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Old March 18 2013, 04:09 AM   #271
Crazy Eddie
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Re: SpaceX is a go for April 30th: 1st commercial launch to space stat

publiusr wrote: View Post
sojourner wrote: View Post
Wait, you're saying a KKV doesn't need a high t/w ratio? Dude, you might want to think on that a little. That KKV is doing exactly what it's supposed to do.
No, it is launched by a missile to hit a warhead
And in order to do that it has to be able to accelerate under very tightly controlled parameters, holding a relative position in the path of an oncoming target that is also moving very very quickly. From the seeker's point of view, it is stationary and everything else around it is moving; it is programmed to keep its target stationary in its field of view no matter where that target actually moves.\

I'm thinking the guys who did this net test expected the actual KKV to use less thrust during an intercept than it did doing this hover.
They did not. The specific point of the test was to see whether or not the MKV had enough precision to follow a pre-programmed test fire routine simulating an actual intercept (with a theoretically high divert trajectory). They performed a similar test with the KKV (which your video does not depict) in which they added a small thruster fed by a pressure hose because the smaller unit's thrusters weren't powerful enough to hover for any amount of time.

The ideal test of the system, of course, would be for it to hold a stationkeeping attitude in freefall -- on a vomit comet or something -- but there's no way anyone's gonna let them actually test that thing on an airplane.

Now the anti-missile defense arguements puzzle me a bit. They say striking a warhead with a KKV is all but impossible
Nobody says that. What they say is that the interceptors that currently exist can't quite pull this off under battlefield conditions because both their timing and their tracking requirements are infeasible under those conditions.

It's a bit like saying it's impossible to do a kick flip on a skateboard during a hurricane. That statement tells you less about kick flips than it does about hurricanes.

Put that another way: how would you assess the feasibility of a Mars Sample Return mission if the Martian government started shooting at your return vehicles?
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Old March 18 2013, 07:12 PM   #272
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Re: SpaceX is a go for April 30th: 1st commercial launch to space stat

newtype_alpha wrote: View Post
Nobody says that. What they say is that the interceptors that currently exist can't quite pull this off under battlefield conditions because both their timing and their tracking requirements are infeasible under those conditions.
But compared to the normal battlefields where we use missile interceptors, the ICBM and LRBM battlefield is pristine, with vastly simpler trajectories (no hard aerodynamic maneuvering), no smoke, no clouds, no birds, and no nearby aircraft with 10,000 pounds of jamming equipment. It might as well be laboratory conditions.

It's a bit like saying it's impossible to do a kick flip on a skateboard during a hurricane. That statement tells you less about kick flips than it does about hurricanes.
Which is why people who've mastered aerial missile combat in hurricanes shouldn't have any problem pulling it off in perfect weather with not only no wind, but no air.

Put that another way: how would you assess the feasibility of a Mars Sample Return mission if the Martian government started shooting at your return vehicles?
Exactly! Anti-missile missiles would make such a mission highly unlikely to succeed.
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Old March 18 2013, 08:15 PM   #273
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Re: SpaceX is a go for April 30th: 1st commercial launch to space stat

gturner wrote: View Post
newtype_alpha wrote: View Post
Nobody says that. What they say is that the interceptors that currently exist can't quite pull this off under battlefield conditions because both their timing and their tracking requirements are infeasible under those conditions.
But compared to the normal battlefields where we use missile interceptors, the ICBM and LRBM battlefield is pristine, with vastly simpler trajectories (no hard aerodynamic maneuvering), no smoke, no clouds, no birds, and no nearby aircraft with 10,000 pounds of jamming equipment. It might as well be laboratory conditions.
Except that in laboratory conditions you know exactly where the missile launched from, exactly what it's trajectory is, and there's no actual risk involved if you intercept it too late or too low, plus there's usually only one target and you know for sure that's the one you're shooting at.

Under battlefield conditions, you have uncertainties in the detection of the launch, the accurate determination of its trajectory and potential questions about whether or not the radar signature you're tracking is a signal object or multiple ones or whether there are others coming up behind it from other launch sites. Either way, you have between 15 and 30 minutes from the time of launch to the time of impact and you have to figure all of this out within a narrow launch window if you're going to really pull off the intercept.

It's actually easier to intercept mortar shells and short range rockets, since the firing solutions and tracking data can be worked out by a single set of sensors and the only trick is positioning those sensors in the right place to direct the interceptor (IOW, not all that different from normal AA warfare).

Which is why people who've mastered aerial missile combat in hurricanes shouldn't have any problem pulling it off in perfect weather with not only no wind, but no air.
That's just it, though: hurricane conditions represent "battlefield" conditions, not merely short range. Put it simply, it's much easier to TEST a weapon system than it is to USE one in uncontrolled conditions. It isn't half as simple as you'd think, especially when the interceptor's infrastructure system is given virtually no warning at all before the actual attack.
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Old March 18 2013, 09:11 PM   #274
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Re: SpaceX is a go for April 30th: 1st commercial launch to space stat

Except that in laboratory conditions you know exactly where the missile launched from, exactly what it's trajectory is, and there's no actual risk involved if you intercept it too late or too low, plus there's usually only one target and you know for sure that's the one you're shooting at.
But for an ICBM intercept you don't need the launch location, just the range and vector range rate. You don't need to know the history of the trajectory, even though you'd know more about that than any conventional tactical launch where unknown aircraft are lobbing missiles on multiple incoming vectors, often from below the radar horizon. The problem is much simpler than warship defense where they have to expect a saturation attack from a variety of platforms and incoming angles simultaneously, possibly coming in with heavy jamming support, and where the warning and flight times are shorter. And with an ICBM intercept, you don't have to worry that some of the incoming missiles are friendlies returning to refuel.

