(SPOILERS) The reasons for the Archangel's return

OrlandoNative wrote:

SWM wrote:You are incorrect. The surviving angels had the Hamilcar--Langhorne's command ship, which was equipped with a complete automated manufacturing plant. David has told us that the Hamilcar was used after the War of the Fallen to completely rebuild the Rakurai. Far from being unable to destroy the Rakurai, they actually replaced it with a new one. The Hamilcar was also used to build the current Temple, including all of it's built-in tech and armor plating. The angels had plenty of technology to build anything they wanted.

Mmm.. while that might be somewhere in the Forums, I've never seen it in the published *books*. Which book tells that tale?

I think the books note that the OBS was rebuilt. I believe the statement that the new OBS and the Temple were built with the Hamlilcar was not in the books, but here in the forums. Unfortunately, I have been unable to locate the threads where he discussed it. (The problem is that David never refers in the forums to the name of the ship that was still in orbit. We get that name from the books. He refers to the weapon system as the OBS, but the word OBS is ignored in a search of the forums. I haven't come up with a search which pulls up the right thread. Can anyone else find it?)

I do have a citation for the capabilities of the ship which was still in orbit (viewtopic.php?f=7&t=4824&p=116032&hilit=obs+deployed#p116032):

runsforcelery wrote:By the time the OBS was deployed, all but one of the colony's ships had been disposed of (as per the original operations plan) by dropping them into the local sun once they were no longer needed. The ship which remained had been Langhorne's flagship all along and he'd been very careful about vetting and reassigning shipboard personnel while Kau-Yung and Shan-Wei were off prepping the planet. By the time he came to join them, he'd had several years to weed out any potential weak spots in the crew.

Now, these were big honking ships, and his flagship had been chosen (and hung onto until last) in part because it was one of the main fabrication vessels --- that is, it represented a very impressive industrial base. Officially, it was retained till last in case something unexpected came up on Safehold which would require industrial support to rectify.

OrlandoNative wrote:In any case, I still stand by my observation that leaving *anything* "unnatural" in orbit is criminally stupid if the overriding concern is to hide from Ghaba scouts. While space is vast, if you're looking for sentient species to destroy, you'd certainly make at least a scan of the near space of any planet you might locate within the "life zone" of a solar system. Having a bombardment system in planetary orbit is like putting up a cosmic "Look Here!" banner. I could see maybe putting such a construct in orbit for a specific engagement, but not leaving it there afterwards for any passersby to notice. Certainly not if one wants to hide one's presence on the planet below.

Here is what David said in response to that criticism (in viewtopic.php?f=7&t=3248&hilit=temple+ship):

runsforcelery wrote:Okay, this is a system which uses solar power collection for its primary operation, is heavily stealthed, and kicks on the onboard fusion plants only when it's time to crank up the kinetic launchers and then turns them off as soon as the strike is over. The support and maintenance systemoperates under exactly the same sort of constraints, as well. As to how the platform(s) are arranged, for now that's for me to know and you to worry about, but I think you can safely assume that the people who put it/them in place weren't stupid enough to design a system that couldn't spot, track, and target objectives wherever they happen to be located on the face of Safehold.

You are absolutely correct that any artificial satellite is going to attract the attention of anyone who sees it. The problem is that if they get close enough to see/detect the kinetic platforms, they will definitely be close enough to realize there's a planet-wide civilization (whether it's "high-tech" or not) on Safehold. While it is fair to question Langhorne's sanity and/or motivations, I think you can take it as a given that he was maniacally careful about hiding all detectable traces of humanity's presence. There were, however, certain things he couldn't hide, and he was perfectly willing to embrace technology which couldn't be detected without the Gbaba coming so close that they couldn't miss the things he couldn't hide anyway.

So, if the Gbaba get close enough to detect the OBS, then they are close enough to notice that the planet is inhabited. It doesn't matter whether they detect the OBS at that point--they will destroy the planet because they can see that there is a civilization down there.

