Solar balloon

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A 10-foot solar "tetroon" Cm529 sb 10ftet.jpg
A 10-foot solar "tetroon"
A 4 meters high solar balloon floats over a meadow. Solarballon Hot 18 Wikipedia.jpg
A 4 meters high solar balloon floats over a meadow.

A solar balloon is a balloon that gains buoyancy when the air inside is heated by solar radiation, usually with the help of black or dark balloon material. The heated air inside the solar balloon expands and has lower density than the surrounding air. As such, a solar balloon is similar to a hot air balloon. Usage of solar balloons is predominantly in the toy market, although it has been proposed that they be used in the investigation of planet Mars, and some solar balloons are large enough for human flight. A vent at the top can be opened to release hot air for descent and deflation.

Contents

Theory of operation

Generating lift

Thermal image showing temperature variation in a hot air balloon Infarot 9.jpg
Thermal image showing temperature variation in a hot air balloon

Raising the air temperature inside the envelope makes it less dense than the surrounding (ambient) air. The balloon floats because of the buoyant force exerted on it. This force is the same force that acts on objects when they are in water and is described by Archimedes' principle. The amount of lift (or buoyancy) provided by a hot air balloon depends primarily upon the difference between the temperature of the air inside the envelope and the temperature of the air outside the envelope.

The lift generated by 100,000 ft3 (2831.7 m3) of dry air heated to various temperatures may be calculated as follows:

air temperatureair densityair masslift generated
68 °F, 20 °C1.2041 kg/m37517 lb, 3409.7 kg0 lbf, 0 kgf
210 °F, 99 °C0.9486 kg/m35922 lb, 2686.2 kg1595 lbf, 723.5 kgf
250 °F, 120 °C0.8978 kg/m35606 lb, 2542.4 kg1912 lbf, 867.3 kgf

The density of air at 20 °C, 68 °F is about 1.2 kg/m3. The total lift for a balloon of 100,000 cu ft heated to (99 °C, 210 °F) would be 1595 lbf, 723.5 kgf. In reality, the air contained in the envelope is not all the same temperature, as the accompanying thermal image shows, and so these calculations are based on averages.

For typical atmospheric conditions (20 °C, 68 °F), a hot air balloon heated to (99 °C, 210 °F) requires about 3.91 m3 of envelope volume to lift 1 kilogram (62.5 cu ft/lb). The precise amount of lift provided depends not only upon the internal temperature mentioned above, but the external temperature, altitude above sea level, and humidity of the surrounding air. On a warm day, a balloon cannot lift as much as on a cool day, because the temperature required for launch will exceed the maximum sustainable for the envelope fabric. Also, in the lower atmosphere, the lift provided by a hot air balloon decreases about 3% for each 1,000 meters (1% per 1,000 ft) of altitude gained. [1]

Solar radiation

Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter (W/m2). Direct insolation is the solar irradiance measured at a given location on Earth with a surface element perpendicular to the Sun's rays, excluding diffuse insolation (the solar radiation that is scattered or reflected by atmospheric components in the sky). Direct insolation is equal to the solar constant minus the atmospheric losses due to absorption and scattering. While the solar constant varies with the Earth-Sun distance and solar cycles, the losses depend on the time of day (length of light's path through the atmosphere depending on the Solar elevation angle), cloud cover, moisture content, and other impurities.

Over the course of a year the average solar radiation arriving at the top of the Earth's atmosphere is roughly 1,366 watts per square meter [2] [3] (see solar constant). The radiant power is distributed across the entire electromagnetic spectrum, although most of the power is in the visible light portion of the spectrum. The Sun's rays are attenuated as they pass through the atmosphere, thus reducing the insolation at the Earth's surface to approximately 1,000 watts per square meter for a surface perpendicular to the Sun's rays at sea level on a clear day.

A black body absorbs all the radiation that hits it. Real world objects are gray objects, with their absorption being equal to their emissivity. Black plastic might have an emissivity of around 0.95, meaning 95 percent of all radiation that hits it will be absorbed, and the remaining 5 percent reflected.

