7 ms·

A novice question. 430K miles per hour is obviously a big number. And I have previously heard of this slingshot approach to increase speed so I am familiar wit

A novice question. 430K miles per hour is obviously a big number. And I have previously heard of this slingshot approach to increase speed so I am familiar with it. However, I believe energy is constant (it can be transformed but unlikely to be created or destroyed). For some object to gain a speed of 430K miles per hour, it must come from elsewhere, obviously it did not burn its own fuel (and I am assuming the slingshot theory). So the Sun transferred it a bunch of energy. I presume that is gravitational energy and to my mind it implies Sun gave away that energy. However, isn't that based on mass? But I do not think the mass would have changed. ELI5 please in terms of energy exchange. Who gained and lost and how?

exitb 2y ago
I mostly got the speed from multiple Venus flybys, which slowed down in its orbit a minuscule amount.
testoo 2y ago
hi kshacker! This is my understanding: That's correct, the energy comes from the body the spacecraft is slingshotting around (the Sun in this case). It's not mass or gravitational energy or anything weird like that, it's actually just a momentum transfer, the same as if the two objects had collided and bounced off each other elastically (i.e. without loss of energy to heat). So a (miniscule amount) of momentum (velocity x mass) is being transferred from the Sun to the spacecraft, and that's where the energy comes from. (source: I studied physics and had a grandparent at NASA who worked on Voyager II and talked about this issue with me; but it's been a while since both of those things, so anyone with more fresh experience feel free to chime in!)
- aio2 2y ago
  I'm studying physics right now, I can say I agree with everything you said. One thing I'd like to expand on to those who don't know how greater energy means greater speed. The kinetic energy equation is 1/2massvelocity^2=KE Since the KE increases from the momentum transfer, and mass of the object stays constant, the only thing that can change is velocity, where it has to go up. ex: KE=2, m=1 2=1/21v^2, v=2 Now if some momentum were transferred, and the kinetic energy increased to KE=8, 8=1/21velocity^2, velocity=4, since the mass can't change
- ShamelessC 2y ago
  Why did this get downvoted so much? Seems accurate enough.
  - deleted 2y ago
    [deleted]
  - testoo 2y ago
    i was wondering too! Do you think it might be because of citing family as a source? I barely ever post here, so don't have a good muscle memory for norms and best practices. (also both scared and curious of what might result from dropping below 0 karma)
    - richrichie 2y ago
      Just ignore it. You will get used to some hyper sensitive HN people that will down vote an apple because it is red.
  - icehawk 2y ago
    Is it though? A vehicle can't use a gravity-assist slingshot around the Sun to maneuver inside the solar system because the sun is at rest with respect to the rest of the solar system.
    - testoo 2y ago
      hey icehawk -- so you can use any celestial object in the solar system to maneuver; all you're doing is basically changing your direction. But you're right, there's something strange going on here. The original article doesn't actually have any information about what this spacecraft is doing, but it links to another one about the speed. I'm looking at that now, gonna add an addendum (or edit the old comment if i can figure out how to do that)
- testoo 2y ago
  update: sorry kshacker, I may have thrown you off the scent here. My explanation of the slingshot effect is right, but it doesn't look like slingshotting is what the spacecraft is using to increase its speed: the original article doesn't actually mention this at all, but it links to another one which tries (so vaguely it's misleading IMO) to explain the maneuver: https://mashable.com/article/nasa-parker-solar-probe-speed https://mashable.com/article/nasa-parker-solar-probe-speed tl;dr: the spacecraft is just falling into the Sun, which is why it speeds up. It isn't gaining speed relative to anything else, and it loses that speed again once it flies away from the Sun. It is using Venus to get closer to the sun each time around by damping its angular momentum, which works but I don't know how to explain that in an ELI5 way. so it's actually a little anticlimactic. BlarfMcFlarf and pfdietz got this right below in their comment thread: "What the Venus flybys did was not add energy so much as remove angular momentum. The hard part about getting close to the Sun is that conservation of angular momentum prevents it." ...and icehawk and vl correctly point out that you can't really use the Sun to increase your within-solar-system speed. Thanks to them for prompting me to look into this further. The cool slingshot maneuvers all involve planets, not the sun. ...but I think the key answer that none of us quite articulated to your question: How is the spacecraft using the slingshot effect to increase its speed each time around? ...is that it isn't! ...the article dramatically describes it as "picking up speed" each time it goes around the sun, but that is misleading. It is just getting closer to the sun every time around, so of course it goes faster the closer it gets. the cool part if any is how it uses Venus to get closer to the sun (by sapping angular momentum), but that's hard to explain in a nutshell and doesn't really relate to your energy question. so that is hopefully now a better answer to this mystery that brings together what some of the other commenters have pointed out.
