How would you designate targets for orbital bombardment?

Question

Throwing big rocks at planets is so passe and any asteroid tug can do that now. The Intergalactic Arms Reduction Treaty forbids the intentional bombardment of a planet's surface with large asteroids. Further, it enjoins all space fairing races to take action to prevent such collisions. So no more big rocks. However, the treaty does not include any language to restrict orbital bombardment by an manned vessel. (There was a suspicious amount of lobbying by many defense contractors and shipwrights. But, anyway.)

Sometimes, an attacker just doesn't care how much collateral damage is done. "Just burn everything" is a valid approach. Sometimes collateral damage is unacceptable and high precision strikes must be made. Weapons systems mounted to orbital vessels include guided missiles and beams weapons. Simple mass driver weapons don't have the needed accuracy.

With massive orbital bombardment potential overhead, what technologies might an attacking force use to designate targets? Terrestrial examples in use today include GPS coordinates or laser designators. What technologies or techniques would work well for the incredible distances inherent in orbital bombardment?

Note the hard-science tag so journal articles and official sources are preferred.

Answer 1

Probably the same as any indirect fire weapon.

It's hard to see everything from orbit and sometimes units on the ground are needed to direct the fire. Like traditional artillery, forward observers might call in orbital bombardment on a specified location. There are a lot of procedures related to the traditional process (sorry, no publications for actual orbital bombardment procedures). In these cases, the forward observers typically use a grid system predetermined for the area, described here:

The observer must locate targets using the most accurate means available. Precision munitions offer both an increased probability of achieving first-round effects on a target and a reduced probability of collateral damage. Because precision munitions are more accurate, target location error must be minimized to achieve effects on a target. The method of target location is normally a grid location, as both polar and shift from known point imply a large target location error. Grid locations are transmitted using the military grid reference system with the 100,000 meter grid square designators and a 10-digit or better grid using a target mensuration system, if available, or an 8-digit grid, if using a less accurate means of target location. Target elevation should be in meters in relation to mean sea level or the ellipsoid using the most current datum available. The observer must specify the datum used, so that the fire direction center can make any necessary conversions.

So, if they want to relay GPS they can, as long as they specify what method they're using the fire center can convert to proper coordinates.

The delay from a call for fire and impact will depend greatly on the type of weapon and the position in orbit of various guns. The response time is not great though, as mentioned in this publication:

To attain velocities in the range of 10 to 11 km/s, satellites must be in orbits with an altitude of more than 40,000 km, but these high-altitude orbits sacrifice responsiveness to achieve high-impact velocities. For instance, a weapon in a 40,000 km orbit would need about five hours to reach the earth’s surface and would have an impact velocity of about 10 km/s.

There are trade offs, of course:

Lower orbits could yield shorter response times; for instance a satellite placed in a 500-mile (926 km) orbit could strike in less than 12 minutes if the orbital geometry was ideal. The trade-off is that a weapon in LEO would impact at less than 5 km/s.

The coordination then will likely be dealing with not particularly mobile targets. Most likely camps and military buildings. Because of this, it's more likely that forward observers would not be calling in orbital bombardment to aid in close quarters battle. Rather they could mark targets and then get to a much safer distance before the bombardment begins.

While an excellent resource, the linked paper has little to say on the actual coordination of attacks, except that perhaps a computer should decide which type of attack to make:

Ideally, a system architecture will ensure that the space based weapons are used in a mutually supporting and coordinated manner. It will have to include a tracking and targeting system that can determine such information as how quickly a target must be destroyed and which satellite or method of intercept will have the highest probability of kill. This information must then be fused and presented in such a manner that a decision maker can quickly select the optimum response. The vast number of variables involved may well argue for a computer to make the decision. This alone would entail a whole new discussion about the desirability of letting a computer decide to employ weapons.

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Unless they can see it from orbit.

Of course, if the bombardment gun has direct sights on the target, they can simply fire at it like any gunner might. Given information on their own troop movements (if any) they can warn friendly forces to stay clear of the target zone.

Answer 2

This has been extensively studied for years, with one of the earliest studies being Project Thor, which Jerry Pournelle has written about from time to time, being one of the investigators of the system.

Like most "smart" weapons, the Thor projectiles have a sensor in the nose, and some aerodynamic surfaces (Pournelle called them "tabs") which are under the control of a guidance mechanism in the weapon. Since "Thor" projectiles were "flying crowbars" made of a dense material like Tungsten, you could consider them to be overgrown variants of the Armour Piercing Discarding Sabot Fins Stabilized projectiles fired from tanks (APDSFS).

So we have a long, slender "dart" with a few differences: the sharp tip is covered with a thimble shaped cap made of some heat resistant material, and the fins are very much smaller than usual (since this will be diving into the Earth's atmosphere at @ Mach 25, large fins are going to be counter productive).

For your question, the Thor would be directed towards advancing Soviet tank columns or surface warships much the same way anything else would, some observer reports the target, provides the location and call for fire. The Space Fire Control officer confirms the target coordinates and passes it electronically to the satellite, which fires it's retrorockets and reenters the atmosphere, releasing the Thor submunitions. It is pointed in the correct direction and will reach the target box very shortly. If you are just looking for a cheap and dirty solution, you can stop right there, each individual projectile will impact with the force of a 250lb HE bomb, and provided you have enough packed in the satellite, you can plough the ground much like Soviet or Russian rocket artillery.

