A research balloon is readied for launch. Credit: NASA.

Balloons provide a long-duration platform to study any atmosphere, the universe, the Sun, and the near-Earth and space environment above as much as 99.7 % of the Earth's atmosphere. Unlike a rocket where data are collected during a brief few minutes, balloons are able to stay aloft for much longer. Balloons for astronomy offer a low-cost, quick-response method for conducting scientific investigations. They are mobile, meaning they can be launched where the scientist needs to conduct the experiment, in as little as six months.

## Balloons

The super pressure balloons flown by the NASA program are essentially very large pressure vessels. Credit: NASA Official: David L. Pierce, Curator: Brandon Wright.{{free media}}
This seven-million-cubic-foot super-pressure balloon is the largest single-cell, super-pressure, fully-sealed balloon ever flown. Credit: NASA.{{free media}}

The Ultra Long Duration Balloon (ULDB) Project is developing new composite materials and a new balloon design, a standard gondola including power, global telemetry/command and an altitude control system. The ULDB is seeking to improve mission control and operations and the integration of scientific instruments. It is the potential for longer duration flights that has been the driver for the resurgence of interest in balloons by the scientific community. In recent years, the manned global ballooning attempts have called attention to the difficulty of achieving “longer”.

"High altitude balloons are an inexpensive means of getting payloads to the brink of space [The first test shown in the image on the left] was launched from McMurdo Station in Antarctica. The balloon reached a float altitude of more than 111,000 feet and maintained it for the entire 11 days of flight. [...] The flight tested the durability and functionality of the scientific balloon’s novel globe-shaped design and the unique lightweight and thin polyethylene film. It launched on December 28, 2008 and returned on January 8, 2009."[1]

"The University of Hawaii Manoa’s Antarctic Impulsive Transient Antenna launched December 21, 2008, and is still aloft. Its radio telescope is searching for indirect evidence of extremely high-energy neutrino particles possibly coming from outside our Milky Way galaxy."[1]

## Planetary sciences

Research balloons are balloons that are used for scientific research. They are usually (though not always) unmanned, filled with a lighter-than-air gas like helium, and fly at high altitudes.

Def. a "branch of science that deals with the [upper] atmosphere of the Earth and the other planets with reference to their chemical composition, physical properties, relative motion, and responses to radiation from space"[2] is called aeronomy.

## Theoretical balloon astronomy

Def. "the branch of meteorology involving the observation of the atmosphere by means of balloons, airplanes, etc"[3] is called aerology.

Def. an "inflatable buoyant item [object], often (but not necessarily) round and flexible"[4] is called a balloon.

## Thunderstorms

Stages of a thunderstorm's life.
Anvil-shaped thundercloud in the mature stage. Credit: .
Lightning, which is responsible for the majority of fires in the American West. Credit: Jrmichae.

A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder.[5] Relatively weak thunderstorms are sometimes called thundershowers.[6]

Thunderstorms can form and develop in any geographic location but most frequently within the mid-latitude, where warm, moist air from tropical latitudes collides with cooler air from polar latitudes.[7]

Warm air has a lower density than cool air, so warmer air rises upwards and cooler air will settle at the bottom[8] (this effect can be seen with a hot air balloon).[9] Clouds form as relatively warmer air, carrying moisture, rises within cooler air. The moist air rises, and, as it does so, it cools and some of the water vapor in that rising air condenses.[10] When the moisture condenses, it releases energy known as latent heat of condensation, which allows the rising packet of air to cool less than the cooler surrounding air[11] continuing the cloud's ascension. If enough instability is present in the atmosphere, this process will continue long enough for cumulonimbus clouds to form and produce lightning and thunder. Meteorological indices such as convective available potential energy (CAPE) and the lifted index can be used to assist in determining potential upward vertical development of clouds.[12] Generally, thunderstorms require three conditions to form:

