New Horizon Spacecraft may be on a Stamp, with your help

•February 6, 2012 • Leave a Comment

You can help to put a spacecraft on a US postage stamp.

The mission team for NASA New Horizon spacecraft, the first spacecraft in human history that will visit Pluto, had come up with the idea of putting the spacecraft on a stamp to commemorate the encounter:

New Horizon left Earth in January 2006, and will reach Pluto in July 2015. New Horizon is the fastest spacecraft ever launched, but it still takes more than 9 years to reach its destination.

According to their news release, “You can help make this happen,” says New Horizons Principal Investigator Alan Stern. “We’re asking people to sign the petition, because the post office considers not just the merits of a new stamp proposal, but also whether it is supported by a significant number of people.” They are starting the process now because it can take three years or longer for a postage stamp proposal to result in an actual stamp, hopefully will coincide with the encounter.

Pluto had made it into a stamp before, in 1990, labelled “Not Yet Explored”. Now New Horizon is on the way to explore it, so I think this stamp serve as an update to its status.

I had signed the petition, if you think you like it, then sign it. I’m not sure how we can get the stamp here (if it really do made into an actual stamp), but I think it’s cool to have a spacecraft on a stamp.

You don’t see it, but it’s there

•January 24, 2012 • Leave a Comment

Dione and Mimas by Cassini. Credit: NASA/JPL-Caltech/Space Science Institute

The bigger moon that filled the view is one of Saturn’s many moons Dione. The night side of Dione blended into the dark space beyond and it seems like there is nothing there. But with the help of the smaller moon Mimas peeking out from behind, we can see the edge of Dione, and realised that there is something there after all.

Let’s Look for Comet Lovejoy Now!

•December 24, 2011 • Leave a Comment

You have to wake up early for this.

Comet Lovejoy. Credit: Colin Legg

Comet Lovejoy has now brightened to naked eye visibility. It can be seen in the morning twilight just before the Sun rises in the constellation Scorpius. You need a clear and unobstructed eastern horizon to increase your chances to see it. If the weather condition is good, even if you can’t see the comet head because of foreground obstruction, you might still be able to glimpse the comet tail.

Comet Lovejoy rising over Western Australia by Colin Legg

The sighting of Comet Lovejoy favours the Southern Hemisphere. Theoretically, we at the equator might be able to see it, but we really need a clear horizon. The visibility of the comet could improve in the days ahead as the comet moves away from the Sun and the background sky darkens accordingly.

Below is a very very stunning image of Comet Lovejoy – a view from space!! This jaw-dropping image of Comet Lovejoy was taken by Dan Burbank, the Expedition 30 commander onboard the International Space Station.

They even created a time lapse video of it!

 

These fantastic images of the comet are only part of the story. Let’s talk a bit on the story before this…

Comet Lovejoy, which bears the official name of C/2011 W3, was discovered by an amateur astronomer Terry Lovejoy early December. This comet is a sungrazer – a comet that passes extremely close to the Sun. The most famous sungrazers are the Kreutz Sungrazers, which all originate from one giant comet that broke up into many smaller comets during its first passage through the inner solar system. Comet Lovejoy belongs to these Kreutz family comets, so did the Great Comets of 1843 and 1882, and Comet Ikeya-Seki in 1965. They were all fragments of the original comet.

Because Kreutz sungrazers are typically small (~10 metres wide), they usually will be completely evaporated during a close approach to the Sun. However, larger ones may survive their passage through the Sun. And Comet Lovejoy is one of those larger one. On Dec 16, Comet Lovejoy plunged through the Sun atmosphere and emerged from the other side intact (the video below is a must see). It was a surprise for the scientists, because they thought that its icy core was not large enough to survive the passage.

Credit: NASA/SDO

After surviving the journey, Comet Lovejoy is now moving away from the Sun and going back to the frozen deep space. As it is backing out, it does not forget to put on a show for us, as can be seen from the picture at the beginning of this post.

I got a place near my house with a unobstructed eastern horizon. I’m going to give the Comet a try (in few hours’ time, actually). Wish me clear sky!

