Friday, February 22, 2013

Instruments for the JUICE Jovian Mission

Artist conception of the JUICE spacecraft encountering Europa.  Credit: ESA/AOES

The European Space Agency (ESA) announced the list of instruments selected for its JUICE mission to explore the Jovian system for three years starting in the 2030 following a 2022 launch.  (NASA is a junior partner on the mission.)  The JUICE spacecraft will make two close flybys of the moon Europa, several flybys of Callisto, and then will settle into orbit around Ganymede for an extended study of that moon.  During the tour of Europa and Callisto, the spacecraft will observe the cloud deck of Jupiter and investigate the magnetosphere surrounding the king of planets.

The JUICE mission will be a worthy successor to the Galileo mission of the 1980s and 1990s that similarly toured the Jovian system.  To keep the cost of the mission around 1B Euro, the spacecraft will have only modest radiation hardening and will only briefly tiptoe into the higher radiation fields close to Jupiter.  Hence, the spacecraft will make just two flybys of Europa where Galileo did a number of flybys.  Unlike Galileo, the JUICE spacecraft will not come closer to Jupiter than the orbit of Europa and hence will not do close flybys of the moon Io.  However, it will observe Io remotely to gauge its volcanic activity. 

ESA’s mission will compliment NASA’s Juno mission that is en route to Jupiter.  Juno will perform extremely close observations of Jupiter, skimming above the top of the atmosphere.  During the close encounters, Juno will see just a tiny slice of the giant planet that lies directly beneath its orbit, but will see the entire area of each pole as it approaches and recedes from Jupiter.  JUICE on the other hand, will see the entire planet and be better able to study broad weather patterns, but only will see the poles obliquely.  Also, Juno will ignore the moons, while JUICE makes the moons the primary focus.

ESA’s press release said very little about the instruments, literally giving just their names.  (I suspect they were leaving the details to be given in the press releases from the individual nations funding the instruments.)  Press releases from NASA and the Jet Propulsion Laboratory provided additional information on the instruments they are participating on.  For the remainder of this post, I've organized the instruments by study area and pieced together the limited information from the three press releases and from the JUICE Assessment Study Report (the “Yellow Book”) that discussed general goals for types of instruments. 

Remote sensing instruments to image and map composition:

  • JANUS: Jovis, Amorum ac Natorum Undique Scrutator, camera system (Google translated the Latin as, “Thursday, love, and children everywhere Examiner,” which put a smile on my face.)  No information was given whether the camera(s) will be narrow angle (telephoto), wide angle, or both.  From the yellow book: A narrow angle camera could, “provide high resolution images of Jupiter and its moons. Global imaging from the high orbit [around Ganymede] and imaging of selected targets with resolution of few meters per pixel from the low altitude at Ganymede will make a breakthrough in our understanding of the geology of the icy satellite and history of its surface.”
  •  MAJIS: Moons and Jupiter Imaging Spectrometer.  From the yellow book, the main goals for this type of instrument, “are to study the composition of the moons’ surfaces and the composition, dynamics, structure and morphology of the Jupiter atmosphere.”
  •  UVS: UV Imaging Spectrograph.  From NASA’s press release: “The principal investigator is Randy Gladstone of Southwest Research Institute in San Antonio. This spectrometer will acquire images to explore the surfaces and atmospheres of Jupiter's icy moons and how they interact with the Jupiter environment. The instrument also will determine how Jupiter's upper atmosphere interacts with its lower atmosphere below, and the ionosphere and magnetosphere above. The instrument will provide images of the aurora on Jupiter and Ganymede.”
  • SWI: Sub-millimetre Wave Instrument.  From the JUICE yellow book: “The main objective of a submillimetre wave instrument is to investigate the structure, composition and dynamics of the middle atmosphere of Jupiter and exospheres of its moons, as well as thermophysical properties of the satellites surfaces.”

