Transcript Yellow book example pages: Plato - Centre for Astrophysics and

Dr. Mark Price: Spring 2011
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We will go through the procedure of a real
example of the mission proposal and
selection process.
In 1 or 2 lectures I can barely scratch the
surface! Even the smallest science mission
costs >£100M and there is quite literally
THOUSANDS of pages of documentation for
even a modest mission.
However, hopefully, it will give you a flavour
for the process.
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Call for proposals:
◦ ESA regularly makes a ‘call for proposals’ – approximately
once every 5 years. (NASA has a ‘decadal’ study).
◦ This is a chance for the scientific community to get
together a proposal for a scientific space mission
◦ Each proposing team is normally made up of 20 – 200
scientists from the relevant field
◦ This call lasts approximately 3-4 months
◦ Warning: ESA and NASA love acronyms! The documentation
is littered with them!
Activity Date: ‘Cosmic Visions’ call 2007
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5 March 2007:
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30 March 2007:
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11 April 2007:
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29 June 2007:
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July - September 2007:
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October 2007:
◦ Release of 1st Call for mission proposals of Cosmic Vision 2015-2025
◦ Deadline for Letters of Intent
◦ Briefing to proposers at ESTEC
◦ Mission Proposals due
◦ Proposal evaluation process by ESA and Peer Review Teams
◦ Working group/SSAC evaluation and selection of:
◦ 3 Class M mission proposals (cost ceiling €470M)
◦ 3 Class L concept proposals (cost ceiling €900M)
ESA headquarters science council meeting
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ESA science programme has three distinct
domains
◦ Astrophysics (Astrophysics Working Group: AWG)
◦ Solar System (Solar System Working Group: SSWG)
◦ Fundamental physics (Fundamental Physics Advisory
Group: FPAG)
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Each group (depending on the mission proposal)
passes its recommendation up to the Space
Science Advisory Committee (SSAC).
The SSAC then passes its recommendation up to
the Science Programme Committee (SPC) which
has delegates from each of ESA’s member
nations. They have final say.
ESA mission selection ‘flow’ chart
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52 proposals received from the community
Of those 6 for each ‘M’ and ‘L’ class proposal
are selected
Principal Investigators (‘PI’s) from each
proposal are invited to ESA headquarters in
Paris to give a talk to the selection board
based on their ‘yellow book’ proposal.
These 6 are then whittled down to a just 3 to
go through to the next evaluation phase.
Timeline prior to any spacecraft construction
Various phases of a mission prior to launch
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ESA received 52 proposals but whittled it
down to 6 candidates
Class M candidates (2 will be successful)
◦ EUCLID
◦ PLATO (we will discuss in detail)
◦ Solar Orbiter
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Class L candidates (1 will be successful)
◦ EJSM-Laplace (we will discuss in some detail, if
there is time).
◦ LISA
◦ IXO
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Each proposer submits a ‘yellow book’ which
is a document describing in detail the science
and the feasibility of the mission.
These documents are hundreds of pages
long!
The ‘yellow book’ must explain to the
selection panel
◦ Why your science is top priority
◦ How can you do your science (does the technology
exist?)
◦ What are the risks?
Plato – main science goals:
1) The detection of extra-solar planetary systems of
all kinds, including small, terrestrial planets in the
habitable zone of solar-type stars.
2) A precise characterization of the basic physical
parameters of the detected exoplanets and the
host stars: radius, mass, age.
3) The identification of suitable targets for future,
more detailed characterization.
(Effectively Plato is a super-sensitive photometer!)
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Plato is a super-sensitive photometer (measures
the amount of light from a star very accurately)
The proposal is to build on Kepler/GAIA results
and detect thousands of Earth-sized exoplanets
in a (near) all-sky survey.
