 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
| HomeDiscussion GroupsSpace ScienceAstronomyAmateur AstronomySpace FlightSpace StationShuttleSpace HistorySpace PolicySETI SpaceKB.com Contact UsLink To UsSearch & Site Map |
Space Forum / Space History / June 2004A few Cassini questions
With the upcoming Cassini-Huygens SOI there's a question that pops up in my mind. Has the ever been a firing of a chemical rocket motor that lasted as long as this is going to (96 min). Of course, there will have been some on test stands, but on a actual mission? Not exactly history, as it lies in the future: I haven't seen plans as to what will be done at the end of the mission. Wouldn't it be nice to do some high-rsik venture like diving through the cassini division (if propellant allows) to get some last spectacular images? Anyway, Cassini-Huygens is *the* mission after Voyager that excites me most. Sorry, but the mars mobiles can't compete. ;-) Hans-Joachim > With the upcoming Cassini-Huygens SOI there's a question that pops up in > my mind. [quoted text clipped - 7 lines] > some high-rsik venture like diving through the cassini division (if > propellant allows) to get some last spectacular images? Cassini-Huygens is meant to pass through the ring plane in between the F and G rings on June 30, so its namesake division be a good finale too. >>With the upcoming Cassini-Huygens SOI there's a question that pops up in >>my mind. [quoted text clipped - 10 lines] > Cassini-Huygens is meant to pass through the ring plane in between the F and > G rings on June 30, so its namesake division be a good finale too. Twice. Once just before SOI and, judging from http://saturn.jpl.nasa.gov/operations/saturn-arrival.cfm, once afterwards. The diagram at the bottom of that page can give you a sense of scale when you consider that the Earth could fit comfortably between Saturn and the spacecraft's path at closest approach. It should be a wild ride on June 30 and an exciting 4 year mission to follow. I've been waiting for this sucker to get to Saturn ever since I sent off my signature to be included on board. It's taken *forever* it seems to get there. I know it's only been 6.7 years give or take but it feels like *decades*.  Signaturebp Proud Member of the Human O-Ring Society Since 2003 (brucepalmero at gmail dot com (remove last 'o')) >Has the ever been a firing of a chemical rocket motor that lasted as long >as this is going to (96 min). Of course, there will have been some on test >stands, but on a actual mission? Can't immediately think of any. Galileo's JOI burn was about half that. Some comsats with liquid-fuel apogee motors make quite long insertion burns, but I don't think they're quite that lengthy. >Not exactly history, as it lies in the future: I haven't seen plans as to >what will be done at the end of the mission. Wouldn't it be nice to do >some high-rsik venture like diving through the cassini division (if >propellant allows) to get some last spectacular images? There was talk of sending Pioneer 11 through Cassini's Division... but it's just as well that it wasn't done, because the Voyager images showed clearly that there's no actual gap in the rings there, just a thin spot. Barring major spacecraft failures, I'd say it's almost certain that the mission will eventually be ended by doing something spectacular and fatal, to definitively terminate the mission (and its operations budget) on a high note. There is now considerable pressure to do that sort of thing, to avoid both never-ending budget extensions and the embarrassment of shutting down a working spacecraft. There will probably be a certain amount of pressure, though, to choose that something to minimize possible future contamination of Titan. So just leaving Cassini in orbit -- let alone in pieces, after a fatal ring-plane penetration -- is unlikely to be favored. I'm not sure what they would pick; perhaps a Ranger-style kamikaze dive into one of the smaller moons, shooting pictures on the way down. (This would require careful trajectory planning, since Cassini's cameras point at a fixed angle to its antenna, and the approach path has to be just right if you want cameras on target and antenna on Earth simultaneously.) Back before Galileo's antenna problem surfaced, there was talk of sending it into Io. Signature"Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | henry@spsystems.net >> Has the ever been a firing of a chemical rocket motor that lasted as >> long as this is going to (96 min). Of course, there will have been [quoted text clipped - 32 lines] > simultaneously.) Back before Galileo's antenna problem surfaced, > there was talk of sending it into Io. They could fly it into that big black monolith on Iapetus... -- Gordon Davie Edinburgh, Scotland "Slipped the surly bonds of Earth...to touch the face of God" > <snip> > > They could fly it into that big black monolith on Iapetus... Only if some well-meaning JPL employee mis-spells it "Japetus"... Doug dvandorn@NOSPAM.mn.rr.com > Barring major spacecraft failures, I'd say it's almost certain that the > mission will eventually be ended by doing something spectacular and fatal, > to definitively terminate the mission (and its operations budget) on a > high note. There is now considerable pressure to do that sort of thing, > to avoid both never-ending budget extensions and the embarrassment of > shutting down a working spacecraft. Perhaps, but funding a Cassini mission extension(s) almost certainly would be much cheaper than flying another spacecraft to the saturnian system. And Cassini's instrument suite is well suited for long-term observations. Needless to say, though, we are getting *way* ahead of ourselves here. But as Bob Mitchell, Cassini's Program Manager, noted at the recent press conference, the current propellant margins would easily support mission extensions of several years (especially if the focus were on a specific target or targets