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The obvious drawback with a flyby mission compared with an orbiter is of course that an orbiter could make several flyby's. I wonder if the following ideas about mission design could help make flyby missions attractive enough to outcompete orbiters for exploration of outer Solar System objects (Uranus, Neptune, dwarf planets, asteroids)?

If a flyby probe splits up into several sub-probes with instruments, they could each fly by the object of study in different trajectories. Images could be taken from several angles and a better 3D measurment of magnetic and gravity fields would be obtained. The main probe would be the only one with Earth communication capability, a long term energy source and apropulsion system. For outer planets, each sub-probe could also pass nearby one moon each. Sub-probes would only be awake on batteries during the flyby and communicate only with the nearby main probe. With 3 sub-probes + the main probe one would have the equivalent of 4 well positioned orbits by an orbiter (near a moon, such as Cassini at Enceladus).

It seems to me that fast flyby missions have several advantages compared to the same investment in an orbiter, for distance objects. Voyager being a triumph and hopefully soon New Horizons too. On the plus side:

  • Earlier arrival by many years, which means that the instruments will the more sophisticated and/or cheaper, giving more science per dollar invested.

  • Earlier science results helps design efficient follow up science, ground based or new flyby's, to target the discoveries and new questions raised.

  • The time value of similar high risk business investments is not rarely 20% per year or so, several years earlier delivery of results could double the present value of the investment.

  • Every flyby mission would fly by Jupiter for gravity assist, and near one of its moons. Then the object of interest, for example Neptune and one of its moons (before which it would split into sub-probes). Then a KBO. It would also test the limits of the heliosphere, like Voyager. So its not exactly a mayfly.

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  • $\begingroup$ Each probe would have it's own avionics, fuel tanks, rocket engines? Each has its own high gain antenna? Sounds like there'd be less mass devoted to scientific instruments. $\endgroup$ – HopDavid Jun 19 '14 at 1:10
  • $\begingroup$ @HopDavid No, a sub-probe in this idea would just be a short lived set of science instruments which is once physically separated from the "mothership" in order to simultaneously pass by on the other side of e.g. Uranus. No avionics, no propulsion. And with an antenna only to transfer data to the nearby mothership. $\endgroup$ – LocalFluff Jun 19 '14 at 1:35
  • $\begingroup$ "...and hopefully soon New Horizons too." Yep you are right! What does "not exactly a mayfly" mean? I think this is a great question, I hope to have another answer in a few days... $\endgroup$ – uhoh Oct 26 '16 at 10:06
  • $\begingroup$ Mayflies have very short lifespans. $\endgroup$ – Camille Goudeseune Jan 7 at 17:23
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The sad reality is that by splitting a probe into a few subprobes you decrease mass, thermal control, and energy budgets available for scientific payloads.

  • mass: you still have to build the frame sturdy enough to withstand high g's at launch; command and data handling equipment is the same for a large and a small probe, etc.

  • thermal control - heaters can serve adjacent instruments in a large probe;

  • power, downlink bandwidth etc. - you can stagger observations/transmissions to get the best value for your money.

Reliability of several probes will also likely be correlated, with an extra twist of managers having no time to control quality of each unit.

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    $\begingroup$ The sturdyness at launch wouldn't be affected. The split up into sub-probes would take place shortly before arrival at the main target. And after that maybe thermal control could be managed by distributing radioactive materials in each sub-probe, not advanced electric producing RTGs, but just for heating like the Chang'e 3 lander on Moon. Power on the sub-probes is needed only short-term, supplied by battery. "Downlink bandwith" would be only to the mother probe nearby. Sub-probes would be identical for testing. I'm not convinced by your arguments! Please come back to kill my darling ;-) $\endgroup$ – LocalFluff Jun 18 '14 at 14:05
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    $\begingroup$ MIRVing flyby probes is recommended if you absolutely need global coverage of the target body but lack the $\Delta V$ for insertion. A very rare case, I'd guess. $\endgroup$ – Deer Hunter Jun 18 '14 at 14:17

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