Text Size
MMS: Frequently Asked Questions
January 26, 2014

Quick Links to Question Content

About the Spacecraft
About the Instrumentation
About Launch and Operations
About the Science
About the People of MMS
About Connecting to the Mission


1. What will power the MMS spacecraft?

MMS is powered by the sun. Each MMS observatory generates electrical power with eight solar panels. During eclipses, energy stored in a battery provides electrical power until MMS passes out of the eclipse, at which point the solar panels recharge the battery and supply power.

2. How big are the MMS spacecraft?

Each MMS observatory, not including antennas and instrument booms, is about 4 feet tall and 12 feet wide. When stacked all together on the launch vehicle, the complete stack of four MMS observatories is over 16 feet tall. In space, with axial booms and wire booms extended, each observatory grows to be about 94 feet tall and 369 feet wide; this size would take up most of Fenway Park!

3. Why are there 4 spacecraft?

There are four spacecraft in order to get three-dimensional science information. Each spacecraft can be thought of as the point of a triangular pyramid, or tetrahedron. As the tetrahedron flies through space, it can measure the three-dimensional properties of magnetic reconnection regions. The separation distances will vary depending on the orbit and can be changed as the mission progresses. The inter-spacecraft distance can be made to be as large as 250 miles (400 km) to as small as 6 miles (10 km).

4. How much will the MMS spacecraft weigh at launch?

At launch, with a full load of propellant, each observatory weighs approximately 2,998 pounds (1360 kg). This is slightly lighter than a 2012 Toyota Prius.

5. What obstacles had to be overcome in development of the mission?

Every space mission has challenges in balancing engineering performance, reliability, cost and schedule. The one technical challenge that stands out on MMS is the need to fly a fleet of four spinning spacecraft in a tight tetrahedron formation. The requirement to fly in a precise formation had technical impacts on the propulsion system design, the accuracy of the on-board accelerometers, the capability of the spacecraft GPS navigation system, and the ground-based flight dynamics systems that are used to determine how to create and maintain the formation -- particularly how to plan, execute and track precise propulsive maneuvers.

6. What is unique about the MMS Spacecraft?

The MMS spacecraft were custom designed and built for the MMS suite of instruments. Although wherever possible, engineers used commercially-built parts and components that are "off the shelf", the bulk of the spacecraft design is one of a kind.

› Back To Top


7. How many instruments are on-board?

Each spacecraft carries 25 instrument sensors.

8. Does each spacecraft carry the same suites of instruments?

Yes. The only difference is that each instrument has individual calibrations for its data.

9. What will the data look like? Will I see images of magnetic reconnection?

Although MMS will not produce images of magnetic reconnection, it will provide novel three–dimensional perspectives into magnetic reconnection that may be able to be easily visualized.

10. How long are each of the antennas and why?

Each of the eight GPS receiver antennas are only 6 inches long. This dimension is based on the GPS transmission wavelength and the antenna design needed to capture a wide field of signals from GPS satellites on the far side of Earth. Each of the two communication antennas are 5 inches long, 24 inches including their bracket. The two magnetometer booms are each 16 feet (5 meters) long when fully extended. This length was chosen to get the sensitive magnetometer sensors as far away from the spacecraft as possible while still being able to fold in two and fit inside the launch vehicle. Each of the two axial double probes are almost 50 feet (15 meters) in length. This length provides the longest possible distance between the sensors on the ends while allowing the stowed booms to fit within the height of the spacecraft. Each of the four SDP wires are almost 200 feet (60 meters) in length. This length maximizes the radial distance of the four SDP sensors while still fitting inside their allotted spaces within the instrument deck before they're deployed.

11. Where can I find more information about each of the instruments aboard the spacecraft?


› Back To Top


12. What type of rocket will be used to launch the spacecraft?

A United Launch Alliance Atlas V 421 rocket.

13. Where is the spacecraft being built?

The spacecraft is being built at NASA's Goddard Space Flight Center in Greenbelt, Md.

14. Where are the instruments being built?

The instruments are built in many places around the United States and the world, including NASA's Goddard Space Flight Center in Greenbelt, Md., Southwest Research Institute in San Antonio, Texas, the Applied Physics Laboratory in Laurel, Md., Aerospace Corp. in El Segundo, Calif., University of California in Los Angeles, the University of New Hampshire, the University of Iowa in Iowa City, ATK Aerospace in Arlington, Va., the Laboratory for Atmospherics and Space Physics in Boulder, Colo., with international collaborations from France, Sweden, Austria, and Japan.

15. What is the MMS orbit?

MMS will have two different orbits around Earth for two different mission phases. The first phase of the mission has an orbit that comes to 1,600 miles (2,550 km) altitude at its closest approach to Earth and at its farthest, extends out to 43,500 miles (70080 km). For the second mission phase, the closest approach remains the same, but the orbit will now extend out to 95,000 miles (152,900 km) at its farthest away from Earth – this is about 41% of the distance to the moon.

16. How will the spacecraft's orbit be controlled during the mission?

The spacecraft orbits will be controlled with an onboard propulsion system that uses 12 thrusters to adjust the orbit of each spacecraft. The spacecraft are tracked and commanded from a control center at NASA's Goddard Space Flight Center in Greenbelt, Md.

