Mars Phoenix Lands In Less Than an Hour
May 25th, 2008
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Just thought I should mention, in case anyone here is not aware that a little before 8 PM Eastern US Time, (1:00 AM GMT, 100 Hours), the Mars Phoenix lander, the latest in NASA’s unmanned Mars exploration program will be arriving on the surface of Mars. Hopefully it will be a landing and not a crash, but one way or another we’re about to find out if the spacecraft arrived. At the moment, all things seem to be going well and indications are that the spacecraft is healthy, but Mars has a history of probe failures, so there’s always suspense, especially because this spacecraft is using a new landing system, as opposed to the well tested and proven airbag system of other recent mars landers, such as the two rovers Spirit and Opportunity.
UPDATE: The spacecraft has landed safely and entirely as planned. After sitting for a short time to allow any dust kicked up to settle (and not get on the solar panels or instruments) the spacecraft has begun taking the first images. The first images typically are low resolution and intended to assess the area and the landing as well as image the spacecraft itself as part of the initial diagnostics.
The Phoenix is not a rover, so it will take measurements from only the area around the lander. It does have the ability to reach out with an arm to take soil and rock samples. The primary goal of this mission is analysis of local material, especially looking for organic materials and water related compounds.
As with all deep space missions, the data will be returned “live” but will actually involve a significant lag of many minutes due to the amount of time it takes data to travel to mars. (In this case, it will be a little more than fifteen minutes due to the position of the planets, which is actually not that long compared to other missions.) Because of this, the spacecraft cannot be controlled in real time and by the time we know if the landing has gone well, the event will already be over.
This entry was posted on Sunday, May 25th, 2008 at 7:13 pm and is filed under Announcements, Good Science, History, Space. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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May 25th, 2008 at 7:55 pm
Touchdown!!
Mars Phoenix is using Twitter
http://twitter.com/MarsPhoenix
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May 25th, 2008 at 10:34 pm
First pictures in. Pity I have to go back to work now! (I just ducked back home to see if all went well during my lunch break… I’ll settle down tonight to read the analysis thus far).
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May 25th, 2008 at 10:55 pm
You know one thing I really would love to see on one of these probes would be full motion video, preferably live. Even if it were only 320×240 at 20 fps and youtube quality, having real video would be really nice. The closest they’ve done is some rapid time-laps that can be somewhat animated.
Scientifically, it would not really be that helpful to anything. It may have it’s uses for diagnostics and assessing the performance of things, but I doubt the value would be that great. The value would be the fact that NASA is trying to keep up the public support for their work. I really think watching the landing as it happens on television would be something people would be excited about and could identify with. It would also be very very cool to simply see a video of driving around mars and also document it for history as one of the first steps of mars exploration by humans.
Of course, it’s technically entirely possible and not that difficult to capture and transmit a digital video stream. The issue is not really weight, but power. Any simple general purpose digital camera, like the low and medium resolution data acquisition cameras can do video. Encoding and compressing video is really not that big a deal to modern computer systems, even for modest hardware.
The reason I’d imagine they do not do it is they are running on solar power and need to squeeze every watt they can out. The data processing on the spacecraft needs to be kept to a minimum. It would not be difficult at all to have the probe encode digital video on the fly from a processing perspective, but it would be difficult to provide that kind of power. The processing on these probes tends to be used very sparingly and they keep all the chips at a low clock speed and try to use them sparingly. Every clock cycle needs energy.
Also, transmitting data is an issue. It comes back so slow for the same reason. They use relatively narrow band transmissions and very effecient modulation, because they have no power to spare.
I’d bet they could easily encode video on the fly and transmit it back to earth with about 30-50 watts of power for the computing and the transmitter. The only problem… that’s more power than the whole damn spacecraft usually operates on.
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May 25th, 2008 at 11:06 pm
drbuzz0 said:
Some people are never happy
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May 26th, 2008 at 4:03 am
DV82XL said:
Well that would be really cool. I agree it is likely a power issue more than the weight of the additional hardware needed, because they really would not need any since a spotting camera could double as a tv camera. I don’t know if it is that they couldn’t put the ecoding on though because these days cell phones can encode video in realtime using just a little power. it can be done with a single multimedia chip.
It is probably the power required to downlink that much data. They have a low baud rate because they need to conserve power and so a powerful radio link is not possible and so they need to go with energy frugality over bandwidth and use more effecient but slower modulation and transmissions.
