Compelling Missions - Part 2

At the moment, news for future planetary missions is scarce as the U.S. waits for the results of the Decadal Survey.  (Other nations continue their own planning cycles, but news is scarce there, too.)  The Decadal Survey has published a list of 25 missions it is considering for the next decade.  I thought that I would take the next few blog entries to pick the five missions from that list that I find most compelling.  I'm under no illusion that I will persuade anyone (especially anyone who influences government spending).  However, I find a well argued (and I hope these will be) argument to help me form my own opinions.  Please provide your opinions, too, in the comments.  You can find the first installment in this series at Thoughts on the Most Compelling Proposed Planetary Mission.

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We live on a terrestrial planet, and one on which we are undertaking a grand experiment to see what happens when we dramatically increase the proportion of greenhouse gases in the atmosphere.  As a result, I think that furthering our understanding of Venus as a terrestrial planet and a greenhouse atmosphere carried to extremes is a compelling target for exploration in the next decade, and is for me, the target for the second most compelling mission for the coming decade.

The complete presentation by VEXAG on goals and objectives for exploring Venus can be found at http://www.spacepolicyonline.com/pages/images/stories/PSDS_IP1_Smrekar_VEXAG.pdf

Venus has been essentially ignored by NASA spacecraft for over 15 years (brief studies by spacecraft en route to other worlds have been the only exceptions).  The Europeans and Japanese, however, have sent orbiters to this world, and the Russians are planning a mission in the coming decade that may include a lander, orbiter, and balloon.  I believe that the U.S. should join the party in the coming decade.

The VEXAG analysis group chartered by NASA has put together an ambitious plan for a highly sophisticated Venus Flagship mission.  This mission would include a very capable orbiter, two balloon platforms, and two atmospheric probes/landers that would survive for many hours on the surface for detailed soil analysis.  Unfortunately, this mission would cost over $3B and requires technology development in several areas.  As a result, it is proposed as a mission for the 2020s and not the coming decade.

Venus Climate Flagship presentation

However, VEXAG members have also proposed a less capable mission, the Venus Climate Flagship, as a possible mission for this coming decade.  In the types of mission elements -- an orbiter, a single balloon, and a single lander -- it seems much like the full Venus Flagship proposal with the duplicate platforms removed.  However, the Climate Flagship would focus on using existing technology, resulting in less capable measurements but doing them as much as a decade sooner.  For example, the full Flagship mission would have brought samples into the landers for analyses that would take several hours to complete.  This would result in expensive sample handling mechanisms, an air lock, and the requirement to survive on the surface for almost a full Earth day.  The Climate Flagship proposal, on the other hand, would  use lasers to illuminate or melt the surface materials with the results analyzed via spectrometry through a porthole in less than an hour.  Similarly, the full Flagship proposal would have carried a radar on the orbiter that would have mapped the surface with resolutions as fine 5 m.  The Climate Flagship would map the surface at "10X" better resolution than the Magellan mission.  This would result in mapping resolutions of several 10s of meters.  (The exact figure depends on whether average or best Magellan resolution would be the baseline, and it's likely that the Climate Flagship proposal hasn't been studied in sufficient detail that the final resolution is known.)

There isn't a firm public estimate for the cost of the Climate Flagship.  A swag in the presentation describing the mission suggests a figure of ~$1.6B, but notes that your "mileage may vary."   However, with international cooperation, the NASA contribution might be substantially less.  Several nations are interested in missions to Venus.  Russia, for example, wants to fly its Venera-D lander this decade.  The Europeans have expressed interest in flying a balloon platform.  NASA might contribute an orbiter for data relay from landers and balloons, to remap portions of the surface with radar at higher resolutions, and carry cameras and imaging spectrometers to extend the atmospheric and surface studies of the European Venus Express and Japanese Akatsuki orbiters.  The RAVEN radar mission has been proposed for the current Discovery mission selection.  NASA also might contribute a lander if the SAGE mission is selected as the next New Frontiers mission.

The Decadal Survey has three flavors of landers and a "climate mission" (no details on what that might include) on its list of candidate missions it is considering.  If any of these missions are recommended, or if the SAGE lander is selected, NASA could participate a series of missions that would perform the science of the Climate Flagship.  (I think it is unlikely that the Decadal Survey would recommend the entire Climate Flagship mission, which as its cost become better understood, might be substantially more expensive than the swag quoted above.)  The Survey could recommend a single element -- the orbiter or a lander -- or a combination such as an orbiter and atmospheric probe.  It could also recommend no NASA-led mission, and instead recommend participation in the missions of others.  The Russians, Europeans, and Japanese could supply missions that meet the goals of the Climate Flagship.  China and India are also on the verge of being able to send probes to other planets and might also participate.

Except for the recent European and Japanese orbiters, our knowledge of Venus is based on missions with decades old technology.  The science questions motivating a return to Venus seem compelling to me.  I believe that NASA should make continued exploration -- preferably as part of an international effort -- a priority for the coming decade.

Landing in Hell

Air and Space magazine has an  article on the challenges of landing on the surface of Venus: Forbidden Planet.  It's even harder than I had thought.

Some Planetary Exploration Challenges

Some of the most interesting places in the solar system unfortunately present some daunting challenges to explore.  The intense radiation fields at Europa are probably the quintessential example of this problem.  With a decade of technology development to push radiation hardened engineering and a $3B+ budget, the proposed Jupiter Europa Orbiter will survive for an estimated 9 months or so after it enters orbit.  With that short of a lifetime and a whole world to explore, a fairly small percentage will be imaged at high resolution.  Eventual lander missions (if the findings of the orbiter warrant what would likely be a Flagship class mission) will be equally time pressed.

