Space Surveillance Telescope Heads to Australia, Space Control and Cosmological Models

The Defense Advanced Projects Agency has transferred the Space Surveilleance Telescope to United States Space Command, whereupon it will be deployed to the Harold E Holt Naval Communication Station in Western Australia.

The Space Surveillance Telescope will be a sensor in the broader Space Surveillance Network. According to DARPA

Current deep space telescopes do not provide a comprehensive picture of all objects in orbit around the Earth. Existing search telescopes have relatively narrow fields of view and cannot reliably detect and track faint objects, including small objects in geosynchronous orbits (roughly 22,000 miles high). There may be as many as hundreds of thousands of additional pieces of debris and asteroids that are too faint to track with current sensors.

The Space Surveillance Telescope program aims to enable ground-based, broad-area search, detection, and tracking of faint objects in deep space for purposes such as space mission assurance and asteroid detection. SST offers improvements in determining the orbits of newly discovered objects and provides rapid observations of events that may only occur over a relatively short period of time, like a supernova. SST’s innovative design allows for a short focal length, wide field of view, and a compact optical train. The SST mirrors are some of the steepest aspherical curvatures ever to be polished and allow the telescope to have the fastest optics of its aperture class. These features combine to provide orders of magnitude improvements in deep space surveillance.

The Space Surveillance Network is part of United States Strategic Command’s space control and space surveillance mission, and the SST has obvious implications for the militarisation of space. This is something we need to think about in Australia, especially given the importance that space security will play over the medium to long term and the vantage point that Australia plays due to the combination of physical fact and the ANZUS alliance.

Our position in the southern hemisphere and our joint facilities with the United States remind me of the role that uranium reserves played in cold war era strategic debates in Australia. Our suitable pieces of real estate may again become controversial as the militarisation of space proceeds.

The design of the telescope is state of the art. Dennis Overbye has a nice article in The New York Times on the SST, and its innovative design

At the telescope’s heart is a 138-inch-diameter highly curved mirror, which has a wider field of view than previous surveillance telescopes. It moves the game, as Darpa said in a statement, “from seeing only a few large objects at a time through the equivalent of a drinking straw, to a ‘windshield’ view with 10,000 objects at a time.”

The result will be an avalanche of data, a terabyte a night, the agency said.

The key to this prodigious capability is a revolutionary curved detector, which could change the way astronomical telescopes are built in the future, astronomers say. Emmanuel Hugot of the Laboratory for Astrophysics in Marseille, France, called the Darpa telescope “a real breakthrough.”

Now Overbye wrote a delightful read on observational cosmology called The Lonely Hearts of the Cosmos, central to which was the depiction of a contest to measure the Hubble constant to the exactness needed to determine at what rate the universe is decelerating in its expansion.

However, we now know that the rate of expansion of the universe is accelerating consistent with a small albeit nonzero value of the cosmological constant. The physical cause of this acceleration is attributed to dark energy, and dark as in we don’t know what it is.

However, is the universe really accelerating?

An interesting report in Physics World, on statistical analysis of Type Ia Supernovae, states

Subir Sarkarof the University of Oxford in the UK, Jeppe Nielsen of the Niels Bohr International Academy in Denmark and Alberto Guffanti of Italy’s University of Turin have done a statistical analysis of data from 740 type 1a supernovae and concluded “that the data are still quite consistent with a constant rate of expansion”…

…Using a technique that Sarkar describes as “industry standard statistics,” the trio took a different approach to dealing with variations in the supernovae. They concluded that the deviation from a constantly expanding universe is less than about 3σ, which is a relatively poor statistical significance. “The evidence for accelerated expansion is marginal,” says Sarkar, who believes that the ΛCDM model needs rethinking.

