Orbital strikes out of MA

[Fact Checking]

Well, if he drags it out long enough, say longer than Mark Cuban did, he could simply take the BFR and go live on Mars. What will the SEC do then?

Also, should by that time Earth buerocrats still insist on unlawful and unjust legal shenanigans, Mars is in a very favorable orbital position to launch kinetic projectiles towards the inner planets, with very little fuel expended. As a warning.

Just saying!

 

[KarenRei]

Also, should by that time Earth buerocrats still insist on unlawful and unjust legal shenanigans, Mars is in a very favorable orbital position to launch kinetic projectiles towards the inner planets, with very little fuel expended. As a warning.

Just saying!

You'd think, but it doesn't actually work like that. Oberth Effect and all - if you want a rocket to get your projectiles up to a high velocity, you want to be closer to the sun, not further away, and in orbit around a strong gravity well, not a weak one. You'll want to boost your projectiles' velocities additionally, aka you'll want gravity assists, which are much more frequent the closer you get to the sun. In short, projectiles launched from LVO (Low Venus Orbit) can get to Earth faster, and harder than from LMO (Low Mars Orbit).

Of course, you have to get projectiles to orbit if they're not already there, and given the much lower dV for escape on Mars, it's in a superior position in that regard. Of course, asteroids require practically no dV to get material off the surface, so they're superior in that regard.

While the moon might look appealing (relatively low dV for escape velocity to ETO, short transfer times), it's of course extremely vulnerable to counterattacks from the SEC

 

[HG Wells]

I don't think Mars has an extradition agreement with Earth, so this may be the ultimate solution.

That's true. There is no extradition treaty. We do have an extraction agreement. But it is one sided.
Martian High Command

Also, should by that time Earth buerocrats still insist on unlawful and unjust legal shenanigans, Mars is in a very favorable orbital position to launch kinetic projectiles towards the inner planets, with very little fuel expended. As a warning.

Just saying!

When the dinosaurs failed to make a payment, we sent them a little present.
Martian High Command

Karen
PS: If you do the orbital mechanics just right, you can have it loop around the sun (very close if its a rock) and then strike the earth. Takes about 4 extra months, but it really packs a wallop !

 

[Fact Checking]

You'd think, but it doesn't actually work like that. Oberth Effect and all - if you want a rocket to get your projectiles up to a high velocity, you want to be closer to the sun, not further away, and in orbit around a strong gravity well, not a weak one.

I think you misunderstood my point: a kinetic projectile, not a missile!

To get a kinetic projectile to high speed cheaply what you need primarily is to be as high in a gravity well as possible, and to have the right vector of velocity: a large rock dropped towards the Earth will gain speed as it gets closer to the Sun, and then gains even more speed as it drops into the gravity well of the Earth.

The Oberth Effect does not apply to passive kinetic warheads.

The rest is timing and precise targeting: a single 10 ton rod of iron, traveling at ~70 km/sec (speed of fastest meteorites hitting the Earth in a counter-orbit) has a kinetic energy equivalent of over 6,000 tons of TNT (!). Even if much of it evaporates as it hits the atmosphere, the plasma strike would probably be devastating.

(Even more devastating are projectiles launched from the Kuiper belt: very little targeting velocity needed, if you are willing to wait years for the strike. Perfect weapons of mutual destruction though, impossible to find and unstoppable at 50+ km/sec.)

Mars is in a superior energetic position when it comes to space warfare.

 

[Fact Checking]

PS: If you do the orbital mechanics just right, you can have it loop around the sun (very close if its a rock) and then strike the earth. Takes about 4 extra months, but it really packs a wallop !

The best kinetic strike from the outer planets would be to loop it around the Sun and both on the way in and on the way out use Venus for a gravity assist and final targeting, then hit Earth almost head on.

The kinetic warhead launch system would be in Jupiter orbit and would use the jovian moons for initial velocity and targeting, via gravity assists.

I think around 100 km/sec relative velocity could be achieved that way, and a strike time of a couple of months.