The hellishly hot surface of Venus provides its own challenge.  Landers and probes have lasted on the surface for an hour or so in the past.  The next generations of landers under consideration by NASA are targeting landed or near surface lifetimes of two-five hours.  These landers extend their life by including phase change materials within the landers.  Much as the ice in your ice chest does, these materials absorb heat as they change from solid to liquid.  Once the phase change is complete, however, the interior of the lander's temperature will rise as heat soaks through the shell.  The lead author of the Venus Mobile Explorer, Lori Glaze at the Goddard Spaceflight Center, explained to me in an e-mail the challenges faced by designers of Venus landers.  "The real challenge here is that if you want to keep the lander 'cool' you have to provide more phase change material, which has mass...At some point, you just can’t get this massive system off the ground at Earth."  As a result, Venus landers seemed destined to have just a few hours to perform their studies.  Long term studies can be done from balloons and orbiters, but long-term surface missions are beyond our capabilities.  (In theory, refrigeration units powered by plutonium 238 could resolve this problem.  However, these systems operate based on the difference in heat between the  plutonium and a thermocouple.  It's hard to "dump" the heat of the Pu-238 into an already hellish hot atmosphere to maintain the temperature difference.)

Titan has neither radiation fields nor heat to deal with.  It's atmosphere and surface are hellishly cold, but nuclear power systems do operate well in cold environments (easy to maintain that heat differnce).  This is a world that has a surface that in many ways may be most Earth-like of any body in the solar system with river valleys, seas and lakes, mountains, and a host of other interesting terrains.  Titan deserves the high resolution imagery that has advanced our understanding of the other Earth-like surface, Mars.  Unfortunately, the atmosphere of Titan and the dim light so far from the sun makes high resolution imaging from orbit almost impossible.  At Mars, orbiters can operate at 150 km altitude, while the atmosphere of Titan requires an altitude of 1500 km.  To see through the haze in a spectral window, a camera has to operate in near infrared bands.  The sun is dimmer at these wavelengths than at visible wavelengths and Saturn is far from the sun.  So to collect enough light to illuminate each pixel sufficiently for a clean image, a large mirror would be needed for high resolution imaging.  As a result of these limitations, the proposed Titan Flagship orbiter would have imaged the surface at 50 m per pixel where Mars is imaged at 30 cm per pixel.  (Radar instruments would have their resolution degraded by the increased altitude compared to what could be done at Venus or Mars.)  In addition, either optical or radar imaging system generate lots of data, which from the distance of Saturn require high powered communications systems.  High power communications systems require large power systems (and likely lots of Pu-238) leading to a large spacecraft.  Net result is that global, moderate resolution (~50 m) mapping of Titan may require a small Flagship-class (($1.5-2.0B?) missions.  In the meantime, in situ probes like the proposed TIME lake lander and the AVIATR plane offer ways to increase our knowledge of Titan at much more moderate costs.

Venus Tessera Lander Concept

Note: A previous version of this entry had the lander crashing onto the surface at 32 km/second -- that should have been 32 km/hour (or 9 m/second * 3600 seconds in an hour / 1000 m in a kilometer).

The Decadal Survey is exploring 25 mission options (at last report) for possible inclusion in the next decade of planetary missions.  (See the complete list of concepts in this blog entry.)  Each mission is initially scoped out by a team at one of NASA's centers or John Hopkin's Applied Physics Laboratory to understand the technical requirements.  An independent firm then assesses the likely costs of the mission.  The results of two concept studies have recently been published as part of the proceedings of the 7th International Planetary Probe Workshop.  In this entry, I'll describe the Venus Intrepid Tessera lander (VITAL) concept, and in the next entry I'll describe the Venus mobile explorer concept.

In many ways, the proposed tessera lander sounds much like the Venus SAGE lander currently in competition for the next New Frontiers mission slot.  While details probably differ between the two proposed missions, what we learn from the from the VITAL concept probably also applies to the SAGE proposal

Broadly speaking, the Venusian surface is covered by extensive plains (which make up the largest portion), large shield volcanoes, the tessera.  The latter are continent-sized regions of highly deformed, folded terrain.  The origin of the tessera is unknown, although there is speculation that they may represent the oldest terrain on Venus.  Measurement of the composition of the tessera is a high scientific priority.  (By contrast, the SAGE mission would go to recently identified terrain on the flanks of a volcano that may be among the youngest terrain on Venus.)

In the past, it's been assumed that the tessera were off limits to landers because the steep terrain would prevent a safe landing.  For this concept study, it was assumed that the slope might be as high as 30 degrees and that the lander might partially sit on a a large rock, creating further tilt.  To deal with these conditions, the probe's pressure vessle is mounted above a heavy outer ring that lowers the center of gravity to provide stability in case of extreme tilt of up to 72.7 degrees.  The lander uses drag plates to slow its descent through the dense lower atmosphere and hits the surface with a speed of 32 km/hour.  The thermal system is designed to allow the probe to function during the one hour descent and for two hours on the surface.

Example sampling area for the Raman/LIBS instruments and context imaging.

A decade ago, it was assumed that high quality compositional measurements of the Venus surface would require a complicated sampling mechanism that would deliver samples to instruments inside the probe through an airlock.  Today's mission concepts instead rely on lasers to illuminate or melt the surface materials with the results analyzed via spectrometry.  (The Mars Science Laboratory's ChemCam will use this technique at Mars.)  Using lasers and spectrometers greatly simplifies the probe design since only a window is needed to access the surface.  The laser will operate in two modes.  In a low power mode, it will illuminate the surface for analysis by a Raman spectrometer.  At higher power, the surface material is vaporized for laser induced breakdown spectrometry (LIBS) and the resulting plasma is spectrally analyzed.  Analysis is carried out across a 0.86 m row of spots each 0.3 mm approximately two meters from the lander.  A camera will take high resolution context images of the sampling area.

Another key goal of the mission is analysis of the atmospheric composition during the descent and on the surface.  A neutral mass spectrometer and a tunable laser spectrometer will perform these tasks.  Another set of instruments will measure the physical charateristics of the atmosphere such as temperature and pressure during the descent.

Two camera systems will provide context images of the landing site.  The descent camera will take a series of nested panchromatic images as the probe nears the surface.  The panoramic imager will take color and near infrared images of the surface in four directions to image a total of 240 degrees of the horizon.

Comparison to the SAGE proposal: Only limited information on the SAGE mission has been publicly released (see this blog entry for a summary).  At the summary level, the two missions seem very similar.  They would carry nearly identical instrument sets, although the SAGE mission apparently would have an arm that could dig a trench to allow the laser to shoot targets 3-10 cm below the surface.  The SAGE lander would be designed to survive for three hours on the surface.

