Scientific Ballooning

PIPER flight closes a weather troubled NASA balloon launch campaign in Fort Sumner

Fort Sumner, New Mexico.- 2017 will be remembered in the annals of NASA's scientific balloon program as a particularly problematic year. Following the loss of the EUSO-SPB balloon in the Pacific in May and the free-fall incident which ended with the destruction of the BETTII telescope in June, the agency's fall campaign held each year at the Scientific Balloon Flight Facility in Fort Sumner, New Mexico, came to an end with only two flights performed of the seven planned, after suffering the worst weather conditions in many years.

After the first balloon mission performed in September 4th for the benefit of the High Altitude Student Platform (HASP) which I've covered in detail in the last update to this website a month ago, the climate did not cooperated for the realization of a second flight until October 13th, when FINALLY the PIPER instrument went aloft.

Believe me, the emphasis of the word above is not a typing error: this experiment was in the launch row of every NASA balloon launch campaign in CONUS since 2016 (more on this later).

Now, what is PIPER?

The instrument's acronym stands for Primordial Inflation Polarization Explorer and was designed and built by NASA's Goddard Space Flight Center, in collaboration with Johns Hopkins University, and the National Institute of Standards and Technology from the United States, and the University of British Columbia in Canada, and the Cardiff University in Wales.

The goal of the instrument is to search evidences of the so called "cosmological inflation" on which the early universe expanded far faster than the speed of light and began growing exponentially almost instantaneously after the Big Bang. This process would have generated gravitational waves, which are small perturbations in the fabric of space-time. These waves would have left an imprint in the polarization of the cosmic background radiation (CBR), the remnant light from the universe's creation that bathes the sky in all directions. This is the observational objective of the Goddard team.

PIPER is composed by two identical telescopes cooled to 1.5 degrees Kelvin within one of the largest liquid helium bucket dewars ever developed for a balloon-borne mission, measuring 3 meters tall and with a volume of 5000 liters, and carrying at launch some 3500 liters of liquid Helium (LHe). There are no windows between the LHe-cooled telescope and the ambient environment as PIPER uses the efflux of boiloff helium gas to prevent the atmosphere at balloon altitudes from condensing on the optics. The later technique was used for the first time a few years ago for another balloon-borne instrument called ARCADE which was also developed by the same team that built PIPER.

Aside the inherited technologies, PIPER incorporates several innovations: an array of advanced bolometer detectors with an unprecedent sensitivity called the backshort under grid (BUG) architecture, a variable polarization modulator made of copper-plated tungsten wires acting like "windows" that only allows the polarized light to reach the detectors, and a device called an adiabatic demagnetization refrigerator that erase the heat signature generated by the instrument itself in order to be able to detect the tiny CBR signal.

PIPER team was looking for a chance to perform the first enginneering flight of their instrument since fall 2016. Then, after three launch attempts the mission was finally cancelled and moved to Palestine in 2017 for the Summer campaign. After the BETTII destruction incident and the halt of operations for a couple of weeks, they had no chance of launch and were finally moved again to Fort Sumner for fall 2017 campaign.

The PIPER team arrived to Fort Sumner in early September just after the first flight of the season. As soon as the instrument was declared "flight ready" it was assigned the top priority for launch and numbered as mission 681N. As it was mandatory to have night observing time and NASA performs launches mostly at dawn, they needed very slow winds at altitude to obtain a long flight before the balloon could reach forbidden zones (California and Mexico border among others).

With all prepared, it was only a mather of finding good weather, but mother nature was not so mercyful this time and the first launch opportunity -although marginal- did not appear before September 21. That day, PIPER was not able even to go to the launch pad before the winds increased to the point to force the cancellation of the operation.

Meanwhile, there were other instruments and missions waiting also their turn to climb to the stratosphere just after PIPER:

• SuperBIT (moved from the 2017 Palestine summer balloon campaign and also flight ready)
• FIREBALL an UV telescope which also was ready to be launched.
• JPL-Remote a multipayload platform for atmospheric science.
• WASP an stabilized platform for astronomical observations.
• 60 MCF Test a qualification test flight of a 60 million cubic feet balloon also planned for the season

The rest of September and the first days of October showed a combination of high winds, storms and rain which made almost impossible any launch attempt. By then, 32 days had passed without flights and 16 days since the first launch chance.

Things started to improve after October 5, so two days later it was the second chance to fly for PIPER, but after moving to the launch pad and even extracting the balloon from its box, the operation was called off due to high surface winds. On October 10 a marginal opportunity appeared in the afternoon so again PIPER was taken to the launch pad, balloon was unboxed and layout and a long wait started. However, this time also the attempt was cancelled due to gusty winds.

With the closing of the launch season approaching, three missions were finally dumped from the wait list: JPL Remote, the 60 MCF balloon flight test and the FIREBALL UV Telescope mission. This late instrument instead of being shipped back to France will remain in storage in Fort Sumner until 2018 when a new attempt will be made. (Note: a couple of days after PIPER's flight there was apparently a launch attempt for SuperBit which nevertheless was cancelled.)

The last launch attempt for the season for PIPER was carried out on October 13th, but this time weather was a little bit more cooperative and allowed to proceed with the operation as intended.

Balloon was laid out at 14.30 utc, and after some tense minutes, finally inflation began about 15:00 utc. The filling operation of the 11 million cubic feet balloon was completed in almost one hour and at 16:12 utc on October 13th, the PIPER balloon was launched starting a more than desired first engineering mission.

Climb to altitude was nominal and ceiling of 98.000 ft was reached about 19:30 utc while flying E of Tucumcari. The balloon moved during the entire flight in a NE direction more or less along along the New Mexico / Texas border, as can be seen in the map below.

The flight was terminated and the payload separated from the balloon at 3:00 utc on October 14th, while flying over Union County in NE New Mexico with a total flight time from launch to landing of 11 hours and 30 minutes.

Thanks to the information that was kindly provided to me by Paul Mirel PIPER's Chief Engineer and Project Manager who designed the polarization variable modulator, I've learned that the landing of the payload was a little rough as it toched ground with a sideways speed around 40 miles/hour and did a cartwheel, landing on the bottom, then on the top, and then on the bottom again. However, the instrument resisted very well the ride and emerged in good shape at all.

According to Mirel the team is very happy with the outcome of the flight, as most of the objectives established for this first engineering flight were succesfuly achieved. Now they are in the process of evaluating the data and preparing for the upcoming flight, which will be performed in late May 2018 from Palestine, Texas. That mission will incorporate to PIPER the science grade version of the detector arrays.

More information on PIPER and the science behind the instrument, can be obtained in the website of the project at Goddard , reading a more technical oriented paper entitled The Primordial Inflation Polarization Explorer (PIPER) at ArXiv and also in their weblog.

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