 

[HG Wells]

I think you misunderstood my point: a kinetic projectile, not a missile!

To get a kinetic projectile to high speed cheaply what you need primarily is to be as high in a gravity well as possible, and to have the right vector of velocity: a large rock dropped towards the Earth will gain speed as it gets closer to the Sun, and then gains even more speed as it drops into the gravity well of the Earth.

The Oberth Effect does not apply to passive kinetic warheads.

The rest is timing and precise targeting: a single 10 ton rod of iron, traveling at ~70 km/sec (speed of fastest meteorites hitting the Earth in a counter-orbit) has a kinetic energy equivalent of over 6,000 tons of TNT (!). Even if much of it evaporates as it hits the atmosphere, the plasma strike would probably be devastating.

(Even more devastating are projectiles launched from the Kuiper belt: very little targeting velocity needed, if you are willing to wait years for the strike. Perfect weapons of mutual destruction though, impossible to find and unstoppable at 50+ km/sec.)

Mars is in a superior energetic position when it comes to space warfare.

Yes, yes we are.

But as to your Kuiper belt comment. Most of them have a high ice component. Once they cross the orbit of mars they start to gas.
Throws off targeting a bit and you can see them from a great distance. Better to use rocky asteroids from the asteroid belt. Some are so dark you won't see them till they are right on top of you.

See Space Commander Kolligs "Planetary Rules of Engagement" Page 342 to 357.

Martian High Command

 

[MarcusMaximus]

The best kinetic strike from the outer planets would be to loop it around the Sun and both on the way in and on the way out use Venus for a gravity assist and final targeting, then hit Earth almost head on.

The kinetic warhead launch system would be in Jupiter orbit and would use the jovian moons for initial velocity and targeting, via gravity assists.

I think around 100 km/sec relative velocity could be achieved that way, and a strike time of a couple of months.

Some mod is going to come along and move this whole conversation, and that makes me sad.

 

[mongo]

Some mod is going to come along and move this whole conversation, and that makes me sad.

But now I'll get to know where it went!

 

[Fact Checking]

But as to your Kuiper belt comment. Most of them have a high ice component. Once they cross the orbit of mars they start to gas.

Actually, we are not 100% sure: while we can see the icy ones with high albedo, but most of the C-type ones ideal for stealth surgical strikes are too dark with their 3% albedo to resolve for even superior Martian phased array sensors based sky surveys. So we have only found and armed around 3,000,000 of them - this limited resource is reserved for special ops use only.

But visibility is not a problem for our most potent retaliatory kinetic strike system: every beltalowda knows that Inners have yet to stop even a single one of our larger icy moons flying at a terminal velocity of 50 km/sec. The targeting solution is also much easier to lock on to with an average moon diameter of 20 km.

 

[ggr]

Some mod is going to come along and move this whole conversation, and that makes me sad.

Damn right. As Sigourney Weaver's character says in Galaxy Quest, "I only have one job to do, and by God I'm going to do it!"

 

[KarenRei]

I think you misunderstood my point: a kinetic projectile, not a missile!

To get a kinetic projectile to high speed cheaply what you need primarily is to be as high in a gravity well as possible, and to have the right vector of velocity: a large rock dropped towards the Earth will gain speed as it gets closer to the Sun, and then gains even more speed as it drops into the gravity well of the Earth.

It's still not clear what you're referring to. Are you talking minimum delta-V Hohmann transfers? If so then all projectiles from all locations will impact the SEC headquarters with the exact same velocity, 11,2km/s. What being further out buys you is minimizing how much energy it takes to go into Earth Transfer Orbit (ETO). The energy requirements of course increased by how much energy it takes for your kinetic projectile to escape from the body in question.

The Oberth Effect does not apply to passive kinetic warheads.

Oberth Effect applies to any application of thrust (including firing a kinetic projectile) in a 3+ body system.

