After a couple of month hiatus from blogging on future planetary exploration (it's that day job), I wanted to return by casting a wider net than normal for topics. Today’s post accumulates a number of news items and ideas that together suggest how rich the coming decades of planetary exploration should be.
I’m always looking for analogies that show how cheap planetary exploration really is when you look at the big picture. To each of us individually, $500 million, $1 billion, or $2 billion for a planetary mission feels like an almost unimaginable amount of money. (I’m assuming few billionaires are read this blog.) A better way is to look at these costs in the context of national economies. NASA’s budget for planetary exploration for 2014, for example, represents a trivial 0.008% of the US economy, or the equivalent of about $4 a year for a family earning $51,000 (the US median family income) a year.
Okay, that was a bit dry, so let’s look at a more fun analogy. Vox.com reports that this year, Americans spent an estimated $350M on pet costumes for Halloween. If NASA had a similar amount each year to spend on its cheapest class of missions (the Discovery program that has funded missions to Mercury and the asteroids Vesta and Dawn among many destinations), it could develop six to seven of these missions a decade instead of the two it developed in the last decade.
The past two months brought news of new planetary missions. India has announced that following the success of its Mars Orbiter Mission currently at the Red Planet, it will launch a follow up mission for 2018 after its second lunar mission to launch in 2016. Both the 2016 and 2018 missions will include a lander and rover.
India’s neighbor China also is planning for an ambitious planetary program. After four successful missions to the moon, China has firm plans for at least one and possibly two lunar sample return missions this decade. China has also discussed plans for a Mars mission later this decade, but it appears that nation’s ambitions are much wider ranging. Chinese space scientists recently published a series of papers describing their priorities across the fields of space science. The suggested mission list for planetary exploration, broken into three stages, through 2030 is ambitious.
First stage of missions
Mars orbiter, lander, and rover
Space-based mission to find near-Earth asteroids
Second stage of missions
Additional Mars mission(s)
Asteroid Ceres sample return
Solar polar observatory
Third stage of missions
Mars sample return
China’s lunar missions have shown that its engineers have the discipline and ability to undertake an ambitious program. If China’s leaders desire, they could fund this program (as I said above, on a national scale planetary missions are affordable). I suspect, though, that this represents the priority list of Chinese scientists, much like the Decadal Survey represents the priority list of US scientists. If the willingness of Chinese politicians to fund planetary missions is similar to that of US politicians, perhaps a third or a half of these missions will see serious development by 2030. Even that fraction, though, would make China a leading player in planetary exploration.
On this list, I’d most like to see the Ceres sample return. We already know that this asteroid is an rock-ice world different than any we've explored to date. I suspect that the Dawn spacecraft will show how intriguing this world is when it arrives in 2015. China’s lunar sample missions will fill a big hole that no other nation currently is addressing. China could fill a similar hole for Ceres, while all the other missions on the list are similar to those already planned by other space agencies (although at each world, there are always opportunities to explore from a new angle).
The next idea jumps from looking at missions across the solar system to enabling micro missions at Mars. NASA is planning a Martian rover mission for 2020 that will duplicate the entry system of the Curiosity rover mission currently on Mars. That entry system has disposable weights that are ejected during the entry and landing process. NASA has issued a challenge to the planetary science and engineering communities to suggest ideas how these could go from dead weights to useful micro-missions. NASA’s call for proposals states, “Proposed concepts should indicate uses for ejectable mass up to 150 kg prior to Mars atmospheric entry and/or another 150 kg during the entry and landing phases of the mission. NASA is seeking concepts that expand scientific knowledge or technological capabilities while exhibiting a high degree of practicality.”
A 150 kg is a lot to work with (although volumes will be constrained). I’m really intrigued to learn what creative ideas will be put forth. NASA expects to announce the winner this January.
The Aviation Week and Space Technology magazine reports that NASA’s Jet Propulsion Laboratory (JPL) and the Aerospace Corporation are exploring a different concept, called MARSdrop, for piggy-back Mars spacecraft. The idea is take advantage of the wealth of spacecraft systems that have been developed for CubeSats that use tiny form factors (as small as 10x10x10 cm) for micro-satellites. In the Mars concept, one or more 10 kg spacecraft would be released from a spacecraft approaching Mars. Each MARSdrop spacecraft would include its own atmospheric entry system and a triangular parachute called a parawing to enable gliding to desired destinations. The landers would be small, perhaps 10 kg, and the first will cost $20M to 50M to develop. The scientific payload would be small, perhaps a video camera or multispectral imager, and the first lander would likely be battery powered, limiting its lifetime to a few days.
