Gravity Effects On Voyager Or Other Probes

light in the tunnel

19th August 2009 - 12:28 AM

I was looking at the NASA webpage about the Voyagers and other probes. Although one of the recent ones used gravity-assist to accelerate it, I believe, the earlier probes seem to be on paths that minimize the effect of gravity on their trajectories.

Do these probes travel in a straight line away from the sun and Earth when they don't come close to the gravitational fields of planets?

Do or will they "fall" into orbit around the sun if their velocity doesn't reach escape velocity for the solar system? (what is escape velocity for the solar system, actually? Is it stronger than that to escape Earth orbit, for example?)

The graphic map shown on the website makes it appear that the probes follow straight-line paths, but it is a pretty basic image, and it may not be intended to be very accurate in terms of the specific shape of the path.

Was the amount of propulsion and acceleration of these probes sufficient to propel them out of the solar system? I guess that goes back to my escape-velocity question, but maybe there's another way of determining the velocity it takes to avoid "falling" into solar orbit.

By the way, sorry for putting "falling" in quotation marks. It seems like there should be a better word but this one seems to be the most tangible where succumbing to gravity is concerned - maybe "entering into orbit" is a better one since, presumably, a satellite can orbit something without the orbit decaying (or don't they always decay, however slowly? This would actually seem more logical to me since gravity should have similar effects on objects at different distances, only at a weaker scale.)

Enthalpy

19th August 2009 - 12:58 AM

Voyager relied heavily (if I dare to say) on gravity assistance by the planets. In fact, the mission was designed, an planned for that date, because a particularly favourable "alignment" of the planets allowed to visit many of them.

The funny part of it is that Nasa sold the mission to the Congress only up to Uranus. As this was brilliantly achieved, Nasa "noticed that" Neptune was by chance on the path and could be visited with little more funding - far less than a new mission.

Sending a probe to Neptune or even outside the Heliosphere would be possible with existing rockets alone, but not the same probe size, and certainly not within two decades journey.

Without planetary assist, the trajectory would be an ellipse or a hyperbola, due to the Sun's gravity.

http://en.wikipedia.org/wiki/Voyager_program

Lunarlanding

20th August 2009 - 01:47 PM

QUOTE (light in the tunnel+Aug 19 2009, 12:28 AM)

Do these probes travel in a straight line away from the sun and Earth when they don't come close to the gravitational fields of planets?

No; typically those sats lauched in the direction of outer planets are launched in a direction that uses the earth's orbital velocity to assist in achieving a more efficient trajectory.

Solar system Escape velocity is determined based upon the distance from the gravitational source....escape velocity depends upon from what graviatational potential the satellite is initially located in. And for satellites using planetary gravity assist there is not a standard figure.

If launched from earth (with no other planetary assist) it would require a speed of around 16.6 km. /sec

Lunar

AlexG

20th August 2009 - 05:42 PM

Here are the trajectories of both Voyager probes.

User posted image: http://voyager.jpl.nasa.gov/science/heliocentric.html

light in the tunnel

21st August 2009 - 01:46 AM

A related question is whether the trajectory of voyager, or other probes, can be predicted into the future. I am guess that if it's possible to determine the direction and speed that it gravity-assisted off the last planet it came close to, it would be possible to use this information to predict the path into the near and distant future.

Specifically, I am interested in whether these probes will go into orbit around the sun or hyperbole out of the solar system indefinitely (can I use "hyperbole" as a verb?). Furthermore I would like to see estimates of the probe's velocity/velocities as it decelerates or accelerates as a result of moving away from or toward the sun or other planets.

Finally I wonder if anyone has tried to look at voyager or any of the other probes using the hubble or another telescope. I know these probes are incredibly small relative to a planet but I thought maybe the hubble is powerful enough to still get an image, especially one of the closer probes, e.g. one that has been launched since hubble has been operating.

By the way, thanks everyone for your thoughtful replies. They were much better than wikipedia.

Quantum_Conundrum

23rd August 2009 - 09:15 PM

QUOTE (light in the tunnel+Aug 20 2009, 08:46 PM)

A related question is whether the trajectory of voyager, or other probes, can be predicted into the future. I am guess that if it's possible to determine the direction and speed that it gravity-assisted off the last planet it came close to, it would be possible to use this information to predict the path into the near and distant future.

Specifically, I am interested in whether these probes will go into orbit around the sun or hyperbole out of the solar system indefinitely (can I use "hyperbole" as a verb?). Furthermore I would like to see estimates of the probe's velocity/velocities as it decelerates or accelerates as a result of moving away from or toward the sun or other planets.

Finally I wonder if anyone has tried to look at voyager or any of the other probes using the hubble or another telescope. I know these probes are incredibly small relative to a planet but I thought maybe the hubble is powerful enough to still get an image, especially one of the closer probes, e.g. one that has been launched since hubble has been operating.

By the way, thanks everyone for your thoughtful replies. They were much better than wikipedia.

Even Hubble telescope wouldn't be able to see anything more than a less-than-pixel-sized speck, if that, of any of these craft.

The (dwarf) planet Pluto is barely able to be seen as anything more than a speck with any telescope, even hubble. I've never been able to find Pluto in my telescope because it is so small and dim you cannot see it with any light pollution whatsoever being present. I have been able to see Jupiter and its 4 biggest moons, and even some of the smaller ones, I think.

Anyway, a probe that is only a few meters wide even w/ solar panels and antenna extended to maximum, and is already beyond Pluto's maximum distance, is not going to be visible in any existing telescope or other device. In order to see something that small at that distance in enough detail to actually identify it, you'd need a telescope over one million times as powerful as Hubble.

The only reason a radio reciever even works at that distance is because NASA knows exactly where to point it based on the original velocity of the probe, and the best calculations for the gravity of the larger objects in the Solar System.

Enthalpy

7th September 2009 - 02:41 PM

Voyagers, as well as Pioneers, have enough velocity to escape the Solar system.

Then, one has to define where our Solar system ends to tell when the probes exit it. One possible definition is where the Solar wind has its shock bow with the interstellar medium, and by this definition, one of these probes has already exited, and another goes in and out as this limit wanders and has an irregular shape.

But if "Escape the Solar system" means to you "got enough speed" then they all escaped long ago, as they passed by Jupiter or even as they got their last impulse by the rocket. New Horizons for instance got the escape speed directly from its rocket.

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