Category Archives: Space Exploration

Interplanetary Copters!

The last decade has seen an incredible bloom in small autonomous and remote controlled helicopters, AKA drones. It isn’t far wrong to call them ubiquitous, and probably the characteristic technology of the 2010s. (Sorry Siri.)

It isn’t surprising, then that NASA (the National Aeronautics and Space Admin.) has some ideas about what to do with robot helicopters.

This month it is confirmed that the next planned Mars rover will have a copter aboard [3].  (To date, this appears to be known as “The Mars Helicopter”, but surely it will need to be christened with some catchy moniker. “The Red Planet Baron”?  “The Martian Air Patrol”? “The Red Planet Express”?)

This won’t be a garden variety quad copter.  Mars in not Earth, and, in particular, Mars “air” is not Earth air. The atmosphere is thin, real thin, which means less lift.  On the other hand, gravity is less than on Earth. The design will feature larger rotors spinning much faster than Terra copters.

Operating on Mars will have to be autonomous, and the flying conditions could be really hairy. Martian air is not only thin, it is cold and dusty.  And the terrain is unknown.  The odds of operating without mishap are small. The first unexpected sand storm, and it may be curtains for the flyer.  Mean time to failure may be hours or less.

Limits of power and radios means that the first mission will be short range. Unfortunately, a 2 kilo UAV will probably only do visual inspections of the surface, albeit with an option for tight close ups.  Still it will extend the footprint of the rover by quite a bit, and potentially enable atmospheric sampling.


This isn’t the only extraterrestrial copter in the works.  If Mars has a cold, thin atmosphere, Saturn’s moon Titan may have methane lakes and weather, and possibly an ocean under the icy surface.   Titan also has a cold thick atmosphere, and really low gravity—favorable for helicopters!

Planning for a landing on this intriguing world is looking at a copter, called “Dragonfly” [1, 2]. The Dragonfly design is a bit larger, and is an octocopter. <<link>>  (It is noted that it should be able to continue to operate even if one or more rotors break.)  Dragonfly is also contemplated to have a nuclear power source—Titan is too far away for solar power to be a useful option.

Titan is a lot farther away than Mars, and communications will be difficult due to radiation and other interference.  The Dragonfly will have to be really, really autonomous.

Flying conditions on Titan are unknown, but theoretically could include clouds, rain, snow, storms, who knows.  The air is methane and hydrocarbons which could gum up the flyer. Honestly, mean time to failure could be zero—it may not be able to even take off.


Both these copters are significantly different from what you might buy at the hobby store or build in your local makerspace.  But prototypes can be flown on Earth, and the autonomous control algorithms are actually not that different from Earth bound UAVs. This is a good thing, because we have to program them here, before we actually send them off.

In fact, I think this is one of the advantages of small helicopters for this use. Flying is flying, once you adjust for pressure, density, etc. It’s probably not as tricky as driving on unknown terrain.  We should be able to design autonomous software that works OK on Mars and Titan.  (Says Bob, who doesn’t have to actually make it work.)


Finally, I’ll note that a mission to Titan should ideally include an autonomous submarine or better, a tunneling submarine, to explore the lakes and cracks. I’m sure this is under study, but I don’t know that it will be possible on the first landing.


  1. Evan Ackerman, How to Conquer Titan With a Nuclear Quad Octocopter, in IEEE Spectrum – Automation. 2017. https://spectrum.ieee.org/automaton/robotics/space-robots/how-to-conquer-titan-with-a-quad-octocopter
  2. Dragonfly. Dragonfly Titan Rotorcraft Lander. 2017, http://dragonfly.jhuapl.edu/.
  3. Karen Northon, Mars Helicopter to Fly on NASA’s Next Red Planet Rover Mission, in NASA News Releases. 2018. https://www.nasa.gov/press-release/mars-helicopter-to-fly-on-nasa-s-next-red-planet-rover-mission

 

We must go to Titan! We must go to Europa!

