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Everything posted by Hesp

  1. Making some assumptions based on Falcon 9 launch profiles, the rocket velocity at 20km altitude is around Mach 2 / 2.5 It's safe to assume that most of the air augmentation will happen below that altitude, so exotic intakes (J58 variable geometry spike) are not needed. A proper designed diverterless supersonic intake could suffice.
  2. Well, if there is a system that allows you to relight your engine an indefinite number of times, why not use it over "old style" solutions that impose a hard limit? (see Falcon heavy splashdown and TEA/TEB exhaustion) The capability of repeated/precisely timed ignition is only an advantage from my point of view, complexity of the system doesn't change much. If the trend is to go towards rocket engine reusability and fast turnaround, a technology (and mindset) transfer from automotive sector would be a great step forward. Cost isn't a barrier for sure, with aerospace budgets you can pick the most advanced solutions and still have a bargain.
  3. I think they will use something comparable to the TJI (Turbulent Jet Ignition) currently applied in Formula1 engines. Basically, a small prechamber with a spark plug and injector. Gaseous methane would work flawlessly with it. At ignition, shaped flame jets are injected into the main combustion chamber. http://www.mahle-powertrain.com/en/experience/mahle-jet-ignition/
  4. Shouldn't GEO be enough for that? Anyway, a dollar bill is 0.11mm thick. 9B$ = 990km
  5. Cheap or not, what I was pointing out was the uncertain mixture and the ability to work with it. Car engines are more omnivorous because they've been conceived and developed to be like that. A F1 (Formula 1) engine without its bespoke fuel won't even start up. Oh, and if a car stops when using appropriate fuel, car manufacturer gets in trouble and loses money -> it's a critical failure as well from an engineering point of view.
  6. Well, commercial LPG is mostly a propane-butane mixture in uncertain proportions, and cars work reliably with it. As told before, if the engine can accept a variable HC mixture some of the ISRU complications can be ignored. What's easier, develop a more tolerant engine or deliver a "perfect" fuel refinery to Mars? I don't have an answer to this. Pure propane at -40°C has a vapour pressure of 1 bar, 0.1 bar at -85°C, 0.03 bar at -100°C. If you can keep it reasonably cool you don't need pressurized tanks at all. It's a tradeoff between cryo CH4 and Kerosene.
  7. The first is a problem that could be solvable using automotive techniques (i.e. a UEGO sensor in closed loop control to adjust Fuel-LOx mixture). Needs to be engineered for a rocket engine, yes, but it removes the need for a laboratory quality fuel and allows to settle for a "good enough" mixture. Boiloff... not sure why nobody is evaluating propane as ISRU fuel. Way more easier to keep liquid than methane, denser and more densifiable when subcooled, almost same ISP. The biggest fraction of the propellant weight will be oxygen anyway, but you can obtain it in a "easier" way from atmosphere. Maybe it's worth to liquify it, keep LOx cool by evaporation, use the GOx for other applications (fuel cells?) instead of going for a zero-boiloff solution.
  8. As an European, my opinion is that they could do way more for the space industry. Close to where I live there are Thales-Alenia and Avio, but they are using only a minimal portion of the engineering, scientific and manufacturing resources available in the area.
  9. About time! Next step would be realizing that big and heavily structured organizations are slow to adapt to changing conditions...
  10. Just having a Launch Escape System decreases dramatically the LOC probability. Regarding Shuttle, risk assessment for STS-114 put a SSME catastrophic failure at 1:610
  11. I'm wondering if they ever considered Propane instead than Methane. It has a higher densification potential when subcooled (less tanks on the vehicle) and storage on Mars should be way simpler (boiling point at 1 bar: -42°C, basically Mars' mean temperature)
  12. Hesp

    Oberth effect

    It was just a simple excel file answering the question: "what V_excess do I need at Mun SOI exit to have the correct V_excess at Kerbin SOI exit?". Nothing much than some basic calculations to see if it was convenient compared to a LKO launch.
  13. Hesp

