Thursday, December 22, 2011

A Vital Cislunar Space Application: Satellite Servicing

In my discussion of the Flexible Path to the Moon, I emphasized the importance of cislunar space.  My view is that developing infrastructure and capabilities in cislunar space is crucial to sustainable and affordable astronaut exploration to more distant destinations like the lunar surface, NEAs, and Mars, and is also vital to enabling exploration efforts to deliver near-term benefits to the taxpayer.  A number of articles have recently appeared that highlight the promise of cislunar space, such as Accelerating the future: human achievements beyond LEO within a decade (The Space Review), Exploration Gateway Platform hosting Reusable Lunar Lander proposed (, and Phase II of “Asteroid Next” missions: Proving Grounds for future crewed Mars missions (also  These have generated considerable interest and discussion, and it would be fun to add my voice to those discussions.

But I'm not going to do that.

Instead, I'd like to focus on a part of the Conference Report for H.R. 2112, the bill that funds NASA for the next fiscal year.  The following excerpt is from the report's Space Technology section:

Satellite servicing.—The conference agreement provides no less than $25,000,000 for satellite servicing activities. This funding will contribute to the planned competitive satellite servicing demonstration mission and shall be managed by the Human Exploration and Operations (HEO) Mission Directorate.

This $25M (at least) is part of the $575M for Space Technology. 

The following excerpt is from the report's Space Operations section:

Satellite servicing.—The conference agreement includes $50,000,000 from Space Operations to continue satellite servicing activities. These funds are in addition to $25,000,000 for satellite servicing in the Space Technology account. The HEO Mission Directorate shall continue to be responsible for the overall direction and management of all agency satellite servicing activities, which are undertaken as a joint project of the HEO, Space Technology and Science mission directorates. Satellite servicing activities shall include mission architecture design, robotic system development, autonomous rendezvous and capture sensor testing, fluid transfer demonstrations and spacecraft design.

Funds are to be used to continue work on a competitive project to develop, in collaboration with a U.S. commercial partner, a satellite servicing mission capable of operating in geosynchronous Earth orbit. The goal for such a mission is to achieve an on-orbit servicing of an observatory-class government satellite by 2016. Any U.S. commercial partner should be willing to invest its own resources in this mission, as it is intended to foster the creation of an ongoing commercial capability that could meet the needs of NASA, other Federal agencies, the commercial satellite sector and the scientific community.

The funds are for a satellite servicing mission involving NASA and a commercial partner with skin in the game operating in geosynchronous orbit.  Demonstration of such a commercial capability could be an important step in opening new robotic commercial satellite servicing markets in cislunar space, and could even lead later to development of human satellite servicing markets there.  Creation of such self-sustaining economic capabilities represents an important milestone in the development of cislunar space, and could be an important step in enabling sustainable exploration and development of more difficult destinations like the lunar surface and NEAs.

The most immediate activity of the NASA Satellite Servicing Capabilities Office is the Robotic Refueling Mission on the International Space Station.  This mission demonstrates robotic technologies to refuel, repair, and otherwise service satellites using various tools.  The office is also investigating a Robotic Servicing Mission.  This would be a robotic mission to demonstrate actual servicing for one or more GEO satellites. 

NASA has released an RFI for development of an on-orbit robotic servicing capability for spacecraft.  In this RFI, NASA shows its interest in a public-private partnership where it uses its satellite servicing capabilities and experience with a commercial partner:

NASA does not intend to establish a Government operated on-orbit satellite servicing capacity but rather to foster the creation of a domestic capability which may meet both future Government and non-government needs. Satellite servicing capabilities may include satellite recovery, repair, relocation, refueling, inspection, subsystem or component replacement, or other services that extend the life or capabilities of on-orbit assets.

The detailed RFI (PDF) gives several examples of the types of partnerships that NASA might be interested in pursuing with private industry.  The RFI makes it clear that the envisioned mission is a robotic one to GEO (as opposed, for example, to a mission where GEO satellites are delivered to and from servicing robots and/or astronauts in LEO), even though Congress's direction is that NASA's HEO Mission Directorate will be in charge of NASA's overall satellite servicing effort.  The RFI lists several contributions that NASA might make to the effort, such as satellite servicing patents, tools for repair, refueling, and other servicing jobs, autonomous rendezvous capability, sensors, test labs, operations support, computer resources, and more.