17. How will you track the location of each spacecraft?

The MMS fleet is tracked in two different ways. The first method uses ground antennas, which use Doppler frequencies and pointing data to determine the location and velocity of the spacecraft. The second method is that each spacecraft contains a very accurate and sensitive GPS receiver that can determine its own position and velocity by picking up the GPS signals and filtering them to calculate position and velocity. Note that the MMS orbit places it above the GPS constellation at times, so the MMS GPS receiver is very sensitive because it must lock onto GPS signals that arrive from the other side of Earth!

18. How, when and where will the spacecraft communicate with Earth?

Each spacecraft uses the same S-Band communication frequency, so only one spacecraft can communicate with Earth at a time. Each spacecraft will communicate with Earth approximately once per day depending on which operations -- such as thruster maneuvers -- are occurring during that orbit. Each spacecraft uses an S-band transponder to communicate either with NASA's Tracking and Data Relay Satellite System, NASA's Near Earth Network of ground station antennas, or the commercial Universal Space Network of ground station antennas. Data is sent from the ground stations to the MMS Mission Operations Center at NASA Goddard. Science data is sent directly to the Science Operations Center at the LASP facility in Boulder, Colo.

19. Who manages the MMS Mission?

NASA’s Goddard Space Flight Center in Greenbelt, Md., manages MMS for NASA’s Science Mission Directorate in Washington and has overall responsibility for MMS mission operations.

› Back To Top


20. What is magnetic reconnection?

Magnetic reconnection occurs when magnetic field lines break and reconfigure, often releasing an explosive burst of energy. It is a fundamental physical process that occurs throughout the universe. The release of energy through reconnection produces massive explosions on the sun, such as giant bursts of radiation called solar flares or eruptions in the sun's atmosphere called coronal mass ejections, or CMEs. Closer to Earth, MMS will study the reconnection in Earth's magnetosphere that helps solar energy and material funnel into near-Earth space. Magnetic reconnection can also occur on the night side of Earth, away from the sun, causing material to slip down toward Earth's poles and enhance the aurora.

21. Why is it important to study magnetic reconnection?

By observing magnetic reconnection, MMS studies one of the most fundamental ways that energy and material is transferred throughout the universe.

With each explosion, magnetic reconnection converts energy stored in magnetic fields into other forms of energy, such as heat or the kinetic energy that accelerates individual charged particles and large-scale flows of gas through the universe. So studying magnetic reconnection helps scientists understand the complicated flows of material in the sun, in space and, indeed, throughout the entire universe. Using Earth's own magnetic environment as a laboratory will help astrophysicists understand this powerful phenomenon in stars and galaxies where it cannot be studied directly.

Magnetic reconnection also has a direct effect on Earth's space environment. Reconnection powers giant explosions on the sun that often send radiation and solar material toward Earth. When this material – made of charged particles, a magnetized material known as plasma -- connects with Earth's magnetic fields, additional magnetic reconnection may occur, altering the shape and size of Earth's own magnetic bubble, the magnetosphere. These space weather events can, at their worst, damage satellites in space, interrupt radio communications, and cause power surges in utility grids. But the physics of what happens during magnetic reconnection is poorly understood. By studying the causes and inner workings of reconnection, scientists hope to be able to better understand space weather events.

22. Where does magnetic reconnection occur?

Magnetic reconnection occurs universally in plasmas, the electrically conducting material that makes up stars, fills space, and accounts for an estimated 99 percent of the observable universe. It also happens in science labs on Earth that perform research on the production of fusion energy: magnetic reconnection is seen inside giant vacuum chambers filled with charged gas, called plasma, much like the material in the sun’s atmosphere and throughout space.

MMS will provide greater understanding for all of these examples, by traveling through and directly measuring regions of reconnection where it occurs in near-Earth space.

23. Where near Earth will MMS study magnetic reconnection?

The orbit for MMS is tailored to hit two areas of magnetic reconnection that occurs on a regular basis at the boundaries of the Earth’s magnetosphere. The first year and a half will focus on the magnetosphere’s dayside boundary with the sun and the last six months on the night side of Earth in the Earth’s magnetic tail.

Previous spacecraft, such as Geotail, Polar, Cluster and THEMIS, have helped narrow down the location of regions near Earth where magnetic reconnection occurs. On the dayside, material from the sun, such as the solar wind, and the occasional coronal mass ejection or CME, travel toward Earth with its own set of magnetic fields. If the two sets of magnetic fields aren't lined up with each other, magnetic reconnection can occur, opening up Earth's magnetosphere to an influx of the material and energy from the sun.

On the night side of the planet, Earth's magnetic tail becomes filled with the solar material, or plasma, and stretches until it can no longer contain it. Portions of the plasma and magnetic field then get disconnected from the rest of the tail and escape downstream from Earth, while the energy released shoots plasma back toward Earth, which in turn can catalyze aurora

24. Why do the spacecraft need to fly in a pyramid-shaped pattern?

A three-dimensional shape is crucial to differentiating between the numerous possible characteristics for any given electromagnetic event, including – as in this case – magnetic reconnection. Specifically, the equations governing electromagnetic occurrences can best be measured with a single base spacecraft and one additional spacecraft for each physical dimension, for a total of four.