Too bad they reserve the RTG’s for the really deep space stuff.
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May 26th, 2008 at 4:04 am
drbuzz0 said:
It would be scientifically valuable for probes to the gas giants, videoing atmospheric phenomena in real time, and possibly for Mars, considering that there may be things we haven’t picked up because we haven’t had that capability (it’s a fluke that we’ve been able to capture some still images of dust devils).
Power is indeed the answer. Power to provide enhanced communications and other capabilities is one of the arguments in favour of nuclear-powered probes.
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May 26th, 2008 at 4:07 am
Actually, the landing was accomplished in an old tech style, like its older cousins, the Viking Landers, using a system that is much like theirs, gyroscopes and accelerometers to provide feedback to the decent computers and monopropellant rockets to provide thrust. The airbag systems used recently are a self correcting systems that are much lower tech (macro scale), heat shield, then solid rocket deceleration, then a small freefall, then the bounce/roll out, the nice thing about the airbag system is it doesn’t care if its on a slope, lands on rocks or whatever, it can even come to rest upside down, when the petals open it will right itself automatically. The drawback is that it requires all of the internal components to be much more robust (not saying Phoenix is a wimp, it handled a rocket boost into orbit, and that’s no small feat (but is very predictable and testable)). GO NASA!!!
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May 26th, 2008 at 4:11 am
I think that full motion video would have a lot more usefulness than just PR and publicity (it’d have that too though).
Like it was mentioned, seeing dust devils and stuff on mars in full motion would help a lot in knowing how they work and move and that would be important for future missions, even manned to understand what kind of problems they could cause and how to avoid them by seeing how they move and how they form and disperse, which you can’t get from still images.
Also, what about just being able to see the vehicles moving on the ground and how they go over rocks and also see how the arms and joints move? If there is a mechanical issue or something I think video would be really helpful for diagnostics to see how things were moving or not moving. also just imaging the landing and motion will help with seeing how the hardware does in real conditions to design more in the future.
So yeah, having a real video link would be really really awesome, but I think it’s too much energy to transmit it now.
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May 26th, 2008 at 4:26 am
Doing some quick searching, it seems it is the transmission thing that would be an issue becasue these mars probes actually have pitiful data rates. The normal data rate is under 120 bits per second. That’s bits, not kilobits or even bytes. I think they can do a little more in a burst, but that’s basically it.
They don’t transmit to earth but transmit to some of the orbiting mars probes that act as relays and some of them have pretty decent theoretical speeds to communicate to earth but they have the benefit of being in space where there is more sunlight for power. The probes have to link up to the orbiters, which are in high orbits and sometimes low on the horizon so that’s why it’s hard to get the transmissions need a fair amount of power and therefore they save it with the extreme narrow bandwidth and speed.
If they don’t link with the satellites then we can still get some data but it’s hard for the DSN to pull that in and they need to commit big radio telescopes to that.
http://www.spectrum.ieee.org/feb06/2810
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May 26th, 2008 at 6:42 am
Is it just me, or do a number of the smallest pebbles in the foreground of the first landscape shot look a bit like the ‘blueberries’ from the Opportunity landing site at Meridiani?
Well, probably not… but this site is supposed to have been beneath the northern sea of Mars (if such a body of water did in fact exist). Perhaps concretions of some sort formed at some point.
Come to think of it, what do the rest of you think of the first images? Lotsa science geeks here (I’m sometimes audacious enough to see myself in that light too), so we should have some informed opinions. How well will the Depleted Craniati do in arriving at the correct interpretation?
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May 26th, 2008 at 8:36 pm
Now THIS is something you Yanks can really be proud of. Not only did you do it, you had the balls to do it on live TV where the world could see you screw up. THAT’S the America I remember from my youth, bold, and full of adventure; leaders in every sense of the word.
It’s time for a few of you to start cracking heads and taking names, and remember who you are again.
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May 27th, 2008 at 12:21 am
DV82XL said:
Yeah, actually for all my criticism of NASA for their handling of manned space flight and the current capabilities of the United States for launch planforms and their development, I’m more than happy and even proud in a slightly nationalistic way for how things have been going the past few years with the unmanned planet exploration program, especially with the mars missions. Despite the fact that there have been some past problems, the recent orbiters and the rovers and other probes have been working far better than even the most optimistic would have expected.