The RFI suggests several potential types of public-private partnerships.  In one partnership model, the commercial partner owns and is responsible for the servicing hardware while the government provides some of the contributions just described as well as an initial satellite to service.  In another model, the government pays a fixed price for commercial services, with both partners contributing hardware and support.  The commercial partner could rent the servicing vehicle for additional servicing missions beyond the government satellites.  In a third model, the commercial partner would be responsible for the entire system, and NASA would not identify a government satellite to service, but could provide intellectual property to the commercial partner.  Other models can be considered.

Several questions and responses (PDF) related to the RFI have also been published.  Some of these deal with foreign participation.  This is not surprising, since MDA is interested in and concerned about the NASA satellite servicing mission. 

Meanwhile, the First Community Workshop on Assessing Capabilities for Human Operations in Cis-Lunar Space: What's Possible Now? includes a presentation on a Manned GEO Servicing Study (PDF) involving NASA and DARPA.  Different satellite servicing missions by astronauts in GEO that would be useful in and of themselves while preparing NASA for future, more distant exploration missions are presented.  Missions could include habitat nodes and tugs to move satellites.  

DARPA has also presented the PHOENIX workshops on a potential satellite servicing program:

The goal of the Phoenix program is to develop and demonstrate technologies to cooperatively harvest and re-use valuable components from retired, nonworking satellites in GEO ...

 There are multiple components in the Phoenix architecture.  Nanosatellites would be launched as secondary payloads.  A satellite servicing component would robotically attach the nanosatellites to an antenna of a dead satellite, enabling the large antenna to be reused.  The nanosatellites are delivered in a new PODS nanosatellite delivery module.  This PODS delivery mechanism meets with the satellite servicing component which can then use the nanosatellites and tools in the PODS as a sort of tool chest.

Like robotic precursor missions to the Moon, NEAs, or Mars, a commercial GEO robotic satellite servicing mission can help set the stage for more ambitious future astronaut servicing missions in the same type of location.  A commercial robotic satellite servicing mission done in partnership with NASA can also strengthen the U.S. commercial spaceflight industry, much like NASA's current approach to send cargo and later crew to the ISS using commercial services.  A commercial robotic satellite servicing mission can demonstrate some of the technologies and capabilities needed by NASA to productively and safely send astronauts to more distant destinations like Lagrange points, the lunar surface, NEAs, and Mars and its moons.  This is especially true of missions that leverage robotic capabilities like telerobotics.  Finally, a commercial GEO robotic satellite servicing mission that involves satellite refueling can develop new markets for fuel that could later come from locations like the lunar surface, thus creating an opportunity for the type of exploration and development using ISRU that can create a strong space economy.

For more information:

On-Orbit Satellite Servicing Study - Project Report - comprehensive 2010 NASA satellite servicing workshop report, including a history of satellite servicing and several potential servicing missions from basic robotic satellite servicing to astronaut assembly and maintenance of large observatories

SSCO - NASA Satellite Servicing Capabilities Office

NASA_SatServ - Twitter account for the NASA Satellite Servicing Capabilities Office

The Future of On-Orbit Satellite Servicing - SpaceRef Forum (article from the September 2011 Space Quarterly (PDF)) - This gives a good overview of the history and recent state of satellite servicing.

Robot Surgeon Tech Aims to Fix NASA Satellites -

Medical Robotics Experts Help Advance NASA’s ‘Satellite Surgery’ Project - Johns Hopkins University

Frank Cepollina, Deputy Associate Director, Space Servicing Capabilities Office, NASA Goddard Space Flight Center - Space News - This covers the Robotic Refueling Mission, a satellite servicing test on Earth, and the potential servicing mission in GEO.

NASA Selects First Payloads For Upcoming Reduced-Gravity Flights - NASA - This includes a Zero-G flight for the Autonomous Robotic Capture payload, similar to the Approach, Rendezvous and Capture Demonstration Cepollina mentioned in the previous article.

