August 2007 Archives

Eclipse night


Lunar eclipse from Melbourne; photo by Ker Fern TanDespite threats from clouds covering the sky, the sky was bright and clear for most of the event last night, which made for great viewing conditions. At the start of the umbral phase of the eclipse, the eastern sky was completely covered from my location, so I missed that. It started clearing up around the time of totality, and the first time I managed to see the Moon (still covered by light clouds) it was already entirely in the dark, with a nice, dark red-orange colour.

It only got better from there as the clouds moved away, so that it was possible to see the whole process of the Moon moving out of the shade and getting progressively brighter. It was beautiful with the naked eye, and even better with binoculars: you could easily see the colour gradient across the lunar globe, and it looked distinctly tri-dimensional.

So, it was a good spectacle. The next one for us, unfortunately, won't be until 2011. We will, however, have a partial solar eclipse next February; I'll write more about it as we get closer to the date.

Carnival of Space #17

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The latest edition of the Carnival of Space is up at the Planetary Blog, edited by Emily Lakdawalla (whom you may know from the Q&A segment in the Planetary Radio show). There are articles about a pulsar just outside the Milky Way, new discoveries about dark matter and about the Phobos-Grunt mission, among others — and two articles from "down under" collaborators, including yours truly.

Up there and down here

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As I write this, space shuttle Endeavour is preparing to return to Earth, one day earlier than expected because of the approach of hurricane Dean. The worry is not so much about bad weather in Florida interfering with the actual landing, but with bad weather in Texas forcing the evacuation of the mission control buildings in Houston. I'm pretty sure everyone will be following the landing closely because of the aforementioned problems with the damaged heat shielding tiles, which NASA chose not to fix (as the process of fixing them could actually make the problem worse). NASA TV will have live coverage of the landing on the web in a few hours.

In unrelated news, the weather forecast for next Monday Tuesday in Melbourne calls for a mostly sunny day with a top temperature close to 20° (and even above 20, depending on your suburb). Great weather for the lunar eclipse of that night; remember that you can join the Astronomical Society of Victoria on the roof of the Victoria Gardens shopping centre, in Richmond, starting from 6:30pm: a gold coin pays for admission, and you get to use the viewing equipment that will be there to look at the moon and the rest of the night sky (I have no idea how to get on the roof, though; my guess is that one would use the garage lifts). But, of course, the only equipment you need to see the eclipse are your own eyes.

And, should you want to go out on the previous night, Mars and the red star Aldebaran will be very close together, presenting a nice show on the night sky to anyone who's up and looking east around 3am; the bright stars Betelgeuse, Rigel and Sirius will not be far off, adding to the show. Mars will put on an even better show in December, at the time of its closest approach to Earth, but we can talk more about that then.

The Shuttle problems

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By now, everyone is certainly aware of the problems found on Endeavour's insulation tiles, caused by fragments of ice hitting the shuttle during launch. The impact cut a gouge in some insulation tiles, and NASA is still deciding what, if anything, to do about it. The astronauts do have materials to fix the insulation, if necessary, but that is a complicated manoeuvre because, well, the tiles are underneath the shuttle. Damaris Sarria, an astronaut-in-training and Thermal Protection Specialist, discusses the possible solutions in her blog, and NASA has a 3D video of the damaged area.

The impact site was photographed from the ISS before the shuttle coupled to it; since the Columbia accident (caused exactly by fragments of, in that case, foam hitting the underside of the orbiter), it is part of the standard procedure to position the shuttle "upside-down" so that it can be seen from the ISS (I don't know what will be done in the Hubble repair mission, though).

I thought this would be a good time to talk a little about the reason why the shuttle keeps being hit by debris during launch. At launch, the shuttle is attached to three other large structures: two solid-fuel rocket boosters, one on each side, and the large, orange fuel tank that is the source of all the problems.

The boosters provide most of the thrust to take the orbiter up, and are solely responsible for holding the weight of the fuel tank and the orbiter while still on the launch pad. On launch, 71% of the total thrust is provided by these rockets, and 100% of the smoke you see coming out of the shuttle when it's already on flight comes from them (most of the "smoke" around the launch pad is actually from the water being used to cool the platform). A failure in one of the boosters is what brought down Challenger, in 1986; a leak ruptured the external tank and caused it to blow up.

The orange external tank carries the fuel for the shuttle's main engines; these engines don't provide much of the power needed for lift-off, but they are what takes the shuttle into orbit, accelerating it from 5,000 to over 27,000 km/h after the boosters separate. The tank is the only part of the shuttle that's not reused; after the engines are turned off, the tank is discarded and falls into the sea (the boosters also fall into the sea, but they have parachutes and are recovered). The landing of the shuttle is mostly unpowered, with aerodynamic braking being used to reduce the speed of the orbiter.

