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.


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?


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) 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.

--
Harry Andreas
Engineering raconteur