Wednesday, May 29, 2013

Implementing Missions Within Budget -- Good News

A few years ago, cost overruns in NASA’s science program were a significant news story.  (See, for example, this post from 2009.)  The major culprits were the two largest missions, the James Webb Space Telescope and the Mars Science Laboratory.  Smaller missions, however, had their share of cost overruns, too.  At one point, for example, NASA cancelled the Dawn mission to the asteroids Vesta and Ceres because of overruns in that mission’s budget.  (Fortunately, NASA reconsidered and re-instated the mission.)

For the last several years, Congress’ General Accounting Office annually has reviewed budget performance on selected NASA missions.  The most recent report got me to relook at cost overruns in NASA’s Planetary Science program.  The news is good, but as so often happens, the good news appears to come with a tradeoff.

The missions of the Discovery program have visited a wide-range of solar system destinations.  These missions also have had a range of cost under- and overruns.  Image from Historic Spacecraft and used under a creative commons license. 

Let’s start by looking at the trends.  Prior to about 2002, some planetary missions came in under budget, others were less than 10% over budget, and two were more than 20% over budget.  (Two of the four missions that came in under budget failed.)  Then, in the mid-2000’s, all missions were more than 19% over their initial estimates.  The Curiosity Mars Science Laboratory began development in 2004 with a planned launch in 2009 (later slipped to 2011).  This mission had the largest absolute and percentage cost overrun since the mid-1990s.   It was towards the end of this period that then NASA science administrator Alan Stern made eliminating cost overruns a central focus.

Trends in NASA planetary mission cost under- and overruns.  Points in red indicate missions in the Discovery and Mars Scout programs (<$500M for the spacecraft) and all other missions are in blue.  Data used is shown at the end of this post.

Following this period, cost overruns in planetary missions all but disappeared.  For missions launched in the last few years, four missions have stayed within their initial budgets and a fifth was less than 10% over budget.

(I was unable to find any information on the Mars Phoenix, Pluto New Horizon, or the Mars Reconnaissance Orbiter missions’ performance against initial cost estimates. The lack of news probably indicates that these missions stayed within budget.)

I hope that the President’s budget office and Congress – which decide whether to reward NASA with funds for new missions or not – take note of this recent accomplishment.  NASA’s Planetary Science Division recognized a problem and appears to have dealt with it.  Unfortunately, I fear that that NASA’s reputation in the near term will be stained by the large overruns in the two flagship programs, MSL and JWST.  Space News reported in January, that future astronomy missions may be limited to approximately $1B, ending a long run of >$1B flagship astronomy missions.  I also wonder how much of the President’s budget office’s refusal to allow development of a Europa mission (estimated $2B) stems from reluctance to trust NASA again on a large science mission.

I also worry about a possible consequence of managing to budget.  Boldly doing new things brings with it the risks of busting budgets.  Look at the string of missions starting in the mid-2000’s that exceeded budgets by 19%+: the Mars Spirit and Opportunity rovers, the Mercury MESSENGER orbiter, the Kepler exoplanet telescope, the Dawn asteroid mission, and the Curiosity rover.  All required new designs and often significant technology development to achieve their goals.

The easiest way to stay within budget is to push the envelope as little as possible.  The Mars MAVEN mission returns to the Red Planet and reuses substantial portions of the Mars Reconnaissance Orbiter’s spacecraft design.  The recently completed lunar GRAIL gravity mapping mission largely reused the spacecraft design of the similar GRACE terrestrial mission.  The 2020 Mars rover mission will reuse the design of the Mars Curiosity rover.  The recently selected Mars InSight lander largely reuses the design of the Phoenix lander. 

InSight’s competitors for selection, by contrast, would have required new designs to either hop across the surface of a comet or to land on a Titan lake.  When NASA selected the InSight mission, its managers emphasized that the science potential of the three were all high, but that the InSight mission had the lowest development risk.

Out of the last nine NASA planetary missions launched or selected for future launch, only two would go to a destination other than the moon or Mars.  This followed a previous string of missions to comets, asteroids, Mercury, and Pluto as well as Mars and the moon.

Managing the tension between fiscal responsibility and doing new things is difficult, but perhaps doable.  The New Frontiers program Jupiter Juno and Pluto New Horizons missions both will boldly go to new destinations.  Both also appear to have done so while staying within their development budgets.  However, both also are among the more expensive missions on the list below.  Perhaps bolder missions require larger budgets.

