U.S. patent application number 15/254323 was filed with the patent office on 2018-03-01 for spherical occulter coronagraph cubesat.
The applicant listed for this patent is U.S.A. as represented by the Administrator of the National Aeronautics and Space Administration, U.S.A. as represented by the Administrator of the National Aeronautics and Space Administration. Invention is credited to PHILLIP C. CHAMBERLIN, JOSEPH M. DAVILA, QIAN GONG, DOUGLAS M. RABIN, NELSON REGINALD, NEERAV SHAH.
Application Number | 20180058922 15/254323 |
Document ID | / |
Family ID | 61242205 |
Filed Date | 2018-03-01 |
United States Patent
Application |
20180058922 |
Kind Code |
A1 |
DAVILA; JOSEPH M. ; et
al. |
March 1, 2018 |
SPHERICAL OCCULTER CORONAGRAPH CUBESAT
Abstract
The present invention relates to a space-based instrument which
provides continuous coronal electron temperature and velocity
images, for a predetermined period of time, thereby improving the
understanding of coronal evolution and how the solar wind and
Coronal Mass Ejection transients evolve from the low solar
atmosphere through the heliosphere for an entire solar rotation.
Specifically, the present invention relates to using a 6U spherical
occulter coronagraph CubeSat, and a relative navigational system
(RNS) that controls the position of the spacecraft relative to the
occulting sphere. The present invention innovatively deploys a
free-flying spherical occulter, and after deployment, the actively
controlled CubeSat will provide an inertial formation flying with
the spherical occulter and Sun.
Inventors: |
DAVILA; JOSEPH M.; (West
Friendship, MD) ; RABIN; DOUGLAS M.; (Arnold, MD)
; REGINALD; NELSON; (Bryans Road, MD) ; GONG;
QIAN; (Columbia, MD) ; SHAH; NEERAV;
(Columbia, MD) ; CHAMBERLIN; PHILLIP C.;
(Gambrills, MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
U.S.A. as represented by the Administrator of the National
Aeronautics and Space Administration |
Washington |
DC |
US |
|
|
Family ID: |
61242205 |
Appl. No.: |
15/254323 |
Filed: |
September 1, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B64G 1/66 20130101; G01J
1/0437 20130101; G01J 1/0271 20130101; B64G 1/1085 20130101; B64G
1/363 20130101; G02B 5/003 20130101; B64G 1/105 20130101; G01J
1/0266 20130101; G01J 2001/446 20130101; G01S 3/7861 20130101; B64G
1/406 20130101; G01J 2001/4266 20130101; G01J 1/4228 20130101; B64G
1/244 20190501; B64G 1/26 20130101; B64G 1/242 20130101 |
International
Class: |
G01J 1/04 20060101
G01J001/04; G01J 1/02 20060101 G01J001/02; G01J 1/44 20060101
G01J001/44; G01J 1/42 20060101 G01J001/42; G01S 3/786 20060101
G01S003/786; B64G 1/10 20060101 B64G001/10; B64G 1/26 20060101
B64G001/26; B64G 1/40 20060101 B64G001/40 |
Claims
1. An occulter coronagraph CubeSat comprising: a spherical
occulter; an occulter release mechanism; wherein said spherical
occulter is deployed from an occulter guide tube disposed in a body
of said occulter coronagraph CubeSat, using said occulter release
mechanism.
2. The occulter coronagraph CubeSat of claim 1, wherein said
spherical occulter is coated with a black paint material which
provides greater than 90% absorption of any scattered light, and is
a conductive surface which provides forward scatter suppression
around said spherical occulter.
3. The occulter coronagraph CubeSat of claim 1, further comprising:
a relative navigation system comprising a plurality of photodiodes,
including first lateral photodiodes, second lateral photodiodes,
full-sun photodiodes, and range photodiodes, said plurality of
photodiodes which sense a translation and range of said spherical
occulter to control a position of the CubeSat relative to said
spherical occulter, and for formation flying feedback of a
plurality of CubeSats.
4. The occulter coronagraph CubeSat of claim 3, wherein said
full-sun photodiodes are disposed on outer edges of a front face of
the CubeSat, and are used to determine a full Sun intensity and
allow for relative measurements of said plurality of photodiodes in
the CubeSat; wherein said first lateral photodiodes are disposed a
predetermined distance from an aperture lens of said spherical
occulter, and are used for lateral motion sensing; wherein said
range photodiodes are used for range measurement and are disposed
at predetermined distances from said aperture lens; wherein said
second lateral photodiodes are disposed at a bottom of said
occulter guide tube proximate to said occulter release mechanism,
and detect lateral movement of said spherical occulter during
release, to confirm that said spherical occulter has left said
occulter guide tube.
5. The occulter coronagraph CubeSat of claim 3, wherein said
spherical occulter is a formation flying, passive, free-flying
occulter, which reduces forward scattering noise contributed by
diffraction around said spherical occulter at an inner half-angle
field-of-view (FOV) of 0.375.degree., corresponding to 1.5
R.sub.Sun.
6. The occulter coronagraph CubeSat of claim 4, wherein a size of
said spherical occulter and said occulter release mechanism is
maximized to an 8 cm diameter to fit into a 1 U unit
allocation.
7. The occulter coronagraph CubeSat of claim 6, wherein the
occulter coronagraph CubeSat measures an electron temperature and a
bulk electron vector velocity of the Sun's corona during one full
Carrington rotation.
