Comments on Rocketpunk Manifesto: Space Warfare I - The Gravity Well

Excellent topic. Very thought provoking. I'd...

2011-08-11T22:52:06.169-07:00

Excellent topic. Very thought provoking. I'd just like to add to Turbo10k's submarine comments:

>I don't think submarines with weaponry to rival that of ground installations feasable.

Cold War era boomers could lurk underwater for 4 months or more (more would be less comfortable for the crew, but potentially feasable in wartime). They could throw enough SLBMs to deliver 200 to 300 warheads each.

Yeah, you could build a bigger, more vulnerable ground installation, but just the two top classes, the Ohios and Typhoons alone, held enough power to throw around 6000 warheads before they needed to reload. And they had stealth and the ability to put a couple hundred meters of ocean between them and an incoming strike. They largely eclipsed the ICBM silos by being potent, mobile, and stealthy.

>Furthermore, a ship in orbit can always parachute a torpedo down to the surface, and hunt the sub in its own element.

Modern torpedos have a fairly short range and aren't that much faster than modern subs (for example, the difference between 40 knots vs 32). ASW helicopters need to get pretty much right over a sub to have a chance of hitting it with a torpedo. You'd have to have incredibly good targeting info and would probably need an insider on the sub feeding you their course and speed in order to threaten subs with torps from space.

Welcome to the comment threads! (A belated welcome...

2011-06-28T11:41:43.370-07:00

Welcome to the comment threads! (A belated welcome for a couple of you!)

The underlying problem with tactical nukes is that once you cross the nuclear threshold you invite retaliation in kind, and it is by no means a sure thing that even interplanetary distances rule out 'strategic' retaliatory strikes.

Martin - by 'the rule' you mean Moore's Law? It will probably not scale indefinitely. That said, we'll probably see growing use of drones in warfare. See Space Warfare XIII: The Human Factor for a discussion with extended comments!

Considering that according to whatever the name of...

2011-06-28T10:02:13.745-07:00

Considering that according to whatever the name of that rule, that a PC will be 13 trillion times smarter than a human in 2100, and that space wars will not be reality until we live both on Earth and on Mars.

Will it not be possible to boost some thousands jet fighter sized smart drones across the solar system, let them survey the planet from high orbit, and enter into the atmosphere, find their targets, and take em out, with no loss of human life on the attackers side? No need of a starship, just a big or several small boosters for the drones.

i no this thread i dead but: like Daniel said it ...

2011-05-02T16:29:32.435-07:00

i no this thread i dead but:

like Daniel said it seems much more sensible to take out enemy infrastructure and production facilities and other soft targets with tactical nukes and Thors and Odins. the ability to penetrate bunkers is not an issue as hey would all be soft targets.
it could then be possible just to wait it out. the planets defenses would collapse through lack of supply, the break down of order among the general population ad even possibly the collapse of the planets government. Pre-infiltrated commandos could possibly add to the chaos.

Sorry to double post, but just found an interestin...

2010-12-04T11:08:23.869-08:00

Sorry to double post, but just found an interesting concept in terms of defeating armor. (obligatory Atomic Rockets link): http://www.projectrho.com/rocket/spacegunconvent.php#Nukes_In_Space~Nuclear_Shaped_Charges
With these, nuclear weaponry would probably be wider used, as smaller warheads could be used with less fallout. I also suspect that tandem charges would show up at some point.

Yay for thread necrothurgy! Railguns: how many sh...

2010-12-04T10:53:59.006-08:00

Yay for thread necrothurgy!

Railguns: how many shots would they get? Everything I've read about current attempts says that barrels are only good for a couple of shots. That doesn't sound like something that could be put aboard something autonomous.

Anyway, attacking a planet from orbit. Everybody seems to be concentrating on hitting bunkers and the comparable costs. Why not just hit the economy? Hit the stockpiles of ready-made materials, factories that make the material, road and rail leading to both bunkers and said places, and earth mover concentrations; in other words, the strategic bombing of world war 2 writ large. Reflecting the differences in economy, I'd also drop something big into bodies of water with oil rigs.

To minimize casualties, the fleet can separate into an autonomous ammunition dispenser part and a manned C&C in higher orbit. Given that the autonomous part doesn't need to remain alive after the initial salvo, it doesn't have to be that much more expensive than the ammunition it carries. All it would need to do would be spread a system of spy, kinetic launcher, and decoy satellites around the planet.

