Print Story What in the fuck, exactly, do you do?
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By ana (Wed Jan 27, 2010 at 04:12:38 PM EST) what do you do exactly (all tags)

So clock wrote,



one of these damned days you and I are going to sit down over a cup of very strong, very black coffee and talk about "stuff." during that time i will ask this question, "what in the fuck, exactly, do you do?" and you'll answer it in one sentence. i'll be satisfied and then we'll get on with other things.


Pour yourself a cup of coffee.

Which reminds me of a time a dozen years ago now that my boss was leaving to accept a faculty job elsewhere. Our trusty group of three walked into his office one day and asked him what he did all day, so that we could split those tasks between us and carry on.

"Um," he said. "Gulp."

As I recall, nothing much that was useful came out of that meeting.



I'm a scientist. I did a PhD in Wisconsin in 1985, with a thesis title of "The Soft X-ray Background as a Blast Wave Viewed from Inside". Basically I do astrophysics, mostly in the x-ray band. I started out as a theoretician; did a 2-year post-doc at the University of Virginia, and decided that space flight hardware is where the money is, and convinced a couple folks in Wisconsin to hire me on to projects like that: building stuff, and analyzing data.

I did a few papers using data from IUE, the International Ultraviolet Explorer, a very small telescope with an ultraviolet spectrometer aboard; basically a fore-runner or pathfinder or something for the Hubble (some of its instruments, at least). That was half of my job, more or less until Hubble was launched. The guy I worked for was part of the team for the Goddard High-resolution Spectrograph (GHRS), and had some observing time because of that. We had to trim the planned program several times when it became apparent that the telescope couldn't be focused because of spherical aberration in the mirror. It was both exciting and sad. But not as sad as another guy in the department there, who'd been Principal Investigator for the High Speed Photometer (HSP), which wasn't very useable with the degraded mirror, and was removed to make room for the corrective optics. Basically, they got nothing.

The other half of my job in those days was working with the hardware team on an attached Space Shuttle payload, the Diffuse X-ray Spectrometer. This was developed by the lab I'd worked in as a grad student (my advisor was their pet theoretician), as a sounding rocket payload for proof-of-concept.

A diversion:

The aforementioned Soft X-ray Background is a diffuse glow of x-ray emission that covers the sky and fills in the space between the stars and galaxies and such that are visible in x-rays. The team in Wisconsin (and several other teams) had mapped the emission using a series of sounding rocket payloads, that basically took images of the sky in various x-ray energy (or wavelength) bands. Think of it as a color picture with R, G, and B broad-band colors.

We think the x-rays come from highly excited atoms in space. There are nowadays two competing ideas: one is that there's a volume of hot gas (about a million Kelvin) more or less centered on the solar system with a radius of about 100 parsecs (300 light-years) and about one supernova's worth of thermal energy in it. You can see the cavity in other wavelength bands because of an absence of absorption towards stars out to roughly 100 parsecs in most directions.

The other idea is that it's coming from the solar wind. The sun spits out gas, mostly H and He, but the heavier elements get ionized 5 to 10 times (if they have that many electrons to give). Neutral atoms from interstellar space (oh, yeah, there's a mostly neutral cloud filling a space about 10 parsecs across right in our vicinity… weird, eh?) stream into the solar system, ignoring all the magnetohydrodynamic shocks and stuff at the edges of the heliosphere. Then you can get reactions like this:


H0 + O+8 --> H+ + O+7*,


where the asterisk denotes the fact that the final ion ends up in a highly excited state. The electron can then cascade down to the ground state, emitting x-rays along the way.


The idea of DXS was to obtain a spectrum of the x-rays in the 0.1 to 0.25 keV energy band (85 down to about 44 angstrom wavelengths) where elements like iron, magnesium, silicon, and sulfur should be emitting, so we could figure out what the temperature is, whether it's thermal or charge-exchange, or what.

Anyway. Building space-flight hardware is much like other engineering projects, except everything has to be highly reliable and work far from help in a hostile environment. We had a team (same guys, give or take, who built the HSP for Hubble) of mechanical, electrical (both digital and analog), software, and systems engineers, basically to take the sounding rocket payload and turn it into an attached shuttle instrument.

Since mechanical and electrical engineers can only just barely communicate, and since there are gadgets like pressure transducers and strain gauges that are mechanical on one end and have wires hanging out the other, there's a problem. The PI's solution to that problem was me: throw a wise guy with a physics degree into the mix. Granted, I don't know shit about engineering, but I do kinda know about the physics behind it, and I'm pretty good at thinking on my feet, and translating. That skill also turned out to be handy for negotiating between the science folks and the software people.

