Some WarShips pretending to be JumpShips

[Dragon Cat]

Nice Q-WarShips

I'd have been tempted to go with Capital Missiles and Lasers especially with the Monolith - a little range couldn't hurt even if you are trying to draw them in.  It would also open a nuke option since your imitating a JumpShip you know its opening up JumpShips to be targeted so might as well break all the rules

[Maingunnery]

On the contrary, observing the drive plume is the most common means of tracking a vessel in the battletech universe, and contains all the information you need. As for variations, the drive plume is a jet of exhaust gasses with a very predictable relation to the acceleration of the target. If it's more or less energetic than expected but the acceleration remains the same, that can only relate to the mass of the craft. Because that's the only other variable in the equation to affect.

Do you have any in-universe examples? I can't think of any examples in which a ship is analyzed to such a degree on the basis of its drive plume.

Also the drive 'plumes' of BT vessels can't be purely gases, for their Isp, a lot of thrust must come from EM radiation (with the gases being reaction by-product). And the radiation can only be accurately measured if the engine pointing at the sensor. So any engine or reactor damage, that mess up the ratios, could lead to bad measurements.

[Daryk]

Using photons for propulsion is horribly inefficient, and would require even more energy than even BattleTech engines can produce.  It's really best not to look too closely there...

As for Liam's point, I believe those rules are in StratOps...

[Maingunnery]

SO, p119

Any Large Craft may detect the drive exhaust plume of any
moving unit. The plume, seen as a moving bar or point of xrays
and light, provides information on heading, velocity and
distance to the target unit.

SO, p247

For all the energy going into the
drive plume, it’s fairly hard to detect in space because the
exhaust is generally collimated and there’s nothing to scatter
the enormous x-ray signatures.

[Maingunnery]

Nice Q-WarShips

I'd have been tempted to go with Capital Missiles and Lasers especially with the Monolith - a little range couldn't hurt even if you are trying to draw them in.  It would also open a nuke option since your imitating a JumpShip you know its opening up JumpShips to be targeted so might as well break all the rules

For the missiles, I have been thinking about a Mammoth PWS design (30 AR-10s). So that is 30x9 launchers.

[Cryhavok101]

In order for drive plumes to allow that level of examination, wouldn't you need to know what kind of ship it was already, so that you can compare expected mass versus actual mass? Otherwise, wouldn't you just end up with: X energy in plume, Y speed, so it must be Z mass, which if you account for variances of fuel, cargo levels, etc. could be any ships in A-G range? The way I (and my not-greatly-educated-in-such-matters imagination) see it, that info would only be really useful for determining things about the ship once you know which of the possible ships it was. Prior to positive identification, it would be useful for plotting interception points, but that is about it (as far as I can tell).

[Dragon Cat]

For the missiles, I have been thinking about a Mammoth PWS design (30 AR-10s). So that is 30x9 launchers.

Essentially "you have AMS?" "Shoot them all down I dare you"

[Liam's Ghost]

Do you have any in-universe examples?

Researching. I wanna say the arrival of the Kell Hounds and Dragoons before the battle of Luthien, but it's been a while so I can't say for certain.

[Cryhavok101]

Essentially "you have AMS?" "Shoot them all down I dare you"

I have a few designs laying around somewhere designed to run canon AMS equipped ships out of ammo ASAP, which leaves everything really wide open to capital missiles. I had some decent success with the strategy, and that was before nukes were available in the rules. If they have LAMS, you can do the same thing, but with heat rather than ammo: "Oh I'm sorry, have all your guns fallen silent due to LAMS activations? My bad."

[CrazyGrasshopper]

So if you fire too much or burn too much fuel, you need to have a Dropship nearby with spare mass to bring the Q-Merchant's mass back up to the safe zone. 

The argument can be that at the beginning of the mission the mass is the same as the mass of the Jumpship it pretends to be. Of course, you do not fire weapons from a get-go and do not use more thrust and thus more fuel than a Jumpship. Your drive signatures still have to mimic the ones of a Jumpship. Once you use thrust, the cover is instantly blown, as it is when you use weapons. So, in the beginning of an operation you do not have a problem you mentioned, and afterwards, the cover does not matter anyway.