OrlandoNative wrote:As for the Rakurai; since obviously Commodore Pei had no means capable of destroying or subverting it (if he had, wouldn't he have left one of any such device in Nimue's cave just in case his nuke attack failed?); and he was the military chief of the Archangels, then why would it *need* replacing? Even with advanced technology, taking out something in orbit from the ground is a non-trivial exercise. Especially if it can defend itself. After the "Fallen" were gone, where was the need for a self-defense-capable platform?

David said this in another thread (viewtopic.php?f=7&t=4824&p=116032&hilit=OBS+deployed#p116032):

runsforcelery wrote:As a result of that uncertainty on his part, the original OBS was a relatively simple (and cheap) system built for a single purpose --- to take out the entire Alexandria Enclave in a single strike --- and it was intended to do so so quickly that neither Kau-Yung and his loyalists among the ex-Navy personnel nor any other "archangels" who might have disagreed with the plan would be able to prevent it from happening.

So, the original OBS was constructed for a very limited purpose. It had a specific target--Alexandria. It did not have any monitoring capability. It did not have any AI. It would only fire when specifically commanded to by authorized personnel. It was merely intended to launch KEWs at a specific, known target at the push of a button. Obviously, whoever built the new OBS wanted to do something more complicated than merely throwing KEWs at Alexandria upon command from the ground.

We don't know exactly what that purpose was, nor do we know what capabilities were built into the new OBS. Merlin fears that it was to prevent high tech from developing, but he doesn't know for sure. Merlin has to use that worst-case assumption as the basis for his decisions, because if it is correct, triggering the OBS will completely defeat his plans.

evilauthor wrote:

OrlandoNative wrote:In any case, I still stand by my observation that leaving *anything* "unnatural" in orbit is criminally stupid if the overriding concern is to hide from Ghaba scouts.

Is it really? If Gbaba scouts are close enough to see the OBS in orbit of the planet, wouldn't they also be close enough to look at the planet itself? And if they actually examine the planet, then humanity is screwed whether the OBS is there or not.

If Gbaba even enter Safehold's solar system, then it's virtually certain that the Gbaba are going to examine Safehold whether there's an OBS or not, because AFAIK, Safehold is the ONLY lifebearing planet in its system. And life bearing planets can produce species that can eventually become space travelers, so the Gbaba will want to see if the planet has such a species.

If the Gbaba DON'T enter the system, then their odds of spotting the OBS at interstellar distances is... probably pretty dismal as long as the OBS isn't giving off any obviously artificial emissions that can be detected at interstellar ranges. It's hard enough to spot individual PLANETS at that range without trying to spot anything in orbit of them.

Actually, no. Safehold is not a technical society at this point. Cities are small, coasts rugged. There really isn't anything artificial *large* enough to be seen even from orbit - much less with just a system "fly-through" - with a cursory search. That point is made way back in OAR; that the *assumption* is that if the Ghaba don't detect any "unnatural" emissions, like those produced by a technical society, they'd probably not look further. Actually makes sense, if the reason behind the Ghaba's genocidal actions is to remove species capable of competing with them. Hominids in a cave even with a fire are not a credible threat; and might never be. A species using radio, having interplanetary travel capabilities, or even just the ability to place satellites in orbit potentially *are*. If the Ghaba are *truly* paranoid, after all, why not just bombard *any* life zone planet they come across; just in case they missed something? How could they be sure they didn't? What if the society, for whatever reason, lived underground; shielded from observation or detection? However, that apparently isn't their way, since the Federation only found devastated worlds that had signs of actual habitation by a technical species prior to encountering the Ghaba themselves.

It was clearly stated that the intent was *not* to give the Ghaba a reason to look closer, if a scout happened to pass through the system. What would be the point if there wasn't some kind of evidence that the Ghaba *wouldn't* look closer unless they noticed something suspicious to begin with? And, again, having a orbital bombardment platform in orbit around the planet is diametrically opposed to that intent.

