Interstellar Mapping and Acceleration Probe

After launch, the spacecraft will take several months to transit to about 1,500,000 km (930,000 mi) away from Earth towards the Sun at what is called the first Lagrange point (L1). The spacecraft will then use on-board propulsion to insert into an approximately 10° x 5° Lissajous orbit around L1, very similar to the orbit of Advanced Composition Explorer (ACE). The baseline mission is 3 years, but all expendables are designed for a lifetime of more than 5 years.[6]

IMAP is a simple spin-stabilized (~4 RPM) spacecraft with ten instruments. Daily attitude maneuvers will be used to keep the spin axis and top deck (with solar arrays) pointed in the direction of the incoming solar wind, which is a few degrees away from the Sun. In the L1 Lissajous orbit, the rear deck, with its communication antenna, approximately points at the Earth.[6]

Particle energy spectra for ions and energetic neutral atoms (inset) at 1 AU and the corresponding particle populations and IMAP instrument ranges.

The ten instruments on IMAP can be grouped into three categories: 1) Energetic neutral atom detectors (IMAP-Lo, IMAP-Hi, and IMAP-Ultra); 2) Charged particle detectors (SWAPI, SWE, CoDICE, and HIT); and 3) Other coordinated measurements (MAG, IDEX, GLOWS).

Shown here (top panel) are oxygen fluences measured at 1 AU by several instruments onboard Advanced Composition Explorer (ACE) during a 3-year period, with representative particle spectra obtained for gradual and impulsive Solar Energetic Particles (SEPs), corotating interaction regions (CIRs), Anomalous Cosmic Rays (ACRs), and Galactic Cosmic Rays (GCRs), and (top panel inset) ion fluxes in the Voyager 1 direction using in situ observations from Voyager and remote ENA observations from Cassini–Huygens and Interstellar Boundary Explorer (IBEX). (Middle panel) SWAPI, CoDICE, and HIT provide comprehensive composition, energy, and angular distributions for all major solar wind species (core and halo), interstellar and inner source pick-up ions, suprathermal, energetic, and accelerated ions from SEPs, interplanetary shocks, as well as ACRs. SWE, CoDICE and HIT also provide energy and angular distributions of the solar wind ion and electron core, halo, strahl, as well as energetic and relativistic electrons up to 1 MeV.[6]

IMAP-Lo is a single-pixel neutral atom imager that gives energy and angle-resolved measurements of ISN atoms (H, He, O, Ne, and D) tracked over >180° in ecliptic longitude and energy resolved global maps of ENA H and O. IMAP-Lo has heritage from the IBEX-Lo on IBEX but provides much larger collection power.[6]

IMAP-Hi consists of two identical, single-pixel high energy ENA Imagers that measure H, He, and heavier ENAs from the outer heliosphere. Each IMAP-Hi Imager is very similar in design to the IBEX-Hi ENA Imager but incorporate key modifications that enable substantially improved resolution, spectral range, and collection power. The instrument also incorporates a time-of-flight (TOF) system for identification of ENA species.[6]

The IMAP-Ultra instrument images the emission of ENAs produced in the heliosheath and beyond, primarily in H atoms between ~3 and 300 keV, but it is also sensitive to contributions from He and O. Ultra is nearly identical to the Jupiter Energetic Neutral Imager (JENI), in development for flight on the European Space Agency's Jupiter Icy Moon Explorer (JUICE) mission to Jupiter and Ganymede. Ultra's primary differences from JENI are the use of two identical copies, one mounted perpendicular to the IMAP spin axis (Ultra90) and one mounted at 45° from the anti-sunward spin axis (Ultra45) for better sky coverage, and the use of slightly thicker, UV-filtering foils covering the back plane MCPs to reduce backgrounds associated with interstellar Lyman-α photons.[6]

The Solar Wind and Pickup Ion (SWAPI) instrument measures solar wind H⁺ and He⁺⁺ and interstellar He⁺ and H⁺ pick-up ions (PUIs). SWAPI is nearly identical to the New Horizons Solar Wind Around Pluto (SWAP) instrument. SWAPI is a simplification of SWAP, and by removal of SWAP's retarding potential analyzer, significantly increases transmission and improves sensitivity, further enhancing PUI observations.[6]

The Solar Wind Electron (SWE) instrument measures the 3D distribution of solar wind thermal and suprathermal electrons from 1 eV to 5 keV. SWE is based on the heritage Ulysses / SWOOPS, ACE/SWEPAM and Genesis/GEM instruments, with updated electronics based on Van Allen Probes/HOPE. SWE is optimized to measure in situ solar wind electrons at L1 to provide context for the ENA measurements and perform the in situ solar wind observations necessary to understand the local structures that can affect acceleration and transport.[6]

The Compact Dual Ion Composition Experiment (CoDICE) measures charged particles in two separate energy ranges in a compact, combined instrument. CoDICELo is an electrostatic analyzer with a time-of-flight versus energy (TOF/E) subsystem to measure the 3D velocity distribution functions (VDFs) and ionic charge state and mass composition of ~0.5–80 keV/q ions. CoDICEHi uses the common TOF/E subsystem to measure the mass composition and arrival direction of ~0.03–5 MeV/nuc ions and ~20–600 keV electrons.[6]

