FOXSI Fires Up
Sounding rocket mission looks at solar flares
by Lindsay Glesener
In the Tularosa desert basin in New Mexico, not far from the White Sands National Monument, a fireball occasionally lights up the sky, climbing higher and higher until it is lost to the observer’s eye. Out of sight, the rocket climbs to a height of 300 kilometers, over 30 times higher than a passenger airplane, and escapes the atmosphere before plummeting back to the grounds of the White Sands Missile Range roughly 15 minutes after its launch. There, a team of scientists eagerly awaits its return.
This story has played out in the New Mexico desert hundreds of times over the last half-century, and quite often the waiting scientists are from Berkeley. This will be the case for an upcoming launch in November 2012, when researchers from UC Berkeley’s Space Science Laboratory will fly an experiment called the Focusing Optics X-ray Solar Imager (FOXSI) onboard a sounding (i.e. “exploratory”) rocket from White Sands. FOXSI will attempt to produce the most sensitive X-ray observations ever made of the Sun using on-board telescopes and cameras. As a graduate student on the FOXSI project, it will be my job not only to perform several scientific tasks, but also to chronicle the preparations and flight for posterity. This article will offer a look at the history of Berkeley rocket science and show what it takes to get an experiment into space.
A better vantage point
Almost five years of instrument design, assembly, and testing will culminate in FOXSI’s 15-minute rocket flight—a significant investment for just a few minutes of data. Yet, for scientists intent on high-altitude experiments, sounding rocket flights are highly sought-after. For astrophysicists, many useful tools are simply not available at ground level. The earth’s atmosphere blocks radiation in many parts of the electromagnetic spectrum, including gamma rays, X-rays, infrared, and some ultraviolet wavelengths. (This is crucial for the presence of life on Earth, as much of this radiation would cause tissue damage.) For high-sensitivity solar X-ray studies, for example, astrophysicists must send their experiments high above the atmosphere to find an unobstructed view of the Sun.
Compared to building a spacecraft, rockets offer a faster and cheaper way to put an experiment into space, albeit for a shorter length of observation time. Scientific rockets are funded by the National Aeronautics and Space Administration (NASA) “Low-Cost Access to Space” program, which offers the opportunity to fly a suborbital project with a construction time of only a few years, at a fraction of the cost of a spacecraft. NASA describes the program as “a low-cost test bed for new scientific techniques, scientific instrumentation, and spacecraft technology” that may eventually end up on satellite missions.
Many astrophysics experiments do indeed use rocket flights as stepping stones to spacecraft status. To win a NASA spacecraft proposal, investigators must prove that all the parts of their hypothetical instrument will work. In some cases this means proving an entirely new concept; in others it means demonstrating that an established technology can withstand the tough physical environment of space. One way to demonstrate that technology is space-ready is to send it there, if only for a few minutes. Rocket-tested technology has formed the basis for hundreds of NASA satellites, past and present. Sometimes spacecraft and rockets fly simultaneously: for example, after the Solar Dynamics Observatory spacecraft was launched in 2010, several rockets were flown to improve the calibration of one of its instruments.
But not all science experiments on rockets gaze at otherworldly objects. Atmospheric and plasma physicists use rocket flights for in situ measurements of the ionosphere and thermosphere plasma, data that is not available to either a ground-based observatory or to a spacecraft. Microgravity experimenters also make use of the rocket’s free-fall to measure the behavior of physical and biological systems in a low-acceleration environment.
Finally, another important scientific component developed by means of rocket experiments is the scientists themselves. Rocket flights have typically been used to train students as physicists and engineers. The short time scale of a rocket project, as well as its greater risk tolerance, allows a PhD student to see a project through from beginning to end and be involved in all aspects of the project, including the design phase, building and testing of the instrument, the flight itself, and data analysis.
