Diapositive 1

1
SWOT mission
Mission objective is to determine the spatial and
temporal variability in freshwater stored in the
worlds terrestrial water bodies spatial
altimetry over oceans. There is numerous
secondary objective achievable such as ice cap
and sea ice measurements.
Coupling with PF2012 No existing PF as is able
to accommodate Karin On going study in France to
develop a new generation of PF product line to
succeed Proteus, Myriade and Spot class. This PF
product line cover micro satellite to large
satellite based on the same avionics SWOT is one
of the 8 reference potential mission for PF2012
Main evolutions vs Water Add ocean
altimetry Orbit requirement based on a
78deg-950km inclination orbit to avoid Tie
Aliasing. Open trade-off on frequency for Nadir
altimeter Open PF compatibility More data to
transmit to ground
2
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

3
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 (gt10years of life duration,
  pointing, DV capacity, data transmission)
• 8 reference potential missions are based on this
  product line including SWOT mission

4
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)

5
Solar array proposed accommodation

• Rotation axis around velocity vector
• Fixed solar array with axis parallel to velocity
• Tilt value constant at 17deg
• Maximum reasonable SAsurface 18 to 20m² (5 to
  5.5kW BOL)
• Yaw flip when Sun crossorbit plane to maintain a
  cold satellite side forthermal dissipation

Velocity

• Advantages of this accommodation
• Maximize power with a fixed SA
• Optimize inertia matrix
• Minimize RF SA/PL interferences
• Optimize payload thermal control
• Minimize drag for POD

Nadir
6
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

7
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?

8
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
9
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

10
Thermal control

• The large power consumption of the payload need a
  large dissipation capability and order of
  magnitude for thermal dissipation
  are(Hypothesis a0.2 _at_10years, e0.76,
  Trad20C, Téq35C without margin)

Without heat pipes With heat pipes
Lateral antiSun side 1m² 280 W/m² 320 W/m²
Lateral Sun side 1m² 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
Total 750 W max 1000 W max
Less stringent than power allocation
11
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