8. The occulter coronagraph CubeSat of claim 7, wherein the
occulter coronagraph CubeSat utilizes a heliocentric orbit.
9. The occulter coronagraph CubeSat of claim 8, further comprising:
a de-tumble or sun finding mode; and an occulter deployment model;
wherein said de-tumble or sun finding mode arrests a tipoff
rotation rate, and a plurality of course sensors are used to find
the Sun and reorient the occulter coronagraph CubeSat to point said
front face to the Sun; and wherein said occulter deployment mode
utilizes said occulter release mechanism to deploy said spherical
occulter.
10. The occulter coronagraph CubeSat of claim 9, further
comprising: a science mode which points said spherical occulter at
<0.5 deg with respect to the Sun, and a jitter of less than 18''
of jitter over a 9-sec integration; wherein said spherical occulter
always occludes the Sun based on a relative position between said
spherical occulter and the occulter coronagraph CubeSat.
11. The occulter coronagraph CubeSat of claim 10, further
comprising: a plurality of micro-cathode vacuum arc thrusters which
are used for in-space micro-propulsion; wherein said thrusters are
fired for a prescribed burn after said spherical occulter is
deployed, in order to move the occulter coronagraph CubeSat away
from said spherical occulter; and wherein on condition that said
spherical occulter has successfully cleared the occulter
coronagraph CubeSat, the thrusters are fired to translate the
occulter coronagraph CubeSat so that said spherical occulter covers
said aperture lens to occult the Sun, and to move the occulter
coronagraph CubeSat further from said spherical occulter along an
optical axis.
12. The occulter coronagraph CubeSat of claim 11, wherein the
occulter coronagraph CubeSat thrusts away from said spherical
occulter with a force of about 1 micro-N.
13. A method of occulting a corona of the Sun, comprising:
deploying an occulter coronagraph CubeSat in a heliocentric orbit;
wherein said occulter coronagraph CubeSat comprises a spherical
occulter, which is deployed from an occulter guide tube disposed in
a body of said occulter coronagraph CubeSat utilizing an occulter
release mechanism.
14. The method of claim 13, wherein said spherical occulter is a
formation flying, passive, free-flying occulter.
15. The method of claim 14, wherein said spherical occulter is
coated with a black paint material which provides better than 90%
absorption of any scattered light as well as being a conductive
surface which provides forward scatter suppression around said
spherical occulter.
16. The method of claim 15, wherein said spherical occulter reduces
forward scattering noise contributed by diffraction around said
spherical occulter at an inner half-angle field-of-view (FOV) of
0.375.degree., corresponding to 1.5 R.sub.Sun.
17. The method of claim 16, wherein a size of said spherical
occulter and said occulter release mechanism is maximized to an 8
cm diameter to fit into a 1 U unit allocation.
18. The method of claim 17, wherein said occulter coronagraph
CubeSat measures an electron temperature and a bulk electron vector
velocity of the Sun's corona during one full Carrington
rotation.
19. The method of claim 18, wherein said occulter coronagraph
CubeSat includes a de-tumble or sun finding mode; an occulter
deployment mode, and a science mode; wherein said de-tumble or sun
finding mode arrests a tipoff rotation rate, and a plurality of
course sensors are used to find the Sun and reorient said occulter
coronagraph CubeSat to point said front face to the Sun; wherein
said occulter deployment mode utilizes said occulter release
mechanism to deploy said spherical occulter; wherein said science
mode includes pointing said spherical occulter at <0.5 deg with
respect to the Sun, and a jitter of less than 18'' of jitter over a
9-sec integration, and said spherical occulter always occludes the
Sun based on a relative position between said spherical occulter
and said occulter coronagraph CubeSat.
20. The method of claim 19, further comprising: utilizing a
plurality of micro-cathode vacuum arc thrusters for in-space
micro-propulsion; wherein said thrusters are fired for a prescribed
burn after said spherical occulter is deployed, in order to move
said occulter coronagraph CubeSat away from said spherical
occulter; wherein on condition that said spherical occulter has
successfully cleared said occulter coronagraph CubeSat, said
thrusters are fired to first translate the occulter coronagraph
CubeSat so that said spherical occulter covers said aperture lens
to occult the Sun, and to move the occulter coronagraph CubeSat
further from said spherical occulter along an optical axis; and
wherein said occulter coronagraph CubeSat thrusts away from said
spherical occulter with a force of about 1 micro-N.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a space-based instrument
which can provide continuous coronal electron temperature and
velocity images, for a predetermined period of time, thereby
improving the understanding of coronal evolution and how the solar
wind and coronal mass ejection (CME) transients evolve from the low
solar atmosphere through the heliosphere for an entire solar
rotation. Specifically, the present invention relates to using a
spherical occulter coronagraph CubeSat, and a relative navigational
system that controls the position of the spacecraft relative to the
occulting sphere.
2. Description of the Related Art
[0002] Conventional solar coronagraphs measure visible photospheric
light Thomson-scattered by coronal electrons, imaging the seemingly
static solar corona including transients, such as Coronal Mass
Ejections (CMEs), as they disrupt the overlying magnetic field.
[0003] However, the resolution of the images in the low corona is
related to the distance that the external occulter is from the
imaging optics; the farther the occulter the better the image. This
is why a total solar eclipse is the ideal coronagraph, as the moon
is over 200,000 miles from the observers. Traditional imagers use
mechanical structures, such as tubes, to mount and align the
occulter to the optics, and these structures limit this distance to
.about.1 meter due to volume/mass limitations to get these
instruments into space.