The idea of small Mars missions seem to be trending, with a Canadian team proposing the Northern Lights mission. The small lander would come with its own instrument suite and arm and would also deploy a small rover that looks to be about the size of the Mars Pathfinder’s Sojourner rover. The program’s web site doesn’t mention any government funding – it appears that the team hopes to raise the few million dollars it believes it needs through crowd sourcing. To me, carrying seven instruments and a rover seems ambitious for first a private Mars mission. Just conducting a successful flight to Mars and then surviving landing (remember that the similar-sized British Beagle 2 lander failed that last test) to take a picture with the equivalent of a cellphone camera would be an outstanding feat. Technology has advanced to the point where micro Mars landers are conceivable; perhaps the Northern Lights team will be the ones to pull it off. Their website is worth a visit because I suspect that some team will put a lander of this scale on Mars in the next two decades.
Each year, NASA solicits ideas for exploration technologies that would push well beyond existing technologies to enable missions that might fly in a decade or two. If these ideas can be made to work, the payback could be enormous (although only a few if any will make it all the way from inspiration to launch pad). This year’s list of funded concept studies was rich in ideas for planetary exploration, and the following paragraphs provide a sampling of the ones I found most intriguing. So that you can get a flavor of the boldness and creativity of these ideas, I’ll let the teams speak for themselves by quoting from their concept summaries.
|Credit: NASA Glenn Research Center|
– Titan’s seas are the only surface oceans other than the Earth’s in the solar system. In the past, several teams have proposed simple floating landers or diving bells to explore these oceans. The Titan Submarine concept, though, would “send a submarine to Titan’s largest northern sea, Kraken Mare. This craft will autonomously carry out detailed scientific investigations under the surface of Kraken Mare, providing unprecedented knowledge of an extraterrestrial sea and expanding NASA’s existing capabilities in planetary exploration to include in situ nautical operations. Sprawling over some 1000 km, with depths estimated at 300 m, Kraken Mare is comparable in size to the Great Lakes and represents an opportunity for an unprecedented planetary exploration mission.” The list of science goals is ambitious: to study the “chemical composition of the liquid, surface and subsurface currents, mixing and layering in the “water” column, tides, wind and waves, bathymetry, and bottom features and composition.”
|Credit: NASA, JPL|
– Balloons to drift across the skies of Titan are another idea with a long pedigree. One limitation of past proposals, though, is that they would have no way to land to conduct studies or collect samples. Similarly, proposed landers would be limited to studying the few square meters around them. The Titan Aerial Daughtercraft would be a less than 10 kg rotocoptor that would, “deploy from a balloon or lander to acquire close-up, high resolution imagery and mapping data of the surface, land at multiple locations to acquire microscopic imagery and samples of solid and liquid material, return the samples to the mothership for analysis, and recharge from an RTG [plutonium power system] on the mothership to enable multiple sorties… This concept is enabled now by recent advances in autonomous navigation and miniaturization of sensors, processors, and sampling devices. It revolutionizes previous mission concepts in several ways. For a lander mission, it enables detailed studies of a large area around the lander, providing context for the microimages and samples; with precision landing near a lake, it potentially enables sampling solid and liquid material from one lander. For a balloon mission, it enables surface investigation and sampling with global reach without requiring a separate lander or that the balloon be brought to the surface.”