Photos of Total Lunar Eclipse – 10 Dec 2011

•December 14, 2011 • 1 Comment

The total lunar eclipse last Saturday was great! The weather cooperated – the sky was partially cloudy, but the clouds were mostly at not where the Moon was. Although occasionally the clouds hide the Moon, overall I still managed to get most of the eclipse progress.

This is my best shot of the night and I like it very much. This image shows 3 things: (1) part of the Moon not in shadow (bright part at the lower right), (2) turquoise colour edge and (3) the reddish Earth’s shadow (see diagram below for illustration).

The turquoise colour in the previous image I took in Jun was not that obvious and this time I was hoping to get a more definite turquoise colour and I’m happy that it turned up nicely in the image. As was explained in my previous post, the turquoise blue colour comes from light passing through the ozone layer, which absorbs red light and makes the passing light bluer. This can be seen as a soft blue fringe around the red core of Earth’s shadow.

 

I had combined all the photos into a short video. Enjoy!

 

This is how the sky looked like at the beginning of the eclipse. Luckily the clouds were moving and it was clear after that.

Credit: all photos by thchieh

Total Lunar Eclipse – 10 Dec 2011

•December 8, 2011 • 2 Comments

Imagine you are outside your house breathing some fresh air and enjoying the night view around you. You look up at the sky, hoping to catch a star or two, but what you saw instead was a reddish orangey full moon hanging in the sky. What happen to our Moon?!?

No fear, there is nothing wrong with our Moon – our Moon is as normal as it always is. It’s just passing through the Earth’s shadow, and we call that a lunar eclipse.

This is going to happen on Saturday (Dec 10), on a convenient time for us (in Malaysia). The Moon starts to enter the penumbral shadow at 7:33 pm and exit by 1:30 am the next day, with maximum eclipse at around 10:30 pm. This means that we no need to stay up late into the night to see it.

Credit: F. Espenak, NASA’s GSFC

For animation, click here. As you can see from the animation, as the Moon enters the Earth’s penumbra (P1 to U1), you may not observe any changes. The show really starts after 8:45 pm (U1), when the Moon starts to enter the umbra shadow. Look for the colour change (to reddish) as the Moon moves deeper and deeper into the shadow. Between 10:06 pm (U2) to 10:57 pm (U3) is what we called totality – this is the time when the whole Moon is in Earth’s umbra. After that, the Moon will slowly come out from the shadow, and by 1:30 am, you can pack and go to sleep.

Total Lunar Eclipse of 16 Jun 2011 taken outside my house. I did not managed to finish the whole sequence because the clouds rolled in. Credit: thChieh.

 

Why does the Moon turns reddish or orangey during totality? Shouldn’t it disappear as it enters the Earth’s shadow? The reason is our atmosphere. Take a look at the diagram below and it’ll explain everything.

If the Earth had no atmosphere, the Moon would be completely dark during an eclipse. The presence of Earth’s atmosphere means that sunlight reaching the Moon must pass through a long and dense layer of air, where the light is scattered. Shorter wavelengths (blue) are more likely to be scattered, so by the time the light has passed through the atmosphere, the longer wavelengths (red) dominate. The scattering depends on the conditions/particles in our atmosphere, which in turns determine the colour of the totality Moon. Anything from bright orange to blood red is possible. If there has been a major volcanic eruption, for example, the atmosphere has so much dust that the shadow on the moon will appear dark throughout an eclipse.

What colour are we going to see this Saturday? It will be a surprise…

(When the eclipsed Moon is bright, the stratosphere is clear. On the other hand, a dark eclipse indicates a dusty stratosphere. There are atmospheric scientists out there who are studying lunar eclipses as a means of monitoring conditions in Earth’s upper atmosphere. How cool is that?)

 

But don’t just look at the red. A more not known colour is the turquoise blue. I’m not sure if it is visible to the naked eye, but I’m sure if you take a picture of it, you will see it (see picture below). This comes from light passing through the ozone layer, which absorbs red light and makes the passing light bluer. This can be seen as a soft blue fringe around the red core of Earth’s shadow. Start looking for the turquoise colour as the umbra eclipse begins (U1), it will be more obvious as the Moon moves into shadow, or when starts to come out of the shadow.

