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ESA ExoMars launch

31 points by leowinterde 11y ago

kartikkumar 11y ago
In case you missed the launch: https://twitter.com/esa/status/709312126356201474 https://twitter.com/esa/status/709312126356201474
sathackr 11y ago
It seems to me that they launched that with a much higher TWR than normal...the rocket seems like it accelerated much faster than I'm used to seeing. Is that just the Russian way?
- mikeash 11y ago
  The Proton-M's initial thrust-to-weight ratio is about 1.5, which is somewhat high. Falcon 9 is about 1.2, and Delta IV Heavy is about 1.25, for comparison. And of course since the Earth subtracts a constant 1, that means the Proton-M's initial vertical acceleration is 2-2.5 times higher than those examples. I'm not sure why it's different. Higher TWR is more efficient (to a point), but it also means there's potentially additional capacity to be had by carrying more fuel. Maybe it has something to do with Proton's origins as a gigantic ICBM, although that was a long time ago. On a tangent, reading the Wikipedia entry for Proton-M, there have been 117 total launches and 11 failures. That's a mildly terrifying failure rate! It occurred to me that with the Russians launching out of central Asia, there must be some chunk of land to the east of there with a ton of rockets falling on it, since even with a successful launch the first stages are just dropped. I couldn't find much info on that, but there are some really cool pictures here: http://www.eurasianet.org/departments/culture/articles/eav041902.shtml http://www.eurasianet.org/departments/culture/articles/eav04... And some history here, but no rocket pictures: http://www.russianspaceweb.com/baikonur_downrange.html http://www.russianspaceweb.com/baikonur_downrange.html
  - sathackr 11y ago
    Thank you...I had googled exomars twr and came up empty.
    - mikeash 11y ago
      I don't think the payload matters much. Certainly its own weight is insignificant compared to the rocket as a whole. I'm not sure if they might load less fuel if the payload doesn't need full performance, but if so I think that would be a relatively small effect as well. I didn't find actual TWRs listed even just for the launchers, but you can find the liftoff mass and thrust pretty easily, and just divide.

31 points by leowinterde 11y ago

In case you missed the launch: https://twitter.com/esa/status/709312126356201474 https://twitter.com/esa/status/709312126356201474

sathackr 11y ago

It seems to me that they launched that with a much higher TWR than normal...the rocket seems like it accelerated much faster than I'm used to seeing. Is that just the Russian way?

mikeash 11y ago
The Proton-M's initial thrust-to-weight ratio is about 1.5, which is somewhat high. Falcon 9 is about 1.2, and Delta IV Heavy is about 1.25, for comparison. And of course since the Earth subtracts a constant 1, that means the Proton-M's initial vertical acceleration is 2-2.5 times higher than those examples. I'm not sure why it's different. Higher TWR is more efficient (to a point), but it also means there's potentially additional capacity to be had by carrying more fuel. Maybe it has something to do with Proton's origins as a gigantic ICBM, although that was a long time ago. On a tangent, reading the Wikipedia entry for Proton-M, there have been 117 total launches and 11 failures. That's a mildly terrifying failure rate! It occurred to me that with the Russians launching out of central Asia, there must be some chunk of land to the east of there with a ton of rockets falling on it, since even with a successful launch the first stages are just dropped. I couldn't find much info on that, but there are some really cool pictures here: http://www.eurasianet.org/departments/culture/articles/eav041902.shtml http://www.eurasianet.org/departments/culture/articles/eav04... And some history here, but no rocket pictures: http://www.russianspaceweb.com/baikonur_downrange.html http://www.russianspaceweb.com/baikonur_downrange.html
- sathackr 11y ago
  Thank you...I had googled exomars twr and came up empty.
  - mikeash 11y ago
    I don't think the payload matters much. Certainly its own weight is insignificant compared to the rocket as a whole. I'm not sure if they might load less fuel if the payload doesn't need full performance, but if so I think that would be a relatively small effect as well. I didn't find actual TWRs listed even just for the launchers, but you can find the liftoff mass and thrust pretty easily, and just divide.