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George
2018-Aug-17, 03:33 PM
How does a probe like Parker use, say, Venus to slow down to obtain its desired near-Sun, and inner aphelion, orbit? I assume there's no atmospheric braking being required. I can imagine zipping around Mercury to force it more into the path of Venus to slow it down but I don't think they do this, or did I miss this?

schlaugh
2018-Aug-17, 04:10 PM
Short answer: Parker is using the gravity of Venus to reduce the angular momentum imparted by the Earth's orbit around the sun, and to reshape its orbit.

Longer answer (https://en.wikipedia.org/wiki/Parker_Solar_Probe#Trajectory):

The Parker Solar Probe mission design uses repeated gravity assists at Venus to incrementally decrease its orbital perihelion to achieve multiple passes of the Sun at approximately 8.5 solar radii, or about 6 million km (3.7 million mi; 0.040 AU).[26] The spacecraft trajectory will include seven Venus flybys over nearly seven years to gradually shrink its elliptical orbit around the Sun, for a total of 24 orbits.[1] The science phase will take place during those 7 years, focusing on the periods when the spacecraft is closest to the Sun. The near Sun radiation environment is predicted to cause spacecraft charging effects, radiation damage in materials and electronics, and communication interruptions, so the orbit will be highly elliptical with short times spent near the Sun.[25]

The trajectory requires high launch energy, so the probe was launched on a Delta IV Heavy class launch vehicle and an upper stage based on the STAR 48BV solid rocket motor.[25] Interplanetary gravity assists will provide further deceleration relative to its heliocentric orbit, which may result in a heliocentric speed record at perihelion.[5][29] As the probe passes around the Sun, it will achieve a velocity of up to 200 km/s (120 mi/s), which will temporarily make it the fastest manmade object, almost three times as fast as the current record holder, Helios-B.[30][31][32] Like every object in an orbit, due to gravity the spacecraft will accelerate as it nears perihelion, then slow down again afterwards until it reaches its aphelion.

Grey
2018-Aug-17, 04:20 PM
How does a probe like Parker use, say, Venus to slow down to obtain its desired near-Sun, and inner aphelion, orbit? I assume there's no atmospheric braking being required. I can imagine zipping around Mercury to force it more into the path of Venus to slow it down but I don't think they do this, or did I miss this?Here (https://medium.com/the-space-perspective/gravity-assists-explained-simply-how-the-voyager-spacecrafts-escaped-the-solar-system-d8aaa4a9273c)'s a nice explanation of the technique for speeding up by gravitational assist. To slow down, you just do the same thing in reverse.

George
2018-Aug-17, 05:12 PM
At the risk of missing something stated due to my work load, it's clear that traveling retrograde will slow the probes. But this requires the prograde orbit, that seems to be in the art and animation videos I've seen -- also only cursory effort to find the one I need, no doubt -- to get a bit of flip, or a special aphelion burn, or something to actually redirect the probe toward Venus to slow it down. What specifically is happening to make the probe change directions and is there an animation that details this a little (lot) more accurately?

schlaugh
2018-Aug-17, 07:17 PM
At the risk of missing something stated due to my work load, it's clear that traveling retrograde will slow the probes. But this requires the prograde orbit, that seems to be in the art and animation videos I've seen -- also only cursory effort to find the one I need, no doubt -- to get a bit of flip, or a special aphelion burn, or something to actually redirect the probe toward Venus to slow it down. What specifically is happening to make the probe change directions and is there an animation that details this a little (lot) more accurately?

I have not found an animation to illustrate the motion, and would like to see one as well. But...no flip or burn. The Delta IV lobbed Parker into an orbit that "chases" Venus. Parker will approach from the leading side in Venus' orbit and gravity will "slingshot" the probe into the desired orbit. Oh, there may be some tweaks but from what I've read the orbital insertion point was planned into the original launch trajectory.

