effect is a clear evidence of the presence of the thermal recoil that accounts up only to 10–20 percent of the overall effect. If the origin of the Pioneer effect is cosmological, it gives a direct access to measuring the numerical value of the Hubble constant independently of observations of the cosmic microwave background radiation or supernova explosions in distant galaxies (Supernova Cosmology Project). Further research avenues It is possible, but not proven, that this anomaly is linked to the flyby anomaly, which has been observed in other spacecraft. Although the circumstances are very different (planet flyby vs. deep space cruise), the overall effect is similar—a small but unexplained velocity change is observed on top of a much larger conventional gravitational acceleration. The Pioneer spacecraft are no longer providing new data (the last contact was on 23 January 2003) and Galileo and Cassini were deliberately disposed of in the atmospheres of Jupiter and Saturn respectively at the ends of their missions. So far, attempts to use data from current missions have not yielded any conclusive results. There are several remaining options for further research: Further analysis of the retrieved Pioneer data. This includes not only the data that was first used to detect the anomaly, but additional data that until recently was saved only in older, inaccessible computer formats and media. This data was recovered in 2006, converted to more modern formats, and is now available for analysis. The New Horizons spacecraft to Pluto is spin-stabilised for much of its cruise, and there is a possibility that it can be used to investigate the anomaly. New Horizons may have the same problem that precluded good data from the Cassini mission—its RTG is mounted close to the spacecraft body, so thermal radiation from it, bouncing off the spacecraft, may produce a systematic thrust of a not-easily predicted magnitude, several times as large as the Pioneer effect. Nevertheless, efforts are underway to study the non-gravimetric accelerations on the spacecraft, in the hopes of having them well modeled for the long cruise to Pluto after the Jupiter fly-by that occurred in February 2007. In particular, despite any large systematic bias from the RTG, the 'onset' of the anomaly at or near the orbit of Saturn might be observed. A dedicated mission has also been proposed. Such a mission would probably need to surpass 200 AU from the Sun in a hyperbolic escape orbit.