What "weed need" is a space mission!

[Uncwilly]

A sun observing probe that orbits the Earth-Sun L3 point. This would help seeing the dark side of the sun, giving us a complete view.


A small cluster of seismographs dropped around on the moon (not unlike the Ranger missions). Then smack the moon 3 different times at different locations with significant different energies.

[retina]

Originally Posted by Uncwilly

A sun observing probe that orbits the Earth-Sun L3 point. This would help seeing the dark side of the sun, giving us a complete view.

How will you communicate with the probe? There is a rather large ball of hot plasma that gets in the way of any signals you might want to transmit between the probe and Earth.

[Uncwilly]

Originally Posted by retina

How will you communicate with the probe? There is a rather large ball of hot plasma that gets in the way of any signals you might want to transmit between the probe and Earth.

Originally Posted by Uncwilly

A sun observing probe that orbits the Earth-Sun L3 point. This would help seeing the dark side of the sun, giving us a complete view.

The probe would not be stationed directly at L3, rather it would orbit the point. It is not crazy. Please read the section on L3 at wikipedia: http://en.wikipedia.org/wiki/Lagrangian_point#L3

[axn]

Originally Posted by Uncwilly

the dark side of the sun

The what?

[Uncwilly]

Originally Posted by axn

The what?

From http://science.nasa.gov/science-news...3jan_darkside/

"This is a perspective we've never had before," says STEREO mission scientist Lika Guhathakurta of NASA headquarters.
"We're now monitoring more than 270 degrees of solar longitude—that's 3/4ths of the star."

"After all these years," she laughs, "we're finally getting to see the dark side of the Sun."

(Editor's note: The Sun has no dark side. That was a solar physics joke.)

[retina]

Originally Posted by Uncwilly

The probe would not be stationed directly at L3, rather it would orbit the point. It is not crazy. Please read the section on L3 at wikipedia: http://en.wikipedia.org/wiki/Lagrangian_point#L3

Thanks for the link. I think at a minimum the orbit has to be double the diameter of the Sun so that we can peek at the probe around the Sun's edges on a continuous basis. But practically I would expect the orbit needs to be larger than that to make signal reception more reliable.

[xilman]

Originally Posted by fivemack

I'm afraid I do get a bit annoyed by the way that, whenever someone mentions space telescopes in quantities greater than one, someone else mentions interferometry. Particularly with the NRO telescopes, which are short focal length and optimised for very-wide-field work in the visual in almost exactly not the way that you'd want for interferometer elements.

NASA put about a billion dollars into space interferometry development, to discover that building an exciting space interferometer cost more than they would be prepared to spend ... planet-hunting by interferometric astrometry is so much more expensive than Kepler.

VLBI with an actually-long baseline is more interestingly practical - big deployable antenna are off-the-shelf, JAXA has launched a test comsat with a 17-metre one. Regrettably the very biggest ones are off the NSA's shelf and so you probably have to pay for the development again.

With current 10,000km baselines you can get 10-microarcsecond precision, which allows pretty good parallax measurements out to 10kpc within the Milky Way, and direct measurements of Keplerian motion of water masers to 60Mpc - there are admittedly issues of getting enough signal for those fairly weak sources. So you probably do need a billion-kilometre baseline for direct parallax to quasars, but the water-maser work might well be possible with sufficiently large dishes at Earth-Sun L4 and L5.

While in the sauna yesterday I came across a flaw in my original mission profile. It may be reparable.

The original had the large antenna doing double duty for down link and astronomy. The former requires that it point at the Earth; the latter that it point almost anywhere but. There's too much noise coming from these parts to be able to see faint astronomical objects. Even if that limitation is overcome, by listening in a particularly quiet band for instance, the geometry is not conducive to parallax measurements.

As I see it, the best solution would be to use a 2-5m dish for comms while near the Earth, up to 30 AU away say, switching over to the big dish once the bandwidth gets too low for the interferometry data. Thereafter, for as long as the spacecraft lasts and anyone cares to listen, there will be adequate bandwidth for the other science packages. The switchover would be done with the same manoeuvring subsystem used to point the big dish at the astronomical sources, possibly augmented by attitude control rockets.

I still wouldn't bother with cameras, though.

[xilman]

Another project came to mind while in the sauna yesterday. This one needs to be flown in relatively low earth orbit.

Quite a few studies have been made of long-term effects on orbiting organisms. Relatively little has been done on genetic adaptability to weightlessness. Ground-based studies of radiation adaptation have been widespread.

The breeding cycle for Drosophila melanogaster is approximately two weeks, though it can vary significantly with living conditions. In stressful environments, thirty to fifty generations is likely long enough for Darwinian evolution to become noticeable. There is probably enough background radiation in earth orbit to induce mutations anyway but a mutagen could be included if needed.

The satellite initially contains 30-50 samples of wild-type Dmel eggs in separate containers each of which are big enough to let them (try to) fly around and indulge in relatively normal behaviour. As Dmel are only a couple of millimeters long, this isn't actually a very large volume. Needless to say, the interior of the space craft has to be fly-rated, so kept warm, lit on a diurnal cycle, pressurized, oxygenated, etc. Every two weeks, or so, one of the remaining containers is depressurized and cryogenically frozen. A mechanism to move it into a permanently shaded part of the craft should be enough to keep it cold.

When all the containers are ready, they are returned to earth for detailed study in the lab.

As you can easily work out, this is a 18-24 month mission.

[Dubslow]

Originally Posted by xilman

Another project came to mind while in the sauna yesterday. This one needs to be flown in relatively low earth orbit.

Ooooohh, good one. It can essentially be done now, at hardly any (extra) cost, and the results would be quite interesting to a significant population of the Earth (where by significant I mean like above 0.001% or so, maybe even more depending on exactly how "interesting" you mean).

[xilman]

Originally Posted by fivemack

With current 10,000km baselines you can get 10-microarcsecond precision, which allows pretty good parallax measurements out to 10kpc within the Milky Way, and direct measurements of Keplerian motion of water masers to 60Mpc - there are admittedly issues of getting enough signal for those fairly weak sources. So you probably do need a billion-kilometre baseline for direct parallax to quasars, but the water-maser work might well be possible with sufficiently large dishes at Earth-Sun L4 and L5.

Here's a quick order of magnitude computation.

Assume the first position measurement is taken at 1G km from the earth (7AU, or half-way between Jupiter and Saturn, probably at a decent period after a Jovian gravity assist). That's 1e5 times the current baselines, so the positional measurements could be good to 10e-6 / 1e5 == 1e-10 arcsec. Wait a few more years and the probe will be over twice as far away so the parallax baseline will be 10AU. Note that this is still well within the orbit of Neptune and is easy to reach even with 40-year old technology.

A parsec is defined as the distance at which a length of 1AU subtends an angle of one arcsec, so a 10AU baseline subtends 1 arcsec at 10pc and 1e-10 arcsec at 1e11pc. 100Gpc is way beyond the edge of the observable the universe and so nearby quasars at a few gigaparsec should show useful parallax.

This pretty much determines the probe trajectory to be as normal as possible to the directions of the largest number of radio-bright quasars.

[chappy]

You space nuts have been busy.