Total Lunar Eclipse of 16 Jun 2011 taken outside my house. The Moon had just fully entered the unbral shadow (U2). The top part is darker because it was deeper in the shadow; the bottom part is bluish due to the reason described above. Credit: thChieh.

If you are in an area without much light pollution, you can actually see the stars around the Moon during totality. Usually the bright full moon will drown all the stars around it, but during a totality, you can take picture of the full moon with the stars.

Go out and take a look at the Moon after dinner this Saturday, you won’t want to miss it, because this will be the last total eclipse until year 2014. Yes, you read it right. There will not be any total lunar eclipse for two whole years. So grab this last opportunity!

When to Launch Spacecrafts to Mars?

•December 4, 2011 • Leave a Comment

Last month, Earthling had launched two spacecrafts to explore Mars – the Russian Phobos-Grunt with China Yinghuo-1 piggybacking and NASA Mars Science Laboratory Curiosity. Curiosity had a successful launch and now is on the way to Mars, but unfortunately for Phobos-Grunt, the engine of its Fregat upper stage failed to ignite and it is now stuck in low-Earth orbit. Currently, engineers are still trying to contact the silent probe, but without much success. You can get more updates from the web.

These mission, however, are not are not the main topic of today.

What I want to talk about is that do any of you ever wondered why these two different missions by two different nations* were launched at almost the same time? Is this a coincidence, or is there a reason? Take a look at the launch histories of Mars mission, and see if you can spot some trends…

Viking 1 (NASA): Aug 20, 1975
Viking 2 (NASA): Sep 9, 1975
Phobos 1 (USSR): Jul 7, 1988
Phobos 2 (USSR): Jul 12, 1988
Mars Observer (NASA): Sep 25, 1992
Mars Global Surveyor (NASA): Nov 7, 1996
Mars 96 (Russian Space Agency): Nov 16, 1996
Mars Pathfinder & Sojourner (NASA): Dec 4 1996
Nozomi (ISAS): Jul 3, 1998
Mars Climate Orbiter (NASA): Dec 11, 1998
Mars Polar Lander (NASA): Jan 3, 1999
Mars Odyssey (NASA): Apr 7, 2001
Mars Express & Beagle 2 (ESA): Jun 2, 2003
Mars Exploration Rover Spirit (NASA): Jun 10, 2003
Mars Exploration Rover Opportunity (NASA): Jul 7, 2003
Mars Reconnaissance Orbiter (NASA): Aug 12, 2005
Phoenix (NASA): Aug 4, 2007
Phobos-Grunt (Russia): Nov 8, 2011
Curiosity (NASA): Nov 26, 2011

We can see that the launches always happened roughly 2+ years apart. Why? Because we want to launch our spacecraft during Mars opposition, and Mars opposition happens every 2 years + 2 months. The reason to launch a mission to Mars during opposition is pretty obvious – this is the time when Earth is nearest to Mars. However, the best time to launch, in terms of how much energy is required for the trip, is a few months before that happens (compare the launch dates above with the Mars opposition dates below).

