Showing posts with label spacecraft. Show all posts
Showing posts with label spacecraft. Show all posts

Monday, June 15, 2015

Viewing Atlas V Launch at Cape Canaveral

Rocket launch up close
Courtesy of www.nasa.gov. Launch of MMS on the Atlas V
A little late is better than never...
This past March, I had the opportunity while visiting Florida to go to Cape Canaveral and watch a launch of a NASA satellite for The Magnetospheric Multiscale Mission (MMS). This is actually a set of four satellites, launched together, which will fly in formation and take measurements of the Earth's magnetosphere. Yeah, I never heard of it either until I found out about the launch. The MMS was launched on a United Launch Alliance Atlas-V 400-series rocket.


Logistics

I had a trip planned to the central Florida area this March, and since I have been several times before to the area, but never during a real launch I was excited to find out that there was indeed a scheduled launch during my trip. I initially just used the Kennedy Space Center (the tourist site company) website, which lists upcoming scheduled launches, and found the post for an Atlas V launch
When: March 12, 10:44 pm

Where: SLC-41, Cape Canaveral Air Force Station
Kennedy Space Center
Rocket Launch: Atlas V | Magnetospheric Multiscale (MMS)

At some point I've subscribed to a Kennedy Space Center "Launch Alert" mailing list, although this particular launch wasn't one that I got an email for. This was probably due to the scheduled time, at 10:44 pm, the official Kennedy Space Center visitor center is closed. I called the day before to the KSC's main number and left a voice message asking if they still had any sort of ticket available to view the launches at night, they did not respond.

After reading a number of other sites with viewing advice for launches, we decided to wing it by going to Cape Canaveral and looking for one of the public viewing areas outside the actual NASA / U.S. Air Force base in the town of Port Canaveral or some of the other nearby state parks. According to launchphotography.com: 
For off-hours/night launches, when no tickets are being sold by the Visitor Complex and Playalinda Beach is closed,
the best option for Atlas 5 launches is Port Canaveral on Route 401, at 11.7 miles from the pad. In that case it is the furthest viewing of any rocket.
Armed with this minimal information we headed off to view the launch!


Night of the Launch

After double-checking the weather reports, the launch appeared to be on schedule. We drove the hour or so to Cape Canaveral in the early evening, the sun was still up and went to get dinner. I think we ate here, which was unremarkable, except for the fact that nearly everyone in there were "space launch groupies" all going to the same launch afterwards. At the table next to us was a couple who apparently had connections to access the base. They were kind enough to suggest we take a look at spaceflightnow.com as the best place to get real-time info on the upcomming launches. After eating our dinner, we drove over to try to get a spot along Rt. 401 which faces the launch pad for Atlas Vs to the North, across an open body of water called the Banana River.
Map of Rt. 401 where we watched the launch
As you may see in from this map image, there is a curve of Rt 401 which goes behind the Port Canaveral cruise terminal. There really isn't an official beach or parking area, people just parked on the north side of the road on some grass next to the water. By the time we got there it was around 8:45 PM and the enter stretch of the road from the entrance to the Air Force base to the East of this map, all the way to the road cornering to the south was taken. Our car was one of the last cars to fit in to a spot before there is a guard rail that prevents any roadside parking on that side, just around that bend. There are "No Parking" signs across the street and there is an active police presence who we saw forced some people who parked on that side to leave. Moral of this story is try to get there early, 2 hrs or more.

After we parked we had two hours to wait. A lot of people were setting up large cameras with zoom lenses on tripods. Since the only people there are the people who drove and were able to park in that area, it wasn't particularly crowded at all, but you had neighbors to your right and left at all times. We sat on the grass in a spot with a good direct view at the rocket on the pad, preparing for launch. From our smart phones, we caught the NASA TV live stream which was mostly just a video of the rocket from close up. Occasionally there would be a feed of some talk of the mission controllers asking for a status check on some system. Things like this were often heard during the hours before the countdown: "The Centaur liquid oxygen pad storage area has been prepped. The next step is conditioning the transfer lines, which is now beginning to prepare the plumbing for flowing the cryogenic oxidizer."

The worst part of this experience was the wait. Right offshore in the shallow water, parallel to the road were some high power lines, which made an incredible loud electrical buzzing the entire time. There were also police patrol cars going up and down the rows of cars along the street, with their lights flashing. The two combined in the most awful synergy to probably qualify as a form of torture in most of the developed world. We spent the next hour listening to updates on my phone, while taking looks at the rocket and the Vehicle Assembly Building which was also nicely lit, and perfectly visible using my binoculars.

