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President Obama’s recently released FY2014 budgetproposal, unfortunately, contains no funding for a mission to Europa. In fact, the budget document states that NASAnot only is not funding such a mission, but that it cannot fund it. Several sources of budget constraints appearto be stalling any new start. In additionto the sequester, NASA’s Science Mission Directorate has the ongoing moneydrain 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 fundingwedge appear at about that time, with a new start for a Europa mission possiblein FY 2015 or 2016. The early years of aspace project require minimal funding, allowing a program to begin Phase A andPhase 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 theEuropa Clipper (seeVan’s post of September 24, 2012). Whenever they are given the “go-ahead” fromthe White House, they will have a mission ready to proceed to implementation.
The Europa science community believe they have developeda cost-effective, yet scientifically compelling, mission to the ice-coveredGalilean satellite. After considering anorbiter, the consensus is that a multi-flyby spacecraft would return morescience for the same cost ceiling. TheEuropa Clipper embodies the modified FBC (faster, better, cheaper)approach. It is seeking to capture asmuch of the Jupiter Europa Orbiter (JEO) flagship science as possible using asmart, elegant, lower-cost design. Thispast January, the Europa team presented the results of their latest “scrub” ofthe Clipper mission. This Europa Clipperdesign refinement can beseen here.
The plan is to launch in 2021, followed by one Venus andtwo Earth gravity assists. Six yearsafter launch, with the gravity assist of a Ganymede flyby, the Clipper willenter orbit around Jupiter. Over thenext 2.5 years, it will perform 32 flybys during its prime mission, withclosest approach altitudes of 25 - 100 kilometers (actually 34 total flybyswill occur, but only 32 are optimal for science). In order to reduce planning costs, thetimeline of each flyby will be essentially identical. (Figure 1)However, the trajectory of each flyby will bring it over a different sector ofEuropa. This will provide globalmedium-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 alsoprovide data that would feed-forward to a future soft lander. This concept of reconnaissance has seen arebirth at NASA, with ongoing orbital missions at the Moon and Mars. The addition of a Reconnaissance Camera wasdeemed 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) willproduce 20 x n km images at resolutions of as fine as 0.5 meters. The limitation on the number of suchhigh-resolution images comes from the large amount of data in each photo. Inturn, the swath length will be determined by the amount of down-linktime available. The Recon camera willutilize an innovative flip-mirror to enable stereo imaging of a scene in asingle pass. It will be able to obtainviews 15 degrees from nadir(Figure 2) It is believed that about 15 candidate landing sites will need to besurveyed in order to be able to down-select to 2, a primary and a backup. That selection will be done by some futureteam 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 thecollection 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 latestiteration, the Europa team was allowed to raise the cost cap from $1.7 billionto a total of $2.0 billion. (This isstill less than half the estimated cost of the previously proposed JupiterEuropa Orbiter.) This increase allowedthe addition of a Magnetometer and Langmuir Probes to the payload suite. Rounding out the instrument complement are anIce-Penetrating Radar, a Thermal Imager, a Neutral-Mass Spectrometer and aShort-Wave Infra-Red Spectrometer. Figure 4 shows some of the payloadcomplement and where they will sit on the spacecraft.
Figure 4. Europa Clipper instruments.
The highly-capable instrument suite is one reason thatthe Europa Clipper would cost more than missions such as JUICE or the proposedIo Observer. The scope and resilience ofthe Clipper mission means that it must survive an intense radiation exposureover its 2.5-year mission. Thisdata-intensive mission must also use a reliable, high-energy power source.
The Europa Clipper spacecraft benefits from the heritageof the Galileo and Juno Jupiter Orbiters in its approach to radiationprotection.The Clipper will utilize 150 kg. of dedicated radiation shieldingwhich is one-half of that planned for the earlier JEO (Jupiter EuropaOrbiter) proposal. The Clipper will use a scheme of nestedradiation protection for its electronics (Figure 5).
Figure 5. Nested radiation protection for the spacecraft's electronics.
For example, the Spacecraft structure and propulsionsystem will provide a measure of radiation protection, essentially forfree. With intelligent placement, theproject will utilize much less expensive 100 and 300 kilo-rad hard parts. Individual payload electronics have their ownshielding, while the use of a central electronics vault is also part of theprotection plan. As a result of thisapproach, the Clipper team will not need to fund an expensive developmenteffort to build mega-rad hard avionics.
The Europa Clipper mission will be data-intensive. In order to downlink this data efficientlyand cheaply, the Clipper will use mass-memory-storage. The spacecraft willleisurely downlink the data from each close encounter with Europa during the two weeks between flybys. This will avoidthe more costly, and power-hungry, approach of near-real-time broadcast duringflyby.
Over the course of its prime mission, the Clipper willreturn 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 robustenergy source is required. There arethree energy supply options, two of which are thermal-electric and one solar.