George
2018-Aug-17, 07:38 PM
I have not found an animation to illustrate the motion, and would like to see one as well. But...no flip or burn. The Delta IV lobbed Parker into an orbit that "chases" Venus. Parker will approach from the leading side in Venus' orbit and gravity will "slingshot" the probe into the desired orbit. Oh, there may be some tweaks but from what I've read the orbital insertion point was planned into the original launch trajectory. Yes, I think this is best illustrated in the animation at the NASA Parker site. For me, the vector math doesn't quite work; shooting at a leading side of Venus will seem to bump velocity more than de-bump it. :)

schlaugh
2018-Aug-17, 07:47 PM
Yes, I think this is best illustrated in the animation at the NASA Parker site. For me, the vector math doesn't quite work; shooting at a leading side of Venus will seem to bump velocity more than de-bump it. :)

It's all about energy transfer relative to the sun. In the Voyager flybys Jupiter lost a bit of energy while Voyager gained by passing around the trailing side of the planet's orbit. With the Venus flybys Parker will lose some energy and Venus will gain by passing on the leading side of the orbit.

George
2018-Aug-17, 08:09 PM
It's all about energy transfer relative to the sun. In the Voyager flybys Jupiter lost a bit of energy while Voyager gained by passing around the trailing side of the planet's orbit. With the Venus flybys Parker will lose some energy and Venus will gain by passing on the leading side of the orbit. Are you saying that they will re-direct Parker so that it will be headed toward (one vector component at least) an on-coming Venus, which seems to be what I see is required in order to reduce its velocity relative to the Sun? If so, how are they doing this re-direction? Throwing something at Venus from behind or transverse to its orbit will get a bump in velocity as Venus drags it forward by its orbital motion, right?

schlaugh
2018-Aug-17, 08:26 PM
Are you saying that they will re-direct Parker so that it will be headed toward an on-coming Venus, which seems to be what I see to reduce its velocity relative to the Sun. If so, how are they doing this re-direction. Throwing something at Venus from behind or transverse to its orbit will get a bump in velocity as Venus drags it forward by its orbital motion, right?

The meeting point with Venus was baked into the original launch trajectory and launch planning, just like with the Apollo missions. (Apollo tweaked their orbits with mid-course corrections because they needed to hit some very specific points in space in order to achieve capture by the moon.)

So that meeting point is ahead of Venus. And yes, if the probe was aimed at the trailing side of Venus then it would gain energy.

I haven't seen a super-accurate diagram but Parker is basically heading roughly perpendicular to the Earth's orbit. By the time it reaches the orbit of Venus then Venus will have caught up to the probe. No major in-flight corrections needed and Isaac Newton does the rest.

Hornblower
2018-Aug-17, 08:34 PM
Are you saying that they will re-direct Parker so that it will be headed toward (one vector component at least) an on-coming Venus, which seems to be what I see is required in order to reduce its velocity relative to the Sun? If so, how are they doing this re-direction? Throwing something at Venus from behind or transverse to its orbit will get a bump in velocity as Venus drags it forward by its orbital motion, right?
Not if we give the spacecraft the correct trajectory on the way in. As it comes in from Earth it will be overtaking Venus on a converging path. Let us transform the motion to Venus-centric and imagine standing on the planet. The spacecraft comes in from the rear, swings around in front of us, and is deflected back to the rear as it goes around in a hyperbolic path relative to us. Now transform it back to heliocentric. We will find that after an initial speed-up on the way in, it will have a slower transverse component once it passes the closest approach and heads back out.

If, for a different mission, we wanted it speeded up by the flyby, we would pass astern of Venus rather than ahead of it.

Swift
2018-Aug-17, 08:48 PM
I found this animation (https://www.youtube.com/watch?v=cMNQeCWT09A) from SciNews, maybe it will help.

And this one from Goddard (https://svs.gsfc.nasa.gov/12998) shows the first couple of encounters with Venus.

