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ESA is planning a "Comet Interceptor" mission that will loiter at the Sun-Earth L2 point for up to three years for something reachable to fly-by: https://en.wi

ESA is planning a "Comet Interceptor" mission that will loiter at the Sun-Earth L2 point for up to three years for something reachable to fly-by: https://en.wikipedia.org/wiki/Comet_Interceptor https://en.wikipedia.org/wiki/Comet_Interceptor Maybe a few more probes like this in suitable locations would give us a better chance of intercepting interesting stuff passing through the solar system.

sandworm101 7y ago
As a general rule, having an interceptor already in an orbit is slower than launching a new one. If the target is coming in on a random orbit, the interceptor floating off in space is in no better a position, on average, than earth. So it is generally more efficient to launch from earth into a more targeted orbit than redirect a craft already in a less-than-ideal position. That said, having dozens or hundreds of probes in random orbits would be advantageous, but still much more costly.
- rtkwe 7y ago
  Maybe faster to reach it but accounting for prep times to ready the probe and rocket the equation probably changes. L1-3 are actually pretty good spots for it though because they're unstable and small perturbations will drastically change the orbit. Parking one is also predictable in budgets where a random emergency launch isn't and will cost more than a planned launch just to get things done quickly.
  - sandworm101 7y ago
    The L points are 'easier' but not any faster. A probe at an L point won't be able to get anywhere any faster than if it were launched from earth directly[1]. And sending a probe on a rocket to park itself at an L point wastes delta-v, as opposed to launching the same rocket directly from earth to the target. [1] Excepting maybe a target that appears conveniently a the same L point.
    - jandrese 7y ago
      The point is that you can't leave a rocket on the pad fueled and ready to go 24/7/365 because those pads are in use for other rockets and keeping them ready to fly is fairly labor intensive. So the advantage of already being in orbit is that you don't have to go through all of the logistics of getting the rocket to the pad, prepping it for flight, getting launch permission, etc... That's a difference of a couple of weeks.
      - HarryHirsch 7y ago
        Here's a silly thought: why can't we put the spacecraft on top of an ICBM in a silo and launch when the next extrasolar object is detected? The American and Russian armed forces worked out 24/7 launch readiness in the 1960s.
        jandrese 7y ago
        Nobody wants to pay for the personal needed to staff that silo.
        sandworm101 7y ago
        Because an ICBM doesn't have anywhere near the power needed for such a mission. A timely flyby of an interstellar object would need something akin to the Saturn-V or Falcon Heavy, or perhaps multiple launches of said. An ICBM is a firecracker in comparison.
        HarryHirsch 7y ago
        I see that now. With the two booster stages, the Ulysses spacecraft weighed > 15 tons in LEO, and the Dnieper rocket has a capacity of 4.5 tons to LTO. And you do need to get to Jupiter to turn the orbital plane of the spacecraft out of the ecliptic.
        rtkwe 7y ago
        ICBMs could only launch a very small probe into orbit and not even a sun centered one. They're meant for basically sub orbital ballistic trajectories for nukes and you don't need the power to put something into orbit for that.
jerf 7y ago
You can't intercept an interstellar object from a loitering orbit around the sun, with something that has basically zero delta-v (in terms of this context) onboard. The loitering orbit, by necessity, has a fairly tightly constrained velocity vector, and the interstellar object, by virtue of having escape velocity from our sun, must have a much higher velocity vector by a certain large number of kilometers per second at a minimum, basically unbounded on the upper end. By the time you have something like a nuclear rocket in space that has the requisite delta-v, there becomes no particular reason to station it around the sun, since you can get to the right vectors from anywhere in the system.
PopeDotNinja 7y ago
I was wondering how the Comet Interceptor could accelerate to follow the same path as some comet thing. The short answer is https://en.wikipedia.org/wiki/Solar_electric_propulsion https://en.wikipedia.org/wiki/Solar_electric_propulsion. It's a pretty cool technology in space, but you wouldn't want to use it for your commute to work here on Earth.

sandworm101 7y ago

As a general rule, having an interceptor already in an orbit is slower than launching a new one. If the target is coming in on a random orbit, the interceptor floating off in space is in no better a position, on average, than earth. So it is generally more efficient to launch from earth into a more targeted orbit than redirect a craft already in a less-than-ideal position. That said, having dozens or hundreds of probes in random orbits would be advantageous, but still much more costly.

rtkwe 7y ago
Maybe faster to reach it but accounting for prep times to ready the probe and rocket the equation probably changes. L1-3 are actually pretty good spots for it though because they're unstable and small perturbations will drastically change the orbit. Parking one is also predictable in budgets where a random emergency launch isn't and will cost more than a planned launch just to get things done quickly.
- sandworm101 7y ago
  The L points are 'easier' but not any faster. A probe at an L point won't be able to get anywhere any faster than if it were launched from earth directly[1]. And sending a probe on a rocket to park itself at an L point wastes delta-v, as opposed to launching the same rocket directly from earth to the target. [1] Excepting maybe a target that appears conveniently a the same L point.
  - jandrese 7y ago
    The point is that you can't leave a rocket on the pad fueled and ready to go 24/7/365 because those pads are in use for other rockets and keeping them ready to fly is fairly labor intensive. So the advantage of already being in orbit is that you don't have to go through all of the logistics of getting the rocket to the pad, prepping it for flight, getting launch permission, etc... That's a difference of a couple of weeks.
    - HarryHirsch 7y ago
      Here's a silly thought: why can't we put the spacecraft on top of an ICBM in a silo and launch when the next extrasolar object is detected? The American and Russian armed forces worked out 24/7 launch readiness in the 1960s.
      - jandrese 7y ago
        Nobody wants to pay for the personal needed to staff that silo.
      - sandworm101 7y ago
        Because an ICBM doesn't have anywhere near the power needed for such a mission. A timely flyby of an interstellar object would need something akin to the Saturn-V or Falcon Heavy, or perhaps multiple launches of said. An ICBM is a firecracker in comparison.
        HarryHirsch 7y ago
        I see that now. With the two booster stages, the Ulysses spacecraft weighed > 15 tons in LEO, and the Dnieper rocket has a capacity of 4.5 tons to LTO. And you do need to get to Jupiter to turn the orbital plane of the spacecraft out of the ecliptic.
      - rtkwe 7y ago
        ICBMs could only launch a very small probe into orbit and not even a sun centered one. They're meant for basically sub orbital ballistic trajectories for nukes and you don't need the power to put something into orbit for that.

jerf 7y ago

You can't intercept an interstellar object from a loitering orbit around the sun, with something that has basically zero delta-v (in terms of this context) onboard. The loitering orbit, by necessity, has a fairly tightly constrained velocity vector, and the interstellar object, by virtue of having escape velocity from our sun, must have a much higher velocity vector by a certain large number of kilometers per second at a minimum, basically unbounded on the upper end. By the time you have something like a nuclear rocket in space that has the requisite delta-v, there becomes no particular reason to station it around the sun, since you can get to the right vectors from anywhere in the system.

PopeDotNinja 7y ago

I was wondering how the Comet Interceptor could accelerate to follow the same path as some comet thing. The short answer is https://en.wikipedia.org/wiki/Solar_electric_propulsion https://en.wikipedia.org/wiki/Solar_electric_propulsion. It's a pretty cool technology in space, but you wouldn't want to use it for your commute to work here on Earth.