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UPDATE: March 30, 2020 - NASA Selects Mission to Study Causes of Giant Solar Particle Storms

NASA has selected a new mission to study how the Sun generates and releases giant space weather storms – known as solar particle storms – into planetary space. Not only will such information improve understanding of how our solar system works, but it ultimately can help protect astronauts traveling to the Moon and Mars by providing better information on how the Sun’s radiation affects the space environment they must travel through.

The new mission, called the Sun Radio Interferometer Space Experiment (SunRISE), is an array of six CubeSats operating as one very large radio telescope. NASA has awarded $62.6 million to design, build and launch SunRISE by no earlier than July 1, 2023.

The Sun Radio Interferometer Space Experiment (SunRISE) is a proposed NASA HeliophysicsÌýExplorer Mission of Opportunity that finished Phase A last year. SunRISE will provide an entirely new viewÌýon particle acceleration and transport in the inner heliosphere by creating the first low radio frequencyÌýinterferometer in space to localize heliospheric radio emissions. Six small spacecraft (S/C) will fly in aÌýsupersynchronous geosynchronous Earth orbit (GEO) within about 10 km of each other and image the Sun in aÌýportion of the spectrum that is blocked by the ionosphere and cannot be observed from Earth. Mission-enablingÌýadvances in software-defined radios and GPS navigation and timing, developed and flown over the past fewÌýyears on the Mars Cube One (MarCO) and DARPA High Frequency Research (DHFR) missions, have finallyÌýmade this concept affordable and low-risk. By determining the location of decametrichectometric (DH) radioÌýbursts from 0.1 MHz–25 MHz, SunRISE provides key information on particle acceleration mechanismsÌýassociated with coronal mass ejections (CMEs) and the magnetic field topology from active regions intoÌýinterplanetary space. SunRISE is highly complementary to current missions, such as Parker Solar Probe andÌýSolar Orbiter, and to the ground-based Daniel K. Inouye Solar Telescope (DKIST).

SunRISE shows that an Explorer Mission of Opportunity can answer fundamental questions in heliophysics,Ìýwith implications for space weather prediction, and serve as a pathfinder for small satellite missions that haveÌýthe potential to revolutionize space science. SunRISE will help us understand the particle acceleration thatÌýoccurs throughout the cosmos and leads to solar flares, solar energetic particles (SEPs), anomalousÌýcosmic rays, and Galactic cosmic rays (GCRs). SEPs and GCRs can damage satellites and lead to radiation sickness (Schwadron et al. 2014). Without new measurement methods (Cucinotta et al. 2010; Schwadron et al.Ìý2015), heliophysics is missing a cornerstone for understanding particle acceleration. Parker Solar Probe (Fox etÌýal. 2016; Kasper et al. 2015) will fly within 10 RS but will not measure particles as they are first accelerated (~3 RS). SunRISE offers the solution: localize radio emission from acceleration source regions and by energeticÌýparticles as they travel interplanetary space, laying the observational foundation for understanding particleÌýacceleration and transport physics at the nearest star.

The SunRISE investigation uses well-studied classes of DH radio bursts: Type II associated with CMEs andÌýType III from electrons escaping from active regions into the solar wind along open magnetic field lines.ÌýSunRISE measures the 3D location of source emission and its evolution in time by determining the emissionÌýfrequency and angular location of the burst on the sky. SunRISE discriminates between competing hypothesesÌýfor the source mechanism of CME-associated SEPs by measuring the location of Type II emission relative to expanding CMEs over distances from 2 RS–20 RS (Objective 1), where the most intense acceleration occurs.ÌýEvery major SEP event seen at Earth is associated with a Type II DH radio burst. Imaging a Type II burstÌýconstrains which major features of a CME are associated with SEP acceleration. SunRISE also determines if aÌýbroad magnetic connection between active regions and interplanetary space accounts for the longitudinal extentÌýof flare and CME SEPs by imaging Type III bursts as they traverse the corona (Objective 2). SunRISE tracesÌýmagnetic field topology from the corona into interplanetary space for the first time.

The theory and implementation of aperture synthesis is well developed for ground-based telescopes. TheÌýSunRISE observatory has three mission-enabling features: Knowledge not Control: The S/C positions do notÌýneed to be controlled to better than 1 km as long as they are known to ~ 1 m accuracy. Integrated Solar DHÌýGlobal Navigation Satellite System (GNSS) Receiver: A Solar DH signal chain measures radio emission at theÌýlocation of the S/C while a GNSS signal chain records signals from GNSS satellites in view. The GNSS signals are used on board to synchronize DH data collection and in ground-based precision orbit determination toÌýprovide accurate S/C location and time. There is no requirement for communication between S/C, whichÌýoperate independently. Correlator Architecture: The DH-GNSS receiver transforms the received DH signals toÌýthe spectral domain. On the ground, the individual S/C data are combined to form SunRISE’s syntheticÌýaperture. This approach provides robustness against interference, reduces on-board computational complexity, and requires only modest downlink data volume. Implementation follows the proven approach of starting fromÌýwell-defined, verifiable Level 1 science requirements that flow to Level 2 project requirements. A passiveÌýformation of six independent and identical S/C, SunRISE drifts in supersynchronous GEO orbit, high above theÌýdisruptive effects of the Earth’s ionosphere.

The SunRISE baseline science mission requires five S/C. An extra S/C provides redundancy. Their orbits areÌýdesigned to keep the formation within a maximum separation of about 10 km, while providing theÌýinterferometer baselines needed to sample a range of angular scales. Nearly all hardware and software designsÌýhave been used before in space. SunRISE integrates them into a 6U form factor, using a standard small satelliteÌýdesign to accommodate the DH-GNSS receiver, GNSS antennas and deployable dipole antennas.ÌýA multi-channel polyphase filter bank processes the full spectrum from 0.1 MHz–25 MHz, allowing dynamicÌýselection of a sufficient number of channels free from S/C generated or terrestrial interference to track radioÌýemission over distances from 2 RS–20 RS. The P/L’s 4-channel GNSS receiver can process up to 42 GNSSÌýsignals simultaneously, providing sub-meter position knowledge (λ/15 at the highest DH frequency) and timeÌýknowledge better than a few nanoseconds. In post-processing conducted on the ground, these GNSSÌýobservables precisely determine the position and time when the DH data were recorded, which are used toÌýcross-multiply the signals coherently, forming a synthetic aperture with the required localization capability.Ìý

SunRISE is operated by JPL during its 12-month mission lifetime, employing existing tools that have been usedÌýfor dozens of missions. Operations consist of regular data collection and orbit maintenance sequences occurringÌýon a 2-week cycle. The science observing profile, with an observing availability greater than 90%, is sufficientÌýto capture the typical duration of Type II bursts. Science data are accumulated continuously, with only briefÌýinterruptions for telecommunications, orbital correction maneuvers and reaction wheel desaturation. DuringÌýdata downlink, small orbital corrections are uplinked, if needed, to maintain the formation without risk ofÌýcollision. SunRISE data flow from the S/C to the Deep Space Network to the JPL Mission Operations CenterÌý(MOC) to the University of Michigan (UM) Science Operations Center (SOC), and finally to the Space PhysicsÌýData Facility.