Or perhaps significant new designs would benefit from longer early design phases than is typically done.  After design began, the Juno mission was delayed approximately two years because of other budget issues at NASA.  At one meeting I listened to, it was stated that the design team put the extra time to good use maturing the design and reducing implementation (and budget) risk. 

It's also likely that NASA and principal investigators have become better at understanding the kinds of missions that are capable in cost-capped programs such as the Discovery program.  The early Discovery missions came in under or near budget.  Then there were a string of more ambitious Discovery missions that came in significantly above their initial estimates.  The last four Discovery and Mars Scout missions appear to have returned to staying within their budgets.

In two years or so, there will be a mid-term assessment of NASA’s performance against the recommendations of the Planetary Decadal Survey that established NASA’s planetary exploration goals.  The budget assumptions in that Survey turned out to be wildly optimistic, and therefore NASA’s capacity to fund missions to new targets was greatly diminished.  I hope that the mid-term update to the Survey will address the proper balance between fiscal responsibility and enabling more frequent exploration of the rest of the solar system beyond the moon and Mars.

In the meantime, NASA’s management team is to be commended for managing recent missions to budget.  Absorbing the budget cuts being imposed on the Planetary Science Division would be much harder to do if one or more of the current missions in development were seriously over budget.

Backup: Mission Cost Data Used

Whenever possible, I used mission cost data from either the National Academies Press Principal-Investigator-Led Missions in the Space Sciences (2006) report or data from the Series of Government Accounting Office assessing NASA’s management of selected projects (downloadable from this link).  For the GAO reports, I compared the earliest firm project cost data with the last reported cost data to compute change.  When these sources failed, I used Wikipedia or press accounts.  For several missions, I was unable to learn whether there had been any significant cost overruns (absence of news probably means there wasn’t any), and I left those columns blank.  It was not always clear from the data sources whether or not mission costs included launch costs.

If any of you have better data for any mission, please send it to me and I’ll correct this post.

If the Mars Science Laboratory is excluded from the list, there is no relationship between final cost and percentage change compared to initial estimated costs.  Because MSL’s cost lies well outside the range of the other missions, it should not be used in an analysis of trends with these much less expensive missions.

There is debate as to when the initial budget for MSL became firm and therefore should be used as the basis for comparison.  I used as the initial cost the budget from the 2009 GAO report.

Lower cost missions from the Discovery and now-cancelled Mars Scout programs (<$500M without launch cost, Principal Investigator-led missions) are highlighted in blue.

Final Cost
Change from initial planned cost
Mars Pathfinder
Mars Global Surveyor
Lunar Prospector
Mars Climate Orbiter
Mars Polar Lander
Mars Odyssey
Mars Exploration Rovers
Deep Impact
Mars Reconnaissance Orbiter
New Horizons
Lunar Reconnaissance Orbiter
Mars Science Laboratory
Mars 2020 rover

TBD – Mission cost estimates to be determined.

Wednesday, May 15, 2013

NASA's Planetary Science Budget Reportedly to be Hit -- Again

The sequester will hit NASA again, with large reported cuts to the Planetary Science program.  NASA's managers have stated for several months that further cuts to the planetary program were likely.  The sequester requires automatic cuts to most federal budgets of approximately 5%.  Congress has given the administration the freedom to apply the cuts disproportionately to lower priority programs within agencies to protect higher priority programs.  For NASA, the planetary program is lower priority, and cuts as large as 15% reportedly are being proposed.  

Mark Sykes, editor of the Planetary Exploration Newsletter, has received advanced information (leaks) on the proposed cuts to the budget for the remainder of fiscal year 2013 (which ends in October).  In recent years, Congress has rarely completed new budgets on time. Agencies have operated under continuing resolutions for months into the following fiscal year, so these budget levels, if they stand, could continue well into FY14.

The administration is expected to release its proposed sequester-adjusted budget for NASA later this month.  It has to notify Congress of the proposed cuts, but it's not clear to me whether Congress can object or if it would formally do so.  (Several representatives and senators have issued statements warning the administration not to disproportionately cut the Planetary Science program, but this is not formal Congressional action.)  The cuts reduce planetary spending substantially below to the recently passed NASA planetary budget for FY13 that was signed into law by President Obama.