The two missions are so similar that if the SAGE mission is selected for the next New Frontiers mission, many aspects of its design likely could be reused for a tessera mission.  No cost estimate is given for the VITAL proposal, but it would seem that if the SAGE mission can be flown within the cost cap of the New Frontiers mission (~$650M for the spacecraft and another ~$550M for other costs), then the VITAL mission could in a similar ballpark, and perhaps less if it can reuse substantial portions of the SAGE design.

You can read the VITAL paper at http://www.planetaryprobe.eu/proceedings/IPPW7%2520Proceedings/Papers/Session2/p385.pdf

Preparing for Japan's Akatsuki Venus Orbiter

Note: A crush of deadlines is largely behind me and I should be able to begin more regular postings again.

Japan is in final preparations for the May 18 launch of its Akatsuki orbiter.  This mission will use a innovative orbit to allow it to study the super rotation of Venus's atmosphere.  While Venus itself rotates at a brisk walking pace (6.5 km/hour or 4 miles/hour), the upper atmosphere rotates at 400 km/hour.  Current models of atmospheric circulation cannot explain the super rotation, suggesting that Venus can teach us some fundamental lessons about how atmospheres work.

The mission will study Venus in a number of wavelengths to study the atmosphere at different levels.  One band will see all the way to the surface and will be used to look for signs of active volcanism.

Akatsuki's five cameras will be optimized to probe phenomenon at different levels of the atmosphere and on the surface.  From Planet-C 2008 VEXAG update

The entire budget for the mission is just $280M (¥25.2 billion), although it's not clear what all is included in that cost beyond the spacecraft (launch vehicle? instruments? mission operations?).  Whatever the full burdened cost of the mission, it appears to be within the scope of what would fit within NASA's Discovery program.  This suggests that there are still interesting missions to the inner planets that would be relatively inexpensive.

As the launch date approaches, articles are beginning to appeal, and I posted a blog entry on the mission some time ago that includes some nice illustrations:

My blog: http://futureplanets.blogspot.com/2009/03/vexag-part-2-japanese-venus-climate.html

Journal Nature: http://www.nature.com/news/2010/100315/full/news.2010.126.html?s=news_rss

Aviation Week and Space Technology: http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/asd/2010/03/18/04.xml

Additional resources:

JAXA Planet-C website

Planet-C 2008 VEXAG update (with information on scientific goals)

Planet-C 2009 VEXAG update (mostly engineering and schedule) Large file!

Russian and European Venus Ambitions

The VEXAG meeting last October (presentations were posted just a couple of weeks ago) had presentations on Russia's Venera-D mission and ESA's possible European Venus Explorer (EVE).   Both are in the definition stage, with the Russian mission apparently funded and a European contribution under consideration.

The Venera-D mission at its most expansive would consist of a capable science orbiter, a lander, and several balloons, and one or more drop sondes that would profile the atmosphere (and take descent images?).  This would be a very sophisticated mission.  A group of U.S. scientists considered a mission of similar scope, the Venus Climate Flagship (or Flagship Lite), and estimated its cost to be $1.7B.  Russia ended its presentation with a slide that read, "We Invite Everybody for Cooperation," suggesting that it would like to share the expenses.

 From the Venera-D presentation.  This scenario appears to be the most ambitious of several configurations of the mission under consideration.

ESA is considering contributing to the mission by providing a balloon platform that would study the upper atmosphere for seven days.  Apparently Japan is considering a second balloon platform that would explore the mid atmosphere.  (It's hard to tell how serious ESA's consideration is.  The presentation to be originally from mid 2008.  EVE was not selected as a candidate for the next round of mission selection.  However, I've read that interest in contributing to Venera-D is growing in Europe.)

From the European Venus Explorer Exploration

Editorial Thoughts: The Venera-D mission is ambitious and would significantly advance our knowledge of Venus.  It's not clear how important international participation would be to see it fully implemented.  If Europe decides not to participate, the mission likely would be less ambitious.  It's not clear how Russia might reduce the scope of the mission.  It might drop the balloon element, or alternatively it might implement its own balloon platform and reduce the capabilities of the orbiter, for example.

NASA's role in the proposed Russia-ESA-JAXA mission apparently would be minor.  However, NASA could potentially make significant complimentary studies.  If the SAGE New Frontiers lander were to be selected, then the NASA and Russian landers could be sent to complimentary sites.  (It appears from the Venera-D presentation that the landers would have similar capabilities.)  Both missions would launch in 2016.

In addition, the Venera-D orbiter apparently would not carry a mapping radar instrument (although a sub-surface sounding radar might be carried).  A NASA mission such as the proposed RAVEN Discovery mission could fill this hole and re-image Venus' surface.

 Venus is currently being explored by Europe's Venus Express mission, and Japan will soon launch an orbiter to study the climate.  Combine these missions with Venera-D and possibly a NASA mission or two, and our knowledge of Venus could see the kind of explosion that has come from the series of Mars missions over the last decade and a half.

Resources:

Venera-D: http://www.lpi.usra.edu/vexag/oct2009/presentations/zasovaVeneraD.pdf

European Venus Explorer: http://www.lpi.usra.edu/vexag/oct2009/presentations/chassefiereEuropeanVenusExplorer.pdf

Venus Flagship Lite

VEXAG (Venus Exploration Analysis Group) was established by NASA "to identify scientific priorities and strategy for exploration of Venus."  Over the last two years, it has developed a robust, full fledged Venus flagship mission consisting of a highly capable orbiter, two balloon platforms, and two landers that would survive on the surface for a day and bring surface sample into the lander for analysis.

The mission also has been estimated to cost over $3B, putting it outside what NASA likely could afford in the coming decade given plans for an aggressive Mars program and the Jupiter Europa Orbiter.  A group of scientists has proposed a lite version of the mission call the Venus Climate Flagship.  Preliminary estimates put the mission at perhaps $1.7B.

