I don't know what "launches from Colorado" you're talking about. United Launch Alliance is *headquartered* in Colorado, but they launch from Florida. The US also has nuclear missile silos in Colorado, but they're suborbital vehicles, not orbital, and their primary location constraint is "somewhere that the enemy can't destroy us before we launch", not "the location that's optimal for minimum delta-V launches"
The vast majority of US launches are done from far-southern, coastal sites, for the aforementioned reasons. It is certainly possible to launch inland, but it requires serious closures downrange and increases liability costs. Likewise, it's possible to launch from more northerly locations, but it costs you serious orbital energy which you have to make up with extra staging. This is the reason why the Soviets, which lacked good southern launch sites, launched so many craft into so-called "Molniya" orbits rather than GEO (it's a pseudo-geosynchronous elliptical orbit that takes less energy to achieve, particularly from northerly latitudes... the downside is that it's not actually geosynchronous).
And to reiterate: an extra couple kilometers in height is irrelevant compared to the 300-400km for orbit, which is in turn a tiny fraction of the energy needed to reach 7800m/s orbital velocity. Ask your "friend's dad" about that.
Throw such a large percent of the US economy at one task, of course you're going to get side benefits. The issue is that Apollo could have been either A) vastly cheaper, or B) have accomplished vastly more, if not for the need to keep the a couple of giant remoras alive for the journey.
The only way to get Apollo again is by socialism, just like the first one.
Perhaps, but whether or not that is true, it glosses over another problem, namely, that Apollo just wasn't that valuable.
Are you kidding? He slayed Pytho, Earth-Dragon of Delphi; he could heal, he brought light and music, and warded away evil. He rescued Aeneas and helped Paris slay Achilles; saved his mother Leto from rape at the hands of Tityos; slayed the cyclopses; and countless other feats.
If it takes socialism to resurrect him, then long live the proletariat and down with the borgiouse swine! I'm kind of curious, what exactly is the summoning ritual like? A laurel branch, a lyre, a copy of Worker's World and a reciting of L'Internationale?
An extra kilometer or two is almost irrelevant in terms of the delta-V required to reach orbit. Meanwhile, launching from near the sea means that ascent (the time when a launch failure poses a serious risk of killing people) is done over open water - also where the noise won't bother people. And hauling things up mountains usually isn't cheap regardless.
Far more important than altitude is latitude. The boost to rockets given by Earth's spin is not insignificant.
Even planes don't help much. A dozen or so kilometers and a few hundred meters per second is nothing compared to the needed 300-400 kilometers and 7800 meters per second (the latter taking an order of magnitude more energy to achieve than the former). That said, there are some advantages to plane launch not at all related to the altitude. One is that it lets your first stage engine be more optimized to low air pressure. Two, it avoids some energy loss to wind resistance on ascent. Three, it makes it easier to move your rocket around (if it's already designed to be plane-carried), and four it makes it easier to launch over the ocean in an equatorial location (for the reasons described above). These latter two are actually the most significant. A few rockets, most notably the Pegasus, are launched in this fashion.
There are some scaleup problems, though. First, the rocket has to be carried somewhere on the plane. Underneath a wing imposes some ground clearance requirements, and underneath a plane altogether imposes huge ground clearance requirements (the reason why the suborbital Virgin Galactic carriers are designed in that unusual shape). Underneath a wing on a regular plane also lopsides the load on the plane and increases wing loadings. Mounting on the top of the fuselage makes launch harder. Some work has been done with carrying rockets inside the fuselage and dropping them out the back, but it imposes some significant maximum size issues.
The second problem, and more fundamental, is that scaling up rockets from Pegasus-size quickly imposes carrier plane size requirements that become ridiculous. The world's largest airplanes already face serious engineering challenges, let alone planes designed to carry many times more. So air launch is pretty much limited to small launches. You could do larger than Pegasus, of course (higher ISP engines, larger custom-designed carriers), but not tremendously larger.
There have been some interesting hybrid concepts proposed. For example, Black Horse / Black Colt was to work around the problem of HTOL spaceplanes facing huge loadings on takeoff by having them takeoff almost empty, meeting up with a refuelling tanker at high altitude, rapidly getting their propellant offloaded there, and then going off to space. I once did some back-of-the-napkin work on a variant that takes off with no propellant at all onboard, being towed up (with fueling lines attached) by a jumbo jet that fuels it during its ascent, to avoid having to do a midair docking on (very limited) rocket power.
Skylon is based on a previous project of Alan Bond, known as HOTOL.[10] The development of HOTOL began in 1982, at a time when space technology was moving towards reusable launch systems such as the Space Shuttle. In conjunction with British Aerospace and Rolls-Royce, a promising design emerged to which the British government contributed £2 million. However, in 1988, the government withdrew further funding, and development was terminated. Following this setback, Bond decided to set up his own company, Reaction Engines Limited, with the hope of continuing development with private funding.
After securing more funding in the 1990s, the initial design underwent radical revision and, since 2000, Reaction Engines has been working with the University of Bristol to develop an engine design vital to the success of Skylon. The STRICT/STERN designs resulting from this programme were deemed a great success.[11] The next stage of development will be to construct a full-sized working prototype of the SABRE Engine.[12]
There are several differences compared with HOTOL. Whereas HOTOL would have launched from a rocket sled, to save weight, Skylon uses a conventional retractable undercarriage. Skylon's revised engine design, the SABRE engine, is expected to offer higher performance.[13] HOTOL's rear mounted engine gave the vehicle intrinsically poor in-flight stability. Skylon solves this by placing engines at the end of its wings, but further forward and much closer to the vehicle's centre of mass longitudinally. Early attempts to fix this problem had ended up sacrificing much of HOTOL's payload potential, and contributed to the failure of the project.[14]
1. Residual formation heat or heat from major ancient impacts. Low, but when you're talking about the tiny inputs needed for cryogenic systems, it's possible.