1. Moisture
2. An unstable airmass
3. A lifting force (heat)

All thunderstorms, regardless of type, go through three stages: the developing stage, the mature stage, and the dissipation stage.[13] The average thunderstorm has a 24 km (15 mi) diameter. Depending on the conditions present in the atmosphere, each of these three stages take an average of 30 minutes.[14]

A "thunderstorm supplies a negative charge to the Earth. The net positive space charge in the air between the ground and a height of ~ 10 km is nearly equal to the negative charge on the Earth's surface".[15]

'Giant' "thunderclouds can produce transverse electric fields of tens of microvolts per meter in the equatorial plane of the midlatitude magnetosphere."[16]

The "contribution to global thunderstorm activity by oceanic thunderstorms should be regarded as itself having a diurnal variation of some 18% in amplitude."[17]

Pyrocumulonimbus are cumuliform clouds that can form over a large fire and that are particularly dry.[18]

There is "a decrease in thunderstorms at the time of high cosmic rays and an increase in thunderstorms 2-4 days later."[19]

## Cosmic-ray telescopes

An increase of ionization with altitude is measured by Hess in 1912 (left) and by Kolhörster (right). Credit: Alessandro De Angelis.
Hess lands after his balloon flight in 1912. Credit: American physical society.

The various background effects OSO 1 encountered prompted the flight of similar detectors on a balloon to determine the cosmic-ray effects in the materials surrounding the detectors.

Then, in 1912, Victor Hess carried three enhanced-accuracy Wulf electrometers[20] to an altitude of 5300 meters in a free balloon flight. He found the ionization rate increased approximately fourfold over the rate at ground level.[20] Hess also ruled out the Sun as the radiation's source by making a balloon ascent during a near-total eclipse. With the moon blocking much of the Sun's visible radiation, Hess still measured rising radiation at rising altitudes.[20] He concluded "The results of my observation are best explained by the assumption that a radiation of very great penetrating power enters our atmosphere from above." In 1913–1914, Werner Kolhörster confirmed Victor Hess' earlier results by measuring the increased ionization rate at an altitude of 9 km. Hess received the Nobel Prize in Physics in 1936 for his discovery.[21][22]

The Hess balloon flight took place on 07 August 1912, providing the first direct evidence of cosmic radiation.

## Neutrons

Space weather conditions are associated with solar activity. Credit: Daniel Wilkinson.{{free media}}

The "effect of time-variations in galactic cosmic rays on the rate of production of neutrons in the atmosphere [was studied using] a series of balloon and airplane observations of the [fast neutron] flux and spectrum of 1-10 MeV neutrons, in flights at high geomagnetic latitude, during [quiet times as well as during Forbush decreases, which are rapid decreases in the observed galactic cosmic rays following a coronal mass ejection (CME), and solar particle events for] the period of increasing solar modulation, 1965-1969. It also included latitude surveys in 1964-1965 and in 1968."[23]

In the image on the right for Forbush decreases, data include GOES-15 X-rays, energetic particles, and magnetometer. Cosmic Rays from the Moscow station show a Forbush Decrease.

## Protons

Antiprotons have been detected in cosmic rays for over 25 years, first by balloon-borne experiments and more recently by satellite-based detectors. The standard picture for their presence in cosmic rays is that they are produced in collisions of cosmic ray protons with nuclei in the interstellar medium, via the reaction, where A represents a nucleus:

p + A → p + p + p + A

The secondary antiprotons (p) then propagate through the galaxy, confined by the galactic magnetic fields. Their energy spectrum is modified by collisions with other atoms in the interstellar medium. The antiproton cosmic ray energy spectrum is now measured reliably and is consistent with this standard picture of antiproton production by cosmic ray collisions.[24]

