The University of Southern California Space
Sciences Center has a long tradition of
Sounding Rocket launches from White Sands Missile Range,
New Mexico. Began in the early 1970s the project
has continually centered upon the Extreme Ultraviolet region of
sunlight which is observable only from space.
The first step in a Sounding Rocket flight is the construction of the
payload section of the rocket. The picture at the left shows the electronics
section of the payload before being
attached inside the 'skin' or shell of the rocket. The power supply,
gas resevoirs, flow regulators, and sequencers are all contained in this
section. For the most recent launch, the payload section was 22"
in diameter and 67" long. The Navy supplies the booster and sustainer. SPARCS, a division of Lockheed Martin, provides the telemetry,
payload pointing, and parachute deployment.
Extensive testing in the lab of the instruments on board is a prerequisite for a successful flight. Every cable, every screw, and every instrument must be secured against high g-forc
d possible resonant vibrations. Once assembled the payload section is taken to White Sands Missile Range for integration, where the payload is attached to the SPARCS section. Integration also includes testing the communication between the two sec
tions and the rocket's stability against vibration.
Once the rocket passes vibrational testing, end to end takes place, where the rocket is attached to the rail and placed atop the engines. the picture at the left shows t
tire rocket being elevated for final testing.
The scientists sit anxiously in a bunker near the
pad monitoring their instruments and hoping for the best. The entire
flight takes about 10 minutes. This allows for about 40
0 seconds of observation time. The peak altitude is about 320 kilometers
and the payload and SPARCS sections land
about 50 miles north of the launch site. The scientists
then hop in a helicopter to retrieve
the payload and SPARCS sections for another flight.
The mission investigators smile at the successful launch and
recovery of another sounding rocket. Now begins the arduous task
of analyzing the data and determining what happened at
each second of the flight.
Unfortunately not every landing is picture perfect.
Every now and then a parachute doesn't work or the
payload lands on a rock and the end
result is what you see at the left. All is not lost
though since much is salvagable from even the most crunched rocket.
A Terrier carrying a USC-designed-and built instrument package soars spaceward from the White Sands test range. "Sounding rocket " launches such as these have set the stage for USC's recent - and upcoming - Space Shuttle missions.
On Dec. 2, 1995, only days after the capsule was returned, another USC-designed-and-built package soared into space, beginning a million-mile journey toward an observation post where it will spend six years gathering data on the sun.
These space spectaculars capped a previous series of 10 suborbital "sounding missions," dating back to 1974, in which USC-built capsules were lofted beyond Earth's atmosphere by small rockets for brief glimpses of the naked sun. The latest of these missions, launched Sept. 12, marked the first working use of a new instrument designed by physicist Melvin D. Daybell, a member of Judge's research group, which specializes in space-based solar astronomy. Another capsule is being readied for a 1997 space shuttle mission.
"We've collected a large amount of data and it looks like we'll be getting a great deal more," Judge said. "The data will help unravel mysteries about the complex workings of the sun and the energy that flows from it, bathing our Earth in radiation, which modifies our ionosphere and drives the photochemistry that further modifies our atmospheric umbrella. Such data may even, ultimately, advance the ongoing effort to understand the consequences of human-caused changes in the Earth's atmosphere.
Judge and his collaborators specialize in the study of a relatively little-known and poorly understood portion of the sun's spectrum, called the extreme ultraviolet (EUV). For more than a century, scientists have known that the light which allows us to see - and which plants use for photosynthesis - is part of an electromagnetic spectrum spanning from the long, low-frequency waves used for radio and television to the short, high-frequency waves called X-rays. Adjacent in wavelength to X-rays is the EUV range, which comprises frequencies much higher and more energetic than the familiar ultraviolet.
The amount of visible light the sun produces is strikingly constant, but at shorter wavelengths the sun is surprisingly changeable. Within an 11-year solar cycle, the sun may increase its production of EUV as much as fourfold. Astronomers believe analysis of these changes could provide important information about the workings of the sun.
The sun's EUV radiation serves as an energy source for the solar system, heating and otherwise affecting the atmosphere of planets (including Earth), moons, comets and the dust and gas found in space.
