Monday, June 6, 2016

Red Dragon and Planetary Exploration



A few weeks ago, as I’m sure most people reading this blog know, Elon Musk, the CEO of SpaceX announced plans to land their Dragon spacecraft, largely at the company’s expense, on Mars.  While this plan is audacious enough, Musk has previously positioned SpaceX’s Dragon capsule as an all-purpose lander suitable to explore almost the entire solar system. 

Since Musk’s announcement, I’ve been doing research and thinking about what the availability of a commercial planetary lander might mean for planetary exploration.  Even if landing the company’s Dragon spacecraft on Mars proves to be a one-time event, it will demonstrate that the technologies for planetary missions have become widely available. 

What if, though, SpaceX’s Dragon spacecraft becomes a standard catalog item that could ordered, the way a launch vehicle is?  What might the impact be on planetary exploration?  As I thought about this, I concluded that three questions are key: How flexible will the Dragon spacecraft be as a payload delivery vehicle?  How far afield can it operate in the solar system without design changes so massive that it becomes necessary to essentially redesign it?  And how will be missions it might fly be paid for?

Mock up of the Dragon version 2 capsule for Earth orbital missions.  Credit SpaceX.

First, some background on the Dragon spacecraft.  SpaceX currently is using the first version of the uncrewed Dragon spacecraft to deliver supplies to the International Space Station.  It is also being being funded by NASA to design a crewed version of the spacecraft to deliver astronauts. (I couldn’t find out what proportion of the Dragon development is being funded by NASA versus by SpaceX’s own funds.)  Musk has ensured that this second version incorporates key technologies such as heat shields that can survive atmospheric entry from interplanetary speeds and built in thrusters that allow soft landings.  (Phil Plait at Slate magazine has an excellent article on the technologies involved.  Wikipedia has additional information.)

Designing a craft for interplanetary flight requires numerous differences from a craft designed to operate in low Earth orbit for short periods of time and then return to our world.  Systems must be able to function for months to years.  Electronics must be able to function in the harsher radiation environment outside the Earth’s magnetosphere.  The communications system must be able to transmit and receive data over distances of hundreds of millions of kilometers.  There will be hours to days between communications periods, requiring the craft to be able to operate autonomously.

Artist's conception of the Red Dragon capsule on the surface of Mars.  Credit: SpaceX.

To operate as a long-lived lander on the surface of a planet, the spacecraft must deploy solar panels to generate power after touch down.  (I’ve not heard of any plans to use plutonium-based power generators for the Dragon spacecraft.)  Batteries must be carried and recharged to keep the spacecraft operating during the night.  And especially on frigid Mars, the spacecraft will need insulation and heaters to keep it warm.

These problems are well known, and we can presume that SpaceX’s engineers have designed the Dragon spacecraft and their subsystems with these issues in mind.  It’s worth pausing for a moment to consider the kind of commitment this implies to SpaceX’s commitment to revolutionize Martian exploration because these enhancements likely aren’t cheap.

By making these investments in the basic Dragon spacecraft design, referred to as the Red Dragon for Mars missions, SpaceX can take advantage of what is likely to be a low volume assembly line building these craft.  While NASA has designs of its own it can reuse to land on Mars, flights are likely to be infrequent enough that their components may gradually become obsolete and the expertise to rebuild and test them may fade.  SpaceX presumably will be building several Dragon spacecraft a decade, allowing it to gradually update the design and keep its expertise intact.  The result will likely be a lander that may be substantially cheaper than NASA reusing its existing designs for some Mars missions.

How Flexible is the Interplanetary Dragon Lander?

I know of two proposals for scientific missions that would use the Red Dragon spacecraft.  One, IceBreaker, led by NASA’s Chris McKay would return to the northern polar plains of Mars to further investigate the subsurface ices found there for habitability and signs of life.  The appeal of the Dragon spacecraft appears to have been its expected low cost.  McKay has also proposed the IceBreaker mission using a near copy of the much smaller NASA Phoenix and InSight landers.  The instruments would have weighed a few tens of kilograms, barely taking advantage of the payload that the Red Dragon could deliver.  The Dragon lander (dubbed the IceDragon for this concept), however, could have carried a much larger drill than the Phoenix-derived lander, allowing samples to be collected from much further below the surface.  (The one published abstract for the IceDragon mission from several years ago proposed a 2 meter drill.  Technology development since then might allow much deeper drilling.)

