NASA Considers Sending Telescope To the Outer Solar System

Nancy_A writes "A mission that astronomers and cosmologists have only dreamed about — until now. A team at JPL and Caltech has been looking into the possibility of hitching an optical telescope to a survey spacecraft on a mission to the outer solar system. Light pollution in our inner solar system, from both the nearby glow of the Sun and the hazy zodiacal glow from dust ground up in the asteroid belt, has long stymied cosmologists looking for a clearer take on the early Universe."

Comments

Upwards?

[Anonymous Coward]

Why couldn't they just send one upwards out of the plane of the solar system? Wouldn't that be quicker?

Re:Upwards?

[Anonymous Coward]

Exactly. The radiation envelope of the solar system is much wider than it is tall. The majority of light-blocking dust is in the plane. So going upwards would get you a clearer view much quicker than going all the way out to the edge along the plane.

Re:Upwards?

[sFurbo]

They are probably going to use gravity assists, and planets are hard to come by outside of the ecliptic. However, I suppose they could use the last gravity assist to deflect it upwards.

Re:Upwards?

[Anonymous Coward]

But there are no survey craft headed in that direction. This sounds like they want to piggyback off some other project.

Plus, you may be able to gather significant radial velocity due to planetary orbits and gravitational slingshots, while acquiring velocity perpendicular to the orbital plane may mainly rely on thrusters, which would be expensive.

Main point being: time is not the problem, expense (in US$) is.

Re:Upwards?

[Anonymous Coward]

Yes, but it's possibly worth bearing in mind that the telescope leaves earth with significant velocity in the plane, at a tangent to Earth's orbit. To send it "up" (i.e., at a normal to the Earth's orbital plane) you would need to shed that significant velocity, and even then it would be just going "up" in a straight line; it wouldn't be in an orbit around the sun or anything.

Of course, for getting "a clearer view much quicker" such a trajectory may be sufficient, but I'd be interested if anyone knowledgeable could comment on the practicalities of sending something in that direction with a sufficiently useful velocity (whether sufficiently useful means to escape the sun's gravity well, or merely to reach a useful "height" fast enough, and stay there long enough before being dragged back in towards the sun).

Re:Upwards?

[Ihmhi]

But there are no survey craft headed in that direction.

When the Zorblaxians invade, it will be because NASA was too lazy to go up or down instead of sideways.

Re:Upwards?

[boristhespider]

No, you're not, you're totally right - if you're pointing away from the sun then it doesn't contaminate anything. It depends where they're pointing it and what they're observing for whether it's an issue. You can mask out the sun but it will still be blocking a part of the sky - and more of it the nearer you are (obviously), and if you're any distance from it at all it will be many years before it gets out of the way.

The dust is probably more a problem though, I agree.

Re:Upwards?

[srjh]

Not necessarily.

Re:Upwards?

[rgbatduke]

Not to be picky, but I don't believe gravitational slingshots work that way. They are basically elastic collisions (mediated by gravity) with a planet, and therefore only give you an increase in velocity if you "recoil" in the direction of motion of the planet. In a nutshell, you borrow a tiny bit of a planet's or moon's forward momentum to come out travelling at twice its speed relative to the Sun. That is, one can slingshot in the ecliptic (in the direction of revolution) and pick up speed, but planets have no velocity/momentum perpendicular to the ecliptic and therefore one cannot borrow any. All one can do with a "collision" that has an outgoing momentum vector perpendicular to the ecliptic is trade around momentum you already have. So single "collisions" won't do.

That means that one requires at least two such collisions/stages to pick up momentum perpendicular to the ecliptic. The first has to do one or more classic slingshots in the plane of the ecliptic to pick up linear momentum. The second has to "collide" with a planet's gravitational well in such a way as to deflect the momentum up or down out of the ecliptic. Sadly, because gravitation is a radial force and conserves angular momentum (in the approximately inertial frame of the collision), one cannot combine the two in a single collision any way I can think of -- you can only pick up slingshot momentum in the plane in a single pass; one cannot also deflect it up.

Voyager (IIRC) did just this sort of things -- engaged in multiple slingshots as it went along both to pick up momentum and energy and to alter direction of that momentum "for free" by selecting specific impact parameters and collision planes with its targets.

