Ramscoops

[rinku]

But looping back to the original question, I can't see how a ramscoop as such would be able to handle the denser atmospheres. It's designed to electromagnetically gather stray hydrogen ions; Gas giant atmospheres are molecular hydrogen. Fuel scoops are funneling in actual gas mechanically, so it's a different design.

And that's before we get to the usual electromagnetic field around a gas giant.

But I could see the area *near* a gas giant, outside its magnetosphere, as possibly being a better place to run a ramjet than in the rarified vacuum of interplanetary space.

 

[Condottiere]

My concept of drop-ships/pods is that they go straight down.

 

[cometyo]

Great comments everyone. Yeah I can accept that the rarified heights of a gas giant might be too dense for ramscoops but not the areas near the gas giant, which might be rich in hydrogen. I wonder, though, if I had a ship designed for deep exploration where redundancy (and not commercial efficiency) might be a good thing, would it be routinely useful to have ramscoops (for gathering hydrogen fuel while transiting to a destination) AND fuel scoops and fuel processors (for harvesting water, ice, hydrocarbons, etc. for fuel at a destination when the ramscoops can't be used)? Or would that not be useful enough to justify the expense and tonnage taken up by these overlapping capabilities?

 

[rinku]

Generally, ramscoops are a very inefficient way to gather fuel. In almost all cases the cost of them would be better spent on a fuel shuttle that would be able to gather conventionally faster.

About the only scenario where I could see them being worth it would be if the ship had to travel outside of M-Drive range and was using reaction drives. The original ramjet concept was just that - gathering fuel to be fused and used as fusion drive for interstellar travel. Although with fusion power plant technology there are other options, such as just using the gathered ions as unfused reaction mass. And Jump Drive largely removes any need to use the ramjet to travel between stars. I see it as more of an alternative tech like solar sails that a useful option.

 

[Condottiere]

You won't need tankers in empty hexes.

 

[Fluffy Bunny Feet]

You won't need tankers in empty hexes.

I have a few designs for what I call Rift Jumpers that use it to fuel the ship where there are no star systems. Also for explorer craft. The idea is that the ram scoop was developed to allow more cargo on the early J-1 ships travelling from Earth as there is no J-1 destination only J-2 or more.

Rather than fuelling them to make back 4 back to back J-1 (there being no portable fuel processors yet) for a round trip they could refuel after each J-1 and have more equipment/personnel to use for exploring purposes even in smaller ships. The ship could still be smaller and cheaper.

Even the first colony vessels to a system would have the same issue till a fuel plant and power plant for it were set up. Early inaccuracy in jumping would have kept them from jumping to a fuel depot at that point in time. The first "portable" fuel processors WERE ram scoops in MY universe.

 

[Condottiere]

Even in the Fifth Millenia, ramscoops can be utilized.

What you have is time and space.

What you don't tend to have is money.

If time is not an issue, you can hop into each (empty) hex, and add a couple of weeks more to the journey time, until you reach the next star.

 

[rinku]

It is worth noting that interstellar space has a higher density of hydrogen atoms (about 1 per cubic centimetre) than within a heliopause. So the trick of jumping into an empty hex and ramscooping to gather enough fuel to jump again might work.

The trouble is, assuming you go with M-Drives needing a gravity well to work, they DO NOT WORK in interstellar space, so you'll (technically) need a reaction drive to make the ramscoop actually work. And... you're probably having to burn most of the hydrogen you gather as reaction mass, so it might take a LONG time to gather.

On the other hand, if you build up a decent velocity before you jump (and rule that going fast IS enough to count as "maneuvering"), that might work for collecting.

The High Guard entry doesn't cover it that well, but how it is meant to work in real life is that the faster you go the more you scoop, within limits. Residual velocity built up before jump plus empty hex that has the expected higher hydrogen density seems pretty solid. Although TBH, the High Guard rule seems overly generous to me. Even in interstellar space you need to be scooping at lot of volume; one litre of liquid hydrogen contains 2.36 x 10^26 H2 molecules. At one *atom* per cubic centimetre, you can get 500 H2 molecules per litre of interstellar space, so you'd need something like 4.72 x 10^23 litres of space scooped. The volume would be the area of scoopfield multiplied by the distance travelled; you could work out the time required if you knew the area of the field and the velocity.

4.72 x 10^23 litres are equal to 4.72 x 10^11 cubic kilometres, which is a handier unit for working this out.

As an example, lets argue the scoop field has a diameter of 1000 km, giving an area of 3,141 km2. That would require a distance travelled to scoop ONE litre of liquid hydrogen to be 4.72 x 10^11 km3 divided by 3,141 km2, or around 1.5 x 10^8 km, which is oddly enough very close to 1AU (149,597,870 km).

So... with PERFECT scoop efficiency and a scoop diameter of 1000km in interstellar space where the hydrogen density is several times higher than inside a solar system, each litre of liquid hydrogen requires the scoop to travel the distance between the sun and the earth.

So... take the High Guard version with a grain of salt. There's also the issue that if more than one ship is scooping in a given volume, the yields will be shared between them. That might be an advantage if they're pooling it, but not if they're in competition.

 

[Fluffy Bunny Feet]

The trouble is, assuming you go with M-Drives needing a gravity well to work, they DO NOT WORK in interstellar space,

In the Primitive Advanced section of High Guard you can make primitive drives that work only to 100 diameters or even to .1 diameter limit. So why not a Advanced limit increase? Pay the max and there is no limit or at least an increase of thrust when you might be limited? (say 1/10 your g rating per advanced step 1 g advanced 3x would let you accelerate at .3 g).

 

[rinku]

In the Primitive Advanced section of High Guard you can make primitive drives that work only to 100 diameters or even to .1 diameter limit. So why not a Advanced limit increase? Pay the max and there is no limit or at least an increase of thrust when you might be limited? (say 1/10 your g rating per advanced step 1 g advanced 3x would let you accelerate at .3 g).

Because the inverse square law will defeat it by the time you get out to interstellar space. It could be a thing to look at for system use, for sure.

100D from the sun is just under 1 AU, something like 147 million kilometres. One parsec is about 30 million million kilometres - call it 200,000 AU or so. Whatever gravitational effect the sun has at 1AU will reduce by 1/(distance in AU)^2 further out, so the gravitational force it has at one parsec is going to be 1/40,000,000,000 of the force at 1AU. 0.000000000025G thrust is going to take you quite a while to get you up to speed.

The 100D etc rules are really just simplifications of how gravity works. In reality you'd expect a drive that needs a given gravitational field to work would still have *some* effect beyond the stated limits, but it should also have a decreasing effect between the listed brackets, too. We simplify that stuff so that Traveller isn't overwhelmed with maths, and some of the magic tech is there specifically to enable that. M-Drives are reactionless, meaning the rocket equation isn't needed and you don't have to account for fuel or really need to concern yourself with orbital dynamics much. Grav compensation allows Star Trek/Wars style deckplans and ships to exceed accelerations that would injure the passengers, etc.

But the background physical reality is still meant to be there - a reaction drive DOES need to account for fuel. A ship without g-compensation DOES need to concern itself with accelerating too hard for too long if it carries meatbags. Gravity IS subject to the inverse square law.

 

[Condottiere]

There is the deepspace manoeuvre drive.

And whatever actual acceleration threshold you establish which picks up free hydrogen.