Thursday, January 13, 2011

A Puzzle to Distract Us From HEFTy Price Tags

With all of the news about the Human Space Exploration Framework Summary and Preliminary Report Regarding NASA’s Space Launch System and Multi-Purpose Crew Vehicle, I thought I'd write a few pages about them.  Then, I changed my mind and decided to ignore them.  I wanted to have some fun instead, and there is nothing fun about unaffordable HEFT reference missions and unneeded rockets designed by a handful of well-placed members of Congress.

I like puzzles, so I made a word search puzzle at to take my mind off the doom and gloom.

I'm not sure, but I may not have completely succeeded in taking my mind off of the train wreck, though:

C  V  N  S  A  S  E  E
A  L  O  B  L  C  T  H
N  H  I  W  L  S  U  E
C  M  R  R  A  O  K  F
E  P  O  W  T  K  A  T
L  C  Q  S  E  R  A  T
T  V  C  O  S  T  L  Y
E  R  I  M  G  A  U  Q
ares late
bloat mpcv
cancel orion
costly quagmire
esas sls
heft waste

Friday, January 07, 2011

Compelling Planetary Science Missions: What Comes After the Top Five?

This completes a series of posts inspired by a similar set of posts at Future Planetary Exploration blog selecting the 5 most compelling missions from the Planetary Science Decadal Survey list.  This presents my point of view of the type of planetary science accomplishments possible through the next Decade's work beyond what I found to be the 5 most compelling missions from the Decadal Survey list.

First, let's review the missions I selected, and their estimated FY15 costs with reserves:
  • Lunar Polar Volatiles Explorer - long-range rover with drill - $1,132M
  • Enceladus Orbiter - Saturn tour followed by Enceladus orbit - $1,613M
  • Mars Polar Climate Mission (2 selections from Decadal Survey options) - climate and weather orbiter and polar subsurface sampler lander - $613M + $860M = 1,473M
  • Mars Geophysical Network - 2 geophysical landers - $1,015M
  • Lunar Geophysical Network - 4 geophysical landers - $903M
This selection is consistent with this blog's theme of restoring the Vision for Space Exploration that was, with some exceptions like LRO and LCROSS, lost in 2005 with the onset of Constellation.  It covers the "Moon, Mars, and beyond" idea almost a bit too literally, since (in my view) Planetary Science should "lean a bit" in this direction while still being driven by science priorities, while a well-funded Robotic Precursor line on the astronaut exploration side should be the main robotic support line for the VSE's robotic needs.  The Lunar Polar Volatiles Explorer is a particularly important mission in support of the VSE goals, whether funded through Planetary Science or Robotic Precursors.  The Enceladus orbiter doesn't quite fit the specific outer planet wording from the Outer Planets section of the VSE, which emphasizes Jupiter's moons and then Titan, but I think it could be justified in the context of the VSE given knowledge gained by Cassini since the VSE was developed.

The total estimated cost in FY15 dollars of these 5 missions (including 8 landers and 2 orbiters) is in the ballpark of $6B.  I could assume the cost would be less, since the missions include significant reserves, and some have substantial heritage.  I could also assume partnerships lower the cost to NASA Planetary Science (e.g.: partnerships with international space agencies, synergy with NASA robotic precursor or technology development lines, commercial participation), but I'll instead assume that such partnerships tend to add capabilities rather than lower cost.  The budget for the Enceladus Orbiter includes operations spending that happens far past the timeframe of the Decadal Survey, so I might be able to overlook some of the budget needs of that mission.  However, I'm more comfortable leaving the estimate for the 5 missions at $6B.

I don't know what the NASA Planetary Science new mission budget will be for the next decade, but let's suppose it's $11.5B in FY15 dollars.  That would leave some money for other areas like Planetary Science technology development, instruments, research, operating long-duration missions, data systems, and so on.  I'll ignore issues like missions whose funding spans multiple Survey decades.  With those simplifying assumptions, with $6B or so for the top 5 missions, we'd still have a healthy $5.5B for other missions.

