Northstar1989

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  1. Northstar1989

    Kevlar in Spacecraft

    I think some people here are under a false impression- that the primary force on a spacecraft to be resisted is the internal pressure of the fuel tanks. It's not. At least not on high-thrust chemical rockets, or any stage launched atop one (electric thruster-propelled spacecraft built in space would be an entirely different story, for instance...) The main force the spacecraft have to contend with is that of their own THRUST: two, maybe three g's of force translating up the entire z-axis of the spacecraft from engines all the way up to the nose. The forces involved are greater than those from the fuel pressing out on the pressure vessels (an interesting aside: the thickness of spherical pressure vessel laws increases in direct proportion to their volume, due to the Square-Cube Law for surface area vs. volume, and the linear relationship between pressure vessel mass and volume. Larger tanks require thicker walls. This is relevant to a few points raised in earlier posts.. ) at many point in the rocket, and so many rockets (especially large, tall ones: *cough* BFR *cough*) require extra structural reinforcement beyond the strength required to contain the internal pressure at many points along their length... --- It is the external shells of large spacecraft, that overlay the pressure vessels and have no direct role in contacting the gasses, that I thought Kevlar (or better yet, Vectran) would be useful for. Structural elements (the use I quite clearly emphasized in the OP: *not* use in strengthening the pressure vessels, which carbon fiber overwraps are actually more appropriate for...), which could, by the way, easily be overlayed with an extremely thin metallic outer coating to reflect UV away from the polymers beneath... --- On Polymers and Ceramics: - Further reading indicates that composites made using spun polymers such as Kevlar are exceedingly strong in tension, but very weak in compression. - By contrast, certain ceramics are exceedingly strong in compression (far stronger, pound-for-pound, than Aluminum: which explains why there has already been substantial research into greater use of ceramics, and ceramic-based composites in spacecraft... https://www.space.com/31516-3d-printed-ceramics-next-gen-spaceships.html https://sbir.nasa.gov/content/ceramic-matrix-composites-spacecraft-propulsion). - Appropriate use of polymers such as Kevlar where tensile forces dominate, and ceramics in places where compression is king, seems to be the key to next-generation, lighter-weight spacecraft design... Indeed a lot of NASA research appears to be focused in precisely this direction. --- In short, further reading indicates that what I was suggesting... has already been considered by much smarter people than myself, and indeed is actually precisely where spacecraft design is headed (although there seems to be more focus on Carbon Fiber than on Kevlar, as it is potentially even stronger: although far less capable of shielding crews and components from radiation...)
  2. Northstar1989

