Retreat From Mars?

"Without more funding and a firm, renewed commitment to Mars from NASA, "MSL will be the last thing we put down on the ground and MAVEN will be the last orbiter we do unless it comes from the Discovery program," said Jim Green, director of NASA's planetary science division."
Will NASA retreat from Mars after string of successes?
- Spaceflight Now

As I write this, the latest news on the Phobos-Grunt spacecraft is that it remains in orbit, apparently operational, but has not communicated with Earth in the last several days.  In the meantime, the Curiosity Mars Science Laboratory launched successfully and its flight so far has been boringly good.

My hopes are with the Russian engineers and scientists as they attempt to re-establish control of the spacecraft and find another target, potentially an asteroid, now that that mission's window to begin the flight to Mars apparently has closed.

Looking to future missions, the news is also mixed.  The only committed and funded mission to follow Curiosity to Mars currently is MAVEN, which is a Discovery-class orbiter to study the Martian upper atmosphere.  (MAVEN was the last mission in the now defunct Mars Scout program which also flew the Phoenix lander.)  The European Space Agency (ESA) and NASA both have hopes of flying a joint orbiter for 2016 and a joint rover for 2018.  Neither has the money currently committed to do the missions alone and neither currently has the committed funding to implement their planned portions.

However, there are encouraging signs of progress.

First a brief recap on the 2016 and 2018 proposals.  The 2016 mission would fly an orbiter that would carry instruments to study the Martian atmosphere and continue high resolution imaging of the surface.  Most critically, this orbiter would also be in place to act as a communications relay for a proposed 2018 rover.  The rover would carry a highly sophisticated ESA instrument suite to examine Mars for signs of life and habitability and NASA equipment to collect and cache samples for eventual return to Earth.  The 2016 mission would also carry an ESA demonstration lander that would function for up to four days on the surface.

A new option is on the table now, that could be an exciting enhancement to the joint program.  When NASA was unable to commit a launch vehicle for the 2016 orbiter, ESA asked Russia to contribute a launcher in return to having its instruments also fly.  The initial reaction reportedly was, nyet!, but recent news sounds more encouraging.  Scientists at Russia's Space Research Institute, IKI, have put together proposals for a minimum and maximum level of participation.  For the minimum proposal, Russia would contribute unspecified instruments for the orbiter that have previously flown on other Russian Earth and planetary missions.  The maximum proposal would add two to four Russian landers to replace the currently planned ESA demonstration lander.  At least one version each of two different landers would fly, and if technical issues could be worked out, two copies of each version might fly.  The first version would be a penetrator that would carry a weather station, and would be similar to the landers jointly developed with the Finns.  The second would be a soft lander that would open up, petal style once on the surface.  The proposed instrument is a French seismometer (which I believe is also the seismometer planned for the Mars GEMS lander in the current NASA Discovery competition).  Power sources aren't mentioned in the news articles, but the implication is that both landers would be long-lived.  Russia reportedly has at least one flight ready copy of each lander left as spares from its Mars-96 mission that experienced a launch failure.

There is no mentioned whether or not the Russian orbiter instruments would be in addition to the currently planned instruments (most supplied by NASA and one supplied by ESA) or would replace one or more of the planned instruments.

Russian scientists are currently in discussions both with ESA and with the Russian political system to secure approval and funding.

On the European front, ESA currently has 850M of the 1B Euros committed from its member nations that it needs to conduct its portion of the currently planned 2016 and 2018 missions.  In the meantime, European financial problems are causing ESA to plan to reduce costs and Europe to debate whether to reduce funding for its flagship Earth observation program (GMES).  I believe that GMES is a European Union program, rather than an ESA program.  Either way, the news speaks to a tightening of budgets for space programs by European governments.  Dropping the ESA lander from the 2016 mission would help reduce the gap between committed Euros for the Mars program and what is needed.

Then there is the American side, which is possibly the most confusing.  At the moment, the President's Office of Management and Budget (OMB) is refusing to allow NASA to commit funds from future budgets to ESA to support the Mars program.  At the same same time, Congress has just passed NASA's Fiscal Year 2012 budget with full funding for the Mars program and a rather pointed requirement that NASA implement the recently completed Decadal Survey that included the Mars program as its highest priority planetary Flagship mission.  (If this seems crazy, welcome to our system of separate powers in government.  Congress can set direction only for the current year's budget; commitments for spending from future budgets (eventually to be ratified or modified by Congress one year at a time) must be approved by OMB.)

