5 ms·

The problem with rockets is the 0 part of H20. 0 = 15.9994, H = 1.00794 so by burning oxygen from the air you drop 15.9994/ (1.00794 * 2 + 15.9994) = 88.8% of

The problem with rockets is the 0 part of H20. 0 = 15.9994, H = 1.00794 so by burning oxygen from the air you drop 15.9994/ (1.00794 * 2 + 15.9994) = 88.8% of the weight of your fuel which makes everything a lot simpler. Less weight takes less fuel to lift which reduces the size of the craft which saves even more fuel or let's you build a stronger craft or one better suited for reentry. An air breathing craft that can get to Mach 10+ would easily drop the cost of getting to space to 1/10th what it is today and let do things like have some reserve fuel in case you messed up the landing and want to come around for another pass. If you can hit Mach 20 then LEO starts to take less energy than flying around the world.

deleted 15y ago
[deleted]
stcredzero 15y ago
The HASTOL scheme was originally proposed with an air-breathing Mach 10 (12?) hypersonic plane.
VladRussian 15y ago
>The problem with rockets is the 0 part of H20. 0 = 15.9994, H = 1.00794 so by burning oxygen from the air you drop 15.9994/ (1.00794 * 2 + 15.9994) = 88.8% of the weight of your fuel which makes everything a lot simpler. there are 2 issues with oxygen from the air: 1. the air is moving fast relatively to the aircraft frame of reference. To burn it, the air should be slowed down in the aircraft frame of reference. That means acceleration of that air in the Earth frame of reference. It isn't a noticeable energy loss below Mach 2, yet above the Mach 2-3 it starts to impact the efficiency of the air breathing scheme to the point that rocket engine carrying oxygen with it (ie. accelerating it in the Earth frame of reference and keeping it non-moving in the aircraft frame of reference) doesn't look that less efficient, and the higher the speed the less the efficiency gap. Scramjets (no slowing down of the air) while seemingly fixing that problem face the other side of the same issue - trying to impact even small amount of additional momentum on the already fast moving air (in the aircraft frame of reference) requires an unproportionally increasing (the same v square) amount of power. 2. due to composition of the Earth atmosphere, to burn 1kg of oxygen, the aircraft need to pump through engine - ie. accelerate as described in the point 1. above to the speed close to its own in the Earth's frame of reference - 5 kg of air. The jet propulsion itself doesn't care that mass m being thrown out of the nozzle with velocity v consists of - H, O2, H2O, steel balls or foam - doesn't make difference as long as it is of mass "m", and the aircraft needs to come up with that mass somehow - carry it with itself or gather from outside (and accelerate the mass or try to impact momentum on the already fast moving mass). Take the points above, add the simplicity and low weight of the rocket engine in comparison with air breathing engines and you will see why rocket engines are dominating the arena.
- onemoreact 15y ago
  1. Scramjet's don't suffer all that much from having extra air move though the engine because they don't slow that air down. 2. Scramjet's have already been demonstrated at over Mach 9.5 and are still more efficient than rockets at those speeds. (aka more thrust per unit fuel.) 3. Scramjet's are actually fairly simple designs compared to a traditional get engines. (Modeling and testing them however is much harder.) Granted, there are plenty of downsides which is why we have not built anything like that. But, the issues are far more in line with heat dissipation and drag vs. limits on the basic physics. Still the main limitation seems to be the far lower thrust-to-weight ratio.
  - VladRussian 15y ago
    >...vs. limits on the basic physics. Still the main limitation seems to be the far lower thrust-to-weight ratio. that exactly the basic physics limit of the scramjet that i was talking about : "the other side of the same issue - trying to impact even small amount of additional momentum on the already fast moving air"

deleted 15y ago

[deleted]

stcredzero 15y ago

The HASTOL scheme was originally proposed with an air-breathing Mach 10 (12?) hypersonic plane.

VladRussian 15y ago

>The problem with rockets is the 0 part of H20. 0 = 15.9994, H = 1.00794 so by burning oxygen from the air you drop 15.9994/ (1.00794 * 2 + 15.9994) = 88.8% of the weight of your fuel which makes everything a lot simpler. there are 2 issues with oxygen from the air: 1. the air is moving fast relatively to the aircraft frame of reference. To burn it, the air should be slowed down in the aircraft frame of reference. That means acceleration of that air in the Earth frame of reference. It isn't a noticeable energy loss below Mach 2, yet above the Mach 2-3 it starts to impact the efficiency of the air breathing scheme to the point that rocket engine carrying oxygen with it (ie. accelerating it in the Earth frame of reference and keeping it non-moving in the aircraft frame of reference) doesn't look that less efficient, and the higher the speed the less the efficiency gap. Scramjets (no slowing down of the air) while seemingly fixing that problem face the other side of the same issue - trying to impact even small amount of additional momentum on the already fast moving air (in the aircraft frame of reference) requires an unproportionally increasing (the same v square) amount of power. 2. due to composition of the Earth atmosphere, to burn 1kg of oxygen, the aircraft need to pump through engine - ie. accelerate as described in the point 1. above to the speed close to its own in the Earth's frame of reference - 5 kg of air. The jet propulsion itself doesn't care that mass m being thrown out of the nozzle with velocity v consists of - H, O2, H2O, steel balls or foam - doesn't make difference as long as it is of mass "m", and the aircraft needs to come up with that mass somehow - carry it with itself or gather from outside (and accelerate the mass or try to impact momentum on the already fast moving mass). Take the points above, add the simplicity and low weight of the rocket engine in comparison with air breathing engines and you will see why rocket engines are dominating the arena.

onemoreact 15y ago
1. Scramjet's don't suffer all that much from having extra air move though the engine because they don't slow that air down. 2. Scramjet's have already been demonstrated at over Mach 9.5 and are still more efficient than rockets at those speeds. (aka more thrust per unit fuel.) 3. Scramjet's are actually fairly simple designs compared to a traditional get engines. (Modeling and testing them however is much harder.) Granted, there are plenty of downsides which is why we have not built anything like that. But, the issues are far more in line with heat dissipation and drag vs. limits on the basic physics. Still the main limitation seems to be the far lower thrust-to-weight ratio.
- VladRussian 15y ago
  >...vs. limits on the basic physics. Still the main limitation seems to be the far lower thrust-to-weight ratio. that exactly the basic physics limit of the scramjet that i was talking about : "the other side of the same issue - trying to impact even small amount of additional momentum on the already fast moving air"