Estimating energy received

[ verification needed ]

A great circle divides the sphere in two equal hemispheres Great circle hemispheres.png
A great circle divides the sphere in two equal hemispheres

If the balloon is imagined as a sphere, the sunlight received by this sphere can be imagined as the cross-section of a cylinder with the same radius as this sphere, see diagram. The area of this circle can be calculated via:

For example, the energy received by a spherical, 5 metre radius, solar balloon with an envelope of black plastic on a clear day with direct insolation of 1000 W/m2, can be estimated by first calculating the area of its great circle:

Then multiplying this with the emissivity of the plastic and the direct insolation of the Sun:

78.54 * 0.95 * 1000 = 74,613 Watts

At sea level at 15 °C at ISA (International Standard Atmosphere), air has a density of approximately 1.22521 kg/m3. The density of air decreases with higher temperatures, at the rate of around 20 grams per m3 per 5 K. Around 1 kilojoules of energy is needed to heat 1 kilogram of dry air by one kelvin (see heat capacity). So, to increase the temperature of 1 m3 of air (at sea level and at 15 °C) 5 °C requires around 5 °C * 1 kilojoules/(kilogram*kelvin) * 1.225 kilograms = 6.125 kilojoules. By doing so, you've reduced the mass of 1 m3 of air by around 24 grams. On a clear day with a black body surface of 1 m2 perpendicular to the Sun and no heat loss, this would take a little over 6 seconds.

Estimating rate of energy lost

Below is the energy balance equation of the rate of energy lost of a solar balloon when drawing the boundary line around the balloon. The Solar Balloon experiences heat transfer due to convection and heat transfer due to radiation.

Ėout= tσπr2(TS4-TF4) + hπr2(TS-TF)

Estimated Change in Entropy

Tds=du+PdV

Δs = ∫(cv/T)dT + Rgasln(V2/V1)

Δs = cvln(T2/T1)

Equilibrium

The system is in equilibrium when the energy lost from the balloon through convection, radiation and conduction, equals the energy received through radiation from the Sun.

History

In 1972, Dominic Michaelis, a British architect and the inventor of many solar utilities and projects, invented and built the first solar balloon, with a clear external surface and dark, heat-catching internal walls. [4] [5]

Manned flight

The first human-carrying pure solar balloon flight was made on 1 May 1973 by Tracy Barnes in his balloon 'Barnes Solar Firefly Tetrahedron'. This balloon was made from a spiral tube of fabric that was formed into a tetrahedron. Dominic Michaelis is recorded as having owned the first pure solar balloon in Europe. This balloon was flown by Julian Nott across the English Channel. Records compiled for the FAI show that on 6 February 1978 Iranian Frederick Eshoo also made a solar flight in a balloon called Sunstat. This used a standard balloon design, but used clear plastic on one side, allowing the Sun's radiation to reflect off the inner surface, heating the inside air. [6]

First antarctic solar weather balloon flight

The first 100% solar weather probe, named Ballon ORA, was launched from the French Antarctic Dumont d'Urville Station in January 2011 by a joint team of students, scientists and engineers. The idea was to assess the feasibility of using solar balloons as probes in remote area, where saving the use of lifting gas, helium or hydrogen, would be precious. The flight was a success, approaching 46,000 ft (14,000 m). The savings do not only concern the lifting gas in itself. The ORA Balloon alleviates the need for the transportation, in and out, of the heavy gas canisters. [7]

Use in planetary exploration

California Institute of Technology's Jet Propulsion Laboratory has conducted a study on the use of solar balloons on several planets and moons in the solar system, concluding they are a viable option for Mars, Jupiter and Saturn. [8]

Safety

Planning and airspace permission may be required by local or national airspace authorities.

Manned flights carry special risks. Unexpected clouds pose a serious risk, akin to regular hot air ballooning without reserve fuel. Solar balloons can descend rapidly when cooling occurs, making ballast very important.