Pictures of the Rocket

Here were some pictures we managed to take. It was dark, and my camera isn't meant for this. My camera is a Sony Cybershot with 20x optical zoom. These were all taken during the fueling stage.
Landscape of the Cape Canaveral base. The Atlas V launch is at center. The VAB is on the left and well lit.

The clearest shot with full zoom

Another zoomed shot of the Atlas V on the launch pad



The Launch

After 2 hours of waiting (and nearly a half day of driving and waiting overall) we finally began hearing the dramatic count down. As I was informed halfway through their count down by a "neighbor" the stream from my smart phone was on about a 20 second delay. So around "T-20" we started seeing the bright orange flames and smoke around the base of the rocket as it silently began to lift off. It was nearly overhead before we heard the loud rumble of the rocket pass by us. I spent most of the launch trying to see something with my binoculars, at first the flame was too bright and I didn't see much. I barely saw it as the first stage separated I think. My mom did the honors and held my digital camera as we filmed a movie.


Aftermath

I can't say I was a big enthusiast for Magnetospheric science, but I have been keeping an eye on the MMS mission since launch. The four satellites in the rocket that were launched together all separated and are flying in a formation in orbit around Earth. They are continuing to take measurements and function as of today. I look forward to seeing what science they are able to do from this mission.

Tuesday, July 9, 2013

Europa Report: Movie Review

I am always a fan of science fiction films and happy for any science fiction that comes my way. In this case Europa Report is a fairly independent movie that is being released online and On Demand before being shown in theaters. I recently watched this through my cable providers "Video On Demand" feature, where you can purchase a rental of this movie for $9.99 (ouch). There are both standard definition and high-definition versions available, but if you get one you don't get the other, so use with caution. I think releasing movies straight to the internet/on demand and skipping the theaters is a new strategy in the movie industry. Hear about that trend in this recent NPR: On Point broad cast: Is the U.S. Movie Industry Broken?
Europa Credit: NASA

Europa Report is about a fictional manned-mission to Jupiter with a landing on the icy moon Europa. One of the four large "Galilean moons" of Jupiter, it has an icy crust, and as we all know, likely to have a sub-surface ocean of liquid water. This near-future sci-fi to stick closely to known technologies and science, might be what one would call "hard sci-fi", more 2001 than Star Wars. But actual science is not usually box-office dynamite (or so studios believe), so as the crew of 6 astronauts approach Europa they fall into increasingly critical misfortunes that threaten their mission and their lives. The movie is foreshadowed by an "executive" talking to the camera, documentary style about the mission and you get the sense something went wrong. Most of the movie is then shown through lost-footage style clips showing bits and pieces of the long journey and the events on Europa. This seems to be a common trope now as it is similar in the style to Apollo 18. Not only is the footage spliced together out of order so you don't get a full understanding of the events until later, but they use a lot of creepy noise effects and interference at times to make it seem "spookier" I guess. I still think Moon did the best job in recent years, to tell a story in space without devolving into a sub-genre of typical horror films, and just having normal drama in a science fiction setting (yes the premise for Moon isn't that realistic). In any case, I don't think it is a huge spoiler, given the trailers for this movie, to tell that things don't ultimately end well for the entire crew.

Thera Macula (false color) on Europa. Credit: Paul Schenk/NASA
Other than the style, I found the characters and story were pretty good, the effects were pretty good overall and didn't seem like overuse of CGI and they did have some weightlessness scenes. The scenes in orbit around Jupiter and Europa were quite impressive, makes you wish we really were going there. There were no explosions in space, super AI, fusion reactors or any other really exaggerated technology. The ship had a rotating living section to simulate gravity which they spent most of their time in. Once they get to Europa they send a large section of the craft down as a lander which will then drill through the ice and hopefully reach the under-ice lake or ocean in order to search for life. That is the plan anyway.

Europa Report currently has a 69% fresh rating on Rotten Tomatoes. Overall I enjoyed the movie. It's probably worth a Netflix rental, rather than paying $9.99 for it.

spoiler alert!

 Stop reading if you don't want critical pieces of the movie spoiled for you.



