Japan has always been regarded as a leader in the field of small
satellite development and operations with considerable expertise in
so-called microsatellites, and even smaller nano-satellites in
particular.
Still, Japan held its first "Nano-Satellite Symposium" only last June.
See http://park.itc.u-tokyo.ac.jp/nsat/NS1/main_e.html
And important organizations which support related research such as the
"Next generation Space system Technology Research Association" (NESTRA)
and the University Space Engineering Consortium (UNISEC) are virtually
brand new.
See http://www.nestra.jp/eng/
and http://www.unisec.jp/
Earlier this month I submitted questions to 3 top Japanese experts
about the work they were undertaking and they were kind enough to
respond promptly.
Part 1 of this post focuses on the work of Professor Shinichi Nakasuka
who is with the Intelligent Space System Laboratory (ISSL) in the
Department of Aeronautics and Astronautics at the University of Tokyo.
He is considered to be a pioneer in microsat and space engineering who
has contributed enormously to development of autonomous / artificially
intelligent space systems. He is also a strong advocate for the
implementation of a shared global Ground Station Network (GSN) to
oversee micro/nanosatellite operations. This project involves
identifying and establishing required functions for the GSN as well as
creating well-defined interfaces and a common architecture.
For readers who do not routinely keep track of these small satellites, I
offer this guide.
Minisatellites weigh between 50 kg to 500 kg
Microsatellites weigh between 20 kg and 50 kg
Nanosatellites weigh between 1kg and 20 kg
Picosatellites weigh between .1 and 1 kg
CubeSats with 1 kg maximum mass can be classified as either large
pico-satellites or small nanosats.
The smallest satellites are so-called femtosatellites which have a mass
of less that 0.1 kg.
Do not be surprised if you find others defining microsatellites as
weighing between 10 kg and 100 kg while designating nanosats as
weighing between 1 kg and 10 kg.
"The Micro-Nano boundary is rather flexble. It depends on the people
involved" said Prof. Nakasuka.
His team at the ISSL built CubeSat XI satellites which were so small -
10x10 cm and 1 kg in total weight - that each was carried in a
briefcase to its launch site at the Plesetsk Cosmodrome in Russia in
2003 and again in 2005.
The pico-satellite known as PRISM - now in orbit- is equipped with a
multi-lens refracting optical system and is capable of performing high
resolution imagery capture with approximately 30 meters of ground
resolution. PRISM's 80 cm (when extended) tube-like telescoping lens is
mounted on a very tiny spacecraft bus weighing just over 8kg.
Next to be launched from Brazil's Alcantara launch facility aboard
a Ukrainian Cyclone -4 rocket will be the Nano-Japan Astrometry Satellite
Mission for Infrared Exploration (Nano-JASMINE) which is a nano-
satellite built to carry out astrometry - determining the very precise
positions of stars. And that mission will be followed in late 2012 by
"Hodoyoshi-1" which is the first satellite in Japan's new nationwide
"Hodoyoshi" project (2010-2014) involving a broad-based emphasis on
practical outcomes for low-cost micro/nano-satellite development and
utilization.
Prof. Nakasuka presented a paper in April at the Small Satellite for
Earth Observation Conference in Berlin which outlined what he expects
to take place as the program gets underway. He is responsible for
setting this joint university - industry program in motion by the way.
Conceptualization and demonstration of a novel reliability concept -
“Reasonable Reliable Systems" or "Hodoyoshi" in Japanese - which is
suitable for micro/nano-satellites is one objective.
Here are 3 other goals -
- Research and development of all the required components for
micro/nano-satellites with advanced technologies, aiming for best of
class performance per size.
- Reduction of development time via innovative satellite development
processes and software tools including standardized interfaces and
ground test procedures.
- Creation of a self-sufficient and all-Japanese micro/nano-satellite
consortium - in effect a robust supply chain network - reinforced by
dedicated user communities, and intensive human resource training, etc.
Pursuit of ultra-high reliability as required in conventional
governmental satellites is very important too.
"The “Hodoyoshi” concept evaluates cost-reliability relationships to
identify relevant and appropriate
design points which yield the highest degree of reliability per cost.