big_paps 2y ago
Potential energy was converted into kinetic energy, not unlike when an apple falls to the ground. So the sun doesn’t really give away this energy, but its the system including these two masses.
vl 2y ago
Increasing speed with slingshot works because you leave vicinity of the planet in the same direction planet travels. Basically this allows you to add planet’s speed to your own. Within solar system you cannot increase speed by slingshotting around the sun. Total energy within system stays the same, some energy is transferred from the planet to the spacecraft.
colechristensen 2y ago
Flybys to boost speed take a tiny tiny tiny part of a planet’s orbital kinetic energy and exchange it with a spacecraft. The silliest way to describe it is kind of like stepping in front of a bus, but instead of actually getting hit you just get close enough for gravity to pull you along with the planet. Orbital mechanics is really just not intuitive so you can’t get an easy explanation as one doesn’t exist, your life experience with momentum and gravity is just too different for it to make sense easily.
BlarfMcFlarf 2y ago
The slingshots used to deorbit were around Venus, so it slightly gained velocity while the Parker probe lost it to get closer to the sun without expending as much fuel. As for its velocity around the sun, it’s intuitively like pendulum. When far away, it’s like the raised pendulum, and when near the sun, it’s like the pendulum at the bottom of its swing. Its a strained metaphor, but if you look at the orbit, it’s a very deep swing and a very large object it’s swinging towards, so it ends up quite fast at the bottom.
- pfdietz 2y ago
  What the Venus flybys did was not add energy so much as remove angular momentum. The hard part about getting close to the Sun is that conservation of angular momentum prevents it. Related to this: a minimum energy transfer between two circular orbits is normally the two-burn Hohmann transfer: an elliptical orbit that is tangent to each circular orbit. But if the radii of the two circular orbits have a sufficiently large ratio, it takes less delta-V to use three burns: go into an elliptical orbit that goes out to very large distance, do a small burn to lower (or raise) the periapsis to be at the other orbit, then circularize with a third burn. This is because doing a burn at large distance adds or removes a very large amount of angular momentum.
testoo 2y ago
there's another cool aspect to your question too! "Who gained and lost [energy] and how?" >there actually is no objective answer as to which body gained and which lost energy! Energy is always conserved, but which way the transfer happened depends on your reference frame! this isn't too difficult to demonstrate: pick an inertial reference frame A such that the spacecraft is at rest following the "collision" (aka the slingshot). In this frame, the spacecraft has 0 kinetic energy post-slingshot; therefore, it lost energy in the slingshot, which was transferred to the Sun. Likewise, pick a frame B such that the Sun is at rest after the slingshot (this would be the more usual frame to pick). In this case, it's the Sun that lost energy, and the spacecraft that gained it. (depending on one's mechanics background this might appear anything from obvious to very weird and unintuitive)
pigpang 2y ago
It's same as for everything: something is going into lower energy state, while something else going into higher energy state via some energy transfer mechanism. We are 100% sure for one side of energy transfer: both spacecraft and Sun are going to higher energy level first, then to lower energy level. Other part of equation is unknown. It's called "Gravitational potential energy", but it's unknown what stores this energy. However, we have few hints: objects creates gravitation waves, gravitational waves are propagated at c (speed of light), there is Higgs field (nature unknown), which is presented everywhere and gives mass, Higgs boson connects objects to Higgs field, gravitational force is proportional to 1/d^2. So, we have a medium (Higgs field), to which objects are connected via Higgs bosons. We can assume that energy can be transferred to/from the medium via bosons, so medium can store the energy and release it. We can speculate that when bosons somewhat connects to medium, it may create a tension in the medium, like bubbles on water, via unknown physical process. As result of that tension, bosons which are closer are spending less energy to create same tension, which makes closer position energetically favorable, so any random motion (because of noise in the medium) in direction of another boson will release some energy, while any movement in opposite direction will require to apply some energy.

