as you can.

    If anybody wants to play with it, here is the save file: Race.sfs   Just make a scratch Sandbox world and reload from this save...  there's an Aquila tanker in 30km orbit with extra fuel onboard, or you can simply go back to the start of the Race save.  [Just don't hurt Leo!!]

    Purpose here is simply to inspire people with what is possible when you Fly The Ball.

  4. I resurrected my old "Race" world from my 1.2.1 workspace.  I refitted the archaic lander I was using in it with my current Hawk, "Gang Star", carrying a Mk 1-3 capsule atop.

    I just tried 2 landings.  Here's the first (note the fuel levels):

    EM7IZXe.png

    Then I repeated the exercise, but went "under the hood" for a purely instrument landing (i.e. performed from inside the cockpit with no external references[*]) as soon as the de-orbit burn had been completed:

    VAjrLHb.png

    I'm trying to figure out now some way to repeat this, perhaps in a video, in some way to "prove" there's nothing fake here.  I know it's probably possible also to record from a camera positioned on the ground.  (I would really like to have seen what that second landing looked like!  My biggest difficulty was, on the ground, trying to be sure I really was on the ground.)

    Incidentally, a huge Attaboy to Leo Kerman who stood in the middle of the triangle and acted as target.  He bet me 1,000 Kroner I couldn't get it in the triangle [he won] and I bet him a 1,000 Kroner he'd run like hell when he saw me coming.  He laughed afterwards that he was so paralyzed by fear that he couldn't run anyway, so he won that bet too.  I'm out 2,000 Kroner to Leo, but it was worth it.

    * All manual in the cockpit: no way I know to set modes on SAS as I usually jump back and forth between SFC Radial and SFC Retrograde.  Had to do it all the old-fashioned glove-and-stick way...

    One more note: both flights were started from a save file with Gang Star in circular 10x10 km orbit just approaching the FAF [Final Approach Fix, 70km].  An inclination change was made by eyeball and then the de-orbit commenced at the 40km mark, reducing speed to 338 m/sec.  Thence, inside the cockpit...  Note the instrument approach took an extra minute since I had to conservatively judge the deceleration burn purely from the navball, not having a DME reading to the target.

  5. 3 hours ago, merlyn63 said:

    Any reason why Mechjeb has trouble flying these particular landers? 

    Imagine you have various thrusters on your craft active and opposing each other, possibly even at odd angles.  Would you expect MechJeb to figure out how to get the most thrust in the direction the maneuver requires?

    It naturally assumes that net thrust will be in the direction of the selected Control From Here point and that you've taken responsibility for setting that up correctly.   MechJeb is a tool with a man/machine interface.  You still have to do your part -- or it wouldn't be any fun.

  6. 9 hours ago, Snark said:

    You can make :retrograde: slide upwards faster by increasing your throttle, or slower by decreasing it.

    I read through your whole description very carefully and it's quite cogent and comprehensible.

    I like this point (quoted above) because it's another technique in the armory to consider.  And I think an experienced pilot will use an amalgam as circumstances indicate.

    My approach is not to keep the engine running, but to turn and use small thrusts to shepherd the markers where I want them.  With experience, this can be done without over-controlling and, generally, the off-pitch angle ["cosine loss"] is not great.  It keeps the approach moving faster until the end (which is good).  It also becomes a bit more necessary when you're intercepting a target that is NOT on the equator.

    In my thinking, where you point the nose and use the throttle in combination repel the marker that indicates direction of flight.  That one in turn repels the target location.  You are the nose.  Your travel is the sheepdog.  The target is the sheep.  And the "zenith" is the pen.  Good teamwork does not chase the sheep all over hill and dale but gently coaxes its trend.

    Really appreciate your input and experience on this [fanatical] subject!

  7. Good to have this discussion with an expert.  I opened a topic on this here: How Do You Fly the Navball? and I think this may be a kind of black art.  I'm always hoping someone could bottle the elixir: i.e. explain this clearly.  It's one thing to do it and another to explain it to someone else.

    There's an algorithm and if you follow it exactly you have a 50% chance of colliding with the target, so the last step actually is reaching a low enough altitude simply desist tracking the target with the navball and just land!

    I think a video would be great.  I landed once on the Mun from inside the cockpit and it was pretty thrilling.  I don't remember how close to the marker I got but I think the supreme challenge would be to lay out 3 flags in a small triangle and land inside them with a non-stop trajectory (no hovering or horizontal translation) from inside the cockpit.  Last time I looked the navball inside the cockpit was somewhat indistinct, but I think it can be done.