## Leptons

Feynman diagram shows the common decays of the tau by emission of an off-shell W boson. Credit: JabberWok and Time3000.
The arrival direction of the anomalous CR event and air shower are described. Credit: P. W. Gorham, B. Rotter, P. Allison, O. Banerjee, L. Batten, J. J. Beatty, K. Bechtol, K. Belov, D. Z. Besson, W. R. Binns, V. Bugaev, P. Cao, C. C. Chen, C. H. Chen, P. Chen, J. M. Clem, A. Connolly, L. Cremonesi, B. Dailey, C. Deaconu, P. F. Dowkontt, B. D. Fox, J. W. H. Gordon, C. Hast, B. Hill, K. Hughes, J. J. Huang, R. Hupe, M. H. Israel, A. Javaid, J. Lam, K. M. Liewer, S. Y. Lin, T.C. Liu, A. Ludwig, L. Macchiarulo, S. Matsuno, C. Miki, K. Mulrey, J. Nam, C. J. Naudet, R. J. Nichol, A. Novikov, E. Oberla, M. Olmedo, R. Prechelt, S. Prohira, B. F. Rauch, J. M. Roberts, A. Romero-Wolf, J. W. Russell, D. Saltzberg, D. Seckel, H. Schoorlemmer, J. Shiao, S. Stafford, J. Stockham, M. Stockham, B. Strutt, G. S. Varner, A. G. Vieregg, S. H. Wang, S. A. Wissel.{{fairuse}}
The second of three ANITA missions as part of NASA’s Antarctica Long Duration Balloon Flight Campaign was successfully launched at 8:10 a.m. EDT, Dec. 2, 2016. Credit: NASA Goddard Space Flight Center from Greenbelt, MD, USA.{{free media}}

"The other two types of electrically charged leptons in the Standard Model, which can annihilate into photons, are the muons μ and tauons τ with masses Mμ = 105.6 MeV and Mτ =1777 MeV, respectively [466]. It is worth noting that in contrast to the electrons and positrons, the muons and the tauons can not be produced in radioactive decays of atomic nuclei, owing to their superior masses. As such, the maps based on the μ+ + μ and/or τ+ + τ annihilation peaks can provide a cleaner signal and a new information about the sites of enhanced [dark matter] DM concentration which would be complementary to the data obtained from the 511-keV surveys."[25]

The tau was detected in a series of experiments between 1974 and 1977.[26][27][28]

"We have discovered 64 events of the form e+
+ e
e±
+ μ
+ at least two undetected particles for which we have no conventional explanation."[26]

"The advantage of using unstable leptons, rather than using electrons, for tracing DM particles is in their finite lifetime. The tauons have a lifetime of 2.9 × 10−13 s, while the muons have lifetimes of 2.2 μs. Their finite lifetimes provide an unique opportunity for mapping of DM regions with an enhanced precision. Thus, for example, DM particles with masses of the order of Mχ = 100 GeV can either annihilate or decay into muons."[25]

Tau mass is 1776.86 ± 0.12 MeV/c2,[29] mean lifetime is 2.903 ±0 .005 x 10-13 s,[29] electric charge = −1 e,[29] and spin is 1/2[29].

"Since a tauon decays into a light meson (lepton) with neutrino(s), the measurements of angular distribution for tauon on ${\displaystyle {\overline {B}}}$ → D(∗)τ${\displaystyle {\overline {\nu }}_{\tau }}$ are difficult."[30]

The tau is the only lepton that can decay into hadrons – the other leptons do not have the necessary mass. Like the other decay modes of the tau, the hadronic decay is through the weak interaction.[31]

The branching ratio of the dominant hadronic tau decays are:[29]

• 25.49% for decay into a charged pion, a neutral pion, and a tau neutrino;
• 10.82% for decay into a charged pion and a tau neutrino;
• 9.26% for decay into a charged pion, two neutral pions, and a tau neutrino;
• 8.99% for decay into three charged pions (of which two have the same electrical charge) and a tau neutrino;
• 2.74% for decay into three charged pions (of which two have the same electrical charge), a neutral pion, and a tau neutrino;
• 1.04% for decay into three neutral pions, a charged pion, and a tau neutrino.

In total, the tau lepton will decay hadronically approximately 64.79% of the time.