    Kevlar in Spacecraft

    Reading about THIS scientific publication, and a related Space.com news article, on The Mars Society page on Facebook, I was inspired by the idea of greater use of Kevlar in spacecraft... https://www.nature.com/articles/s41598-017-01707-2 Basically, pound-for-pound, Kevlar is just as effective as Polyethylene as radiation-shielding in space (and MANY times more effective than Aluminum). It's also denser (Kevlar has a density of about 1.44 grams/cm^3, vs. a maximum density of about 0.975 grams/cm^3 for Polyethylene)- meaning that a tile providing the same level of protection (measured in grams/cm^2) would also be thinner: https://www.ptonline.com/columns/density-molecular-weight-in-polyethylene http://www.dupont.com/products-and-services/fabrics-fibers-nonwovens/fibers/articles/kevlar-properties.html But more interesting, Kevlar is also STRONGER than Aluminum. Looking at two of the most important parameters describing strength (Tensile Strength, and Yield Strength) it is substantially stronger: Kevlar Tensile Strength: 3620 MPa Yield Strength: 898.5 Mpa*m3/kg http://www.tsgc.utexas.edu/tadp/1996/reports/tech/material2.html https://en.m.wikipedia.org/wiki/Kevlar Temper 6061 Aluminum Tensile Strength: 290 MPa Yield Strength: 240 MPa https://en.m.wikipedia.org/wiki/6061_aluminium_alloy#Standards 7068 Aluminum Alloy Tensile Strength: 710 MPa Yield Strength: 683 MPa https://en.m.wikipedia.org/wiki/7068_aluminium_alloy 7068 Aluminum Alloy is basically one of the strongest aluminum alloys that sees any actual commercial use, and is currently being considered as an UPGRADE for many spacecraft designs (weaker, but more workable alloys are currently used). It currently sees its greatest use in military ammunition. 6061 is a relatively strong, basic form of extruded Aluminum, which sees many commercial uses. ------ My basic idea is this: since Kevlar is both stronger (pound-for-pound) and better at radiation-shielding than Aluminum, why not make greater use of it in spacecraft? Particularly, why not work it into the structural elements of more spacecraft? Regards, Northstar
  3. As a published Biologist with a graduate degree, substantial research experience in Reproductive Biology (and *specifically* an entire year spent researching Spermatogenesis), and one of my areas of focus being Genetics and Development, I can state that is categorically false. Sperm do *NOT* live "only a day or so" (in fact they take about 70-90 days just to form), and new ones are not generated from scratch on a daily basis (although new sperm are continuously being formed). The man's Spermatogonial Stem Cells, Sertoli Cells, and various other cells of the testis that support Spermatogenesis are NOT "fresh" 10 years after a space mission, and because the woman's eggs that are active 10 years later were completely dormant and inactive during the space mission (and thus at minimal risk for radiation-induced mutagenesis) she is actually at lower risk of reproductive complications due to the radiation exposure than the man... --- The formation of Sperm (Spermatogenesis) takes 10 to 12 weeks (as much as 3 months!) from start to finish. What's more, since Spermatogenesis is continuous in the testis, on any given day there are MILLIONS of cell divisions going on associated with it. You really should at least read the Wikipedia article on the topic before presuming to make statements on sperm formation: https://en.m.wikipedia.org/wiki/Spermatogenesis The male reproductive system is actually far MORE vulnerable to radiation exposure than the female system for the following reasons: 1. Cells are most vulnerable to radiation while they are actively undergoing cell division. A woman is born with all the immature eggs she will ever have, but all but a handful are frozen in Meiosis I at any given point in her lifetime- and active cell division of the follicles only occurs at certain times of the month (as opposed to 365 days a year in men), as dictated by the hormonal cycle. Follicular development also occurs at a much slower pace overall- a single egg takes 10 months to develop, as opposed to 3 months for sperm. 2. There are no active germline stem cell populations in the postnatal (after birth) human female. All ovarian follicles have already been formed long before birth, and the germ cells are merely frozen in their development. The germline stem cell populations that give rise to new germ cells from scratch degenerated before she was even born. By contrast, males still have active germline stem cell populations- which are capable of accumulating mutations during cell division due to radiation exposure and sustaining the effects of these mutations in ALL future sperm generated from those mutated stem cells (a female can have half her actively-dividing follicles mutate, and they will all be gone in a year- with the dormant eggs that later become active as good as new. A male can accumulate mutations in half his dividing spermatogonial stem cells, and it will affect his fertility and risk of cancer for the rest of his life...) Stem Cell mutations also *greatly* increase the risk of cancer compared to somatic cell mutations, consider the "Cancer Stem Cell Theory"... There are other reasons, but after writing this much, I don't really feel like going into them... It suffices to say that men are actually at greater risk of radiation exposure affecting their fertility than women. --- Not to mention women make better astronauts for a variety of other reasons, including lower metabolic rate (for long-duration missions, the cost of food for the crew is a very significant consideration. Females burn through substantially fewercalories in a day than men on average, in part due to their smaller bodies...), lower incidence of aggressive/violent behaviors (on long-duration missions, the risk of crew attacking