The only good news in the budget changes is that $67M would be spent to further studies on a mission to Europa.  However, the President's proposed budget for FY14 has no money for this program, so this could be a one year project.  (As I understand the rules of the sequester, whole programs in enacted budgets cannot be eliminated, so the administration may not have had the freedom to cut the Europa mission studies.)

To pay for the Europa studies, the sequester-adjusted budget would cut the Discovery program (missions <$500M) by 33% and the New Frontiers program (missions ~$1B) by 7%.  The Discovery program cuts would, I think, delay the start of the competition for the next mission from early next year to sometime in the future.  (I don't know if the cuts are large enough to impact to delay the current Discovery mission in development -- the Mars InSight geophysical station -- or not.  Sykes does not mention any slip.)  The research and analysis budget that supports the scientific community that analyzes planetary data would be cut by 9% and could cause scientists without funding to leave the field.  (All cut percentages are relative to the current approved Planetary Science budget for FY13 that was passed by Congress.)

Cuts to programs could have potentially larger impacts than the simple percentages imply because they must be applied in the few months remaining in this fiscal year.

You can read the full details of the proposed cuts at the Planetary Exploration Newsletter site.  (I read this newsletter regularly and recommend it to you.)

Sunday, May 12, 2013

ISIS: Blasting a Crater on Asteroid Bennu

NASA’s OSIRIS- REx asteroid mission may get much more exciting thanks to an innovative proposal from a group led by Steve Chesley at the Jet Propulsion Laboratory.  The main goal of the OSIRIS-REx mission will be to gather and return to Earth up to two kilograms of material from the surface of the primitive asteroid Bennu (previously known as 1999 RQ36).  Prior to collecting the sample, the spacecraft will also carry out extensive imaging and spectral analysis of the surface and by mapping the gravity field investigate the interior structure.  (See here and here for my posts on the OSIRIS-REx mission.)

The proposed ISIS spacecraft nearing its impact with the asteroid Bennu.  Credit Steve Chesley.

Chesley proposes to send a second spacecraft, named ISIS, to Bennu that would perform a high speed crash on the surface.  You may remember that the Deep Impact spacecraft similarly delivered an impact projectile to comet Tempel  1.  That mission was partially skunked when the dust cloud raised by the collision prevented the main spacecraft from imaging the resulting crater, whose size and shape would have provided important clues about the structure of comets.  (A second spacecraft later imaged the crater.)

Under Chesley’s plan, the impact would occur while the OSIRIS-REx spacecraft lingers (at a safe distance) near Bennu following its initial study and the collection of the samples.  At the time of the impact, the OSIRIS-REx cameras would watch the cloud of ejected material for clues to the composition and size of the blocks of material making up the surface.  Once the ejecta had safely dissipated, OSIRIS-REx would move in for a close look at the ISIS impact crater to examine the composition of Bennu a few meters below the surface.  The spacecraft would also remap the asteroid surface to see what changes occurred as the result of the seismic shock created by the impact, which will help us understand the role impacts have in shaping the surface of small bodies.  (There is no plan to risk the OSIRIS-REx spacecraft by having it sample within the newly created crater.)

Image of the Deep Impact strike on comet Tempel 1.  Credit NASA/JPL.

While the impact would further our scientific exploration of asteroids, the ISIS mission also would contribute to other goals.  If astronomers discover an asteroid on a collision course with Earth, one idea would be to send an spacecraft to change the asteroid’s trajectory through a high speed impact.  Small asteroids like Bennu are believed to be rubble piles, and it’s difficult to model how an impact would affect an asteroid’s trajectory.  The OSIRIS-REx mission team would measure Bennu’s trajectory before and after the impact to determine the resulting miniscule change in Bennu’s orbit about the sun.  This would help us better understand whether future impactors could divert asteroids from collision courses with the Earth.  (Bennu is among the known asteroids with the largest (but still small) probability of hitting the Earth in the future.)

NASA also has goals to send humans to explore small near Earth asteroids like Bennu.  Before astronauts arrive, the space agency would like to better understand these bodies’ surface mechanical properties, their local and global stability, and the environment of small particles likely to surround them.  The ISIS impact experiment would further our understanding in all three areas.