The Pluto mission as well as their development of relatively low cost missions that have demonstrated ion thrusters and other innovative systems have been extremely successful. Also, some of the asteroid probes and research has been extremely successful.
So yeah, NASA can do stuff right sometimes too. Beyond that, they can do things spectacularly well on occasion.
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May 27th, 2008 at 3:25 am
Real time video from mars would be very very cool, especially if they had a camera on it as it was coming down. Can you imagine how exciting it would have been to watch the surface come up and see the engines fire and then the ground start to become clear as the dust settles? That would be something to tune in for.
Of course, it would also be great to have that kind of power and transmitting ability for other purposes and to run the scientific payloads on. With these missions, power is always a limiting factor of what kind of experiments can be done and how far a rover can travel or when it can be activated and when it must be left in hibernation.
Plutonium-238 happens to be expensive. It might be less so if we could make it ourselves, but right now it is coming from Russia and even the Russians have a limited production capacity and are already busy using many of their materials reactors to produce other isotopes.
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May 27th, 2008 at 5:12 am
Having been able to take a look at more images this evening, I hereby withdraw my assertion that the pebbles in some images may be concretions.
I’d still be interested to hear the take of others on the images and info coming in, and to come.
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May 27th, 2008 at 3:44 pm
A digital watch has the horsepower to encode video as long as you don’t much care how long it takes. Short video bursts (10 seconds?) could be encoded and transmitted over time allowing a lower energy accumulation rate as long as nobody is in a hurry. It would require more memory.
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May 28th, 2008 at 12:00 am
Chuck said:
That might be true, but I think right now the time and data on the probes is at such a premium that they won’t waste it on something that does not have a very high scientific value.
Maybe on the rovers though, actually, I could see them doing it. They’ve been going so much longer than expected that I think they’ve analyzed most of the interesting stuff in the area around them. Maybe they could send up a software update to take some video while in motion and then encode and send it back. That would be cool!
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May 28th, 2008 at 12:58 am
Finrod said:
The terrain reminds me of the area on the south shore of Great Bear Lake in The Northwest Territories, which is a stony wasteland scoured and ground by glaciers during the last ice-age.
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May 28th, 2008 at 1:09 am
DV82XL said:
That would make sense. This is the summer in the area and there’s relatively little ice right now. However, during winter it is covered with a sort of glacier of sublimated Co2. It may have been covered with even more thick deposits of CO2 and water ice in the past.
Assuming the probe lasts the entire season, it will be interesting to watch the ice return as winter begins to set in. Of course, it’s anyone’s guess how far along we’ll get before the probe quits, but it will eventually fail as the winter sets in and sunlight begins to become more scarce, while at the same time night temperatures will drop lower and lower. Eventually it’ll be encased in dry ice, so it’s a given that the mission will fail by the time full on winter arives.
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May 28th, 2008 at 1:18 am
drbuzz0 said:
Remind me again why NASA isn’t flying a nice hot radioisotope thermoelectric generator on this mission. That and a few radioisotope heater units would keep the unit running sun or no sun regardless of the ambient temperature.
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May 28th, 2008 at 9:58 am
DV82XL said:
Well, a single RTG can cost around $100 million and there have been struggles to provide enough plutonium-238 for them recently as noted here: http://www.space.com/spacenews/businessmonday_041004.html
The US has zero capability at the moment to manufacture Pu-238, which is sad because in the 1960’s and 70’s we could crank the stuff out and had plenty. They rely on Russia and even the Russians have a somewhat limited capability to product it at the moment.
You’d need a fair amount, I would imagine to not only run the RTG but add some pellets of it around the spacecraft as a general purpose heater.
I suppose the alternative would be to use something other than Pu-238. Sr-90 would work and is just about free since it’s a fission byproduct, but you would need three times as much plus for the same amount of heat. However, I’m starting to think that adding a few pounds to the mission might be worth offsetting the enormous cost of Pu-238. I don’t know though, weight is always such a big concern with these things.
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May 28th, 2008 at 11:15 am
One step at a time. Keeping down costs by using already-manufactured components and not spending big on research for an entirely new RTG system is understandable in this case. Aside from the scientific objectives, this mission had an important engineering objective: To demonstrate soft landing using retro-rockets employing current equipment. That aspect is so important to the future of the Mars program that I’m not suprised other engineering goals were secondary on this occasion.