like Titan or the icy moons) and, in the instance of a "fields and particles-only" focus extension(s), which do not have as stringent navigation and pointing requirements, possibly 10-15 years. SignatureAlex R. Blackwell University of Hawaii >> Barring major spacecraft failures, I'd say it's almost certain that the >> mission will eventually be ended by doing something spectacular and fatal... > >Perhaps, but funding a Cassini mission extension(s) almost certainly >would be much cheaper than flying another spacecraft to the saturnian >system... Quite so, but it will not be competing against a new Saturn orbiter. Rather, it will be an extension of an old mission which has long since stopped making headlines, competing against new missions -- mostly cheaper ones to easier targets -- which could well make new headlines. In that arena, it's fighting with one foot in a bucket. Oh, I expect there will be at least one Cassini mission extension, if there are no bad hardware failures. But comes the time to ask for the third or fourth extension, it will be made clear that only one more is available, and that the price of getting it is that the extension plan must include killing the spacecraft somehow. Moreover, this is not entirely a bad thing. While it largely precludes long-term monitoring missions, it also permits doing things that would never otherwise be done, precisely because they *do* involve killing an expensive spacecraft. Signature"Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | henry@spsystems.net > Oh, I expect there will be at least one Cassini mission extension, if > there are no bad hardware failures. But comes the time to ask for the > third or fourth extension, it will be made clear that only one more is > available, and that the price of getting it is that the extension plan > must include killing the spacecraft somehow. I don't doubt that the mission extensions, assuming there are any, will come to an end. However, I'll predict that the reason will be because of spacecraft health rather than funding. Given the considerable investment in the Cassini-Huygens primary mission to date, any mission extensions, even two or three, which is where MGS is at the moment, are paltry sums in comparison. As for terminating the mission by killing the spacecraft, we'll see. I've seen a couple of mission extension options that do not involve killing the spacecraft and that preclude (or at least reduce to negligible levels) the risk of impacting Titan, thereby effectively negating any forward contamination concerns. SignatureAlex R. Blackwell University of Hawaii > As for terminating the mission by killing the spacecraft, we'll see. > I've seen a couple of mission extension options that do not involve > killing the spacecraft and that preclude (or at least reduce to > negligible levels) the risk of impacting Titan, thereby effectively > negating any forward contamination concerns. Might be the time for a few runs through the rings, "Silent Running" style. Pat >Might be the time for a few runs through the rings, "Silent Running" style. ...Actually, when it comes to that scene, one thing I'd love to get from Doug Trumbull is exactly *how* he composed the ring scenes using the Slitscan rig. A step-by-step would be nice :-) OM Signature"No bastard ever won a war by dying for | http://www.io.com/~o_m his country. He won it by making the other | Sergeant-At-Arms poor dumb bastard die for his country." | Human O-Ring Society - General George S. Patton, Jr >...Given the considerable >investment in the Cassini-Huygens primary mission to date, any mission >extensions, even two or three, which is where MGS is at the moment, are >paltry sums in comparison. True, but the paltry sums still have to be found, and patience tends to run out as the science return and the publicity taper off. I think MGS would be in real danger if it wasn't making itself conspicuously useful in support of newer missions. I can't see any new Saturn missions being approved soon, so Cassini won't have that excuse -- hypothetical future missions won't count. >As for terminating the mission by killing the spacecraft, we'll see. >I've seen a couple of mission extension options that do not involve >killing the spacecraft... Oh, certainly such concepts exist. They existed for Galileo too. But there's not much chance they'll actually be approved. NASA HQ doesn't want the political embarrassment of ordering a functioning spacecraft turned off, so it is politically mandatory that the spacecraft die when the funding is about to end. And I really doubt that today's NASA will buy into a long-term commitment to keep on operating a complex, costly spacecraft into the vague future (even granted that the operations team and the DSN support will be slimmed down from what they are now). Signature"Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | henry@spsystems.net > True, but the paltry sums still have to be found, and patience tends to > run out as the science return and the publicity taper off. I think MGS > would be in real danger if it wasn't making itself conspicuously useful in > support of newer missions. I can't see any new Saturn missions being > approved soon, so Cassini won't have that excuse -- hypothetical future > missions won't count. As for your skepticism about "new Saturn missions," your *guess* is as good as mine. However, I can easily see two or even three Cassini mission extensions primarily focused on Titan, which would be a great deal cheaper than some of dedicated Titan mission concepts I've seen. And who knows what Cassini-Huygens will reveal about Titan during the primary mission? > Oh, certainly such concepts exist. They existed for Galileo too. But > there's not much chance they'll actually be approved. Perhaps, but we'll see. And "not much chance" is a nice snippet to archive ;-) SignatureAlex R. Blackwell University of Hawaii >And who knows what Cassini-Huygens