    I actually set up a world save with this scenario prepared for a challenge: Instrument Landing.  Land within the markers -- from inside the cockpit (once the de-orbit burn is made) -- pilot down with the most fuel still onboard takes the prize.

    Kinda breath-taking to consider...  :wink::)

     

  8. 8 hours ago, LordFerret said:

    engines fall off the first time wheels hit the runway

    If they're not already attached to the fuselage (but are attached to their natural, visible position (such as the wings), take a deep swallow and use the Gizmo to attach everything to the fuselage no matter where it goes in the layout.)

    This is the lesson I was given in the SPH first time round by the Masters of the Craft...

    8 hours ago, Kronus_Aerospace said:

    any of y'all can guess which aircraft I'm making solely off of the engines?

    I'd say it's Boeing's Elaborate New B737 Test plane (737MAX) for its new GE9X engines...

    ..and I base that on a Google search: "Which airplane is @Kronus_Aerospace building now with huge fat-ass engines?"

  9. 7 hours ago, Whisky Tango Foxtrot said:

    begin my hiatus from KSP right away

    Say it ain't so...!  :(

    I've had my mid-life crisis [Jool] already so I foresee the next big crisis coming for me is retirement -- and have started planning.  New Horizons or maybe Kolonization?  Too addicted to stop...

  10. I think my ultimate objective is to perform an efficient de-orbit burn followed by an efficient deceleration burn that places my vessel in a cone above the target at low speed and altitude such that I have just enough time and maneuvering room to tune the approach to touch-down 10m from the target.

    This "cone above the target" is a vertical simile  to the ILS localizer/glide slope used in aviation.

  11. I think there is also a discrepancy in my approach due to the rotation of the surface body.  On departure, the truck is chasing you.  On arrival, the truck is fleeing.

    Dunry did it twelve times and put it on the orbital line with some deviation up and down it, generally about a hundred meters from the truck, except one time he got off focus.  [We had a spat then when I called him "Dunderhead"...]

    But I can say that the results were excellent.  It does work as desired.  The numbers depend totally on how you fly the lift-off.  I have another set today: 5.3km, 435 m/s, 64.2km.  This is a much flatter departure/approach and potentially much more efficient.  The margin for error may be smaller.

    Lastly, for anyone who doesn't think this is a suicide burn, I recommend you try it.  Done right, I guarantee you'll live but you won't be confused about the relevance anymore, either!  Dunry assured me it was "very exciting".  He was quite agitated.  :)

  12. 14 minutes ago, Snark said:

    I say "nearly" true, above, because the analogy between takeoff and landing isn't perfect.

    Yup.  Thanks for yours above.  I resurrected an old thread (of mine) here:
    https://forum.kerbalspaceprogram.com/index.php?/topic/143921-pinpoint-landings-again/&do=findComment&comment=3334163

    to mention a refinement in my previous approach and that I had recently investigated some approach via calculus to account for diminishing fuel.  I determined it wasn't worth thinking about.

    But the general problem with my old approach is that you stopped precisely over the target but way too high, which is a waste of fuel. 

    This new approach can be potentially tuned as low as you want to risk.  :)

    23 minutes ago, MechBFP said:

    I’m so confused right now. What does this have to do with suicide burns?

    I understand the confusion.  A suicide burn to the surface is suicidal.  My aim is to come to a dead-stop just a few hundred meters above the target.  Which doesn't seem so suicidal at all.  But a lot more useful.

    The most important thing about the term is actually that full-throttle SFC retrograde is the most efficient use of fuel in deceleration.  Snark summed it up very well.

  13. My buddy, First Lieutenant Dunry Kerman, spent yesterday evening doing "bump and grinds" on the Mun in a Hawk tug/lander configured with a fuel pod.  I took cover on the surface at a safe distance with a stopwatch and clipboard.  We stayed up all night while Dunry did a total of a dozen cycles up and down to/fro the Mun orbital fuel dump.

    Best thing about this is that there is NO math.  :)

  14. My buddy, First Lieutenant Dunry Kerman, spent yesterday evening trying out an idea for me.

    This is Dunry in the jump seat of a Hawk tug/lander with an empty fuel pod attached.  It's in the landing configuration: Hawk tanks are full and the fuel pod is bone dry.

    16La3cq.png

    First task was to have Dunry take the Hawk to a 10 x 10km orbit using his standard departure procedure, which is:

    1. lift-off checklist complete; SFC Radial Out; 1/4 throttle to get off the surface 100m;
    2. cut engine; rotate nose to a few degrees above the easterly horizon and go full throttle
    3. cut engines when 10km apoapsis is established
    4. coast to 10km and then circularize.

