# Interstellar Mapping and Acceleration Probe

The Interstellar Mapping and Acceleration Probe (IMAP) is a heliophysics mission that will simultaneously investigate two important and coupled science topics in the heliosphere: the acceleration of energetic particles and interaction of the solar wind with the local interstellar medium. These science topics are coupled because particles accelerated in the inner heliosphere play crucial roles in the outer heliospheric interaction. In 2018, NASA selected a team led by David J. McComas of Princeton University to implement the mission, which is currently scheduled to launch no earlier than September 2025. IMAP will be a Sun-tracking spin-stabilized satellite in orbit about the Sun–Earth L1 Lagrange point with a science payload of ten instruments. IMAP will also continuously broadcast real-time in-situ data that can be used for space weather prediction.
It is the fifth mission selected in the Solar Terrestrial Probes program, after TIMED, Hinode, STEREO and MMS.

## Science

Acceleration of charged particles up to high energy is ubiquitous throughout the universe, occurring at stars, magnetospheres, black holes, neutron stars, supernova remnants, and other locations. The precise processes behind this acceleration are not well understood. There are intermediate suprathermal particles which have energies between the energetic particles and the bulk thermal plasma. Understanding how these particles are energized and form the seed population of the energetic particles is one of the science topics that IMAP will investigate.
The solar wind and its associated magnetic field have blown a bubble in interstellar space called the heliosphere. IMAP will study the heliosphere boundary where the solar wind collides with material from the rest of the galaxy. Using Energetic Neutral Atoms (ENAs), IMAP will image this interaction region from the inner Solar System. In addition, IMAP will also directly measure the neutral particles of the interstellar medium, because they flow through the heliosphere relatively unmodified.
IMAP will also investigate the source of the IBEX ribbon.
IMAP's science goals are based on the four science objectives specified in the IMAP Announcement of Opportunity (from the outside in):
* Improve understanding of the composition and properties of the local interstellar medium (LISM).
* Advance understanding of the temporal and spatial evolution of the boundary region in which the solar wind and the interstellar medium interact.
* Identify and advance the understanding of processes related to the interactions of the magnetic field of the Sun and the LISM.
* Identify and advance understanding of particle injection and acceleration processes near the Sun, in the heliosphere and heliosheath.

## Mission
### Profile

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.

### Spacecraft

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.

### Instruments

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.

#### IMAP-Lo

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.

#### IMAP-Hi

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.

#### IMAP-Ultra

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.

#### Solar Wind and Pick-up Ion (SWAPI)

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.

#### Solar Wind Electron (SWE)

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.

#### Compact Dual Ion Composition Experiment (CoDICE)

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.

#### High-energy Ion Telescope (HIT)

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.

#### Magnetometer (MAG)

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 sensors are based on the Solar Orbiter mission magnetometers and are built by Imperial College London.

#### Interstellar Dust Experiment (IDEX)

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 cm$^2$ [110 sq in]), which allows it to collect a statistically significant number of dust impacts (> 100/year). This instrument was constructed at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder.

#### GLObal solar Wind Structure (GLOWS)

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).

### Communications

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. 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.

### Space weather data

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.

### Management

This is the fifth mission in NASA's Solar Terrestrial Probes program. 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.
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. As of April 2020, the preliminary total cost of the mission is estimated to be US$707.7 million to US$776.3 million.

## Missions of Opportunity

NASA plans on including an EELV Secondary Payload Adapter (ESPA) (Evolved expendable launch vehicle) Grande ring below the IMAP spacecraft, which will give the opportunity for 4 or 5 secondary payloads to ride along with the IMAP launch. Deployment of the secondary payloads will occur after IMAP deployment into a transfer orbit to the Earth-Sun L1 Lagrange point. Some of the slots may be used by other divisions in the Science Mission Directorate and some may be used by other government agencies. Two opportunities for slots were competed for the Heliophysics Science Division as part of the Third Stand Alone Missions of Opportunity Notice (SALMON-3) Program Element Appendix (PEA), with proposals for both due on 30 November 2018. Selection for Phase A studies should be announced in 2019.