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this post was submitted on 14 Nov 2023
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A lot of the energy comes from orbital speeds.
The Hypervelocity Rod Bundles project proposed 6,1x0,3 m tungsten rods, weighing about 8200 kg, impacting at about 3000 m/s, meaning about 42 GJ of energy per projectile [wikipedia].
The weakest recorded nuke, the Davy Crocket Tactical Nuclear Weapon, is estimated at about twice that (84 GJ), and the largest, Tsar Bomba, at about 3 000 000x the yield (210 PJ).
That’s their point, how do you get such a heavy thing to orbital speed without spending all that energy? You can’t unless you build it from materials harvested in space.
Oh, I apologise, I suffered some curse of knowledge there, the answer is time.
A blast is a release of energy over a short time, the whole point of building weapons is to store and handle energy in safe amounts over time.
Global electric energy consumption is about 200 PJ a day, approximately the same as the Tsar Bomba, but there's no risk for a huge explosion neither when you incinerate trash or turn off the AC.
Because time.
Although we could explode a nuke and propel things ballistically, it turns out it's a lot easier to use rockets. A rocket, although carrying frightening amounts of fuel and exploding spectacularly when it fires wrong, has several safeguards to not expend all that fuel at once. And also gives the opportunity to correct course along the way.
Now imagine that the same amount of energy has been expended many many many times over the course of the space era, and almost any mass in orbit has serious potential for damage.
For example, the MIR was 130 tons, orbiting at about 7,8 km/s, for a kinetic energy of 4 TJ, and another 235 GJ of potential energy. Totalling about a tenth of Little Boy that levelled Hiroshima.
Edit: Specifying and correcting the global energy consumption.
Right, and tungsten rods are dangerous because they don’t slow down and burn up in the atmosphere like most spacecraft do (like you said, spreading out that energy over time and space). As long as you can deorbit them accurately, they are devastating since they convert the entire orbital potential energy into surface kinetic energy all at once. (Oddly, orbital potential energy and surface kinetic energy are the same thing, just from different points of reference.)
Agreed. On all points.
Moreover, the Tungsten rods are quite dense and thus small, and thus very hard to spot on radar or hit with countermeasures.
I'm not sure countermeasures would even work. Even if you could blast it with a half dozen CWIS for the entire duration it's in the atmosphere, hitting every shot, you might change the impact zone by a few hundred meters. A high-angle trajectory would be completely unaffected.
One of the things that's stuck with me during my time on Lemmy is someone remarking that the only difference between a battery and a bomb is how controlled the release of energy is. Having seen what happens when you puncture a LiPo battery, I believe it 😰
There is another factor here which is the base energy level of a battery. LiPo batteries still have a relatively high base level, so even when discharged can still burn/explode. There are other battery chemistries that have a lower base and are therefore safer when fully discharged.
Wait this can't be right or I am missing something. Are you saying that the Tsar Bomba released 10 PetaJoule of energy more than our current world uses in a year?
It's.... definitely not right. Most estimates I found from a quick Google search put global energy consumption at a bit under 600,000 PJ per year, so even if they meant to say daily energy consumption or something they'd still be off by an order of magnitude.
The closest I can get to the number they gave is that global daily electricity consumption is a little over 200 PJ, so right on par with estimates for the Tsar Bomba.
Daily electricity is right, I'll edit
Tsar Bomba released 210–240 PJ of energy according to Wikipedia. Not sure about global energy consumption.
https://en.m.wikipedia.org/wiki/Tsar_Bomba
Still you need that much energy. And it all needs to be on that rocket. So if anything goes wrong with that rocket, it will burn and release the energy of a nuclear explosion. It will be less devastating than a nuke, because it is burning fuel as opposed to a huge shockwave and temperature, but still it would insanely dangerous.
And i've yet to come across a space program that didn't include catastrophic failure rocket launches.
Isn’t this system a rather normal payload? We had really large rockets with the Apollo program.
We've seen this already. Starship should be capable of at least 100t to orbit, which is about 40TJ of energy on orbit. The Little Boy was 63TJ, so accounting for losses, Starship flight test 1 was exactly what that would look like.
Do note that much of the energy was lost because most of the fuel didn't burn, it just evaporated. The Beirut fertilizer explosion was 1/30th the energy, but all released at once.
The mass to orbit isn't the hard part. A reusable Falcon 9 can put 18,400 kg in low Earth orbit. That should cover two rods, plus hardware to hold and deploy them.
And then you would either need to wait for your satellite to get over the target, or add a lot more weight to maneuver it to the target.
If you add wings for precision you are adding drag and heat, both sapping from your destructive power.
If your weapons satellites all start maneuvering to cross your opponents' cities then they probably would have a bit of a warning that you are planning something, and likely just shoot them down at a much cheaper cost. Anti satellite missiles have been shown to work, and it would be easy to overheat a satellite with lasers.
You also have to contend with them just nuking you in response. If Moscow were to be destroyed in a single blast they would not wait to determine if it was nukes or something else, they would fire.
You can definitely make some stealthy satellites.
I was thinking for release you could actually fold out wings/parachute to increase drag so it would deorbit faster and with less propellant.
Don’t think you can target a satellite with a laser, it’s too far away and you’d have to find it first.
But overall it doesn’t seem particularly efficient or useful.