will reveal about Titan during the >primary mission? ...Ah, but with our luck, it'll auger without sending any data back, and Jonathan will have to change his .sig again :-) OM Signature"No bastard ever won a war by dying for | http://www.io.com/~o_m his country. He won it by making the other | Sergeant-At-Arms poor dumb bastard die for his country." | Human O-Ring Society - General George S. Patton, Jr > Barring major spacecraft failures, I'd say it's almost certain that > the mission will eventually be ended by doing something spectacular > and fatal, to definitively terminate the mission (and its operations > budget) on a high note. Unfortunate, since it precludes someday recovering the spacecraft and putting it in a museum. And in the shorter term, what if something spectacular like the crash of that comet into Jupiter were about to happen at Saturn, but Cassini had been deliberately destroyed a few months earlier? > There will probably be a certain amount of pressure, though, to > choose that something to minimize possible future contamination > of Titan. And what keeps Huygens from contaminating Titan? SignatureKeith F. Lynch - http://keithlynch.net/ Please see http://keithlynch.net/email.html before emailing me. >> There will probably be a certain amount of pressure, though, to >> choose that something to minimize possible future contamination >> of Titan. > >And what keeps Huygens from contaminating Titan? You'll note that I said "minimize", not "prevent". Signature"Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | henry@spsystems.net >>And what keeps Huygens from contaminating Titan? >> > >You'll note that I said "minimize", not "prevent". Given Titan's surface temperature (around -290 degrees F) I'm pretty sure any Earth organisms would have a very hard time doing anything more lively than shattering like glass if touched. That is of course assuming that the probe is not instantly eaten by the ravenous Titanic Methane Muskies, always on the lookout for something to liven up their normal diet of Methane Minnows and frozen tar as they drive themselves forward through the chilled depths- via a violently ejected bubbling stream of nearly constant flatulence. :-) Pat > Given Titan's surface temperature (around -290 degrees F) I'm pretty > sure any Earth organisms would have a very hard time doing anything more [quoted text clipped - 4 lines] > drive themselves forward through the chilled depths- via a violently > ejected bubbling stream of nearly constant flatulence. :-) That started out perfectly plausible until I remembered the cardinal rule about Pat's posts: there's always a second paragraph :) >That started out perfectly plausible until I remembered the cardinal rule >about Pat's posts: there's always a second paragraph :) Laugh while you can, cute, personality filled Monkey Boy! Those fish are'a born killers! Pat Warflan Yoyodyne Industries "The Future Begins Tomorrow At Yoyodyne!" >>Barring major spacecraft failures, I'd say it's almost certain that >>the mission will eventually be ended by doing something spectacular [quoted text clipped - 6 lines] > happen at Saturn, but Cassini had been deliberately destroyed a few > months earlier? This is an especially good point for several reasons. First, Cassini is in much, much better shape than Galileo was at the same time in its mission. Cassini, for example, is not significantly crippled as Galileo was. Second, Saturn does not have near the radiation environment that Jupiter has, which will further tend to keep Cassini in good shape. Third, Cassini's basic subsystems should be able to survive as long as other similar interplanetary spacecraft, such as the Voyagers or Pioneers. Perhaps longer, as Cassini's designs favor solid state systems. Fourth, unlike Galileo, Cassini's basic control systems should be in good enough shape to trust letting it stay around a while, provided you don't do anything to damage them, and still have the opportunity to do a Saturn dive at the actual end of the spacecraft's useful life, should that merit serious concern (personally I don't think it does). Given all this there's a good case to be made for putting Cassini in a high Saturnian orbit and a low-maintenance quasi-sleep configuration for an extended period of time. It could then be used for occasional imagery of Saturn or the Moons (probably the engineers could come up with the command sets, at considerable cost savings) to monitor long term changes, and it could be pulled out of retirement for a brief period if anything interesting looked likely to happen, such as an impact or dramatic weather changes on Saturn or Titan. Note that this is hardly unprecedented, as it has been done with several spacecraft in the past. There's little reason to suppose that Cassini can't still be around as long as Voyager has been. Which would be nice, I think, because it would sort of morph into this long lived deep space "asset" like MGS or SOHO has. I think it's past time we stopped looking at interplanetary space as something we venture into rarely and briefly and instead look at it as a place we can go to and stay. There is little merit in the idea of junking Cassini and there is great potential benefit of keeping it around as long as possible. Don't recall off the top of my head (and too tired to look it up now) but how long will the nuke power last? >>>Barring major spacecraft failures, I'd say it's almost certain that >>>the mission will eventually be ended by doing something spectacular [quoted text clipped - 48 lines] > there is great potential benefit of keeping it around as > long as possible. Signaturerk, Just an OldEngineer "Dealing properly with very rare events is one of the attributes that distinguishes a design that is fit for safety-critical systems from one that is not." -- John Rushby in "A Comparison of Bus Architectures for Safety- Critical Embedded Systems," March 2003 >Don't recall off the