
The U.S., Russia, and China Prepare for Satellite Warfare - Parbeyjr
https://edgylabs.com/2016/12/01/us-russia-china-satellite-warfare/
======
partycoder
This started a long long time ago.

Positioning satellites are likely targets of a satellite war. There was a
strong emphasis to have the European satellite positioning system (Galileo) to
use different frequencies than GPS (e.g: so they could be jammed without side
effects on each other). GPS jammers have been a thing for a while too.

Then, spy satellites get occasionally targeted by light beams so they cannot
take pictures.

Then, both China and the US have destroyed decommissioned satellites with
missiles. When China did it, they were denounced publicly for increasing the
amount of space debris.

So naturally satellite-on-satellite fun was naturally going to be a thing.

A predicted satellite weapon system are rods of tungsten (or whatever) dropped
from space as a mean of very powerful kinetic bombardment... something that
has received the name of "rod of god". Can cause large damage without side
effects (e.g: radiation, public outcry).

Rods of god however have a prohibitive cost due to the cost of lifting objects
to orbit. Eventually the first superpower to get their hands in a space
elevator will fill space with rods of god. Space elevators however would need
some shielding to pass through the nasty Van Allen belt radiation, since space
elevators are slower than rockets exposing the payload to radiation for longer
periods of time.

~~~
gozur88
The big problem with Rods of God isn't cost. We just spent $10bn on a carrier,
after all. The real problem is it's destabilizing - potential adversaries have
to consider the very short time frame of that kind of attack and adjust their
defensive posture accordingly, i.e. shoot-on-warning.

~~~
credit_guy
The bigger problem with Rods of God is that they just wouldn't work.

There are several reasons, let's take them one by one.

1\. Kinetic energy is not that high compared to chemical energy, and is
completely negligible compared to nuclear energy. For a kinetic(non-explosive)
projectile to deliver the energy of its mass equivalent in TNT, it needs to
travel at about 2.9km/s, or Mach 8.5. In other words, a rod weighing one ton
hitting a target at 2.9km/s delivers a destructive energy equivalent to one
ton of TNT. Since kinetic energy goes up with the square of the speed, such a
rod traveling at the first orbital speed, 7km/s, would have a yield of about
5.8 tons TNT equivalent. For comparison, the largest non-nuclear bomb used in
WW2 was the Grand Slam, with a yield of 6.5t TNT equiv, and the Hiroshima bomb
had a yield of about 15000t TNT equiv.

2\. Losses due to atmospheric drag. An orbital body can't magically hit the
ground with its full orbital speed. It will lose a lot of its energy to air
drag. The wikipedia page on the "Rods of God" [1] mentions a 2003 US Air Force
study where the terminal velocity of these rods was Mach 10. That's only
slightly higher than the Mach 8.5 I mentioned above, so the final conclusion
was a bit underwhelming: "the practical applications of such a system are
limited to those situations where its other characteristics provide a clear
and decisive advantage—a conventional bomb/warhead of similar weight to the
tungsten rod, delivered by conventional means, provides similar destructive
capability and is far more practical and cost effective."

3\. You can't simply drop something from orbit. A fun little experiment is
this: you are a cosmonaut doing an EVA (extra-vehicular activity) and just for
the fun of it you throw a small object towards Earth, at about 10m/s. What
happens to the object? The cosmonaut's name was Leonov, who told the story to
V.V. Beletskiy, who did the math, and the story is told beautifully by V.I.
Arnold in [2]. The object goes initially towards Earth, but then starts
turning, and does a full ellipse, and meets again the space station about 1.5
hour later, coming from above (well, technically it doesn't meet it, it has a
deviation of a few dozen meters). The moral of this story is that you need
some sort of launching mechanism to make the rod leave the satellite and go
towards its target, maybe a rocket or some sort of a gun. If you want to
deorbit something in the optimal way, you use a Hohmann transfer; I did a back
of the envelope calculation and the propellant mass needed to deorbit is a bit
less than 10% of the mass of the projectile. However, with a Hohmann transfer
we are talking about more than an hour from the start of the strike to hitting
the target. If you want to achieve minutes, you need to pay a price. I don't
know how to do this calculation, maybe a KSP aficionado can help here, but it
would not surprise me if the propellant ratio shot up to 30%. On top of that
you need propellant to maintain the altitude of the satellite over the years.
This adds mass and complexity to the satellite. Let's say you want to have a
bundle of 20 Rods of Gods up there, 10t each. You get 200t, and then you add
propellant, rocket engines, solar panels, etc, etc, I can't imagine you get
away with less than 400t. For comparison the current mass of the ISS (the
biggest satellite every built) is 370t and that cost so far $150BN.

