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Pictures from Galileo 
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Joined: Fri Mar 13, 2009 4:18 pm
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The space probe Galileo launched in late 1989 for Jupiter, where it took some cool photos and probably did other scientific stuff until late 2003, when they decided to wrap up the mission by crashing it into the planet.

But Galileo didn't just take photos of Jupiter and its moons! For instance, on the way there, it flew through the asteroid belt, and made the first ever asteroid fly-bys. The second was asteroid 243 Ida, and, approaching within a mere 2400 km of the roughly 50 km rock

(image from NASA (source))

Galileo found something that had never been seen before: an asteroid's moon!

(image from NASA (source))

Yep, the 50 km asteroid has a tiny 1.5 km moon, given the name "Dactyl" (phallic beings who inhabited Mount Ida in Greek mythology, according to Wikipedia--oh those nutty astronomers!). It's about orbiting about 90 km (56 miles) from Ida here. Aren't they a cute pair? Aw.

Galileo also got the best pictures of Jupiter's comet Shoemaker-Levy 9 crashing into that planet in 1994--the first observation of interplanetary bodies smacking together like that! SL9 was probably a 5 km comet orbiting the Sun, but was picked up by Jupiter in maybe the 60's or 70's, and in 1992 began to break up when it got so close to the planet that the tidal force of Jupiter's gravity overcame the comet's internal gravity and cohesion, and started to pull it apart; it was in about 21 major chunks when it hit Jupiter. This is Galileo's sequence of the massive fireball from planet "W":

(image from NASA (source))

Doesn't look like much on the computer screen, but that's like an Earth-sized fireball! The fragments hit the planet at about 60 km/s, and the estimated total impact force of just this one of 21 fragments was about 600 times Earth's entire nuclear arsenal--and that's from just maybe 1/21st of a 5 km comet hitting at a "mere" 1.67% light speed. Phew! W and a few other fragments its size left dark spots twice the size of Earth on Jupiter's gas surface, and were visible for months afterwards, much more prominently than Jupiter's usual prime feature, the red "Eye" storm.


Just to throw in some more about ships getting close to asteroids, there've been some other interesting happenings aside from Galileo's flybys, including one that's still ongoing.

Space probe NEAR-Shoemaker was sent out to probe the 30 km "near-Earth" asteroid 433 Eros, one of the largest NEAs, and due to get within 70 lunar distances of Earth in 2012.

The probe got some nifty photos of Eros, including this one:

(image from NASA (source))

It tried going into orbit around Eros, but a glitch occurred just after its thrusters engaged, shutting them off. A cascading series of failures followed during the control "anomaly," with the probe firing its thrusters thousands of times, burning all the spare fuel the mission had, and going out of control; they didn't get control back for about 24 hours. Anyway at the end of the study period they landed it on the asteroid, in the "saddle" part you can see in the photo. Neat maneuver! So now it's just sitting there in the saddle for all eternity, more or less.

The other asteroid ship story doesn't have cool pictures (oh wait yeah it has some of the tiny asteroid, for instance here), but it's another drama of cascading failures, this one still ongoing! Probe Hayabusa, of the Japan Aerospace Exploration Agency ("JAXA"), launched in 2003 for a rendezvous with NEA 25143 Itokawa, with the ambitious plan of actually making contact with the asteroid, collecting surface samples (not by actually landing, but by firing pellets to knock bits off its surface), and flinging them back to Earth in a special capsule, which can be collected and studied.

Hayabusa had a "safe mode" glitch when trying to "land," just like NEAR-Shoemaker did during its orbital insertion attempt! Two attempts to knock bits off the asteroid into the sample collector were made, but both times something didn't quite work out, and they aren't actually sure they got anything. Gee!

The Hayabusa has had some really rough luck altogether, though. To name just a few...

- Its solar cells were damaged by solar flares on the way out, slowing it down and cutting the amount of time it could stay at the asteroid, and reducing the number of landing attempts it could make from 3 to 2.
- It had a 12 cm mini-lander, MINERVA, that was supposed to be launched to the surface of the asteroid and "hop" around with an internal flywheel, but the deploy command came when Hayabusa's autopilot had kicked in a course correction, so MINERVA missed, and went spinning off into space. Poor little thing!
- The probe wasn't actually supposed to land on the asteroid, but in fact it ended up doing so when autopilot kicked in at one point during the massive control snafus in the first sampling attempt, and was on the surface for about 30 minutes.
- Two US-made flywheels for maneuvering failed at separate times, so Hayabusa has to do its maneuvering with its propellant thrusters. The failed "reaction wheels" were US-made, oooh.
- After the landing attempts, it sprung a fuel leak. This caused a power outage and forced a course correction. Later, the craft went into an out of control spin, possibly due to evaporation of leaked fuel. They had to wait from December 2005 to March 2006 for its spin to stabilize.
- They weren't actually able to get it under control and headed back toward Earth until April 2007, limping along on two of its four ion drive engines, and 7 of its 11 batteries.
- Earlier this month, one of the remaining ion drives failed. A week ago, they announced that they'd been able to cobble together partial thrust from two of the other broken drives, which should be enough to get the return capsule back to Earth.

If nothing else calamitous occurs, the probe will release its return capsule in June of next year. The capsule is supposed to via parachute in Australia, while the probe burns up in re-entry (it's a tough life for a probe). We can hope that it actually got some asteroid chunks in the capsule!

Hm somewhere in all this, I think maybe with NEAR-Shoemaker, I also found another interesting tidbit about NASA: they've got a Deep Space Network of communication installations on Earth that cooperate in sending and receiving the transmissions for NASA's probes and ships. There are currently three of these, spaced evenly around the world in California, Madrid, and Australia. Each one has at least four deep-space antennae, going up to a fairly massive 70-meter dish. The DSN has been in operation since the late 50's, though (before that, the Army ran this stuff), and those 70-meter dishes in particular (which probably weren't up in the late 50's, but I didn't find when they were made) are aging and in need of repair/replacement; currently they can be out of service for months at a time. Save the Deep Space Network! :o

Sat Nov 28, 2009 7:02 am
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Joined: Fri Mar 13, 2009 4:18 pm
Posts: 4209
Hayabusa's capsule landed in the Australian Outback today; they still have to locate it and see if it actually got any samples.

EDIT: Article updated: they recovered the capsule.

The article mentions that Hayabusa would be the fourth "space sample" returning mission, the others being moon matter by the Apollo series (A* forum article here), comet material by Stardust (previous A* forum mention here), and solar wind material from Genesis. So of course I had to look up Genesis, which was a NASA solar probe that launched in 2001, went to Earth's L1 point (gravitationally stable point between the Earth and the Sun--about 1.5 million km from Earth, which is about four times the distance of the Moon from Earth)) collect solar wind particles, and returned to Earth in 2004. Just to show that unlike with Hayabusa's capsule, these things don't always work as planned (like most of the rest of Hayabusa's mission, too!), Genesis's capsule crashed when the parachute didn't deploy. Ouch! But it landed in soft muddy ground at "only" 193 mph, so they were actually able to recover some of the samples.

An interesting side note in the Wikipedia article is that the design error that prevented the Genesis capsule's chute from deploying--an incorrectly oriented accelerometer--was the same type of error that led aerospace engineer Edward A. Murphy, Jr, to coin "Murphy's Law": "Anything that can go wrong will go wrong."

Mon Jun 14, 2010 12:08 am
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