Best method for destroying/clearing the rubble of many planets/solar systems

Question

In this world we have made contact with many other intelligent species. Using our combined knowledge, we were able to devise a first form of FTL travel! These aliens wish to engage in trading activities but there's one problem; the FTL ships can't maneuver at those speeds and once the drive is engaged it can only turn off at a preset date: like a timer. This problem is being combated by stopping and starting which makes a slow and inefficient journey through the galaxy to our trade partners.

This can be used just fine for short distance travel but.... we need a Highway, the plans are already underway we have just faced one problem. how should the people of the galaxy go about destroying and (if necessary) clearing the rubble of these planets and even entire solar systems?

Tech level is far more advanced than us so hypothetical weaponry is acceptable.

Answer 1

Statistics show that there will be very little need for stellar demolition for star highways.

In our region of the galaxy the stellar density is about 0.004 stars per cubic light year. The density is higher in some galactic regions and lower in others.

Suppose that a galactic highway is going to cross the entire diameter of the galactic disc, 80,000 or 100,000 or 120,000 light years. Suppose that if a starship using FTL drive passes within 0.000001 or one millionth of a light year of a star it will suffer bad effects from interacting with that star. One millionth of a light years is about 5,878,000 miles.

The proposed star highway will have to be a clear cylinder of space with radius of 0.000001 light year and a height of 80,000 or 100,000 or 120,000 light years. The formula for the volume of a cylinder is pi times the radius squared times the height. One millionth times one millionth is one trillionth.

The proposed galactic highway will thus need a clear volume of space equal to 251,327.2 multiplied by one trillionth cubic light years, or 314,159 multiplied by one trillionth cubic light years, or 376,990.8 multiplied by one trillionth cubic light years. And if you bother to do the math you will find that the total volume of space occupied by one trans galactic space highway will be less than one millionth of a cubic light year.

Suppose that FTL ships need a much greater radius of clear space to operate well. Suppose that they need a clear radius of one thousandth (0.001) of a light year, or 5,878,000,000 miles, for safe operation.

Thus a trans galactic highway 80,000 light years long will have a volume of 0.213274 cubic light years, a trans trans galactic highway 100,000 light years long will have a volume of 0.314159 cubic light years, and a trans galactic highway 120,000 light years long will have a volume of 0.3769908 cubic light years. Since there are about 0.004 stars per cubic light year or about 250 cubic light years per star, there would be about one star in over 500 trans galactic highways 120,000 light years long.

Actually the galactic disc is about 1,000 or 2,000 light years in thickness. Actually the galactic disc doesn't have a sharp edge, as you travel higher and higher "above" the galactic disc the star density gets less and less and less. At distances a few thousand light years "above" or "below" the galactic disc the stars are very thinly spread compared to in the galactic disc.

So a logical form of galactic navigation would be to travel straight "up" (or "down") from the departure solar system until the star ship is several thousand light years "above" (or "below") the galactic disc. Then aim for a point in space several thousand light years "above" (or "below") the destination star system. Then travel 10,000 light years or 50,000 light years or whatever the distance is to the point "above" (or "below") the destination star system. Then head vertically "down" (or "up") to reach the destination star system.

Answer 2

This is a navigation problem, not a planet destroying problem

This problem is similar to what is encountered by ships moving in and out of harbors. Many big harbors, like New York, Lagos Nigeria, Rotterdam, or Shanghai are built at the mouth of large rivers and have to deal with deposits of silt moving around and changing the depth. To avoid ships running aground, the solution is to mark and maintain shipping channels.

First surveying ships make detailed maps of the bottom and any obstacles (sand bars, rocks, other sunken ships). Then safe courses that bypass those obstacles are charted. If the passage around obstacles is too narrow, or not deep enough, the obstacles are fixed. Rocks are blown up, bottoms are dredged, etc.

In space, the problems would be similar. A big galactic civilization would have pre-marked 'hyperlanes' that ships would follow. Government agencies and treaties between planetary systems would create and manage a system of markers to make sure ships were following the right paths.

At FTL speeds (however your FTL works) any impact of anything bigger than atom will have the energy of a nuclear weapon. Destroying a planet is going to leave a lot of atomic sized debris, so its going to take a lot of work to get every last atom out of the way of the hyperlane. Better off just routing the hyperlanes into the most barren parts of deep space. To be clear, none of the hyperlanes would be a straight shot. Most likely they would exist as a series of shorter jumps, each well marked. A ship would enter the hyperlane, set its FLT 'timer' then pop out at a junction point on the other end, where would have one or more new hyperlane segments to jump on.

The real maintenance problem would be sweeping the hyperlanes of any sort of debris of any size. That would be the fix for your advanced technology. Maybe powerful forcefields to act like a plow to clear anything out of the space, or ships that ionize all particles with high voltage, then use a magnetic field to repel them out of the hyperpace lanes. For larger particles and objects, ablating them with a laser would be effective. A ship with a powerful laser would heat up one side of the object until it turns to plasma. That expanding plasma will act as a rocket engine, firing that object in a direction away from any other travel lanes.