5 ms·

It is stated multiple times across the article that the probe would need a means of changing is trajectory, but not even a hint of idea how that could possibly

It is stated multiple times across the article that the probe would need a means of changing is trajectory, but not even a hint of idea how that could possibly be done is given. So the most important and blocking aspect of the mission is simply skimmed over, and the rest of it is built upon this omission as if it was something trivial to come up with. Does anyone have an idea how to equip a 1g spacecraft with any means to steer itself at 1/3 speed of light? The kinetic energy at that speed would seem to require something very incompatible with the weight constraint, to my understanding.

antonvs 1y ago
Easy fix: change the description to "Interstellar Mission to the General Galactic Vicinity of a Black Hole"
dvh 1y ago
Simply. You do Monte Carlo with the probes. You fire 1000 and one or two will have perfect trajectory so that no correction is needed.
- magnat 1y ago
  Did you, by any chance, play Outer Wilds recently?
- gus_massa 1y ago
  I don't think 1000, or even 1000000 are enough if you use random directions. Space is <huge>huge</huge>. This has been posted here afew times https://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html https://joshworth.com/dev/pixelspace/pixelspace_solarsystem....
estimator7292 1y ago
Solar sails. You can fire a shit ton of lasers from the planet (or orbit) at the probes and very,very slowly boost them up to the desired velocity.
marcellus23 1y ago
It's not skimmed over, they cover it near the end in the "Requirements and challenges" section: > The most challenging phase of the mission may be related to how the nanocraft can transfer from an unbound to a bound orbit and start orbiting around the compact object. All possible solutions should be considered carefully. In the case the transfer is not possible, we may redesign the mission to perform the scientific tests when the nanocraft passes close to the black hole. For example, when the nanocraft is close to the black hole, it may separate into a mother-nanocraft (with a wafer and sail) and a number of small nanocrafts (without sails). The nanocrafts could communicate with each other by exchanging electromagnetic signals. The mother-nanocraft could compare the trajectories of the small nanocrafts to those expected in a Kerr spacetime and send the data to Earth. Light sales can theoretically be used to not only accelerate away from Earth, but also decelerate at the end of an interstellar journey (see Robert L Forward's work). The practicality of that is another matter.
- hinkley 1y ago
  There’s a really straightforward way to avoid a parabolic trajectory with a black hole. But data retrieval gets a bit difficult. More seriously, it floors me how often and consistently people forget that the accretion disk is essentially a partial accelerator and crossing or entering it will probably pulverize you to radioactive dust. Possibly before you could hit the event horizon.
  - marcellus23 1y ago
    Not every black hole has an accretion disk, especially not isolated ones.
    - hinkley 1y ago
      So the question there is if it’s worth it for us to study a naked singularity. What would it teach us? And how do you get into orbit?
      - celticninja 1y ago
sigmoid10 1y ago
People don't realise this, but you can steer perfectly fine with a solar sail. That's because photons transfer momentum not just when they hit the sail, but also when they are emitted after reflection. So just by turning the sail at an angle, you can create a force in any direction perpendicular to the velocity vector. Using a two sail system, you can even accelerate and slow down along a single beam path. So you could theoretically travel to mars with a constant acceleration/deceleration phase (like a flip-and-burn in the Expanse) using only one beam emitter on earth.
- kragen 1y ago
  How long would it take for a person to get to Mars with a sail powered by an Earth-based laser?
  - lazide 1y ago
    Infinite time since we have no realistic way of making such a laser at this time - and anyone trying it is likely to get nuked before they finish their massive death ray.
    - kragen 1y ago
      Stipulate that we have the laser.
      - sigmoid10 1y ago
        Depends entirely on the power output of the laser, the dispersal length and the size, weight and reflectivity of the sail. Since we are already talking about imaginary technology, any answer between "slower than current chemical rockets" and "some significant fraction of the speed of light" could be valid.
        kragen 1y ago
        I don't think that is correct. I think there's a rather disappointing limit on the acceleration a laser sail can reach with known materials.
palmotea 1y ago