McGuiness wrote:But that knowledge could very well have come at the cost of waking up something under the Temple that the good guys would prefer to remain asleep for as long as possible - at least until they can get their grubby mitts on it to control or destroy whatever it is.

Another aspect that's occurred to me is that Merlin made the decision early on that he wouldn't use TF technology to make himself appear as an archangel, or to prey on the teachings of the Writ and the CoGA to further his cause.

True. But he's never been all that worried about "technology" waking something up if it's used *outside* the immediate area of Zion and the Temple. He uses SNARC's; comms, skimmers, etc. Even visited Zion himself. While it's true the original Archangels probably used such gear themselves; it's also true that if they were truly worried about any developing technology, they would have made sure to turn on monitoring of anything similar to what they themselves used when they "left". Thus, theoretically *nothing* should be safe. However, we know that obviously isn't so; at least at a distance from the Temple.

Since the islands used for testing were *far* away from Zion and the Temple, the chances of detection were probably virtually indistinguishable from non-existent.

Your point about *using* obviously advanced technology in his day-to-day life is sound, but he *does* use it in disguised forms. His swords, for example, couldn't be duplicated by the current technology. Probably couldn't even be *analyzed* by it. But, then again, they're not really *available* for others to really examine, are they. since he's always got them with him? He has no qualms about using the skimmers if no one can see them.

Similarly, he could realistically use energy weapons in scenarios where there won't be any survivors to note their use. Eg, when the Navy of God sailed, he could have destroyed the entire fleet; without requiring the costly (as far as casualties go) interception by the only partially shell armed Charisian galleons. After all, sailing ships *do* sink for various reasons. For all those expecting the fleet to eventually arrive know, it could have encountered a devastating storm at sea and gone down that way, similar to what happened to the fleet China sent to conquer Japan in our own history.

OrlandoNative wrote:

evilauthor wrote:Is it really? If Gbaba scouts are close enough to see the OBS in orbit of the planet, wouldn't they also be close enough to look at the planet itself? And if they actually examine the planet, then humanity is screwed whether the OBS is there or not.

If Gbaba even enter Safehold's solar system, then it's virtually certain that the Gbaba are going to examine Safehold whether there's an OBS or not, because AFAIK, Safehold is the ONLY lifebearing planet in its system. And life bearing planets can produce species that can eventually become space travelers, so the Gbaba will want to see if the planet has such a species.

If the Gbaba DON'T enter the system, then their odds of spotting the OBS at interstellar distances is... probably pretty dismal as long as the OBS isn't giving off any obviously artificial emissions that can be detected at interstellar ranges. It's hard enough to spot individual PLANETS at that range without trying to spot anything in orbit of them.

Actually, no. Safehold is not a technical society at this point. Cities are small, coasts rugged. There really isn't anything artificial *large* enough to be seen even from orbit - much less with just a system "fly-through" - with a cursory search. That point is made way back in OAR; that the *assumption* is that if the Ghaba don't detect any "unnatural" emissions, like those produced by a technical society, they'd probably not look further. Actually makes sense, if the reason behind the Ghaba's genocidal actions is to remove species capable of competing with them. Hominids in a cave even with a fire are not a credible threat; and might never be. A species using radio, having interplanetary travel capabilities, or even just the ability to place satellites in orbit potentially *are*. If the Ghaba are *truly* paranoid, after all, why not just bombard *any* life zone planet they come across; just in case they missed something? How could they be sure they didn't? What if the society, for whatever reason, lived underground; shielded from observation or detection? However, that apparently isn't their way, since the Federation only found devastated worlds that had signs of actual habitation by a technical species prior to encountering the Ghaba themselves.

It was clearly stated that the intent was *not* to give the Ghaba a reason to look closer, if a scout happened to pass through the system. What would be the point if there wasn't some kind of evidence that the Ghaba *wouldn't* look closer unless they noticed something suspicious to begin with? And, again, having a orbital bombardment platform in orbit around the planet is diametrically opposed to that intent.