Do you have any in-universe examples?

The class of the Warship belonging to the Green Ghosts was identified by its signature (Interstellar Players 3). In Jihad sourcebooks you can find some other instances, IIRC.

[Dragon Cat]

I have a few designs laying around somewhere designed to run canon AMS equipped ships out of ammo ASAP, which leaves everything really wide open to capital missiles. I had some decent success with the strategy, and that was before nukes were available in the rules. If they have LAMS, you can do the same thing, but with heat rather than ammo: "Oh I'm sorry, have all your guns fallen silent due to LAMS activations? My bad."

That's it defences are not guaranteed to succeed they just make it a lot harder

[idea weenie]

In order for drive plumes to allow that level of examination, wouldn't you need to know what kind of ship it was already, so that you can compare expected mass versus actual mass? Otherwise, wouldn't you just end up with: X energy in plume, Y speed, so it must be Z mass, which if you account for variances of fuel, cargo levels, etc. could be any ships in A-G range? The way I (and my not-greatly-educated-in-such-matters imagination) see it, that info would only be really useful for determining things about the ship once you know which of the possible ships it was. Prior to positive identification, it would be useful for plotting interception points, but that is about it (as far as I can tell).

Most locations already have a book of common Jumpship types (Merchant, Scout, Invader, aso).  The local sensors can measure the output from the exhaust in terms of tons of thrust (brightness, spectral shift, spectral composition, etc), compare that to known Jumpship hulls, and if it falls outside that range will contact the Q-Jumpship with "Hey, we don't recognize your ship, what type is it?" hail.  Usually followed by "we don't recognize that design, we're going to make a health & safety examination, plus Kevin wants to add a note to his scrapbook of Jumpship types".  At that point, the Q-Jumpship has to make a choice to allow the other guys on board.  If they get close enough to recognize it as a Merchant Jumpship but you are only putting out 10,000 tons of thrust and getting .1G acceleration, that means your 'Merchant' is 20,000 tons underweight, and the locals start getting suspicious.

The argument can be that at the beginning of the mission the mass is the same as the mass of the Jumpship it pretends to be. Of course, you do not fire weapons from a get-go and do not use more thrust and thus more fuel than a Jumpship. Your drive signatures still have to mimic the ones of a Jumpship. Once you use thrust, the cover is instantly blown, as it is when you use weapons. So, in the beginning of an operation you do not have a problem you mentioned, and afterwards, the cover does not matter anyway.

True, on the way in it would be imitating its Jumpship profile, so no problems there.

On the way out it needs to be taking back routes (i.e. transiting through uninhabited systems) if it can't refill its fuel tanks and add cargo to bring it up to proper mass range.

[Maingunnery]

Most locations already have a book of common Jumpship types (Merchant, Scout, Invader, aso).  The local sensors can measure the output from the exhaust in terms of tons of thrust (brightness, spectral shift, spectral composition, etc), compare that to known Jumpship hulls, and if it falls outside that range will contact the Q-Jumpship with "Hey, we don't recognize your ship, what type is it?" hail.  Usually followed by "we don't recognize that design, we're going to make a health & safety examination, plus Kevin wants to add a note to his scrapbook of Jumpship types".  At that point, the Q-Jumpship has to make a choice to allow the other guys on board.  If they get close enough to recognize it as a Merchant Jumpship but you are only putting out 10,000 tons of thrust and getting .1G acceleration, that means your 'Merchant' is 20,000 tons underweight, and the locals start getting suspicious.

I haven't found any reference that the thrust can be calculated to such accuracy. The sources that are present do say that X-rays are a large part of the thrust (see my earlier post), so that would make it really difficult to make accurate measurements. At best one could make an identification and thrust estimation based upon the dispersal pattern/shape of any plasma left by the plume plume.



The references for the Peregrine do make me think that it might be a Clan-spec Surveillance ship, beneath 200kt, low on weaponry, was mistaken for a Jumpship at first. This could make it a surveillance ship based upon the look of the Invader JumpShip. It would also explain why it was made in small numbers and later taken out of service.

