Good question -- I am not sure the reason for the remaining approximately 2 arcmin residual error.
For our purposes for the time being, though, as long as we have the payload on the (15 x 15 arcmin) field of view, we're good enough -- it's only a big problem if it is outside the field of view. So I think we're OK at least for now as long as we align to that precision. (We might have to improve further at a later point, but 2 arcmin is good enough for now.)
thanks, justin
On Mon, 19 Aug 2013 17:09:54 GMT, Karun Thanjavur wrote:
> Hi Yorke and Justin, > Very well done with this flight, and thanks very much for this > detailed account as well. I am sorry the tracking on the telescope was > off and prevented you from getting much 'science' data; glad to note > you have traced and rectified the cause. What do you think is reason > for the remaining 2 arc.min residual error? with the built-in GPS, the > pointing should be much better than that, I would presume? > > We owe much to Todd for the safe retrieval of the payload, quite the > adventure. If frozen dew is indeed the cause of the parafoil malfunction, > we'll obviously have to devise a way to avoid this in future. Perhaps both > of you have ideas already? > > Hope the Hanover weather permits many more such flights soon, permitting > us to move operations down to Mt. Hopkins in the near future. > Clear skies > Karun > > > > > *** 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 > > > > ------------------------------------------------------------- > > Visit this projectALTAIR.org message (to reply or unsubscribe) at: > > http://projectaltair.org/HyperNews/get/balloon/14.html > > >