|Credit: John Hopkins University|
– Many of the moons of the outer solar system are believed to harbor oceans beneath their icy crusts. A key question for future missions will be how thick those overlying crusts are. Current methods require either power and data hungry and heavy ice penetrating radar systems or prolonged measurements from orbit to measure tides on the surface. One of this year’s funded proposals would take an entirely new approach. The team proposes “to exploit a remarkable confluence between methods from the esoteric world of high energy particle physics and an application to delineate habitats suitable for life within the solar system. PRIDE (Passive Radio Ice Depth Experiment) is a concept for an innovative low cost, low power, low mass passive instrument to measure ice sheet thickness on outer planet moons, such as Europa, Ganymede, and Enceladus, some of which may harbor the possibility of life in under-ice oceans. The proposed instrument, which uses experimental techniques adapted from high energy physics, is a passive receiver of a naturally occurring signal generated by interactions of deep penetrating cosmic ray neutrinos. It could measure ice thickness directly, and at a significant savings to spacecraft resources. In addition to getting the global average ice thickness this instrument can be configured to make low resolution global maps of the ice shell. Such maps would be invaluable for understanding planetary features and finding the best places for future landers to explore.”
|Credit: NASA, JPL|
– One of the primary limitations on our ability to explore the solar system is the amount of fuel a spacecraft can carry. One proposal would develop a system that would use the mass of small comets or asteroids as a substitute for fuel. “The comet hitchhiker concept is literally to hitch rides on comets to tour around the Solar System. This concept is implemented by a tethered spacecraft that accelerates or decelerates itself without fuel by harvesting kinetic energy from a target body. First, the spacecraft harpoons a target as it makes a close flyby in order to attach a tether to the target. Then, as the target moves away, it reels out the tether while applying regenerative brake to give itself a moderate (less than 5g) acceleration as well as to harvest energy.” The proposers provide two example of how this system could be used. “1. Fuel-less landing and orbit insertion. We estimate that a comet hitchhiker spacecraft can obtain up to ~10 km/s of delta-V by using a carbon nanotube (CNT) tether. This level of delta-V enables a spacecraft to land on/orbit around long-period comets and Kuiper belt objects (KBOs), which have not been even visited by any spacecraft yet. With existing technologies only a fly-by is realistic for these targets. 2. Non-gravitational slingshot around small bodies. A comet hitchhiker can obtain ~5 km/s of additional delta-V by utilizing just 25% of the harvested energy for reeling in the tether and/or driving electric propulsion engines. The tether is detached from the target after the desired delta-V is obtained. Our concept enables to design a fast trajectory to a wide range of destinations in the Solar System by taking full advantage of the high relative velocity, abundance, and orbital diversity of small bodies. For example, by hitching a comet with q=0.5 AU, a comet hitchhiker can reach the current orbital distance of Pluto (32.6 AU) in 5.6 years and that of Haumea (50.8 AU) in 8.8 years.”
|Credit: Draper Laboratories|
Through enabling technologies, such as high-accuracy quantum, or cold-atom, inertial sensors based on light-pulse atom interferometry (LPAI), and the extreme miniaturization of space components into fully functional spacecraft-on-a-chip systems (ChipSats), these combined missions can perform decadal-class science with greatly reduced time scales and risk.” Draper Lab’s media relations department, though, got the word out, and this idea received considerable press (see, for example, here and here). This concept has three parts. First, a CubeSat spacecraft that might be the size of a loaf of bread would be designed that would be capable of interplanetary flight and operations. Second, an extremely miniaturized accelerometer (that’s the “high-accuracy quantum, or cold-atom, inertial sensors”) would enable high resolution gravity measurements of a planet or moon. Third, a flock of tiny landers that are each a single computer chip would be released for surface studies. Draper Labs concept image and press released emphasized this concept as a way to explore Europa, which would probably be about the most difficult target imaginable: high radiation that kills electronics and little ability to add shielding to the tiny CubeSat or a ChipSats, no meaningful atmosphere to allow the ChipSats to flutter to the surface safely, and a distant sun that limits the effectiveness of solar panels. I will be interested to see if this team releases further information on how they would deal with these challenges. However, the same approach could also be used at Mars where the science potential is strong and the specific challenges of Europa’s environment are absent. For these technology development projects, teams sometimes will take on the most difficult challenge to help force creative solutions. – Sometimes a title that seems to border on technobabble hides an exciting idea, or in this case, three. The summary on NASA’s web site doesn't help much: “
Space limitations prevent me from summarizing all the solar system concepts selected for funding this year. There are also concepts for testing the ability of terrestrial plants to grow in a greenhouse on Mars, propel a spacecraft quickly into interstellar space, and precisely measure the gravity field and hence internal structure of asteroids and comets during brief flybys. You can read the summaries of these concepts and others addressing non-solar system exploration at this site.