Ice Worlds, Ho!

Robot Wednesday

The Water Plumes Of Europa

Europa is interesting.  Very interesting.

It is one of at least seven “ocean worlds” in our solar system.

Orbiting Jupiter, Europa is warped and headed by the tides generated by Jupiter’s gravitation. This means that there is an ocean of liquid water, possibly larger than all of Earth’s oceans.

This ocean is covered by ice. The ice shell has not been conclusively measured, but it seems to be thin (10s of KM), and full of cracks through which tides drive ligquid water to the surface.

This active, water rich geology appears to have all the prerequisites for life. Water, chemicals, energy, tidal action, gnarly geometry.  These are the signatures of fertile habitats on Earth.  Is there life under the ice?  I, for one, want to know.

To date, we have limited direct measurements of Europa.  Hubble and ground based telescopes have imaged it from afar. In the first wave of exploration, the Voyagers flew by, and the Gallileo probe obtained the best images so far of Europa, with old and only partly working technology [2].

It is obvious why Europa is a high priority for additional visits with much better instrumentation and eventually, landers.

In the mean time, we can pour over the data we have.

This month researchers report an analysis of data from the Galileo mission from 1997.  The data is measurements of the magnetosphere and plasma that the spacecraft encountered as it passed close to Europa (200 KM).  This data features a transient event, which was difficult to interpret.

The new study suggests that the measurements are related to Europa, and, in fact, represent traces of a volcanic plume of water spewed into space.

This study developed a detailed computational simulation of the plasma and ions near Europa.  Introducing a plume consistent with the telescope observations, and showed that the model closely aligns with the hitherto unexplained measurements from Galileo.  They conclude that the spacecraft did, in fact, fly through the traces of a plume of water from inside Europa.

In itself, this result isn’t too surprising.  It does support hypotheses that Europa not only has an ocean and an active icy crust, but like Enceladus, Titan, and other moons, is volcanically active.

Where there are volcanoes, there is the possibility of life as we know it.

We must go to Europa.

  1. Kenneth Chang, Europa, Jupiter’s Ocean Moon, May Shoot Plumes of Water Into Space, in The New York Times. 2018: New York. https://www.nytimes.com/2018/05/14/science/europa-plumes-water.html
  2. Richard J. Greenberg, \Unmasking Europa: the search for life on Jupiter’s ocean moon. 2008, Copernicus Books: New York.
  3. Xianzhe Jia, Margaret G. Kivelson, Krishan K. Khurana, and William S. Kurth, Evidence of a plume on Europa from Galileo magnetic and plasma wave signatures. Nature Astronomy, 2018/05/14 2018. https://doi.org/10.1038/s41550-018-0450-z

 

Ethereum in Space!

Cryptocurrencies have attracted far thinking people, including utopians ideas of “disrupting” money.

But the farthest thinking must involve getting off the planet or even out of the solar system altogether.

NASA is tasked with thinking about and developing concepts for space exploration, and they are certainly aware of the need for decentralized protocols.  NASA missions, by definition, go far beyond Earthbound infrastructure, not to mention beyond the possibility of direct human control.  (Even human spacefarers can only control things within a tiny sphere.)


Many research teams are investigating autonomous systems, which can operate without direct programming from Earth.  This year, Professor Jin Wei Kocsis  of the U. of Akron is looking at Ethereum “smart contracts” as a model for part of the system [2].

[T]his project intends to develop a resilient networking and computing paradigm (RNCP) that consists of two essential parts: (1) a secure and decentralized computing infrastructure and (2) a data-driven cognitive networking management architecture.

Ethereum is a decentralized more-or-less secure infrastructure, with both storage and computation.    Ethereum-style executable contracts are decentralized and Turing complete.  One could imagine Ethereum nodes on a constellation of loosely cooperating spacecraft, and one can imagine Ethereum contracts executing in such a network.

Cool.