Solar panels would be the lowest cost, highest massoption. However, they pose the risk ofnot providing enough power over the lifetime of the mission. The Europa Clipper's orbit has a lowinclination causing it to pass through the most intense radiation environmentin the solar system.This would cause aggressive degradation of solar cells,such that their power output would be increasingly compromised as the missionprogressed. The Juno orbiter is able touse solar power because its high-inclination polar trajectory enables it toavoid most of the high radiation zones that are concentrated over Jupiter'sequator. This is true even though itflies much closer to the gas giant than the Clipper ever will. ESA’s JUICE spacecraft is able to use solarenergy mainly because it only flies near Europa twice during its mission.
The proposed IoObserver would also use solar panels. Itavoids high doses of radiation by orbiting Jupiter in an inclined orbit. Europa Clipper is unable to utilize such ahigh-inclination orbit because that would result in flyby velocities too greatto allow its Infra-Red and Ice-Penetrating Radar to gather useful data.
This leaves the two thermal-electric options. These power systems utilize the heatgenerated by the decay of Plutonium-238 to drive thermal-electric power conversionunits. One of these, the AdvancedStirling 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 utilizedone of these units. In light of thatdecision, the agency will still take the two ASRG development units to flightstatus this year. They will then beplaced in storage, awaiting a mission. If this power source is chosen, then the Clipper would utilize four ASRGunits.
However, before the ASRG design would be approved forthe Europa Clipper, more work would needto be done. The radiation hardness ofthe Generation-1 ASRG units is not sufficient for the Europa mission and thereare also lifetime demonstration issues.
The other thermal-electric option is the Multi-MissionRadioisotope Thermal-electric Generator design (MMRTG). This system is the 1stnew radioisotope power system developed in over 20 years.It has advanced toactual flight status, with the first MMRTG flight unit, F-1, now sitting on thesurface of Mars, powering the MSL rover. Its backup, F-2, is in bonded storage at the Rocketdyne plant in CanogaPark. It has been operated and has showngood performance. It is now slated tofly 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, withcompletion set for this month. If notneeded for the Mars 2020 rover, then F-3 would be available for a mission toEuropa.In addition to F-3, three more MMRTG units would be needed for theClipper. There are plans for infusingnew technologies in the next generation of MMRTG.These would produce 150, oreven 180 watts, as compared to 120 watts for the 1stgeneration.
There are anumber of issues that need to be considered if one of the thermal-electricoptions is chosen. ASRG developmentseems to have begun during the short-lived Prometheus program. An engineering unit at NASA Glenn hasaccumulated over 10,000 hours (14 months) of operation so far. The maturity level for the ASRG units ishigh, but they are more expensive than an MMRTG and have yet to fly inspace. On the other hand, their powerconversion 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 theASRG. First, as noted, an MMRTG is nowin space. The design has highreliability and low cost. In addition,the ASRG utilizes kinetic energy as one stage in it power conversion. It is still to be determined whether theresulting vibrations would make it incompatible with a Europa mission. If so, then the vibration-free MMRTG would beat an advantage. In addition, there-start of Plutonium production in the U.S. may make the use of an MMRTG forEuropa more plausible. One factor thathad favored the use of ASRG units for space missions was the shrinkinginventory of Pu-238 in this country. However, if the goal of producing 1.5 – 2.0 kg of Pu-238 per year ismet, then that concern will be eased.America now has about 10 kg of older,aging Pu-238. The new Pu-238 can beblended with the old material producing the desired power density.
Over the next 18 months the Europa project team will beconducting a comprehensive trade study, comparing all viable energyoptions. The variables to be consideredinclude cost, risk, robustness, design compatibility, and implementationfeasibility. This effort will go a longway towards choosing the most appropriate system for the Clipper.
The Clipper team is very interested in the idea ofhosting several nanosats that would be deployed in the vicinity of Europa. This is contingent upon the use of the SpaceLaunch System (SLS) heavy-lifter. Onlythat rocket would provide the needed mass margin required if the Clipper is tocarry small satellite payload elements. However, if pursued, the working concept for the Clipper could providethe necessary housekeeping, deployment and radio-relay capabilities. In addition, thought is being given toutilizing an intermediate orbit insertion module that would allow severalnanosats to enter orbit around Europa.
