Jump to content

Lukaszenko

Members
  • Posts

    357
  • Joined

  • Last visited

Posts posted by Lukaszenko

  1. I don't think it's that simple. Reentry vehicles are especially shaped to push the hot plasma away and create a cooler boundary layer between the vehicle and the hot gas. And even then, they use special materials and various tricks to withstand the extreme heat. A grid fin, at first glance, is a smack in the face to this design concept. You're basically asking it to go directly through the hot plasma, and even adding extra surface area for it to impinge upon. 

    I'm confident that using everyday materials such as titanium as a heat shield would be catastrophic. I'm also confident that a grid-fin out of purpose-made reentry material (if even possible) would fail. 

    A titanium grid fin though? There would be no chance. 

  2. I'm guessing that making the 2nd stage reusable can't be worse (payload wise), but probably even much better than attaching a Dragon 2 to it, since a Dragon 2 already has all the things necessary for reusability. If my math is correct, you would then be left with a ~10,000 kg payload. Not that bad, really. It's what the original Falcon 9's payload was, except now all the hardware is reusable. 

  3. 1 hour ago, kunok said:

    You could change the suborbital capsule in the NS to a second stage with a payload of the same total mass. It won't be in a Falcon9 class but it would be in a Falcon 1 class, but reusable.

    But they didn't, and that makes all the difference. Even the difference between *almost* to orbit and TO orbit is a world of difference, because one stays up and the other doesn't. 

    And on the same note, you could also just slap 3 Falcon 9s together and have a Falcon Heavy. And yet somehow it's not there, despite being worked on for the better part of a decade. 

    Turns out that in aerospace, seemingly simple things have a way of not being so. 

  4. 18 hours ago, Shpaget said:

    F9 first stage does not deliver payload to orbit, it's the second stage that is responsible for almost 80% of the total speed. At the moment of staging, the first stage is traveling at 1660 m/s (in the specific case of CRS-10), which is not a whole lot faster than New Shepard (aprox. 1300 m/s).

    That's like saying it's not the gun that does the killing, it's the bullet. The point is, they're part of a system designed for a specific goal, and one is useless without the other. 

  5. 12 hours ago, Nothalogh said:

    They built Grasshopper just to prove it was possible

    Falcon Heavy is just a couple Falcons tie-wrapped together, and yet it's taking the better part of a decade to get it made. Similar story with the SLS. Sometimes aerospace seems to have a way of making seemingly simple things not-so-simple, unless apparently they REALLY REALLY push for it. 

  6. On 2/3/2017 at 3:58 PM, DerekL1963 said:

    How the hell do I get rid of this quote? I'm not trying to quote anybody.

    The size of wafers is nowhere near limited by gravity yet. It is limited by economics. The amount of chips you can print on a wafer is only one ever-decreasing part of the overall cost of a chip, and it just isn't worth it anymore to go larger. To go larger AND do it in space would be economic suicide.

  7. Seems like they were always aware of the cracks, and the turbines are designed with them in mind. Cracks are not an ideal thing to have, but they are not necessarily catastrophic as long as you are aware of them and the design can cope. Airliners routinely fly with cracks, for example, with exact specifications on how long they can grow to before refurbishment is needed.

    The fact that SpaceX's turbopumps aren't really known for blowing up, despite numerous reuses, kind of aligns with SpaceX's explanation.

     

     

  8. On 1/3/2017 at 7:20 AM, Blaarkies said:

    I love the design, sleek and pretty. How do you land that, and how does the kerbal get into the command pod?

    How is the drag losses compared to a 2.5m only rocket?...the 3.75m parts add lots of cross-section based on my experiments

    Thanks. The pic is just the naked ascent vehicle I used for testing. I added labels to the picture of the whole stack I posted above. You can see the lander and some ladders attached to one of its sides. They are jettisoned prior to takeoff. It enters the atmosphere using an inflatable heat shield on both ends (for stability). It also has a science package and a 4 parachutes above the command module (jettisoned using a launch abort system). The 4 parachutes slow it enough to land on its landing foot. 

