Orbiter: 2016 vs. 2010

As I wrote recently in this blog and in an article in The Space Review, Orbiter 2016 was released in September. This is the first major release of this freeware space flight simulator since Orbiter 2010, and as I mentioned, not all of the many third-party addons for the 2010 version are working in Orbiter 2016. If you are familiar with Orbiter, you know that it's quite easy to have multiple installations of the software on the same PC, so there is no need to replace the 2010 version with the 2016 version -- as long as you have the disk space, you can keep multiple copies of both versions installed in separate folders and just run the one that has the features and addons of interest at the moment. In the picture pairs below, the top screenshot is from Orbiter 2010, the bottom one is from Orbiter 2016. 

You should also know that although there are some user interface changes in the 2016 version, they are really quite minor, so even if you are new to Orbiter, you can install and use both the 2010 and 2016 versions quite easily. Some developers have already updated their addons for 2016, and others no doubt will when they have the time and inclination. But Orbiter 2010 is still readily available, so if you are interested in the Apollo program, the advanced Shuttle Fleet, the fictional spacecraft of 2001: A Space Odyssey (sample screenshot at the top of this post) or Colliers Magazine, and many other addons, there's no need to wait for 2016 versions to come along. Note that the final version of Orbiter 2010 is often called 2010-P1 (patch-1) or 100830 (August 30, 2010).

Here are some observations and tips for working with both Orbiter 2010 and the new Orbiter 2016:

1. The biggest user interface difference is that the "no-cockpit" full screen pilot view has a control bar that appears when you hover the mouse near top edge in the 2016 version. In the 2010 version, the F4 key will pop up a small menu bar with same controls (in the 2016 version, F4 will toggle the top edge menu between "on" and "auto-hide"). See "no-cockpit" comparison screenshots above. 

2. The biggest visible difference in the 2016 is in its support for highly detailed surface terrain data complete with elevations, so mountains and craters are true 3D objects. This makes for some incredible eye-candy especially when you are flying low over the terrain, but in most situations in Orbiter, you are orbiting (oddly enough) 200 km or more from the surface, and the flat 2010 terrain textures look just fine. 

3. In addition to the general high-res 3D surface data for all of Earth, the Moon, Mars, and some other bodies, Kennedy Space Center (cockpit view above) and the Edwards AFB/Mojave region (see shuttle final approach screenshot below) have been given super-detailed makeovers in Orbiter 2016. Again, this doesn't matter much if you are in orbit or cruising to the Moon or Mars, but it does add a lot to the realism before you launch or when you are landing at Edwards AFB. 

4. There is a thread on the Orbiter Forum that reports addons that are known to work in Orbiter 2016. There are quite a few and there are probably many others that have not been tested but may work. Orbiter Sound 4.0 works with Orbiter 2016 though there are a few minor glitches such as incorrect audio feedback for some actions (e.g., the G key for "landing gear" in the Deltaglider will deploy the gear but audio will say "radiator deployed"). 

5. Some popular addons that currently seem to work only in Orbiter 2010 include AMSO (Apollo program in great detail), Shuttle Fleet V4.8 (which is freaking amazing), and the excellent "World of 2001" and "World of Colliers" addons by "Sputnik." Note that even for 2010, some addons may only work with Orbiter's "native" graphics (not the D3D9 Orbiter_NG client which offers better graphics quality and frame rate). I'm not sure how to know this for sure, but if you find that your spacecraft are invisible in the D3D9 client, you should try the native graphics version. 

6. One addon I especially like is the videnie module for orbital path drawing by "artlav." It renders orbital paths for spacecraft, planets, and other bodies in exterior views (green, red, and purple lines around Earth in screenshot above from Orbiter 2010). This is super cool and very helpful in understanding orbital paths, but it only works in native graphics mode (not orbiter_ng) with Orbiter 2010.

7. If you have plenty of hard drive space available, a good general tip is to create two separate "clean" installation folders, one for Orbiter 2010-P1 and one for Orbiter 2016, including whatever terrain data you prefer, and perhaps with Orbiter Sound 4.0 installed. Make a copy of the clean installations and install any desired addons there. Note that Orbiter 2016 installations with full terrain data can be very large (I have one installation that is 58 GB). 

8. Orbiter Sound supports mp3 playback with control over when the music plays (e.g., exterior views only). But since modern versions of Windows support multi-source sound multiplexing, I tend to just stream music from Amazon or iTunes while running Orbiter. An album of Strauss waltzes is a particular favorite, especially with the World of 2001 addon.

Note: The screen shots here are from Orbiter 2010 and Orbiter 2016, without modification. You can find them and various others in full screen resolution in this Flickr album. 

SevenEves: Bye Bye Moon

When I got super interested in space flight technology and orbital mechanics back in 2005, I played with the Orbiter space flight simulator for a few months and wrote a 181 page tutorial book for it called Go Play In Space. When Neal Stephenson got interested in space technology and orbital mechanics, he researched it for 9 years and wrote 880 pages to create a novel called SevenEves. The only common thread I can claim is that Neal and I both did our homework on the physics of space flight. But Neal did his homework on much more than this, and tied it all together into a fantastic story. Two major stories, actually -- one an extremely detailed, near-future "disaster movie" (the first two thirds of the book), the other an imaginative and ultimately exciting speculation on the lives of the survivors' descendants, 5000 years in the future. How many survivors were there? The book's title gives a clue that's at least partially correct (it's also a palindrome).