But astronomers trying to observe the sun's EUV emissions face severe obstacles. First, the Earth's atmosphere, which allows visible light to pass through, is completely opaque to EUV, making impossible any such observations from the planet's surface. EUV is absorbed not only by the ozone layer, which partially shields Earth from sunburn-producing "near" ultraviolet rays, but also by many other atmospheric gases.
With rocket technology, scientists can lift instruments above Earth's atmosphere, making EUV astronomy possible. But this led to a second problem. The design of the instruments themselves proved unreliable. The highly energetic EUV radiation, scientists found, quickly degraded materials used in the instruments, so that the sensitivity of a single instrument changed over time.
To build stable detectors, therefore, became the key to the whole field of EUV astronomy, according to Judge. And USC has become a world center in the design and construction of these new instruments.
The research group developed a unique four-instrument cluster called the Solar Extreme Ultraviolet Hitchhiker (SEH). To avoid problems inherent in earlier EUV-measuring instruments, the four devices were designed using "optics-free" engineering.
The instruments check each other by using three different mechanisms to measure the number of individual units - or photons - of EUV radiation striking in a given time. One sensor depends on helium gas as a measuring medium; the second neon gas; the third a silicon electronic device.
These instruments, however, can only measure the total number of photons at all EUV wavelengths. The fourth instrument, a spectrometer built without lenses or prisms, allows the scientists to distinguish different "colors" (wavelengths) of EUV from this gross total.
The four instruments were all designed and built at USC. The designs of all have been refined since 1974, when Judge first began working on the problem.
According to research laboratory supervisor Donald R. McMullin, who served as payload coordinator on USC missions, the designs have been thoroughly calibrated. "We now have high confidence that the numbers we are getting are in fact an accurate and consistent measurement of EUV."
The SEH package components were developed, tested and have gathered data in a series of "sounding rocket " flights fired at the White Sands test range in New Mexico. The "sounding rocket " soared above the atmosphere for approximately 10 minutes - long enough to take some useful measurements, but these amounted to little more than snapshots.
In the Space Shuttle, with observation periods lasting days rather than minutes, SEH could attempt far more ambitious experiments.
For example, Jupiter and its moon, Io, form a system that generates and emits EUV. But to understand the dynamics of the two masses, scientists need to know how much EUV solar radiation is entering the system. SEH measurements of the sun - taken while another specially designed instrument simultaneously looked at Jupiter and Io - successfully gathered the data.
USC-made instruments worked almost perfectly on the Shuttle flight. The only glitch involved a sticky part, but this malfunction didn't interfere with data collection.
Data collection, itself, was an arduous task. During the flight, the USC researchers had to man the instrument package's ground-control chair around the clock at the Houston Control Center. Judge, McMullin and research scientist Howard Ogawa rotated the duty, with occasional relief from graduate student Jerry Hoffman.
Likewise, functioning perfectly are the instruments sent aloft in the new SOHO (Solar Orbiting Heliocentric Observer) mission - which will observe the sun's ultra-hot atmosphere (or "heliosphere") from a unique orbital point (where the gravitational attraction of the Earth and the sun cancel each other out).
And a new instrument is ready to join the lineup. The new Daybell design was recently tested for the first time on a White Sands Shuttle flight. Alex Small, an 18-year-old undergraduate and Trustee Scholar, worked with Daybell to transform the design from a raw concept into an actual instrument, helping with calculations, drawings and testing.
Besides analyzing the flood of data expected from the SOHO instrument, the group - which also includes 1995 graduate Michael Banks, graduate students Jerry Hoffman and Nathan Rodgers and undergraduate Jeff Nuttall - is looking ahead to another sounding rocket launch in June, and to a two-week Shuttle mission in 1997.
Beyond that, the group hopes to get its own dedicated EUV satellite, to be controlled directly from USC. In the meantime: as the group's NASA web page (http://sspp.gsfc.nasa. gov/seh.html) reports:
Judge, McMullin and undergraduate Nathan Rogers retrieve the instruments launched on a Terrier "sounding rocket "