"Harry Andreas" wrote in message
...
In article , "Kevin Brooks"
wrote:
"Harry Andreas" wrote in message
...
In article , "Kevin Brooks"
wrote:
"D. Strang" wrote in message
news:1%obc.4658$zc1.3787@okepread03...
The F/A-22 also has an inherent air-to-surface
capability." It can already lug a couple of JDAM's. So how does
that
even
*require* an optimized ground mapping radar to allow it to
strike
ground
targets with significant precision?
I'm not a bombardier, but I think the SAR radar is necessary for
the
INS
inputs. The INS being only updated by the GPS, and only if the
GPS
isn't being jammed (which will be unlikely down the road). I
think I
read
where GPS only doubles the accuracy of the INS (50 feet versus 100
feet).
Without SAR, and GPS being jammed, you'll need a good pair of
TACAN's,
which some enemies don't seem to provide :-)
I have yet to hear that a SAR update is required. Doing so would
require
the
preloaded data for the terrain (so that the SAR would have something
to
relate its picture to). From what i understand, the weapon gets its
update
from the aircraft (through its own INS), then after release it uses
GPS
to
improve the accuracy of its own INS. If SAR was required, then I
guess
the
A-10 would never be certified to carry JDAM...?
That's ridculous.
No, what is ridiculous is your misunderstanding of my statement. As you
acknowledge later, SAR is NOT required to launch a JDAM. And correct me
if I
am wrong, but you do indeed have to have a digital terrain model data
set
loaded in order to use the SAR to update a location--merely looking at
the
screen and saying, "Yep, that's a bridge!" doesn't cut it--the system
would
have to know that the bridge is at (insert 10 digit grid for
centerpoint),
either by vurtue of having access to a DTM or by inputting the accurate
coordinates? The following article indicates that the basic procedure
for
JDAMS usage is as I described it--the carrying platform updates the
weapon
through both its own INS and GPS systems; use of a SAR, as in the case
of
the B-2 JDAM usage in Kosovo and Afghanistan, does indeed increase the
accuracy further.
http://www.aero.org/publications/cro...er2002/05.html
It's ridiculous that anyone would think SAR is required. That has been
discussed
here over and over. BTW, DTM is not required either.
All that's required is GPS, INS, and for better accuracy, SAR.
Which is why I argued that SAR is NOT required; maybe you were addressing
your "that's ridiculous" elsewhere and mistakenly appended it after my
response? As to DTM, I guess it would not be required if the coordinates of
the target or the IP (or whatver point is chosen as an update location) are
known and input into the equation; the system takes the known point and then
compares the chosen point on the SAR output to further refine the "where am
I at release" info. OK, that makes sense.
SAR updates to pre-programmed INS settings have been used since the
early 90's to improve the accuracy of GPS aided munitions.
Uhmmm...Harry, what GPS guided munitions were in service during the
"early
90's"? JDAMS was not; perhaps the ALCM or SLCM used GPS updates in
conjunction with their stored DTM (but there you go again, that pesky
DTM...); I can't think of any others that used GPS during that
timeframe.
SAR updated GPS aided munitions were used by the B-2's in Bosnia with
eye-opening effect. You don't think that happened overnight?
Actually, B-2's were not used in the first (Bosnia) episode--they came later
during the Kosovo operation. So unless you are thinking that 1999 was "early
90's".... :-) Another poster has noted that GPS was used earlier, in the
case of SLAM, but not IAW any SAR usage that I am aware of--it instead,
along with an INS, got the missile to the general target area, where an
optical system took over, the signal being datalinked back to the launch
aircraft.
You don't need the SAR update to launch a JDAM, but it dramatically
improves the CEP of the weapon and essentially means that you can use
a smaller weapon to take out a target.
Well, it improves it, but not sure how "dramatically"; dramatic
improvement
of JDAMS appears to be dependent upon use of a secondary IR imaging
system
not IR. SAR. And the amount depends on the performance of the radar.
Numbers will not be mentioned here.
DAMASK is not IR? According to the following (amongst other sites), it does
indeed use an imaging infrared seeker:
http://www.nationaldefensemagazine.o...cle.cfm?Id=667
(DAMASK) or ISAR input after the drop, as was tested in the joint F-16
dropped, and E-8 updated AMSTE (Affordable Moving Surface Target
Engagement) JDAM.
Hmmm. DAMASK at least has a future.
Can't imagine flying an E-8 close enough to a potential target to
get useful data without becoming a target yourself.
Well, maybe in the future if they port it to a UAV.
That is one possibility. But also recall that the E-8 can look pretty deep
into a battlefield; one orbiting fifty miles behind the FLOT can see, under
optimal conditions, some 100 miles beyond the FLOT, if you use the FAS
numbers (actual range being classified, no doubt). Being able to kill mobile
targets of opportunity with JDAM to that depth would seem to be a rather
valuable capability.
Brooks
--
Harry Andreas
Engineering raconteur