Gravity-assist flybys of Earth itself are also out of the question: the probe’s power supply includes plutonium – and while there is only about one-quarter as much as on the Cassini Saturn probe, there’s enough unease about such flybys that NASA has now decided that no plutonium-powered space probe will be making Earth flybys anytime soon.
In another flight plan, the probe might be attached to an ion-drive engine module exactly like the one used with great success on the Deep Space-1 probe., and powered by big extendable solar panels.
In this plan, the probe would make only one gravity-assist flyby of Venus but with the additional push from months of thrusting with the ion engine, it would have enough thrust to be propelled out to Pluto in under 10 years.
The ion engine would be switched off and separated midway through the Asteroid Belt, since it would no longer be receiving enough solar energy for the high-voltage ion engine to operate at all.
This scenario, however, may involve higher total cost even though it may allow the probe to be launched on a smaller and cheaper regular Delta 2 booster.
And the real problem is that this mission is under real time constraints and will suffer significant scientific losses from any delays of few years more.
Pluto is currently moving farther away from the Sun on its highly lopsided orbit, and will soon become cold enough that its atmosphere will freeze out onto its surface.
This atmosphere – containing nitrogen along with an uncertain mixture of other gases – is incredibly thin: only a few hundred-thousandths as dense as Earth’s.
But it’s nevertheless very interesting scientifically: its analysis will allow the composition and history of Pluto itself to be better understood. Moreover, Pluto’s atmosphere is thought to stretch hundreds (or even thousands) of kilometers above the low-gravity planet’s surface in a way which may be unique in the Solar System.
Current estimates are that it will be completely frozen out onto Pluto’s surface by about 2020 — and the resultant frost layer would also interfere somewhat with another of the Pluto-Kuiper Express’s goals: making near-IR maps of Pluto’s surface composition.
It’s just starting to disappear now, and any probe arriving after about 2015 would very likely have trouble studying the small remaining trace of atmosphere. But if Savage’s claim is correct, 2015 is now probably about the earliest we can hope for Pluto Express to arrive.
NASA is currently close-mouthed about its plans for reorganizing yet again its space science program — but it’s obvious that some very painful choices will have to be made, and the Pluto-Kuiper Express will apparently be one of their victims.
But it’s not the only one — Savage also confirmed rumors first reported by NASA Watch that the Extreme Ultraviolet Explorer astronomy satellite may have to be turned off next year simply because of inadequate funds, although it’s still operating perfectly and making useful observations. Savage repeated, however, that this is only a possibility, and the Agency was nowhere near a final decision point.
Finally, Savage insisted that NASA’s sudden snap decision to consider launching a second Mars rover in 2003 without waiting for input from Mars scientists has had no impact on these considerations.
Savage said that the money for such a rover would have to come out of NASA’s FY 2001 budget, and the current debate over cuts applies only to its 2002 budget request.
It’s hard to see, however, how such a sudden new mission – probably costing around 175-200 million additional dollars – would not have a serious impact on the funding of NASA’s other space science programs.
