The Science

The Sun

Space Weather

The term Space Weather refers to the entire space environment between the Sun and the Earth. More specifically, the study of space weather focuses on the impacts this weather has on satellites in orbit as well as technology on Earth. Space weather originates from the Sun, typically in the form of solar wind, coronal mass ejections, or solar flares. This barrage of particles and energy from the Sun hits the Earth’s magnetosphere, energizing the particles as they accelerate towards Earth’s ionosphere, thermosphere, and upper atmosphere. These interactions can have many consequences. For example, solar flares can produce strong x-rays that can block high-frequency radio communication, while coronal mass ejections can create geomagnetic storms that induce an excess current that can impact and even shut down power grids. These potentially severe impacts highlight the importance of understanding space weather to better forecast and ultimately prepare for extreme space weather events.

Coronal Mass Ejections

A Coronal Mass Ejection (CME) is a solar event characterized by the eruption of plasma and magnetic fields at the corona of the Sun. CMEs eject a great amount of mass, sometimes equal to the amount of water in Lake Michigan, and travel at millions of miles per hour. CMEs originate from twisted magnetic fields within the sun that explode after abrupt realignment of those fields. As CMEs travel away from the Sun, they accelerate Solar Energetic Particles (SEPs), such as electrons and protons. When these particles reach Earth, they can cause disruption to Earth’s own magnetic fields affecting radio, GPS, and electrical grids. CMEs are of great interest to scientists. Specifically, scientists would like to better understand the structure of CMEs and how they accelerate SEPs. Understanding CMEs would allow scientists to make better predictions of when CMEs may occur and help set up warning systems for when CMEs do occur.

Solar Radio Bursts

Solar bursts are an influential type of space weather, as they can greatly affect life on the surface of the Earth, particularly due to the increase of technology. Solar bursts are low-frequency solar radio emissions that arise from the solar atmosphere. The solar bursts that SunRISE cares about can be categorized as Type II or Type III. Type II bursts are produced by shock accelerated electrons, while type III bursts are produced by flare accelerated electrons. By understanding the process in which these bursts progress and are developed, we can better predict space weather.

Magnetosphere

The magnetosphere is the region of space around the object in which the object’s magnetic field is dominant. While not all planets have magnetic fields, The Earth’s is created by the moving molten iron in the core. Because of the electrical currents in the Sun, the Sun also has a magnetic field. This includes the solar wind that permeates throughout the solar system and beyond. The Sun’s magnetosphere interacts with the Earth’s and shortens the size of the Earth’s magnetosphere that faces towards the Sun. Like a magnet, the Sun’s magnetic field has poles that flip at the peak of solar activity every 11 years. Both the Earth’s magnetic field and the Sun’s work together to help decrease the amount of radiation that reaches the Earth – the Earth’s helps to protect us from UV rays and other forms of radiation coming from the Sun and the Sun’s field helps to protect us from galactic cosmic radiation.

Layers of the Atmosphere

An atmosphere is a set of layers of gases that are mutually buoyant (held by gravity) in the sky. The higher the layer is, the less of air there is. Overall, Earth’s atmosphere is composed of nitrogen in the majority, oxygen as the runner-up, and a perceptible amount of argon and carbon dioxide to fill the rest. There are a total of seven layers in the Earth’s atmosphere, with the troposphere at the bottom and the Exosphere at the top. From the ground up to 12 miles (20 km) is the troposphere, where life is harbored and clouds are seen. From the 12-mile mark to the 31-mile (50 km) mark is the stratosphere, where the Ozone helps keep us warm and absorb radiation from the Sun. The air here is about a thousand times tinier than it is at sea level, and this is where jets are confined to. Going up is the mesosphere, ranging from 31 miles (50 km) and 53 miles (85 km). This layer is the coldest part of Earth’s atmosphere, with temperature averaging about -130 F (-90 C). Meteors usually burn up in this layer. The next layer is the thermosphere, which extends from 56 miles (90 km) to between 310 and 620 miles (500 and 1,000 km). This is where auroras would occur when particles get ionized by solar radiation. In particular, parts of the mesosphere, thermosphere, and exosphere are generally called the ionosphere, where ionized particles are observed. This ionized layer poses a great challenge to the astronomers who use ground telescopes to study the Sun because it rejects any radio signals that is less than 15 MHz, where Solar Energetic Particles fall under. Thus, it is important that we establish space-based telescopes in order to obtain a relatively unobtrusive view of the Sun.