The story of science rockets
Rockets certainly weren’t invented just to suit the whims of scientists who wanted to get their experiments into space. The evolution of space rocketry is intertwined with that of military rocketry. Rudimentary military rockets were built almost as soon as gunpowder was discovered, and solid-fuel rockets were used in battles throughout the 1800s. But by the early 20th century, rockets began to excite the human imagination as a way of turning science fiction into reality, by exploring space. In the 1920s, Hermann Olberth, a German physicist, proposed that rockets could be used to either place artificial satellites around the Earth or to escape the Earth’s gravitational field entirely, and thus could serve as a useful tool for space exploration. Around the same time in the United States, Robert H. Goddard experimented with liquid fuels, stabilizing systems, and multiple stages, the building blocks of space-capable rockets. For this work, Goddard would later become known as the father of modern rocketry.
It didn’t take long for military personnel to realize that these principles would also be useful for building powerful weapons of war. Throughout the 1930s, aggressive rocket development programs took place in several countries, particularly in Germany. A large and well-funded team of rocket scientists led by Werner von Braun developed the V-2, a liquid-fuel, single-stage military rocket. The V-2 was used against several Allied targets in World War II, and in 1944 became the first man made object to fly into space.
The end of the war marked an important turning point for space rocketry. The United States competed with other Allied forces for custody of captured V-2 rockets, along with their creators. German rocket experts, having surrendered to the Allies, immigrated to the United States and continued development of rocket systems (the United States’ secret effort to recruit German rocketeers was known as “Operation Paperclip”). Von Braun himself remained the leader of this team, working first in White Sands, and later in Huntsville, Alabama. In 1960 the newly-formed NASA established the Marshall Space Flight Center in Huntsville, with von Braun as director. This facility designed and built the rockets that powered the American side of the space race, culminating in the development of the Saturn V rocket, which would eventually be used to launch the Apollo Moon missions.
Along with human spaceflight, the newly formed space agency recognized the value of sending scientific instruments to make measurements in space. At birth, NASA inherited hundreds of retired Army rockets and immediately put them to use, putting out calls for academic physicists to propose rocket experiments. Thus, NASA’s sounding rocket program was born. The term “sounding rocket” comes from nautical use, in which “sounding” is a method to gauge distance. In this sense, to “sound” via a rocket is to explore an unknown realm. These flights are also known as sub-orbital flights, since the rockets enter space but do not stay there for an entire orbit of the earth. Early NASA sounding rockets carried instruments designed to study cosmic rays, atmospheric composition, the Sun, the aurora borealis (northern lights), and X-ray and UV-emitting astronomical sources, among many others. Experiments not only made new measurements, but also tested out groundbreaking new technology. Later on, the best of this technology would be used to build spaceborne astronomical observatories. University professors and their students carried out many of the experiments, and typically a student was given the main responsibility for the project. In this way, rockets were not only a platform to develop new technology and science, but also one to develop new scientists for the space age.
UC Berkeley’s involvement in sounding rocket expeditions goes back to the very beginnings of the field. In 1958, Berkeley faculty recognized the opportunities for research offered by newly available rockets and satellites, and proposed a new research center called the Space Sciences Laboratory (SSL). SSL began operations in 1960, constructing experiments for flight on rockets, high-altitude balloons, and spacecraft. Over the last 58 years, almost 400 PhDs have been awarded for experiments flown on NASA sounding rockets, with 40 of them from Berkeley.
Michael Lampton, a retired physicist at Lawrence Berkeley Laboratory (LBL) and a former NASA payload specialist, was one of the first Berkeley students to fly a rocket. In the late 1960s he and his advisor, physics professor Kinsey Anderson, won a proposal to do daytime studies of the aurora. They built and launched four Nike rockets with Apache stages from Fort Churchill, Canada into Hudson Bay and found the first evidence of auroral activity during the daytime. After graduating in 1969, Lampton flew several X-ray astronomy rockets from White Sands, where, he said, the projects would amass a large crew. “We called them ‘rocket roadies.’ Other students, girlfriends, friends, dogs, everyone would pile into campers and trucks and make the drive out to the desert,” he recalled. The rocket roadies would help out with manual labor and moral support, and were rewarded with the chance to help with and witness an exciting rocket launch.