I really enjoy most of Neal Stephenson's writing, and when I learned that his next book would be based in space, I pre-ordered it immediately. When it was released last Monday, it jumped the queue of all the books I was reading or planning to read. I saw a couple of early reviews, including a fairly negative one focused on Stephenson's relative lack of character development and other novelish niceties, in favor of nerdish discussions of all technical sorts. To me, this is a feature, not a bug. I loved the wide-ranging and carefully researched details, and I thought the characters were mostly well drawn. The storytelling and pace are good, although I did feel that it bogged down in the first third of part 3 (the 5000 years from now part). In fairness, there's a lot of explaining to do when you introduce a complex future civilization and many new characters, and after all that setup, the last 300 pages are quite thrilling. Good save, Neal!

The book starts with the moon exploding for no apparent reason. It initially breaks into seven major pieces, but a popular public outreach astrophysicist nicknamed "Doob" (clearly modeled on Neil Degrasse Tyson) and his grad students figure out that it will soon break further into trillions of pieces, many of which will reenter Earth's atmosphere, destroying the atmosphere and everything in it. In 25 months (plus or minus 2 months). Scientists in many other countries independently reach the same conclusion.

Two years is not much time to get ready for the end of the world, so most of the 7 billion people and virtually all other living things will die.  And unfortunately, the incoming swarm of debris dubbed "hard rain" is estimated to continue for some 5000 years. So immediate repopulation of Earth's surface will not be possible. People will have to learn to live deep underground or in space, indefinitely -- somehow. The first 600 pages are mainly focused on a gigantic space lifeboat effort, although it's clear that only a relative handful of people (a few thousand at most) can make it to space in that short time, even with all of Earth's resources, industry, and minds focused on this.

Of course this immediately answers the question, what is the International Space Station good for? Why, to serve as the centerpiece of a swarm of hastily constructed and launched habitat spacecraft that will be used to save this small number of humans in hopes of some sort of future. It's fortunate that in this near future world, the ISS has been expanded to include an experimental rotating habitat and a captured asteroid for experimentation with mining using a fleet of small robots. That at least gives the planetless survivors a fighting chance. But to say there are challenges is a vast understatement. There are many close calls and heroic efforts that turn out to be essential -- like a hastily organized mission led by an Elon Musk-like space entrepreneur to retrieve a chunk of a comet.  This huge mass of water is needed for radiation shielding and to make rocket fuel. You can do that (extract hydrogen and oxygen) if you have enough electric power, like a nuclear power plant repurposed from a submarine. Since part 3 takes place 5000 years in the future, you know that somehow humanity makes it, but it is by the very thinnest of margins.

Is this book realistic? You have to just accept the premise that the Moon just blows up for some reason. The "agent" responsible for this is never really explained, but it doesn't really matter. Everything else within parts one and two ("now") is constrained by realistic physics and plausible current or near-future technology. Orbital mechanics is a major constraint and is handled very well. The problems of radiation, microgravity, growing food in space, living in crowded spaces, and many other issues are handled realistically. Space debris is a constant problem, especially once the "hard rain" starts throwing parts of the former moon in all directions. Space construction requires the help of thousands of small robots, but these are not especially smart robots -- plausible extrapolations of things I have read about in MIT Technology Review. All in all, I consider parts 1 and 2 to be some of the best "hard SF" that I've ever read.

Part 3 is more problematic for me, though ultimately enjoyable. The future space construction technology is massive, though still believable by extrapolation of robotic capabilities. But the tight connection between the personalities of the few survivors and the characteristics of the resulting race-driven civilization in 5000 years often did not ring true to me. There are a lot of interesting and plausible ideas, but also a lot that I thought was very silly, seemingly just made up, "because I said so." These are extrapolations of genetic and social engineering over 5000 years. I don't think you can say anything definitive about this based on anything we know, even if you accept genetic manipulation of the human genome as a required and well-understood tool.

Of course it is all just made up by the author. But it is in part 3 that I have to say to myself, "that's why they call it science fiction." It's still more than fantasy or magic, though I wouldn't call it hard SF. But overall, it's a really good book, and most of those 880 pages flew by over the last six days (actually 14,403 Kindle "locations," read mostly on my iPad).

It's a long book, full of interesting ideas and good writing. I learned a lot, as I always do from Stephenson's books. It is ultimately a hopeful book -- humans are resourceful and manage to barely survive, and eventually go on to build a new and very different civilization and to start to repopulate the Earth (with genetically engineered plants and animals, synthesized from a comprehensive DNA database that was saved from "Old Earth," since no actual animals and very few plants were brought to space -- the Old Earth mission planners did manage to preserve much of Earth's knowledge, genetic and otherwise). But as different as their new civilizations are, aggression and racial stereotypes remain -- even though the races are completely new. Even if we were capable of building a future "paradise," even a small handful of people will fail to agree that it is paradise -- some will want something else. Humans are difficult creatures. It will always be so.

The images here are my own screen captures from the Orbiter space flight simulator, loosely inspired by early events in the book. Some of them are from a project I did in 2006 called "Mars for Less," a partial simulation of a human Mars mission using existing launch vehicles and orbital assembly. We used some of the techniques discussed in SevenEves, such tethering two spacecraft together and rotating them to generate artificial gravity. There are better artists' conceptions of some of the objects in the book here. There's a companion website for the book here, including the author's book tour schedule. He's in Cambridge, MA next Friday, so I'm going to hear him speak about the book. I hope to learn a little about how you go from a palindrome and some concerns about space debris to an 880 page book.