[0004] Thus, a coronagraph that is capable of eliminating any
mechanical structure and utilize inertial formation flying of two
separate spacecraft, one containing the occulter and the other the
spacecraft, is desired.
SUMMARY OF THE INVENTION
[0005] The present invention relates to a space-based instrument
which can provide continuous, high-resolution coronal electron
temperature and velocity images, for a predetermined period of time
(i.e., one month), thereby improving the understanding of coronal
evolution and how the solar wind and CME transients evolve from the
low solar atmosphere through the heliosphere for an entire solar
rotation. Specifically, the present invention relates to using a
spherical occulter coronagraph (SOC) CubeSat, and a relative
navigational system (RNS) that controls the position of the
spacecraft relative to the occulting sphere.
[0006] In one embodiment, the present invention relates to a novel
6U (U-type spacecraft) spherical occulter coronagraph Cubesat,
which can meet science observations from 1.5R.sub.Sun to 5
R.sub.Sun. In one embodiment, the novel spherical occulter
coronagraph of the present invention innovatively deploys a
free-flying spherical occulter (instead of a flat disk), and after
deployment, the actively controlled CubeSat provides a novel
inertial formation flying with the sphere and Sun using a novel
relative navigational system (RNS).
[0007] In one embodiment, the RNS includes a plurality of RNS
photodiodes for sensing the translation and range of the spherical
occulter relative to the spacecraft, and for formation flying
feedback.
[0008] In one embodiment, the spherical occulter coronagraph of the
present invention has greater than 2.25 m separation between the
occulter and optics, greater than prior art separations which are
approximately 0.8 m to 1.3 m. This larger separation improves the
signal-to-noise ratio due to reduced diffraction intensities off
the occulter, a dominant noise source in coronagraphs. The
spherical occulter coronagraph's separation also leads to greatly
improved spatial resolution over current externally occulted
coronagraphs in the diffraction-limited region, from vignetting in
the low corona.
[0009] Additionally, the spherical occulter coronagraph CubeSat of
the present invention is a pathfinder directly scalable to
coronagraphs with even larger separations, possibly hundreds of
meters in length, using inflatable spherical occulters. The
spherical occulter coronagraph of the larger-scale coronagraphs
will have even better signal/noise ratio and spatial resolution,
providing high-resolution images and plasma diagnostics down to
<1.05 solar radii.
[0010] In one embodiment, the spherical occulter coronagraph
CubeSat of the present invention can be used in any Earth-escape
orbit that will take the spherical occulter coronagraph CubeSat out
of the influence of Earth's atmospheric density variations and
changing gravitational forces, simplifying formation flying while
providing a 100% view of the Sun.
[0011] In one embodiment, the spherical occulter coronagraph
CubeSat of the present invention includes a plurality of novel
technology features, including: 1) inertial formation-flying with a
passive secondary including release technique, control scheme, and
software; 2) theoretical diffractive performance of a spherical
occulter, expected to be superior to the traditional flat
knife-edge occulters; 3) fine Sun-pointing from a CubeSat platform;
4) interplanetary communication from a CubeSat; 5) .mu.CAT
microthrusters; and 6) approximately 1 U volume coronagraph optics
and filter wheel, not including the occulter.
[0012] In one embodiment, the occulter coronagraph CubeSat of the
present invention includes: a spherical occulter; an occulter
release mechanism; wherein the spherical occulter is deployed from
an occulter guide tube disposed in a body of the occulter
coronagraph CubeSat, using the occulter release mechanism.
[0013] In one embodiment, the spherical occulter is coated with a
black paint material which provides greater than 90% absorption of
any scattered light, and is a conductive surface which provides
forward scatter suppression around the spherical occulter.
[0014] In one embodiment, the occulter coronagraph CubeSat
includes: a relative navigation system (RNS) including a plurality
of photodiodes, including first lateral photodiodes, second lateral
photodiodes, full-sun photodiodes, and range photodiodes, the
plurality of photodiodes which sense a translation and range of the
spherical occulter to control a position of the CubeSat relative to
the spherical occulter, and for formation flying feedback of a
plurality of CubeSats.
[0015] In one embodiment, the full-sun photodiodes are disposed on
outer edges of a front face of the CubeSat, and are used to
determine a full Sun intensity and allow for relative measurements
of the plurality of photodiodes in the CubeSat; wherein the first
lateral photodiodes are disposed a predetermined distance from an
aperture lens of the spherical occulter, and are used for lateral
motion sensing; wherein the range photodiodes are used for range
measurement and are disposed at predetermined distances from the
aperture lens; wherein the second lateral photodiodes are disposed
at a bottom of the occulter guide tube proximate to the occulter
release mechanism, and detect lateral movement of the spherical
occulter during release, to confirm that the spherical occulter has
left the occulter guide tube.
[0016] In one embodiment, the spherical occulter is a formation
flying, passive, free-flying occulter, which reduces forward
scattering noise contributed by diffraction around the spherical
occulter at an inner half-angle field-of-view (FOV) of
0.375.degree., corresponding to 1.5R.sub.sun.
[0017] In one embodiment, a size of the spherical occulter and the
occulter release mechanism is maximized to an 8 cm diameter to fit
into a 1 U unit allocation.