While the Europa Report was pretty good, but the "science" part of the plot kept reminding me of List of things I did not care for in Prometheus. Basically it comes down to: "We are going to go halfway across the solar system, for the first time in humanity, but as soon as we get there we have no ability to actual get any scientific research done without being eaten by monsters". One the main claims to fame this movie has is the supposed realism and authenticity of the mission. I feel their hearts were in the right places, and it's basically a movie about every space geek's fantasy about what might be on Europa, but they fell into too convenient plot devices I found hard to swallow, despite enjoying the movie.

Among my issues with the plot:
  • No redundancy of communications... what!? Isn't that the most important thing for a mission to another planet/moon? Not to mention they apparently did have a way to repair it, but chose not to until the very end. Oh and genius idea that the life-support subsystem can swap parts with the communication subsystem.
  • No redundancy of their drilling probe? They lose one and all is lost. They can't improvise a camera on a pole and look under the ice?
  • Apparently, there was no firm plan to have the crew explore the ice surface after landing, no radiation protection, no way to deal with hazards of walking on ice, no vehicles to use other than walking. Why send humans at all in that case?
  • When they do send a scientist outside, they have no safety harnesses, they don't use a buddy system like mountain climbers (were the Apollo astronauts ever alone?). Let alone have any sort of a rescue plan i.e. a jet-pack or other person suited up ready to go out in an emergency. Maybe flotation devices might be useful on a planet with liquid water? For that matter, I wonder how buoyant a space suit is with low gravity, since I believe in those neutral buoyancy tanks on Earth they weigh down the suits with additional weight. She basically sinks like a stone in falling through the ice, they don't even bother to go after her, but it's implied she is eaten/killed by the monster. This is like horror movie 101 stuff, never go out alone, never walk towards the mysterious light.
  • So they go all the way to land on Europa and they don't have a reliable way to go outside, so you would think the lander would have all sorts of robotic arms, scoops and other sensors to get as much science, like any other lander NASA has ever sent to another world, but other than the one drill probe, apparently not. Wouldn't a major effort be to take back "Europa-rocks" of ice samples or whatever they can find and bring back to Earth for research?
  • You would think to support such a mission there would be a network of probes either in orbit around Europa or in the Jovian system which would be taking images of them and the landing site (maybe to see aerial view of the "lights" they are so desperate to see up close), able to relay communications, etc.. Like we have on Mars now with NASA's MRO
  • 6 crew all the way to Europa and only 2 scientists doing anything while they are there.
  • They didn't exactly explain how long they planned to live on Europa, similar to some missions to Mars, the return window is some length of time away, so they need to have some semi-permanent base to live and work out of for an extended stay. For Mars exploration there are ideas to send unmanned supply/cargo craft that would already be there on the moon for them to use to set up some sort of base. It didn't look like they had any plan like this, and it seemed like they had an all or nothing EVA to get scientific data before trying to come home? It wasn't clear if the rapid take off was due to the crew death's or because they weren't going to stay long anyway.

Maybe the idea (I doubt the writers even thought this far ahead) was that the mission was really just a "plant the flag" expedition to Europa, without much plan for hard science, but to promote the Europa Ventures company. Something like the quick and dirty ways they could get to Mars really fast without doing anything useful while there. But then again, they probably wouldn't need 6 crew for that. On the other hand, the one thing they did have redundancy for was the lives of the crew!


Some unresolved questions or plot points, and maybe I just missed them:

Why couldn't they leave theAndrei in the orbiter? Not that it mattered I guess, did they imply he had radiation poisoning or just that he was depressed?
 
Why did that male scientist die at the end, did he just fall because of an "ice quake" or did the monsters get him?
 
Hopefully the monsters' ecosystem isn't waiting for spacecraft to land, be attracted to their lights and fall through the ice so they can be eaten. They would get very hungry.
 
Wasn't the monster creature attracted to light almost directly taken from Arthur C. Clarke's "2061: Odyssey Three"?
 
It was implied that there was some connection between radioactivity interference and the monsters, could be interesting if there were alien life that could somehow use radiation in the environment directly as a food or heat source. But this was never really "answered" within the movie.

Tuesday, July 17, 2012

List of things I did not care for in Prometheus

spoiler alert!