    This is typically a very flat and horizontal trajectory.

    In this case, I had Dunry climb 300m before the orbit injection burn.  We later realized that 1km is better.  I also had him set Target on the fuel truck on the ground at the departure point, so as to measure distance from it.

    Dunry departed and noted the following 3 numbers for me:

    1. D1: distance from the fuel truck, 3.6km, as soon the Reliants shut down after the orbit insertion burn
    2. V1: speed at commencement of the circularization burn, 338 m/s.
    3. D2: distance from the fuel truck when the circularization burn reached completion, 43.1 km

    Second task, which Dunry practiced maybe about a dozen times last night was to reverse-engineer this sequence:

    Starting from a 10 x 10km orbit, reaching 40 km [*], D2, from the truck, use Surface-Retrograde to reduce speed to V1:  338 m/s.  Now on a hockey-stick trajectory back to a point 300m [*] directly above the target!

    A very exciting trajectory, Dunry told me after the first go, with tears of joy still streaming down his cheeks.

    Don't Panic.  (We're having a little placard made up for the tank on the Hawk, just in front of the jump seat.)  Wait for it; wait for it, D1: 3.6km.  Full Surface-retrograde burn upon reaching 3.6km DME to the target truck.  Burn until motionless and find oneself 600-800m above the target.  Land as usual.

    Needless to point out, if the departure trajectory at your surface base is clear of obstructions, such as e.g. mountains, but the approach path is not, you need to apply some common sense about all this.

    * the departure is flatter than a hockey-stick Surface-retro burn, which is the way we aim to return, so we found that 1km would have been a better safety margin to use in the first task above.  We compensated for this simply by using D2 = 40km, instead of 43.1km, which extends the landing trajectory over the target, which effectively just builds a slight amount of altitude into the curve above the target.

  15. Earlier in this thread, I proposed that you could start a de-orbit burn for a target on the surface of an airless body when:

    S = v^2/(2 * a)

    [substitute t = v/a into s = 1/2.a.t^2]

    where S is the distance indicated to the target when the burn should commence, v is your orbital speed and a is the (KER-reported) max acceleration rate of your craft.

    ---

    I investigated the effect of reduction of vessel mass during the burn due to consumption of fuel and concluded that, even for relatively light vessels, it was not significant.

    What is a good refinement however is to make the following compensation.  Your distance to the target is reported line-of-sight, which means that it contains a vertical as well as horizontal component.  We can use Pythag as follows.

    If my orbital altitude is 10km and the target on the surface is known to be at 4km altitude, then the vertical component is 6km.  If the equation above indicates that the deceleration should start at 10km horizontal distance, then using Pythag:

    sqrt(10 * 10 + 6 * 6) = 11.66km.  So you should commence your de-orbit burn when the target is at 11.7km.  This may seem like a small difference in distance but it works out to being whether you land 1.7km from the target or a mere 20 meters from it.

    It really is quite an exhilarating feeling to pull to a dead stop on that ole fire pole and then just slide down to the target and land next to it.

    ---

    That having been said, the most efficient burn is a full-throttle Surface retrograde burn.  Not a complete stop in the horizontal direction and then a long fall to the target.

    Therefore, use the above to perform a full-throttle Surface retrograde burn.  The result is a hockey stick trajectory that is mostly horizontal until the final moments.    But as some of the thrust will naturally then be directed against the vertical motion (induced by Old Man Gravity), be aware that the maneuver is going to have a slight overshoot built into it.  Rather than a bad thing, this will probably just prevent you from colliding with your target on the ground and ending your day in a fiery conflagration.

    Good luck.

  16. 2 hours ago, Ace in Space said:

    I love modular design!

    Me too.  My architecture is based on 2.5m.  Using radially-attached boosters, as you do with asparagus, means that you wind up with a lot of power being exerted through the central column.  With heavy loads, this causes a catastrophic collapse.  Plus, you need an attachment point for nukes.  This suggested to me that I needed a top deck with 6-way radially-attached 2.5m tanks that effectively become a payload deck to which you can attach anything; and through which the thrust can be distributed.  If the load is too heavy to fully pack the deck at lift-off, you can pack more on it (consolidation) once in LKO.  You can also then gang several.  That became my Aquila transporter.

    When 1.3 wrecked Aquila's fuel sequence, I got expert help to sort it out but not before I went nuts and created GizmoGizmo breathes Brute Force into a 2-stage package.  Once Aquila was resurrected for me by expert help, I looked at Gizmo and saw that I had had a psychotic episode.  Because Gizmo makes everything way too easy.  (Gizmo is basically 7 rockets joined together at the hip and is named after the VAB device that made it possible.)