David Weber disagrees with you. A couple posts ago, I quoted David's response to almost exactly the same question. Basically, he said that if they were close enough to detect the heavily stealthed OBS, they were close enough to notice signs of civilization on the planet.

The intent was not to give the Gbaba a reason to look closer if a scout happened to pass near the system. If the Gbaba actually enter the system, the gig is up. They will detect a habitable planet, investigate further, discover civilization, and destroy it. The presence of a heavily stealthed and nearly inactive satellite will not make a difference.

OrlandoNative wrote:

McGuiness wrote:But that knowledge could very well have come at the cost of waking up something under the Temple that the good guys would prefer to remain asleep for as long as possible - at least until they can get their grubby mitts on it to control or destroy whatever it is.

Another aspect that's occurred to me is that Merlin made the decision early on that he wouldn't use TF technology to make himself appear as an archangel, or to prey on the teachings of the Writ and the CoGA to further his cause.

True. But he's never been all that worried about "technology" waking something up if it's used *outside* the immediate area of Zion and the Temple. He uses SNARC's; comms, skimmers, etc. Even visited Zion himself. While it's true the original Archangels probably used such gear themselves; it's also true that if they were truly worried about any developing technology, they would have made sure to turn on monitoring of anything similar to what they themselves used when they "left". Thus, theoretically *nothing* should be safe. However, we know that obviously isn't so; at least at a distance from the Temple.

Since the islands used for testing were *far* away from Zion and the Temple, the chances of detection were probably virtually indistinguishable from non-existent.

Your point about *using* obviously advanced technology in his day-to-day life is sound, but he *does* use it in disguised forms. His swords, for example, couldn't be duplicated by the current technology. Probably couldn't even be *analyzed* by it. But, then again, they're not really *available* for others to really examine, are they. since he's always got them with him? He has no qualms about using the skimmers if no one can see them.

Similarly, he could realistically use energy weapons in scenarios where there won't be any survivors to note their use. Eg, when the Navy of God sailed, he could have destroyed the entire fleet; without requiring the costly (as far as casualties go) interception by the only partially shell armed Charisian galleons. After all, sailing ships *do* sink for various reasons. For all those expecting the fleet to eventually arrive know, it could have encountered a devastating storm at sea and gone down that way, similar to what happened to the fleet China sent to conquer Japan in our own history.

The advanced tech Merlin avoids using would be that which gives off a strong energy signature. The SNARCs and all other high tech devices he and the inner circle use are heavily stealthed and were also used by the archangels. (Although Merlin is betting on the SNARC's stealth features, not on them being off the "shoot on sight" list.) The SNARC's remotes are apparently small, emit very little energy as they send a line of sight signal, and they are undetectable by the OBS or anything the archangels might have left around.

Merlin has a very different view about the possibilities of sensors near and inside the Temple though, which is why he won't go within miles of it, nor does he ever have SNARC remotes broadcast from there. For example when the last of the Charisian POWs were put to death in the Plaza of Martyrs, a SNARC's remote recorded the event using a very long distance lens, then moved considerably further away from the Temple before uploading the video. (Which is why Merlin is unlikely to be able to be in position with an M96 at a time when Clyntahn walks out of the Temple.) Bummer!

From the records in Nimue's cave which don't include any accounts of the War of the Angels, Merlin doesn't know what the reaction of the OBS would be to the use of TF energy weapons. He and the inner circle discussed using the skimmer's weapons to sink any ship that might possibly carry the Charisian POWs to Zion, but ruled it out as an option since Merlin felt it would be too likely to set off a response from the OBS. This was before they learned of the Key of Schueler and the millennial return of the archangels.

