by Paul Gilster | May 23, 2005 | Deep Sky Astronomy & Telescopes, Exoplanetary Science
The mundane facts of finance continue to threaten our far-flung Voyager spacecraft as NASA looks for dollars to keep the missions alive. Adding further significance to the issue is the upcoming news conference on May 24, in which Voyager scientists will present information that has led them to conclude Voyager 1 has reached the heliosheath — that area between 80 and 100 AU from the Sun just inside the boundaries of the heliosphere.
The heliosphere is that region carved out by the solar wind from the Sun within the larger interstellar medium. The ‘termination shock’ is the zone where the solar wind is slowed by interstellar gas, dropping abruptly from its 300 to 700 kilometer per second velocity (the solar wind seems to change in speed and pressure, causing the termination shock to expand and contract). Having apparently exited the termination shock, Voyager 1 is in the heliosheath, on its way to the outer boundary of the Sun’s magnetic field and solar wind.
What tells us that Voyager 1 has entered the heliosheath? On December 17, 2004, at a distance of 94 AU, the spacecraft noted an increase in the strength of the magnetic fields around it; particle beams in the area reversed direction and became steady in strength, markers of the passage. More on this on Tuesday, when we will also hear about “…some puzzling and unexpected aspects of these observations…” and predictions about what comes next. All this takes place within the context of the American Geophysical Union’s 2005 Joint Assembly, which runs from May 23 to 27 in New Orleans.
These findings, of course, are all the more reason we must find a way to sustain funding for the Voyagers. But the NASA budget crunch doesn’t stop here. NASA administrator Michael D. Griffin has sent a letter to Congress noting the agency’s $2 billion shortfall in the current year. Among the undesirable effects of the budget squeeze may be to stretch the timelines of both the Space Interferometry Mission (currently scheduled for 2011 launch) and Terrestrial Planet Finder (2012-2015).
The worst problem of all may be cutbacks and a delay in the launch of the James Webb Space Telescope, a 6.5-meter infrared observatory designed to study the earliest galaxies. The JWST is being jointly developed by NASA, the European Space Agency and the Canadian Space Agency. The delay would set the telescope’s launch back at least to 2012, with possible increases to mission costs also coming into the picture. The Webb telescope’s current budget is $3.5 billion.
Image: Artist’s conception of the James Webb Space Telescope. Credit: TRW and Ball Aerospace.
According to Sky & Telescope, NASA is now asking the project to consider a scaled-down JWST, perhaps a 4-meter telescope with fewer instruments. It is hard to see how such a minimized telescope could be justified, given the rapid increases in giant ground-based telescopes that could outperform it.
Science Magazine has a news feature on this story: “NASA Astronomy: New Space Telescope May Be Scaled Back,” Science 308 (2005), p. 935. And note this story from the Rocky Mountain News, seen through the eyes of JWST subcontractor Ball Aerospace & Technology. From the story:
“I’d say it is a crisis,” said John Mather, project scientist for the telescope at NASA’s Goddard Space Flight Center in Maryland.
“(NASA) headquarters just doesn’t have any more money for us,” Mather said. “Something’s got to give, but we don’t know what it’s going to be.”
Centauri Dreams‘ note: A panel of astronomers is to meet over the next two months to rank the JWST’s science priorities, but it’s hard to see how cutting deeply into the mission can avoid having a catastrophic effect on this successor to Hubble. Yes, it could still do good science, but its original mission goals (the study of galaxies that first appeared as early as 200 million years after the universe formed) would have to be abandoned because they’re based on the larger instrument. In what may now be seen as an ironic twist, the National Academy of Sciences has ranked the JWST as the most important NASA science project of the decade. Let’s hope it stays that way.
by Paul Gilster | May 21, 2005 | Culture and Society
“The space program stands with the cathedrals and pyramids as one of the great ‘central projects’ of history, epic social feats embodying the worldview of a culture and the spirit of an age. On the launch pads, the rockets point heavenward like Gothic spires. Searchlights intersect on a waiting ship to form a great candescent pyramid, ablaze on the black horizon like some alien encounter, radiating light to the heavens. To reach for the heavens seems almost the signature of the central project. The pyramid was called the ‘stairway to heaven,’ the cathedral the ‘gate of heaven.’ The archetype is in Genesis: ‘let us build us a city and a tower, whose top may reach unto heaven.’
“Literature on the pyramids, cathedrals and moon shots has tended to miss the significance not only of great height as the signal feature of central projects, but also their function as means through which whole cultures have found symbolic expression. Writers often pay lip service to the official rationales — immortality for the Pharaoh, a shrine to the Holy Virgin, or the quest for the grail of lunar rocks — while stressing the negative function of these projects as a source of shallow political pride…or as a display of collective vitality… Though some have noted that the central project focuses the energies and educates the consciousness of a population during periods of cultural transition, attracting the best and most adventurous minds of the age, most of the interpretation has been narrowly political, reflecting the pedestrian, power-oriented, if not paranoid, slant of contemporary social science. Thus the pyramids become a ploy for political control, the Gothic cathedral is rooted in royal squabbles, and the space program is but a product of WASP prejudice or cold war hypocrisy — themes that lack all perception of the projects as spiritual quests in the broadest and deepest sense.”
