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Unmanned Spaceflight.com _ Exploration Strategy _ Anti-satellite weapon test?

Posted by: Thu Jan 19 2007, 02:39 PM

According to this link, China fired a missile to destroy an orbiting weather satellite last week: http://www.spacewar.com/reports/China_Trashes_LEO_With_Debris_From_Anti_Satellite_Test_999.html

I am curios about what kind of projectile could be used? A "smart" one with on board guidance system or just a dumb one? How close did the "killer satellite" came to the target?

Does anybody have an idea?

Posted by: climber Jan 19 2007, 03:06 PM

QUOTE (Thu @ Jan 19 2007, 03:39 PM) *
According to this link, China fired a missile to destroy an orbiting weather satellite last week: http://www.spacewar.com/reports/China_Trashes_LEO_With_Debris_From_Anti_Satellite_Test_999.html

I am curios about what kind of projectile could be used? A "smart" one with on board guidance system or just a dumb one? How close did the "killer satellite" came to the target?

Does anybody have an idea?

OK, weather forcasts are sometimes very bad. I didn't thought China will get THAT angry about it biggrin.gif

Posted by: Lorne Ipsum Jan 19 2007, 06:51 PM

Nobody really knows the details, but most reports I've read say the satellite was hit with a kinetic warhead (i.e., no explosives, just a direct hit with the sensor head). This pretty much mandates a "smart" projectile.

Lorne

Posted by: nprev Jan 20 2007, 01:59 AM

Anybody know what the inclination of the target satellite's orbit was? I got a sinking feeling that it might well have been in a polar orbit...worried a bit about the NOAA polar orbiters & that debris cloud... unsure.gif

EDIT: Yep, it was in a polar orbit, but a bit below the NOAA POES... smile.gif

Posted by: OWW Jan 20 2007, 12:12 PM

QUOTE (nprev @ Jan 20 2007, 02:59 AM) *
I got a sinking feeling that it might well have been in a polar orbit...worried a bit about the NOAA polar orbiters & that debris cloud... unsure.gif

EDIT: Yep, it was in a polar orbit, but a bit below the NOAA POES... smile.gif


According to Jonathan's Space Report ( http://www.planet4589.org/space/jsr/latest.html ):

The FY-1C was in an 843 x 862 km x 98.7 deg orbit; the debris cataloged so far ranges from
165 x 850 km to 850 x 3500 km, a wide range of heights indicating an
energetic fragmentation with delta-Vs of -190 to +550 m/s. Of course,
we are missing the tail of dV significantly less than -190 since those objects
would reenter immediately.


Correct me if I'm wrong, but doesn't this put ALL satellites from 165 to 3500 km at risk and not just the ones around 850 km? blink.gif

Posted by: Thu Jan 22 2007, 04:42 PM

Thank you all for your information. Still no official speak from China yet so I do believe the test was real sad.gif
There is no international law against this kind of test? How about the Outer Space Treaty?

Posted by: djellison Jan 22 2007, 04:53 PM

Very very close to becoming a political thread here - but the USA recently refused to sign up to an agreement banning such tests.

Doug

Posted by: Chmee Jan 22 2007, 05:55 PM

The US did develop an anti-satellite weapon back in the 1980's and actually shot one down in 1985. I beleive the weapon was actually carried on an F-15 and shot into space (Pagasus style). While the US has not conducted such tests since then (that we know of..) it is beleived they still have the capability.

As for the Chinese anti-sat weapon being 'smart' or 'dumb' it is hard to say. You would not have to do a 'bullet hits a bullet' type of kill vehicle to accomplish this. Rather, a 'dumb' weapon could be used to spray some material, over a large area, in the path of the intended satellite, like sand or ball bearings. The relative speed would between the objects would be all thats needed.

Posted by: djellison Jan 22 2007, 06:29 PM

QUOTE (Chmee @ Jan 22 2007, 05:55 PM) *
like sand or ball bearings. The relative speed would between the objects would be all thats needed.


That's what I was imagining this to have been. Launch - on a high sub-orb trajectory, and disperse a cloud of lead shot etc - through the satellite goes - 7.5k/sec impacts - the remaining shot just re-enters harmlessly but the sat is blown to pieces.