Even more devastating are projectiles launched from the Kuiper belt: very little targeting velocity needed, if you are willing to wait years for the strike

If you're talking minimum energy transfers, you're not just talking "years", you're talking decades to centuries. The SEC attorneys would be dead by the time the projectiles arrived.

Mars is in a superior energetic position when it comes to space warfare.

Further out in the solar system, contrary to intuition, is just simply worse. Less Oberth Effect, rarer launch windows, longer transit times, fewer opportunities for gravity assist. And some of those factors are quadratic scaling

The best kinetic strike from the outer planets would be to loop it around the Sun and both on the way in and on the way out use Venus for a gravity assist and final targeting, then hit Earth almost head on.

Earth-Venus offers so many opportunities for gravity assists Really, talking about minimum energy direct transfers is pointless, the real issue is, where do you get the best gravity assist opportunities? And Venus and Earth align frequently, and you can set up repeat Venus-Earth or even Earth-Earth or Venus-Venus assists. A popular arrangement starting from Earth involves two Venus flybys and one Earth flyby in order to reach a high-energy destination (usually the outer solar system, but also Mercury). Transit times are just a few years and windows open up fairly frequently.

Of course, if we want to go into so much detail, we also have to account for the energy to get off of the surface, which obviously is a big hit to Venus, but still a meaningful hit to Mars. Your best bet for minimizing energy to get your mass off the surface and giving it frequent launch windows and good gravity assist opportunities is to launch from an Aten asteroid, or perhaps a Venus crosser.

 

[JRP3]

It's still not clear what you're referring to. Are you talking minimum delta-V Hohmann transfers? ...

My favorite off topic post to date

 

[JRP3]

Damn right. As Sigourney Weaver's character says in Galaxy Quest, "I only have one job to do, and by God I'm going to do it!"

And yet blatant FUDsters post repeatedly with a delayed response while an interesting discussion is quickly moved...just sayin...priorities?

 

[HG Wells]

OUR OWN THREAD !

Makes my second and third heart skip a beat.

Martian High Command

 

[TSLA_Hopeful]

Why is this a thread....

 

[JRP3]

Why not?

 

[mongo]

Option strikes
Orbital strikes
It's all good in the investor thread
But no poetry
-rule 201

 

[ggr]

And yet blatant FUDsters post repeatedly with a delayed response while an interesting discussion is quickly moved...just sayin...priorities?

If that's a serious question, here's the serious answer: it is possible to move a handful of posts on a single off-topic subject to a thread of their own, where it will actually be possible to find them in future if you want to. It is simply not possible for any of us to continually stay on top of what's happening minute-to-minute in terms of fudsters, and people who might actually mean well (or, I agree, might not). Anyway, thanks for making it clear that I needn't waste any more of my time on this.

 

[Fact Checking]

Oberth Effect applies to any application of thrust (including firing a kinetic projectile) in a 3+ body system.

If you are gaining kinetic energy via an impulse rocket then the Oberth Effect indeed offers an approximate propulsion energy advantage of +~40% near the surface of Earth (on the surface and in LEO) when reaching velocities required for minimal Hohmann Transfer to Mars transfer orbit - while the Oberth Effect from the surface of Mars is less than +20%, so on paper Earth has a ~20-25% propulsion energy generation advantage there. This is the rough scope of the Oberth Effect advantage you are referring to I believe.

But you are missing two points:

1)

Even assuming chemical propulsion missile strikes (which my original post didn't, see further below) Mars has an Oberth Effect advantage:

• Even the highest specific-impulse chemical rockets are awfully inefficient and mass-intensive to gain kinetic energy. A Falcon 9 for example spends 99% of its launch mass on gaining minimal orbital velocity (!): the tyranny of the rocket equation.
  
• When launching from Earth surface there's a much deeper gravity well to climb out of to begin with. Even from LEO there's a ~3 km/sec Δv cost in escaping Earth - while only about 1 km/sec when escaping from Low Mars Orbit (!). This cost is counting against any Oberth Effect advantages gained.
• Another cost when launching from Earth surface is the ~10% efficiency loss that sea level pressure causes in rocket engines, while Mars surface is vacuum in comparison and chemical rockets work at 99% efficiency levels already.
  
