MIT-3 Flight Info (April 13, 2008)

This flight is a test of an experimental balloon envelope. Hopefully it will acheive float at some altitude.

Launch Time: Approx 5pm Eastern, 4/13/08
Launch Location: Cambridge, MA
Downlink Frequency: 10.143 MHz
Reception Reports to: w1mx-balloon AT mit.edu

• Launch at 5:20pm EST
• UPDATE (6pm): Became roughly neutral at around 10,000 feet and is now sinking slowly.
• UPDATE (6:20pm): Seems that for some reason the low-order digits of the altitude are getting dropped ocassionally. Valid altitudes have five digits, followed by 'M' for meters.
• UPDATE (7:05pm): GPS has lost lock for some reason, last fix at 230210z.
• UPDATE (10:00pm): After a long outage, GPS has returned. Balloon has landed on ocean surface, and is drifting along. Still transmitting. Please send your reports!

MIT-2 Flight Info

The first test flight of the HF beacon is MIT-2, scheduled for launch on March 2, 2008 around 5pm eastern. This flight will use a standard latex balloon , and is expected to float to burst altitude before falling into the ocean. It is primarily a test of the HF beacon.

UPDATE (11:57pm): Balloon burst and crashed into the ocean. Final position message put it at 4045.16N 06912.97W at 015935Z. Backsolving the altitude messages gave us an ascent rate just shy of 500 feet/min, and a burst altitude of around 100,000 feet. We lost GPS completely for about 30 minutes during the flight. Altitude information was bogus (aside from the 10x error) for about 2/3 of the flight. It seems we need a better GPS system. The final track is on a map, here.

UPDATE (7:12pm): About 100 miles southeast of Boston. CW has been heavily corrupted for the entire duration, but Hell has been very clear. The position data seems fine, but the altitude values are wrong... we are working to figure out why.

Launch Time: Approx 5pm Eastern, 3/2/08
Launch Location: Cambridge, MA
Downlink Frequency: 10.143 MHz
Reception Reports to: w1mx-balloon AT mit.edu

Low-cost HF Beacon Transmitter

The above transmitter outputs around 1.5W on 30 meters using a 12V supply. It is on-off keyed, and the included Atmel microcontroller receives NMEA sentences from a GPS, and generates CW and Hellschreiber messages, which are sent via radio. The beacon was designed to be low cost (about $25 per unit) so it can be used as part of an Atlantic-crossing balloon program. We expect to lose a lot of them, so low cost and repeatability are important.

Schematics are here (PA) and here (digital section).

Message Formats

Position message format:

[time] [grid] [grid] [lat] [lon] [heading] [speed] [altitude] [sats] [board temp]

CW substitudes 'T' for 0 to speed things up.

Time Slot	Message Type
0,3,4,5,8,9 minutes	Hell Position Message
1,6 minutes	CW Position Message
2,7 minutes	Text Message in Hell, then CW

Transmit slots are referenced to GPS time, in the case that GPS signal is lost, a timeout will expire after 2 minutes to cause a transmission.