It would have been easy to have chosen 5 missions that together cost far more than $6B, since the Decadal Survey list concentrates on New Frontiers and Flagship missions (i.e. ambitious but expensive ones).  For example, here are the listed FY15 costs for 3 particularly capable, long-sought-after, and undeniably compelling missions that very well might be emphasized by the Decadal Survey:
  • Jupiter Europa Orbiter - $3,897M ($1,200M of this is reserves)
  • Mars 2018 MAX-C Caching Rover - $2,196M (and this requires 2 more large missions before the biggest reward - Mars sample return - happens)
  • Titan Saturn System Mission - $3,456M
As you can see, if we go with those 3 missions, and assume a total Planetary Science budget of $11.5B for missions, we aren't left with much else for the other 2 of the top-5 missions, let alone other missions.  The Mars 2018 MAX-C mission assumes an earlier ESA/NASA ExoMars mission for telecommunications, so we have even less room for flexibility if we select these 3 missions.  Those would be 3 great missions, but I don't think I'd want Planetary Science to be limited almost entirely to these 3.  I'd also consider the impact to Planetary Science if any of these 3 suffered serious cost overruns or a major technical failure, considering how many eggs would be in so few baskets.

Since I happen to have picked some of the less-expensive missions from the Survey list, though, I now have a chance to provide some depth to what would be, if left to stand by itself, a fairly unbalanced set of missions in my top 5.  I seem to have emphasized Mars, the Moon, and geophysical networks at the cost of sample return, Venus, small bodies, and other priorities.  Can that be fixed?  What should we do with the "leftover" mission funding?

The first thing I'd do with that extra $5.5B is establish a funding block (for the sake of discussion, let's say $1B over the decade) for "frequent, very low cost missions".  This would be in addition to existing areas like flights of opportunity for instruments on non-NASA missions.  This might sound like the Discovery line of missions, but for various reasons, the Discovery line is getting a bit expensive.  The FY10 Discovery mission limit used in the Survey studies is $580M for FY2010; it's assumed to be $666M in FY2015.  That includes $155M (FY10) or $178M (FY15) for an assumed Atlas V 401 launch.  The new mission line that I'm proposing would be for lower cost Planetary Science missions than that.  You might think of some of the early Discovery missions, the new "Venture Class" Earth observation missions, or astrophysics and heliophysics Explorer, MIDEX, and SMEX missions.  This line would seek to take advantage of opportunities like
  • potential lower-cost launchers, such as the Falcon 1e, Falcon 9, and Taurus II
  • potential increased availability of secondary payload slots on launchers
  • commercial data purchases, similar to NASA's Innovative Lunar Demonstrations Data contracts, but for planetary science data rather than engineering data
  • other cooperative arrangements with non-NASA partners such as commercial vendors
  • cooperative missions with other NASA areas like Space Technology, Exploration Technology Development and Demonstration, and Robotic Precursors, or even entire small space missions whose main purpose is to demonstrate products of the Planetary Science technology development budget
  • focused, low-cost mission approaches (for example, penetrators like the Deep Space 2 Mars technology demonstrators)
  • favorable trends in the small satellite field
Such missions would probably tend to go to some of the Planetary Science destinations that are easier to reach quickly, such as the Moon, Venus, Mars, comets, and NEOs.  If that happens, they could fill in some of the gaps of my original 5 mission list (Venus, NEOs, comets) while strengthening the Moon and Mars focus of that list.

If we used $1B for that, we would have $4.5B left.  I think we should have at least 3 Discovery missions (4 if you count the Mars Scout-like Mars Climate Orbiter I selected in the most compelling missions as a Discovery mission).  There are a lot of gaps left in my mission choices that these Discovery missions could fill in.  For example, even with my predisposition to favor missions with "astronaut robotic precursor" potential, I didn't select a single Near Earth object mission, even though Near Earth objects are often discussed as the first beyond-LEO destination in NASA's new Flexible Path plan for astronaut missions.  (Actually the first beyond-LEO mission destination in that plan is cislunar space - possibly lunar orbit or an Earth-Moon Lagrange point - but those early beyond-LEO missions are often overlooked when the new plans are discussed).