The rule that the inner-circle is using regarding TF weapons is to avoid anything with a large energy signature, which the skimmer's weapons certainly have. It's possible that the OBS is programmed to ignore that sort of weapon in the same way it ignores the skimmer, but they don't know that, and they can't afford to be wrong, especially now that they know for sure that there's something in the basement of the Temple that they really don't want to wake up!

SWM wrote:

Keith_w wrote:Would you mind explaining WHY I couldn't get a KEW to another planet? I am glad that you are a planetary scientist, which I am not, so you should be aware that Safehold is a planet, which could be used to provide the initial gravity boost. We don't even know if there are other celestial objects in the solar system. There has been AFAIK no mention of astronomy on Safehold.

We are talking about an orbital bombardment system. Such a system depends on using the gravity of the planet to accelerate the weapon downward. A system like that does not launch things upward. The system cannot provide enough force to launch the weapon with escape velocity.

No, Safehold cannot provide the initial boost. A gravity assist requires coming from outside the planetary gravitational field, coming up from behind the planet as it orbits around the star. Basically, the vehicle is falls toward the planet, being accelerated by its gravity. But the planet is moving in the same direction as the vehicle. In essence, this gives the vehicle more time to fall and be accelerated by the gravity. The vehicle eventually reaches closest approach, swings around the planet, and comes out at right-angles to the motion of the planet. Since the planet and vehicle are no longer moving in the same direction, the vehicle spends less time moving out of the gravitational field. So it doesn't lose as much energy as it gained while approaching. The planet gives up some of its kinetic energy while the vehicle gains some kinetic energy.

But this doesn't work if you are already in orbit around the planet. The planet is not moving away from you. If you fall toward the planet and swing around it, you will lose as much energy as you gained while falling. If you are in orbit, you cannot use a gravity boost around the planet. The only way to boost your weapon out of orbit to interplanetary space is by having a powerful launcher or by putting a rocket on the weapon.

I never suggested that you launch things upward. However, there is no evidence that the OBS is in a stable permanent orbit. Indeed, it is probably not, even the ISS has to correct it's orbit on a regular basis. I would not be surprised to discover that the OBS also has to do so, which means it has the means to adjust it's orbit, which means that it can change its orientation, and thus, if it wanted to, launch "upward".

Apparently you have never circled something that is moving. You spend a portion of the time moving in the same direction as the direction of motion and part of the time moving in the other direction.

And exactly what evidence do you have that there aren't rockets on the weapon? Unless the OBS moves to position itself correctly to simply drop the weapon(s) on someone's head, they have to be guided there using some sort of thrusting system, if only to deorbit the weapon.

OrlandoNative wrote:

Keith_w wrote:Would you mind explaining WHY I couldn't get a KEW to another planet? I am glad that you are a planetary scientist, which I am not, so you should be aware that Safehold is a planet, which could be used to provide the initial gravity boost. We don't even know if there are other celestial objects in the solar system. There has been AFAIK no mention of astronomy on Safehold.

As for the rest, I didn't say that it would be particularly effective, just that it could be done. As it was pointed out in OAR, coasting missiles are easy to avoid for spaceships, but not for planets.

It's not so much that you possibly couldn't get a KEW to another planet, it's that a orbital bombardment system wouldn't be the *kind* of KEW one would use to do so. Such a system has minimal capabilities for flight. Basically a way to slow down (so the projectile falls from orbit) and possibly some steering capability while still in space.

For a projectile to travel to another planet, it would need the capability to boost itself out of the gravity field of the planet it's orbiting. That would require significant thrust. For example, the moon trips couldn't just "slingshot" themselves from Earth to Moon, though they could from Moon to Earth if they needed to; due to the Moon as a starting point being "higher" in the gravity well than low Earth orbit was.

"Slingshot" maneuvers require either (1) the projectile *not* being part of the planetary "system" being used for the slingshot (ie, having more than escape velocity to begin with) or (2) significant propulsive assist at some point during the trajectory. Otherwise, the velocity gained diving into the gravity well is lost again as the projectile climbs back out. Conservation of energy - you can't get something for nothing. It's really more of a course *correction* implementation; where one can alter course with minimal fuel usage.

