Chandra X-Ray Observatory

Chandra Extremely Large Projects

Chandra ELP


Part 1 of this message describes the parameters of a possible program for Extremely Large Projects which we are considering for Chandra. Once every three years, one such program ranging from 3 to 5Ms exposure time could be selected if we establish the ELP program.

Part 2 of this message describes a call for brief white papers which will be used to assess the potential scientific merit of a Chandra ELP program. The deadline for submission of these white papers is February 1, 2007.

Part 1 - Parameters for Chandra ELP

1. We are contemplating the establishment of Extremely Large Projects (ELP) for Chandra. The purpose of such a category would be to enable science programs which can not be accomplished within time allocations currently available for Guest Observer, Large, and Very Large Projects (GO, LP, and VLP).

2. If ELP are established, we envision a solicitation once every 3 years, with 5Ms for ELP allocated from the 6Ms which would otherwise have been available for LP and VLP in that year/cycle. The remaining 1 Ms would be allocated for a reduced LP program for that year. If we proceed with ELP, we anticipate including them for the first time in the Call for Proposals (CfP) for Cycle 10 to be released in Dec 2007. Subsequent ELP opportunities would be placed at 3 year intervals.

Proposals for ELP would be solicited with no restriction or pre-selection of science topics. The review process would be embedded within the Chandra Peer Review with nominally 2 topical panels reviewing each ELP (and LP in the same cycle) and forwarding their recommendations to the Big Project Panel (BPP) for final evaluation and ranking of ELP. For cycles involving ELP, we intend to involve additional relevant expertise by increasing the number of "pundits" on the BPP. The CXC Director remains the formal selection official for ELP as well as other Chandra proposals.

Current VLP programs can request up to the 3Ms, so ELPs would cover the range from 3 to 5Ms, with at most 1 selected per review (once every 3 years). 5Ms represents approximately 3 months of Chandra observing time, so the amount of time contemplated for ELP is quite substantial. The plan to solicit, review, and potentially select 1 ELP once every 3 years was structured so as to limit the impact on the ongoing LP and VLP programs and to have no impact at all on GO proposals. Given the exposure time for an ELP, the scheduling constraints associated with Chandra, and other programmatic considerations, we intend to carry out approved ELP over a nominal period of up to 2 years, compared to the nominal 1 year for other categories of Chandra programs.

3. If ELP are established, the Peer Review process through the BPP would be permitted to recommend the rejection of all proposals if in their judgment none merited the allocation of this large block of Chandra time. They could also recommend reduction in time from that requested if based on a sound scientific argument. However, the general intent would be for them to recommend implementation of 1 ELP and, if merited, for the full time requested. The instructions to the Peer Review would reflect this intent. While a modest amount of any unallocated ELP time might be returned to the GO and/or LP pool for that cycle, it is unlikely that much time would be reallocated in such a manner should no ELP be selected. The CXC will be charged with establishing a process for time allocations which will ensure continuity in the Chandra observing program whether or not an ELP is selected.

4. Teams proposing for ELP would be required to provide a modest management plan as part of their proposal. They would also be expected to identify special data products or other appropriate deliverables as part of their proposal, and possibly a preliminary cost estimate. Funding for ELP would be drawn from the funds nominally available for VLP plus 2/3 of the LP for a given cycle. Based on recent years, this would provide ~$1.5M to support a selected ELP. Some fraction of this funding (perhaps 1/2 to 2/3) would be the nominal "fair share" for the successful proposing team with the actual allocation to be decided as part of the Chandra stage 2 cost review process. The remaining funds would be available to investigators chosen from a separate competitive review of proposals to exploit the data for different or complementary science objectives, to apply novel analysis methods, to obtain corollary or ancillary data including those at other wavelengths, and to provide theoretical expertise in interpreting the observations. This separate competition would take place after the successful ELP is announced and before the observations actually begin.

At present Chandra VLP do not carry proprietary rights and the data are released as they are acquired, processed, and certified. As a baseline we anticipate handling the ELP data in a similar way, but we invite feedback from those potentially interested in proposing for ELP as part of the process described below.

