principal investigators and mission leadership

Available online at www.sciencedirect.com

Space Policy 25 (2009) 181e186www.elsevier.com/locate/spacepol

Principal Investigators and mission leadership

Susan M. Niebur*

Niebur Consulting, 418 Hillsboro Drive, Silver Spring, MD 20902, USA

Available online 26 June 2009

Abstract

Principal Investigators of small and medium sized space and earth science missions face many challenges during formulation, design,development, integration and test, launch, and operations; these challenges may be more easily met by team leaders with prior missionexperience. This paper reports the results of the first known demographic study of NASA’s Principal-Investigator-led missions and makesrecommendations for preparing additional space scientists to lead. The addition of a Deputy Principal Investigator to proposal teams couldreduce the burden on the Principal Investigator and provide an opportunity for additional scientists to gain mission leadership experience usefulon future missions. The pool of mission-knowledgeable scientists could further be expanded to include scientists earlier in their careers viacarefully managed Participating Scientist Programs. Adding Deputy Principal Investigators and Participating Scientist Programs to missions asa matter of course would reinforce effective management practices, open the field of proposers, and provide concrete ways to mentor the nextgeneration of Principal Investigators.� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

In recent years, the National Aeronautics and SpaceAdministration (NASA) has invested an increasing amount ofresources in small, frequently launched, Principal-Investi-gator-led (PI-led) missions, in addition to the larger institu-tion-led missions that fly once a decade. Small missions, suchas those in the Discovery, Explorer, Mars Scout, and EarthSystem Science Pathfinder lines, and medium missions, suchas those being proposed for the New Frontiers mission line,are able to accomplish focused science investigations forlimited cost. Costs vary by mission line: Small Explorer(SMEX) missions, for example, are allotted up to $105million, excluding launch vehicle [1]; New Frontiers missionscan cost up to $650 million [2]. With these smaller cost caps(large missions are typically $1 billion or more) comesrecognition that the investigations must be tightly focused,development time kept short, and teams well managed. Fifteenyears after the first of these PI-led missions was competitively

* Tel./fax: þ1 301 754 0939.

E-mail address: [email protected]

0265-9646/$ - see front matter � 2009 Elsevier Ltd. All rights reserved.

doi:10.1016/j.spacepol.2009.05.009

selected, with dozens of missions successfully launched andoperated, the concept has been validated. Today there is a fleetof small, focused scientific investigations throughout the innerSolar system, and a set of Principal Investigators (PIs) provencapable of leading their teams to success.

As missions become more complex and risk tolerancecontracts, however, increasing attention is being paid to thequalifications of scientists proposing to lead future missions.The primary criterion to date has been prior mission experi-ence. Project management skills, scientific productivity,innovative thinking, and instrument building experience arealso critical to properly lead a mission to success on time andon budget, but these factors have been rolled up by NASA’sScience Mission Directorate (SMD) into a single emblem ofqualification: prior mission experience in one of four specificleadership roles [3]. While the requirement seems reasonableinitially, new data presented in this paper show that sucha strictly defined gate would severely limit future proposalsand inhibit new ideas from experienced investigators who havenot officially served in one of these key roles. The number ofexperienced investigators so defined is small, limiting optionsfor future missions unless NASA management and the spacescience community act to increase the number of qualified

mailto:[email protected]

http://www.elsevier.com/locate/spacepol

182 S.M. Niebur / Space Policy 25 (2009) 181e186

scientists through training, mentoring, and/or hands-on expe-rience with current and upcoming missions. This paper willdiscuss the scientific management of these missions, define thekey roles, postulate a typical PI’s career path, begin to quantifythe experience of selected PIs, and highlight what can be doneto expand the field of scientists with qualifying missionexperience.

2. Mission management

The Discovery mission line, implemented in 1994, encap-sulated a new way of doing business at NASA, one that wassoon replicated by Explorer, Mars Scout, ESSP, and NewFrontiers. As funding becomes available in one of thesemission lines, NASA releases Announcements of Opportunity(AOs) for scientists to propose new mission concepts in therelevant science disciplines. A strict cost cap is imposed, withthreat of termination if the cost cap is exceeded. Developmenttime is capped as well, with no more than two to five yearsbetween confirmation and launch. New flexibility in missionmanagement was initially encouraged with the realization thatlaunching a mission in a short amount of time and on budgetrequires lean teams and potentially innovative managementpractices. Some of this flexibility was removed in 1999, afterthe failure of Mars Polar Lander and Mars Climate Orbiter,similar-sized and -managed missions. Since then, themanagement teaming arrangements have had to adhere morestrictly to standard NASA policies and practices.

