Nike Missile Flight Sequence

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Please note: for a computer guidance perspective, please see Missile guidance summary
Also, for an actual flight path, see Intercept

This information is grouped into the following sections:

Time 0 sec, Electric Signal Ignites Booster
Time 3.4 sec, End of Booster, Start Roll then 7 g Dive
Quick discussion of "Dead Zone"
Determining when to end the 7 g dive
Time (approx.) 12 sec, End 7 g dive, start cruise
Time (later), Burst Command
Preparing for the Next launch

Time 0 sec, Electric Signal Ignites Booster

Remember, from the Pre-Launch Sequence (preceding), the following has happened
  • (in Launcher Area) Missile Safety Devices remove, Missile on surface, Electrically Connected
  • (in Launcher Area) Missile Vertical, Missile Selected, Launch Officer Safety Key in.
  • (in IFC Area) Target Tracked, Computer Settled, Red Alert,
  • (in IFC Area) Battery Commander Safety Key Inserted,
  • (in IFC Area) Predicted Intercept Point gyro angle sent to selected missile
  • (in IFC Area) Missile Radar Tracking Selected (un-launched) Missile,
  • (in IFC Area) Fire Switch Activated (nothing will happen if all above not true)
  • (in Launcher Area) Fire Signal passes through Launch Control to missile booster
The 1st moment of truth has arrived - a great deal of training, preparation and checking has been performed to get the battery personnel, radars, computer, communication cables, launchers, launch control and missile to this point. Can all of this happen correctly?
Remarkably, the answer is "yes" a very high percentage (99+? percent) of the time.

The booster igniters (one for each of the four booster tubes) almost explode into large flames which ignites the main "cruciform" shaped solid propellant (potassium perchlorate and a rubber compound?). In just a tenth of a second, full thrust is attained and the missile starts to move upward at an acceleration of 25 times the acceleration of gravity. (The acceleration of gravity is about 32 feet per second per second)

The missile guidance is active, keeping the missile vertical (0 g's turning) and the bottom of the missile pointing in the same direction as at launch (no roll).

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Time 3.4 sec, End of Booster, Start Roll then 7 g Dive

After 3.4 seconds, the missile is going straight up at 2000 miles per hour and is almost 1 mile high, The booster cluster has burned all its fuel (0 thrust). The booster cluster has more aerodynamic drag than the missile, and uncouples (the missile slides out of the cone shaped holder). The lanyard (a short cord connecting the missile from the booster) is pulled, pulling a pin from the missile. This pin operation closes an electric circuit informing the missile circuitry of booster separation. The following happens:
  • A roll maneuver is executed to bring the bottom the missile into the rotational plane of the gyro. This synchronizes "up/down" with the ground radar and the computer.
  • Either
    • the sustainer motor is ignited,
    • or an 8 second delay is started so that the upcoming 7 g dive will be performed and a lower speed and be smaller radius (decreasing the "dead zone" where the missile can't reach)

The roll maneuver is allowed one second to complete then the computer and missile radar command the missile to "dive" at 7 g's. This dive starts the missile toward the Predicted Intercept Point, since "down" for the vertical missile is in that direction.

The computer will continue sending this 7 g command until missile tracking shows that the missile is on a 0.5 g flight path to the Predicted Intercept Point. This path means that the missile will "fall" at an acceleration if 0.5 g s, and be supported by its fins by 0.5 g s (1/2 of the weight of the missile will be supported by the fins). This low weight on the fins decreases the missile drag, and the thin air of this high flight path will also decrease missile drag (keeping the speed high while decreasing the need for a larger sustainer motor).

The above paragraph means that 7 g dive is stopped a little early so the missile will make a shallow arc to the Predicted Intercept Point. If the Predicted Intercept Point is low and relatively near, the 7 g dive lasts longer. If the Predicted Intercept Point is high and relatively far, the 7 g dive lasts a shorted time.

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Quick discussion of "Dead Zone"

The "Dead Zone" as a donut shaped area around the site that the missile is not capable of entering. This limit is because the missile is launched straight up, and has a maximum dive capability of 7 g's due to fin strength limits.

A method of decreasing the size of the dead zone is to cause the missile to go slower so that the turning radius is decreased. Delaying the start of the sustainer motor eliminates the normal missile speed increase during the 7 g (later 10 g) dive, decreasing the turning radius, and decreasing the size on the dead zone. This method is chosen when the predicted intercept point is close and low.

The minimum dead zone using this method is about 21,000 ft high and about 4 miles in radius.

If the predicted intercept point is more than 10 miles away, or above 30,000 feet, the firing of the sustainer motor is not delayed and the missile starts gaining speed to mach 3.5 earlier in its flight.

Nike sites were frequently patterned so that the dead zone of one site was in the firing or accessible zone of one or more other sites. Also Hawk batteries were sometimes placed near Nike sites as area defense (and they also defended the dead zone of a particular Nike site).