> It is stated multiple times across the article... I was a bit confused by your comment, but I think the article you're referring to is not the OP, but the article the OP was commenting on: https://www.cell.com/iscience/fulltext/S2589-0042(25)01403-8?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS2589004225014038%3Fshowall%3Dtrue https://www.cell.com/iscience/fulltext/S2589-0042(25)01403-8... > Does anyone have an idea how to equip a 1g spacecraft with any means to steer itself at 1/3 speed of light? The kinetic energy at that speed would seem to require something very incompatible with the weight constraint, to my understanding. I'm also wondering how such a thing is supposed to communicate back to us over dozens of light years. That also seems incompatible with the weight constraint.
- NoMoreNicksLeft 1y ago
  >I'm also wondering how such a thing is supposed to communicate back to us over dozens of light years. Split particle pairs. We just need to repeal the no cloning theorem, maybe if we promise to not use it for FTL communication the legislators would go for it.
  - VonTum 1y ago
    We could call them "Sophons" while we're at it.
- floxy 1y ago
  >I'm also wondering how such a thing is supposed to communicate back to us over dozens of light years. Just spit-balling here. Send out the first batch of probes and then 5 years later send another batch of probes. The first batch of probes does their surveying for 5 years, when the later batch of probes start arriving. The data is uploaded to the late-comers, who aren't on an intercept course. Instead they are on a trajectory that causes them to swing around the black hole, and head on back to earth with the data.
  - palmotea 1y ago
    > Send out the first batch of probes and then 5 years later send another batch of probes. What's the separation there, at 0.33 lightspeed? 1.65 light years? Wikipedia says Voyager is 168.35 AU away, and Google says that's 0.00266 light years. Voyager has 23-watt radio focused by a 3.7m dish and its signals are received by a 70-meter dish on Earth. So you're talking about a 1g spacecraft signaling another 1g spacecraft over 620 times the distance to Voyager, without any of the beefy equipment that exists on both ends of the Voyager link.
floxy 1y ago
Since momentum is conserved, why not just have a 2 of the 1 g probes strapped to each other with a spring in between. When you need a course correction at 100 AU out (or whatever). The probes calculate how much of a correction is needed, adjusts a screw that tightens or loosens tension on the spring, reorients itself appropriately with a reaction wheel, then the two probes are released from each other, begin pushed apart with the spring. One probe gets the trajectory correction it needs, and the other gets further off course. Maybe with some gravity assists with nearby objects. https://en.wikipedia.org/wiki/Gravity_assist https://en.wikipedia.org/wiki/Gravity_assist also: Roundtrip Interstellar Travel Using Laser-Pushed Lightsails https://ia800108.us.archive.org/view_archive.php?archive=/24/items/wikipedia-scholarly-sources-corpus/10.2514.zip&file=10.2514%252F3.8632.pdf https://ia800108.us.archive.org/view_archive.php?archive=/24...
- vjvjvjvjghv 1y ago
  Isn’t that basically how a rocket works? Throw stuff out one side to get the thing on the other side moving. Not sure how this would compare to a rocket engine with hyperbolic fuel.
  - floxy 1y ago
    Yes.
  - dylan604 1y ago
    It compares in that it doesn't require said hyperbolic fuel. That fuel is heavy and finite.
    - lazide 1y ago
      Uh, it does - the ‘fuel’ is the other probe. Notably, this also has a particularly bad ISP? Also, probes are presumably also heavier and rarer?
    - mlsu 1y ago
      You can think of the hypergolic fuel as a type of spring. The chemical energy stored in the bonds of the fuel is what pushes the fuel products apart when it reacts. This is what pressure is, it's nothing more than KE of molecules. The 'spring action' of fuel is very good because there's a lot more energy (per unit mass) stored in the bonds. Orders of magnitude more than a mechanical spring.
stronglikedan 1y ago
gyroscopes?
bawolff 1y ago
> So the most important and blocking aspect of the mission Idk, i think the fact they are using statistical arguments that there should be a nearby black hole, but haven't actually found any or have any idea where they are, is pretty blocking.
ithkuil 1y ago
"steering" is a word that can lead to confusion because it leverages the intuition that we have with our ground vehicles. A change in direction in space requires accelerating the vehicle in some direction, the effect of which is just simple vector addition of the velocity vector of the vehicle. So if you are going with a huge velocity in one direction and you want to change direction significantly in another direction you have to change velocity (accelerate) a lot in order for the combined vectors to produce a significantly different final velocity vector
- deleted 1y ago
  [deleted]
deleted 1y ago
[deleted]

antonvs 1y ago

Easy fix: change the description to "Interstellar Mission to the General Galactic Vicinity of a Black Hole"

dvh 1y ago

Simply. You do Monte Carlo with the probes. You fire 1000 and one or two will have perfect trajectory so that no correction is needed.

