Call for a Fast (F) mission opportunity
in ESA's Science Programme
for a launch in the 2026-2028 timeframe

Questions & Answers


Please check this page periodically for new questions and answers while this Call for a Fast mission is open.


Added: 2019-02-06
Q22: What specific tasks are expected for Phase A/B for payload to reach TRL 6?

A22: The proposing team must provide evidence that the technology is available and at TRL 6; this could be based on bread-boarding, testing, simulation, modelling, etc.


Added: 2019-02-06
Q21: Could you provide more information on the F-mission schedule?

A21: In general terms the schedule reported in the Call is confirmed. The detailed schedule for the F-mission is not yet further developed as this will depend very much on the nature and details of the selected mission. A refinement to the schedule will be done during/after Phase 0. Payload reviews are usually carried out somewhat ahead of the system reviews (up to ~6 months), but in some cases they may be together/in-line with the system reviews.

The dates of the reviews refer to when the reviews should be completed – so the start will be defined to comply with the completion date.

Here is a list of expected reviews:

  • At the end of Phase 0 we will have a Mission Definition Review (to check readiness for Phase A/B) including payload: this could be around September/October 2019 (TBC).
  • In the middle of Phase A there will be a Mission Configuration Review (MCR; to verify that a mission baseline is selected/defined).
  • At the end of Phase A there will be a Mission Formulation Review (MFR; at the level of Preliminary Requirements Review (PRR), but with wider scope).
  • At the end of Phase B1 there will be the Mission Adoption Review (MAR; at the level of System Requirements Review (SRR) but with a wider scope, to demonstrate readiness for adoption).
  • Soon after that the payload Preliminary Design Review (PDR) will happen.


Added: 2019-01-29
Q20: If daughter spacecraft are provided by an international partner, how might ESA view sharing of operations between the international partner and ESA? For example, if communications of a partner spacecraft are routed via the mother spacecraft does this greatly increase the operations complexity in ESA’s view or can operations teams in other nations pass commands via ESA with little oversight?
A20:The routing itself is not driving, unless it requires:
  • additional equipment,
  • frequent repointing of the spacecraft to point an antenna to the other spacecraft, finding of the other spacecraft (position for the pointing),
  • or involves very high data rates, which drive the downlink to Earth and hence number of hours of Ground Stations, or asks for more expensive onboard Telecommunications (TC) equipment.
  • Also, when several different operational modes are required as this needs development and testing of operation infrastructure and onboard procedures.

We cannot express this in M€ unless detailed requirements are on the table and analysed. The proposing teams should consider that complexity translates to cost (independent of the procurement scheme). Therefore, to avoid to become a cost driver and result in the proposed mission exceeding the cost cap proposers should maintain operation as simple as possible.

Added: 2019-01-29
Q19: Is there a way to understand ESA expectations for data archive costs? What saving in the budget might be possible if archiving is handled by a third party?
A19: Data from ESA science missions have to be properly archived in the ESA Space Science repository (in ESAC) for proper preservation and dissemination to the broad community. It is difficult to define expected costs for data archiving. They depend on what needs to be archived and what data processing is requested beforehand (pipeline complexity and who develops and maintains it). At the end, cost comes down to manpower need and equipment/facilities needs.
Added: 2019-01-29
Q18: Will the F-Class schedule follow the common ESA mission development schedule? i.e. there should be a PDR before adoption in 2022 and payload engineering models should be developed for CDR in 2024. Furthermore, could engineering models be started before adoption to ease the overall schedule if designs are mature before the end of Phase A/B?
A18: As indicated in Section 8 of the Call the development schedule foresees Phase 0, Phase A/B and mission adoption with relevant reviews. It is up to the proposing team to propose a model philosophy and a credible development plan that meets the launch date.
Added: 2019-01-29
Q17: How will ESA deal with TRL and schedule of international partner contributions? For example, may a JAXA contribution start with lower TRL if the JAXA management commit to a schedule that raises TRL and thus meets the F-Class mission requirements at Adoption?
A17: Low TRL levels for contributions from international partners can be acceptable provided that the partners will confirm commitment to reach the required TRL in interactions with ESA.

