AE 426 Space System Design
Spacecraft Array for Asteroid Characterization via Stellar Occultation:
PTAR Results
Design Team No. __1___
1. Mission Design Introduction :
Nice charts, easy to understand, info good. Great visual for formation flying.
2. Trade Options Discussion:
Not hearing about trades – focus on selected option. Use of ### reduces duplication
and increases robustness against failure.
3. Design Description:
Robust design option discussion – good. Nice views of CubeSat designs. Good
summary of design data.
Unclear how they know where each sat is located in the constellation. Cost
discussion confusing. Incorrect orbit detail (over CS every 90 minutes?!?)
Nice sim of Y formation orbits – but a better understanding of the orbit dynamics is
necessary. Really nice CubeSat designs – both types of spacecraft. 90 minutes per
passage over CS? The earth rotates. Follow-on work needed: Power budget
accounting for eclipse; GPS for formation control.
4. Summary of Advantages:
The lack of trades weakens conclusions
1
Design Team No. __2___
1. Mission Design Introduction :
Best introduction.
Cute cartoon
2. Trade Options Discussion:
I’m confused about the number of satellites. 12 and 45 were mentioned, but some
graphics showed as few as 10. Was donation of the satellites an option that should
appear in the cost discussion? Cost is independent of where the $ comes from.
Selection criteria are well explained. Lots of formation geometry options. Addressed
stray light. Extendable secondary, Chose cold gas thrusters.
3. Design Description:
One image shows a Maksutov cassegrain, which is not what they chose. Altitude?
Investigated 12 CubeSat option – it’s good to have a “Plan B”. Need better
understanding of the formation dynamics.
4. Summary of Advantages:
Recommend a “ride-along” launch deal. How bright are the stars that need to be
used.
2
Design Team No. __3___
1. Mission Design Introduction :
Decided on 12 CubeSats. What about an additional option?
2. Trade Options Discussion:
They needed to give justification for the expensive sensor
Interesting P-Pod arrangement. Note: each sat downlinks is raw data – a simple
solution. Follow-on work: More complete delta-V estimation.
3. Design Description:
Altitude?
CCD Fairchild Imaging – But each sat does not need to form an image, just count
photons. Cost: Total CubeSat budget ~ 1.2M?? Could we purchase a Pegasus?
4. Summary of Advantages:
Cheapest star tracker ~ 100K. Later work: more detailed delta-V calc. Is a de-orbit
burn necessary? What’s the CubeSat ballistic coefficient, and the orbit lifetime?
3
Design Team No. __4___
1. Mission Design Introduction :
Need bottom line up front.
2. Trade Options Discussion:
Optics good!! – Boom solution good! Great optics design. Formation nice – trades
are solid. Comm – good.
Most promising approach to secondary deployment with stray light protection.
Speaker mentioned this came out of University of Tokyo – bur details of boom
design are not given in the Powerpoint.
3. Design Description:
Formation study very good
Best info on deployment of the optics, attention to stray light.
Good CubeSat design.
4. Summary of Advantages:
Need a star tracker for attitude control. Need to formulate pointing requirements.
Need to cool the detectors to reduce dark count.
4
Design Team No. __5___
1. Mission Design Introduction :
Presented a good outline at the outset.
2. Trade Options Discussion:
Good look at unusual solutions.
Nice trade trees. Lots of interesting options. Deployable primary, photon sieve,
cloud formation, deployable/inflatable comm. antennas.
3. Design Description:
Most information. Greatest clarity. I like the unique (within the class) look at the
cloud deployment and the unusual mirror
Deployable primary gets larger photon collecting area (proportionate to the increase
in radius). Photon sieve is interesting but may be inconsistent with the need to
collect as many photons as possible. Cloud design is interesting – this might suggest
that we can relax formation-keeping constraints. Need GPS on each sat anyway.
GNC uses horizon sensors and magnetometers. The latter are probably too course
to be useful. Good options discussion in Data handling and computation – suggested
an automated occultation detector.
4. Summary of Advantages:
Strongest case.
Vegi-patch primary is pretty neat, but need to trade off SNR improvement versus
need, complexity and robustness. Someone suggested putting photodetector at the
primary focus – increases noise due to running wires up to focus position; also
detector is less protected from thermal and radiation.
5
Contractor
Presentation
(average)
Content
(average)
Total
1
8.0
7.75
15.75
2
8.25
7.88
16.13
3
8.0
7.62
15.62
4
8.38
8.62
17.00
5
8.35
8.54
16.89
6
Team
1
Subsist,
component
No. of “eye”
CubeSats
No. of
“Master”,
comm. sats
Telescope
type
Aperture
diameter
2nd–ary
mirror
assembly
Light
detector
Formation
geometry and
size
Orbit:
Altitude and
inclination
Launch
strategy
Attitude
sensors
Attitude
control
actuators
Comm
subsyst
Data
handling and
computing
Propulsion
Power and
thermal
Structure of
Master sat
Structure of
Eye sat
39
2
3
4
5
12
21
?
3
45 (+ 12
option)
1
0
2
3
Cassegrain
Cassegrain
Cassegrain
Cassegrain
Cassegrain
10 cm
10 cm
10 cm
10 cm
>10cm
Entire optic
contained
in 2U of the
3U
1261000nm
Y-shape
Diam=?
Deployable
arm (use
cold gas
pressure)
?