2. Radiothermal heating. Again, low given Pluto's small size, but see #1
3. Solar heating. Again, see #1.
4. Chemical reactions in Pluto's rock. This is what's believed to be a major contributor to Enceladus's oceans (serpentinization of rock leading to a "soda sea")
5. Subduction. The subduction of denser materials and the rising of lighter materials is an energetically favorable process. In particular, during cooling liquid nitrogen would have tended to rise over water ice (water ice being denser than liquid nitrogen), but solid nitrogen (when compacted) is denser than solid water, so after it froze it would be energetic for it to subduct.
6. Relaxation. Any layers in non-gravitational equilibrium form due to Pluto's history relaxing to a more gravitational equilibrium (regardless of whether subduction is occurring) yields a release of energy.
7. Transitions between different ice phases. At temperatures and pressures we're used to most matter that we encounter in our daily lives only comes in one crystalline phase. But the various ices found on Pluto have numerous different ice phases, with different energies and densities associated with them. Most of these can metastably persist for long periods of time but transition when conditions favor doing so. The transitions can even sometimes be explosive.
8. Solar wind-driven sublimation. At one point it was thought that the solar wind had taken off nearly a thousand meters of nitrogen ice from Pluto, which would of course cause a redistribution of Pluto's mass and resettling. However this now seems unlikely as the extent of Pluto's atmosphere has been refined downward, reducing the rate of mass a thousandfold.
And many more - there are vast numbers of possibilities. That said, calling these ice volcanoes still sounds weird to me. Nitrogen, methane, and carbon monoxide ices are too readily flowing to support structures this high - it was well known in advance of the mission that any high contours would have to be water ice. But Pluto appears to have a mantle of nitrogen ice (exposed at Sputnik) under a water ice crust (possibly with layers of denser high pressure water ices underneath the nitrogen, although who knows). So how are flows of liquid water coming up through easily-flowing nitrogen ices? That doesn't make any sense to me. Also, that surface texture doesn't look anything like lava flows, at least on the large scale (some of it kind of looks like pillows, but there's no logical reason that pillows could be produced on such absurdly large scales on Pluto). The stuff nearest the "crater" looks tectonic. Honestly, I'd be less surprised to learn that it's some kind of huge frost heaving structure rather than a cryovolcanic one, maybe driven by solid-state ice phase transitions. Frost heaving tends to produce "hummocky" terrain like is seen in the pictures, and some frost heaving structures have central "craters". Another possibility would be mass loss rather than eruption. Perhaps there was a pocket of nitrogen, methane, or carbon monoxide ice long ago embedded in a large chunk of water ice that has since all sublimated away, leaving a giant collapsed sinkhole (which is being interpreted as a "crater"). Maybe it even happens regularly, some lighter ices seeping in, building up a chamber, then subliming away. Yet another possibility would be mildly analogous to pseudocraters on Earth - perhaps there are explosive events there (such as self-propagating solid state ice transitions, or rapid vaporization of "warm" nitrogen/methane/carbon monoxide ices suddenly released from pressure) that eject material and form a structure looking like a volcanic crater without actually having volcanic "roots" feeding liquid water in.
The rocket equation is not cost. Cost is cost. Proposing an expensive system to reduce fuel and tankage mass is not a money-saving concept. They get some reduction in the required launch thrust, not not incredibly, and at the cost of far more complex engines.
It's not clear to me from your description whether the oxidiser is to be solid or liquid
How can that not be clear? It says many times that the oxidizer is ammonium perchlorate. That's a solid. Polymer/perchlorate mixes are pretty standard solid rocket fuels.
If it's solid, what you've described is a solid rocket motor; if it's liquid, you've described a hybrid rocket motor.
Conventional solid and liquid rockets do not consume their "casing" and "engine" as they fly
You've described the propellant block as being shaped similarly to an aerospike, presumably for the same reason. But it's critical to the operation of an aerospike that the exhaust gases are released at the base (top) of the spike, and expand as they travel along its length
I wrote twice, "although the ideal shape would be different from an aerospike" The presence of exhaust gases being released both at the top and further down changes the ideal shape from a spike to a more conical form. Note of course that even in most conventional aerospike designs, a fraction of the exhaust (usually from that which is used to drive the turbopumps) is exhausted through the bottom of the spike.
Since the exhaust gases in your design are released from the entire surface of the spike, you don't get that benefit; you're essentially just running a rocket without a nozzle.
I think you're confused about how aerospikes (and rocket engines in general) work. The aerospike isn't what causes the gases to compress - just the opposite, it's an expansion nozzle, akin to the bell-shaped traditional expansion nozzle. There are one or more combustion chambers above the spike which are responsible for creating the compressed gas stream, which emerges at high velocity through the throat. In a conventional bell nozzle, this gas streams out straight downward and is constrained in outward expansion by the bell on all sides, up until (ideally) it reaches ambient pressure. In an aerospike, it emerges angled inward, with the ultimate expansion force being directed downward due to the action of the low pressure wake in the center, which effectively acts as an extension of the spike out to infinite length. At high pressure, the expansion remains angled inwards for a long period due to the exterior air pressure, and tracks its path away from the rocket. At low pressures the exhaust stream angles more outward and forms a broader expanding column, but still linearly directed away from the rocket. The exact process is complex and involves the reflection of compression waves, but that's getting a bit off topic here.