The team claims to have a superior technique of statistical analysis and access to significantly more data from more supernovae than the teams that announced the original discovery of the accelerating expansion had available to them. One of the sceptics, Sarkar, observes, at Physics.Org, that the veracity placed in the lambda cold dark matter model of the universe could be misleading and

The apparent manifestation of dark energy is a consequence of analysing the data in an oversimplified theoretical model – one that was in fact constructed in the 1930s, long before there was any real data. A more sophisticated theoretical framework accounting for the observation that the universe is not exactly homogeneous and that its matter content may not behave as an ideal gas – two key assumptions of standard cosmology – may well be able to account for all observations without requiring dark energy. Indeed, vacuum energy is something of which we have absolutely no understanding in fundamental theory.’

Both articles above make the point that there exists other types of evidence to support accelerating expansion and the cosmological constant beyond that of standard candles, such as Type Ia supernovae. The Physics.Org article above observes,

There is other data available that appears to support the idea of an accelerating universe, such as information on the cosmic microwave background – the faint afterglow of the Big Bang – from the Planck satellite. However, Professor Sarkar said: ‘All of these tests are indirect, carried out in the framework of an assumed model, and the cosmic microwave background is not directly affected by dark energy. Actually, there is indeed a subtle effect, the late-integrated Sachs-Wolfe effect, but this has not been convincingly detected.

Studying voids in the universe promises to shed light on cosmology as much as study of galaxies, supernovae and such. The integrated Sachs-Wolfe effect is,

A supercluster is a huge region of the Universe with relatively many galaxies; a supervoid is a huge region with relatively few. When light travels into a supercluster, it heats up, gaining energy as though it were rolling into a valley. When the light leaves the supercluster, it must give that energy back. But dark energy stretches and flattens the valley in the meantime, and lets the light keep some of the warmth it had in the supercluster. Similarly, light leaving supervoids gets a slight chill as a souvenir.

The integrated Sachs-Wolfe effect has just been detected

A team of astrophysicists at the University of Portsmouth have created the largest ever map of voids and superclusters in the universe, which helps solve a long-standing cosmological mystery. The map of the positions of cosmic voids – large empty spaces which contain relatively few galaxies – and superclusters – huge regions with many more galaxies than normal – can be used to measure the effect of dark energy ‘stretching’ the universe.

The results confirm the predictions of Einstein’s theory of gravity…

…”This is known as the integrated Sachs-Wolfe (ISW) effect. When this effect was studied by astronomers at the University of Hawaii in 2008 using an older catalogue of voids and superclusters, the effect seemed to be five times bigger than predicted. This has been puzzling scientists for a long time, so we looked at it again with new data.”

To create the map of voids and superclusters, the Portsmouth team used more than three-quarters of a million galaxies identified by the Sloan Digital Sky Survey. This gave them a catalogue of structures more than 300 times bigger than the one previously used.
The scientists then used large computer simulations of the universe to predict the size of the ISW effect. Because the effect is so small, the team had to develop a powerful new statistical technique to be able to measure the CMB data.

They applied this technique to CMB data from the Planck satellite, and were able to make a very precise measurement of the ISW effect of the voids and superclusters. Unlike in the previous work, they found that the new result agreed extremely well with predictions using Einstein’s gravity.

So, we have two teams with refined statistical techniques reporting two different things about the universe.

Lies, damned lies and statistics.

The Space Surveillance Telescope’s revolutionary design, according to Overbye, could be incorporated into the European Extremely Large Telescope

Dr. Hugot said European astronomers would be meeting this month to talk about how to incorporate curved detectors into the European Extremely Large Telescope, a behemoth under construction in Chile that will be the world’s largest ground-based telescope.

What remains to be seen is when the technologies developed by Darpa will spread to civilian astronomers. The main obstacles, Dr. Hugot and his colleagues said in their paper, were manufacturing costs and the need for a parallel commercial market that would make it worthwhile for big companies to invest.

The EELT might give us the final word, to cite Sarkar from Physics.Org

Significant progress will be made when the European Extremely Large Telescope makes observations with an ultrasensitive “laser comb” to directly measure over a ten to 15-year period whether the expansion rate is indeed accelerating.’

The technology behind the Space Surveillance Telescope promises to provide us with a rich stream of data. Let us hope that the statistical techniques to analyse that data are just as sophisticated.


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