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-   -   How big would a Lander be? (http://www.travellerrpg.com/CotI/Discuss/showthread.php?t=40169)

bjjones37 July 3rd, 2019 09:17 AM

How big would a Lander be?
 
I have never designed a ship yet and looking over High Guard I am left with some uncertainties. I want to design a lander that that is a small craft. But I want to be able to unclamp from the mainship hull from orbit about 250 miles up, make a safe descent to the planet surface, do some exploratory flying, and then ascend back up to the mainship 250 miles up in orbit.

How big would such a ship need to be? What would it's power requirements be?

And since it is not jump capable, how much larger percentage wise would the mainship need to be for it to catch a ride?

Just for comparison an F-22 Raptor (although not an orbiter) loaded weighs between 32 and 41 tons. SpaceshipTwo is about 10 tons not counting the launch aircraft. And the X-15 was about 17 tons but also launched from an aircraft. I am guessing that for a lander I would need something in the vicinity of 35 to 40 tons (with about half of that being reaction mass). But I have no intuitive feel for the efficiency of Traveller ship technology.

McPerth July 3rd, 2019 09:42 AM

I'd say this will depend on the cargo you want it to be able to land...

In my designs (mostly for MgT and MgT2300, you have the links in my blog) for the Jump (Warp in MgT2300) Frame and Barges and Planetary Invasión Ships, the barges/landers in both cases were 400 dtons...

bjjones37 July 3rd, 2019 09:58 AM

The lander would not be a cargo transport or combat craft, more a survey small craft carrying only mission essential equipment. It would have a crew of one with a one or two passenger potential along the lines of SAR (search air rescue). I had in mind something small enough to be carried by a standard scoutship (for jump purposes) but that may not be feasible.

AnotherDilbert July 3rd, 2019 10:00 AM

Quote:

Originally Posted by bjjones37 (Post 603628)
I am guessing that for a lander I would need something in the vicinity of 35 to 40 tons (with about half of that being reaction mass). But I have no intuitive feel for the efficiency of Traveller ship technology.

Traveller craft don't use reaction mass...

You can use anything from about 10 displacement ton (≈100 tonnes) and up.

Minimum would be something like this:
Code:

QN-0203301-000000-00000-0        MCr 6,7          10 Dton
bearing                                            Crew=1
batteries                                          TL=12
                        Cargo=5 Fuel=1 EP=0,33 Agility=3

                                                      5      6,7
                                    USP    #      Dton      Cost
Hull                Custom            0            10         
Configuration      Cone              2                      1,1
Scoops              Streamlined                                 
Armour                                0                       
                                                               
Manoeuvre D                            3    1        1      0,5
Power Plant                            3    1        1        3
Fuel, #J, #weeks    J-0, 4 weeks                      1         
                                                               
Bridge                                                         
Computer            m/1                0    1        1        2
                                                               
Couch                                      2        1      0,1
                                                               
Cargo                                                5         
                                                               
                                                               
Nominal Cost        MCr 6,65            Sum:        5      6,7

It has 5 Dton (≈50 tonnes) payload, and a 0.33 EP = 83 MW power plant.

AnotherDilbert July 3rd, 2019 10:05 AM

Quote:

Originally Posted by bjjones37 (Post 603630)
It would have a crew of one with a one or two passenger potential along the lines of SAR (search air rescue).

How about:
Code:

QN-0205501-000000-00000-0        MCr 6,2          6 Dton
bearing                                            Crew=1
batteries                                          TL=12
                        Cargo=1 Fuel=1 EP=0,33 Agility=5

Single Occupancy                                      1      6,2
                                    USP    #      Dton      Cost
Hull                Custom            0              6         
Configuration      Cone              2                      0,7
Scoops              Streamlined                                 
Armour                                0                       
                                                               
Manoeuvre D                            5    1        1      0,5
Power Plant                            5    1        1        3
Fuel, #J, #weeks    J-0, 4 weeks                      1         
                                                               
Bridge                                                         
Computer            m/1                0    1        1        2
                                                               
Couch                                      2        1      0,1
                                                               
Cargo                                                1         
                                                               
                                                               
Nominal Cost        MCr 6,21            Sum:        1      6,2

6 Dton, 5 g acceleration, 2 seats, 1 Dt payload (≈10 tonne).

bjjones37 July 3rd, 2019 10:32 AM

Quote:

Originally Posted by AnotherDilbert (Post 603631)
Traveller craft don't use reaction mass...

MGT2 Traveller Highguard P.16

"Maneuver drives do not require fuel but, though reaction drives do.
The amount of fuel a reaction drive requires is determined as the percentage of ship's total tonnage and is equal to 2.5% per Thrust hour."

I am assuming that you are referring to using a gravity drive for maneuvering and I am not sufficiently informed as to the pros and cons of a gravitic drive, and what forces it exerts on its surrounding environment.