5. The mechanics and guidelines for possible Chandra ELP have been discussed by the Chandra X-ray Center, the Marshall Space Flight Center Project Scientist, and the Chandra Users Committee (CUC). The consensus is that the merits of such a program should be further evaluated before it is initiated. A process to carry out such an assessment is described below and formally established via this communication.

Part 2 - Call for Chandra ELP White Papers


1. We solicit brief white papers from the community of maximum length 3 pages describing possible science projects which they might carry out under a Chandra ELP. The white papers should summarize the anticipated science objectives conveying a sense of why these are of great import and worthy of 3-5Ms of Chandra observing time. The white papers should explain why an ELP is needed to accomplish these objectives (explaining why they can not be achieved under existing GO/LP/VLP programs). Finally the white paper should provide a preliminary assessment of feasibility - via calculations or simulations showing that the required counts, spatial or spectral resolution, signal to noise, or other appropriate parameters can be acquired.

The white papers should assume that the readers will be knowledgeable and should not devote time or space to a lengthy introduction, background, or other unnecessary information. The purpose of these white papers is to provide examples of science so compelling that the establishment of Chandra ELP is warranted. If you are aware of any special observing constraints which are required for your conceptual program (along the lines of constraints already applied to Chandra GO/LP/VLP) please make note of these in your white paper. As part of your white paper you may make a case (briefly) for why there should be a period of proprietary time for a successful ELP proposing team (up to the nominal 12 months accorded to GO programs). You may also state that you support the current baseline of making such large data sets public as they are acquired. These inputs will help us to decide whether we should have a proprietary period for ELP data (with a similar period then being established for VLP as well).

In principle (and for fairness) if you are opposed to the establishment of Chandra ELP, you may also submit a white paper indicating the science which you envision being adversely impacted by an ELP program.


3. These white papers are also not the equivalent of letters of intent. You are not required to submit a white paper in order to be eligible to propose an ELP if the program is eventually established. We do encourage you in the strongest possible way to submit a white paper with your best ideas if you are interested in there being a Chandra ELP program. Our decision on whether or not to establish the ELP will be based primarily on our assessment of the merit of the science described in these white papers.

We have considered a range of options for review of these white papers. On the one hand extensive participation by the community at large would provide wide-ranging expertise for this assessment. On the other hand, there were concerns that ideas presented in the white papers constitute intellectual property meriting strong assurances of confidentiality, so as to encourage people to submit their best ideas for ELP science in what is still a pre-proposal phase. Ultimately we decided that the white papers would be read by a small number of reviewers who would agree in advance not to propose as PI or Co-I for any Cycle 10 ELP. Moreover, the starting position is that the reviewers will come from a small core of Chandra science leaders - CXC Director Harvey Tananbaum, MSFC Project Scientist Martin Weisskopf, and CXC Assistant Director Belinda Wilkes. A few additional reviewers may be asked to assist in this process but possibly only after the white papers are received. The names of any other reviewers will also be publicly released, and they too will be required to opt out of any Cycle 10 ELP proposals.

Following review of the white papers, we will formulate a recommendation about ELP and a formal set of guidelines if the intent is to proceed with the program. These will be posted, reviewed with the CUC, and eventually submitted to NASA for formal concurrence to proceed.

4. Questions about this notification should be addressed to Harvey Tananbaum ( with cc's to Martin Weisskopf ( and Belinda Wilkes (

White papers can be submitted in the format of choice by those responding (pdf seeming to be a standard for many such submissions these days). REMEMBER: WHITE PAPERS ARE DUE FEBRUARY 1, 2007.

Please submit your white paper via e-mail to: Harvey Tananbaum ( with cc's to Belinda Wilkes ( and Martin Weisskopf (

Either Harvey or Belinda will acknowledge receipt of your submission via e-mail within 3 days. If you do not receive an acknowledgment please inform us via e-mail.

Last modified: 12/14/16

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