I watched the movie Prometheus a few weekends ago, it was a decent sci-fi movie, in my opinion the more big sci-fi epics that are made, the better. Others have said similar things as I am about to. I recommend everyone read Bad Astronomy's review. In this post going to stick more to the bad science than the bad plot. Except for FTL travel, I don't care about that, I hate when people bring that up as a problem in movies, yes we know there is no currently known way to travel faster than light according to the General Theory of Relativity.


List of things I did not care for in Prometheus.

Sound in space. If there are no lasers or big explosions to make things exciting, you don't need sounds in space. You didn't need it in 2001: A Space Oddessy, so I don't know why every sci-fi movie since then feels the need to add sounds when there is an external shot of a space ship. Silence is unnatural and heightens the spookiness of space travel.

The spaceship Prometheus directly lands on the planet. Ok so they must have some super source of energy to fly FTL, but for some reason it bugs me they land their main ship directly on the planet surface. In Alien the Nostromo separated from the cargo portion of the ship, same thing in Aliens with the drop ship bringing the crew from the Sulaco which remained in orbit. Both of those movies are set at a later date, so it may be implying that these are one of the first expeditions to other star systems? Even so, it would seem technologically easier to construct an interstellar FTL ship without having to worry about landing it in on a planet with gravity and an atmosphere, let alone taking off again.

Another way you might expect them to economize their travel is by manufacturing things from the planet when they land, either fuel, or oxygen, water, etc.. all things you might not want to carry all that extra mass. I assume if you have some kind of infinite fusion drive energy source you might be able to get away with not bothering to do that, although unless they have super compression techniques, there didn't seem to be big storage tanks or anything on the Prometheus to hold the matter they would need for things like breathing and drinking. Another area where it would have been a nice thing to show them actually do for once in a sci-fi movie.

The purpose of the trip is supposed to be a scientific study but all the scientists immediately run out and dive into the first structure they see. There is no systematic mapping of the area, they landed near the first spot they came across. Even if they just land somewhere that seems interesting, if they had left the main ship in orbit or even just some remote satellites they could have begun mapping the entire world for any other interesting areas. That's not to mention that there are no efforts to survey the outside of the structure.

As has been pointed out elsewhere, the scientists run around touching everything they see. The one thing they do which makes sense are sending those small robots to map out the interior, the one good idea they have seemingly. David has some ulterior motives in his programming, so I can give him a pass, although it seemed silly for the android to be the one to take the "touch first, ask questions later" approach to levels higher than the other scientists could possibly do. Overall everyone seemed pretty underwhelmed that they had in fact found an alien civilization at all! Even the remains of one would be a momentous archaeological find. It seemed like they were not interested in studying anything, and I guess it would be emotional but they seemed more greedy than amazed by anything they saw. If I remember the Alien series, there was no confirmed alien/xenomorph life on any planet ever surveyed, and since this was earlier than those movies, this would be the first proof of life outside of Earth, another amazing discovery by itself.

What was the one Engineer alien doing there asleep all this time? Did he come there after everyone else died and was trying to do something? Or did he go to sleep before all the others and didn't know that things went to shit for all the other Engineers? If so why wouldn't no one wake him? Or why would he be sleeping on a stationary ship in the first place while the others were there doing some work.

The first thing the Engineer does is start trying to kill everyone.  That was probably the low-point for me in the movie. So predictable and B-movie-ish. No dialog, no explanation, nothing profound from the mouth one of the creators of the human race, not even a thank you for waking him from his several thousand year hibernation or sleep. Maybe they are inherently violent, although the opening scene would seem to imply some sort of more thoughtful existence. It would have been better if he didn't physically try to hulk smash everyone but instead if his actions were more intelligently shown to trick or trap the humans, or even experiment on them. At that moment he would have no idea whether or not there were 100 armed soldiers just outside, what he did was careless and incomprehensible.

