The first definitely interstellar object 1I/’Oumuamua (previously A/2017 U1) observed in our solar system provides the opportunity to directly study material from other star systems. Can such objects be intercepted? The challenge of reaching the object within a reasonable timeframe is formidable due to its high heliocentric hyperbolic excess velocity of about 26 km/s; much faster than any vehicle yet launched. This paper presents a high-level analysis of potential near-term options for such a mission. Launching a spacecraft in a reasonable timeframe of 5-10 years requires a hyperbolic solar system excess velocity between 33 to 76 km/s for mission durations between 30 to 5 years. Different mission durations and their velocity requirements are explored with respect to the launch date, assuming direct impulsive transfer to the intercept trajectory. Several technology options are outlined, ranging from a close solar Oberth Maneuver using chemical propulsion, and the more advanced options of solar and laser sails. To maximize science return decelerating the spacecraft at ‘Oumuamua is highly desirable, due to the minimal science return from a hyper-velocity encounter. It is concluded that although reaching the object is challenging, there seem to be viable options based on current and near-term technology.
Best current technology would enable a flyby in 2035-2050 if we were able to launch quickly
Chasing 1I/‘Oumuamua with a realistic launch date (next 5-10 years), is a formidable challenge for current space systems.
A realistic launch date for a probe would be between 5 to 10 years in the future (2023 to 2027). At that point, the required hyperbolic excess velocity for the mission is between 33 to 76 km/s, for mission durations between 30 to 5 years. These values highly exceed the current chemical and electric propulsion system capabilities for deceleration and orbital insertion, and hence a fly-by would be more reasonable.
A rapidly cloned New Horizons Pluto mission vehicle might be launched within 5 years.
Nominally a single launch architecture, via the Space Launch System (SLS) for example, would simplify mission design. However other launch providers project promising capabilities in the next few years. One potential mission architecture is to make use of SpaceX’s Big Falcon Rocket (BFR) and their in-space refueling technique with a launch date in 2025. To achieve the required hyperbolic excess (at least 30 km/s) a Jupiter flyby combined with a close solar flyby (down to 3 solar radii), nicknamed “solar fryby” is envisioned. This maneuver is also known under “Oberth Maneuver”.
The architecture is based on the Keck Institute for Space Studies(KISS) and the Jet Propulsion Laboratory (JPL)interstellar precursor mission studies. Using the BFR however eliminates the need for multi-planet flybys to build up momentum for a Jupiter trajectory. Instead via direct launch from a Highly Eccentric Earth Orbit (HEEO) the probe, plus various kick-stages, is given a C3 of 100 km²/s² into an 18 month trajectory to Jupiter for a gravity assist into the solar fryby. A multi-layer thermal shield protects the spacecraft, which is boosted by a high thrust solid rocket stage at perihelion. The KISS Interstellar Medium study computed that a hyperbolic excess velocity of 70 km/s was possible via this technique, a value which achieves an intercept at about 85 AU in 2039 for a 2025 launch. More modest figures can still fulfill the mission, such as 40 km/s with an intercept at 155 AU in 2051. With the high approach speed a hyper-velocity impactor to produce a gas ‘puff’ to sample with a mass spectrometer could be the serious option to get in-situ data.
Develop more advanced laser sail then we could send small probes to this object and many other missions
The above architecture emphasizes urgency, rather than advanced techniques. Using more advanced technologies, for example solar sails, laser sails, and laser electric propulsion could open up further possibilities to flyby or rendezvous with 1I/‘Oumuamua. In the following, first order analyses for solar and laser sail missions are given.
There are probably many interstellar objects passing through our solar system which are now getting the ability to detect. We should develop a reusable laser sail probe launching capability.
For the solar sail mission, a launch from Earth orbit is assumed, given a time to launch of 3 to 4 years. The velocity requirement is ~55 km/s, suggesting a lightness number for the mission of 0.15, and a characteristic acceleration of 0.009 m/s2. This requires a sail loading of 1 g/m², advanced materials with light payloads might achieve 0.1 g/m². Given this, for different spacecraft masses assuming a sail loading of σ = 1 g/m² sail design leads to the values shown in Table 1 for a circular and square-shaped sail.
The most appropriate and practical design would assume a launch in 4 years and a 1 kg spacecraft mass and lower.
Laser-pushed sail-based missions, based on Breakthrough Initiatives’ Project Starshot technology , would use a 2.74 MW laser beam, with a total velocity increment of 55 km/s, launched in 3.5 years (2021), accelerating at 1g for 3,000s, the probe size would be about 1 gram. It would reach 1I/‘Oumuamua in about 7 years. With a 27.4 MW laser then a 10 gram probe could be used. Higher spacecraft masses could be achieved by using different mission architectures, lower acceleration rates, and longer mission durations.
However, with such a laser beaming infrastructure in place, hundreds or even thousands of probes could be sent, as illustrated in Figure 8. Such a swarm-based or distributed architecture would allow for gathering data over a larger search volume without the limitations of a single monolithic spacecraft.
Another concept proposed by Streeman and Peck is to send ChipSats into the magnetosphere of Jupiter, then using the Lorentz force to accelerating them to very high velocities of about 3,000 km/s. However, controlling the direction of these probes might not be trivial.
An important implication is that once an operational Project Starshot beaming infrastructure has been established, even at a small scale, missions to interstellar objects flying through the solar system could be launched within short notice and could justify their development. The main benefit of such an architecture would be the short response time to extraordinary opportunities. The investment would be justified by the option value of such an infrastructure.
Regarding deceleration at the object, obviously existing propulsion systems could be used, e.g. electric propulsion, though limited by the low specific power of RTGs as a power source. With an intercept distance beyond the Heliosphere, into the pristine Interstellar Medium (ISM) more advanced technologies such as magnetic sails, electric sails, and the more recent magnetoshell braking system are worth investigating. The Technological Readiness of these more advanced technologies is currently low, dependent on breakthroughs in superconducting materials manufacture, but they would multiply the scientific return by orders of magnitude.
The small size of the object and its low albedo will make it difficult to observe it once it has entered deep space again. This means the navigation problem of getting a sufficiently accurate fix on 1I/‘Oumuamua to get close enough to the object to send back useful data is considerable. Due to the positional uncertainty of such a difficult-to-track object, a distributed, swarm-based mission design that is able to span a large area, should be investigated.
Arxiv – Project Lyra: Sending a Spacecraft to 1I/’Oumuamua (former A/2017 U1), the Interstellar Asteroid. 8 Nov 2017. Andreas M. Hein, Nikolaos Perakis, Kelvin F. Long, Adam Crowl, Marshall Eubanks, Robert G. Kennedy III, Richard Osborne
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