[0018] In one embodiment, the occulter coronagraph CubeSat measures
an electron temperature and a bulk electron vector velocity of the
Sun's corona during one full Carrington rotation.
[0019] In one embodiment, the occulter coronagraph CubeSat utilizes
a heliocentric orbit.
[0020] In one embodiment, the occulter coronagraph CubeSat further
includes: a de-tumble or sun finding mode; and an occulter
deployment model; wherein the de-tumble or sun finding mode arrests
a tipoff rotation rate, and a plurality of course sensors are used
to find the Sun and reorient the occulter coronagraph CubeSat to
point the front face to the Sun; and wherein the occulter
deployment mode utilizes the occulter release mechanism to deploy
the spherical occulter.
[0021] In one embodiment, the occulter coronagraph CubeSat further
includes: a science mode which points the spherical occulter at
<0.5 deg with respect to the Sun, and a jitter of less than 18''
of jitter over a 9-sec integration; wherein the spherical occulter
always occludes the Sun based on a relative position between the
spherical occulter and the occulter coronagraph CubeSat.
[0022] In one embodiment, the occulter coronagraph CubeSat further
includes: a plurality of micro-cathode vacuum arc thrusters which
are used for in-space micro-propulsion; wherein the thrusters are
fired for a prescribed burn after the spherical occulter is
deployed, in order to back the occulter coronagraph CubeSat away
from the spherical occulter; and wherein on condition that the
spherical occulter has successfully cleared the occulter
coronagraph CubeSat, the thrusters are fired to translate the
occulter coronagraph CubeSat so that the spherical occulter covers
the aperture lens to occult the Sun, and to move the occulter
coronagraph CubeSat further from the spherical occulter along an
optical axis.
[0023] In one embodiment, the occulter coronagraph CubeSat thrusts
away from the spherical occulter with a force of about 1
micro-N.
[0024] In one embodiment, a method of occulting a corona of the
Sun, includes: deploying an occulter coronagraph CubeSat in a
heliocentric orbit; wherein the occulter coronagraph CubeSat
includes a spherical occulter, which is deployed from an occulter
guide tube disposed in a body of the occulter coronagraph CubeSat
utilizing an occulter release mechanism.
[0025] In one embodiment, the method of occulting a corona of the
Sun further includes: utilizing a plurality of micro-cathode vacuum
arc thrusters for in-space micro-propulsion; wherein the thrusters
are fired for a prescribed burn after the spherical occulter is
deployed, in order to back the occulter coronagraph CubeSat away
from the spherical occulter; wherein on condition that the
spherical occulter has successfully cleared the occulter
coronagraph CubeSat, the thrusters are fired to first translate the
occulter coronagraph CubeSat so that the spherical occulter covers
the aperture lens to occult the Sun, and to move the occulter
coronagraph CubeSat further from the spherical occulter along an
optical axis; and wherein the occulter coronagraph CubeSat thrusts
away from the spherical occulter with a force of about 1
micro-N.
[0026] Thus has been outlined, some features consistent with the
present invention in order that the detailed description thereof
that follows may be better understood, and in order that the
present contribution to the art may be better appreciated. There
are, of course, additional features consistent with the present
invention that will be described below and which will form the
subject matter of the claims appended hereto.
[0027] In this respect, before explaining at least one embodiment
consistent with the present invention in detail, it is to be
understood that the invention is not limited in its application to
the details of construction and to the arrangements of the
components set forth in the following description or illustrated in
the drawings. Methods and apparatuses consistent with the present
invention are capable of other embodiments and of being practiced
and carried out in various ways. Also, it is to be understood that
the phraseology and terminology employed herein, as well as the
abstract included below, are for the purpose of description and
should not be regarded as limiting.
[0028] As such, those skilled in the art will appreciate that the
conception upon which this disclosure is based may readily be
utilized as a basis for the designing of other structures, methods
and systems for carrying out the several purposes of the present
invention. It is important, therefore, that the claims be regarded
as including such equivalent constructions insofar as they do not
depart from the spirit and scope of the methods and apparatuses
consistent with the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a block diagram of the spherical occulter
coronagraph CubeSat of the present invention, showing exemplary
subsystems and interface connections, according to one embodiment
consistent with the present invention.
[0030] FIG. 2 is a perspective view of a spherical occulter
coronagraph CubeSat, showing the front panel and top panel,
according to one embodiment consistent with the present
invention.
[0031] FIG. 3 is a view of the spherical occulter coronagraph
CubeSata, where the right-most version is clear of any labels and
shows the umbral and penumbral shadow of the spherical occuler on
the front panel, and the left version shows symbols and annotations
describing the components of the relative navigation system (RNS),
according to one embodiment consistent with the present
invention.
[0032] FIG. 4 is a rear, open panel view, showing the components
within, of the spherical occulter coronagraph CubeSat according to
one embodiment consistent with the present invention.
DESCRIPTION OF THE INVENTION
[0033] The present invention on relates to a space-based instrument
which can provide continuous coronal electron temperature and
velocity images, for a predetermined period of time (i.e., one
month), thereby improving the understanding of coronal evolution
and how the solar wind and Coronal Mass Ejection (CME) transients
evolve from the low solar atmosphere through the heliosphere for an
entire solar rotation. Specifically, the present invention relates
to using a novel spherical occulter coronagraph (SOC) CubeSat, and
a relative navigational system (RNS) that controls the position of
the spacecraft relative to the occulting sphere.