George
2018-Aug-17, 09:38 PM
Not if we give the spacecraft the correct trajectory on the way in. As it comes in from Earth it will be overtaking Venus on a converging path. Let us transform the motion to Venus-centric and imagine standing on the planet. The spacecraft comes in from the rear, swings around in front of us, and is deflected back to the rear as it goes around in a hyperbolic path relative to us. Now transform it back to heliocentric. We will find that after an initial speed-up on the way in, it will have a slower transverse component once it passes the closest approach and heads back out.
I kinda get that, but not quite. see next post...

George
2018-Aug-17, 09:43 PM
I found this animation (https://www.youtube.com/watch?v=cMNQeCWT09A) from SciNews, maybe it will help.

And this one from Goddard (https://svs.gsfc.nasa.gov/12998) shows the first couple of encounters with Venus.

Yes, but those don't quite reveal how the speed is reduced, at least within the confines of the neuron group that I've freed at the moment for this purpose.

So the following may help address this issue. I have drawn the two vectors that seem important: Parker vector as it would be at or near the point in front of Venus; and the orbital path vector for Venus that, when added, at least partially, are supposed to give us path #2. I keep trying to look for a -X vector component to slow Parker down. Where is that sucker, or is the sucker just me?

23500

Added.... I do get that we can fling Parker into a path #2 or even flip it back outward, away from the Sun, but flinging it inward and giving it much greater speed (right?) in doing so may be more my hang-up. Increasing the radial velocity, as at least one article depicts, does not necessarily produce a closer aphelion.

grapes
2018-Aug-18, 01:50 AM
Increasing the radial velocity, as at least one article depicts, does not necessarily produce a closer aphelion.
They are shooting for closer perihelion, of course.

DaveC426913
2018-Aug-18, 04:43 AM
Are you saying that they will re-direct Parker so that it will be headed toward (one vector component at least) an on-coming Venus, which seems to be what I see is required in order to reduce its velocity relative to the Sun? If so, how are they doing this re-direction? Throwing something at Venus from behind or transverse to its orbit will get a bump in velocity as Venus drags it forward by its orbital motion, right?
Looking at an ideal two-body system, such as just the probe and Venus, for a moment, the probe will always lose as much speed on the way out as it gained on the way in (in a two-body scenario, the path is completely reversible in time).


The issue is not where it comes from or goes to - but on what face (front or back) it passes. And 'front or back' refers to Venus' motion, requiring a third reference point by which to reference that motion.

The energy being used is Venus' motion around the sun (i.e. a three body system), thus the motion gained is relative to the Sun.

So:

If it passes behind Venus, then the probe steals some of Venus' forward motion, gaining forward motion in the process, while Venus slows down.
If it passes in front of Venus, then Venus steals some of the probe's forward motion, gaining forward motion in the process, while the probe slows down.

cjameshuff
2018-Aug-18, 01:54 PM
Are you saying that they will re-direct Parker so that it will be headed toward (one vector component at least) an on-coming Venus, which seems to be what I see is required in order to reduce its velocity relative to the Sun? If so, how are they doing this re-direction? Throwing something at Venus from behind or transverse to its orbit will get a bump in velocity as Venus drags it forward by its orbital motion, right?


For a given probe velocity wrt. the sun, the resulting velocity wrt. the planet is at a minimum when the probe's incoming trajectory is aligned with that of the planet, and a maximum when it is opposed.
For a given probe velocity wrt. the planet, the resulting velocity wrt. the sun is at a minimum when the probe's outgoing trajectory is opposed to that of the planet, and a maximum when they are aligned.
The probe's velocity wrt. the planet is the same on the outbound trajectory as it is on the incoming trajectory.


To accelerate, you need to exit the flyby on a trajectory that aligns more closely to the planet's motion than the incoming trajectory. To decelerate, you need your entry trajectory to align with the planet's motion more than your exit trajectory.

