Less drag for the same blade velocity, but less lift in the same proportion, and what matters is lift to drag ratio, which isn't as good at high speeds (and a Martian helicopter would likely require a supersonic rotor).
And fundamentally, a hovering Mars drone is constantly accelerating by 3.7 m/s^2 by accelerating the nearby atmosphere downward. This is energy intensive, entirely apart from the drag losses. The thinner the surrounding atmosphere, the lower the mass flow rate and higher the velocity you have to accelerate it to, and higher the energy requirements...if a 1 kg drone accelerates 100 g of atmosphere (about 10 m^3) per second to 37 m/s to maintain a hover, it's doing about 70 watts of work, without even looking at losses. For reference, Curiosity gets about 125 W of continuous electrical power from its RTGs.
Weather balloons are quite large and delicate. You need something that can be deployed from a rover without any assistance, and which can survive being tethered to that rover while fully inflated...recall that weather balloons are barely inflated at launch because they expand during ascent, when they actually reach those high altitudes they are far larger than they appear on the ground. We're talking tens of meters across, a hundred cubic meters per kg of payload and balloon, made out of a fragile plastic film...and the goal is to make a rover *more* mobile, so it has to be tethered to something trundling along the surface, or self-propelled effectively enough to stay with it.
There would also be a risk of fouling the rover when the thing inevitably ruptures, something there'd be a particular risk of during inflation. A free-flying balloon probe would be possible, though very difficult and limited, a balloon drone to assist a ground rover is much less practical.
A blimp would suffer the same problem, but even worse. A cubic meter of unpressurized helium will only lift about 10 grams at the surface, and there's nothing you can do about that. The helicopter could at least spin its blades faster, though there's the problem of a power source...
Apart from being at the wrong end of a rather long vehicle, for most of the landing process the turbopumps aren't running. The engines do use RP-1 pressurized by the fuel turbopump for things like the gimbaling hydraulics, but the fins have to work even while the engines are shut down, and so have a separate system.
They only use fuel as hydraulic fluid for the engines, the fins use a different system that has to operate when the engines (and the turbopumps pressurizing the fuel) are shut down. If you're out of fuel, you don't need to gimbal the engines. And it was rather clearly not out of fuel, considering the big plume of fire coming out of the bottom of the rocket.
The fluid requirements would depend on how much the fins were actually being moved around during descent. That's something difficult to estimate without ever having actually flown a stage back to the surface under control of the grid fins.
It's not just the pumps and piping, they also save having to carry a power source for those pumps, which all adds up to a mass equivalent to quite a lot of fluid. Are you going to stick a big battery pack and electrically powered pump on the rocket? Or maybe use something driven by toxic hydrazine monopropellant? Or ditch the pump entirely and make the fluid reservoir and one of the existing pressurized helium tanks slightly bigger?
An open system with larger reserves of fluid is also less susceptible to leaks.
Return to launch site has been their goal all along. It's only in the last few months that they started talking about the seagoing landing platform approach, and then only for those situations where there wasn't enough propellant left to return, which were previously expected to require more expensive launches that expended cores instead of recovering them (the Falcon Heavy center core and geosynchronous launches, mainly).
If air breathing doesn't reduce the cost of the first launch, it won't reduce the cost of the second, and reuse works at least as well at reducing costs for Skylon's competitors. Actually considerably better for SpaceX and those who choose to take their approach, due to the efficiency gains of staging as well as a much less extreme reentry for the first stage (which constitutes the great majority of the vehicle).
Assuming the first flight is the most reliable one. They may instead start offering a discount to those willing to risk a payload on a vehicle that's never flown before.
Skylon also launches with all the oxygen it needs to reach orbit, it does not extract oxygen from the air or store it for later use. Doing so would require even more machinery to extract and liquefy the oxygen, even more hydrogen to cool and power the machinery, etc.
