Knight Hawks - ADF explained

Anonymous's picture
Anonymous
May 29, 2008 - 8:16am
Can someone explain to me how a ship a ship can have the same acceleration and deceleration without turning around? Do they use powerful attitude thrusters or something?

Curosity killed the dralasite. ;-)

Comments:

AZ_GAMER's picture
AZ_GAMER
May 29, 2008 - 8:39am

I guess it would depend on the model of propulsion you were using. For example if you were using some form of field propulsion then the process would be reversing the field. If you were using a direct thrust type propulsion you would have to be able to either vent the thrust in the opossing direction, use some kind of engine rotation, actually turn the ship around, or use some form of attitude thrusters. The ship configuration would probably have a lot to do with it. On the other side of the coin, maybe just the reduction of constant thrust in conjunction with RCS or attitude thrusters/retros would slow the ship. Now were getting in math, I hate math, Terlo is really good at figuring this stuff out, he is a rocket scientist after all.


Sam's picture
Sam
May 29, 2008 - 9:17am
It really depends on how much "hard" science you inject into the game. But unless your drives are field based (or you have some sort of inertial dampening device???), you would still have to thrust in the direction of your original vector to slow down/eliminate that vector.  

Anonymous's picture
w00t (not verified)
May 29, 2008 - 9:37am
I was referring to the board game and the RPG rules that expand AD.
Perhaps it's a simple mechanic in the game.



TerlObar's picture
TerlObar
May 29, 2008 - 10:32am
Yes, it is just a simple mechanic in my opinion.  The way I read the rules all the engines in SF are thrust based, not field based.  So in real-life you would have to flip your ship around and thrust in the "forward" direction to slow down as Sam indicated.  That being said, since the boardgame turns are 10 minutes long, it really isn't that big a deal to imagine the ship turning around and thrusting to slow down.  The rotation maneuvers don't really take that long compared to 10 minutes.

MR on the other hand is 100% a game mechanic, there is no way to reconcile that with real life.
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Will's picture
Will
May 29, 2008 - 2:39pm

And, I believe the originial KH rules do require you turn around to decelerate. If not, they should've.

"You're everything that's base in humanity," Cochrane continued. "Drawing up strict, senseless rules for the sole reason of putting you at the top and excluding anyone you say doesn't belong or fit in, for no other reason than just because you say so."


—Judith and Garfield Reeves-Stephens, Federation

AZ_GAMER's picture
AZ_GAMER
May 30, 2008 - 6:11am

Well it sounds practical, however I just have a little difficulty envisioning a gigantonormous battleship flipping a 180' to turn around. I have always played this rule during game sessions but until know I never considered how this might look. I may come around on this but it does seem a little awkward.

Now are we pretty much all in agreement that their probably is some form of RCS thrusters to move the ship around for minor manuvering, say around a station or in port, that would not require the beast to flip around to speed up or slow down?

Terl what do you think about the speculative tech of field based proplusion, would this rule still apply or just need a house rule re-write.


Corvus's picture
Corvus
May 30, 2008 - 6:49am
AZ_GAMER wrote:

Well it sounds practical, however I just have a little difficulty envisioning a gigantonormous battleship flipping a 180' to turn around.



If you think that's hard, try getting your head around the image of a 3500-meter superdreadnought from the Honor Harrington universe doing the same thing. Wink
If you wish to make an apple pie from scratch, you must first invent the universe. -- Carl Sagan

Imperial Lord's picture
Imperial Lord
May 30, 2008 - 7:10am
You are not required to turn around in the canon rules to decelerate.  Not at all.

My guess is that there are some kind of retro rockets that take care of that.

Anonymous's picture
w00t (not verified)
May 30, 2008 - 8:04am
Imperial Lord wrote:
You are not required to turn around in the canon rules to decelerate. Not at all.

My guess is that there are some kind of retro rockets that take care of that.