Mission leadership authority now rests unquestionably withthe PI. PIs are given latitude to propose complete missionpackages, including instrument design and development,spacecraft bus specifications, integration and testing proce-dures, launch parameters, and operations. PIs rely on projectmanagers and project system engineers for much of the dailyengineering leadership, but all trades that may affect theacquisition of the science or the integration of the instruments,as well as any that would significantly change the budget orrequire greater reserves, must be presented to the PI for finalapproval.

Consequently, the demands on a selected mission PI aregreat. NASA charges the PI with primary responsibility forimplementing and executing the selected investigations, asstated in this excerpt from the 2009 New Frontiers AO: ‘‘TheMission PI is accountable to NASA for the success of theinvestigation, with full responsibility for its scientific integrityand for its execution within committed cost and schedule.’’[2]Clearly, any selected PI must have sufficient experience toplan and execute mission design, development, review, andoperations.

One way to augment the PI’s effectiveness is to appoint keyplayers to assist. At the PI’s discretion, key scientists can becharged with roles such as managing the science team, inter-acting with the engineering leads, overseeing instrumentdevelopment, and planning for operations. Popular optionsinclude a Deputy Principal Investigator (DPI), whose role isdefined by the PI at proposal, a Project Scientist (PS), andperhaps a Deputy Project Scientist (DPS). The latter two

positions are typically appointed by and located at themanaging and/or implementing institutions, in most casesa NASA Center or the Applied Physics Laboratory (APL) atJohns Hopkins University. PSs provide day-to-day support andcommunication between the scientists who have defined therequirements and the engineers building the hardware.

Mission management organization, including the use of keyroles such as these, is evaluated for NASA by scientific andengineering experts, unaffiliated with competing proposals,who are charged with review of the scientific, technical, merit,and cost aspects of each competing proposal. The existence ofthese key roles is currently value-neutral in the reviews;NASA allows but does not explicitly encourage or require anyof those positions in the AOs or supporting documents. Afterrigorous review of the proposals, NASA selects three to fivemission concepts for further study; these are further narrowedto one or two missions for implementation every two to fouryears.

Each mission is selected as a complete package, includingthe mission leadership outlined in this section and all othermembers of the science team necessary for design, develop-ment, implementation, mission operations, and preliminarydata analysis. These other science team members named atproposal are called Co-Investigators (Co-Is).

3. The role of PI: experience

The charge to design, develop, implement, and operatea space or earth science mission on time and on budgetencompasses many tasks and skill sets. In recent years NASAhas increased its emphasis on evaluating the experience of thePI, the project manager, and the managing institution, partic-ularly in relation to previous execution of small flight missionsor instruments on larger flagship missions flown over the pastseveral decades. Very few PIs have led a mission before,because of the longtime scales required for comprehensivemission development, but experience working with othermission teams has served them well. The career path fora PI varies, but it typically includes a PhD, many years per-forming independent research, possibly serving as a Co-I onone or more missions, and then a series of unsuccessfulproposals to competitive AOs leading to successful selectionof a mission with the scientist as a PI. (The series of proposalsis key: in the Discovery Program, for instance, seven of thenine competitively selected missions selected to date were firstproposed in some form in 1992 and/or 1994. The need forsuccessive proposals over a decade further lengthens the timeelapsed between PhD and selection as a PI.)

In 2007 SMD announced a new policy limiting proposersfor PI-led missions to those who had served in specific scienceleadership roles on missions in the past. The text of this policywas first published in the notice of an upcoming proposalopportunity: ‘‘A proposal PI for this AO must have demon-strated sufficient experience to successfully lead a SMEXmission by having held a key position (PI, PS, Deputy PI,Deputy PS) for a space project (orbital or suborbital or deepspace, mission or experiment or instrument) that has launched

183S.M. Niebur / Space Policy 25 (2009) 181e186

[4].’’ Many in the community of planetary scientists objectedto this policy, as this action restricted the vast majority fromproposing to lead a new mission, thereby reducing the diver-sity of new mission concepts eligible for proposal. The policyalso had the effect, if not necessarily the intent, of barringyounger investigators and almost all women from submittingproposals, because of their lack of previous experience inthese specific science leadership positions, despite missionexperience as members of the science team in numbers moreproportionate to their representation in the field as a whole.The policy undervalued the contribution of Co-Is, who may beresponsible for design and delivery of an instrument,completion of a scientific investigation, mission operations,and/or coordinating supporting observations from ground-based telescopes or other space assets, without providing anyavenue for these Co-Is to become qualified under the newdefinition.