To achieve those costs, the orbiter would have a less capable radar imager and the mission would fly a single balloon and lander.  The biggest change would be that the lander would no longer bring samples into the craft but would instead remotely study the surface chemistry through gamma ray spectrometry and Laser Induced Breakdown Spectroscopy (LIBS) with a Raman spectrometer.  With this technique, a laser would vaporize surface material and spectrometers would analyze the resulting gases.  (The Mars Science Laboratory will carry an LIBS instrument.  Lab experiments have shown that the technique should work on the surface of Venus.  Combining an LIBS instrument with a Raman spectrometer would enhance the analysis capabilities.) [The proposed lander sounds very much like the SAGE lander that is a candidate for the next New Frontiers mission.]

Editorial Thoughts: This proposal seems to retain the critical elements necessary to move Venus science forward.  I suspect that the $1.7B price tag would still be hard to fit in NASA's budget for the coming decade.  However, the capabilities proposed could be implemented by a consortium of space agencies.  Both ESA and Russia are pursuing joint programs, and the latter has announced plans for the Venera-D lander for mid decade.  I would like to see NASA dedicate $750M to a $1B to Venus exploration, with the specific mission chosen to maximize synergy with contributions by other agencies.

Resources:


Venus Flagship Lite Presentation

Venus Flagship Proposal

LIBS/Raman Spectroscopy for Venus

Venera-D

Proposed Discovery Venus Radar Mission

A few posts ago (http://futureplanets.blogspot.com/2009/10/venus-new-frontiers-radar-mapping.html), I wrote about proposed radar missions to remap Venus at higher resolution.  At that time, the idea of doing this within a New Frontiers budget (~$650M) was an eye opener for me.  I listened into part of the most recent VEXAG meeting, and learned of a Discovery mission (~$425M) that could remap Venus.

The principle investigator, Dr. Sharpton, sent me the following synopsis of the mission: "RAVEN, utilizes the latest in the RADARSAT lineage, extending back to 1996 (RADARSAT 1 launched in Nov. '95).  We can accomplish reconnaissance level mapping of Venus at 30-m/px and map about 25% of Venus each cycle (a venusian day).  Alternatively, we could map about 3% of the planet at 3-m resolution each cycle.  Obviously, we would want to have a combination of resolution modes and have overlap so that we can extract topography.  Topographic resolutions would be on the order of 20m vertical resolution and either 300-m postings (if using 30-m images) or 30-m postings (with 3-m images).  If InSAR turns out to be feasible (we believe it will), the vertical resolutions would drop to a meter or less."

Dr. Sharpton pointed me to an AGU abstract about the mission.  Since there is no easy way to link to AGU abstracts, I'm posting parts of it below.  You can search for it and other planetary abstracts athttp://agu-fm09.abstractcentral.com/planner

RAVEN – High-resolution Mapping of Venus within a Discovery Mission Budget
V. L. Sharpton1; R. R. Herrick1; F. Rogers2; S. Waterman3
1. University of Alaska Fairbanks, Fairbanks, AK, USA.
2. The Boeing Company, Huntington Beach, CA, USA.
3. Alliance Spacesystems, Boulder, CO, USA.

It has been more than 15 years since the Magellan mission mapped Venus with S-band synthetic aperture radar (SAR) images at ~100-m resolution. Advances in radar technology are such that current Earth-orbiting SAR instruments are capable of providing images at meter-scale resolution. RAVEN (RAdar at VENus) is a mission concept that utilizes the instrument developed for the RADARSAT Constellation Mission (RCM) to map Venus in an economical, highly capable, and reliable way. RCM relies on a C-band SAR that can be tuned to generate images at a wide variety of resolutions and swath widths, ranging from ScanSAR mode (broad swaths at 30-m resolution) to strip-map mode (resolutions as fine as 3 m), as well as a spotlight mode that can image patches at 1-m resolution. In particular, the high-resolution modes allow the landing sites of previous missions to be pinpointed and characterized... Our current estimates indicate that within an imaging cycle of one Venus day we can image 20-30 percent of the planet at 20–30-m resolution and several percent at 3-5 m resolution. These figures compare favorably to the coverage provided by recent imaging systems orbiting Mars. Our strategy calls for the first cycle of coverage to be devoted to imaging large geographic areas (e.g., Thetis Regio) at 20–30-m resolution with interleaved observation of pre-selected targets at high resolution. The second cycle will include additional imaging, but the focus will be repeat-pass coverage to obtain topography for a significant fraction of the first-cycle targets... All components of the spacecraft are expected to remain operational well beyond the nominal mission time, so global mapping at 10 m or better resolution during an extended mission is conceivable."

Japan's Planet-C/Akatsuki

Japan has just announced a name for its forthcoming 2010 Venus orbiter. The spacecraft will be called "Akatsuki," meaning Dawn.

This is a clever mission that will focus on the super rotation of Venus' atmosphere. While the solid body of Venus rotates very slowly (243 Earth days), the atmosphere itself rotates very quickly and circumnavigates the globe in 4 to 5 days. This mismatch has lots of scientific implications, which are nicely summarized on the science background tab of JAXA's Akatsuki web page (http://www.stp.isas.jaxa.jp/venus/E_sci.html).

Resources:

Mission webpage: http://www.stp.isas.jaxa.jp/venus/top_english.html

An earliers summary on this blog: http://futureplanets.blogspot.com/2009/03/vexag-part-2-japanese-venus-climate.html

Venus New Frontiers Radar Mapping Mission

A number of previous blogs have looked at possible NASA missions to explore Venus in the coming decade. (See this blog entry for links to the full set.) As discussed in those blogs, exploration of our sister world is hampered by the lack of funds for a Flagship (>$1B) mission given likely commitments of Flagship class missions to Mars and Jupiter-Europa. A number of missions ideas to study the planet from within the atmosphere or on the surface have been proposed. More recently, a proposal for a New Frontiers (~$650M) mission to continue the radar mapping of Venus has been published in a Decadal Survey White Paper.

Until this paper, I had been under the assumption that radar mapping missions that would meaningfully exceed the Magellan resolution (more on that below) would require a Flagship class mission. In fact, an orbiter estimated at over a $1B to do this has been proposed as part of a Flagship mission for the 2020s. This White Paper and an abstract for the upcoming Fall American Geophysical Union (AGU) meeting makes the case that a capable mission could be done in the New Frontiers program. (It's not clear whether the AGU abstract is discussing a Flagship or New Frontiers class mission, but the science rational remains the same either way. There doesn't appear to be any overlap in the authors of the White Paper and the AGU abstract, so different classes of missions may be being proposed.)

