Babur Cruise Missile - Database

[amardeep mishra]

@The Deterrent
@Oscar

We all very well know the importance of INS+GPS package for guidance of missiles.I will begin my analysis from briefly describing the INS+GPS and then eventually building on TERCOM and DASMAC guidance schemes. I have certain reservations regarding pakistani access to accurate maps- but i am guessing china would provide these to pakistan?
There are Two GPS/INS integration approaches commonly used. These are

(a) the tightly coupled integration approach, which yields higher accuracies; and
(b)the loosely coupled integration approach used for short time and/or ranges,yielding lower accuracies
Normally the GPS receiver of the missile is interfaced with
(1)altimeter
(2)flight control system,
(3)the INS’s serial/digital interface,
(4) and the carrier aircraft/launching platform

The navigator (i.e., dynamic navigation equations), consisting of a 15-state Kalman filter(in case anyone of you want an elaborate analysis of how KALMAN filters are used to fine tune/filter various sensor outputs,i can provide an indepth analysis as well- for more advanced readers- Amardeep Mishra), is normally updated by the onboard navigation computer every 50 milliseconds (or a 20-Hz rate),while the GPS is updated at1-Hz rate.The GPS will normally consist of a 8-state Kalman filter,so that both the INS and GPS Kalman filters operate in a cascaded mode.Inertial aiding provided to the GPS receiver- tracking loop is at a 10-Hz rate. (Note that the INS is of the strap down class. Thus,the basic strap-down INS algorithms that maintain the body-to-level-axis transformation matrix and transform the body-axis velocity increments to a locally level coordinate frame can be performed at a rate of 50 Hz, while the basic INS algorithms can be performed at an iteration rate of 10 Hz.).

A significant characteristic of the ALCM is the high accuracy at long missile ranges provided by its terrain correlation updated navigation system. In order to implement a terrain correlation updated navigation system, reference terrain elevations must be stored in the missile’s computer prior to launch.This elevation data must be gathered, stored in ground computers, precisely selected for each mission, stored in the carrier aircraft, and transmitted to the missile prior to launch. More specifically, the missile’s navigation and guidance unit uses a terrain contour matching (TERCOM) system that periodically updates the missile’s inertial navigation system by comparing terrain over which the missile flies with stored mapping data.

Now here is the trouble,where does pakistan sources,such an "elevation data"?In USA's case,this data is collected by Defense Mapping Agency-Aerospace Center (DMAAC).In india's case this data is gathered by most probably the RISATs in orbit(more preferabbly by RISAT-2 that has an x-band AESA SAR that can map very very accurately)

The above figure shows visually the steps involved in planning a test mission from launch
point (Point 0) to the target (Point 6). The planner first selects a path from launch to the target in the horizontal plane that passes through the required maps (maps 1 and 3, in the example). In the horizontal plane selection, the mission planner takes into account the terrain over which the missile will fly,special test objectives,and distance between maps. The mission planner has two ALCM simulation tools (or modules) available to aid him in planning missions. These are
(a) the clobber analysis module
(CAM), and
(b) the navigation accuracy module (NAM)

Both these programs reside in a ground-based computer. CAM provides the capability to the mission planner to compute either probability of ground clobber given a specified ground clearance, or ground clearance given a specified probability of clobber. CAM can operate in a rapid mode or a slower mode that provides more detailed results. NAM predicts accuracy and map crossing probabilities along the route of the mission from launch to target. Each of the horizontal maneuvers or any missile mode or speed change requires a missile waypoint. A waypoint is defined as an action point.
The vertical profile is then selected. Here again, a waypoint is needed for each vertical change either in terrain following or barometric hold. Once the mission is selected and all way point and maps defined,the defined mission is inputed to the mission data preparation system

 

[amardeep mishra]

Contd

The guidance software modules provide the command signals used by the auto- pilot modules to control vehicle heading, crosstrack, and altitude. The guidance modules are
(a) route definition module,
(b) lateral guidance module, and
(c) vertical guidance module.
The route definition module provides
(1) launch turn control to permit launch in a direction away from the first waypoint,
(2) calculation of unit vectors in a tangent plane coordinate frame for use in the lateral guidance module
(which will be discussed below),
(3) data control logic to sequence through profile segment data and waypoint definition data, and
(4) control of logic flags that initiate turns to change from one mission segment (or leg) to the next.