Like in a traditional aerospike, in what I was talking about, the spike isn't what causes the gases to compress. The gases are compressed because the burning propellant is in channels inside an aluminum structure. It has nowhere to go but out one end, but the tight channel limits the rate at which it can escape. Each little channel - space between wires or aluminum corrugations - is like a micronozzle. The spike itself is, as in an aerospike, the core of an expansion nozzle. Its purpose is not compression - it's expansion.
your exhaust gases are being emitted laterally
Again, quoting the above: " The angle of the channels would direct the stream largely along the spike"
Laterally? Why on Earth would one angle the channels laterally? What's the logic in directing your stream outward?
Lastly, see the comments above: there's actually an Air Force patent for something similar (although it relies on bow shock for compression rather than microchannels, and is thus limited to high speed atmospheric usage and lower compression ratios). If the Air Force saw fit to patent a related concept (to avoid having to pay royalties to others if they should build it, according to the patent), then it's certainly not absurd.
Similar, but not the same. Their design calls for no reinforcement at all - pressure is to come only from the bow shock. That significantly reduces the potential for pressure (as well as making the rocket more fragile), and thus the efficiency - particularly at low velocities and low external pressures (hence their focus on hypersonic missiles). In particular, due to the need for a bow shock to compress the exhaust gases, at zero velocity there is zero compression - they have to launch it from a cannon to get it going. My proposal would certainly benefit from a bow shock but does not fundamentally require one, as the eroding aluminum structure provides compression as well. Ironically, they also, include the aluminum in the propellant mix, but include it as a powder, where it's not doing any good toward increasing the pressure. Sure, the powder burns much faster, but the whole purpose of the aluminum in my variant is to not burn too quickly, so that it's around long enough to do some good.
Still, neat to see that they were exploring some of the same concepts.
Skylon's payload is comparable to that of the Falcon 9 V.1.1, but its engines are nonetheless still 70% the thrust of Falcon 9 V1.1 first stage. And a LOT more complex.
There's a number of other problematic things about Skylon. One is the very HTOL design itself. Rockets (including skylon) are cylinders under some degree of pressure - that's the natural shape for them due to wind resistance. This is a very strong design against loads along its length, not so much for loads applied by stubby wings in the middle. VTOL keeps the loads vertical the whole time, which is a big structural mass savings (it also allows for the use of landing struts rather than landing gear, which are lighter and simpler, and much smaller highly reinforced concrete pads - Skylon requires a whole highly-reinforced runway). VTHL is the next best - you still have to be able to bear lateral loads, but on landing your craft is a tiny fraction of its launch mass, so the lateral loads are a tiny fraction of what they would be with horizontal takeoff. But Skylon is HTOL - it must bear its whole loaded mass at takeoff. It has a takeoff weight like a jumbo jet, yet they want it to have an empty weight a tiny fraction of an unfurnished jumbo jet - yet have far more complicated, powerful engines, to be spaceworthy, to be hauling cryogenic propellants, etc. It's a tall order. Jumbo jets have such high empty weights in large party to withstand their takeoff loads.
Takeoff is even worse that cruise at full mass, as there's higher pressure, and you have so much force concentrated on the tiny points of your landing gear. It's so much of an issue that some HTOL designs have even tried to work around it by having the craft empty on takeoff and be fueled midair (see "Black Horse" as an example). Some extant systems do this indirectly, for example Pegasus, by employing an airplane to get them off the ground. The airplane doesn't give the rocket much altitude or delta-V, so it's not immediately obvious what advantages it gives that justify the added expense and complexity, but it's a whole host of small side benefits: great flexibility of launch locations, ease of transportation of the rocket, allowing the first rocket stage to be optimized for thinner air, and yes, avoiding the mass penalty of having to withstand the forces of takeoff. The plane has to do that, not the rocket. Other variants that have been investigated have been tow-launch with midair refueling and launch out the back of a cargo plane.
High launch frequency != mass production and continued refining between releases. It doesn't matter how often you launch if you only have a couple vehicles. Airplaines would simply be nothing like the refined vehicles that they are today if there were only five of them out there - no matter how often they flew.
Airplanes used to be terribly unreliable as well. The first cross-country "flight" in the US involved several dozen crashes. Mass production combined with the extensive design experimentation and process refinement that it enabled allowed airplanes to become the reliable, relatively quick turnaround vehicles that they are today (note: while a typical turnaround may be 30 minutes, they still have to be taken out of service regularly for more expenensive go-overs). How do you plan to get this sort of mass production-enabled experimentaiton and process refinement with Skylon? The Shuttle could likewise have been refined to reduce maintenance.... but the vehicle wasn't in the sort of production/design environment that jets are in that enables such refinement.
Tankage mass is not generally that expensive, so reducing your tankage by reducing your propellant is not the huge money-saver you're envisioning. It's your engines and particularly all of the components that drive them that make rockets expensive. And Skylon involves totally new, rather complex engines that run in two different operating modes.
And really, you think Skylon engines wouldn't have to be taken apart, examined, and refurbished just like the shuttle engines? Like jet engines?
