ASCENT RATE VARIATIONS
Ralph Wallio, WRPK   WRPK  at  netINS.net


The ascent rate of a high altitude balloon and payload is created by imbalance between buoyant lift and the combination of total weight and aerodynamic drag. Buoyant Lift results from the difference in density between equal volumes of lifting gas and displaced air. Total Weight includes all mass being lifted, the balloon envelope, payload, parachute, et al. Aerodynamic Drag slows ascent rate because air must be pushed aside as the balloon rises.

These factors are brought together in a formula of equilibrium,
LIFT = DRAG + WEIGHT

LIFT is calculated using Volume [m3] (equal volumes of lifting gas and displaced air), Density [kg/m3] of Air minus Density [kg/m3] of liftring gas, and the Acceleration of Gravity [9.8m s-2]:

LIFT = (4pi/3)Radius3(Densityair-Densityhelium)9.8m s-2   (assumes balloon is spherical)

DRAG is calculated using Drag Coefficient, projected Area [m2]of balloon, Density of Air, and Ascent Rate

DRAG = Cd(pi)Radius2(Densityair)Ascent Rate2/2



High altitude balloon track and touchdown prediction accuracy is dependent on the quality of winds aloft observations and forecasts, ascent and descent rate predictions and burst altitude estimates. This discussion looks at ascent rate variations while hoping that they might be managed to improve track prediction accuracy. It is going to take all the king's horses and all the king's men to make sense out of what we find.

Current and all past versions of track prediction programs allow use of only one ascent rate value. These programs use wind direction and speed values at increasing altitudes to laterally move balloon and payload while they are ascending. Assumption of a constant ascent rate makes programs insensitive to variations in vertical velocity. The result is reduced accuracy in track and touchdown predictions.

Navigation telemetry files containing GPS based time stamp, latitude, longitude and altitude information have been collected for numerous high altitude missions. This study includes only those missions that flew after GPS Selective Availability inaccuracies were turned off on
May 2, 2000. Ascent rate is calculated between consecutive GPS records using altitude and time stamps:

Ascent Rate = (New altitude - old altitude)/(New time - old time)

EXCEL charts are then constructed comparing ascent rate vs. altitude. Ten point moving average trend lines of data points are plotted and average ascent rates are given as straight lines (average for the entire ascent, release to burst). Ascent rate vs. altitude curves are then collected in monthly charts (data for any flights in January and March is not available).

We can now look through these charts attempting to find characteristics that might be useful. I have noted a few interesting details that immediately come to mind.

MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

EOSS-47

25Feb01

Colorado

40dN

93,811

1045

~1300

129

na




MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

EOSS-48

01Apr01

Colorado

40dN

90,045

905

~1000

140

na

EOSS-49

21Apr01

Colorado

40dN

88,056

687

unk

143

Data stops at 12,240ft descending

EOSS-50

21Apr01

Colorado

40dN

103,984

501

unk

215

Data stops at 91,051ft descending

NSTAR01A

14Apr01

Nebraska

41dN

60,321

1172

~1700

135

na

EOSS-50 (April) achieved equilibrium and was floating when it burst. EOSS-49 and EOSS-50 flew at the same time from the same launch site but curves are very different below 35,000ft.


MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

BEAR-1

27May00

Alberta

53dN

104,211

455

~900

254

Edmonton, Alberta, Canada

NSTAR-01B

19May01

Nebraska

41dN

95,384

1046

~1000

265

na

TVNSP-01C

12May01

Idaho

43dN

67,012

808

unk

336

Altitude hold during descent

BEAR-1 appears to be approaching equilibrium and float state just before burst.


MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

NSBG1-3

30Jun01

Kansas

38dN

78,247

964

unk

131

Data stops at 60,751ft descending

NSTAR-01C

24Jun01

Nebraska

41dN

83,625

1099

~1000

196

na

NSTAR-01D

30Jun01

Kansas

38dN

91,365

986

~1150

208

na

TVNSP-01D

30Jun01

Kansas

38dN

83,099

446

~1000

293

na

NSBG1-3, NSTAR-10D and TVNSP-01D flew at the same time from the same launch site.


MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

ANSR-2

28Jul01

Arizona

35dN

85,742

401

unk

349

16,818ft ascend to 14,206ft descend

HABET-L49

26Jul01

Iowa

42dN

85,970

1266

na

1956

Descent via small balloon

ANSR-2 appears to have a much tighter data point plot than HABET-L49(?)


MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

BEAR-2

05Aug00

Alberta

53dN

99,482

714

~1150

165

Edmonton, Alberta, Canada

EOSS-51

25Aug01

Colorado

39dN

91,458

1178

~1000

207

na

TRAVELER1

04Aug01

Kansas

38dN

90,139

1291

unk

50

na

TVNSP-01F

12Aug01

Idaho

42dN

85,439

919

unk

93

Data stops at 32,982ft descending




MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

NSTAR-01E

01Sep01

Nebraska

41dN

54,380

879

~900

414

na

TVNSP-01G

29Sep01

Idaho

43dN

44,113

800

~600

299

na




MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

ANSR-3

14Oct01

Arizona

32dN

98,581

642

~1150

103

na

EOSS-52

20Oct01

Colorado

39dN

92,224

1198

unk

212

na

NSTAR-00A

07Oct00

Nebraska

40dN

83,675

972

~1400

200

na




MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

HABET-L44

15Nov00

Iowa

42dN

59,999

1326

~500

1436

na

HABET-L52

15Nov01

Iowa

41dN

90,078

1126

~600

1985

na

NSTAR-00B

04Nov00

Nebraska

41dN

74,242

1029

~1200

189

na




MISSION

DATE

LOCATION

LATITUDE

MAX ALT

ASCENT

DESCENT

RECORDS

REMARKS

ANSR-4

01Dec01

Arizona

32dN

90,226

1159

~1200

50

Data starts at12,058ft ascending

EOSS-53

01Dec01

Colorado

39dN

94,755

1065

~1000

236

na


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