The moon's surface is kind of boring, as far as geology goes. Aluminum oxide, titanium oxide, iron oxide, silicon dioxide... by and large it's stuff that's really common on Earth. And not much of the common stuff that's super-useful, like water. And really, it's way more of a gravity well than is ideal to have.
But gasoline is one of the more expensive thermal fuels. 34kWh (122MJ) is 4,2kg of coal. Coal is about $45 per short ton, aka per ~1100kg, aka $0,04/kg, aka the coal equivalent of one gallon of gasoline costs only $0,17.
No no, we can get much more than a 1-2% improvement in chemical rocket performance. The issue is that for our needs thusfar (large objects to LEO and GEO, small objects further out with long transit times and gravity assists or ion propulsion), H2/O2 has been fine and it's not been worth all of the headaches of more energy dense fuel mixtures, like Li-(LF2|FLOX|OF2)-LH2 triprop. But we can indeed get a 25% improvement in ISP if we're willing to work with very hazardous, toxic chemicals (at least the resultant LiF isn't as toxic as F2!). It was already done in a lab-scale development back in the late 1960s. And let's not kid ourself, NASA has indeed launched successful missions using toxic, corrosive and dangerous chemicals as propellants. But this would be a new upper bound in this regard. I doubt they'd ever use a propellant like that on a lower stage, but for an upper stage or a return stage... it's a possibility.
Without invoking significant toxicity we can improve the picture somewhat. Burning the lithium with O2 (and of course H2 for exhaust flow reasons) is also a very high energy propellant, but it still means working with metallic lithium in some form or another (liquid, hybrid, slurry, cryosolid, etc), which most people would really like to avoid. But it is possible to do.
A small boost to H2/O2 can be made with aluminum - it only boosts the Isp a few percent (I believe about 4%-ish, though I'd have to double check), but it also gives a nice secondary bonus of really increasing your propellant density. Aluminum is neither dangerous nor toxic, but burning it with the H2/O2, and in a reliable manner, hasn't been tackled yet.
Boron is another high-energy compound one can use. As is beryllium (Be-F2-H2 is even more powerful than Li-F2-H2 by a small margin), but it's hugely expensive and extremely toxic in dust form.
Beyond all of the "familiar" stuff there's a lot of research on more exotic compounds with strained chemical bonds which remain in a metastable state until burned; there's way too many such compounds to list here. But at present they all generally suffer from either production cost issues or problematic instabilities.
Oh, and you can also improve performance by increasing the chamber pressure. That said, it's rather modest - if I recall a doubling of chamber pressure is usually on the order of a 7% ISP boost. But it does mean that advances in material technologies can translate to advances in rocket ISP. And there's also a wide range of other modifications to engine design that could boost rocket ISP to lesser extents.
Staging works pretty well to get around the energy density problem, at least early on.. though the rocket equation starts getting pretty tyrranical when it comes to returns from other planetary bodies. It's really hard to conceive of a manned Mars mission with return that doesn't involve at least the return ascent stage being fueled by one of the following:
1) In-situ propellant production 2) Extreme-ISP chemical propellant 3) Nuclear thermal
You can't rely on ion propulsion (even higher power variants like VASIMR) to get you off the ground. Nuclear thermal (1) should work (NERVA showed promise), but the development costs will be huge and it'd face massive public opposition, having that much nuclear fuel on a single craft. It also puts a rather large minimum size for your ascent stage - fission doesn't scale down well, and even as big as it was NERVA only had a thrust to weight ratio of 3 to 4. And the mass of that large, heavy ascent stage imposes significant mass penalties on your earlier stages, partially negating the benefit of that 800-1100 sec ISP.
For more advanced chemicals (2), there's lots of theoretical stuff, but with stuff that we could do today for a practical cost, it'd probably pretty much have to be some variant of lithium/fluorine/hydrogen triprop. The oxidizer could be LF, FLOX, OF2, or a couple other possibilities... but if you want an ISP(vac) from chemical propellants in 500-550 range and good density, that's pretty much what you have to do (yes, the LM and CSM used toxic, corrosive, dangerous propellants too, and NASA managed fine, but these are even worse). And even still, 500-550 sec is low enough that you'd probably still want some sort of ion "tug" cycler to move you between LEO and LMO, with your fuel only used for ascent.