Mars Oppositions: Dec 1975, … , Sep 1988, Nov 1990, Jan 1993, Feb 1995, Mar 1997, Apr 1999, Jun 2001, Aug 2003, Nov 2005, Dec 2007, Jan 2010, Mar 2012 …

~~~~~

“The launch window for Curiosity is from Nov 25 to Dec 18, 2011.”

“Although the launch window for a round-trip to Mars closed yesterday (November 21, 2011) for the Russia’s Phobos-Grunt probe, a one-way flight to the Red Planet will still be possible for another few weeks.”

“A delay that interferes with the launch window can cause the entire launch to be scrubbed.”

In spaceflight term, the time period in which a particular mission must is launched is called the “launch window”. If a spacecraft wants to meet with another spacecraft (for example a Soyuz wants go to the ISS), or go to a planet, an asteroid, or any other objects in space, the launch must be carefully timed so that the orbits overlap at some point in the future (meaning both objects will meet each other in the future). If the weather is bad or a malfunction occurs during a launch window, the mission must be postponed until the next launch window appropriate for the flight.

But why do we need a launch window? Why can’t we just find where Mars is now, point our rocket and launch it any time we like? To answer that, imagine you are standing in the middle of a field watching a 400 m running race in a stadium. Now, if you want to catch one of the runners, how would you do it? One way would be to simply chase the runner, and provided that you are fast enough, you might eventually catch him only after using up lots of energy and travelling a long way. Not efficient.

A better way to intercept your target is simply to walk to the other side of the running track. It uses a lot lesser energy and time to get there. But there is a catch – you have to time your walk carefully so that you reach there at the same time as the runner does. If too early, then you’ll have to wait; if too late, then you’ll miss him completely.

The same thing applied in spaceflight. Now you are Earth and the runner is Mars. The calculations are actually more complicated then the example above since both Earth and Mars are moving in space. In order to reach Mars, we do not aim our spacecraft at where the planet is now, because by the time we reach the planet has already moved and is no longer there. Instead, spacecraft will travel in an elliptical orbit around the Sun that will eventually intersect Mars**. If the spacecraft reach the intersection point too early or too late, it’ll miss its target. (In the above example, if you are early you can wait, but in spaceflight a spacecraft cannot wait.) So timing the launch to allow a spacecraft and Mars to arrive at the same point and at the same time is important, and that’s how launch window comes in. If you miss your launch window, you miss your target.

The distance between Earth and Mars, the launch vehicle’s power, the spacecraft’s weight, and the desired geometry of approach to Mars are all factors in determining the range of possible launch dates.

A launch vehicle from Earth will take advantage of the Earth’s spin for an added boost, which translate to fuel saving. The point at which a launch vehicle uses the least amount of fuel to push a spacecraft onto the proper trajectory for Mars identifies an ideal launch date. The length of launch window for a mission is often determined by the type of launch vehicle, which has been designed to launch a certain amount of load at a certain velocity.

The farther the launch is from the optimal time for lift-off, the more energy needed to get to the target. If a rocket is just slightly more than enough to do its assigned job under the best launch conditions, the launch window becomes very narrow. The more energy a rocket delivers for a particular payload, the wider the range of conditions it can handle, thus the launch window widens. However, this consumes more fuels and money. Therefore, there has to be a balance between the mass of the payload and the energy capabilities of the launch vehicle.

You may think that a straight line is the best way to get to Mars, but that straight line translates into a huge, inefficient orbit around the sun. The launch vehicle required to put the spacecraft in such an extreme solar orbit would have to be very large, very powerful, very expensive and would waste an inordinate amount of fuel. Source: http://athena.cornell.edu/

For a mission to Mars, launch is usually scheduled prior to an ideal launch day, but within acceptable conditions for the launch vehicle. This allows for weather-related delays or delays in getting the vehicle ready. Other launch windows include a range of days after the ideal launch date. If these windows were missed, the trajectory to Mars becomes more difficult, the thrust of the launch vehicle becomes inadequate, and the window of opportunity for a mission to Mars closes for another two years.

~~~~~

*three is you include China, but China Yinghuo-1 was launched by Russian rocket, so here I take it as two.

**In addition, the direction in which the spacecraft moves when it arrives should make it easy to match velocities with Mars, so that it is easier to enter Mars orbit. These trajectories and orbits are collectively referred to as Hohmann transfer orbits, first proposed in 1925 by the German engineer Wolfgang Hohmann. This will be a story for another post.

Moons and Rings

•November 6, 2011 • Leave a Comment

A quartet of Saturn’s moons posing for a picture with the planet’s rings taken by Cassini spacecraft. Credit: NASA/JPL-Caltech/SSI

The largest moon at the back is Titan with its hazy atmosphere. The white moon superimposed on Titan is Dione. The oblong-shaped moon to the right of the rings is Pandora while little Pan can be seen in the Encke Gap on the left of the picture.

 
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