(SPOILERS) The reasons for the Archangel's return

Keith_w wrote:

SWM wrote:I am fully aware of the list of interplanetary probes that used gravity assist. I know several of the project scientists who worked on those probes. Notice that none of those probes used gravity assist to escape the Earth's orbit. They all used gravity assist on other planets, and they always approached that planet with a speed greater than escape velocity.

Let me show you why the velocity of the object relative to the planet matters. Imagine a satellite in orbit around the Earth with an orbital speed of 5 km/s (well below escape velocity). Sometimes it is moving in the direction opposite to the Earth's motion, sometimes it is moving in the same direction as the Earth's motion. The orbital velocity of the Earth around the Sun is 30 km/s. What is the velocity of the satellite relative to the Sun? When it is moving opposite to the Earth's motion, the velocity relative to the Sun is 25 km/s. When it is moving in the other direction, it is moving 35 km/s. The velocity of the satellite relative to the sun oscillates between 25 km/s and 35 km/s. The act of swinging around the backside of the Earth increases the velocity of the satellite with respect to the Sun--this is exactly the same thing that happens with a gravity assist. But since it does not change the speed of the satellite with respect to the Earth, the Earth's gravity will slow it down until it swings back the other way. It never gets away from the Earth--it never breaks out of orbit. And "break out of orbit" is what you say you are trying to do.

Velocity with respect to the planet you are trying to swing around is critical. Swinging around the planet is not going to give the satellite more energy with respect to the planet. If it is bound to the planet, it stays bound to the planet, unless you give it more energy from elsewhere. Swinging around the planet when you don't have enough energy to escape the planet will temporarily increase your velocity with respect to the star. And then decrease it again, in a never-ending cycle.

Why are you so hung up on the relative to the planet being used to do the G-A? Who cares about relative to the non-Safehold planet (which we don't even know if the exist)? We care about the speed relative to the local stellar object and the other objects in the local stellar neighbourhood, and if that didn't work why would we bother doing it for our own interplanetary probes?

The original suggestion was to use gravity assist a.k.a. slingshot effect around other (possibly existing) planets to use KEWs as an anti-Ghaba device. Then someone said, nono you can't do that because you can't get them out of orbit, at which time I suggested that the G-A could be used to get them out of Safeholdian orbit, and which has been your focus ever since. Fine, you can't use G-A that way. I don't think and never did think that you needed to.

It was just a suggestion and not really a very good one in the first place since the Ghaba would see them coming and get out of the way anyway.

What really surprised me was the lack of imagination shown here. This is science fiction folks. The Terran Federation had compensatory that allowed them to travel at 400Gs. Presumably they had a power source which would allow them to reach that speed, and probably more if it wasn't necessary to protect the protoplasmic objects within.

BarryKirk wrote:Don't know if it applies here, but the KEW used in the Honorverse was travelling at least 10% the speed of light.

That KEW was a simple projectile. No guidence other than the original launcher.

The projectile itself had relatively little mass... With that velocity, it doesn't take much mass to get to truly huge amounts of energy.

With that velocity, you don't have to futz around with any orbital manuovers... Orbital speeds for planets and solar systems are teeny tiny by comparison.

All you need is a launcher with a couple million Gs grav generator to make it work.

SWM wrote: quote="Keith_w quote="SWM"
I am fully aware of the list of interplanetary probes that used gravity assist. I know several of the project scientists who worked on those probes. Notice that none of those probes used gravity assist to escape the Earth's orbit. They all used gravity assist on other planets, and they always approached that planet with a speed greater than escape velocity.

Let me show you why the velocity of the object relative to the planet matters. Imagine a satellite in orbit around the Earth with an orbital speed of 5 km/s (well below escape velocity). Sometimes it is moving in the direction opposite to the Earth's motion, sometimes it is moving in the same direction as the Earth's motion. The orbital velocity of the Earth around the Sun is 30 km/s. What is the velocity of the satellite relative to the Sun? When it is moving opposite to the Earth's motion, the velocity relative to the Sun is 25 km/s. When it is moving in the other direction, it is moving 35 km/s. The velocity of the satellite relative to the sun oscillates between 25 km/s and 35 km/s. The act of swinging around the backside of the Earth increases the velocity of the satellite with respect to the Sun--this is exactly the same thing that happens with a gravity assist. But since it does not change the speed of the satellite with respect to the Earth, the Earth's gravity will slow it down until it swings back the other way. It never gets away from the Earth--it never breaks out of orbit. And "break out of orbit" is what you say you are trying to do.

Velocity with respect to the planet you are trying to swing around is critical. Swinging around the planet is not going to give the satellite more energy with respect to the planet. If it is bound to the planet, it stays bound to the planet, unless you give it more energy from elsewhere. Swinging around the planet when you don't have enough energy to escape the planet will temporarily increase your velocity with respect to the star. And then decrease it again, in a never-ending cycle. /quote

Why are you so hung up on the relative to the planet being used to do the G-A? Who cares about relative to the non-Safehold planet (which we don't even know if the exist)? We care about the speed relative to the local stellar object and the other objects in the local stellar neighbourhood, and if that didn't work why would we bother doing it for our own interplanetary probes?

The original suggestion was to use gravity assist a.k.a. slingshot effect around other (possibly existing) planets to use KEWs as an anti-Ghaba device. Then someone said, nono you can't do that because you can't get them out of orbit, at which time I suggested that the G-A could be used to get them out of Safeholdian orbit, and which has been your focus ever since. Fine, you can't use G-A that way. I don't think and never did think that you needed to.

