• Content count

  • Joined

  • Last visited

Community Reputation

4,137 Excellent


About sevenperforce

  • Rank
    Physics Superhero

Recent Profile Visitors

5,448 profile views
  1. That's what they pretended to do in Armageddon.
  2. Sounds like dragonskin body armor. They made quite a bit deal of out it a few years ago. IIRC it degraded really quickly under high temperature fluctuations and couldn't handle grit or sand. May also have had a shrapnel effect with multiple hits to the same area -- i.e., plate fragmentation would end up sending ceramic shards through the inner lining if you got hit more than once.
  3. @Mad Rocket Scientist So here's the kicker. Adding 100 m/s of dV adds 100 m/s of dV. That doesn't change. 100 m/s of dV is the same instantaneous change in velocity regardless of where it is applied, at that moment. However, if you add 100 m/s of dV to your velocity while your fuel is moving very very fast, then you end up leaving with far more velocity than if you added that 100 m/s while your fuel is moving relatively slow, because fuel that is moving fast has a greater amount of inertia/momentum/impulse than fuel that is moving slow. That's the way to think about it, conceptually. The math is...the math. The math works out on its own.
  4. Good example by @FleshJeb above. Another, less mathy way of looking at it: Suppose you do a burn out in empty heliocentric space. You're pushing fuel out the back of your rocket, which slows the fuel down (relative to the sun) and speeds you up. You're throwing something in one direction and it pushes you in the other direction. It's an exchange of momentum. Makes sense so far, right? Now, suppose you do a burn deep in a planet's gravity well. This time, you're still doing an exchange of momentum (pushing the fuel in one direction which pushes you in the other direction), but this time, the fuel you're pushing away has much more momentum to begin with because it's been sped up by the gravity well. When you push it away, you're pushing against something that is, effectively, "heavier"; as a result, it gives you more of a kick, relative to the original heliocentric orbit. This doesn't violate conservation of momentum, because the momentum left behind is (essentially) added to the gravity of the planet.
  5. The one nice thing about the MMU was that an astronaut could use it to "fly out" and grab a derelict spacecraft and push it inside the orbiter's payload bay for repairs. Or, you know, the orbiter could simply fly a little closer and grab the spacecraft with the Canadarm.
  6. sevenperforce

    SpaceX Discussion Thread

    Concern would probably be getting the reactor to sit dormant for a decade then pop online autonomously and start working.
  7. sevenperforce

    JWST: it's done!

    JWST won't have any orientation problems because the sunshade is symmetric with respect to the sun, but it does have a propellant budget for counteracting the outward thrust produced by the solar wind. It can be turned to the ecliptic, but that's not the primary goal.
  8. sevenperforce

    JWST: it's done!

    Sunshade isn't large enough to run into solar wind problems. As far as survey is concerned, JWST will primary point toward polar objects. This, incidentally, is one of the reasons why TESS had a sky-survey designed to maximize the amount of time spent looking due north and due south.
  9. Too bulky, not necessary, replaced with the SAFER jetpack.
  10. sevenperforce

    SpaceX Discussion Thread

    Driving a rover from your computer is tricky with the 3-second lightspeed delay. Better to have a bunch of tiny autonomous rovers doing a Google Street View thing, and then you could have human people navigating the existing data and flagging stuff that way.
  11. sevenperforce

    Russian Launch and Mission Thread

    Y u no haz pictures?!
  12. sevenperforce

    SpaceX Discussion Thread

    And just like that you would have 100 male organs drawn on the surface of the moon. Rover McRoverFace all over again.
  13. sevenperforce

    SpaceX Discussion Thread

    Ah, very good point. I wonder if you could use an excess-hyperbolic Type I transfer out of LEO to Neptune, and then use a Neptune flyby to lower velocity to reach Pluto with lower excess hyperbolic velocity. Might lower intercept speed to something that a big hydrazine (or even hypergolic biprop) tank could handle.
  14. sevenperforce

    SpaceX Discussion Thread

    On Pluto... If you want to do a Pluto mission, just wait until BFR is flying. Build a massive 30-tonne Pluto science robot spaceship with an orbiter, a lander, and a sample return capsule. Send up a BFS tanker and refuel it in LEO with two additional launches. Mate your Pluto spaceship to a 110-tonne hydrolox Earth Departure Stage (Vacuum New Shepard or the like) and shove the whole affair into a cargo BFS. BFS launches to LEO, rendezvouses with the tanker, refuels, and burns to Earth escape. Open the clamshell, release the payload, and then turn around and burn slightly so the BFS can re-enter after a single eccentric orbit. The hydrolox stage burns the rest of the way to Pluto intercept, no Jupiter flyby or ion kick stage necessary.