The High-energy Ion Telescope (HIT) uses silicon solid-state detectors to measure the elemental composition, energy spectra, angular distributions, and arrival times of H to Ni ions over a species-dependent energy range from ~2 to ~40 MeV/nuc. HIT, heavily based on the Low Energy Telescope (LET) on the Solar Terrestrial Relations Observatory (STEREO), delivers full-sky coverage with a large geometry factor. A portion of the HIT viewing area is also optimized to measure 0.5 - 1.0 MeV electrons.[6]

The IMAP magnetometer (MAG) consists of a pair of identical triaxial fluxgate magnetometers that measure the 3D interplanetary magnetic field. Both magnetometers are mounted on a 1.8 m boom, one on the end and the other in an intermediate position. This configuration, through gradiometry, reduces the effect of spacecraft magnetic fields on the measurements of the instrument by dynamically removing the spacecraft field. The MAG are based on the Magnetospheric Multiscale Mission magnetometers.[6]

The Interstellar Dust Experiment (IDEX) is a high-resolution dust analyzer that provides the elemental composition, speed and mass distributions of interstellar dust particles. IDEX's sensor head has a large effective target area (700 cm² [110 sq in]), which allows it to collect a statistically significant number of dust impacts (> 100/year).[6] This instrument was constructed at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder.[7]

The GLObal Solar Wind Structure (GLOWS) is a non-imaging single-pixel Lyman-α photometer that will be used to observe the sky distribution of the helioglow to better understand the evolution of the solar wind structure. The helioglow is formed by the interaction between interstellar neutral hydrogen (ISN H) and solar photons in a specific ultraviolet region called the Lyman-α waveband.

Photons enter the detector through a collimator with a baffle that restricts the photons to those only from GLOWS’ field of view (FOV). A spectral filter allows only photons found in the Lyman-α wavelength band into a channel electron multiplier (CEM) detector that counts them. GLOWS’ FOV shifts with IMAP's daily spin axis redirection, allowing for sequential observations of the structure of the solar wind from separate locations around the Sun. The Lyman-α photon counts from these observations can be used to build a more comprehensive picture of the solar wind structure and how it changes through the solar cycles.

GLOWS design and assembly is led by the Space Research Center, Polish Academy of Sciences, Warsaw, Poland (CBK PAN).[8][9]

[6]

Nominally, IMAP will have two 4-hour contacts per week through the NASA Deep Space Network (DSN). This is sufficient to upload any commands, download the week's worth of science data and housekeeping, and perform spacecraft ranging required for navigation. DSN will communicate with the IMAP Mission Operation Center (MOC) at Johns Hopkins University Applied Physics Laboratory, which will operate the spacecraft. All science and ancillary data will pass through the MOC to the Science Operations Center (SOC) at LASP.[7] The IMAP SOC at LASP will be responsible for all aspects of instrument operations: planning, commanding, health and status monitoring, anomaly response, and sustaining engineering for the instruments. The SOC will also handle science data processing (including data calibration, validation and preliminary analysis), distribution, archiving, and maintaining the IMAP data management plan. Science data will be produced centrally using algorithms, software, and calibration data provided and managed by each instrument team.

All science and other data will be shared with the heliophysics community as rapidly as practical with an open data policy compliant with the NASA Heliophysics Science Data Management Policy. The NASA Space Physics Data Facility (SPDF) is the final archive for IMAP, with regular transfer of data to the SPDF so that the data can be made available through their Coordinated Data Analysis Web (CDAWeb) site.[6]

IMAP will supply critical real-time space weather data through its "IMAP Active Link for Real-Time" or I-ALiRT. IMAP will continuously broadcast a small subset (500 bit/s) of the science data for I-ALiRT to supporting ground stations around the world when not in contact with the DSN. During DSN tracks, the flight system includes the space weather data in the full-rate science data stream, which the MOC receives from the DSN and forwards to the SOC. In either case, the SOC processes these real-time observations to create the data products required by the space weather community. Data include all of the important parameters currently provided by Advanced Composition Explorer (ACE), but at significantly higher cadence, and also include several new key parameters.[6]

This is the fifth mission in NASA's Solar Terrestrial Probes program.[10] The Heliophysics Program Office at NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the STP program for the agency's Heliophysics Science Division in Washington, D.C.

The mission's principal investigator is David J. McComas of Princeton University. The Johns Hopkins University's Applied Physics Laboratory in Laurel, Maryland, will provide project management.[4]

The mission is cost-capped at US$564 million, excluding cost for the launch on a SpaceX Falcon 9 launch vehicle from Cape Canaveral Space Launch Complex 40 (SLC-40) at Cape Canaveral Space Force Station (CCSFS) in Florida.[11] As of April 2020, the preliminary total cost of the mission is estimated to be US$707.7 million to US$776.3 million.[1]

The Announcement of Opportunity for the 2018 Heliophysics Science Missions of Opportunity (MoO) included the option of proposing a Small Complete Mission (SCM) to utilize the IMAP ESPA Grande to launch a secondary payload. Up to two ports on the ESPA Grande ring may be allocated for Science MoOs. The payloads are designated as Class D as defined in NPR 8705.4.[12]

The Announcement of Opportunity for the 2018 Heliophysics Technology Demonstration (TechDemo) Missions of Opportunity requested SCM proposals for spaceflight demonstration of innovative medium Technology Readiness Level (TRL) technologies that enable significant advances in NASA's Heliophysics Science Objectives and Goals. TechDemo investigations must be proposed for flight as a secondary payload with the IMAP mission. Up to two ports on the ESPA Grande ring may be allocated for TechDemo. The payloads are designated as Class D as defined in NPR 8705.4. Down-selection is targeted for the third quarter FY 2020.[13]