    I quickly ruled out using only 2.5 m parts, due to how long and unstable for landing it would be, but I will still be interested to test it.

    Anyway, I still hadn't flown a full mission with this thing. I am doing that right now, and taking some pics. 

    EDIT:

    So I did change the lower tank to a 2.5 m one as per your suggestion. Indeed it still easily made it to orbit, despite less fuel (and ~4 tons less weight and a sloppy ascent). I couldn't do a proper back to back test, however, but there's clearly a difference.

    screenshot84.png

    Still, I like the looks of the previous one better :P

  9. By tweaking the above, I've made this ~50t, ~6000 dv vehicle which can claw its way from Eve surface to its orbit, with hundreds of delta-v to spare:

    It's not the lightest, but it's compact, simple, and can be piloted by any idiot. It needs some sort of gravity turn, but it can handle any that I threw at it. It can be made even simpler.

     E.g. remove the aerospike for less performance (but still orbit capable), as per the the TWR point.

    It can also, with few modifications, be augmented to give you ~1000 dv to spare in orbit, even despite a sloppy ascent. 

     

    Untitled_2.jpg

     

     

  10. I've been messing around with an EVE lander for a while now, optimizing and testing the tiniest changes. Just a few tips:

    • TWR: VERY important. The more the better, because the gravity losses are MUCH greater than the aerodynamic ones (if you streamline properly).

    I'm talking a TWR of at least 2 and maybe even 3 (Eve, atmospheric), especially on the first stage, before the weight of the engines gives diminishing returns. You might think otherwise, but it's worth it, despite the expense of delta-v. Vectors are really good here.

    • STREAMLINING: Aerodynamics is VERY important. Just like the gravity losses, it can quickly make your theoretical delta-v a moot number. Gravity and atmosphere are the biggest bottlenecks in getting to orbit.

    Seemingly stupid things, such as solar panels or radiators (the ones that go "flush" with the fuselage), can make a difference. Even a fairing that angles a bit too high or a bit too low, can make a difference. It's subject to experiment, but it's good to know. Use pointy nose cones, they are are demonstratively better than even the narrowest docking port, despite the temptation (that at least I've had) to use one. I've even experienced the same amount of engines at the bottom of the rocket (supposedly secluded from the airstream), give hugely different performance depending simply on how they were positioned. That said, some wings and winglets give surprising little drag, making them quite useful when compared to the (much needed) stability they provide.

    • CONTROL: I've seen the theoretical delta-v take a dump when I realized I can't utilize it, because my rocket goes out of control.  

    Stabilizing wings and/or powerful vectoring engines give good control and can make a large difference between orbit or not. 

  11. On 10/8/2016 at 6:46 AM, Northstar1989 said:

    This is a perfect example of how the human brain is bad at comparing probabilities, and why we need to do the math...

    It's an example of MY brain calculating the wrong numbers. I assumed you were talking about a larger number of less reliable landers. In fact, your calculations (and indeed previous posts) show that you were actually talking a larger number of MORE reliable landers. I don't need to do the math to see that this will be safer.

    Obviously if you compare putting your eggs into one basket or putting your eggs into more and stronger baskets, the more & stronger will be the safer option.

  12. 2 hours ago, Northstar1989 said:

    Risk equations are probability times consequence.  For instance a 1% chance of losing a million dollars is a much larger risk than a 10% chance of losing 10 dollars.  There is a much larger chance of something going wrong with the lander architecture (say a bad docking causing a tiny hull breach near one of the dicking ports, or one of the landers becoming inoperable), but the consequences are much less for most such failures.

    The overall risk is less because, for example, losing one of four redundant landers (and 2-3 crew members with it) in a crash due to a landing computer failure is not nearly so bad as losing the entire ITS due to a couple of the thermal tiles failing in a repeat of the Columbia disaster.  Putting all your eggs in different baskets increases your chances of losing an egg or two- but greatly decreases your chances of losing ALL your eggs...