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June 2nd, 2008 at 11:56 am
Personally, I’m really looking forward to having the Mars Science Laboratory in action.
It’s running on a nice, sensible energy source
It’s awesome; bigger and faster and more feature packed than any mars craft before it.
Did I mention it’s got a great big laser on it?
If they don’t land it properly, or crash it, or somehow lose or destroy it, I will be really, really disappointed.
PS: I think Sr-90 is less favourable for RTGs because you tend to prefer nuclides with as little neutron, beta or gamma emission as possible, as they make handling on earth harder, and interfere more with the spacecraft’s instruments, and shielding is intrinsically heavy, which is not good on a spacecraft.
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June 2nd, 2008 at 1:16 pm
Luke said:
Do you know if they have decided if they are going with the standard Boeing design or with the Lockheed Martin’s Stirling?
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June 3rd, 2008 at 5:33 am
I think they’re leaning towards Boeing’s new RTG, as opposed to the radioisotope Stirling engine, which isn’t quite developed to the stage where they’re ready to gamble the entire spacecraft on it.
The Boeing RTG is still a new and improved RTG, although it’s still fundamentally the same familiar RTG technology.
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September 5th, 2008 at 4:10 pm
drbuzz0 said:
This is an interesting mathematics and computer science problem as well. You want to use good compression with efficient error checking (ie good at correcting errors, but not very large) to be able to move as much data as possible across a narrow point to point link (the point on Earth will decompress the stream and restream it out to other places). You also want a video codec that encodes the video stream itself to a very small size without loss of visual quality.
Since it’s point to point there’s no way for a bandwidth-sparing protocol (eg BitTorrent) to help, but there are some interesting proprietary protocols that I haven’t really looked into yet for doing high-quality streaming video over narrower and narrower bandwidths. BitGravity is one company doing such a thing but I haven’t looked into how they’re doing it. (If they’re using a bandwidth-sparing protocol then that won’t help, but I don’t think they are.)
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September 5th, 2008 at 4:28 pm
Chem Geek Gregor said:
Ok, this is probably more than coding theory can solve then
I agree, more power! An RTG would be a good start, followed by an improved relay network. Could they deploy a payload of several small dedicated RTG-powered relays to be placed in orbits that would provide coverage for all probes on the surface and transmit their data back to Earth?
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September 5th, 2008 at 4:50 pm
mlp said:
That’s an interesting idea, but I’m not sure that RTG’s would really be that much of an improvement for the orbiting spacecraft. Solar panels work quite well in space, and in martian orbit there would be less sun than earth but probably still enough to get some good power. Solar panels on a satellite can enable several kilowatts of operating power in earth orbit, but I’m not sure about mars – it’s probably still pretty decent. I’m not sure 200 pounds worth of RTG would do that much better than 200 pounds worth of solar panels, and for one thing, space solar panels can be light because they don’t need to even support their own weight.
I believe the issue is more likely linked to the fact that there is a lot of singnal loss and poor signal to noise when transmitting from mars and possibly also the fact that the orbiting spacecraft were not purpose-built to act as data relays from surface probes. They can do that, but that’s a secondary concern and might not be a design priority. I believe the surface probes can communicate directly with the earth in most cases, which would be a capability you’d want so you would not lose the mission if the orbiters didn’t work properly, but for a little surface probe to communicate with the earth would be a lot more difficult and probably cause a much greater power usage and poorer signal.
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September 5th, 2008 at 5:15 pm
drbuzz0 said:
Yeah, I have no idea what kind of power can be reasonably obtained by solar cells in martian orbit. It’s something to ask my buddy who works on the Mars Phoenix project next time I talk to him though.
It would be fun to start with that and then work out what sort of small dedicated orbiting relays could be built…
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September 5th, 2008 at 8:15 pm
Actually I did some reading and the mars reconnaissance orbiters has a maximum theoretical transmission rate of 6mbps using a new Ka-band transmitter link. I believe it’s considerably less when you account for error correction, but that’s still pretty good. However, it seems that it can only do this in relatively short bursts, at least partially because it is only oriented properly for high bandwidth transmissions during a small portion of the orbit. It probably could be for longer if it was continuously adjusted to keep the high gain antenna pointed at earth, but that would complicate things.