Kerbal Space Program?!?

I read something about KSP (Kerbal Space Program) a couple of years ago but I didn't do anything about it. Then the other day I saw this comic on xkcd, referencing KSP. If you hover your mouse over the comic, the comment says "Ahem. We are STRICTLY an Orbiter shop." Me too! But I was curious about what had happened to KSP since it was last (vaguely) on my radar.

Quite a bit, it turns out. It's still in an extended alpha development phase, but it's already got some interesting capabilities for people who like to "play in space" (something I once wrote a book about). After looking at a few web sites and videos, I decided to download and try KSP for myself (current version is 0.21.1, and it costs $23, including future updates). So what is KSP? From the web site:

KSP is a game where the players create and manage their own space program. Build spacecraft, fly them, and try to help the Kerbals to fulfill their ultimate mission of conquering space.

Essentially it's a space flight simulator with reasonably accurate physics, wrapped in a game-like interface with pretty decent graphics and some quirky alien-like astronaut characters (KSP's developers also seem to have a quirky sense of humor). It is just now starting to emerge from its "sandbox" phase (with the ability to build and fly your own spacecraft, but without any specific game-like goals). At this point, it's something like 3D simulated model rocketry, but with the ability to launch the rockets you design into space (orbital mechanics is involved, but the math is hidden behind clever controls and displays). You can dock with space stations, travel to and land on other planets, and try to navigate your spacecraft back to Kerbin for a safe landing.

Yes, Kerbin, not Earth. This fictional solar system has real physics (orbital mechanics and atmospheric flight) but it doesn't use the names and specific physical properties of our own solar system. Kerbin is an Earth-like "exoplanet" with two moons (Mun and Minmus - you can fly to and land on them).

So far I've only scratched the surface of KSP, and I don't know how much time I will spend with it. It depends in part on whether I start to do some space-related educational outreach again. I haven't done any for quite a while. When I have done school presentations, I have generally used Orbiter to dynamically demonstrate certain aspects of space flight and the solar system. That's cool for demos, and it beats simply using PowerPoint, but Orbiter's learning curve is quite steep, and it's hard for me to recommend to any students younger than maybe 11 or 12. KSP is definitely more kid-friendly. The rocket building section (see picture at top of this post) is simple yet powerful (though there is no guarantee that what you build will fly well or at all - the physics is pretty realistic, so you have to worry about mass, thrust, stability, etc.). As the Minecraft craze shows, kids (and adults) love to build stuff inside virtual worlds (and real ones). While building your own spacecraft for Orbiter is certainly possible, it's a separate "add on" development process, not integrated with the simulation itself.

KSP also integrates the instruments and controls needed to change orbits directly within the 3D views (spacecraft and map), making it easier and less abstract to see the effects of firing your rockets at certain times, locations, and directions. The screenshot above is from the integrated Orbiting 101 tutorial, and it shows the "maneuver node system" being used to predict the effect of a pro-grade burn at the low point of the orbit (periapsis). Dragging the pro-grade symbol changes the delta-V (speed change) value, and the dotted orbital path shows the predicted effect in real time (your path doesn't actually change unless you make that proposed burn at the proper time and with the correct ship orientation). Orbiter has similar capabilities (and much more) with its various "MFD" instruments, but these work like display screens in the cockpit, not directly in the 3D view. More realistic but also harder to visualize and understand.

KSP allows you to build and fly some pretty cool and complex space vehicles such as multi-stage rockets with strap-on boosters, and even Apollo LM-like landers such as the one shown above (docked with an Apollo-like command module housing three Kerbals who are about to land on the Mun - this is a supplied sample scenario). Although it's easy to build monster rockets with many engines, you do need to pay attention to structural integrity, symmetry, and stability or your giant booster may tumble out of control, crash, and burn. Unlike in Orbiter, things can and do blow up in KSP, though at the moment the hardy Kerbal astronauts are immune to G-forces, allowing you to perform high-G atmospheric entries and the like with impunity (this will undoubtedly change in future versions).

Future versions will also include a flight sim-like "career mode" with awards for completing certain missions or milestones like docking or landing on the Mun). I suppose that training options will also expand, although there is already some basic training in the game, and a variety of user-created tutorial videos and PDF's available on the web. Note that since changes between versions can be pretty extreme, there is no guarantee of backwards compatibility for previously built things when you upgrade.

I think KSP is already a great educational tool, because it is sufficiently "toy like" to be fun and non-threatening (think building robots with Lego MindStorms, but much cheaper), but powerful enough to allow really interesting and challenging activities. I really like the emphasis on what is essentially engineering - designing, building, testing, and thinking about why things work or don't work so the next iteration can be better. And remember, to engineer is human (and sometimes fun too).

JPL's Basics of Space Flight

Serendipity works in mysterious ways. While updating the Kindle app on my iPad, the installation got hung up somehow. I tried various things and finally deleted the app and all its data, i.e., all my local e-books. No worries for the purchased Kindle books as Amazon keeps backups for you on its cloud server. But I also had a bunch of PDF files. I wasn't sure exactly which ones, so I searched my laptop's external drive for larger PDF files. I found several PDF books I had lost or forgotten about, including a wonderful book called The Ascent of Science, and a JPL work called "The Basics of Space Flight."