Wyn Wachhorst, The Dream of Spaceflight (New York: Basic Books, 2000), pp. 99-100.
by Paul Gilster | May 20, 2005 | Autonomy and Robotics, Culture and Society
Sometimes the fuzziest image carries a sense of awe that later, far more detailed photographs do not quite convey. Such were the early photographs from the Palomar Observatory showing planetary images that forever fixed in my mind the dream of seeing these places up close; even Cassini’s extraordinary views can’t eclipse the memory of Palomar’s Saturn as seen through a boy’s eyes forty-five years ago. And it may be that the image below carries a bit of the same awe.
Fuzzy it may be, but you’re looking at an image of the Mars Odyssey spacecraft as seen by another craft, the Mars Global Surveyor using its Mars Orbiter Camera. This and another Mars Orbiter Camera image, that one of the European Space Agency’s Mars Express spacecraft, mark the first time a spacecraft in orbit around another planet has taken pictures of another spacecraft orbiting that planet. You can compare the actual image of Mars Odyssey with the computer-generated view of the spacecraft below to interpret what you’re seeing.
Image (above): This view is an enlargement of an image of NASA’s Mars Odyssey spacecraft taken by the Mars Orbiter Camera aboard NASA’s Mars Global Surveyor while the two spacecraft were about 90 kilometers (56 miles) apart. The camera’s successful imaging of Odyssey and of the European Space Agency’s Mars Express in April 2005 produced the first pictures of any spacecraft orbiting a foreign planet taken by another spacecraft orbiting that planet. Image and caption credit: NASA/JPL/MSSS.
Mars Orbiter Camera can resolve Martian features down to a few meters across from the Mars Global Surveyor orbit (350 to 405 kilometers). The image of Mars Odyssey is taken from about 90 kilometers. Both craft are in nearly circular near-polar orbits, with Odyssey in a slightly higher orbit; the craft occasionally close to within as little as 15 kilometers. Malin Space Science Systems, JPL, and the Mars Global Surveyor operations teams (Lockheed Martin Space Systems, Denver) obtained the images in April.
There is something that sends a tingle up the spine about seeing human technology viewing itself, and the mind is immediately drawn back to the image of the Huygens probe as it departed the Cassini Saturn Orbiter back in December. Our probes are machines driven by computers and the complex commands of long-range communications. Ultimately, they must become fully autonomous as we push past the outer Solar System and into interstellar space. In a deep sense, their design is a legacy of the curiosity and aspirations of a technological civilization.
More photos from the Mars Orbiter Camera, including its view of Mars Express, can be found at the Malin Space Science Systems site.
by Paul Gilster | May 19, 2005 | Breakthrough Propulsion, Deep Sky Astronomy & Telescopes
The expansion of the universe ought to be slowing down — gravitational attraction working on the ordinary matter of the cosmos should see to that. So evidence produced during the last eight years that the universe’s expansion seems to be speeding up continues to confound astrophysicists. To explain it, a provocative notion has been introduced: two-thirds of the entire energy density of the universe consists of a new kind of energy. This ‘dark energy’ has the opposite effect of gravity, pushing away rather than attracting.
But is there such a thing as dark energy, or is it just a way to explain something so baffling that we have no other models to describe it?
“We don’t know,” comments Professor David Spergel of Princeton University. “It could be a whole new form of energy or the observational signature of the failure of Einstein’s theory of General Relativity. Either way, its existence will have profound impact on our understanding of space and time. Our goal is to be able to distinguish the two cases.”
Spergel is referring to work he and Mustapha Ishak-Boushaki (also of Princeton) have presented to the Canadian Astronomical Society meeting in Montreal. They have come up with a technique for determining whether dark energy is indeed operational or whether (and the flip side is also startling) Einstein’s General Relativity breaks down at the largest scales.
Image: Is it possible that a new form of energy accounts for cosmic expansion throughout the universe? Here is a typical patch of sky, as seen by Hubble’s Advanced Camera for Surveys. The jumble of galaxies in this image, taken in September 2003, includes a yellow spiral whose arms have been stretched by a possible collision [lower right]; a young, blue galaxy [top] bursting with star birth; and several smaller, red galaxies. Credit: NASA, ESA, J. Blakeslee and H. Ford (Johns Hopkins University).
Consider, for example, how physics would be changed if this cosmic acceleration is showing us a new theory of gravity, perhaps one that can be explained by superstring theory with its numerous additional dimensions. That would be, if confirmed, an enormous breakthrough for superstring advocates, but we’re a long way from knowing for sure.
Ishak-Boushaki and team think there is a way to test for dark energy. From a Princeton press release available at the Canadian Astronomical Society site:
If the acceleration is due to Dark Energy then the expansion history of the universe should be consistent with the rate at which clusters of galaxies grow. Deviations from this consistency would be a signature of the breakdown of General Relativity at very large scales of the universe. The procedure proposed implements this idea by comparing the constraints obtained on Dark Energy from different cosmological probes and allows one to clearly identify any inconsistencies.