Three instruments will map the physical structure of the moons during close encounters and from Ganymede orbit:

  • GALA: Ganymede Laser Altimeter.  From the yellow book, “A Laser Altimeter (LA) will contribute to the characterisation of the icy moons. It will provide data about the topography, shape and tidal deformation of the icy surfaces. It will also be crucial for studies of the spacecraft orbit in the gravity field of a satellite by providing accurate range data.” 
  • RIME: Radar for Icy Moons Exploration.  From the NASA press release: “The principal investigator is Lorenzo Bruzzone of Universita degli Studi di Trento in Italy. The U.S. lead is Jeffrey Plaut of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. Under the lead of Bruzzone and the Italian Space Agency, JPL will provide the transmitter and receiver hardware for a radar sounder designed to penetrate the icy crust of Europa, Ganymede, and Callisto to a depth of about 5 miles (9 kilometers). This will allow scientists to see for the first time the underground structure of these tectonically complex and unique icy worlds.”
  •  3GM: Gravity & Geophysics of Jupiter and Galilean Moons  From the yellow book: This instrument will perform the, “Characterisation of internal structure and subsurface oceans at Ganymede and Callisto and possibly at Europa by tracking the spacecraft”

Several instruments will study the magnetospheres of Jupiter and Ganymede and the particles trapped within them:

  • J-MAG: Magnetometer for JUICE.  From the yellow book: “The [magnetometer] instrument will characterize the permanent internal/intrinsic magnetic field of Ganymede; establish and characterize magnetic induction signatures in possible subsurface oceans at Ganymede, Europa and Callisto; investigate Ganymede’s mini-magnetosphere which is embedded within the Jovian magnetosphere; observe magnetic field signatures within the Jovian magnetosphere and aid in characterizing the dynamics within this magnetosphere.”
  •  PEP: Particle Environment Package.  From the NASA press release: The principal investigator is Stas Barabash of the Swedish Institute of Space Physics. The U.S. lead is Pontus Brandt of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md. Under the lead of Barabash and the Swedish National Space Board, APL will provide instruments to this suite to measure the neutral material and plasma that are accelerated and heated to extreme levels in Jupiter's fierce and complex magnetic environment.
  •  RPWI: Radio & Plasma Wave Investigation.  From the yellow book (and this is a mouthful of physics-speak): , “RPWI consists of a set of sensors that measures the dc electric field (two E-field dipole sensors), the electric component of plasma waves (E-field sensors and use of the radar antenna), magnetic field component of electromagnetic waves (Search Coil Magnetometer), radio emissions (triad of radio antennae) as well as some detailed characteristics of the thermal plasma (Langmuir Probes) including electric conductivity. Most of the proposed measurements have never been carried out before around Jupiter and its moons.” 

A final instrument “does not include spacecraft hardware but will exploit VLBI – Very Large Base Interferometry – to conduct radio science.”  I'm not sure what that means, but here is the instrument's name: 
  • PRIDE: Planetary Radio Interferometer & Doppler Experiment

When more information becomes available, I’ll write additional posts on the instruments.

Tuesday, February 19, 2013

Brother, Can You Spare $1B for a Planetary Space Telescope?

Imagine you had a Hubble-class telescope and could use in any way you wanted to explore planets.  What would you do with it?

A number of scientists have had the chance to explore that question courtesy of an American spy agency.  A year ago, NASA received a surprise phone call from the National Reconnaissance Agency (NRO), which flies spy satellites, asking if it would like two spare, Hubble-class space telescopes.  NASA’s managers said,”Yes!,” and now the agency is looking for the best uses for the telescopes.  The highest priority is to see if one telescope could be used to meet the needs for the Wide-Field Infrared Survey Telescope (WFIRST) to study dark energy.  That potentially leaves a second telescope for other deep space or solar system studies.

Before I describe the concepts discussed at a recent conference, a truth in advertising statement is required.  Each telescope represents $250M worth of hardware.  However, not all the systems needed for an actual satellite are included, instruments are not included, and the whole lot would need to be launched.  Figures I’ve read suggest that turning each telescope into a working observatory would cost approximately $1B, depending on the specifics of the mission.  NASA’s current budgets have no room to fund a single mission, much less two.  In a few years, there may be room for a mission or two, so the space agency is soliciting ideas.

Some assembly required: The hardware provided by NRO.  NASA would be required to provide all the additional hardware, launch, and mission operations support to turn the core telescope into a working space telescope.  Image from this presentation.

At the conference, researchers presented ideas for both deep space astronomical targets and a variety of planetary targets.  The latter were divided between exploring Mars, monitoring the solar system, and examining any planets orbiting stars in the stellar neighborhood.

The original mission for the telescopes was to take very high resolution images of the Earth’s surface.  Two of the proposals would repurpose those terrestrial imaging capabilities to spy the surface of the Red Planet in very high resolution.  The Mars Reconnaissance Orbiter’s instruments are the current high resolution champs at Mars with 90 cm resolution for images and 18 m for multi-spectral imaging.  By using the NRO’s telescope, those numbers improve to 23 cm and 1 m.  A second proposal would improve those numbers to 8 cm and 21 cm.  (Those improvements appear to also come in part from more modern instruments as well as the larger telescope.)  The high resolution comes with a tradeoff, and only a handful of sites could be studied each day.  Depending on the resolution, the images taken would be stripes along the surface less than two or even one kilometer wide.