If you don't want to or can't do either of those two options (#2 and #3), you're pretty much stuck with in-situ production (unless you want to have to launch a LOT of tonnage into orbit!) Which is why that's SpaceX's focus... it probably is the best option. Still, though, it's a challenge and a risk, no question.
Indeed. Did you see his interview with Colbert about Pluto? He talks about everyone who disagrees with him about the IAU decision (a group that includes most of the New Horizons scientific team) as though they's ignorant little children who just don't "understand" like he does.
I think his job is more "ticking large numbers of people off". For example, he was one of the leaders behind the "Pluto, Eris, Ceres, etc aren't planets" movement - he had references to Pluto being a planet removed from the Hayden Planetarium years before the IAU vote. He's not exactly popular among those who felt that hydrostatic equilibrium was the relevant constraint and that the "cleared the neighborhood" definition is fundamentally flawed.
Which is silly, because the Apollo mission was primarily oriented around the physics of getting a bunch of large mammals into space, keeping them alive on the way to the moon, landing them on the moon, keeping them alive down there while they explore, and then doing all of that in reverse. If they hadn't brought a single rock back the total change to the mission cost would have been almost unnoticeable.
Furthermore, who's focused on mining the moon? Most mining proposals focus on mining NEOs. It's way easier to get material from a NEO to Earth aerocapture. You could do it with a coilgun with no expenditure of consumables, again and again for years on end. They're also far more rich in interesting materials - much better than the best mines on Earth, and with no overburden.
Actually they very well might. The strongest individual SWNTs measured thusfar are, what, 60GPa? That's way too weak to make a practical space elevator. And that's for individual tubes. Ropes are only held together by VDW and break at their weakest points, which will invariably exist - as a result it's hard to get ropes more than a couple GPa. There may be some better structures out there, but I wouldn't hold my breath waiting for an Earth-based space elevator.
If you want a physical structure reaching to space, go for a Lofstrom loop.
Where are you getting those prices? NASA was paying $3,60/kg for LH in 1980, so that's probably, what, $7/kg for LH today? Remember, this is LH, not gaseous - you not only have to cool it to extreme temperatures, but you also have to catalyze the conversion of orthohydrogen to parahydrogen - which is exothermic, yielding enough heat to nearly boil off everything you just cooled. NASA was paying $0,08/kg for LOX in 1980, so probably around $0,15 today. The Shuttle ET holds 630 tonnes of LOX and 106 tonnes of LH, so $836k.
The SRBs are 70% ammonium perchlorate, which is about $3/kg. 16% aluminum (about $1,50/kg), 12% PBAN binder (about $1/kg), 2% epoxy (about $5/kg), and an irrelevant amount of iron oxide. The total propellant was about 500 tonnes. Total propellant cost, $1,3m.
So the total propellant cost between the two, about $2m. To lift 27,6 tonnes of cargo to LEO, or $72 per kilogram. Now, people shouldn't fall for the fallacy that you just multiply that by how much a person weighs or a little more and that's the per-person cost to go to space - you actually have to launch many times more than a person's weight to get them there and keep them alive. But yes, propellant costs are not the key issue - if costs were close to propellant costs, rocketry would only cost about $25-100k to bring people to orbit in bulk.
Unfortunately, that's not the case.
Mind you, it's even possible to get significantly lower than that, but you can't rely on the rocket equation. And even if Space Elevator unobtanium existed, it wouldn't actually get you down to the levels one wants - there's no practical way to pump the climbing power up the tether, and beaming efficiencies with such a small receiver are unfortunately very low over such long distances. Much more practical is something like a Lofstrom loop - one might get power transfer efficiencies upwards of 50% or so. In such a case, you need about 70MJ per kilogram (19,4kWh). At industrial power rates of, say, $0,08/kW, that's a cost of a mere $1,56/kg. Sending people up in bulk might cost on the order of $800-ish per person in energy costs.
In both cases, though, it's not the propellant/energy costs that are killer, it's the hardware.You're asking structures to perform some borderline magical tasks in terms of the challenges that are put on them.
Anyway, enough Slashdot for now... back to working on simulating my caseless rocket design in OpenFoam and optimizing propellant combinations in CEA.;)
What's the worst thing that could happen with a multi-tonne chunk of metal full of potentially explosive, potentially toxic, at a bare mininum highly flammable propellants, flying overhead at thousands of meters per second?
It was hit by something else, damaged, and landed.
That would be even more impressive on the rebel's part. In your telling, they hit it twice, with two separate weapons systems, one while it was flying?
