Monday, May 07, 2012

Why Not Build Planetary Resources a NEOSSat?

PR co-founder Eric Anderson.
The mass media, in their rush to judgment over the current financial state of the Canadian Space Agency (CSA) and the ongoing confusion over recent proposals from the billionaire backed Planetary Resources (PR) to mine the asteroids, seems to have completely forgotten how very well positioned Canada is to take advantage of this new entrepreneurial environment.

First of all, we already have what is arguably the best tax code in the world for terrestrial mining operations. As outlined in my June 20th, 2010 post "Mining as a Model for the Commercial Space Industry" it would take only a very few legislative changes plus the reassessment of only one international treaty (the 1967 Outer Space Treaty, as per my April 7th, 2012 post "Do Current Laws Support Private Space Activities?") to make Canada the best place in the world to set up a "space" mining company.

The proposed LEO space telescope.

But Canada also has at least two examples of the technology required for the proposed Arkyd 101, or Leo Space telescope, which PR promotes as being the core of its "phase-1" plan to first inventory and then mine near Earth asteroids for water and various metals.

Those two examples are the Microvariability and Oscillations of STars (MOST) space telescope and the Near Earth Object Surveillance Satellite (NEOSSat).

MOST principal investigator Jaymie Matthews.

According to the May 6th, 2012 post on the HobbySpace website titled "Planetary Resources Arkyd 101 - not the first smallsat asteroid finder" the Canadian MOST micro-satellite (which has been in orbit since 2003) also uses a small telescope for stellar photometry. Although it uses only a 15-cm aperture for its telescope, the MOST is able (through the use of four reaction wheels, devices which aim a spacecraft in different directions without firing rockets or jets) to achieve a pointing error of less than one arc-second, which is the level of accuracy listed as being required for the LEO space telescope to effectively search for near Earth asteroids.

Of course, MOST is designed to monitor variations in star light and doesn't officially look for asteroids.

However, NEOSSat, based around the same 15-cm aperture telescope technology first used in MOST, is specifically designed and built to be the world's first space telescope dedicated to detecting and tracking asteroid and space debris. According to the CSA NEOSSat website:
... it will circle the globe every 100 minutes (when launched in the fall of 2012), scanning space near the Sun to pinpoint asteroids that may someday pass near our planet. NEOSSat will also sweep the skies in search of satellites and space debris as part of Canada’s commitment to keeping orbital space safe for everyone. NEOSSat applies key technology already demonstrated in Canada’s very successful MOST satellite.
A model of NEOSSat, from the 2011 IAA Planetary Defense Conference.

This sounds a lot like what PR is planning to do.

According to Kieran Carroll, the mission and system architect for MOST, the key to achieving an accuracy of less than one arc-second depends on two main innovations. The first is:
The development of a star-tracker that has accuracy at the arc-second level.
This level of accuracy is hard to achieve, requiring a narrow field of view for the star tracker, which is rather narrower than that used in most commercially available star trackers. What we decided on for MOST was to use the same set of optics for the star tracker and for the satellite's science instrument (in essence, putting two CCDs at the focal plane of the optics). 

This trick (which the Hubble Space Telescope also uses) allowed us to not have to carry a second set of optics (which are large, heavy and expensive), and also avoided the need to keep two sets of optics co-aligned to arc-second level (which is a very difficult thing to accomplish). 

Each CCD on MOST has a 0.86 degree field of view (3070 arc/sec), each having  1024x1024 pixels, so that each pixel sees a 3 arc/sec x 3 arc/sec patch of sky. We use made the image slightly out of focus, smearing the star images over several pixels, which enables us to do "sub-pixel interpolation" in order to measure star centroids down to better than 3 arc/sec --- I think that with software upgrades over the years, the guys eventually got the measurement accuracy down to 0.5-1 arc/sec.
Kieran Carroll.
The second innovation was the development of very small reaction wheel actuators. According to Carroll:
Larger reaction wheels had existed for many years before MOST, but we couldn't afford the mass or volume they'd need, and also they were pretty darn expensive, given our budget.

Instead, we developed a new reaction wheel design, meant not only for MOST but as a commercial product. It was designed to be small, low-mass and low-cost. Also, it was designed to have a very low power consumption (to avoid driving up the cost of the power subsystem since photovoltaic cells are also pretty expensive), and to have a really very good speed/torque controller built into it, to minimize the errors between the torque we were commanding the actual torque delivered (too much torque jitter would have resulted in too-large errors in MOST's line of sight).
While there are a number of current suppliers of similar reaction wheels on the market today, the star tracker system is still a unique Canadian innovation and only really available here.

Someone should call up PR co-founder Eric Anderson and tell him about this. We could end up building him a NEOSSat.

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