If I sends a fleet that takes out your ability to reconstruct for the same cost as the bunkers the you used to kill it, I still have shipyards to make another fleet. I just cost you not only the cost to replace everything just destroyed, but also the wealth that could have been made by the targets during the period when they don't have a replacement.

For less collateral, I think something can be done with fighters. Not Hollywood's image of semi-streamlined airplanes, but jets with a disposable heat shield. They probably wouldn't need to be manned. Just some basic AI for navigation and collision/munitions avoidance, with a pilot in high orbit for the trigger. That way we get to bring in point-blank toys like bunker-busters and HARMs under the radar. To be reusable, drop a tanker with a large booster either with them or right before they need to leave.

We all here 'ships' and think maritime models. Maybe we should head back to the Air Force model.

Part 3 Enough replying to the others. My own voic...

2010-07-28T15:44:20.596-07:00

Part 3

Enough replying to the others. My own voice now;

What if...it wasn't the whole planet the attacking fleet is fighting? Several nations on the surface, some friendly, others hostile? Not so much a 'balkanised earth' setting than today's map, or even simpler, US vs USSR or somethink like than.

If you keep that in mind, then you can forget half of the defender's options. Can't run away indefinitely, can't build launchers and guns over the planet, can't always have access to mountain-tops or favourable ground, and now you got an ally that negates ground/air supremacy of the defender in ways Space Marines (R) and Aerospatial fighters can never do.

It alse makes things more complicated. Attackers would have to avoid commercial/allied orbits, and can't send down raining hell for fear of hitting friendlies. Defenders would have to identify targets before ingaging in 'Fast responce' maneouvers. Even worse, it now has to deal with fighters, armies and navies from neighbouring countries. Mix in ambiguity about who's targeting who with nuclear missiles and nations switching sides and you'll get strategic headaches to no end.

Food for thought!
:))

Part 2 Rick: Subs are great, yep. However, depth ...

2010-07-28T15:32:32.944-07:00

Part 2

Rick: Subs are great, yep. However, depth pressure constraints have reduced submarines mostly to the size we find them today ie cylindrical, length/radius ratio not too large or small, ballast tanks proportionate to density....
All the above creates a situation where supermassive submarines would be very slow , turn even slower, and surface/dive with difficulty. In other words, I don't think submarines with weaponry to rival that of ground installations feastable.

<>

Except that they don't pop up, steel ain't THAT strong a material. Furthermore, a ship in orbit can always parachute a torpedo down to the surface, and hunt the sub in its own element.

Hope my first post is up to standard!

P.S. 1: I think the latest metrological satellites can detect underwater mountains and elevations by measuring how the surface rises relative o the rest of the area. A 'congregation' of submarines in calm weather could be detected by this method by superfine sensors...

P.S. 2: I think of my lasers as very large, very expensive and very heavy things. More 'jet engines with a mirror at the end' than clinical 'zap, your dead as many times as I want' view of them. Otherwise my second argument (use by planetary defence vs LO ships) for railgun/coilguns is void.

Part 1 W00t Thread revival FTW! I'm new here...

2010-07-28T15:31:53.564-07:00

Part 1

W00t Thread revival FTW!

I'm new here, and after doing quite a bit of reading (Whole Atomic Rocket site, the Space fighter threads (whole two years of them) and this...), I think I can join in.

My thing to say;

Byron: I believe the Railgun/Coilgun launch concept works only in two situations. First would be deccelerating a Thor rod from orbit without a long, highly visible flare. Angled, it can even give quite a kickstart to the rod, reducing the altitude it has to be launched from.
Advantages: -Lower altitude launch
-No visible flares, except after heat sink is cooled down (quite a delay in my opinion for laser-equipped warships)
-Only uses a fraction of *limitless* power supply a nuclear generator makes

Disadvantages: -Uses up heat sink, not good if has to be saved for laser point-defence.
-Low penetration. After launch, speeds only increase until the lower atmosphere. Might prove problematic with rods melting due to friction before hitting the ground.