I agree this is the way KH is written.
So... I should be able to enter the Void -- in reverse. Laughing

Imperial Lord's picture
Imperial Lord
May 30, 2008 - 8:21am

Well Larry, come to think of it, sure...


TerlObar's picture
TerlObar
May 30, 2008 - 10:20am
You asked for it and I don't really feel like working today (my kids are out of school and I leave on Sunday for a week on Florida to watch my satellite launchCool). Here we go:

Imperial Lord is right, in the canon boardgame rules you do not have to turn around to deccelerate, you just slow down with your current facing. Of course I've always taken the boardgame rules as an abstraction of the way things really work.

For example, in the KH Campaign Book on page 33 it describes space travel for a jump as accelerating toward your destination until nearing jump speed, making the jump, taking "several minutes" to turn around and then decclerate with the engines in the direction of motion to slow down. I've always assumed that it took "several minutes" because they were being careful and making sure everything worked after the jump. The ships should be capable of making the turns on the order of a single minute, not several. Thus the concept is that to slow down you have to turn around.

So how fast can the ships turn? Some examples I know about.
  1. The satellite I work on (GLAST) is slow and it takes about 10s to turn one degree or a half hour to turn 180 degrees. However, it doesn't need to turn quickly for it's science so it wasn't designed to. For reference it is about 3m long.
  2. The Swift satellite (about 6m long) turns 50 degrees in 75 seconds or about 4.5 minutes to do a 180. Now both of these satellites are not using RCS thursters to turn but are using flywheels mounted in the body of the space craft.
  3. The Space Shuttle (hereafter SS), which is effectively a HS 2 ship in SF terms, can do a 180 degree turn in less than 30 seconds if it needed to. I don't think they really ever turn it that fast but it is possible. I don't have exact numbers on this one but based on the Orbiter flight simulator, which is supposed to be a very realistic replication of the SS, it took 20s to do a 180 degree flip. If my Space Shuttle Operatator's Manual wasn't packed in a box somewhere I might be able to to the math and get exact numbers as I believe it had acutal numbers for the thrust provided by the engines and the moments of inertia for the orbiter.
Now the SS RCS thrusters are 540 times smaller than it's main engines and there are engines out there that provide ~2.5 times the thrust of the shuttle main engines. So making the assumtion that the mass of the Star Frontiers ships scales linearly with their volume (a very rough approximation) and that the SS is equivilent to a HS 2 ship, you could use these large engines as the RCS engines on the bigger ships and have a HS 13 ship that could turn 180 degrees in 20 seconds in a pinch (i.e. combat). Now the SS uses 3 of it's RCS engines together in a pod to achieve those rotation rates. So you'd have to gang 3 of the big ones together to get the same effect. If you ganged 5 of the big ones together per pod you could spin a HS 15 ship 180 degrees in about 30 seconds and a HS 20 ship in about 1.5 minutes.

Using those numbers, we get the following forces felt during the turn. On the bridge of the Battleship turning in 80 seconds, you would feel about 1/20th of a gee of sideways acceleration which is no big deal. Remember you are strapped into an acceleration couch capable of handling at least 2 g but more likely 5+ g. On the HS 15 ship turning in about 30 seconds, you'd get about .3 gees. On the HS 13 ship (a Light Cruiser) turning in 20 seconds you'd feel 1/2 a gee. On the SS turning in 20 seconds you'd only feel 0.05 gees. If you mounted big enough engines on the battleship to turn 180 degrees in 30 seconds you'd feel 0.4 gees of acceleration. If you turned the battleship in 20 seconds you feel 0.94 gees sideways. Those numbers are for the extremities of the ship. The forces get smaller as you move closer to the center of mass.

The bottom line is that you can spin ships that fast even with modern technology and there is no reason to believe that in the SF universe there are not more powerful and more efficient engines (and they don't have to be that much better). The gee forces involved are not that big and the ships should easily be able to handle the stresses.

