The big news for future planetary exploration
this month is likely to be the announcement of the instrument selection for
NASA’s 2020 Mars rover that will define how it will fulfill its scientific
goals. In the meantime, there have been
several announcements for proposed missions to Mars and on the planning for a
NASA return to Europa that highlight the contrasts in planning missions for
these two high priority destinations.
China’s chief scientist for its lunar program
has stated
that China is planning a rover mission to Mars for 2020 and a sample return
from that planet by 2030. The Chinese
space program tends to be tight lipped about its plans (especially those still
several years out), and I’ve been unable to find any more information. Is this mission a placeholder on the space
agency’s roadmap – much like an eventual Martian sample return for NASA – or an
approved and funded program? Would the
rover be delivered by a small lander and therefore be small itself, perhaps
like NASA’s 1996 Sojourner rover? Or perhaps
it would be a medium sized rover like China’s Yutu lunar rover and NASA’s
Opportunity rover. Given China’s string
of successes and careful build up to more complex missions, if a Martian rover
is firmly in their plans, they seem likely to succeed.
A Chinese rover would find itself part of a
crowd on the Martian surface in 2020. As
mentioned above, NASA plans its own Curiosity-class rover for that year. Europe’s ExoMars rover is likely to still be
operating along with its Russian stationary lander. I’m willing to bet that NASA’s 2016 InSight
lander and Curiosity rover will still be functioning, and I have some hope that
the Energizer bunny-Opportunity rover will still be alive (although perhaps as
a stationary platform by then).
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| Mars exploration has reached the point where private organizations can promote credible plans for complex Mars missions on the web. Credit: BodlyGo Institute and Mars One |
If two private organizations have their way,
the party at Mars will be more raucous still.
The BoldlyGo Institute would like to raise funds for its SCIM
spacecraft that would dip briefly into the
upper atmosphere during a high speed flyby to snag dust and atmosphere samples
to return to Earth. While we have some
130 rocks delivered as meteorites that are believed to be from Mars, this
mission would return samples of the dust that ubiquitously blankets the
planet. If this idea seems familiar, it
was proposed twice before in NASA’s Mars Scout and Discovery mission
competitions. Now its backers hope that
this mission will have better success at securing private funders.
Another organization, Mars One has been
planning to land humans on Mars in about a decade’s time. Recently, it announced plans for a Martian lander for 2018 built on the
same platform as NASA’s Phoenix and InSight landers. Mars One is seeking proposals for instruments
that would be useful to eventually colonization of Mars. For example, the organization is requesting
proposals to demonstrate water extraction from the soil. It would also deliver one instrument
developed by a university to the surface of Mars.
Both of these missions depend on finding
funding from some combination of rich donors, corporate sponsors, and crowd
sourcing from small donors. I’m never quite certain how much hope to hold out
for missions that depend on private donations.
Given their scope, these two missions would likely costs of several
hundred million dollars; each mission would either need a fantastic number of
small contributors or one or more wealthy contributors. While rich space enthusiasts exist (I’m
thinking of Elon Musk of SpaceX as an example), if you are very,
very rich and have the slightest inkling towards philanthropy, then fund
raisers from many worthy causes from universities to global health to saving
species are already in touch with you.
Rather than dividing potential support,
having multiple organizations trying to raise funds may benefit private
planetary exploration. We can’t know
beforehand which, if any, approaches will open check books and competition may
help us learn what will work. (The B612
Foundation is another player looking to
finance a challenging mission, in their case a space telescope to search for
near Earth asteroids.)
Jeff Foust at The
Space Review had a story recently on the
potential for private funding of space missions. While raising hundreds of millions of
dollars my prove too daunting, technology is on the cusp of enabling small
planetary spacecraft based on CubeSat
and SmallSat
technologies that would cost just a few tens of millions of dollars. The Planetary Society’s LightSail project is an example of such a mission (although it
will test critical hardware in Earth orbit rather than fly to another world).
If planning for Mars missions is becoming
commonplace, NASA is still trying to find a plan to for a dedicated mission to
Europa. In a step forward, the agency has
released a request for proposals to the scientific community for instruments
for a Europa mission. It did so,
however, in a rather odd fashion.
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| Reddish features in this colorized image of Europa's surface likely contain water ice mixed with hydrated salts, potentially magnesium sulfate or sulfuric acid that may represent material from the interior ocean. Full caption available at http://www.nasa.gov/content/reddish-bands-on-europa/. Credit: NASA/JPL-Caltech/SETI Institute |
Usually when NASA requests instrument
proposals, it has a solid mission concept in mind. For this call, NASA said that the Europa
mission might be an orbiter or might be a multi-flyby spacecraft. The request document was vague as to the
budget for instruments and just said that past studies assumed it would likely
be around 15% of the total mission cost.
While many instruments by their nature have modest costs, some could be
quite costly and it might help proposers to know whether the total instrument
budget is closer to $150M (for the $1B total mission cost NASA would like) or
to $300M (for the ~$2B that past studies have said is needed to achieve all the
high priority scientific goals).
For some instruments, proposers will have to
bet that NASA either selects a multi-flyby spacecraft or an orbiter. For example, measuring Europan tides would
help pin down the depth of the ice covering the ocean. A laser altimeter could accurately measure
the tides, but it requires an orbiting platform to pin down the size of the
tides. If NASA goes with a flyby
spacecraft, any group that proposed an altimeter is likely to be out of luck.
