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PH 711: Spacecraft mission design and selection: real examples

PH 711: Spacecraft mission design and selection: real examples. Dr. Mark Price: Spring 2011. Mission selection. We will go through the procedure of a real example of the mission proposal and selection process.

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PH 711: Spacecraft mission design and selection: real examples

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  1. PH 711: Spacecraft mission design and selection: real examples Dr. Mark Price: Spring 2011

  2. Mission selection • 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.

  3. ESA mission selection (NASA is very similar, but US-centric). • 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!

  4. ESA selection timeline ActivityDate: ‘Cosmic Visions’ call 2007 • 5 March 2007: • Release of 1st Call for mission proposals of Cosmic Vision 2015-2025 • 30 March 2007: • Deadline for Letters of Intent • 11 April 2007: • Briefing to proposers at ESTEC • 29 June 2007: • Mission Proposals due • July - September 2007: • Proposal evaluation process by ESA and Peer Review Teams • October 2007: • Working group/SSAC evaluation and selection of: • 3 Class M mission proposals (cost ceiling €470M) • 3 Class L concept proposals (cost ceiling €900M)

  5. ESA mission selection ESA headquarters science council meeting

  6. ESA mission selection • 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) • 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.

  7. ESA mission proposals ESA mission selection ‘flow’ chart

  8. 2007 call: ESA mission proposals • 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.

  9. ESA mission proposals Timeline prior to any spacecraft construction

  10. ESA mission proposals Various phases of a mission prior to launch

  11. ESA mission proposals • 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 • Class L candidates (1 will be successful) • EJSM-Laplace (we will discuss in some detail, if there is time). • LISA • IXO

  12. ESA mission proposals • 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?

  13. Yellow book example pages: Plato 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.

  14. Yellow book example pages: Plato (Effectively Plato is a super-sensitive photometer!)

  15. Yellow book example pages: Plato • 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]

  16. Plato: concept A (Astrium) • 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

  17. Plato: concept B (Thales) • 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

  18. Plato: concept C (PPLC) • 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

  19. Yellow book example pages: Plato

  20. Yellow book example pages: Plato

  21. Yellow book example pages: Plato

  22. Yellow book example pages: Plato GANTT chart for Plato operations to launch

  23. Yellow book example pages: Plato Spacecraft to be placed at ‘L2’ point to minimise radiation from the Sun (thermal and ionising). Ideal location for astronomy missions

  24. Yellow book example pages: Plato • 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

  25. Yellow book example pages: Plato 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.” • (Basically: we don’t really know yet).

  26. Yellow book example pages: Plato 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 30.0kg Total 124.4 kg

  27. Yellow book example pages: Plato 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

  28. Yellow book example pages: Plato Engineering drawings of payload (concept ‘A’) and how it mounts inside the proposed Soyuz launch vehicle.

  29. Yellow book example pages: Plato Plato Mass budget

  30. Yellow book example pages: Plato • Plato power budget for all three concepts

  31. Yellow book example pages: Plato • ‘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.

  32. Yellow book example pages: Plato • “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.” • Plato requires a LOT of space qualified CCDs so need to start producing them ASAP.

  33. Yellow book example pages: Plato • Data download • Only (up-to) 48 hours of data will be stored on-board. • 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

  34. Yellow book example pages: Plato The mission operations can be broken down into the following tasks: • 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)

  35. ESA response to Plato proposal • 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.

  36. ESA IRR for Plato IRR risk summary for Plato: 4 areas are identified

  37. Plato: CCD requirement “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.”

  38. Plato: CCD requirement • “When the Gaia bench mark is applied to the two industrial studies and the PPLC the following schedule can be deduced for the Phase B2/C/D:” • Astrium (concept A): • 214 CCDs (BB + EM + FM + FS) - 6 years • Thales (concept B): • 128 CCDs (EM + FM) - 3.6 years • PPLC (concept C): • 168 CCDs (FM) - 4.7 years • (This is just the length of time needed to produce enough space-qualified CCDs for the mission!)

  39. Plato: optical configuration • 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.

  40. Plato: optical configuration IRR optical design assessment and recommendations

  41. Plato: technology readiness The IRR summarises the risk of the technology for Plato as follows

  42. Plato: IRR summary The following summarises the main conclusions of the review team: • 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.

  43. Plato: IRR summary 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 ESA-developed 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” • 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.

  44. Conclusions • 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!

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