Their design was kind of problematic. People naturally gravitate towards polybutadiene because of its use as a binder in solid rockets. But hybrids are not solids. Hybrids are great in most regards except for generally pathetic burn rates. Rather than consider other fuels, SS1 just used a typical solid rocket binder. One can compensate for the low burn rate, of course - usually by trying to increase the area by making many, smaller channels - this they did. But the more your propellant looks like swiss cheese, the more likely you are to have chunks break off as the rocket burns down. Which is exactly what happened on one flight, they had such a loud bang during the strike that the pilot thought his engine had exploded.
The proper solution is pointed to by research. Rather than polybutadiene the propellant should be something like paraffin or polyethylene. They melt at lower temperatures and become very fluid. The combustion basically whips up a "spray" off of the surface, making for very rapid combustion. With rapid combustion you don't have to "swiss cheeseify" your propellant. The polyethylene and the high melting point paraffins also are very strong and stable at room temperature.
a feat that not even government space programs have achieved
Because they haven't seen fit to waste any money on it because it's such a meaningless endeavour. There's so little money in it, except for tourism, which government space programs (possibly excepting the Russians) have no interest in.
As a general rule, when governments shoot something up, they want it to stay up.
But the public confuses space and orbit. To them they're synonymous. It is not technically incorrect to call it "reaching space", but it's also not wrong to point out that "reaching space" and "reaching orbit" are not even in the same ballpark.
Anyway, the oxidizer is HTP, so we can look forward to this company going bust shortly after they suffer from a catastrophic tank explosion - hopefully while nobody is around. Seriously, why did every other little suborbital rocket startup in the 1990s and 2000s suddenly decide that in contrast with the vast amount of evidence amassed earlier, HTP is in reality an easy, convenient, safe oxidizer choice? Because they can find household peroxide in their medicine cabinet and gee, it seems safe enough?
(It's not impossible to use HTP safely - for example, it's used for maneuvering in Soyuz - but it usually takes a number of explosions to get your process refined to the point that that doesn't happen any more)
In general, rocketry has pretty much well settled on the right general formula for liquids and hybrids: LOX (clean, absurdly cheap, relatively dense, low viscosity, stable and (by oxidizer standards) non-corrosive in the right conditions, and although cryogenic we've gotten good at dealing with that) burned with hydrogen or alkanes of varying lengths (depending on the desired balance between efficiency and temperature/density/power; they're clean, cheap, stable, low viscosity and readily vaporized, non-corrosive, etc) and optionally fine-grained aluminum if one can work it (up to 20% - cheap, rather clean, very stable, dense, and very energy-rich). Some of the alternatives under research may provide some benefits, and in certain particular situations there might be a need for "special cases" (for example, where hypergolics or monoprops are essential), but by and large for bulk "lifting" it's about refining designs, not propellant combinations.
To put it another way: the Falcon 9 first stage has a loaded mass of 418 tonnes and an empty mass of 23 tonnes, or a ratio of 18,2 to 1. New Shepard has a loaded mass of 75 tonnes and an empty mass of 20,5 tonnes, or a ratio of 3,66 to 1. Noticing a bit of difference here? New Shepard has, proportionally, 5 times more mass to throw around toward making their landing easy. How easily do you think they could cut their spacecraft to 20% of its current weight and still land? And on top of that, they face far lower wind loadings and heat loadings to boot and have far less crossrange to deal with, making it that much easier on them.
Suborbital spaceflight is the special olympics of spaceflight.
Again: "from space" is not the same thing, or even close, to "from orbit". It's not the height that causes problems, it's the velocity. And more importantly than that, it's the extreme mass limitations that reaching that velocity imposes on your craft. With suborbital flight you can dedicate all the mass in the world to making the task as easy on yourself as possible.
Flights that just pop up to the Karman line and back down are virtually nothing like flights that actually go to orbit. Even the X-15, which actually reached a quarter of orbital velocity, was far more like an orbital flight than a straight up/down jaunt.
The Karman line is only 1/3rd to 1/4 of the way to proper orbital altitude. And the energy required to achieve orbital altitude is only a tiny fraction of that required to reach orbital velocity. And the rocket equation means that the faster you want to go, the exponentially more mass it takes. These little up-down jaunts do nothing except to confuse the general public into thinking that they're doing something similar to orbital spaceflight.