There is no space savings. You can't put oxygen in the hydrogen tank. In fact, Skylon has to carry extra hydrogen for cooling, and the extremely low density of liquid hydrogen makes it an enormous vehicle. This coupled with the need to stay in the atmosphere to breathe air vastly increases losses from aerodynamic drag...something that is actually almost insignificant for a non-airbreathing rocket (only around 100 m/s total, considerably less in some cases) becomes a major loss. There's also the little problem of the oxygen not moving along with the vehicle, it starts off with high relative motion in the direction you're trying to accelerate it in (and is also diluted heavily with nitrogen, and is in the form of low density gas that has to be compressed many times over...). Energy that goes into accelerating oxygen carried by a rocket isn't wasted, it gets that oxygen moving with the rocket so it can later produce full thrust when it is burned. And then there's all the extra structure and equipment that you have to carry to breathe air, which in the case of SSTO vehicles has to be hauled all the way into orbit, and that still has to be done mostly on pure rocket power.
If you do the math, it turns out you need air breathing engines with extremely high thrust and lift surfaces with very high lift to drag ratios at hypersonic speeds (not typical characteristics of hypersonic engines and lift surfaces) in order to avoid having aerodynamic losses eat up all the specific impulse advantages of air breathing engines. The main thing you accomplish by breathing air in an orbital launch system is replacing dense, easily handled liquid oxygen with low-density, tricky liquid hydrogen and adding vast amounts of complexity to the system.
That's often cited as an advantage, but jets that have to take off and potentially land (in the case of an abort) while carrying extremely heavy, hazardous, fragile, billion-dollar payloads are not particularly tolerant of bad weather.
Rockets can be *more* tolerant due to their excess of power, rapid ascent, and lack of large aerodynamic surfaces, but rocket operators have been far more risk averse due to the cost of failure. Even so, they've launched in conditions such as heavy snow that might have grounded a carrier aircraft.
The solids were partially reused...they used heavy steel casings that survived recovery. You couldn't exactly say the same booster flew twice, though, and the casings were probably one of the cheapest components of the entire system (being steel drums wrapped around a low-performance solid rocket motor that just got the vehicle off the pad and was dropped off early in the launch). The Orbiter was heavily refurbished after each flight, but was reused. The external tank could have been brought into orbit and repurposed there, but NASA never mustered the ambition and focus to do so...they just dropped them to burn up in the atmosphere.
SpaceX doesn't seem interested in burdening their spacecraft with wings, and they are very focused on cost reduction, so their eventual reusable upper stage (for the next rocket after the Falcon 9, most likely) will hopefully avoid the problems the Shuttle had.
It's not about minerals to be sent back to Earth, it's about volatiles for use in orbit. Platinum group metals might someday become a minor side business, but the real potential is in supplying propellant in orbit that doesn't cost as much as its mass in precious metals. This would allow a major expansion of orbital operations, with further reduction of costs and risk due to the additional flexibility in handling failures via robotic assembly and servicing, as well as largely solving the orbital debris problem.
They've specifically said that second stage reuse probably won't happen on the Falcon 9, but that the next vehicle (the gigantic methane-powered monster using the Raptor engine) will be fully reusable. Still, bringing the substantially larger tanks and structure of the first stage and 9 of 10 engines (27 of 28 engines for Falcon Heavy) back for reuse is likely to do more than halve costs as Teancum is assuming, even without considering that it'll allow simultaneous easing of pressure on the manufacturing end while increasing the launch rate.
What SpaceX is doing isn't just a self landing rocket, it's operational medium (and soon heavy lift lift) orbital launch vehicles with first stages that can restart their engines multiple times and return through a powered reentry for a precision landing and reuse. That *is* new, in fact the supersonic retroburn is something that nobody was even certain was possible. They're also doing propellant crossfeed on the Falcon Heavy...they may not have invented the concept, but they are the only ones to implement it. Also new: record setting thrust to weight and specific impulse from a simple gas generator engine design, and successful clustering of 9 engines for the first stage and a single near-identical engine for the second. And then there's the fact that they've disrupted the entire industry with their cost reductions. It takes a particularly blatant form of denial to claim SpaceX is doing nothing new.
Simple: you have to perform your launch from a balloon. You have to cram any support gear that would normally go on a pad into the balloon, and hopefully work out some way to get it back. You can't do any test fires or pad aborts, you're committed to either a successful launch or loss of vehicle and payload once the balloon leaves the ground. You can only launch when the weather's good enough to inflate and fly the carrier balloon, which is far more sensitive to bad weather than rockets. Even gigantic balloons would be limited to tiny rockets...for example, the Falcon 9 v1.1 masses over 500 metric tons, and SpaceX has bigger and more capable rockets planned.
