Realistic targets at 1000Â AU for interstellar precursor missions

The nearest stellar system, the Alpha Centauri three star system, is located at about 4.40 light-years away. This amounts to 278,261 AU. But at only 550 AU, or, more generally, at only about 1000 AU, the focus of the gravitational lens of the Sun is found, that is then 278 times closer than our nearest interstellar target. In other words, assuming equal engineering problems, the trip to the Sun focus takes 278 times less than the time to the nearest stellar target. This makes the Sun focus a reasonable target for our probes to reach within this century. It also plainly appears that, before we send a probe towards anyone of the nearest stellar systems, we will need a detailed radio map of that stellar system. In other words, we need a huge radio magnification of all objects located in that neighbourhood, and nothing is better than the huge magnification provided by the gravitational lens of the Sun. Thus, sending a preliminary probe to 1000 AU in the direction opposite to the target stellar system clearly must be done before any interstellar flight to that stellar system is designed, not to say attempted. In this paper, a status review is presented about the “FOCAL” probe to 550 or 1000 AU. The relevant scientific, propulsion and telecommunication issues are briefly summarized and updated.