Getting this large of a telescope to Mars, however, would be a challenge.  Both proposals would use a solar electric propulsion stage.  While smaller planetary spacecraft have used solar electric propulsion, I believe this would be the first with such a large spacecraft.  One of the proposals points out that this would be a demonstration of solar electric propulsion capabilities that may eventually be used for a human Mars mission.

Comparison of potential capabilities of the NRO telescopes in Mars orbit for visible camera images and for an imaging spectrometer compared to the capabilities of the currently operating Mars Reconnaissance Orbiters HiRISE camera and CRISM imaging spectrometer.  While the NRO telescope would improve resolution, the size of the images would be much smaller (look at the swath widths).  From Zachary J. Bailey and colleagues abstract submitted to the conference.  Click on the table for a larger image.
Several of the proposals would keep the telescope near Earth, but would use it to watch the bodies of the solar system.  The studies proposed are not that different than what can be done with Hubble today.  However, the Hubble telescope spends just a small portion of its time looking at the neighborhood.  As one proposal summary states: “The advanced instruments on [Hubble] are rarely trained on solar system targets due to high oversubscription and an increasing focus on deep field observations.” 

The solar system watch proposals presented at the conference point out that the instruments proposed would also be useful for deep space studies, the allocation of observing time would be reversed.  The telescope’s resolution and would allow it to be a planetary mission to many worlds.  Many of the studies would repeat observations over months and years: the change in weather patterns on the gas planets as well as Saturn’s moon Titan; and the evolution of outgassing by comets as they approach and recede from the inner solar system; and volcanism on Io and Enceladus (with searches for volcanism on other worlds).  Other observations would study large numbers of asteroids and Kuiper belt objects in the distant solar system to measure their size and composition.  Depending on the specific proposal, the instrument complement would include some combination of a camera for high resolution images and/or ultraviolet and near infrared spectrometers for composition measurements.

A number of the proposals would use an NRO telescope to perform long term solar system studies.  This image shows Uranus as imaged by the  Hubble Space Telecope.

A number of the proposers would look beyond our solar system to study planets orbiting stars in our stellar neighborhood up to 60 light years away.  While the specifics of each proposal varied, most proposed would use one or more of three techniques: 

  • A coronagraph could block the bright light of the target star, allowing planets to be visible for spectrographic studies of their composition.  If the coronagraph is built into the telescope, it appears that gas giants and possibly super Earth-sized planets could be studied.  If a co-orbiting stellar shade were used instead, Earth-sized worlds within inner stellar systems could be detected.
  • A second instrument could use astrometric techniques to measure extremely faint wobbles in the star’s motion to determine the mass of visible planets and to detect smaller planets too small to image.  While similar techniques have been used to discover numerous exo-planets with Earth-bound telescopes, a large telescope above Earth’s atmosphere would allow much more sensitive searchers
  • A third instrument could measure the spectral change that occurs when planets cross in front of their stars.  The bright light of the star shining through the atmosphere enables more precise compositional measurements for planets with atmospheres than is possible with a coronagraphic spectrometer, which can examine only the faint reflected light.  For all planets that happen to cross in front of the star, the dimming of the light received provides information about the size of the planet.

We know so little about planets orbiting other stars that even simple measurements of colors can tell us what type of world they are.  In this figure from Timothy A. Livengood's proposal, ratios of colors (indicated by their wavelengths) sort the planets into distinct groups using color information.  The Earth, with its water and life, is distinct from the other planets in the solar system.

While this blog is about planetary studies, exciting, potentially ground breaking astronomical missions also were proposed – it is not a given that a mission using the second telescope would have a planetary focus.  But if I were to answer my own question about what I would use a Hubble-class telescope for, my first choice would be to study planets around nearby stars.  This would be ground breaking research.  If the budget and spacecraft capabilities permitted, I’d then add instruments for studying solar system objects and dedicate large blocks of time to solar system studies.  (These instruments also could be similar – but with more modern technologies – to those currently on Hubble and therefore would also be useful for continuing Hubble astronomy studies.)