[0034] In one embodiment, the present invention relates to a novel
6U (U-type spacecraft) spherical occulter coronagraph (SOC) Cubesat
100 (see FIGS. 1-4), which can meet science observations from
1.5R.sub.Sun to 5R.sub.Sun. In one embodiment, the novel spherical
occulter coronagraph of the present invention innovatively deploys
a free-flying spherical occulter 201 (see FIG. 2) (instead of a
flat disk), and after deployment, the actively controlled CubeSat
100 will provide a novel inertial formation flying with the
spherical occulter 201 and Sun.
[0035] System Design
[0036] In one embodiment, FIG. 1 shows exemplary components of the
novel spherical occulter coronagraph CubeSat 100 of the present
invention. In one embodiment, a spacecraft and payload interface
board 101 enables communication to the computer standardized bus
(i.e., PC/104) 102 subsystems: space Electrical Power System (EPS)
103, batteries 104, and X-band transceiver 105. A CHREC (Center for
High-Performance Reconfigurable Computing) space processor (CSP
107) is connected to the bus 102 via a connector 119. The interface
board 101 enables communication to non-PC/104 subsystems such as
and X-ray advanced concepts testbed (XACT) sounding rocket 106, the
CSP 107, the science complementary metal-oxide semiconductor (CMOS)
imager board 108, and a plurality of micro-cathode vacuum arc
thrusters (CAT) 109 with electric propulsion boards 110. The
micro-cathode vacuum arc thrusters (.mu.CAT) 109 are used for
in-space micro-propulsion applications, and are high specific
impulse (Isp), low-thrust electric propulsion suitable for small
satellite attitude control, precision orbit control or extended
low-thrust maneuvers. In one embodiment, the CubeSat 100
compatible, Deep Space Network (DSN) 118 compatible X-band
transponder 105 can operate on any channel in deep space or the
near Earth X-band.
[0037] In one embodiment, the optical equipment 114 of the
spherical occulter 201 was designed to be placed in a 6U CubeSat
100. In one embodiment, the optical design of the present invention
meets all science-derived requirements, and the entire optics
package 114 (see FIGS. 1 and 4), including focusing lenses (i.e.,
entrance aperture lens 207 etc.), as well as the filter wheel 115,
all fit into just over a 1 U volume package.
[0038] In one embodiment, the flight software of the CSP 107 has
communication and control of the science electronics board 101, the
guidance, navigation and control (GNC) relative navigational system
(RNS), and the detection of a CME. The CFE allows for custom
applications to be developed independently. This is especially
useful for the relative navigational system (RNS) as it will run as
a separate process within the CFE and communicate via the messaging
middleware.
[0039] In one embodiment, the XACT 106 is one of two subsystems of
the guidance, navigation and control system (GNC) of the spherical
occulter coronagraph CubeSat 100--namely, the attitude control
system (ACS), which controls the attitude of the 6U spacecraft 100
relative to the Sun; and the novel relative navigational system
(RNS).
[0040] In one embodiment, as part of the ACS, a course sun sensor
(CSS) photodiode 205 (see FIG. 2) is placed on each of the
satellite faces (bottom panel 200, top panel 202, front panel 204,
and back panel) for course Sun-sensor positional knowledge. The CSS
photodiodes 205 are small photodiodes used for course determination
of the Sun's position, and are used only in the initial de-tumble
and sun-finding modes (discussed later).
[0041] In one embodiment, also as part of the ACS, a Fine Sun
Sensor (FSS) 117 is incorporated in the XACT 106 and used to
maintain fine pointing (<0.3.degree.) to the Sun. Further, the
FSS 117 is mounted such that it does not protrude past the outer
surface (front panel 204) of the spacecraft body (see FIG. 2) in
order to not reflect light into the optics 114.
[0042] In one embodiment, a plurality of .mu.CAT thrusters 109 are
mounted on the payload 100 at each corner of the top panel 202 and
facing outward (see FIG. 2), while the set is mirrored on the
bottom panel 200 (see FIG. 3). In one exemplary embodiment, an
arrangement of eight .mu.CAT thrusters 109 is the minimum number
needed at each of these corners of the CubeSat 100 to produce
motion in both translation and rotation on each body axis. This
will allow for control of the spacecraft 100 relative to the
spherical occulter 201 as well as allow for dumping momentum (i.e.,
allowing the momentum wheels from the XACT 106 system to spin down
to maintain spacecraft 100 attitude), if needed (but which is not
expected). However, one of ordinary skill in the art would know
that the placement and number of thrusters may change depending on
requirements.
[0043] As noted above, in one embodiment, the second subsystem of
the GNC is the novel relative navigation system (RNS) that controls
the position of the spacecraft 100 relative to the occulting sphere
201. In one embodiment, the inertial navigation includes a
plurality of RNS photodiodes (see FIG. 3)--for example, four
Lateral photodiodes 301, four Full-Sun photodiodes 302, two Range
photodiodes 303, and two other Lateral photodiodes (not shown)--for
sensing the translation and range of the spherical occulter 201
relative to the spacecraft 100, and for formation flying feedback.
However, one of ordinary skill in the art would know that the
placement and number of photodiodes may change depending on
requirements.
