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A mainstay of science fiction games is the idea that infantry can be deployed from space based platforms to act as some component of a QRF, or as a replacement for paratroopers. But how feasible is this in real life, disregarding treaties that prohibit the militarization of space?

Assumptions :

We are in the not so far future, and humanity has developed a space based platform using current or near future tech that is able to sustain life for an extended amount of time. This platform has artificial gravity and a life support system that can operate indefinitely, but it is dependent on the Earth for some maintenance supplies and food.

Questions :

How would these infantry units be deployed in the correct area? I'm thinking that either the re-entry vehicle has to have some type of guidance and boosters to get to the landing zone, or the space platform itself has to re-position.

How quickly can these men be on the ground? Using reasonable advances in technology, can this platform really offer a faster response time than a network of paratroopers stationed around the world (current US capabilities).

If this method of deployment has a tactical value and is more effective than other means of troop deployment, then is it even remotely cost effective? Space vehicles are expensive, making reentry vehicles are also expensive. The answer to this would determine whether this tech gets handed out to a battalion sized group of space marines, or whether it only goes to the space Navy Seals.

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Were you thinking a space station, or dozens of them? Reentry is not a simple thing, and neither is major orbital changes. We may think of them more like a navy, with mutliple carrier fleets. Instead of a carrier in one ocean, you have a plaform in space on an orbit. However, you'd want a lot of them because changing orbits is pricey in terms of fuel. – Cort Ammon Feb 17 at 16:03
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So this is a la Starship Troopers? – HDE 226868 Feb 17 at 16:08
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Somebody wake up Hicks. – Scott Downey Feb 17 at 16:23
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Beam me up, Scottie. – XandarTheZenon Feb 17 at 17:35
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13 Answers 13

up vote 26 down vote accepted

It's technically viable, but horribly expensive. It's also not subtle.

Unless launching was a lot cheaper you would need a ridiculous amount of resources to keep an army in space. You then get problems with them atrophying unless you can also provide them with training missions and simulated gravity.

So no army then, how about a small special forces group?

Once the cost problems are overcome the actual re-entry process is very obvious. We're talking balls of fire in the sky and sonic booms. They are not going to be subtle at all. Not great for special forces.

The great ball of fire is also a perfect target for defenders to use to pinpoint the soldiers as they come in, but trying to decelerate by any other means would be incredibly expensive in fuel or very slow, or both.

A vehicle shaped for re-entry is also not well shaped for flying in regular conditions, you would have limited maneuvering ability. In fact the most likely scenario is a drop pod that after re-entry the military forces bail out of and then use parachutes (possibly HALO) to close in on the target.

So you're expensive, noisy, obvious and vulnerable. Not a great combination. The one thing you do have going for you is speed. You would orbit the planet 15 times every day which means you could deploy to any location within a few hours.

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Would it be viable to put small boosters on the reentry vehicle to make small corrections in space? That way, any errors in the path of the craft could be accounted for before it reaches the atmosphere. – Carlos Danger Feb 17 at 16:31
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Course corrections isn't the problem. The problem is decelerating from 28,080 km/h ... objects in orbit are moving FAST. – Tim B Feb 17 at 16:35
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So all you need is a propulsion system with basically unlimited delta-V - perhaps a space modulator powered by illudium or unobtanium. – Bob Jarvis Feb 17 at 17:35
    
Regarding "a vehicle shaped for re-entry is also not well shaped for flying in regular conditions", you may want to have a look at SpaceShipTwo's feathering system ( youtube.com/watch?v=3n8q41DWhQk ) which I believe solves this problem. – Ajedi32 Feb 17 at 22:22
    
@Ajedi32 Interesting video, thanks for the link. That does improves the situation but you're still not going to have the resulting ship maneuvering like a jet fighter or even a troop transport though, the requirements are just so different. – Tim B Feb 17 at 22:31

Military commanders tend to be reluctant to deploy troops to areas from which they can't be recovered if things go wrong -- even paratroops landing behind enemy lines have lines of retreat mapped out as contingencies. So you can't in general deploy troops from space unless you can also recover them back into space. And that is a much harder problem -- it's certainly not feasible with contemporary technology, or anything we expect to develop this century.