By the 1980s, when LBL physicist Pat Jelinsky was a PhD student, SSL had become an assembly line of both rockets and students. Berkeley rockets were flown almost every year, and each new student was trained by the previous one. Jelinsky flew three rockets (two Aries and one Black Brant) to perform extreme-ultraviolet astrophysical studies. The earliest of these rockets suffered problems with the alignment system and the pressure environment and were unsuccessful. Later flights were able to fix these problems and produced the first extreme-ultraviolet studies of the local interstellar medium. In this way, rockets were used to successively iron out problems, culminating in a tested instrument capable of groundbreaking new science.
The FOXSI mission
Berkeley’s participation in sounding rocket programs lagged in the new century: the last Berkeley rocket was an auroral experiment flown from Alaska in 2000. That will change this year, however, with the November launch of the FOXSI mission, which continues the long tradition of building rocket experiments at the Space Sciences Laboratory. FOXSI promises to reveal a new view of the quieter parts of the Sun at elusive high X-ray frequencies.
X-ray telescopes are notoriously difficult to engineer because traditional telescope configurations won’t work. X-rays do not reflect or refract as easily as visible light does, so traditional telescopes with large reflecting mirrors or refracting lenses can’t be used. In the past, to image high-energy X-rays from astronomical objects, scientists had to resort to indirect imaging techniques that are limited in sensitivity and dynamic range. But producing focused X-ray images is not an impossible task, though the technological requirements are high. X-rays need to reflect on a mirror at a very small angle (less than half a degree). The mirror also needs to be carefully shaped and needs to be smooth down to the scale of a few atoms. Recent advances at NASA’s Marshall Space Flight Center (NASA/Marshall), among others, have produced telescopes that can focus high-energy X-rays.
One of the fields that could benefit most from such a telescope is the study of solar flares. Solar flares, or giant explosions on the Sun, occur frequently and are the most powerful accelerators in the solar system. Radiation and high-energy particles released during flares often reach the Earth, affecting communications and power systems and placing satellites at risk. Understanding how solar flares happen and what triggers them is an important goal of solar physics. Because X-rays are emitted from high-energy charged particles traveling through the solar plasma, they give us important clues into the underlying processes of solar flares.
FOXSI was born five years ago in a proposal to NASA by UC Berkeley scientists that aimed to study flares in the quietest regions of the Sun. Since it is so far impossible to predict large solar flares and time a rocket accordingly, the team chose instead to focus on small flares theorized to occur frequently. FOXSI combines focusing X-ray telescopes made by NASA/Marshall with X-ray cameras from Japanese collaborators to be able to image faint solar X-ray sources. Säm Krucker, the principal investigator of FOXSI and a senior physicist at the Space Sciences Laboratory, emphasizes that this science can only be done from a rocket or a spacecraft. He also underscores the importance of rockets as a training tool. “With their quick turnaround times, rockets are a great low-cost way to try out new instrumentation and train students. To accomplish this, SSL’s heritage in building rocket experiments is essential. We rely on scientists and engineers with decades of experience in building space projects.” New students tasked with building and testing rocket payloads can draw from this wealth of institutional knowledge to help them build instruments that will work in space.
After about four years of work, FOXSI is ready for its first flight. But the populous, crowded Bay Area is no place to fly a rocket —that requires an isolated area where a rocket can launch and land without posing a danger to anyone. So the FOXSI team will take their experiment to one of the birthplaces of US rocketry: White Sands.
FOXSI in the desert
The White Sands Missile Range is geographically the largest active military base in the country, covering over 3000 square miles of New Mexico desert. Located an hour north of El Paso, TX, and a half hour east of Las Cruces, NM, the range is like a small town in itself. Families of active military personnel live there, and a tour of the base reveals houses, schools, playgrounds, and a golf course. There’s even a bowling alley, which is a good place to take a break from work for a burger and a chocolate shake—important for scientists working around the clock to put the finishing touches on their experiment.
White Sands is a military and scientific facility with an illustrious history. It was here that the first atomic bomb was exploded in 1945 at the Trinity Site. It was here that the Operation Paperclip rocket scientists arrived along with truckloads of V-2 rockets after the end of World War II. And it hosts a facility used by NASA for launching scientific rockets for the last 50 years.