Also, based on the content of the received proposals, contributions from international partners will be negotiated and agreed by ESA with them.
Added: 2018-12-18
Q16: Could you clarify the operations cost for a low thrust transfer using EP?
A16: The ~ 15-20 % (of the ESA CaC) figure given as an indication in the Technical Annex of the F-class call (Table 5) is supposed to include the cost of all mission operations of at least the mothercraft (in the cases of mother-daughters configuration). This would include the transfer to the target object provided that manoeuvres are not frequent and that the EP trajectory can be pre-loaded and only "routine" checks are necessary. In other words, to fit in that cost figure the number of operations/manoeuvres during the cruise phase should be kept to a minimum.
Added: 2018-12-18
Q15: Concerning the Small Planetary Platforms (SPP) CDF study report, could you please clarify the mass budget?
  • The SPP mothercraft design assumed the use of a dual launch adapter and, therefore, its structure was not designed to carry the ARIEL spacecraft on top. For this reason, the structural mass of the mothercraft would need to be increased to something in the order of ~ 175-200 kg also to include both I/F rings (towards the launcher and towards ARIEL).
  • Following some further studies on the smallsats conducted after the SPP study, a reasonable mass figure to assume for a scientific smallsat for deep space applications (carrying instruments in the order of ~ 5-8 kg) would be ~ 35-40 kg (TBC by dedicated design).
  • So, although it is correct that the propellant mass reported in the SPP document for the NEO case might be conservative (i.e. computed for a larger mass than the figure obtained through the bottom-up exercise), due to the two points mentioned above and the fact that the updated mass cap for the F-mission is at ~ 850-900 kg (TBC), it is recommended to constraint the mission DV (with electric propulsion) to ~ 4.5 km/s at least for the proposal phase. Further dedicated analysis for the selected mission will determine if some optimisation to increase the mission DV figure would be possible, but for the moment we recommend to keep the missions as simple as possible.
Added: 2018-12-14
Q14: Regarding a possible contribution by JAXA. Does this need to be accompanied by a letter of endorsement at the letter of endorsement deadline date showing full support, or is this fully up to ESA to negotiate after selection for Phase 0?
A14: Discussion with JAXA (and other international partners) about their potential participation in candidate missions will be managed directly by ESA. The proposing teams are invited to indicate clearly in the proposal what their view is about a contribution potentially coming from JAXA (or other international partners) for spacecraft and/or payload elements.
Added: 2018-12-14
Q13: ESA in principle is willing to directly support some necessary development, even of instruments if really needed, starting from the beginning of the Phase 0 study, e.g. July 2019, given that it is laid out in the proposal and counted within the 150 ME. Is this correct?
A13: It is correct that ESA is available to discuss with the proposing teams support for both the mission preparation and implementation phases, also for payload elements, for ensuring the schedule feasibility. The preparation phase budget (Phases 0/A/B, until mission adoption) is not part of the 150 ME, which are devoted to the mission implementation (phases C/D/E/F). It is expected that ESA support for nationally provided payload elements will have to be coordinated/agreed with the relevant Funding Agencies.
Added: 2018-10-01
Q12: Is the 80 kg limit for the mass of the scientific payload correct? 80 kg seems to be low compared to a total mass of 1 ton.
A12: The quoted limit is a requirement given in the Annex of the Call, driven by the fact that the payload mass limit is related to the overall cost and schedule constraints of this class of mission.  Even if specific technical solutions could allow for a higher share, increased complexity of the payload would very likely drive the cost of the mission to ESA beyond the foreseen envelope. 
Added: 2018-09-21
Q11: According to §5 of Annex, contingency cost was not included.  Since the spacecraft cost will be 95-105 Meur, and ESA project cost is about 20-25 Meur, upper boundary of operation cost varies from 15 Meur (max <6 month operation)  to 30 Meur (1 year operation) depending on whether we should include contingency cost or not.  Could you clarify this?