Conceptual design for the IceDragon version of the Red Dragon capsule that could be sent to sample the icy plains of Mars' arctic regions.  Human figure shown for scale.  Credit: NASA.

The second proposal would be to use the Dragon spacecraft to deliver a launch vehicle to return samples directly from the surface of Mars to the Earth.  This concept takes full advantage of the payload mass and volume offered by the Dragon.  Other concepts proposed to return samples to Earth envision two missions.  The first would land on Mars and launch a sample canister into Martian orbit.  The second would retrieve the canister and perform the voyage to Earth.  The large ascent vehicle enabled by the Dragon would, the proposers argue, combine these two functions to lower costs, complexity, and risk. 

Unfortunately, this proposal requires that a rover already be on Mars that could deliver a canister with samples to the Dragon spacecraft.  While NASA’s planned 2020 Mars rover will collect samples, it will leave them on the surface for a later rover to collect and return to an ascent vehicle.  There isn’t the payload mass for the proposed Dragon mission to carry its own fetch rover and a direct-to-Earth ascent return vehicle, although it could launch samples into Martian orbit if it has to carry its own fetch rover according to the proposers.

Conceptual design for the Red Dragon used to carry a Mars Ascent Vehicle (MAV) and an Earth Return Vehicle (ERV).  Credit: NASA.

There’s much we don’t know about the Red Dragon design.  Will it be suited only to missions where the scientific investigations are limited to the immediate landing site where robotic arms could reach such as these two proposals?  That would suggest missions to locations where homogenous conditions exist over large areas such as the polar plains of Mars. 

A variation of the proposal to use the Dragon design to return samples from Mars would be to use it to return samples from different regions of the moon or from some of the larger asteroids.  Since the scientists proposing lunar sample returns are interested in broad regional differences in composition, grabbing samples with an arm in the immediate vicinity of the lander would meet their goals.

However, many of the goals for lunar and Martian exploration require rovers that can reach and study or sample multiple locations across within a much larger study area.  I have not seen any analysis about whether delivering a capable rover would be a feasible extension of the Red Dragon’s design.  Could the Dragon design host a moderately large rover (smaller than the Curiosity rover but perhaps bigger than the Opportunity rover) and deploy it to the surface by including a large hatch and a ramp or crane? 

NASA already has two current, proven designs for Martian landers.  The first, used for the Phoenix and InSight missions, delivers a few tens of kilograms of instruments using a small, stationary lander.  The key advantage of this platform is that it provides a soft landing, and its low stature provides easy access to the surface.  The second system used parachutes and a rocket-powered skycrane to deliver the Curiosity rover to the surface (and the design will be reused for the 2020 rover).  It also places up to 930 kilograms of rover directly on the surface, eliminating the need for ramps to get the rover off the lander.  The landing system is also designed with the myriad of safety requirements needed for a rover/lander to use a plutonium power supply.

The Red Dragon will be able to deliver a slightly more massive payload, about 1000 kilograms.  While the payload space appears large by the standards of most planetary landers, it doesn’t appear large enough to carry a duplicate of the Curiosity rover.  Unlike the skycrane landing system, the payload will sit inside a large spacecraft, well above the ground.  Long robotic arms or drills would be needed to bring surface samples to instruments inside the spacecraft or place small instruments on the surface.  Delivering a large package such as a rover to the surface would require ramps or a crane.  I expect that these problems are solvable, but they create a level of complexity that NASA’s skycrane system was invented to avoid.

Comparison of the sizes of the Dragon capsule (left) and the Curiosity rover entry and descent system.  The Dragon capsule would not have the width to carry a Curiosity-sized rover, but likely could carry a smaller rover to the Martian surface.  Credit: NASA.