magnat 1y ago
Did you, by any chance, play Outer Wilds recently?
gus_massa 1y ago
I don't think 1000, or even 1000000 are enough if you use random directions. Space is <huge>huge</huge>. This has been posted here afew times https://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html https://joshworth.com/dev/pixelspace/pixelspace_solarsystem....

estimator7292 1y ago

Solar sails. You can fire a shit ton of lasers from the planet (or orbit) at the probes and very,very slowly boost them up to the desired velocity.

marcellus23 1y ago

It's not skimmed over, they cover it near the end in the "Requirements and challenges" section: > The most challenging phase of the mission may be related to how the nanocraft can transfer from an unbound to a bound orbit and start orbiting around the compact object. All possible solutions should be considered carefully. In the case the transfer is not possible, we may redesign the mission to perform the scientific tests when the nanocraft passes close to the black hole. For example, when the nanocraft is close to the black hole, it may separate into a mother-nanocraft (with a wafer and sail) and a number of small nanocrafts (without sails). The nanocrafts could communicate with each other by exchanging electromagnetic signals. The mother-nanocraft could compare the trajectories of the small nanocrafts to those expected in a Kerr spacetime and send the data to Earth. Light sales can theoretically be used to not only accelerate away from Earth, but also decelerate at the end of an interstellar journey (see Robert L Forward's work). The practicality of that is another matter.

hinkley 1y ago
There’s a really straightforward way to avoid a parabolic trajectory with a black hole. But data retrieval gets a bit difficult. More seriously, it floors me how often and consistently people forget that the accretion disk is essentially a partial accelerator and crossing or entering it will probably pulverize you to radioactive dust. Possibly before you could hit the event horizon.
- marcellus23 1y ago
  Not every black hole has an accretion disk, especially not isolated ones.
  - hinkley 1y ago
    So the question there is if it’s worth it for us to study a naked singularity. What would it teach us? And how do you get into orbit?
    - celticninja 1y ago

sigmoid10 1y ago

People don't realise this, but you can steer perfectly fine with a solar sail. That's because photons transfer momentum not just when they hit the sail, but also when they are emitted after reflection. So just by turning the sail at an angle, you can create a force in any direction perpendicular to the velocity vector. Using a two sail system, you can even accelerate and slow down along a single beam path. So you could theoretically travel to mars with a constant acceleration/deceleration phase (like a flip-and-burn in the Expanse) using only one beam emitter on earth.

kragen 1y ago
How long would it take for a person to get to Mars with a sail powered by an Earth-based laser?
- lazide 1y ago
  Infinite time since we have no realistic way of making such a laser at this time - and anyone trying it is likely to get nuked before they finish their massive death ray.
  - kragen 1y ago
    Stipulate that we have the laser.
    - sigmoid10 1y ago
      Depends entirely on the power output of the laser, the dispersal length and the size, weight and reflectivity of the sail. Since we are already talking about imaginary technology, any answer between "slower than current chemical rockets" and "some significant fraction of the speed of light" could be valid.
      - kragen 1y ago
        I don't think that is correct. I think there's a rather disappointing limit on the acceleration a laser sail can reach with known materials.

palmotea 1y ago

> It is stated multiple times across the article... I was a bit confused by your comment, but I think the article you're referring to is not the OP, but the article the OP was commenting on: https://www.cell.com/iscience/fulltext/S2589-0042(25)01403-8?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS2589004225014038%3Fshowall%3Dtrue https://www.cell.com/iscience/fulltext/S2589-0042(25)01403-8... > Does anyone have an idea how to equip a 1g spacecraft with any means to steer itself at 1/3 speed of light? The kinetic energy at that speed would seem to require something very incompatible with the weight constraint, to my understanding. I'm also wondering how such a thing is supposed to communicate back to us over dozens of light years. That also seems incompatible with the weight constraint.