After hue and cry, and a change of Associate Administra-tors at NASA, the explicit requirement stated above was notincluded in the 2008 AO, a standard version proposed for useby all PI-led mission lines. The expectation of extensiveexperience, however, remains, as does confusion about whatexperience is considered sufficient, how to obtain such expe-rience, and what an aspiring PI might do to increase the oddsof selection in the future. The 2009 New Frontiers AO textdefines the requirement as follows:

Requirement 36. Proposals shall identify which manage-ment positions will be filled by key management teammembers (including as a minimum the PI, PM, PSE [ProjectSystems Engineer]), and, where appropriate, PS and partnerleads. Proposals shall describe the qualifications and experi-ence of the key management team members, where named,and shall demonstrate that the qualifications and experienceare commensurate with the technical and managerial needs ofthe proposed investigation [2].

This requirement is immediately preceded in the AO by thestatement, ‘‘The commitment, spaceflight experience, and pastperformance of the PI and of the implementing institutionswill be assessed against the needs of the investigation.’’

The flexibility inherent in this text is an improvement overthe 2007 requirement, but it replaces absolutes with ambiguity.The reader is left wondering whether there is an unwritten rulethat adequate spaceflight experience include positions in thekey roles as mandated the year before. In the absence ofdirection, there is no clear confirmation that, for example,experience as a DPS, or as a Co-I on several successfulmissions, would be considered sufficient. The reader is leftwith uncertainty about the agency’s expectations.

This uncertainty leads to broader questions of PI experi-ence, such as acceptable career stage and expected previousparticipation on missions, as well as questions of adequateopportunity for newer scientists to gain such pre-PI experi-ence. To quantify some of these issues, it is useful to look in-depth at the set of PIs who have been selected to date ina single mission line. This paper will discuss the previousexperience of scientists filling the key roles of PI, DPI, PS, andDPS on the small planetary science missions selected through

the Discovery Program, a mission line encompassing explo-ration of comets, asteroids, moons, and the inner planets of theSolar System.

4. Case study: the Discovery Program

Demographic data are not collected or used by NASA. Toperform this study, the author used data collected frompublicly available sources, such as press releases and missionwebsites. Collated lists of names were then confirmed withNASA representatives and mission Principal Investigators foraccuracy. All analysis was done specifically for this study andis outside of the selection process at NASA. The resultsreported in this paper represent the first known demographicstudy of scientists selected to lead NASA missions.

The Discovery Program, the first of the PI-led missionlines, was selected for the case study because of its large rangeof missions and broad community participation. TenDiscovery missions have launched; another is currently indevelopment. The Discovery missions are NASA’s leastcomplex planetary science missions and can be characterizedas relatively low in cost (less than $425 million), straightfor-ward in development (less than 35 months from the beginningof implementation to launch), and without constraint ofa particular management structure imposed by NASA [4]. TheDiscovery missions are Mars Pathfinder, NEAR, Lunar Pros-pector, Stardust, Genesis, CONTOUR, MESSENGER, DeepImpact, Dawn, Kepler, and Grail. The early missions, MarsPathfinder and NEAR, had project scientists in charge of thepayload; all subsequent missions were PI-led and competi-tively selected as full mission proposals.

PI leadership of such demanding missions requiresa tremendous amount of dedication, experience, and time.Currently, the flight rate is insufficiently high (with a launchevery 18e24 months), and appointment of scientists to keyleadership positions too low (the positions of DPI, PS, and/orDPS are not routinely utilized), to guarantee the developmentof a number of new mission PIs eligible and prepared topropose future missions. This case study will look at thetraditional use of scientists in the DPI, PS, and DPS roles andshow how the PI-eligible field can be expanded to increase thetalent pool available for future missions.