Beyond the Moon and Mars

Musk has been quoted saying that the Dragon capsule can be used to explore almost any world in the solar system: “With Dragon launched on a Falcon Heavy, it can go pretty much anywhere in the solar system, because that’s a heck of a big rocket…  Dragon 2 is capable of transporting scientific payloads to anywhere in the solar system, with a liquid or solid surface, with or without an atmosphere. So Dragon is really a crew transport and science delivery platform…  Dragon, with the heat shield, parachutes and propulsive landing capability, is able to land on a planet that has higher entry heating, like Mars. It can also land on the Moon, or potentially conduct a Europa mission.”

Musk’s claim appears to touch on three separate issues.  The first is whether the Falcon Heavy could propel a Dragon spacecraft to any location in the solar system.  The answer likely is yes.  For our moon, Mars, and Venus, the launcher will be able to send the Dragon directly to these worlds.  If the Falcon Heavy cannot send a Dragon directly to Mercury or the outer planets, it certainly could launch it on a trajectory that would use Venus and/or Earth gravity assists to provide the additional velocity needed.

The second issue is whether the Dragon could land on these more distant worlds, which breaks into two parts.  The first is how the Dragon capsule would kill the high approach velocity when it reaches its destination.  The atmospheres of Mars, Venus, and Titan can kill much of the speed.  It’s less clear to me whether the Dragon spacecraft would carry enough fuel to first brake into, say, Jovian orbit and then kill the remaining velocity to land on Europa.  (A direct landing on Europa without entering Jovian orbit also would need to kill a lot of speed.)  Musk’s statements suggest it could, but for now we lack details.

The third issue is whether the Dragon spacecraft could deal with the special environmental issues at various worlds.  The moon and Mars are reasonably straightforward challenges both because of their proximity and their comparatively (for planetary destinations) benign environments. By contrast, while the Mercurian poles are cool, the spacecraft would need to deal with intense solar heating on the way to this world.  The surface of Venus is intensely hot and has a crushing atmospheric surface pressure.  Jupiter’s moon Europa sits deep within an intense, electronics frying, radiation belt.  Titan’s surface is as bitterly cold as Venus’ is broiling.  Landing on a small asteroid or comet may require special adaptations such as harpoons to hold the capsule on the surface.  Traveling to any world beyond Jupiter will require a radioisotope generator for power (Saturn might be an exception). 
It is possible to design spacecraft to handle any of these challenges.  Missions have been proposed to land on each of these worlds, but using custom designs that take into account the unique challenges of each environments.  Would it be cost effective to modify the Dragon spacecraft to handle the challenges of any of these worlds, or more cost effective to design a custom spacecraft?  

There’s also the question of whether a prior scouting mission would be needed.  For the moon and for high priority locations on Mars, existing high resolution images would allow mission planners to identify precise locations of safe terrain within otherwise rugged but scientifically interesting terrains.  The same will be true for selected sites on Europa following NASA’s planned Europa Multiple Flyby mission.  What about a world with only coarse resolution mapping or none at all?

Example of the rugged terrain the salt deposits of Ceres are found on.  Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

As a thought experiment, I considered a Dragon mission to land on the asteroid Ceres to explore the salts on the surface that have erupted from a likely (now frozen?) subterranean ocean.  We have moderate resolution (35 meters) images of the surface from the Dawn spacecraft currently orbiting that world.  The images of the terrain where the exposed salts are found that I’ve seen, however, appear quite rugged at 35 m resolution.  And a lot of lander-killing ruggedness can hide within that scale of resolution.  For assessing a potential Martian landing site, by comparison, NASA likes to have images with sub-meter resolution.
I’m sure that the Dragon capsule or its service module could physically carry a high resolution camera to scout for safe landing sites.  But would the spacecraft have the precise pointing capability to accurately aim the camera and the stability to prevent image jitter?  Again, solutions to these problems are well known, but is this something that would have to be added to the Dragon spacecraft?