each other is, once again, a significant consideration. I believe it was a Russian male cosmonaut who once wrote in his diary about a space station mission that on an extended stay in a crasmoed space station "all the conditions necessary for murder are present" and that he personally fantasized at times of bashing one particular comrade's head in...), and greater tendency to behave cooperatively and follow instructions ratger than behaving easily or independently (indeed NASA once experienced a small "mutiny in space" of sorts when some of their astronauts stopped following orders...) --- No, the reason Russia no longer relies as heavily on female cosmonauts as it once did has nothing to do with biology or the relative suitability of male vs. female cosmonauts (because females are actualky BETTER suited for the demands of extended space missions). My best guess is it has to do with creeping conservatism in the later years of the USSR (as others have suggested) and sexist attitudes ultimately gaining more dominance in the Russian space program and political arenas, as others suggested..
  4. Exactly. I don't see why they couldn't at least allow Scenarios to be played like Career Mode...
  5. I persist in asking about being able to take on contracts and manage Funds/Reputation/Science in custom Scenarios. If I'm correct, we currently can't create a Custom Scenario just to, say, play an all-stock game out of an alternative launch site and still manage the Career aspects of the game. Or am I mistaken?
  6. You still don't get it. I'm talking about being able to play scenarios like Career Mode, with Funds and missions, *not* "regular Sandbox mode". This is a Sandbox *Game*, and we already have tons of ability to customize our Career games (starting off with piles and piles of Funds and Science on Custom Difficulty, for instance). This would just be one more way.
  7. You completely miss the point that this is a Sansbox game, and players should be able to do as they wish in it. Not to mention, it would still be a "Scenario"- just having the ability to take missions and manage Funds in a Scenario like in Career is all I'm asking for...
  8. How hard is it to get a precise location on the first try? I.e. what if I wanted to add a launchpad in the mountains west of KSC, or in one of the even taller ranges elsewhere on Kerbin. How hard would it be to get a launchpad on a mountaintop, rather than side? Also, I understand that Mission Control, Administration etc. are all disabled in a Scenario?
  9. Please do. The ability to place custom/alternate launchpads is what had me the most excited. However I don't see why they couldn't have also thrown in custom/alternate runways as well... And, of course, the whole thing really needs Career Mode integration. What I really want to do is play Career Mode with a mountaintop launchpad (probably in the mountains west of the KSC) available for an alternate launch location. Or, extra landing-pads for precision-landings, SpaceX style (yes, I've managed to return launch stages to the KSC pad, and once even to a floating barge before. It's incredibly difficult, though...) In one previous save I literally went so far as to *FLY* an Extraplanetary Launchpads pad (as well as several storage tanks for RocketParts and fuel) out to those mountains with a giant nuclear-electric helicopter I built for a challenge. I then used Fuel Balancer mod to edit in full loads of RocketParts and fuel after each launch... (rather than waste time flying resupply missions) I would much rather have worked with a Stock alternative launchpad feature. It took me *hours* to fly the pad out (less time for the fuel tanks, once I figured out how to better sling payloads beneath the chopper using multiple KAS winches with different attachment points and levels of tension in the lines so I could fly at a greater Angle of Attack for the chopper blades- made me really wish I had gotten to attend Army Air Assault School back in my ROTC days, since one of the many lessons learned there is how to sling payloads beneath a Chinook...)
  10. I second that. The game has desperately needed the ability to add more launch sites and runways for some time now- and runways in particular really ought to have been included in this expansion... Better yet, a toolkit to allow players to add multiple different building-types (using the models for the existing buildings in-game, plus making the runway segments individually peaceable), including runway segments, using the Mission Builder. That way players could, for instance, build a longer/wider runway than the KSC one out in a desert somewhere for a Scenario... If players can build missions that essentially become a custom Sandbox setup (i.e. players can keep playing after any objectives are complete, take contracts, etc.) this become a even more useful... If they can't, they should be able to. Adding launch sites is, besides the 5 meter rocket parts, really the only thing in this expansion I consider worth buying. But right now it seems like a half-finished idea that could have been so much more...
  11. You're not trying to get *out* of orbit, just maintain an orbit- which can be done with a few dozen millinewtons of thrust for most satellite designs... Even something the size of the ISS could maintain orbit at 200 km with less than a newton of thrust- which its panels provide enough power for...
  12. Nobody said anything about using this engine to boost a satellite from LEO to GTO. Doing so would just be silly. But if you used these engines to maintain a Propulsive Fluid Accumulator, and transferred collected gasses to a depot in a higher orbit (say 600 or 700 km) you could refuel chemical upper stages with fresh Liquid Oxygen (or Liquid Nitrogen for Thermal Rockets) at 600-700 km before sending them to GTO, the Moon, Mars or wherever...
  13. Northstar1989

