Here it is, practically missing the month of December in all of its entirety, my promised science post. The first topic of conversation is the Spitzer Space Telescope, which was brought to my attention by a very pretty pin I received commemorating its 10,000th hour of scientific observation. Our second topic is slightly old hat, but always interesting, the MER rovers. The PI of this project gave a talk back in July of 2005 that was one of the best talks I have yet seen, titled “MER: Stealing Success from the Jaws of Failure.” And finally, I will point you in the direction of this very accessible and interesting NY times article on quantum “cat” states, which have been verified at the National Institute of Standards and Technology in Boulder, Colorado. Think about it for a minute, and after you read the article, come back here and read this sentence: We can’t know which state a particle is in (e.g. whether the cat is dead or alive), but we can know that it’s in two states at once; is that deterministic? And finally, if you have Griffiths’ Intro to Quantum Mechanics book, read the discussion on philosophies of quantum mechanics in Chapter 1 (I’ll add page numbers when I get back to LA). This is going very interesting places.
SPITZER (from a talk by Michael Werner, Project Scientist, 12/13/2005):
The Spitzer Space Telescope, part of the SIRTF project, was launched August 25, 2003 and is now on of the great telescopes of our time, among the Hubble Space Telescope (1993), the Chandra X-ray Observatory (1999) and the Compton Gamma-Ray Observatory (1991). These four telescopes pretty much cover the entire spectrum of light. As most of you know, Hubble takes data in the visible light range, and has returned some of the most stunning images of space ever seen. Chandra is in the x-ray region and is studying primarily the remnants of exploded stars. Compton covered energies from 30 keV to 30 GeV and its data spans 6 decades of the electromagnetic spectrum. Spitzer fills in the gap in the infrared range of light. IR data supplies scientists with completely different data that is complementary to that supplied by Hubble, Chandra, and Compton. The image in the upper left compares a Spitzer image to that of the same galaxy in visible light (lower left of image). Galaxies that are dim in the visible and bright in the infrared are the prime candidates for the oldest galaxies in the universe, and studying these galaxies is one of the best ways we have of trying to paste together the years of our early universe. Spitzer has found galaxies that formed 800 million years ago—earlier than we had originally thought galaxy formation was possible.
The reason that the light from the oldest galaxies in the universe would be in the IR has to do with the expansion of the universe. As a galaxy’s light started to move toward us (200-800 Myr ago), the actual fabric of space was (still is) stretching, and the light wave is literally stretched along with it. This is much like the pitch of the horn of a car changing as it moves further away from you while you stand on the side of the street (likely selling lemonade). The sound is obviously still coming toward you, but the source is moving away, so the sound wave gets stretched out (longer wavelength). Originally visible light from galaxies that started moving away from us the earliest will be the most stretched, thus in the infrared.
IR observation is also a very good way to study star formation, another important element in our spotty ‘history of the universe’ text. In particular, Spitzer is looking at polycylic aromatic hydrocarbons (yes, car exhaust). Until the mid 80’s, there were unexplained anomalous bands in the IR spectrum of young stars, dubbed ‘Unidentified Infrared Bands’ (UIBs). The current hypothesis, proposed by Puget and Leger in 1989, is that these bands are in fact polycylic aromatic hydrocarbons, and this is now generally accepted. If correct, this discovery would prove that these stars are in fact prebiotic, which is a huge step towards understanding the latter stages of the stellar life cycle. I’m in way over my head, here; this is a huge topic and still very controversial. For a more complete explanation, explore this site (which actually references Mr. A. Costa’s research group because of their fancy ion trapping mechanisms), and this site, by NASA AMES.
Last bit of Spitzer science: the instruments are able to deduce the temperature of planets by waiting for them to eclipse behind their sun. This is actually just a subtraction problem: measure the IR radiation from the sun alone, wait for the planet to sneak behind it, and look for a little blip. Because of background radiation, you cannot determine this information from looking at the planet alone; there is too much noise. Spitzer has found these eclipsing planets to be ~100 K and planets in these ranges at these temperatures have no business existing–a new mystery! Of course this technique will only work when Spitzer is in the orbital plane of the eclipsing planet.