Okay, now for needing to turn around to slow down. The KH rules (again on page 33 but also in other places) specifically states that there is only artificial gravity when under thrust. If you don't have your engines on, you are in a zero-gee environment. This is not Star Wars or Star Trek where you have artificial gravity generators to keep your feet on the floor whether you are drifting or if you are accelerating at 5g perpendicular to the direction you are standing (i.e. you should be smashed against the back wall). So, if you don't turn around to deccelerate the forces you experience would be working to pull you out of your acceleration chair against the restraints instead of pushing you into it like it was designed for. That could be painful.Cry Not to mention the fact that anything not secured would go flying up and smash into the celing of the room.

As for field propulsion, I've never really thought much about it. If it were possible, you still have the issue of the force vectors being in the "wrong" direction relative to the design of your ship if you didn't turn around to do the decceleration.

So I think Star Frontiers ships do have to turn around to deccelerate but that the rotations can happen quick enough that you can be chasing a target, rotate, deccelerate for the round, rotate back and fire you cannon all in the same 10 minute turn if you need to. Now if you scale down the combat turn, then you can't do that and you need a completely new game mechanic.

Also, these rotations are completely separate from the ship's "MR". That particular statistic has to do with changing the direction of the ship's motion and is completely unrealistic at any speeds greater than about half the ships ADF in hexes per turn. For travel in some medium (e.g. air or water) the MR concept makes sense, it is just the turn speed using friction with the medium to help you turn (lift on an aerodynamic body, pressure against the rudder and/or sails in water, etc). In the vacuum of space, there is no medium by definition and all you have is your engines and Newton's Laws of Motion. To turn you have to stop all your motion in the direction you don't want to be going and then thrust in the direction you do want to go.
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TerlObar's picture
TerlObar
May 30, 2008 - 10:22am
w00t wrote:
Imperial Lord wrote:
You are not required to turn around in the canon rules to decelerate. Not at all.

My guess is that there are some kind of retro rockets that take care of that.


I agree this is the way KH is written.
So... I should be able to enter the Void -- in reverse. Laughing

Or sideways if you wanted to.  I always took it that you used the RCS thrusters to nudge you up over the 0.01 c mark so you could theoretically do it in any orientation you wanted.
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Will's picture
Will
May 31, 2008 - 1:09am
Corvus wrote:
AZ_GAMER wrote:

Well it sounds practical, however I just have a little difficulty envisioning a gigantonormous battleship flipping a 180' to turn around.



If you think that's hard, try getting your head around the image of a 3500-meter superdreadnought from the Honor Harrington universe doing the same thing. Wink


Or a Greenfeld super-battlewagon from the Kris Longknife series.

"You're everything that's base in humanity," Cochrane continued. "Drawing up strict, senseless rules for the sole reason of putting you at the top and excluding anyone you say doesn't belong or fit in, for no other reason than just because you say so."


—Judith and Garfield Reeves-Stephens, Federation

AZ_GAMER's picture
AZ_GAMER
May 31, 2008 - 6:01am

It's good to have a rocket scientist in the forumCool Thank you. I will have to re-read the post a couple of times to digest all that data but it is very helpful.

So when I am working on an art project showing this manuver how does everyone think this should look?

If I understand the posts correctly, it is assumed that on the game board the counter doesn't have to flip around to simulate decelleration but it is assumed that the ship has done this in the course of the turn. Or are the engines capable of producing reverse thrust to decelerate without any turn.

I think I like the simplicty of artificial gravity generator technology on larger ships like in the Star Trek Universe, at least for faster game play...lol. However, a small POS craft made of scrap and duct tape would be fun to have no gravity generators and make the PC's work around that environment....muhuhaaaaaahhahahahaahahaaa....ack, cough, choke, gasp, wheeze, huhahahahaaahaa! Sometimes the evil Ref just has to be let out to harass the PC's Kiss


TerlObar's picture
TerlObar
May 31, 2008 - 7:06am
Quote:
Or are the engines capable of producing reverse thrust to decelerate without any turn.
If you want artificial gravity generators and field-based propulsion in your campaign you can do that. If the engines have to throw stuff out the back to provide thrust or you can't compensated for the reversed force vectors throwing you against they ceiling, then yes you have to turn around to deccelerate. And as soon as you have artifical gravity generators, you don't need the perpendicular to axis deckplans descibed in the KH rules either. As you said, in the end it's up to the referee. Personally I don't use them.
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Will's picture
Will
June 1, 2008 - 1:39pm
Terl Obar's a rocket scientist.