Turkey has released a radar track (I could dig it up if you want). See that little lobe that dips into Syria south of Yayladagi? The track shows that the plane flew straight across it rather than going around it.
Nor is the FSA. JaF is, however, and they work with the FSA. The US isn't arming Jaf, but they're not bombing them either, as Jaf is actively fighting Daesh and seems to have no interest - at least at present - in attacks against the west.
It's really not, at least among the major players. In the north (where the most relevant fronts are, even if there is still lots of random fighting elsewhere) you have Daesh in the east, the YPG (kurdish "Peoples' Defense Units") to the north of them, and JaF (Jaish al-Fatah, "Army of Conquest")/FSA alliance in the center (down to just north of Hama, and edging into Latakia by the Turkish border). The FSA has many different brigades but they're all pretty unified by wanting to fight Assad and Daesh and being composed of members who explicitly didn't join the (formerly much more powerful) Islamist militias. JaF is comprised of a number of militias, mostly islamist, the two most powerful being Ahrar ash-Sham ("Supporters of the Levant") and Jabhat al-Nusra ("The Support Front for the People of the Levant").
Let's break down the players.
The YPG, opposed by Turkey (out of fear of links to the PKK), controls a long strip along Turkey's northeast border, as well as a couple of pockets west of there. They have a long border with Daesh territory and fight almost exclusively against Daesh (even though there's one or two Assad pockets within their territory). Recently they've launched a major anti-Daesh campaign, using US-supplied weapons, in an alliance with Arab anti-Daesh forces, under the banner of Syrian Democratic Forces. So far it seems to be progressing well.
Daesh (aka IS/ISIS/IL) is, of course, Daesh. A group of Islamists so radical that even al-Qaeda thinks they're nuts. That said, it should be reiterated that not everyone who fights for them shares their ideology. They literally do run what is effectively a state, with locally sourced money (based around oil pumping, refining with truck-mounted mini-refineries, and sales - both domestic, to Turkey (black market), and even to Assad, who they're vehemently against. This money funds a militia far larger than their ideological base, often made up of the poor and displaced in the conflict who need the work. That said, literally armed entitity who's not part of Daesh in this conflict is an enemy of Daesh, so it's hard to imagine them surviving in the long run.
The FSA was once the largest fighting force in early post-revolution Syria, but atrophied to a lack of financing and weaponry, becoming a paper tiger. Since 2014 however a joint US/Saudi/Turkey program under the auspices of the CIA (not to be confused with the gigantic-failure Pentagon program) has funnelled them a basically unlimited supply of TOWs, which they've been making good use of - their kill rate is reportedly about 6 out of 7 fired. Their numbers have increased since then. So far they seem to have managed their assets quite well, with reports stating that only 2 (some say 4) have fallen into other hands (Jabhat al-Nusra), and they seem to have used them. FSA works closely with JaF but is not part of the alliance itself.
Jaish al-Fatah is as mentioned a coalition, largely Islamist, although its individual members vary significantly. Let's go into the two biggest ones.
Ahrar ash-Sham can be thought of as sort of like the Muslim Brotherhood: Islamist, supporting sharia, but locally focused. Saudi Arabia and Qatar seem to have this group as their favored dog in the game.
Jabhat al-Nusra is a branch of al-Qaeda operating in Syria. Strangely despite this they haven't been behaving very much like al-Qaeda usually does, and they've been a very effective force against both Assad and Daesh. While they still take part in things like suicide bombings and human shields, they have a policy of not taking any anti-western activity and have worked hard to try to not engender local resentment, such as not imposing sharia on Christian towns. Qatar has been reportedly working to try to get them to break with al-Qaeda, but so far this campaign has not yielded any fruit. A large chunk of al-Nusra's fighters are foreign volunteers attracted by the name and they would risk losing them if they were to break with al-Qaeda.
JaF is really tricky on how one should deal with it. Ahra
Oh hey, speak of the devil, they just released a video of the hitting of the helicopter: link "Hard landing" my arse.
They'd really be nowhere today if it wasn't for those TOWs. They film every attack - footage and return of the tubes is apparently part of the deal to get more, to prevent them from stockpiling them or transferring them to other militias, so there's a couple new videos put out every day. Saudi Arabia reportedly purchased 13k of them from the US which it routes through Turkey in batches of a couple hundred at a time.
Slashdot Mirror
The moon's surface is kind of boring, as far as geology goes. Aluminum oxide, titanium oxide, iron oxide, silicon dioxide... by and large it's stuff that's really common on Earth. And not much of the common stuff that's super-useful, like water. And really, it's way more of a gravity well than is ideal to have.
