# Feasibility of "stealthily deployed missiles" in 0G

Please focus your evaluations only on the maneuver, not any aspect of stealth in space. I repeat: Stealth in space is not asked for, just the maneuver.

Let's take a more advanced world based on today. Due to increased efficiencies commercial and military spaceflight in the solar system became feasible enough to colonize the inner planets. Detection equipment such as cameras, radar and IR detectors remain mostly unchanged though, energy shields are a nono.

Now, my sleep deprived brain cooked up this possible 'stealth' missile deployment system and... now that I think of it needs concept evaluation:

Some kind of spacefighter flies with speed $\vec{v_0}$ and just disengages the missile during a maneuver (like in the middle of a hohman transfer to get into direcct weapon range) without engaging the missile's engines. For this one moment, the missile moves with $\vec{v_0}$, as does the spacefighter.

Subsequently, the spacefighter continiues the maneuver, not influencing the missile anymore. According to Newton's first law, the missile just goes on on its new orbit, reads passive data (radar or IR signature) and generates only minimal EM emission, only having the residual heat from when it was attached to the fighter - just enough to keep the electronics operational.

Once the missiles distance is short enough or some timer ran out, it uses maneuvering thrusters to turn to the needed new vector, starts up the engine and homes in. A particularly clever design variant might even just do a short corrective burn before 'hibernating' once again for a bit, trying to not being estimated as a big threat by the target as a hot burning item.

Now: Is this method for deploying your missiles in a tactical scale (single ship to single ship encounter) feasible or do I miss out some blatant flaw?!

I am not trying to disguise the ship dropping the missile or the missile at all. It is the basic maneuver that shall be evaluated: Does it give a tactical benefit to start a maneuver (like changing orbit), dropping the (mostly passive) missile as a 'dead drifting' object during this and having it launch later from its own orbit?

Since everybody is going over the BASICS of stealth in space: Yes, I read "There is no stealth in space.

• @StephenG The main issiue is efficiency and energy generation just as much as life supoort - but that is not part of the question, it's about "cold dropping a missile that only fires on the last part". A fighter also doesn't need extended alone operation time (think 5 hours tops). May 31, 2018 at 12:43
• @StephenG You are concearned with things that don't impact the core of the question at all May 31, 2018 at 13:24
• The kind of tech available fundamentally affects the nature of the answer. May 31, 2018 at 14:02
• Rereading, there's a lot of concerns which aren't addressed. Time, distance, engines, doctrines, levels of alert, all of these radically affect whether this tactic is useful. I do want to point out that 100% of spacecraft launched today use this method. However, instead of calling it a "spacefighter," we call it a "booster." For a real life practical example, look at Hohmann transfers, where there's real life physical reasons to have a long delay between burns. May 31, 2018 at 16:24
• @CortAmmon It is pretty much Hohmann transfer battle... and I am aware. The basic idea behind the plpy is to drop the missile(s) during a maneuver that is somewhat expected, and launch them from a position when they are in a better position to the target than the own ship, most likely from a position where they are close enough to just boost forward. As practically 'dead', they might get assumed to be some piece of debris if the launching pilot gets lucky. May 31, 2018 at 16:30

## TL,DR;

Yes, it makes great tactical sense to do this.

## Details

In addition to the "There's no Stealth in Space" articles, another article is pertinent to the discussion. Its conclusion is that space fighters are generally a Bad Idea (TM). But that is not why you should read the section.

It states that it makes more sense to replace the space fighter with an expendable missile bus.

Basing the weapons on current and extrapolated propulsion systems, the missile bus would possess a high Isp, low thrust engine capable of supplying a large delta V and low acceleration.

The missiles would possess lower Isp, higher thrust engines to ensure the target couldn't "jink" out of the way or shoot it down.

When the targeting computer on the missile bus calculated the missile's delta V would permit an intercept, it would drop missiles for the intercept. It's conceivable that the missile bus would hold many missiles and make several such drops for each target.

Each missile's targeting computer would calculate its optimal & terminal burns (a maneuvering missile is harder to shoot down) to ensure intercept. The missiles would fly ballistically (no propulsion) until it reached one of those burn windows.

The benefit this tactic provides is manifold. The target will see the missile bus (or fighter) as it uses its propulsion. The missile bus can eject missile pairs in opposite directions and impart a large separation force. These means each missile will arrive on different trajectories (making defense harder). Because the missile hasn't used its propulsion yet, it's possible the defender won't see the missile ejections. The missile bus and missile on-board computers will have shared planned trajectories so that all dropped missiles arrive at similar times.

The target will see the missile bus and know it has been engaged. Depending upon the details of the engagement, it might not see the actual missiles until after the first time it sees each missile make its optimal trajectory change burn, the target will know for sure that it was fired upon. Also due to the nature of ballistic flight, it will be trivially easy for the target to compute the missile's location. A smart defender would use this knowledge to try to maneuver out of the threat envelop of the missile, shoot it down, engage ECM, or all the above.