The transmission rate from the ground probes looks to be limited to about 1200 baud, but perhaps a little more for bursts. Remember that to use a satellite of mars as a relay the satellite needs to both have a good line of sight with the probe AND have a good line of sight at earth. For this reason a lot of the transmissions and store-and-forward and not live. The orbiter records the data when it is able to receive it and then retransmits it when it has good alignment with earth.
Of course, mars is rotating all the time, so sometimes one side is facing earth and sometimes another. The satellites are constantly orbiting mars and coming in and out of proper alignment with earth. If you wanted to be able to stream data directly you’d likely need to have a few satellites around mars to relay the data from the ground to a satellite that had a good signal from the ground probe, to a satellite in a good alignment with the earth.
The satellite would also need to have the ability to run the transmitter and the receiver simultaneously and receive a signal from a different heading than it transmits it at. For satelite-to-satellite relays the antenna would not have to be that precise a beam vector, because the signal would be fairly strong. It would just have to be pointed in the right general direction. It could even have a 180 degree beam. But for earth, it would have to be a very narrow, high gain directional antenna to get the signal properly transmitted back to earth.
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September 5th, 2008 at 9:28 pm
Yeah, that’s why I’m wondering if it would be possible to build several small relay satellites and deploy them as part of one payload (ie deploy a circum-Mars satellite relay network in one shot). Unfortunately I’m embarrassingly ignorant about orbital mechanics, so I don’t have any idea where the optimal orbital points to deploy them would be or how many you would want, but the idea would be to have four or five satellites in orbit so that they could receive data from ground probes, then relay that data to whichever orbital satellite has the best shot at earth at that time (which would of course vary over time based on the difference in planetary orbits around the sun). If the orbiting relays are in communication with each other then a ground probe just needs to reach one of them, and the receiver then figures out how to route the signal to the relay that will get it to earth fastest.
Or if you wanted to get into very-near-future science fiction, you could have hundreds of orbital satellites in a mesh network configuration, thereby raising the number of satellites with a good alignment with earth at any given time
802.11s has some serious problems, but mesh networking in general is a big research area in CS and EE departments right now and I think as more and more small devices become internet-enabled we’ll see some cool advances in the kind of store-and-forward protocols that sparse meshes require.
It’s an interesting math problem to be sure! I don’t expect it’s a priority for NASA, but a more robust earth-Mars communications link would be of huge benefit to future research, particularly if we ever get around to a manned Mars mission. And of course if we ever end up colonising Mars, we’re going to need a high-bandwidth “pipe”.
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September 5th, 2008 at 10:14 pm
The closest thing I can think of to this would be the iridium network of satellites which provides mobile phone service around the world via satellite. There are only a couple of downlink stations for the satellites to connect to so if you want to make a call it links to a satellite and they relay the data to one in range of the earthstation via KA-band hookups.
However those are LEO. I think the best way to have a satellite system for covering mars would be to have them at a very high altitude. Something close to what geostationary satellites of earth are at (about 30,000 miles) because then you could cover most of the martial surface by three satellites – maybe four.
Also at least one of the satellites would be in constant view of the earth. There are antenna arrays on earth satellites that have been developed with enough gain to allow for direct communication with low power portable devices on the surface. Obviously this needs a high gain antenna because the device is far away on the surface and the power produced is only a small amount from a low gain antenna.
Here’s an image of the Thuraya satellite, which is for low-powered handheld mobile satellite phones. AS you can see, the special aray antenna is enormous. This technology was developed for military satellites, but the antenna folds up and is deployable only in space because its far too flimsy to support itself in gravity or against even gentle winds. It floats:
http://www.boeing.com/defense-space/space/bss/factsheets/geomobile/thuraya2_3/01pr_01515.jpg
So three or four of those will give coverage to a planet and the transmitters on the surface don’t need to be big and powerful. Just a few watts will work fine. And you could get basic broadband speeds with that.
Then you’d have to relay it between the satellites (comparatively easy – a couple phased arays)
Then you need another big antenna to downlink to earth. The antenna would need to be steerable. That’s totally doable. The big issue would be that each satellite weighs a good couple of tons and that is not easy to get all the way to mars.
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September 5th, 2008 at 11:32 pm
Sweet! That’s what I love so much about this blog, how wonderfully polymathic you and your regular commenters are.
So really it’s an engineering question — can the size and cost of telecommunications satellites be reduced to the point where the cost of getting them all the way to Mars is justified by the scientific benefit of having them there.
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