Why didn't I select any Near-Earth asteroid planetary science missions?  Well, for one thing, there weren't any on the Decadal Survey list.  I didn't allow the current batch of New Frontiers missions, including the Near-Earth asteroid sample return mission OSIRIS-REX, in my selection.  The Decadal Survey studies include an analysis of "Near Earth Asteroid Trajectory Opportunities", but I didn't consider that to be an actual mission.  The list also includes an affordable "Trojan Tour Concept", but Trojan asteroids are by definition the "cloud" estimated to include hundreds of thousands of objects (if we only count those greater than 1 km in diameter) around the L4 and L5 Jupiter-Sun Lagrange points.  Those are not candidates for early astronaut exploration missions, and in fact, it could be a couple of decades before the Trojan Tour robotic mission would get there if it was selected - with 1 decade for the actual trip.  Nevertheless, the Trojan Tour is affordable and would cover a set of bodies that has never been visited before, so it is certainly worth consideration.  There is also an affordable Chiron Orbiter mission in the Decadal Survey list, but this would take even longer to launch and to reach its destination.

So, with the most compelling missions I've selected, we probably have a coverage gap in the area of Near Earth objects, or at least primitive bodies in general.  One or two Discovery missions to fill that gap might be in order.  We also have coverage gaps at Venus and Jupiter.  So, if we add 3 Discovery missions, we might be able to let the Discovery mission selection process fill some of the gaps I left with my top 5 selections.

If we assume the Discovery missions cost $700M each, that leaves us with $2.4B.  What should we do with that?  There are a number of interesting possibilities:
  • Upgrade the Enceladus Orbiter to a full-blown Titan Saturn System mission, or switch it to the Jupiter Europa Orbiter after all.  This would make a lot of the planetary science community and international partners happy, although I would still worry about mission cost until data starts coming in (upon which time I would undoubtably forget cost).
  • Fly the Mars 2018 MAX-C Rover after all.  This would make a different, but also big, part of the planetary science community and international partners happy.  With $2.4B available and a mission estimate of about $2.2B, there would be a little bit of slack to also cover NASA's contributions to the earlier Mars Trace Gas mission (e.g.: the rocket, instrumentation, telecommunications), but one of the Discovery missions might need to be traded or postponed to fully cover that.  Because of the amount of planning and interconnected missions involved, this selection might make a great deal of sense, in spite of my serious worries about mission cost.
  • Fly a variant of the Venus Climate Mission (which barely missed my 6th-place spot).  The basic mission should allow room for anther Discovery mission, which is the approach I would tend to take.  Alternately, the Venus Climate Mission could fill up the $2.4B by taking on some of the capabilities of the more ambitious Venus Climate Flagship reference mission.
  • Assuming the current New Frontiers selection picks one out of MoonRise (lunar sample return), SAGE (Venus lander), and OSIRIS-Rex (Near-Earth asteroid sample return), we should be able to afford to fly the other 2 with the leftover $2.4B.  I find this to be a particularly attractive option, since these missions should be in a more well-developed state than some of the others in the Decadal Survey list, since they address sample return (which I've completely skipped in my selections), since they have significant "robotic precursor" and "exploration technology demonstration cooperation" potential, and since they partially address some of the content that I lost by letting the Venus Climate Mission slip into 6th place on my list.
  • Fly 3 more Discovery missions, giving a total of 6 - a good decade for this class of missions.  I tend to think of Discovery missions as the "meat and potatoes" of Planetary Science, so I'd seriously consider this option.  One of those Discovery missions (or a mission with similar cost but selected and managed differently) might be a second Lunar Polar Volatiles Explorer, just like the first one but at another lunar location (e.g.: the other pole).
  • All sorts of other possibilities.
We can't do everything, but picking one of these would at least fill in some of the gaps that I've left with my original 5 selections.

Sunday, January 02, 2011

Compelling Planetary Science Missions: Showdown Between Lunar Geophysical Network and Venus Climate Orbiter

This continues a series of posts inspired by a similar set of posts at Future Planetary Exploration blog selecting the 5 most compelling missions from the Planetary Science Decadal Survey list.  This presents my personal selection for the 5th and last most compelling mission from the list.

I'd like to select a mission that fits well with one of the Mars missions I selected as my 3rd and 4th most compelling mission: a 2-part Mars Climate mission and a Mars Geophysical Network.  The obvious choices to me were the Venus Climate Mission and the Lunar Geophysical Network.  First, let me described these 2 contenders for the 5th spot as presented by the Decadal Survey mission concept studies.