I wrote about JPL's "Basics" back in 2007. It's a really great educational web site developed by JPL spaceflight engineer Dave Doody. The web site has a number of interactive features (including quizzes) and is maintained and updated by JPL. There have been PDF versions available too, but they have carried a disclaimer that they are not maintained, and past versions were not very nicely formatted (essentially PDF captures of the web pages). When I found a PDF dated 2001, I decided to check JPL for a newer version. Sure enough, I found a 2011 version that Doody had reformatted specifically for e-book and print purposes. It's really great.

The home page for the JPL Basics of Space Flight website is here, and this is definitely the most complete and up-to-date version if you wish to explore interactively. If you want a nicely formatted, albeit slightly older and non-interactive PDF version, click here (it's about 17 megabytes). There is also a paperback version available from Amazon.

In reading the introduction to the PDF, I learned about a more technical book that Dave Doody published in 2009, Deep Space Craft: An Overview of Interplanetary Flight. I read a few pages through Amazon's "Look Inside" feature, and it's definitely a piece of space-geek heaven. But it's a $92 textbook and I wasn't going to buy it (no Kindle version, and I very rarely buy paper books these days). But just now I saw a "like new" copy from a third party seller for $32 so I decided to go for it. What can I say about an addiction?

Rocket Science for Fun

I'm making slow progress on the third edition edits for Go Play In Space for the Orbiter 2010 space flight simulator. I sometimes need to present various aspects of "rocket science" in the course of explaining the intricacies of maneuvering in space (otherwise known as orbital mechanics) in Orbiter. This has led me to look into how other authors handle these explanations, so I've revisited a favorite book and have bought a new one. My perspective is a bit more practical than for many general readers - I am trying to teach my readers how to operate realistically simulated spacecraft, so when they encounter things like ascending nodes, they want to know what they can do with them (like align the plane of their current orbit with that of the ISS in preparation for rendezvous and docking), whereas other readers might just say, "that's nice" and turn the page.

The new book is It's ONLY Rocket Science by Lucy Rogers (I bought the Kindle version). Dr. Rogers is a British mechanical engineer and freelance journalist on space and astronomy topics (perhaps among others).She says on her website that she aims to write about science in plain English, and she pretty much succeeds in this book. For example, her explanations of orbital elements, Lagrange points, and ground tracks are quite clear and include some simple illustrations (including ones for Molniya and geosynchronous orbits). On the other hand, her explanation of rendezvous and docking is rather too brief, and could use some more illustrations for someone who wants the background needed to actually do rendezvous and docking in a real spacecraft (or in Orbiter, for most of us). The book also covers the space environment, rockets and spacecraft, types of missions, propulsion systems, communications, humans in space, and other topics in addition to the basics of orbital mechanics. There's a website with information and book excerpts here.

My old favorite is Wayne Lee's To Rise From Earth (Second Edition), which is sadly out of print (used copies are available on Amazon). I wrote about this book in some detail in 2006. The subtitle "an easy-to-understand guide to spaceflight" is really true, and Lee (who works as an interplanetary space flight engineer at JPL) covers a lot of ground in this book, including a lot of space history with detailed information on the Apollo program and the space shuttle. In the orbital mechanics area, the explanations are detailed, and there are many excellent color illustrations that support the explanations. Rendezvous and docking and ground track explanations are especially well done. As I wrote in 2006:

Both the book and Orbiter provide an essentially non-mathematical introduction to space flight - the book approaches this through geometry, using a large number of excellent diagrams as well as clear analogies and other text descriptions and many photographs. Orbiter takes the first-person approach of putting you in the pilot's seat and providing various instruments to guide you as you control the spacecraft to change orbits, rendezvous with another spacecraft, or fly to the Moon or to Mars.

So if you are a budding astronaut (or Orbinaut), which book should you choose? Ideally you should read both - Rogers covers some topics better than Lee (for example, Lagrange points) and you may find some explanations to be clearer in spite of the small number of illustrations. But if you want to really understand how orbits work and how you change them to get where you want to get in space, you should grab a copy of Wayne Lee's book before the used copies run out. Rogers' 2008 book is still in print (paper and Kindle).

Cassini Tour Guide

Busy week, not much time for reading or blogging. One thing I noticed that is really cool is this guest post on the Planetary Society blog. John Smith is a planetary tour designer at JPL, one of just two or three people who work on designing the orbital journeys of the Cassini spacecraft since it arrived in Saturn orbit in 2004. His article is really fascinating, and it doesn't even delve into much in the way of orbital mechanics. It's amazing how many constraints they have to meet to try to achieve the many science goals (all within the constraints of orbital mechanics, i.e., physics).

Just as we optical engineers will say "it's all done with mirrors" (not really), orbital engineers will say, "it's all done with gravity," and of course it is. The "engine" that really allows Cassini to travel in the wide range of orbits needed to visit the various moons of Saturn is actually the gravity of Titan, Saturn's largest moon. Every time Cassini passes near Titan, its orbit can be slightly or dramatically changed, with full control depending on the location and closeness of the orbital path to Titan. Cassini has thrusters and a small fuel supply for attitude control and for minor adjustments to some orbits, but Titan's gravity is what does the "heavy lifting" when it comes to changing the orbit.

I've simulated a few close passes to Titan in Orbiter (with the Cassini add-on or other spacecraft, it doesn't really matter), usually when something interesting has happened recently with Cassini (like finding those methane/ethane lakes) and I want to show this in a space demo. I've always gotten specific orbit data from JPL's Horizon's database so I know it will work (then I play around with the views in Orbiter so it looks really cool in the demo, especially with time acceleration), but you can also use Orbiter to experiment with gravity-assist maneuvers on your own, using the scenario editor and navigation tools like IMFD.