Who Will Pay for Interplanetary Dragon Missions?

Until we know more about the capabilities of the Red Dragon capsule, it is hard to know what its advantages and disadvantages will be compared to existing lander designs.  It may provide a significant cost advantage – remember that likely assembly line of Dragon spacecraft.  However, the lander hardware is just one part of the cost of a mission.  There is still the cost of the launch, the instruments, potentially a rover or a launch vehicle for sample return, and operations. 

Even if the cost of a Red Dragon landing were free, these other costs would drive the total mission costs to several hundred millions of dollars.  This puts a Red Dragon-based mission in competition for funding with all the other missions planetary scientists would like to conduct.  A lunar or Martian landing mission may be selected by NASA only once a decade, and the Red Dragon may or may not be the most suitable design. 

As an alternative, perhaps SpaceX will schedule a Martian landing every two years or so and will sell payload space to space agencies, universities, and even private companies to cover costs.  Then the cost to any individual space agency, university research group, or company might be relatively small – a few million or tens of millions of dollars. 

Or Musk may use the profits from SpaceX or a portion of his personal fortune to drive his own program of Mars robotic exploration.  From his statements we know he wants to eventually take humans to Mars.  Perhaps Red Dragon is a stepping stone to that grander vision.

Red Dragon is possible because of the vision and drive of its founder, Elon Musk.  He made a strategic decision to build a capsule that could land on Mars as well as meet NASA’s needs in near Earth orbit.  We will need to wait to learn what types of landed missions that vision will encompass and which worlds beyond Mars Musk wants to explore.

Friday, April 8, 2016

Defining the Missions for the Ocean Worlds



One of the major revolutions in planetary science that I’ve seen in my lifetime is the discovery that the solar system contains not just one ocean world – our Earth – but several ocean worlds.  Unlike or planet, which has its oceans on the surface, these other worlds trap their oceans beneath a surface layer of ice (or in the possible case of the asteroid Ceres, beneath a rocky shell).  For several of these worlds such as Jupiter’s moons Ganymede and Callisto, the oceans appear to be locked between layers of ice and therefore would be unlikely candidates for abodes of life.  For two of the moons, Jupiter’s Europa and Saturn’s Enceladus, the oceans appear to lie directly on top of a rocky core that would provide key elements needed to support life as well as energy from possible hydrothermal vents.  Saturn’s moon Titan is a unique case, with seas of liquid ethane, methane, and propane on the surface and a water ocean in the interior that may or may not be in contact with the rocky core and occasionally interact with the surface.  (This article and poster give more background on these worlds and their oceans.)

NASA’s managers, at the direction of Congress, have begun to put together an Ocean Worlds program to explore Europa, Titan, and Enceladus.  At a recent meeting of an advisory group for NASA, the Committee on Astrobiology and Planetary Science (CAPS), Jim Green, the head of NASA’s Planetary Science Division, and Barry Goldstein, from the Jet Propulsion Laboratory, provided updates on plans to explore these worlds.  In this post, I’ll report on the highlights of their talks (the presentations will be posted to this site (scroll down to the March 29-31 meeting) sometime in the future).


Europa Multi-flyby Mission

The only currently approved mission in the Ocean Worlds program is the Europa multi-flyby spacecraft.  This mission, estimated to cost ~$2 billion, will orbit Jupiter and will take approximately 45 toe dips into the high radiation belts surrounding this moon to make close flybys.  In between flybys, the spacecraft will have time to transmit the volumes of data it collected up close back to Earth.  (This presentation gives a good overview of the mission design and science goals while this presentation summarizes the instrument payload.)

The mission is well into its design phase.  At the CAPS meeting, the project manager, Barry Goldstein with the Jet Propulsion Laboratory, updated the committee members on refinements to the design.