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Any "Space Marine" style attack is pretty much a one way mission. – Qwerky Feb 18 at 11:36
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I agree with your premise but, disagree with your conclusion that "...you can't in general deploy troops from space unless you can also recover them back into space." That's like saying that you can't deploy forces into an area by parachute, unless you can also do an extraction by air. Forces may well be dropped into an area, then have to extract on foot or by other means. – Doug R. Feb 18 at 12:39
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Additionally in many eras dropping men in and letting them fight their way out would be perfectly acceptable. It's just in the last 50 years or so we've become more squeamish about such things. – Tim B Feb 18 at 19:10

I think that this method, if it becomes technically feasible, would only be used to insert very highly trained special forces type of teams behind enemy lines, and not for massive invasions, or assaults.

Reason 1: sending people to space is expensive.

It requires a lot of fuel. It requires some very expensive to build/maintain technology. It requires special training. Sending thousands of troops and their gear up there would be cripplingly expensive for any combination of countries you care to name.

Reason 2: too easy to defend against

If I'm the leader of a regime unfriendly to the one who runs this orbital platform, and I know that they are planning to drop 10 000 space marines on me I would make certain to either:

  • Target your orbital base with all sorts of weapons (such as launching a fake satellite which is actually full of missiles, or mines into orbit)

or

  • To invest very heavily in the sort of Anti-Air (AA) tech that will shoot your drop pods / orbital reentry vehicles out of the sky.

Most likely both.

Conclusion

Deploying your troops to the right area is actually the easiest part of this venture, and possible even using today's technology.

The problems are costs, and the fact that your base/reentry vehicles are very vulnerable

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*Sending people to space is expensive" - Damnable Guild – Azor-Ahai Feb 17 at 21:52

First question: Maneuver the reentry vehicle, not the station.

  • The reentry vehicle will be smaller, so it requires a lower total amount of fuel.
  • You can use aerodynamic control for part of the maneuvering. This is impossible if the station is supposed to stay in orbit.

Second question: Depending on the number of stations, an hour to several hours. This is faster than a global deployment with subsonic transport planes.

  • With a station in LEO, a global reach would require either lots of delta-V or a large number of separate stations. Then you take the one with the best position.
  • For reaction times, look at proposed designs for orbital bombardment systems. A soft landing will be slower, but not much.
  • Current airborne forces have to account for a delay because the troops don't sit in or next to their planes. The spaceborne forces can't be away on leave.

Third question: Not even remotely cost-effective with current technology.

  • "Space SEALs" are right out. The landing will be impossible to hide.

More comments:

  • Human health deteriorates in zero-G. The troops won't be fit when they arrive.
  • The space troops would have to go to orbit with all their gear and all their specialists. It will be difficult to add interpreters, drug-sniffing dogs, etc. on short notice.
  • Troops can be regionally based and trained, e.g. with the US CENTCOM for the Middle East and surrounding areas. A force in orbit would have to be global.
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As the other answers have pointed out, there is a huge cost in resources and energy to get stuff into orbit, and having the right supplies in orbit would be hard to plan for unless you had an orbiting city. However, getting things down from orbit is pretty straightforward, and the speed would be stunning, very probably overcoming most defenses.

If the station is in LEO, it will be orbiting Earth in 90-120 minutes. The reentry 'pod' could be launched at the optimal point in the station's orbit to put it in an orbit to come down on top of the target. When it nears the target, the pod could do a rapid deceleration descent, landing like the SpaceX rockets do. So, station's orbit is 90-120 minutes. If the target is under the station's orbit, there is very little adjustment needed for the pod's orbit. Assuming the pod has infinite orbit adjustment energy, the pod would need at most .25 orbit to reach the destination (15-20 minutes). Reentry from 7.8 km/s at a steady 4g's would take 200 seconds. So, in a worst case scenario, it would take 144 minutes to hit the ground, and in a best case (directly under the orbital path right now) it would take 4 minutes.

Targeting could land on a small target very easily. SpaceX and the Martian landers have shown how getting a rocket to a 100m landing area is very doable.