As mentioned, it's contained within the aluminum channels. A sizeable chunk of the mass of the "engine"/propellant would be aluminum metal (whether wires, corrugated sheets, etc, brazed together), meaning rather tremendous total structural strength. Each individual channel has little strength, but on the other side of each channel is another channel - the outward-pushing pressure from combustion in one channel is countered by the opposite pressure from the adjacent channels.
I've sometimes pondered the concept of a self-consuming rocket engine - basically infinite-staging.
Picture a spike (although the ideal shape would be different from an aerospike) comprised of small channels between aluminum - for example, assembled via fine aluminum wires or finely corrugated aluminum sheets, all the way through, thus leaving empty space between them. The wires or sheets would be joined together by having any surface oxide removed (or inhibited altogether by alloying agents), and heated enough in a non-oxidizing environment to braze them together. The channels would be filled with an oxidizer-rich polymer/ammonium perchlorate mixture (very mainstream as far as propellants go).
The engine would need to be lit off across its entire surface, so all channels ignite (or be designed such that neighboring channels ignite neighbors who fail to ignite).
The propellant mixture would burn down into the channels (as even fine aluminum wire/sheeting takes time to burn through) - lacking any area within the channels to expand into, it remains compressed and accelerates linearly as it moves through the channel (design parameters set such that the compression ratio achieved is the desired compression ratio for the engine). The angle of the channels would direct the stream largely along the spike, so that the gases expand along an ideal expansion profile for generating forward thrust. Since the entire spike would be comprised of channels, again, the ideal shape would be different form an aerospike; the exhaust gases don't simply come from the top.
As the oxidizer-rich propellant burns down, it progressively erodes the aluminum making up its channels (again, alloying agents in the aluminum may be used to help or hinder this process). Since the exterior ends of the channels would be exposed to the oxidizer-rich exhaust for the longest, they'd progressively burn down from their ends. Since the exhaust burns further as it flows (and the oxidizer would be more liberated), again the erosive potential of the stream would be highest near the end of the channels. So like a wick keeping pace with a candle as it burns down, the channels would be expected to erode away at approximately the same rate that the propellant burns down.
Aluminum metal is itself is a very energetic-burning compound - aluminum dust is often included in solid rocket mixes, so the erosion of the aluminum channels is a significant thrust contributor. Lithium-aluminum would be even better - lithium-aluminum is stronger than aluminum, and lithium is even more energetic than aluminum. It would also help neutralize the hydrochloric acid that occurs in most ammonium perchlorate-based solid propellants (although there are other techniques as well, such as burning magnesium and/or sodium nitrate with it).
In a naive implementation, the spike would change from the ideal shape to a progressively suboptimal shape as it burned down. But the rate of propellant burn and aluminum erosion could be controlled by tweaking the parameters of the system such that the areas of the spike you want to last longer can burn down slower than the areas you want to burn down faster. Hence the ideal spike shape can be retained as the engine burns down, all the way to right before it burns out.
Basically, your rocket would be... no rocket at all; just propellant. The entire thing is consumed. It'd be useless for orbital maneuvering**, but to get to orbit, the rocket equation likes nothing better than non-stop continuous staging with no tankage or engine mass at all (a caveat in this regard: your gimbaling system and interstage would still have to be sized for when it's at full size and max thrust). No complex systems at all. No exotic manufacturing techniques needed. No exotic, expensive materials. Just aluminum and a not-particularly-unusual solid rocket propellant. Getting the details of the mix right to ensure 1) even ignition, 2) even burndown, and 3) aluminum erosion at the proper rate would take research and experimentation, but I would e
Skylon is reusable? So was the shuttle. Skylon saves propellant? Propellant is cheap. Reusable and low propellant consumption are not the key factors - maintenance costs are. And how Skylon will fare in that regard is very much an unknown at this point.
Part of the problem with building these sorts of reusables is that they're such low volume that you never achieve economies of scales or significant stocks of parts, and have a lot more trouble refining the design with time. SpaceX's approach where the rockets are designed to be reusable but are still an affordable option as a disposal - and starting with the disposable route - works around this problem. They produce them in bulk while progressively refining the reusable aspects.
That doesn't mean that SABRE/Skylon (which, by the way, is quite an old concept) shouldn't be pursued. It could be a quite useful concept. But it's really not answering the key question. That said, one nice thing about Skylon: being basically a giant hydrogen tank, it has a very low mass/surface area ratio when empty - namely because it has such a big bloated volume due to hydrogen's low density. This gives it a big advantage against craft like the shuttle on reentry - the energy you have to lose is proportional to your mass but the amount of surface you have to lose it from is proportional to your surface area. A reentering Skylon is a whole lot of... well, nothing. Just a big hollow shell for the most part.
And found an overwhelming ratio of "an average AQ score of 21.9 compared to a score of 18.9". Stop the presses, it's time to draw all sorts of wide ranging conclusions based on a single study finding a difference 3 points in AQ score.
I love how Slashdot is a hotbed for people arguing that:
A) People who think that ISS, a permanent human presence orbiting our planet, is a huge financial boondoggle that we never should have done; and B) Establishing a permanent human presence on the surface of Mars will be cheap and we should have done it long ago.
They're not talking about capturing wild bees and covering them in pesticides - they're talking about bred bees. And by means of using them to target applications, there would be vastly less in the environment (versus just mass-spraying orchards). And if their bred bees die, then they're not going to be achieving their goal. Hence the chemicals must be compatible with bees.
People deploy insects for agricultural purposes all the time - predators, sterilized pests, pollinators, etc. This is just another use.