If George Washington were alive today he'd be rolling over in his grave.
(And banging on the lid of his casket, screaming "Let me out!!!!")
But gasoline is one of the more expensive thermal fuels. 34kWh (122MJ) is 4,2kg of coal. Coal is about $45 per short ton, aka per ~1100kg, aka $0,04/kg, aka the coal equivalent of one gallon of gasoline costs only $0,17.
All forms of energy are not equivalent.
No no, we can get much more than a 1-2% improvement in chemical rocket performance. The issue is that for our needs thusfar (large objects to LEO and GEO, small objects further out with long transit times and gravity assists or ion propulsion), H2/O2 has been fine and it's not been worth all of the headaches of more energy dense fuel mixtures, like Li-(LF2|FLOX|OF2)-LH2 triprop. But we can indeed get a 25% improvement in ISP if we're willing to work with very hazardous, toxic chemicals (at least the resultant LiF isn't as toxic as F2!). It was already done in a lab-scale development back in the late 1960s. And let's not kid ourself, NASA has indeed launched successful missions using toxic, corrosive and dangerous chemicals as propellants. But this would be a new upper bound in this regard. I doubt they'd ever use a propellant like that on a lower stage, but for an upper stage or a return stage... it's a possibility.
Without invoking significant toxicity we can improve the picture somewhat. Burning the lithium with O2 (and of course H2 for exhaust flow reasons) is also a very high energy propellant, but it still means working with metallic lithium in some form or another (liquid, hybrid, slurry, cryosolid, etc), which most people would really like to avoid. But it is possible to do.
A small boost to H2/O2 can be made with aluminum - it only boosts the Isp a few percent (I believe about 4%-ish, though I'd have to double check), but it also gives a nice secondary bonus of really increasing your propellant density. Aluminum is neither dangerous nor toxic, but burning it with the H2/O2, and in a reliable manner, hasn't been tackled yet.
Boron is another high-energy compound one can use. As is beryllium (Be-F2-H2 is even more powerful than Li-F2-H2 by a small margin), but it's hugely expensive and extremely toxic in dust form.
Beyond all of the "familiar" stuff there's a lot of research on more exotic compounds with strained chemical bonds which remain in a metastable state until burned; there's way too many such compounds to list here. But at present they all generally suffer from either production cost issues or problematic instabilities.
Oh, and you can also improve performance by increasing the chamber pressure. That said, it's rather modest - if I recall a doubling of chamber pressure is usually on the order of a 7% ISP boost. But it does mean that advances in material technologies can translate to advances in rocket ISP. And there's also a wide range of other modifications to engine design that could boost rocket ISP to lesser extents.
Staging works pretty well to get around the energy density problem, at least early on.. though the rocket equation starts getting pretty tyrranical when it comes to returns from other planetary bodies. It's really hard to conceive of a manned Mars mission with return that doesn't involve at least the return ascent stage being fueled by one of the following:
1) In-situ propellant production
2) Extreme-ISP chemical propellant
3) Nuclear thermal
You can't rely on ion propulsion (even higher power variants like VASIMR) to get you off the ground. Nuclear thermal (1) should work (NERVA showed promise), but the development costs will be huge and it'd face massive public opposition, having that much nuclear fuel on a single craft. It also puts a rather large minimum size for your ascent stage - fission doesn't scale down well, and even as big as it was NERVA only had a thrust to weight ratio of 3 to 4. And the mass of that large, heavy ascent stage imposes significant mass penalties on your earlier stages, partially negating the benefit of that 800-1100 sec ISP.
For more advanced chemicals (2), there's lots of theoretical stuff, but with stuff that we could do today for a practical cost, it'd probably pretty much have to be some variant of lithium/fluorine/hydrogen triprop. The oxidizer could be LF, FLOX, OF2, or a couple other possibilities... but if you want an ISP(vac) from chemical propellants in 500-550 range and good density, that's pretty much what you have to do (yes, the LM and CSM used toxic, corrosive, dangerous propellants too, and NASA managed fine, but these are even worse). And even still, 500-550 sec is low enough that you'd probably still want some sort of ion "tug" cycler to move you between LEO and LMO, with your fuel only used for ascent.