The recently completed conference was intended to look at a wide range of concepts.  NASA intends to select six for more in-depth studies.  It is likely to have plenty of time to do so.  Given current budgets, the second telescope (assuming the first is used for the WFIRST mission) seems unlikely to fly until the mid-2020s, if ever.


Selected proposal abstracts that provide a broad background for each proposed planetary mission type:

Thursday, February 14, 2013

Sequester Update

When I started this blog, I decided to include posts on the political and budget issues that impact future planetary missions as well as plans for specific missions.  I try to keep the former to a minimum, but this month the all news has been the sequester.  As you may recall, this is the poison pill US law intended to force Congress to make difficult decisions on how to reduce budget deficits.  As the month progresses, it looks more likely that the sequester will happen on March 1.  

If the sequester occurs, agencies like NASA will have to cut each program (but with wiggle room to move cuts around) by 5% relative to their Fiscal Year 2012 spending.  Since half of the current fiscal year has passed (the fiscal year starts October 1), the cut to the remainder of the year spending will be 9%.  (Some agencies have been under spending so far this year to bank money in case the sequester occurs; I don't know if NASA has been one of them.)

NASA has now sent Congress a letter giving examples of how the sequester will impact each of its programs.  Because its Science program absorbed a 3.2% budget cut in FY13 compared to FY12, the program would have to absorb just(!) an additional 1.8% cut to the FY13 budget. (NASA's letter says the additional cut would be $51.1M.  My spreadsheet says it would be $91.1M, so either the letter has a typo or more probably the budget summary I work from doesn't have the complete picture.) 

NASA's Planetary Science program absorbed a 20.5% cut from FY13 to FY12, so in theory it might be spared any sequester cuts.  However, NASA has some discretion to move cuts from higher priority programs such as the James Webb Space Telescope (with a 20% FY13 budget increase) to programs it considers lower priority.  The Planetary Science program might see some sequester cuts, if the sequester occurs, but perhaps less than the 5%.  The two specific examples of programs provided by NASA for the Science program shows that the amount of cuts is flexible between programs.  The low cost Earth Science and Astrophysics mission programs would have a 10-15% cut while the research and analysis program that supports individual scientists would have a 2% cut.

Still not good news -- the Science program already is hurting from the FY13 cut and paying for the cost overruns on the James Webb Space Telescope.  However, the addition sequester cuts to the Planetary Science program -- if they happen -- may not be as bad as I had feared.  I also still have some hope that in the end, the two political parties will blink and either cancel the sequester (everyone agrees that blanket cuts are terrible policy) or substitute it with a more thoughtful approach to reducing the deficit.

You can read my original post on the sequester here and a previous update here.  You can read the text of NASA's letter here on the Space Ref website.

Tuesday, February 5, 2013

Sequestration for the Perplexed and Minor Corrections

The journal Science has posted an article on the sequester for the perplexed that left me even more perplexed (and it's not because the writing isn't clear).  (The sequester would be automatic budget cuts applied to most US Federal programs at the beginning of March.)  It appears that the cuts that will be implemented this year may be 8.2%, 6.4%, or 5%.  The wording suggests, however, that any smaller cut this year may have to be made up for with larger cuts in future years to hit a total of $1.2 trillion over ten years.  It's also not clear what at what level of programs the cuts must be applied -- for NASA it might be the entire science division, each major science program (planetary, astrophysics, Earth science, etc.), or by budget category (for example, the Mars program).

Having had to decide where to cut programs in my former career, I know how painful this is and my sympathies are with the managers who have to plan for this.  My hope is that the political process will work at the last moment and we never have to learn what was on the chopping block.

In the charts showing the budgets for the Maven mission development and Curiosity rover operations in my post, Sequestration and Planetary Exploration, my spreadsheet software showed incorrect percentages (but correct dollar amounts).  I've corrected these charts, and I thank Duane for pointing out the problem.

Casey Dreier (I presume this is the same Casey who is the Planetary Society's Advocacy and Outreach Strategist) in the comments points out that the sequester will be calculated from Fiscal Year 2012 budgets.  NASA's overall budget for that year and this year are almost the same, so if NASA is given discretion on how to distributed the cuts, this may not make much of a difference.  However, if the sequester is applied to each program, the news might be better for the planetary program if FY12 is the basis:

Budget    8.2% cut Remainder
FY12 $1,501 -$123 $1,378
FY13 $1,192 -$98 $1,094

(All figures are in millions of dollars.)

If the planetary science program is cut less, though, other NASA programs likely will be cut more.