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Call for Submission of Letters of Intent to Propose Instruments for the Solar Orbiter Mission

Call for Submission of Letters of Intent to Propose Instruments for the Solar Orbiter Mission

11 July 2006

Note - Deadline for submission has passedSubject to resource availability and schedule viability, Solar Orbiter is under consideration to be the next mission in the Science Directorate's planning for the current Cosmic Vision Programme. The Science Programme Committee (SPC) of the European Space Agency has requested that Solar Orbiter remain targeted to a May 2015 launch date, even though current constraints on financial planning can accommodate a launch no earlier than 2017.

The chairperson of the SPC, Geneviève Debouzy, summarised recent discussions of the Solar Orbiter mission at the May 2006 SPC meeting by proposing several elements that would need to be addressed by the Executive. First, a primary element was to establish the interest in the science community in providing payload by calling for Letters of Intent (LoI) to provide instruments. Second, she also urged that all effort be made to establish the possibility of international cooperation, particularly as interest had been present in the United Sates. 
This call is to request such letters (LoI) from interested parties in ESA Member States and, in light of potential cooperation, in the United States.

A third element was to put in place a "Review Team" to look at the proposed payload,  mission plan and cooperation possibilities in order to propose ways in which major cost reductions could be achieved. To fulfil this set of objectives, the Review Team will most likely interact with responders to this call for Letters of Intent. 

In the meantime, the Executive has met with NASA in June to open discussions on possible collaboration on Solar Orbiter. It has been agreed to review the outcome of such discussions in the end of September/early October timeframe before the start of the technology study of the crucial instrument Heat shield. 

All aspects of the project will then be reviewed in the coming year and a final decision on how to proceed is expected to be made by the SPC at its November 2007 meeting.

As currently foreseen, the Solar Orbiter mission consists of a single spacecraft designed to provide unique observations of the Sun and inner heliosphere from an elliptical orbit with a minimum pericentre of about 0.22 AU and an inclination of up to 35 degrees.  Such an orbit will provide the closest ever views of the sun, the possibility of near co-rotation during part of the orbit and opportunities to examine regions out of the sun's equator.

The spacecraft will carry a combination of in-situ instruments and remote sensing instruments that will satisfy the scientific objectives as defined by the Science Definition Team appointed by the European Space Agency.  The scientific objectives and an outline of the basic payload complement are provided in the Science Requirements Document and Payload Definition Document that are both available as PDF:

Clarification Document 88 kb


Payload Definition Document 4.4 Mb


Science Requirements Document 580 kb


Additional Clarification - 7 September 2006

Question 1
Is it possible (and perhaps nominal?) for the spacecraft to track a given feature since it necessitates only knowledge of orbital parameters and solar target coordinates. Such ability will be especially useful in phases of co-rotation, at perihelion. Could you confirm, and possibly provide us with related technical elements.

Answer 1
The nominal operational approach is to be nadir pointed, with a possible offpointing of +/- 1.25 deg. This should inherently provide some tracking capability by preplanning the attitude profile with some offsets, if the feature to be observed remains within the +/- 1.25 deg limit. It is unlikely but there could be some constraints to this capability from the attitude control system of the spacecraft, to avoid saturating wheels for example. This still needs to be further studied. From an operational point of view, a safe approach would be to perform a first perehelion pass fully nadir pointed which is more thermally robust. Off-pointing might then be implemented as part of the next pass if it is confirmed to be compatible with the fundamental NADIR pointing requirements. This will be addressed in the coming industrial studies.

Question 2
It would be interesting to learn about the envisaged implementation of the last paragraph of the Science Requirements Document. What action do you foresee an instrument might take in response to triggers? We consider scenarios where some instrument of the payload would suggest a new pointing (only when the whole mission is in such a temporary mode). This would greatly enhance the chances to catch less frequent events with the high-resolution instruments but we need to learn about all boundary conditions.

Answer 2
Concerning the question about the last paragraph of the Science Requirements Document, the current baseline is that all science operations during the perihelion passages (particularly when no high-gain antenna contact is possible) will be pre-planned. We do not plan to implement autonomous re-pointing of the S/C based on instrument event recognition. This does not exclude the possibility of "burst-mode" triggering by one of the in-situ instruments, but this would only affect the mode of data acquisition, not the S/C attitude.

Descriptions of the Instrument operational scenarios including their justification with respect to these two aspects should be included in the response to the Call for LOI.

Additional Clarification - 11 September 2006

Question 3
What is the sequencing of instrument commanding, instrument operation and telemetry generation ? Could this have an impact on the need for instrument buffers and instrument operations planning ?

Answer 3
The whole mission will be operating on a store and forward basis. Once the instrument is on and in science mode, it will produce science data at a given rate. For the time being, the rates defined in the PDD are assumed. All the science data produced will be stored in the spacecraft on-board storage device (SSMM). The on-board storage will then be dumped at the earliest opportunity when a ground station is visible. This opportunity will depend on the position of the spacecraft with respect to Earth (hence data rate and ground station visibility) and the backlog of data to be transmitted. Instrument buffers are therefore not required for large on-board data storage as this will be performed by the spacecraft. Limited instrument buffers/drivers will however be needed for the implementation of the link from the instrument to the spacecraft on-board storage device but this is the subject of detailed interface work to be carried out later.