Code: [Select]

                    AeroTech 2 Vessel Technical Readout
                                  VALIDATED

Class/Model/Name:  Peregrine (Surveillance) WarShip
Tech:              Clan / 2969
Vessel Type:       WarShip
Rules:             Level 2, Standard design
Rules Set:         AeroTech2

Mass:              150.000 tons
K-F Drive System:  (Unknown)
Length:            505 meters
Sail Diameter:     878 meters
Power Plant:       Standard
Safe Thrust:       5
Maximum Thrust:    8
Armor Type:        Ferro-carbide
Armament:         
   18 AMS
   24 Large Pulse Laser
    6 NL45
    1 AR10 Launcher
    1 Large Naval Comm-Scanner
------------------------------------------------------------------------------
Class/Model/Name:  Peregrine (Surveillance) WarShip
Mass:              150.000 tons

Equipment:                                                            Mass 
Power Plant, Drive & Control:                                       45.000,00
Thrust:  Safe Thrust: 5
      Maximum Thrust: 8
Kearny-Fuchida Hyperdrive:  Compact (Integrity = 5)                 67.875,00
Jump Sail (Detachable): (Integrity = 3)                                 38,00
Structural Integrity: 46                                             6.900,00
Total Heat Sinks:    350 Double                                          5,00
Fuel & Fuel Pumps:                                                   3.060,00
Bridge, Controls, Radar, Computer & Attitude Thrusters:                375,00
Fire Control Computers:                                                   ,00
Armor Type:  Ferro-carbide  (180 total armor pts)                      136,00
                           Capital Scale Armor Pts
   Location:                            L / R
   Fore:                                 30
   Fore-Left/Right:                   30/30
   Aft-Left/Right:                    30/30
   Aft:                                  30

Cargo:
   Bay 1:  Small Craft (2) with 2 doors                                400,00
           Cargo (1) with 2 doors                                      566,00
   Bay 2:  Cargo (1) with 1 door                                    14.687,00

DropShip Capacity:  3 Docking Hardpoints                             3.000,00
Grav Deck #1:  (65-meter diameter)                                      50,00
Escape Pods:  6 (7 tons each)                                           42,00

Crew and Passengers:
     17 Officers (16 minimum)                                          170,00
     70 Crew (58 minimum)                                              490,00
     14 Gunners (14 minimum)                                            98,00
     25 Marine Battle Armor Troopers/Elementals                        175,00
     10 Bay Personnel                                                     ,00
Weapons and Equipment      Loc        SRV    MRV    LRV    ERV  Heat    Mass
------------------------------------------------------------------------------
3 AMS(120 rounds)          Nose        --     --     --     --    3      6,50
3 Large Pulse Laser        Nose     3(30)  3(30)  3(30)     --   30     18,00
3 NL45                     FL/R        14     14     14     14  420  5.400,00
3 AMS(120 rounds)          FL/R        --     --     --     --    6     13,00
3 Large Pulse Laser        FL/R     3(30)  3(30)  3(30)     --   60     36,00
3 Large Pulse Laser        L/RBS    3(30)  3(30)  3(30)     --   60     36,00
3 AMS(120 rounds)          AL/R        --     --     --     --    6     13,00
3 Large Pulse Laser        AL/R     3(30)  3(30)  3(30)     --   60     36,00
3 AMS(120 rounds)          Aft         --     --     --     --    3      6,50
3 Large Pulse Laser        Aft      3(30)  3(30)  3(30)     --   30     18,00
1 AR10 (5 KW, 5 WS, 5 B)   Aft          *      *      *      *   20    850,00
1 Large Naval Comm-Scanner                                             500,00
------------------------------------------------------------------------------
TOTALS:                                              Heat: 698     150.000,00
Tons Left:                                                                ,00

Calculated Factors:
Total Cost:        4.454.746.000 C-Bills
Battle Value:      23.268
Cost per BV:       191.453,76
Weapon Value:      16.030 (Ratio = ,69)
Damage Factors:    SRV = 607;  MRV = 504;  LRV = 339;  ERV = 90
Maintenance:       Maintenance Point Value (MPV) = 178.730
                   (57.444 Structure, 103.588 Life Support, 17.698 Weapons)
                   Support Points (SP) = 223.650  (125% of MPV)
BattleForce2:      Not applicable


[idea weenie]

I haven't found any reference that the thrust can be calculated to such accuracy. The sources that are present do say that X-rays are a large part of the thrust (see my earlier post), so that would make it really difficult to make accurate measurements. At best one could make an identification and thrust estimation based upon the dispersal pattern/shape of any plasma left by the plume plume. 

