RLV Spaceports etc
Thanks to Fred's reminder (and a little spare time before bed), I'm going to try and lay out a few of my recent thoughts about RLV Spaceport locations and a few other things.
Ever since the start of the space age, most US launches have been done from coastal areas, heading out over the water. This was due to the dangerous nature of early rockets. Simply put, they tended to blow up, or veer off-course on a far to frequent basis. More importantly, all US launches to date have involved the anti-social behavior of dropping multi-ton pieces of litter. The Russians launch a lot of their rockets over land from Kazakhstan, but they can only get away with this because there's this big desert downrange of Baikonur that very few people live in. Even then, Russia is often getting in trouble with Kazakhstan for dropping stages full of nasty propellants where they aren't supposed to when something goes wrong. Case in point, the most recent Dnepr launch.
However, I started wondering if this same situation would also hold for RLVs. What got me thinking about this was our avionics provider, Tim Bendell of Frontier Astronautics. Sometime around February, he let us know that he decided to buy an old Atlas-E silo outside of Chugwater, Wyoming in order to turn it into a space launch and rocket testing facility. Chugwater has only 244 people living in it, giving it an even lower population density than Mojave, CA. While I was playing around looking at the site, something interesting dawned on me--that you could actually launch into a space station orbit without crossing over enough people to drive your Ec unnacceptably high. The more I thought about it, the more benefits I could see for launching RLVs over land instead of water, enough so that I think there's a good chance that inland spaceports may become the norm, not the exception, once commercial orbital RLVs hit the market.
Inland Orbital Spaceports: Benefits
The most important reason I can think of is that if you launch over water, there is a substantial window of time during the launch where an abort may well mean ditching the vehicle into the ocean. Not only is that expensive, but it's also dangerous to passengers and cargo.
More importantly, if you drop your RLV into the drink, it's going to be very difficult to figure out exactly what went wrong, and thus it will be more difficult to get the reliability you need in an RLV. Intact abort is really important in driving down costs, and getting high reliability. If you have a problem with an RLV, you want to get it back in one piece so you can make sure you know exactly what happened, then fix it and verify that it isn't going to happen again. That's hard to do if your vehicle is in a "fishing orbit".
Additionally, having land down-range makes getting a first stage back a lot easier. While there are definitely some trajectories that can be done that don't involve a downrange landing for the first-stage (such as the K-1's planned trajectory, or the trajectories discussed in the book The Rocket Company), there are still big advantages to letting it land downrange some of the time. Basically, any sort of flyback or return to launch site type maneuver costs a lot of propellant weight or vehicle mass or complexity (or all of the above). If you can just allow it to land downrange, you can save all that weight, and put a much heftier payload into orbit with the same vehicle.
Inland Orbital Spaceports: Challenges
One of the biggest challenges for over-land orbital launch trajectories is third party safety. However, while over-land launch is more difficult from a third-party safety standpoint, there are actually plenty of places in the continental US where you could do an orbital launch from without crossing over large population centers until you're going fast enough that your Instantaneous Impact Point (the point where your vehicle would crash if it lost power at any given time during the flight) crosses those areas fast enough to not drive up your Ec (Pronounced E-sub-C, short for Expected Casualties--basically the number of casualties statistically expected from a given launch and reentry--US law requires this number to be less than 30x10^-6 casualties per flight). Particularly out West, there are plenty of potential sites such as Mojave, Las Cruces, places in Nevada, Utah, Chugwater, anywhere else in Wyoming for that matter, Alaska, places in Texas, and the list goes on. The cool thing is that as flights get more common, and demonstrated reliability goes up, more and more potential flight corridors open up. Once you've flown ~30 consecutive flights succesfully, you can claim a 90% reliability with a 95% confidence interval, which means that your Ec number can be revised downward by an order of magnitude, which means you can effectively overfly an area with 10 times the population density of a new and untried vehicle without driving Ec past where it can go. Most RLVs will likely fly at least that many times during the qualification and testing program.
The other big challenge is that most of these launch sites can only launch into higher inclination orbits. But I'm not sure this is such a bad deal. Sure, you get a definite payload benefit from launching closer to the equator, but much of that benefit is probably outweighed by the added cost of launching from low-inclination launch sites. Look at how much of a challenge Kwajelein has been for SpaceX. You may very well be able to put more payload up over a given amount of time, for a lower cost into one of those denigrated 51.6 degree orbits that the Russians like than you could out of an Equatorial launch site. Unlike all the weather delays you run into in Florida, you could likely launch out of Mojave almost any day of the year, and unlike Kwajelein, tanker cars of LOX and fuel are never more than a day or two away. Also for space tourism, you might actually want to launch into a higher inclination orbit. The scenery is a lot more varied with a 56 degree orbit than it is with a 23.8 degree orbit. Not to mention the fact that you're more likely to overfly the customer's hometown in a high inclination orbit than a low-inclination one. Also, a friend of mine who knows a lot about orbital mechanics mentioned that there are some resonant orbits near the space station's inclination (but at a slightly higher altitude) that provide daily launch and reentry opportunities from many useful locations.