• The Oberth Effect also gets much weaker at higher kinetic energies: the Oberth Effect scales up with the depth of the gravity well, but scales down with the ratio between exhaust velocity and current projectile velocity. The ~40% advantage during launch to Earth orbit gets reduced to 20% and less once projectile speed gets much larger than exhaust velocity, which is 3-4 km/sec for the best chemical propulsion engines we know at the moment.
  
• But most importantly, the mother of all Oberth Effects is not the gravity well of Earth, but the very deep gravity well of the Sun - and Mars Missile Command has a better access to that one too, because it has lower orbital velocity to transfer from: Earth orbital velocity is ~30 km/sec, while Mars orbital velocity is ~24 km/sec, so there's a 6 km/sec Δv advantage Mars has when accessing low Sun orbits - a much higher advantage in most launch scenarios than the Oberth effect advantage of launches from Earth surface.

2)

But my main point was that the Oberth Effect is largely immaterial if most of the kinetic energy is gained not via inefficient chemical propulsion (the only currently known method of propulsion that can make significant use of the Oberth Effect in Earth orbit), but by converting high gravitational potential energy into kinetic energy:

Earth-Venus offers so many opportunities for gravity assists

It's still not clear what you're referring to. Are you talking minimum delta-V Hohmann transfers? If so then all projectiles from all locations will impact the SEC headquarters with the exact same velocity, 11,2km/s. What being further out buys you is minimizing how much energy it takes to go into Earth Transfer Orbit (ETO). The energy requirements of course increased by how much energy it takes for your kinetic projectile to escape from the body in question.

Striking the Earth-Moon system from Mars, the jovians or the Kuiper belt is still much, much more favorable energetically than striking Mars from Earth:

• Most of the energy gained from a Venus assist will be spent on reaching Mars orbit energy levels: at least 3 km/sec Δv is lost when launching from Earth to Mars, even during the most favorable launch window (which ideal launch window has a periodicity of ~2.2 years), but the minimum transfer energy requirements can be as bad as a Δv loss of 9 km/sec (!).
  
• The Δv gained by the final approach is much higher when striking objects close to Earth surface: almost 12 km/sec when impacting Earth, while only 6 km/sec when impacting the surface of Mars: a factor of 4x difference in kinetic energy from this source alone. The deep gravity well that creates an advantageous Oberth Effect contribution to chemical rockets is a big disadvantage when being the target of kinetic strikes.
  
• If an up to 30 days additional launch window is not a problem then the Moon can add another 1 km/sec gravity assist, while the contribution of Phobos and Deimos is negligible.

And yes, I'm talking about all orbits that kinetic strikes could use: from the simplest 4-body Hohmann transfers to highly complex 10+ body gravity assists that are using very little initial kinetic energy to get going.

The advantage Mars has in energy requirements is so massive for the vast majority of realistic strike scenarios that it overwhelms any advantage the Oberth Effect offers to Earth Command.

I'll admit that Earth has one advantage though: a much thicker atmospheric shield, which makes surgical strikes harder. Negotiations tend to get emotional when the best targeting granularity of your surgical strikes is not single person size but to take out an entire city...

But Earth atmosphere won't help the SEC much once they relocate their headquarters to Elysium!

 

[JRP3]

If that's a serious question, here's the serious answer: it is possible to move a handful of posts on a single off-topic subject to a thread of their own, where it will actually be possible to find them in future if you want to. It is simply not possible for any of us to continually stay on top of what's happening minute-to-minute in terms of fudsters, and people who might actually mean well (or, I agree, might not). Anyway, thanks for making it clear that I needn't waste any more of my time on this.

Not to drag this off topic thread off topic, but it just seems easier to ban the obvious fudsters than try to chase their individual posts. I've been trying to convince the mods to make their lives easier, and the board better, by being less tolerant of repeat offenders.