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Determining when to end the 7 g dive

The above diagram shows three (of many) possible flight paths. The paths start from the missile's 7 g dive ( about 27,000 feet altitude ) and end at the Predicted Intercept Point.

The "0 g" flight path is not supported by any air lift on the wings of the missile. The missile basically acts like a bullet, falling freely due to the acceleration of gravity. A person riding on the missile would not feel any gravity, would feel "weightless".

  • The advantage of this flight path is minimum air friction (drag). The missile is at zero angle of attack (through the air) giving minimum friction. A side benefit is that the flight is high - through thinner air.
  • The disadvantages are:
    1) Longer flight time
    2) On high, distant targets, the missile could be above effective air so that it could not dive quickly if needed

The "1 g" flight path is fully supported by the missile wings. It is similar to driving an airplane straight from point a to point b. A person riding on the missile would feel normal gravity, would feel full weight.
  • The advantage of this flight path is it is the straightest and may yield the shortest flight time.
  • The disadvantage is that the missile flies through thick (dense) air yielding higher friction and shorter range

The "0.5 g" flight path is the flight path chosen for the Nike Ajax (an probably for the Nike Hercules). A person riding on the missile would feel 0.5 normal gravity, would feel one half weight. This path is a reasonable compromise between advantages and disadvantages of the options above. For further details of the 1/2 g flight path, see page 64 of TM9-5000-3 (4.5 MBytes).

The computer determines when to end the 7 g dive to enter the 0.5 g path, ( this signal is called "On Trajectory" ) then steers the missile to follow this flight style.

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Time (approx.) 12 sec, End 7 g dive, Start Cruise

At the end of the 7 g dive, normal steering commands are sent to the missile to send it to the constantly updated Predicted Intercept Point. The computer continues to accept tracking information from the Target Tracking Radar and the Missile Tracking Radar, uses a missile speed profile built into the computer, and updates the probable remaining flight time and Predicted Intercept Point.

Steering commands are as gentle as possible until the last 10 seconds to decrease steering caused drag, and thereby maintaining highest possible speed.
( For details see Computer Solving and Computer Steering.)
The steering commands during the first part of the normal flight are decreased to allow for the following effects:

  • Normal target tracking of a weak signal (lots of electrical noise in relation to signal from the target) is by definition noisy, but not nearly as noisy as the following:
  • Tracking a jamming target can be quite noisy, operators changing tracking modes to fight jamming, the system occasionally locking onto chaff dropped by the target, etc.
  • The target aircraft itself may be wildly evading fighter planes, other missiles, trying to confuse tracking, struggling with air turbulence, etc.
The above conditions can cause large swings (as much as 15 degrees azimuth and 15 % range) in the Predicted Point of Impact, especially when there is a long time to Predicted Intercept.

Commanding the missile to steer hard for each wild change causes large g force commands, and the high "aerodynamic angle of attack" to produce the large g forces produce high drag. High drag reduces missile speed, causes longer flight time, and reduces range (all bad).

The reduced steering command scheme tends to average out the large swings, giving a faster flight. During the last 10 seconds of flight, full steering commands are sent.

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Time (later), Burst Command

About 120 milliseconds before expected missile impact with (or closest approach to) the target at the Predicted Intercept Point, a "missile burst" command is issued by the computer through the Missile Tracking Radar. Some milliseconds are required for the missile to decode this command - then - oblivion - for the missile and hopefully the target.

Preparing for the Next launch
After the burst command is sent, the Missile Tracking Radar (MTR) automatically slews (moves rapidly) to the next designated missile in the launcher area. The MTR can "lock on" to this next missile with in 5 seconds. It probably takes the battery commander more than this 5 seconds to evaluate if the target has been disabled (see below). If the target has not been disabled, the next missile could be on its way to this target in another 2 seconds.

To help the battery commander to decide quickly if the target is disabled, there is a "Target Ground Speed" dial in front of him. If the target speed suddenly slows, and the target elevation suddenly drops, the battery commander may decide that the target has been disabled.

If the target appears disabled, a new target may be designated. This could be quite quick as there has been relative idle time during the missile flight for continued viewing and analysis of the defense area. Area control could well have designated the next target for this battery.

It will take the Target Tracking Radar maybe 10 seconds to slew to the next designated target, find the target in range and azimuth and elevation, and lock onto it. There is a PPI scope in the Radar control van showing the target tracking operators the same picture that the battery commander sees. This shows both the target and the azimuth and range of the TTR. This aids target acquisition in azimuth and range. The elevation operator has fewer aids. He may have been given advisories from the acquisition radars or area control about the height of the target, such as "appears high", "on the deck", but the target search in elevation has no real mechanical aid. He searches up and down quickly trying to find a target at the correct range.

The computer will take probably another 5 seconds to "settle" and give predicted intercept point, and the battery commander needs time to analyze the situation with this next target before committing a missile to it.

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If you have comments or suggestions, Send e-mail to Ed Thelen

Updated April 7, 2013