Since the tauonic lepton number is conserved in weak decays, a tau neutrino is always created when a tau decays.[31]

The branching ratio of the common purely leptonic tau decays are:[29]

• 17.82% for decay into a tau neutrino, electron and electron antineutrino;
• 17.39% for decay into a tau neutrino, muon and muon antineutrino.

The similarity of values of the two branching ratios is a consequence of lepton universality.

The tau was anticipated.[32]

An "upward traveling, radio-detected cosmic-ray-like impulsive event [has] characteristics closely matching an extensive air shower. This event, observed in the third flight of the Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload, is consistent with a similar event reported in a previous flight. These events may be produced by the atmospheric decay of an upward-propagating τ-lepton produced by a ντ interaction, although their relatively steep arrival angles create tension with the standard model (SM) neutrino cross section. Each of the two events have a posteriori background estimates of ≲10−2 events. If these are generated by τ-lepton decay, then either the charged-current ντ cross section is suppressed at EeV energies, or the events arise at moments when the peak flux of a transient neutrino source was much larger than the typical expected cosmogenic background neutrinos."[33]

The upward traveling event is detected and described in the image and graph on the lower right. "Top: Interferometric map of the arrival direction of the anomalous CR event 15717147. Bottom: ANITA combined amplitude spectral density (ASD) for the event, from 50-800 MHz, including data from the ANITA Low Frequency Antenna (ALFA). A simulated upward-propagating extensive air shower spectral-density curve is overlain."[33]

## Electrons

"The conventional procedure of delta-ray counting to measure charge (Powell, Fowler, and Perkins 1959), which was limited to resolution sigmaz = 1-2 because of uncertainties of the criterion of delta-ray ranges, has been significantly improved by the application of delta-ray range distribution measurements for 16O and 32S data of 200 GeV per nucleon (Takahashi 1988; Parnell et al. 1989)."[34] Here, the delta-ray tracks in emulsion chambers have been used for "[d]irect measurements of cosmic-ray nuclei above 1 TeV/nucleon ... in a series of balloon-borne experiments".[34]

## Positrons

Measurements "of the cosmic-ray positron fraction as a function of energy have been made using the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument."[35]

"The first flight took place from Fort Sumner, New Mexico, [on May 3, 1994, with a total time at float altitude of 29.5 hr and a mean atmospheric overburden of 5.7 g cm-2] ... The second flight [is] from Lynn Lake, Manitoba, [on August 23, 1995, with a total time at float altitude of 26 hr, and a mean atmospheric overburden of 4.8 g cm-2]".[35]

There is an "unexpected rise of the positron fraction, observed by HEAT and PAMELA experiments, for energies larger than a few GeVs."[36]

"[T]he HEAT balloon experiment [30] ... has mildly indicated a possible positron excess at energies larger than 10 GeV ... In October 2008, the latest results of PAMELA experiment [36] have confirmed and extended this feature [37]."[36]

"The major problems associated with the balloon borne positron measurements are (i) the unique identification against a vast background of protons, and (ii) corrections for the positrons produced in the residual atmosphere."[37]

"[T]o account for the atmospheric corrections ... first [use] the instrument to determine the negative muon spectrum at float altitude. ... [Use this] spectrum ... to normalize the analytically determined atmospheric electron-positron spectra. ... most of the atmospheric electrons and positrons at small atmospheric depths are produced from muon decay at [the energies from 0.85 to 14 GeV]."[37]

## Gamma rays

On June 19, 1988, from Birigüi (50° 20' W 21° 20' S) at 10:15 UTC a balloon launch occurred which carried two NaI(Tl) detectors (600 cm2 total area) to an air pressure altitude of 5.5 mb for a total observation time of 6 hr.[38] The supernova SN1987A in the Large Magellanic Cloud (LMC) was discovered on February 23, 1987, and its progenitor is a blue supergiant (Sk -69 202) with luminosity of 2-5 x 1038 erg/s.[38] The 847 keV and 1238 keV gamma-ray lines from 56Co decay have been detected.[38]

