Red Bull Stratos – a supersonic flight from the stratosphere

Preparations for the mission jump that was to allow the first human to become supersonic in freefall involved massive equipment testing. For example, the high-tech capsule, the custom-made pressurized suit with its life support system, helium balloons in different sizes, as well as state-of-the-art still and video camera gear that would document the attempted jump needed to undergo thorough testing, and of course demanded considerable financial resources.

Finally, in early 2012 the project entered into its ultimate rehearsal phase comprising two high-altitude manned test jumps, following two earlier unmanned flights conducted in December 2011 and January 2012, respectively.
Felix Baumgartner's first stratospheric test jump took place on 15 March 2012 from an egress altitude of 21,828 m (71,615 ft) over Roswell, New Mexico (USA). According to official data from the Fédération Aéronautique Internationale (FAI), Baumgartner during a freefall duration of 3 minutes and 40 seconds reached a top speed of 586.92 km/h (163,03 m/s or 364.69 mph), deploying his parachute at 2,503 m (8,211 ft) above sea level.
The second and final test jump took place in the same location on 25 July 2012. According to FAI data, the actual egress altitude this time was 29,610 m (97,146 ft), some 2,000 m higher than planned. He reached a top speed of 863.71 km/h (239.92 m/s or 536.80 mph) during a freefall of 3 minutes and 48 seconds, deploying his parachute at 3,930 m (12,894 ft) above sea level. The whole descent lasted 10 minutes and 36 seconds.

Exactly 65 years to the day when US Air Force pilot Capt. Chuck Yeager was the first to break the sound barrier in his rocket-powered Bell X-1 plane reaching a maximum speed of Mach 1.07, Red Bull Stratos took to the skies over Roswell, New Mexico (USA), on Sunday, 14 October 2012.

After the first scheduled launch window six days earlier (on Monday, 8 October 2012) had passed due to unfavourable ground winds, the second attempt on Wednesday, 10 October 2012, had to be scrapped when the helium balloon during filling was hit by wind gusts at the top of the balloon which partly forced it down on the ground potentially damaging its super-thin (0.02 mm) polyethylene foil. The first of two available balloon hulls was thus lost in that attempt. With only one more, slightly larger balloon hull left the countdown for the final jump resumed on Sunday, 14 October 2012, at six o'clock in the morning local time.

Though the Red Bull Stratos team again had to wait for several hours in order to pick the right window for filling the almost 850,000 m³ large balloon with helium, everything went smoothly this time. At 9:29 hrs. local time the huge balloon with Felix Baumgartner's capsule suspended below performed a text book launch. The official target altitude for the mission jump was 35,576 m (120,000 ft). This altitude was considered to provide for sufficient margin for Baumgartner to actually break the sound barrier which, while being dependant on temperature, was calculated to be around 1,110 km/h (308.3 m/s) at 30 kilometres of altitude.

Due to the second balloon being larger than the one spent on the Wednesday before, it ascended to a peak altitude of 39,068.5 m (128,177.5 ft). The actual egress altitude according to final Red Bull Stratos data became 38,969.4 m (127,852.4 ft). After jumping from the capsule's doorstep, Baumgartner within some 34 seconds became supersonic, i.e. passed Mach 1.0 (equivalent to 1,115 km/h), at an altitude of 33,446.0 m (109,731.0 ft), still massively accelerating at this point. According to final Red Bull Stratos data, he reached a vertical top speed of 1,357.6 km/h (377.1 m/s or 843.6 mph) at an altitude of 27,833.0 m (91,315.6 ft) after 50 seconds spent in freefall, translating to a Mach number of 1.25! He then slowed down to subsonic speed at an altitude of 22,960.7 m (75,330.4 ft) after some 64 seconds into freefall. At that point a sonic boom could be heard and was indeed recorded on the ground. Based on these updated information, the supersonic section of Baumgartner's freefall amounted for exactly 10,485.3 m (34,400.6 ft).

The freefall duration was clocked at 4 minutes 20 seconds, interestingly short of Joe Kittinger's record set in 1960. However, Kittinger then descended with the assistance of a drogue chute that apparently extended his freefall. The Mach number achieved indeed topped even the most optimistic estimates which had anticipated a likely maximum Mach 1.17. The whole descent lasted a mere 9 minutes and 18 seconds, and Baumgartner deployed his main parachute at approximately 1,525 m (5,003 ft) above ground.

Felix Baumgartner successfully avoided the automatic deployment of a safety drogue chute during the fastest section of the freefall. This drogue chute would have been triggered by a G-force sensor once Baumgartner had been in a dangerous flat spin for more than six consecutive seconds at more than 3.5 G. Additional POV video footage, released one year after the successful jump, confirmed that Baumgartner was successfully battling violent flat spins after already being supersonic. Thus, the possible deployment of the drogue chute would likely not have compromised the mission's key objective, i.e. to become faster than the speed of sound during freefall. Baumgartner in interviews after the successful jump admitted not noticing the moment of going supersonic; he even wasn't sure whether he had accomplished his key objective. Part of the ground team, however, stated they heard the familiar sonic boom during Baumgartner's descent. The full POV video indeed suggests that speeds above some Mach 0.85 are particular prone to causing flat spins. Baumgartner managed to fully stabilize his freefall while decelerating to Mach 0.86 at an altitude of some 19,500 m (64,000 ft).

The capsule safely landed 88 km away from the launch site after a 24 minute ride, while the balloon hull landed 11 km away from the capsule after a 15 minute descent. Both pieces of equipment were recovered by the team and immediately ferried back to Roswell airfield the same afternoon.