Pournelle was after a much more elegant solution. Spending millions of dollars to launch a satellite to simply provide area fire was far too expensive for the effect you would get. Once the satellite had been given instructions to deorbit, it would be arriving inside the "target box" and the submunitions would all be inside a defined boundary where the target was identified. In Pournelle's vision, once the reentry period passed, the heat resistant nose caps would be ejected and the seeker heads would look for the targets on their own, using millimetric radar or some form of thermal imagery to strike individual tanks or plunge through the upper decks of Soviet warships. Realistically, even in the 1980's this would be straining contemporary technology, so many of the Thor's would probably be fitted with laser seekers, and on the ground or aerial spotters would use laser designators to mark the targets, and the Thor's wold make corrections using their small "tabs" to home in on the target. Helicopters like the Apache and the various scout helicopters, as well as A-10 Thunderbolts and other FAC airplanes would all make excellent markers against Soviet land forces, while the Navy would have to make due with laser targeting pods on F-18's or Seahawk helicopters in this time period.

Today of course, a greater portion of the Thor's would be smart or even brilliant, capable of seeking their own targets, while drones and UAV's would do much of the target marking for laser seekers. We should also expect that a multitude of different mechanisms would be used, so only a small portion of the Thor projectiles could be spoofed or otherwise misdirected from their targets. In the end, a soldier on the ground still has to see the targets and identify their location to define the target box for these smart and brilliant weapons to work.

Answer 3

The best and simplest way to guide an attack is to have some sort of a beacon you're aiming at, rather than coordinates.

A good example of such beacon would be a mobile phone. It has been successfully used for such purpose as early as in 1996:

https://en.wikipedia.org/wiki/Dzhokhar_Dudayev#Death_and_legacy

Of course the technology has greatly matured since then. Now all cell phones have some sort of tracking technology embedded - for your convenience!

You can start your reading here and move forward to the sources:

https://en.wikipedia.org/wiki/Mobile_phone_tracking

Now, what if you want to shoot some lonely hermit, who dwells on some mountain's peak, and has never heard of a shower, much less about about a cell phone?

Well, the obvious answer would be "send a meatbag with a beacon on a suicide mission", but let's not murder our own soldiers just yet.

You're probably thinking now, that I'm going to suggest local equivalent of GPS, but after my personal experience with a navigation with my car, I will never entrust a weapon to that system.

Instead I present you: Pigeon Missile!

Homing pigeons can find their destination with perfect accuracy over 1800 km:

https://en.wikipedia.org/wiki/Homing_pigeon

That's quite impressive for peanut-sized-brain bird, don't you think? Surely, we are not sure how it works now, but in the future we'll probably crack that mystery. And what's better use of such knowledge than bombing your neighbour?

So, instead of going super-high-tech I advise you to look no further than to Mother Nature and use locally available homing system used by native species.

EDIT:

What technologies or techniques would work well for the incredible distances inherent in orbital bombardment?

Split the hard problem in smaller, easier problems and solve them separately.

1. First solve "hit the planet" problem, which is easy, because the planet is damned big rock
2. Before the missile hit the ground, switch to guiding system from "space" to "local" and pick something from the answers.

There is really no point in flying precisely at the intended target all the way from space - just last few kilometres are enough.

Answer 4

The same ones we use today

Michael brings up a good point: orbital bombardment would be very similar to attack by ballistic missiles (only you can skip the first half of the trajectory).

As any textbook on orbital mechanics will tell you (e.g. Chapter 6 of Bate, Mueller and White [pdf]) ballistic missile trajectories have apogees of thousands of kilometers, well beyond low Earth orbit. They can also be highly accurate: the Peacekeeper missile has an accuracy (circular error probable) of just 90 meters. This means that ICBMs are a possible template for orbital bombardment guidance.

One of the many factors that ballistic missile designers consider is resistance to enemy jamming. If an ICBM (or our orbital bombardment system, for that matter) used something like a laser target designator or even GPS guidance, there would be the possibility that an enemy could disrupt the guidance signal or substitute their own signal to redirect the warheads. The best way to avoid this is to keep the guidance system entirely self-contained.

That is where inertial guidance systems come in. The concept is very simple: if you know where you start from, by integrating the accelerations that you feel over time you can determine your current position. You simply input the initial position and the target position just before launch, and the munition can guide itself to the target with no further input. Note that this only allows you to attack targets that are stationary (on the order of the ten to fifteen minutes it takes to reach the surface): for moving targets you can employ one of the many techniques developed for guided missiles and "smart bombs."

In practice this is very difficult, since (due to the integration) any tiny measurement error accumulates over time. However, extremely precise inertial guidance systems like the Advanced Inertial Reference Sphere do exist. Used together with a highly-accurate model of the Earth's gravitational field, this system is what gives US ballistic missiles like Minuteman and Peacekeeper their accuracy.

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Note that the inertial guidance system (according to the above reference) only contributes around 1% of the total inaccuracy of the missile: most of the inaccuracy comes from the warhead's inability to maneuver (remember that a ballistic missile coasts unguided for the majority of its trajectory). With a much shorter trajectory from LEO to the surface and with better maneuvering ability, inertial navigation should give you practically pinpoint accuracy.

Answer 5

Use laser designators, inertial guidance, coordinates or beacons for terminal guidance for guided missiles. Use coordinates for beam weapons. Modern technology already has equivalents for these guidance techniques.

There needs to be something that can provide terminal guidance for guided missiles. As shown in this answer about hitting precision targets from orbit, it's not possible to fire a projectile with sufficient accuracy for a precision strike from orbit. Any projectile from orbit requires some way to know where to strike. Laser designation, coordinates, optical guidance all provide the kind of guidance needed. There are modern equivalents of all these techniques so we know they work.

Beam weapons only require a point to aim at. A special operations team should be able to generate this kind of target data.

Get the guidance system right and you get to see something like this.