[alexitorg]

For military purposes, my idea for Starship would be the following. Starship aims to put a 150tonne payload to orbit for a few million dollars. I would look at non-nuclear kinetic perpetrators.

Put a 100 tonne tungsten rod into space (cost ~$10m), or more likely some cheaper metal. Maybe 10m long with 25cm radius. Stick a cold gas reaction control system, maybe some gridfins and a guidance package. Put it in orbit, Put some ablative on the leading edge. Once in orbit the cold gas system slows the weapon to put it on target. The gridfins and cold gas thrusters control the guidance. The gridfins wouldn't work for long before the burnt off, but recessed cold gas thrusters could continue to work. Ionisation and intense heat would stop any optical sensors or outside guidance, so aiming it would be problematic.

A kinetic warhead with a mass of 100tonnes going at sub orbital speeds (say 7000m/s) would have 2.45x10^12 joules, which is around 0.58kt of tnt. If I remember correctly once it is going past a critical speed the penetrator and target act like fluids and the rod would penetrate a depth based on the relative density of the two materials time the length. Tungsten is about 6 to 12 times as dense as rock, so it might go through 60 to 120m meters of rock.

Non-nuclear, pretty hard to detect or stop. Competitive in price with cruise missiles. Accuracy could be a problem.

[gpm]

Storing weapons in space is really scary. It's practically impossible to reliably detect when they are "fired", which makes the people with nuclear bombs waiting to fire back antsy, which increases the risk of a nuclear war accidentally starting. I hope no one carries out this idea of yours.

Using starship to launch rods that immediately come down on people instead of loitering in space sounds like a much safer use.

[ColanR]

Those rods are designed for precision targets on the order of a few meters in diameter. I would much rather both sides of the conflict had those in play, than a nuclear alternative.

[gpm]

Unfortunately it's not a question of one or the other, but of nuclear or both.

[ColanR]

Then both would be preferable. :)

[Aperocky]

> practically impossible to reliably detect

I call the opposite, it is extremely easy to detect and track their orbits, a single personal computer can probably track them all and calculate the potential strike point over points in orbits.

Any attempt to deviate from an existing low earth orbit is extremely energy intensive. It also can't strike anywhere - it can be more than 24 hours before its in position over the location it wants to be.

[gpm]

It doesn't take much Delta v (energy) to move a low Earth orbit into a suborbital collision course. You don't kill all of your velocity, just enough of it that your orbit intersects Earth.

The orbital period for low Earth orbit is closer to 1 hour than 24, and you further reduce that to only a dozen or so minutes by spacing out rods over the orbit... Much like starlink satellites.

[Aperocky]

Yeah it's 1 hour but what if your orbit doesn't intersect with where you want to strike? What if the city is 5000 km _sideways_? Then you wait for the rotation of Earth to bring that location into your orbit path.

Keep in mind an orbit does not cover all of the Earth surface. And unless the target is on the equator, there is no low earth orbit that can maintain it's path over a target consistently.

[Arelius]

I understand your point on tracking orbits.

But for detection, Is that actually easy? I don't know much about it, would it be done optically, or is there a better way? Are there concealment strategies? How about say painting the satellite black?

[ColanR]

Otherwise known as the "Rods from God". https://en.wikipedia.org/wiki/Kinetic_bombardment

[alexitorg]

Nice link. I am not surprised that the concept is that well developed. I'm surprised they slow down to terminal velocity before impact.

Fun to think about but I also hope they don't build these things.

[ceejayoz]

Terminal velocity for a streamlined rod of metal is pretty high. You're talking about tactical nuke levels of energy, delivered to a foot-wide spot on the ground.

[Aperocky]

De-orbiting them would consume a lot of delta-V.. plus if they're 'stored' in orbit they have a very narrow path where they can go in a certain period of time.

[FeepingCreature]

Could de-orbiting be partially managed by shooting them backward from the platform, using atmospheric resistance to bleed off the gained velocity of the platform?

[saagarjha]

Deorbiting them so their periapsis intersects with the earth is not hard from LEO.

[Aperocky]

If you don't mind aero capturing over multiple orbits that is.

[saagarjha]

They're already in orbit, though?