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The Dragon capsule is more "payload" than "stage". The Falcon 9 will have two stages (hopefully both eventually landing themselves). The Dragon (not always us

by jlgreco 13y ago

The Dragon capsule is more "payload" than "stage". The Falcon 9 will have two stages (hopefully both eventually landing themselves). The Dragon (not always used. Sometimes they may just stick a satellite or something on top) will also be able to land itself. Sort of like how the Saturn V is considered a 3-stage rocket, even though during the later Apollo missions it had on top a service module, a command module, and a (two stage!) lunar module.

lobster_johnson 13y ago
So what modules does the video show? Also, if the mission is something like transport astronauts to the ISS, why eject any stages at all? Why not just make the rocket capable of flying to the ISS, let the whole thing dock to the ISS, exchange astronauts, then detach and land back on Earth? (Of course, if there are tons of missions happening around the same time, all requiring a first stage rocket, and each mission has a period that doesn't require any rocket, then I see the point of letting the rocket go back and be used for other things.)
- nawitus 13y ago
  >Also, if the mission is something like transport astronauts to the ISS, why eject any stages at all? Because that requires a single-stage-to-orbit vehicle, which has never been done before. Yes, in the future that might be possible.
- jlgreco 13y ago
  The video shows the lower stage and upper stage of a Falcon 9 taking off, then landing. These two stages are shown launching a Dragon spacecraft. The Dragon spacecraft is shown docking with the ISS. The pressurized half of the Dragon spacecraft is then shown landing (the unpressurized trunk section, with the solar panels attached, burns up in the atmosphere (though this is not shown in the video)). Staging is done because not doing it ("SSTO" or "single stage to orbit") is extremely hard. In fact, it has never been done before from earth. When that second stage burns, it is only accelerating the mass of itself and the Dragon spacecraft on top. Having it accelerate the mass of the lower stage as well would be massively inefficient, requiring much more fuel to be used. So much more fuel that there most likely would no be any mass left over for the Dragon spacecraft. Without staging we wouldn't be able to put things in orbit at all (today and in the past anyway), let alone reuse rockets.
  - lobster_johnson 13y ago
    Thanks. I assumed the section with the solar panels somehow retracted the panels before re-entering the atmosphere, but they skip that part, and I now see that the part re-entering is actually a bit smaller.
    - jlgreco 13y ago
      Yup, that part burns up. It's not a complete waste though. I believe at the ISS they usually pack those sorts of parts (parts that burn up that is. Other examples being the Russian "Progress" spacecraft or the ESA's ATV) full of garbage before sending them off. Intact reentry volume/mass is valuable (currently only the Soyuz and the Dragon can do that) so they just let all of their trash burn up. Here's a neat picture of the first ATV, carrying a bunch of ISS trash, burning up: http://en.wikipedia.org/wiki/File:Jules_Verne_Automated_Transfer_Vehicle_re-enters_Earth%27s_atmosphere.jpg http://en.wikipedia.org/wiki/File:Jules_Verne_Automated_Tran...
- shabble 13y ago
  > Also, if the mission is something like transport astronauts to the ISS, why eject any stages at all? Why not just make the rocket capable of flying to the ISS, let the whole thing dock to the ISS Essentially, Physics. To a lesser extent, practicality and cost. See The Tyranny of the Rocket Equation[1] or the "Model Rocketry" entry of xkcd What-If[2] [1] http://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html http://www.nasa.gov/mission_pages/station/expeditions/expedi... [2] http://what-if.xkcd.com/24/ http://what-if.xkcd.com/24/
- rbanffy 13y ago
  The delta-v the first, more massive, stage has to deal with is much smaller than the one the second-stage has to deal with. The second stage is more or less on LEO when the Dragon is released and uses atmospheric braking just like most returning spacecraft do. Braking a single stage like that would require lots of structural reinforcements that would increase vehicle weight. Also, the lower stage engines are optimized for working in the low atmosphere while the second stage only needs to operate in a vacuum and therefore, has a different design.
- PhasmaFelis 13y ago
  Several folks have answered already, but here's another attempt: getting stuff into orbit takes so much fuel that any launch vehicle must devote something like 90%+ of its mass to fuel tanks. Once a fuel tank is empty, it's worthless, dead weight. If you tried to carry all that dead weight into orbit, you would never make it; it would pull you down. So you drop the empty tanks as you go, until the part that finally reaches orbit is only a small fraction of the original launch vehicle. An SSTO--single stage to orbit--vehicle would be safer, more reliable, and above all cheaper to operate than a multi-stage vehicle, but every attempt to make something light enough that it can reach orbit with all its fuel tanks still aboard has failed. A two-stage rocket where the stages return to the pad under their own power is still a big improvement over the traditional model, with three or more stages that are simply dropped into the ocean to be recovered later.