As Samburaj Das remarks, “Details remain slim” [1].

But we can speculate.

<SET MODE = SPECULATE>

The overall goal is “autonomous” spacefaring, i.e., pushing as much sensing and decision-making to the spacecraft.

I hope to develop technology that can recognize environmental threats and avoid them, as well as complete a number of tasks automatically,”  Professor Jin Wei Kocsis quoted in [1]

Reading between the lines of the abstract, it seems likely that the system is expected to incorporate data from many sources, e.g., from planetside radar and swarms of spacecraft.  In such a scenario, the spacecraft needs to get data from many sources and automatically combine and filter it to keep a current assessment of hazards and possible responses.  It is also possible that the assessments (i.e., the computations) might be shared, so the whole system can learn and refine awareness of the whole area.

The scenario I describe is often solved using some form of shared memory, e.g., as a scratchpad or chalkboard shared among many nodes.  Clearly, a blockchain can function as such a shared memory, with the advantage of being completely distributed and robust regardless of nodes dropping out or communication problems.  Ethereum executable contracts offer the additional advantage of distributed computation, which can filter and analyze data on the blockchain.

This is surely the essence of how Ethereum will be used, presumably integrated as storage for their control algorithms.


There are other features of Ethereum that may or may not be important or even relevant for this project

It is possible that the cryptographic signatures may be useful as well.  Data on the blockchain is signed and can’t be fiddled with.  Cryptographic signatures mean enable the network to potentially detect and ignore intruders, errors, and false signals.

Speculating further, it is possible that the Nakamotoan distributed consensus mechanisms may be useful in the event that not all nodes are known or trusted.  The blockchain is a ledger designed to be trustworthy without relying on specific nodes to be correct or honest.  Out in space for years with no supervision, being able to trust the data even if you can’t trust the network nodes is probably valuable.

In summary, there is certainly a case for a distributed memory, and something like Ethereum is a useful testbed for these ideas.


On the other hand, I’m not sure if the currency aspects of Ethereum will be particularly useful, or if so, how.

I wonder if the incentives for miners make sense for this use case.  Would autonomous spacecraft want to operate as miners, or would they rely on other nodes (e.g., motherships and dirtside servers)?  It seems unlikely that the energy budget of a spacecraft can afford the costs of mining.

In the case of Ethereum, there is also the question of “gas” to run contracts.  This is extremely important for the correct operation of executable contracts (among other things, it assures that a contract will not run forever).  How are autonomous spacecraft going to be provisioned with Ether to buy gas?  Surely it isn’t reasonable to upload Ethereum coins from Earth.

Perhaps they going to buy and sell data or other services with their peers?  Maybe.  But this seems kind of out of scope, and potentially a huge resource hog for a very constrained system.  (It would be bad to be churning away doing some kind of micro transactions, and not have enough CPU time to actually do the navigation, no?)

(Combining these two possibilities:  maybe the spacecraft will charge for downloads.  “You want the data I collected?  That will be 100 ETH, please.”)


I imagine that these questions are some of the things the research will investigate.

Let me be clear. I know that Ethereum is just a testbed, not proposed to actually use on a mission.

It isn’t likely (or even possible) for Ethereum to be used in real spacecraft.

But Ethereum can help identify the features for a distributed storage and computation system that could be used.


I’ll add that distributed algorithms and storage are scarcely new to NASA.  NASA has been exploring these architectures for a long, long time [4,5].  Nevertheless, it is very interesting to see how these contemporary systems might be applied to specific missions.