And the big one: if you're going to orbit, there's just no reason to launch from a balloon. Gaining altitude is a small part of reaching orbit, balloon launch is really only useful for small suborbital rockets where the starting altitude more or less directly adds to the peak altitude reached. And even then, for rockets like Starscraper, there's the above limitations with weather, mass, etc, and the additional added trouble with recovery due to the drift of the balloon before the rocket launches.
It may take less mass in hydrogen, but you also need insulation and cooling systems to keep it liquid, and tanks large enough to contain enough liquid hydrogen. The big winner is to use water, and to obtain that water from local sources on Mars.
Except that SpaceX has performed multiple supersonic retro burns, so your chain of reasoning breaks at the first step. Supersonic retro burns have been avoided previously due to uncertainty as to whether it'd work, not because of certainty that it wouldn't. They have now been flight proven.
It's the other way around, the retrograde (which is only "counterclockwise" when viewed from one side) motion causes tidal drag which causes the orbit to decay.
Tidal forces produce bulges on large objects, and the resulting non-spherical shape allows gravity to apply torque to objects and transfer angular momentum between their rotation and their orbital revolution. This tends to bring rotation and orbital revolution into sync: it locked the moon's rotation to its orbit around the Earth, and the reverse process transferred angular momentum from Earth's rotation to the moon's orbit, slowing the Earth's rotation and pulling the moon to a higher orbit. Triton happened to be captured on the "wrong" side of Neptune and end up in a retrograde orbit, so the same tidal drag is pulling it into a lower orbit.
Phobos is in a similar situation despite having a prograde orbit: it's low enough that it orbits faster than Mars rotates (appearing from the surface to cross the sky in the opposite direction as Deimos), so the tidal drag that is pulling the more distant and slower-orbiting Deimos into an even higher orbit is pulling Phobos into a lower one.
Scaling the reactor is nothing at all like that joke. For one thing, simple realities of available room generally make use of superconducting magnets impractical on small reactors. Further, every reactor benefits from larger sizes simply due to square-cube scaling, with less surface area for heat loss for a given volume of fusing plasma, and the various plasma and electromagnetic field behaviors follow their own scaling laws, dependent on the design but frequently favoring larger scales. The Polywell, for example, is expected to have power output proportional to the seventh power of size.
You are assuming that increasing the size of the reactor is no different from building duplicates of the reactor. The reality is that they're nothing at all alike.
Price was supposedly the highest-weighted factor for this particular contract, so they aren't entirely unjustified in their complaint. However, NASA also has good justification for their decision: there's quite a bit of uncertainty with the DreamChaser. For instance, they apparently haven't settled on something as basic as a propulsion system. There's talk of them replacing the hybrids with ORBITEC's Vortex engines, but at a recent presentation they appeared to still be undecided (https://twitter.com/jeff_foust/status/517341940073787392). That's somewhat of a significant shortcoming.
It's a precursor, but not one that's stable in an atmosphere exposed to sunlight in the long term. Early Earth may have had some delivered by icy impactors. Titan has a significant quantity in the atmosphere, but even out in Saturn orbit there's enough sunlight that it's constantly being broken up and recombining into heavier hydrocarbons and other photochemical smog components. Titan is largely composed of ices and cryovolcanism is a likely source of replacement methane. There's no obvious sign of similar reserves on Mars, and traces of methane could be a sign of microbial life that are actively producing it.
Dragon actually is man-rated and has actually had people inside it, while in orbit and attached to the ISS, without killing anyone. It's just not a man-rated *launcher*, which would require a launch escape system, various additions to support people, etc. The requirements for man-rating Dragon 2 and the Falcon 9 are more extensive but not overwhelmingly different. They've already had people bouncing around inside the Dragon while in orbit, there's no reason to think they won't get this done.
And 12 launches without a single loss of vehicle or failed primary mission, and one partial failure of a secondary mission due to ISS safety rules is hardly "an abysmal safety record". It's arguably a better start than either the Atlas V or Delta IV had...the first 12 launches of both of which included a partial failure that left the *primary* payload in the wrong orbit.
