3 ms·

The really interesting question - does the modest increase in initial velocity and altitude with a boost out of the lower atmosphere make it practical to build

by ufmace 9y ago

The really interesting question - does the modest increase in initial velocity and altitude with a boost out of the lower atmosphere make it practical to build a Single Stage To Orbit rocket? If they can, then it's an impressive achievement. If not, then it doesn't really seem worth the trouble.

averagewall 9y ago
While having fewer stages sounds simpler and easier, that's not necessarily a major cost. Having a big and powerful 1st stage is a major cost so this should allow either a cheaper 1st stage or a heavier payload.
PhasmaFelis 9y ago
Technically I think the carrier plane counts as a stage, so two-stage-to-orbit is the minimum. Yes, I know what you meant. :) Interesting question.
Symmetry 9y ago
The altitude boost is certainly not worth the work. The velocity from the plane is small but since fuel requirements go up exponentially with necessary velocity every bit helps. More important than that is that the rocket doesn't have to punch through as dense of an atmosphere when getting up to speed. That means you don't have to reinforce the rocket as much since it's maximum dynamic pressure (maxQ) is lower giving you a better mass ratio and it means that you're not losing as much delta-v to air resistance but that's only another 100 m/s or so for a decently sized rocket like the one being launched here. But more importantly you can design your engines so that they don't have to work at higher atmospheric pressures. https://en.wikipedia.org/wiki/Rocket_engine_nozzle https://en.wikipedia.org/wiki/Rocket_engine_nozzle A Merlin engine with a bell designed for taking off from sea level has a trust at sea level of 845 kN but a thrust in Vacuum of 914 kN all while burning the same amount of fuel. And a Merlin with a nozzle sized for vacuum use can go up to 934 kN when firing in vacuum, again for the same fuel flow rate.

by ufmace 9y ago

averagewall 9y ago

While having fewer stages sounds simpler and easier, that's not necessarily a major cost. Having a big and powerful 1st stage is a major cost so this should allow either a cheaper 1st stage or a heavier payload.

PhasmaFelis 9y ago

Technically I think the carrier plane counts as a stage, so two-stage-to-orbit is the minimum. Yes, I know what you meant. :) Interesting question.

Symmetry 9y ago

The altitude boost is certainly not worth the work. The velocity from the plane is small but since fuel requirements go up exponentially with necessary velocity every bit helps. More important than that is that the rocket doesn't have to punch through as dense of an atmosphere when getting up to speed. That means you don't have to reinforce the rocket as much since it's maximum dynamic pressure (maxQ) is lower giving you a better mass ratio and it means that you're not losing as much delta-v to air resistance but that's only another 100 m/s or so for a decently sized rocket like the one being launched here. But more importantly you can design your engines so that they don't have to work at higher atmospheric pressures. https://en.wikipedia.org/wiki/Rocket_engine_nozzle https://en.wikipedia.org/wiki/Rocket_engine_nozzle A Merlin engine with a bell designed for taking off from sea level has a trust at sea level of 845 kN but a thrust in Vacuum of 914 kN all while burning the same amount of fuel. And a Merlin with a nozzle sized for vacuum use can go up to 934 kN when firing in vacuum, again for the same fuel flow rate.