Instrument commanding will be for the most part preprogrammed by uplinking to the spacecraft a set of commands covering a given period. The commands will be typically stored in the spacecraft on-board storage device (SSMM or CDMU). The spacecraft on-board data handling will then execute the commands at the required time. The frequency of uplink of the commands will vary during the mission and will be defined later after review of ground station coverage, of communication outages and of high gain antenna characteristics. Internal instrument buffering of received commands is not required by the spacecraft.

Question 4
The Solar Orbiter LOI webpage at only lists the electronic addresses for Dr. Marsden, Mr. Mccoy and Mr. Coradini. Do you prefer the Solar Orbiter LOIs to be submitted electronically or as a hardcopy? If you prefer for these to be submitted by mail, could you please provide me with the desired mailing addresses.

Answer 4
The Letter of Intent along with any supporting documentation shall be sent to the e-mail addresses given in the Solar Orbiter Website. No hardcopies are requested. In the event that the e-mail system of the sender or the Agency blocks the data exchange, a special FTP will be set-up specifically for the transfer of the electronic data for the specific proposer involved. This will be done on an ad-hoc basis and will be coordinated by Mrs. Elisabeth Zondag in ESTEC who may be contacted by e-mail ( or by telephone in case of general e-mail problems (+31 71 565 5192) between 09:00 and 17:00 CEST [07:00 - 15:00 UT].

Because of the present constrained financial prospects for the Cosmic Vision programme, at this point, the conclusions of the Science Definition Team must remain tentative for the moment. The precise form of the mission should be made clear in the coming year and the technical uncertainties should be further refined. Descoping of mission capabilities should be considered and the potential for international cooperation be fully explored. The Review Team established by ESA should monitor the evolving redefinition process and look at the proposed payload, mission plan and cooperation possibilities and potentially propose ways in which major cost reductions could be achieved whilst safeguarding as much as possible the mission science objectives. 

The mission has already been studied with the support of European industry and the scientific community to prove its feasibility and to scope its fundamental resource requirements in terms of cost, schedule needs and physical resources for launch.  For this purpose, a basic payload complement has been defined for study purposes to identify any enabling technologies that might be needed to successfully proceed with the mission. The results of the assessment studies as provided in the Payload Definition Document are considered a reference point in terms of resources and envelopes and one of the goals of this call is to identify the groups who are potential proposers for Solar Orbiter. The responses to the call will accordingly refine knowledge of what a realistic mission payload could be.

The outcome of the call will be used for three purposes:

  1. To help the Review Team understand how not only present science objectives can be met but also how they might be efficiently adjusted in the frame of proposals for possible descoping of the mission.
  2. To advance the readiness of the mission by a further refinement of the instruments based on interactions with potential principal investigator teams to enable the ESA technical team to continue work on technology required for developing the spacecraft systems and to be able to match that closely to realistic payload requirements thereby further consolidating the overall mission design and refining cost, schedule and resources.
  3. To enable the Executive to assess the state of technical readiness of payload items to be provided by sources outside the Agency and to work with the ESA Member States and agencies responsible for funding any potential non-ESA payload providers to establish overall resources required for the mission.

To accomplish the next step in preparing the Solar Orbiter mission, the Agency is issuing this call for Letters of Intent. LoI's should be sent by scientists or groups of scientists who intend to propose instruments if an AO for Solar Orbiter is issued.  In light of the considerable challenges facing the mission (technical, financial, managerial), the objective of this interim activity requires substantially more effort from interested groups than a simple letter since it is the intention of the Executive, the Review Team and those who will be responsible for payload provision to gain insight into the details of the proposed instrument's management structure, industrial organisation, technical design, technology development and overall technical readiness. In order to facilitate this process and to advance the objectives in a structured manner, the Agency will expect to be able to request technical documentation from each interested group after the LoI submission. 

Moreover, the ESA project group will expect to be able to undertake technical and managerial reviews with the potential instrument teams to clarify and define the instrument design, interfaces and development plans to the fullest extent possible.  This will be performed in parallel with the work of the competing industrial prime contractors during the 12-15 month period that is structured to advance the technology for the crucial Heat Shield interface to instruments.  It must be clear that the groups who respond to this call may be asked to interact with the industrial contractors so that sufficient resources must be identified for the teams to be able to support interaction with the Agency and, as required, the two contractors during this period. It follows that a brief management/financial plan is requested that will detail the short term resource requirements to ensure adequate support is available from the proposing groups to participate in the ESA led Heat Shield/System Study activities.

This call for submission of Letters of Intent does not constitute a commitment on the part of the Agency to select an instrument for the Solar Orbiter mission.  

The deadline for submission of the LoI along with a brief management/financial plan for those interested in the Solar Orbiter mission is 15 September 2006. 

In order to keep potential national funding authorities informed, responders are invited to submit a copy of their response to the relevant national authorities.

All information submitted for each instrument will remain confidential with the Agency and will be used in a confidential manner by European industry for assessments and accommodation in spacecraft designs. Industrial participants will be bound to a confidentiality agreement with the Agency concerning all instrument data.

The duration of the LOI assessment activity will be on the order of 12-15 months.


Submissions should be addressed to:

Dr. Marcello Coradini
Solar System Missions Coordinator, ESA HQ

With copies to:

Dr. Richard Marsden
Solar Orbiter Study Scientist, ESA ESTEC


Mr. Don McCoy
Solar Orbiter Project Manager, ESA ESTEC

Last Update: 1 September 2019
7-Feb-2023 11:29 UT

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