The lateral guidance module calculates the bank angle commands used by the autopilot modules in controlling vehicle heading and cross track position. In particular,the lateral guidance module provides bank angle commands for steering to the ground track defined by waypoints. Near a waypoint, the desired path (i.e., the reference for determining lateral displacement and heading) is a circular arc transition between the two directions defined by adjacent great circle path segments, as illustrated in Figure 7.3(that i have attached below for the reference). To recapitulate, the cruise missile is directed along the proper course between waypoints by the lateral steering system. The steering plane, that is, a plane containing the two waypoints and the Earth’s center, defines the course between two waypoints. The perpendicular distance between the air vehicle position and the steering plane is the crosstrack error, and its time derivative is the crosstrack error rate

During turns, the crosstrack error may be defined as follows. A turn center is defined (see the figure above) that is the center of the circle containing the desired ground track during the turn. As a result, the crosstrack error then becomes the difference in the lengths of two vectors from the turn center. One of the vectors defines air vehicle position, and the other, the ground velocity.

The third module, the vertical guidance module, calculates the vertical acceleration commands used by the autopilot module(i.e., vertical acceleration control) to control air vehicle altitude. Specifically, the vertical guidance module commands normal accelerations based on clearance altitude error and a selected form of feedback. Note that climbing flight generally employs a clearance rate feedback, while diving flight is executed with inertial rate feedback.

@Oscar

here is my brief analysis of TERCOM-
Terrain contour matching(TERCOM) can be defined as a technique for determination of the position location of an air borne vehicle with respect to the terrain over which the vehicle is flying.More specifically, TERCOM is a form of correlation guidance based on a comparison between the measured and the pre stored features of the profile of the ground(i.e.,terrain)over which a missile or air craftisflying.Generally,terrain height forms the basis of this comparison.Reference terrain elevation source data descriptive of the relative elevations of the terrain in the fixpoint are as are stored in the airvehicle’s onboard computer. Obtaining the reference data requires prior measurement of the ground contours of interest. These data are in the form of a horizontally arranged matrix of digital elevation numbers. A given set of these numbers describes a terrain profile. The length of contour profile necessary for a unique fit is a function of terrain roughness, but is in the range of 6 to 10 km and can be a curved path. The TERCOM profile acquisition system consists of a radar terrain sensor (RTS) or a radar altimeter and a reference altitude sensor (RAS) or barometric altimeter.
As the vehicle flies over the matrix area, data describing the actual terrain profile beneath the vehicle are acquired. That is, the actual profile is acquired using a combination of radar and barometric altimeter outputs sampled at specific intervals, and when compared against the stored matrix profiles provides the position location. This type of guidance is used for updating a midcourse guidance system on a periodic basis, and has been applied to the guidance of cruise missiles, which usually fly at subsonic speeds and fairly constant altitude. With regard to midcourse guidance, it is well known that the simplest midcourse guidance is the explicit guidance method.The guidance algorithm has the capability to guide the missile to a desired point in the air while controlling the approach angle and minimizing an appropriate cost function. Furthermore, the guidance gains of the explicit guidance law are usually selected to shape the trajectory for the desired conditions.