"Gamma rays at energies of 0.3 to 8 megaelectron volts (MeV) were detected on 15 April 1988 from four nuclear-powered satellites including Cosmos 1900 and Cosmos 1932 as they flew over a double Compton gamma-ray telescope."[39]

## X-rays

The MeV Auroral X-ray Imaging and Spectroscopy experiment (MAXIS) is carried aloft by a balloon. Credit: Michael McCarthy and NASA.
Between January 12-30, 2000 the MAXIS balloon successfully circumnavigated the South Pole. Credit: Michael McCarthy.{{free media}}
The Crab Nebula is a remnant of an exploded star. This image shows the Crab Nebula in various energy bands, including a hard X-ray image from the HEFT data taken during its 2005 observation run. Each image is 6′ wide. Credit: CM Hubert Chen, Fiona A. Harrison, Principal Investigator, Caltech Charles J. Hailey, Columbia Principal, Columbia, Finn E. Christensen, DSRI Principal, DSRI, William W. Craig, Optics Scientist, LLNL, Stephen M. Schindler, Project Manager, Caltech.

The MeV Auroral X-ray Imaging and Spectroscopy experiment (MAXIS) was carried aloft by a balloon for a 450 h flight from McMurdo Station, Antarctica. The MAXIS flight detected an auroral X-ray event possibly associated with the solar wind as it interacted with the upper atmosphere between January 22nd and 26th, 2000.[40]

"Between January 12-30, 2000 the MAXIS balloon successfully circumnavigated the South Pole at altitudes of about 120,000 feet and was similar to the 1998 northern hemisphere balloon flight in its science objectives. During the mission, the auroral x-ray instruments on MAXIS recorded an event between 21:20 UT January 19 and 00:20 UT January 20. Also, an auroral x-ray event possibly associated with a shock in the solar wind was observed between January 22-26, 2000."[41]

"The scientific purpose for the MAXIS flight is to study electron precipitation from the magnetosphere into the ionosphere. This electron precipitation creates the aurora (northern and southern lights) along with X-rays which can be observed with our balloon instrumentation. The MAXIS balloon was terminated on January 30, 2000 at 22:13 UT after a successful 450 hour flight. The balloon was cut-down over Victoria Land, approximately 390 nautical miles from McMurdo Station. On February 3, 2000 the recovery team (Steven Peterzen and Robyn Millan) reached the payload via Twin Otter and found the gondola in relatively good condition considering it had come to a stop upside down following landing. The data vault containing the hard drive, the UW x-ray imagers, the BGO detector, and three of the four sun-sensor arrays were among the components successfully recovered."[41]

Balloon flights can carry instruments to altitudes of up to 40 km above sea level, where they are above as much as 99.997% of the Earth's atmosphere. Unlike a rocket where data are collected during a brief few minutes, balloons are able to stay aloft for much longer. However, even at such altitudes, much of the X-ray spectrum is still absorbed. X-rays with energies less than 35 keV (5,600 aJ) cannot reach balloons.

"On July 21, 1964, the Crab Nebula supernova remnant was discovered to be a hard X-ray (15 – 60 keV) source by a scintillation counter flown on a balloon launched from Palestine, Texas, USA."[42] This was likely the first balloon-based detection of X-rays from a discrete cosmic X-ray source.[43]

"The high-energy focusing telescope (HEFT) is a balloon-borne experiment to image astrophysical sources in the hard X-ray (20–100 keV) band.[44] Its maiden flight took place in May 2005 from Fort Sumner, New Mexico, USA. The angular resolution of HEFT is ~1.5'. Rather than using a grazing-angle X-ray telescope, HEFT makes use of a novel tungsten-silicon multilayer coatings to extend the reflectivity of nested grazing-incidence mirrors beyond 10 keV. HEFT has an energy resolution of 1.0 keV full width at half maximum at 60 keV. HEFT was launched for a 25-hour balloon flight in May 2005. The instrument performed within specification and observed [SN 1054] Tau X-1, the Crab Nebula."[42]

One of the recent balloon-borne experiments was called the High-resolution gamma-ray and hard X-ray spectrometer (HIREGS).[45] It was launched from McMurdo Station, Antarctica in December 1991, steady winds carried the balloon on a circumpolar flight lasting about two weeks.