The second situation would be planetary defences trying to hit low-orbit ships VERY quickly. Especially combined with air-launch or mountain-top defences.
Advantages: -You could get a projectile 'up there' much faster than a rocket.
-Launches would be hard to detect, and projectiles cannot be stopped by point defence.
-Does not have to worry about power loss as lasers do (given enough initial speed that is)

Disadvantages:-Just like lasers, is only useable until the gun is found, unlike for mobile missile launchers.
-Slower than lasers.
-Cannot be course-corrected.

I hope I haven't made any gross inconsistencies yet :P

W00t Thread revival FTW! I'm new here, and af...

2010-07-28T15:30:52.138-07:00

W00t Thread revival FTW!

I'm new here, and after doing quite a bit of reading (Whole Atomic Rocket site, the Space fighter threads (whole two years of them) and this...), I think I can join in.

My thing to say;

Byron: I believe the Railgun/Coilgun launch concept works only in two situations. First would be deccelerating a Thor rod from orbit without a long, highly visible flare. Angled, it can even give quite a kickstart to the rod, reducing the altitude it has to be launched from.
Advantages: -Lower altitude launch
-No visible flares, except after heat sink is cooled down (quite a delay in my opinion for laser-equipped warships)
-Only uses a fraction of *limitless* power supply a nuclear generator makes

Disadvantages: -Uses up heat sink, not good if has to be saved for laser point-defence.
-Low penetration. After launch, speeds only increase until the lower atmosphere. Might prove problematic with rods melting due to friction before hitting the ground.

The second situation would be planetary defences trying to hit low-orbit ships VERY quickly. Especially combined with air-launch or mountain-top defences.
Advantages: -You could get a projectile 'up there' much faster than a rocket.
-Launches would be hard to detect, and projectiles cannot be stopped by point defence.
-Does not have to worry about power loss as lasers do (given enough initial speed that is)

Disadvantages:-Just like lasers, is only useable until the gun is found, unlike for mobile missile launchers.
-Slower than lasers.
-Cannot be course-corrected.

I hope I haven't made any gross inconsistencies yet :P

Rick: Subs are great, yep. However, depth pressure constraints have reduced submarines mostly to the size we find them today ie cylindrical, length/radius ratio not too large or small, ballast tanks proportionate to density....
All the above creates a situation where supermassive submarines would be very slow , turn even slower, and surface/dive with difficulty. In other words, I don't think submarines with weaponry to rival that of ground installations feastable.

<>

Except that they don't pop up, steel ain't THAT strong a material. Furthermore, a ship in orbit can always parachute a torpedo down to the surface, and hunt the sub in its own element.

Hope my first post is up to standard!

P.S. 1: I think the latest metrological satellites can detect underwater mountains and elevations by measuring how the surface rises relative o the rest of the area. A 'congregation' of submarines in calm weather could be detected by this method by superfine sensors...

P.S. 2: I think of my lasers as very large, very expensive and very heavy things. More 'jet engines with a mirror at the end' than clinical 'zap, your dead as many times as I want' view of them. Otherwise my second argument (use by planetary defence vs LO ships) for railgun/coilguns is void.

What about using kenetic weapons launched by coil/...

2010-03-19T11:52:07.990-07:00

What about using kenetic weapons launched by coil/railguns. I know that the atmosphere has usually been seen as the problem with that, but I did some rough calculations and to launch something up 100 km, not counting air resistance, would only take Mach 4 from sea level. That would run into air resistance, but if you launched from either a mountain or some sort of balloon it could work without the thermal flare of a missile launch.
Also, why does a laser only have to have one mirror? I know that there is a discussion on atomic rocket of a ship with one generator and multiple mirrors, so why not do the same with ground defenses?

Welcome to the discussion boards! Submarines defi...

2010-02-14T15:15:13.304-08:00

Welcome to the discussion boards!

Submarines definitely have potential as a planetary defense weapon, for the reasons you give. A full circle of sorts, since early naval submarines were regarded as largely a coast defense weapon.

Submarines got mentioned a bit but I suspect are u...

2010-02-13T13:24:44.918-08:00

Submarines got mentioned a bit but I suspect are underrated. More expensive and smaller than bunkers, but both mobile and somewhat stealthy. Can pop up to fire missiles -- or a laser!, with ocean as nice heat sink compared to a spaceship -- then submerge and move away from orbital response. And have meters or hundreds of meters of water as shielding against a fast response.

Concentration of force got mentioned; it was rebutted by noting orbital can't actually orbit well, except in geosync or Molniya (high elliptical) orbits, but space forces can still share orbit and rain down fire in a pass. Bunkers can't move, but submarines could congregate, if there's a reason.