    Oberth effect

    Honestly I did not perform further calculations, but my gut feeling is that could be a plausible explanation. I have to remark that @HebaruSan wrote a great tool to plan this kind of manouvers with his Astrogator. After completing that Duna mission i restarted a career in a 2.5x scale "real" system, and I should perform soon some calculations on where to place the Lunar fuel depot. The current Lunar station for surface operations is in a 100x100km orbit at 28.5° inclination from Earth equator (no plane changes needed if the launch is correctly timed). For the fuel depot I'm planning to keep an higher orbit (tentative 300x300) and aligned to the Ecliptic plane for interplanetary missions.
  14. There has been at least a materials experiment payload launched with a Shuttle and retrieved with a Dragon (MISSE-8), and other experiments are already up there: https://www.nasa.gov/mission_pages/station/research/experiments/2531.html http://www.alphaspace.com/about-misse-ff.html Hint: for moving big items around ISS you don't have to rely on what an astronaut can handle, there is a robotic arm and all you need to do is to design the item with adequate attachment points (see berthing operations of cargo capsules)
  15. I read that report but the only useful slide is the #21, and yet they don't specify HOW delivering from the Moon to LEO will be cheaper than launching directly from Earth. Bringing fuel down a gravity well only to refuel a ship that has to climb that gravity well again is plain stupid, and should be done only when other options aren't available. Personally, if we need fuel in EML1, I'd start research on some "dumb" ion tankers that travel from LEO without hurry. I don't have the competences to say what could be a profitable business on the Moon. Before reaching that stage it should be only seen as a research outpost, in my opinion.
  16. A lunar base in my opinion is a logical step to do along the path of exploration and research. Honestly I'm skeptic about the main purpose of the base (ISRU plant). If they told "we need some ISRU to fuel the reusable landers" [Lunar surface -> LLO] it would make sense to ease the transfers to the surface, but basing all the papers on the hypotesis to SELL the produced fuel to third parties using EML2 and LEO [why LEO??] depots is unrealistic. As others said, fuel is cheap and we don't have the need to develop a completely new technology to fill the tanks in our backyard. Just send up a Falcon 9 RTLS with 12t of fuel... Should be around 5k$ per kg of fuel delivered in LEO, less if launch prices go down. Good luck beating that price with the ISRU from lunar surface. For the base the joint operation between space agencies (ISS style) is the most probable to succeed because it's already been proven, although the progress will be rather slow. I cannot see any chance of a "space race 2.0" coming in the next years.
  17. I did some calculations and experiments on another old thread, but it was meant for a fuel station in Mun orbit:
  18. @wumpus Basically you need the know-how. To build that you need engineering time, prototypes, measuring lab and testing equipment, and failures. Lots of them. Any failure you investigate correctly gives you further knowledge of the topic. Building a system that works at the first attempt without having previous experience and know-how is pure luck. On a side note, that's why every aerospace supplier must have a AS9100 or EN9100 certification.
  19. Got it, what you say regarding the new capabilities of the process is true and i completely agree. If SLS is the only way you can manufacture a part, it qualifies automatically for production rather than just prototypes. My remark was that we both stated the same thing, when saying that it's not an alternative to machining for things that can be machined.
  20. We said the same thing, read again. In my current job 3d printing it is an alternative to metal CASTING or FORGING for single or very small batches of prototypes. It makes you save the cost and the design time of all the casting/forging toolings and fixtures, really prohibitive if you need only a small lot, quickly.
  21. I have some work experience in simulations and design of turbochargers... Making a functional turbopump is something way beyond the amateur/hobbist territory.
  22. I wasn't referring to the F1 engine, specifically. To 3d print it you'll need the technical drawing and the 3d model of every single component, good luck getting those from NASA. And yes, internal surface roughness will be different from original since they are coming from a different process. Plumbing is not a big issue today with hydroforming and a certified welder doing the job. Metal 3D printing is increasingly common in prototype manufacturing compared to other processes like casting and forging, it's not an alternative to CNC milling. No need to laser sinter a part that can be obtained only by machining.
  23. The technology you are looking for is called DMLS (Direct Metal Laser Sintering), a branch of SLS (Selective Laser Sintering). While the cost for one of these machines ranges from 50k to 500k€, there is plenty of existing companies able to "3d print" your parts. These printed parts usually need to be finished on a CNC center to achieve the required tolerances, anyway.