Eight Things To Know About Our Flying Observatory

Eight Things to Know About Our Flying Observatory

Our flying observatory, called SOFIA, is the world’s largest airborne observatory. It is a partnership with the German Aerospace Center (DLR). SOFIA studies the life cycle of stars, planets (including Pluto’s atmosphere), how interstellar dust can contribute to planet formation, analyzes the area around black holes, and identifies complex molecules in space.

1. A Telescope in an Airplane

SOFIA stands for the Stratospheric Observatory for Infrared Astronomy. It is a Boeing 747SP aircraft that carries a 100-inch telescope to observe the universe while flying between 38,000 and 45,000 feet – the layer of Earth’s atmosphere called the stratosphere.

2. The Short Aircraft Means Long Flights

SP stands for “special performance.” The plane is 47 feet shorter than a standard 747, so it’s lighter and can fly greater distances. Each observing flight lasts 10-12 hours.

3. It Flies with A Hole in the Side of the Plane…

The telescope is behind a door that opens when SOFIA reaches altitude so astronomers on board can study the universe. The kind of light SOFIA observes, infrared, is blocked by almost all materials, so engineers designed the side of the aircraft to direct air up-and-over the open cavity, ensuring a smooth flight.

4. …But the Cabin is Pressurized!

A wall, called a pressure bulkhead, was added between the telescope and the cabin so the team inside the aircraft stays comfortable and safe. Each flight has pilots, telescope operators, scientists, flight planners and mission crew aboard.

5. This Telescope Has to Fly

Water vapor in Earth’s atmosphere blocks infrared light from reaching the ground. Flying at more than 39,000 feet puts SOFIA above more than 99% of this vapor, allowing astronomers to study infrared light coming from space. The airborne observatory can carry heavier, more powerful instruments than space-based observatories because it is not limited by launch weight restrictions and solar power.

6. Studying the Invisible Universe

Humans cannot see what is beyond the rainbow of visible light. However, many interesting astronomical processes happen in the clouds of dust and gas that often surround the objects SOFIA studies, like newly forming stars. Infrared light can pass through these clouds, allowing astronomers to study what is happening inside these areas.

7. The German Telescope

The telescope was built our partner, the German Aerospace Center, DLR. It is made of a glass-ceramic material called Zerodur that does not change shape when exposed to extremely cold temperatures. The telescope has a honeycomb design, which reduces the weight by 80%, from 8,700 lb to 1,764 lb. (Note that the honeycomb design was only visible before the reflective aluminum coating was applied to the mirror’s surface).

8. ZigZag Flights with a Purpose

The telescope can move up and down, between 20-60 degrees above the horizon. But it can only move significantly left and right by turning the whole aircraft. Each new direction of the flight means astronomers are studying a new celestial object. SOFIA’s flight planners carefully map where the plane needs to fly to best observe each object planned for that night.

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Voyager: The Spacecraft

The twin Voyager 1 and 2 spacecraft are exploring where nothing from Earth has flown before. Continuing their more-than-40-year journey since their 1977 launches, they each are much farther away from Earth and the Sun than Pluto.

The primary mission was the exploration of Jupiter and Saturn. After making a string of discoveries there – such as active volcanoes on Jupiter’s moon Io and intricacies of Saturn’s rings – the mission was extended.

Voyager 2 went on to explore Uranus and Neptune, and is still the only spacecraft to have visited those outer planets. The adventurers’ current mission, the Voyager Interstellar Mission (VIM), will explore the outermost edge of the Sun’s domain. And beyond.

Spacecraft Instruments

‘BUS’ Housing Electronics

The basic structure of the spacecraft is called the “bus,” which carries the various engineering subsystems and scientific instruments. It is like a large ten-sided box. Each of the ten sides of the bus contains a compartment (a bay) that houses various electronic assemblies.

Cosmic Ray Subsystem (CRS)

The Cosmic Ray Subsystem (CRS) looks only for very energetic particles in plasma, and has the highest sensitivity of the three particle detectors on the spacecraft. Very energetic particles can often be found in the intense radiation fields surrounding some planets (like Jupiter). Particles with the highest-known energies come from other stars. The CRS looks for both.

High-Gain Antenna (HGA)

The High-Gain Antenna (HGA) transmits data to Earth on two frequency channels (the downlink). One at about 8.4 gigahertz, is the X-band channel and contains science and engineering data. For comparison, the FM radio band is centered around 100 megahertz.

Imaging Science Subsystem (ISS)

The Imaging Science Subsystem (ISS) is a modified version of the slow scan vidicon camera designed that were used in the earlier Mariner flights. The ISS consists of two television-type cameras, each with eight filters in a commandable Filter Wheel mounted in front of the vidicons. One has a low resolution 200 mm wide-angle lens, while the other uses a higher resolution 1500 mm narrow-angle lens.

Infrared Interferometer Spectrometer and Radiometer (IRIS)

The Infrared Interferometer Spectrometer and Radiometer (IRIS) actually acts as three separate instruments. First, it is a very sophisticated thermometer. It can determine the distribution of heat energy a body is emitting, allowing scientists to determine the temperature of that body or substance.