The Lunar Geophysical Network includes 4 similar landers that would arrive at different locations on the Moon.  These landers would have goals that are not very different from those of the Mars Geophysical Network.  They would be expected to determine information about the lunar crust, mantle layers, and core (e.g.: size, state, composition, temperature), assess lunar heat flow, and measure moonquakes.  Each lander would include a seismometer, magnetometers, electric field sensors, a Langmuir probe, retroreflectors, and a heat flow sensor.  As with the Mars Geophysical Network seismometers, the 4 seismometers on 4 landers in the lunar network concept would work together simultaneously to produce results that are much more useful than measurements from a single seismometer.  The heat flow sensor would be deployed under the regolith up to 3 meters, possibly delivered by a "mole".  The retroreflectors are targets for Earth-based lasers that precisely measure the distance from the laser to the retroreflector. 

The lunar day/night cycle encourages use of ASRGs, which in turn encourages use of an Atlas V variant for launch.  The Falcon 9 is not certified for launch of ASRGs, but a less capable mission variant is depicted using Falcon 9 to launch 2 solar-powered landers.  There is a tradeoff between expensive ASRGs (and related certification) and heavy, less capable solar power and batteries.  My mission selection for the top 4 most compelling missions is already ASRG-heavy, so the ASRG option might be problematic in that context.

Clive Neal presents more justification for a mission like this one in The Rationale for Deployment of a Long-Lived Geophysical Network on the Moon.

One of the nice things about this proposal is that it can start to produce results quickly.  The mission could launch and begin to return data in FY16.  Compare that to my second most compelling mission choice, the Enceladus Orbiter, which might launch in the mid-2020's and arrive at Saturn in the 2030's.

Another attraction compared to many other missions in the Decadal Survey list is the estimated cost, $903M in FY15 dollars with reserves included.

On the other hand, if I were selecting a lunar mission, I would put some thought into selecting a second Lunar Polar Volatiles Explorer rover (which I suspect would be quite affordable assuming the first is built) sent to another region (perhaps the other lunar pole), or a lunar sample return mission like MoonRise, before this geophysical mission.  However, I bent my own rules enough by choosing 2 of the Decadal Survey's Mars Climate Orbiter concepts.  I didn't include carbon copies of earlier choices or current New Frontiers mission contenders as possible choices in the first place - I only want to select unique missions from the Decadal Survey's mission list.

Now let's take a look at the ambitious Venus Climate Mission.  This mission is intended to study the origin, variability, suspected major ancient climate change, and interaction with the surface of the mostly carbon dioxide atmosphere of Venus.  One angle of this study is to learn about potential climate change on Earth by comparison, and to test terrestrial General Circulation Models using Venus as a model test scenario.  The mission includes several distinct pieces of Venus hardware.

There is a Venus orbiter spacecraft that serves as a carrier and telecommunications rely for the other components.  The orbiter also includes a "Venus Monitoring" camera that gives context for the measurements from the elements of the mission that reach Venus itself.

There is a balloon that itself serves as a carrier and deployer for other mission elements.  The balloon is intended to last at least 3 weeks, floating 55km in the Venusian atmosphere and going around Venus up to 5 times during its journey.  The balloon has instruments that sample the atmosphere and clouds of the planet.  For example, it includes a Neutral Mass Spectrometer that can carefully measure noble gas isotopes.  A Tunable Laser Spectrometer measures trace gases.  The NMS and TLS should give even better results together than they would do individually.  A Nephelometer studies cloud particles.  Clues on atmospheric circulation are revealed by tracking the balloon as the atmosphere moves it about the planet.   

At 2 different times during the balloon mission, it deploys is a pair of small Drop Sondes.  These measure pressure, temperature, acceleration, and wind speed as they fall from the balloon to the surface over the course of 45 minutes using "Atmospheric Structure Instrumentation".  The balloon and Mini-Probe (which I will describe momentarily) also include similar instrumentation.  The Drop Sondes also include a Net Flux Radiometer to measure solar and Venus-based radiation.  Again, the balloon and Mini-Probe host similar instruments.  The Drop Sondes are tracked by the balloon to gain more data about winds at the various levels the Drop Sondes fall through.