    I don't know man...something's off in these risk calculations.

    Which lander would you rather be on? The 1 of many that has a 10% chance of failing, or the single one with many more people....that has a 1% chance of failing?

    I'm pretty sure a tiny lander with 2-3 people crashing would be pretty darn bad. Maybe not as bad as a 100 person lander crashing, but certainly not merely 2-3% as bad. If there's a situation where putting all your eggs in one basket, and making sure that basket is as good as you can make it, then this one is it. 

  13. 10 hours ago, Northstar1989 said:

    And on that note, it's extremely easy to plan an aerocapture to orbit anyways- you just aerocapture into an elliptical orbit and the raise your periapsis so there's no chance of re-entering instead of aerobraking on the next pass.  Aerobraking is easy so long as you're conservative and give yourself a good 20-30% margin for error (that is, you assume you'll slow down more than expected, and so make shallower passes).

    Aerobraking is easy and done all the time, because you can always make a shallower pass. You don't even need heat shields. Aerocapture to orbit on the other hand has never been done, because you CAN'T always make a shallower pass, and you don't really know what's up with the atmosphere at the exact instant you want to use it.

  14. 2 hours ago, WhereAmI said:

    So, now we finally know what happened to the rocket parts overhaul... To say honestly, I am not surprised.

    I always wondered how it works with the international employees. It was either Squad was paying them waaay more than everyone else at Squad, or they were getting paid waaay less than everyone else in their country. 

    Didn't seem ideal for anybody.

  15. Could also be that indeed this is some 1-in-a-million-thing that everybody's been overlooking since the 50s and eventually it had to happen, and SpaceX simply drew a short straw. Happened many times in the airline industry, where nobody could foresee it until it actually happened.

    The fact that they're having trouble figuring this out could very well indicate what I just said. Such a case would certainly be less damaging to SpaceX's reputation than "oh we forgot to plug in the ground cable".

  16. 4 hours ago, mikegarrison said:

    Don't know where you got that, but if it's in reference to a commercial airplane then a gap in the windows has nothing to do with uncontained engine failures. When you are looking at a commercial airplane and you see places where there appears to be a window missing, that's because the cabin air riser duct goes through there.

    Wouldn't it make sense then to place that duct where the engine pieces are likely to hit? (if it actually improved the plane's and/or peoples' likelihood of surviving)

  17. 4 hours ago, Frozen_Heart said:

    Is there really much debris to work with? How do they tell what is damaged from the explosion and what broken part actually caused it?

    You can tell a lot actually. Fatigue stress cracks look different than something failing due to overstress. Or compression. Or an explosion. Or getting stressed in a completely different manner than its used in (such as due to an explosion). How fast the failure occurred also results in different looking debris. There's so many clues left behind even when the debris is barely recognizable.

    Remember, information cannot be destroyed. Except in a black hole...and even that's debatable I think.

  18. On 9/2/2016 at 7:52 AM, kerbiloid said:

    Imagine, if it bursts when booster gives 4g, so effective acceleration of the capsule relative to the fairing is 1-2 g...

    Here we can get that T/W of LES should be not 6, but 6+4 = 10 at least. (Usually 12..18)

    Either the booster blew up, in which case it's not giving 4g, or when they hit the "abort" button, the booster simultaneously turns off. In this post-moon-landing-rockets-returning-and-landing-by-themselves era, this shouldn't be too hard to conceptualize and implement. 

  19. On 7/14/2013 at 9:46 AM, Justy said:

    On second thought, you probably don't leave it on Earth, you leave it in Earth *orbit*. You can't afford to lose laser output as heat before it leaves the atmosphere. 

     

    Oooh I don't know about that man. That thing is not going to stay in orbit very long...you know, the whole action/reaction thing :)

  20. I don't. Damn video games are like drugs to me; it's best to stay away altogether.

    Maaaybe if it's some mindless game that I can finish in a couple sittings and put away for good. But, after KSP, I'm afraid to risk playing anything.

×
×
  • Create New...