Launching a rocket at White Sands now is a different story than it was 50 years ago. Security regulations do not allow for non-essential personnel; ‘rocket roadies’ are no longer permitted. During the launch, scientists, engineers, and observers will be located in a sturdy block house near the launch rail or else a viewing location miles away; outdoor viewing bleachers right next to the rail are a thing of the past. Anyone wishing to attend the launch should get there early; a few hours before the launch, the nearby highway as well as the adjacent national park will be closed to traffic and visitors.
Though FOXSI will have its first shot at space in late 2012, it has already been introduced to the range. In March of 2012, FOXSI was brought to White Sands for a first flight attempt, but the flight was delayed due to unexpected problems with the experiment. The time on the missile range was instead used as a dry run of the flight preparation, in which each essential step leading up to the launch was practiced.
One of the first steps in preparing the rocket was to line up the telescopes with the X-ray cameras. To get the needed precision, this had to be done using a high-power X-ray generator located 60 feet away from the instrument. Since X-rays are undetectable to the naked eye and can be harmful in high doses, this was done in a carefully controlled environment so that no personnel could be exposed to the X-ray beam.
The next step was “integration,” meaning that all rocket components, including the instrument, were attached together for the first time. This was followed by a “sequence test” of the entire instrument. In this test, events during the countdown, launch, and flight of the rocket were simulated. Power and communications systems were switched on at the appropriate times. The shutter door that will expose the telescopes to the Sun was opened. Members of the FOXSI team in a control room practiced receiving the experimental data and making command decisions based on it. The appropriate times for the parachute to open and for the payload to hit the ground were called out.
Next was an important milestone: the vibration test. When the rocket fires, the entire structure will be subject to strong vibrations, with amplitudes up to 10 times the force of gravity. Naturally, it is necessary to make sure the experiment and all the rocket parts can hold up under this extreme stress. To check this, the rocket was placed on a special vibrating table that simulated the launch environment. Over the loud rumble of the vibrating table, a high-pitched squeal could be heard from the telescope, caused by resonances in the telescope shells. At many times, it was difficult not to anthropomorphize the experiment, and hearing FOXSI “scream” on the vibration table was one of those times. Everyone held their breath in hopes that the instrument was unharmed, and it was.
With a little luck and a lot of hard work, FOXSI will be back in the desert in October of this year for its first launch attempt. The experiment will be launched via a Black Brant Mark II rocket and will fly for a total of 15 minutes. For five of these minutes, the telescope will be in space with an unhindered view of the Sun. FOXSI will aim at two targets: first, it will record the hot, active part of the Sun where most flares arise, as a check of the instrument’s capabilities. Then the telescope will switch to a less active area, searching for never-before-seen X-rays from the quiet regions of the Sun.
While most of the excitement lies in the preparation and launch of the instrument, the work does not end there. Launched at an almost vertical angle, FOXSI will return to earth within about 60 miles of its launch site. A parachute will slow its descent once it re-enters the atmosphere and a metal crush bumper beneath the telescope will take the brunt of the impact with the ground. Members of the science team will travel by helicopter to recover the rocket and check the instrument for damage. With any luck, the instrument will be recovered in good shape, intact and ready to fly again.
The future of FOXSI
One of the reasons to hope for a good recovery is that FOXSI is just beginning its life as a solar observer. FOXSI’s second flight has been funded and will take place in two years. Sounding rocket experiments can typically be flown several times, with each flight gathering more data or making improvements and upgrades to the instrument. After this adolescence, it is hoped that FOXSI will mature into an orbiting observatory, with several rocket flights having provided the proof that it is space-worthy. As a spacecraft, FOXSI could study the Sun with a far better sensitivity than any current instrument, and could help us understand how the giant explosions seen in solar flares come about.
Evolving FOXSI into a spacecraft is one of the main goals of Krucker and his team. The motivation and idea for FOXSI came from studying data from a previous solar X-ray observing spacecraft, named RHESSI, which greatly advanced our knowledge of solar flares and gave clues about what to look for next. Once FOXSI, now a temporary flame in the sky, has matured into a spacecraft, its results will surely spark new ideas, which will be tested on rockets and balloons. With each of these, young scientists will be trained to build and run a mission. In this way, the cycle of space science continues.