I don't get this. These conversations always summon these sorts of people:
"The sensors are wrong and the scientists aren't doing any sort of correction to remove bad data or adjust the data to cancel out the errors - GLOBAL WARMING IS A LIE".... people who then in an unrelated article proceed to argue:
"The scientists are applying so-called "correction factors" to the data rather than using the raw data, so that they can make up whatever they want - GLOBAL WARMING IS A LIE!"
Limited uses due to the limited payload and the fact that they'll largely just touch the flowers, but where that's "good enough" it's an interesting possibility. Rather than dousing whole fields in pesticides and fungal innocculants you only touch the flowers - but you get almost every last flower. That's pretty darned targeted.
Obviously they're going to be using pesticides and fungal species compatible with the bees. Otherwise the plan wouldn't work at all. They probably use a reverse of the technique used to treat honeybees for parasites - a material that they have to brush against when they enter/leave the hive.
Slashdot Mirror
I don't know what "launches from Colorado" you're talking about. United Launch Alliance is *headquartered* in Colorado, but they launch from Florida. The US also has nuclear missile silos in Colorado, but they're suborbital vehicles, not orbital, and their primary location constraint is "somewhere that the enemy can't destroy us before we launch", not "the location that's optimal for minimum delta-V launches"
The vast majority of US launches are done from far-southern, coastal sites, for the aforementioned reasons. It is certainly possible to launch inland, but it requires serious closures downrange and increases liability costs. Likewise, it's possible to launch from more northerly locations, but it costs you serious orbital energy which you have to make up with extra staging. This is the reason why the Soviets, which lacked good southern launch sites, launched so many craft into so-called "Molniya" orbits rather than GEO (it's a pseudo-geosynchronous elliptical orbit that takes less energy to achieve, particularly from northerly latitudes... the downside is that it's not actually geosynchronous).
And to reiterate: an extra couple kilometers in height is irrelevant compared to the 300-400km for orbit, which is in turn a tiny fraction of the energy needed to reach 7800m/s orbital velocity. Ask your "friend's dad" about that.
No, now the US is "pissing it away" on the SLS.
I'll contribute toward the goal of sealing up the Kardashians in tubes and firing them off to Mars.
Throw such a large percent of the US economy at one task, of course you're going to get side benefits. The issue is that Apollo could have been either A) vastly cheaper, or B) have accomplished vastly more, if not for the need to keep the a couple of giant remoras alive for the journey.
Are you kidding? He slayed Pytho, Earth-Dragon of Delphi; he could heal, he brought light and music, and warded away evil. He rescued Aeneas and helped Paris slay Achilles; saved his mother Leto from rape at the hands of Tityos; slayed the cyclopses; and countless other feats.
If it takes socialism to resurrect him, then long live the proletariat and down with the borgiouse swine! I'm kind of curious, what exactly is the summoning ritual like? A laurel branch, a lyre, a copy of Worker's World and a reciting of L'Internationale?
No, Charon and Pluto are tidally locked. That said, any changes in mass distribution on one can impart energy to the other.
An extra kilometer or two is almost irrelevant in terms of the delta-V required to reach orbit. Meanwhile, launching from near the sea means that ascent (the time when a launch failure poses a serious risk of killing people) is done over open water - also where the noise won't bother people. And hauling things up mountains usually isn't cheap regardless.
Far more important than altitude is latitude. The boost to rockets given by Earth's spin is not insignificant.
Even planes don't help much. A dozen or so kilometers and a few hundred meters per second is nothing compared to the needed 300-400 kilometers and 7800 meters per second (the latter taking an order of magnitude more energy to achieve than the former). That said, there are some advantages to plane launch not at all related to the altitude. One is that it lets your first stage engine be more optimized to low air pressure. Two, it avoids some energy loss to wind resistance on ascent. Three, it makes it easier to move your rocket around (if it's already designed to be plane-carried), and four it makes it easier to launch over the ocean in an equatorial location (for the reasons described above). These latter two are actually the most significant. A few rockets, most notably the Pegasus, are launched in this fashion.
There are some scaleup problems, though. First, the rocket has to be carried somewhere on the plane. Underneath a wing imposes some ground clearance requirements, and underneath a plane altogether imposes huge ground clearance requirements (the reason why the suborbital Virgin Galactic carriers are designed in that unusual shape). Underneath a wing on a regular plane also lopsides the load on the plane and increases wing loadings. Mounting on the top of the fuselage makes launch harder. Some work has been done with carrying rockets inside the fuselage and dropping them out the back, but it imposes some significant maximum size issues.
The second problem, and more fundamental, is that scaling up rockets from Pegasus-size quickly imposes carrier plane size requirements that become ridiculous. The world's largest airplanes already face serious engineering challenges, let alone planes designed to carry many times more. So air launch is pretty much limited to small launches. You could do larger than Pegasus, of course (higher ISP engines, larger custom-designed carriers), but not tremendously larger.
There have been some interesting hybrid concepts proposed. For example, Black Horse / Black Colt was to work around the problem of HTOL spaceplanes facing huge loadings on takeoff by having them takeoff almost empty, meeting up with a refuelling tanker at high altitude, rapidly getting their propellant offloaded there, and then going off to space. I once did some back-of-the-napkin work on a variant that takes off with no propellant at all onboard, being towed up (with fueling lines attached) by a jumbo jet that fuels it during its ascent, to avoid having to do a midair docking on (very limited) rocket power.
From Wikipedia:
.
Lots of possibilities.
1. Residual formation heat or heat from major ancient impacts. Low, but when you're talking about the tiny inputs needed for cryogenic systems, it's possible.