Venus has previously been mapped by NASA's Magellan spacecraft in the early 1990s. The resolutions were crude: 100 - 150 meters horizontal resolution in the mapping mode and 80 meter vertical topography measured every 8 - 10 km. Imaging radar mapped the terrain at 100 - 150 m. As the AGU abstract states, "Our state of knowledge about Venus is currently analogous to our knowledge of Mars in the post-Viking era, and a high-resolution imaging radar mission to Venus could revolutionize our understanding of Venus in the way that the Mars Global Surveyor mission did for Mars."

From http://www.lpi.usra.edu/decadal/vexag/venusGeoFinal.pdf

The crux of the proposed New Frontiers mission is to improve topographic resolution dramatically. Several schemes are discussed that would return different resolutions, presumably at different mission costs. One to two meter vertical resolution at 1 km spacings is given as an example of a reasonable implementation. A synthetic aperture radar (SAR) could also image selected targets at ~10 m for a few percent of the planet. (This is much the same strategy that the very high resolution cameras on Mars orbiters have employed to revolutionize our understanding of that world.) The paper also briefly discusses how the Venus Express instruments have mapped albedo differences in the surface of Venus in the near IR band, with the suggestion that enhanced mapping using this approach might be an additional study for this orbiter.

The White Paper gives a number of examples of how the enhanced radar mapping would advanced our understanding of Venus. I'll give a summary of one example here. Roughly 20% of Venus is covered by highland "continents" which are crossed by linear features known as tesseras. Currently, there are two theories about the origin of the highlands: They represent ancient crustal units, or they have been gradually built up over the history of Venus. The proposed mission would be able to determine if the surrounding plains intersect the tesseras at a sharp angle (indicating ancient origin for the tessaras) or a gradual angle (indicating gradual formation).

The AGU abstract gives a long summary of what might be learned. (I normally don't like to quote this much material from other websites, but the AGU abstracts can't be linked with simple URLs.) The abstract states, "Such a mission would substantially further our understanding of Venus by means of: (1) assessing the fundamental framework of the planet's geologic history (e.g., catastrophic change, slow evolution, uniformitarian) by imaging key stratigraphic contacts; (2) expanding the global framework of geomorphic unit types and relative stratigraphy with reconnaissance surveys of large geographic provinces; (3) directly detecting volcanic and tectonic activity through imaging of flows and fault-related activities (e.g., landslides) that occur between imaging passes; (4) monitoring present-day volcanic and tectonic activity with repeat-pass InSAR deformation studies; (5) constraining the nature of Venusian geologic volcanic and tectonic processes, and their relationship to mantle convective processes; (6) understanding the role of eolian processes in modifying the surface and the use of eolian features as stratigraphic markers (e.g., parabolic features) through detailed examination; (7) constraining Venusian impact processes, particularly the role of the atmosphere in the ejecta emplacement process; (8) constraining the processes responsible for the abrupt decrease in emissivity at high altitudes; (9) selecting landing sites for future missions; and (10) identifying past landers/probes to place them in geologic context."

Resources:

Past blog entries on Venus mission concepts

White Paper http://www.lpi.usra.edu/decadal/vexag/venusGeoFinal.pdf

AGU website http://agu-fm09.abstractcentral.com/login Search for abstract, P33A-1281, "The Rationale for a New High-resolution Imaging Radar Mission to Venus."

Options for Venus in the Coming Decade

In a previous blog entry, I discussed the quandaries that scientists focusing on the inner planets (ex Mars) face. That seems especially true for Venus science. First, Venus is just plain hard to study: the atmosphere is opaque except for a few narrow spectral bands and the surface is literally hell that requires advanced engineering to even reach, much less to operate on for several hours. In addition, many of the easy missions have been done. The basic radar mapping was completed in the 1990s. ESA's Venus Express and Japan's upcoming orbiter address the obvious atmospheric questions. The next steps in Venus exploration will require highly capable orbiters with advanced radars or difficult to design and test landers. The only easy missions left that I'm aware of are balloons to float in the upper atmosphere for long term chemical and dynamics studies. (In this, Venus is one of the easier planets to study since its dense atmosphere makes balloons extra buoyant, although there are the problems of designing the deployment system and surviving air laced with sulfuric acid.)

Despite these challenges, Venus is a world ripe for study because it is the only other large terrestrial planet in the solar system (Mars and Mercury being substantially smaller). Understanding why Venus ended up so different from Earth is likely to tell us a lot about how terrestrial worlds operate.

From http://www.spacepolicyonline.com/pages/images/stories/PSDS_IP1_Smrekar_VEXAG.pdf

The U.S. Venus science community is advocating a $3+B flagship mission for the 2020s that would involve a sophisticated orbiter, two landers that could survive for a day to make in-depth analysis of surface samples, and two balloons. The technology for this mission is not yet ready, and NASA is already committed to two to three flagship class missions for the coming decade between Mars and Jupiter-Europa. So for this decade, the request is for the technology development that would enable this mission to be ready for selection a decade hence.

In the meantime, the Venus science community would like to see one or more Discovery (~$450M) and New Frontiers (~$650M) missions sent to the evening star. In the former category, the community lists several concepts. (As an editorial aside, I'll note that a number of Venus Discovery missions have been proposed, but none selected. It's not clear what is necessary to break this track record.) In a previous blog entry, I discussed a number of New Frontiers mission concepts. One of those has been described in more detail in a White Paper, and I'll describe it in more detail in the next blog entry.

From http://www.spacepolicyonline.com/pages/images/stories/PSDS_IP1_Smrekar_VEXAG.pdf

Editorial Thoughts: For this blog entry, I'll close with a couple of observations. It appears that the VEXAG (an advisory group of Venus scientists) would prioritize a Venus atmospheric probe/lander as its highest New Frontiers priority, a balloon mission as its second highest priority, and a radar mapper as its third priority. All of these capabilities are included within the concept of Russia's Venera D mission for mid to late this decade. From what I can tell, Venera D is in the early planning stages and the Russian's are seeking international participation. One approach to NASA participation would be to provide one or more of the elements within these three concepts. I expect that Russia would prioritize a lander that builds on its history of Venus landers as something it will do in house. The French, with their expertise in balloons and experience with the Vega balloons, might contribute the balloon portion. NASA could contribute the orbiter. All partners could contribute instruments to each platform.