Doug

Posted by: tty Jan 22 2007, 07:34 PM

Actually a satellite in LEO is not a particularly challenging target. Its position and trajectory is known in advance and it is usually a non-maneuvring target. Also it usually has a nice big cross-section in both the radar, IR and visual band and operates in a very uncluttered environment.

All that is needed is a reasonably precise suborbital rocket and a suitable warhead. However I doubt that the "ball-bearing/sand" solution is cost effective. Unless You release quite close to the target they would probably disperse too thinly to ensure a kill. It would probably be better to use a homing warhead with a proximity fuse. Anybody having the technology for the carrier rocket should be able to handle the guidance system and the warhead too.

tty

Posted by: Bob Shaw Jan 22 2007, 08:18 PM

QUOTE (tty @ Jan 22 2007, 07:34 PM) *
It would probably be better to use a homing warhead with a proximity fuse. Anybody having the technology for the carrier rocket should be able to handle the guidance system and the warhead too.

tty


It's a tad more difficult than it looks. Most aircraft missile systems don't use thrust to control attitude, but instead rely on aerodynamic forces. An exoatmospheric vehicle has to be precisely stabilised, and because it has to actively hunt down a target then spinning probably won't do. You're looking at 3-axis attitude control, plus an ability to change direction at very short notice. Some of the Star Wars kinetic kill vehicles not only were 3-axis stabilised, but also spun to deploy arms at the last moment and then also disintegrated to provide further frontal area. All this has to be arranged in a space of seconds, with space-hardened computers. All in all, it's a very tough call, and the US has done it only a very few times (and sometimes by moving the goalposts after the event). China's success is a major milestone, and speaks highly of their space technology.


Bob Shaw

Posted by: helvick Jan 22 2007, 08:46 PM

So with a bit of luck they might now consider that they have successfully shown all interested parties that they are well in contention in LEO and that they now need to demonstrate some serious long range remote capability - expect Chinese Moon, Mars and outer planets missions to follow shortly.

So it's time to go and learn Chinese folks so we can stay on top of CNSA's PR department.

(Just looking for the bright side since this is my 1000'th post. smile.gif )

Posted by: djellison Jan 22 2007, 09:01 PM

Just thinking in terms of 'impact window' - i.e. the time taken for the target to cover it's own size in terms of distance - the variable that identifies how accurate something has to be to hit something rushing past - not totally analogous ( you could drive 'down' the velocity vector for instance ) - but it gives you a sense of the scale of the problem.

Car - 4.3 metres - 26 m/sec - window is 0.165 seconds.
Jumbo Jet - 57 metres - 223 m/sec - window is 0.255 seconds ( this is why a jumbo 'looks' so slow in the sky - it covers it's own length slower than a small car rushing past). F22 - .030 seconds.

Satellite - 3 metre sized bus - 7500 m/sec - window is 0.0004 seconds

i.e. stood watching the thing fly past - you've got to be 412 times more accurate hitting a spacecraft than a car doing 60 mph. 637 times more accurate than hitting a flying jumbo - and 75 times more accurate than hitting an F22 raptor.

It's a big ask - I don't know how hard it actually is - but this isn't "let's modify a sidewinder' type thing.

Doug

Posted by: helvick Jan 22 2007, 09:24 PM

Your calculations are only valid for an orthogonal impact, that's probably not the ideal way to do this.

Taking x-axis to be cross track relative to the target, y-axis to be on track and z-axis to be vertical. If you are going to rely on kinetics alone to do the work for you the ideal approach would be to lob your "warhead" into a z-axis ballistic curve that tracks along the targe's y-axis (so x-axis velocity relative to the target is negligable) timed to reach zenith just ahead of the target's arrival (so the z-axis velocity relative to the target is very small). The high y-axis relatively velocity then becomes an advantage as the probe will impact the "warhead" if it intersects the probe at any stage during it's "hang time". For a 25cm "warhead" that impact window is almost a quarter of a second assuming you can target the orbital track and altitude with the same precision. That is obviously not a trivial task but I think it should be simpler than active targetting with a 0.4 microsecond window.

Posted by: tty Jan 23 2007, 07:32 AM

QUOTE (djellison @ Jan 22 2007, 10:01 PM) *
It's a big ask - I don't know how hard it actually is - but this isn't "let's modify a sidewinder' type thing.