Defending against an object moving at ballistic speeds is really hard. AA systems would have a few minutes to detect the incoming pod, target, and fire at something travelling at 17,000 mph and decelerating at 87 mph per second. The landing pod would begin firing 780km away from the target and 200 seconds later would land. A precursor to the marines landing could be space rockets or bombs. They wouldn't need to worry about human survivability so they would not need to decelerate, just change directions. High explosive needles similar to bunker buster bombs could be released from the pod before or during reentry and would strike anywhere from 100 seconds (if released from pod as the pod starts decelerating) to immediately before the pod.

Decelerating faster than 4g would allow faster re-entry and greater surprise, but at some point tech to protect human passengers would be necessary. The space shuttle experienced 3g in descent, the Soyuz can reach 15g. Drones or weapons would be able to re-enter much faster, and would not necessarily need protection during re-entry, allowing more useable mass (1000kg landing pod that is a missile = 1000 kg of ordinance, drones with shielding might be 600kg of ordinance and 400kg shielding, 1000kg human pod might carry 4 humans, 300kg, plus 100kg of ordinance).

Compared to a space-deployed bomb, cluster-bomb, or drone, humans would be much more expensive and delicate.

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You don't drop straight down (technically nadir) from orbit, unless you have truly unlimited delta-v available. Instead, you alter your orbit such that it intersects the appreciable atmosphere, and then decelerate from there. Normally touchdown occurs approximately half an orbit after the deorbit burn, but the specifics depends on the exact velocity change, the newly resultant orbit and atmosphere involved. Compare How could a 90 m/s delta-v be enough to commit the space shuttle to landing? on Space Exploration. – Michael Kjörling Feb 18 at 14:08
    
You are correct, the trajectory would curve around the earth. The example you give of the space shuttle is that of the minimum power needed to successfully deorbit. They apply modest thrust for a short time to lower perigee exactly opposite the current location in orbit, then let gravity bring them in. A fully powered descent would be a much steeper curve. – user15741 Feb 18 at 15:06
    
Yes, like I said, the difference between what is technically possible and what is normally done. – Michael Kjörling Feb 18 at 15:07

Use nukes instead

No matter how the deployment is done, if this all happens on a single planet then sending couple infantrymen up to space and then down again takes more resources than building and sending down a nuke to the same spot. If you're averse to nukes, then even https://en.wikipedia.org/wiki/Kinetic_bombardment can do more damage as the same weight of soldiers during their (probably short) lifetime after being dropped this way with no symmetrical option for retreat. You could utterly destroy huge territories with less energy than you'd need to get a single infantry company up to space and down to a soft (nonfatal) landing - just aim a similar amount of missiles directly at the enemy instead of orbit.

Thus, for all missions that aim to destroy enemy personnel, facilities or equipment (in a major war, this means the vast majority of them) the cheap and efficient way would be to use high-tech weapons, and the rare and expensive approach would be to send a limited number troopers if you need to achieve some special goals - espionage, high-stakes sabotage of something that can't be bombed, capture and/or interrogation of very important people.

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Sometimes you want boots on the ground, if you want to take control of something with minimal collateral damage. – Dave Halsall Feb 18 at 12:49
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Pretty much any facilities, vehicles or equipment in the limited amount that, say, four men can capture and control is worth less than the resource cost of bringing four men to orbit. If that something has exceptional strategic, political or propaganda value, then you may want to infiltrate some special forces to capture that, but for anything that's just a valuable resource it would still be more efficient to just destroy it and rebuild it rather than avoid collateral damage but spend the enormous amount of supplies required to send stuff to space. – Peteris Feb 18 at 19:53

You've said near future, but then granted the space platform artificial gravity. That implies that in the near future, we get a much better grip on the nature of gravity and how to manipulate it.

With a low-energy consuming, solid state anti-gravity available, war becomes much more three dimensional. You wont just be fighting on the ground. You'll be fighting in the clouds and in low orbit.

The spectrum of options for offense and defense expand exponentially, lending a whole new definition to the idea of higher ground. If projectile weapons are still the norm, the warrior with a few miles of height advantage is safe while his enemy is not.