[0044] FIG. 3 also shows the extent of the umbra boundary 304 and
penumbra boundary 305 from the novel spherical occulter 201 on the
face of the occulter coronagraph CubeSat 100. In one embodiment,
four exemplary Full-Sun photodiodes 302 on the outer edges of the
science (front) face 204 are used to determine the full sun
intensity and should never be shadowed unless the spherical
occulter 201 has drifted and the spacecraft 100 has not compensated
for it. In one embodiment, the Full-Sun photodiodes 302 allow for
relative and not absolute measurements of all inertial alignment
diodes to remove other variables from the system (e.g., thermal,
proton storms, etc.).
[0045] In one embodiment, the occulter/aperture distance, given the
occulter 301 diameter, was iterated with the signal calculation,
which was limited by the occulter diffraction, to define the inner
FOV cutoff to be 1.5R.sub.sun. Note that the spherical occulter 301
spatial resolution from vignetting is moderate until about
1.75R.sub.Sun. The spherical occulter coronagraph CubeSat 100 of
the present invention is utilizing formation flying, thus, if the
noise and diffraction are lower than theoretically calculated it is
easy to adjust the distance control algorithm via upload command to
move the spherical occulter 301 farther away, enabling observations
lower in the solar corona. This leads to a separation of 2.25 m
with the 50 cm aperture, resulting in a much better
vignetting-limited spatial resolution than current
coronagraphs.
[0046] In one embodiment, the exemplary inside Lateral diodes 301,
which are disposed, for example, at 4 cm from the aperture lens
207, are used for lateral motion sensing. When the spherical
occulter 201 is centered over a CMOS detector 403 (see FIG. 4), the
shadow it casts will have equal intensity on all four exemplary
Lateral sensors 301. The Lateral photodiodes 301 are insensitive to
the range, as they are located at a radius equal to the radius of
the spherical occulter 201. The CMOS detector 403 is optimal due to
the power limitation on a CubeSat 100, and it interfaces with the
interface board 101 to transfer data into the CSP 107 for further
handling.
[0047] In one embodiment, there are two other sensors--Range diodes
303--used for range measurement, and that may be located in an
exemplary location, such as 4.25 cm and 4.5 cm from the aperture
lens 207 center. The relative intensity of the sun light going from
the umbra 304 through the penumbra 305 to full sun light on the
spacecraft front face 204, changes for a number of ranges
corresponding to different solar radii. By using the difference in
intensities on each of these range photodiodes 303, the range can
be determined. As the spacecraft moves further away from the
spherical occulter 201, and the effective solar radius of the
spherical occulter 201 gets smaller, the penumbra grows.
[0048] In one embodiment, the Lateral motion sensors 401 are
shadowed for all ranges. In one embodiment, the Ranging diodes 403
are placed such that they will be more accurate at long ranges. Any
effect on the estimation of range inside the 1.5R.sub.Sun baseline
is irrelevant as fine control is not needed here.
[0049] In one embodiment, the two remaining Lateral photodiodes
(not shown) are on the inside edges at the bottom of the occulter
guide tube 206 near the release mechanism 402. The Lateral
photodiodes detect if the spherical occulter 201 first moves
outward during the release and pullback by the spacecraft 100 until
the spherical occulter 201 is clear and followed by the translation
maneuver of the spacecraft 100 until the now free-flying spherical
occulter 201 is in position in front of the instrument aperture
lens 207, providing knowledge that the occulter 201 has left the
occulter guide tube 206 and is centered on the aperture lens 207.
In one embodiment, based on estimated noise of the photodiodes
301-303 and accompanying electrical circuits to read them, the
intensity of the photodiodes 301-303 can conservatively be
estimated within 1% of full scale which gives a range accuracy of
.about.13 cm and a lateral accuracy of .about.1 mm for a shadow
from the sphere relative size of 1.5R.sub.Sun.
[0050] In one embodiment, the spherical occulter coronagraph
CubeSat 100 of the present invention uses two space 6U single-sided
long-edge deployable solar panels 111, 112, each panel 111, 112
containing a plurality of solar cells (for example, 21 solar cells
of which seven (7) are in series and three (3) in parallel--7s3p
configuration) on only the outer face (see FIG. 2). The solar cells
provide power to the CubeSat 100 when the panels 111, 112 are
stowed prior to panel deployment. The operating temperature of the
solar cells 111, 112 is around +80.degree. C.
[0051] In one embodiment, in addition to the two 6U deployable
solar panels 111, 112, and filter wheel 115, the spacecraft 100
includes other onboard mechanisms such as a release mechanism 402
(see FIG. 4) for the occulter 201. In one embodiment, the spherical
occulter's 201 size, along with its deployment or release mechanism
402 (see FIG. 3), was maximized to an 8 cm diameter to fit into a 1
U unit allocation.
[0052] In one embodiment, the 6U deployable solar panels 111, 112
include all necessary mounting hardware and release mechanisms that
incorporate a thermal knife and time driver system (not shown).
When deployed, the spring loaded hinge system (not shown) of the
release mechanism 402 will open the panels to a 90.degree. position
to be normal to the Sun for maximum power production.
[0053] The occulter release mechanism 402 contains a pin puller
among other components. A cupped plunger (not shown) is used to
hold the occulter 201 against the wall of the occulter guide tube
206. Upon actuation of the pin puller (not shown), a compression
spring pushes the plunger away from the occulter 201 such that it
is free to move. The compression spring (not shown) maintains force
on the plunger so that it will not return to the occulter guide
tube 206.