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Less drag for the same blade velocity, but less lift in the same proportion, and what matters is lift to drag ratio, which isn't as good at high speeds (and a Martian helicopter would likely require a supersonic rotor).
And fundamentally, a hovering Mars drone is constantly accelerating by 3.7 m/s^2 by accelerating the nearby atmosphere downward. This is energy intensive, entirely apart from the drag losses. The thinner the surrounding atmosphere, the lower the mass flow rate and higher the velocity you have to accelerate it to, and higher the energy requirements...if a 1 kg drone accelerates 100 g of atmosphere (about 10 m^3) per second to 37 m/s to maintain a hover, it's doing about 70 watts of work, without even looking at losses. For reference, Curiosity gets about 125 W of continuous electrical power from its RTGs.
Weather balloons are quite large and delicate. You need something that can be deployed from a rover without any assistance, and which can survive being tethered to that rover while fully inflated...recall that weather balloons are barely inflated at launch because they expand during ascent, when they actually reach those high altitudes they are far larger than they appear on the ground. We're talking tens of meters across, a hundred cubic meters per kg of payload and balloon, made out of a fragile plastic film...and the goal is to make a rover *more* mobile, so it has to be tethered to something trundling along the surface, or self-propelled effectively enough to stay with it.
There would also be a risk of fouling the rover when the thing inevitably ruptures, something there'd be a particular risk of during inflation. A free-flying balloon probe would be possible, though very difficult and limited, a balloon drone to assist a ground rover is much less practical.
A blimp would suffer the same problem, but even worse. A cubic meter of unpressurized helium will only lift about 10 grams at the surface, and there's nothing you can do about that. The helicopter could at least spin its blades faster, though there's the problem of a power source...
Apart from being at the wrong end of a rather long vehicle, for most of the landing process the turbopumps aren't running. The engines do use RP-1 pressurized by the fuel turbopump for things like the gimbaling hydraulics, but the fins have to work even while the engines are shut down, and so have a separate system.
They only use fuel as hydraulic fluid for the engines, the fins use a different system that has to operate when the engines (and the turbopumps pressurizing the fuel) are shut down. If you're out of fuel, you don't need to gimbal the engines. And it was rather clearly not out of fuel, considering the big plume of fire coming out of the bottom of the rocket.
The fluid requirements would depend on how much the fins were actually being moved around during descent. That's something difficult to estimate without ever having actually flown a stage back to the surface under control of the grid fins.
It's not just the pumps and piping, they also save having to carry a power source for those pumps, which all adds up to a mass equivalent to quite a lot of fluid. Are you going to stick a big battery pack and electrically powered pump on the rocket? Or maybe use something driven by toxic hydrazine monopropellant? Or ditch the pump entirely and make the fluid reservoir and one of the existing pressurized helium tanks slightly bigger?
An open system with larger reserves of fluid is also less susceptible to leaks.
Environmental assessment for their landing sites at LC13 at the Cape:
http://www.patrick.af.mil/shar...
Return to launch site has been their goal all along. It's only in the last few months that they started talking about the seagoing landing platform approach, and then only for those situations where there wasn't enough propellant left to return, which were previously expected to require more expensive launches that expended cores instead of recovering them (the Falcon Heavy center core and geosynchronous launches, mainly).
If air breathing doesn't reduce the cost of the first launch, it won't reduce the cost of the second, and reuse works at least as well at reducing costs for Skylon's competitors. Actually considerably better for SpaceX and those who choose to take their approach, due to the efficiency gains of staging as well as a much less extreme reentry for the first stage (which constitutes the great majority of the vehicle).
Assuming the first flight is the most reliable one. They may instead start offering a discount to those willing to risk a payload on a vehicle that's never flown before.
Skylon also launches with all the oxygen it needs to reach orbit, it does not extract oxygen from the air or store it for later use. Doing so would require even more machinery to extract and liquefy the oxygen, even more hydrogen to cool and power the machinery, etc.