I always thought he was a Psyclone(sic)....

"You're everything that's base in humanity," Cochrane continued. "Drawing up strict, senseless rules for the sole reason of putting you at the top and excluding anyone you say doesn't belong or fit in, for no other reason than just because you say so."


—Judith and Garfield Reeves-Stephens, Federation

AZ_GAMER's picture
AZ_GAMER
June 2, 2008 - 1:19am
Terlobar - Okay ya' got me thinking now on the subject deck plans perpendicular to ship axis. I always recognized this but never gave it a lot of serious thought. From your earlier explanation about ADF relating to the hard science examples makes a lot of sense. However, I would like to try and reconcile this if possible with the common sci-fi media concept which often uses a horizontal to axis deck arrangement much like that of modern millitary naval craft. I will be opening a new discussion about this but wanted to get the ball rolling here since this is where it got brought up. I hope the community can help me out with some thought provoking discussion in another topic forum. Can horizontal deck placement be used? If so what hard science would be needed or support this (conventional or speculative)? How does this effect atmo capable vessels with perpendicular deck placement?, and finally thoughts on why most artistic depictions seem to be of horizontal deck placement and how to reconcile to keep with the continuity and spirit of the game's vision. Thanks meet me at the new topic to discuss.

Shadow Shack's picture
Shadow Shack
June 8, 2008 - 6:50am
Simple answer is thrust deflectors, like an airliner uses to shed speed after touching down on the runway. What happens is the tail cone splits like a clamshell to cover the afterburner, and when the thrust is applied as such the air is directed forward instead of aft, thus slowing the plane down. Episode 3 of Star Wars opens with a similar visual, Greivous' ship uses thrust deflectors to get out of the nose dive.

Game mechanics the rules state (as well as at least one module) the tail coming around to decelerate. Simply put, some ships would not be able to turn around during the 3-15 seconds in the void in order to decelrate as such (such as any ship with a MR less than 3, meaning it would take at least two ten minute turns to rotate 180º), so both systems are used...thrust deflectors in combat or void hopping, rotational maneuvers for standard 1G operation.
I'm not overly fond of Zeb's Guide...nor do I have any qualms stating why. Tongue out

My SF website

Will's picture
Will
June 8, 2008 - 8:56am
In Stover's novelization, Anakin opened the airlocks to slow down the chunk of Invisible Hand prior to landing it.

"You're everything that's base in humanity," Cochrane continued. "Drawing up strict, senseless rules for the sole reason of putting you at the top and excluding anyone you say doesn't belong or fit in, for no other reason than just because you say so."


—Judith and Garfield Reeves-Stephens, Federation

Shadow Shack's picture
Shadow Shack
June 8, 2008 - 12:25pm
There was a lot that transpired in the novel that we didn't see on the big screen or DVD. Including the conspiring discussion that transpired between Dooku and Palpatine before Anakin and Obi-Wan arrived.

Although if memory serves me the airlocks were at least mentioned in the flick before the ship snapped in two, I believe the line was "Open all airlocks and extend all drag fins."
I'm not overly fond of Zeb's Guide...nor do I have any qualms stating why. Tongue out

My SF website

Will's picture
Will
June 9, 2008 - 1:03am

By Jove, you're absolutely right.... 

"You're everything that's base in humanity," Cochrane continued. "Drawing up strict, senseless rules for the sole reason of putting you at the top and excluding anyone you say doesn't belong or fit in, for no other reason than just because you say so."


—Judith and Garfield Reeves-Stephens, Federation