The arrival of 3I/ATLAS in our solar system has led to several proposals for rendezvous missions to study it up close. As the third interstellar object (ISO) ever detected, the wealth of information provided by direct study will be groundbreaking in many ways. However, the architecture of a mission to intercept an interstellar comet poses a number of significant challenges for mission designers and planners. Chief among them is the technology readiness level (TRL) of proposed propulsion systems, ranging from conventional rockets to directed energy propulsion (DEP).
Mission proposals so far have focused on chemical rockets that launch from Earth, such as NASA’s Janus mission or ESA’s Comet Interceptor, or existing missions such as the Juno spacecraft, which would adjust its orbit to rendezvous with Earth. In a recent paper, researchers at the Initiative for Interstellar Research (i4is) propose postponing a direct transfer mission scheduled to launch from Earth today. Instead, they demonstrated how a mission launching in 2035 could intercept 3I/ATLAS using indirect solar-overs maneuver.
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The main challenges for a direct mission to rendezvous with 3I/ATLAS stem from the celestial dynamics of the target object, high geocentric velocity, and initial detection delay. The first problem effectively eliminates rendezvous missions that rely on onboard propulsion systems to match the comet’s velocity, thereby enabling long-term close-up studies of the object. As a result, fly-by missions are the preferred option. However, the second and third considerations exclude direct missions. Because the optimal launch date had already passed before it was discovered. In an email, Hibberd told Universe Today:
“In the case of the Direct mission, object 3I/ATLAS was already traveling within Jupiter’s orbit at speeds in excess of 60 km/s, so it was discovered too late. In the end, this turned out to be past the optimal launch date for the Direct mission to intercept it. One paper states that 3I/ATLAS was already in the Sun/Earth’s L2 It turned out that if it had been anchored at the same point, it would have been difficult to create a “comet interceptor” probe.” ”
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This is where the Hibbard-designed Optimal Interplanetary Orbit Software (OITS) was used to assess the feasibility of direct and indirect missions to intercept ISO. This software has a track record of solving missions with Solar Oberths. This includes previous i4is research on the mission to intercept ‘Oumuamua, the first ISO ever detected (Project Lyra). Integral to the Rila mission and other missions utilizing OITS is the use of gravity assist (GA) and overbert maneuvers.
The former involves slingshot maneuvers that use the gravity of a planet (or moon) to increase speed. The latter consists of a spacecraft under the gravitational influence of a large celestial body (the Sun), waiting to reach its point of closest approach (perihelion) and applying thrust to achieve a high geocentric velocity. The spacecraft could achieve escape velocity from the solar system in this way, or gain enough speed to rendezvous with the ISO, which has already traveled a long distance by this point. Hibbard said:
“In the case of the Direct mission, object 3I/ATLAS was discovered too late, as it was already moving within Jupiter’s orbit at speeds in excess of 60 km per second. In the end, this turned out to be past the optimal launch date for the Direct mission to intercept it. One paper states that when 3I/ATLAS was launched, it was already in the Sun/Earth’s L2 It turned out that if we had patrolled the area, it would have been difficult to create a “comet interceptor” probe.” ”
The Solar Oberth option is designed for cases where an interstellar object is passing through perihelion (closest approach to the Sun) and is rapidly moving away from the Sun. Recognizing the fact that capturing such objects requires the spacecraft to generate enormous velocities, it exploits the so-called “oververse effect” to generate this velocity. As the spacecraft approaches the Sun, the Sun’s gravity increases its speed until it reaches perihelion, at which point the spacecraft fires its solid fuel engines to maximize the “slingshot effect” and rapidly accelerate the spacecraft toward the target object, in this case 3I/ATLAS.
Based on OITS simulations, the research team found that interception could be achieved with a solar-Obert maneuver, but that the launch would have to occur in 2035 to achieve optimal alignment between Earth, Jupiter, and 3I/ATLAS. The flight period would be 50 years (although Hibbard said this could be shortened slightly). “2035 is optimal because the configuration of the bodies involved (i.e., Earth, Jupiter, Sun, and 3I/ATLAS) is most favorable for reaching 3I/ATLAS with the minimum Solar Oberth propulsion requirements from the spacecraft, the minimum performance requirements for the launch vehicle, and the minimum flight time to the target.”
Although it takes a long time for such a mission to intercept ISO, the scientific results are nothing short of revolutionary. Asteroids and comets are essentially leftover material from the formation of planetary systems. So ISO research will reveal things about other star systems without sending missions to them, which could take centuries or more. DEP is being researched as a possible solution, as is Swarming Proxima Centauri (another i4is project), but the TRL for this concept is likely decades away.
On the other hand, spacecraft developed with current technology that relies on solar-Obert maneuvers could potentially reach ISO and provide detailed analysis within the same time period. Even if we never send a mission to a nearby star to observe what’s out there, ISO interceptors could tell us everything we need to know about systems beyond our stars.
A version of this article originally appeared on Universe Today.
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