If you don't want to or can't do either of those two options (#2 and #3), you're pretty much stuck with in-situ production (unless you want to have to launch a LOT of tonnage into orbit!) Which is why that's SpaceX's focus... it probably is the best option. Still, though, it's a challenge and a risk, no question.
Indeed. Did you see his interview with Colbert about Pluto? He talks about everyone who disagrees with him about the IAU decision (a group that includes most of the New Horizons scientific team) as though they's ignorant little children who just don't "understand" like he does.
I think his job is more "ticking large numbers of people off". For example, he was one of the leaders behind the "Pluto, Eris, Ceres, etc aren't planets" movement - he had references to Pluto being a planet removed from the Hayden Planetarium years before the IAU vote. He's not exactly popular among those who felt that hydrostatic equilibrium was the relevant constraint and that the "cleared the neighborhood" definition is fundamentally flawed.
Which is silly, because the Apollo mission was primarily oriented around the physics of getting a bunch of large mammals into space, keeping them alive on the way to the moon, landing them on the moon, keeping them alive down there while they explore, and then doing all of that in reverse. If they hadn't brought a single rock back the total change to the mission cost would have been almost unnoticeable.
Furthermore, who's focused on mining the moon? Most mining proposals focus on mining NEOs. It's way easier to get material from a NEO to Earth aerocapture. You could do it with a coilgun with no expenditure of consumables, again and again for years on end. They're also far more rich in interesting materials - much better than the best mines on Earth, and with no overburden.
The price of electricity is not the price of energy. Not all forms of energy are equal.
Actually they very well might. The strongest individual SWNTs measured thusfar are, what, 60GPa? That's way too weak to make a practical space elevator. And that's for individual tubes. Ropes are only held together by VDW and break at their weakest points, which will invariably exist - as a result it's hard to get ropes more than a couple GPa. There may be some better structures out there, but I wouldn't hold my breath waiting for an Earth-based space elevator.
If you want a physical structure reaching to space, go for a Lofstrom loop.
Where are you getting those prices? NASA was paying $3,60/kg for LH in 1980, so that's probably, what, $7/kg for LH today? Remember, this is LH, not gaseous - you not only have to cool it to extreme temperatures, but you also have to catalyze the conversion of orthohydrogen to parahydrogen - which is exothermic, yielding enough heat to nearly boil off everything you just cooled. NASA was paying $0,08/kg for LOX in 1980, so probably around $0,15 today. The Shuttle ET holds 630 tonnes of LOX and 106 tonnes of LH, so $836k.
The SRBs are 70% ammonium perchlorate, which is about $3/kg. 16% aluminum (about $1,50/kg), 12% PBAN binder (about $1/kg), 2% epoxy (about $5/kg), and an irrelevant amount of iron oxide. The total propellant was about 500 tonnes. Total propellant cost, $1,3m.
So the total propellant cost between the two, about $2m. To lift 27,6 tonnes of cargo to LEO, or $72 per kilogram. Now, people shouldn't fall for the fallacy that you just multiply that by how much a person weighs or a little more and that's the per-person cost to go to space - you actually have to launch many times more than a person's weight to get them there and keep them alive. But yes, propellant costs are not the key issue - if costs were close to propellant costs, rocketry would only cost about $25-100k to bring people to orbit in bulk.
Unfortunately, that's not the case.
Mind you, it's even possible to get significantly lower than that, but you can't rely on the rocket equation. And even if Space Elevator unobtanium existed, it wouldn't actually get you down to the levels one wants - there's no practical way to pump the climbing power up the tether, and beaming efficiencies with such a small receiver are unfortunately very low over such long distances. Much more practical is something like a Lofstrom loop - one might get power transfer efficiencies upwards of 50% or so. In such a case, you need about 70MJ per kilogram (19,4kWh). At industrial power rates of, say, $0,08/kW, that's a cost of a mere $1,56/kg. Sending people up in bulk might cost on the order of $800-ish per person in energy costs.
In both cases, though, it's not the propellant/energy costs that are killer, it's the hardware.You're asking structures to perform some borderline magical tasks in terms of the challenges that are put on them.
Anyway, enough Slashdot for now... back to working on simulating my caseless rocket design in OpenFoam and optimizing propellant combinations in CEA. ;)
What's the worst thing that could happen with a multi-tonne chunk of metal full of potentially explosive, potentially toxic, at a bare mininum highly flammable propellants, flying overhead at thousands of meters per second?