George
2018-Aug-18, 03:29 PM
They are shooting for closer perihelion, of course. Yes and at least one animation pushes that argument, but it is misleading since shooting it faster and closer will just produce greater eccentricity, which produces a greater aphelion. Pushing a marble and forcing it more to the center of a frictionless bowl will not cause it to rise less in the bowl. Everything shown is to have both a tighter perihelion and a tighter aphelion.

But I thought a little more on Hornblower's point and I think I have it. I am fairly sure that if I see something peculiar than the other average Joe's will be puzzled, too, if they bother to wrap their head around all the nuances.

George
2018-Aug-18, 03:56 PM
Looking at an ideal two-body system, such as just the probe and Venus, for a moment, the probe will always lose as much speed on the way out as it gained on the way in (in a two-body scenario, the path is completely reversible in time). Yes, and I have assumed the gravity well effects would be separate from its orbital motion. I think Venus being closer to it, as planned, as Parker departs changes the symmetry of the path in and out regardless of the orbital motion of Venus. I ignore the gravity well effect when considering probes that are boosted outward because it's the planet's orbital motion itself that is the key to greater net velocity (after the gravity well effect). I suppose that the circumstance of a rear approach for boosting may have the affect of slowing the probe when considering the gravity well effect alone because of the likely greater time near the planet upon departure. Is this right?

Let's simplify and maybe then I can see better...

So if one pictures an object falling radially toward the Sun, as it nears the intersection of the orbit of and on-coming Venus it will accelerate toward Venus and we have our -X vector component working to slow it down in this direction. But Venus will drag it faster as it goes by. Yet if Parker is far enough away by then, then the net effect will be to have slowed it as desired. I think this is the key to my confusion-- I imagined Venus close as it sailed onward, and in any animation I've seen, the lack of a zoomed view for the encounter has limited my understanding of what takes place.



So:

If it passes behind Venus, then the probe steals some of Venus' forward motion, gaining forward motion in the process, while Venus slows down.
If it passes in front of Venus, then Venus steals some of the probe's forward motion, gaining forward motion in the process, while the probe slows down.It seems to me it also depends on the trajectory so, for the second case, if Venus is close as it sails by, then Venus will drag the probe with it. Or is no such trajectory possible?

George
2018-Aug-18, 04:06 PM
To accelerate, you need to exit the flyby on a trajectory that aligns more closely to the planet's motion than the incoming trajectory. To decelerate, you need your entry trajectory to align with the planet's motion more than your exit trajectory. Yes, and it's not hard to see that as the probe approaches the planet's orbital path, the planet will pull it with that -X vector component I was looking for. But the hard part is knowing that Venus doesn't stop but will pass ahead of the probe and will now pull our probe faster (+X). In a simple gravity well, what goes down comes back up, but the nuance is the trajectory that times it where it is close to Venus to get the drag-back effect yet far away by the time Venus is ahead of it. I think it's that simple and I think it would be helpful for others if it were shown that way.

I still recall the first real puzzle that hit me hard when I was very young. It was of a plane stationary in mid-air. It struck me as extremely odd because I was too young (I prefer a youthful excuse :)) to recognize that it was just a picture that was not demonstrating, perhaps by an expected image blur of the jet, that it was moving. Motion and, in this case, trajectory must be considered to "get the picture".

cjameshuff
2018-Aug-18, 06:20 PM
Yes, and I have assumed the gravity well effects would be separate from its orbital motion. I think Venus being closer to it, as planned, as Parker departs changes the symmetry of the path in and out regardless of the orbital motion of Venus. I ignore the gravity well effect when considering probes that are boosted outward because it's the planet's orbital motion itself that is the key to greater net velocity (after the gravity well effect). I suppose that the circumstance of a rear approach for boosting may have the affect of slowing the probe when considering the gravity well effect alone because of the likely greater time near the planet upon departure. Is this right?

Let's simplify and maybe then I can see better...