Your space platforms will be equivalent to modern day battleships or carriers. Their movement into orbit over an area will be not only a military tactic but also have political weight. With that in mind, subtlety is not part of the goal. When you finally deploy thousands of troops into descent over an enemy capital, you want them to burn through the sky like falling stars, their ablative armor glowing brilliantly as the swoop down upon a terrified enemy.

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Artificial gravity can be achieved by spinning. – Stig Hemmer Feb 18 at 8:53
    
@StigHemmer Well, yes and no. Yes in that the resultant force keeps you against the floor. No in that this is a centrifugal force, not gravitational. – Michael Kjörling Feb 18 at 14:14

In some science fiction it make more sense because troops arrived from other planet, so they need to get down somehow.

For Earth -> Earth in near future it is extremely expensive, not subtle but it is faster than deploying from home (Other answers cower this).

Speed wise - it can be faster or slower than predeployed troops, depends how close to target area troops are. But if you need to send them anywhere and can't have them everywhere it is faster.

Unsubtle approach is still problem. You can limit yourself to areas without AA and accept jumping on prepared enemy/to areas cleared by orbital bombardment (can solve part of AA problem too), or you can make it more subtle.

Instead of jumping from edge of space, use reentry vehicle capable of aerodynamic flight, enter somewhere else slow down to subsonic speed and fly to target area and perform normal paradrop. But such vehicle itself would be extremely expensive itself and bringing it to orbit even more.

Maybe ^^ could be modified by dropping in Star ship troopes-esque drop pods and gliding on squirrel suits. Against long range AA it would be same as dropping directly on target, but if enemy don't have it or its dealt with somehow (counter measures/bombardment) it can achieve tactical surprise (enemy knows you are coming, but don't know where, unless they know that THEY must be target).

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Very Feasible

The entire premise of SpaceX is that launch costs can be reduced by 10-100x by building reusable rockets (believe it or not, the fuel is actually a minor cost of rocket launches). We do not have artificial gravity space stations yet, but there are no obvious physical barriers to doing so (mostly engineering and cost barriers).

Why

The problem with jets is that we have a very mature set of weapons systems designed to defeat them, from SAMs to interceptor aircraft. And transports are almost never designed to be very fast, because they are almost always used after air superiority has been achieved. Rather, they are designed to be flexible, so they can deliver troops to inhospitable terrain (c.f. Osprey, Chinook, etc.).

Right now, the only weapons systems we have for anti-space defense are ICBM interceptor batteries, which are mostly untested and probably unreliable. Most tests of such systems fail to reach the target or fail to destroy the target. An orbital delivery vehicle would presumably be armored if there were credible defenses which could attack it. Combined with thrusters for evasive maneuvers, such a vehicle should be extremely hard to hit.

Where

If you look at the placement of AA defenses, they are situated on the borders of countries and around high-value targets. Space offers a border with the entire surface area of the country. You can't blanket all of China or Russia with AA batteries. But clearly, an orbital drop would be a good choice away from conventional AA defenses.

Who

Obviously, you wouldn't use an infantry drop to shoot a thug or blow up a building. You would use it for target extraction or minimal collateral damage or to reach targets which are hardened against other kinds of attacks (like deep underground facilities).

Logistics

In addition to having multiple space barracks, you could rotate your marines/Spec Ops teams so they don't spend too much time in space (where they are exposed to a lot more radiation than on the ground), say, every 3 months. And obviously, you would not just put average grunts in space. You would want highly trained fighters, at the least, and possibly your best troops, if that becomes the most effective way to deliver them to the battlefield in the future.

Limitations

Although an orbital drop lacks subtlety, what it gains is logistical speed. It would be easy to drop into an area which does not have ready defenders, and gain a significant time advantage against a less protected target. Of course, dropping into an area with a lot of defenders is probably a very poor strategy. Even then, the battlefield can be prepped via kinetic bombardment (though defeating air forces would be harder from space, unless you also have energy weapons).

If you consider how long it took to get F-16s on station on 9/11, it is easy to see how soft the interior of most countries is. That was just a few jets. Imagine trying to mobilize a squadron against an orbital drop. It would be very difficult to get them prepped and ready in time to meet the space marines, even if you knew where they were going to land 30 minutes in advance. And if they were snake eaters, then they could land well away from the intended target and infiltrate the countryside, making it extremely difficult to find them.