Well, not early Sidewinder at least since they used pursuit-curve logic. This would be a collision-course interception, preferably from nearly dead ahead and would probably use constant-bearing logic. That is: if You keep the bearing to the target constant you are bound to hit it sooner or later.
The main problem in this case is the very high closure rate which means that tracking and manoeuvring have to be precise at fairly long range otherwise very large and fast corrections will be needed at a late stage in the interception. The proximity fuse will also need to be fast and precise. The latter is more difficult than it sounds. Sufficiently precise fusing is one of the main challenges in building implosion-type nuclear weapons.

tty

Posted by: djellison Jan 23 2007, 08:47 AM

You don't need fusing - this was a kinetic impact...it just what WHACK not BOOM.

Doug

Posted by: climber Jan 23 2007, 08:55 AM

QUOTE (helvick @ Jan 22 2007, 09:46 PM) *
(Just looking for the bright side since this is my 1000'th post. smile.gif )

My 900 was yesterday wink.gif
I was wondering if it was their first try of if we have infos that they've missed previously!

Posted by: Bob Shaw Jan 23 2007, 11:11 AM

QUOTE (djellison @ Jan 23 2007, 08:47 AM) *
You don't need fusing - this was a kinetic impact...it just what WHACK not BOOM.

Doug



Doug:

They probably broke the kill vehicle up just before impact to increase their ability to whack the target, so a proximity fuse (or some other method of breaking the thing up) would have been needed.

The bottom line remains the same: this is an impressive bit of engineering. Perhaps less so in terms of the political repercussions (eg Sino/US space collaboration will now be more difficult), but that's another matter.


Bob Shaw

Posted by: Bob Shaw Jan 23 2007, 11:31 AM

QUOTE (helvick @ Jan 22 2007, 08:46 PM) *
(Just looking for the bright side since this is my 1000'th post. smile.gif )



1,000? Pah! Amateurs, don't know what things are coming to, mumble, why in my day, I remember back in '05...

Keep up the good work!


Bob Shaw

Posted by: Bob Shaw Jan 23 2007, 11:42 AM

QUOTE (climber @ Jan 23 2007, 08:55 AM) *
My 900 was yesterday wink.gif
I was wondering if it was their first try of if we have infos that they've missed previously!


Interesting point. The ASAT engine plume would be highly visible in IR, so the US would almost certainly have seen the whole thing. Whether or not they'd have told anyone about previous attempts is a moot point, as the NRO (or whoever is running staring IR sensors in GEO) is notoriously shy and they'd rather not release any information which can be reverse-engineered to reveal their actual capabilities to any potential opponent. So the internal hierarchy of the US may well have known, and they may have told some of their regional allies, but that'd be about it - there's no international requirement for a nation to tell anyone else about sub-orbital activity if they don't want to, and the Chinese wanted a success rather than anything which might be seen as a failure. Personally, I'd be surprised if the Chinese managed an ASAT demonstration first time out, though the US appears to have done exactly that when they tried it. As an example of just how difficult it can be to launch big(ish) missiles from an aeroplane, see the whole NOTSNIK story!


Bob Shaw

Posted by: mchan Jan 24 2007, 04:39 AM

There was an article quoting unamed sources that there were three previous unsuccessful attempts.

Regarding detecting / tracking the ASAT engine plume, the ASAT would only need course correction maneuvers in the end game. These burns are relatively low energy. Early warning sats are required to detect rocket plumes during boost phase which are much larger. Whether their sensors are sensitive enough to detect small ASAT course correction burns is unknown outside the classified realm, but my guess is not likely.

Regarding staring sensors, the operational US early warning sats in geosynchronous orbit still use a scanning sensor. There have been tests of staring senors in add-on payloads to other military sats in high elliptical orbits. I don't recall reading that these are in operational use.

Posted by: Bob Shaw Jan 24 2007, 12:11 PM

QUOTE (mchan @ Jan 24 2007, 04:39 AM) *
There was an article quoting unamed sources that there were three previous unsuccessful attempts.

Regarding detecting / tracking the ASAT engine plume, the ASAT would only need course correction maneuvers in the end game. These burns are relatively low energy.



I'm not surprised to hear that, three sounds sorta sensible for a demo programme.