4.1. Methodology

The first task for this study was to create a data set, usingpublicly available information, of the most basic biographicalinformation for each of the scientists selected as a mission PI,DPI, PS, DPS, or Co-I. PIs and program scientists at NASAHeadquarters were then asked to verify the names of thesescience team members; their changes were incorporated andthe data set updated.

Relevant experience was quantified using two objectivevariables: previous experience on a flight mission and timespent as a practicing scientist. Data on the first were obtainedusing PI curriculum vitae and interviews; data on the secondwere confirmed using curriculum vitae, citations, and date of


publication for doctoral dissertations. Mission selection datesare a matter of public record. The second variable, calculatedas time elapsed between terminal degree and selection asa mission PI, gives a measure of career stage at selection. Withfew exceptions, data are reported here as median time todegree for all scientists across a category. Medians are usedinstead of means because of the small statistics; one or twoextreme selections in any category would bias an average, butnot a median.

4.2. Principal Investigators

A study of the characteristics of the nine competitivelyselected Discovery PIs shows that only three of the nine hadprevious mission experience as a Co-I on a planetary sciencemission. None, in fact, had previously served as a DPI, PS, orDPS. This may be partially explained by the relatively smallnumber of missions flown in the 1980s, but it does reveala steep learning curve for newly selected PIs.

PIs are generally between 20 and 35 years post-PhD. Thesole exception is the lone PI without a doctoral degree; histime was calculated post-MS and is therefore four years longerthan the next most experienced PI. The median value for PIs atselection is 28 years post-PhD (see Fig. 1).

The long interval between degree and first selection asa PI actually puts selected PIs at a disadvantage for proposingfuture missions. Consider the following steps in a potential PI’scareer. The proposer nominally finishes college at age 22 andgraduate school at 27. After 28 years in the workforce, theproposer is selected as a mission PI. After four years of missiondesign and development, the spacecraft mission launches andbegins a cruise phase of up to 10 years for planetary missions,concluding with additional time for mission operations.(Median time elapsed for the current set of Discovery missions iseight years from selection to end of mission.) At the end of

Fig. 1. The time elapsed between PhD and selection as a mission PI, DPI, PS,

DPS, Co-I, or participating scientist follows some expected, and some unex-

pected parameters. The median time elapsed for a PI, 28 years, is generally

what would be expected for this group of senior scientists. Co-Is, on the other

hand, are significantly more senior than generally realized, indicating highly

experienced teams. The positions of DPI and PSþDPS are strangely diver-

gent, indicating that, while PS and DPS may be perceived as training positions,

DPI is not. Participating Scientists are typically younger than either Co-Is or

scientists in the first four leadership roles, reinforcing the fact that this group is

an appropriate training ground for future mission leadership.

mission, this PI is between 33 and 42 years post-PhD. (Actualtime since degree at end of mission for the current set ofDiscovery PIs ranges from 18 to 51 years post-PhD.) Since fewmissions are selected at first proposal, and it is nearly impossibleto propose a new mission while managing an operating missionwell, it is scarcely possible that the PI would be selected again atthe first opportunity; he would probably have to wait an addi-tional two to five years to win a second mission. At this point, hewould be between 35 and 47 years post-PhD at proposal; hischronological age for proposing this second mission will thenbe, at a minimum, between 62 and 75, depending on the length ofdevelopment, cruise, and operations of the first mission he led.Another eight years of mission development and cruise wouldmake the PI between 70 and 83 when the second mission ended.As this analysis makes clear, it is very unlikely that a PI will leadtwo missions in a lifetime.

NASA’s interest in selecting a PI who has PI’d before mayunintentionally limit choices to those who have led missionswith short cruise phases (i.e. to nearby targets), those whowere selected much younger than their peers, and those whosemissions failed to complete their prime mission. There aresimply not many other options that would make it possible fora PI to complete a mission and then go on to propose andcomplete another.

4.3. Deputy Principal Investigators

It is widely assumed that PIs routinely name DPIs to helpwith workload management and succession planning, partic-ularly in cases where the missions are designed with a longcruise time between launch and arrival at the planetary target.Many new proposals incorporate this as a best practice.However, the results of this case study show that this has nothistorically been the case. In fact, of the six cases where a DPIhas been named for a mission, the DPI has been older than thePI more often than not. The median value for DPIs at selectionis 32 years post-PhD., which puts their chronological agecloser to 60.