## Optical turbulence profiling

An "in situ technique [measures] the microstructure of the temperature field in our atmosphere. It consists of an autonomous [balloon] payload that computes the structure function of the temperature, along with an off-the-shelf meteorological sonde that gives air pressure, temperature, humidity, and wind speed. This technique, which has been intensively cross-calibrated, gives a high spatiotemporal resolution, [...] to achieve an optical turbulence profile ${\displaystyle C_{N}^{2}(h)}$ with a better than 6 m vertical resolution. It has been designed to allow simultaneous measurements of the temperature structure function in various geometrical configurations."[46]

"Since the 1960s, modern astronomy in the visible range has required quantitative measurements of the optical turbulence strength at different altitudes to improve the seeing at the focus of already existing telescopes and to search for new sites where a new class of instrument (4 m at the beginning and then 8 m and more) could be installed. First, a geographical study was performed to select the best potential areas, and then attention was concentrated on a few sites where intensive investigations were set up, including mast, balloon, and seeing monitors (such as the differential image motion monitor; DIMM), a generalized seeing monitor (GSM), SCIDAR (scintillation detection and ranging), then generalized SCIDAR (GS), and finally meteo- rological models."[46]

"Image motion, blurring, and scintillation are responsible for the majority of loss in angular precision of large, ground-based telescopes, due to phase and amplitude distortion at the entrance pupil. These disturbances occur when the optical beam, un- affected at the top of our atmosphere (≈30 km), reaches the first turbulent layers, which generate refractive index fluctua- tions, mainly related to the temperature turbulent field, in the visible range. In radio and millimeter astronomy, the refractive index is related to humidity changes (Bean & Dutton 1968)."[46]

"The applications [...] come from various site testing campaigns that took place at Aire sur l’Adour, Haute Provence Observatory, and Toulouse in France, Cerro Paranal and Cerro Pachón in Chile, Observatorio Roque del los Muchachos in Spain, and finally South Pole, in Antarctica."[46]

"Modern techniques in astronomy, such as adaptive optics and interferometry, require a precise and quantitative knowledge of seeing 􏰂𝜀, isoplanatic angle 𝜃, coherence time 𝜏, and cone effect d0. These quantities are related to the vertical profiles of ${\displaystyle C_{N}^{2}}$ and ${\displaystyle V(h)}$ above the observatory, along the optical path. The above mentioned quantities are defined within a four-dimensional cube (x, y, z, t), and up to now no experiment exists that is able to assess the optical properties within such a cube. Even GS might give different ${\displaystyle C_{N}^{2}}$ profiles when exploring different parts of the sky, as discussed by Masciadri et al. (2002). In the case of the balloons, they are dragged away by the wind during their ascent. A typical balloon flight will take 1.5 hr to reach 20 km, an altitude at which the balloon might be 100 km away from its launch pad, depending on the wind speed. This distance is much larger than the 20 km radius of a 45􏰁 cone of observation centered around an observatory at 20 km altitude. Nevertheless, a lot of comparisons have been performed in the past with optical devices such as SCIDAR, GS, DIMM, which demonstrate good qualitative and quantitative coherence. This might be explained by (1) the large horizontal extent of the turbulent layers, which fluctuate but remain active over many hours, and (2) the fact that optical turbulence is concentrated within hundreds of thin “laminae” (Coulman et al. 1995), which compensates for the poor accuracy achieved in each layer."[46]

## Submillimeters

BLAST is hanging from the launch vehicle in Esrange near Kiruna, Sweden before launch June 2005. Credit: Mtruch.
NASA's balloon-carried BLAST sub-millimeter telescope is hoisted into launch position on Dec. 25, 2012, at McMurdo Station in Antarctica. Credit: NASA/Wallops Flight Facility.