My guess is that space will be militarized with marines just as soon as countries can afford it and have a good reason to do so.

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Stationing infantry in space

  • As has already been pointed it would be very expensive.

  • The vehicle to get them back to earth would be very easy to shoot down, due to the issues of re-entry that Tim B explained.

  • The troops will not be able to exit back to space, so will be on a one way mission or have another exit route planned.

  • The R&D costs will be very high.

Supersonic “transport” aircraft

  • Given the same R&D spending, I expect that a supersonic “transport” aircraft that is deployable from an aircraft carrier would be cheaper to developer.
  • I expect that operating a few aircraft carriers along with supersonic “transport” aircraft would be a lot cheaper then basing the troops in space.
  • To get a response time of a few hours to anywhere in the world not need many such setups.
  • As the mission is one way or has anther exit route, parachutes can be used to get the troops from the supersonic “transport” to the ground.
  • I also expect that entry vehicle could be lunched from the supersonic “transport” aircraft if that was considered to give an advantage.

So for must less cost than deploying infantry from space, you can set a system that gives all of the advantages with less problems, along with the world wide quick deployment.

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Getting down from orbit is not about the distance - it is just 100 - 200 km high. It is about slowing down from orbital speed of about 8 km per second which is about 28 times the speed of sound.

In obligatory XKCD explainer space is not far - space is FAST.

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The ISS orbits at 400 km high. Problem is, in order to stay in orbit you have to really fast, so the time required to land is really the time required to break to survivable speeds. This is done with air breaking because it's the only cost effective option. It takes a lot of time. The IIS moves at 7.66 km/s.

Next problem is that the space marines are zipping around the earth in orbit. Making a considerable change to a given orbit takes time, so If you orbit the equator you may need to add a few extra hours depending on where you want to deploy.

At an ISS-like orbit, it takes them 90 minutes to go around the earth once, so if you need rapid deployment and you just missed the window, you now have to wait 90 minutes.

All in all, even with 4 or 5 different space barracks, your average response time would be somewhere around 2 hours.

Compare this with a supersonic delivery system, lets say something based on blackbird technology (3500km/h). If we include acceleration and deceleration, it should easily beat response times of orbital drops anywhere within 3000 km of its base. And the response time is predictable, because it's based on distance, while the space marines zipping along in orbit really make timing difficult for everyone else. Military Commanders always prefer predictable, because there are already more than enough other unpredictables they have to deal with.

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It's been mentioned a couple times, but I think that the use of hypersonic transport planes would be more viable than deploying troops from a space station. The space station itself would make a decent platform for kinetic bombardment, but a major problem is that as soon as one country developed a militarized space platform and a way to put soldiers in it consistently, every single country with the capabilities to do so would immediately begin working on how to shoot that platform down. It also would be difficult to counter new anti-space platform threats because the space station is in space and thus it would be (possibly prohibitively) expensive to upgrade a station's offensive and defensive capabilities. It's also worth noting that international organizations such as the U.N., as well as geopolitical rivals, would fiercely denounce such a space station. In extreme cases, a nation may even go to war preventatively to avoid being permanently outmatched when the space station is armed and fully operational...

Recently, the U.S. military tested an unmanned aircraft that flew at Mach 20 ( 15,345.3 mph) for three minutes in a stable and controlled manner. Major military powers around the world are also placing some focus on developing hypersonic missiles, so we see that already, the use of hypersonic speeds for military purposes is gaining momentum.

Fast forward a few decades, and it's conceivable that we will have developed some kind of effective hypersonic aircraft for military purposes. Put an advanced targeting system, an electronic warfare suite, a railgun, a laser, and maybe a couple missiles on it, and then stuff a platoon or a light infantry company into the cargo bay, and a Mach 20-capable aircraft (or greater) could cover the circumference of the earth and deploy its human cargo via parachutes, pods, whatever your imagination can come up with, very quickly. Hypersonic military aircraft would likely be significantly less destabilizing to the international order than a space station that poses significant threats to other nations.

You could also time your orbital space station to launch a kinetic bombardment on a target that impacts very shortly before the airborne soldiers leave their hypersonic ship, which would likely destroy and/or scare the crap out of any military force present.

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