Should this kind of cooperation not be possible, then if NASA and Russia both build one or more landers, then Venus is a big and varied place. Eventually, we'll need a number of landers to understand its story.

Resources:

Venus VEXAG justification for exploring Venus and mission priorities (from a Decadal Survey meeting)

Venus Flagship mission concept (from a Decade Survey meeting)

Summary of New Frontiers mission concepts (from this blog)

Venus New Frontiers lander concept (from this blog)

Venus balloon concept and a Discovery mission concept (from this blog)

Venera -D Plans

The BBC has a long article on plans for Russia's Venera-D lander. The mission would include an orbiter, a lander that would survive on the surface for a day, multiple balloons, and perhaps even a free flying kite. Details on the mission apparently haven't been worked out. Russia recently hosted a conference inviting international participation in the mission. The current launch target is for 2016, but the French space agency CNES has said a delay until 2018 would be needed for it to participate. The article points out that the recent delay of the Phobos-Grunt mission could have a ripple effect, pushing Venera-D to 2018.

Editorial Thoughts: It's good to see Russia building on its Venus mission experience with a return to this planet. This is an ambitious plan. It's equivalent to at least a small flagship mission (~$1.2B) in NASA's planning.

The solar system is a large place. The bulk of NASA's planetary spending for the next decade is likely to go to Mars and Jupiter-Europa. ESA's planetary budget will largely go to its Mercury mission and (if approved) a Jupiter-Ganymede mission and possibly a series of joint Mars missions with NASA. Venus has been an ignored step child for too long. Venus Express broke a long drought in missions, and it will soon be joined by a Japanese orbiter. It's been 26 years since a probe (the Soviet Union's Venera 16) entered the atmosphere, though, to conduct in situ measurements.

I hope that Venera-D will be just the first of a series of Russian missions that will involve the world-wide Venus science community.

Resources

BBC article

Venera-D webpage

Venus New Frontiers Mission Concepts

The Venus Exploration Analysis Group (VEXAG), which provides inputs into NASA's Venus exploration plans, has posted a presentation on possible New Frontiers ($650M) missions to Venus. The same group has also proposed a >$3B flagship mission to the same world. That mission would be composed of an orbiter/data relay that would image small portions of the planet with radar at ~5 m resolution. (The strategy is similar to the HiRise camera used at Mars, which photographs a small fraction of that globe at high resolution.) Two balloons would conduct long term atmospheric measurements while two landers would survive at least a day to make detailed chemical measurements of the surface. This presentation will serve as input into setting priorities for planetary exploration in the Decadal Survey.

The first part of the presentation lays out the case for exploring Venus. It's a long list, but key argument is that Venus is the third example of a terrestrial planet with an atmosphere. While Mars has received considerable attention in the last 15 years, only the Venus Express mission has conducted in-depth studies of that world in the same time frame. Studying Venus provides a contrast that can help us understand the role of early planet evolution, plate tectonics, and atmospheric change on the evolution of terrestrial worlds. The three primary questions that underlie the goals for Venus exploration are:

• "How did Venus originate and evolve, and what are the implications for the characteristic lifetimes and conditions of habitable environments on Venus and similar extrasolar systems?"
• "What are the processes that have shaped and still shape the planet?"
• "What does Venus tell us about the fate of Earth's environment?"

The missions proposed in the presentation are pieces of the Flagship proposal. They are:

Venus In-Situ Explorer (VISE) that would be a combination atmospheric probe to measure atmospheric composition to the from the upper atmosphere to the surface and then measure surface composition. The focus of this mission would be to understand the accretion of terrestrial planets including whether Venus had an ocean, how the atmosphere has evolved, and the type of volcanism. Instruments would include, "cameras, spectrometers, NMS/GS [neutral mass spectrometer/gas chromatograph], meteorology package," and instruments to, "determine mineralogy, elemental composition, and surface texture." While the presentation is silent on the topic, this would presumably be a short-lived lander that would function for only one to a few hours on the surface.

Long-lived balloons with drop sondes and a data relay orbiter to address the question of how the planet's atmosphere works. Apparently multiple balloons would be used that would float at different altitudes and each carry a gas chromatograph/mass spectrometer, radio tracking, an atmospheric structure instrument, a nephelometer to measure cloud particles, a lightening detector, and a TLS (tunable laser spectrometer?). Drop sondes would be released from the balloons to drop to the surface and would carry one or more instruments for trace gas measurements, imaging the surface, and measuring pressure and temperature. (No details on how many drop sondes per balloon or whether they would function all the way down to impact on the surface.) The orbiter would carry a near infrared imager and topographic radar (which presumably would measure only surface elevations and not image the planet).

Venus Global Surveyor orbiter that would focus on the evolution of the crust, shallow interior, and search for active volcanism from a circular orbit. The instrument list includes a radar altimeter, imaging radar, and a near infrared imaging spectrometer. No information is given on the potential resolution of the radar images, although there would presumably be more detailed than Magellan's.

Venus atmospheric sample return that would focus on the origin and evolution of the atmosphere. The atmospheric sample would be collected from an altitude of 110 km during a brief run through the atmosphere. (A similar mission was proposed for Mars several years ago.) Earth-based instruments would be able to make much more detailed measurements of atmospheric composition than could be done from an in-situ instrument that must survive the rigors of launch and atmospheric entry while meeting stringent weight, size, and power limitations.

Next Generation Geochemical Lander would focus on surface composition and gasses trapped in the surface material to study how the crust formed and the chemical interaction of the atmosphere and surface. The lander would be targeted to a site expected to have vesicular basalt (so trapped gasses can be examined) and would survive for 24 hours to allow detailed chemical analysis. The choice of sampling site(s) near the lander would be made by operators on Earth, so this wouldn't be a blind sample grab. Instruments would include a 10 cm depth drill, mass spectrometer, x-ray diffraction, x-ray fluorescence, cameras for descent and surface panoramas, and a microscopic camera.

