Voyager spacecraft, which left our Solar System?

[donsignori]

In the November 23, 2004 edition of 'Today on Space.com', titled "Fact vs. Fiction: 10 Questions to Test Your Space IQ" we see number 5 making this statement, <br /><br /> "We currently have the technology necessary to send astronauts to another star system within a reasonable time span. The only problem is that such a mission would be overwhelmingly expensive." <br /><br /> and asking whether its Fact or Fiction. <br /><br /> The answer is correctly given as fiction. However part of the answer is also Fiction and leaves the general public with misleading information. <br /><br /> The following part of Space.coms answer is not Science Fact but is an all too common misconception of the dimensions of our Solar System;<br /><br /> " Even the unmanned Voyager spacecraft, which left our solar system years ago at a breathtaking 37,000 miles per hour".<br /><br /> Given the fact that our Solar System is believed to have a radius of 'At Least' one Light Year from our Sun to the edge of the Oort Cloud, the Voyager spacecraft travelling at 37,000 mph will take some 18,000 years to leave our Solar System.<br />

 

[robnissen]

That statement is not completely inaccurate. One way to look at the solar system is to measure it to the edge of the heliosphere (which is where the solar wind is reversed course and pushed back by the intersteller medium.) The heliosphere is shaped like the bow of a boat with a much shorter wake in front of the direction of travel of the sun (boat) then behind it. As the voyagers were both send off towards the front of the boat (sun), they are both fairly close to crossing the heliosphere, but that is still more than a decade away. One of the voyagers, however, will very soon, perhaps already, cross the heliopause (which is where the solar wind starts to get pushed backwards, but has not yet reversed course). At least an argument can be made, that the solar system ends at the heliopause, or at least the heliosphere. But I agree that to the extent that part of the Oort cloud is in front of the sun as it orbits through the Milky Way, to say that the solar system ends at the Heliosphere is probably not completely accurate.<br /><br />This is a space.com article discussing Voyager and the heliosphere:<br /><br />http://www.space.com/missionlaunches/missions/heliosphere_shock_010706.html

 

[CalliArcale]

It is worth pointing out that even the Voyager team (perhaps understandably) uses this definition of the edge of the solar system. <img src="/images/icons/wink.gif" /><br /><br />Of course, gravitationally speaking, the Voyagers left the solar system years ago. Neither is in orbit around the Sun, and is thus in a very real sense no longer a part of the solar system, but simply an object passing through its outer reaches. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[meteo]

Well, I think we "could" send a nuclear powered rocket but you would have to expand the reasonable definition to 100-200 years. It would cost trillions but it I think it would be possible.

 

[donsignori]

While I believe there is only one definition to our Solar Systems dimensions (to the outer edge of the Oort Cloud) the statement in the Space.com article would still be inaccurate if one wishes to define it as the edge of the Heliopause/Helioshphere or the Termination Shock. It says that the Voyager left the Solar System years ago. Now I do believe there is an area where the Solar wind meets interstellar medium and that our spacecraft are speeding towards it. But we don't know for sure where the Termination shock is or how far out it is. The Voyagers we are told could reach it in a year or ten or........ Whichever definition we use the Voyagers clearly have not left our Solar System. Unless, and only unless the Solar System being referred to in these stories is the distance to the edge of the furthest point of our ninth planets orbit. Pluto. However leading people to believe that that's the extent of our Solar System would be IMHO a mistake.

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p> It says that the Voyager left the Solar System years ago.<p><hr /></p></p></blockquote><br /><br />In which case, they are clearly referring to the gravitational definition, which is quite true. They have left the solar system in the sense that they are no longer part of it. Neither are Pioneers 10 and 11. In fact, Voyager 1 became no longer a part of the solar system in the 80s, during its encounter with Saturn. I'm not sure whether Voyager 2 acheived escape then or during one of its subsequent planetary encounters. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[nexium]

Lets try some arithtmetic on the trip to Centarri or a bit farther. In 40 years 2 Voyagers and 2 Pioneers have traveled about 6 billion miles. With twice as much fuel and four times as much money, we can expect to go twice that far in the next 40 years. We can double again, and again, perhaps before diminishing returns make a 5th doubling too costly with that technology = chemical rockets and sling shot manuvers. Since we can expect diminishing returns, we will develop ten more propulsion systems, over the next 50 years, which is about the least time possible to properly evaluate the first 3 doublings. Generally it is not productive to attempt bigger scale ups than double. With very good luck, one ot two of the other ten propultion systems will have caught up with chemical rockets and sling shot manuvers, so we can do 3 or 4 more doublings of the distance with perhaps only 50 years of travel time. That however puts us at 2104 (a century from now) before we launch what we hope will be the 8 th doubling to about 1570 billion kilometers in 50 years. That distance is 0.064 light years, so you see we still have annother 1/2 century of doubling before we can hope to send probes to the Centarri system in less than a century. Worse, that assumes we keep finding propulsion systems that are not killed quickly by diminishing returns.<br /> A practical probe is more than a propulion system, so we must make equally rapid advances in other systems to actually launch probes to the Centarri system 150 years from now, at a cost of many trillions of dollars. A major break though could get us there sooner, but I have no idea what it might be. The thermal nuclear rocket also requires reaction mass to be expelled at rather low speeds, so it has less potential than ion propulsion which can theoretically expell reaction mass at 0.9999999 c. Neil