SWOT mission
Mission objective is to determine the spatial and temporal
variability in freshwater stored in the world’s terrestrial water bodies
+ spatial altimetry over oceans. There is numerous secondary
objective achievable such as ice cap and sea ice measurements.
Main evolutions vs
Water:
Coupling with PF2012:
Add ocean altimetry
No existing PF “as is” able to
accommodate Karin
Orbit requirement
based on a 78deg950km inclination orbit
to avoid Tie Aliasing.
On going study in France to
develop a new generation of PF
product line to succeed Proteus,
Myriade and Spot class.
Open trade-off on
frequency for Nadir
altimeter
This PF product line cover micro
satellite to large satellite based
on the same avionics
Open PF compatibility
SWOT is one of the 8 reference
potential mission for PF2012
More data to transmit
to ground
07/07/2005
Agenda
 Situation on Platform studies
 Main key points studied for payload accommodation
 Power versus “Drifting orbit + roll stability + fixed yaw” constraints
 Data transmission to ground
 Payload thermal control
07/07/2005
Platform situation
 No existing PF available after 2012 and compatible with SWOT
constraints in Europe
 On going activity in CNES to define a new generation of PF to
succeed Myriade, Proteus and larger satellite: called PF2012
 Concept with 3 nominal mechanical architecture to cover a large flight
domain
 Standardized avionic with power modularity such as on Telecom PF
 High performances (>10years of life duration, pointing, DV capacity,
data transmission…)
 8 reference potential missions are based on this product line
including SWOT mission
07/07/2005
Power versus
“Drifting orbit + roll stability + fixed yaw” constraints
 SWOT need a « state of the art » stability in roll (few 0.1 arcsec over 10s)
 Need a fixed solar array during measurements to avoid SADM perturbation
 SWOT need a fixed yaw (antennas parallel to velocity vector)
 Not compatible with yaw steering such as on Topex/Jason
 SWOT need a drifting orbit to avoid tie aliasing
 Sun elevation versus orbit plane varies from 0 to 90 deg
 SWOT need a large payload power consumption
 The sum of these constraints lead to a solar array efficiency over an orbit of 30%
instead of 68% for a mission such as Jason.
 The solar array surface shall be of 2m² per 100W of satellite power
(with the most efficient existing solar cells: 3J AsGa and without margin)
07/07/2005
Solar array proposed accommodation
 Rotation axis around velocity vector
 Fixed solar array with axis parallel to velocity
 Tilt value constant at 17deg
 Maximum “reasonable” SA
surface 18 to 20m² (5 to 5.5kW BOL)
 Yaw flip when Sun cross
orbit plane to maintain a
cold satellite side for
thermal dissipation
Velocity
Optimum if constant = 17deg
 Advantages of this accommodation
Nadir





Maximize power with a fixed SA
Optimize inertia matrix
Minimize RF SA/PL interferences
Optimize payload thermal control
Minimize drag for POD
07/07/2005
Power availability with Fixed (or semi-fixed) solar array
 Perform a satellite YAW FLIP each time the SUN cross the orbit plane to
maintain a cold side for thermal dissipation
110,00
105,00
100,00
95,00
90,00
85,00
80,00
75,00
70,00
65,00
60,00
55,00
50,00
45,00
40,00
35,00
30,00
25,00
20,00
15,00
10,00
5,00
0,00
Sun distance effect
Eclipse effect
Seasonal solar array efficiency with semi-fixed tilt between 0 and 90deg
Seasonal solar array efficiency with semi fixed tilt between 0 and 30deg
Day
07/07/2005
30-déc
16-déc
2-déc
18-nov
4-nov
21-oct
7-oct
23-sept
9-sept
26-août
12-août
29-juil
15-juil
1-juil
17-juin
3-juin
20-mai
6-mai
22-avr
8-avr
25-mars
11-mars
26-févr
12-févr
29-janv
15-janv
Seasonal solar array efficiency with constant tilt of 17 deg
1-janv
efficiency(%))
Seasonal solar array efficiency
Inclination 78 deg - altitude 950 km
Constraint on the payload power consumption versus orbit
 There is no significant constraint on a 6h SSO orbit
 In order to avoid a very specific satellite design, it is recommend to limit solar array
surface at 20 m² in the case of a drifting orbit

allow 1000 W for satellite mean power
 With an assumption of 300W for PF and 20% of system margin:
 Allocation for payload mean power consumption is 560W including data storage,
transmission consumption, and payload thermal control
 If SSO orbit is definitely discarded, it is strongly recommend to limit payload mean
power under 500W for phase 0 and phase A
 A so large solar array need as a minimum a 2.38 internal diameter launcher fairing
 Which US launch vehicle (s) shall be consider for studies?
07/07/2005
KaRIN data rate is the second key parameter
KaRIN data rate (without margin) : 256 Mbit/s (TBC)
Maximum downlink data rate in X : 620 Mbit/s only over ground stations
It is impossible to downlink all data even with Ka band with these inputs
Altitude 813 km - site min 5deg
90
SPITZBERG
FAIRBANKS
60
Europe
FUCINO
WALLOPS
30
0
-30
-60
07/07/2005
Data transmission
 Need to optimize transmitted data rate:
 on board treatment (systematic or over limited zone)
 mask on data over zone without water
 With an objective of mean data rate of 30 (TBC) Mbit/s even if the
peak rate reach 256 Mbit/s
07/07/2005
Thermal control
 The large power consumption of the payload need a large dissipation
capability and order of magnitude for thermal dissipation are:
(Hypothesis: a=0.2 @10years, e=0.76, Trad=20°C, Téq=35°C without margin)
Without heat pipes
With heat pipes
280 W/m²
320 W/m²
0 W/m²
60 W/m²
2 velocity and anti-velocity
side – 2m²
200 W/m²
260 W/m²
Earth side 0.5m²
140 W/m²
200 W/m²
750 W max
1000 W max
Lateral antiSun side – 1m²
Lateral Sun side – 1m²
Total
Less stringent than power allocation
07/07/2005
conclusion
 SWOT is a reference potential mission for the new PF product line PF2012
 The platform and satellite may be provided by NASA or CNES
 Phase 0/A in CNES are performed on the basis of PF2012
 No work are done for an accommodation on a US platform
 The payload power consumption is the first key parameter (with a drifting orbit) to
avoid a specific and expensive platform development, the solar array is fix during
nominal operations.
 The mean payload data rate is the second key parameter for the mission feasibility
 The large size of solar panel will probably not be compatible with very small launch
vehicle fairing
 Need a dedicated launch (due to the specific orbit) with 2.38 m minimum fairing diameter
07/07/2005