...And with it, routine space access, the hydrogen economy, room-temperature superconductivity, and ultra large telescopes.

Very interesting article here reporting on researchers who had previously announced a rapid means of producing synthetic gem sized diamonds, now believe their methods will work to produce diamonds of arbitrary size:

Artificial diamonds - now available in extra large.
18:11 13 November 2008 by Catherine Brahic.
"A team in the US has brought the world one step closer to cheap, mass- produced, perfect diamonds. The improvement also means there is no theoretical limit on the size of diamonds that can be grown in the lab.
"A team led by Russell Hemley, of the Carnegie Institute of
Washington, makes diamonds by chemical vapour deposition (CVD), where carbon atoms in a gas are deposited on a surface to produce diamond crystals.
"The CVD process produces rapid diamond growth, but impurities from the gas are absorbed and the diamonds take on a brownish tint.
"These defects can be purged by a costly high-pressure, high-
temperature treatment called annealing. However, only relatively small diamonds can be produced this way: the largest so far being a 34-carat yellow diamond about 1 centimetre wide.
"Microwaved gems
"Now Hemley and his team have got around the size limit by using microwaves to "cook" their diamonds in a hydrogen plasma at 2200 °C but at low pressure. Diamond size is now limited only by the size of the microwave chamber used.
"The most exciting aspect of this new annealing process is the unlimited size of the crystals that can be treated. The breakthrough will allow us to push to kilocarat diamonds of high optical quality," says Hemley's Carnegie Institute colleague Ho-kwang Mao."
http://www.newscientist.com/article/dn16036

 Original research article:

Enhanced optical properties of chemical vapor deposited single crystal diamond by low-pressure/high-temperature annealing.
Yu-fei Meng, Chih-shiue Yan, Joseph Lai, Szczesny Krasnicki, Haiyun Shu, Thomas Yu, Qi Liang, Ho-kwang Mao, and Russell J. Hemley
Published online before print November 12, 2008, doi: 10.1073/pnas.0808230105
PNAS  November 18, 2008 vol.105 no. 46 17620-17625
http://www.pnas.org/content/105/46/17620  [abstract]

 I had discussed the earlier research that showed they could make synthetic diamonds of perhaps 50% greater hardness than natural diamond. From this I suggested this should mean the strength should also be increased by this amount and could result in ultra large telescope mirrors, perhaps to 30 meters across, if the process could be scaled to arbitrary sizes, as now appears likely:

Newsgroups: sci.astro, sci.physics, sci.optics, sci.materials
From: "Robert Clark" <rgregorycl...@yahoo.com>
Date: 11 Dec 2004 12:48:10 -0800
Local: Sat, Dec 11 2004 3:48 pm
Subject: Re: Can diamond now be used for telescope mirrors?
http://groups.google.com/group/sci.astro/msg/8d2744a0b5fa94b4?hl=en

 Here I suggested that use of ultra high strength microspheres or microfibers would be able to solve the problem of finding lightweight storage tanks for the hydrogen fuel on the VentureStar reusable launch vehicle:

Newsgroups: sci.astro, sci.space.policy, sci.physics, sci.energy
From: Robert Clark <rgregorycl...@yahoo.com>
Date: Fri, 5 Sep 2008 20:32:39 -0700 (PDT)
Local: Fri, Sep 5 2008 10:32 pm
Subject: High strength microspheres for hydrogen storage (was: High strength fibers for hydrogen storage on the VentureStar.)
http://groups.google.com/group/sci.astro/msg/4bddfa864aa04056?hl=en

 If the high strength material at the microscale were diamond, the weight of the propellant tanks could be reduced by a factor of 100, which would make feasible not only the VentureStar but also the other competing NASA reusable launch vehicle proposals. With the newly announced process now being able to make diamond in bulk sizes, the tanks would not need to consist of numerous microspheres or microfibers but a single macrosized tank. Note that such lightweight, high strength tanks would also solve the storage problem for hydrogen for the hydrogen economy.
 Not only could the diamond be used for the propellant tanks but also for the strength bearing structures of the entire craft since diamond also has ultra high compressive strength as well as tensile strength.
The weight of the vehicles could conceivable be reduced by a factor of 100: instead of 200,000 lbs., only 2000 lbs.

 Metallic hydrogen has been considered an ideal rocket fuel if it could be produced because it is of high density yet it's energy content would give it a fuel efficiency of 4 times that of the best chemical propellants now used. Theoretical modeling also suggests it could be stable at room temperature once produced and would be a superconductor.
Experimental and theoretical work suggested metallic hydrogen would be produced at pressures of 4.5 megabars, 450 GPa:

Apr 10, 2002
Hydrogen metal on the horizon.
"Scientists have long expected solid hydrogen to become a metal when it is compressed, but so far electrical conductivity has only been detected in liquid hydrogen. Now an experimental study of solid hydrogen at pressures up to 320 GPa predicts that it will become metallic at a pressure of 450 GPa – over four million times atmospheric pressure. René LeToullec and co-workers at the CEA in France also found that solid hydrogen becomes opaque – or ‘black’ – under compression (P Loubeyre et al 2002 Nature 416 613)."
http://physicsworld.com/cws/article/news/5307

 Attempts to create ultra high pressures in the megabar range
frequently involve using diamond anvils at the microscale. However, natural diamond has maximum compressive strength of about 400 GPa. If it is indeed the case that the 50% increase in hardness of the new synthetic diamonds over natural diamond also indicates a corresponding increase in compressive strength, this would put diamond anvils using
these synthetic diamonds within the compressive strength range required to produce metallic hydrogen.

    Bob Clark