  1. Samburaj Das, NASA Researches Ethereum Blockchain Tech for Deep Space Exploration, in Ethereum News. 2018. https://www.ccn.com/nasa-researches-ethereum-blockchain-tech-for-deep-space-exploration/
  2. Loura Hall, RNCP: A Resilient Networking and Computing Paradigm for NASA Space Exploration, in NASA -Early Career Faculty Awards. 2017. https://www.nasa.gov/directorates/spacetech/strg/ecf17/RNCP
  3. Alex Knisely, Researcher and NASA work to help spacecraft avoid floating debris, in University of Akron – News. 2018. https://www.uakron.edu/engineering/ECE/news-detail.dot?newsId=c9a2717e-4327-4dcb-9040-87e788d068c4&pageTitle=Recent%20Headlines&crumbTitle=Researcher%20and%20NASA%20work%20to%20help%20spacecraft%20avoid%20floating%20debris
  4. J. Russell Carpenter, Decentralized control of satellite formations. International Journal of Robust and Nonlinear Control, 12:141-161, 2002. https://pdfs.semanticscholar.org/2c1a/d1206eb750399bc3728ee644ae8146f13fa5.pdf
  5. Wei Ren and A Randal Beard, eds. Distributed Consensus in Multi-vehicle Cooperative Control: Theory and Applications. Springer Publishing Company, Incorporated: London, 2010.

 

Space Saturday

Jupiter Science from Juno Coming Out

The Juno spacecraft has been in orbit around Jupiter since July 2016, and will complete at least two more orbits under current funding (July, 2018).

One of the goals of the mission is to look in detail at the atmosphere of this gas giant.  From Earth, we can see the stripes, which are vast wind streams (in opposite directions ?!), and the Great Red Spot, the largest hurricane in the solar system. But what is going on under the cloud tops?

After more than a year of data collection, results are starting to come in.  Jonathan Fortney summarizes three new papers appearing this spring in Nature [2].  Fortney points out that Earth bound experiments and  theory have not been able to describe the complicated Hydrogen / Helium atmosphere below the surface we can see.

One study investigated the mass distribution of Jupiter by measuring the Doppler effects on the radio signals from the Juno spacecraft as it swooped past [4].  Fortney notes that this was a very finicky process, which had to account for tiny amounts of acceleration including the absorption and re-radiation of sunlight!  The researchers conclude that the bands we see extend quite deep into the atmosphere.

A second study extends this work to conclude that the strong winds decay slowly down some 3.000 kilometers [5].  I.e., the bands we see probably extend down some 3,000 kilometers into the atmosphere.

A third study finds that below that depth, the planet rotates as a solid [3]. At that depth, the pressure is such that the hydrogen ionizes and electromagnetic forces bind the material into a liquid. (This core is the source of the strong magnetic field.)  Obviously, there must be a very turbulent area at the boundary of these two regions, with huge bands of wind ripping East and West across an inner core.

These studies give a picture of a dense interior, with a deep atmosphere dominated by huge bands of strong winds.  An extremely stormy planet!

See swirling cloud formations in the northern area of Jupiter’s north temperate belt in this new view taken by NASA’s Juno spacecraft. The color-enhanced image was taken on Feb. 7 at 5:42 a.m. PST (8:42 a.m. EST), as Juno performed its eleventh close flyby of Jupiter. At the time the image was taken, the spacecraft was about 5,086 miles (8,186 kilometers) from the tops of the clouds of the planet at a latitude of 39.9 degrees. Citizen scientist Kevin M. Gill processed this image using data from the JunoCam imager.

(Caveat:  these studies are based on the theory of gravitational harmonics which I don’t understand at all.)

Fortney suggests that Juno may be able to make further detailed observations of the Red Spot and other storms, which would be interesting details to have.  He also notes that data returned by the Cassini probe of Saturn should yield comparative measurements for the its less dense and probably deeper atmosphere.

Stay tuned. There is lots of other science coming.

The current funding ends in July, but the mission could continue for several more years if supported.