[1]
[https://en.wikipedia.org/wiki/Kinetic_bombardment](https://en.wikipedia.org/wiki/Kinetic_bombardment)
[2] [https://www.amazon.com/Mathematical-Understanding-Nature-
Phe...](https://www.amazon.com/Mathematical-Understanding-Nature-Phenomena-
Mathematicians/dp/1470417014)

~~~
gozur88
A reasonable impact speed for a Rod would be more than mach 20. That's what we
get out of ICBMs today. And that's including atmospheric drag.

As far as dropping something from orbit, the concept was each rod would have a
tiny booster and be in its orbit. You'd put a few dozen (or a few hundred) in
polar orbits, and that way you'd always have one lined up.

The equation you're looking for in your third point is this one:

[https://en.wikipedia.org/wiki/Vis-
viva_equation](https://en.wikipedia.org/wiki/Vis-viva_equation)

Exactly how long it would take for the Rod to arrive on target depends on how
much control authority you have at hypersonic speeds. Not really sure what's
possible there.

~~~
credit_guy
A Rod at Mach 20 only has four times the energy of a Rod at Mach 10. Not
really a game changer (in my first point I used 7km/s which is Mach 20.6).

The vis-viva equation doesn't change what I was saying in my third point. I
didn't know about it, thanks for pointing to it, but implicitly I applied it.
I found a Hohmann calculator online, and I got that the delta v for going from
a 400km orbit to a 100km orbit is about 175m/s. I plugged that in the rocket
equation assuming a decent solid propellant (APCP used in the retrorockets of
the descent stage of NASA's Curiosity and Spirit, for example, an application
similar to the retrorocket needed here) and I got a propellant fraction of
6.7%. Now, at 400km you still have atmospheric drag, and you need a delta v of
about 25m/s per year to maintain your orbit. If you want to go to 600km, you
pay a price in the deorbiting delta v. At any rate, let's say the optimal
poster that brings you down from space is between 5 and 10% of the mass of the
Rod. We can agree to tall this "tiny". But this will need at least a
revolution around the Earth (at 7km/s that's more than 95 min). The fact that
you have plenty of Rods all over the place doesn't help you. A perfectly place
Rod will still take 95 min to get from LEO to surface.

If you want to hit the atmosphere in minutes instead of 1.5 hours, you need to
pay a price in delta v, but you don't have a problem with the control at
hypersonic speeds - we are still in vacuum. Once you hit the atmosphere you
need control to hit the target, not to get to the target faster.

Now let's see what happens if you put a few dozen or hundred in space. What
can you do with a single Rod? Sure, you can destroy a civilian building, and
that could be a skyscraper and you kill a few thousand civilians. I don't
think either the US or Russia would adopt such a strategy (North Korea maybe).
But in terms of military targets, what good are these? Remember, they are tiny
in comparison with nuclear weapons. You can't destroy nuclear bunkers, you
can't acquire mobile targets.