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| Examples of instruments that the scientific community may propose to study Europa. From the Europa instrument Announcement of Opportunity available here. |
The request for proposals gives two roadmaps
for how NASA will select the winning proposals.
Its managers expect that they will select up to 20 proposals in April
2015 for which they will fund further development towards a final selection of
approximately eight instruments a year later.
NASA also reserves the right to simply select the final instrument suite
in April 2015. The document implies that
the longer timeline assumes a launch no earlier than 2021, while the shorter
timeline could either reflect a possible earlier launch date or the possibility
that the proposals seem ready for selection without an additional year of
maturation.
With this request, NASA appears to be showing
its commitment to an eventual Europa mission, but it still hopes to find a
cheaper alternative that will win the allegiance of the scientific
community. The large cost overruns on
the Curiosity Mars rover and James Webb Space Telescope have made the White
House’s budget managers and NASA’s senior managers wary of multi-billion dollar
missions.
SpacePolitics.com reports that NASA has received a number of concepts
for Europa missions that might cost no more than $1B. The agency is currently assessing these ideas
for their cost, technical, and scientific feasibility. Comments by NASA’s chief scientist suggest
that these missions likely would perform only a fraction of the science
considered high priority by the scientific community (and that would be
accomplished by the current ~$2B mission concept).
In the request for instrument proposals, NASA
specifically asked for instruments that could study possible plumes of water erupting
from Europa. The recent possible
discovery of plumes at Europa has raised the question of whether and how planning
to explore this world should be changed.
If the plumes are verified, then they represent a chance to directly
study material being ejected into space from beneath Europa’s surface as
Cassini has been able to do for Saturn’s moon Enceladus.
The request comes despite the recommendations
a few weeks earlier of NASA’s Europa Science Definition Team. They reviewed both the evidence for Europan
plumes and the experience studying plumes erupting from Saturn’s moon Enceladus
with the Cassini spacecraft. Their
recommendation was that a mission to Europa should be capable of exploring
plumes if they exist, but that a dedicated focus on the plumes would not be
appropriate.
First of all, the team noted, only one
observation made by the Hubble Space Telescope saw possible plumes. Other searches for plumes by telescopes and
by the Galileo spacecraft when it orbited Jupiter have not found unambiguous
evidence for plumes. (Some Galileo data
is consistent with plumes but also have other possible explanations.) Even if the Hubble did observe one or more
plumes, they may occur at sporadic intervals separated by years or
decades. If so, they would be more like
the sporadic eruptions of each volcano on Io than the so-far continuous
eruptions seen at Saturn’s Enceladus. A
mission to Europa lasting a few years might entirely miss plumes if they
sporadically erupt.
Second, Cassini’s observations of Enceladus’
plumes have shown the power of a diverse instrument set to characterize plumes.
Instruments already recommended for the
~$2B Europa mission concept could be used to search for and study any
plumes. A mass spectrometer, for
example, could determine the composition of the gases expelled from the
surface, while the thermal imager could look for warm spots that would be the
source of the plumes. A couple of
instruments such as a UV spectrometer and a dust spectrometer that haven’t made
the straw man list of instruments used for mission studies to date would
enhance plume studies, but these instruments also would be useful for studying
the rest of Europa.
The instrument request document acknowledges
the science team’s assessment, but states that, “the scientific potential
presented by the plumes is sufficiently high that NASA will continue to
emphasize the importance of plume investigations and encourages instrument
investigations focused on this area.”
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| Draft summary of findings by the Europa Science Definition Team regarding possible Europa plumes and planning for a mission to that moon. Entire presentation available here. |
While NASA’s management decides the scope of
a Europa mission, engineers at JPL continue to refine the design of the current
leading concept, the Europa Clipper that comes with an estimated cost of
$2.1B. The current concept would have
the Clipper spacecraft make 45 dashes through the radiation fields surrounding
Europa for close up looks at the surface and interior. Building a spacecraft and instruments that
can survive that radiation exposure is one of the factors that has driven the
cost well above the $1B NASA’s senior managers would like to see.
A presentation made to the science team also
provides more insight as to why a large number of encounters are required to
study Europa. The science team has
carefully justified what measurements are needed at Europa to understand this
world and to enable planning for a lander that would follow the Europa Clipper.
As an example, the science team has stated a requirement that the composition of 70% of the surface be mapped at resolutions of less than 10 kilometers by an instrument known as a short-wave infrared spectrometer. With 45 encounters, this goal would be just missed with 68% of the surface mapped. (Thirty flybys would map 50% at this resolution or better.) Similarly, mapping 70% of the surface with an imaging camera at resolutions of 1 kilometer or better would require 38 flybys. A global distribution of flybys to study the structure of the ice and ocean beneath the surface with an ice penetrating radar would not be met until 43 flybys.
If the radiation belt did not exist, the next
stage to exploring Europa would be to orbit it instead of frantically gathering
data during numerous brief flybys. (Europe,
for example, will send the JUICE spacecraft to orbit Europa’s sister moon
Ganymede, but that moon lies outside the harshest portions of the radiation
belt.) JPL’s studies suggest that a
Europa orbiter would cost about the same as the Europa Clipper, but its
lifetime would be so short that the Clipper with its many flybys would better
study this moon.
We are left with contrasting opportunities
for studying these two worlds. Mars is
close enough and benign enough that both China and private organizations can
seriously consider challenging missions.
Europa’s location within harsh radiation belts leaves it as both a
technical and a budget challenge.