Then there might be submersible 'bunkers', much larger, that don't move fast laterally but can pop up for heavy fire then submerge again.

I like seeing old posts show life! After all, the ...

2009-08-20T18:08:09.177-07:00

I like seeing old posts show life! After all, the space fighters post is still going strong after two years.

Kinetic bombardment of planets strikes me as one of those generally overrated things, where conceptual coolness trumps practicality. The Sandia people have (shock!) a good point that uber-fast impacts turn any impactor into a fluid, and its kinetic energy gets transferred quickly.

Note that 1 km/s is near the muzzle velocity of conventional artillery.

I hate to keep resurrecting ancient threads, Rick,...

2009-08-20T12:45:41.420-07:00

I hate to keep resurrecting ancient threads, Rick, but this stuff is just so much fun, and I kind of came to the party late.

I think the case for Rods from God is not nearly as open and shut as lots of people are thinking. Sandia actually did quite a bit of examination on the topic- granted, for the modern era, and not for whatever shiny fusion powered future we are conjecturing about, but all the same, their analysis was not terribly rosy.

First (not a notion raised by Sandia, but I thought of it) most of the references to kinetic impactors speak of releasing them, when in truth, you need to deorbit them, or in the classical Pournelle scheme, cancel all orbital motion so they simply fall- a maneuver that takes a rather substantial burn that can be observed.

Second (and this point is raised by Sandia) the super high energy impactors will take forever to get there. A fall from a sufficient height to deliver one rick of damage is 460km, with a fall time of 12 minutes- insufficient warning to move out of the way of a nuclear blast, but if all you have to dodge is a conventional equivalent bomb, its fine. A fall from geosync altitude delivers ten ricks, but also takes six hours- with the deorbit/orbit cancelling manuever making a big observable exhaust, and six hours to look, I doubt any asset that could conceivable be moved would be in the same county.

The last issue is penetration. Sandia did penetration tests with long rods of all different materials (the stronger the better) and their conclusion was that maximum penetration occurs at 1km/s. Beyond that, you simply can't make a penetrator strong enough to not functionally liquify at impact and thus dump all its energy into the uppermost layers of the target. Of course, at 1km/s, the altitude it can be dropped from is much lower and the warning time and booster exhaust plume associated with deorbit are much smaller-but at that speed the projectile deal 1/9th of a rick in damage-not so thrilling, and probably in need of a real warhead.

So, in conclusion:

TNT-equivalent impactors have a long enough warning time to conceivably scoot something mobile. Conceivably being the operative word- it's the the same sort of destructive energies, detection possibilites and response times we associate with strike aircraft, which sometimes make the mark and sometimes don't.

Two, geosync level rods provide nice intermediate levels of destructive force between nukes and bombs-but with their cripplingly long response time and low penetration, they can really only threaten fixed surface targets- certainly a big category, but most things that shoot, also move. It just changes the nature of the battlespace.

Third, kinetic rods are in no way a panacea against deeply buried targets- far from it. If you want to take out bunkers, you are dropping the rods from very low, and they are packed with explosives.

The situation involves aliens who think that th...

2009-06-16T06:37:37.054-07:00
The situation involves aliens who think that there is room for only one intelligent species in the universe

There's some harrowing commentary on this at the Atomic Rockets site that I'm gonna have to take up at some point.

As for using the oceans and icecaps as heat sinks, those must be whomping powerful weapons! And a scenario where global warming is distinctly the lesser of evils ....

Coming in late to this discussion, but I though I ...

2009-06-15T22:14:45.965-07:00
Coming in late to this discussion, but I though I should mention the space battles in _Antares Dawn_ by Michael McCollum. He seems to have though of most of these points when he wrote the book in the 1980s.

The situation involves aliens who think that there is room for only one intelligent species in the universe & immediately start trying to exterminate humanity one contact is made. FTL in this ficton is similar to the Alderson drive in _The Mote in Gods Eye_.

The battle involves an attacking force getting some ships through the jump point defences & the defenders using lancer tactics to destroy some of the incoming fleet so planet based defences can take out the rest.

The planet based defences use oceans & ice caps as heat sinks for their massively energetic weapons.

This thread is pretty outrageous! It's the mos...