Support
frame slides
out
30cm
deployable
truss w light
baffle
MicroFB30050-SMT
Y-shape
Diam. =?
Vegetable
patch –
segmented
primary
?
450 km
?
Alt=?
28.5degr
450 km
28.5degr
?
Dedicated
vehicle
Dedicated
vehicle
?
Pegasus XL
Piggyback
?
Blue Canyon
XACT
Blue Canyon
XACT
Gyroscope and
sun sensor
Thrusters,
magnetorquers
GPS, Sun,
gyro, mag
Magtorque,
Wheels,
thrusters
S-band
patch
“Eye” data
-> grnd
ISIS UHF, up
VHF down
“Eye” data
->“Master”
->grnd
Deploy tape
Spring
“Eye” data
>Relay
->grnd
Electric
VACCO
MiPS
Photovolt.
Gyros,magnet
in solar ps
CCD 595
Fairchild
Circle
Y-shape
Diam. =?
Magnetorq
uers
?
VHF/UHF
S-band
“Eye” data
>“Master”
->grnd
?
Plasma
thruster
Solar
panels
Cold Gas
?
Pulse
Plasma
Solar panels,
Li-Poly
batteries
2U, 3.51kg
?, 1.3kg
N/A
NanoPower
P31U Supply
ISIS Cube-Sat
panels
3U, 1.967kg
3U, 2.47kg
2U, 1.3kg
3U, ?kg
2U, 1.506kg
“Eye” data
>“Master”
->grnd
7
Cloud
?
3U, ?kg
Recommendations and Further Study
Secondary Mirror Assembly:
Recommend Team 4’s deployable truss approach
 System already developed – but we need corroborating references
and details on performance
 If you can add a flexible wrapping that is consistent with
deployment, then the stray light problem is properly addressed
 Team 1 also addressed the stray light problem by entirely
enclosing the optic in the CubeSat body – but we may need some
volume margin for the remaining equipment.
Team 5’s Vegetable Patch Optic:
 Good thinking “outside the box” – this option was worth
consideration
 Segmented primary mirrors tend not to be chosen for imaging
systems – but for flux collector optics, they are feasible.
 On the one hand, there’s modest SNR improvement (by the ratio
of the primary radii). On the other, it’s very hard to address stray
light with a deployable light baffle, and there’s lots of moving
parts.
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 Not suitable for tech validation mission with CubeSats, but very
possible solution for the operational system (bigger spacecraft,
much larger apertures needed.
Telescope Type
It’s unanimous! Cassegrain is the choice.
Formation Design:
The Y shape is chosen. It is simple and efficient. Before going forward,
however, Team 5’s cloud concept deserves discussion:
 Again, this is avant-garde. A formation that has aperture density
increasing toward the center provides more flexibility in
addressing asteroids of varying size.
 There are also advantages in a pseudo-random distribution.
 However, it will take a lot of development and analysis to use this
concept.
 Thus the concept is premature for this validation experiment but
remains a candidate for the full operational system.
9
Orbit and Launch Mode:
Recommend 450km altitude, Cape Kennedy launch as a secondary
payload. Also, Team 3 proposed a Pegasus launch with an interesting
radially directed “fan” of P-Pods (see below). This should be considered
further.
Number of Light-Collecting Apertures – System scope
Recommend, besides a high capability baseline design, formulation of a
12-aperture, “Plan B”, system as was done by Team 2.
CubeSat Design Presentation
Team 1 produced very high quality and detailed CAD renderings of
their CubeSat design. We want the same quality and completeness in
our final presentation.
Comm Architecture and Data Handling
Let us stick with the concept of “Eye” (light collecting) satellites with
relatively lower data rate, and “Master” spacecraft specializing in
communication (relatively high data rate), tracking and overall
formation coordination. This offers the most fault tolerance. We need
to do link budgets to compare the various distributions of data handling
and computation efforts.
Position of the Detectors
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Detectors should be mounted behind the primary, within the CubeSat
volume, and not at the primary focus. The latter location exposes them
to thermal and radiation loads, while the recommended position offers
them some protection.
Areas for Refinement
 Formation Dynamics and Deployment: A better understanding of
the orbit dynamics is absolutely necessary. The formation shape is
made possible because all the satellites are to follow equi-energy
orbits (see the dynamics homework). That means that, once
deployed, the formation rotates like a rigid body without (to at
least first order) the need for additional thrusting. Many of the
deployment diagrams are not actually feasible. The deployment
needs more analysis to produce a technically correct video.
 The V budgets need to be worked out. Orbit maintenance
analysis will need to look at various disturbances including the J2
perturbations
due
to
Earth’s
oblateness.
 Attitude control has to consider not only requirements to slew the
“eye” sats, but also to counter various disturbances such as solar
pressure torques, magnetic torques, aerodynamics, etc.
 Pointing budgets must be drawn up based on flux collector
requirements (e.g. telescope field-of-view, etc.), then select sensors
with the requisite precision. Star trackers are probably essential.
 Time in View Analysis: The average fraction of time in view of the
CS ground station should be calculated. The telecommunications
homework gives you a reasonable algorithm to accomplish this.
 Photodetectors and Dark Count: We need to determine the “dark
count”, which is the rate at which false pulses are produced
independent of the light source being viewed. This information,
which is a function of temperature, is then used to determine how
much cooling of the detectors is required to keep dark count from
degrading the SNR.
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Nominal
operation with
Peltier cooler:
4500 phot/s
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