5 ms·

Reusing the 1st stage seems to impose a massive penalty on the payload. Chopping it down to 1/3 for the Falcon Heavy to GTO (8000 kg vs 22000 kg). In case I'm

by Hondor 10y ago

Reusing the 1st stage seems to impose a massive penalty on the payload. Chopping it down to 1/3 for the Falcon Heavy to GTO (8000 kg vs 22000 kg). In case I'm misunderstanding, do these term have these meanings? mT = metric tonne? The standard symbol is "t". It's odd that they also use kg on the same table for the same quantity so maybe it really means something else? Not millitesla I'm sure :P "fully expendable vehicle" means dumping the 1st stage into the sea instead of landing and recovering it?

rtkwe 10y ago
Yes fully expendable means dumping the whole rocket like other launches. It takes a good amount of fuel to kill all the horizontal velocity the first stage built up before detaching and then a bit more for landing. Due to just the physics you're losing some of the most effective (in terms of dV per unit mass of fuel) burn in the first stage.
- Klathmon 10y ago
  So hopefully someone can answer this, but what's the reason they don't put the droneships WAY down range of the rockets? So instead of having to fully stop and reverse, they position them so they can arc back down and only has to stop its momentum.
  - rtkwe 10y ago
    CRS-8 which was the one that successfully landed on the barge recently was going 6600 kmph at 71 km when the first stage cut off, most of that was horizontal speed. They have to reduce that speed to both not break apart in the atmosphere. They can't have a lot of horizontal momentum low in the atmosphere and still land straight up on the barge. The rocket has hard limits on how much it can control it's orientation inside the atmosphere because it only has small cold gas thrusters and the grid fins to really control roll pitch and yaw.
rm445 10y ago
Yes, apart from the coincidental sharing a name with Elon Musk's car company, a moderate amount of magnetic field strength is an odd thing to care about putting into orbit. I think it's just some poor, ad-hoc made-up notation. I have a little bit of sympathy with Te (occasionally pronounced 'tunny') to distinguish ton from tonne, but really if you want other people to understand your units you have to go with what the BIPM recommend.
Symmetry 10y ago
Reusing the 1st stage imposed a penalty but not a massive one. For the Falcon it means a 30% to 40% penalty, not a 66% one. The 22000kg to 8000 kg difference is due to the speed you need to send the payload out at. For a GTO the payload will be in an eliptical orbit traveling between 35,786 km and 120km. For a GEO launch it will just stay at 120km or so. The GTO orbit requires much more energy per kg of payload so the Falcon 9 can't launch as much mass to GTO as it can to GEO, that doesn't have anything to do with reusability. Yes, American space companies use mT for metric tons. They normally use imperial units so please forgive them. Yes, that's what fully expendable means.

by Hondor 10y ago

rtkwe 10y ago

Yes fully expendable means dumping the whole rocket like other launches. It takes a good amount of fuel to kill all the horizontal velocity the first stage built up before detaching and then a bit more for landing. Due to just the physics you're losing some of the most effective (in terms of dV per unit mass of fuel) burn in the first stage.

Klathmon 10y ago
So hopefully someone can answer this, but what's the reason they don't put the droneships WAY down range of the rockets? So instead of having to fully stop and reverse, they position them so they can arc back down and only has to stop its momentum.
- rtkwe 10y ago
  CRS-8 which was the one that successfully landed on the barge recently was going 6600 kmph at 71 km when the first stage cut off, most of that was horizontal speed. They have to reduce that speed to both not break apart in the atmosphere. They can't have a lot of horizontal momentum low in the atmosphere and still land straight up on the barge. The rocket has hard limits on how much it can control it's orientation inside the atmosphere because it only has small cold gas thrusters and the grid fins to really control roll pitch and yaw.

rm445 10y ago

Yes, apart from the coincidental sharing a name with Elon Musk's car company, a moderate amount of magnetic field strength is an odd thing to care about putting into orbit. I think it's just some poor, ad-hoc made-up notation. I have a little bit of sympathy with Te (occasionally pronounced 'tunny') to distinguish ton from tonne, but really if you want other people to understand your units you have to go with what the BIPM recommend.

Symmetry 10y ago

Reusing the 1st stage imposed a penalty but not a massive one. For the Falcon it means a 30% to 40% penalty, not a 66% one. The 22000kg to 8000 kg difference is due to the speed you need to send the payload out at. For a GTO the payload will be in an eliptical orbit traveling between 35,786 km and 120km. For a GEO launch it will just stay at 120km or so. The GTO orbit requires much more energy per kg of payload so the Falcon 9 can't launch as much mass to GTO as it can to GEO, that doesn't have anything to do with reusability. Yes, American space companies use mT for metric tons. They normally use imperial units so please forgive them. Yes, that's what fully expendable means.