2009-06-14T20:33:07.962-07:00
This thread is pretty outrageous! It's the most replies I've had on this blog, and heavyweight replies to boot, stuff that makes my brain explode.

Your summary of the scenario is correct, but Thors are potentially cheap, just big spikes. A couple of transports could carry a lot of them. Probably they're not quite so cheap in practice, since they need some kind of precision guidance to hit point targets.

I ignored orbital defenses for this discussion; though part of a planetary defense their tactical role falls under 'space battles.' And you might want your costly space forces taking the war to the enemy, not in defensive orbits!

The general argument of this post is not that 'planets are invulnerable' - they aren't - but that surface-based defenses are more formidable than commonly imagined, and pose space forces with challenges not unlike those naval forces have historically faced against coast defenses.

Ok,first: I'm amazed that this is post is stil...

2009-06-14T17:29:06.256-07:00
Ok,first: I'm amazed that this is post is still getting replies. Second, let me see if I've understood correctly what we're talking about: We have a planet that's being assaulted by an enemy spacefleet; the planet has many defensive bases capable of orbital defense as well as many moble units of various types also capable of defense of LEO and upper atmosphere. The spacefleet has point-defense weapons(lasers) and Thor type ground attack weapons.

Now, how does the spacefleet replenish it's stock of Thors? Does it mine asteroids, do supply ships shuttle back and forth beteween their base and the fleet, or do the attacking spacecraft periodically withdraw to resupply? Because, let's face it; the planet defense bases can each have many times the spares/supplies/weapons/ammo than the entire enemy fleet combined.

Another question would be; what kind of orbital-based defenses do they have and how quickly/easily can the planet replace them?

If the attacking spacefleet can't defete the space defenses of the planet pretty quickly, then they will be forced to withdraw, simply so they can refit.
Ferrell

Mark - Very good point about orbital decoys. The s...

2009-06-14T16:04:09.453-07:00
Mark - Very good point about orbital decoys. The standard rap on decoys (at least in the haunts of SFConsim-l) is that they can't maneuver without giving themselves away. But forces in orbit don't necessarily HAVE to maneuver, and until/unless they do they are not so easily distinguished from decoys (or general clutter).

Which somewhat anticipates an upcoming post!

Sundog - On one level this is one of the most basic military realities: If you come to the party with enough toys, I can break a lot of them and you'll still take my cake.

But there are two different cases to consider. If really long range ground based zappers are available, they will scrag ships even in high orbit. If they are not available, I'll concede high orbit, and defend low orbit with mobile based SOMs. Which are hard for kinetics launched from high orbit to take out, since they can move during the kinetics' flight time. (And in the case of truck launched SOMs, the trucks are low value targets once they've launched their shots.)

All of this is dealing with tactical combat. You have the option of falling back on strategic targeting of my supply chain. Here a completely different dynamic comes into play. My gut feeling is that soft area targets are extremely vulnerable to attack from space, to the point that MAD rules apply. This requires that I have a space based deterrent, but it does not have to have much tactical fighting power.

Okay, I think we can reasonably state that, with a...

2009-06-14T14:40:25.366-07:00
Okay, I think we can reasonably state that, with assistance from point defence systems and mobile launchers, a system of well-emplaced planetary defence centers (PDCs) can stop an invasion force from taking low orbit and fight for a considerable time against high orbit opponents.

However, I think the final word is going to be with the orbitals. Thor shots can be stopped, one way or another, but can you stop the orbitals from upscaling?

After a relatively short period of the siege, they're going to get a pretty good idea of where the PDCs are. At this point they pull out Thor's big brother - in keeping with the theme, let's call it Odin.

Odin is just Thor writ large. Where Thor shots might come in at a quarter tonne, Odin shots weigh in at 20 Tonnes. And Odin is not a slim, precise rod of metal - it's just a solid ball. Drop half a dozen of these on each PDC - remember, all you need to do is kill that big E-Weapon and the PDC is just another bunker for your ground troops to worry about.

The sad thing is, the orbital side can keep on "raising the stakes" like this as long as they like, up to the point where they are doing significant climatological damage (or even after - if they're careful, the climate damage can inconvenience and demoralize the planet owners, but still clear up in a few decades). Big Bunkers are just big targets.

Decoys might be useful in an orbital "blockad...

