Gravity getting in the way of Scooping Fuel

[ColinD]

As I sit here drinking Hot Chocolate from my Traveller Mug (Thanks TravellerCon/USA) my thoughts turn to High Gravity and Starships. On page 79 of the Starship Operators Manual, the blue box states,
"If the ship only has 1G of thrust, avoid landing on worlds with Size code B or higher unless there is good reason to believe that ship can take back off again." It seems that High Gravity Worlds might permanently ground a Starship with an insufficient Manoeuvre Drive.

So if your starship ends up around Terra/Sol (Earth) with a pick of 4 Gas Giants to choose from, would Jupiter have too big of a Gravity Well for a Starship that has an M Drive of 1? Would it only be able to skim fuel from Saturn with an escape velocity of 10.44 m/s2 and a gravity of 1.065 g or
Neptune with it's escape velocity of 11.15 m/s2 and a gravity of 1.137 g rather than Jupiter (24.79 m/s2 and a gravity of 2.528)?

I would imagine that if you ended up in a System with a Gas Giant that had a high surface gravity like HD 80606 b with a gravity of 9.6 g you would not be able to get close enough in your starship to use the fuel scoops.

What do you all think?

 

[Fluffy Bunny Feet]

I use the assumption that since 1g ships are VERY common especially among freighters they must be able to handle launch from higher g worlds so therefore the M-Drive is more efficient the deeper you are in a gravity well so you can land and take off from higher g locations. So 1g vessels don't really make a lot of sense to have landing ability.

Now without that assumption you might achieve orbit by using a long runway and your aerodynamic surfaces to get into the air and keep accelerating and achieving higher altitude till you (hours later) finally get to orbit. Your pilot rolls would be used mostly to reduce the time (or lengthen it) and you might need more than 1 pilot to relieve one another. Might not be viable on thinner atmosphere worlds.

On the other hand I'm thinking also of a launch grid based on repulsors (which are also tractors) to land/launch spacecraft. The larger they are the lower TL they are. So establish your own minimum TL and use them as a launch system to put all those 1 g craft in orbit (and land them in the first place). Range is short but that gets you to LEO (or equivalent). Low TL worlds might have trouble building them but then again colonizing without them would be difficult anyhow so there should be 2g freighters to bring in components.

 

[Sigtrygg]

I assume that streamlined and airframe ships generate lift as they accelerate horizontally at 1g continuous acceleration. This allows them to fly.

As to skimming a ship does not need to re-orbit the gas giant to skim fuel, they adjust their orbit such that it takes them into the atmosphere to skim fuel, the m-drive can be used to correct for any velocity lost to drag.

Once skimming is complete it is a matter of adjusting the orbit again to swing the ship a long way from the gas giant, at which point the m-drive can be used to break orbit.

 

[Condottiere]

Slingshotting would give enough momentum not to get trapped, though not sure how much you can gas up with each flyby.

Ye high burn thruster, which takes up additional volume, and will eat through some of that gas.

 

[ColinD]

Thanks everyone! This will make the fuel scooping a little more interesting in my games.

 

[AnotherDilbert]

As I sit here drinking Hot Chocolate from my Traveller Mug (Thanks TravellerCon/USA) my thoughts turn to High Gravity and Starships. On page 79 of the Starship Operators Manual, the blue box states,
"If the ship only has 1G of thrust, avoid landing on worlds with Size code B or higher unless there is good reason to believe that ship can take back off again."

The start of the text-box explains how generally assumed lifters and M-drives can counteract more than 1 G gravity together.

It seems that High Gravity Worlds might permanently ground a Starship with an insufficient Manoeuvre Drive.

Yes, where insufficient is 1 G M-drive on a 1.5 G world (≈size B).
1 G drives and lifters are enough to take off from most size A worlds, hence the vast majority of inhabited worlds.

So if your starship ends up around Terra/Sol (Earth) with a pick of 4 Gas Giants to choose from, would Jupiter have too big of a Gravity Well for a Starship that has an M Drive of 1? Would it only be able to skim fuel from Saturn with an escape velocity of 10.44 m/s2 and a gravity of 1.065 g or
Neptune with it's escape velocity of 11.15 m/s2 and a gravity of 1.137 g rather than Jupiter (24.79 m/s2 and a gravity of 2.528)?

You don't stop or land when you scoop, you pass through the upper atmosphere (where apparent gravity hence escape velocity is lower) with enough velocity to escape again, at least together with the acceleration from your drive.
Note that lifters would reduce escape velocity significantly.

If you want to hide for a long time deep in the GG atmosphere (like an SDB) you need enough acceleration to overcome GG gravity.

I would imagine that if you ended up in a System with a Gas Giant that had a high surface gravity like HD 80606 b with a gravity of 9.6 g you would not be able to get close enough in your starship to use the fuel scoops.

That's the "surface" gravity at some depth in the atmosphere. What's the gravity at the top of the atmosphere?
Do faster, shallower scoop runs and you'll be fine...