Related Research Articles

<span class="mw-page-title-main">Solar energy</span> Radiant light and heat from the Sun, harnessed with technology

Solar energy is radiant light and heat from the Sun that is harnessed using a range of technologies such as solar power to generate electricity, solar thermal energy, and solar architecture. It is an essential source of renewable energy, and its technologies are broadly characterized as either passive solar or active solar depending on how they capture and distribute solar energy or convert it into solar power. Active solar techniques include the use of photovoltaic systems, concentrated solar power, and solar water heating to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light-dispersing properties, and designing spaces that naturally circulate air.

<span class="mw-page-title-main">Sunlight</span> Light emitted by the Sun

Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere as daylight when the Sun is above the horizon. When direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat (atmospheric). When blocked by clouds or reflected off other objects, sunlight is diffused. Sources estimate a global average of between 164 watts to 340 watts per square meter over a 24-hour day; this figure is estimated by NASA to be about a quarter of Earth's average total solar irradiance.

<span class="mw-page-title-main">Hot air balloon</span> Lighter-than-air aircraft

A hot air balloon is a lighter-than-air aircraft consisting of a bag, called an envelope, which contains heated air. Suspended beneath is a gondola or wicker basket, which carries passengers and a source of heat, in most cases an open flame caused by burning liquid propane. The heated air inside the envelope makes it buoyant, since it has a lower density than the colder air outside the envelope. As with all aircraft, hot air balloons cannot fly beyond the atmosphere. The envelope does not have to be sealed at the bottom, since the air inside the envelope is at about the same pressure as the surrounding air. In modern sport balloons the envelope is generally made from nylon fabric, and the inlet of the balloon is made from a fire-resistant material such as Nomex. Modern balloons have been made in many shapes, such as rocket ships and the shapes of various commercial products, though the traditional shape is used for most non-commercial and many commercial applications.

<span class="mw-page-title-main">Aerobot</span>

An aerobot is an aerial robot, usually used in the context of an uncrewed space probe or unmanned aerial vehicle.

<span class="mw-page-title-main">Passive solar building design</span> Architectural engineering that uses the Suns heat without electric or mechanical systems

In passive solar building design, windows, walls, and floors are made to collect, store, reflect, and distribute solar energy, in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design because, unlike active solar heating systems, it does not involve the use of mechanical and electrical devices.

Direct insolation is the insolation measured at a given location on Earth with a surface element perpendicular to the Sun's rays, excluding diffuse insolation. Direct insolation is equal to the solar irradiance above the atmosphere minus the atmospheric losses due to absorption and scattering. While the solar irradiance above the atmosphere varies with the Earth–Sun distance and solar cycles, the losses depend on the time of day, cloud cover, humidity, and other impurities.

<span class="mw-page-title-main">Thermal</span> Column of rising air in the lower altitudes of Earths atmosphere

A thermal column is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example of convection, specifically atmospheric convection.

<span class="mw-page-title-main">Solar thermal collector</span> Device that collects heat

A solar thermal collector collects heat by absorbing sunlight. The term "solar collector" commonly refers to a device for solar hot water heating, but may refer to large power generating installations such as solar parabolic troughs and solar towers or non-water heating devices such as solar cookers or solar air heaters.

<span class="mw-page-title-main">Balloon (aeronautics)</span> Type of aerostat that remains aloft due to its buoyancy

In aeronautics, a balloon is an unpowered aerostat, which remains aloft or floats due to its buoyancy. A balloon may be free, moving with the wind, or tethered to a fixed point. It is distinct from an airship, which is a powered aerostat that can propel itself through the air in a controlled manner.

<span class="mw-page-title-main">Solar irradiance</span> Measurement of electromagnetic radiation

Solar irradiance is the power per unit area received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre (W/m2) in SI units.

This is a list of meteorology topics. The terms relate to meteorology, the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting.

<span class="mw-page-title-main">Ed Yost</span> American balloonist inventor

Paul Edward Yost was the American inventor of the modern hot air balloon and is referred to as the "Father of the Modern Day Hot-Air Balloon." He worked for a high-altitude research division of General Mills in the early 1950s until he left to establish Raven Industries in 1956, along with several colleagues from General Mills.