The good news is that NASA has funding to support the development of its instruments for the 2016 orbiter and the 2018 mission remains a priority -- for the remainder of FY12.  OMB has promised to make clear its position on NASA's ability to make future commitments to enable ESA to continue to count on NASA for 2016 and 2018 in its FY13 budget to be revealed in February.  Reportedly, the responsible OMB official has stated that a key concern is that going forward with the 2018 mission is just the down payment on a program of missions to return samples that could cost $8.5B.

Editorial ThoughtsE: The 2016 and 2018 missions are both excellent missions, and I hope to see them fly.  Even without NASA's equipment to collect and cache samples, the 2018 rover mission should fly.  All of this political maneuvering is frustrating as hell, and my hat is off to the NASA officials who are handling this situation as the professionals that they are.

The addition of Russian instruments and landers would only make the 2016 mission more exciting assuming all the technical and managerial issues can be worked out without unacceptable additions to technical, schedule, or budget risk.

I can understand, however, OMB's position.  It is looking at a suite of programs for human spaceflight and the over budget James Webb Space Telescope that it and Congress have agreed are NASA's top priorities and for which the current NASA funding likely is insufficient.  The American budget problems are likely to reduce NASA's funding or at very best keep it flat.  Commitments made in haste may be undone later.

I have come to wonder whether the American political process will approve the start of a Mars sample return program without the discovery of strong signs of life or at least habitability on Mars.  If Curiosity or another mission (such as the 2018 rover) finds complex hydrocarbons consistent with life, for example, I think support for the sample return will be strong.  Without it, it has proven difficult over the past twenty years to convince the political process that bringing back "a bunch of rocks" justifies the expense of many billions of dollars.

So, to address the question in the title of this post, I don't yet know if this will be a retreat from Mars.  The fact that Congress held a hearing on NASA's Mars program budget impasse and required continued spending on it for this year is an encouraging sign.  The scientific community remains committed to supporting the program.  In normal times, I would be optimistic that these problems would be worked out.  Given the budget problems and politics in the US, Europe, and Russia, I am only hopeful that they will be.

Resources:

Russia's proposals for the 2016 mission article at Russian Space Web and a shortened version at the BBC website.

Aviation Week article on NASA budget situation regarding its Mars program, U.S., Europe, Russia To Talk Mars Mission

"...land at Thera, and you might be able to taste Europa's ocean!"

Artist's conception of a lake beneath a chaos region on Europa but above the global ocean.

Courtesy of University of Texas at Austin

"So for all of you people who were secretly hoping the thin-icers would win the argument because you are hoping to see humans send a probe onto Europa's surface and maybe even drill through the ice to its ocean, you have a consolation prize... land at Thera [Macula], and you might be able to taste Europa's ocean!"

Emily Lakdawalla, 

Is Europa's ice thin or thick? At chaos terrain, it's both!, 

The Planetary Society Blog   

As many of you probably know by now, a paper to be published in the journal Nature next week postulates a new theory for the chaos terrain on Europa.  As the nomenclature implies, 'chaos terrains' are jumbled areas on the surface of Europa that appear to be huge blocks of ice scattered across the surface with rifts between them.  This new theory suggests that these areas are caused by the formation of large subsurface lakes beneath the surface.  Initially, the formation of the lake reduces volume beneath the surface (water fills less volume than ice), causing the surface to crack and collapse.  When the lake eventually refreezes, the volume expands pushing the shattered surface up into a dome.  The surface of a chaos region, then, is a mixture of surface ice and water that upwelled from the subterranean lake.  Current imaging suggests that up to 50% of Europa's surface represents chaos terrains ranging from fresh to old.  One area that looks to represent chaos terrain with an active lake with greater volume than all the great lakes of North America combined is Thera Macula.


These chaos regions appear to represent the best locations to sample the ocean that underlies the surface of ice at Europa.  Beneath that ocean lies a rocky core, which is tidally flexed and heated by the gravitational pull of Jupiter.  That puts the ocean in contact with minerals and energy (think of the hot vent plumes beneath the Earth's oceans) that could provide the mixture needed to support life.  In this respect, Europa may be unique among the icy worlds believed to have subterranean oceans.  On Ganymede and Titan, by contrast, the oceans would be sandwiched between layers of ice, removing the oceans from the minerals and heat needed to support life.  (A lively debate continues as to whether or not Enceladus' plumes come from an ocean in contact with the rocky core.)