If these nanosats can be accommodated, then the Europateam would like to cooperate with the growing American small-satcommunity. There is a desire to getfeedback from engineers and scientists on the best way to use theseprobes. There are a variety of optionsthat could use a single smallsat, or a network, with instruments such asmagnetometers or cameras. These probescould be orbiters, “Ranger-style” crash landers, or even hard landers thatmight operate for a short time after impact. Resource and cost constraints will be tight, but if thesemini-probes could fit, then the Europateam 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 fordevelopment of a Europa mission. Therehave been rumors that NASA’s operating plan for this year’s budget, due to bedelivered to Congress soon, will seek to spend that money on other agencyprojects. In response to such concerns,Senators Diane Feinstein and Barbara Boxer joined with Congressmen Adam Schiff and John Culberson insending aletter to NASA. They point out to NASA thatfunding levels for its science programs “will remain consistent with thestructure directed by Congress.” Essentially, they are reminding the agency that the Constitution givesthe power to say how the nation’s money is spent to the Congress. The Executive branch has limited leeway inhow it interprets Congress’ appropriations legislation.
How this will turn out is difficult to gauge. This is not the first time such a strugglehas occurred. For years, the Congressearmarked funds for development of a Solar Probe mission. Eventually, NASA got the message and awardeda new start for the Solar Probe Plus spacecraft. About 10 years ago, when NASA was trying toeliminate funding for the New Horizons Pluto probe, Congress specificallyearmarked funding for that mission, enabling it to proceed.More recently, afterthe Obama Administration canceled the Ares 5 heavy lift rocket in its FY 2011budget proposal, the Congress (especially the Senate) was not pleased. They directed NASA to pursue an alternate heavylifter, the SLS (Space Launch System), which is essentially a scaled-backversion of the Ares 5.That launcher is now on track for its first mission in2017.
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 vehiclerequirements and power system options could be funded, as well as studies todefine the loads on the Clipper during launch. Much will also depend on whether Congress again earmarks funds for aEuropa mission in the new FY 2014 budget. If it does, then the tug-of-war with the Administration will continuewith 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 thePlanetary Society's website for instructions on how to do so. You can also follow the latest information on the budget on Twitter at #fundPlanetary.
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What about a VASIMR subsidy of $200M to the first mission for each major planetoid system? It would be a good space platform for the GOP. What helps one mission helps the ice moon microbe searches. Ev en if we don't find much more, we might be able to improve the Drake Equation solution.
ReplyDeletePhil Phil Phil...what planet are you on?
DeleteVASIMR, being able to go fast or slow and alter the speed, on the same platform...it seems simple enough to work and with radiator costs should be economical. Risky robot missions are okay. VASIMR can't get humans to the nearest star, so shouldn't anger ET.
ReplyDeleteThis is an exciting mission that appears to be maturing in time to begin a new start in time for the 2021 launch.
ReplyDeleteIt is important to continue pressuring congress to impart their will on the administration to enable this mission by that launch date.
I remember when Pluto Express was canceled prompting the Planetary Society to become involved with a letter writing campaign. The result was the New Horizons mission. It too was funded at the objection of the administration at the time.
I want to correct an error that I made in the article. The actual time between flybys for the Europa Clipper will be more like 2 weeks, rather than the 4 weeks which I indicated in the article. Please excuse the mistake.
ReplyDeletePromising progress is being made it seems, good news, good article! Such a shame that the current priorities are all dictated by politics and pork to congressional districts. Imagine if the Planetary Science community had the final say in what missions get flown and how much they should cost. Scientists decided on what science should get funded! Gosh, I get chills up my spine just thinking about it! Maybe one day in an enlightened future age.
ReplyDeleteScientists DO decide what science they want to see funded--see the Decadal Survey link. It's my understanding this mission has not yet made the cut, perhaps partly because of the MMRTG/plutonium-shortage issue, partly because of the great cost of the previous iteration of this design, etc.
ReplyDeleteMentioning using SLS in the context of a planetary science mission is laughable--that would drive up the LAUNCH price by at least a billion, much less the development cost of all the additional science payloads. Not to mention the increased risk of tying your mission to an as-yet-undeveloped launch platform.
The fact that all the members of Congress upset about the $75 million represent districts where that money would be spent (JPL) makes this look much more like pork. Not that it doesn't have SOME merit--most pork does in fact have local merit. It's just not what would be chosen, considering the entire American interest (for example, other very good planetary exploration projects).
Scientists get the _final_ say on funding, when they provide all the funds. Since the entire American people provide the funds, the entire American people get a say in how they are spent. That is how it should be.
Anon -
ReplyDeleteThe Decadal Survey listed a Europa mission as its second priority large (Flagship-class) mission if the estimated cost could be cut in half. The Europa Clipper proposal would do that.
- Van
IMO, SLS is a bigger drain on NASA resources than JWST. When i was a kid, i thought that the USSR could use a couple Proton launches and beat us to the Moon. Maybe more than two would have been needed. These days, i think a bunch of Falcon 9 launches would get us to Mars.
ReplyDeleteAssuming that NASA doesn't get a budget, perhaps ESA could pick up the mission. And after all. Any life found on Europa would be Europeans.
This is cool!
ReplyDeletePhillip Huggan is still kicking around eh? Look me up.
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