The TERCOM technique, first patented in 1958, relies for its operating principle on the simple fact that the altitude of the ground above sea level varies as a function of location. For example, if one were to make a rectangular map of an area 2 km ×10 km long, divide the map into squares, say, 100 meters on a side, and record in each square the average elevation of the ground in it, one would then obtain a digital map consisting of 2,000 numbers, each number corresponding to the elevation of a point of known coordinates on the ground. A set of such maps, which can be made much larger and can have squares with smaller sides if required, is stored in the memory of the missile’s onboard computer. The missile is provided with a downlooking radar altimeter capable of resolving objects on the ground smaller than the map squares from a height of several kilometers.Consequently, as the missile approaches the region for which the computer memory has a map, the altimeter starts providing a stream of ground-elevation data. Furthermore, the computer, by comparing these data with the elevation data it has in its memory, can determine the actual location of the missile with an accuracy comparable to the size of the map cell. It then instructs the autopilot to take any corrective steps necessary to return the missile to its intended trajectory. More than 20 such maps can be stored in the missile’s on board computer,enabling the missile to update its location information and correct its trajectory frequently during its overland flight

TERCOM is somewhat of a misnomer, since the process does not accurately match terrain contours to determine a fit,and thus the missile’s location.Rather,the“match” occurs by determining the minimum value of a summation of terrain altitude differences.The altitude for each cell of a reference strip is subtracted from cell altitudes derived from a combination of the missile’s radar altimeter and air data system to obtain these differences. The map strip identified by the minimum summation locates the crosstrack position of the missile. The downtrack position of the missile is deter-
mined from the time that the minimum value occurred. Significant in this process is the fact that the reference map data are stored as a 4-bit words, limiting the number of possible altitudes to 16 quantized levels. Radar altimeter data are stored as 4-bit words. It should be noted that TERCOM fix accuracy degrades with increasing altitude. Above a radar altitude of 4 to 5 times the cell size, the accuracy degrades to the point that terrain correlation is not feasible.

@Oscar

Now, the question i have is-
1)Does babur have onboard radar imaging seeker?
2)How does pakistan acquire precise altitude maps of the region?

 

[SQ8]

Now, the question i have is-
1)Does babur have onboard radar imaging seeker?
2)How does pakistan acquire precise altitude maps of the region?

Babur Cruise Missile - Database | Page 17

Precision of maps is limited to available commercial DeD sources.

 

[amardeep mishra]

Precision of maps is limited to available commercial DeD sources.

But what about the seeker?does babur have any kind of active radar,either for measure altitude,or even for altitude correlation?

 

[shaheenmissile]

But what about the seeker?does babur have any kind of active radar,either for measure altitude,or even for altitude correlation?

Has RADAR altimeter. That is an integral part of TERCOM.

 

[amardeep mishra]

Has RADAR altimeter

Hi!
I am guessing the source of this radar altimeter is again china?just like the turbojet that powers it? And finally are there no programs to indigenously design radars?i mean,radars form the basis of a lot of modern weapon systems,ranging from missiles,surveillance systems etc!
It would be great if you can shed some light on that based on credible research literature!

 

[SQ8]

But what about the seeker?does babur have any kind of active radar,either for measure altitude,or even for altitude correlation?

It has a basic radar altimeter to correlate the data with.

 

[Stephen Cohen]

@amardeep mishra

What matters from India's point of view is that whether
our SAM systems are able to destroy Sub sonic missiles or not

 

[amardeep mishra]

What matters from India's point of view is that whether
our SAM systems are able to destroy Sub sonic missiles or not

Hi
Dr saraswat in one his seminars revealed that india does have interceptor capability to take down the cruise missiles.However the main challenge associated is the early warning of cruise missiles(He mentioned this some 6-7 years back,when they were still perfecting the AAD design).To that effect DRDO is working on aerostats with longer ranges(450kms ranged aerostats is in development).The typical requirement of a aerostat radar is to have decent MTI capability(by having relatively low PRF) to detect a small cruise missile flying very low against the ground clutter. He also mentioned a network of multi-static systems to be deployed as early warning for cruise missiles.
Apart from all these,various LRDE developed LOW LEVEL RADARs are already in service to provide early warning against cruise missiles or for that matter any low level object(however their range is pretty much limited to ~50kms).
One should also note that in one the recent test launches of akash SAM,it intercepted a target merely 30m above the ground

@Oscar
Does pakistan operate any LLRs(low level radars) like LRDE's bharani and ashlesha?