For those who don’t remember their ancient Egyptian mythology, Osiris was a god ruler of Egypt.  Following his murder and dismemberment, his wife and queen Isis gathered together his scattered body parts and resurrected him.  While there’s no murder in this story, the proposed ISIS mission would be enabled by taking advantage of various existing components. 

First, the OSIRIS-REx spacecraft will be at Bennu and will have several months available in its schedule to watch the impact and study the aftermath.  The 2016 InSight Mars mission provides an option to launch ISIS at negligible additional cost on an orbit would take it twice past Mars and then to Bennu.  The ISIS spacecraft itself would be built around an adapter ring designed to mate a main spacecraft to its launch vehicle and also provide attach points for small secondary spacecraft.  The components needed to turn the adapter ring into a spacecraft – electronics, solar panels, propulsion, and a camera that would be used to track Bennu – would take the place of the secondary spacecraft.    The final collision would be enabled by a JPL-developed AutoNav system, has been used for five previous NASA comet encounters, that would image Bennu in the final hours and steer the spacecraft to an impact.

Current concept for the ISIS spacecraft.  The ESPA ring is the adapter between the launch vehicle and the InSight Mars lander  Ballast can be added to maximize the impact weight of the ISIS spacecraft within the overall launch weight constraints for the InSight and ISIS missions.  Credit Steve Chesley.

The InSight Mars lander and ISIS asteroid impact spacecraft stack atop the launch vehicle.  Credit Steve Chesley.

The goal of the mission would be to maximize the wallop of the impact by maximizing the impact velocity and the mass of the spacecraft.  The maximum velocity of the collision would be determined by the constraints of terminal approaches in which the AutoNav system can ensure an impact.  The design team has approximately 1000 kg of spare launch mass on the InSight mission to use in designing the ISIS spacecraft, with a good portion of that needed for propellant for the trajectory maneuvers.  The current nominal mission design would impact Bennu at 13.4 kilometers a second (48,000 kilometers or 30,000 miles per hour) with a dry spacecraft mass of around 420 kg.  Chesley’s team estimates the energy of the impact would be equivalent to approximately nine tons of TNT, enough to create a crater tens of meters across.

The ISIS mission would be a planetary exploration bargain.  While Chesley’s team is continuing to refine the mission design, current cost estimates are somewhat above $100M.  NASA’s cheapest class of planetary missions from its Discovery program cost approximately $450M not including the launch vehicle.  Time, though, is short to develop a spacecraft in time for launch in 2016, and NASA’s budgets are tight.  At the moment, NASA is funding further design pending a decision on whether it can fund the ISIS mission this coming fall. 

If the ISIS mission gets its go ahead, the timeline would play out as follows:

  March: ISIS and InSight launch
  July: ISIS 1st Mars flyby
  September: OSIRS-REx launch
  October: OSIRIS-REx reaches Bennu
  January: ISIS 2nd Mars flyby
  January: OSIRIS-REx completes planned Bennu observations and sampling
2021 -    
  February: ISIS impacts Bennu
  May: OSIRIS-REx completes post impact observations
  June: OSIRIS-REx departs for Earth
  Bennu samples returned to Earth

I’m impressed the cleverness behind the acronyms for the missions involved.  The OSIRIS-REx team began the Egyptian theme with a mission acronym that spells the name of an Egyptian diety: Origins Spectral Interpretation Resource Identification Security Regolith EXplorer.  The asteroid’s new name, Bennu, comes from an Egyptian god usually depicted as a heron, which OSIRIS-REx will resemble as it extends its sampling probe to the asteroid’s surface.  That resemblance was noticed by nine-year-old Michael Puzio, who won a contest to name the asteroid. Chesley proposes to continue the Egyptian them with ISIS:  Impactor for Surface and Interior Science.  I think a safe prediction is that the features identified on Bennu will also follow an Egyptian theme.

You can read a presentation by Chesley on the ISIS mission here.  Leonard David at also wrote an article about this mission.

Monday, May 6, 2013

Europa Clipper Update

Planetary geologist Philip Horzempa returns with a new post giving an update on the proposed Europa Clipper mission.  