2009-06-14T11:20:49.108-07:00
Decoys might be useful in an orbital "blockade" (keeping with the nautical terminology) you won't fool anyone into thinking they are spacecraft, but if you flood LEO with cheap inflatable decoys it will probably create enough clutter to hide a constellation of spy satellites (especially if they are also inflatable), and if they shoot down the decoys then every SOM they use isn't killing something important, and if they use lasers that's wear and tear for every shot (and each decoy would require a shot instead of putting shrapnel in LEO to scrape it clean like you could with a SOM)
-Mark

Both of these points sound valid, though for desta...

2009-06-13T12:21:06.394-07:00
Both of these points sound valid, though for destabilizing a Thor it may not be necessary to tumble it directly, just create an asymmetrical airflow. (In which case the higher you do it, the more time for it to tumble.)

Another question for Thors is the nature of the targets. If the defense is mobile missiles, or 'guns' of whatever sort that are light enough to be mobile, there may not be many tactical targets to shoot at except by lasers that have no delay.

Et All- as far as I can tell, if a relitively smal...

2009-06-13T11:06:55.010-07:00
Et All- as far as I can tell, if a relitively small force is applied asymetically (i.e. hits it off-center), it will disrupt the Thor and cause it to tumble and explode; however, this asysmetircal force is differnt at different altitudes and entry speeds as well as the mass of the weapon. So, a hand grenade-sized explosive going off slightly to one side might be enough to cause the distruction of the Thor projectile, it greatly depends on where in the reentry track the weapon is.

Because ground based instillations have greater redundency than a spacecraft, the builders of the spacecraft must either choose the absolute best weapon for a very narrowly defined mission, or the best-all-around-weapon for a much more broadly defined mission or range of missions. The Thor, I think, falls into the latter. The real question comes down to: will the percentage of individual weapons that get through the defenses do enough damage to accomplsh the mission? Unfortunately, that question probably can only be answered by actual combat and probably will, sometime in the future.
Ferrell

Ian - last point first, agree that these defensive...

2009-06-12T17:50:12.432-07:00
Ian - last point first, agree that these defensive systems are not mutually exclusive!

Impact explosives could be a nice options, though they actually won't add much more energy than the impact itself, which releases several times the energy per unit mass of TNT.

Tumbling the Thor is exactly my objective. Sophisticated calculations are way above my skill level, but here is my basic take, from pretty much high school physics:

Thors, except for jumbo ones (in the tons), have to be long and slender to minimize their cross section so that they don't shed their speed = kinetic energy by punching through the atmosphere.

A column of air 10 cm in diameter extending up through the atmosphere has a mass of about 80 kg, and a Thor with a diameter of 10 cm has to push this air aside, so to speak. To first approximation, the air is slapped aside at roughly the speed that the Thor hits it - so if the Thor also weighs 80 kg it will transfer much of its energy to the air, and by the time it hits the ground it will be a 'spent bullet,' with a much lower impact speed and thus much less kinetic energy and penetrating power. A sphere 10 cm in diameter, even of dense stuff, would only weigh about 10 kg.

A long slender rod with a sharp nose means more mass per cm of cross section AND the air does not get pushed aside as fast, so less energy is lost. (This is a REALLY crude model, but you get the idea.)

But at supersonic and especially hypersonic speeds most of the decelerating force acts near the nose, so the Thor is doing a dynamic balancing act; if knocked slightly off true it will tend to tumble. And if it tumbles, its cross section is larger, and the decerating forces are greater.

This is what did it for the shuttle Columbia. I believe it was killed not directly by heat getting inside, but by unbalanced aerodynamic forces. So long as the tumbling forces were small enough to be counterbalanced by the attitude jets its reentry remained controlled, but once the attitude jets were overpowered it tumbled and almost immediately broke up.

A solid Thor is vastly stronger, but the lower atmosphere is 4000 (!) times denser than at 60 km where the Columbia broke up. Also a fair amount of the energy lost to deceleration is converted into heat. So if a Thor tumbles it is subjected to enormous stresses and heating.

The devils are in the details, AKA the specific numbers and dynamics, but I suspect that a Thor that tumbles will break up and explode in the air. At minimum it will hit a lot slower, and with a lot less penetrating power due to greater impact cross section as well as lower speed. The key question is how much disruption of air flow is needed to tumble it. Which this crude modeling doesn't answer at all.