There is no space savings. You can't put oxygen in the hydrogen tank. In fact, Skylon has to carry extra hydrogen for cooling, and the extremely low density of liquid hydrogen makes it an enormous vehicle. This coupled with the need to stay in the atmosphere to breathe air vastly increases losses from aerodynamic drag...something that is actually almost insignificant for a non-airbreathing rocket (only around 100 m/s total, considerably less in some cases) becomes a major loss. There's also the little problem of the oxygen not moving along with the vehicle, it starts off with high relative motion in the direction you're trying to accelerate it in (and is also diluted heavily with nitrogen, and is in the form of low density gas that has to be compressed many times over...). Energy that goes into accelerating oxygen carried by a rocket isn't wasted, it gets that oxygen moving with the rocket so it can later produce full thrust when it is burned. And then there's all the extra structure and equipment that you have to carry to breathe air, which in the case of SSTO vehicles has to be hauled all the way into orbit, and that still has to be done mostly on pure rocket power.
If you do the math, it turns out you need air breathing engines with extremely high thrust and lift surfaces with very high lift to drag ratios at hypersonic speeds (not typical characteristics of hypersonic engines and lift surfaces) in order to avoid having aerodynamic losses eat up all the specific impulse advantages of air breathing engines. The main thing you accomplish by breathing air in an orbital launch system is replacing dense, easily handled liquid oxygen with low-density, tricky liquid hydrogen and adding vast amounts of complexity to the system.
That's often cited as an advantage, but jets that have to take off and potentially land (in the case of an abort) while carrying extremely heavy, hazardous, fragile, billion-dollar payloads are not particularly tolerant of bad weather.
Rockets can be *more* tolerant due to their excess of power, rapid ascent, and lack of large aerodynamic surfaces, but rocket operators have been far more risk averse due to the cost of failure. Even so, they've launched in conditions such as heavy snow that might have grounded a carrier aircraft.
The solids were partially reused...they used heavy steel casings that survived recovery. You couldn't exactly say the same booster flew twice, though, and the casings were probably one of the cheapest components of the entire system (being steel drums wrapped around a low-performance solid rocket motor that just got the vehicle off the pad and was dropped off early in the launch). The Orbiter was heavily refurbished after each flight, but was reused. The external tank could have been brought into orbit and repurposed there, but NASA never mustered the ambition and focus to do so...they just dropped them to burn up in the atmosphere.
SpaceX doesn't seem interested in burdening their spacecraft with wings, and they are very focused on cost reduction, so their eventual reusable upper stage (for the next rocket after the Falcon 9, most likely) will hopefully avoid the problems the Shuttle had.
It's not about minerals to be sent back to Earth, it's about volatiles for use in orbit. Platinum group metals might someday become a minor side business, but the real potential is in supplying propellant in orbit that doesn't cost as much as its mass in precious metals. This would allow a major expansion of orbital operations, with further reduction of costs and risk due to the additional flexibility in handling failures via robotic assembly and servicing, as well as largely solving the orbital debris problem.
They've specifically said that second stage reuse probably won't happen on the Falcon 9, but that the next vehicle (the gigantic methane-powered monster using the Raptor engine) will be fully reusable. Still, bringing the substantially larger tanks and structure of the first stage and 9 of 10 engines (27 of 28 engines for Falcon Heavy) back for reuse is likely to do more than halve costs as Teancum is assuming, even without considering that it'll allow simultaneous easing of pressure on the manufacturing end while increasing the launch rate.
What SpaceX is doing isn't just a self landing rocket, it's operational medium (and soon heavy lift lift) orbital launch vehicles with first stages that can restart their engines multiple times and return through a powered reentry for a precision landing and reuse. That *is* new, in fact the supersonic retroburn is something that nobody was even certain was possible. They're also doing propellant crossfeed on the Falcon Heavy...they may not have invented the concept, but they are the only ones to implement it. Also new: record setting thrust to weight and specific impulse from a simple gas generator engine design, and successful clustering of 9 engines for the first stage and a single near-identical engine for the second. And then there's the fact that they've disrupted the entire industry with their cost reductions. It takes a particularly blatant form of denial to claim SpaceX is doing nothing new.
Simple: you have to perform your launch from a balloon. You have to cram any support gear that would normally go on a pad into the balloon, and hopefully work out some way to get it back. You can't do any test fires or pad aborts, you're committed to either a successful launch or loss of vehicle and payload once the balloon leaves the ground. You can only launch when the weather's good enough to inflate and fly the carrier balloon, which is far more sensitive to bad weather than rockets. Even gigantic balloons would be limited to tiny rockets...for example, the Falcon 9 v1.1 masses over 500 metric tons, and SpaceX has bigger and more capable rockets planned.