President Obama’s recently released FY2014 budget proposal, unfortunately, contains no funding for a mission to Europa.  In fact, the budget document states that NASA not only is not funding such a mission, but that it cannot fund it.  Several sources of budget constraints appear to be stalling any new start.  In addition to the sequester, NASA’s Science Mission Directorate has the ongoing money drain of the Jams Webb Space Telescope (JWST).  That funding burden will not lessen until about 2017 – 2018.  One could imagine that NASA may see a funding wedge appear at about that time, with a new start for a Europa mission possible in FY 2015 or 2016.  The early years of a space project require minimal funding, allowing a program to begin Phase A and Phase B (design and definition) a few years before the fiscal “heavy-lifting” of Phases C and D (detailed design, construction and testing) .In the meantime, the Europa team has continued to refine the design of what they refer to as the Europa Clipper (see Van’s post of September 24, 2012).  Whenever they are given the “go-ahead” from the White House, they will have a mission ready to proceed to implementation. 

The Europa science community believe they have developed a cost-effective, yet scientifically compelling, mission to the ice-covered Galilean satellite.  After considering an orbiter, the consensus is that a multi-flyby spacecraft would return more science for the same cost ceiling.  The Europa Clipper embodies the modified FBC (faster, better, cheaper) approach.  It is seeking to capture as much of the Jupiter Europa Orbiter (JEO) flagship science as possible using a smart, elegant, lower-cost design.  This past January, the Europa team presented the results of their latest “scrub” of the Clipper mission.  This Europa Clipper design refinement can be seen here.

The plan is to launch in 2021, followed by one Venus and two Earth gravity assists.  Six years after launch, with the gravity assist of a Ganymede flyby, the Clipper will enter orbit around Jupiter.  Over the next 2.5 years, it will perform 32 flybys during its prime mission, with closest approach altitudes of 25 - 100 kilometers (actually 34 total flybys will occur, but only 32 are optimal for science).  In order to reduce planning costs, the timeline of each flyby will be essentially identical. (Figure 1) However, the trajectory of each flyby will bring it over a different sector of Europa.  This will provide global medium-resolution coverage from the Topographic Imager. 

Figure 1.  Flyby timeline.  Click on image for a larger version.

It was felt that the Europa Clipper mission should also provide data that would feed-forward to a future soft lander.  This concept of reconnaissance has seen a rebirth at NASA, with ongoing orbital missions at the Moon and Mars.  The addition of a Reconnaissance Camera was deemed to be essential for providing images for landing site surveys ( lander-scale characterization of the surface is needed).  The Recon camera (a push-broom design) will produce 20 x n km images at resolutions of as fine as 0.5 meters.  The limitation on the number of such high-resolution images comes from the large amount of data in each photo.  In turn, the swath length will be determined by the amount of down-link time available.  The Recon camera will utilize an innovative flip-mirror to enable stereo imaging of a scene in a single pass.  It will be able to obtain views 15 degrees from nadir (Figure 2)  It is believed that about 15 candidate landing sites will need to be surveyed in order to be able to down-select to 2, a primary and a backup.  That selection will be done by some future team of Europa Lander scientists and engineers.

Figure 2. High resolution camera flip mirror to allow stereo imaging.

A separate, smaller, and gimbaled gravity science antenna will allow the collection of gravity data during flybys. (Figure 3).  Because the cameras and other remote sensing instruments are mounted to the spacecraft body, the main antenna cannot be pointed to Earth during flybys to allow tracking for gravity measurements.  The separate antenna will be kept pointed at Earth during flybys to permit the important gravity measurements that will reveal much of the internal structure of Europa.

Figure 3. Gravity science antenna.

During this latest iteration, the Europa team was allowed to raise the cost cap from $1.7 billion to a total of $2.0 billion.  (This is still less than half the estimated cost of the previously proposed Jupiter Europa Orbiter.)  This increase allowed the addition of a Magnetometer and Langmuir Probes to the payload suite.  Rounding out the instrument complement are an Ice-Penetrating Radar, a Thermal Imager, a Neutral-Mass Spectrometer and a Short-Wave Infra-Red Spectrometer.  Figure 4 shows some of the payload complement and where they will sit on the spacecraft. 

Figure 4.  Europa Clipper instruments.

The highly-capable instrument suite is one reason that the Europa Clipper would cost more than missions such as JUICE or the proposed Io Observer.  The scope and resilience of the Clipper mission means that it must survive an intense radiation exposure over its 2.5-year mission.  This data-intensive mission must also use a reliable, high-energy power source. 

