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Comment by yaix | Hacker News Reader

It would be great if we would send one or two such probes out per year, in different directions. We could find so many interesting things. There are currently only two.

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You can not do this.

The Voyager probes where only able to escape the solar system because Jupiter, Saturn, Uranus, and Neptune where aligned, and they could use the slingshot effect to accelerate when passing by them. These planets will not be aligned in a similar way until the 22nd century [1][2].

[1] http://en.wikipedia.org/wiki/Planetary_Grand_Tour [2] http://en.wikipedia.org/wiki/Gravity_assist#Limits_to_slings...

What about New Horizons[1], launched in 2006? It's supposed to leave the solar system in 2029, according to wikipedia (granted, citation needed).

[1] http://en.wikipedia.org/wiki/New_Horizons#Key_mission_dates

Exactly. Just think of all the robots and probes we could've created with the money spent on the shuttle program.

The shuttle programme was good and necessary.

But maybe we could have used some of the x trillion dollars spend on killing people in the past few decades.

It would be especially great if we could send one out of the plane of the ecliptic (i.e. out of the "top" of the sun rather than the "side").

Unfortunately in this case we cannot use the slingshot effect.

Why not? Doesn't gravity work in the Z coordinate?

But seriously - is there a physical reason not to send a probe "over the top" of the sun and fling it up, rather that out?

[Edit] Note to self. Always consult Wikipedia before opening your trap on HN. http://en.wikipedia.org/wiki/Slingshot_effect

I suspect the energy requirements to do so would so large as to be impractical.

The "slingshot effect" or gravity assist involves a vessel robbing angular momentum from a large body.

If you launch a vessel towards a planet (so that you come near but don't collide with it), then in the reference frame of the planet your vessel will leave with the same velocity going away from the planet as the velocity of your approach. However, since the planet was moving with respect to the Sun, you will have gained or lost velocity with respect to the Sun, depending on whether your space craft approached from behind or in front of the moving planet. Typically in these assist maneuvers, you wait for a large planet to be a bit ahead of the Earth's orbit. You launch towards that planet, and the gravity assist accelerates the space probe. Some of that acceleration will be tangential (mostly useless to you) but some will be radial, increasing your velocity from the Sun.

The Voyager probes took advantage of a once-in-every 180 year planetary alignment, with all of the outer planets mostly aligned. See http://en.wikipedia.org/wiki/File:Voyager_2_path.png for a good illustration. All the outer planets are traveling in a counter clockwise direction, and you can clearly see the outer planets accelerating Voyager 2 tangentially. It should be clear that there will be a radial component to that acceleration as well.

I don't think you can use the Sun in these circumstances; it doesn't have any angular momentum for you to steal.

Incidentally, the discovery of this method is sheer brilliance; without using gravity assists it would have taken prohibitively long and required a prohibitive amount of propellant to reach the outer planets.

A theoretical and probably ridiculous question here, but... does not the probe thus reduce the planetary orbital speed by the same amount (relative to mass, I guess), that it gains?

Momentum is conserved in the system (total momentum of probe and planet is always the same). Momentum = mass x velocity, so yes, the planet will slow down, but it's a ridiculously small amount. Think of shooting airgun pellets at a tank barelling down on you to slow it down, but even less effective.

The tank is powered though... if it were COASTING at me, that'd be closer... ;-)

The slingshot effect lets you add or subtract a fraction of the orbital motion of a planet you closely fly by. The key is that the speed relative to the planet will be the same going in as coming out, however the angle of the trajectory of the spacecraft relative to the planet's orbit can be different. If you want to change the plane of an orbit the slingshot effect can still be worthwhile, since it can help kill some of the speed in the ecliptic plane, but it won't help adding to the speed perpendicular to the ecliptic.

Could you not build up a lot of speed in the ecliptic plane with the slingshot effect, and then use the gravity of a planet or the sun to deflect the orbit perpendicular to the ecliptic? (I mean in practice this maybe be unlikely to be feasible, but in theory it is with the right planet arrangement)

Yup, you can do that, but the faster you go the less you'll be deflected, and you won't get a speed increase as you would with a normal planetary assist.

I think the NASA/ESA Ulysses probe did that - it used Jupiter to flip the probe out of the plane of the ecliptic:

http://en.wikipedia.org/wiki/Ulysses_%28spacecraft%29

Maybe, but with a limited budget for probes there's a lot of things I'd rather see than "what empty space looks like, in different directions"

It's not empty! That's what's so fantastic!

Voyager1 and 2 were sent around 30 years back. If we send now, we will get results only after 2040 only.

well you got to think about the future or else voyager 1 and 2 never would been sent out.

they would have just thought "lets not do it because we may not get interesting stuff until 2011"

if something takes time, the smartest thing is to start as quick as possible so you get results that much quicker

Well, the more reason to launch them now and not wait another year.

I don't think a new one would take 30 years.

http://www.grc.nasa.gov/WWW/ion/overview/overview.htm

It tops out at 90,000 meters per second.

http://voyager.jpl.nasa.gov/mission/interstellar.html

The furthest one out is 17 billion kilometers.

http://www.google.com/search?sourceid=chrome&ie=UTF-8...

That's about six years, though I don't know how long it would take to reach the top speed.

How long does it take the data to reach us?

Speed of light, baby! IIRC, on the order of 4 hours from Pluto. 16 hours (one-way) out to Voyager 1 where it is now.

Wolfram Alpha excels in that type of questions:

http://www.wolframalpha.com/input/?i=distance+pluto+%2F+ligh...

http://www.wolframalpha.com/input/?i=distance+voyager+1+%2F+...

P.S. You are correct.

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

"astronomical units per day: 173"

http://en.wikipedia.org/wiki/Astronomical_unit#Examples

"94 AU: Termination shock between Solar winds/Interstellar winds/Interstellar medium"

I think astronomers would prefer data move back and forth faster, but they're used to waiting that long and more for things to happen.

That's my point exactly. Don't wait. Send probes out every year. Because it takes so long for them to get to these places. A few may get lost on the way. Some instruments may malfunction. So better send out more. What would that cost? Half a billion dollars a year? Probably much less, because construction would get more efficient.

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