So if one pictures an object falling radially toward the Sun, as it nears the intersection of the orbit of and on-coming Venus it will accelerate toward Venus and we have our -X vector component working to slow it down in this direction. But Venus will drag it faster as it goes by. Yet if Parker is far enough away by then, then the net effect will be to have slowed it as desired. I think this is the key to my confusion-- I imagined Venus close as it sailed onward, and in any animation I've seen, the lack of a zoomed view for the encounter has limited my understanding of what takes place.


It seems to me it also depends on the trajectory so, for the second case, if Venus is close as it sails by, then Venus will drag the probe with it. Or is no such trajectory possible?

There isn't a separate "gravity well effect" and "orbital motion effect". With no gravity well, there is no change in direction and no slingshot. With no orbital motion there is no change in velocity and no slingshot. The sun itself has a gravity well that dwarfs everything else in the system, but it can not be used to change an object's solar orbit.

To decelerate, the probe needs its velocity vector to align with that of Venus at the start of the flyby, and to diverge from it after the flyby. This subtracts Venus' orbital velocity from the probe's and results in the lowest encounter velocity. At any given distance from Venus, the magnitude of the velocity of the probe with respect to Venus on the outbound part of the flyby maneuver is the same as it was on the inbound part, but its direction is different, and its velocity with respect to the sun is lower.

It doesn't matter which one "comes up behind" the other. The maneuver is most effective for deceleration if done near aphelion or perihelion of the probe. If the flyby is done at aphelion, the probe will have a lower sun-relative velocity than Venus and Venus will pass it from behind. If it is done at perihelion, the probe will be the one that catches up to Venus.

Hornblower
2018-Aug-18, 08:57 PM
Yes, and it's not hard to see that as the probe approaches the planet's orbital path, the planet will pull it with that -X vector component I was looking for. But the hard part is knowing that Venus doesn't stop but will pass ahead of the probe and will now pull our probe faster (+X). In a simple gravity well, what goes down comes back up, but the nuance is the trajectory that times it where it is close to Venus to get the drag-back effect yet far away by the time Venus is ahead of it. I think it's that simple and I think it would be helpful for others if it were shown that way.

I still recall the first real puzzle that hit me hard when I was very young. It was of a plane stationary in mid-air. It struck me as extremely odd because I was too young (I prefer a youthful excuse :)) to recognize that it was just a picture that was not demonstrating, perhaps by an expected image blur of the jet, that it was moving. Motion and, in this case, trajectory must be considered to "get the picture".

When you mentioned the idea of the spacecraft being dragged along, it appeared to me that you may have initially envisioned the action as equivalent to throwing out a hook and line and snagging the spacecraft as you fly by. In actual fact, at any given position shortly after the flyby the gravitational force on the spacecraft is exactly the same as it would have been with the planet stationary at the same position. Since the separation is increasing faster than with a stationary attractor, the gravitational action is weakened in this leg of the trip, just the opposite of what a hook and line would have done. This was an easy intuitive trap to fall into, and I had to do some head scratching to solve it.

George
2018-Aug-19, 10:19 PM
There isn't a separate "gravity well effect" and "orbital motion effect". With no gravity well, there is no change in direction and no slingshot. With no orbital motion there is no change in velocity and no slingshot. The sun itself has a gravity well that dwarfs everything else in the system, but it can not be used to change an object's solar orbit. Yes, gravity doesn't bifurcate. Like rolling a marble from one side of a bowl to the other, is different than the vectors that we use when moving the bowl at the same time. The net must be together, which we all know, but I was attempting to focus on the relative motions more than just a gravity well, which requires the well, of course. It's probably wiser to not try this simplified approach, after all.


At any given distance from Venus, the magnitude of the velocity of the probe with respect to Venus on the outbound part of the flyby maneuver is the same as it was on the inbound part, but its direction is different, and its velocity with respect to the sun is lower. I disagree unless you are addressing the non-moving gravity well simplification only. Increasing the outbound speed is the point of a gravity boost for probes headed away from the Sun. I know you know that so maybe I'm missing your point, admittedly.


It doesn't matter which one "comes up behind" the other... I can't imagine how this could be true. I planet ahead of an oncoming probe will be propelled by the planet's motion giving it and increase in velocity.