  1. Jonathan Amos, Jupiter’s winds run deep into the planet, in BBC News – Science & Environment. 2018. http://www.bbc.com/news/science-environment-43317566
  2. Jonathan Fortney, A deeper look at Jupiter. Nature, 555:168-169, March 7 2018. https://www.nature.com/articles/d41586-018-02612-y
  3. T. Guillot, Y. Miguel, B. Militzer, W. B. Hubbard, Y. Kaspi, E. Galanti, H. Cao, R. Helled, S. M. Wahl, L. Iess, W. M. Folkner, D. J. Stevenson, J. I. Lunine, D. R. Reese, A. Biekman, M. Parisi, D. Durante, J. E. P. Connerney, S. M. Levin, and S. J. Bolton, A suppression of differential rotation in Jupiter’s deep interior. Nature, 555:227, 03/07/online 2018. http://dx.doi.org/10.1038/nature25775
  4. L. Iess, W. M. Folkner, D. Durante, M. Parisi, Y. Kaspi, E. Galanti, T. Guillot, W. B. Hubbard, D. J. Stevenson, J. D. Anderson, D. R. Buccino, L. Gomez Casajus, A. Milani, R. Park, P. Racioppa, D. Serra, P. Tortora, M. Zannoni, H. Cao, R. Helled, J. I. Lunine, Y. Miguel, B. Militzer, S. Wahl, J. E. P. Connerney, S. M. Levin, and S. J. Bolton, Measurement of Jupiter’s asymmetric gravity field. Nature, 555:220, 03/07/online 2018. http://dx.doi.org/10.1038/nature25776
  5. Y. Kaspi, E. Galanti, W. B. Hubbard, D. J. Stevenson, S. J. Bolton, L. Iess, T. Guillot, J. Bloxham, J. E. P. Connerney, H. Cao, D. Durante, W. M. Folkner, R. Helled, A. P. Ingersoll, S. M. Levin, J. I. Lunine, Y. Miguel, B. Militzer, M. Parisi, and S. M. Wahl, Jupiter’s atmospheric jet streams extend thousands of kilometres deep. Nature, 555:223, 03/07/online 2018. http://dx.doi.org/10.1038/nature25793

 

Space Saturday

 

Life On Ocean Worlds

One of the great philosophical mysteries of our age is, in the words ascribed to Enrico Fermi (AKA, “the pope of physics”): “Where is Everybody?” [3]  (This is known as Fermi’s Paradox, though he didn’t originate it, nor is it really a ‘paradox’.  It’s still a Fermi-grade question, though.)

Humans have been watching the skies for millennia, and in the past century have looked ever wider and deeper into the universe, not to mention into physics and the biology. Everything we know indicates that there could very well be life and even technological civilizations everywhere in the vast universe.  But we have never seen evidence of life beyond Earth.

Where is everybody?

Coming up with answers to Fermi’s question is a great scientific parlor game.

In 2002, Stephen Webb describes 50 answers [2], and in his 2015 update he gives 75 (!) [3].  The “solutions” listed by Webb range from “they are already here”, through “they are so strange we don’t recognize that they are there”, as well as the possibility that life really is very, very rare.

Along the way, he points out many uncertainties in our estimates of how likely the development of life and “intelligent” life may be (e.g., we have only our own planet to extrapolate from), as well as unknowable hypotheses about the possible psychology or politics of putative non-human civilizations (e.g., just because we want to talk to everyone doesn’t mean anyone wants to talk to us).

There are also disturbing warnings that “civilizations” are likely to self-destruct before escaping their home planet, or, even worse, may be snuffed out in the nest by predators or catastrophes. (With this in mind, blasting our electromagnetic presence in all directions might not have been a healthy life style choice.)

Webb’s compendium of “solutions” is fun to read, but the game is hardly over.


At the 2017 Habitable Worlds workshop, S. Alan Stern proposes yet another solution to the Fermi Paradox: most life evolves in “interior water ocean worlds”, i.e., in oceans under thick ice covers [1].

most life, and most intelligent life in the universe inhabits interior water ocean worlds (WOWs) where their presence is cloaked by massive overlying burdens of rock or ice between their abode and the universe.

There are several such worlds in our own solar system, and at times in the past the Earth itself flirted with such conditions, covered over with a kilometer of ice.