It would not need to boost itself. It could be boosted by the launcher, and when it gets to the other planet, it doesn't need to boost itself out of the gravity well, the vector of transit will do that for it. After all, we do that for our planetary probes and they sure don't carry enough fuel to do that - if they did, they could boost themselves to decent speeds and not worry about slingshotting.

Keith_w wrote:

OrlandoNative wrote:
It's not so much that you possibly couldn't get a KEW to another planet, it's that a orbital bombardment system wouldn't be the *kind* of KEW one would use to do so. Such a system has minimal capabilities for flight. Basically a way to slow down (so the projectile falls from orbit) and possibly some steering capability while still in space.

For a projectile to travel to another planet, it would need the capability to boost itself out of the gravity field of the planet it's orbiting. That would require significant thrust. For example, the moon trips couldn't just "slingshot" themselves from Earth to Moon, though they could from Moon to Earth if they needed to; due to the Moon as a starting point being "higher" in the gravity well than low Earth orbit was.

"Slingshot" maneuvers require either (1) the projectile *not* being part of the planetary "system" being used for the slingshot (ie, having more than escape velocity to begin with) or (2) significant propulsive assist at some point during the trajectory. Otherwise, the velocity gained diving into the gravity well is lost again as the projectile climbs back out. Conservation of energy - you can't get something for nothing. It's really more of a course *correction* implementation; where one can alter course with minimal fuel usage.

It would not need to boost itself. It could be boosted by the launcher, and when it gets to the other planet, it doesn't need to boost itself out of the gravity well, the vector of transit will do that for it. After all, we do that for our planetary probes and they sure don't carry enough fuel to do that - if they did, they could boost themselves to decent speeds and not worry about slingshotting.

Putting my physicist hat on....
If you are talking about a yield anything higher than a kiloton and you don't want to annihilate the target planet you do need to accelerate the projectile as you cant gain sufficient energy form a standing start (i.e. free fall) without dropping a mountain on the target. A small high velocity projectile has the advantage of a smaller launcher and less time to respond. Dropping a rock from low earth orbit under gravity first requires killing the orbital velocity - which is essentially wasted energy, this would be better used for either a higher velocity non vertical strike or scaling up the velocity (and the projectile down further) a vertical strike at relativistic velocities (if you are fast enough then orbital physics becomes irrelevant (short of strange objects like black holes). It take the same energy either way. (BTW a rock free falling from orbit will not dig a significant crater - you have to be at well above escape velocity for that).
As for firing from the ground, your biggest problem would be muzzle blast, this is substantial as a relativistic projectile (or even one at escape velocity) will radiate energy at a fierce rate as the atmospheric air ahead of it is either compressed and moved aside or at relativistic velocities simply annihilated in a gamma ray burst. Think moderate sized nuclear bomb. Not un-obvious. The higher the altitude the lower the blast (less air on the projectile). NASA has done studies on this and yes its possible, even human survivable, if the muzzle is at Everest level heights, and post launch boosted, but much harder and more expensive than a simple rocket launch for one off's, for a lot of small shots it becomes cheaper but the initial infrastructure required is in GDP level numbers. BTW the entire first stage of the Saturn V was to get to 30000ft and Mach 1 and accounted for over half the launch weight.

Keith_w wrote:I never suggested that you launch things upward. However, there is no evidence that the OBS is in a stable permanent orbit. Indeed, it is probably not, even the ISS has to correct it's orbit on a regular basis. I would not be surprised to discover that the OBS also has to do so, which means it has the means to adjust it's orbit, which means that it can change its orientation, and thus, if it wanted to, launch "upward".

Apparently you have never circled something that is moving. You spend a portion of the time moving in the same direction as the direction of motion and part of the time moving in the other direction.