 

[Arkathan]

Consider our current solar robot: the Parker Solar Probe.
No M-Drive, but it dives through the solar atmosphere.
Get sufficient velocity while plotting a gravitationally advantageous course and you will come out the other side.
Whether or not important pieces fall off in the process depends on your piloting skill roll.

 

[ColinD]

Consider our current solar robot: the Parker Solar Probe.
No M-Drive, but it dives through the solar atmosphere.
Get sufficient velocity while plotting a gravitationally advantageous course and you will come out the other side.
Whether or not important pieces fall off in the process depends on your piloting skill roll.

I do wonder how do you think those inside will handle the heavy gravity.

 

[Condottiere]

Upto two and nine tenths, if presumably, temporarily.

 

[Sigtrygg]

I do wonder how do you think those inside will handle the heavy gravity.

What heavy gravity, those on board are weightless without artificial gravity.

 

[Arkathan]

I do wonder how do you think those inside will handle the heavy gravity.

As Sig said, weightless. The gravitation pull of Earth at the space station's orbit is .75 g. The crew doesn't notice that.

 

[Jame Rowe]

I do wonder how do you think those inside will handle the heavy gravity.

I always figured that the m drive has inertial compensation, and some anti grav lifters like a grav vehicle does, so that it can take off and land from planets with various gravity.
The tonnage of the lifters and compensators is subsumed into the tonnage of the drive, and therefore not described.

 

[ColinD]

I always thought that if you were on a heavy gravity planet, or even skimming its surface, it would affect those inside the ship. Say a Beowulf style far trader skims the surface of a gas giant with an gravity of say 6 g. They could build up enough inertia to skim the gas surface and get fuel, but would their be no effect on the crew?

 

[Sigtrygg]

If you are in free fall you are weightless, if you are in orbit you are in free fall. You can orbit a supermassive black hole.

Changing your orbit to dip into the atmosphere still has you in free fall, your orbit just now dips into the atmosphere.

You experience weight in an aircraft as a reaction to lift, the plane is pushing you up, so you push back, you have weight. If the plane falls out of the air and no longer has lift then you are in free fall within the plane, you are both moving at the same velocity.

 

[ColinD]

If you are in free fall you are weightless, if you are in orbit you are in free fall. You can orbit a supermassive black hole.

Changing your orbit to dip into the atmosphere still has you in free fall, your orbit just now dips into the atmosphere.

You experience weight in an aircraft as a reaction to lift, the plane is pushing you up, so you push back, you have weight. If the plane falls out of the air and no longer has lift then you are in free fall within the plane, you are both moving at eh same velocity.

Great! So just keep the right trajectory and you will be fine.

 

[Arkathan]

Great! So just keep the right trajectory and you will be fine.

Yes, but buckle up. Free fall does not preclude sudden winds hear that might overcome your gravitic's ability to compensate.

 

[To Tha Moon!]

As I sit here drinking Hot Chocolate from my Traveller Mug (Thanks TravellerCon/USA) my thoughts turn to High Gravity and Starships. On page 79 of the Starship Operators Manual, the blue box states,
"If the ship only has 1G of thrust, avoid landing on worlds with Size code B or higher unless there is good reason to believe that ship can take back off again." It seems that High Gravity Worlds might permanently ground a Starship with an insufficient Manoeuvre Drive.

So if your starship ends up around Terra/Sol (Earth) with a pick of 4 Gas Giants to choose from, would Jupiter have too big of a Gravity Well for a Starship that has an M Drive of 1? Would it only be able to skim fuel from Saturn with an escape velocity of 10.44 m/s2 and a gravity of 1.065 g or
Neptune with it's escape velocity of 11.15 m/s2 and a gravity of 1.137 g rather than Jupiter (24.79 m/s2 and a gravity of 2.528)?

I would imagine that if you ended up in a System with a Gas Giant that had a high surface gravity like HD 80606 b with a gravity of 9.6 g you would not be able to get close enough in your starship to use the fuel scoops.

What do you all think?

MegaTraveller came up with an idea that you can overdrive the Maneuver drive. I made a conversion of sorts for Mongoose Traveller. But I want to redo the System Crosschecks part. Seems clunky.

MGT Only: - Tasks from the MegaTraveller Starship Operator's Manual for Mongoose v2

I've been wanting to do this for a while. Porting over some ideas from MegaTraveller's Starship Operator's Manual and Imperial Encyclopedia. I worked on it a little the other day, but embellished it more. Let me know if you see anything wrong. Maneuver Drive Overdrive According to...

www.travellerrpg.com

 

[Condottiere]

You still can, though I prefer the previous edition.

 

[MarcusIII]

would Jupiter have too big of a Gravity Well for a Starship that has an M Drive of 1?

Of course not. You aren't landing on Jupiter but "skipping" through its extreme upper atmosphere. You calculate your trajectory so you don't get so low in the atmosphere that your speed doesn't drop too low to get back into low orbit.