FOXSI launch day, part II

The countdown continued.  I felt strangely detached.  The countdown hit zero.  On the TV screen there were smoke and flames and the rocket leapt up off the ground.  Before that moment FOXSI had always seemed kind of small on the launch rail, at least compared to the gigantic rockets you see in pictures of spacecraft launches.  But at that moment FOXSI was huge and powerful and dangerous, an object visible from all over the desert.

The sound hit us later, having taken several seconds to travel the miles between the launch rail and our building.

FOXSI was in the air, climbing slowly.  The second stage motor ignited, there was another bright flash, and FOXSI shot off unbelievably fast, now truly on its way to space!

I was floored by what I had just witnessed, but now there was work to do!  The most important step was to send the uplink command to turn on the voltage to our detectors.  If this command were to fail for any reason then our X-ray cameras would not work.  It was for this reason that I was inside, watching the launch on a TV, rather than outside with the others -- I wanted to be focused and ready for this crucial step.   At 30 seconds after the launch, I sent the command and watched the data to see that it had registered.  It did, and the detectors immediately began to respond.

There were about 70 seconds more to wait for FOXSI to get to space, the shutter door to open and reveal our telescope, and the pointing system to find the Sun.  We would start observing when the rocket was about 150 kilometers (100 miles) high, well above the dense parts of the Earth's atmosphere.  The other team members ran back in to take their places by my side and we eagerly watched our screen to see the data streaming in…

…and we saw nothing.

Well, not exactly nothing.  There were a few X-ray hits here and there on our detectors, but the rate was quite small and they did not come from a concentrated spot on the Sun as we had expected.  We looked at each other and calmly made the decision to switch to a backup target.  Säm (our principal investigator and the "driver" for our payload) sent the command to change targets.

The second target showed no improvement.  Again, no concentrated spot appeared, but only random hits here and there.  At this point it looked as if the mission might be a failure; with no recognizable image at all it would be difficult to prove we had even been looking at the Sun.  Despite this, we moved on to a third target. 

 This target showed nothing much as well.  Now about three minutes had gone by, which is half our observation time, and all of our best prospects for finding an X-ray source were gone.  The rocket reached its peak height of 300 kilometers and then started on its way down.

We switched to a fourth target, one of two we had programmed in as last resorts.  (We had appropriately nicknamed these "Hail" and "Mary.")  We did not expect much, if any, emission from these targets, but they were regions on the Sun we hadn't looked at yet.

And suddenly there it was!  The count rate jumped up significantly, and an X-ray image started to build up.  Excitedly, we yelled at Säm to center the image!  He sent the command to do this, and the image disappeared.

That's right, it disappeared.  We had gone the wrong way!  If you ever needed an "undo" button, this was the time!  And luckily we *did* have an undo button.  Säm steered us back to the target and we found our image again.  (Later, we found that a problem in the way we had written our software was responsible for our wrong turn.)  We were in instant agreement not to touch anything more; we stayed right where we were for the last minute of the observation time.

And then it was done.  The rocket was descending back into the atmosphere.  The shutter door closed over our optics.  I sent the command to begin the shutdown of our detectors.  The parachute opened and FOXSI slowly continued its descent back to the desert sands, so much more carefree and calmly than the manner in which it had left.

Steven gave me a high-five that nearly broke my hand, and that began the celebration…we had done it!  FOXSI had done it!  We had made a focused image of X-rays from the Sun, the first ever made in this particular way in this energy range.  At that point we did not really understand what it was we had seen, but the important thing was that the instrument had worked.

Later we would learn that we had been extremely lucky.  The solar object we imaged was not a sunspot, as we had expected, but a solar flare in progress!  It was a small flare, but it appeared at just the right time and in just the right place for FOXSI to see it.  Without this flare, it is possible that we may have had no recognizable signal from the Sun.  Hail Mary, indeed…

So what to make of our other targets?  Why did we see no, or very little, X-ray emission?  There are several possibilities.  The active region targets could have been either cooler or fainter than we expected.  Our sensitivity could have been reduced for an unknown reason.  The quiet-Sun signal could have been extremely faint or even nonexistent.

But here is where the solar flare we caught really comes into play.  With this flare we can do a cross-calibration of our instrument with an existing spacecraft, RHESSI.  With this proof of a working instrument we can then make a case for what the X-ray flux actually was from the quiet Sun (and from the active regions).  If we find that there was no detectable emission, this is in itself an important science result.  But there may be emission after all.  As I mentioned, there was a very small rate of X-rays even before we saw the flare.  At this point it is not clear whether this signal was from the Sun or from the background X-ray flux that persists throughout the solar system.  It will take a tremendous amount of work to properly make that distinction!

But I digress…at this point there was a helicopter about to arrive to take us to the landing site and recover our payload.  We grabbed a couple bags of gear for the ride and took off for the helipad.

Stay tuned…part 3 will describe the journey into the desert to retrieve FOXSI!