Greetings from CalCon. I gave my talk yesterday, although I didn't
exactly cover myself with glory, nobody walked out, either.
A few minor comments on Justin's account of the A10 flight:
o Tracking actually worked quite well. I aligned the finder scope
very carefully and have measured its FoV. The target appeared very
consistently about 1 deg down and right of the aim point. Since the
FoV of the science camera is 0.25 deg, that put the target out of the
field. This sort of dc offset is to be expected based on our
experience with the telescope. I have included in the software a
facility for entering an offset, but being single-handed at the
downrange station, I didn't attempt to apply it. I certainly wish I
had, but things were happening pretty fast and I didn't want to miss cutdown.
o I made three attempts to align the telescope. On the first
attempt, I was probably aligning to the wrong stars since Autostar
was not selecting the very brightest stars for alignment. I presumed
that the second alignment star was Vega, but apparently it was
something nearby. (It's too bad the system doesn't tell you what
star it's aligning to!) On the second attempt the motor stalled
because I had not positioned the azimuth at midrange before starting
the alignment, and it ran up against the end stop while trying to
slew to the second star. On the third attempt, I went ahead and took
the brightest star within five degrees or so of the optical axis, and
it seems to have worked.
o When Justin and I were experimenting with the telescope a few days
later, we had the same experience of the alignment stars not being
the obvious choice, and pointing being a bit off. Still, when
properly aligned, the target is near the center of the finder scope,
so as a matter of course, it will be very practical to bring it onto
the field of the science camera. By the way, I always carefully
level the tripod using the installed bubble level.
o A10 was our third successful tracking experience. Max actually
got photos on A2; Will observed through the eyepiece on A5, and I
monitored it through the finder scope on A10.
o I understand Karun's reference to a 2 arcmin deficit to correspond
to Justin's comment that properly aligned, the LX200 is still a
"couple of arcminutes" off. I'd estimate it at more like "as much as
20 or 30 arcmin," but I think this is just normal for this telescope
and concur with Justin's assessment. It's expected that we will need
to tweak the pointing once Autostar gets the target in the field of
view. As we experimented with the scope last Wednesday, targets
generally appeared in the FoV of the 26 mm ocular, but never
centered. I'm not worried about this issue. If Autostar gets the
target into the field of the finder, our software will put it into
the field of the science camera. Optical guiding may not be
practical since in practice the source is not continuously.
o Dew fighting has been on our list of things to address for some
time now. I think a simple space blanket will address the problem of
the gondola and parachute getting wet. I've used a nylon poncho
successfully in protecting my computer and note-taking
equipment. (It's awkward.) During A10 I kept the cap on the LX200
except when actively catching photons.
o The tree was actually a maple, not an oak. ;)
o I'm suspicious that some of our problems may actually have been
due to weak batteries, but I haven't had a chance to think this
through. The temperature data is funky...
o As for all flights, there's a brief account on my website.
o Here's some preliminary data analysis from A9 and A10 that
suggests problems with parachute deployment:
ALTAIR 9-4
Descent speed = 3.03 m/s
Forward velocity (wind calm, so this is airspeed)
vx = 0.81 m/s
vy = 3.12 m/s
v = 3.22 m/s
Glide Ratio 1:1
ALTAIR 10
He qty = 2x 150 CF
Climb Rate = 5.84 m/s
Cutdown Alt = 3000 m
Descent Rate = 5.48 m/s
Forward ground speed = 8.17 m/s
Wind velocity 850 m (from climb 800-900 m)
vx = 6.16 m/s
vy = 4.13 m/s
Forward velocity at 850 m (on descent 900-800 m)
vx = 6.55 m/s
vy = 4.88 m/s
Airspeed
vx = 0.39 m/s
vy = 0.75 m/s
v = 0.84 m/s
Glide Ratio = 0.10 !! In other words, not gliding.
--Yorke
At 11:24 PM 8/18/2013, Justin Albert wrote:
>*** Discussion title: ALTAIR Balloon
>
>Hi,
>
>For documentation, the below is a brief summary of the ALTAIR flight
>that Yorke and I did in the early morning hours last Sunday (Aug. 11,
>2013), and the recovery of the payload from a tall tree by Todd
>Anderson, assisted by Yorke (with me observing), the following day
>(Mon., Aug. 12).
>
>Please do just follow up with anything I happen to miss, or get wrong,
>Yorke and Todd -- since I'm posting this without checking first to make
>sure we have the story straight!
>
>Yorke and I began to set up at just before 2 am on Aug. 11 for a launch
>from Garipay Field in Hanover, NH. Yorke had determined, for a launch at
>around 4 am, the winds would carry ALTAIR approximately to the location
>of Robert Frost Lane in Etna, NH (approximately 5 km away from the
>launch site) if we cut the payload down when it reached 3000 m altitude.
>The purpose of the flight was to attempt to observe and get image(s) of
>the payload in flight via the Harvard Meade LX200 portable telescope and
>SBIG camera (using the green LED beacon rather than the full laser diode
>and integrating sphere payload, to get experience with getting telescope
>images without risking the full payload). The telescope+camera and
>recovery tracking station were set up by Yorke at the Robert Frost Lane
>location.
>
>The weather was fairly good: clear skies, and predicted and actual winds
>low enough so that we could at least get up to 3000 m without the
>payload ending up in deep forests outside the region. There was quite a
>bit of early morning dew at the launch site.
>
>The setup for the launch went well: we were set up, balloon filled and
>ready for launch at around 3:20 am. Yorke then proceeded to the Robert
>Frost Lane location to setup the telescope and recovery tracking
>station, and I remained at Garipay Field to pull the cord to launch and
>to man the launch tracking station.