The instrument flew on the STS-54 mission of the Space Shuttle Endeavour in January, 1993, just prior to Bill Clinton's inauguration. We controlled it from a windowless room at the Goddard Space Flight Center (GSFC) in Greenbelt, MD.

The mission was a qualified success. There was a roughly 24 hour period (of the six-day mission) when the instrument wasn't working, so we reshuffled all the shiftwork, leaving me running the 6pm to 6am shift while the PI consulted with the brain trust to resuscitate the instruments. Which we managed to do, get them running, and obtain sufficient data to show that, in fact, the diffuse soft x-ray background has emission lines in its spectrum (not a surprise, but it was the first time anybody'd actually seen them). Here is a little article I wrote about it shortly after the mission. (Credit for web design goes to reel_life.)

Figuring out what that means beyond that it probably comes from one of the two ideas outlined above is a really hard problem, it turns out, exacerbated by the fact that nobody has either measured or calculated in detail what highly ionized atoms of silicon, sulfur, magnesium, iron and so forth should actually *do*, in terms of emitting x-rays.

So in 1995 that job was mostly done except for the data analysis and interpretation, it turned out that there was a project to build a high-spatial resolution general purpose x-ray telescope and fly it, and they were hiring.

That telescope became the Chandra X-ray Observatory. I went to work for them at the Smithsonian Astrophysical Observatory (SAO), which shares a building, a director, a library, and some other stuff with the Harvard astronomy department, to form the Harvard/Smithsonian Center for Astrophysics. In some senses this is The Place To Be for astrophysics in the US. It's often the case that I can walk down the hall and knock on the door of the world's expert on some obscure bit of astronomy or astrophysics.

My part of the action before launch was to participate in the ground calibration, where we put the mirror assembly on its side in a big vacuum tank at the Marshall Space Flight Center, shone real x-rays through it from a source 600 meters away, and measured the results at the focal point. This was to verify a very fancy ray trace code that several of my colleagues had built to predict the performance of the telescope. We had an array of x-ray detectors to use for the calibration, including a microchannel plate camera, some proportional counters (basically geiger counters that were tuned differently) and some solid-state detectors (germanium in our case). Trying to calibrate anything to 1% accuracy is seriously a bitch. There was an attempt to build detectors as nearly identical as possible, put one (or more) in the beam beside the telescope, and one at the focal point of the telescope, and divide the signals, hoping the instrumental details would all cancel.

Ten years later, no 13 now, we're still trying to get that to happen.

Getting the absolute sensitivity of an astronomical instrument is tricky. In the optical, a lot of stuff is tied to the brightness of the star Vega, which by definition is apparent magnitude zero in whatever optical band you pick. But how bright is Vega, in real units? We set out to create an absolute standard in x-rays. I think we accomplished that, to an accuracy certainly better than 10%, and maybe as good as 3%. The details are ugly and still controversial.

Chandra was launched from the Space Shuttle on STS-93 in July 1999. I got to go to Cape Canaveral and watch. A night shuttle launch is well worth seeing; lights up the whole county. The VIP stand is 3 miles from the launch pad, near a little museum which houses one of the few remaining Saturn V rockets.

Around the time of launch, the guy on the calibration team who was tasked with organizing the calibration of the prime camera, a CCD camera called ACIS (Advanced CCD Imaging Spectrometer) decided he'd rather be in academia. So my boss looked at the dozen or so scientists in her group and asked the fateful question: "Who in the Calibration Group knows about instruments?" You might think a properly staffed program, especially a 2 Gigabuck program, would never have to ask that question, but hey. My number came up.

So as a day job, I calibrate ACIS.

What does that mean, exactly? I like to summarize it by saying that we make numerical models of the telescope, so that people can tell the difference between astrophysics and instrumental hallucinations.

Another aside might be in order.


ACIS is a CCD camera, not unlike the ones in digital cameras nowadays. When used as optical detectors, a CCD accumulates charge in each pixel in proportion to the amount of light it sees during what are often very long exposures in astronomical uses, and then reads the whole image out at once and digitizes it. For x-ray use, the array is read out often (every 3.2 seconds by default). The idea is to have only one x-ray photon in any area of the chip. The amount of charge deposited is proportional to the energy in the x-ray photon. The on board software then looks at the image, snips out 3x3 pixels around each local maximum, and sends the information to the ground. There's not enough bandwidth to send the whole images, so just sending snippets near what might be x-ray events has to suffice.