Artist’s concept of Europa’s frozen surface. Credit: JPL-Caltech

Stern notes that these worlds appear to be highly conducive to the development of life.  The ice cap protects and stabilizes the ocean environment, providing a nest for fragile life to develop over long, evolutionary periods of time.  Thus, however likely life is to develop, ice worlds are prime candidates for successful evolution.

However, Stern also makes the interesting inference that life that evolved under a deep ice cap would have no direct view of the universe.  The protective shield overhead would also block out most evidence of other stars and planets. An emerging civilization under the ice would not know about the universe, at least until technology develops that detects (indirectly) the space above the ice.  Even then, intelligent beings might have difficulty imagining life that does not live under ice, so they might not think to look for signals from us or send signals we could detect.

Stern also argues that life adapted to an ice-covered ocean would find space travel difficult, at least compared to species adapted to the surface under a gaseous atmosphere. In addition to the technical challenge of penetrating many kilometers of rock hard ice, life-support would be necessary to support a dense, liquid environment.

He combines these arguments to answer the “Where is everybody?” question:  if much life develops in ice covered oceans, and any civilizations in such environments unlikely to know or care about the wider universe, then this explains why we haven’t heard from them.

This is an interesting idea to think about.  It is certainly useful to break out of the parochial idea that an Earthlike planet is the only or ideal locus for life or “civilization”.  In fact, we know that life on Earth has just barely survived at least five major extinction events, and an ice world might well be a safer crèche.

I’ll also note that his comment that life on such a planet “either cannot communicate or are simply not aware that other worlds exist” works both ways.  It is difficult for us to detect such inhabitants, and we haven’t be looking until recently.  In our own solar system, there are several ice worlds, but we still have no idea if they are inhabited or not.


On the other hand, several aspects of Stern’s argument are less convincing to me.

An ice-covered ocean world might be a favorable site for life to start, but it might also be a closed system that is quickly exhausted.  Experience on Earth certainly indicates that a closed “ark” will rapidly be overgrown, clogged, and die out.   It is likely that only some ice worlds will be sufficiently “active” or open enough for life to persist.  But who knows until we actually check.

I have to say that I find the arguments about the supposed psychology of native to ice worlds highly speculative, to say the least.  It is true that life on Earth can directly sense the solar system and wider universe, and there are plausible arguments that this knowledge has strongly influenced the development of what we call intelligence.  But it is very difficult to guess the implications of not having an open sky.

I also think that, should a technological civilization develop under an icecap, it will surely develop undertanding of the outside universe. They’ll surely learn about gravity, and when they learn to detect and manipulate electromagnetism, they’ll soon notice a lot of interesting stuff coming in through their icy roof.  For that matter, no matter how difficult space travel might be, wouldn’t they deploy robot explorers and harvesters on the outer side of the ice.  And from that perch, who would not look up and see other worlds?

In short, I’ll buy the idea that ice worlds are good places for life to develop, though they may not be great places to sustain life for billions of years.  But I reserve judgement on questions of how the lack of a sky might influence the development of “civilizations”.


In this article, Stern describes yet one more case for why there could be some extraterrestrial civilizations that we have not seen or heard.  But this clearly isn’t “the answer”. He joins the roster of all the dozens of other hypotheses (Indeed, Webb has a solution called “Cloudy Skies Are Common” ([3], p. 183), which probably subsumes Stern’s solution as a sub case.).

On the other hand, this thesis is yet more reason why icy ocean worlds are really interesting and really need to be explored..  There very well could be life under the ice, and we really should find out what we can.

We have several such worlds close at hand in our solar system that we could visit and actually see what is down under the ice. (EuropaEceladus!  Titan!)

Let’s go, already!