    Is that bad?

    :)

  17. Here's an interesting idea -- and, yes, I bet many have already discovered this.

    I just rendez-voused a big, hulking ship with a space station.  I didn't want to dock it, but just keep it close.  They are currently 245m apart and the target-relative speed is 0.4 m/s, orbiting the Mun at an altitude of 50km.  How fast are they drifting apart?

    Well, before you answer that, the orbital period of these two has been adjusted by me to be just 1 (one) millisecond apart.  (As close as I could get it with RCS.)  51m 21.588s and .587.

    So the question really is: "how far apart can they drift?"  And the answer is "not much".  The closer you get them when you synchronize, the less it's likely to be and very likely always within quick "vessel switch" range during the whole orbit.

    I really like this: "invisible tethering"!  A few hundred meters is a very easy trip for a fuel tender to make from an OFD (Orbital Fuel Dump) to a client vessel.

    OK, so here's another good question: "why would you want to do that?".  (Here's my answer: "sick to death of the Kraken".)

    [Somebody's gonna chime in to ask incredulously: "you didn't know that?"  :)  Very good.  Take a number...]

    Update: it's also really easy to re-adjust.  Align pro/retro-grade and bring up the Rendez-vous Planner (if you use MechJeb) and use RCS to simply dial-in a shorter or longer orbital period that brings your closest encounter back down really low.  Set a KAC alarm for one loop later.  Synchronize orbital periods again.

    ---

    After I read this thread, I decided to put five space stations into orbit around Kerbin.  One of the CommNet tutorials describes the usage of the Law of Cosines.  You can use it to adjust the orbital period of one ship to acquire a rather exact line-of-sight distance to another, e.g. the distance equivalent to 72 degrees ahead in the orbit.  You can get within a few meters.  But it is then tuning the orbital period down to milliseconds that really holds tight formation.

  18. 17 minutes ago, Geonovast said:

    I believe what you're trying to do is exactly what I do.

    Perfect!  Yes.  That is what I want.  I assume you achieved this by placing the links side-by-side on the same line and I further intuit that this is superior to a table for the same effect because it allows the browser to break the images vertically for small-screen devices.  (Resizing wasn't my issue.)

    I will try this next time.  Thank you. 

    Update: @Geonovast  Also, it appears that the slide-show feature operates for all images on the post, including ones in subsequent spoiler sections which is provides the Ultimate in User Preservation.

     

  19. 39 minutes ago, Geonovast said:

    Are you doing the table to essentially make them thumbnails?

    Not thumb-nails, or at least, not their conventional size, as they would be too small to engender any interest.

    In the general case, I'd like two screen-shots side-by-side in the width.  Big enough to see what is in each screen-shot and have interest captured, but easy enough to scroll on by, because I'd aim to have all screen-shots fit on a page or not much more.  (I have had, on occasion, to scroll through 40 pages of shots I didn't want to see, so I figure the Golden Rule applies.)

    And I'd like to provide the option that the interested reader can see a shot enlarged and then easily slide to the next, if interested.

    So, I'm looking for that middle ground.

    I'd settle for a format of one "heading" shot followed by the rest in a spoiler, especially if I could make the one-click slide-show available.  Scrolling full-scale shots is not much fun.

     

  20. 7 minutes ago, Ace in Space said:

    keeps driving a rustbucket

    At least nobody has brought up the rustbucket rocket vehicles I slap together.  [Uh, I think I just did.  :) ]

    I'm not gonna be throwin' stones this day, brother.

    :)

  21. 5 minutes ago, qzgy said:

    Wonder if spoilering it would help....

    Yup, the table is an in-between measure.  A spoiler would mean that people who might enjoy my schtick would just scroll on by.  In some cases, I've put up the first screenshot and then the rest in the spoiler...  I'll revert to considering use of that again for people who can't afford large monitors.  :)  But this one HAD to be a cartoon strip.  It was yelling for it.

    Thanks for the feedback.

    UPDATE: OK, maybe a 5-row, 1-col table would have worked better...  I'll experiment.

  22. 4 minutes ago, CatastrophicFailure said:

    Hey, how are you posting your pictures?

    Sorry about that.  I'm posting them in a 1-row, 5-col table, which means the pictures render quickly on a desktop so people who prefer to skip my schtick [and there are a few -- I know, because they write in!  :) ] can just scroll on by...  (I liked the cartoon strip feel to that, too.)

    Then if you click the first shot to enlarge it, you can use a right-arrow to go through a slide-show.

    Hadn't thought about small screen devices...  I'll have to rethink it.

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