Anyhow, I could go on, but it's turning into Sunday, so I'll wrap it up for now. What do you all think?
Ever since the start of the space age, most US launches have been done from coastal areas, heading out over the water. This was due to the dangerous nature of early rockets. Simply put, they tended to blow up, or veer off-course on a far to frequent basis. More importantly, all US launches to date have involved the anti-social behavior of dropping multi-ton pieces of litter. The Russians launch a lot of their rockets over land from Kazakhstan, but they can only get away with this because there's this big desert downrange of Baikonur that very few people live in. Even then, Russia is often getting in trouble with Kazakhstan for dropping stages full of nasty propellants where they aren't supposed to when something goes wrong. Case in point, the most recent Dnepr launch.
However, I started wondering if this same situation would also hold for RLVs. What got me thinking about this was our avionics provider, Tim Bendell of Frontier Astronautics. Sometime around February, he let us know that he decided to buy an old Atlas-E silo outside of Chugwater, Wyoming in order to turn it into a space launch and rocket testing facility. Chugwater has only 244 people living in it, giving it an even lower population density than Mojave, CA. While I was playing around looking at the site, something interesting dawned on me--that you could actually launch into a space station orbit without crossing over enough people to drive your Ec unnacceptably high. The more I thought about it, the more benefits I could see for launching RLVs over land instead of water, enough so that I think there's a good chance that inland spaceports may become the norm, not the exception, once commercial orbital RLVs hit the market.
Inland Orbital Spaceports: Benefits
The most important reason I can think of is that if you launch over water, there is a substantial window of time during the launch where an abort may well mean ditching the vehicle into the ocean. Not only is that expensive, but it's also dangerous to passengers and cargo.
More importantly, if you drop your RLV into the drink, it's going to be very difficult to figure out exactly what went wrong, and thus it will be more difficult to get the reliability you need in an RLV. Intact abort is really important in driving down costs, and getting high reliability. If you have a problem with an RLV, you want to get it back in one piece so you can make sure you know exactly what happened, then fix it and verify that it isn't going to happen again. That's hard to do if your vehicle is in a "fishing orbit".
Additionally, having land down-range makes getting a first stage back a lot easier. While there are definitely some trajectories that can be done that don't involve a downrange landing for the first-stage (such as the K-1's planned trajectory, or the trajectories discussed in the book The Rocket Company), there are still big advantages to letting it land downrange some of the time. Basically, any sort of flyback or return to launch site type maneuver costs a lot of propellant weight or vehicle mass or complexity (or all of the above). If you can just allow it to land downrange, you can save all that weight, and put a much heftier payload into orbit with the same vehicle.
Inland Orbital Spaceports: Challenges
One of the biggest challenges for over-land orbital launch trajectories is third party safety. However, while over-land launch is more difficult from a third-party safety standpoint, there are actually plenty of places in the continental US where you could do an orbital launch from without crossing over large population centers until you're going fast enough that your Instantaneous Impact Point (the point where your vehicle would crash if it lost power at any given time during the flight) crosses those areas fast enough to not drive up your Ec (Pronounced E-sub-C, short for Expected Casualties--basically the number of casualties statistically expected from a given launch and reentry--US law requires this number to be less than 30x10^-6 casualties per flight). Particularly out West, there are plenty of potential sites such as Mojave, Las Cruces, places in Nevada, Utah, Chugwater, anywhere else in Wyoming for that matter, Alaska, places in Texas, and the list goes on. The cool thing is that as flights get more common, and demonstrated reliability goes up, more and more potential flight corridors open up. Once you've flown ~30 consecutive flights succesfully, you can claim a 90% reliability with a 95% confidence interval, which means that your Ec number can be revised downward by an order of magnitude, which means you can effectively overfly an area with 10 times the population density of a new and untried vehicle without driving Ec past where it can go. Most RLVs will likely fly at least that many times during the qualification and testing program.
The other big challenge is that most of these launch sites can only launch into higher inclination orbits. But I'm not sure this is such a bad deal. Sure, you get a definite payload benefit from launching closer to the equator, but much of that benefit is probably outweighed by the added cost of launching from low-inclination launch sites. Look at how much of a challenge Kwajelein has been for SpaceX. You may very well be able to put more payload up over a given amount of time, for a lower cost into one of those denigrated 51.6 degree orbits that the Russians like than you could out of an Equatorial launch site. Unlike all the weather delays you run into in Florida, you could likely launch out of Mojave almost any day of the year, and unlike Kwajelein, tanker cars of LOX and fuel are never more than a day or two away. Also for space tourism, you might actually want to launch into a higher inclination orbit. The scenery is a lot more varied with a 56 degree orbit than it is with a 23.8 degree orbit. Not to mention the fact that you're more likely to overfly the customer's hometown in a high inclination orbit than a low-inclination one. Also, a friend of mine who knows a lot about orbital mechanics mentioned that there are some resonant orbits near the space station's inclination (but at a slightly higher altitude) that provide daily launch and reentry opportunities from many useful locations.