>
>Yorke had set up the telescope and recovery station, and called me by
>about 4:20 am. He noted that there was some difficulty with the
>telescope star alignment (needed to track and take images of the payload
>in flight), and he wanted to try aligning again.
>
>Yorke called again at around 4:35 am, and said that the alignment was
>likely as good as it would get during the launch window before sunrise
>(and before sky background would start to increase dramatically) and
>that we should thus proceed with launch. I thus turned the payload and
>LED beacon on and, after countdown, launched the balloon and payload at
>approximately 4:45 am.
>
>The LED beacon was easily visible by eye throughout the entire flight,
>by both Yorke and myself. Other than the moon, it was the brightest
>object in the sky throughout essentially all of its flight -- even at
>apogee it was approximately 1st magnitude. When Yorke performed the
>cutdown at 3000 m altitude via the recovery station, I could easily see
>its effects from the launch site a few kilometres both away and below,
>via the LED beacon and payload shaking, and thus the green light
>blinking in and out of view. A few cell phone pictures of the green LED
>beacon during its flight are attached.
>
>Unfortunately, the star alignment of the telescope was not sufficient to
>get telescope images of the payload in flight. The pre-alignment
>automatically performed by the Meade LX200 using its level sensors and
>compass is sufficiently off such that the stars that it then selects for
>the user's star alignment are actually outside the field of view of the
>telescope. Yorke and I later (on Wednesday night) diagnosed and
>(hopefully) solved this issue, but it prevented us from obtaining
>telescope images of the payload in flight on Sunday.
>
>After Yorke performed the cutdown, he then actively controlled the
>parafoil in order to attempt to have the payload land as close as
>possible to the recovery station. Yorke noted that the parafoil did not
>appear to be responding to commands as much as it should have been.
>Yorke and I both lost contact with the payload at about 2000 m altitude,
>and the payload landed approximately 1 km beyond (i.e. east of) the
>recovery site.
>
>After packing up our respective sites, Yorke and I went driving around,
>Yorke with an antenna and receiver, to attempt to get a signal and thus
>GPS location of the payload. At first we were unsuccessful, but after
>Yorke briefly went home to obtain an improved flight-path prediction of
>where the payload might be, we then drove to an area that looked like
>the best possibility, and Yorke fortunately obtained a signal and GPS
>info. The GPS location of the payload was on land behind the Morton
>Farm, which is land on the outskirts of Hanover owned by Dartmouth and
>is the Dartmouth Equestrian Center.
>
>We then proceeded to the Morton Farm to see where the payload had ended
>up. Behind the Morton Farm there are trails in the woods, one of which
>took us to approximately 300 m from the GPS location of the payload. We
>then went off the trail through the woods to the GPS location. The
>payload was found to be at the GPS location, very high in an oak tree,
>hanging from the parafoil approximately 60 ft above the ground, with
>green LED beacon still on. A technical climb, with climbing equipment
>which we would have to bring later, would be required to retrieve the
>payload. Location noted, we returned to our vehicles. From our vehicles,
>Yorke used the antenna to obtain a connection with the payload and turn
>the LED beacon off, to save the battery from running completely to zero.
>We then went back to our respective homes to get some rest (at that time
>it was about 10 am on Sunday morning).
>
>Yorke realized that the dew that collected on the parafoil prior to
>launch had likely frozen during flight and prevented the parafoil from
>steering and performing nearly as well as it should have. This
>definitely seems like the most likely explanation for that.
>
>Todd returned on Sunday evening from a trip to Utah, and is an
>experienced climber, so he very kindly volunteered to be the tree
>climber on Monday to retrieve the payload. This is a very hazardous
>technical climbing task, especially with the payload in a very
>dangerously high location, so Yorke and I both owe a very great deal to
>Todd for successfully getting the payload, and more importantly himself,
>as well as all the ropes, carabiners, and climbing equipment, down from
>over 60 ft up in a very tall forest tree. Yorke is also an experienced
>climber, with his own equipment, so he performed the extremely critical
>tasks of both belaying Todd, and also getting the top-rope started on a
>branch about 20 feet off the ground. Todd successfully retrieved the
>payload, and got it and himself down, belayed by Yorke, at about 3:30 pm
>on Monday afternoon. This was extremely fortunate because early the
>following morning (Tuesday), starting at about 4 am, heavy rain began,
>and fell steadily throughout Tuesday.
>
>On Wednesday the skies began to clear, and on Wednesday evening Yorke
>and I got the telescope out to see if we could understand the alignment.
>Yorke set it up, and after doing the automatic pre-alignment, he
>determined the stars which it was then suggesting for the star alignment
>were both a few degrees outside the two fields of view. Yorke aligned to
>those stars, and then found that the telescope was then in good
>alignment, demonstrated by it then being able to accurately and
>precisely enough (i.e. within no more than a couple arcminutes, which is
>definitely good enough) being able to find Saturn, Vega, Altair (the
>star, not the payload), Deneb, etc.
>
>Early the following (Thursday) morning, I had to fly out to go back to
>the west coast.
>
>Please follow up with what I have missed and got wrong!
>
> thanks,
> justin
>
> Attachment:
>
>http://projectaltair.org/HyperNews/get/AUX/2013/08/18/20.23-87912-light_CellphoneImage1.JPG
>
>http://projectaltair.org/HyperNews/get/AUX/2013/08/18/20.23-29230-light_CellPhoneImage2.JPG
>
>http://projectaltair.org/HyperNews/get/AUX/2013/08/18/20.23-73793-PayloadInTree.JPG
>
>http://projectaltair.org/HyperNews/get/AUX/2013/08/18/20.23-40301-ToddRecoveredPayload.JPG
>
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