And the big one: if you're going to orbit, there's just no reason to launch from a balloon. Gaining altitude is a small part of reaching orbit, balloon launch is really only useful for small suborbital rockets where the starting altitude more or less directly adds to the peak altitude reached. And even then, for rockets like Starscraper, there's the above limitations with weather, mass, etc, and the additional added trouble with recovery due to the drift of the balloon before the rocket launches.
It may take less mass in hydrogen, but you also need insulation and cooling systems to keep it liquid, and tanks large enough to contain enough liquid hydrogen. The big winner is to use water, and to obtain that water from local sources on Mars.
Except that SpaceX has performed multiple supersonic retro burns, so your chain of reasoning breaks at the first step. Supersonic retro burns have been avoided previously due to uncertainty as to whether it'd work, not because of certainty that it wouldn't. They have now been flight proven.
It's the other way around, the retrograde (which is only "counterclockwise" when viewed from one side) motion causes tidal drag which causes the orbit to decay.
Tidal forces produce bulges on large objects, and the resulting non-spherical shape allows gravity to apply torque to objects and transfer angular momentum between their rotation and their orbital revolution. This tends to bring rotation and orbital revolution into sync: it locked the moon's rotation to its orbit around the Earth, and the reverse process transferred angular momentum from Earth's rotation to the moon's orbit, slowing the Earth's rotation and pulling the moon to a higher orbit. Triton happened to be captured on the "wrong" side of Neptune and end up in a retrograde orbit, so the same tidal drag is pulling it into a lower orbit.
Phobos is in a similar situation despite having a prograde orbit: it's low enough that it orbits faster than Mars rotates (appearing from the surface to cross the sky in the opposite direction as Deimos), so the tidal drag that is pulling the more distant and slower-orbiting Deimos into an even higher orbit is pulling Phobos into a lower one.
Scaling the reactor is nothing at all like that joke. For one thing, simple realities of available room generally make use of superconducting magnets impractical on small reactors. Further, every reactor benefits from larger sizes simply due to square-cube scaling, with less surface area for heat loss for a given volume of fusing plasma, and the various plasma and electromagnetic field behaviors follow their own scaling laws, dependent on the design but frequently favoring larger scales. The Polywell, for example, is expected to have power output proportional to the seventh power of size.
You are assuming that increasing the size of the reactor is no different from building duplicates of the reactor. The reality is that they're nothing at all alike.
Price was supposedly the highest-weighted factor for this particular contract, so they aren't entirely unjustified in their complaint. However, NASA also has good justification for their decision: there's quite a bit of uncertainty with the DreamChaser. For instance, they apparently haven't settled on something as basic as a propulsion system. There's talk of them replacing the hybrids with ORBITEC's Vortex engines, but at a recent presentation they appeared to still be undecided (https://twitter.com/jeff_foust/status/517341940073787392). That's somewhat of a significant shortcoming.
It's a precursor, but not one that's stable in an atmosphere exposed to sunlight in the long term. Early Earth may have had some delivered by icy impactors. Titan has a significant quantity in the atmosphere, but even out in Saturn orbit there's enough sunlight that it's constantly being broken up and recombining into heavier hydrocarbons and other photochemical smog components. Titan is largely composed of ices and cryovolcanism is a likely source of replacement methane. There's no obvious sign of similar reserves on Mars, and traces of methane could be a sign of microbial life that are actively producing it.
Dragon actually is man-rated and has actually had people inside it, while in orbit and attached to the ISS, without killing anyone. It's just not a man-rated *launcher*, which would require a launch escape system, various additions to support people, etc. The requirements for man-rating Dragon 2 and the Falcon 9 are more extensive but not overwhelmingly different. They've already had people bouncing around inside the Dragon while in orbit, there's no reason to think they won't get this done.
And 12 launches without a single loss of vehicle or failed primary mission, and one partial failure of a secondary mission due to ISS safety rules is hardly "an abysmal safety record". It's arguably a better start than either the Atlas V or Delta IV had...the first 12 launches of both of which included a partial failure that left the *primary* payload in the wrong orbit.