Geophysical Lander to study the interior structure and thermal evolution. Details on this idea are limited (and it is new to me, so perhaps it is a recent concept still being fleshed out). Instruments would include a magnetometer, a corner cube reflector (to allow precise location determination by radar, although I don't know if this would be from an orbiter or from Earth), electromagnetic sounding (presumably to detect subsurface layering), heat flow (I was under the impression that heat flow measurements are both hard (they've only been done for the Earth and moon) and require long times, so I'm not sure what approach would be used), and panoramic camera, and a gamma ray spectrometer (presumably for bulk surface composition measurements).



Editorial Thoughts: Two immediate issues come to mind for me. The first is how many of these missions would really fit within a $650M New Frontiers budget. The VISE and long-lived balloons have both been proposed for previous New Frontiers competitions, so they seem like the most likely candidates. I sat in on a VEXAG-sponsored meeting last December and the comments there were that the Flagship orbiter with high resolution imaging and the long-lived (24 hours (this is Venus, so long-lived is relative!)) landers would cost approximately a $1B each. Perhaps the orbiter listed here is less capable and flying just a single lander (instead of the two planned for the Flagship mission) reduces costs sufficiently. I have no idea how difficult the other two missions would be to conduct.

The second issue is that this is a long list of missions. Realistically, only one -- and at the outside, two -- would likely fly in the next decade. What is the priority for these missions? From the last Decadal Survey (completed in 2003), VISE was the highest priority (and it still hasn't flown). What is the priority now? I hope that VEXAG will make this clear as this Decadal Survey progresses over the next few months. One factor that could change the priorities is Russia's plans to send Venera-D to Venus in 2016 with an orbiter to conduct radar imaging at higher resolutions than Magellan did and to send a short-lived lander to the surface. Apparently this will be the first in a series of new Venus missions for Russia.

If Russia is successful and shares the data with the world-wide scientific community, then the urgency for NASA to prioritize Venus might be less. (Or perhaps there are still key holes that NASA could fill, hopefully in cooperation with Russia.) The solar system is a big place, and it would be easy to argue for making Mars, Venus, Jupiter/Europa, or Titan/Enceladus the focus of any single space agency's priorities. Perhaps Russia could focus on Venus and NASA and ESA on Mars and possibly Jupiter/Europa.

Resources:

VEXAG presentation on New Frontiers mission goals and concepts: http://www.lpi.usra.edu/decadal/vexag/InnerPlanetsPanel08272009_v3.pdf

Summary of Venara D: http://en.wikipedia.org/wiki/Venera-D

VEXAG Flagship proposal: http://vfm.jpl.nasa.gov/

Venus Flagship Proposal

Bruce Moomaw has kindly provided a summary of the new proposed Venus Flagship meeting:

NASA's Venus Science and Technology Definition Team -- chartered by NASA to design an ambitious $2 to $3 billion flagship mission to the hot planet -- has just issued an extremely detailed report:
http://vfm.jpl.nasa.gov/files/Venus+Flagship+Mission+Study+090501-compressed.pdf .
http://vfm.jpl.nasa.gov/ - website summary

It's extremely unlikely that Congress or any reasonably near-future administration would back such a costly mission; but (unlike the design for the Europa Flagship mission) it's broken up into individually built and launched spacecraft which could also be descoped scientifically, with the separate pieces being launched as New Frontiers or perhaps even Discovery-class missions.

The mission as designed involves two Atlas 5 launches within 6 months of each other. The first is an orbiter which will radar-map Venus at two orders of magnitude better than the Magellan craft did, as well as carrying out other scientific studies and serving as a com relay for the separate craft that make up the second launch. That second launch, in turn, would be a carrier spacecraft delivering two landers and two smaller balloon spacecraft to Venus, with the landers working for 5 hours after touchdown and the balloons being blown around Venus at cloud-level altitudes (55 km) about seven times over the course of a month before their batteries fail.

This mission -- unlike previous concepts for an advanced and comprehensive Venus mission -- doesn't utilize revolutionary new electronics that could operate at Venus temperatures, or an RTG-powered refrigeration unit. Thus the short lifetimes of its landers, which cannot carry out seismic or long-term weather observations from the surface and would instead focus on analyzing surface composition. Even such a short-lived mission, however, if properly instrumented, could provide massively new scientific information on Venus, whose savage environment has up to now greatly curtailed its exploration even given the Soviet Union's long-time interest in sending surface landers to it.

One of the landers would land on the "Alpha Regio" -- one of the patches of highly fractured "tessera terrain" which are scattered around Venus and (judging from their somewhat heavier cratering) may very well be remnants of its original crust which survived the "catastrophic resurfacing" which seems to have struck the planet about 3 billion years ago and flooded most of its surface with basalt lava flows at that time. It's possible -- although far from certain -- that the tesserae are actually the surviving remnants of granite continents that formed on Venus during its earliest days when it may still have had a liquid-water ocean, which seems to be required for granite to form. Thus simply analyzing their rocky composition might confirm one of the most intriguing speculations about Venus. The other lander would touch down on a lava-flow region similar in some ways to the basalt plains that all the previous Soviet surface-analyzing landers landed on and analyzed; but it would analyze it in much greater detail -- in particular, the landers would use X-ray diffractometers and infrared spectrometers to identify actual minerals on the surface instead of just measuring total percentages of elements as the Soviets did.

Although the probe carrier spacecraft would be launched six months before the Orbiter, it would actually arrive at Venus four months later, giving the Orbiter time to set itself up in an elongated Venus orbit to perform its radio-relay duties. The probe carrier would drop two entry vehicles off at Venus, with each one inflating a 7-meter balloon on the way down that would be released along with its small instrumented gondola to bob around in the cloud level, carrying out detailed studies of the composition, cloud structure and wind patterns of Venus' atmosphere as the planet's high-speed cloud-level "superrotation" winds blow the balloons around the planet once every four days. (Again, even given the number of American, Soviet and European spacecraft dispatched to Venus, the remaining scientific mysteries about its atmosphere are numerous, and they may have some relevance to climate-change studies of Earth's atmosphere. These include measurements of the trace components in both its atmosphere and cloud droplets, as well as the question of just what drives the atmosphere's high-speed rotation around the slowly turning planet.)