That's the actual battlefield environment we're used to. The battlefield environment for space is vastly cleaner, the sensor data is better, the background problems are gone, the targets have almost no ability to maneuver without creating an instantaneous and large IR signature, they follow a purely ballistic path in between maneuvers, and they're very, very fragile compared to conventional targets (a slightly damaged warhead isn't going to survive re-entry, but a flaming Kamikaze can still hit).

It's a much easier targeting environment than the early Sidewinders had to cope with, and they could complete an intercept using just half-a-dozen vaccuum tubes for a control system, yet were able to distinguish targets from bright background clouds, adjust their control sensitivity for differing air-speeds and air-densities, and make off-angle lead intercepts.

The difficulty with ABM intercepts is the massive delta-V required to get the terminal package into the target environment.
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Old March 19 2013, 07:14 PM   #275
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Re: SpaceX is a go for April 30th: 1st commercial launch to space stat

gturner wrote: View Post
But for an ICBM intercept you don't need the launch location
You do if you're pre-positioning tracking radars with the intention of quickly obtaining an accurate firing solution for the interceptor. If the radars are in the wrong position or if the attack comes from an unexpected direction (say, someone launching a missile on a polar orbit that comes up from south to north) your sensors could give a false reading on its course and speed, or fail to detect it altogether.

The last rounds of ABM tests were fired against targets whose exact launch points were known ahead of time so the tracking systems could be placed in an optimal position to acquire the target and guide the missile to a hit. You don't have the luxury of doing this in battlefield conditions, because you 1) Can't know ahead of time when someone's going to launch an ICBM at you and what launch site they're using and therefore cannot position your sensors to watch all likely approaches and 2) don't necessarily know what kind of missile is going to be launched at you or its flight profile. ABMs appear to be optimized for certain types of ground-based ICBMs like the kind China and/or Russia still use in their land-based silos, and they aren't particularly good at intercepting those anyway; they're virtually useless against SLBMs, which are often launched at closer range using much flatter trajectories.

The problem is much simpler than warship defense where they have to expect a saturation attack from a variety of platforms and incoming angles simultaneously, possibly coming in with heavy jamming support, and where the warning and flight times are shorter.
And much more complicated due to the fact that the thing you're defending is a thousand kilometers wide and the thing that could attack it could be just about anywhere. And that too ignores the fact that anyone who is going to fire an ICBM at the United States probably isn't going to fire just one, and probably isn't going to use one that'll be easy to intercept (even the older Russian missiles have decoy launchers and electronic warfare systems).

The difficulty with ABM intercepts is the massive delta-V required to get the terminal package into the target environment.
No, the difficulty with ABM intercepts is the problem of scale. You're not shooting a missile at another missile in the same battlespace, you're shooting a spacecraft at another spacecraft half a world away on a path that will bring them into contact with one another at exactly the right moment in their respective flight profiles. Even when you have the timing down perfect -- which you can't in a battlefield situation -- the degree of uncertainty in both the target and interceptor's flight path is huge and grows exponentially larger the less accurate your targeting fix is.

When you factor in the fact that the United States only has about 24 ABMs of capable of intercepting an ICBM for the more than 200 missiles possessed by both China and the Russian Federation, ultimately those missiles are more for peace of mind than an actual defense against ICBMs.
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Old March 23 2013, 07:41 PM   #276
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Re: SpaceX is a go for April 30th: 1st commercial launch to space stat



Fun recent interview with Musk. I like how he has began to refer to the Mars round-trip reusability with more certainty now, and more confidence that he can bring the price down dramatically. In previous interviews, he was cautious even when talking about LEO reusability. I can't wait for that Falcon Heavy-Grasshoper hybrid he could be having in mind.
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Old March 28 2013, 07:26 PM   #277
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Re: SpaceX is a go for April 30th: 1st commercial launch to space stat

YellowSubmarine wrote: View Post

Fun recent interview with Musk. I like how he has began to refer to the Mars round-trip reusability with more certainty now, and more confidence that he can bring the price down dramatically. In previous interviews, he was cautious even when talking about LEO reusability. I can't wait for that Falcon Heavy-Grasshoper hybrid he could be having in mind.
I noticed this too. Also since the last post the mission was a success...so congrats to all involved.

Still pretty anxious about the SLS, a multi-tiered space race is really heating up. The video from the SLS tests remind me of the footage from Apollo's early days.

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Old March 28 2013, 11:35 PM   #278
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Re: SpaceX is a go for April 30th: 1st commercial launch to space stat

They're talking about doing a first-stage flyback/return next year.
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Old March 29 2013, 12:37 AM   #279
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Re: SpaceX is a go for April 30th: 1st commercial launch to space stat

They're going to try and soft land the first stage in the ocean on the next few flights as build up to land landings.
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