Until recently, NASA’s managers had hoped that the main spacecraft could carry a 250 kilogram free flying daughter spacecraft to conduct complimentary studies.  Ideas ranged from a simple Europa lander, to a spacecraft that would divert to flyby the volcanic moon Io, to a spacecraft dedicated to flying through any plumes ejecting material from the surface of Europa.  NASA had invited the European Space Agency to propose (and pay for) a daughter spacecraft.  In addition, a group at NASA’s Goddard Space Flight Center had developed a proposal for a free flyer that would swoop even lower to the surface than the main spacecraft to fly through any plumes while carrying a mass spectrometer more tuned to identifying bio signatures than the main spacecraft’s instruments.

Unfortunately, it appears that NASA has decided to drop the idea of a daughter spacecraft.  I’m told that ESA’s managers determined that they had no way to fund such a spacecraft on the timeline for the Europa mission.  NASA’s managers may have also decided they lacked the funding to build their own daughter spacecraft.

Dropping the daughter spacecraft opens up new possibilities for launching the multi-flyby spacecraft to Jupiter.  NASA’s primary plan for sending this spacecraft on its way is the Space Launch System (SLS) that would enable a direct launch.  This extremely large booster could launch the spacecraft directly to Jupiter with a flight time of 2.1 to 2.5 years.  It will have sufficient heft to give the project a 33-35% mass margin, providing a cushion should the actual spacecraft as finally implemented weigh more than its designers currently think it will (which usually happens). 

The SLS, however, is still in development and its reliability will only be proven through one or more future flights.  In addition, this program is something of a political football, and so assuming it will be funded through development and into the time period of the Europa launch is a risk.  It’s also unclear what an SLS launch would cost and whether or not the planetary science program could afford it.  The project’s managers, therefore, are designing the spacecraft to also be capable of being launched on a less powerful commercial launch vehicle. 

Currently that backup would be either an Atlas V 551 or Delta IV Heavy booster followed by three Earth and one Venus flybys to receive gravity assist boost that would enable the final flight to Jupiter (known as the EVEEGA trajectory).  This extended looping flight would take 7.4 years to reach the Jovian system.

Dropping the 250 kilogram free flyer (plus supporting equipment on the main spacecraft) opens up an alternative launch plan.  By enlarging the spacecraft’s propellant tanks to allow a large deep space maneuver to set up a single Earth gravity assist (known as the ∆v/EGA trajectory), a Delta IV Heavy vehicle could deliver the Europa mission in just 4.7 years while still providing a healthy mass margin of 34%.  (For Falcon Heavy fans, NASA’s managers will consider this booster, too, once they have its final specifications, but they believe it would have similar performance to the Delta IV Heavy.)

This new launch backup is not yet an official plan as engineers and NASA’s managers examine it in more detail.  If they decide they can adopt it, the net savings in flight time if the SLS launch is unavailable is 2.7 years.

The current baseline plan for launching the Europa multiple flyby mission is the Space Launch System.  A new backup plan under consideration could reduce the alternative flight from over seven years to less than five years. Credit: NASA/JPL


Titan and Enceladus

The Ocean Worlds program now includes Saturn’s moons Titan and Enceladus as target worlds.  Previous mission proposals were for either for expensive Flagship missions (with estimated costs of ~$1.5 billion to ~$6 billion) or the inexpensive  Discovery missions (~$450 million).  The former doesn’t fit within NASA’s budget and the latter appears to be too little to reach and explore these distant moons.  In the past few months, NASA’s managers have opened up the intermediate cost (~$850 million) New Frontiers mission class to explore these worlds.

Science objectives for Enceladus and Titan presented by Dr. Green.  Credit: NASA
 
At the CAPS meeting, Green presented draft science objectives for a possible New Frontiers mission to Enceladus and/or Titan along with example goals for measurements that would meet those objectives.  For Enceladus, the goals relate to understanding the composition of the material within the plumes erupting from the moon’s southern pole.  What are the organic molecules in the plume detected by the Cassini spacecraft, but which its instrument lacked the sensitivity to analyze in detail?  Do these compounds suggest possible present life or a geological origin from hydrological activity?  Does the chemistry suggest that the ocean below the icy crust has the necessary chemicals to support life?