Centauri Dreams‘ take: What this means is that the Princeton team believes it can identify the signature of modified gravity models and separate it from those involving dark energy. Future experiments will be needed to distinguish the two, but the theoretical basis for making the call is now being developed.
For more on this, read Ishak-Boushaki’s “Probing decisive answers to dark energy questions from cosmic complementarity and lensing tomography” (2005), the preprint available here. The paper has been submitted to Monthly Notices of the Royal Astronomical Society. From the abstract: “…the requirement for very ambitious and sophisticated surveys in order to achieve some of the constraints or to improve them suggests the need for new tests to probe the nature of dark energy in addition to constraining its equation of state.”
Spergel and Ishak-Boushaki also consider dark energy constraints in relation to the Terrestrial Planet Finder mission in a JPL white paper called “General Astrophysics and Comparative Planetology with the Terrestrial Planet Finder Missions,” based on a 2004 Princeton workshop and available here in Microsoft Word format.
by Paul Gilster | May 18, 2005 | Sail Concepts
Robert Forward’s early work on the beamed-energy lightsail, exemplified by the 1984 paper “Round-trip Interstellar Travel Using Laser-Pushed Lightsails,” came to grips with the central challenges of interstellar travel. As described in a recent paper on beamed energy requirements for laser sails, these are:
How to reach a nearby star within a human lifetime?
How to achieve this with known physics?
How to hold down the cost, which also means minimizing the energy requirements?
How to return the crew to Earth at the end of their explorations?
Forward’s methods involved huge laser installations near the Sun, lenses fully 1000-kilometers in diameter in the outer Solar System, and a vast sail constructed in three parts so it could be separated (staged), with the outer ring projecting light back on the inner two for deceleration at destination, using the still powerful laser beam from the Sol system. The method is complicated, ingenious and extraordinarily creative. But can we improve on its physics?
Image: Forward’s lightsail separating at the beginning of its deceleration phase. Laser sailing may be the best way to the stars, provided we can work out the enormous technical challenges of managing the outbound beam. Credit: R.L. Forward.
Recent work on these issues is summarized in “Space Based Energy Beaming Requirements for Interstellar Laser Sailing,” by Travis Taylor, R. Charles Anding, D. Halford and Gregory Matloff. The authors quickly point to a major limitation of laser propulsion: the beam must be aimed precisely and kept tightly collimated (avoiding beam spread) “…to an accuracy defined by a 100-km sail size at the far end of a trillion-kilometer acceleration ‘runway.'”
One method for doing this is Forward’s, constructing an O’Meara para-lens, which is a huge Fresnel lens made of concentric rings of some lightweight, transparent material, with free space between the rings and spars to hold the vast structure together. The lens would be constructed in the outer Solar System between the orbits of Saturn and Uranus. Supplying it would be a laser beam from an installation near Mercury’s orbit, one demanding laser power to the tune of roughly 1000 times our civilization’s current power consumption.
Other possibilities for energy beaming include accelerating micro-sails in the beam; these would impact upon the larger spacecraft, transferring their momentum to it. Matloff has also determined that some sail shapes may be able to automatically correct for small beam drift. And it may be possible in some way to employ gravitational lensing; just as the light from an object occulted by the Sun, when seen from a distance greater than 550 AU from the Sun, is focused into an amplified and narrow beam, perhaps beamed energy from the Earth could be similarly tailored to reproduce this effect.
Other items of interest in this wide-ranging paper include an analysis showing that instead of Forward’s para-lens design, a solid optic might have better optical and structural properties. The authors experiment with a small-scale prototype of an electrically controlled membrane reflector as a proof-of-concept, confirming that curvature produced in the reflector by electrostatic forces made it into a useful antenna.
The huge power requirements of laser sailing will demand large solar collector arrays based in space. In this context, the authors consider the precise control system demands needed to keep the laser beam on the sail at large distances from the Sun. From the paper:
The analysis given here, which did not take into account pointing jitter, suggests a minimum of about 15 km in radius for the collector. If pointing error is considered, it appears that the current state-of-the-art of jitter control is many orders of magnitude from enabling a laser sailing mission. Beam control is the largest obstacle for laser sailing.
And later:
Preliminary analysis suggests that the standard O’Meara para-lens would be inefficient and most likely difficult to control or steer. More analysis and experiment should be conducted, however, before the idea is completely discarded. On the other hand, the current status of large reflective optics seems more likely to be technologically feasible in the near future.
The paper is T. Taylor, R.C. Anding et al., “Space Based Energy Beaming Requirements for Interstellar Laser Sailing,” CP664, Beamed Energy Propulsion: First International Symposium on Beamed Energy Propulsion, ed. By A.V. Pakhomov (2003), American Institute of Physics 0-7354-0126-8. The original Forward paper — now considered a classic — is “Roundtrip Interstellar Travel Using Laser-Pushed Lightsails,” Journal of Spacecraft and Rockets 21 (1984), pp. 187-195.
