"Harry Andreas" wrote in message
...
In article , "Kevin Brooks"
wrote:


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.


Sorry if I was not more clear. My statement was meant to cast aspersion
on the statement that SAR is somehow needed, so I was actually agreeing
with you.


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.

Say, rather the mid 90's. I know that work was being done earlier, but the
engineering world usually predates the operational world by quite a lot.
Sometimes it's hard to keep straight.

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:

My statement is intended to counter your statement that
"dramatic improvement of JDAMS appears to be dependent upon use of a
secondary IR imaging"
Dramatic improvement does not depend upon IR imaging if you have
a high accuracy SAR aboard.

Which is why I had the *or* in the original statement, mentioning AMSTE,
which does indeed use radar. DAMASK and AMSTE appear to offer "dramatically
improved" accuracy, IMO (to the point that the latter can engage a mobile
target). Use of SAR with "vanilla" JDAMS does improve the accuracy, but I am
not sure if that level of improvment merits the moniker "dramatic"--the
JDAMS without SAR but with a decent INS/GPS update prior to release
apparently offers pretty good accuracy as is.



(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.

Remember that the further away you are, the more range error you
accumulate.
If you want a high accuracy solution, you need either a very high powered
SAR system (more than an E-8) or need to be closer. Closer brings it's
own jepardy.

Eh? The E-8 is operating at that range--you think that the range error of
the E-8's ISAR itself increases significantly through the depth of its
coverage? The platform doing the weapons release would have to be about on
top of the target. This configuration, using AMSTE, was credited with a
successful strike in its first test drop, from what I have read. Of interest
would be how much the E-8 "sees"--can it also pick up the aircraft dropping
the munition (regular JDAM in this case)(as I believe the follow-on E-10
will be able to do)? If so, then it would appear to offer the dropping
aircraft the same accuracy enhancement that its own SAR would afford--the
E-8 would have the target and the delivery platform in the same frame of
reference, so any ranging error would be largely negated?

Brooks


--
Harry Andreas
Engineering raconteur