The goals for Titan mission broke into two sets.  The first related, as with Enceladus, to questions of chemistry.  How are complex organic molecules created, modified, and stored in the upper and lower atmosphere and in the surface lakes and seas?  Do any of these compounds suggest possible pre-biotic or even biotic origin?  The second set of goals focus on the structure of the interior ocean (for example, is it in contact with the silicate core that would provide many of the elements needed for life?) and whether material from that ocean may have reached the surface (as evidenced by past resurfacing).

Previous studies have looked at a number of mission concepts to continue the exploration of these two moons following the Cassini mission.  At the high end – and almost certainly outside the cost cap of a New Frontiers mission – were Titan and Enceladus orbiters and Titan balloons. 

In the past two Discovery competitions, three missions to Enceladus and Titan were proposed (but not selected to fly).  By law, NASA’s managers can’t reveal the results of their evaluations of these proposals – that’s proprietary information for the proposing teams who may well propose future missions in these competitive selections.  However, comments by managers in public meetings have said their science was compelling and that missions to the Saturn system don’t fit within the cost cap of the Discovery program.  The implication is that the higher mission costs allowed by the New Frontiers program could enable a mission to the Saturn system.  These past proposals for Discovery-class missions suggest possible New Frontiers-class missions to these worlds.

Two of the Discovery proposals replaced orbiters with spacecraft that would – like the Europa multiple flyby mission –that would study these Saturnian moons with multiple flybys.  The Enceladus Life Mission (ELF) would have flown through Enceladus’ plumes with two cutting edge mass spectrometers that would have studied the chemistry of the ocean’s volatiles and silicates.  The Journey to Enceladus and Titan (JET) would have carried a mass spectrometer to study the volatiles in the plumes and Titan’s upper atmosphere.  It would also have carried a thermal imaging camera that would have imaged Titan’s surface at up to an order of magnitude higher resolution (as fine as 25 m) than the Cassini spacecraft has done.  The imager would also have imaged the sources of the plumes on Enceladus’ surface in much higher resolution than Cassini has.

A possible New Frontiers proposal might combine the ELF and JET proposals by carrying ELF’s mass spectrometers and JET’s thermal imager and conduct multiple flybys of Enceladus and Titan.  Such a mission could address the composition questions posed by Green for Enceladus and Titan’s upper atmosphere.  The thermal imager could address the questions of whether Titan’s surface morphology indicates that the subsurface ocean has interacted with Titan’s surface. 

Possible enhancements to this type of mission might include an ice penetrating radar to study the subsurface structures of their icy shells.  Or the thermal imager could be enhanced by adding an imaging spectrometer that would search for variations in the surface composition of Titan.  Both of these latter ideas have been included in previous, Flagship-class mission proposals and would address the goal to better understand the structure of the interior oceans and their interaction with the surface.

Both Discovery proposals included high speed flybys of Enceladus.  While these flybys are relatively easy to set up, the velocity (typically ~4 kilometers per second) could destroy any highly complex organic molecules as they impact the mass spectrometer instruments.  One mission option would instead use a number of flybys of the moons Rhea, Dione, and Tethys to lower the orbit over two years to enable Enceladus flybys at ~1 kilometer per second.  Affording the additional costs of two years of mission operations likely is hard in a Discovery mission proposal but might be an option that could fit within a New Frontiers budget.

The third Discovery proposal, the Titan Mare Explorer (TiME), would have landed a probe to float on one of the moon’s large polar seas.  These lakes are believed to be stews that absorb and release gases into the atmosphere, receive a rain of complex organic molecules created in the upper atmosphere, and interact with the ices forming the shores and bottoms of the lakes.  A future mission could replicate TiME’s goal to study Titan’s chemistry.  The TiME proposed mission focused tightly on science conducted on a lake. A plusher New Frontiers mission might add instruments that could enhance atmospheric composition measurements as the probe descends to a lake landing as was proposed for a Flagship version of this mission several years back.