Second, the IRIS is a device that can determine when certain types of elements or compounds are present in an atmosphere or on a surface.

Third, it uses a separate radiometer to measure the total amount of sunlight reflected by a body at ultraviolet, visible and infrared frequencies.

Low-Energy Charged Particles (LECP)

The Low-Energy Charged Particles (LECP) looks for particles of higher energy than the Plasma Science instrument, and it overlaps with the Cosmic Ray Subsystem (CRS). It has the broadest energy range of the three sets of particle sensors.

The LECP can be imagined as a piece of wood, with the particles of interest playing the role of the bullets. The faster a bullet moves, the deeper it will penetrate the wood. Thus, the depth of penetration measures the speed of the particles. The number of “bullet holes” over time indicates how many particles there are in various places in the solar wind, and at the various outer planets. The orientation of the wood indicates the direction from which the particles came.

Magnetometer (MAG)

Although the Magnetometer (MAG) can detect some of the effects of the solar wind on the outer planets and moons, its primary job is to measure changes in the Sun’s magnetic field with distance and time, to determine if each of the outer planets has a magnetic field, and how the moons and rings of the outer planets interact with those magnetic fields.

Optical Calibration Target The target plate is a flat rectangle of known color and brightness, fixed to the spacecraft so the instruments on the movable scan platform (cameras, infrared instrument, etc.) can point to a predictable target for calibration purposes.

Photopolarimeter Subsystem (PPS)

The Photopolarimeter Subsystem (PPS) uses a 0.2 m telescope fitted with filters and polarization analyzers. The experiment is designed to determine the physical properties of particulate matter in the atmospheres of Jupiter, Saturn and the rings of Saturn by measuring the intensity and linear polarization of scattered sunlight at eight wavelengths.

The experiment also provided information on the texture and probable composition of the surfaces of the satellites of Jupiter and Saturn.

Planetary Radio Astronomy (PRA) and Plasma Wave Subsystem (PWS)

Two separate experiments, The Plasma Wave Subsystem and the Planetary Radio Astronomy experiment, share the two long antennas which stretch at right-angles to one another, forming a “V”.

Plasma Science (PLS)

The Plasma Science (PLS) instrument looks for the lowest-energy particles in plasma. It also has the ability to look for particles moving at particular speeds and, to a limited extent, to determine the direction from which they come.

The Plasma Subsystem studies the properties of very hot ionized gases that exist in interplanetary regions. One plasma detector points in the direction of the Earth and the other points at a right angle to the first.

Radioisotope Thermoelectric Generators (RTG)

Three RTG units, electrically parallel-connected, are the central power sources for the mission module. The RTGs are mounted in tandem (end-to-end) on a deployable boom. The heat source radioisotopic fuel is Plutonium-238 in the form of the oxide Pu02. In the isotopic decay process, alpha particles are released which bombard the inner surface of the container. The energy released is converted to heat and is the source of heat to the thermoelectric converter.

Ultraviolet Spectrometer (UVS)

The Ultraviolet Spectrometer (UVS) is a very specialized type of light meter that is sensitive to ultraviolet light. It determines when certain atoms or ions are present, or when certain physical processes are going on.

The instrument looks for specific colors of ultraviolet light that certain elements and compounds are known to emit.

Learn more about the Voyager 1 and 2 spacecraft HERE.

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The aligned spin of a black hole

A black hole in traditional theory is characterized by having "no hair," that is, it is so simple that it can be completely described by just three parameters, its mass, its spin, and its electric charge. Even though it may have formed out of a complex mix of matter and energy, all the specific details are lost when it collapses to a singular point. This is surrounded by a "horizon," and once anything – matter or light (energy) – falls within that horizon, it cannot escape. Hence, the singularity appears black. Outside this horizon a rotating, accreting disk can radiate freely. Astronomers are able to measure the spins of black holes by closely modeling the X-ray radiation from the environment in one of two ways: fitting the continuum emission spectrum, or modeling the shape of an emission iron line from very highly ionized iron. $$!ad_code_content_spilt_video_ad!$$ So far the spins of ten stellar-mass black holes have been determined and the robustness of the continuum-fitting method has been well demonstrated. Recently one bright black hole, "Nova Muscae 1991," was found to be rotating in a sense opposite to the spin of its disk, a very unusual and curious result since both might be expected to develop somewhat in concert. The spin of this black hole had previously determined to be small, about ten percent of the limit allowed by relativity. CfA astronomers Jeff McClintock, James Steiner and Jainfeng Wu and their colleagues have re-reduced archival data for this source, and obtained much improved measurements for the three key parameters needed in the continuum-fitting method: mass (11.0 solar-masses), disk inclination (43.2 degrees), and distance (16,300 light-years), each with a corresponding (and modest) uncertainty. Using the new numbers to reevaluate the model of the Nova Muscae 1991 spin, the scientists report that the spin is actually about five times larger than previously estimated. More significantly, that the spin is definitely prograde (aligned with the direction of the disk spin), and not retrograde. The new results resolve a potential mystery, and offer a confirmation of the general methods for modeling black holes. *Source: Harvard-Smithsonian Center for Astrophysics*

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