Super-Cool Spacecraft

The Hubble Space Telescope is a cool spacecraft, and the STS-125 astronauts are busy working on making it better than ever. Despite difficulties with some bolts, yesterday's EVA team removed the workhorse WFPC2 and replaced it with the new WFC3 camera system. Today the second EVA team has replaced RSU's (Rate Sensor Units, part of the telescope's attitude sensing system) and is now working on replacing batteries.

Update: I wasn't following the EVA earlier in the day and I missed the trouble that Mike Good had with installing one of the new RSU's, requiring the installation of an older but refurbished unit that was carried as a backup. Those NASA folks think of everything, but the trouble put them significantly behind schedule and required extending the EVA duration to allow enough time to do the critical battery task. I bet those guys sleep well tonight! Even for well-trained astronauts in great physical shape, a 7.5+ hour space walk has got to be exhausting.

As cool as Hubble is, the Herschel spacecraft that was launched by ESA earlier this week is super-cool. Literally. This advanced telescope for far-infrared and millimeter-wave observations has a supply of liquid helium on board to keep its sensors cooled below 2 K (less than 2 degrees above absolute zero). As an optical engineer, I'm impressed that this Cassegrain telescope has a 3.5 meter primary mirror, the largest yet launched into space (Hubble's primary is 2.4 m in diameter). Using these long wavelengths, Herschel will be able to image very distant, cold, and dust-shrouded objects to investigate the early history of the universe.

Herschel was launched with a companion spacecraft called Planck, which is a microwave observatory designed to study tiny fluctuations in the cosmic microwave background radiation (CMB), allowing scientists to infer the structure of the early universe as early as 380,000 years after the Big Bang (that's only about 0.003% of the estimated age of the universe, 13.5 to 14 billion years). ESA has a lot of online information on both Herschel and Planck.

Both satellites will operate quite far from Earth, at the Sun/Earth L2 Lagrangian point. They will be established in separate Lissoujous orbits around the L2 point. If you would like to see what this looks like for yourself, you can do so in Orbiter, courtesy of Brian Jones and Papyref, whose latest add-on simulates the Herschel and Planck spacecraft and also provides a special tool for viewing their orbits around the L2 point (screen shot at top). The models and included materials for this add-on are quite detailed. There is one L2 scenario provided, plus two launch-related scenarios (these require additional add-ons for the Ariane 5 launch vehicle and the ESA Kourou launch site.

Super cool!

Carnival of Space Turns 100!

This week's Carnival of Space is hosted by One-Minute Astronomer, and it's a big one, number one-hundred! It's also a really cool one, with quite a lot of new information for me, starting with One-Minute Astronomer itself. It's an excellent observation-oriented and educational astronomy site.

Other special points of interest for me:

Mang's Bat Page has an introduction to interactive orbit simulators available through JPL's Small-Body Database Browser (I searched for Eros) and other online resources.

Beyond Apollo has a great post on Wernher von Braun's 1969 proposal for a nuclear-rocket Mars mission. Of course this never happened, but this post shows well how it might have been done.

And most amazing of all (partly because I knew nothing of the 2008 Orbiter add-on that is featured) is a post and video on The Discovery Enterprise blog of another Apollo-based Mars mission that never was, this one based on Stephen Baxter's alternate history SF novel Voyage. I loved that book, and I knew there had been an Orbiter add-on based on the book, but it was for an early version of Orbiter. This new add-on is called Baxter's Voyage Beta and was uploaded by "belisarius" in May 2008. The video by "rseferino" is really cool. He has some other Orbiter-based videos that also look interesting including one based on the amazing 2001: A Space Odyssey add-on (Floyd's Journey).

Interplanetary Trajectories

The MESSENGER spacecraft is closing fast on its close encounter with Mercury tomorrow (the Planetary Society has a detailed preview here, flyby simulation video here). This will be the first close approach to Mercury since Mariner 10 in 1974-75, and it will be very close - only about 200 kilometers from the surface! This is the first of three flyby encounters in 2008-2009, designed both for imaging/science and for trajectory modifications that will help MESSENGER to match Mercury's orbit and allow Mercury orbit insertion in March 2011. The 2008 passes should finally give us imagery of Mercury's entire surface (Mariner 10 was only able to photograph about half of the planet on its three flyby encounters). The planned one-year orbital phase will allow much more detailed study of this relatively unknown planet.

Launched in August 2004, MESSENGER's journey to Mercury has taken a rather indirect path, looking something like a pinball in a pinball machine in in the animated GIF above (linked from the Planetary Society web site). MESSENGER got trajectory help from several gravitational-assistance passes (Earth flyby in 2005, two Venus flyby's in 2006 and 2007, and the upcoming Mercury passes in 2008 and 2009 - here's a great diagram of the stages of the trajectory). Since Mercury is close to the sun, you might wonder why all this bouncing around is necessary, since it's pretty much "downhill" from Earth to sun-hugging Mercury, gravitationally speaking. While I don't know the specific constraints on the MESSENGER trajectory design, there are always complex trade-offs among payload (the mass available for instruments and spacecraft structures), propellant mass and usage, and timing. If you can wait longer to get there and use gravitational assistance from planets, you can carry a larger payload while needing less propellant to arrive precisely at your target at the right time and with the right velocity to do what you need to do.

