Orbital Bombardment from Retrograde Solar Orbit

[SunJumper]

A while ago, Scott Manley made a video about re-entering Kerbin's atmosphere from a retrograde orbit, at 19km/s. Now, I thought about an interesting purpose of this: A Rod from the Gods. How much more effective would a RFTG be when launched from retrograde solar orbit, than simply from low Kerbin orbit?

A test with Sal Vager's RFTG mod may be useful.

Preliminary testing with a modded cockpit with mass 100 tonnes and drag value 0.01 and atmo entry speed 19km/s, gives an impact velocity of 15.8km/s (mach 45), and a penetration depth of about 100m. This is mind numbingly impressive, as KSP does not simulate hypervelocity ground penetration!

Impact pic:

If the altimeter above is accurate, I actually penetrated about 1.5km.

Dropping my test pod from orbit (entry velocity 2.1km/s) causes an impact velocity of about 1km/s.

This means that the RSO rod brings 69% of its energy to the ground, and the LKO rod only 23%. From E=0.5mv^2, assuming no mass loss.

Edited April 19, 2013 by SunJumper

[Nibb31]

Probably not very effective, as it would take 6 months to reach its target and a LOT of ÃŽâ€v.

[SunJumper]

For a sufficiently advanced civilisation, 10 to 100km/s delta-v is peanuts.

[Rune]

For a sufficiently advanced civilisation, 10 to 100km/s delta-v is peanuts.

Which means they could accelerate it during the plunge from orbit, and then why take the extra months to circle around the sun, complicating targeting? Impressive test, BTW.

[Scotius]

Holy impact Batman! That is very impressive, but i agree with Rune - it's not very feasible. Civilisation advanced enough to build such system should have much more "imminent" ways to vaporise a chunk of the terrain. Weapon is best when you can use it wherever you want, whenever you want. Weapon that you have to launch 6 months or more prior to attack is best suited for terrorists, or Bond-style supervillain.

[UltraVires]

Nice testing! But the regular RFTG's would actually have about the same level of impact ability if KSP actually had a good model of atmosphere drag... In real life, the study that I read (it may have even been the one that Jerry Pournell wrote, but I have forgotten) was talking about impact velocities of 10,000 mph plus There was even a section on rocket boosted "Final Impactors" that would give you even more penetrating power... Lol This would be a valid and devastating weapons system... if there weren't already weapons that can do about the same thing (the RFTG's are the Ultimate ground penetrators!) much cheaper... Once again the penny pinchers rob us of our Space Fighters!!! Grrr Nice Discussion!

[Felsmak]

Weapon that you have to launch 6 months or more prior to attack is best suited for terrorists, or Bond-style supervillain.

Lots of time to prepare that final villain speech!

[PIRATEONTHERUN]

I guess theoretically you could keep a bunch of RFTG's fitted with small engines in a retrograde orbit around the Sun out of inclination with Earth, and if you wanted to use them you would just adjust the orbit to where you wanted it to go with the nearest one, but then there's the problem of keeping 100,000's of RFTG's in orbit and of when their orbits eventually intersect the Earth and they're out of fuel...

[The Jedi Master]

Theory:

MWUWWHAHAHA *Earth blows up*

Practice:

MWUWHAHAHAHA * missile burns up in atmosphere within seconds*

[Rune]

Theory:

MWUWWHAHAHA *Earth blows up*

Practice:

MWUWHAHAHAHA * missile burns up in atmosphere within seconds*

Not if you have some knowledge about how these things work and make it a rod of tungsten with a decent ballistic coefficient (long and pointy). Look at the beginning of thethread to see what percentage of the energy gets dissipated as heat. Then divide by the energy necessary to vaporize each unit of mass of tungsten. Increase mass so final impact mass is the one you want, by perhaps a few of kilograms per delivered ton.

Rune. It's called ablative heatshield, and tungsten makes a hell of a good one.

[SunJumper]

Don't forget that a retrograde RFTG will only spend literally 1 second in the part of the atmosphere that is non-negligible in re-entry.

[magnemoe]

I guess theoretically you could keep a bunch of RFTG's fitted with small engines in a retrograde orbit around the Sun out of inclination with Earth, and if you wanted to use them you would just adjust the orbit to where you wanted it to go with the nearest one, but then there's the problem of keeping 100,000's of RFTG's in orbit and of when their orbits eventually intersect the Earth and they're out of fuel...

You could but this would reduce the rate of fire, say you have 1000 in orbit, you would then have 6 to use each day in 180 days, if you wanted to use 100 the first day in the war, then between 10 and 20 the following days and the war last an month it would not be an very useful weapon.