That's what I get for trusting Astronautix - looks like their info is outdated. :
That would be even more impressive on the rebel's part. In your telling, they hit it twice, with two separate weapons systems, one while it was flying?
Their design was kind of problematic. People naturally gravitate towards polybutadiene because of its use as a binder in solid rockets. But hybrids are not solids. Hybrids are great in most regards except for generally pathetic burn rates. Rather than consider other fuels, SS1 just used a typical solid rocket binder. One can compensate for the low burn rate, of course - usually by trying to increase the area by making many, smaller channels - this they did. But the more your propellant looks like swiss cheese, the more likely you are to have chunks break off as the rocket burns down. Which is exactly what happened on one flight, they had such a loud bang during the strike that the pilot thought his engine had exploded.
The proper solution is pointed to by research. Rather than polybutadiene the propellant should be something like paraffin or polyethylene. They melt at lower temperatures and become very fluid. The combustion basically whips up a "spray" off of the surface, making for very rapid combustion. With rapid combustion you don't have to "swiss cheeseify" your propellant. The polyethylene and the high melting point paraffins also are very strong and stable at room temperature.
Because they haven't seen fit to waste any money on it because it's such a meaningless endeavour. There's so little money in it, except for tourism, which government space programs (possibly excepting the Russians) have no interest in.
As a general rule, when governments shoot something up, they want it to stay up.
But the public confuses space and orbit. To them they're synonymous. It is not technically incorrect to call it "reaching space", but it's also not wrong to point out that "reaching space" and "reaching orbit" are not even in the same ballpark.
Anyway, the oxidizer is HTP, so we can look forward to this company going bust shortly after they suffer from a catastrophic tank explosion - hopefully while nobody is around. Seriously, why did every other little suborbital rocket startup in the 1990s and 2000s suddenly decide that in contrast with the vast amount of evidence amassed earlier, HTP is in reality an easy, convenient, safe oxidizer choice? Because they can find household peroxide in their medicine cabinet and gee, it seems safe enough?
(It's not impossible to use HTP safely - for example, it's used for maneuvering in Soyuz - but it usually takes a number of explosions to get your process refined to the point that that doesn't happen any more)
In general, rocketry has pretty much well settled on the right general formula for liquids and hybrids: LOX (clean, absurdly cheap, relatively dense, low viscosity, stable and (by oxidizer standards) non-corrosive in the right conditions, and although cryogenic we've gotten good at dealing with that) burned with hydrogen or alkanes of varying lengths (depending on the desired balance between efficiency and temperature/density/power; they're clean, cheap, stable, low viscosity and readily vaporized, non-corrosive, etc) and optionally fine-grained aluminum if one can work it (up to 20% - cheap, rather clean, very stable, dense, and very energy-rich). Some of the alternatives under research may provide some benefits, and in certain particular situations there might be a need for "special cases" (for example, where hypergolics or monoprops are essential), but by and large for bulk "lifting" it's about refining designs, not propellant combinations.
To put it another way: the Falcon 9 first stage has a loaded mass of 418 tonnes and an empty mass of 23 tonnes, or a ratio of 18,2 to 1. New Shepard has a loaded mass of 75 tonnes and an empty mass of 20,5 tonnes, or a ratio of 3,66 to 1. Noticing a bit of difference here? New Shepard has, proportionally, 5 times more mass to throw around toward making their landing easy. How easily do you think they could cut their spacecraft to 20% of its current weight and still land? And on top of that, they face far lower wind loadings and heat loadings to boot and have far less crossrange to deal with, making it that much easier on them.
Suborbital spaceflight is the special olympics of spaceflight.
Again: "from space" is not the same thing, or even close, to "from orbit". It's not the height that causes problems, it's the velocity. And more importantly than that, it's the extreme mass limitations that reaching that velocity imposes on your craft. With suborbital flight you can dedicate all the mass in the world to making the task as easy on yourself as possible.
Cue the hordes of Slashdotters who don't know the difference between orbital and suborbital flight.
Flights that just pop up to the Karman line and back down are virtually nothing like flights that actually go to orbit. Even the X-15, which actually reached a quarter of orbital velocity, was far more like an orbital flight than a straight up/down jaunt.
The Karman line is only 1/3rd to 1/4 of the way to proper orbital altitude. And the energy required to achieve orbital altitude is only a tiny fraction of that required to reach orbital velocity. And the rocket equation means that the faster you want to go, the exponentially more mass it takes. These little up-down jaunts do nothing except to confuse the general public into thinking that they're doing something similar to orbital spaceflight.