The basic data product is a list of "events" (which may be x-rays, cosmic rays, or some other kind of "background"). Each has a time of arrival (when it was read out on the satellite), a bunch of coordinates from raw chip coordinates to computed sky coordinates, the raw pulse heights in the nine pixel island, their sum, and the energy derived from that. Probably some other stuff as well; I forget. In addition, the user gets lots of "engineering data" about the state of the satellite, where it was pointed, the temperatures, voltages, currents, etc. etc. etc., most of which is used by the data "reduction" software (it makes the data set larger) but can otherwise be ignored.

The camera has 10 CCD chips, roughly a square inch each. These are arranged in two arrays, one 2x2 chips for imaging, and one 1x6 chips for use as a readout for the grating spectrometers (which disperse x-rays in proportion to their wavelengths).


So many pixels (10 million), so little time. We have an onboard calibration source; it's a small amount of radioactive iron-55 which fluoresces lines of Manganese, Titanium, and Aluminum which have known energies. We use those data to calibrate the energy response of the CCD chips.

We also observe various sky sources periodically for various reasons. One of my personal favorites is the supernova remnant 1E0102-72.3 in the Small Magellenic Cloud (a companion galaxy to the Milky Way). It's been the Astronomy Picture of the Day poster child a few times. E0102. It's bright, and it has a simple x-ray spectrum: the x-rays come from gas that's almost exclusively oxygen and neon that was ejected during the supernova explosion and is now being shocked to temperatures of about two million Kelvin.

As you can imagine, with 10 megapixels to characterize, there needs to be a lot of automation. The full-fledged data reduction software is written by professionals, most of them on contract with us. (You want a job?) But there's a fair amount of fiddly little scripting (to get tool A to talk to tool B) or minor programming work (algorithm development, proof of concept, etc) that we do ourselves, in whatever language comes to hand. In my case that's usually perl, C, Fortran, IDL (the Interactive Data Language; see also GDL. Not to be confused with the Interface Design Language), or S/Lang. Or sometimes several different languages (C-shell scripts to run a bunch of tools end to end, for example).

The ultimate product of the calibration is a so-called Calibration Database, which contains various products such as a bad pixel list, the quantum efficiency of the CCD camera (probability of a photon being detected, given that it hits the front surface of the filter) as functions of time, position, photon energy. The response function, which is the distribution of pulse heights you get for photons of a given energy (it's not a perfect spectrometer, so this has a finite width, which again depends on the position and photon energy, and changes slowly with time over the years).

Lately I've been working on "trap maps" which characterize the charge transfer inefficiency (CTI), i.e. the amount of charge that's lost clocking the signal across the chip to the readout. We have some software to correct some of the effects of CTI, and it feeds on one of these trap map files.

Supposedly, I have 30% of my time to do my own science, either with Chandra data or on any other subject in astrophysics I might choose (and can get funded). It doesn't work out that way, but in the summer of 2008 a couple of us split the time and attentions of an undergraduate intern from Michigan who did some interesting work setting limits on how much energy in the Cygnus Loop (a.k.a. Veil Nebula) supernova remnant blast wave can be going into accelerating charged particles to cosmic ray energies. We published this paper on that work.

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What in the fuck, exactly, do you do? | 35 comments (35 topical, 0 hidden) | Trackback
Interesting by sasquatchan (4.00 / 1) #1 Wed Jan 27, 2010 at 04:29:21 PM EST
I follow maybe 50% of it..

... nobody has either measured or calculated in detail what highly ionized atoms of silicon, sulfur, magnesium, iron and so forth should actually do, in terms of emitting x-rays.

Really ? I thought the specs were well known (as you say later), and is it hard to get those elements to such an ionized state to see on earth ?

(been 15 years since I dealt with PChem, so ... )

Can be done by ana (2.00 / 0) #2 Wed Jan 27, 2010 at 04:32:42 PM EST
It can be done either in plasma physics machines like Tokamacs, or in gadgets like the Electron Beam Ion Trap (EBIT). It's kind of time consuming, and they do it one ion at a time. There's been some progress since the middle 90s. We also have Chandra spectra of cool stars like Alpha Centauri, with coronal temperatures more or less like what we think the local interstellar bubble might have.

Some Day SoonTM I'm gonna look up some of those spectra, convolve them with the DXS response, and see how they compare to the diffuse background data.

"And this ... is a piece of Synergy." --Kellnerin

[ Parent ]
very cool. by MillMan (4.00 / 1) #3 Wed Jan 27, 2010 at 05:59:09 PM EST
I have long wondered what sort of back magic you get up to in that place.