The incredible miniaturization of space components and systems now
underway separates small let alone tiny satellites from conventional
mid-sized or large satellites. Vastly different operating
characteristics come into play based on the satellite's size and the
power levels involved. More innovative subsystem design concepts are
needed, and this program encourages the development of an innovative
concept for each component via large scale, multi-player collaboration.
Hodoyoshi-1 will be used for remote sensing and earth observation,
introducing an innovative design concept for the satellite itself and a
new onboard optical sensor system. Hodoyoshi-1 will open anew chapter
in sensor design by nhancing the flexibility of sensors so that they
can address a wide range of applications and/or constraints. The
objective is to move away from overspecialized sensors that only fit
specific applications or function well under specific constraints.
Creating sensors that are optimized for reasonably high performance in a much broader range of applications and constraints
only makes sense.
"Specifically, we aim to develop a 'flexible' sensor in terms of (1)
selectability of wavelength bands, (2)
adaptability to the required Ground Sample Distance (GSD), and (3)
optimal performance under a wide range of environmental temperatures,"
said Prof. Nakasuka.
This means that refractive optics will be in the spotlight because it
outperforms reflective optics in terms of its ability to capture a wide
field of view and do so on the basis of higher practical performance.
Refractive optics is simply more tolerant of several
types of misalignment of optical elements. In addition, lens elements
can be supported on both sides of the lens surfaces, although mirror
elements are often difficult to support in the same way due to
significant deformation of mirror surfaces.
The method of scanning in this instance involves staring via
two-dimensional CCDs as photodetectors on account of the much less
strict requirements
for a satellite’s attitude stability.
Prof. Nakasuka's discussion of the selectability of wavelength bands
and the functionality of the optics
will be omitted here. He does address the tendency of refractive optics
to defocus as the environmental temperature changes.
"In the proposed concept, we aim at overcoming this weakness by
designing athermal and apochromatic optics, whose focus position stays
extremely flat over a wide range of wavelength and temperature," said
Prof. Nakasuka. "To design athermal and apochromatic optics, first, we
have described the wavelength and the temperature dependences of
optical and structural parameters of glass materials as a mathematical model.
Second, we select glass materials with a specific power as a result of the optimization of the established model."
Prof. Nakasuka informed his audience in Berlin that the
optical design for the first sensor based on the proposed concept is
now in progress.
Hodoyoshi-2 will be a purely scientific satellite open to
researchers other nations. More than 12 proposals
have been submitted thus far from several countries.
Hodoyoshi-3, Hodoyoshi-4, and Hodoyoshi-5 will constitute a single
constellation of micro/nano-satellites An international "Mission Idea
Contest" has been recently conducted to identify appropriate and
attractive missions for this specific constellation.
In addition to seeing the Hodoyoshi project accomplish its goals,
Prof. Nakasuka looks forward to the future deployment of an earth
observation constellation consisting of more than 100 tiny satellites.
"A space science mission which requires very special technology is the
also most interesting," said Prof. Nakasuka. "More 'soft' entertainment
applications would be a new area and we expect to see some new ideas
emerging from outside of established space community."
He politely declined when asked to describe these things in greater
detail.
"I am sorry, but these special technologies are secret. We are
developing several new applications of microsatellite technology, and
the details and required technologies cannot be shared with your
readers at this time," replied Prof. Nakasuka. "What sort of
entertainment might be promising is also secret. Sorry about that. The
key point is that applications of microsat are very broad and we can
expect many new types of applications introduced by many new types of
players."
He is eager to start testing new propulsion systems too.
"We are planning to use a small hydrogen peroxide (H2O2) propulsion
system, and we also plan to use an ion thruster which was specially
configured to be installed on a 50kg satellite" said Prof. Nakasuka.
JAXA appears to be meeting the demand for launch services required by
Japanese microsat researchers. Other launch options are available if
needed too.
"JAXA's H-IIA is providing launch services to accommodate a total of 9
micro/nano/pico satellites in Japan. The JEM module attached to the
International Space Station will be used to deploy 4 satellites next
summer," said Prof. Nakasuka. "But the number of slots are not enough
and we are negotiating in order to gain access to India's PLSV,
Russia's Dnepr and Rockot, and Ukraine's Cylone-4, to name a few."
Part 2 will examine cutting edge projects undertaken by a pair of top researchers, Prof. Kazuya Yoshida of Tohoku University and Prof. Yukihiro Takahashi of Hokkaido University.
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