Three different spacecraft optical configurations
(telescope design and CCDs) proposed from
three different contractors:
◦ Astrium (‘Concept A’)
◦ Thales (‘Concept B’)
◦ PPLC (‘Concept C’) [PPLC = Plato Payload Consortium]
•Uses 12 reflecting telescopes to achieve
a field-of-view of 1800 deg2
•Optical structure is silicon carbide to reduce
thermal expansion/contraction
•Mirrors are aspheric and require special
manufacture
•Has a sunshield deployed in space
•Requires 176 CCDs with a resolution
of 2080x2574
•54 refracting telescopes
mounted on optical baseplate
•Telescope primary lenses made
of BaF2 to cover wavelength
range 450 – 1000nm
•Total field-of-view ~ 625 deg2
•Each telescope to have
3000x6000 pixel CCD
Telescope based on known design
•42 refractive telescopes
•Each with its own sunshade
•Total field-of-view = 1800 deg2
•Each telescope has 6 BaF2 lenses
•Requires 168 CCDs with
a resolution of 3584x3584
GANTT chart for Plato operations to launch
Spacecraft to be placed at ‘L2’ point to minimise radiation from
the Sun (thermal and ionising). Ideal location for astronomy missions
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How does Plato’s ‘Yellow Book’ address the
environments we have discussed in this module?
Thermal control:
◦ Telescope is passively cooled. The spacecraft structure is
kept at ~150K using a sunshield and passive radiative
cooling
◦ The CCDs and optics are coupled to the spacecraft
structure through a silicon carbide baseplate to cool
them ~170K
◦ The electronics will operate at 320K and are thermally
isolated from the focal plane array
◦ Spacecraft is at L2 point, and thus radiation from the Sun
is minimised
Radiation environment
“The radiation levels for PLATO are calculated to be
10 times higher than for GAIA. A proper radiation
analysis is needed in a possible future phase in
order to better characterise and estimate the
radiation effects.
A possible mitigation action against radiation
damage would be to add a protective silica plate
on top of each focal plane. Assuming 10mm
thickness for this plate, the mass impact is an
additional 30kg.”
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(Basically: we don’t really know yet).
Mass budget: optical array – concept A
Telescope mass budget for each telescope
and Telescope Assembly (TA).
Telescope TA (3 telescopes) PLM (4 TA)
M1
9.8kg 29.4kg
117.6kg
M2
6.4kg 19.2kg
76.8kg
Protective silica plate
2.5kg 7.5kg
Total 124.4 kg
30.0kg
Mass budget: optical support – concept A
Item Mass [kg] incl. margin
M1 supporting plate
171.2
M2 supporting plate
62.7
Struts
39.2
Interfaces fixation devices
10.5
Secondary structures and baffles 2.1
Fixation H/W (screws, etc.)
6.3
Interface base plate
104.7
Isostatic I/F with SVM
20.0
Total
416.7
Engineering drawings of payload (concept ‘A’) and how it
mounts inside the proposed Soyuz launch vehicle.
Plato
Mass budget
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Plato power budget for all three concepts
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‘Technology Readiness Level ’ (TRL) – i.e. can
we build what we say we can build.
◦ “For design concept A, the Deployable Sunshield is
identified as a critical area in which the TRL needs
to be raised before a possible implementation
phase. In particular, the HDRM that will need to
provide structural stability during launch needs to
be developed...” (HDRM=Hold Down and Release
Mechanism)
◦ This basically says that the technology needed to
unfold the sunshield for concept A isn’t mature
enough.
◦ “Common for all concepts is the need for an early
CCD design activity so that there is sufficient time
to produce all the CCDs needed. The specifications
of the CCDs are not more complex compared to
other programs such as GAIA, but the designs
require many CCDs due to the large FoV. So the
critical issue is rather in having enough time to
produce and test all CCDs instead of new, complex
CCD designs. This is why a development activity in
phase A/B1 is needed to ensure that production of
the FM CCDs can start as soon as possible.”
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Plato requires a LOT of space qualified CCDs
so need to start producing them ASAP.
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Data download
◦ Only (up-to) 48 hours of data will be stored onboard.
◦ Data will be downloaded once-per-day for a period
of 3.5 hours in a 24 hour cycle
◦ Data transmit rate will be 8.7 Mbps
◦ Data will be transmitted in the X-band (10 MHz)
using standard GMSK modulation
The mission operations can be broken down into the following tasks:
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Mission Planning: long term, medium and short term planning (24 hours to one
week time frame, it is assumed that only very limited short term planning
activities are required for PLATO.)
Spacecraft control, following the Flight Operations Plan and the short-term plan
Spacecraft status monitoring and off line performance analysis.
Instrument control, implementation of the observation schedules
Collection of the instrument HKTM telemetry and instrument status monitoring.
Orbit determination and control using tracking data and implementing orbit
manoeuvres.