[0054] In one embodiment a three (3)-node thermal mode provides
operating temperatures for the solar panels 111, 112, and also
ensures that the CMOS chip 403 can be run at -20.degree. C. (to
reduce detector 403 noise) using a simply conductive thermal strap
404 (see FIG. 4) tied to a dedicated 10 cm by 20 cm white paint
radiator patch on the aft end 203 of the spacecraft 100. There is
also a significant margin to dissipate the rest of the internal
heat sources given the rest of the CubeSat 100 faces 300, 302 303,
305 behind the solar panels 113, 114.
[0055] In one embodiment, the power system is designed such that
power experiment is only during the science window; power
transmitter is only during the exemplary transmit time (e.g., 240
minutes per day); and power guidance, navigation and control (GNC)
and command and data handling (C&DH) (science and housekeeping)
is conducted 100% of the time.
[0056] In one embodiment, the batteries 104 are configured in a
2s3p configuration, and are designed to integrate with a suitable
EPS 103 and the solar arrays 111, 112 to form a complete power
system for the spherical occulter coronagraph CubeSat 100.
[0057] In one embodiment, the spherical occulter 201, as a
formation flying, passive, free-flying occulter 210, reduces the
forward scattering noise contributed by diffraction around the
occulter 201, by over an order of magnitude versus the traditional
knife-edge disk occulter at the occulter 201 inner half-angle FOV
of 0.375.degree., corresponding to 1.5R.sub.Sun. The noise
reduction is also more than 7 orders of magnitude greater at the
occulter 201 outer FOV cutoff of 5R.sub.Sun.
[0058] In one embodiment, sunlight reflected/scattered off the
spacecraft 100, or directly from the Earth or lunar albedo, hitting
the spherical occulter 201 could possibly be scattered into the
entrance aperture. However, the worst-case scatter light path (Sun
to solar panels 111, 112 to occulter 201 into aperture) is reduced
by nine orders of magnitude. This large reduction is due to
insuring there are no direct reflection paths, only Lambertian
scattering, as well as black painting the sphere and the small
(1.degree. FOV) of the sphere 201. So these scatter paths off of
the back of the occulter 201 are not a significant source of
noise.
[0059] In one embodiment, although there is no "tube" between the
occulter 201 and the aperture to block light, there is no concern
regarding scattered light entering into the optical path/aperture
off the passive occulter 201. In one embodiment, the spherical
occulter 201 is coated with a black paint material which provides
better than 90% absorption of any scattered light as well as being
a conductive surface which provides forward scatter suppression
around said spherical occulter.
[0060] In one embodiment, the instrument optics 114, filter wheel
115, and CMOSIS Chip and Board 503 are enclosed on their sides with
sheet metal closeouts to keep out stray light. In one embodiment,
the four telemetry cards 401 (see FIG. 4) and EPS 103 are
maintained in a stack in order to best utilize a CubeSat Kit
connector 405 to the interface 101. In one embodiment, custom
mounting brackets are used to place each of the eight propulsion
thrusters 109 at the corners of the spacecraft body 100 and
maintain the desired 45.degree. orientation.
[0061] In one embodiment, in order to use the temperature and
velocity ratio techniques described below, four bandpass filters
(not shown) are used. A visible filter position, which is used to
reduce the noise signal, is used to obtain standard broadband white
light coronagraph images. A dark position for dark-image
subtraction is also needed, and this will also be used for
optics/CMOS protection during launch and times in the mission prior
to occulter 201 deployment when the full Sun enters the optics 114.
This leads to six total filter positions needed in the filter wheel
115. In one embodiment, the diameters of the four bandpass filters
will be adjusted to the spherical occulter coronagraph optical
design and placed in the filter wheel 115 to automatically cycle
through the four different wavelengths along with the visible Sun
and dark filter positions.
[0062] In one embodiment, a soft X-ray photodiode 208 (e.g., AXUV20
with Beryllium filter) is used to detect flares. It is a smaller
photodiode 208 than existing X-ray photodiodes in order to reduce
resources, and is a thicker filter to reduce dynamic range. An
intensity level is set at about C-class flare level, that when
breached, will flag upcoming observations for the next three hours
as a priority for downlink.
[0063] Science Mode
[0064] In one embodiment, the components described above of the
spherical occulter coronagraph CubeSat 100 of the present invention
are used to perform the tasks of determining the bulk electron flow
velocity and plasma temperature of the Sun's corona throughout one
full Carrington rotation (i.e., 27 days for a solar rotation), and
to determine the bulk electron flow velocity and plasma temperature
of Coronal Mass Ejections (CMEs).
[0065] In one embodiment, the CubeSat 100 of the present invention
will provide information on how the temperature and flows in these
large scale coronal structures change over a single Carrington
rotation due to the underlying emerging, evolving, and decaying
active regions and the subsequent changes these drive in the
overlying solar corona, as well as the dynamics of the solar wind
and multiple CMEs that disrupt the steady state corona, and which
can have significant Space Weather impacts.
[0066] In one embodiment, the CubeSat 100 provides the white-light
image of the solar corona from 1.5 solar radii (R.sub.Sun) out to
5R.sub.Sun, but with its set of an exemplary four bandpass filters,
it will also be able to produce the first-ever continuous
space-based maps of the coronal temperature and bulk electron
velocity.
[0067] In one embodiment, the spherical occulter coronagraph
CubeSat 100 of the present invention will provide additional
measurements of the electron temperature and the bulk electron
vector velocity--not just the transverse velocity--significantly
increasing understanding of the dynamics and evolution of these
complex events.