    Vacuum Engines

    Most afterburning jet engines *do* expand their exhaust to some degree at certain altitudes and speeds. Just because it's not as obvious as with a rocket doesn't mean it's not happening. In fact, let me clarify something- rocket engines *ARE* jet engines. Rockets are actually just a subtype of jet engine that relies on internal propellant. Don't just take my word for it, though- It's literally in the first paragraph of the Wikipedia page on jet engines: "A jet engine is a reaction engine discharging a fast-moving jet that generates thrust by jet propulsion. This broad definition includes airbreathing jet engines (turbojets, turbofans, ramjets, and pulse jets) and non-airbreathing jet engines (such as rocket engines). In general, jet engines are combustion engines." https://en.m.wikipedia.org/wiki/Jet_engine Internal Combustion Airbreathing Jet Engines (what most people think of when they use the term "jet engine") and rockets can actually be understood with many of the same equations, and share many of the same design-principles... Both generally include a narrow throat (much narrower than the rest of the engine) that compresses the exhaust stream to the speed of sound (Mach 1), and most high-performance jet engines that are designed to operate at supersonic speeds (i.e. most afterburning jets in things like fighter aircraft, but NOT the jets you see on large subsonic passenger aircraft) then expand the exhaust- because that is the only way to accelerate the exhaust beyond Mach 1 (you also got more Thrust that way- right up until you expand the exhaust to ambient atmospheric pressure...) --- So, it's the same principle in an internal combustion airbreathing jet engine designed to fly at supersonic speeds as in a rocket nozzle, really. Compress the exhaust from a combustion chamber until its velocity reaches Mach 1, then expand it to accelerate it further (ideally, enough to equal ambient pressure). The nozzle may look a bit different, but the working principles are largely the same. One of the biggest differences that DOES exist, however, is that many high-performance jets have variable-geometry "petals" that determine the final aperture the exhaust passes through- allowing the jet to produce exhaust at different pressures depending on the altitude as well as throttle/afterburner setting (increasing the throttle or igniting the afterburner increases the Mass Flow Rate through the engine- resulting in higher exhaust pressure unless you increase the expansion-ratio...), such as to better match the ambient pressure. Ideally, the petals should be opened wider at higher altitudes, higher throttle settings, and when using the afterburner... --- I also have a sneaking suspicion you don't fully understand how Expansion Ratio is defined. If you have a 1.25 meter combustion chamber and turbofan on a jet engine, then a 0.05 meter throat, then a variable-geometry nozzle that can be anywhere from 0.600 meters to 1.25 meters in diameter, the Expansion Ratio varies between 12 and 25, not between 0.5 and 1. The Expansion Ratio is determined by the ratio of diameters of the throat to the end of the nozzle, *NOT* by the ratio of diameters of the nozzle-end to the combustion chamber or the rest of the engine. The throat diameter and nozzle diameter are the *only* numbers that matter here, in fact you can increase the Expansion Ratio just by making the throat diameter smaller while keeping the final nozzle diameter the same, although this can create problems with turbulent flow or excessive chamber pressures (higher than the walls of the combustion chamber can handle) if you take this too far...
  14. Northstar1989

    Vacuum Engines

    Well said. I hope you don't think I was saying anything differently than that. Just to be clear, you can *always* increase ISP by increasing chamber pressure or expansion-ratio (keeping one the same and increasing the other), it's just that, as you said, those improvements become progressively smaller and smaller as you approach a mathematical limit. Your math is off, though. It's not nearly as simple as dividing the chamber pressure by the final exhaust pressure to find the percentage of thermal energy you harness. A rocket that expands its exhaust from 100 atmospheres to 1 atmosphere is *a lot* less than 99% efficient. The math involved actually really hard- as in beyond my mathematical abilities hard (my abilities are just advanced single-variable calculus, basic statistics, and very limited amounts of multivariable calculus)- although there are simpler equations that exist that give a reasonable first approximation of the efficiency...
  15. Your math is wrong. If you are traveling at 7.7 km/s and you need to expel exhaust at 4 times that velocity to maintain orbit, then this only amounts to an exhaust velocity of (7700 * 4=30800 m/s) 30.8 km/s, which is an ISP of (30800 / 9.8066 = 3140.7 seconds) 3140.7 s, not 3300 s. Any Gridded Ion Thruster (a type closely related to this airbreathing design) can easily beat this ISP- indeed the Dual Stage 4 Grid design can achieve exhaust velocities of 210 km/s (21,414 seconds ISP). https://en.m.wikipedia.org/wiki/Gridded_ion_thruster KSP isn't real life. Real electric thrusters have much higher ISP, and much lower Thrust, than the ion thrusters in KSP. Or maybe your figures came from the Dawn/DS1 probes, which both used the NSTAR design, which maxed out its ISP around 3100 seconds... https://en.m.wikipedia.org/wiki/Dawn_(spacecraft) Problem is, that's not even close to the best ISP thst can be achieved. Even the NEXT thruster, developed as a successor to the Dawn/DS1 thrusters and using similar ion thruster technology, can achieve an ISP of 4190 seconds: https://en.m.wikipedia.org/wiki/NEXT_(ion_thruster) Once again, though, the ESA airbreathing thruster is a dual-stage design (one that, interestingly, thermalizes the flow before ionizing it). Which means it's going to have higher ISP but lower Thrust than any design similar to NSTAR or NEXT... https://m.esa.int/Our_Activities/Space_Engineering_Technology/World-first_firing_of_air-breathing_electric_thruster Regards, Northstar