The NASA press site has a summary of the findings and nice illustrations.  I recommend reading Emily's write up even if you've read this or other press accounts.  She does a nice job expanding on the press release.  


Fortuitously, NASA has also asked a team of scientists and engineers to develop the concept for a minimalistic Europa lander mission.  This follows the definition of minimalistic mission concepts for an Europa orbiter and a multi-flyby mission (see my post, Europa - New Options) that would each cost approximately $1.5B (not including launch).  The hope is that the lander mission will also cost ~$1.5B, but that's not a requirement.


Since the team has yet to formulate it's plan, all details are subject to change.  However, I'll summarize the presentations giving the current thinking captured in the kick off meeting (presentations posted here).  

Europa's surface roughness presents a landing challenge.

Except as noted, all illustrations are from the Europa Lander Forum presentations posted at http://www.lpi.usra.edu/opag/Oct2011/lander_forum_presentations/

The surface of Europa at all scales at which it has been imaged (the best images come from the Galileo mission) looks forbidding to land on.  Jumbled surfaces of ice appear everywhere, especially in the now high priority chaos regions.  For this reason, the current concept includes two landers in the hope that one would make it to the surface intact.  The landers would descend under rocket power, much like the Mars Phoenix lander.  An instrument (lidar) would scan the surface to find the location with the smoothest surface, and the lander would steer itself to land there.

Radiation levels on the trailing side of Europa.  The red line shows the boundary between the high radiation trailing hemisphere (left) and the low radiation leading hemisphere (right).

The jagged surface presents one problem.  The radiation at Europa presents another problem.  A radiation field surrounds Jupiter that becomes more intense closer to the planet.  Europa lies fairly deep within this field and an unshielded spacecraft either would have a short life (~1 month) or would require expensive radiation hardened electronics and a price tag well above $1.5B.  Here, the current concept proposes to use Europa itself as a radiation shield.

Cumulative radiation dose for a spacecraft in orbit around Europa (blue line) and a lander on the leading hemisphere of Europa (red line)

The major moons of Jupiter and its radiation field both rotate counter clockwise when viewed from above Jupiter's north pole.  The radiation field is trapped within Jupiter's magnetic field and so rotates at the same speed as the planet, every 9.9 hours.  Europa, however, orbits at the more leisurely pace once every three and a half Earth days.  As a result, the radiation field slams into the trailing hemisphere of Europa full on, but not its leading side. (Remember that Europa is tidally locked with Jupiter and keeps the same face to the planet throughout its orbit as our own moon does with the Earth.  As a result, the same face of the moon is always the leading hemisphere, and the opposite face the trailing hemisphere.)   On the other hand, the leading hemisphere experiences just a fraction of the radiation of the radiation hitting the trailing hemisphere.  (Thera Marcula lies near the edge between the two hemispheres just on the leading hemisphere side.  )

Concept for the orbiter and two lander stack

The landers would be carried into Europa orbit by a carrier spacecraft.  After entering Jupiter orbit, the combined spacecraft would perform sixteen Ganymede and Callisto flybys before entering Europa orbit.  (The presentation doesn't specify how many Europa flybys would be performed, although the goal would be to get into Europa orbit as quickly as possible to minimize time in the high radiation fields.)  After a few orbits around Europa, the first lander would be released with the second lander released at the same time or a few orbits later.  Once on the surface, the landers might either communicate directly with Earth or use the orbiting carrier craft for data relay.

Concept for the lander

Many details of the mission are still to be worked out.  For example the landers might either be battery powered if they are to last just a few days or carry nuclear ASRG power sources to enable life for several weeks until radiation kills the electronics.  The concept images in the presentation show ASRG's on the carrier spacecraft and on each lander.


The minimum instrument compliment for the landers is one of the decisions to be made by the lander concept team.  The slides suggest that the minimum might a mass spectrometer to measure the surface composition, a seismometer to examine the subsurface structure, and a suite of physical state instruments to measure temperature, radiation, light levels, and acceleration (presumably from surface flexing).  An enhanced instrument suite might have more comprehensive chemistry and geophysical instruments as well as cameras.  A likely key decision for the concept team would be how the samples would be acquired for composition measurements -- arm and scoop, drill, ?