The Europa Clipper spacecraft benefits from the heritage of the Galileo and Juno Jupiter Orbiters in its approach to radiation protection.The Clipper will utilize 150 kg. of dedicated radiation shielding which is one-half of that planned for the earlier JEO (Jupiter Europa Orbiter)  proposal.  The Clipper will use a scheme of nested radiation protection for its electronics (Figure 5).

Figure 5. Nested radiation protection for the spacecraft's electronics.

For example, the Spacecraft structure and propulsion system will provide a measure of radiation protection, essentially for free.  With intelligent placement, the project will utilize much less expensive 100 and 300 kilo-rad hard parts.  Individual payload electronics have their own shielding, while the use of a central electronics vault is also part of the protection plan.  As a result of this approach, the Clipper team will not need to fund an expensive development effort to build mega-rad hard avionics.

The Europa Clipper mission will be data-intensive.  In order to downlink this data efficiently and cheaply, the Clipper will use mass-memory-storage. The spacecraft will leisurely downlink the data from each close encounter with Europa during the two weeks between flybys.  This will avoid the more costly, and power-hungry, approach of near-real-time broadcast during flyby.

Over the course of its prime mission, the Clipper will return a Terabit of data, including high-resolution images, radar soundings, magnetic field measurements, compostion spectra, and gravity science.  In order to return all of this date, a robust energy source is required.  There are three energy supply options, two of which are thermal-electric and one solar.

Solar panels would be the lowest cost, highest mass option.  However, they pose the risk of not providing enough power over the lifetime of the mission.  The Europa Clipper's orbit has a low inclination causing it to pass through the most intense radiation environment in the solar system.This would cause aggressive degradation of solar cells, such that their power output would be increasingly compromised as the mission progressed.  The Juno orbiter is able to use solar power because its high-inclination polar trajectory enables it to avoid most of the high radiation zones that are concentrated over Jupiter's equator.  This is true even though it flies much closer to the gas giant than the Clipper ever will.  ESA’s JUICE spacecraft is able to use solar energy mainly because it only flies near Europa twice during its mission. 

The proposed Io Observer would also use solar panels.  It avoids high doses of radiation by orbiting Jupiter in an inclined orbit.  Europa Clipper is unable to utilize such a high-inclination orbit because that would result in flyby velocities too great to allow its Infra-Red and Ice-Penetrating Radar to gather useful data. 

This leaves the two thermal-electric options.  These power systems utilize the heat generated by the decay of Plutonium-238 to drive thermal-electric power conversion units.  One of these, the Advanced Stirling Radioisotope Generator (ASRG) design is actually still in development, although at a high level of maturity.  NASA chose not to pursue a Discovery mission that would have utilized one of these units.  In light of that decision, the agency will still take the two ASRG development units to flight status this year.  They will then be placed in storage, awaiting a mission.  If this power source is chosen, then the Clipper would utilize four ASRG units. 

However, before the ASRG design would be approved for the Europa Clipper,  more work would need to be done.  The radiation hardness of the Generation-1 ASRG units is not sufficient for the Europa mission and there are also lifetime demonstration issues.

The other thermal-electric option is the Multi-Mission Radioisotope Thermal-electric Generator design (MMRTG). This system is the 1st new radioisotope power system developed in over 20 years.It has advanced to actual flight status, with the first MMRTG flight unit, F-1, now sitting on the surface of Mars, powering the MSL rover.  Its backup, F-2, is in bonded storage at the Rocketdyne plant in Canoga Park.  It has been operated and has shown good performance.  It is now slated to fly onboard the 2020 Mars Rover, i.e., MSL-2. 

The next unit, F-3, is the flight spare for Mars 2020.It is now under construction, with completion set for this month.  If not needed for the Mars 2020 rover, then F-3 would be available for a mission to Europa.In addition to F-3, three more MMRTG units would be needed for the Clipper.  There are plans for infusing new technologies in the next generation of MMRTG.These would produce 150, or even 180 watts, as compared to 120 watts for the 1st generation. 

There are a number of issues that need to be considered if one of the thermal-electric options is chosen.  ASRG development seems to have begun during the short-lived Prometheus program.  An engineering unit at NASA Glenn has accumulated over 10,000 hours (14 months) of operation so far.  The maturity level for the ASRG units is high, but they are more expensive than an MMRTG and have yet to fly in space.  On the other hand, their power conversion efficiency of 30% means that they are more frugal than MMRTG units (9% efficiency) with the Plutonium supply. 