Anyhow, I could go on, but it's turning into Sunday, so I'll wrap it up for now. What do you all think?
posted by Jon Goff at 11:07 PM
7 Comments:
Interesting. I just posted some similar thoughts here:
http://cosmiclog.msnbc.msn.com/archive/2006/08/09/1938.aspx
...and considered adding a personal thought that one may want to launch RLVs (espically single stage) eastward from the *west* coast, specifically so as to keep dry land beneath the launcher during ascent, to accomodate aborts and emerency landings during that time.
Some major airports are costal, but not because of anything resembling 'range safety' issues (though that may be an afterthought), but because approach and departure is simplified when there are no potential terrain, and fewer noise-abatement issues.
Of course, eventually, you want to be able to launch from anywhere that you'd be willing to fly aircraft out of....
You missed one big problem with inland ports and one big advantage of coastal ones - access. Landing your first stage on land (for example) doesn't do you much good if you can't get it back to the spaceport! Shipping anything much over 10' is going to be rough sledding in many parts of the country - and keeping costs down rules anything but road or rail right out.
Derek,
While road shipability is quite important, there are some ways around that issue. The biggest one for an RLV first stage is to just fly the thing there. If it has the ability to make it from point A to point B, while hauling an upper stage up to high enough speed and altitude for staging, it can most definitely fly back from point B to point A sans upper stage.
There are some other tricksy tricks one can use, but that's by far the most straighforward.
~Jon
Sure - you can fly it back, once you get propellant trucks out to it.
And what exactly will the Podunk County airport managers think of you after your aborted first stage has been decorating the middle of their runway for a week? or Farmer John whose beet field now has a scar in it? or various govermental bodies whose parkland you have to drive over?
The only other option is to increase operating costs by maintaining your own set of abort sites... (Or hope that a spaceport has been built in the general vicinity of your routine landing and abort zones.)
It's not as straightforward as you paint it.
Derek,
Sure - you can fly it back, once you get propellant trucks out to it.
Which with a few exceptions isn't really that tough in the continental US. Much less difficult than trying to fish a piece of expensive aerospace hardware off the bottom of the ocean (or trying to mount a rescue operation for the crew/passengers).
I don't disagree with you that smaller spacecraft that can be hauled overland do have some substantial advantages over vehicles that can only self-ferry or be carried by boat.
And what exactly will the Podunk County airport managers think of you after your aborted first stage has been decorating the middle of their runway for a week?
Just because a vehicle can't be hauled easily over the highway doesn't mean that it can't at least be hauled off the side of the runway pending reflight. Of course, once it's out of the way, I'm sure they'd be happy to have you stay as long as you can afford....
or Farmer John whose beet field now has a scar in it?
In Farmer John's case, that's why AST requires you to insure against your maximum probable loss.
or various govermental bodies whose parkland you have to drive over?
Well, the thing to remember is that if the vehicle is recoverable at all, it had to be under at least *some* control. If it was under control, there's a good chance that the person doing the landing would try to place it down in as accessable of a position as possible. But once again, this is why AST requires you to get insurance for flights. Maybe some care will need to be excercised in laying out your flight paths so that you avoid as much as possible flying over areas where recovery would be impossible.
I mean, there is some thought that needs to go into this, but from a safety, reliability, and reusability standpoint, I don't see how any of these problems are harder than dealing with a crash landing out in the middle of the ocean.
The only other option is to increase operating costs by maintaining your own set of abort sites... (Or hope that a spaceport has been built in the general vicinity of your routine landing and abort zones.)
It's not as straightforward as you paint it.
Sure, but it is fairly straighforward to say that it's probably easier than dealing with just launching over the ocean. Yes, AST will require you to take that sort of thing into consideration. Yes, there is no easy out. But no, I still am not convinced that it would be more economical or safer for crew/passengers/cargo to do all of your flights over the ocean.
~Jon
Yes, there is no easy out. But no, I still am not convinced that it would be more economical or safer for crew/passengers/cargo to do all of your flights over the ocean.
I agree that overland, if possible, is the way to go - I'm just (as usual) poking around behind the curtains to make sure that there are no hidden assumptions etc... etc... You should know that by know Jon.
Derek,
I agree that overland, if possible, is the way to go - I'm just (as usual) poking around behind the curtains to make sure that there are no hidden assumptions etc... etc... You should know that by now Jon.
Sorry bout that, I wasn't sure if this was Derek Lyons or someone else. But yeah, there is a lot of detail work to be figured out in the process. The biggest challenge is that reflights will need to be licensed or permitted one way or another, so there will need to be some cleverness factored in in advance for the launch licensing (or experimental permitting) process.
I can just see the look on George Nield's face when you first suggest the idea..."You want to do what?!?"
~Jon
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