A11: The F-class has a cost cap to ESA of 150 M€.  This includes all elements to be funded by ESA except for the launch services and excludes Member State and potential international partner contributions.  Margins must be included within this cost cap and should be according to estimated cost risk (typically 10-15%). 
Added: 2018-09-21
Q10: The spacecraft cost of 65-70% (95-105 Meur) is similar value of estimated cost for single spacecraft by ESA for M4/M5 (< case of wet mass of 500 kg).  Does this mean we should search national agency or partner agency to provide sub-spacecraft?  
A10: The cost breakdown for an F mission will vary with the mission concept and with the foreseen contributions from Member States and/or international partners.   Table 5 was provided as an indication of a potential cost breakdown.  The cost of the space segment has to cover all proposed elements  for which ESA is proposed to fund, irrespective of mothercraft and/or number of sub-craft.  Note: the indicative amount of 95 – 105 M€ has no relation to M4/M5 cost estimates.
Added: 2018-09-21
Q9: Is cubesat allowed as sub-spacecraft?  
A9: There is no minimum size of the ‘sub-spacecraft’ required, but: as a rule, the standard ECSS requirements are applicable to the entire spacecraft, including the daughtercraft.  However, deviations from these requirements for the F mission concept will be assessed on a case by case basis.  As an illustrative example, Table 4 (in the Annex) has been established by assuming no single point failures for the mothercraft, while tolerating single point failures for the probes, for maximising the payload mass availability.  The underlying assumption is that a mission with multiple smallsats/probes would be conceived with some intrinsic failure tolerance, e.g. by providing a graceful degradation scheme and guaranteeing a core science return in case of a single probe failure.  Conversely, robustness against single point failures could be enforced in some cases to the detriment of the useful payload mass.
Added: 2018-09-05
Q8: Could you please give some guidance on the use of COTS parts?
A8: The use of any technology must demonstrate compatibility with the particular environment to ensure a reasonable probability of function.  For that reason, testing and delta development is likely needed and will require further investigations of suitability of the technology for a particular case.  On page 14 of the Annex of the Call for a Fast Mission is stated: "As a rule, the standard ECSS requirements are applicable to the entire spacecraft, including the daughtercraft.  However, deviations from these requirements are allowable for the F mission concept and will be assessed on a case by case basis.  As an illustrative example, Table 4 has been established by assuming no single point failures for the mothercraft, while tolerating single point failures for the probes, for maximising the payload mass availability.  The underlying assumption is that a mission with multiple smallsats/probes would be conceived with some intrinsic failure tolerance, e.g. by providing a graceful degradation scheme and guaranteeing a core science return in case of a single probe failure.  Conversely, robustness against single point failures could be enforced in some cases to the detriment of the useful payload mass."
Added: 2018-09-03
Q7: The F1 Call Annex 3.5 gives the link budget considerations for the communication between s/c HGA and Earth.  Are there similar numbers of the link budget considerations available for the mother - daughter communication?  Maybe based on the earlier cdf studies or some other ongoing studies.
A7: The link budget between the mother and daughter(s) depends on several parameters, including: the inter-satellite distance,  the available RF power, the visibility between them, the duty cycle required to transfer the desired data volume, the antennas available on each side of the link, etc.  Estimate cases can be found in the internal Small Planetary Platforms (SPP) CDF study report, available at, where typical data rates considered for the Inter Satellite Link (ISL) varied between a minimum of 10 kbps and a maximum of 600 kbps for satellite distances of tens of metres.