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a submillimeter telescope that hangs from a high altitude balloon. It has a 2 meter primary mirror that directs light into bolometer arrays operating at 250, 350, and 500 µm. BLAST's primary science goals are:[47]

• Measure photometric redshifts, rest-frame [Far infrared] FIR luminosities and star formation rates of high-redshift starburst galaxies, thereby constraining the evolutionary history of those galaxies that produce the FIR/submillimeter background.
• Measure cold pre-stellar sources associated with the earliest stages of star and planet formation.
• Make high-resolution maps of interstellar medium diffuse galactic emission over a wide range of galactic latitudes.

High-altitude balloons and aircraft can get above [much] of the atmosphere. The BLAST experiment and SOFIA are two examples, respectively, although SOFIA can also handle near infrared observations.

At left above "NASA's balloon-carried BLAST sub-millimeter telescope is hoisted into launch position on Dec. 25, 2012, at McMurdo Station in Antarctica on a mission to peer into the cosmos."[48] The giant helium-filled balloon is slowly drifting about 36 km above Antarctica. It was "[l]aunched on Tuesday (Dec. 25) from the National Science Foundation's Long Duration Balloon (LDB) facility ... This is the fifth and final mission for BLAST, short for the Balloon-borne Large-Aperture Submillimeter Telescope. ... "BLAST found lots of so-called dark cores in our own Milky Way — dense clouds of cold dust that are supposed to be stars-in-the-making. Based on the number of dark cores, you would expect our galaxy to spawn dozens of new stars each year on average. Yet, the galactic star formation rate is only some four solar masses per year." So why is the stellar birth rate in our Milky Way so low? Astronomers can think of two ways in which a dense cloud of dust is prevented from further contracting into a star: turbulence in the dust, or the collapse-impeding effects of magnetic fields. On its new mission, BLAST should find out which process is to blame. ... [The 1800-kilogram] stratospheric telescope will observe selected star-forming regions in the constellations Vela and Lupus."[49]

## Microwaves

WMAP 3-year Power spectrum of CMB is compared to recent measurements of BOOMERanG, CBI, VSA and ACBAR. Credit: NASA/WMAP Science Team. {{free media}}

The figure at the right "shows the three-year WMAP spectrum compared to a set of recent balloon and ground-based measurements that were selected to most complement the WMAP data in terms of frequency coverage and l range. The non-WMAP data points are plotted with errors that include both measurement uncertainty and cosmic variance, while the WMAP data in this l range are largely noise dominated, so the effective error is comparable. When the WMAP data are combined with these higher resolution CMB measurements, the existence of a third acoustic peak is well established, as is the onset of Silk damping beyond the 3rd peak."[50]

## Milky Way

"By using a balloon borne telescope, an extensive survey of the [CII] line emission of the Galaxy has been undertaken. To minimize the instrumental emission, an off-axis telescope with a Newtonian-Nasmyth focus was used in conjunction with a liquid helium cooled Fabry-Perot spectrometer. The beam size of the telescope was 12' in diameter and the spectral resolution of the spectrometer was 175 km/s in velocity scale."[51]

"The balloon flights were made from Palestine, TX in 1991 and from Alice Springs, Australia in 1992. By both observations, the major part of the galactic plane in the northern sky and the southern sky has been scanned. As a result, a complete map of the [CII] line intensity distribution has been constructed for the region from—100° to 80° in galactic longitude and within ±4° in galactic latitude. In addition to the general scan of the galactic plane, the observations were extended to some individual sources, such as Cyg-X region, p-Oph dark cloud and Large Magellanic Cloud."[51]

"The observed maps reveal strong [CII] line emission extensively distributed in the galactic plane, as well as many discrete sources associated with HII regions and/or molecular clouds. The distribution is more or less correlated with far infrared continuum and CO line intensity distributions."[51]