Turkey has released a radar track (I could dig it up if you want). See that little lobe that dips into Syria south of Yayladagi? The track shows that the plane flew straight across it rather than going around it.
Nor is the FSA. JaF is, however, and they work with the FSA. The US isn't arming Jaf, but they're not bombing them either, as Jaf is actively fighting Daesh and seems to have no interest - at least at present - in attacks against the west.
It's really not, at least among the major players. In the north (where the most relevant fronts are, even if there is still lots of random fighting elsewhere) you have Daesh in the east, the YPG (kurdish "Peoples' Defense Units") to the north of them, and JaF (Jaish al-Fatah, "Army of Conquest")/FSA alliance in the center (down to just north of Hama, and edging into Latakia by the Turkish border). The FSA has many different brigades but they're all pretty unified by wanting to fight Assad and Daesh and being composed of members who explicitly didn't join the (formerly much more powerful) Islamist militias. JaF is comprised of a number of militias, mostly islamist, the two most powerful being Ahrar ash-Sham ("Supporters of the Levant") and Jabhat al-Nusra ("The Support Front for the People of the Levant").
Let's break down the players.
The YPG, opposed by Turkey (out of fear of links to the PKK), controls a long strip along Turkey's northeast border, as well as a couple of pockets west of there. They have a long border with Daesh territory and fight almost exclusively against Daesh (even though there's one or two Assad pockets within their territory). Recently they've launched a major anti-Daesh campaign, using US-supplied weapons, in an alliance with Arab anti-Daesh forces, under the banner of Syrian Democratic Forces. So far it seems to be progressing well.
Daesh (aka IS/ISIS/IL) is, of course, Daesh. A group of Islamists so radical that even al-Qaeda thinks they're nuts. That said, it should be reiterated that not everyone who fights for them shares their ideology. They literally do run what is effectively a state, with locally sourced money (based around oil pumping, refining with truck-mounted mini-refineries, and sales - both domestic, to Turkey (black market), and even to Assad, who they're vehemently against. This money funds a militia far larger than their ideological base, often made up of the poor and displaced in the conflict who need the work. That said, literally armed entitity who's not part of Daesh in this conflict is an enemy of Daesh, so it's hard to imagine them surviving in the long run.
The FSA was once the largest fighting force in early post-revolution Syria, but atrophied to a lack of financing and weaponry, becoming a paper tiger. Since 2014 however a joint US/Saudi/Turkey program under the auspices of the CIA (not to be confused with the gigantic-failure Pentagon program) has funnelled them a basically unlimited supply of TOWs, which they've been making good use of - their kill rate is reportedly about 6 out of 7 fired. Their numbers have increased since then. So far they seem to have managed their assets quite well, with reports stating that only 2 (some say 4) have fallen into other hands (Jabhat al-Nusra), and they seem to have used them. FSA works closely with JaF but is not part of the alliance itself.
Jaish al-Fatah is as mentioned a coalition, largely Islamist, although its individual members vary significantly. Let's go into the two biggest ones.
Ahrar ash-Sham can be thought of as sort of like the Muslim Brotherhood: Islamist, supporting sharia, but locally focused. Saudi Arabia and Qatar seem to have this group as their favored dog in the game.
Jabhat al-Nusra is a branch of al-Qaeda operating in Syria. Strangely despite this they haven't been behaving very much like al-Qaeda usually does, and they've been a very effective force against both Assad and Daesh. While they still take part in things like suicide bombings and human shields, they have a policy of not taking any anti-western activity and have worked hard to try to not engender local resentment, such as not imposing sharia on Christian towns. Qatar has been reportedly working to try to get them to break with al-Qaeda, but so far this campaign has not yielded any fruit. A large chunk of al-Nusra's fighters are foreign volunteers attracted by the name and they would risk losing them if they were to break with al-Qaeda.
JaF is really tricky on how one should deal with it. Ahra
Oh hey, speak of the devil, they just released a video of the hitting of the helicopter: link "Hard landing" my arse.
They'd really be nowhere today if it wasn't for those TOWs. They film every attack - footage and return of the tubes is apparently part of the deal to get more, to prevent them from stockpiling them or transferring them to other militias, so there's a couple new videos put out every day. Saudi Arabia reportedly purchased 13k of them from the US which it routes through Turkey in batches of a couple hundred at a time.