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Goddard Space Flight Center

Astrophysics Science Division | Sciences and Exploration

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Eric Christian's
Questions and Answers

Eric Christian's Field Journal from 2003 Campaign

2003 Campaign
Wildlife Seen on the 2003 Campaign
Vehicles Seen on the 2003 Campaign

Questions from Old Bridge High School

When it comes to finding the mass of a cosmic ray, will there be a magnetic field generated from OWL? If not, then where is it generated? Are both methods for determining cosmic ray mass used? Which method is preferable and which is more efficient?

OWL will not use a magnetic field because you couldn't generate a large enough magnetic field to bend these high energy particles (even the Earth's field doesn't bend them much). These particles are moving at about 0.99999999 times the speed of light. The way we will get more information about them is by determining where the particles interact in the atmosphere and what is the shape of the air shower of particles they create. A heavier particle will interact closer to the top of the atmosphere and the air shower will grow faster (at a certain height below the start of the shower there will be more particles and thus more light).

As with much of physics, the method that is most "efficient" depends upon the circumstances, in this case the energy. Magnetic fields are good at low energies, but are not really useful above about 1 GeV, which is seven or eight orders of magnitude in energy below the particles that OWL and EUSO will measure.

How long is it expected to take before considerable data is obtained from this mission?

We'll start taking data the first night NIGHTGLOW is up in the air. The longer the flight, the more and better data we'll get. Some nights are also better than others (due to the phase of the Moon - we get better data for more of the night close to the new moon).

What are the current theories concerning the origins of these high-energy cosmic rays?

The current theories can be divided into two groups. There are the "Bottom Up" theories that say that these cosmic rays start at lower energies (like ordinary galactic cosmic rays) and get somehow accelerated up to these enormous velocities. The problem with these theories is that we don't see any place close enough to us (within about 50 megaparsecs) that could do the acceleration.

The other group is called "Top Down". These theories say that there is "Something" (super-strings, small black holes, dark matter?) that has more energy than these particles, and then it decays into these very energetic cosmic rays. There is not enough data yet to confirm any of these theories, which is why we need OWL and/or EUSO. For more information, see the OWL website.

How will determining the origin of these high-energy cosmic rays further our efforts in space exploration? What relevance does this information have in regard to exploration?

The highest energy cosmic rays have the potential to be really important to physics (and maybe in the long term to space exploration). The current physical theories say that we shouldn't see any particles with energies about a few times ten to the 19th electron volts, yet we see some. This could mean that there is something there that is beyond our current understanding of the universe. Who knows where such new physics will lead us?

What do you think will be gained by studying the light pollution?

Light pollution increases the background against which OWL and EUSO will have to observe the very dim cosmic ray tracks. Understanding how widespread the light pollution is, and how it changes with time, will help us to design and understand the data from OWL and EUSO.

What would be the ideal weather for NIGHTGLOW's launch?

Low (but not zero) winds all the way up to 1000 feet coming from a steady direction. Our problem up to now (Feb. 12) is that when the winds are slow at the surface, there have been high winds (>20 knots) up a few hundred feet. Since it is almost 1000 feet from the top of the balloon to the instrument, this wind shear is not acceptable for launch. And one night, the winds looked OK, but then they took a sudden shift in direction, luckily before the balloon was prepared. If the wind shift had happened while they were filling the balloon, we could have lost it.

What do you hope to find in your experiments?

With NIGHTGLOW, it is not so much a matter of finding something new, it's a matter of understanding what exists so that we can better design future experiments, such as EUSO and OWL. EUSO and OWL will look for very faint UV tracks in the atmosphere left by the highest energy cosmic rays. We need to know the UV background and how it changes with time, cloud conditions, position over the Earth, etc. otherwise we might have trouble seeing and understanding the cosmic ray data.

What were some of your obstacles in developing and designing the mission?

The main obstacle was money. The data NIGHTGLOW collects will enable excellent science in the future (understanding the origin of the highest energy cosmic rays), but is not important scientifically right now. Because of this, we had to work with a limited budget, and so borrowed equipment and tried to do this as cheaply as possible.

What are the specifications of the balloon, mass, volume, pressure, gas pressure, etc.?

The balloon has a volume of over 600,000 cubic meters (over 21 million cubic feet) and weighs 2470 kg (5445 lbs). Its diameter, at "float" altitude (33.5 km or ~110,000 feet) is 121 meters. Its surface area is over 40,000 square meters (430,000 square feet or almost 10 acres of plastic). It also has 290 rope tendons that stretch from top to bottom to help take the pressure (it is these tendons that give the balloon its "pumpkin" shape.

How heavy are the instruments on NIGHTGLOW?

NIGHTGLOW as a whole is 800 kg (1750 lbs). Most of that is what is called structure (the mechanical support for everything). Each of the three telescopes (two that rotate, one that always looks straight down) weigh about 35 kg apiece. There are also 110 kg (240 lbs) of batteries. The solar arrays charge the batteries during the day, and NIGHTGLOW uses the battery power at night. There are also several "piggyback" experiments, each of which weighs about 10 - 15 kg (22 - 33 lbs).

How did you develop the instruments to see the sensitivity needed to see the nightglow, when in the past, instruments lacked the sensitivity needed to see the nightglow?

It wasn't so much that earlier instruments couldn't see nightglow if they had wanted to, it's just that they didn't want to. Earlier measurements in this wavelength were designed to see the very much brighter dayglow, which is important for the dynamics of the atmosphere. The much dimmer levels of UV at night weren't important for the atmosphere, and so the instruments weren't designed to measure them.

Do you plan to collect any data while NIGHTGLOW is traveling during daylight?

No, because the photomultiplier tubes (the devices that turn the light into electrical signals) are designed to be really sensitive and measure very dim light, they can't handle the bright light of daytime.

What is NIGHTGLOW made of?

Most of NIGHTGLOW is made of aluminum, because most of it is structure (the support frame that the telescopes, computer, etc. are attached to). There are also glass mirrors and photomultiplier tubes, electronics boards and parts (computers, power supplies, etc.) and lots of wire and cables.

How thin is it?

I don't understand this question, there are many different pieces, all with different thicknesses. Here's a side view: Side view of NIGHTGLOW

How many layers are on the balloon?

The balloon is made of three layers of plastic, with the outer layers being the same chemical composition, sandwiching a different plastic. However, the three layers are made together (this type of plastic film is "extruded") and the long plastic polymer strands are so intertwined that there is no way to tell the three layers apart.

Will people be tracking the balloon by land, in case that it prematurely lands?

In the first couple of hours after launch, there is a chase plane that will follow the balloon and mark where it lands if it comes down prematurely. It would be too hard to follow it over the ground here in the outback (not many roads and very rough terrain).

This file was last modified February 20, 2003