Heliosphere

In simplest terms, the Heliosphere is the range of space that is mainly under the influence of a star: specifically its solar wind. This range of space not only includes the solar system but expands far beyond. As a star emits its solar wind in all directions, the space this wind travels makes up the Heliosphere. Eventually, the pressure from the interstellar medium – the matter that takes up the space in between star systems – overpowers the solar wind and creates the edge of the Heliosphere. The bubble of space inside the Heliosphere has lower radiation levels than outside because the Heliosphere helps to protect against galactic cosmic radiation. As the solar wind encounters more pressure from the interstellar medium, at about 100 AU (100x the distance from the Sun to Earth) for the Sun, it encounters the termination shock and slows down. After this slow down the solar wind is said to enter the region known as the heliosheath as it transitions to the edge of the Heliosphere. The outermost edge of the Heliosphere is known as the Heliopause. Two Human-made spacecraft have recently traveled into the Heliopause – Voyager 1 and 2 – and thus are said to have left the solar system.

Radio Instrumentation

CubeSats

CubeSats are a type of small satellite that is commonly used in space research because of their ability to be assembled with commercial off-the-shelf electronic and structural components. They also have specific criteria for shape, size, and weight which helps reduce costs for building and deployment and allows them to be mass-produced. The standard unit of a CubeSat is 1U or 10 cm by 10 cm by 10 cm and is 1-1.33 kg. CubeSats are made in multiples of these units which allow for sizes of 1.5U, 2U, 3U, and 6U. The CubeSats deployed in SunRISE are 6U. CubeSats require a dispenser system that interfaces between the CubeSat and the launch vehicle (LV). This provides an attachment to the launch vehicle and protects the CubeSat during launch. Dispenser systems are designed to hold satellites that conform to the standard form factor (size, shape, mass).  

Long Wavelength Antenna

The Long Wavelength Array (LWA) is a specialized antenna receiver that’s able to receive radio waves at extreme distances at relatively low frequencies. This antenna is a cross-dipole receiver that can be connected in a variety of different configurations. A dipole antenna is the most simple and common form of an antenna where two conductors of opposite charge are connected together by a feed line. The cross-dipole antenna is a slight modification of this where an additional dipole is added perpendicular to the other allowing it to be used in both horizontally and circularly polarized modes. The ability to receive signals using multiple polarizations is important for tuning out interference.   The motivation behind the LWA design is that for antennas to obtain resolution at long wavelengths, the diameter of the instrument must be increased significantly. This is often impractical due to manufacturing costs and mechanical considerations. The front end electronics convert the balanced dipole to an unbalanced 50-ohm impedance and around 35 dB gain to each dipole that’s connected to its own receiver. By changing the phase relationship between the dipoles to create a circular polarization, the antenna can discriminate a certain direction of rotation. For the SunRise missions ground-based prototype, we will be using the LWA antenna from Reeve and operating from a frequency range of 20-90 MHz. The spectral targets will include Jovian emissions, Auroral kilometric radiation, medium frequency bursts, and other interfering satellites.

Radio Interferometry

Sounds cool, right? What’s even cooler is the science behind it! Radio interferometry is what allows us to see and capture low-frequency signals. Signals are invisible to naked/unaided eyes as they travel through walls, buildings, even human bodies without anyone noticing it. In order to analyze or see them, scientists have pooled together the brightest minds of the world and built numerous telescopes to observe what cannot be seen. In the last century, scientists discovered that the longer wavelength of a signal, the larger a telescope is required for observation. This put a limit to a range of signals scientists could see, and that was problematic since many signals of interests were on the lower half of the electromagnetic spectrum, commonly known as the radio range. It was when people realized building increasingly larger telescopes not only was not economical but also was restricted by various mechanical constraints. Enters radio interferometry. Radio interferometry uses sophisticated mathematical and physical models to patch incoming signals received by different telescopes together. It takes temporal and geospatial variances into account to reconstruct images that would have required a telescope that is hundreds, if not thousands, times in size. Now, we are using the diameter of the Earth as the size of an imaginary telescope to make groundbreaking discoveries every day.

