ment18

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About ment18

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    Spacecraft Engineer in Training

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  1. ment18

    SpaceX Discussion Thread

    By not having COPVs. Shooting regular tanks simply causes fuel to slowly leak out and boil off, nothing catastrophic. They intentionally did this to safe vehicles in the past. If you are talking about sniping passengers themselves, not sure anything reasonable can be done, for any vehicle.
  2. ment18

    SpaceX Discussion Thread

    They scrubbed at 30s. They waited until then to see if the upper winds would improve enough to fly.
  3. ment18

    SpaceX Discussion Thread

    My guess is that the booster is still composite bc they can check up on it after every flight and it is in a much less severe heating environment, while the spaceship is titanium or some new alloy. The spaceship needs to be much better proven than the booster because it has much longer missions and is more important to cree safety. By still doing the composite booster they gain experience allowing future spaceships to be made in composites, and the dry mass of the booster still matters a lot because it does RTLS, which costs several km/s of dv.
  4. ment18

    NASA SLS/Orion/Payloads

    It appears that the core stage of SLS is way overweight. The core stage is pretty close in size to the ET, which was about 26.5t empty. Each RS-25 is about 3.5t, so the theoretical attach 4 RS-25s to the ET should weight around 40.5t. However, the SLS core stage weighs 85t, which seems quite ridiculous to me, even accounting for all the extra structure you would need. Also, the throw weight of shuttle include the SSMEs, and SLS does not, which accounts for some of the mass difference. It doesn't matter if BFR is terribly managed because it is an order of magnitude cheaper and unquantifiably more capable. SpaceX literally can't afford to be as bad as SLS. We know from Falcon 9 that SpaceX is far more money efficient than NASA/Boeing b/c it took them $400 million to do a project NASA expected to cost $4 billion. Elon Musk is behind his schedule and exceeds his cost estimations, but this is disingenuous b/c his schedules are at least 3x more aggressive then anyone else's and his cost estimations are at-least 10x more smaller than anyone else's. Even if Elon does 50% worse than he plans, he still does 2x better than anyone else in the aerospace industry. If you can actually meet your cost and time plans, than you aren't working at your full potential, your plans aren't challenging enough. The mistakes being made by Boeing are similar in magnitude to the entire SpaceX Falcon 9 Project. If you like space travel, why go against SpaceX. They are not hurting anyone unless you think SLS is so garbage that it risks cancellation, which basically says you think SLS is worse then BFR. If SLS is any good, BFR is not a threat so you should want BFR to succeed because it never hurts to have more rockets and it might make space travel massively better.
  5. ment18

    3d Printed Pulsejet Project

    does that require a metal surface and no air to seal?
  6. ment18

    3d Printed Pulsejet Project

    http://www.pulse-jets.com/phpbb3/viewtopic.php?t=2701 -- Pulse Jet Tube Temperature >800C https://www.lifewire.com/specs-on-3d-printing-materials-2232 -- ABS Melting Point: 240C Its gonna require a massive performance hit to make up for that disparity, physics of engine might not even allow it because the air flow rate it based on the power of the engine.
  7. ment18

    3d Printed Pulsejet Project

    I think the temperatures involved mean the plastic is useless, easily liquified far before you get any performance. It needs to be easy to melt to print, unless you have a special printer. I think joining metal components is really the only option. Valves or no?
  8. ment18

    3d Printed Pulsejet Project

    Its probably easier to connect metal piping together than trying to use plastic, though I'm not familiar with how well shaped pulsejets need to be. How much in the way of tools do you have access to?
  9. ment18

    SpaceX Discussion Thread

    nope, hes still ceo, just not board chairman for 3 years
  10. ment18

    BFR concepts and ideas thread.

    A couple of other points: Musk talked about how many easy manned missions would fly at lower gees, reducing payload for those missions, but tankers onviously go all out. Additionally, BFRs minimum size might be controlled by the propellant plant. I'd want the first plant just to be bolted into a BFR and pretty work light since you have to do everything robitically, just plug in solar, open vents, and add water. This decrease in mass suggests that the factory is more volume limited than mass. I also really like the external cargo bays for their ease of loading in space. For cargo missions, BFS has way more performance than it needs, and the external racks could be loaded up with high density stuff once in space more easily than the internal cargo bay. They could probably pack over 100t of metal 3D printer material into them.
  11. ment18

    BFR concepts and ideas thread.

    The presentation said >100 tons, Which I interpreted as less than 150, but they dont really know specifics. Someone earlier had math suggesting that the lack of vacuum isp reduced payload by about 20tons. I also think spacex had found their payloads to be less dense than expected, so have focused less on payload mass. Musk also acted much less sure than he has before, so I think they've started to have difficulties in making the vehicle as light as they want. So all of the above, probably around 125 tons.
  12. ment18

    SpaceX Discussion Thread

    The things at the bottom are cargo racks, they are in no way a nozzle. They can be replaced by vacuum nozzled engines later. Also said that vacuum nozzles wouldnt gimbal.
  13. ment18

    Amateur rocket to orbit

    Pressure fed is probably easier, which is more important than performance. Why bother with trying to figure out hybrid rockets instead of just building more liquid cores? Building gimbal would probably be the hardest part.
  14. ment18

    Amateur rocket to orbit

    I've built an extremely simple liquid fueled rocket engine. From my experience and reading of rocket literature, the injector is a major sticking point, but I think a pintle would be relatively simple. Pumping is hard, but electric gets rid of the really hard part in the pre-burner. Liquids also have much higher standards than hydrid or solid.
  15. ment18

    Amateur rocket to orbit

    I don't know for sure, but wouldn't LNG/LOX be safer? It also gives much more performance, and i think those factors combined make up for the annoyance of cryogenics. Amateur rockets aren't going to get close to the optimal performance of rocket engines, so you need all the base performance you can get. Plus, the goal of this project is probably to prove yourself to some organization, and both SX and BO are doing Methalox. Definitely do ablative nozzles, I don't know how exactly they work, and you might need to put some fuel next to the walls for cooling. Electric pumps are probably easier and safer then pressurization, since both lox and lng can do pressurization relatively on their own and you don't need some high pressure helium container. I think launching from a boat in the ocean is easier and cheaper, plus you can go out in the middle of nowhere so you don't hurt anything.