Artist's concept of landing within a chaos region on Europa

Editorial Thoughts:  Given the recent study suggesting ideal landing spots on Europa -- fresh chaos regions -- the idea of a landed mission as our next Europa mission becomes very attractive; hell, it is exciting.  To temper that excitement, however, remember that a simple orbiter with a few instruments or a simple multi-flyby spacecraft with a few instruments would each cost ~$1.5B.  This mission would require an orbiter plus two landers that each would have the approximate sophistication of the Mars Phoenix lander.  That feels tight for a $1.5B budget.


There is also the practical problem that most of Europa has not been imaged or spectrally mapped to determine surface composition at high resolution.  When we had a similar situation with Mars and the MER rovers, we selected a landing site for Spirit that looked at moderate resolution to be a lake bed but turned out to be a lava flow bed.  (Fortunately, Spirit reached hills above the lava flow that retained clear evidence for past watery environments.)  Unfortunately, our highest resolution imaging of Europa is on the trailing hemisphere, leaving the highly desirable low radiation leading hemisphere terra fuzzy.


So, should the carrier spacecraft include a high resolution camera and spectrometer to image Europa during flybys prior to orbit insertion to select the best landing locations?  Orbital mechanics plays a dirty trick on us here.  Galileo imaged the trailing hemisphere at highest resolution because the natural location to encounter Europa at around the 3 o'clock position (again, looking down from above the northern hemisphere of the Jovian system).  At that position, the trailing hemisphere is fully illuminated and the desirable leading hemisphere is in darkness.  A mission that tries to get into Europa orbit as quickly as possible would face a similar problem.  Gravity assists can be used to walk the location of Europa encounters around the clock (so to speak) but at the cost of a longer mission and higher operation costs.


Once the carrier craft is in orbit, should it carry any instruments?  For a truly minimalistic mission, the simple answer is no.  However, much of the cost of the orbital science is getting to Europa and orbiting for a few days to a few weeks.  The orbiter's radio system would allow gravity mapping, a high priority measurement to study the interior of the moon.  I suspect that the temptation to carry at least a camera and a magnetometer (which enables inferences about the subsurface ocean through magnetic induction) would be strong.  (The orbit would dip to just five kilometers above the surface to deploy the probes where a simple camera's resolution might be ~5 m.)  The laser altimeter to measure the flexing of the surface to estimate ice thickness and the Langmuir probe to measure the particle and fields environment (and isolate their impact on the magnetometer measurements) might be too much.  I think a camera to document the terrain of the landing sites both to pick safer spot and to put the surface measurements in context would be strongly desired.


I would not be surprised to learn that the final cost estimates for this mission with any carrier craft instruments deemed necessary or minimal added cost will be above $1.5B.  Given that NASA's projected budgets cannot afford even a $1.5B mission, selling the political system on a, say, $2B orbiter plus two landers is probably not much harder than selling them on a $1.5B orbiter or multiflyby mission.


I'm hoping for good news out of this task force.

JUICE – Jupiter Ganymede Orbiter Revised Proposal

Current concepts for the JUICE spacecraft.  All illustrations are from the JUICE presentation at the recent OPAG meeting.

This time last year, both NASA and ESA were considering a joint mission to the Jovian system, with the former to concentrate on Europa and the latter on Ganymede.  Today, NASA’s budget outlook has caused it to abandon its plans for the Jupiter Europa Orbiter (although it is looking at ways to reduce costs to enable a Europa mission should budgets become increase).  ESA, however, is still considering its Jupiter-Ganymede orbiter as part of a competition to select is next large science mission.  The new moniker for the mission is JUICE for JUpiter ICy moon Explorer. 

At the recent Outer Planets Analysis Group (OPAG) meeting, two members of the JUICE proposal team provided an update on their proposal.  Ganymede remains the focus of the mission, with the spacecraft studying it from orbit about the moon for the better part of a year with the final orbits just 200 kilometers from the surface.  The original mission also included a number of Callisto flybys that have been retained in modified form in the latest proposal.

The focus of the JUICE mission remains the study of Ganymede from orbit around that moon

In the last few months, the JUICE team has looked at whether the mission could be enhanced to more thoroughly study the rest of the Jovian system, including Europa.  From the point of view of celestial mechanics, adding Europa flybys to the mission would be relatively straightforward.  Unfortunately Europa orbits Jupiter deep within that planet’s radiation belts.  Targeting Europa requires enhancing the radiation hardening of the spacecraft and instruments, increasing mass and costs.