With the four MMS spacecraft in a three-sided pyramid, or tetrahedral, pattern, three of the spacecraft measure the difference relative to the “base” spacecraft, thus providing the necessary 3-dimensional measurement of reconnection.

In addition, the four MMS observatories can observe a broad swath of space simultaneously, and thus determine whether reconnection events occur in an isolated locale, occur in many places simultaneously, or travel across space. The spacecraft might spot, for example, triggers or results of reconnection that travel through space over a distance.

25. What results are expected from MMS science?

MMS seeks to understand the special conditions necessary to initiate or sustain magnetic reconnection and therefore to differentiate between numerous current theories on the mater. Such theories vary dramatically from those that state magnetic reconnection is initiated by certain microscopic conditions and those that state it is initiated by specific large-scale conditions. The comprehensive suite of MMS instruments will provide a wide range of observations – including magnetic field strength and direction, electric field strength and direction, particle composition, temperature and speed -- with the detail required to distinguish between these many theories.

26. How will the data from the MMS mission further our understanding of space weather?

The transfer of energy through magnetic reconnection powers the origins of space weather events at the sun – such as solar flares and CMEs. It also affects space weather near Earth, such as variations in Earth's own magnetic fields, which accelerate energetic particles that can damage sensitive instrumentation on satellites. By understanding the process in more detail, scientists will be able to improve models of space weather events that will, in turn, improve our forecasting ability.

27. Can the data from this mission support other research programs?

NASA currently supports nine missions in space that observe the magnetic environment near Earth. While these do not focus on magnetic reconnection specifically, they all either measure or observe the effects of incoming radiation, solar material, and magnetism from the sun. Data from MMS will provide a key component to understanding Earth's magnetosphere as a whole by comparing its data with, among others, such missions as:

28. What is unique about the science capabilities of MMS?

MMS is the first NASA multi-spacecraft mission to study magnetic reconnection. Each area of reconnection in space near Earth is just a few miles across – so a spacecraft traveling through one of these regions at some 30 to 60 miles per second will have just a tenth of a second to capture data. Previous missions have, mostly by chance, traveled through such regions but did not have the capacity to capture large amounts of information or to observe the action at its origin.

The MMS orbit will put the spacecraft in the right place to fly directly through regions of magnetic reconnection on a regular basis. In addition—with only a tenth of a second to capture information on any given fly-through -- MMS will be prepared to measure particle velocities and electric and magnetic fields with a time resolution on the order of milliseconds. One instrument, for example, called the Fast Plasma Instrument will collect data 100 times faster than any previous similar instrument.

› Back To Top


29. How many people work on a mission like MMS?

Over 1,000 people have worked to help build MMS.

30. What types of careers are needed for a mission like MMS?

NASA must draw from a wide range of careers in order to successfully design, build, launch and operate a complex mission such as the MMS mission. MMS careers include project scientists, spacecraft system engineers, program managers, technologists, resource analysts, technical photographers, digital artists, science writers, communications experts and trained educators. To learn more about these careers and many others, visit http://bit.ly/W1wtCO.

31. Where can I learn more about the people of MMS?

The MMS Website: http://mms.gsfc.nasa.gov/epo_faces_of_mms.html
Faces of MMS YouTube Channel: http://bit.ly/W1wtCO

› Back To Top


32. What is the best way to follow the progress of the mission?

There are several ways to follow the progress of the MMS mission. Regular updates will be posted at http://www.nasa.gov/mms. While there you can learn more about each of the four spacecraft, the launch vehicle, instrumentation, team members and science.

You can also download and watch the growing collection of NASA Edge vodcasts about the progress of the MMS mission. With a few simple clicks from this page, you'll be on your way to an unscripted and unpredictable look into some of the latest information about this mission including a close-up look at the propulsion systems, hardware, clean room facilities and more! Visit http://mms.gsfc.nasa.gov/epo_nasa_edge.html

Stay in touch with the latest from the mission by following us on FaceBook, Twitter, Pinterest and YouTube.

33. How can I locate MMS visuals?

Images, magnetic reconnection visualizations, and movies about MMS may be found at http://www.nasa.gov/mission_pages/mms/multimedia/index.html or you may take advantage of the growing multimedia gallery at http://mms.gsfc.nasa.gov/images_multimedia.html, which includes the updated images and videos of the MMS observatories, spacecraft assembly and future orbital paths.

34. Where can I find educational resources (materials, lesson plans, podcasts, etc.) related to the MMS mission?

A growing collection of lesson plans, easy-to-do activities and videos can be used to bring the science, technology, engineering and mathematics of the MMS mission to an educational setting. These pages can help one teach everything from building models of the four MMS spacecraft to showing an audience how to explore magnetism and space weather. Visit http://mms.gsfc.nasa.gov/education.html.

Image Token: 
Image Token: 
Image Token: 
Page Last Updated: November 26th, 2014
Page Editor: Holly Zell