The figure below indicates the theoretical physical limits of an ISL communication over a range of distances with a RF power of 1, 2 or 5 Watt assumed, and based on S-band and the use of (non-directive) low gain antennas (LGAs).  For small distances, the maximum data rate is probably limited by the capabilities/specification of the proposed ISL equipment (and to a lesser extent by the link budget).  For larger distances, the link budget will dominate, data rates could be increased with increased RF power (depending on DC power availability and RF amplifier equipment specifications) and/or with antennas with higher gain (therefore with reduced FoV and therefore more demanding pointing requirements for the link and at some stage driving the AOCS system).
Theoretical physical limits of an Inter Satellite Link (ISL) communication over a range of distances. This figure is also available to download in pdf format. Credit: ESA
Added: 2018-08-31
Q6: Under F1 Call Annex 4.3.3 there are given the cost drivers and listed many requirements related to approaching target bodies. What are the cost driving considerations as seen from the ESA point of view for the formation flying. For example, having 4 or more daughter s/c flying in a formation?
A6: The term "Formation Flying" is rather vague and can lead to a wide range of development complexity. In general, it is reserved to constellations requiring a tight control of the formation with demanding requirements on the position control or knowledge (millimetric or submillimetric, often coupled with stringent velocity and/or attitude requirements).  Such requirements would have major programmatic impacts (on hardware and operation costs, and on schedule), and are hardly compatible with the F-Call boundaries.  Conversely, a constellation of spacecraft with a loose formation - for example driven by celestial mechanics with virtually no impact on routine operations - can be envisaged.  For any multiple spacecraft configuration, the spacecraft must be small enough (e.g. maximum a few tens of kg), ideally identical (as a bare minimum the platform must be fully recurring), relying on available technologies, and requiring "simple" operations (e.g. basically not too different from a single spacecraft case).  Furthermore, as a general rule, flight hardware and in-orbit operations must be simplified if and where possible by using data post-processing on ground.
Added: 2018-08-22
Q5: Would it make sense to let international partners participate in an F-class mission proposal?
A5: The Call is indeed open for international collaborations (as specified and according to the conditions indicated in Section 3.5 of the Call document).
 As is customary for competitive calls, it is entirely up to the relevant international partners to consider if and according to which scheme they could support contributions to proposals; this applies also to the F-class mission Call.
As indicated in Section 3.5 of the Call, "The Agency (ESA) would contact international partners mentioned in the proposal to verify the feasibility of the proposed scheme."
More generally, considering the calibre of the F-class missions, we encourage proposers to evaluate carefully the complexity of the proposed concept, also in terms of technical and management interfaces.
Added: 2018-08-22
Q4: Is it possible to be part of more than one proposal?  For example, is it possible to be a PI in one proposal, and participant in another?
Also, is it possible for a consortium to send more than one phase-1 proposal?
  • there is no restriction for one individual to participate in different proposals
  • there is no restriction to the number of proposals that can be submitted by an institution or research team, provided that the roles and responsibilities of participating people are clarified in each proposal
  • it is highly recommended that a Lead Proposer leads only one proposal
Added: 2018-08-22
Q3: We were wondering if there would be any interest from ESA to also include a cubesat-size mission along/within the 1000 kg that are allocated for the F-class mission.
A3: As clearly stated in the Call document, the Call aims at the selection of an F mission candidate.  All proposals received according to the deadlines stated in Section 8 will be subject to the evaluation process indicated in the Call, in competition with all other received proposals.
Added: 2018-07-25
Q2: The Technical Annex document refers to [RD1] “Small Planetary Platforms CDF Study Report, CDF-178, January 2018.” Can you please advise on how that document may be obtained?
Added: 2018-07-18
Q1: Could you clarify the mass that is available for the F mission?
A1: From page 5 of the technical Annex: "The likely scenario is to launch in a stacked configuration, with ARIEL mounted on top of the F mission spacecraft."
This is a single launch where the F mission has to carry ARIEL. T his is a mass efficient solution compared to the relatively heavy dual launch adapter (the best custom-made solutions would be around 450 kg; the A64 dual launch adapter is more massive).
Using the above approach leaves up to 1,000 kg for the F mission spacecraft.