  1. S. Alan Stern, An Answer to Fermi’s Paradox in the Prevalence of Ocean Worlds?, in Habitable Worlds 2017: A System Science Workshop. 2017: Laramie, Wyoming. https://www.hou.usra.edu/meetings/habitableworlds2017/pdf/4006.pdf
  2. Stephen Webb, If the Universe Is Teeming with Aliens … WHERE IS EVERYBODY? Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life, New York, Copernicus Books In Association With Praxis Pub, 2002.
  3. Stephen Webb, If the Universe Is Teeming with Aliens … WHERE IS EVERYBODY? Seventy-Five Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life, New York, Springer, 2015.

 

Space Saturday

Cassini End of Mission

After twenty years in space (launched 10 years Bi, Before iPhone), traveling over a billion KM, and returning data for 13 years from more than a light-hour from Earth, the Cassini Spacecraft ended its mission this week.

The project has accomplished lots of amazing science, represented by 3,948 papers so far. There will surely be a few more—lets go for 5K papers!

The end was a planned dive into the atmosphere of Saturn, collecting a few more bits of data on the way down, and assuring the complete destruction of the spacecraft.

As has been explained before, the spacecraft needed to be vaporized to prevent even the slighted chance that it might contaminate the area with Earth microbes. Aside from not wanting to harm any life that might exist on the moons or dust, we also don’t want to accidentally leave something that a later spacecraft might find and not realize was inadvertently sent from Earth.

(Which, if you think about it is way, way cool. How many human endeavors have to worry about the possibility of contaminating alien ecosystems, even in principle?)

Hence, the final dive.

This montage of images, made from data obtained by Cassini’s visual and infrared mapping spectrometer, shows the location on Saturn where the NASA spacecraft entered Saturn’s atmosphere on Sept. 15, 2017. Credit NASA/JPL-Caltech/Space Science Institute

Cassini signed off permanently on September 15. Loss of Signal. End of Mission. Lots of accomplishments.

 

Space Saturday

Interplanetary Networking

Space travel faces inevitable communication challenges. Even within the solar system, distances are light minutes to hours, which means round trip latencies that preclude easy conversation. In addition, signals decay quadradically, so there is a brutal power-to-distance relationship—and power is precious in space.

Can we do better than radio signals?

Gregory Mone reports in CACM that the answer is, lasers, man! [2]

Lasers are higher frequency and narrower beams, so they can transmit more data for the same power. This can’t eliminate the latency, but can push more data in a given time. As much as 10-100 times the data, which is worth a lot of effort to make happen.

A laser is much more directional than radio, and the receiver is a telescope. The narrow beam is a challenge, because the signal has to be aimed precisely. Given than everything is moving rapidly relative to everything else, it isn’t trivial to keep a signaling laser pointed at a very distant target.

If you were to aim a beam of radio waves back at Earth from Mars, the beam would spread out so much that the footprint would be much larger than the size of our planet. “If you did the same thing with a laser,” Biswas  [of NASA JPL] says, “the beam footprint would be about the size of California.”” ([2], p. 18)

Experiments have demonstrated space laser communication, utilizing error correcting codes (to mitigate lost signals) and advanced nanoactuators to precisely aim the laser. At very large distances, power will be at a premium, so there will be no bits to spare for error correction.

The receivers are essentially telescopes, which are a very well known technology. Receiving weaker signals from farther away means bigger telescopes. Mone says that signals from the solar system need a 10-15 meter scope.

These links will still have extremely long latencies compared to terrestrial networks. This means that our Earth bound protocols need to be redesigned for the Interplanetary Internet. (Hint: timeouts don’t work well if the round trip time for an ACK is variable and measured in hours.) This work is well underway [1].

Cool!

  1. InterPlanetary Networking Special Interest Group (IPNSIG). InterPlanetary Networking Special Interest Group (IPNSIG). 2017, http://ipnsig.org/.
  2. Gregory Mone, Broadband to Mars. Commun. ACM, 60 (9):16-17, 2017. https://cacm.acm.org/magazines/2017/9/220434-broadband-to-mars/fulltext