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.