[0068] Flight Operations
[0069] In one embodiment, the reasons that a heliocentric orbit is
ideal for formation flying include, but are not limited to:
[0070] 1) It is free from high-frequency external forces present in
low-Earth orbit, such as those from density perturbations in the
Earth's atmosphere or from the Earth's varying gravitational
influence that would act differently on the two different
spacecraft 100 in formation flying (see FIG. 3). The inertial
formation flying corrections that will need to be made are much
less frequent and are slowly changing. The solar radiation pressure
will act on both spacecraft 100 in the same direction, and solar
wind and CMEs are insignificant due to their small densities.
[0071] 2) The heliocentric orbit also provides a continuous view of
the Sun that is free from eclipses, leading to 100% observation
time to view eruptive events in their entirety.
[0072] 3) The heliocentric orbit is also free from elliptical
orbital perturbations that would restrict formation-flying missions
that are in orbit around Earth, to once per orbit. Inertial
formation-flying dynamics require the two spacecraft 100 to have
the same semi-major axis in order to have the same orbital period,
so almost all locations along the orbit are useless.
[0073] The spherical occulter coronagraph CubeSat 100 of the
present invention includes two operational modes.
[0074] Mode 1 is the De-tumble/Sun finding mode. In one embodiment,
the De-tumble mode starts after spherical occulter coronagraph
separation when the spacecraft 100 comes alive, when the ACS
switches to De-tumble mode and arrests the tipoff rotation rates.
The course sun sensors 205 are used to initially find the Sun and
reorient it to point the correct face at the Sun. The solar panels
111, 112 are deployed once the fine sun sensors (FSS) 117 register
that the Sun has been obtained and the FSS 117 take control. The
spacecraft 100 will wait in the De-tumble mode until the second
mode--Occulter deployment--which will occur after lunar swing-by,
to ensure the occculter 201 will not be lost during swing-by.
[0075] In Mode 2--Occulter deployment--the spherical occulter 201
is released so as to not impart an unknown velocity between the two
objects 100. After the spherical occulter 201 is released, the
thrusters 109 are fired for a prescribed burn to back the 6U
spacecraft 100 away from the spherical occulter 201, where a
photodiode at the base of the occulter guide tube 206 registers
that the spherical occulter 201 has successfully cleared the
spacecraft 100. The CSP 107 will then fire the thrusters 109 to
first translate the CubeSat 100 so that the spherical occulter 201
covers the lens 207 to occult the Sun; and second, to move the
spacecraft 100 further from the spherical occulter 201 along the
optical axis.
[0076] In another mode--the Science Mode--the ACS and RNS
algorithms will run continuously throughout the Science mission
ensuring 100% views of the Sun with inertial alignment to within
the pointing requirements. The science operation is simply either
taking data or transmitting data, and pointing at the Sun
continuously; no additional pointing offsets are needed for
transmission or receiving.
[0077] In one embodiment, the science requirement for pointing is
<0.5 deg with respect to the Sun and a jitter of less than 18''
of jitter over a 9-sec integration. The spacecraft 100 position
relative to the occulting sphere 301 must be maintained such that
the Sun is always occluded. The relative movement during an
exposure is not as critical, but should be kept to less than 0.1
cm, which is easily accommodated.
[0078] In one embodiment, in a heliocentric orbit, the primary
forces and torques on the spacecraft 100 will be due to solar
pressure. The spherical occulter 201 has a much smaller area than
the spacecraft 100 but weights much less; therefore, it will want
to move towards the spacecraft 100 after deployment. In order to
maintain a desired range, the spacecraft 100 will have to thrust
away from the sphere 201 with a force of about 1 micro-N. In one
exemplary embodiment, if the center of gravity is 5 cm away from
the center of pressure, the torque from solar pressure will be
about 4e-8 Nm which equates to about 3.5 mNms per day. At tipoff,
if a 3 deg/sec body rate is assumed, the momentum wheels need to
absorb about 8 mNms momentum with at least 2 mNms to spare for a
rotation maneuver to find the Sun for a total capacity needed of
about 10 mNms.
[0079] In one embodiment, the spherical occulter coronagraph of the
present invention measures the electron temperature and bulk
electron velocity in the corona, providing additional continuous
measurements of physical variables beyond the current standard
imaging coronagraph. With the addition of polarization filter,
application of this technique can be made further out in the solar
corona.
[0080] Not only does the spherical occulter coronagraph of the
present invention have stand-alone science achievements, it also
addresses technology that can be used for larger, higher-class
missions, including: 1) inertial formation flying with a passive
secondary including release technique, control scheme, and
software; 2) theoretical diffractive performance of a spherical
occulter, expected to be superior to the traditional flat
knife-edge occulters; 3) fine Sun-pointing in a CubeSat; 4)
interplanetary communication from a CubeSat; 5) .mu.CAT
microthrusters; and 6) approximately 1 U volume coronagraph optics
and filter wheel, not including the occulter.
[0081] It should be emphasized that the above-described embodiments
of the invention are merely possible examples of implementations
set forth for a clear understanding of the principles of the
invention. Variations and modifications may be made to the
above-described embodiments of the invention without departing from
the spirit and principles of the invention. All such modifications
and variations are intended to be included herein within the scope
of the invention and protected by the following claims.
* * * * *