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."

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 [wikipedia.org], 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.

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: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