There is no assurance that an Ocean Worlds mission will be selected as the next New Frontiers mission, which will launch in the mid-2020s.  These missions are selected through open competitions.  The other missions on the candidate list – a Venus lander, lunar sample return, comet sample return, a Saturn atmospheric probe, and Trojan asteroid tour – are scientifically compelling in their own right and several may be less risky and expensive to implement.  We should learn which mission is selected in 2019.

On a side note, not discussed at the CAPS meeting (at least while I was listening), is the question of international cooperation in exploring Titan and Enceladus.  An obvious idea would be to combine the Titan lake lander with the multi-flyby spacecraft that could act as carrier and data relay in addition to its own scientific duties.  Fitting both within a New Frontiers budget seems unlikely to me.  However, other space agencies, particularly ESA, are also interested in exploring these worlds.  It may be possible that NASA would provide one craft within a New Frontiers budget while another space agency provides the complimentary craft.  Timing the funding for cooperative missions can get tricky (as shown by the inability of ESA to pay for a Europa mission free flyer on NASA’s schedule), but it is an obvious idea that I’m sure will be explored.

Examples measurements a New Frontiers mission to Enceladus or Titan might make to meet the science goals.  Credit: NASA
  
An Ocean Worlds Lander

In addition to providing an update to the Europa multiple flyby mission, JPL’s Goldstein provided the first public look at the current concept for a Europa lander.  In the normal progression of exploring a world, NASA would not look at detailed plans for lander until the results from a mission orbiting that world (replaced with multiple flybys for Europa) were in.  However, Congress has directed NASA to add a lander to the currently planned Europa mission.

JPL’s engineers have decided to make the lander an entirely separate spacecraft from the multi-flyby spacecraft.  To find the spot on this moon that best combines scientific value and landing safety, the multi-flyby spacecraft must first complete its examination of the surface.  As a result, a landing would come at least two to three years after the arrival of the multi-flyby spacecraft.  The lander spacecraft could either launch with the multi-flyby spacecraft and park itself in Jovian orbit while waiting for the reconnaissance to be complete or the lander could be launch later.  (I’m betting on the latter.  NASA’s Green described the current design state of the lander concept as “immature” and it’s not clear that NASA will receive sufficient time or funding to mature the design in time for launch with the multi-flyby spacecraft.)

A Europa lander, whose design could be used for landing on other ocean worlds, would consist of four major elements, a carrier craft that would also relay the lander's data, a solid rocket motor to slow the lander, a sky crane descent stage, and the lander itself.

The lander itself would look much like and be about the size of the Mars Pathfinder that landed on the Red planet in 1997 (but without the Pathfinder’s small rover).  The lander would be encased in petals that would deploy, allowing the lander to right itself if necessary after touchdown and that could also act as “snowshoes” in case the landing is on a soft surface.  A mass spectrometer and a Raman spectrometer would study the composition of the surface material, panoramic and microscopic cameras would provide context and close up images, and a geophone would provide seismic measurements.  The lander would include an arm that could scoop or drill samples from the surface to deliver to the instruments.  Batteries would power the lander for up to 21 days.

The proposed Europa lander would look much like and be roughly the same size as the Mars Pathfinder lander (bottom).  Credit: NASA/JPL

 While the initial target for this lander design is Europa, Goldstein pointed out that the design could be used to land on a number of ocean worlds including Enceladus and Jupiter’s Ganymede.  (As discussed above, a Titan lander will need enter and descend through a thick atmosphere and then float on a sea.  Its design is likely to be quite different.)  Perhaps, if the funding gods are kind, we could see both multiple flyby missions to these moons and landers for these moons launch in the next decade or two.

Additional Material

Current launch plans for the Europa multiple flyby mission.  Credit: NASA/JPL.
The proposed multiple flyby tour of Titan and Enceladus for the Journey to Enceladus and Titan (JET) mission (top) and the ground tracks below each flyby (top panel of bottom slide) and the imaging resolution for Titan and the height of the flyby through the plumes for Enceladus.  Credit: JPL