George
2018-Aug-19, 10:27 PM
When you mentioned the idea of the spacecraft being dragged along, it appeared to me that you may have initially envisioned the action as equivalent to throwing out a hook and line and snagging the spacecraft as you fly by. In actual fact, at any given position shortly after the flyby the gravitational force on the spacecraft is exactly the same as it would have been with the planet stationary at the same position. Since the separation is increasing faster than with a stationary attractor, the gravitational action is weakened in this leg of the trip, just the opposite of what a hook and line would have done. This was an easy intuitive trap to fall into, and I had to do some head scratching to solve it.[my bold] Yes, I think this is the real story of what is happening to slow its speed relative to the Sun. The animators seem content to show Venus sailing along ahead of the probe without considering the ambiguity that introduces into the very thing they were trying to demonstrate, oddly enough. But, it would take a separate zoomed animation to illustrate this nuance, though I think it is interesting to see and worthy for someone to do it. Perhaps Tony will answer this call...HINT. :)

cjameshuff
2018-Aug-20, 01:09 AM
I disagree unless you are addressing the non-moving gravity well simplification only. Increasing the outbound speed is the point of a gravity boost for probes headed away from the Sun. I know you know that so maybe I'm missing your point, admittedly.

An unpowered flyby maneuver does not change the speed of the spacecraft with respect to the body it's doing the maneuver around. v = sqrt(mu*(2/r - 1/2)).

Increasing the outbound speed is not the point, changing the direction is. The velocity of the spacecraft with respect to the sun is then changed depending on the relative velocity of the body being used for the gravity assist and the direction of the spacecraft's motion on its inbound and outbound legs.

ngc3314
2018-Aug-20, 01:06 PM
Another wrinkle in this instance - reducing aphelion is not the goal, reducing perihelion is (and aphelion must grow if the orbit is to stay resonant with Venus for future slingshot maneuvers). The redirection reducing the probe's angular momentum is probably the best bumper-sticker description.

George
2018-Aug-20, 02:02 PM
An unpowered flyby maneuver does not change the speed of the spacecraft with respect to the body it's doing the maneuver around. v = sqrt(mu*(2/r - 1/2)). Yes, thanks for clarifying. I was thinking about the Sun's reference frame instead.


Increasing the outbound speed is not the point, changing the direction is.Are you saying the speed increase for, say, New Horizons was not important but changing its direction was? Or are you saying outbound speed is not the point in the Parker mission?


The velocity of the spacecraft with respect to the sun is then changed depending on the relative velocity of the body being used for the gravity assist and the direction of the spacecraft's motion on its inbound and outbound legs.Agreed. I now see better how the speed will decrease if the probe passes in front of the oncoming planet, but it seems as if the window is both narrow and timing is critical. This is logical given that probes require multiple passes to get the desired trajectory and speed. Messenger, I think, took about 6 planetary encounters to get its speed and trajectory right to allow orbital insertion.

So, are these windows (fly-by paths) fairly delicate? They must be.

George
2018-Aug-20, 02:11 PM
Another wrinkle in this instance - reducing aphelion is not the goal, reducing perihelion is (and aphelion must grow if the orbit is to stay resonant with Venus for future slingshot maneuvers).Ah, so the aphelion chosen is to set it up for other slingshots. That makes sense and I assume it could even get bumped to the outer planets as well. A lower aphelion would increase the number of perihelion passes over time, but at the eventual loss of an expensive probe. [I wondered why the aphelion was that far out.]


The redirection reducing the probe's angular momentum is probably the best bumper-sticker description.Yep, sharing is a good thing, when done right. :)

Hornblower
2018-Aug-20, 02:18 PM
Yes, thanks for clarifying. I was thinking about the Sun's reference frame instead.

Are you saying the speed increase for, say, New Horizons was not important but changing its direction was? Or are you saying outbound speed is not the point in the Parker mission?