exitb 2y ago

I mostly got the speed from multiple Venus flybys, which slowed down in its orbit a minuscule amount.

testoo 2y ago

hi kshacker! This is my understanding: That's correct, the energy comes from the body the spacecraft is slingshotting around (the Sun in this case). It's not mass or gravitational energy or anything weird like that, it's actually just a momentum transfer, the same as if the two objects had collided and bounced off each other elastically (i.e. without loss of energy to heat). So a (miniscule amount) of momentum (velocity x mass) is being transferred from the Sun to the spacecraft, and that's where the energy comes from. (source: I studied physics and had a grandparent at NASA who worked on Voyager II and talked about this issue with me; but it's been a while since both of those things, so anyone with more fresh experience feel free to chime in!)

aio2 2y ago
I'm studying physics right now, I can say I agree with everything you said. One thing I'd like to expand on to those who don't know how greater energy means greater speed. The kinetic energy equation is 1/2massvelocity^2=KE Since the KE increases from the momentum transfer, and mass of the object stays constant, the only thing that can change is velocity, where it has to go up. ex: KE=2, m=1 2=1/21v^2, v=2 Now if some momentum were transferred, and the kinetic energy increased to KE=8, 8=1/21velocity^2, velocity=4, since the mass can't change
ShamelessC 2y ago
Why did this get downvoted so much? Seems accurate enough.
- deleted 2y ago
  [deleted]
- testoo 2y ago
  i was wondering too! Do you think it might be because of citing family as a source? I barely ever post here, so don't have a good muscle memory for norms and best practices. (also both scared and curious of what might result from dropping below 0 karma)
  - richrichie 2y ago
    Just ignore it. You will get used to some hyper sensitive HN people that will down vote an apple because it is red.
- icehawk 2y ago
  Is it though? A vehicle can't use a gravity-assist slingshot around the Sun to maneuver inside the solar system because the sun is at rest with respect to the rest of the solar system.
  - testoo 2y ago
    hey icehawk -- so you can use any celestial object in the solar system to maneuver; all you're doing is basically changing your direction. But you're right, there's something strange going on here. The original article doesn't actually have any information about what this spacecraft is doing, but it links to another one about the speed. I'm looking at that now, gonna add an addendum (or edit the old comment if i can figure out how to do that)
testoo 2y ago
update: sorry kshacker, I may have thrown you off the scent here. My explanation of the slingshot effect is right, but it doesn't look like slingshotting is what the spacecraft is using to increase its speed: the original article doesn't actually mention this at all, but it links to another one which tries (so vaguely it's misleading IMO) to explain the maneuver: https://mashable.com/article/nasa-parker-solar-probe-speed https://mashable.com/article/nasa-parker-solar-probe-speed tl;dr: the spacecraft is just falling into the Sun, which is why it speeds up. It isn't gaining speed relative to anything else, and it loses that speed again once it flies away from the Sun. It is using Venus to get closer to the sun each time around by damping its angular momentum, which works but I don't know how to explain that in an ELI5 way. so it's actually a little anticlimactic. BlarfMcFlarf and pfdietz got this right below in their comment thread: "What the Venus flybys did was not add energy so much as remove angular momentum. The hard part about getting close to the Sun is that conservation of angular momentum prevents it." ...and icehawk and vl correctly point out that you can't really use the Sun to increase your within-solar-system speed. Thanks to them for prompting me to look into this further. The cool slingshot maneuvers all involve planets, not the sun. ...but I think the key answer that none of us quite articulated to your question: How is the spacecraft using the slingshot effect to increase its speed each time around? ...is that it isn't! ...the article dramatically describes it as "picking up speed" each time it goes around the sun, but that is misleading. It is just getting closer to the sun every time around, so of course it goes faster the closer it gets. the cool part if any is how it uses Venus to get closer to the sun (by sapping angular momentum), but that's hard to explain in a nutshell and doesn't really relate to your energy question. so that is hopefully now a better answer to this mystery that brings together what some of the other commenters have pointed out.

