HCREM, a rendezvous mission to comet Halley

1 - Introduction

We propose a Halley Comet Rendezvous Mission (HCREM) feasible with currently available propulsion technology with a target launch date around 2040. The mission concept has been developed to reach comet 1/P Halley well before it crosses Saturn’s orbit, i.e. before the onset of major activity driven by the sublimation of super-volatile gases, as CO and CO2, or water ice. Even considering potential future development in nuclear propulsion systems, launches beyond 2040 cannot be taken into account, as they would prevent the observation of the crucial starting phases of comet activity.

An interplanetary low-thrust gravity-assisted trajectory design strategy is proposed. The trajectory design combines gravity-assist maneuvers with electric propulsion arcs to maximize the allowable scientific payload mass while keeping the transfer duration reasonable. To ensure the propellant budget remains within acceptable limits, most plane change maneuvers are achieved via either a Jupiter or a Saturn flyby.

Additionally, an innovative very wide angle camera is proposed as part of the instrumentation complement.

2 - The 1/P Halley Comet

1P/Halley remains one of the most scientifically valuable comets due to its well-documented periodic appearances (approximately 75 years) and historical significance. Previous flyby missions in 1986—such as Giotto and Vega—offered precious scientific insights but were inherently limited due to fast passage, i.e. brief observation windows, and by the challenges posed by the comet high-speed retrograde motion.

Thus, the return of 1P/Halley in 2061 is promoting a wide interest in ground and space observations ([1][2]). This work proposes an ambitious rendezvous mission that seeks to overcome the previous limitations by enabling extended, in-depth study of the Halley comet in situ.

3 - Scientific Objectives

The primary objective of the mission is to analyze the comet nucleus and coma before water sublimation begins. A rendezvous mission, rather than another flyby, could significantly enhance cometary science by allowing extended, close-range observations of both its surface composition and activity. This will provide crucial insights into primordial matter from the early solar system, aiding our understanding of planetary formation and evolution.

Key scientific goals include:

• Characterizing surface morphology and geological processes.
• Investigating the composition and evolution of volatile materials.
• Tracking ejected particles to understand coma formation dynamics.
• Monitoring changes over time as solar radiation influences activity.

The mission would also provide a rare opportunity to study the comet evolution since its last return, yielding crucial insights into cometary aging, sublimation processes, and volatile preservation.

4 - Trajectory and payload

One of the major technical challenges is reaching Halley’s comet when it is beyond Saturn’s orbit while ensuring that the spacecraft remains operational under extreme conditions. The authors propose a trajectory utilizing gravitational assists from a giant planet, maximizing fuel efficiency and enabling an optimal rendezvous ([3][4]).

A critical aspect of the spacecraft design is the source of power for the propulsion system. To produce the power needed by the electrical  thruster at large distances from the Sun, where solar radiation is scarce, the spacecraft will rely on radioisotope thermoelectrical generators. In this way, extended operations deep within the coma will be possible without risking damage to solar panels from high dust densities.

Given Halley's comet orbital dynamics, the mission requires early preparation and strategic planning. A launch before 2040 is necessary to ensure proper alignment for gravitational assist maneuvers.

The transfer is made possible by the gravitational assistance of a giant planet. The resulting mission will be capable of reaching the comet beyond the distance of Saturn, when the sublimation of super-volatile species will be ongoing, and well before the onset of the sublimation of water (4 AU). After rendezvous, the spacecraft will accompany the comet for several years before, around and after perihelion (July 2061).

An innovative imaging system is proposed as part of the payload. A very large field of view (100°) camera will allow the simultaneous acquisition of the comet surface and the surrounding environment. Trajectories of chunks and clouds ejected by pits or fractures, crucial to understanding the cometary activity, could be followed for several degrees [2].

5 - Conclusions

This work highlights the scientific value of a rendezvous mission to Halley's comet in 2061, underlining that early preparation and technological innovation will be key to mission success.

By overcoming previous limitations, this mission would answer fundamental questions about cometary evolution and provide unprecedented insights into Halley’s activity. It could allow scientists to monitor the comet for years, study how cometary volatiles evolve, and refine theories about comet formation and preservation.

References

[1] J. Horsewood, R. McNutt, A. Delamere, “Preparing for the Return of Comet Halley in 2061”, OPAG June 2024 Meeting (2024).

[2] C. Barbieri, A. Beolchi, I. Bertini, V. Da Deppo, E. Fantino, R. Flores, C. Pernechele, C. Pozzi, “Preparing for the 2061 return of Halley’s comet – A rendezvous mission with an innovative imaging system”, submitted to PSS (Special issue) (2025) https://arxiv.org/pdf/2502.12816

[3] A. Beolchi, C. Pozzi, E. Fantino, R. Flores, I. Bertini, C. Barbieri, “Low-Thrust Gravity-Assisted Rendezvous Trajectory to Halley’s Comet”, Proceedings of the 75^th International Astronautical Congress, Paper IAC24-C1.8.7 (2024).

[4] R. Flores, A. Beolchi, E. Fantino, C. Pozzi, M. Pontani, I. Bertini, C. Barbieri, “Design of a low-thrust gravity-assisted rendezvous trajectory to Halley's comet”, submitted to Acta Astronautica (2025) https://doi.org/10.48550/arXiv.2503.05358