The fuel inside the external tank is liquid oxygen and liquid hydrogen (which burn into water, thus no smoke from it), and herein lies the problem. Liquid hydrogen needs to be cooled down to -252.8 degrees Celsius (just over 20 kelvin), which means that the tank needs to be very well insulated. Because of that, it is covered with a 2.5-centimetre thick coating of polyisocyanurate foam (which also protects the tank for aerodynamic heating during launch).

And this is the foam that falls off during launch. Also, as it is not a perfect insulation, sometimes ice forms on the tank (especially if it's a humid day and the shuttle has been fuelled for a while before it's launched), and ice fragments can also fall off. The foam can't be more securely attached to the tank without increasing weight and cost significantly (it's worth noting that, in the first few launches of the shuttle, the tank was painted white; that alone adds almost 500kg to the launch weight, and that's why it's not done anymore), so there's no easy solution to the problem.

The routine of inspecting the shuttle from the ISS seems to be the best procedure to deal with the problem of damage to tiles from falling debris, especially considering that the shuttle is not going to be used for much longer; it's indeed best that NASA spend its money and energy in the next generation of vehicles, rather than trying to re-engineer the aging shuttles. Still, that will make every launch and landing very tense for all involved, including interested amateurs like me and you.

Endeavour was launched

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Endeavour launchSpace shuttle Endeavour was launched this morning from Florida, as 8:36am Melbourne time (6:36pm yesterday, Florida time). STS-118 takes with it a new segment for the International Space Station, almost three thousand kilos of supplies and equipment and, more importantly, a school teacher.

Barbara Morgan was the back-up crew member for Christa McAuliffe on STS-51, the ill-fated Challenger flight of January 1986. After that, she continued working with NASA and eventually completed a full astronaut training program; this is her first flight, and she is the first teacher to successfully fly into space.

Endeavour is expected to land in 11 days, back in Florida, weather permitting. As with the previous missions, the shuttle will be thoroughly inspected while in orbit to ensure that it is fit to re-enter the atmosphere. NASA has pictures and videos of the launch, and will have all the updates as the mission progresses.

Lunar eclipse this month

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As I've mentioned before, there will be a total lunar eclipse later this month, visible from Melbourne (and from the Americas and most of Asia as well). The eclipse happens on Tuesday, 28 August, and starts at 17:52 Melbourne time (07:52 UTC), which is three minutes before sunset and nine minutes after the moon rises (here; check your local times). Eastern Australia will be able to see the whole eclipse (assuming a clear view of the eastern horizon from your location), while the west will see the moon rise with the eclipse already in progress. Totality starts at 19:52 (09:52 UTC) Melbourne time, and lasts for a bit over 90 minutes. Details and maps here.

That, of course, assumes that the rain gods will look kindly on us. Should we miss this one, the next total eclipse visible from here will happen in late 2011.

For those interested, the Astronomical Society of Victoria is organising a public viewing of the eclipse on the roof of the Victoria Gardens shopping centre (top deck of the car park, actually), and telescopes will be available to the public. I assume this event will only happen with good weather, but check the details closer to the date.


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Somehow, I allowed the whole month of July to go by without a single post here. And now, this blog comes back from its own ashes, nicely tying with the launch of the new Mars Lander...

Phoenix was, finally, launched last Saturday at 5:26am Florida time (7:26pm Melbourne time), and it should land on 25 May next year (no word on the expected time of the landing so far) near the north pole of the red planet.

The Phoenix lander is very different from its more famous cousins, the rovers Spirit and Opportunity; Phoenix will not move across the planet once it touched down. Instead, it will make detailed studies of the area on which it lands with the explicit intent of finding water. With that goal, it will land on an arctic region (close to, but outside, the polar ice cap) that seems to have a high amount of water under the ground (these observations were made by the Mars Odyssey orbiter) and will use an impressive array of instruments to explore its neighbourhood.

Most impressive of all is its robotic arm, which is almost 2.4 metres long and capable of digging up to half a meter into the soil; it is expected to reach a hard layer of ice before going that deep, though, and if it does it will scrape the ice to get samples, which will then be analysed by a collection of devices, including optical and atomic-force microscopes, a gas analyser and a conductivity probe. It also carries a full weather station and an stereo imaging camera, not to mention a further camera positioned at the tip of its arm.

This is the third lander intended for a polar region of Mars; the previous ones, the Mars Polar Lander, failed at landing due to human error in its programming. Let's hope that the Phoenix fares better; we shall now in 9 months.

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This page is an archive of entries from August 2007 listed from newest to oldest.

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