This one is an AESA(designed by LRDE) and tbh,it looks a smaller variant of your TPS-77 radar

 

[SQ8]

@Oscar
Does pakistan operate any LLRs(low level radars) like LRDE's bharani and ashlesha?

Army:
GIRAFFE Radar - Wikipedia, the free encyclopedia
Giraffe 40 upgraded locally to near AMB standards in signal processing.

LAADS system from the US, upgraded version based on MPQ-46
AN/MPQ-49 Forward Area Alerting Radar - Wikipedia, the free encyclopedia

Air Force:
YLC-6
More here
PLA Air Defence Radars

From what I remember from when I worked(2010-12) is there are two other low level Radar systems said to be local(as they were to be part of the 3rd and 4th layer of Net Centric system under development at the time. .no idea what nomenclature, how developed etc.

 

[Muhammad Omar]

Pakistan test fires Babur missile-Pakistan-World-TIMESNOW.tv - Latest Breaking News, Big News Stories, News Videos

Showing NASR Missile and Saying BABUR Missile

 

[amardeep mishra]

From what I remember from when I worked(2010-12) is there are two other low level Radar systems said to be local(as they were to be part of the 3rd and 4th layer of Net Centric system under development at the time. .no idea what nomenclature, how developed etc.

Hi oscar,to be honest,i never really knew that pakistan has MPQ-49! Anyways,if possible,can you shed some light on the part i have highlighted above?

 

[amardeep mishra]

Terrain Hugging capability can be derived from GPS/BEIDOU or any satellite navigation system,provided the positioning is accurate enough

hi there!
you seem to have gotten the concept of TERCOM all wrong!-Terrain hugging capability is actually autonomous to GPS and to be honest,this was developed way earlier than the GPS(the actual development of GPS aided cruise missile guidance was pioneered by USA in mid 80s and it was only in early 90s that GPS aided guidance was put to use!) In modern times though the TERCOM is usually coupled with GPS to improve accuracy.
For TERCOM you'd need altitude maps of the region- again for that you'd need MAPPING SATELLITES and not navigational satellites!- i hope now itz clear?

 

[shaheenmissile]

hi there!
you seem to have gotten the concept of TERCOM all wrong!-Terrain hugging capability is actually autonomous to GPS and to be honest,this was developed way earlier than the GPS(the actual development of GPS aided cruise missile guidance was pioneered by USA in mid 80s and it was only in early 90s that GPS aided guidance was put to use!) In modern times though the TERCOM is usually coupled with GPS to improve accuracy.
For TERCOM you'd need altitude maps of the region- again for that you'd need MAPPING SATELLITES and not navigational satellites!- i hope now itz clear?

Yes true. TERCOM needs altimeter and terrain altitude data. Not GPS as per say. But the basic purpose of TERCOM was not position finding but missile survivability in stealth,as TERCOM helped missile to maintain a constant low altitude by following altitude contours of the land.
But not technology has improved.ELINT/SIGINY is much advanced and so is GPS posotioning.
An altimeter is a transmission which can give away Missile's position. Thats why radar altimeter may be switched off or replacef with an accurate satellite positioninh system to keep missiles stealth.
Although no evidence yet of this technology in Babur. But both Babur and Raad are fitted with 2d/3d pitot tubes. Your article does not cover working and purpose of pitot tubes in missile.

 

[Bossman]

Hi!
I am guessing the source of this radar altimeter is again china?just like the turbojet that powers it? And finally are there no programs to indigenously design radars?i mean,radars form the basis of a lot of modern weapon systems,ranging from missiles,surveillance systems etc!
It would be great if you can shed some light on that based on credible research literature!

Check PAC and AERO websites. Pakistan produces various types of radar altimeters. No need to set your self up for failure by starting every thing from scratch like DRDO. We design what we can, we manufacture what we can if it makes economic sense, we buy what is viable to buy. The idea is to have a credible defense at minimum cost and don't waste resources on basic research. You want basic research you go to the universities. The defense establishment is not for basic research