In the end, the team is recommending just two flybys of Europa as a compromise.  The team looked at two options for those flybys.  One would have the spacecraft make its closest approach to Europa at different faces of the moon to maximize geophysical measurements of the gravity (mass distribution) and interaction of the subsurface ocean with Jupiter’s magnetosphere.  The second option would have the spacecraft fly over the same hemisphere and would focus on remote sensing surface composition measurements of high priority areas.  The team has chosen the latter approach both because detailed composition measurements of Europa from the Galileo mission were limited and to simplify the spacecraft design.  The proposal team recognizes that two flybys capture just a tiny fraction of the science that NASA Europa orbiter would have.  However, the team estimates that as many as 50 - 100 flybys would be needed to fully replace a dedicated Europa orbiter, which would require radiation hardening not feasible within the mission’s budget but which would also result in the loss of the rest of the science objectives of the mission, that of Ganymede and Jupiter system science.

Example ground tracks and focus areas for remote sensing during the two Europa flybys.

The team also looked for ways to enhance studies of Jupiter’s atmosphere and magnetosphere.  For both sets of studies, scientists would like to move the spacecraft out of Jupiter’s equatorial plane.  By doing so, the instruments can view the atmosphere at higher latitudes and get a better understanding of the three dimensional structure of Jupiter’s magnetic field and plasma fields.


The team proposes to incline the spacecraft’s orbit around Jupiter by 29 degrees by using the Callisto flybys to first pump up and then pump down the inclination.  There will be a price to pay for these orbital maneuvers.  The previous mission plan had the closest approaches to Callisto well distributed around the moon’s surface.  The new plan fixes the approach geometry so that the spacecraft follows nearly the same ground track for each flyby.  As a result, the instruments will see the same portion of the surface and sense the same area of the gravity field as a measure of internal structure for each flyby.

Inclined Jovian orbits to study the Jupiter atmosphere and magnetosphere at higher latitudes

In the new plan, the JUICE spacecraft would follow nearly the same ground track for each Callisto flyby (left) instead of distributing the ground tracks around the moon as previously planned (right)

Unfortunately, Io remains too deep in Jupiter’s radiation field for the mission to flyby it.  Future studies of this moon will depend on the success of the proposers of the Io missions in future NASA New Frontiers and Discovery mission selections.

Currently three missions, JUICE and two astrophysics missions, are in contention for the single funding slot for the next ESA large science mission.   In February, ESA plans to select either its final choice or to eliminate one of the three with a final winner selected after further study.  If JUICE is selected, it would launch in 2020, with a backup launch opportunity in 2022.  Approximately six years later, the spacecraft would reach orbit.  Another two and a half years would be spent exploring the Jovian system and preparing to enter Ganymede orbit for ten months of orbital science observations before the mission ends.

Editorial Thoughts:  The budget for ESA’s next large science mission is capped, and major changes to the original Jupiter Ganymede Orbiter proposal are not possible.  The proposal team has done a nice job of enhancing the proposal with limited additional studies of Europa, Jupiter’s atmosphere, and the magnetosphere. 

The other two missions in competition for selection by ESA are exciting astrophysics missions in their own right.  The competition is likely to be tough.   Barring a significant budget increase for NASA, however, JUICE appears to be our only option for exploring the icy moons of Jupiter in the next two decades.


My thanks to Michele Dougherty, Professor of Space Physics at Imperial College and Lead of the JUICE Science Study Team, for reviewing a draft of this post.

Return to Venus

Portion of Venera 14 landing image.  Ted Stryk's website has the nicest versions of these images I've seen.

A bit over a year ago, I wrote that a return mission to Venus would be compelling because "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."

While NASA has taken a pass on Venus for now, Europe has no missions in the offering, and Japan's Akatsuki mission is struggling to reach orbit, Russia has a mission planned for 2018.

Russia's Venera-D mission has gone through several iterations.  At one time, Russia had hoped that international cooperation might lead to a truly ambitious flotilla consisting of advanced orbiters, multiple balloons, and multiple landers.  The new plan appears to be a Russia-only mission, but one that is still ambitious with a capable orbiter and lander.  It is really three missions in one, with significant capabilities for studying the atmospheric structure and composition, the plasma environment enveloping the planet, the surface geology.