As for the rocket plume, I'll grant that control inputs will lessen as 'rendezvous' (haha) approaches, but you still need a reasonable belt to get up there in the first place, and that's the signature which would be detected. I'd also wager that the test took place over some appropriate part of China and that the USAF had a good idea of which might be a target satellite well in advance, thus making detection almost a numbers game. And that numbers game would serve to obfuscate the exact capabilities of US space intelligence assets, too... ...staring IR or not!


Bob Shaw

Posted by: climber Jan 24 2007, 03:56 PM

Interesting article on this topic on Aviation Week.
US intelligence were ready to monitor the trial, so they knew about it ahead of time.

Posted by: tty Jan 24 2007, 07:46 PM

QUOTE (Bob Shaw @ Jan 24 2007, 01:11 PM) *
As for the rocket plume, I'll grant that control inputs will lessen as 'rendezvous' (haha) approaches



Nix - that is true for a slow "friendly" rendezvous like ISS/STS. For a high speed interception it's the other way around. The need for control inputs increases dramatically at the end when the relative angular velocity goes up and the inevitable minor initial errors must be corrected.

tty

Posted by: Bob Shaw Jan 24 2007, 09:14 PM

QUOTE (tty @ Jan 24 2007, 07:46 PM) *
The need for control inputs increases dramatically at the end when the relative angular velocity goes up and the inevitable minor initial errors must be corrected.

tty



I'll buy that - however, with (presumably) burnout of the main stage the vehicle mass will be way down so smaller burps will do the job. One of the 1980s-era US kill vehicles had a (IIRC) *five* terminal engine setup, and these could actually support the thing (though briefly) in a 1G static environment. They did some testing with the thing flying free over a big a net, into which it dropped at the end. Something I just noticed is that some (early) reports spoke of an air-launch, while the latest are talking about the thing being on top of an IRBM. Somehow, I think the IRBM carrier version, knocking out a satellite in a well-known orbit is rather less of an achievement than the air-launched scenario.

I don't think the whole affair has made Sino/US space co-operation more likely, but international diplomacy is a funny old game.


Bob Shaw

Posted by: Thu Jan 25 2007, 01:07 AM

Finally, we have an official announcement from China http://www.spacewar.com/reports/China_Officialy_Announces_Anti_Satellite_Test_Successful_999.html

Posted by: CosmicRocker Jan 25 2007, 06:13 AM

I rarely stray into this section of the Forum, and I don't appreciate all of the important intricacies that some of you apparently do, but this really is a "funny game" as Bob pointed out. It is especially so when all you have to go on are published reports.

A comment I noticed in an IRC discussion on this topic kind of put it into perspective for me. Didn't China use remaining fuel to move the target into an orbital position that would be easy to hit? Will China declare it a success? Heck yes, it was a success. Will other nations complain? Yes, again. Can one dispute Chinese Foreign Ministry spokesman Liu Jianchao's response claiming that his country had displayed a "responsible attitude" and that it had "upheld the peaceful use of outer space? It gets kind of dicey at this point for me. If it wasn't gong to be a threat to people on the ground, or other satellites, was this a responsible action? It seems to me that the important question here is, was there a threat that needed to be minimized, or not?

Posted by: tty Jan 25 2007, 07:07 AM

QUOTE (Bob Shaw @ Jan 24 2007, 10:14 PM) *
I think the IRBM carrier version, knocking out a satellite in a well-known orbit is rather less of an achievement than the air-launched scenario.


That is definitely true. It also makes the chinese system much less capable since it can only be used when the satellite track passes close to the launch site. An aircraft carried ASAT allows much more flexible targeting.

tty

Posted by: nprev Jan 26 2007, 02:35 AM

Just to put a bit of (hopefully) UMSF-related spin on this: The guidance & control technologies used for ASAT ops probably will mature at a rapid rate because of this event and be available for other applications such as asteroid/comet interdiction, or even adaptive autonomous terminal guidance for risky outer-planet missions such as landing on Triton.

Admittedly, Deep Impact had a nice big target...but wouldn't it be nice if we could hit a potentially threatening comet in a very precise fashion in order to deflect its orbit just enough (like by exposing a deposit of volatiles near perihelion) to miss us?

Just makin' lemonade here, don't mind me... smile.gif

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