This surprising result could indicate the desire of youngerPIs to have a more experienced Deputy PI on board, exceptthat even the ‘‘youngest’’ of the PIs is 21 years post-PhD andhas been a Co-I on several previous missions. Perhaps morePIs are treating the Deputy PI as an advisor close in age, orchoosing a longtime colleague for other reasons. Regardless ofthe rationale, this analysis highlights an opportunity for NASAto encourage hands-on training and mentoring of futuremission leaders.

If indeed NASA desires to select experienced PIs who haveserved in a key role on a past mission, a concentrated effortmust be made to select and train younger scientists for thesekey roles, perhaps by redefining the role of the DPI. Witha few sentences in an AO, NASA could explicitly encouragePIs to appoint junior colleagues as DPIs, exposing them to thereal work of mission leadership and mentoring them as themission progresses. If each selected PI were to mentor a wellqualified DPI, the pool of available talent would increase twiceas fast. The position of DPI could prove to be of great value to

185S.M. Niebur / Space Policy 25 (2009) 181e186

both the PI and the future of NASA missions, as the workloadand lessons learned are shared across generations.

To increase the number and quality of experiencedPI candidates, NASA and/or the community should considerredefining the role of Deputy PI to incorporate training andhands-on mission leadership experience for junior scientistswho may propose to lead missions in the future.

4.4. Project Scientists

The roles of PS and DPS, in contrast, bring some demo-graphic diversity to the mission leadership. The PS role is onethat was established in 1959 as a necessary role for eachscience team, with the charge ‘‘to understand and interpret thelegitimate requirements of the scientists to the project teamand to interpret and explain the project team’s requirements tothe scientists [5].’’ In contrast to the PI and Co-Is, the PS andDPS are appointed by the managing institution. For each of thefive missions where a PS, and, in one case, a DPS, wasrequired by the managing institution, the PS and DPS havebeen significantly more junior than the managing PI. Themedian time between degree and selection is 18 years.

As scientists have been appointed PS and DPS a full decadeearlier than their colleagues are winning mission proposals asPI and DPI, it may appear that their experience in these roleswould be excellent preparation for future missions. Thissupposition is supported by the SMEX AO requirement thatproposing PIs have had experience in ‘‘a key position (PI, PS,Deputy PI, Deputy PS) [3].’’ If the role of PS is such goodtraining for future PIs, one would expect to see more scientistsfilling the roles sequentially. In fact, in all of planetary science,no PS has yet gone on to PI another mission, inside or outsideof the Discovery Program. This result indicates that one of thefollowing alternatives must be true: PSs are not interested inbecoming PI, PSs are not winning proposals to become PI, orthere is an unrecognized institutional barrier.

Both NASA and PSs could benefit from a study examiningwhether the role of PS/DPS is a desired entry point to the roleof a PI and how to leverage the role to maximize benefit forfuture mission proposals.

4.5. Co-investigators

The number of scientists in the key roles discussed so far isadmittedly small. Of the 257 times NASA has confirmedparticipation of a planetary scientist on a Discovery Programmission, only 22 have been named PI, DPI, PS, or DPS. Toinvestigate whether these key leaders are in fact more expe-rienced than the rest of the Co-Is at selection, a data set of 179Co-I selections was assembled. For these Co-Is, the timeelapsed between PhD and selection varied more widely, butthe median was 22 years.

This six-year difference between the median age of the PIsand the median age of these Co-Is is surprisingly small. TheCo-I teams are, as a whole, quite experienced and composedlargely of more senior scientists than would have beenexpected for these small mission opportunities. In fact, the

median age of the Co-Is is seen to increase over time, withsmaller, earlier missions populated by more junior scientistsand larger, more recent missions populated by more seniorscientists. Two underlying trends help to explain this: missionteams tend to select the most experienced scientists available,overlooking their younger colleagues, and the cohort of Co-Isis aging with the program.

4.6. Participating Scientists

Occasionally, NASA, the mission team, or both wish to addmore investigators to the science team. To select these newinvestigators, called Participating Scientists, NASA, in coop-eration with the PI, releases a NASA Research Announcementrequesting proposals for complete science investigations thatmay be performed by the proposer using one or more instru-ments on a particular operating mission. These proposalsundergo a rigorous peer review that considers the proposedinvestigation, how the proposed investigation would comple-ment those already planned by the science team, potentialcontribution to mission operations and planning, possibleimprovement in the planned data products for team use anddelivery to the Planetary Data System, and the need of theproposer to be on the team to ensure the acquisition of theappropriate data during the mission’s operation [6].

