Jerry the Vampire wrote:I didn't mean to imply that because she struggled with pen and paper arithmetic she doesn't know Newtonian Physics. But from what I can tell she only has a secondary school level maths background which usually covers only basic mechanics..
You don't really need to be able to cope with nutation and moment of inertia tensors to be able to talk about special relativity. Special relativity is actually very
simple; it's GR that's hard.
Broomstick wrote:Her mission profile seems quite logical to me. The 'capture' ship would have to accelerate to match velocities with the target, then speed up a bit more to overtake it.
You don't need to overtake it, just match velocities. You "merely" calculate everything so that when you finally match velocities you're close enough to reach out and grab it. That's one reason for having an AI on board, to make the necessary very fine course corrections when getting close to the target.
Thing is, if you're chasing the target then at some point you need to travel faster than it does. I had just... assumed this was a tail-chase scenario, or would turn into one. It doesn't have to, I guess, if you launch the relativistic interceptor before the target even passes near your star system. Months before.
Again, no need to slow down or stop prior to direction change. Change direction and slow down at the same time. Like I said, you'll have a huge turn radius but I'm guessing it will still be less fuel than coming to a halt.
I'm actually not sure. I suspect it cancels out. For the record, you
are talking about just burning the engines at right angles to your path to describe a large circle in interstellar space, yes?
What you'd need to do is compare the required radial acceleration and duration for a 180-degree turn at relativistic speeds, to the acceleration required to come to a stop and get back up to speed. Either plan is somewhat time-consuming, so it really is important from a plot standpoint: do you need to retrieve this cargo "as fast as possible," or can you take your sweet time coming back once you've caught it in the first place?
It's not like the planet you left behind is standing still, it's moving too. You'll have to intercept it just as you intercepted the Mysterious Object. Returning home is the exact same sort of problem as going out.
Relative to a spacecraft moving at relativistic speeds, planets are standing still
for purposes of calculating total fuel consumption required to get back to them.
We're comparing speeds on the order of a hundred thousand km/s for the ship, to speeds on the order of ten km/s for the planet. It's more relevant than continental drift moving the airstrip would be for someone flying a plane, but not much.
I'm thinking a rendezvous (or several) with resupply drones. Again, it would extremely tricky to launch and time everything so that on the return the drones are in the right place at the right velocity and direction for a pick up but it's at least plausible.
The drones might also need to be impractically big, depending on details of the math I've avoided doing.
The other thing is that school districts are far more lenient about making such arrangements - back in my day it was breaking all sorts of rules and could have gotten the teacher into very serious trouble, but I appreciate what he did because it enabled me to pass with a decent grade.
Well, on my own tests (i.e. most of the ones I give for calc) I can damn well do what I please. On state benchmark tests, you only get extra time if you're special ed.
Broomstick wrote:And here I'm not convinced you're visualizing things properly. We're going away from a star (unless we catch the Mysterious Object as it goes by a star, but that wasn't my intention), the whole time outbound we're counteracting the star's gravity. On the way back, our thrust changes direction and starts working with the star's gravity although certainly at the early part of the return trip that gravity assistance will be meager.
The total delta-v you can get from a star's gravity well is pretty limited relative to the speeds involved, and it would take centuries of repeated passes for it to add up to much.
It's a matter of there is the capability to rendezvous rapidly, and start slowing it down, but the cargo may not be able to withstand such high acceleration as well as it might be easier to re-supply on the return trip, when supply drones won't have to play catch up.
Well.
While you're still outbound, any supply drones have to have been launched before you even intercepted the target, and would have to move at relativistic speeds in their own right. The real challenge is slowing down from high-relativistic (.9c and up) speed down toward something less crazy like .5c. Once you get down there, it's drastically easier for future resupply drones to catch up with you.
One might imagine, say, two payloads being launched more or less simultaneously. One is the "catcher," the other is the "tanker." The "catcher" is responsible both for intercepting the cargo AND for snagging that tank of fuel. It's comparable in mass to the entire weight of the catcher payload, and exists solely to help slow down the "catcher" a bit so that it can later match courses with the NEXT tankload of fuel. And the next. And the next.
Subsequent tankers actually carry considerably more fuel- because they were launched at lower speeds, so they never reach the same extreme peak velocity as the "catcher" payload. Potentially you could even
very slowly (say. 0.2c) 'toss' a very large fuel tanker out to the place you expect your catcher to end up after braking to a stop, to gas up for the return trip.
Incidentally, this kind of tanker problem is one reason NOT to have your "catcher" describe a huge 180 degree turn in space- it makes the intercept problem of delivering extra refueling tankers to the moving target more complicated. Because at certain points on the trajectory, you have to burn a lot more fuel to accelerate your care package onto the right vector so that the "catcher" can catch it.
Commander of the MFS Darwinian Selection Method (sexual)