## Cygnus X-1

The X-ray emitter Cygnus X-1, in the constellation of Cygnus, is imaged by a balloon born telescope. Credit: NASA/Marshall Space Flight Center.{{free media}}

A balloon was launched for the High Energy Replicated Optics project on May 23, 2001, from Fort Sumner, New Mexico, USA, reaching an altitude of 39 km. Using a telescope containing unique X-ray mirrors, a team from NASA's Marshall Space Flight Center in Huntsville, Ala., has obtained the world's first focused high-energy X-ray images of any astronomical object, e.g., Cygnus X-1.

"This is the first step toward opening the high-energy, or 'hard,' X-ray spectrum for high sensitivity exploration."[52]

"The ability to collect focused hard X-ray images has the potential of allowing us to observe objects in the heavens which are 10 to 100 times fainter than those which can be detected with current instruments. This development gives us new eyes - enabling new understanding about our violent universe."[52]

"The [High Energy Replicated Optics] HERO team launched the experimental telescope on May 23, 2001, from Fort Sumner, N.M., using a 40 million cubic-foot (1.1 million cubic-meter) balloon that carried the payload to an altitude of 128,000 feet (39,000 meters). At this altitude, the telescope is above 99.7 percent of Earth's atmosphere, which absorbs X-rays and many other wavelengths of electromagnetic radiation."[52]

"An image of the Cygnus X-1 binary star system [on the right] is the second of the first two focused high-energy X-ray images of any astronomical object. The images were captured by a team from NASA's Marshall Space Flight Center on May 23 using a telescope containing unique X-ray mirrors."[52]

## Galactic center

On November 25, 1970, from Paraná, Argentina, latitude 32° S, "[a] balloon-altitude observation was conducted ... of the galactic-center region, at energies between 23 and 930 keV. ... evidence for a spectral feature at 0.5 MeV is [detected]."[53] The radiation detected over about 300 to 103 keV fit a power law of

N(E) = (10.5 ± 2.2) E-(2.37±0.05) photons cm-2 s-1 keV-1.[53]

The 0.5 MeV peak is broad at 473 ± 30 keV and "is consistent with a single γ-ray spectral line [of flux] (1.8 ± 0.5) x 10-3 photons cm-2 s-1 keV-1 at the top of the Earth's atmosphere ... Gamma-ray lines in the 0.5-MeV energy region may arise from either the annihilation of positrons or from the de-excitation of nuclei. However, it seems likely, on the basis of evidence presented herein, that the energy of the peak is not at 0.511 MeV (unless the radiation is redshifted by ~0.07 in energy)."[53].

More recent measurements from 1979 through 2003 with germanium detectors observed the peak at 511 keV.[54] "[A] single point source is inconsistent with the data. Formally, we cannot exclude the possibility that the emission originates in at least 2 point sources."[54]

## Technology

It is discovered in an early balloon flight by experimenters in the 1960s that passive collimators or shields, made of materials such as lead, actually increase the undesired background rate, due to the intense showers of secondary particles and photons produced by the extremely high energy (GeV) particles characteristic of the space radiation environment.

## Facilities

The Columbia Scientific Balloon Facility operates and launches balloons from its remote site in Fort Sumner, New Mexico, USA. The Columbia Scientific Balloon Facility (CSBF) itself is located in Palestine, Texas, from which earlier balloon launches took place.

## Hypotheses

1. The use of satellites should provide ten times the information as sounding rockets or balloons.

A control group for a radiation satellite would contain

1. a radiation astronomy telescope,
2. a two-way communication system,
3. a positional locator,
4. an orientation propulsion system, and
5. power supplies and energy sources for all components.

A control group for radiation astronomy satellites may include an ideal or rigorously stable orbit so that the satellite observes the radiation at or to a much higher resolution than an Earth-based ground-level observatory is capable of.

## References

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