The MMRTG design has several advantages over the ASRG.  First, as noted, an MMRTG is now in space.  The design has high reliability and low cost.  In addition, the ASRG utilizes kinetic energy as one stage in it power conversion.  It is still to be determined whether the resulting vibrations would make it incompatible with a Europa mission.  If so, then the vibration-free MMRTG would be at an advantage.  In addition, the re-start of Plutonium production in the U.S. may make the use of an MMRTG for Europa more plausible.  One factor that had favored the use of ASRG units for space missions was the shrinking inventory of Pu-238 in this country.  However, if the goal of producing 1.5 – 2.0 kg of Pu-238 per year is met, then that concern will be eased.America now has about 10 kg of older, aging Pu-238.  The new Pu-238 can be blended with the old material producing the desired power density.

Over the next 18 months the Europa project team will be conducting a comprehensive trade study, comparing all viable energy options.  The variables to be considered include cost, risk, robustness, design compatibility, and implementation feasibility.  This effort will go a long way towards choosing the most appropriate system for the Clipper. 

The Clipper team is very interested in the idea of hosting several nanosats that would be deployed in the vicinity of Europa.  This is contingent upon the use of the Space Launch System (SLS) heavy-lifter.  Only that rocket would provide the needed mass margin required if the Clipper is to carry small satellite payload elements.  However, if pursued, the working concept for the Clipper could provide the necessary housekeeping, deployment and radio-relay capabilities.  In addition, thought is being given to utilizing an intermediate orbit insertion module that would allow several nanosats to enter orbit around Europa. 

If these nanosats can be accommodated, then the Europa team would like to cooperate with the growing American small-sat community.  There is a desire to get feedback from engineers and scientists on the best way to use these probes.  There are a variety of options that could use a single smallsat, or a network, with instruments such as magnetometers or cameras.  These probes could be orbiters, “Ranger-style” crash landers, or even hard landers that might operate for a short time after impact.  Resource and cost constraints will be tight, but if these mini-probes  could fit, then the Europa team is interested. 

Still to be decided this year is how, or if, a total of $75 million of new funding is to be spent.  In this year’s budget, Congress specifically earmarked that sum for development of a Europa mission.  There have been rumors that NASA’s operating plan for this year’s budget, due to be delivered to Congress soon, will seek to spend that money on other agency projects.  In response to such concerns, Senators Diane Feinstein and Barbara Boxer joined with  Congressmen Adam Schiff and John Culberson in sending a letter to NASA.  They point out to NASA that funding levels for its science programs “will remain consistent with the structure directed by Congress.”  Essentially, they are reminding the agency that the Constitution gives the power to say how the nation’s money is spent to the Congress.  The Executive branch has limited leeway in how it interprets Congress’ appropriations legislation.

How this will turn out is difficult to gauge.  This is not the first time such a struggle has occurred.  For years, the Congress earmarked funds for development of a Solar Probe mission.  Eventually, NASA got the message and awarded a new start for the Solar Probe Plus spacecraft.  About 10 years ago, when NASA was trying to eliminate funding for the New Horizons Pluto probe, Congress specifically earmarked funding for that mission, enabling it to proceed.More recently, after the Obama Administration canceled the Ares 5 heavy lift rocket in its FY 2011 budget proposal, the Congress (especially the Senate) was not pleased.  They directed NASA to pursue an alternate heavy lifter, the SLS (Space Launch System), which is essentially a scaled-back version of the Ares 5.That launcher is now on track for its first mission in 2017.

If NASA does agree to spend the $75 million (more like $70 million after sequestration) this year for Europa mission preparation, there are several ways that the money could be usefully spent.  Instrument development, launch vehicle requirements and power system options could be funded, as well as studies to define the loads on the Clipper during launch.  Much will also depend on whether Congress again earmarks funds for a Europa mission in the new FY 2014 budget.  If it does, then the tug-of-war with the Administration will continue with the future of Europa exploration hanging in the balance. 

Editorial Note from Van: If you are an American citizen and you would like to see NASA continue work on the Europa Clipper, remember to let your Congressional representatives know.  Visit the Planetary Society's website for instructions on how to do so.  You can also follow the latest information on the budget on Twitter at #fundPlanetary