top of my head (and too tired to look it up now) but how >long will the nuke power last? ...Rich, remind me to pop you silly with a wet towel for top-posting :-P OM Signature"No bastard ever won a war by dying for | http://www.io.com/~o_m his country. He won it by making the other | Sergeant-At-Arms poor dumb bastard die for his country." | Human O-Ring Society - General George S. Patton, Jr > >Don't recall off the top of my head (and too tired to look it up now) but how > >long will the nuke power last? [quoted text clipped - 3 lines] > > OM Maybe it was the top of his head top-posting? > Don't recall off the top of my head (and too tired to look it up now) but how > long will the nuke power last? I'm not sure. But it's easy to work out that it should be a tremendously long time. First, Cassini starts off with more electric power from its RTGs relative to Voyager, which I'll use as a baseline from now on. Second, Cassini has more instruments, meaning that it has more margin for limited and partial power configurations so that it can keep operating a few critical instruments. Third, I believe Cassini is designed for much higher data rate transmissions (and thus more transmission power) as well as the ability to use its HGA as a RADAR transmitter and receiver, implying yet larger power margins for that "minimal operating power" configuration. The unknown is the GPHS construction, which hasn't been tested to the extreme durations that the MHW and SNAP RTGs on Voyager and Pioneer have been. Though the Galileo RTG fared just fine over its nearly two decade trek from intended launch through end of mission. Otherwise, I think the basic control systems ought to actually take less power to run than Voyager's, but that's just a hunch based on the abundance of solid state components. My gut says Cassini could probably survive out to 2050 if nursed along, but don't quote me on that. >There's little reason to suppose that Cassini can't still >be around as long as Voyager has been. Which would be [quoted text clipped - 6 lines] >there is great potential benefit of keeping it around as >long as possible. [Insert thundering rounds of applause] ...Well said, brother. OM Signature"No bastard ever won a war by dying for | http://www.io.com/~o_m his country. He won it by making the other | Sergeant-At-Arms poor dumb bastard die for his country." | Human O-Ring Society - General George S. Patton, Jr >...there's a good case to be made for putting Cassini >in a high Saturnian orbit and a low-maintenance [quoted text clipped - 4 lines] >looked likely to happen, such as an impact or dramatic >weather changes on Saturn or Titan. The trouble is, particularly if you want the option of being able to revive it on short notice, you need to keep an operations team together. These are not simple, standardized spacecraft; running one properly is a sizable job, and training and experience with the particular spacecraft are important. You can dial the level of spacecraft activity up and down pretty easily, but you can't do the same for the ops team. If you want them to be available and up to speed when opportunity strikes, they've got to have ongoing activity. (Moreover, the skill set used in a low-budget monitoring-and-maintenance mission typically isn't the same one needed to form the core group of a rapidly-assembled ops team for a brief period of heavy activity.) >Note that this is hardly unprecedented, as it has been >done with several spacecraft in the past. Which ones? Please be specific. My recollection is that on the few occasions when a retired or semi-retired spacecraft was pulled out of retirement, it was (a) unplanned, and (b) quite difficult. This is not at all the same as simply keeping the mission going at a steady but lower level. Note that one major reason why the Voyagers' camera systems were shut down and abandoned (after shooting the last "family portrait" images) was that the expense of maintaining the camera operations team was no longer thought worthwhile. Signature"Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | henry@spsystems.net > The trouble is, particularly if you want the option of being able > to revive it on short notice, you need to keep an operations team > together. These are not simple, standardized spacecraft; running > one properly is a sizable job, and training and experience with the > particular spacecraft are important. Perhaps what is needed is a fleet of simple, standardized mass-produced space probes, which will be permanently stationed in pairs in various key locations around the solar system. Whenever one of a pair stops working, a replacement will promptly be launched. > Note that one major reason why the Voyagers' camera systems were > shut down and abandoned (after shooting the last "family portrait" > images) was that the expense of maintaining the camera operations > team was no longer thought worthwhile. Could the cameras be turned back on if there were any reason to? SignatureKeith F. Lynch - http://keithlynch.net/ Please see http://keithlynch.net/email.html before emailing me. >Could the cameras be turned back on if there were any reason to? ...I've gotten two answers on this one in the past: 1) "No, once they're off, they're off." ...Which, when it was pointed out that they were shut down several times in transit and restarted fine, the answer went to: 2) "Well, there's not enough power to run any imaging as the RTGs are just too spent." ...Answers courtesy of a rather wimpy NASA PAO geek, natch. OM Signature"No bastard ever won a war by dying for | http://www.io.com/~o_m his country. He won it by making the other | Sergeant-At-Arms poor dumb bastard die for his country." | Human O-Ring Society - General George S. Patton, Jr >> The trouble is, particularly if you want the option of being able >> to revive it on short notice, you need to keep an operations team [quoted text clipped - 6 lines] >pairs in various key