Plenty of unanswered plot points (I can't take full credit for these, thanks to my bro for expressing better than I can):
-- Why did the engineers, create humans billions of years ago, then come back to earth several times over our history to tell us about a military base they were building to eventually use to destroy us? Were those runes or cave paintings an invitation or warning?
-- So the engineers were planning on wiping out Earth with the goo, but something went wrong and they all died except for the one engineer who went to sleep before the others? Why are only the corpses of the engineers left but not the xenomorphs or whatever it was that killed them?
-- Did the rest of the engineers, the one not on the base just abandon the whole thing? The goo base and humans?
-- What happened to the two scientists who were trying to put the main woman [Shaw] under?
-- How does the main woman do this major surgery on herself, but no one seems to know, or notice, or react at all to it?
-- Why is no one particularly surprised that a stow-away, a man who had supposedly been dead for two years, turn up on the ship?
-- Where does EVERYBODY go? We see some people get off-ed but its a crew of 17. [>> So there were at least 3 in the bridge of the ship at the end. The Biologist, Geologist and Charlie killed by various alien things. Vickers met her end too. Thats seven. If David counts, 8, there were at least an orderly and two security guards with Weyland too, and presumably some of them were killed by the Engineer in the alien ship? I think you could count 3-4 more killed in the cargo hold by the zombie-Geologist, even if the number was only 3, then you're up 14. Two aforementioned scientists operating on Shaw, they vanished after being beat up. And Shaw herself being the 17th, not counting Weyland. ]



(Full disclosure, I wrote most of this the week after the movie came out when it seemed to matter more)

Saturday, June 23, 2012

Book Review: Von Braun Dreamer of Space...

I recently finished this book Von Braun: Dreamer of Space, Engineer of War by Michael Neufeld.

This post is a reprint of my book review on Amazon.com

Debbie Downer History of Von Braun
This deeply detailed biography seems to say that von Braun's popular image was more about fame and personality than real accomplishments or importance in the history of the Space program and even before. Not having studied the man before, I have to admit to buying in the general mythology of his too until reading this. From an American perspective, there is something very positive about his life, he is the ultimate immigrant success story, a case of American pragmatism to accept a national of a former enemy and promote him to the very heights of power in our government, that opportunism (on both sides) is very Stangelove-ian and in strange way admirable to me. He was apparently a likeable and charismatic man with big dreams when the country was thinking big, so its not hard to see his rise to fame and power. The book, though, takes a hard look at his active cooperation with or at best neutrality towards the highest levels of the Nazi regime and the crimes of war in the production of the V2. Further complicating is the probable deceitfulness he expressed in later denying much of the story of his true involvement and an apparent lack of personal guilt. I am sure if I agree with the author that this criticism is deserved, but it is quite surprising to find out he was an SS officer.

I found that overall it seemed like the author was a little lopsided in the flow of the narrative, usually moving between personal/political challenges then various technical issues without any real success. It almost seemed like he never actually got any rockets or missles to actually work. Usually by the time the technical issues are sorted, the discussion moves to some other crisis, or the next project, with rarely discussing the actual successes. For instance, based on the way the book describes it, it didn't seem like they actually had any completely successful tests of the A4/V-2 before it was put into production and active duty, yet didn't thousands not in fact hit London and Antwerp (very little about the actual V2 bombings was mentioned)? After the war it seemed as of Von Braun and the rest of the paperclip scientists spent 5-6 years doing little of anything in Texas, later Huntsville, AL, which if totally accurate is amazing considering how much attention that group of scientists was given supposedly. His group's contributions to the overall American rocket and missile field appear modest, without much impact on the Cold War. Whole chapters deal with the US Army's efforts to develop ballistic missiles, such as Redstone and Jupiter-C, were either ever used for anything in practice? The book basically portrays these efforts as one development issue or lack of mission crisis after the other with little mention of any actual outcome from these efforts. Its hard to miss the success of the Saturn V and von Braun's central role in that effort, due to the Apollo moon landings, though great pains are taken to portray him as as subordinate center director in NASA rather than a leading figure. In the end his tenure at NASA headquarters is described as a depressing frustration and his post-NASA career also at Fairchild is also portrayed with mix results.

Maybe the author was purposefully trying to contradict some other more glowing histories of the man, though I suspect the truth is somewhere in between. A lot of the details of his personal and professional life still do impress, even if he didn't really do anything successfully, he seemed to work pretty hard for his entire career.

The more I read about the subjects of NASA (To the Ends of the Solar System, Moon Hunters), the more of a happy coincidence we had to even get to the moon (Kennedy's promise, followed by a pro-space successor in Johnson). It is quite eye opening to read these behind the scenes accounts of the political and budgetary battles in government that ended up killing any really expansive manned space program after Apollo that we've all read about. Its amazing how the government made it seem like we were on this mission to the next big thing it just needed more time, when in reality they were consciously killing programs that would get us to Mars or put stations in space.

