Project Rahu 

The official Project Rahu webpage has now been updated with additional details about our project. This temporary page does still contain some information about our test launch and early preparation that hasn’t made it to the main site yet.

August 21: Eclipse Day was a success!

August 16-20: Eclipse Prep in Oregon


August 3: Rahu 0 Test Flight

Rahu I, Rahu II, Rahu III, Rahu IV

Preliminary flight stats

August 21: Eclipse Day was a success!


We’re Craig Butz and David Friedlander-Holm, faculty at the Bay School of San Francisco (cbutz AT and dfriedlander-holm AT On August 21, 2017 we launched four camera-equipped weather balloons from NW of Madras, OR into the path of the total solar eclipse. Our goal, besides experiencing the eclipse on the ground, was to see what the complete umbra looks like from above most of the atmosphere, something only a handful of photographs had been taken of prior to this eclipse.

View of the shadow of the eclipse approaching from the Oregon coast from Rahu IV at 83,000 feet at 10:16am.

Rahu I at 86,000 feet is just visible as a tiny speck of white over the shadow.

Umbra engulfing Mt. Jefferson at 10:18am from Rahu IV.

Mt. Jefferson completely in the shadow at 10:18 from Rahu I.

The eclipse completely filling the space between the Three Sisters and Mt. Hood.

Mt. Jefferson is in complete darkness at 10:19.

View of the shadow of the eclipse receding from Rahu I at 90,000 feet at 10:23am.

Rahu IV at 87,000 feet is clearly visible as a white dot in front of the shadow.

After months of prep, we released our balloons at 7:28 (Rahu I), 7:34 (Rahu IV), 7:40 (Rahu II), and 7:48 (Rahu III). We recovered equipment from all four balloons, though trackers from Rahu II became separated from the rest of the payload, so we lost those four cameras. As we sort through the hours of video footage and thousands of still images, we will continue to update this page over the coming days and weeks. You can watch a timelapse of the eclipse shadow passing on YouTube.

The stabilized version of the timelapse can be found here.

Our primary tracking was done via Tracksoar APRS transmitters, designed by Mike Bales. The balloons transmitted on 144.39 as KJ6DYP-11, KJ6DYP-14, KJ6DYP-12, and KJ6DYP-13.

Backup satellite tracking was by Spot Trace. Payloads also included Xiaomi Yi cameras for stills and 808 keychain cameras for video, both with supplemental batteries. The 720g payloads are carried by 1000g Kaymont balloons.

You can see the tracks of all of our balloons online via APRS.

Diagram of the eclipse path and shadow showing our launch site NE of Madras

August 16-20: Eclipse Prep in Oregon

We arrived in Oregon and camped out in the Crooked River National Grasslands (on the site of the Emerson Fire). We observed several fires to our West, making for impressive sunsets! We prepared more for our launch before the eclipse. Here are some images of that process.

Our soldering iron wasn’t powerful enough to repair a heavy-gauge battery connection so Craig had to use two.

Verizon has better service than AT&T most of the time…

Our home for four days!


August 3: Rahu 0 Test Flight

We released and recovered a test balloon in California’s Central Valley on the morning of August 3rd. During the 3½ hour flight, our tracking equipment and cameras made it to an altitude of 103,045 feet and traveled 54 miles.

Google Earth visualization of the flight path, looking toward The Bay Area.

Map of APRS repeaters that relayed our tracking transmissions. The outer circle is the horizon at peak altitude. The inner one is the area where the balloon was 5º above the horizon.

Flight path via



Still images from the Xiaomi Yi action camera.

We encountered two problems with this camera that we were able to correct for the eclipse flights. The case developed condensation in front of the lens, which was solved by removing the glass in front of the lens. The camera also shut down early. After ground tests with dry ice, we insulated the camera with mylar space blanket material inside the case and black-painted foam outside, which we hoped was enough to get the cameras to last through passage of the eclipse.

Video still from the 808#16 camera from over 98,000 feet.


Images of an inflated balloon in the inflation bag we sewed and the payload components hanging from a carbon fiber kite strut.

Rahu I, Rahu II, Rahu III, Rahu IV

From its lower altitude at the back of the pack, the Yi camera on Rahu III was able to capture all three of our other balloons, as well as two other eclipse-day balloons.