Agreed. I now see better how the speed will decrease if the probe passes in front of the oncoming planet, but it seems as if the window is both narrow and timing is critical. This is logical given that probes require multiple passes to get the desired trajectory and speed. Messenger, I think, took about 6 planetary encounters to get its speed and trajectory right to allow orbital insertion.

So, are these windows fairly delicate? They must be.

My bold. Yes indeed. If I am not mistaken it required the advent of supercomputers to enable the computational tour de force that makes this technique practical. There is no exact analytic solution for a multibody problem like this, and it takes a tremendous amount of number crunching to do the numerical integrations with the necessary precision and accuracy.

George
2018-Aug-20, 03:25 PM
My bold. Yes indeed. If I am not mistaken it required the advent of supercomputers to enable the computational tour de force that makes this technique practical. There is no exact analytic solution for a multibody problem like this, and it takes a tremendous amount of number crunching to do the numerical integrations with the necessary precision and accuracy. The deeper we go the more interesting this topic becomes. I recall an ME 101(?) textbook intro saying how many years it would have taken to calculate what was required of Apollo 13 to make it back home if all we were using were slide rules. It may have even been the textbook for the class on how to use a slide rule. :) I recently read of a brilliant mathematician (19th century) that published about 6 books on the Moon's orbit, three were just formulae and calculations, IIRC.

I appreciate all the help!

selden
2018-Aug-20, 06:37 PM
My bold. Yes indeed. If I am not mistaken it required the advent of supercomputers to enable the computational tour de force that makes this technique practical. There is no exact analytic solution for a multibody problem like this, and it takes a tremendous amount of number crunching to do the numerical integrations with the necessary precision and accuracy.

Supercomputers are not needed to produce the initial approximations for multibody transfer orbits. Although it hasn't been available for free downloading since the company changed ownership, JAQAR Space Engineering used to provide a software package which included the ability to calculate orbits which used multiple intermediate planetary "swing-bys" which would run on desktop PCs. For details, see http://trajectory.estec.esa.int/Astro/3rd-astro-workshop-presentations/DATO%20%28Descent%20and%20Ascent%20Trajectory%20Op timisation%29-%20%20A%20tool%20for%20quick%20evaluations%20of%20 descent%20and%20ascent%20trajectories.pdf

tony873004
2018-Aug-21, 06:46 PM
Here is a link to an animated GIF of Parker's trip to the Sun including the 7 Venus flybys.
It also includes a link to a numerical integration simulation. This simulation will run in your browser.

https://twitter.com/tony873004/status/1028388156981239808

Grey
2018-Aug-21, 11:32 PM
Here is a link to an animated GIF of Parker's trip to the Sun including the 7 Venus flybys.
It also includes a link to a numerical integration simulation. This simulation will run in your browser.Very nicely done.

George
2018-Aug-22, 02:09 PM
Here is a link to an animated GIF of Parker's trip to the Sun including the 7 Venus flybys.
It also includes a link to a numerical integration simulation. This simulation will run in your browser.

https://twitter.com/tony873004/status/1028388156981239808 Thanks Tony. I was hoping you might step in with one of those. It allows us to see that the probe leads Venus, which is necessary to help see it lose speed and get the desired perihelion, though taking a number of orbits to do so. Other than the yellow Sun, it's wonderful! :)

Jean Tate
2018-Aug-23, 12:03 AM
If a probe like Parker had been launched from Mercury, could it reduce its perihelion by flybys of Venus or Earth? Would it be possible to keep its aphelion near either planet?

Jens
2018-Aug-23, 01:31 AM
If a probe like Parker had been launched from Mercury, could it reduce its perihelion by flybys of Venus or Earth? Would it be possible to keep its aphelion near either planet?

I think that if it were to be launched from Mercury, a good strategy would be to do a flyby of Venus and then of Mercury. There isn't anything wrong with getting a gravity assist from the planet that you launched from, as long as the math works out (the earth has been used for gravity assists).