NoMoreNicksLeft 1y ago
>I'm also wondering how such a thing is supposed to communicate back to us over dozens of light years. Split particle pairs. We just need to repeal the no cloning theorem, maybe if we promise to not use it for FTL communication the legislators would go for it.
- VonTum 1y ago
  We could call them "Sophons" while we're at it.
floxy 1y ago
>I'm also wondering how such a thing is supposed to communicate back to us over dozens of light years. Just spit-balling here. Send out the first batch of probes and then 5 years later send another batch of probes. The first batch of probes does their surveying for 5 years, when the later batch of probes start arriving. The data is uploaded to the late-comers, who aren't on an intercept course. Instead they are on a trajectory that causes them to swing around the black hole, and head on back to earth with the data.
- palmotea 1y ago
  > Send out the first batch of probes and then 5 years later send another batch of probes. What's the separation there, at 0.33 lightspeed? 1.65 light years? Wikipedia says Voyager is 168.35 AU away, and Google says that's 0.00266 light years. Voyager has 23-watt radio focused by a 3.7m dish and its signals are received by a 70-meter dish on Earth. So you're talking about a 1g spacecraft signaling another 1g spacecraft over 620 times the distance to Voyager, without any of the beefy equipment that exists on both ends of the Voyager link.

floxy 1y ago

Since momentum is conserved, why not just have a 2 of the 1 g probes strapped to each other with a spring in between. When you need a course correction at 100 AU out (or whatever). The probes calculate how much of a correction is needed, adjusts a screw that tightens or loosens tension on the spring, reorients itself appropriately with a reaction wheel, then the two probes are released from each other, begin pushed apart with the spring. One probe gets the trajectory correction it needs, and the other gets further off course. Maybe with some gravity assists with nearby objects. https://en.wikipedia.org/wiki/Gravity_assist https://en.wikipedia.org/wiki/Gravity_assist also: Roundtrip Interstellar Travel Using Laser-Pushed Lightsails https://ia800108.us.archive.org/view_archive.php?archive=/24/items/wikipedia-scholarly-sources-corpus/10.2514.zip&file=10.2514%252F3.8632.pdf https://ia800108.us.archive.org/view_archive.php?archive=/24...

vjvjvjvjghv 1y ago
Isn’t that basically how a rocket works? Throw stuff out one side to get the thing on the other side moving. Not sure how this would compare to a rocket engine with hyperbolic fuel.
- floxy 1y ago
  Yes.
- dylan604 1y ago
  It compares in that it doesn't require said hyperbolic fuel. That fuel is heavy and finite.
  - lazide 1y ago
    Uh, it does - the ‘fuel’ is the other probe. Notably, this also has a particularly bad ISP? Also, probes are presumably also heavier and rarer?
  - mlsu 1y ago
    You can think of the hypergolic fuel as a type of spring. The chemical energy stored in the bonds of the fuel is what pushes the fuel products apart when it reacts. This is what pressure is, it's nothing more than KE of molecules. The 'spring action' of fuel is very good because there's a lot more energy (per unit mass) stored in the bonds. Orders of magnitude more than a mechanical spring.

stronglikedan 1y ago

gyroscopes?

bawolff 1y ago

> So the most important and blocking aspect of the mission Idk, i think the fact they are using statistical arguments that there should be a nearby black hole, but haven't actually found any or have any idea where they are, is pretty blocking.

ithkuil 1y ago

"steering" is a word that can lead to confusion because it leverages the intuition that we have with our ground vehicles. A change in direction in space requires accelerating the vehicle in some direction, the effect of which is just simple vector addition of the velocity vector of the vehicle. So if you are going with a huge velocity in one direction and you want to change direction significantly in another direction you have to change velocity (accelerate) a lot in order for the combined vectors to produce a significantly different final velocity vector

deleted 1y ago
[deleted]

deleted 1y ago

[deleted]