The landers would then proceed all the way down to the surface -- taking photos during the last few km of their descent -- and, after landing, they would drill up two samples of the surface each and stuff the samples through a tiny airlock into their instrumented interiors, as well as obtaining more photos and infrared spectra of the surrounding landscape during their 5-hour surface lifetimes.

After spending a month relaying the data from the balloons back to Earth, the Orbiter would aerobrake itself down (as Magellan finally did) into a low circular orbit and focus on its own scientific instruments -- including both more studies of the atmosphere (to help put the balloon measurements into context) and very detailed radar mapping with a two-antenna "interferometric synthetic-aperture radar" system using fully 2 to 3 kilowatts of power to provide images with a 50-meter resolution (and only 6 meters in some chosen areas). It would spend at least two years making these studies.

This summary doesn't list all the scientific instruments carried by each of the three types of exploratory spacecraft. Suffice it to say that -- even given the short lifetimes of the insulated landers -- the mission would be a quantum leap in the exploration of Venus. It would, however, be an expensive quantum leap. Despite the fact that it was designed not to require any revolutionary high-temperature electronics or high-powered refrigeration systems, the cost estimate runs between $2.7 and 3.8 billion -- making this a mission that Congress would be reluctant to fund any time in the reasonably near future. In my next installment, I'll examine how the Venus Flagship Mission might be chopped into separate, lower-cost pieces.

Editorial notes: I had a chance to sit in on a briefing of scientists on this proposal last December at the American Geophysical Union meeting. Bruce's summary prompted me to go back through my notes. A key element of the proposal was the simultaneous operation of the mission elements -- a highly capable orbiter for relay, simultaneous balloon and descent measurements. While the elements could be flown separately, the Venus science community clearly is hoping that their turn for a big piece of the planetary budget (after Mars and Jupiter-Europa) is coming.

A key requirement of the lander is the multi-hour lifetime that allows long integration times for the surface composition samples. This longer life is a key difference between these landers and that proposed at one time for the New Frontiers mission series. The difference in lifetimes would add $250M to the cost of the landers.

The radar imager proposed would be an extremely complex and expensive instrument. My notes list $200M, but it isn't clear whether this was just for the radar or for all the orbiter's instruments. I remember a price tag of ~$1B for the orbiter element of this mission and my notes say that the radar measurements probably cannot be done within a New Frontiers ($650M) budget.

One melancholy note: The proposal is to fly this mission in the 2020s. As was stated in the meeting (which had middle aged participants for the most part), this will be a mission for our children.

As soon as Bruce writes his follow up piece, I'll post it.

ASRG Missions: Venus Balloon

In a previous post, I discussed the a new generation of plutonium-powered power sources for future planetary missions. NASA is funding mission studies to determine whether or not lightweight radioisotope power sources would enable one or more low cost (Discovery class, or ~$450M) missions.

Kevin Baines of JPL has proposed a number of Venus Discovery missions including an orbiter to study the atmosphere (whose goals were more than fulfilled by the Venus Express mission), and two balloon missions. The earlier balloon proposal, the VEVA (Venus Exploration of Volcanoes and Atmosphere) would have had been the most complex with a number of elements, while the second would have had just two balloon platforms. At least twice, to my recolleciton, Baines has been a finalist in the Discovery selection process, and both times other missions were selected.

The previous proposals suffered the limiation of being battery powered (solar cells are of questionable to no use within Venus' clouded atmosphere). Baines' current proposal would use an ASRG power source to enable much longer operation (a month instead of hours to days) and over ten times the data return. Baines and his collaborator, Tibor Balint of JPL, were kind enough to send me a copy of a poster on the mission they presented at a recent conference, and I've reproduced the abstract here:

"In situ exploration of Venus is expected to answer high priority
science questions about the planet’s origin, evolution,
chemistry, and dynamics as identified in the NRC Decadal
Survey and in the VEXAG White Paper. Furthermore,
exploration of the polar regions of Venus is key to
understanding its climate and global circulation, as well as
providing insight into the circulation, chemistry, and
climatological processes on Earth. In this paper we discuss
our proposed Nuclear Polar VALOR mission, which would
target one of the polar regions of Venus, while building on
design heritage from the Discovery class VALOR concept,
proposed in 2004 and 2006. Riding the strong zonal winds at
55 km altitude and drifting poleward from mid-latitude this
balloon-borne aerial science station (aerostat) would
circumnavigate the planet multiple times over its one-month
operation, extensively investigating polar dynamics,
meteorology, and chemistry. Rising and descending over 1
km altitude in planetary waves – similar to the two VEGA
balloons in 1985 – onboard instrumentation would accurately
and constantly sample and measure other meteorological and
chemical parameters, such as atmospheric temperature and
pressure, cloud particle sizes and their local column
abundances, the vertical wind component, and the chemical
composition of cloud-forming trace gases. As well, when
viewed with terrestrial radio telescopes on the Earth-facing
side of Venus, both zonal and meridional winds would be
measured to high accuracy (better than 10 cm/sec averaged
over an hour). Due to three factors: the lack of sunlight near
the poles; severe limitations on the floating mass-fraction
available for a power source; and the science requirements for
intensive and continuous measurements of the balloon’s
environment and movement, a long-duration polar balloon
mission would require a long-lived internal power source in a
relatively lightweight package. For our concept we assumed
an Advanced Stirling Radioisotope Generator (ASRG). In
return, this mission would provide two orders of magnitude
more science data than expected from the original batterypowered
VALOR concept, and could reduce measurement
uncertainties by a factor of five. In addition to the science
return, the secondary objective of this proposed mission would
be to space qualify ASRGs through all mission phases and in
various operating environments. Lifetime testing would be
demonstrated using a second ASRG on the carrier that would
keep operating after the in-situ element is delivered. Based on
the results of this and another eight ongoing NASA funded
studies, NASA will make a decision about the inclusion of
ASRGs in the next Discovery AO, due in the summer of 2009."