I read the book in paperback edition. One improvement is that it could have used some maps of Europe and Germany, especially for the Peenemünde era and World War II. As an aside his name is pronounced in German: "Vairner fon Brown"

Thursday, November 4, 2010

Deep Impact makes closest approach to comet Hartley 2

The NASA probe, Deep Impact, is currently making its closest approach to comet Hartley 2. It will eventually fly within 700km of the comet. During the fly-by the antenna will be not be oriented towards Earth so it will be some time before photos come out. They didn't want to fly any closer due to the risk that the comets debris 'tail' would damage the spacecraft.

http://www.space.com/scienceastronomy/comet-hartley2-poison-gas-jets-101103.html

The comet Hartley 2 is now visible from Earth as well.

http://www.skyandtelescope.com/observing/home/102632669.html


11/7/2010 - Edit Pictures came out:


http://www.jpl.nasa.gov/news/news.cfm?release=2010-371

Saturday, May 15, 2010

Exploring the Milky Way

I was sent to South Africa for work during April for about three weeks. I brought a long plenty of reading material (not safe to walk outside supposedly). The first book I read was Exploring the Milky Way by Donald Goldsmith (1999) which I checked out of my local public library. Let's just say that reading this book lit a fire under me, I want to learn more about how they actually write software for a probe that is millions of miles away and 10hrs away from any instruction from Earth. So how do they actually write that code? Did they program an AI in C++? Is it some crazy assembly language? I am guessing Java or .NET isn't a skill that would be particularly useful for the Cassini and Galileo missions. I think my basic questions are echoed by others, for example this poster(Developer.*: "Code for Nasa space probes" By berrydoo)
I've been reading a lot lately about the two Mars rovers, and the Galileo space probe thats orbiting Saturn's moon Titan. And I'm really curious to read about the software design of those machines. That must be some of the most complicated code ever written. These machines have to be "smart" enough to manage navigation through space, communication with earth, management of sensors and storage of sensor information, create and possibly interpret diagnostic data, and be smart enough to recover if a problem occurs. What should it do if it cant communicate with earth any more? What should it do if one of it's systems fails? I'd venture to say that code is about as close as we come right now to artificially intelligent machines.

Does anybody know where I could read more about this topic? I've looked around, but I cant find anything on the internet. That information might be classified, but I just thought I'd ask.


Well sir, I had the exact same questions, so I started to google it. My own particular interest had more to do with the deep space missions to the outer solar system, Jupiter, Saturn, etc. That limits it down to the Voyagers (software probably written in the 70s), Galileo (Jupiter mission, 1989 - 2003), Cassini (Saturn, 1997 - present). Certainly there a couple missions underway or to be launched (e.g. Juno).

I decided to look into Cassini. In the end I found a number of resources that help explain how the software was designed and what it does. (Cassini software was written in Ada)

So if you want to know more about Cassini or other spacecraft implementation details these are some useful resources I've found:


  • Basics of Space Flight, JPL
    http://www2.jpl.nasa.gov/basics/index.php
    Top to bottom introduction to physics, mission operations and spacecraft components. Useful reference or for putting it all together. Much higher level than many of the technical papers describing the actual software or components that assumes this knowledge.

  • The Cassini Spacecraft: Object Oriented Flight Control Software, Hackney, J., Bernard, D.Rasmussen, R.
    http://hdl.handle.net/2014/34861
    Article about how they used OO methodology for design of components to steer/orient the spacecraft.

  • An Attitude Control Design for the Cassini Spacecraft, Wong, Edward
    http://hdl.handle.net/2014/30851
    How the spacecraft determines attittude and estimates attitude for pointing (Star-sensor, sun-sensor, gyros, etc..)

  • System Fault Protection Design for the Cassini Spacecraft, Slonski, John P.
    http://hdl.handle.net/2014/31814
    Attempts at generic or reusable fault protection models, designs and algorithms for fault protection.

  • Cassini Star Tracking and Identification Algorithms, Scene Simulation, and Testing, Alexander, James W.
    Chang, Daniel H.
    http://hdl.handle.net/2014/26388
    How the spacecraft's star tracker, literally takes an "image" of the sky, on the fly looks up the configuration of stars in an on-board "database", calculates relative distance between stars, and then based on that can give an estimate of where it is pointing. Amazing stuff.


More public domain, articles in PDF format are also available for many subjects on BEACON eSpace at Jet Propulsion Labratory.