2. Radiothermal heating. Again, low given Pluto's small size, but see #1
3. Solar heating. Again, see #1.
4. Chemical reactions in Pluto's rock. This is what's believed to be a major contributor to Enceladus's oceans (serpentinization of rock leading to a "soda sea")
5. Subduction. The subduction of denser materials and the rising of lighter materials is an energetically favorable process. In particular, during cooling liquid nitrogen would have tended to rise over water ice (water ice being denser than liquid nitrogen), but solid nitrogen (when compacted) is denser than solid water, so after it froze it would be energetic for it to subduct.
6. Relaxation. Any layers in non-gravitational equilibrium form due to Pluto's history relaxing to a more gravitational equilibrium (regardless of whether subduction is occurring) yields a release of energy.
7. Transitions between different ice phases. At temperatures and pressures we're used to most matter that we encounter in our daily lives only comes in one crystalline phase. But the various ices found on Pluto have numerous different ice phases, with different energies and densities associated with them. Most of these can metastably persist for long periods of time but transition when conditions favor doing so. The transitions can even sometimes be explosive.
8. Solar wind-driven sublimation. At one point it was thought that the solar wind had taken off nearly a thousand meters of nitrogen ice from Pluto, which would of course cause a redistribution of Pluto's mass and resettling. However this now seems unlikely as the extent of Pluto's atmosphere has been refined downward, reducing the rate of mass a thousandfold.
And many more - there are vast numbers of possibilities. That said, calling these ice volcanoes still sounds weird to me. Nitrogen, methane, and carbon monoxide ices are too readily flowing to support structures this high - it was well known in advance of the mission that any high contours would have to be water ice. But Pluto appears to have a mantle of nitrogen ice (exposed at Sputnik) under a water ice crust (possibly with layers of denser high pressure water ices underneath the nitrogen, although who knows). So how are flows of liquid water coming up through easily-flowing nitrogen ices? That doesn't make any sense to me. Also, that surface texture doesn't look anything like lava flows, at least on the large scale (some of it kind of looks like pillows, but there's no logical reason that pillows could be produced on such absurdly large scales on Pluto). The stuff nearest the "crater" looks tectonic. Honestly, I'd be less surprised to learn that it's some kind of huge frost heaving structure rather than a cryovolcanic one, maybe driven by solid-state ice phase transitions. Frost heaving tends to produce "hummocky" terrain like is seen in the pictures, and some frost heaving structures have central "craters". Another possibility would be mass loss rather than eruption. Perhaps there was a pocket of nitrogen, methane, or carbon monoxide ice long ago embedded in a large chunk of water ice that has since all sublimated away, leaving a giant collapsed sinkhole (which is being interpreted as a "crater"). Maybe it even happens regularly, some lighter ices seeping in, building up a chamber, then subliming away. Yet another possibility would be mildly analogous to pseudocraters on Earth - perhaps there are explosive events there (such as self-propagating solid state ice transitions, or rapid vaporization of "warm" nitrogen/methane/carbon monoxide ices suddenly released from pressure) that eject material and form a structure looking like a volcanic crater without actually having volcanic "roots" feeding liquid water in.
The rocket equation is not cost. Cost is cost. Proposing an expensive system to reduce fuel and tankage mass is not a money-saving concept. They get some reduction in the required launch thrust, not not incredibly, and at the cost of far more complex engines.
How can that not be clear? It says many times that the oxidizer is ammonium perchlorate. That's a solid. Polymer/perchlorate mixes are pretty standard solid rocket fuels.
Conventional solid and liquid rockets do not consume their "casing" and "engine" as they fly
I wrote twice, "although the ideal shape would be different from an aerospike" The presence of exhaust gases being released both at the top and further down changes the ideal shape from a spike to a more conical form. Note of course that even in most conventional aerospike designs, a fraction of the exhaust (usually from that which is used to drive the turbopumps) is exhausted through the bottom of the spike.
I think you're confused about how aerospikes (and rocket engines in general) work. The aerospike isn't what causes the gases to compress - just the opposite, it's an expansion nozzle, akin to the bell-shaped traditional expansion nozzle. There are one or more combustion chambers above the spike which are responsible for creating the compressed gas stream, which emerges at high velocity through the throat. In a conventional bell nozzle, this gas streams out straight downward and is constrained in outward expansion by the bell on all sides, up until (ideally) it reaches ambient pressure. In an aerospike, it emerges angled inward, with the ultimate expansion force being directed downward due to the action of the low pressure wake in the center, which effectively acts as an extension of the spike out to infinite length. At high pressure, the expansion remains angled inwards for a long period due to the exterior air pressure, and tracks its path away from the rocket. At low pressures the exhaust stream angles more outward and forms a broader expanding column, but still linearly directed away from the rocket. The exact process is complex and involves the reflection of compression waves, but that's getting a bit off topic here.
Like in a traditional aerospike, in what I was talking about, the spike isn't what causes the gases to compress. The gases are compressed because the burning propellant is in channels inside an aluminum structure. It has nowhere to go but out one end, but the tight channel limits the rate at which it can escape. Each little channel - space between wires or aluminum corrugations - is like a micronozzle. The spike itself is, as in an aerospike, the core of an expansion nozzle. Its purpose is not compression - it's expansion.
Again, quoting the above: " The angle of the channels would direct the stream largely along the spike"
Laterally? Why on Earth would one angle the channels laterally? What's the logic in directing your stream outward?