This whole orbital mechanics business has interested me since high school. Aside from library books, I'm sure that the many "NASA Facts" and other documents that I got by writing to NASA played a big part. That was the Apollo era, so I was reading about free-return trajectories and orbital rendezvous and the like at a young age. At one point I thought that this might even be my career, since I was so interested in space and computers, but I took a path not unlike MESSENGER (with a music-assisted change in direction and university) and ended up in optics software instead.

Nowadays at places like JPL, interplanetary trajectory design is incredibly sophisticated. Simulation, optimization, and visualization software make it possible to meet all sorts of constraints and requirements and to perform and pre-visualize all sorts of "what ifs." If you would like to play around with this sort of stuff yourself, there is the great combination of Orbiter and IMFD (Interplanetary MFD by Jarmo Nikkanen, a wonderful planning tool that runs inside Orbiter itself, now up to version 5.1d). Gravity Simulator 2.0 is another great and free tool for playing with orbits and trajectories. You can even use JPL Horizons data to get real spacecraft data to use in your own simulations (see my earlier tutorial post on this).

Speaking of tutorials, I just found one for IMFD 5.0 that I had not seen before. It's a 20 minute narrated video tutorial by Robert Denny, and it's really cool (he has done earlier text/picture tutorials on IMFD which are still available, though they are based on an earlier version of IMFD). While this "simple tutorial" is very well done and clear, you should note a few points. One is that he assumes some basic familiarity with Orbiter and with orbital mechanics terminology. Another is that he is only showing the "MFD" instrument windows, not the full Orbiter screen. Orbiter has cockpit views, external views, and full 3D graphics, but for this tutorial, you are essentially "flying on instruments" and don't need to see that other stuff, though you would see the outside view if you were running this in Orbiter. Third is that Denny has chosen to transfer from Europa to Callisto, two moons of Jupiter. Jupiter is like a mini (but still huge!) solar system, so it's quicker and simpler in some ways to learn to do orbital transfers between moons there than between widely separated planets orbiting the sun. The same methods would apply to flying from (say) Earth orbit to Mars orbit. Even if you don't understand everything, you can see from this tutorial what a powerful tool IMFD can be, and it goes much farther than what is shown here. There are other (non-video) IMFD tutorials on Jarmo's site.

Free Fall Physics

One of the things that confuses people about space flight is the whole "weightless" or "zero-G" thing. I was once discussing space flight with a man on an airport bus. He was a Ph.D. biochemist and had just attended a shuttle launch at KSC. He was pretty interested in space and said he had read a few articles and books, so I was surprised when he asked me, "At what altitude does gravity fall to zero so the astronauts can be weightless?" I explained that while gravitational force does fall off with increasing distance (squared), it is only slightly lower at the shuttle's typical orbital altitude than it is at the surface. The astronauts are not really in zero-G or weightless, but rather in a continuous free-fall around the Earth, and that this is essentially what an orbit is, just a really long fall as gravity pulls the spacecraft and astronauts toward the center of the Earth, and the Earth's surface "bends away." He was surprised and even somewhat skeptical of this. I guess the common terms "weightless" and "zero-G" are pretty misleading and influential. Free-fall is a better term.

This is explained in many places, starting with Newton's Principia in 1686-87. I even have a discussion in my Go Play In Space. But one of the best explanations I've seen is in a video of a physics lecture by Richard A. Muller, professor of physics at UC Berkeley. His course "Physics for Future Presidents" (Physics 10, for non-majors) is one of the most popular introductory classes at Berkeley, and his lectures are available as live webcasts and on YouTube. He also wrote a textbook for the class (several chapters are available on his teaching web site). The video above is lecture #3 on gravity and satellites (the orbit explanation starts at around 20 minutes). He does a few demos, but it's mostly blackboard and talking, with many real-world examples and great analogies and explanations. I've only watched this one lecture so far (69 minutes), but he's obviously really good. It's great that stuff like this is on the web and free to all (he has people all over the world auditing his webcast lectures and listening to his podcasts, which are also available free on iTunes).

The Saturn Show

Just back from two weeks in Europe and there's a lot to catch up on at the office and at home. I have some interesting things to blog about once I can find some time - maybe this weekend. In the meantime, let me point you to a really nice JPL slide show marking Cassini's three years at Saturn. The picture here compares the size of a radar-imaged lake on Titan (most likely liquid ethane and methane) with our own Lake Superior. That's a lot of rocket fuel!

Cassini happens to be making another planned low pass over Titan today. I grabbed today's orbital state vectors from the JPL Horizons system yesterday and used them in Orbiter to simulate the low pass at an outreach event at my local library last night. I started about 138,000 km out and used a view option (target-to) to keep the camera pointed at Titan through the pass, getting as low as 2000 km above the clouds. Time acceleration makes this pretty dramatic to watch - it looks like a crash is inevitable, but of course that's just the design of the orbit.

I Feel the Earth Move

One of the blogs I discovered through recent space carnivals is Astropixie, which I really like. Her recent post on heliocentrism referred to a blog where the idea is seriously considered that the Earth is the fixed center of the universe, around which everything else revolves. It’s essentially Ptolemy’s ancient Greek “music of the spheres,” although I’m sure its proponents don’t especially like Ptolemy because he wasn’t a Christian (he couldn’t help it, he was born too soon).

The “proof” of this fixed Earth theory seems to consist of three things: (1) I don’t FEEL the Earth moving, (2) the sun, stars, and planets APPEAR to move around us, and the clincher, (3) the Bible says the Earth is fixed. As with people who believe in Creationism, Intelligent Design, Intelligent Falling, or that humans are a plague on the Earth and should become extinct, this got me thinking: what is up with that?