locations around the solar system. Whenever one >of a pair stops working, a replacement will promptly be launched. And with what instruments shall they be equipped? What scientific goal would be achieved? D. SignatureTouch-twice life. Eat. Drink. Laugh. On Sat, 26 Jun 2004 05:05:21 GMT, fairwater@gmail.com (Derek "Captain Schnook of the USS Killfile Your Colleagues" Lyons) wrote: >And with what instruments shall they be equipped? What scientific >goal would be achieved? ...Here's your chance, kids: if you had to design a generic purpose probe that could be produced on an assembly line, and you had only, say, six instruments besides the mandantory, non-negotiable, has to be installed or the contract is cancelled, high-res visible spectrum camera and the data storage device that best suits the level of technology at the time that's space-rated, what six would you choose? Ergo, design the SAP - Swiss Army Probe. OM Signature"No bastard ever won a war by dying for | http://www.io.com/~o_m his country. He won it by making the other | Sergeant-At-Arms poor dumb bastard die for his country." | Human O-Ring Society - General George S. Patton, Jr > On Sat, 26 Jun 2004 05:05:21 GMT, fairwater@gmail.com (Derek "Captain > Schnook of the USS Killfile Your Colleagues" Lyons) wrote: [quoted text clipped - 10 lines] > > Ergo, design the SAP - Swiss Army Probe. mass spectrometer magnetometer infrared imaging untraviolet imaging cosmic ray detector gravity wave sensor (in concert with the rest of the "fleet") Signaturebp Proud Member of the Human O-Ring Society Since 2003 > > On Sat, 26 Jun 2004 05:05:21 GMT, fairwater@gmail.com (Derek "Captain > > Schnook of the USS Killfile Your Colleagues" Lyons) wrote: [quoted text clipped - 10 lines] > > > > Ergo, design the SAP - Swiss Army Probe. Is an antenna an instrument? >> > On Sat, 26 Jun 2004 05:05:21 GMT, fairwater@gmail.com (Derek "Captain >> > Schnook of the USS Killfile Your Colleagues" Lyons) wrote: [quoted text clipped - 12 lines] > >Is an antenna an instrument? ...Nope. It's standard gear, like the casing of the knife. The HQVL camera is there as well, and is telescopic, so don't waste a slot by adding that in there again *unless* you've decided to do real-time stereo pair imaging and not time-space delayed pair 3D synthesis. OM Signature"No bastard ever won a war by dying for | http://www.io.com/~o_m his country. He won it by making the other | Sergeant-At-Arms poor dumb bastard die for his country." | Human O-Ring Society - General George S. Patton, Jr >gravity wave sensor (in concert with the rest of the "fleet") Nice touch, but that's going to be a bit on the heavy side, isn't it? Pat > On Sat, 26 Jun 2004 05:05:21 GMT, fairwater@gmail.com (Derek "Captain > Schnook of the USS Killfile Your Colleagues" Lyons) wrote: [quoted text clipped - 8 lines] > camera and the data storage device that best suits the level of > technology at the time that's space-rated, what six would you choose? A wide-field visible light camera, a good telescopic VL camera, a good telescopic IR camera, a spectrometer. Pretty much everything else is nitpicky secondary stuff. It's not magnetic field readings that interest the people paying the bills. It's not cosmic ray traces that people buy posters of to inspire the kiddies. SignatureScott Lowther, Engineer Remove the obvious (capitalized) anti-spam gibberish from the reply-to e-mail address > ...Here's your chance, kids: if you had to design a generic purpose > probe that could be produced on an assembly line, and you had only, [quoted text clipped - 4 lines] > > Ergo, design the SAP - Swiss Army Probe. - Wide field hyper-spectral near-IR through near-UV imager - Narrow field Visible-Infrared imaging spectrometer - Magnetometer - Gas and dust analysis mass spectrometer / impact detector - Laser rangefinder - Neutron/Gamma Ray spectrometer - Microwave radar / radar sounder That ought to do it. > > ...Here's your chance, kids: if you had to design a generic purpose > > probe that could be produced on an assembly line, and you had only, [quoted text clipped - 15 lines] > > That ought to do it. Without antennas, where does the data go? >> > ...Here's your chance, kids: if you had to design a generic purpose >> > probe that could be produced on an assembly line, and you had only, [quoted text clipped - 17 lines] > >Without antennas, where does the data go? ...As I posted earlier, the antennas are part of the core package. Perhaps I need to clarify this a bit. The core probe package consists of: * General purpose bus structure * Solar array (2) * RTG and extendable boom * High-Resolution Telescopic Visible Light camera * HGA Dish antenna - solid, not mesh * Additional antennas for LGA backup X/R * Solid-state data storage properly hardened for space use. * RCS and navigation systems * Primary orbital insertion motor * Gold plaque with nekkid pictures of a couple etched on the casing * One 2' RG59-U coaxial cable with BNC connectors for hooking up to 23rd century tricorders * Mounting points for ESA piggyback payloads when they want to embarass themselves again * Small container for cremated human remains to be deposited off-world. ...Anything else I forgot? OM Signature"No bastard ever won a war by dying for | http://www.io.com/~o_m his country. He won it by making the other | Sergeant-At-Arms poor dumb bastard die for his country." | Human O-Ring Society - General George S. Patton, Jr > ...Anything else I forgot? Backwards compatibility with MS-DOS? >> ...Anything else I forgot? > >Backwards compatibility with MS-DOS? ...CP/M, actually :-) OM Signature"No bastard ever won a war by dying for | http://www.io.com/~o_m his country. He won it by making the other | Sergeant-At-Arms poor dumb bastard die for his country." | Human O-Ring Society - General George S. Patton, Jr >> ...Here's your chance, kids: if you had to design a generic purpose >> probe that could be produced on an assembly