Lastly, see the comments above: there's actually an Air Force patent for something similar (although it relies on bow shock for compression rather than microchannels, and is thus limited to high speed atmospheric usage and lower compression ratios). If the Air Force saw fit to patent a related concept (to avoid having to pay royalties to others if they should build it, according to the patent), then it's certainly not absurd.
You're envisioning the world launching many tens of millions of tonnes of payload into orbit any time soon? Yeah, good luck with that dream.
Similar, but not the same. Their design calls for no reinforcement at all - pressure is to come only from the bow shock. That significantly reduces the potential for pressure (as well as making the rocket more fragile), and thus the efficiency - particularly at low velocities and low external pressures (hence their focus on hypersonic missiles). In particular, due to the need for a bow shock to compress the exhaust gases, at zero velocity there is zero compression - they have to launch it from a cannon to get it going. My proposal would certainly benefit from a bow shock but does not fundamentally require one, as the eroding aluminum structure provides compression as well. Ironically, they also, include the aluminum in the propellant mix, but include it as a powder, where it's not doing any good toward increasing the pressure. Sure, the powder burns much faster, but the whole purpose of the aluminum in my variant is to not burn too quickly, so that it's around long enough to do some good.
Still, neat to see that they were exploring some of the same concepts.
Skylon's payload is comparable to that of the Falcon 9 V.1.1, but its engines are nonetheless still 70% the thrust of Falcon 9 V1.1 first stage. And a LOT more complex.
There's a number of other problematic things about Skylon. One is the very HTOL design itself. Rockets (including skylon) are cylinders under some degree of pressure - that's the natural shape for them due to wind resistance. This is a very strong design against loads along its length, not so much for loads applied by stubby wings in the middle. VTOL keeps the loads vertical the whole time, which is a big structural mass savings (it also allows for the use of landing struts rather than landing gear, which are lighter and simpler, and much smaller highly reinforced concrete pads - Skylon requires a whole highly-reinforced runway). VTHL is the next best - you still have to be able to bear lateral loads, but on landing your craft is a tiny fraction of its launch mass, so the lateral loads are a tiny fraction of what they would be with horizontal takeoff. But Skylon is HTOL - it must bear its whole loaded mass at takeoff. It has a takeoff weight like a jumbo jet, yet they want it to have an empty weight a tiny fraction of an unfurnished jumbo jet - yet have far more complicated, powerful engines, to be spaceworthy, to be hauling cryogenic propellants, etc. It's a tall order. Jumbo jets have such high empty weights in large party to withstand their takeoff loads.
Takeoff is even worse that cruise at full mass, as there's higher pressure, and you have so much force concentrated on the tiny points of your landing gear. It's so much of an issue that some HTOL designs have even tried to work around it by having the craft empty on takeoff and be fueled midair (see "Black Horse" as an example). Some extant systems do this indirectly, for example Pegasus, by employing an airplane to get them off the ground. The airplane doesn't give the rocket much altitude or delta-V, so it's not immediately obvious what advantages it gives that justify the added expense and complexity, but it's a whole host of small side benefits: great flexibility of launch locations, ease of transportation of the rocket, allowing the first rocket stage to be optimized for thinner air, and yes, avoiding the mass penalty of having to withstand the forces of takeoff. The plane has to do that, not the rocket. Other variants that have been investigated have been tow-launch with midair refueling and launch out the back of a cargo plane.
High launch frequency != mass production and continued refining between releases. It doesn't matter how often you launch if you only have a couple vehicles. Airplaines would simply be nothing like the refined vehicles that they are today if there were only five of them out there - no matter how often they flew.
Airplanes used to be terribly unreliable as well. The first cross-country "flight" in the US involved several dozen crashes. Mass production combined with the extensive design experimentation and process refinement that it enabled allowed airplanes to become the reliable, relatively quick turnaround vehicles that they are today (note: while a typical turnaround may be 30 minutes, they still have to be taken out of service regularly for more expenensive go-overs). How do you plan to get this sort of mass production-enabled experimentaiton and process refinement with Skylon? The Shuttle could likewise have been refined to reduce maintenance.... but the vehicle wasn't in the sort of production/design environment that jets are in that enables such refinement.
Tankage mass is not generally that expensive, so reducing your tankage by reducing your propellant is not the huge money-saver you're envisioning. It's your engines and particularly all of the components that drive them that make rockets expensive. And Skylon involves totally new, rather complex engines that run in two different operating modes.
And really, you think Skylon engines wouldn't have to be taken apart, examined, and refurbished just like the shuttle engines? Like jet engines?
As mentioned, it's contained within the aluminum channels. A sizeable chunk of the mass of the "engine"/propellant would be aluminum metal (whether wires, corrugated sheets, etc, brazed together), meaning rather tremendous total structural strength. Each individual channel has little strength, but on the other side of each channel is another channel - the outward-pushing pressure from combustion in one channel is countered by the opposite pressure from the adjacent channels.
I've sometimes pondered the concept of a self-consuming rocket engine - basically infinite-staging.
Picture a spike (although the ideal shape would be different from an aerospike) comprised of small channels between aluminum - for example, assembled via fine aluminum wires or finely corrugated aluminum sheets, all the way through, thus leaving empty space between them. The wires or sheets would be joined together by having any surface oxide removed (or inhibited altogether by alloying agents), and heated enough in a non-oxidizing environment to braze them together. The channels would be filled with an oxidizer-rich polymer/ammonium perchlorate mixture (very mainstream as far as propellants go).
