You are correct in asking this question.. And answer lies in the beauty of A2A missiles.. I may not be very precise as my field knowledge and class notes are pretty old and i have forgotten a lot too.. But let me try and give a little brief
First Derby Missile
http://www.rafael.co.il/Marketing/331-887-en/Marketing.aspx
View attachment 291975
So we know Derby's guidance system is Active Radar Seeker
Now theory states that
- Radar guidance system detects and move over their flight path towards end target by sensing EM waves reflected from target aircraft's surface
- These reflected radiation requires a radar transmitter to continuously illuminate the target
- Thus there are different sources of such guidance as under
- View attachment 291980
- The role of transmitter is clearly to beam EM waves at the target, receive the reflected data to the receiver antenna of the missile, analyse it further and determine the course and corrections if any to the guidance computer to steer the missile towards the target to achieve a kill.
- Of course there are issues which the receptor must tackle like reflections to quality etc etc in order to ensure the determination is accurate.
Now comes the bigger issue. Once a A2A missile is launched there are 3 phases of guidance
1. Launch Phase/ Program Maneuver phase
2. Mid course phase
3. Terminal phase
The Program Maneuver phase is simply the separation of missile from the aircraft and is clear of the aircraft just after launch. its full independent of anything related to the target or its position.
The Mid course Phase comes online or initiated just after the first phase completion and its major function is to place the missile within terminal acquisition range of the target with the seeker pointed at the target.
The moment Missile comes within Terminal acquisition phase the last phase or Terminal phase is initialized. Its basically the last part of the flightpath and is the most crucial part as its success determines a successful hit or miss. In the terminal phase, based on the reflections received at the receiver antenna, the objective is clearly to place the missile to get a successful hit on the aircraft. It basically locks on the target and tries to cover the distance as quickly as possible with two possible chief challenges of limited on board fuel and maneuvering limitations. More than directly scoring a hit, its more of a proximity detonation. Thus the effectiveness of this phase is based on how close the missile gets to the target
See this to quickly understand what i said above
View attachment 291982
Source old notes
and in terminal phase see this
View attachment 291983
Source:
http://www.rafael.co.il/Marketing/331-887-en/Marketing.aspx Derby Brochure..
The same points in guidance is there in a SAM too but first phase of launch phase is known as boost phase.
Now some more concepts.. Different category of homing guidance
Active Homing : An active homing guidance system is one in which both the source of energy to illuminate the target and the receiver of the energy reflected from the target are carried in the missile. Hence, the missile contains a transmitting
antenna, a receiving antenna, and a receiver. It also carries within it the signal processor and the guidance computer.
View attachment 291985
Semi-Active Homing : A system wherein the transmitter of the energy is at a point external to the missile, but the receiver is inside the missile. The missile contains a receiving antenna, a signal processor, and a guidance computer. Since the
transmitting antenna is located externally normally carried by launch craft or ground antenna it has less autonomy than active homing guidance.
View attachment 291988
Passive Homing : In this system, in which the receiver, placed inside the missile, utilizes the energy emanating from the target. It does not require a transmitter. A heat seeking missile uses such a system. The missile contains the receiver for the the receiver, placed inside the missile, utilizes the energy emanating from the target. The missile contains the receiver for the kind of energy that the target emanates, a signal processor, and a guidance computer.
View attachment 291991
Derby uses Active Radar Homing but in terminal phase. Thus, the missile during mid course needs a link via which it gets information for its course and correction requirement. Thus the aircraft and missile via a DATALINK must share this information and the launch aircraft must continue to illuminate the target so that the mid course can steer the missile uptill the terminal acquisition phase when the terminal guidance takes over. This is very important as the target plane may be using different air maneuvers to continuously try and change position to evade correct course of the missile. The other possibility is use of GPS which takes over the responsibility of the launch aircraft providing illumination.
Derby does nt have GPS guidance.Now sadly by continuous illumination the launch aircraft is putting itself on risk. Certain times illumination duty is taken over by AWACS/Mini AWACS as their longer range and a separate entity solves the problem of illumination based targeting of the launch aircraft.
And last 2 concepts
LOBL: lock on before launch and LOAL: lock on after launch
The LOBL mode allows the launch aircraft pilot to confirm the missile is locked on to the designated target prior to launch, gives high kill probability against short-range high-maneuvering targets and enables the engagement of designated targets by on board guidance normally used in terminal phase. The LOAL mode basically does everything that LOBL does with just one difference that lock on happens after the launch and is basically guided terminal course to the lock.
If the target is within seeker acquisition range which is generally very short and is estimated to be just above minimum range, the missile is launched in LOBL mode. If the target is beyond seeker acquisition range the missile is launched in LOAL mode. The seeker searches for the target and switches to homing phase when the target is acquired. Both the Derby and the Python 5 missiles can operate in LOBL and LOAL modes.
This means Derby operates in LOBL mode for short-range target engagement and LOAL mode for medium-range engagements.
By the use of BNG (Ballistic Non Guided) mode it seems the Tejas has not provided the mid course guidance. It can imply that range of Derby fired is small and just above its minimum range. Normally its assumed that minimum range is 10-15% of declared range which in this case is 10-15% of 65 Km or 6.5-10 Kms (Derby has a range of 65 km when launched by an aircraft travelling at 0.9 M at 25000 Ft head on.. While actual max range or minimum range is classified)
So being just above minimum range, at the time of launch itself its basically LOBL, the terminal acquisition phase is activated right after Program Maneuverable Phase/Launch phase and skipping Mid course phase. Thus no guidance provided and is non guided terminology
It looks like there would be a series of tests with increase in ranges to see how the mid course guidance works out in a phased manner. Especially bcz the radar used may be EL/M 2032 MMR the limitation of range will definitely effect the guidance part for Derby maximum range which will be corrected with more powerful 2052 AESA. This makes me believe strongly every test will see a phase wise increase in range and through evaluation of system working optimally at every phase of the missile guidance.
Hope it clears all the doubts..
@cerberus @MilSpec @Abingdonboy @AUSTERLITZ @SpArK @The Deterrent @Oscar @others
Pls feel free to correct any mistakes and add to it..