Off line attitude determination and control based on the processed attitude
sensors data in the spacecraft telemetry and by commanded updates of control
parameters in the on-board attitude control system.
On-board S/W maintenance (OBCP programming and maintenance, and
application and payload software update management).
Data distribution and data archiving (science data are archived at ESAC)
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ESA has an internal review to determine the
feasibility (scientific and engineering) and risk
associated with each mission.
Referred to as an ‘Internal Review Report’
(shortened to ‘IRR’).
This document outlines the risks to the
Science Programme Committee (SPC) and
makes recommendations.
These recommendations effectively ‘make’ or
‘break’ a mission proposal.
IRR risk summary for Plato: 4 areas are identified
“Given the high number of CCDs to be produced in
all studies, a key element which will impact the
spacecraft development is their manufacturing
time. In order to evaluate the proposed schedules
for the development and production of the
potential PLATO CCDs, the GAIA CCDs
development, manufacturing and test rate was
used as a benchmark. In Figure 2-1 the time line
of the GAIA CCD program is shown.
Based on that, a reasonable production rate is
about 3 CCDs per month.”
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“When the Gaia bench mark is applied to the two
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Astrium (concept A):
industrial studies and the PPLC the following
schedule can be deduced for the Phase B2/C/D:”
◦ 214 CCDs (BB + EM + FM + FS) - 6 years
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Thales (concept B):
◦ 128 CCDs (EM + FM) - 3.6 years
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PPLC (concept C):
◦ 168 CCDs (FM) - 4.7 years
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(This is just the length of time needed to produce
enough space-qualified CCDs for the mission!)
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The IRR flags concerns about the optical
configuration for all three concepts:
◦ The mirrors for concept A are aspherical, non-standard
and made of SiC.
◦ The estimated time to manufacture one M1 mirror is ~27
months. Therefore total manufacture time is >6 years
(estimate).
◦ The refractive designs are simpler, and use known
technologies but BaF2 lenses are expensive and the
crystal has to be custom grown.
◦ Estimated time to grow a large BaF2 crystal ~2-3
months.
◦ Lenses are hygroscopic and thus need environmental
control
◦ 250-300 lenses are needed for either concept B or C.
Lens manufacture time is unknown.
IRR optical design assessment and recommendations
The IRR summarises the risk of the technology for Plato as follows
The following summarises the main conclusions of the review team:
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The mission requirements are reasonably well defined to start the Phase
B1.
The spacecraft design does not show peculiar complexities beyond the
state of the art achieved with Gaia and/or Corot. The mission is
reasonably straightforward.
The mass is underestimated. Compatibility with the Soyuz launcher
requires downsize of the S/C by, at least, 5 %.
The only identified critical technology is the manufacturing of the
primary mirror M1 in the reflective system due to the very peculiar shape
of the surface.
The schedule is strongly underestimated. Main driver is the high number
of CCDs to be manufactured (other elements are the high number of
optical elements and the not fully thought verification at payload system
level).
Assuming start of the phase B2/C/D middle of 2012, a “realistic” launch
date will be 2021. This assumes that the phase B1 is used to freeze the
CCD design and prototyping; otherwise a further year shall be added.
Main recommendation to SPC
“The current design is not compatible with a 2017/2018 launch. To
achieve end 2018 a major reduction (order of > 30%) of the
payload module (number of CCDs and optics) is required. This
would result in a positive mass margin, which can be used for
increasing the pupil diameter and recovering at least part of the
science performance. Considering mission extension in orbit
could also help recovering performance. Using the ESAdeveloped instrument performance model for PLATO, preliminary
results obtained by the study team at the end of the review
indicate that the proposed way forward is viable with moderate
impact on science performance if any”
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Effectively says that for a 2018 launch, the mission has to be
‘descoped’ by 30%! But, due to the nature of the mission (no
cryogenics, exoplanets aren’t going anywhere etc) science could
be recovered by extending the baseline mission from 6 years.
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The procedure to select a space mission is
complicated!
Lots of documentation has to be produced and
meetings held before a single nut is purchased.
Missions can be ‘descoped’ (‘Exomars’ for
example) to cut costs and to meet launch
windows.
Past a certain point in the process, the external
science community has very little say in the final
mission profile.
The time from ‘call’ to ‘launch’ is normally 10+
years!