line, and you had only, [quoted text clipped - 13 lines] > - Neutron/Gamma Ray spectrometer > - Microwave radar / radar sounder Now that I think about it, the laser rangefinder is mostly made redundant by the radar. I'd probably replace it with a UV instrument, some sort of uber, imaging spectrometer, natch. On second thought, I'll toss in, oh, I dunno, an inanimate carbon rod on an articulated frame. Why? Because I can! MUAHAHAHAHA!! (Note that there are seven instruments, because I actually read OM's instructions properly, the first instrument, listed separately, is the gimme camera.) Interestingly, this thread isn't too far off from current practices in the field. Instruments are getting good enough, especially hyper spectral imagers and imaging spectrometers, to where you can reduce the instrument count a lot and still get along quite nicely. A lot of recent and upcomming missions will use a surprisingly similar set of instrumentation. The core seems to be the high-res super imager (preferably with oodles of color channels or operating as an imaging spectrometer) married with a wide-field "context camera" or survey camera. Following that is usually either a sounder of some sort (laser rangefinder or radar) or a radiation instrument (neutron/gamma-ray spectrometer) or both, and then maybe a magnetometer and related instrumentation. > Now that I think about it, the laser rangefinder is > mostly made redundant by the radar. But weight should play a part in this also, and the antenna that will give you accuracy to the degree that a laser rangefinder will as far as height of terrain goes is going to weigh far more than the rangefinder....if weight is taken completely out of the equation, I'd hang a radar antennae the size of Jodrell Bank's on one side, and a telescope the size of Palomar's on the other. Then there is that giant solid-lead gravity wave detector to contend with. Pat >> Now that I think about it, the laser rangefinder is >> mostly made redundant by the radar. [quoted text clipped - 6 lines] >telescope the size of Palomar's on the other. >Then there is that giant solid-lead gravity wave detector to contend with. Can't you use an ultra-stable radio signal (or a laser signal) to detect gravity waves, the way Cassini did? SignatureWhat have they got to hide? Release the full Beagle 2 report. Remove spam and invalid from address to reply. >say, six instruments besides the mandantory, non-negotiable, has to be >installed or the contract is cancelled, high-res visible spectrum >camera and the data storage device that best suits the level of >technology at the time that's space-rated, what six would you choose? I'm going to assume that we're talking about an orbiter/flyby spacecraft, since landers tend to want to be custom-built for the environment and the mission constraints. You want to extend imaging into the IR and UV as well. Cassini is already giving us images of surface features on Titan, which the Voyagers saw only as a featureless ball of haze because they had no significant IR imaging capability. Extending a visible camera's spectral range moderately one way or the other is not too hard, but doing both is tricky, and the IR in particular goes a long way down with a lot of interesting things to see. Probably the thing to do is to add UV capability to the visible camera, and have a separate IR camera. Moreover, it's also useful to be able to get actual spectra, either with a spectrometer or, more ambitiously, a hyperspectral imager that gives a low-resolution spectrum for each image point. Mind you, a hyperspectral imager needs more light than a regular camera, because it spreads it thinner. That aside, you can always *reduce* the spectral resolution by combining in software, turning the hyperspectral imager into a versatile multi-band camera. My impression is that spectral data is most revealing in IR. So one reasonable combination would be a UV/visible camera, a visible/near-IR hyperspectral imager, and a (probably low-resolution) far-IR camera. The overlap also gives us some backup capability if one breaks. The cameras have filter wheels to give some spectral selectivity, and we could also borrow a trick from Mariner 10: one position on the filter wheel is a mirror that redirects the view from the main telescope (the cameras will all be telescopic, of course) to a small wide-angle lens. This avoids a separate wide-angle camera. There are a dozen different flavors of specialized spectrometers and radiometers for looking at various details of surfaces and atmospheres, but my (vague) impression is that they *are* rather specialized, and probably aren't versatile enough to merit taking up one whole slot on a general-purpose probe. One thing that probably is worth including, however, is a laser altimeter. Not only will this give you accurate topography, but in combination with one of the cameras it might give you limited ability (at close range) to do low-grade imaging of areas which don't get sunlight. That's three optical instruments (in addition to the main camera), and that's probably enough for the optics mafia. :-) First on my non-optical list would be a radar sounder, for low-resolution subsurface exploration. We know almost nothing about the *insides* of most solar-system bodies, and there is much to be learned from penetrating radar. There's room for a lot of complexity here, but a simple sounder instrument does not need massive electronics, a lot of power (it sends brief pulses fairly infrequently), or complex antennas. It does require fairly short range. I've never been terribly impressed with X-ray and gamma-ray spectrometry. The information content is limited, and penetration is so poor that you're studying only a thin surface layer. Neutron spectrometry is a little better, but penetration is still very limited and I wouldn't give it high priority in general. I think second on my non-optical list would be some flavor of