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> How has the situation been improved relative to previous proposals that were judged unfruitful in an era when first stage landings didn't exist? Those propos

by T-A 2y ago

> How has the situation been improved relative to previous proposals that were judged unfruitful in an era when first stage landings didn't exist? Those proposals did not use a sled and aerodynamic lift on the way up, lighter and stronger composite materials are available and rocket engines have evolved. > Far more efficient at fighting gravity? Ask anyone who's compared how high and fast you can get a fixed-wing drone powered by one engine and a quad-copter powered by four. A serious assessment of this design would require detailed specifications and a fair amount of calculation. I am not inclined to summarily dismiss it based on generic hand-waving.

mapt 2y ago
The math is complex, but this approximation is true enough for government work: You don't need to get high to get to orbit per se. You need to get flying horizontal, much faster than the atmosphere will allow you to sustain; This is the only reason you need to get out of atmosphere. About 10% of the work in conventional spaceflight is attempting to get to >100km above your head, and about 90% of the work is in attempting to get >100km above your head, flying parallel to the Earth's surface at ~8000m/s. Those wings are useful at mach 0.7 and much less useful at mach 2 and a loss-creating pain in the ass at mach 5. You need to get to mach >20, and the longer it takes you to do so, the more you pay to the aero and gravity gods. Wings with a glide ratio of N at low speed allow a plane to divide what they pay to gravity per unit time by about N, at the cost of paying a bit more to aero losses. But as soon as you get significantly supersonic/hypersonic, the aero costs ramp to impractical levels. In airplanes, that reduction in gravity losses per unit time translates to lower needed thrust to weight ratio. Most planes fly with a TWR much lower than 1, being incapable of flying straight up. This is useful because jet engines are incredibly expensive, complex pieces of technology compared to rocket engines per unit thrust. Rockets more often fly up at a craft TWR artificially limited to "Whatever the humans and the structure will tolerate without falling apart", which changes as the craft gets lighter.
- T-A 2y ago
  > Those wings are useful at mach 0.7 and much less useful at mach 2 and a loss-creating pain in the ass at mach 5. You need to get to mach >20, and the longer it takes you to do so, the more you pay to the aero and gravity gods. If you stay at the same altitude. You are arguing by analogy with aircraft and hypersonic missiles designed to stay in the atmosphere, not to efficiently climb above most of it.

by T-A 2y ago

mapt 2y ago

The math is complex, but this approximation is true enough for government work: You don't need to get high to get to orbit per se. You need to get flying horizontal, much faster than the atmosphere will allow you to sustain; This is the only reason you need to get out of atmosphere. About 10% of the work in conventional spaceflight is attempting to get to >100km above your head, and about 90% of the work is in attempting to get >100km above your head, flying parallel to the Earth's surface at ~8000m/s. Those wings are useful at mach 0.7 and much less useful at mach 2 and a loss-creating pain in the ass at mach 5. You need to get to mach >20, and the longer it takes you to do so, the more you pay to the aero and gravity gods. Wings with a glide ratio of N at low speed allow a plane to divide what they pay to gravity per unit time by about N, at the cost of paying a bit more to aero losses. But as soon as you get significantly supersonic/hypersonic, the aero costs ramp to impractical levels. In airplanes, that reduction in gravity losses per unit time translates to lower needed thrust to weight ratio. Most planes fly with a TWR much lower than 1, being incapable of flying straight up. This is useful because jet engines are incredibly expensive, complex pieces of technology compared to rocket engines per unit thrust. Rockets more often fly up at a craft TWR artificially limited to "Whatever the humans and the structure will tolerate without falling apart", which changes as the craft gets lighter.

T-A 2y ago
> Those wings are useful at mach 0.7 and much less useful at mach 2 and a loss-creating pain in the ass at mach 5. You need to get to mach >20, and the longer it takes you to do so, the more you pay to the aero and gravity gods. If you stay at the same altitude. You are arguing by analogy with aircraft and hypersonic missiles designed to stay in the atmosphere, not to efficiently climb above most of it.