The other element of the mission is a Mini-Probe that is larger and more capable than the 2 Drop Sondes.  It is released by the entry system at the same time as the balloon system, and falls for 45 minutes.  In addition to instruments like those the Drop Sondes carry, like the balloon system, it carries a Neutral Mass Spectrometer to measure aspects of Venus's atmospheric chemistry.  In this case the profile is taken vertically (i.e. the probe falls through the atmosphere as it takes measurements), whereas the balloon profile is generally horizontal.

The Venus Flagship Reference Mission has some commonalities with the Venus Climate Mission, but it's even more ambitious.  It includes 2 landers that last for several hours on the surface, 2 balloons, and a much more capable orbiter able to map Venus at a much higher resolution than Magellan did.  That mission is also much more expensive, and was not one of the ones on the Decadal Survey list, so I'm not considering it.

The Venus Mobile Explorer, another concept on the Decadal Survey list, also includes a Neutral Mass Spectrometer, Tunable Laser Spectrometer, and pressure/temperature/wind sensors for analysis of the atmosphere at different altitudes.  It's able to land and later float to one other location on the surface.  It has fewer climate/atmosphere capabilities than the Venus Climate Mission and may cost a bit more, but it gains surface capabilities and imaging.

The Venus Intrepid Tessera Lander, another mission studied by the Decadal Survey, includes similar atmosphere instrumentation on a lander mission, but at a projected cost ($1.3B in FY15 dollars with reserves) that is lower than either the Venus Mobile Explorer or the Venus Climate Mission.

When finding a partner for the Mars Climate Mission, the Venus Climate Mission comes to mind first, but these other missions should also be considered, since they have some climate capabilities mixed in with surface analysis.

As with the lunar geophysical mission, I would consider the SAGE (Surface and Atmosphere Geochemical Explorer) Venus mission in the current New Frontiers competition as a strong alternative to the Venus Climate Mission.  SAGE consists of a lander that would survive for at least 3 hours on a Venus volcano.  It can dig and analyze samples, and also includes a number of instruments to study the climate and atmosphere of Venus (including the Atmospheric Structure Investigation, Tunable Laser Spectrometer, and Neutral Mass Spectrometer, which I assume are similar to the ones of the climate mission).  However, SAGE is not on the Decadal Survey list, so I'm not including it as a possible choice.  Allowing the 3 current New Frontiers competitors could have taken a lot of the fun out of this survey of Decadal Survey options since I could very well have given 3 of the top 5 spots to them.

The combination of a Venus Climate mission, various climate studies of Earth (including those based on satellite data), and surface and orbiter Mars Climate missions (as I already selected for the 3rd most compelling mission) should give us a lot of practical data to allow us to compare climate at these planets.  Of course learning about implications for Earth from the other 2 planets is the immediately practical aspect, and it's a compelling one.  However, I'm concerned about the cost of the Venus Climate mission, estimated at $1.577B in FY15 dollars with reserves.  I already selected the Enceladus Orbiter as a Flagship class mission, and I'm inclined to limit the number of flagship missions to allow a greater number of less costly (but, it should be admitted, less capable) missions to fly.  As a result, even though in one sense I consider the Venus Climate mission to be the more compelling of the 2 missions by a hair, when factoring in cost, the Lunar Geophyiscal Network wins.  I select LGN as the 5th and last of my "top 5 most compelling missions" from the Decadal Survey.  The LGN folks shouldn't rest easy, though, because if an international partner picks up the costs for one or two of the significant components of the Venus Climate mission, thereby lowering the cost of the mission to NASA (which I think could be done given the several distinct parts of the mission), the Venus mission would probably bump LGN off the list and into spot #6.

Now that I've selected my personal top 5 selections from the Planetary Science Decadal Survey, in the next post I'll take a look at some ideas for the rest of NASA's Planetary Science mission budget.  I've come up with a top 5 list that only gets to 3 destinations, so it would nice to see where else we can go.  I may also discuss how my 5 most compelling selections fit with the theme of this blog.