The engine would need to be lit off across its entire surface, so all channels ignite (or be designed such that neighboring channels ignite neighbors who fail to ignite).
The propellant mixture would burn down into the channels (as even fine aluminum wire/sheeting takes time to burn through) - lacking any area within the channels to expand into, it remains compressed and accelerates linearly as it moves through the channel (design parameters set such that the compression ratio achieved is the desired compression ratio for the engine). The angle of the channels would direct the stream largely along the spike, so that the gases expand along an ideal expansion profile for generating forward thrust. Since the entire spike would be comprised of channels, again, the ideal shape would be different form an aerospike; the exhaust gases don't simply come from the top.
As the oxidizer-rich propellant burns down, it progressively erodes the aluminum making up its channels (again, alloying agents in the aluminum may be used to help or hinder this process). Since the exterior ends of the channels would be exposed to the oxidizer-rich exhaust for the longest, they'd progressively burn down from their ends. Since the exhaust burns further as it flows (and the oxidizer would be more liberated), again the erosive potential of the stream would be highest near the end of the channels. So like a wick keeping pace with a candle as it burns down, the channels would be expected to erode away at approximately the same rate that the propellant burns down.
Aluminum metal is itself is a very energetic-burning compound - aluminum dust is often included in solid rocket mixes, so the erosion of the aluminum channels is a significant thrust contributor. Lithium-aluminum would be even better - lithium-aluminum is stronger than aluminum, and lithium is even more energetic than aluminum. It would also help neutralize the hydrochloric acid that occurs in most ammonium perchlorate-based solid propellants (although there are other techniques as well, such as burning magnesium and/or sodium nitrate with it).
In a naive implementation, the spike would change from the ideal shape to a progressively suboptimal shape as it burned down. But the rate of propellant burn and aluminum erosion could be controlled by tweaking the parameters of the system such that the areas of the spike you want to last longer can burn down slower than the areas you want to burn down faster. Hence the ideal spike shape can be retained as the engine burns down, all the way to right before it burns out.
Basically, your rocket would be... no rocket at all; just propellant. The entire thing is consumed. It'd be useless for orbital maneuvering**, but to get to orbit, the rocket equation likes nothing better than non-stop continuous staging with no tankage or engine mass at all (a caveat in this regard: your gimbaling system and interstage would still have to be sized for when it's at full size and max thrust). No complex systems at all. No exotic manufacturing techniques needed. No exotic, expensive materials. Just aluminum and a not-particularly-unusual solid rocket propellant. Getting the details of the mix right to ensure 1) even ignition, 2) even burndown, and 3) aluminum erosion at the proper rate would take research and experimentation, but I would e
Skylon is reusable? So was the shuttle. Skylon saves propellant? Propellant is cheap. Reusable and low propellant consumption are not the key factors - maintenance costs are. And how Skylon will fare in that regard is very much an unknown at this point.
Part of the problem with building these sorts of reusables is that they're such low volume that you never achieve economies of scales or significant stocks of parts, and have a lot more trouble refining the design with time. SpaceX's approach where the rockets are designed to be reusable but are still an affordable option as a disposal - and starting with the disposable route - works around this problem. They produce them in bulk while progressively refining the reusable aspects.
That doesn't mean that SABRE/Skylon (which, by the way, is quite an old concept) shouldn't be pursued. It could be a quite useful concept. But it's really not answering the key question. That said, one nice thing about Skylon: being basically a giant hydrogen tank, it has a very low mass/surface area ratio when empty - namely because it has such a big bloated volume due to hydrogen's low density. This gives it a big advantage against craft like the shuttle on reentry - the energy you have to lose is proportional to your mass but the amount of surface you have to lose it from is proportional to your surface area. A reentering Skylon is a whole lot of... well, nothing. Just a big hollow shell for the most part.
And found an overwhelming ratio of "an average AQ score of 21.9 compared to a score of 18.9". Stop the presses, it's time to draw all sorts of wide ranging conclusions based on a single study finding a difference 3 points in AQ score.
I love how Slashdot is a hotbed for people arguing that:
A) People who think that ISS, a permanent human presence orbiting our planet, is a huge financial boondoggle that we never should have done; and
B) Establishing a permanent human presence on the surface of Mars will be cheap and we should have done it long ago.
They're not talking about capturing wild bees and covering them in pesticides - they're talking about bred bees. And by means of using them to target applications, there would be vastly less in the environment (versus just mass-spraying orchards). And if their bred bees die, then they're not going to be achieving their goal. Hence the chemicals must be compatible with bees.
People deploy insects for agricultural purposes all the time - predators, sterilized pests, pollinators, etc. This is just another use.
I don't get this. These conversations always summon these sorts of people:
"The sensors are wrong and the scientists aren't doing any sort of correction to remove bad data or adjust the data to cancel out the errors - GLOBAL WARMING IS A LIE" .... people who then in an unrelated article proceed to argue:
"The scientists are applying so-called "correction factors" to the data rather than using the raw data, so that they can make up whatever they want - GLOBAL WARMING IS A LIE!"
I wish they'd make up their minds.
Limited uses due to the limited payload and the fact that they'll largely just touch the flowers, but where that's "good enough" it's an interesting possibility. Rather than dousing whole fields in pesticides and fungal innocculants you only touch the flowers - but you get almost every last flower. That's pretty darned targeted.
Obviously they're going to be using pesticides and fungal species compatible with the bees. Otherwise the plan wouldn't work at all. They probably use a reverse of the technique used to treat honeybees for parasites - a material that they have to brush against when they enter/leave the hive.