big_paps 2y ago

Potential energy was converted into kinetic energy, not unlike when an apple falls to the ground. So the sun doesn’t really give away this energy, but its the system including these two masses.

vl 2y ago

Increasing speed with slingshot works because you leave vicinity of the planet in the same direction planet travels. Basically this allows you to add planet’s speed to your own. Within solar system you cannot increase speed by slingshotting around the sun. Total energy within system stays the same, some energy is transferred from the planet to the spacecraft.

colechristensen 2y ago

Flybys to boost speed take a tiny tiny tiny part of a planet’s orbital kinetic energy and exchange it with a spacecraft. The silliest way to describe it is kind of like stepping in front of a bus, but instead of actually getting hit you just get close enough for gravity to pull you along with the planet. Orbital mechanics is really just not intuitive so you can’t get an easy explanation as one doesn’t exist, your life experience with momentum and gravity is just too different for it to make sense easily.

BlarfMcFlarf 2y ago

The slingshots used to deorbit were around Venus, so it slightly gained velocity while the Parker probe lost it to get closer to the sun without expending as much fuel. As for its velocity around the sun, it’s intuitively like pendulum. When far away, it’s like the raised pendulum, and when near the sun, it’s like the pendulum at the bottom of its swing. Its a strained metaphor, but if you look at the orbit, it’s a very deep swing and a very large object it’s swinging towards, so it ends up quite fast at the bottom.

pfdietz 2y ago
What the Venus flybys did was not add energy so much as remove angular momentum. The hard part about getting close to the Sun is that conservation of angular momentum prevents it. Related to this: a minimum energy transfer between two circular orbits is normally the two-burn Hohmann transfer: an elliptical orbit that is tangent to each circular orbit. But if the radii of the two circular orbits have a sufficiently large ratio, it takes less delta-V to use three burns: go into an elliptical orbit that goes out to very large distance, do a small burn to lower (or raise) the periapsis to be at the other orbit, then circularize with a third burn. This is because doing a burn at large distance adds or removes a very large amount of angular momentum.

testoo 2y ago

there's another cool aspect to your question too! "Who gained and lost [energy] and how?" >there actually is no objective answer as to which body gained and which lost energy! Energy is always conserved, but which way the transfer happened depends on your reference frame! this isn't too difficult to demonstrate: pick an inertial reference frame A such that the spacecraft is at rest following the "collision" (aka the slingshot). In this frame, the spacecraft has 0 kinetic energy post-slingshot; therefore, it lost energy in the slingshot, which was transferred to the Sun. Likewise, pick a frame B such that the Sun is at rest after the slingshot (this would be the more usual frame to pick). In this case, it's the Sun that lost energy, and the spacecraft that gained it. (depending on one's mechanics background this might appear anything from obvious to very weird and unintuitive)

pigpang 2y ago

It's same as for everything: something is going into lower energy state, while something else going into higher energy state via some energy transfer mechanism. We are 100% sure for one side of energy transfer: both spacecraft and Sun are going to higher energy level first, then to lower energy level. Other part of equation is unknown. It's called "Gravitational potential energy", but it's unknown what stores this energy. However, we have few hints: objects creates gravitation waves, gravitational waves are propagated at c (speed of light), there is Higgs field (nature unknown), which is presented everywhere and gives mass, Higgs boson connects objects to Higgs field, gravitational force is proportional to 1/d^2. So, we have a medium (Higgs field), to which objects are connected via Higgs bosons. We can assume that energy can be transferred to/from the medium via bosons, so medium can store the energy and release it. We can speculate that when bosons somewhat connects to medium, it may create a tension in the medium, like bubbles on water, via unknown physical process. As result of that tension, bosons which are closer are spending less energy to create same tension, which makes closer position energetically favorable, so any random motion (because of noise in the medium) in direction of another boson will release some energy, while any movement in opposite direction will require to apply some energy.