## Reference

• So Tl/Dr: Use a multi-stage booster, like every other spacecraft? May 31, 2018 at 17:50
• In essence yes. I imagine that missile bus + missile weapons for long range / higher delta V engagements. For shorter / low delta V engagements, just the missiles should be sufficient. May 31, 2018 at 18:04

Practically speaking, no. This tactic is a reasonable tactic, but it is about as stealthy/subtle as pointing a loaded gun in someone's face.

First off, I'd like to point out the similarities between this and a much simpler answer a. la. Jim2B's answer. Consider the case where, instead of doing these maneuvers, you simply launched a 2-stage weapon. The first stage does the same maneuver you described for your spacecraft, jettisons the cold and quiet 2nd stage before going somewhere (it just has to burn a little in some direction). The only difference between this and your maneuver is that, in your maneuver, its plausible that the opposing fleet may think they are observing nothing more than a orbital maneuver, and not bother to look for the missile.

Practically speaking, navies which think this way don't live very long.

In both your maneuver and the 2stage missile example, the key is that whenever you are on an intercept trajectory, you can drop an object which will continue along that path. Thus any objects which are on near-intercept trajectories must be assumed to be dangerous. Being on an intercept trajectory with a military spacecraft is analogous to pointing a gun at them. Militaries which don't respond to that also don't live very long.

As such, you can be 100% certain that a competent adversary who is tracking you is going to treat you as a threat while you are still on an intercept trajectory with them, whether you are mid-maneuver or otherwise. The longer you stay on that trajectory, the more hostile they will treat you.

Now in your example, you're trying to be casual about this, so you'll likely not be on that trajectory long. Just long enough to release your package. However, this poses a problem for your maneuver. You just pointed a gun at them, and now they know where in space a cold quiet package could be. Now they can look for it very intently, rather than having to scour the skies. They will have a rather small region of space where an object could be if it were undetectably-launched during your maneuver in the right direction.

What happens next depends on their missile defense systems, but again, militaries that don't react to a gun being pointed at them don't live long. You can be guaranteed that they have some solution to this problem.

There's three cases where this would not apply:

• They aren't looking at you. If they're not looking at you, then they wont see you point the loaded gun. Shame on them. However, that also means you could have simply fired a 2-stage missile and achieved the exact same results without committing yourself to a new orbit.
• If there's a planet nearby, you could hide in the shadow of the planet. Once again, any 2-stage missile would be effective from this position. The tactic didn't buy anything.
• A cheap-shot at the start of a war might work. If you had hundreds of spacefighters "doing peaceful things," and one of them did such a maneuver, the enemy might not find it worth responding to.

So basically, it's a good idea in the sense that the general structure of it is required for any missile launch, no matter how you approach it. However, it's as stealthy as pointing a loaded gun in someone's face. Expect the enemy to respond without being tricked in any way.

Not being a scientist, I'd consider it viable under certain conditions. It's used occasionally in sci fi already.

## Ways to detect such a stealth missile

The missile will most likely have a temperature above the surrounding space, so a temperature sensitive sensor might detect it, unless it approaches from the direction of another "hot" object that obfuscates readings in that direction, e.g. a sun. The chances for detection are probably very small, but definitely non-zero.

The missile might also have emissions, e.g. radiation from a nuclear core. Shielding will reduce or remove that, but improper shielding like on an improvised or damaged missile will increase the chances of detection.

The missile will most likely be made of or contain steel or other materials with magnetic properties, which could lead to detection by sensors working with magnetism.

Every object has gravitational pull. Even a small missile could potentially be detected by it's gravitational effect. The larger the missile, the easier it is to detect.

## Limits to its usability

Space is big. Really, really big. Sending a missile on it's way from outside of detection range will mean that it will take a long time to reach it's target. That means that it will only really work on targets that aren't moving a lot or are moving in predictable patterns, e.g. space stations, asteroids or planets. You won't hit another space ship, unless you allow for a longer homing phase, which would then in turn allow for countermeasures, reducing the effectiveness of the missiles. If the enemy is coming straight at you and moving predictably, it's still a possibility, but warfare would eventually evolve to a point where such missiles are at least accounted for in standard military procedures.

## Use in tactical situations

For tactical situation, a lot depends on the actual situation, e.g. tech level, distance, speed, size of the ships (starfighters or starships) and predictability of the enemy.

You are describing a missile that stays 'dead drifting' until it gets triggered later, which is certainly possible. The missiles inherit the momentum of your ship, so the launch system is feasible. It might even be useful, depending on how much of the stealth aspect you are willing to handwave.

You can drop all your missiles one by one and then have them target the enemy ship in one wave at a later time. The main problem with that is knowing where the enemy ship will be at some point in the future, because if it doesn't get close enough, e.g. stays on the other side of a planet, then your missiles might not be able to reach him and you probably won't have a system to pick missiles back up quickly to reposition them. It also might require the missiles to be self-guided and not wire-guided. If the missiles need to be guided by the ship, i.e. wire-guided (technically incorrect term, but used a lot in sci-fi for remotely guided missiles), the guidance systems might not be able to handle more than the normally launched number of missiles.

