4 ms·

Why is it using a solid second stage? What are the advantages beyond weight? It isn´t more risky if you have to compensate for some kind of 1st stage under or o

by omegant 14y ago

Why is it using a solid second stage? What are the advantages beyond weight? It isn´t more risky if you have to compensate for some kind of 1st stage under or over burn?

wolf550e 14y ago
It's a solid upper stage because of time-to-market considerations, not because it's a good idea. For the first stage, thrust is more important than fuel efficiency, so a solid first stage (or boosters) make sense (at least for unmanned flights where there is no escape system), but for upper stages the fuel efficiency is more important than thrust so the upper stages should be liquid and if possible LH2/LOX, though that is the most expensive to develop (up front cost) and handle (recurring cost). Castor 30 has vacuum isp of 300sec, while Merlin 1Dvac is around 340sec. There are rumors of SpaceX working on a closed cycle methane engine, which should have even better fuel efficiency. http://www.spacelaunchreport.com/taurus2.html http://www.spacelaunchreport.com/taurus2.html http://www.spacelaunchreport.com/falcon9.html http://www.spacelaunchreport.com/falcon9.html
- InclinedPlane 14y ago
  It's not a rumor, SpaceX has stated publicly that they're working on LOX/Methane engines. There are two big reasons for this. On the one hand, it's just a good idea, liquid methane is a pretty decent compromise between LH2 and kerosene in terms of Isp vs. density (both of which affect overall stage performance) and since LCH4 exists at a similar temperature to LOX it doesn't add any exceptional problems into vehicle design or operations the way LH2 does. But perhaps more profoundly, methane is actually shockingly easy to manufacture on Mars with a very small amount of industrial equipment (we're talking about mere kilograms, provided there's sufficient power available). So the development of methane fueled rockets is also very much a way to build the systems and technology necessary for facilitating exploration and colonization of Mars.
Zuph 14y ago
Orbital has scads of experience with solid rocket motors. Simplicity is the major advantage (and disadvantage).

by omegant 14y ago

Why is it using a solid second stage? What are the advantages beyond weight? It isn´t more risky if you have to compensate for some kind of 1st stage under or over burn?

wolf550e 14y ago

It's a solid upper stage because of time-to-market considerations, not because it's a good idea. For the first stage, thrust is more important than fuel efficiency, so a solid first stage (or boosters) make sense (at least for unmanned flights where there is no escape system), but for upper stages the fuel efficiency is more important than thrust so the upper stages should be liquid and if possible LH2/LOX, though that is the most expensive to develop (up front cost) and handle (recurring cost). Castor 30 has vacuum isp of 300sec, while Merlin 1Dvac is around 340sec. There are rumors of SpaceX working on a closed cycle methane engine, which should have even better fuel efficiency. http://www.spacelaunchreport.com/taurus2.html http://www.spacelaunchreport.com/taurus2.html http://www.spacelaunchreport.com/falcon9.html http://www.spacelaunchreport.com/falcon9.html

InclinedPlane 14y ago
It's not a rumor, SpaceX has stated publicly that they're working on LOX/Methane engines. There are two big reasons for this. On the one hand, it's just a good idea, liquid methane is a pretty decent compromise between LH2 and kerosene in terms of Isp vs. density (both of which affect overall stage performance) and since LCH4 exists at a similar temperature to LOX it doesn't add any exceptional problems into vehicle design or operations the way LH2 does. But perhaps more profoundly, methane is actually shockingly easy to manufacture on Mars with a very small amount of industrial equipment (we're talking about mere kilograms, provided there's sufficient power available). So the development of methane fueled rockets is also very much a way to build the systems and technology necessary for facilitating exploration and colonization of Mars.

Zuph 14y ago

Orbital has scads of experience with solid rocket motors. Simplicity is the major advantage (and disadvantage).