"Just as there are no atheists in foxholes, there are no libertarians in financial crises." -Krugman

(Comment Deleted) by xth (4.00 / 5) #4 Wed Jan 27, 2010 at 06:58:26 PM EST

This comment has been deleted by xth

and this is why by LilFlightTest (4.00 / 1) #5 Wed Jan 27, 2010 at 07:08:31 PM EST
you're the reason I passed physics...
if de-virgination results in me being able to birth hammerhead sharks, SIGN ME UP!!! --misslake
Thats not one sentence by greyrat (2.00 / 0) #6 Wed Jan 27, 2010 at 08:30:15 PM EST my dad would say.

True. by ana (2.00 / 0) #7 Wed Jan 27, 2010 at 09:14:51 PM EST
Sorry I overran the word limit.

"And this ... is a piece of Synergy." --Kellnerin

[ Parent ]
Ever met Larry Niven? by ammoniacal (2.00 / 0) #8 Wed Jan 27, 2010 at 09:33:25 PM EST
I like his take on the potential militarization of space: It ain't viable because every tool you might have on you is a potential WMD.

Including x-ray commo lasers. lol.

"To this day that was the most bullshit caesar salad I have every experienced..." - triggerfinger

ok. by clock (4.00 / 2) #9 Wed Jan 27, 2010 at 10:20:05 PM EST
that makes a lot of sense.  i'll nitpick the length of the answer later...maybe.  i was half expecting you to say you were an ordinary rocket scientist but my dad used to work with the ordinary ones and you're more fun.

and i should say, it makes sense in that "that sounds really complicated and yet pretty f'n cool" sort of way and not in the " that all?" way.  know what i mean?


and dayum.  that's really, really cool.

I agree with clock entirely --Kellnerin

That's because by notafurry (3.00 / 2) #24 Thu Jan 28, 2010 at 12:47:01 PM EST
Ordinary rocket scientists (or, well, rocket engineers) are bitter husks that used to be men who spend all their time staring into their drink, doodling really cool shit on napkins, and voting Republican because, while they're irritating shitholes who fuck up everything about the rest of our lives, the goddamn pissbucket Democrats keep axing the entire fucking program.

That would be why I'm in IT these days.

[ Parent ]
One of the guys in our group by ana (4.00 / 1) #25 Thu Jan 28, 2010 at 12:54:01 PM EST
in Wisconsin was trying to drag us kicking and screaming into the century of the fruitbat, by teaching us to use some kind of version control. He created a document called "Version Control for the Ordinary Rocket Scientist", and it really did explain the basics of what you had to do and how in terms an ordinary rocket scientist could understand.

"And this ... is a piece of Synergy." --Kellnerin

[ Parent ]
Is that online anywhere? by wiredog (2.00 / 0) #26 Thu Jan 28, 2010 at 04:18:11 PM EST

Earth First!
(We can strip mine the rest later.)

[ Parent ]
Don't think so by ana (2.00 / 0) #27 Thu Jan 28, 2010 at 05:04:44 PM EST
It described SCCS if I'm not mistaken, because that came with Ultrix in the mid-1990s. He may have updated it.

"And this ... is a piece of Synergy." --Kellnerin

[ Parent ]
sccs! by Tonatiuh (2.00 / 0) #35 Sun Jan 31, 2010 at 08:50:20 PM EST
The new kids in the block would not be caught dead using that.

<evil_voice>They need GUIs</evil_voice>

[ Parent ]
That's a catchy thesis title. by Scrymarch (4.00 / 2) #10 Thu Jan 28, 2010 at 12:36:53 AM EST

Iambic Web Certified

One Sentence for me... by anonimouse (2.00 / 0) #11 Thu Jan 28, 2010 at 07:31:39 AM EST
I create intranet web-sites which present monitoring data to management and weenies so that when one of the graphs spikes they can run around like headless chickens claiming the sky is falling in, my current sites being in the banking sector.


Girls come and go but a mortgage is for 25 years -- JtL
There are some really smart people in this place by wiredog (4.00 / 2) #12 Thu Jan 28, 2010 at 08:45:17 AM EST
And then there are the average guys, like me.

Scary that I've read enough SF, and S non-F, to actually understand most of what you wrote.

Earth First!
(We can strip mine the rest later.)

That was kind of the point... by ana (4.00 / 1) #13 Thu Jan 28, 2010 at 09:21:48 AM EST
explaining it to intelligent non-specialists.

"And this ... is a piece of Synergy." --Kellnerin

[ Parent ]
And you did a good job of it, too. by wiredog (4.00 / 1) #19 Thu Jan 28, 2010 at 10:47:21 AM EST
Have you considered a teaching position?

Earth First!
(We can strip mine the rest later.)