If someone could solve the mobile target acquisition problem, these would be
really good at killing tanks and armored vehicles. This could be useful, but
this is hardly the application the alarmists on the internet have in mind. The
typical perceived threat is some type of decapitation strike (alluded by the
comment I was answering to). This simply is far from realistic.

~~~
gozur88
>If you want to hit the atmosphere in minutes instead of 1.5 hours, you need
to pay a price in delta v, but you don't have a problem with the control at
hypersonic speeds - we are still in vacuum. Once you hit the atmosphere you
need control to hit the target, not to get to the target faster.

If you're in low orbit you'll drop into the atmosphere almost immediately when
you burn retrograde. And you can hit your target faster by entering the
atmosphere later than you otherwise would and steering _down_. The question is
when you really have enough control to make that happen.

>Now let's see what happens if you put a few dozen or hundred in space. What
can you do with a single Rod?

The earth turns. Within 24 hours all your rods will have been in a position to
hit any target on the surface.

>But in terms of military targets, what good are these? Remember, they are
tiny in comparison with nuclear weapons. You can't destroy nuclear bunkers,
you can't acquire mobile targets.

You could most certainly destroy missile bunkers if your targeting was
accurate enough even with a relatively small rod. But there's no reason to
assume the rods are small - 50 tons is a nice round number. Assuming you can't
get volume pricing SpaceX will loft 100 of them for about the price of a
carrier.

And I don't see why you think you couldn't hit a moving target (assuming there
exists a moving target worth destroying that way). The MRBM missile the
Chinese have developed to destroy carriers can hit a moving target, and that's
substantially the same bit of engineering.

>If someone could solve the mobile target acquisition problem, these would be
really good at killing tanks and armored vehicles.

As I pointed out, this is already a solved problem. That said, it would be
pointless to use something that expensive to destroy a tank. There are all
sorts of ways to kill tanks and armored vehicles for a tiny, tiny, tiny (and
that's not really enough "tinys") fraction of the cost. You're already a
sitting duck in a tank.

No, the role for the Rods would be strategic - bunkers, ports, airfields.

------
truetraveller
It boils down to your definition of "patriotism" vs "terrorism". "good" vs
"evil". When China does it, it's bad, right? And the same done by the U.S.
good? Or is it the other way around?

I think SpaceX's revenue is inevitably going to be tainted with money derived
from major military purchases.

Would love to know Musk's views.

~~~
mzw_mzw
> When China does it, it's bad, right? And the same done by the U.S. good? Or
> is it the other way around?

Neither.

Instead of flashing an applause light (on HN, that would be "The United States
Government is evil!" but, to be fair, in lots of other places it would be
yelling about the evil Chinese) we can look at the situation as it develops
and why. It would depend on how the war came about, it would depend on the
different actors' behaviors and motives. It would require thinking, and
honesty.

That whole world-weary "well, who knows what the distinction is between
patriotism and terrorism really?" is quite foolish in general, and an excuse
to avoid making hard moral choices or, worse, to avoid siding with people who
are unpopular in one's social milieu. Yes, there are gray areas. There are
also areas which are quite black and white. Should satellite warfare ever
happen, something we should all hope is not the case, there's every chance
will be able to figure out who was right and who was wrong.

~~~
robotomir
Neither side will make a move without a decade of preparation, and every act
during that decade needs to be judged against a common moral standard.

Also we need orbital brooms, even second-class powers these days can trigger a
Kessler syndrome. Several powerful laser installations, maybe on ships, will
do fine.

~~~
mzw_mzw
Hmm, I've never heard that proposal before. Is anyone seriously investigating
the use of ground-based lasers to clear orbiting debris? It's plausible that a
powerful and well-controlled laser could damage large satellites, but could
that be done carefully enough to safely deorbit them instead of breaking them
apart? And would the lasers be capable of clearing smaller pieces of debris?

~~~
germinalphrase
Apparently, yes. [0]

Lasers would not be used to destroy the debris. Instead, they would be used to
burn off particles from the space debris causing them to prematurely de-orbit
and burn up in the atmosphere.

[0] www.space.com/29271-space-station-laser-cannon-orbital-debris.html

~~~
mzw_mzw
That's fantastic, thank you. Obviously the researchers are going to be
optimistic about their own project but if it's even a tenth as good as they
claim, this could genuinely solve the problem.

