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About sevenperforce

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  1. SpaceX Discussion Thread

    This matches what I was expecting. They'd take some steps to try and get it back but reuse is not the goal. Economics of reuse on the second stage just doesn't close, not with the current design. Good to hear updates on the small vs large Raptor. I wasn't sure whether they'd built the larger one yet. I wonder what happens if they end up getting combustion instabilities in the larger Raptor and end up making the scaled version the flight one. Might see BFR scaled even further down.
  2. SpaceX Discussion Thread

    Original grid fins are fine for reuse after LEO entries but get torched on GTO entries. The biggest surprise for me was seeing plasma streams coming off the base of the rocket. I'm guessing they are burning through their supply of aluminum grid fins in anticipation of Block 5.
  3. SpaceX Discussion Thread

    Far and away has to be the hottest re-entry so far. The plasma and sparking right before the downlink cut out was spectacular. I'm guessing BulgariaSat must have had a flatter trajectory? Probably more total heating, but not as high a peak heat nor as rapid a deceleration.
  4. SpaceX Discussion Thread

    As I understand it, Al grid fins can be reused after LEO re-entries but get torched in GTO re-entries. So there's no reason to use the new titanium ones on LEO launches, but if they are used on GTO launches then they are expected to be expended. (The grid fins, not the stage).
  5. SpaceX Discussion Thread

    I feel like you can just drop the rest of the sentence after "do not stay inside a star" and it's equally-good medical advice. Looks like aluminum grid fins again. Surprising.
  6. SpaceX Discussion Thread

    Damn you Klingon sympathizer! Per above -- A Jupiter is a unit of planetary mass, an Amazon is a unit of volumetric flow, a daraf is an inverse Farad, a hiroshima is a unit of energy, and both electrons and faradays are units of charge. So Jupiter-Amazons*daraf2 / hiroshimas3 electron-faradays2 simplifies to kg*m3*s/J3*F2*C4, for which simplifying to meters per second is left as an exercise for the reader. Of course seconds are a unit of distance thanks to the definition of c, so m/s really simplifies to a unitless value.
  7. SpaceX Discussion Thread

    Okay, I think I've got the perfect unit for SpaceX to use in its webcast. Jupiter-Amazons of square darafs per cubic hiroshimas of square electron-faradays.
  8. SpaceX Discussion Thread

    Furlongs per shake. Ells per dog year. Horselength per lightfoot. Siriometers per galactic minute. Gigafurlongs per nanofortnight?
  9. SpaceX Discussion Thread

    Second stage restart and SECO2 confirmed. Prepping for sat deployment.
  10. SpaceX Discussion Thread

    T+9:30. SECO, good orbit on S2. Entering 41-minute coast.
  11. SpaceX Discussion Thread

    T-30! Nominal liftoff! Foggy view from the ground. Passed Mach 1. Really weird view from below through the fog...the plume keeps fading in and out of view as the cloudbank alternately thickens and thins. Looked like normal flames for a bit. Underexpansion clearly visible. T+2:29, MECO and S2 startup! Boostback ignition at just under T+3 minutes. Really eerie night view of the plume around the boostback burn. Fairing jettison! S1 apogee at T+4:00 at 107 km. I can come back and get a pretty good idea of the horizontal speed component by comparing the change in altitude over time to the change in overall speed over time. Entry burn ignition. 1, then 3, then cutoff; brief glimpse of the grid fins in the glare from the entry burn plume. Wondering what kind of droneship view we'll get with how dark it is. T+6:55, landing burn ignition! Plume coming through clouds is fantastic. I see the droneship! Legs out! And down! Falcon has landed! Gorgeous view of the landing with only a momentary pause from the link on JRTI.
  12. SpaceX Discussion Thread

    Logged into my work PC and opened the webcast during the opening credits; perfect timing! This is a new booster, correct? The grid fins are white so they must be aluminum, not titanium. I guess they are from the stockpile. Is this Block 3, Block 4, or Block 3/4? It's so weird that all the SpaceX media images and mockups have black legs but all the rockets so far have had white legs. The LOX vent from S2 seems much more intermittent than usual. Ah, confirmed. "These are the aluminum grid fins; we are using these today instead of titanium because the return is less extreme than a geostationary transfer launch." I wonder if they are still manufacturing the Al ones, then. I don't remember the ten deployment points being individually indicated on the launch sequence at the bottom for Iridium I or II. I think he said that even though this is a droneship landing, it'll still have a boostback burn. I don't see it on the sequence at the bottom, though.
  13. SpaceX Discussion Thread

    Has this successfully happened at least once? Which imho means. ITS/BFS is useless here even more. Putting a huge ship much heavier than its cargo, into high orbit to refuel another ship?.. Maybe just spiral up the lifeless and calm fuel with low thrust or long-lasting nuketug? No, it hasn't happened once, because the whole BFS architecture revolves around on-orbit propellant transfer. That's precisely the thing being proposed.
  14. SpaceX Discussion Thread

    I doubt Raptor could run on alt prop.
  15. SpaceX Discussion Thread

    Nose-to-nose docking and docked burns aren't necessary. Position two full tankers in high-elliptic Earth orbit (using as many launches as necessary to do this). Tank up your mission vehicle in LEO, then have it boost up to high-elliptic earth orbit to rendezvous with the two waiting tankers. At perigee, all three vehicles burn to trans-martian injection together. Immediately thereafter, while still near perigee, one of the tankers docks with the mission vehicle, transfers its propellant to the mission vehicle, then decouples and burns retrograde for just long enough to bring its apogee back into Earth's SOI. It can then progressively aerobrake and eventually re-enter and land. In transit, the mission vehicle adjusts its trajectory for EDL, while the tanker adjusts its trajectory for aerocapture. The tanker aerocaptures into a high-elliptic Martian orbit which will be circularized slowly via aerobraking while the mission vehicle enters and descends for a landing. It will have enough reserve propellant to abort the landing and change landing sites, or to return to low Martian Orbit. Alternately, even after landing, it will have enough propellant to return to LMO if ISRU doesn't end up working out. In nominal missions, it would refuel via ISRU and return to LMO, at which point both vehicles would return to Earth together. In abort scenarios, it would return to LMO, rendezvous with the tanker, and drain the tanker in order to get enough fuel for the trip home, leaving the tanker behind. The Zubrin plan was to bring the hydrogen, react it with atmospheric CO2 to make methane, and crack more atmospheric CO2 into O2. The latter uses solid-oxide electrolysis. SpaceX's plan is to react atmospheric CO2 with Martian H2O via the Sabatier process to make methane and LOX directly.