Ralph McNutt’s recent update on the progress of the Innovative Interstellar Explorer concept elicited plenty of comments, enough that Dr. McNutt wanted to answer them in a new post. Now at Johns Hopkins University Applied Physics Laboratory, McNutt
Ralph McNutt’s recent update on the progress of the Innovative Interstellar Explorer concept elicited plenty of comments, enough that Dr. McNutt wanted to answer them in a new post. Now at Johns Hopkins University Applied Physics Laboratory, McNutt is Project Scientist and a Co-Investigator on NASA’s MESSENGER mission to Mercury, Co-Investigator on NASA’s Solar Probe Plus mission to the solar corona, Principal Investigator on the PEPSSI investigation on the New Horizons mission to Pluto, a Co-Investigator for the Voyager PLS and LECP instruments, and a Member of the Ion Neutral Mass Spectrometer Team on the Cassini Orbiter spacecraft. With all that on his plate, it’s hard to see how he has time for anything else, but McNutt also continues his work as a consultant on the Project Icarus interstellar design study. His Innovative Interstellar Explorer is a precursor mission designed to push our technologies hard.
by Ralph McNutt
I typically do not get involved with commenting on comments just because of the time constraints of protracted discussions, but some of the questions raised by your readers are, I think, very good and deserving of a response. [The original post is Update on Innovative Interstellar Explorer -- readers may want to skim through the comments there to get up to speed -- PG].
Let me try to take the comments, for the most part, in order. At one point we did take a look at Sedna and the other large trans-Neptunian Objects (TNOs). The orbit of Sedna (can be found here) will move through ~60° of arc and through its perihelion between now and 2100 (just prior to the aphelion of Pluto) — this is out of an orbital period of ~12,600 years. All of this motion is within 90 AU of the Sun, the orbital inclination is ~12° and is certainly accessible with the appropriate “tweak” at a Jupiter gravity assist. Such an aim point also puts constraints on exactly where with respect to the direction of the incoming interstellar wind one is aiming. To exit the solar system rapidly, one wants a speed as high as possible. Traveling “only” ~17 km/s (about the flyby speed of Voyager 1 past Titan and faster than the speed of New Horizons past Pluto of ~13 km/s), close imaging is problematic (with a radius of 1500 km, this is an object radius travelled in ~100s). Several months of high resolution imaging are possible with a large camera such as LORRI on New Horizons but not with a cell phone camera (which would die rapidly in the space radiation environment shortly after launch anyway).
Eris, with an orbital inclination approaching 45° is currently about 97 AU from the Sun (orbit here) and is inbound to perihelion, crossing the plane of the ecliptic at ~90 AU in the early 2070′s, but still outside of 83 AU in 2100. Makemake (orbit) is currently well above the plane of the ecliptic, passing through the plane of the ecliptic just after the end of this century and just inside of 50 AU; its orbit has a relatively small eccentricity of ~0.16 and an inclination of ~29, etc. The real problem is that doing a flyby of a TNO really is a different mission.
It is perhaps also worth noting that nuclear electric propulsion has been looked at – and in some detail under NASA’s Project Prometheus. The problem is that the power system needs to have a specific mass no greater than ~30 kg/kW (something noted by Ernst Stuhlinger back in the 1960′s — Stuhlinge