AnotherDilbert July 3rd, 2019 10:56 AM

OK, MgT2.

Gravitic drives are far more efficient, they work for weeks on end. Reaction drives are generally used as an addition or on very low tech level craft.

Gravitic drives interact with the gravity field of any nearby planet, and produce no noticeable effect except perhaps a slight glow, no exhaust or radiation. A factor 1 manoeuvre drive produces 1 g (≈10 m/s˛) acceleration.


A minimun lander might look something like this:
https://i.imgur.com/sdMaqD9.png
10 Dt, 4 g acceleration, 2 seats, 5 Dt payload, 4 weeks endurance.


With a reaction drive instead it would be:
https://i.imgur.com/7eMyalE.png
10 Dt, 2 g acceleration, 2 seats, 4 Dt payload, 2 hours endurance.

kilemall July 3rd, 2019 11:33 AM

Most Traveller versions don't have reaction mass type drives, a few do or have hypereffecient ones such as the HEPLAR drive.
The Mongeese have pretty much the option outlined above.


The big question you have to ask yourself is what sort of universe do you want with the primary focus being what feel and options do you want to present to the player?


Reaction mass only milieus are going to do a LOT of low vee coasting and not a lot of operational/tactical vector changes, and a big dependence on jump drives for even interplanetary travel.
Classic type Traveller postulates jetting around realspace with ridiculously low fuel use but big fuel use for jump. So small craft such as what you are asking about are as likely to be making high speed interplanetary trips as doing a planet landing.


A common later Traveller version thing is that grav drives are useless past a 1000D limit to a grav source. So outer systems and spaces between systems are off-limits unless you know of some rock you can maneuver against out there.
For MTU, that's no good as a big part of the environment is the Oort Cloud, both refueling point for J-1 only ships AND the interstellar communities backwoods/swamp lowlife/illegals operating area. So I redid the drive tech to support that play choice.

So my recommendation is learn the MgT2 system including the two ones outlined, maybe one of the other Traveller versions closer to your preference, then make tech 'homerule' choices that support what sort of play you want to engender that works for your players.

bjjones37 July 3rd, 2019 11:33 AM

It looks very nicely done. But I could use some clarification.

My book does not make reference to a dton. I looked up displacement tonnage but it refers to water displacement of naval vessels. Is there a conversion factor to straight tonnage? My examples in the book are all simply listed as tons.

And a question about gravitic drives. How does it interact with the gravitational field? I am visualizing a column of reverse gravitational force focused with a gravity lens to be perpendicular to a planetary surface focused with a gravity lens comparable to the mass of the object. While the lens could be used to widen the arc a disperse the force somewhat, a hovering multi-ton craft would still crush whatever was under it unlike say a helicopter which uses air flow to generate lift. It has some downward component, but just a fraction of it's actual mass. While the gravity component would be no issue at a spaceport, it could severely impact the special purpose application of this lander.

kilemall July 3rd, 2019 11:43 AM

Quote:

Originally Posted by bjjones37 (Post 603640)
It looks very nicely done. But I could use some clarification.

My book does not make reference to a dton. I looked up displacement tonnage but it refers to water displacement of naval vessels. Is there a conversion factor to straight tonnage? My examples in the book are all simply listed as tons.

And a question about gravitic drives. How does it interact with the gravitational field? I am visualizing a column of reverse gravitational force focused with a gravity lens to be perpendicular to a planetary surface focused with a gravity lens comparable to the mass of the object. While the lens could be used to widen the arc a disperse the force somewhat, a hovering multi-ton craft would still crush whatever was under it unlike say a helicopter which uses air flow to generate lift. It has some downward component, but just a fraction of it's actual mass. While the gravity component would be no issue at a spaceport, it could severely impact the special purpose application of this lander.


A dton is usually defined as a metric ton of hydrogen in liquid state. That is a very light density thing, so dton for the purposes of ship design is a displacement/volume thing. Usually defined as 14 or 13.5 cubic meters. This link goes into it.
https://www.freelancetraveller.com/f...d/tonnage.html

We have massively gearhead conversations about weight vs. volume, so we can point you to threads if you want to explore that. In most versions mass is neutralized or not a major factor, some versions or homerules scratch the wonk itch and it does count.
The grav thing has been defined various ways, including some explicit shots at it in some versions. I'd go ahead and learn the various options, which others can explain better then I (a lot of of it is neutralization/buoyancy rather then the repulsion you describe and I prefer), but again it's going to ultimately be what works for your universe.


Speaking of grav, grav vehicles are low orbit capable at least, so an option for your lander is something like the classic GCarrier, found in most versions. A lot cheaper then small craft, but also typically not interplanetary/out of planet 10D capable or safe for radiation hull if nothing else, and usually does not tote ship-level weaponry.

That too is something to think about when considering which tech prevails in your universe.


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