versatile charged-particle detector, for radiation belts and the solar wind (and their interactions with small bodies). Lots of options for the last slot. I think I would give the nod to a dust instrument, although a neutral-atom imager is an interesting alternative. Finally, something that isn't an instrument, but is nevertheless highly desirable for a general-purpose orbiter, is radio relay equipment to allow it to serve as a comsat for landers and other small probes in the immediate vicinity. Signature"Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | henry@spsystems.net >I'm going to assume that we're talking about an orbiter/flyby spacecraft, >since landers tend to want to be custom-built for the environment and the [quoted text clipped - 4 lines] >as a featureless ball of haze because they had no significant IR imaging >capability. Cassini is using a polarization filter as well as the carefully selected wavelengths to see through the haze: http://spaceflightnow.com/cassini/040625titan.html Does the Huygens lander have it's cameras optimized to also see through the haze as it descends? It's going to be a shame if all we get images of is featureless orange haze as it parachutes toward the surface. I'm really hoping that the new images are showing us the methane seas. Pat >I'm going to assume that we're talking about an orbiter/flyby spacecraft, >since landers tend to want to be custom-built for the environment and the >mission constraints. ...You know, I was going to be a real sh.t and say "no, Henry, the core of the Swiss Army Probe has landing gear, parachutes, airbags *and* landing retros!", and *then* demand an ICH T-Shirt, but somehow I just couldn't pull that stunt this time :-) :-) :-) OM Signature"No bastard ever won a war by dying for | http://www.io.com/~o_m his country. He won it by making the other | Sergeant-At-Arms poor dumb bastard die for his country." | Human O-Ring Society - General George S. Patton, Jr >...You know, I was going to be a real sh.t and say "no, Henry, the >core of the Swiss Army Probe has landing gear, parachutes, airbags >*and* landing retros!"... Tsk tsk, you forgot the aerodynamic skirt (Venus atmosphere probes) and the balsawood sphere. Signature"Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | henry@spsystems.net >>...You know, I was going to be a real sh.t and say "no, Henry, the >>core of the Swiss Army Probe has landing gear, parachutes, airbags >>*and* landing retros!"... > >Tsk tsk, you forgot the aerodynamic skirt (Venus atmosphere probes) and >the balsawood sphere. ...I also left out the pentagonal fragments casing with pictures of Lenin on them, but then again I had to leave you *something* to correct me on :-) OM Signature"No bastard ever won a war by dying for | http://www.io.com/~o_m his country. He won it by making the other | Sergeant-At-Arms poor dumb bastard die for his country." | Human O-Ring Society - General George S. Patton, Jr [ massive snipping ] > One thing that probably is worth including, however, is a laser > altimeter. Not only will this give you accurate topography, but in > combination with one of the cameras it might give you limited ability (at > close range) to do low-grade imaging of areas which don't get sunlight. And although not my speciality to comment on the why and why not, I believe that measuring the energy returned from a pulse gives the scientists some information. Ready for an IWCBHA [1] since too lazy now to look that up. ;-) > That's three optical instruments (in addition to the main camera), and > that's probably enough for the optics mafia. :-) > I think second on my non-optical list would be some flavor of versatile > charged-particle detector, for radiation belts and the solar wind (and > their interactions with small bodies). One thing to think about is do you want just one spacecraft type? Perhaps one spacecraft that is three-axis stabilized and another spinner for the particles and fields guys. If I recall correctly, Cassini had a turntable that was axed. And the Galileo dual-spinner design was a tad problematic; the spacecraft did go through multiple configurations in its development history. > Finally, something that isn't an instrument, but is nevertheless highly > desirable for a general-purpose orbiter, is radio relay equipment to > allow it to serve as a comsat for landers and other small probes in the > immediate vicinity. I think this relay is one of the real unsung heroes of the MER missions. And there is science by using the radio as an instrument. [1] I Was Corrected By Henry Again Signaturerk, Just an OldEngineer "Dealing properly with very rare events is one of the attributes that distinguishes a design that is fit for safety-critical systems from one that is not." -- John Rushby in "A Comparison of Bus Architectures for Safety- Critical Embedded Systems," March 2003 >> Finally, something that isn't an instrument, but is nevertheless highly >> desirable for a general-purpose orbiter, is radio relay equipment to >> allow it to serve as a comsat for landers and other small probes in the >> immediate vicinity. > > I think this relay is one of the real unsung heroes of the MER missions. Is it accepted as standard for all future Mars orbiters, now? I mean, I assume MRO is flying with one, but stands to reason that you should run with them regardless... because it doesn't take *that* long to approve and fly a lander mission, and your orbiter might well just be around then. In engineering terms, what are the penalties associated with flying relay equipment like this? I mean, is it significant enough that you're talking about bumping instrumentation, does it have notable power or space requirements, or is it essentially a "free ride"? > And there is science by using the radio as an instrument. Indeed, some of the earliest planetary stuff was done solely with a radio signal... > [1] I Was Corrected By Henry Again not As