Initial proposal (2019-2024)
Each probe is to weigh about 200 kilograms, to use radioisotope thermoelectric generators for power, and to carry 50 kilograms or more of scientific instruments such as optical cameras, magnetometers, dust detectors, and neutral atom and particle payloads. They will also study anomalous cosmic rays, interplanetary dust and the interstellar medium. Depending on whether monopropellant or ion propulsion is used, the probes would be launched using either Long March 3B or Long March 5 rockets. While IHP-1 and IHP-2 will use RTGs for power, IHP-3, if approved, would use a nuclear reactor.
The dwarf planet Quaoar and its moon Weywot were considered as potential flyby targets for IHP-1. Centaur exploration has also been considered for both probes.
While a 2024 launch date was targeted, the COVID-19 pandemic has caused some delays, which rendered it to launch at a later date. Future dates of 2026 launches have been considered.
The stated goal of the spacecraft was to travel a total of 100 astronomical units by 2049, which is the centennial celebration of the People's Republic of China's founding.
If IHP-1 would have been launched in May 2024, it was planned to return to Earth in October 2025 for a gravity assist, then loop back in December 2027 for yet another gravity assist before flying by Jupiter in March 2029 to proceed on a trajectory toward the nose of the heliosphere and potentially make observations of centaurs or Kuiper belt objects, including the flyby of Quaoar, along the way.
IHP-2 was expected to launch before May 2026 and was proposed to receive two gravity assists from Earth in May 2027 and March 2032, respectively. A flyby of Jupiter in May 2033 is then proposed to send it on a path to fly by Neptune in January 2038 at only 1,000 kilometers above its cloud tops. The probe may also release an atmospheric impactor prior to the flyby.
If IHP-2 launch combines with another planned Chinese interplanetary mission Tianwen-4, there may be a chance for comparative planetology in some form because IHP-2's proposed flyby of Neptune and Triton in 2038 and Tianwen-4's possible additional probe for Uranus flyby could also be in 2039, allowing for comparisons of similar planetary cohorts within short span of few years. Earlier IHP-1's Quaoar flyby was also planned to occur in 2040.
Scientific payload
The probes were proposed to carry the following suite of instruments:
| Instrument |
Dimension, range, resolution |
| Vector Atomic Magnetometer |
Electromagnetic radiation:
8–70,000 nT; sensitive to 0.001–0.05 nT/Hz1/2, accurate to 0.005–3 nT |
| Plasma Analyzer |
Plasma wave observations:
0.005–30 keV, resolution 8% |
| Pick-up Ion Analyzer |
Ion counter: 0.002–40 keV/e, energy resolution 5%; mass resolution of H+, He+, He2+, N+, O+, Ne+ |
| High Energy Particle Analyzer |
Ionization analysis:
Protons, 7–300 MeV
Electrons, 200 keV – 10 MeV
Heavy ions, 10–300 MeV/n |
| Energetic Particle Analyzer |
Ionization analysis:
Protons, 20 keV – 7 MeV
Electrons, 20–400 keV
Heavy ions, 0.5–20 MeV/n |
| Energetic Neutral Atom Analyzer |
Images emission of energetic neutral atoms; ~1–100 keV H |
| Dust Particle Analyzer |
Dust analysis: 400 cm2 area, 10−17–10−9 kg range, 1 – 103 km/s impact, 10−16–10−13 charge |
| Camera |
Narrow-angle: 1,200 mm focal length, 150 mm aperture; 0.78°×1.05° FOV, 40–1,000 nm wavelength, 6–8 spectra channels
Mid-angle: 150 mm focal length, 37.5 mm aperture, 6.28°×8.34° FOV, 460–1,000 nm wavelength, 6–8 spectra channels
Wide-angle (4×); 38 mm focal length, 20 mm aperture, 30°×23.4° FOV, 600–1,000 nm wavelength |
| UV photometer |
Ultraviolet mapping: 121.6 nm, 58.4 nm wavelength, 4°×4° FOV |
| Infrared spectrometer |
Infrared mapping: 1–16 μm spectrum range, 9 cm−1 spectrum resolution, 0.5° FOV |
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