From Mercenary's Star p51:

"My Lord, we ran a careful analysis of the Dropship's drive flare, course, and delta-V.  The starship's transmission indicated the Dropship to be a Union class, but there are discrepancies.  A Union class masses 3500 tons, and-"
(other person talking)
"Of course, my Lord.  The . . . intruder masses 3200 tons. . . ."

This was when the Dropship was 10 hrs away at 1G thrust, for a distance of ~6.35 million km.

This means they were able to tell that the Dropship was at 8.6% off its listed mass.  I don't know if that is an upper or lower limit of their detection systems though.

(Upper limit means that they would not have spotted if it was smaller percentage, lower limit means they could have gotten the tens place of the Dropship's tonnage depending on the cargo.)

[Maingunnery]

Interesting reference, according to the text they used a telescope? Also this check does not seem routine, it looks like the check was only made because of the presence of a blockade, the Trojan DS using obsolete IFF codes and it not being on any schedule.

But then again, Mercenary Star, is one of the oldest works of fiction with plenty of odd things.
Do we have anymore references? There isn't a consistent picture right now, unless we disregard old fiction or having DS drives be more vulnerable to thrust checks.

[CrazyGrasshopper]

The sources that are present do say that X-rays are a large part of the thrust (see my earlier post), so that would make it really difficult to make accurate measurements.

As it was already pointed out, photons are not effective in propelling the Warship. At all. And I do not understand what you mean by being "a large part of the thrust."

Drives accelerate charged particles (ions) via electric field, that's how you get propulsion. That's how drives work in BTU, and I, actually, do not know any other fundamentally different way for drives to work with the stated effectiveness. Of course, since charged particles have tremendous accelerations, they radiate a lot. There will be components for any frequency in the radiation spectrum, not just X-rays. I'm a bit lazy to make a calculation to determine which part of the spectrum contains the majority of radiation, but the spectrum will be broad for sure. There also can be beaming effects, but they play role only during the later stages of acceleration.

Tl;dr: drives should radiate quite a lot of electromagnetic energy in all directions in a wide spectral range. This happens to be a byproduct of their work. Now, I say "a lot", but there are also space scale distances to consider in order to decide how detectable this radiation is. You need someone with astrophysics expertise to answer such question.

[HobbesHurlbut]

As it was already pointed out, photons are not effective in propelling the Warship. At all. And I do not understand what you mean by being "a large part of the thrust."

Drives accelerate charged particles (ions) via electric field, that's how you get propulsion. That's how drives work in BTU, and I, actually, do not know any other fundamentally different way for drives to work with the stated effectiveness. Of course, since charged particles have tremendous accelerations, they radiate a lot. There will be components for any frequency in the radiation spectrum, not just X-rays. I'm a bit lazy to make a calculation to determine which part of the spectrum contains the majority of radiation, but the spectrum will be broad for sure. There also can be beaming effects, but they play role only during the later stages of acceleration.

Tl;dr: drives should radiate quite a lot of electromagnetic energy in all directions in a wide spectral range. This happens to be a byproduct of their work. Now, I say "a lot", but there are also space scale distances to consider in order to decide how detectable this radiation is. You need someone with astrophysics expertise to answer such question.

Well, Cray is an engineer and he has written for the current rulebooks. He also collaborated to make a fan setting based on BT for the spaceship aspect.

[Black_Knyght]

This was kind of the idea behind the Doppleganger class SpecOps Warship too  O0

http://bg.battletech.com/forums/index.php?topic=56016.0