Advantages of stratospheric balloons as scientific instrument platforms include:
- Stratospheric balloons fly above 99.5% of Earth atmosphere giving access to spectral bands not observable from ground-based observatories or airborne platforms like the SOFIA aircraft.
- Stratospheric balloons fly above the turbulent air mass that can degrade the quality of images being captured by the various sensors onboard the balloon platform.
- Balloon-platforms provide access to near-space at a fraction of the cost of spacecraft missions. Typical balloon mission development costs range from about $5 million to $10 million and typical balloon launch costs range from about $500,000 to about $1.5 million – a fraction of what spacecraft mission development and spacecraft launch vehicles cost.
- Balloon payloads can be recovered more than 95 percent of the time. These payloads can be refurbished and re-flown multiple times. Plus, since the payload is still within the protection of the Earth’s radiation belts, there is no need for radiation-hardened electronics.
- Since balloon missions are developed on relatively quick time-scales (within a year or two), they are perfect training opportunities for young space engineers & scientists.
How does the atmosphere interfere with viewing comets?
The atmosphere is relatively clear at visible wavelengths but is opaque at many other wavelengths. It acts like a filter of light, hindering our ability to observe objects in deep space, in our Solar System, and beyond. Specifically, CO2 and water vapor within the atmosphere absorb the wavelengths of these same species from comets, which are what BOPPS will observe. So BOPPS needs to fly at high altitude, above nearly the entire atmosphere, in order to observe the comet emissions before they are absorbed.
The atmosphere also bends rays of light irregularly as they pass through turbulent air masses, causing stars to twinkle as we watch them, and causing stars in images to become fuzzy instead of sharp points. These effects are called “seeing”. By flying in the stratosphere, above most of the atmospheric turbulence, scientific balloon platforms can see sharper images, undistorted by atmospheric seeing. BOPPS carries the UVVis instrument, which will demonstrate image stabilization with its fine steering mirror.
Finally the atmosphere emits light, including both thermal emissions and scattered sunlight. The atmospheric emissions are a source of background which must be removed to measure the signal from an object in deep space. If the atmosphere is too bright, it may be difficult to see the tiny contribution from the object. When the Sun is up, and the sky is bright, you can’t see the stars, but when the Sun goes down and the sky becomes dark, you can see the stars through the atmosphere (unless it is cloudy).
So the atmosphere can block the light from objects in space, absorbing particular wavelengths; it bends the light and blurs images; and it emits light (also at particular wavelengths). In all these ways it interferes with observations of objects in deep space.
The BOPPS ballooncraft is made of two primary components.
First is the large, helium-filled balloon, also referred to as a stratospheric scientific balloon, which will lift the scientific payload into the stratosphere to altitudes as high as 130,000 ft, almost into space. BOPPS will use a 40 million cubic foot balloon which is, when fully inflated at altitude, longer from the top of the balloon to the payload than the height of the Washington Monument. An entire football field could fit inside the balloon when it is inflated. It is made of more than 22 acres of thin (0.0008 inch) polyethylene film.
Second is the gondola, an aluminum structure which houses the scientific instrument payload. The payload includes a refurbished telescope with sensors in the near-infrared, near ultra-violet and visible wavelength ranges.