Map showing relative locations of balloons as they became large enough to see each other clearly. Red circles are burst points. Colored spots are approximate locations of balloons when others burst.

 Video from Rahu III shows the balloon closest to Rahu II rising from below and suddenly blinking out above Rahu II, presumably when it burst. The two balloons appear to have been about half a mile apart. Unfortunately, the Rahu II cameras were not recovered. Rahu IV burst immediately after the image above was taken.

Rahu III closed to within 1.2 miles Rahu II, and took its final shots of Rahu II before the camera failed about a minute before Rahu II burst.

Rahu II at around 105,000 feet just before burst with parachute and payload faintly visible, taken from Rahu III.

Rahu I captured these stills showing Rahu IV’s burst from 1.5 miles away.

Gif excerpt from the timelapse video of the umbra sweeping over Oregon.

Recovering all four payloads took up the remainder of Eclipse Day. Since the balloons exceeded the altitude of the test by 2300 to 4600 feet, they drifted considerably further west than predicted, landing in the Deschutes National Forest rather than farm or grassland. A number of roads were too rough to travel; other roads were private and gated, but after driving south and then back north, we were able to get within a few hundred yards of all the landing locations. At least there weren’t any traffic jams!

Rahu I landed entirely intact with the parachute having functioned correctly.

Only the Spot and Tracksoar tracking devices were located from Rahu II--a few dozen yards apart--after become separated from the cameras and parachute. Footage from Rahu III, which suffered a similar, but less catastrophic failure, suggests the looped and taped, but untied string holding the tracking end of the carbon strut came free at burst, allowing the trackers to work their way off the end. The balloon cam would also have slid off if the trackers did, but we did not locate it in a half-hour sweep of the area. The rest of the cameras, parachute, and balloon remains likely drifted further southwest.

Spot 2, found without the rest of its payload.

Tracksoar 2 (with the yellow Lego stratonaut) fell not far from the Spot module.

Rahu III came apart similarly to Rahu II. The tracksoar module slid off after one of its straps broke in the turbulence of descent and was recovered a few hundred feet away. The balloon cam seemed to have come off at impact.

The balloon of Rahu III was severely tangled with the line and parachute.

David locates the tracksoar module of Rahu III after a frustrating search of the relatively small area it was transmitting from.

Rahu III fell from 20 miles in 21 minutes, even faster that the solo trackers of Rahu II and more than twice as fast as the payloads with functional parachutes. Rahu IV, on the other hand, drifted down over 47 minutes and came to rest hanging from a tree a few inches off the ground a quarter mile from where the Rahu II trackers landed.

Preliminary flight stats

Rahu 0 (Test)

Rahu I

Rahu II

Rahu III

Rahu IV

Release time

11:37 Aug 3

7:28 Aug 21

7:40 Aug 21

7:48 Aug 21

7:34 Aug 21

Burst time






Landing time






Ascent time

3 hours 1 min

3 hours 32 min

3 hours 36 min

3 hours 32 min

3 hours 23 min

Descent time

38 min

40 min

28 min

21 min

47 min

Total flight time

3 hours 39 min

4 hours 12 min

4 hours 4 min

3 hours 53 min

4 hours 10 min


54 mi

30.5 mi

28.4 mi

26.8 mi

28.4 mi

Initial ascent rate

613 ft/min

461 ft/min

379 ft/min

481 ft/min

470 ft/min

Final ascent rate

544 ft/min

238 ft/min

352 ft/min

325 ft/min

512 ft/min

Max descent rate

4521 ft/min

7115 ft/min

4306 ft/min (over 15 min)

7339 ft/min

6476 ft/min

Landing speed

1185 ft/min

13.5 mph

1319 ft/min

15 mph

2696 ft/min

30 mph

2629 ft/min

30 mph

1283 ft/min


Max altitude

103045 feet

107707 feet

105581 feet

105981 feet

105354 feet

Lowest internal temp

14ºC @ 57000ft

-30ºC @ 92000ft


-26ºC @ 81000ft


-28ºC @ 78500ft


-32ºC @ 88000ft


Lowest pressure

1502 Pa

836 Pa

995 Pa

1102 Pa

1154 Pa

We will continue to update this page as our project progresses. While you wait for us to get back, here’s a 90s Angelfire page under construction GIF:


Info about Bay’s earlier high altitude balloon flights.