Figure 1. Vesta, as photographed by Dawn on 23 July, 2011.



Sol Sun

MercuryMercury ____________

VenusVenus crescent

Earth &
Earth's Moon

Mars Mars: Spirit 
       Sol 30 ____________

Asteroids Vesta

Jupiter Jupiter storm 
       north of Great Red Spot ____________

Saturn Saturn's Rings

Uranus Uranus' Rings

Neptune Neptune

Pluto & Pluto Kuiper Belt

Comets &
Oort Cloud

Comments & Submissions ____________

Beyond the Solar System

- A Modest Proposal -

By F. E. Harris

March 10, 2012


Given the immensity of interstellar space, planning either a manned or unmanned interstellar mission at this time faces many difficulties. However, both manned and unmanned expeditions to the Oort Cloud and beyond, may have advantages.

Section 1: The Disadvantages of Interstellar Flight

There are several disadvantages to mounting an interstellar mission. The first is that the distances are large, so it would be a very long, slow journey. With present technology, such a trip, whether manned or unmanned, would take over 50,000 years, longer than the span between now and the old stone age. Assuming such a probe is launched a century from now, using technology capable of maximum speeds equal to 1% the speed of light, such a probe would still take over 400 years to reach the nearest star beyond the Solar System, Proxima Centauri.

Four problems present themselves.

  1. The probe (or manned spaceship) would have to keep functioning for a very long time, longer than humanity has known how to use electricity.
  2. People back in the Solar System would have to remember to receive the signal, when the probe reached the star, and was ready to send back the data it had recorded. Humanity has a poor record when it comes to keping projects going for multiple centuries.
  3. Given the distance, the power requirements for sending back data, and the low data rate for a signal sent so far, not vey much information could be returned.
  4. A probe (or manned expedition) sent a few decades later might be capable of much higher speeds, thus rendering the probe obsolete before it arrived.
The third point is worth considering. Every few years there are advances in optics, radio, and microwave astronomy. Instruments on or near the Earth can see farther, fainter, and in more detail than they could a decade ago. It is quite likely that by the time a probe to another star system arrived, instruments in the Solar system would be able to collect more data about the nearby star system, than the probe could. Also, such instruments would not be limited to reporting back on one star system, but could examine all of the nearby stars.

The last point, of course, is particularly galling. One could launch a probe that cost vast amounts of money, resources, and effort to send, only to have it become obsolete before it arrives. The case is even worse for a manned expedition, that might arrive at a fully populated planet, colonized by expeditions that started the trip a century after them.

Section 2: The Alternative: Exploring Nearby Interstellar Space

The Oort Cloud, the outermost zone of our Solar System, is believed to contain billions of comets, and also larger bodies whose gravitational influence flings thousands of comets sunward each year. Beyond the Oort Cloud is interstellar space. Recent studies suggest there are many rogue planets in interstellar space, but they are very difficult to detect from the Earth. At present the only way to detect them is if they pass in front of a star that is being constantly observed, like those that are now being studied by the Kepler space telescope. Then, gravitational lensing and occultation may produce variations in the brightness of the star that indicates a planet passed between it and the Earth.

To map the dwarf planets in the Oort cloud and the rogue planets of interstellar space, space telescopes must be placed beyond the orbit of Neptune. This is because interplanetary dust reflects enough light to prevent viewing of these very faint objects.

Section 3: A Modest Proposal

Interferometry is the technique whereby several telescopes are linked together, to see greater detail than any of them can see alone.1 The longer the distance between the telescopes, the "baseline," the greater the detail that can be observed.

The technique was first used with radio telescopes. Later, as technology improved, it was applied to shorter wavelengths and higher frequencies. Now, microwave and infrared telescopes use interferometry to see greater detail. In the furure, visible, UV, and X-ray telescopes may be able to adopt the technique.

At present, the limit for long baseline interferometry is the diameter of the Earth. There is no reason why space based telescopes could not extend baselines to vastly larger distances.

Here is my proposal: Send out 2 deep space probes with really large radio telescope antennas, following directly behind Voyagers 1 and 2.2,3,4 These would be able to relay data and commands to and from V1 and V2, keeping them operational for decades longer. These probes would also be able to send back their own observations. Linked to radio telescopes still in the inner solar system, they would make an interferometer capable of picking out unprecedented detail from objects within and outside our galaxy.

The next step is to send 2 more probes in roughly the opposite directions to those traveled by V1 and V2. This would double the capability of our interferometer, as well as providing interstellar gas, plasma, and magnetic field measurements.

Finally, these 4 probes (6 if you count V1 and V2) define a plane. Send out 2 more probes, like the others with really big radio telescopes, in the up and down perpendicular directions to the plane. Now we have a really big interferometer, capable of imaging anywhere in the sky, in unprecedented detail.

I would want to put power supplies and ion drives (for steering) on these probes capable of operation for centuries. When they are almost too far out to communicate with Earth, send 6 more radio telescope probes out to follow them, and extend the lines. The capabilities of this system would just keep increasing.

Section 4: Conclusion

The network of probes has other uses besides long baseline interferometry. Each probe can relay data and commands to probes farther out, so that communications can be maintained at longer distances and higher data rates than direct transmissions would permit. In this way they function somewhat like a cellular telephone network, where a web of low power transmitters carry more messages than a single transmitter ever could.

As I envision them, each probe is a substantial collection of telescopes. I imagine each probe equipped with large radio and microwave antennas, that can be linked together with other probes to perform interferometry, timed by comparison to pulsars. With such very long baselines, imaging planets and moons in nearby star systems should be possible. I also envision each probe equipped with an infrared telescope, to look for nearby rogue planets. These probes will eventually be thousands of AU from the inner Solar System, so each probe will be scanning the whole sky, for about 100 AU around the probe, in the infrared.

In the visible wavelengths, the probe should have a powerful laser and telescope, for communications to its neighbors, and back to Earth. Last and not least, I think each probe should possess a set of low powered visible light telescopes, much like the one on the Kepler space telescope, that scan the nearby stars in the entire sky, watching for planetary occultations, both in other stellar systems and from rogue planets. Detections could be followed up by direct observations in infrared, microwave, and radio wavelengths, and in some cases, triangulations with other probes might be possible.


Fifty years or more from now, when this network of probes has mapped the Oort cloud and the rogue planets within a light year of Earth, it will be time to consider whether robotic factories should be sent to dwarf planets in the Oort cloud and beyond. The purpose of these factories would be to build resupply and repair bases to support future manned interstellar expeditions. Such expeditions would not have to launch with all the supplies they needed, if an unmanned probe, built by robots on a dwarf planet, could match velocity with the expedition and deliver needed consumables. Repair parts and new, improved technologies such as better drives and life support might also be delivered by unmanned supply ships.


1. "Very Long Baseline Interferometry," Wikepedia, 29 February 2012, latest edit.
2. "Voyager: The Interstellar Mission,"
3. "Voyager 1," Wikipedia, 1 March 2012
4. "Voyager 2," Wikipedia, 29 February 2012

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