References

1. Alibay, Farah et al. “SunRISE Status: Concept Development Update.” IEEE Aerospace Conference Proceedings. Vol. 2018-March. IEEE Computer Society, 2018. 1–11. IEEE Aerospace Conference Proceedings. Web.

2. “Coronal Mass Ejections.” Coronal Mass Ejections | NOAA / NWS Space Weather Prediction Centerwww.swpc.noaa.gov/phenomena/coronal-mass-ejections.

3. Ellingson, Steven W, et al. “The Long Wavelength Array.” Proceedings of the IEEE, vol. 97, no. 8, Aug. 2009, pp. 1421–1430.

4. Garner, Rob. “Solar Storm and Space Weather – Frequently Asked Questions.” NASA, NASA, 19 Mar. 2015, www.nasa.gov/mission_pages/sunearth/spaceweather/index.html.

5. Gregersen, Erik. “Heliosphere.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 10 Sept. 2018, www.britannica.com/science/heliosphere. 6. “Heliosphere.” NASA, NASA, science.nasa.gov/heliophysics/focus-areas/heliosphere.

7. Kasper, Justin C. SunRISE, Sun Radio Interferometer Space Experiment. July 30th, 2018.

8. Kasper, Justin. “The Sun Radio Interferometer Space Experiment (SunRISE): Revealing How Energetic Particles are Accelerated and Released into Interplanetary Space.” 42nd COSPAR Scientific Assembly 2018, Pasadena, California, July 14-22. Presentation.

9. Layers of Earth’s Atmospherescied.ucar.edu/atmosphere-layers.

10. “Magnetosphere.” Magnetosphere – an Overview | ScienceDirect Topics, 2015, www.sciencedirect.com/topics/earth-and-planetary-sciences/magnetosphere. “Magnetospheres.” NASA, NASA, science.nasa.gov/heliophysics/focus-areas/magnetosphere-ionosphere.

20. Potter, Sean. “NASA Selects Mission to Study Causes of Giant Solar Particle Storms.” NASA, NASA, 30 Mar. 2020, www.nasa.gov/press-release/nasa-selects-mission-to-study-causes-of-giant-solar-particle-storms.

21. Reeve, Whitham D. “Long Wavelength Array Active Crossed-Dipole Antenna.” LWA Active Crossed-Dipole Antenna, 22 Feb. 2014, www.reeve.com/RadioScience/Antennas/ActiveCrossed-Dipole/LWA_Antenna.htm.

22. Space Weather Impacts. www.swpc.noaa.gov/impacts. “Structural Dynamics Test of Spiral Tube Actuator for Controlled Extension / Retraction (STACER) Antenna Deployment in Microgravity.” NASA, NASA, flightopportunities.nasa.gov/technologies/55/.

24. Thompson, A. R., et al. Interferometry and Synthesis in Radio Astronomy. 3rd ed., Springer Open, 2017.

25. US Department of Commerce, NOAA. Layers of the Atmosphere. 12 Aug. 2019, www.weather.gov/jetstream/layers.

26. Zell, Holly. “The Difference Between Flares and CMEs.” NASA, NASA, 10 Feb. 2015, www.nasa.gov/content/goddard/the-difference-between-flares-and-cmes.

27. Zell, Holly. Earth’s Atmospheric Layers. 2 Mar. 2015, www.nasa.gov/mission_pages/sunearth/science/atmosphere-layers2.html.

28. Zell, Holly. Space Weather. 18 May 2015, www.nasa.gov/mission_pages/rbsp/science/rbsp-spaceweather.html. “Space Weather Phenomena.” Space Weather Phenomena | NOAA / NWS Space Weather Prediction Center, www.swpc.noaa.gov/phenomena.