astronomical institute university of bern 64 th international astronautical congress 23-27 september...
TRANSCRIPT
Astronomical Institute University of
Bern
64th International Astronautical Congress
23-27 September 2013, Beijing, China
Assessment of possible observation strategy in LEO regime
A. Vananti, T. Schildknecht
Astronomical Institute, University Bern (AIUB)
G.M. Pinna, T. Flohrer
European Space Agency (ESA)
Slide 2 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Introduction
European Space Situational Awareness (SSA) system: Network of optical telescopes Established concepts for GEO/MEO Few studies for LEO
LEO regime: Traditionally covered by radars Telescopes for upper LEO is more cost
efficient Assessment of LEO strategy:
Visibility of LEO objects Coverage simulations Orbit determination simulations
Slide 3 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Observation concept (Cibin et al. 2011)
Fly-eye telescope
1m, 6.7 x 6.7 deg2, 1.5“/px
Complex optical system (splitter, lenses)
Dynamic fences
Fields close to shadow border
Fields in low phase angle region
Slide 4 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Visibility
Based on dynamic fences concept Stripe around the shadow region Tenerife latitude = ~ 30°
120°90°
φ
site
= ± 23°
0 Limitation is the minimal elevation Reduced visibility around midnight in September With stripe at = 0° no visibility Station at high latitude needed for better coverage
Slide 5 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Visibility
Better visibility in Summer (from Northern emisphere)
Coverage like a sliding window that covers around 30° or 2 h of the moving station
Stripe at = 30° allows better visibility in September
But it does not cover low-inclination orbits
Slide 6 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Phase angles
Phase angles show a gap around midnight similarly to visibilities In summer, phase angles are slightly better reaching around 90° In general, when visibility is allowed are the phase angles around reasonable values < 60°
Slide 7 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Phase angles
For the fixed declination stripe in the visibility region the phase angles show big variation Smallest phase angles are well below 20° High phase angles exceed 100°
Slide 8 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Coverage simulations
LEO TLE population (~ 2000 objects) Eccentricity = 0 - 0.05 Inclination = ~ 50° - 100° Satellites at 1000-2000 km altitude Stations in Tenerife (TEN) and Azores
(AZR) Stripe declination = 30° Simulations without detection model 10° minimal elevation
Dec. Jun. Sep.
TEN. 312 989 661
TEN. AZR.
456 1286 895
Missed objects are: Visible only below the minimal elevation In the twilight region
Neglecting twilight constraints and assuming 0° for minimal elevation
=> 1953 objects
Slide 9 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Coverage during night
0
10
20
30
40
50
60
70
80
90
-5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8
Ob
ject
s
Hours after midnight UTC
Tenerife, September
0
5
10
15
20
25
30
35
40
45
50
-5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8
Ob
ject
s
Hours after midnight UTC
Tenerife, December
Also about 4 hours idle time In winter the nights are longer But the visibility is very reduced
Reduced visibility due to Earth shadow
4 hours idle time around local midnight
Covered range: ~ 2 h or ~ 30°
Slide 10 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Coverage during night
0
10
20
30
40
50
60
70
80
90
100
-5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8
Ob
ject
s
Hours after midnight UTC
Tenerife, June
No gap in summer (3 months) Only reductions due to:
Minimal elevation Twilight constraints
Almost full coverage with: No twilight constraints 0° minimal elevation
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
-5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8
Pe
rcen
t
Hours after midnight UTC
Tenerife, June, 0 deg min. elev., no twilight constraints
Slide 11 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Orbit determination simulations
Simulated 100 orbits in LEO regime: Altitude: 1000 km – 2000 km Eccentricity 0 – 0.01 Inclination 60° - 85°
Simulated observations (0.5“ error) from Tenerife, midnight UTC, 21.09.2012
Orbit determination with observations at different time intervals, assuming tracklet correlation
Examined angular position error after 24 hours Examined radial and along-track components of position error after
24 hours Requirements for orbit accuracy:
Radial component: 4 m Along-track component: 30 m
Slide 12 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Orbit determination simulations
Object discovery at plot origin Observations after 5 minutes The error strongly diverges after
only 1 follow-up
Histogram of angular position error Δ after 24 hours Observations after 5 min and 2 hours After 5 min: object observed from same station on a
second stripe After 2 hours: object observed after one revolution
from same station
Slide 13 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Orbit determination simulations
Observation intervals: 20 min, 2 h After 20 min: object observed from site at
same longitude in the opposite hemisphere Slight improvement compared with the
intervals 5 min, 2 h
Observation intervals: 5 min, 2 h, 4 h Assuming observations after 4 h from
a different longitude (> 30° shift) Error for most of the orbits < 1“
Slide 14 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Orbit determination simulations
Observation intervals: 5 min, 2 h, 4 h , 6 h, ... , 24 h Assuming a perfect coverage from all longitudes (12 or
more sites)
Slide 15 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Orbit determination simulations
Analysis of the position error Required accuracy: radial (4 m) and along-track component (30
m) Observation intervals: 5 min, 2 h
Radial error < 600 m Along-track error ~ 7 km Follow-up after 5 min and 2 hours:
=> not enough to satisfy requirements
Slide 16 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Orbit determination simulations
Observation intervals: 20 min, 2 h Required accuracy: radial (4 m)
and along-track component (30 m)
Requirements are partly satisfied: ~ 50 % radial ~ 35 % along-track
Slide 17 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Orbit determination simulations
Required accuracy: radial (4 m) and along-track component (30 m)
Observation intervals: 5 min, 2 hours, 4 hours Requirements are partly satisfied:
~ 45 % radial ~ 50 % along-track
Slide 18 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Orbit determination simulations
Required accuracy: along-track component (30 m) Observation intervals: 5 min, 2 h, 4 h , 6 h, ... , 24 h Requirement is well satisfied:
=> > 90% orbits within the required along-track accuracy
Slide 19 Astronomical Institute University of
Bern
Ass
ess
men
t of
poss
ible
ob
serv
ati
on
str
ate
gy in
LEO
reg
ime, IA
C 2
01
3, 2
3-2
7 S
ep
., B
eiji
ng Conclusions
Ideal strategy follows the contour of the Earth shadow Visibility window ~ 30° along the stripe During 9 months, 4 hours idle time per night Additional sites at higher latitude are an advantage, but not
indispensable 2 sites: 25% - 65% of objects covered depending on season For orbit determination 2 considered situations:
1 site North. and 1 site South. Hemisphere, same longitude => observations after 20 min and 2 hours 2 sites same Hemisphere, > 30° longitude separation => observations after 5 min, 2 hours, and 4 hours
On average 40 % - 50% objects with required accuracy after 24 hours