I never learned to build or fix a car or airplane engine, and I know only broadly how they operate, but I can still drive a car and fly a small airplane. I know that engines work on physical principles that are well understood by many people, and that specialized engineers and technicians understand these principles (and a lot of practical details) especially well and can design, build, and fix engines so I can safely drive or fly. If I believed instead that Carburetor Fairies, the Magneto Demon, the Spaghetti Monster, or the Hand of God caused the engine to produce power, I could still drive or fly. The existence of such beliefs doesn’t especially hurt anything as long as there are people who can actually build and fix engines so they work. And of course there are many people (perhaps most) who have no special beliefs about how their car engine works and don’t especially care as long as it runs, and when it doesn’t, they take it to a mechanic.

The fixed Earth people might be similar to this – on the basis of their direct senses and their belief in the Bible, they maintain that the Earth is obviously fixed, and that everything rotates around us. As long as these people don’t try to launch satellites or space probes, or make their opinions about this subject the law of the land, no great harm done. Just as quantum mechanics is implicitly proved every time you turn on a device with transistors or lasers in it, a rotating Earth is required (along with the rest of the well understood and well demonstrated heliocentric system) every time a satellite is launched in an eastward direction to take advantage of the velocity boost provided by the spinning Earth. If you make use of satellite based weather reports, satellite TV, or GPS, you are benefiting from the knowledge and work of people who understand these principles and how to apply them. You don’t have to know or care how these things work (or even that they exist at all) unless you want to.

The funny part is when someone with such a belief tries to straddle the fence, accepting and applying certain parts of physics and rejecting others to try to build a case for their alternate view – “teach the controversy,” as it were, though the controversy here is comparable to the question of who is the stronger god, Zeus or Thor? (obviously Thor, duh).

An example is this page on a fixed Earth web site “falsifying the geosynchronous satellite concept.” Assuming these people are serious (they seem to be), they go to some pains to explain that GEO orbits are based on various unproved assumptions. Although you can’t see GEO satellites with the naked eye, they do accept as directly observable that there are satellites which remain fixed at a distance of 22,236 miles above certain points on the equator, but since they deny that the Earth rotates and that the satellites are in circular orbits with periods set to match the Earth’s rotation rate, they need a way to explain why these satellites don’t simply fall straight down.

Their answer: electromagnetism (they show a small metallic globe that is suspended magnetically to illustrate this idea). They don’t say how these powerful “beams of magnetism” are generated, and of course no one has ever observed or measured the alleged tubes of localized electromagnetic forces that keep these satellites suspended over the supposedly fixed Earth. But it works for a 3 inch model Earth, so why not for a 22,236 mile high tube of magnetic force?

Of course if any of this were true, rocket launches and satellites (not to mention the Moon) would have to operate quite differently from what physicists, astronomers, and engineers have been telling us since Newton in 1687. This would involve a vast and intricate conspiracy of government, private industry, scientists, engineers, and many others all around the world. Why wasn’t I asked to join when I got my physics degree? It is not clear whether this is a conspiracy to launch spacecraft that operate differently from what we have learned in school, or whether the conspiracy has simply faked every space flight since 1957 (with great special effects, I especially like that GPS trick). None of this is very clear actually.

I suppose I’ve spent more time on this than it’s really worth and I should simply accept that whatever it is, there is probably someone somewhere who believes it. It’s just really astounding to me. There’s a lot of stuff in the Bible that is debatable, and probably a lot that is valuable. But as an orbital mechanics resource, it’s just plain wrong. I don’t expect to convince anyone who accepts the Bible as fact to change their opinion based on my remarks here. But considering the political source of Astropixie’s original link to this fixed Earth stuff, I wanted to also point out that depending on how things go in November 2008, science may not quite be out of the woods when Bush finally leaves office.

Learning the Orbital Ropes

I write a lot about Orbiter, and a little bit about other software tools such as Gravity Simulator, and I've written Go Play In Space to help people get started with Orbiter (it includes quite a lot of background material too). But there's a lot of stuff that I more or less assume that people know if they're interested in space, and I have to admit that this is not always a good assumption. Fortunately we have the web, and I want to mention two sites that I have found really useful for understanding space flight and orbital mechanics.

JPL Basics of Space Flight - Quite complete, richly illustrated, essentially non-mathematical, and with brief quizes for each section to check your understanding. It's best used in the interactive mode though there is a PDF version as well.

Rocket & Space Technology by Robert A. Braeunig - Not as comprehensive but the explanations are clear and compact. There is a fair amount of high-school-algebra-level math. Also includes an excellent page clearly and simply debunking the "we never went" Moon-landing-hoax nonsense. Very nicely done.

Rocket Science for... um, Dummies?

The "for dummies" thing seems to be permanently with us, alas, though I supppose that's better than "for the complete idiot" (another popular book series). Rocket Science for Dummies isn't a book, it's a web tutorial on applied orbital mechanics using Orbiter. It's been around for a few years (since 2004) and is actually quite good - it's one of the things that helped me learn Orbiter back in 2005 and then inspired me to write my full-blown tutorial book, Go Play in Space.

The original version of Dummies was written by "Windlepoons" as a series of posts in a gaming forum. Last fall "Enjo" (Simon Ender) updated the tutorial for Orbiter 2006 and posted it in four parts on "Falcoleprof's" excellent orbiterschool.com educational support site. It includes some starting scenarios, good diagrams, and good explanations to help you get up and orbiting (and even docking in part 4) in almost no time.

