Missile contrails in space

[jgrose]

So this conversation came up in the office today while discussing the effects in Sci-Fi Channel's Battlestar Galactica remake. I figured I'd pose this question to you guys as many of you are well versed in aerospace fun and factoids and hell, some of you even make a living in the business. Would a contrail form nicely behind a missile as it streaks along, or would it quickly dissipate in the vacuum of space? We see plenty of contrails in Macross with all those massive volleys flying about, so maybe this discussion has come up here before?

Thoughts, questions, complaints...?

Jeff Grose

AN

Edited December 10, 2003 by jgrose

[Zentrandude]

depends on whats used as fuel and its waste as its burn off. i guess it would be same as in air but minus the wind effect.

[Daishi3500]

Maybe space would getal foggy. The smoke would naturally spread, cuz there is more presure in a clump of smoke than in no smoke. Plus the rocket crapped it out rearward, and unless friction stops the particles, won't they keep on going.

I have to wonder if space in modern day will ever be a battlefield. I suppose this subject will be swarmed with treaties and pacts first. But what the hell would be those weapons in space??. BTW, does oxygen have to be present in order to ignite gunpowder from a bullet (guns in space)?? And one more; how would you get a missile to home in on something with no gravity. Wouldn't the missile have to constantly cancel out its direction to turn. O well, sorry for egendering all these extra questions into your topic.

[Uxi]

A missile would have to maneuver like a small spacecraft. It would need manuevering jets and thrust vectoring, not control surfaces... So they'd either be fairly large and expensive (much moreso than something like the AMRAAM or Phoenix). And they need to carry all their reaction mass with them. So they'd probably be short ranged or they'd be so large that they would be prohibitively expensive. Plus, depending on the technology available any kinetic energy missile (that needs to make contact with its target) in space is gonna get pretty easy to hit assuming any decent lasers are available. An alternative is to make the missile dodge (but that will necessitate even more manueverability, and the reaction mass that goes with it) or armor it up. In either case, it gets larger and larger (and needs correspondingly larger engine and thus reaction mass, etc etc) and more and more expensive. To say nothing of the need for more advanced targetting system capable of dodging.

In short, they'll probably become less and less viable, especially once directed energy weapons (lasers, etc) become common. Alternatives are nuclear pumped gamma or x-ray missiles (seen in the Niven & Pournelle's Footfall and the Traveller RPG) where the missiles are essentially laser carriers that only need to get within 30,000km or so and then fire off a small number (< 10) of lasers themselves.

Edited December 11, 2003 by Uxi

[ComicKaze]

So how realistic are Macross's missiles?

They are micro-missiles, seem to have ruthless homing capbility, manage to avoid each other when flying in an incredible swarm, and leave ridiculous amounts of contrails in space! Maybe that's a sign of inefficient combustion?

Edited December 11, 2003 by ComicKaze

[NERV]

does oxygen have to be present in order to ignite gunpowder from a bullet (guns in space)??

you do need oxygen to ignit but the oxygen is alreayd inside each chamber and easch chamber is airtight so yes, a gun could work in space

[David Hingtgen]

Contrails are ice crystal formations (actually a cloud, just an unusual shape), formed by when the hot vapor exiting an engine's exhaust encounters the cold dry air at high altitude, and it takes the right temp/pressure/altitude to do so. Also, the vast majority of water vapor in contrails comes from the surrounding air, not the plane itself. No contrails in warm air/low altitudes. And no contrails at extremely high altitudes.

Thus, no contrails in space, since the pressure is zilch, and water vapor is zilch.

PS---contrails are nearly identical to when you can "see your breath" in cold weather---warm moist air from your mouth condenses when exposed to cool dry air.

[Mr March]

Strictly speaking, there should not be contrails in space when you fire a missile. The definition of a contrail is the humid air that forms from the hot exhaust of a jet engine mixing with a low pressure, low temperature atmosphere (typically at high altitudes). Since there is no atmosphere in space, the mixing of the two never takes place and hence no contrail.

Space is low temperature, but there is no humidity coming from the propulsion system of a Valkyrie or it's missiles. Nor is there any humidity in space, because it's a vacuum.