by jlgreco 13y ago

lobster_johnson 13y ago

So what modules does the video show? Also, if the mission is something like transport astronauts to the ISS, why eject any stages at all? Why not just make the rocket capable of flying to the ISS, let the whole thing dock to the ISS, exchange astronauts, then detach and land back on Earth? (Of course, if there are tons of missions happening around the same time, all requiring a first stage rocket, and each mission has a period that doesn't require any rocket, then I see the point of letting the rocket go back and be used for other things.)

nawitus 13y ago
>Also, if the mission is something like transport astronauts to the ISS, why eject any stages at all? Because that requires a single-stage-to-orbit vehicle, which has never been done before. Yes, in the future that might be possible.
jlgreco 13y ago
The video shows the lower stage and upper stage of a Falcon 9 taking off, then landing. These two stages are shown launching a Dragon spacecraft. The Dragon spacecraft is shown docking with the ISS. The pressurized half of the Dragon spacecraft is then shown landing (the unpressurized trunk section, with the solar panels attached, burns up in the atmosphere (though this is not shown in the video)). Staging is done because not doing it ("SSTO" or "single stage to orbit") is extremely hard. In fact, it has never been done before from earth. When that second stage burns, it is only accelerating the mass of itself and the Dragon spacecraft on top. Having it accelerate the mass of the lower stage as well would be massively inefficient, requiring much more fuel to be used. So much more fuel that there most likely would no be any mass left over for the Dragon spacecraft. Without staging we wouldn't be able to put things in orbit at all (today and in the past anyway), let alone reuse rockets.
- lobster_johnson 13y ago
  Thanks. I assumed the section with the solar panels somehow retracted the panels before re-entering the atmosphere, but they skip that part, and I now see that the part re-entering is actually a bit smaller.
  - jlgreco 13y ago
    Yup, that part burns up. It's not a complete waste though. I believe at the ISS they usually pack those sorts of parts (parts that burn up that is. Other examples being the Russian "Progress" spacecraft or the ESA's ATV) full of garbage before sending them off. Intact reentry volume/mass is valuable (currently only the Soyuz and the Dragon can do that) so they just let all of their trash burn up. Here's a neat picture of the first ATV, carrying a bunch of ISS trash, burning up: http://en.wikipedia.org/wiki/File:Jules_Verne_Automated_Transfer_Vehicle_re-enters_Earth%27s_atmosphere.jpg http://en.wikipedia.org/wiki/File:Jules_Verne_Automated_Tran...
shabble 13y ago
> Also, if the mission is something like transport astronauts to the ISS, why eject any stages at all? Why not just make the rocket capable of flying to the ISS, let the whole thing dock to the ISS Essentially, Physics. To a lesser extent, practicality and cost. See The Tyranny of the Rocket Equation[1] or the "Model Rocketry" entry of xkcd What-If[2] [1] http://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html http://www.nasa.gov/mission_pages/station/expeditions/expedi... [2] http://what-if.xkcd.com/24/ http://what-if.xkcd.com/24/
rbanffy 13y ago
The delta-v the first, more massive, stage has to deal with is much smaller than the one the second-stage has to deal with. The second stage is more or less on LEO when the Dragon is released and uses atmospheric braking just like most returning spacecraft do. Braking a single stage like that would require lots of structural reinforcements that would increase vehicle weight. Also, the lower stage engines are optimized for working in the low atmosphere while the second stage only needs to operate in a vacuum and therefore, has a different design.
PhasmaFelis 13y ago
Several folks have answered already, but here's another attempt: getting stuff into orbit takes so much fuel that any launch vehicle must devote something like 90%+ of its mass to fuel tanks. Once a fuel tank is empty, it's worthless, dead weight. If you tried to carry all that dead weight into orbit, you would never make it; it would pull you down. So you drop the empty tanks as you go, until the part that finally reaches orbit is only a small fraction of the original launch vehicle. An SSTO--single stage to orbit--vehicle would be safer, more reliable, and above all cheaper to operate than a multi-stage vehicle, but every attempt to make something light enough that it can reach orbit with all its fuel tanks still aboard has failed. A two-stage rocket where the stages return to the pad under their own power is still a big improvement over the traditional model, with three or more stages that are simply dropped into the ocean to be recovered later.