The other way to use drifting objects is as moving mines, triggered by enemies approaching it. In that case they need to maintain their own sensors, which can make them easier to detect, but they work even if your own ship can't provide direct guidance to the missiles.

In a starfighter versus starfighter close combat situation, you could decelerate for a moment, drop the missile and accelerate again, if the enemy is behind you. That would cause the missile to move slower than you and your pursuer will fly directly towards it. However, since the enemy is behind you, you'll probably do a lot of evasive maneuvers, which might pull the pursuer of course. His shots might also destroy the missile accidentally. Depending on whether such a tactic becomes commonplace enough in starfighter vs starfighter combat, your maneuver will lead the pursuer to evade the missile, whether he detected it or not.

The deciding factor is how close you can have the path of your drifting missile interject with the path of the enemy ship(s). If the enemy is moving unpredictably, your missiles will probably end up far away from the enemy and need a long burn phase, which gives the enemy plenty of time to react.

• @Trish see edit. Jun 2, 2018 at 7:37

The image of a burning engine can give an estimation of the energy output. During the first burn the estimated energy use and observed course change would give a guessed mass. After releasing the weapon the mass drops, so during the second burn less energy is needed to effect the same course change.

If the weapon is a significant fraction of the total mass it is obvious. If the characteristics of fighter are well known even a small discrepancy might be interesting causing an investigation.

If your ships are poorly made their characteristics might vary widely between units making discrepancies less interesting, may require many small course corrections which might make investigation all the possible drift trajectories obnoxious, and waste enough fuel mass or leak enough whatever to make non-launch differences plausible. Setting up a pattern of non-weapon things falling off your space craft may limit the defenses' reaction if you only need a single strike.

If IFF is clear and fuel is limited opposition will try to put something on collision with the drift trajectory to kill the fighter or force a burn at a non-ideal time, which would then catch your missile.

## Orbital Mechanics

This depends significantly on what it is orbiting, even in interstellar space, you are still orbiting the galactic core, and the closer you are to the centre of the gravitational field the more of a difference this makes. and often the direction you would need to speed up and "fire" the missile would not actually be toward the ship, often its away form it, Scott Manley does a very good youtube video explaining this in Kerbal Space Program, might be worth having a watch of it.

## Accuracy

The next issue is that warfare in space will most likely take place at very very long range, so accuracy is all important. an initially dumb warhead would need a very advanced computer system to launch it on the right path in the right direction so that it ends up on a collision course with the target.

That aside, say you could make that work, if the weapon was located on a hardpoint outside the ship similar to fighter jets today, then in theory it will not be a huge amount above the background temperature of the ship, the electronics will still work fine, and the engines should still fire if necessary to adjust the trajectory. even then if the missile was stored in an insulated sleeve, which held it in pressurized Liquid Nitrogen, then the drop in pressure of the launch would keep it cold enough to not be easily noticed.

## Maneuvering

If the maneuvering "thrusters" were simply very compressed gas, that are released from various ports around the missile to changes its rotation/orientation then it would be horribly inefficient in terms of fuel but would also not generate heat as it adjusts (Due to going from high pressure to Low pressure has a cooling effect (yes i know this is very basic description of the process)) think of a deodorant can. this is impractical in a regular missile as the changes would be very inefficient and less effective but for the weapon you describe it would probably have the pros outweigh the cons to keep it as a stealth projectile. again this is not as efficient as an active engine and would not offer much in the way of DeltaV

## Why not go backwards?

You could fire the weapon retrograde (against the direction of orbit) this could be done from one side of the ship, while the target is on the other, and then it would be travel exceedingly fast towards the target while the target would be travelling exceedingly faster towards it, less time to evade. but this would only work when low orbit of a planet, and also would need someway of predicting where the enemy ship is going to be. but it would mean the no need to be stealth, by the time the target sees it coming over the "horizon" of the planet, so it's easy miss in the thermal radiation of the planet, and as orbital speed for Low Earth Orbit is about 7.8 km/s then a weapon going twice that relative to the target, so 15.6 km/s is going (around Earth at least)

• Retrograde orbits can happen at any altitude, but the further out they are the more time for the target to see them... and also the HUGE amount of DeltaV need to perform them. May 31, 2018 at 12:52
• please reread the question and revise as you see needed. May 31, 2018 at 14:40

The problem I see is that even with massive advances to current engines, any and all traffic in space would still happen according to current orbital mechanics and very similar to current engines.

You'd accelerate, either in a quick burst (like current chemical rocket engines) or constantly (like current ion thrusters) and then decelerate when reaching the orbit or around a half way point, again depending on the engine type.

If you want to attack a target that does a maneuver like that, you can extrapolate its path and send an object on a collision course. That is done by releasing it at the correct speed/trajectory or by making it do an own burn (which is more efficient) or by having it burn constantly, once more depending on the type of engine.

In other words, that kind of missile would already be the way missiles work.

• please reread the question and revise as you see needed. May 31, 2018 at 14:40