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I am wondering that if missiles fired from jet fighters can ascend or descend?

Are they going to aim only horizontally?

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Yes, they can. Air-to-Air or Air-to-Ground missiles are often equipped with little fins that allow certain maneuverability or also with thrust vectoring.

AIM9 Sidewinder
(Image Source: WikiPedia - Author: USAF)

Thrust Vectoring
(Image Source: WikiPedia - Author: Titimaster)

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Long range missiles benefit from the lower air density at higher altitudes. Short-range missiles normally fly line-of-sight to the target, but for distances of more than 8 or 10 km, the range of the missile increases significantly if it first climbs for the cruise phase, and only descends when it closes in on the target.

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  • $\begingroup$ Which missiles do this? I know the F14's Phoenix missiles could do this, but those were exceptionally long range missiles. $\endgroup$ – MSalters May 28 '15 at 14:01
  • $\begingroup$ Do you have any references? $\endgroup$ – Manu H May 28 '15 at 14:05
  • $\begingroup$ @MSalters - probably the AMRAAM missiles as well - most other western missiles are shorter range (Sidewinder, Sparrow, ASRAAM) and don't benefit since they don't have the range $\endgroup$ – SSumner May 28 '15 at 14:58
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    $\begingroup$ Just an appeal to authority but I know the AIM-120 AMRAAM is designed to climb after launch and descend as described. It's all about energy management; the missile keeps more of the energy it gets from its motor (which doesn't last the full 45 seconds it might take to get to its target) so it remains more energetic when it reaches the target. I think the Sparrow was designed to do this too but don't quote me on that one. $\endgroup$ – KeithS May 28 '15 at 14:59
  • $\begingroup$ @KeithS typically anti-air rocket motor burn times are going to be measured in single digit seconds. $\endgroup$ – Rhino Driver May 31 '15 at 3:24
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I am wondering that if missiles fired from jet fighters can ascend or descend?

Almost every AAM ever built can ascend, while some could descend. Every missile made today can do both. It has to do with the seeker.

With an IR seeker the target is a point source that is very strong against anything other than the sun, or sometimes the reflection of the sun off of clouds. So even if the aircraft is flying below you, their IR signature is visible and the missile can track - in fact, it might help when the background is cold or snow covered. Against a target above it, the sky is mostly cold with the exception of the sun, so it can track pretty well there too.

Radar seekers are another issue. In this case the signal is not coming from the target, but is the reflection of a signal from the launching aircraft (in most cases anyway). When the target is below the aircraft, its radar will hit the ground at some point, which scatters some of the signal back towards the launch aircraft. This results in a powerful signal that overwhelms the signal from the target. There is a lot of geometry involved; if the aircraft is directly below you then this is a problem, but if you are flying at, say, 30,000 and they are at 25,000, then they may still be above the horizon or close enough to it that your signal never returns (the horizon might be 500 miles away). Ground return was a significant problem with missiles like the Sparrow, which couldn't reliably be used against targets very far below the fighter.

Since the 1970s there have been a number of improvements that have largely eliminated this problem. One of the first was to use monopulse radars, which have additional coding in the signal, normally polarization, which allows it to filter out ground returns. When they were testing the Skyflash they could hit targets right on the ground, but had to keep the targets above 75m so their cameras could track them properly.

A more general solution is Doppler filtering, which lets you measure the relative speed of the returns, and filter out anything that has the speed of the ground as seen at that angle - the ground right below you isn't moving relative to you unless you're climbing or diving, but the ground in front of you is "moving" backward at whatever speed you're moving forward, and between those two the relative speed is changing based on the angle so its not entirely trivial. Well, at least until we had IC's, at which point it was trivial. Every modern radar missile I am aware of, and "modern" means "since the 1980s", uses this method.

As others have noted, it is also common for long-range missiles to climb to very high altitudes during the midcourse. This is known as a "lofted trajectory" or some variation on that theme. In addition to some of the ones mentioned above, the MBDA Meteor can do this, as well as any number of really long-range designs like the Seekbat, Eagle and R-37. Lofting is even more common in SAMs, where it is used by everything since the Nike Ajax - the Hercules used to go up to something like 120,000 feet before descending IIRC, and the Blue Envoy would have cruised at around 100,000 feet.

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