A 1m Resolution Camera
For Small Satellites
Paper SSC06-X-5
Presenter: Jeremy Curtis
1
Introduction
• TopSat launched October 2005 carrying
RAL’s 2.5m GSD camera into a 686km
orbit
• Built and operated by consortium: SSTL,
RAL, QinetiQ and InfoTerra
• Over 500 usable images, operating
continuously for 9 months
• Success has encouraged RAL to set-up a
commercial business to exploit this
technology
• New company (Orbital Optics Ltd) has
initiated development of 1m GSD camera
2
Typical mission for 1m camera
Mission
Altitude
~ 600km
Orbit
Sun-synchronous ~ 10:30 LTAN
Lifetime
5 years
Spacecraft per launcher
3
Camera
GSD
1m
Swath width
>10km
Target mass
<40kg (excluding on-board storage)
Imaging method
Bushbroom, no pitch compensation
Channels
Panchromatic
R,G,B & NIR (desirable)
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Optics Design
• Short trade-study of optical designs undertaken
• Scaling the TopSat optical design (a TMA) would not lead to a
particularly compact camera design
• Build spacecraft around the camera - on-axis cylindrical design best
4
Optics Design
•Ritchey-Chrétien design with a three lens corrector group selected
•Focal plane sized for four identical CCDs – R, G, B and NIR (pan can be
achieved by combining the RGB channels)
•Lightweight Zerodur mirrors for primary and secondary mirrors
~0.5m
4 Detectors & filters
- NIR
- RED
- GREEN
- BLUE
~1.1m
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Detector Electronics
• TDI CCDs needed to get sufficient exposure without pitching spacecraft
• Commercial CCD with 12,228 pixels (8µm), and 96 selectable TDI stages
• At 600km altitude it takes 145µs to traverse 1m - readout rate
>10.6Mpixels/s through each of eight output amplifiers
• Pixel data contained within 2 bytes, so data rate for each output amplifier
is 21.2 Mbytes/s
• Overall data rate for all four CCDs will be 668.8 Mbytes/sec (a CD per
second!)
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Detector Electronics Packaging
Enclosure
ADC board
CCDs
8 Spacewire connections per board
7
Structure Design
• Primary structural components made from low CTE composite material
(graphite epoxy), based on TopSat heritage
• Stability requirements relaxed through the use of adjustable (on-orbit) M2
mirror assembly
• Actuators located outside of the aperture preventing any further obscuration
of the system
• Two options for mounting the spacecraft possible: one inside a central
cylinder, and the other to a flat panel
• Breadboard model of primary structure and mirror adjustment mechanism
under design. Plan is to build and test these items early to de-risk the flight
model programme
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Structure Design
Baffle
M2 adjusters
Focal Plane Assembly
M2 Mirror Cell
Metering Tube
M1 Support Plate
9
Section View
10
Primary Mirror Design
Ø480mm
• Machining of Zerodur has advanced
considerably and it is now possible to achieve
a high degree of light-weighting at relatively
low cost
Method
Mass (kg)
% Lightweight
Honeycomb
15.8
65
Pocketing
10.0
77
Double arch
22.0
51
Primary mirror with pockets
11
Spacecraft Layout
Two cameras plus
spacecraft under a
Kosmos-3M fairing.
Could possibly
accommodate a third
spacecraft on an
upper platform.
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Mass Budget
Item
Mass (kg)
M1 assembly
13.7
Bulkhead assy.
4.2
Lens barrel assy.
4.2
FPA & Ebox.
2.9
M2+spider assy.
3.7
Tube assy.
4.3
Camera mounts
2.7
Actuators + harness
1.5
Thermal subsystem
2.0
Total
39.2
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Technology Transfer
•
•
•
•
•
2.5m imagery from a small satellite has
been demonstrated
Technology and IPR has been spun out of
CCLRC-RAL into a commercial company
CCLRC retains majority shareholding (~
40% is held by investors and TopSat
inventors)
Investment into the new company has
enabled a 1m GSD breadboard
programme to be started, with the majority
of work subcontracted back to CCLRCRAL
Orbital Optics Ltd will develop and market
a range of low cost camera solutions, and
will eventually become less dependent on
CCLRC-RAL for development support
Washington, USA 31st Mar ‘06
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The future
•
•
•
Low cost cameras and platforms will
make constellations affordable,
allowing greater global coverage
than is currently possible with a
single platform
The 1m camera design will be
complete by the end of August, with
the hardware expected to take about
6 months to procure.
A test programme will start early next
year, to confirm the primary structure
stability and the effectiveness of the
M2 adjustment system
Dartford, London 7th Dec ‘05
15
Contacts
Jeremy Curtis
Rutherford Appleton Laboratory
[email protected]
www.sstd.rl.ac.uk
John Ellis
Orbital Optics Limited
[email protected]
www.orbitaloptics.com
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