Having said that, the nature of the propulsion systems used in Macross is somewhat vague. The contrails could be artificially produced, much like the smoke trails we see on land-to-air based missile systems. In this case it's not so much an atmosphereic interaction, but a chemical byproduct of the actual propoulsion process (I think). How visible they would be and how they would form outside of an atmosphere is beyond me.

Not much help, but hopefully I made ya think

Edited December 11, 2003 by Mr March

[VF-17]

I don't think the term was supposed to be literally taken as contrails, but more of the trails of burnt fuel in space. I really don't know if this can happen, but it sounds possible. But, the trails would stay as nice lines for long since the "smoke" is mass and would continue to move until something stops it. As for the way it flies, since this is sci fi and evidently they have artificial gravity, hypothetically, they may have a device in them that makes gravity pockets around it to make the rocket turn. And who knows, the devices may be smaller and cheaper than fuel burning motors. Just a thought

[F-ZeroOne]

I have to wonder if space in modern day will ever be a battlefield. I suppose this subject will be swarmed with treaties and pacts first. But what the hell would be those weapons in space??. BTW, does oxygen have to be present in order to ignite gunpowder from a bullet (guns in space)?? And one more; how would you get a missile to home in on something with no gravity. Wouldn't the missile have to constantly cancel out its direction to turn. O well, sorry for egendering all these extra questions into your topic.

For a pretty good "hard-SF" book series with a good deal of high-G, thrust vectoring, kinetic impact, gamma-laser bursting, cluster warheaded, anti-matter fuelled action, try the "Nights Dawn" trilogy by Peter F. Hamiliton.

[ewilen]

I thought at least some of the "contrail-like" lines made by airplanes weren't from the engines at all, but from low-pressure vortices created by the wings, which in turn induce condensation out of the air. Am I completely off on that? Isn't that semi-famous picture of a Hornet "defolding" through a globe of white vapor caused by a similar phenomenon?

Anyway, I'm inclined to agree with VF-17 & Mr. March--the byproducts of the chemical reaction used to propel the missiles could leave a trail in space. Much of it would likely be water vapor and CO2 (combustion of organic fuels with an oxidizer). How visible it would be, I don't know.

Comment on Uxi's comments. First off, all missiles carry their reaction mass with them. About whether the missiles need to be big to maneuver, on the one hand, by ducting some of the thrust through side openings, swivelling the nozzels, or using small ancillary thrusters operating on something as simple as compressed air, I think you could change the missile's axis and let the main thrust handle changing the vector. On the other hand, I think a Sidewinder only accelerates for a brief period of time; a lot of its maneuvering is done by means of the fins while effectively coasting. That option doesn't exist in space.

As for dodging, I think the Macross approach is to fire a bunch of missiles whose trajectories diverge and then converge on the target, which complicates interception/evasion.

Edited December 11, 2003 by ewilen

[Commander McBride]

A space missile would not be prohibitively expensive at all. Missiles with thrust vectoring already exist. And having a missile steer with thrusters (hell, it could even be compressed CO2 or Nitrogen, that's what is used in some current day thrusters) would not be any more complex than having motor driven fins for steering. And, the lack of gravity makes it easier, as th emissile will fly straight instead of having to account for gravity, and the vacuum would allow for very little propulsion fuel, as there would be no loss of speed, only necessitating a very short burn time, or, alternately, a missile with insanely high velocity.

[David Hingtgen]

ewilen---those aren't contrails. Basically the opposite--only visible at low altitude. Contrail=CONdesation TRAIL. Not vortex trails. If you see something coming off a wingtip, or strake, or even flaps, it's caused by a vortex. This is also the "cloud" enveloping the Concorde's wings at high AOA. (Concordes fly via vortex-generation, unlike most aircraft)

Now as for a sonic-boom-style cloud: well that's yet another thing. For that, as you approach Mach 1, the air gets SO compressed it literally squeezes the water vapor out of the air and all the vapor has nowhere to go so it condenses, thus making a visible cloud.

The end results all look the same, but the reasons are different.