Orbiter for Educators: Using JPL Horizons

JPL's Horizons system is a public-access database with current orbital data on many, many objects in the Solar System (both natural objects and spacecraft). Orbiter is a space flight simulator which includes a "scenario editor" that lets you interactively change the orbital data for any spacecraft in the scenario you are currently running. I was going to write an entry on how to use the web interface for Horizons to get information on (say) the Saturn-orbiting Cassini spacecraft and then transfer it to Orbiter using the Orbiter Scenario Editor. But before I could write this up, I found a better way, thanks to Tony Dunn, author of Gravity Simulator 2.0 (and also an Orbiter user).

First some general information. I won't attempt to explain Horizons itself - the FAQ and web access tutorial can do that. There are two basic types of data you can get, orbital ELEMENTS, and VECTORS (called "state vectors" in Orbiter), which we will use here. These are basically the (x,y,z) position and (Vx,Vy,Vz) velocity of the object relative to some reference body (e.g., Sun, Earth, Saturn, etc.), at a specific date and time. The date and time are encoded as a number called the "Julian Date" (JD), though Orbiter uses a modified version called (logically enough) "Modified Julian Date" (MJD). The idea is to get accurate information on an object of interest from Horizons, convert it if necessary, and enter it into Orbiter, so you can answer a question like "what does Saturn look like from Cassini right now?"

Conceptually this is quite easy (grab the date and vectors and pop them into the scenario editor), but there are a few things to learn, including the right questions to ask Horizons, and how to get the resulting data into Orbiter. Units, dates, coordinates, and reference bodies require a bit of explaining and possibly some conversions (m vs. km etc.). Nothing terrible, mind you, just a few details to keep straight.

Tony Dunn provides an easier way with his simple little utility program cfgData.exe (120 KB .exe file download) and the Horizons "batch" email interface. Download the program to any convenient directory (no installation needed) and run it. You can then enter the desired date/time and choose the object (e.g., Cassini Spacecraft, object -82 for JPL) and "center body" (e.g., Saturn barycenter, object 6 for JPL) from drop down lists of available JPL objects. Choose VECTORS, click [Create E-mail], and copy the resulting block of text to the clipboard with the button that appears. Go to your email program and create a new message. Paste the text into the body of a new email window, enter job as the subject, email to horizons@ssd.jpl.gov, and wait for the reply (usually very quick).

Select ALL the text of the reply and copy to the clipboard (check for error messages first - I just requested Cassini data for March 2009 and it's not available). Back in the cfgData window, click the [next > ] button (a new window appears), paste the return text into the new window, and click the [Create Data] button...

This is where it gets slightly tricky. The MJD and state vector data has to be copied and pasted into the right spot in an Orbiter scenario (.scn) file using a text editor like Notepad. It's easiest if you already have a scenario that is generally doing the right thing (like orbiting Saturn), so you only have to paste in the new MJD, RPOS, and RVEL data over the prior data, save it, then launch Orbiter and run your new scenario.

How do you get that starting scenario? If you've installed the Cassini add-on (shown above on 3-27-07) you will have a scenario (in the Grand Explorations folder) called Cassini Phoebe Flyby.scn which will have Cassini with STATUS Orbiting Saturn. Just copy the new date (MJD) and replace it in this file, copy the RPOS and RVEL lines in place of the old ones, Save As with a new name, and you're ready to run. Or take any Earth-orbiting scenario with a spacecraft (Deltaglider or whatever) with STATUS Orbiting Earth and change Earth to Saturn, paste MJD, RPOS, RVEL data, save, and run.

Note: You can also get orbital elements from Horizons for natural bodies such as asteroids and use this data in configuration files to add these objects to your Orbiter solar system. This has more steps, and you might consider using this utility to easily define minor planets in Orbiter.

Gravity Simulator: Funky Music of the Spheres

Gravity is strange stuff, and you don't even need General Relativity to see it do weird things. The book Fly Me to the Moon got me curious about low energy transfer orbits to the Moon that take advantage of "chaotic" behavior, and I'm now experimenting with Tony Dunn's freeware program Gravity Simulator 2.0, though I haven't gotten too far with it yet. I've created some simple models from scratch and played around with some of the scenarios supplied with the program and downloadable from his web site, especially some Earth-crossing asteroid cases (picture shows A2004 MN4, otherwise known as Apophis, one that will pass very close to us in the 2029-2036 time frame). It's pretty cool.

Using Gravity Simulator's ability to reference your view to any object, and to establish reference frames that rotate with particular objects, you can start to see "hidden" behaviors and patterns such as resonances with planets that can lead to surprising (chaotic?) changes in an asteroid's orbit (see Toutatis, for example - scroll down to the animated GIF - Cruithne is pretty weird too). User note: the scroll bar on the right controls the angle of your view of the orbits you create, and when you change the view or the scale, any object tracks that have been drawn are erased, which seems odd at first (you have to wait for them to re-draw, running time backwards if necessary to get back to an earlier point so you can redraw an interesting part of your path, like that asteroid buzzing the Earth).

I've found some web references with orbital data for low-energy Earth-Moon transfers, but so far I haven't been able to generate any of the odd looping orbits that are shown in this huge (4 MB PDF) "atlas" article covering some 280 families of these orbits. At least I'm getting a handle on it. GS is a much better tool than Orbiter for experiments like this that focus mainly on gravity and orbital mechanics and don't need the 3D views and other goodies that Orbiter provides.