But this doesn't make this a bad idea, only a more complicated one than "just" a slingshot off of e.g. the moon. The other nifty thing they could probably manage with such a craft is doing some serious parallax measurements, ones with a baseline much larger than 2 AU. Put a really precise observatory in an orbit out at (say) 20 AU and you extend our ability to measure distances to nearby stars out by a factor of 10 -- 1000 times as many stars, probably even more if getting out of the haze reveals e.g. nearby brown dwarfs and stellar objects that are too faint to see. This in turn could alter things like estimates of the total mass or mass distribution of the galaxy if the numbers turn out to be very different from what we think they are now. So it isn't only a matter of the distant Universe -- the near Universe could benefit from this sort of out-of-ecliptic study, although it is long term science, since the further out you make the orbit, the longer you have to wait for a full parallax baseline.

rgb

Re:Upwards?

[agentgonzo]

Not to be picky, but I don't believe gravitational slingshots work that way. They are basically elastic collisions (mediated by gravity) with a planet, and therefore only give you an increase in velocity if you "recoil" in the direction of motion of the planet. In a nutshell, you borrow a tiny bit of a planet's or moon's forward momentum to come out travelling at twice its speed relative to the Sun.

Yes, they can do that. It is essentially an elastic collision as you say, but it doesn't have to result in the gained momentum being in the same direction as the planet's motion. Extrapolating your analogy, if you had an elastic collision between the probe and a high-latitude region of the planet (rather than at the equator) then your resulting trajectory would have a 'vertical' (meaning perpendicular to the ecliptic) component. This can be done by having your encounter with the planet you are using to gain the gravitational assist happen at a high inclination. Take a look at Voyager 2. From a quick wiki search, it's currently travelling on a trajectory 30 below the ecliptic after it's encounter with Neptune and Triton.

Earth's orbit and slingshots

[captainpanic]

Why couldn't they just send one upwards out of the plane of the solar system? Wouldn't that be quicker?

Costs. And time.

We already have a certain velocity in the plane (earth is going around the sun, and we have to escape the sun's gravity well). We have practically zero velocity in the upwards direction. This is also who rockets are launched from near the equator.

Add to that possible slingshots around other planets, and you have your whole answer.

Bandwidth make it improbable?

[Jane Q. Public]

There is likely a bandwidth problem. Near-earth objects like Hubble and others can send us high-speed data streams. But while a distant telescope might see more, we would probably not be able to receive anywhere near the same data rate as for a closer object.

So... super-high resolution images at maybe one per day?

Maybe I have that wrong, but I don't think so. Higher-frequency (and therefore higher bandwidth) signals tend to attenuate more rapidly than lower-frequency signals do.

Re:Bandwidth make it improbable?

[Sockatume]

Maybe the smart thing to do is have the 'scope do the data processing for us. In astronomy there's a lot of preprocessing from a large volume of redundant data to a small volume of high-value data, why not have a telescope that's got the intelligence (constantly updated and amended from Earth) to do some of that work before transmission.

Re:Bandwidth make it improbable?

[hackertourist]

Distance is the main factor. By the time you're far enough away, you need really big antennas (the Deep Space Network) of which there aren't many; you don't want to keep one of the few DSN antennas pointed at this probe 24/7.
On the transmitter side, the power and size/weight budgets limit the signal strength.

Re:Um, will they get funding for it?

[Silpher]

The reign of a great empire has come to an end. I think we'll dive into a quasi modern dark ages for the next period. With the collapse of the world economy wars will break out even more one even might consider WW3. The U.S.A. became unimaginable rich and prosperous with cheap borrowed energy (fossil fuel) and later borrowed money. With this they could achieve things which were awesome and great. Alas with great effort too they destroyed the pillars of their own success and the U.S.A has now become a hollow shell of what they've once been. The world has to stabilize again first before we're going to see great and whole hearty efforts in space again. And with powers shifting don't be surprised if some country else will take the lead. At least IMHO.

Re:not a good idea with current technology

[addie]

Well then it's a good thing they're only hoping to go as far as Jupiter, where "the zodiacal light is 30 times fainter than at Earth". But don't take my word for it, try reading the article.

Congratulations!

[clyde_cadiddlehopper]

You have managed to come up with a topic for which there is no article in Wikipedia . I am duly impressed.

Re:Xena

[Coisiche]

Xena was just a temporary suggestion for the name; since 13th September 2006 it's actually been called Eris.