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Cezary

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    SweetJet: Reaching Mach 3 (966 m/s) [0.15 STOCK]

    in KSP1 The Spacecraft Exchange

    Posted

    I\'ve been playing around with the different engine types in KSP 0.15 and I decided to build a super sonic jet. For those of you not familiar with the speed of sound, it is roughly 340 m/s at sea level and goes down as the air gets colder and altitude gets higher. By my rough estimation, the velocity required for Mach 1 at 15,000 - 20,000 meters (on Kerbin, not Earth) is 322 m/s. Mach 3 would therefore be 966 m/s.

    If you think about it, reaching that kind of velocity is easy. We\'ve all done it before using rockets. It\'s even possible to go that fast in the atmosphere with enough thrust. So where lies the challenge? I\'m glad you asked.

    Here\'s the criteria for my super sonic jet:


    • [li]No cheating (use Space Plane parts only)[/li]
      [li]Takeoff and land horizontally[/li]
      [li]No decoupling boosters (every original part has to be attached during Mach 3)[/li]
      [li]Completely reusable (no detaching landing gear, etc...)[/li]
      [li]Balanced for atmospheric flight AND high-altitude speed attempt[/li]

    Easy, easy, easy, easy, um... what?

    Step five is the tricky part. A poorly designed jet will pull up or down on you, even with ASAS turned on. The balance of your plane depends not only on lift surfaces like your wings, but also on engine location and power. Even if you manage to place all of your components such that your plane flies straight at sea level, higher altitudes provide less lift and less air for your engines. So what do you do?

    I designed the awesomely named SweetJet to balance both at sea level and at 15 - 20km altitudes. The trick is that it\'s not perfectly balanced between those altitudes. At sea level, the wings and canards combined with the main engines provide a smooth ride that begins to pull upwards the higher you go. This is mainly because the engines gain thrust faster that the wings lose lift in the thinner air. Rather than the basic jet engines, I chose the TurboJets for their ability to get me to 15km.

    Once high enough, the Toroidal Aerospike Rocket activates and in conjunction with the TurboJets propels the craft up to Mach 3. The high-altitude 'nose up' behaviour is corrected by the position of the rocket engine and the jet becomes balanced yet again. I highly advise to keep the altitude under 20 km as the air becomes too thin for the control surfaces to keep the jet steady.

    Once the Rocket runs dry, you should descend to 12 km and fly your plane to the nearest landing zone. I tested the SweetJet by rotating it 180 degrees so that I would be over land instead of water.

    *** Ship download link ***

    screenshot30.png

    screenshot25.png

    screenshot26.png

    screenshot27.png

    screenshot28.png

    1062 m/s = Mach 3.3

    Making the orbit smaller

    in KSP1 Gameplay Questions and Tutorials

    Posted

    First of all, your Mun-bound path should look like this.

    screenshot31.png

    Your ship AND the Mun will get to the same point (the Apoapsis) at the same time.

    Once you\'re there, the Mun will capture you and your path will look something like this.

    skeletor-mun-approach.png

    The next step is to wait until you are at your Periapsis, turn your ship backwards, and burn to SLOW DOWN. Your orbital path will narrow until it closes into a large ellipse.

    skeletor-mun-orbit-slowdown-burn.png

    Keep burning (slowing down) and lower your thrust as your orbital path looks more and more like a circle. When it is circular (or when the [A] and [P] suddenly switch places) turn off your engine with the [X] key. You should have a nice Mun orbit like this.

    skeletor-mun-orbit.png

    Don\'t worry about which direction your orbit is in. You\'ll learn how to perform a plane change maneuver once you\'re comfortable with attaining orbit.

    Help with a KEO Satellite Constellation

    in KSP1 Gameplay Questions and Tutorials

    Posted

    Do the spent stages explode when they hit the ground? My experience has always been that one parachute isn\'t enough to keep them from having a rough landing.

    Fantastic job!!! That looks amazing, congrats.

    In regard to the spent stages, they do explode upon terrain impact as the parachute only slows them to about 20m/s, which is way too fast. I plot my course and design my ship so that the spent stages will end up over water. This gives me a more real-life feel to managing spent stages, even though they still splash-down too hard. I don\'t want to use mods for now, and the stock parts don\'t allow enough parachute placement to do the job.

    Help with a KEO Satellite Constellation

    in KSP1 Gameplay Questions and Tutorials

    Posted

    Ok, tough question. You want 3 satellites in geosynchronous orbit, 120 degrees apart, on one orbital plane. Sounds simple enough. You make a good point in that the satellites would end up in the same place, since they would launch from the same place and end up geosynchronous (assuming 3 IDENTICAL launches).

    First things first, I need to watch that part about the Iridium Satellite Network @ 3:11 again. :o Whew, that\'s gonna be my next project. Now, back to your question. I crunched the numbers, compared using Hohmann and Bi-elliptic transfers, and came up with a few solutions you could use.

    1. Use lower orbits first, then calculate the transfer time to line up your satellites

    Example:


    • [li]LEO @ 150 km (orbital period 00:36:12)[/li]
      [li]Transfer 150 km -> 2,868.4 km (transfer time 01:25:22)[/li]
      [li]KEO @ 2,868.4 km (orbital period 06:00:00)[/li]

    You begin your burn on the opposite side of Kerbin (180 degrees from the target point) @ 150km at the exact moment that your destination is 85.37 degrees away from the target point. Both you and your destination will arrive at the target point at the same time and @ 2,868.4 km. You only need to burn again to circularize your orbit. You can find your target point when your first geosynchronous satellite is 120 + 85.37 - 180 = 25.37 degrees behind you. This may sound impossible to do by eye or without mods and plugins, but the stock game has something that can help you time this perfectly. The Mission Elapsed Time (MET) visible in the Tracking Station can help you calculate the angle of the satellite it belongs to. 360 degrees around takes exactly 360 minutes when in geosynchronous orbit.

    2. Line up all 3 satellites in LEO, 120 degrees apart, and send them all to KEO at the same time*

    (*) technically impossible**

    (**) nothing is impossible

    Setup:


    • [li]Launch Satellite One to 150 km orbit, time warp until MET is 00:12:04[/li]
      [li]Launch Satellite Two to 150 km orbit, time warp until MET is 00:12:04[/li]
      [li]Launch Satellite Three to 150 km orbit, check the Tracking Station to verify timing and position[/li]

    Now the perfect solution would be to do a Hohmann transfer with all three satellites AT THE SAME TIME to 2,868.4 km and they would remain at exactly 120 degrees apart. Then do a second burn, again simultaneously, to circularize all three orbits. So how do you do it? Could you burn REALLY quickly, one satellite after another (trading accuracy for speed) and hope they end up close enough? Perhaps. Could you do minor burns with each satellite, cycling through all of them numerous times, pushing the apoapsis further and further until all three are at 2,868.4 km? More precise, for sure. Technically if you do it slowly enough, the time it takes to switch between ships becomes less and less of an issue. The only downside is that it\'s tedious and will take time***. Oh yeah, and you have to do it again once near apoapsis to bring the periapsis to 2,868.4 km just as accurately.

    ***Tediousness and large time requirements are EXACTLY why I play KSP

    3. Do a crap-load of math and use your imagination to find other ways

    There are countless ways to do this. You can use orbits that are slightly too high or too low and wait until the positions align. You could build ONE ship, with 3 satellites, and decouple them at each place after changing orbits and positions 3 times. It\'s up to you. All I ask is that you take screen shots and post your adventures for all to see.

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