It was just a suggestion and not really a very good one in the first place since the Ghaba would see them coming and get out of the way anyway.

What really surprised me was the lack of imagination shown here. This is science fiction folks. The Terran Federation had compensatory that allowed them to travel at 400Gs. Presumably they had a power source which would allow them to reach that speed, and probably more if it wasn't necessary to protect the protoplasmic objects within. /quote
It sounds like we have been talking at cross purposes. I thought you were still talking about getting the KEW out of Safehold orbit by doing a gravity assist around Safehold. I have not been talking about the velocity relative to other planets--I have been talking about the velocity of the KEW relative to Safehold, because I thought that's what you were still talking about. You never actually said that you had given up on the idea of using a slingshot to get out of orbit. Your responses made me think you were still arguing with my evidence that you can't get it out of orbit that way.

If you are talking about using some other method to get the KEW out of orbit, and using gravity assist around other planets to change the trajectory and velocity of the KEW, then I totally agree with you. If you had some method to get the weapon out of orbit, you could do that. In fact, I've said that several times. And I also agree that Federation technology could have done it. My only disagreement with the idea (which I have also explained several times) is that I don't think the OBS is equipped with anything to get the KEWs out of orbit. That is only my own opinion, of course, and my only objection to your proposal. This is not a matter of lack of imagination--it is an understanding of the most efficient way to design an orbital KEW.

SWM wrote:

BarryKirk wrote:Don't know if it applies here, but the KEW used in the Honorverse was travelling at least 10% the speed of light.

That KEW was a simple projectile. No guidence other than the original launcher.

The projectile itself had relatively little mass... With that velocity, it doesn't take much mass to get to truly huge amounts of energy.

With that velocity, you don't have to futz around with any orbital manuovers... Orbital speeds for planets and solar systems are teeny tiny by comparison.

All you need is a launcher with a couple million Gs grav generator to make it work.

I'm afraid it doesn't apply here, and you are also wrong in at least one point. The kinetic energy weapons used by Manticore have a built-in impeller drive; this is likely true of KEWs used by other Honorverse navies. Since they have a drive, they almost certainly also have a guidance package. This does not apply to Safehold.

SWM wrote:

BarryKirk wrote:Don't know if it applies here, but the KEW used in the Honorverse was travelling at least 10% the speed of light.

That KEW was a simple projectile. No guidence other than the original launcher.

The projectile itself had relatively little mass... With that velocity, it doesn't take much mass to get to truly huge amounts of energy.

With that velocity, you don't have to futz around with any orbital manuovers... Orbital speeds for planets and solar systems are teeny tiny by comparison.

All you need is a launcher with a couple million Gs grav generator to make it work.

I'm afraid it doesn't apply here, and you are also wrong in at least one point. The kinetic energy weapons used by Manticore have a built-in impeller drive; this is likely true of KEWs used by other Honorverse navies. Since they have a drive, they almost certainly also have a guidance package. This does not apply to Safehold.

Keith_w wrote:

SWM wrote:I'm afraid it doesn't apply here, and you are also wrong in at least one point. The kinetic energy weapons used by Manticore have a built-in impeller drive; this is likely true of KEWs used by other Honorverse navies. Since they have a drive, they almost certainly also have a guidance package. This does not apply to Safehold.

And why shouldn't they include a propulsion system? And they certainly need to include a guidance system unless you are planning to shotgun the whole planet. Remember, Safeholdian gravity is approximately the same as earth's, ie, 32feet/sec, squared. Terminal velocity on earth for a human being (and yes, I know we are not talking about dropping human beings), is about 122 Miles/ 195KM per hour
in the facedown free fall position. If you put a motor on that, you get to go a lot faster, and faster, for the same weight, means more kinetic energy.

SWM wrote: quote="Keith_w" quote="SWM"
I'm afraid it doesn't apply here, and you are also wrong in at least one point. The kinetic energy weapons used by Manticore have a built-in impeller drive; this is likely true of KEWs used by other Honorverse navies. Since they have a drive, they almost certainly also have a guidance package. This does not apply to Safehold.
/quote

And why shouldn't they include a propulsion system? And they certainly need to include a guidance system unless you are planning to shotgun the whole planet. Remember, Safeholdian gravity is approximately the same as earth's, ie, 32feet/sec, squared. Terminal velocity on earth for a human being (and yes, I know we are not talking about dropping human beings), is about 122 Miles/ 195KM per hour
in the facedown free fall position. If you put a motor on that, you get to go a lot faster, and faster, for the same weight, means more kinetic energy. /quote
I already said that I believe the Safehold KEWs do have a guidance system, and there has to be some propulsion (either in the launcher or the KEW itself) in order to alter the KEW orbit to intersect the planet. I just don't think it is much more powerful than is necessary to do that.

The reason I said that the Honorverse example does not apply to Safehold is because the Federation does not have impeller wedges to accelerate projectiles at nearly 100,000 gees.

BarryKirk wrote:I know it's a different universe, but in the Honorverse, the initial pods for launching missiles had a problem. They couldn't kick the missiles out with a high initial velocity.

Standard ship based launchers and later pods could kick missiles out with a fairly high initial velocity.

In one of the Honorverse books, can't remember which one, it was mentioned that KEW's were launched out of standard missile tubes. Those KEWs may have been inert super high speed projectiles... No guidence or impeller wedges.