And exactly what evidence do you have that there aren't rockets on the weapon? Unless the OBS moves to position itself correctly to simply drop the weapon(s) on someone's head, they have to be guided there using some sort of thrusting system, if only to deorbit the weapon.

I actually believe that there are rockets on the weapon. David has hinted that the weapons are not mere dumb rocks, which suggests to me that they have guidance systems. But I also believe that they do not have rockets powerful enough to produce escape velocity. The point of these weapons is that they gain their kinetic energy relative to the planet by falling.

I misstated some details of how the gravity assist works. You actually want to approach the planet from any direction except from directly behind, and you want to end up turning towards the direction of motion of the planet. The best boost you can get is to approach the planet from ahead of the planet and end up moving in the same direction as the planet. I also used loose language, because I didn't want to get you bogged down in technical details. So let's get into a little more detail to straighten this out.

Suppose weapon W and planet P are headed toward each other, relative to the local star. W is moving at velocity V relative to the star, and P is moving at velocity U relative to the star, in the opposite direction. Notice that this means the velocity of weapon W relative to planet P is V+U. W just misses the planet, swings around in a tight parabola, and ends up heading in almost the opposite direction it started in. If the planet is so massive that the loss in its velocity is negligible, then the planet P still have a velocity of approximately U relative to the star. But the weapon W now has a velocity approximately V+2U relative to the star! According to the star, the weapon has gained up to twice the velocity of the planet. It is similar to an elastic collision.

But what is the velocity of weapon W with respect to planet P? Before the close approach, the relative velocity of W to P was V+U. After the close approach, the velocity of W to P is V+2U-U, which equals V+U. The velocity of the weapon with respect to the planet is the same before and after! The weapon does not gain any velocity with respect to the planet.

If the weapon did not have escape velocity before the close approach, it will still not have escape velocity after the close approach. Sure, you gain velocity relative to the star, but that doesn't help you escape the planet. Your velocity relative to the star will oscillate up and down, as you continue to orbit around the planet. That's what happens in any orbit. You never escape the planet.

Gravity assist never changes your velocity relative to the planet; it only changes your velocity relative to other objects which are moving relative to the planet. If you are in orbit around the planet, you have to use some other means to get escape velocity. And as I said earlier, I don't believe that the guidance rockets on the OBS are strong enough to give escape velocity.

Sorry to be so long responding, we are away from home for the weekend visiting family. I hope everyone has a good Easter.
SWM, Thank you for that paraphrase of this Wikipedia article. http://en.wikipedia.org/wiki/Gravity_assist. The fact that the object does not change velocity with regard to the planet it is using for the gravity assist is unimportant, what is important is that it changes velocity relative to the neighbourhood stellar object.

It would seem that we have made a lot of assumptions, so I thought it would attempt to detail some of the things that we know about the OBS and point out some of those that we don’t. I may get them wrong, I am, as I said, away from home and don’t have access to the books. Feel free to correct me or add to the lists, but please provide the Textev to support your changes.

Things we know:
1. Langhorne built it without the knowledge of Pei Kau-yung
2. It dropped multiple KEVs across Alexandria in multiple passes
3. It was used against the Abbey and Grave of Khody’
4. It can defend itself
Things we don’t know:
1. Can it reload itself
2. How does it maintain its orbit
3. Is it repositionable
4. What type of orbit is it in
5. How far out is its orbit
6. What do the KEVs consist of:
a. Are they objects floating in space awaiting orders to de-orbit themselves
b. Are they objects loaded into launching platforms grouped together ready to be launched
c. Do they carry thrusters or other means of changing vector both in and out of atmosphere
7. Is it independent or is it under control, ie is it active or is it passive?
8. Where is the control centre
We know that the TF had control of gravity to a certain extent (Compensators, Tractor beams)
We know that they had quite miniature fusion reactors.
We know that they were able to defeat certain sizes of Ghaba fleets
Feel free to add to the list.