NASA balloon program Analysis Group recently presented a roadmap to NASA to guide them on how to plan and fund future balloon astronomy programs. Balloons have been used for over a century to conduct physics experiments, astronomical observations and Earth observation work, but remain relatively unknown to the general public. Balloon astronomy shares many advantages with space telescopes, but at a fraction of the cost.
The first modern scientific experiment based on balloons took place in 1912 when Austrian physicist Victor Hess raised 3 electroscopes to an altitude of over 17,000 feet (although meteorologists used balloons to measure air temperature at different altitudes from the end of the 19th century).
Hess was trying to prove that background radiation emanates from radioactive minerals in the ground, but instead found that levels of ionizing radiation actually increased at high altitudes. This experiment, which discovered the high-speed particles we now call cosmic rays, and which won Hess a Nobel Prize, marked the beginning of the field of high-energy astrophysics.
Modern balloon missions serve a wide range of scientific fields. Observations of cosmic rays are a valuable source of data for particle physics experiments. Cosmic ray particles often carry energies far beyond what scientists can achieve at particle accelerators like the Large Hadron Collider, so these missions can collect valuable data by monitoring collisions between cosmic rays and molecules. of air in the upper atmosphere.
But balloons often also perform more traditional astronomical observations. Small telescopes (less than a meter wide) are often hoisted above the atmosphere to study exoplanets. They can directly observe protoplanetary dust belts around stars and detect new exoplanets using the transit method.
The high altitude of balloon flights means that infrared (IR) telescopes can be placed above the water vapor in our atmosphere. Because water vapor absorbs infrared light very efficiently, these telescopes can make high-resolution observations of very faint stars that would be impossible from the ground. Likewise, radio telescopes operating in the terahertz (THz) band, which is also blocked by atmospheric water vapor, can be lifted high enough to study the interstellar medium.
Advantages of the ball
Balloons can position scientific instruments and observatories high enough to gain many of the advantages of observatories in space, but with few disadvantages.
The most obvious advantage of balloons over satellites is their cost; the James Webb Space Telescope (JWST) costs nearly $9 billion, and even modern commercial launchers, with their reusable rockets, are still beyond the reach of smaller research programs and institutes. Balloons can lift extremely large and heavy payloads to the far reaches of space and stay aloft for long periods of time, at a tiny fraction of the price of a rocket launch.
Because these missions are inexpensive, they can tolerate a much higher level of risk. This not only means that junior or undergraduate researchers can get directly involved in the development of the instruments, but also that the experiment can be more ambitious; it’s much easier to accept a failed experiment if it didn’t cost too much!
Balloon missions also have a very high recovery rate. Satellites tend to either be dropped in space or re-enter the atmosphere. Balloon missions, on the other hand, are usually equipped with GPS receivers and constantly transmit telemetry, so their owners know exactly where to find them, and then they eventually return to Earth.
Testing and development
One of the effects of the benefits listed above is that balloons are often used as a test bed for new observation technologies and instruments. Many instruments sent into space, both in orbital observatories and on probes sent to other planets, are based on designs first tested in balloons.
For example, scintillating fiber optic hodoscopes are instruments that detect cosmic rays and are commonly used in space. One was used in the Cosmic Ray Isotope Spectrometer (CRIS), which has worked flawlessly on the ACE spacecraft for 23 years.
Another is part of the CALorimetric Electron Telescope (CALET), which has been working on the International Space Station (ISS) since 2015. These instruments were first used with balloon cosmic ray experiments, and therefore benefited from years development and testing. even before being launched into space.
Similarly, the payload for Matter Antimatter Exploration and Light Nucleus Astrophysics (PAMELA) and the second ISS Magnetic Alpha Spectrometer (AMS02) both rely on instrumentation originally designed for high altitudes close to space where balloons operate.
Balloons used for balloon astronomy have three basic design requirements: they must be able to float at very high altitudes, they must be able to lift heavy payloads, and they must be able to fly for a very long time before returning to Earth.
Helium balloons are only partially filled at launch. As they rise and atmospheric pressure drops, the helium inside the balloon expands so that it is only fully inflated when it reaches its working altitude and bursts not going up. It’s not a stable situation, however. As the local temperature and pressure change, the gas inside the balloon expands and shrinks, causing the balloon to rise or fall to different altitudes, or even burst. To handle this, NASA uses two different designs.
Zero pressure balloons (ZPB) carry a supply of ballast or helium and are able to control their altitude as needed. If a ZPS balloon begins to rise too high, it vents some of the gas, slightly deflating the balloon, and if it begins to fall, it can either re-inflate the balloon or drop some ballast. This is a very effective method of maintaining a stable altitude, but it limits the life of the mission – when the gas or ballast runs out, it can no longer maintain altitude and must descend.
Super Pressure Balloons (SPB) are made from much stronger materials – they don’t stretch, so the gas volume doesn’t change during flight. This requires the gas inside the balloon to be at a higher pressure than the surrounding atmosphere at all times, hence its name. SPBs are designed to maintain a relatively constant altitude during the day-night cycle, without the need to carry consumables, allowing them to perform missions for very long periods of time.
ZPBs can fly for up to eight weeks during the Antarctic summer, but typically they only handle shorter flights of a few days. They can hoist payloads of up to about 4 tons in the lower stratosphere, but less than a ton in the upper stratosphere. SPBs, on the other hand, can handle flights of up to 100 days, but cannot fly as high as ZPBs, nor can they handle such heavy payloads.
This article was originally published on Universe today by Allen Versfeld. Read the original article here.