Spitzer has a finite lifetime. To do infrared photography, your instruments have to be very cold; otherwise you would be recording blackbody radiation from the hot objects all around the camera. Spitzer was launched with a 5 ½ year supply of liquid helium, and when this runs out the quality of the data will decrease tremendously as the telescope warms up. However, there is a period that the telescope will be used in its “post-cryo” stage and there is still a lot of useful data to be gotten with a warm (though still 30 K) instrument, particularly in the short IR range.
Spitzer is a very successful instrument in terms of both science and efficiency. In fact, Spitzer collects scientific data an unprecedented 65.97% of the time. The rest of the time it has to perform tasks such as downlinks to Earth, calibration, slews (changing direction), and dealing with anomalies. The priority of the data taken by the instrument is first taken from its original proposal, and then the rest of the time is competed for by anyone who wants to submit a proposal. Its schedule is planned yearly, and proposals are still being accepted. So far, it has completed a survey of the Milky Way, which –haha!—I saw pictures from that won’t be released to the public until mid January; the GLIMPSE (it’s ridiculous that I’m typing this out: the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire–not kidding); and the MIPSGAL (whose acronym is not expanded that I can see). Stay tuned, the results are awesome.
MER (from a talk by Rob Manning, Project Manager, 07/08/2005):
The Mars Explorer Rovers have been a huge success, and to a large degree, have repopularized space exploration. However, as I found when attending Manning’s talk (”Stealing Success From the Jaws of Failure”), the project was always hectic, rushed, and undergoing constant redesign. Manning is very entertaining and has a quality sense of humor; an example is the disclaimer on his first slide:
“Mistakes presented here were performed at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration (Clearance number CL#TBD)”
The original plan for MER was to mostly use a design from the 2000 proposal by Rob Manning, Mark Alder et. al for the rovers that was already in existence. Analysis concluded that this design could not be used as is and the MER team would have to completely redesign the rovers in a very short period of 30 months. Below is Manning’s comparison of the usual NASA ABCD phase flow to the MER phase flow:
4 years in Phase ABCD:
Year 1: Team gets to know, like each other and agree. (A)
Year 2: Team gets to design it. (B)
Year 3: Team gets to build it. (C)
Year 4: Team gets to test it and launch it. (D)
Post launch: Team gets to happily operate it (E)
The MER way:
Year 1: Team thinks it is designing it.(A)
Year 2: Oops. Team re-designs it. Finally agrees.(AB)
Year 3: Team gets to know each other, fabs it, build it, test it, launch it. (CD)
Post launch: Team gets to really test it. (E)
(Team really likes each other after landing successfully.)
And his “lessons learned” from the mistakes of the MER project are:
1. Volume is a real constraint
2. Even if the volume is constrained, it can always get heavier
3. It can always get more complex (wiring, programming, weight, volume)
4. Do not skip a year (complete redesign)
5. Do not take soft good for granite (failing parachutes)
6. Ignorance is not bliss (are there winds on Mars?)
7. Knives and electricity do not mix (breaking the fuse 8 weeks prior to launch)
8. Simultaneously: There is more time to solve problems than you think.
There is less time to Solve problems than you think. (surprises 30 hrs prior to launch)
9. And the final lesson: Spacecraft are built by people, not processes.
Good processes should help them succeed.
Manning concluded by saying that MER was lucky. But luck only goes so far without a team of over-dedicated scientists, technicians, and engineers–many working 80-100 hr weeks–and the strong and constant support from both NASA and JPL.
If you are interested, I have found a couple more MER stories from the project scientists here and here.
It is both amazing and not at all surprising that the MER project is so successful. Dedication has a lot to do with it, and, though scattered, the MER story is pretty inspirational–in the end, they made it happen. Both Spirit and Opportunity have now spent over an entire Martian year on the surface of the planet, taking incredible data, and helping us prepare to get there ourselves someday.