Of the missions in our case study, only four (Mars Pathfinder,NEAR, MESSENGER, and Kepler) have employed thisprocess, selecting 56 Participating Scientists to date. Themedian age of the aggregate set of Participating Scientists is 13years post-PhD, almost a decade younger than the originalCo-Is. It should be noted that on any given mission, theperceived difference is even larger, as four to eight years havepassed between the selection of the mission proposal andoriginal Co-Is and the selection of these new ParticipatingScientists. For example, on NEAR, a young team of Co-Isselected in 1994 was supplemented in 1999 with ParticipatingScientists with a median age only two years younger at selec-tion, resulting in a median age difference of seven yearsbetween original and new science team members. At the otherextreme, in 2007, the MESSENGER mission added a group ofParticipating Scientists 20 years younger than its original Co-Is.

From these data, it can be seen that implementinga Participating Scientist Program is an effective way to recruityounger scientists onto a NASA mission.

5. Conclusions

This work has shown that eligibility requirements thatspecifically require previous experience as a mission PI, DPI,PS, or DPS without corresponding attention to the filling ofsuch positions drastically restricts the pool of eligibleproposers.

If NASA values experience on past space and earth sciencemissions for its future PIs, the agency has an opportunity toexpand the pool of qualified proposers and manage upcomingmissions more effectively by making a simple change inmission AOs. A clause should be added in the AO not only


encouraging but requiring prospective PIs to name a DPI andoutline his role on the mission. The role would then be eval-uated by the science, technical, management, and costreviewers and NASA officials during the peer review of themission proposal.

Adding the requirement of a named DPI would benefitNASA, the PI, and the community. NASA would increase theexperience of scientists in management roles in preparation forfuture missions. The PI would receive additional assistance,making it more possible for PIs to balance mission leadershipwith institutional commitments, such as teaching of under-graduates and mentoring of graduate students. The communitywould benefit not only by adding a leadership role for whichmembers might be eligible, but from the perceived increase inopportunity for themselves and the younger scientists whothey mentor. Taking this step could rejuvenate the missionproposal opportunities, as parts of the community who hadbeen shut out under the 2007e2008 rules would now feelwelcomed as valuable contributors to missions and to NASA’sfuture.

Those not ready to propose as DPIs should be brought intothe fold for missions through increased usage of ParticipatingScientist Programs, particularly as a tool to bring youngerscientists and underutilized members of the community intothe most active part of the life of a NASA scientist: involve-ment on a flight mission. NASA, PIs, and the community allstand to gain by implementing these two straightforwardchanges, the first of which has no net cost to the mission lines.Adding DPIs and Participating Scientist Programs as standardmission components would reinforce effective management

practices, open the field of proposers, and provide a concreteway to mentor the next generation of PIs.

Acknowledgement

This work was produced under contract to NASA (ContractNNH08CC65C) in the program The History of ScientificExploration of Earth and Space. The views expressed in thisarticle represent only those of the author.

References

[1] National Aeronautics and Space Administration, Science Mission Direc-

torate. Announcement of opportunity: Small Explorer (SMEX) and

missions of opportunity. NASA Announcement of Opportunity

NNH07ZDA003O; September 28, 2007.


torate. New Frontiers announcement of opportunity 2009. NASA

Announcement of Opportunity NNH09ZDA007O; April 20, 2009.


torate. Information notice: NASA Explorer Program announcement of

opportunity. Available from: http://explorers.gsfc.nasa.gov/042407.html;

April 24, 2007 [accessed 30.11.08].


torate. Announcement of opportunity: Discovery Program 2006 and

missions of opportunity. NASA Announcement of Opportunity

NH06ZDA001O; January 3, 2006.

[5] Naugle JE. First among equals: the selection of NASA space science

experiments (NASA SP-4215); 1991.


torate. Research Opportunities in Space and Earth Sciences e 2006:

MESSENGER Participating Scientist Program, section C.16. NASA

Research Announcement NNH06ZDA001N-MESSPS; 22 January 2006.

http://explorers.gsfc.nasa.gov/042407.html

principal investigators and mission leadership

Documents