questions about horizontal distance and wind influence

[David Levy]

Many people were surprised that the balloons did not land further away
from the launch point given the amount of time they had been in the air.
I think this topic was mentioned before in one of the discussions or
maybe the data was revealed in one of the published graphs. In any case
maybe this is a good place to summarize the data again.

Some questions from individuals:

1) How far were the recovery points from the initial launch location?
2) Does the altitude band of the "jet stream" have the most impact on
horizontal distance? What was the impact of the jet stream on both the
ascent and descent?
3) How did these launches compare to prior years' launches ( with
respect to recovery location)
4) Is the Earth rotation not a factor at the higher altitude ( like
100,000 feet)

Thanks
David Levy
FLL Team 90 Payload Coach

[David Levy]

question #4 should read

4) Is the Earth rotation a factor at all? What about at the higher altitude of 100,000 feet)?

[Eric]

1) your payload was recovered 44.9 miles from the launch point
the first balloon launched went 42.7 miles
Lil' Joe went 34.9 miles

These distances are "great circle" or "as the crow flies" distances
between the launch and landing points. I don't know the actual total
distance traveled (for example, each went at least 40 miles - 20 up
and 20 back down - in addition to the 45 horizontal miles). I'm sure
there is a program out there somewhere that can calculate the total
distance traveled based on the GPS data.

2) the jet stream is typically the cause of most of the distance
traveled, but it wasn't very strong on the day we launched. We've put
balloons into the jet stream in the past on purpose and they really
get moving (over 200 mph horizontal speed).

We actually predicted the balloons to go much further in terms of
distance and much more East. We were off by a good 30 miles in our
predictions - mainly because of the front that came through that
morning. During changing weather, it is hard to predict what the winds
aloft are like - the weather models are just not that good. We
typically do a prediction the night before the launch after the 6PM
weather data become available - but we were camping and were out of
WiFi range and unable to do the prediction so we were going off of
data 24 hours old.

3) In terms of the landing location, the recovery of the first balloon
was one of the longest (time-wise) hikes we've ever had. In terms of
distance, HALE was pretty standard. The shortest distance between
launch and touchdown we've ever had was just about 2 miles. The
longest is around 90 miles (to the best of my recollection). 30-50
miles is fairly typical. The direction the balloons went (mostly
North) is very atypical. Again, the storm front that came through
really messed us up (but kept us cool on the hike). You can see from
the photos that we were pretty well covered in clouds. Remember that
Nevada is a desert - we only get 7 inches of rain a year and have over
300 cloudless days per year. So getting a storm in July is pretty
unusual and took us by surprise.

Knock on wood - we've been very lucky in that most of the time the
payloads are recovered within a mile of a road (although some "roads"
we use are on the GPS and topo maps but apparently were never
installed by the department of transportation). Even when they land
close to a road, it is pretty hard to find the payloads. GPS gets you
close, but we have to deal with the error of the GPS on the payloads
and the error of the GPS we are using in the cars (or handhelds).
Getting to within a hundred feet is typical. Then we have to wander
around an look. If it's flat - no problem. If it's hilly - like the
first balloon - then it's more difficult. We can't complain though,
we've read about other folks who have landed a payload in a cornfield
or in a the top of a tree in a forest. Oregon Space Grant once took
several weeks to find a payload that was up in a tree in a dense
forest.

Jeff and I have already decided that HALE2 will not take place in the
middle of the summer. We want it to be much cooler next time :)

4) I am not sure how much of a factor it is. But we're 20 miles up and
the earth is 8000 miles in diameter (I think), so we're not really too
far off the Earth's surface in the grand scheme of things. Brian may
be able to answer this better as the physicist in the group :)

Eric

[Brian Davis]

On Aug 16, 2:40 am, Eric <lego.profes...@gmail.com> wrote:

> I'm sure there is a program out there somewhere that can
> calculate the total distance traveled based on the GPS data.

Actually, we could do it in Excel again. Just add up the distance
between each GSP fix. I just haven't bothered because I can't see any
use for the information.

> 4) I am not sure how much of a factor it is. But we're 20 miles up and
> the earth is 8000 miles in diameter (I think), so we're not really too
> far off the Earth's surface in the grand scheme of things. Brian may
> be able to answer this better as the physicist in the group :)

Always scary when you punt to the physicist :). The Earth rotation, in
this case, is pretty much a non-issue. Right now a point on the ground
in Nevada is moving at about 1280 kph (790 mph), while a point 30 km
above it would have to be moving faster to keep up (it's further from
the center)... but just 0.47% faster, or a speed difference of 6 kph
(3.7 mph) - walking pace at best. Technically that's due to what's
called the Coriolis effect... and you can see here, it makes for a
trivial difference in velocity.

With the atmosphere, you have to remember that while you are moving in
a circle at a really high rate of speed... so is all the air around
you, even at high altitude. If it was moving relative to you, then
friction and turbulence match the velocities rather rapidly *unless*
there's some input of energy, like heat or moisture condensing
(actually, another version of "heat" as far as the weather is
concerned).

--
Brian Davis