[ Parent ]
I have done some teaching. by ana (2.00 / 0) #20 Thu Jan 28, 2010 at 10:50:57 AM EST
I spent 4 years between my BA and going to grad school teaching at the US Navy Nuclear Power School, which in those days was in Orlando. And I was a TA for a couple years in grad school, and taught intermittently to make ends meet when the research funding was slow. I kind of miss it, I think, but hereabouts there are lots of PhDs per student, so teaching opportunities are few.

"And this ... is a piece of Synergy." --Kellnerin

[ Parent ]
My brother by garlic (4.00 / 1) #28 Fri Jan 29, 2010 at 05:18:48 PM EST
went to the US Navy Nuclear Power school. Although not while you were teaching there.

[ Parent ]
Very cool. by mrgoat (4.00 / 2) #14 Thu Jan 28, 2010 at 09:28:54 AM EST
This should be a regular feature. Though I imagine some of our jobs are much less interesting to read about.

--top hat--
<shuffles feet, looks at ground> by Phage (4.00 / 2) #15 Thu Jan 28, 2010 at 10:06:25 AM EST
That's a vicious slander by someone who knows me...I do plenty of interesting stuff. Somewhere in the attic, is a box with my life in it.

[ Parent ]
That would be cool. by ana (4.00 / 1) #18 Thu Jan 28, 2010 at 10:11:18 AM EST
Hence the "what do you do exactly?" tag. I'd be thrilled if other people used it.

"And this ... is a piece of Synergy." --Kellnerin

[ Parent ]
I help our customers print junk mail by georgeha (4.00 / 1) #21 Thu Jan 28, 2010 at 11:08:37 AM EST

[ Parent ]
I help our customers create/maintain search apps by infinitera (2.00 / 0) #22 Thu Jan 28, 2010 at 11:18:07 AM EST
Really, it's all the same, REC diaries are the best description.

[…] a professional layabout. Which I aspire to be, but am not yet. — CheeseburgerBrown

[ Parent ]
Ooooh by Phage (2.00 / 0) #16 Thu Jan 28, 2010 at 10:07:42 AM EST
Damn near a cosmologist if I read that correctly.
Well I'll be damned.
Very cool, sir. One day I'd like to shake your hand.

Cosmology... by ana (2.00 / 0) #17 Thu Jan 28, 2010 at 10:09:18 AM EST
is not even wrong. Most of the time. Though they seem to have some measurements lately that are actually statistically significant.

"And this ... is a piece of Synergy." --Kellnerin

[ Parent ]
My god it... by duxup (4.00 / 2) #23 Thu Jan 28, 2010 at 12:13:40 PM EST
Let me know when you find a monolith.

My job is far less complex and I just respond with "Computers." and when needed "No, not home computers."

There are complexities to lots of our jobs. by garlic (4.00 / 1) #29 Fri Jan 29, 2010 at 05:21:27 PM EST
Ana could have said "rocket scientist" or "astrophysicist" and been done. I can say "computer chip designer" or if I'm trying to show off "anti-rocket scientist" but that doesn't really get into the cool details.

[ Parent ]
I sometimes use by duxup (2.00 / 0) #30 Fri Jan 29, 2010 at 09:28:57 PM EST
Consumer Drone.

[ Parent ]
my job is complex enough by LilFlightTest (4.00 / 2) #31 Sat Jan 30, 2010 at 11:00:50 AM EST
but hard to describe. I'm in IT, but "I arrange for the purchase of computer equipment" makes it sound like i'm in purchasing...but this is not something you want purchasing to do. I have a lot of other job functions, all of which are vital, but...again, hard to describe. Half the time, I feel like a better description might be "I make magic happen."
if de-virgination results in me being able to birth hammerhead sharks, SIGN ME UP!!! --misslake
[ Parent ]
I used to think my job was not complex. by Tonatiuh (4.00 / 1) #34 Sun Jan 31, 2010 at 08:47:48 PM EST
But I still don't find that many  people that know enough about the kind of stuff I know how to do, so it must be complex enough ....

[ Parent ]
Cool by jimgon (2.00 / 0) #32 Sat Jan 30, 2010 at 11:12:21 AM EST
I knew you were an astrophysicist, but didn't know the specifics.  Cool stuff.

Technician - "We can't even get decent physical health care. Mental health is like witchcraft here."
If you programmed in perl.... by Tonatiuh (2.00 / 0) #33 Sun Jan 31, 2010 at 08:45:28 PM EST
.... your spaceships would not be able to reach escape velocity, they would be dragged down by the language's verbosity.

What in the fuck, exactly, do you do? | 35 comments (35 topical, 0 hidden) | Trackback