On Sunday, June 28, 2020 at 3:54:25 AM UTC-4, JF Mezei wrote:
On 2020-06-27 18:19, wrote:

space cheap enough for the rest of us. While a conventional rocket engine must
carry giant tanks of fuel and oxidizer on its journey to space, an air-breathing
rocket motor pulls most of its oxidizer directly from the atmosphere.


*Most* of its oxydizer?
Until what altitude is there enough air to run a rocket engine?
How long out of the roughly 8 minutes for first stage engine firing does
it take to reach that altitude?

Could such an engine be efficent when what it breathes in is 80%
nitrogen and 20% oxygen?

Would such an engine have both a LOX turbopump as we know it, and a
separate one that pushes gaseous air into combustion chamber? (with the
LOX turbopump activated once a certain altiutude is reached.

Is it theoretically possible to design the injectors and combustion
chamber to handle both gaseious pure oxygen at high pressure (after
pre-burner) and gaseous mix of nitrogen and oxygen (air) ?

If you read the article, everyone of your questions was addressed.