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NASA - THEMIS Mission Manager Answers Your Questions
February 16, 2007
 

Garrett Skrobot, THEMIS mission manager. Did you ever wonder who helps to bring the right rocket together with a spacecraft to ensure a successful mission? That person is called a mission manager. Throughout the process, the mission manager serves as the primary interface between the spacecraft and the launch vehicle.

THEMIS Mission Manager Garrett Skrobot answers some of the questions submitted to the question board.




Bonnie from Daytona Beach asked: "Why does THEMIS have five probes and when do they separate from each other?"
Answer: "The purpose of the THEMIS mission is to distinguished between two proposed models for the release of solar wind energy stored in the Earth's magnetic field. We can do that by using the five spacecraft to pinpoint when and where the release occurs. In one model, the release occurs at a location about a six of the distance to the moon. In the other model, the release occurs at a location somewhere between a third and a half the distance to the moon. To determine which model is correct, we need to place spacecraft just earthward, and just beyond, each location. That makes four spacecraft. The fifth spacecraft is there to help out if any of the other four gets in trouble.

Now about separation, that occurs 73 minutes after launch. First the top probe pops off and then 3 seconds later the other probes are released. If we launch at 6:05 PM on February 16, 2007, the probes will separate at 7:21 PM Eastern Standard Time.
Aren from Vermont asked: What can we learn from auroras? How will this knowledge benefit us on Earth?
Answer: Auroras are the visible manifestation of dynamic processes happening within the Earth's magnetic field. The Earth's magnetic field captures energy from the solar wind and releases it somewhere between a sixth and half the distance to the moon. Observations of the aurora can help us determine when and where the release occurs, how big it is, and how long it lasts. The fundamental physical processes that drive the release occur throughout the plasma universe, at other planets, at the Sun, and at other stars. Understanding the processes that cause the aurora can help us predict when and where the energy releases occur. With that knowledge, we will be better able to protect astronauts and spacecraft from harmful radiation, to predict intervals when GPS and radio communication will be disrupted, and to predict current surges that can blow out power line transformers and cause massive power blackouts.
Paul from West Palm Beach asked: What is the projected lifetime of THEMIS, and if a particularly strong solar storm were to hit during its mission, would it be able to survive?
Answer: The THEMIS spacecraft have been designed to last for 2 years. The spacecraft and instruments are shielded to protect them from both solar storms and traversals of the Earth's Van Allen radiation belts. A very large storm could harm the spacecraft, but we think the chances of this are very small. First, the spacecraft spend most of their orbit outside the Earth's radiation belts. Second THEMIS is launching during solar minimum, so the chance of a severe solar storm is lower.
Mary from White Plains asked: How long is the THEMIS mission going to last and is it long enough to gather the information needed?
Answer: The THEMIS mission lifetime is 2 years. The THEMIS spacecraft spend January to March each year on the nightside of the Earth, i.e. on the other side of the Earth from the Sun. Their orbits have been selected to enable them to observe the abrupt releases of energy that occur during substorms. We expect the spacecraft to observe more than two dozen substorms during the 2-year nominal lifetime. That will be more than enough to determine what causes substorms.
Marylou from Iowa asked: Why are we studying auroras? What is the benefit to us taxpayers?
Answer: Aurora represent the visible signatures of fundamental physical processes occurring within the Earth's magnetic field, processes that can have a severe impact upon our technological systems. The Earth's magnetic field captures solar wind energy, stores it, and suddenly releases it in the form of energized particles and strong currents. Some of the particles enter the Earth's atmosphere and produce aurora, while others are dumped into the Earth's Van Allen radiation belts where they can harm both spacecraft and astronauts. Particles within the Earth's radiation belts could cause the loss of communications spacecraft and cut telephone communications. The strong currents can flow through power lines, blow out transformers, and cause massive power blackouts. One such event occurred in March 1989, when a major blackout lasting more than 9 hours occurred in Quebec. The blackout cost the power company $10 million dollars, while customer losses were many times larger. By understanding the cause of auroras and substorms, we hope to learn how to predict them and protect ourselves from their harmful space weather effects.
Glen from Omaha asked: When was the THEMIS mission conceived of and planned, and will the mission also provide us data toward the question of our shifting magnetic poles?
Answer: THEMIS dates back to 1996, when the Space Science Laboratory of the University of California, Berkeley (UCB) proposed a small University class Explorer (UNEX) to NASA. The THEMIS mission evolved into its current concept in 2001, in collaboration with Swales Aerospace. UCB proposed THEMIS to NASA's Middle Explorer (MIDEX) program and it was selected for development in 2003. THEMIS studies the interaction of the solar wind with the Earth's magnetic field, in particle the release of solar wind energy stored within the Earth's magnetic field during substorms. Substorms occur about once every 3 hours, storage takes about an hour, and the release occurs within a matter of minutes. By contrast, significant changes in the locations of the Earth's magnetic poles take place over hundreds to thousands of years, a very different time scale.
Tim from Stockton asked: Who decided which rocket to use for THEMIS and why?
Answer: During the formulation of the THEMIS mission, the THEMIS principal investigator team at the University of California at Berkeley made the decision to use the medium-class launch vehicle performance range in 2001. This decision was based on optimizing science per total mission cost. The five spacecraft of THEMIS plus their carrier weigh about 800 kg. The origin of the auroral energy is near Earth's equator; the rocket, starting from an inclination of 28 degrees at Cape Canaveral, has to reduce the payload inclination and place it about 60,000 miles away from Earth to optimize the science return. Once THEMIS has completed the requirements for a launch vehicle, NASA's Launch Services Program sends a "request for proposals" to our contractors. A Source Evaluation Board is formed to review the proposals, and a launch vehicle is selected and put on contract. The Delta II 7925, one of the largest vehicles available to NASA for the medium-class missions, was selected.
Ashleigh from San Francisco asked: What makes a Delta II rocket the right one for this mission? How is it different from the Delta IV or Atlas V?
Answer: When determining which launch vehicle to use for the mission, the mass of the spacecraft and where it needs to be released plays a major role in selecting the launch vehicle. The weight of THEMIS at the time of launch vehicle selection was not to exceed 829 kg. This weight makes the Delta II performance a perfect fit for the THEMIS. The Delta II vehicle is what we call a medium-class launch vehicle and is used to place NASA's medium spacecraft into space. The Delta IV and Atlas V rockets are much bigger and are used to place NASA's large spacecraft into space, or even send the spacecraft to other planets.
John from Timonium, MD asked: What trajectory will the rocket take? Will it be visible going up the East Coast due to the nighttime launch, or is it headed out over the Atlantic?
Answer: THEMIS will be flying from Space Launch Complex 17B at Cape Canaveral Air Force Station in Florida. The trajectory for the launch vehicle will be a flight azimuth of 93 degrees. With this flight azimuth, THEMIS will be heading over the Atlantic Ocean for its ascent phase of flight, so it will not be going up the East Coast. Sorry!
 
 
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