<span class="mw-page-title-main">Colonization of Venus</span> Proposed colonization of the planet Venus

The colonization of Venus has been a subject of many works of science fiction since before the dawn of spaceflight, and is still discussed from both a fictional and a scientific standpoint. However, with the discovery of Venus's extremely hostile surface environment, attention has largely shifted towards the colonization of the Moon and Mars instead, with proposals for Venus focused on habitats floating in the upper-middle atmosphere and on terraforming.

<span class="mw-page-title-main">Hot air ballooning</span> Activity of flying hot air balloons

Hot air ballooning is the recreational and competitive adventure sport of flying hot air balloons. Attractive aspects of ballooning include the exceptional quiet, the lack of a feeling of movement, and the bird's-eye view. Since the balloon moves with the direction of the winds, the passengers feel absolutely no wind, except for brief periods during the flight when the balloon climbs or descends into air currents of different direction or speed. Hot air ballooning has been recognized by Fédération Aéronautique Internationale (FAI) as the safest air sport in aviation, and fatalities in hot air balloon accidents are rare, according to statistics from the National Transportation Safety Board (NTSB).

<span class="mw-page-title-main">Julian Nott (balloonist)</span> American balloonist (1944–2019)

Julian Nott was a British balloonist who later lived in Santa Barbara, California. He was known for his record-setting achievements. Nott set 79 world ballooning records and 96 British aviation records. He developed balloons for flights to Solar System destinations, particularly Titan. He flew a working prototype Titan balloon at minus 175 Celsius, approximately the temperature of Titan's atmosphere.

A lifting gas or lighter-than-air gas is a gas that has a density lower than normal atmospheric gases and rises above them as a result, making it useful in lifting lighter-than-air aircraft. Only certain lighter than air gases are suitable as lifting gases. Dry air has a density of about 1.29 g/L at standard conditions for temperature and pressure (STP) and an average molecular mass of 28.97 g/mol, and so lighter-than-air gases have a density lower than this.

<span class="mw-page-title-main">Solar air heat</span> Solar thermal technology

Solar air heating is a solar thermal technology in which the energy from the sun, insolation, is captured by an absorbing medium and used to heat air. Solar air heating is a renewable energy heating technology used to heat or condition air for buildings or process heat applications. It is typically the most cost-effective out of all the solar technologies, especially in commercial and industrial applications, and it addresses the largest usage of building energy in heating climates, which is space heating and industrial process heating.

<span class="mw-page-title-main">Dominic Michaelis</span> French inventor

Dominic Michaelis was an Anglo-French architect, inventor, and solar energy advocate.

The following outline is provided as an overview of and topical guide to solar energy:

Exposing Microorganisms in the Stratosphere (E-MIST) is a NASA study to determine if a specific microorganism could survive conditions like those on the planet Mars. The study transported Bacillus pumilus bacteria and their spores by helium-filled balloon to the stratosphere of Earth and monitored the ability of the microorganisms to survive in extreme Martian-like conditions such as low pressure, dryness, cold, and ionizing radiation.

References

  1. "How to Calculate the Weight of Air and Model Hot Air Balloon Lift" . Retrieved 2008-01-01.
  2. Satellite observations of total solar irradiance
  3. "Construction of a Composite Total Solar Irradiance (TSI) Time Series from 1978 to present". Figure 4 & figure 5. Archived from the original on August 1, 2011. Retrieved February 2, 2009.
  4. "Solar Balloons, a very short History" . Retrieved 2011-04-11.
  5. "The solar hot air balloons of Dominic Michaelis" . Retrieved 2011-04-11.
  6. "School Project Information - Solar Ballooning" . Retrieved 2009-07-18. According to Ballooning magazine article "Sunstat - a balloon that rides on sunbeams (Ballooning Journal, Vol XI Num 2, March April 1978)" (PDF). Retrieved 2011-04-11.
  7. "Ballon ORA". Ecole Centrale Lyon. Retrieved 2011-01-30.
  8. "Inflatable robotics for planetary applications" (PDF). Beacon eSpace at Jet Propulsion Laboratory. Archived from the original (PDF) on 2010-05-26. Retrieved 2011-04-09.