The orbiter will carry a number of spectrometers that will measure the structure and composition of the atmosphere from its top to the planetary surface.  One of its instruments, the interferometer spectrometer, will replace the Planetary Fourier Spectrometer that failed on the Venus Express mission that would have measured the atmospheric structure below the cloud tops.

A second suite of instruments on the main orbiter and a small sub-satellite will extend our studies of the plasma environment.  A key problem with studying plasmas environments is that they are dynamic, and it is hard to separate local conditions surrounding a single spacecraft from more global conditions.  The sub-satellite will provide a second point of measurement to compare results.

The atmospheric and plasma experiments will continue, and significantly extend, studies that have been made by previous missions extending as far back as the Pioneer Venus orbiter in the late 1970s and continuing today with the Venus Express mission and hopefully continuing with the Akatsuki mission if it can reach orbit.

For me, though, the key contribution of the Venera D mission will be a return to the surface.  The lander will explore a different terrain than previous landers, which landed either on the basaltic plains that cover most of the planet or on the fringes of the highlands.  Venera D will be targeted to explore the tessera highlands of Venus that rise, like continents, above the surrounding lowlands.

NASA studied a tessera lander as part of its recent Decadal Survey.  The authors of the report on the mission concept summarized the importance of a mission to these highlands: "The key science driver... is to measure the mineralogy and major elemental composition of tessera terrain, which is distinct from the plains and is yet unsampled... Tesseara terrains appears.. as the oldest material on a planet where the average surface age is ~500 million years.  Thus, the tessera proved the best chance to access rocks that are derived from teh first 80% of the history of the planet, an era for which we currently have no information."

While the probe is called a lander, it is just as importantly, an atmospheric probe.  The NASA report continued, [Previous] "compositional measurements of the atmosphere constrain atmospheric evolution, but to date, very little compositional or physical information has been garnered [below 16 km altitude], which is key to understand both atmospheric evolution and the surface-atmospheric interactions."

In many ways, the lander portion of Venera D is similar to the twice proposed New Frontiers SAGE Venus lander.  A comparison of their instrument lists shows that both missions would have similar capabilities.  In its most recent incarnation, the SAGE lander was targeted toward an area that Venus Express scientists believe may have been covered with recent lava flows.  Should both missions fly, we will have sampled the dominant younger (<500 M years old) plains of Venus with the older Venera landers, possibly the much older surface on a tessera, and possibly the some of the youngest surface with SAGE.

Location of previous Venera landing sites from the Wikipedia article on the Venera landers.

Editorial Thoughts: Venera D is an exciting mission.  I don't know whether it is a fully approved mission, or whether it is still a mission concept that needs to be formally approved by the Russian government.  (If any of you have insight into its status, please post a comment.)  A recent conference abstract (link below) says the mission is in Phase A, which is the earliest phase of a mission's conceptual definition and design.  This would be normal for a mission still six years from launch.

Resources:

You can read Ted Stryk's summary of the Venera D mission (which provided essential background for this post) at http://planetary.org/blog/article/00003210/.  He also posted a photograph of a poster on the mission from a recent conference.

A Russian space agency website on the mission can be found at http://www.venera-d.cosmos.ru/.  While the website is in Russian, Google Translate produces a reasonable English translation, and likely does well for other languages.  A recent conference abstract on the mission can be found at http://meetingorganizer.copernicus.org/EPSC-DPS2011/EPSC-DPS2011-1334.pdf.  My thanks to colin_wilson at the Unmanned Spaceflight Forum for these two links.

I wrote a post on NASA's tessra lander concept, which you can read at http://futureplanets.blogspot.com/2010/06/venus-tessera-lander-concept.html.You can read NASA report on its tessera mission concept at http://ia600505.us.archive.org/30/items/VenusIntrepidTesseraLanderConceptStudy/03_Venus_Intrepid_Tessera_Lander.pdf

There is a summary of the SAGE mission proposal at http://lasp.colorado.edu/sage/archives/PDF/SAGE%20Fact%20Sheet-p6_for%20print_April-21-2010.pdf

I wrote a post on previous concepts for international Venus missions that would have been more capable than the current concept for Venera D: http://futureplanets.blogspot.com/2010/01/russian-and-european-venus-ambitions.html