Always? ;-) Signature-Andrew Gray andrew.gray@dunelm.org.uk > Is it accepted as standard for all future Mars orbiters, now? I mean, I > assume MRO is flying with one... Yes, MRO will fly the JPL-designed Electra relay package, which is far more capable than MGS MR or even the 2001 Mars Odyssey UHF relay. SignatureAlex R. Blackwell University of Hawaii >>> desirable for a general-purpose orbiter, is radio relay equipment to >>> allow it to serve as a comsat for landers and other small probes in the [quoted text clipped - 3 lines] >assume MRO is flying with one, but stands to reason that you should run >with them regardless... It's considered highly desirable, at the very least. A specialized small orbiter conceivably might not be able to accommodate a relay package, but anything which can, should. >In engineering terms, what are the penalties associated with flying >relay equipment like this? I mean, is it significant enough that you're >talking about bumping instrumentation, does it have notable power or >space requirements, or is it essentially a "free ride"? Assuming you've already got serious data storage capacity, it's likely to be a fairly small electronics package and a small antenna or two. Mass and power requirements will not be entirely insignificant but shouldn't be substantial enough to endanger instruments, unless the orbiter and its instruments are very small indeed. >> And there is science by using the radio as an instrument. > >Indeed, some of the earliest planetary stuff was done solely with a >radio signal... Note, though, that it's not entirely free. To really do it well, it's desirable to have an Ultra Stable Oscillator to ensure a highly stable transmitter frequency even when you haven't got an uplink signal to reference it against, and those things do require some mass and some power (although not as much as they used to). Signature"Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | henry@spsystems.net > Note, though, that it's not entirely free. To really do it well, it's > desirable to have an Ultra Stable Oscillator to ensure a highly stable > transmitter frequency even when you haven't got an uplink signal to > reference it against, and those things do require some mass and some power > (although not as much as they used to). Definitely not free or extremely cheap but the modern units aren't really bank breakers. Signaturerk, Just an OldEngineer "Dealing properly with very rare events is one of the attributes that distinguishes a design that is fit for safety-critical systems from one that is not." -- John Rushby in "A Comparison of Bus Architectures for Safety- Critical Embedded Systems," March 2003 > One thing to think about is do you want just one spacecraft type? Perhaps one > spacecraft that is three-axis stabilized and another spinner for the particles > and fields guys. If I recall correctly, Cassini had a turntable that was > axed. Actually, the original Mariner Mark 2 design (CRAF/Cassini) had *two* scan platforms on deployable booms that were baselined for each spacecraft: a high-precision *scan* platform and a low-precision *pointing* platform (on Cassini, the latter was to be replaced by a turntable and a ram-direction platform). As you alluded to, the scan platforms were eliminated for cost and complexity reasons, as was the proposed steerable medium gain antenna (MGA) proposed for Cassini, which would have also relayed data from Huygens. SignatureAlex R. Blackwell University of Hawaii >> Perhaps what is needed is a fleet of simple, standardized >> mass-produced space probes, which will be permanently stationed in >> pairs in various key locations around the solar system. Whenever one >> of a pair stops working, a replacement will promptly be launched. > And with what instruments shall they be equipped? The usual. Camera, spectrometer, magnetometer, dust detector, solar wind detector, radiation meter, radar mapper, etc. Even if some of these make no sense for a particular probe, they'll be left in, since that's easier than removing them. Of course I'm only talking about orbiters, not landers. A Mars lander would have little in common with a Venus lander. On the other hand, why not have a dozen identical wheeled Mars landers, each robust enough that they can be driven all the way around the planet multiple times? > What scientific goal would be achieved? A greater understanding of the solar system. SignatureKeith F. Lynch - http://keithlynch.net/ Please see http://keithlynch.net/email.html before emailing me. >>> Perhaps what is needed is a fleet of simple, standardized >>> mass-produced space probes, which will be permanently stationed in [quoted text clipped - 5 lines] >The usual. Camera, spectrometer, magnetometer, dust detector, solar >wind detector, radiation meter, radar mapper, etc. Am I right in thinking that no-one's yet flown a dust detector to Mars? > Am I right in thinking that no-one's yet flown a dust detector to Mars? That'd be like flying an ice detector to Antarctica. In message <40de38f4$0$24743$5a62ac22@per-qv1-newsreader-01.iinet.net.au>, Neil Gerace <geracen@iinet.net.au> writes >> Am I right in thinking that no-one's yet flown a dust detector to Mars? > >That'd be like flying an ice detector to Antarctica. Sorry! What I meant was "has anyone flown a dust detector on an orbiting or fly-by spacecraft, to look for dust in space near Mars". Stuff coming off the moons, for instance. > Sorry! What I meant was "has anyone flown a dust detector on an orbiting > or fly-by spacecraft, to look for dust in space near Mars". Stuff coming > off the moons, for instance. Heh, I was just being a smartarse, sorry :) >> Note that one major reason why the Voyagers' camera systems were >> shut down and abandoned (after shooting the last "family portrait" >> images) was that the expense of maintaining the camera operations >> team was no longer thought worthwhile. > >Could the cameras be turned back on if there were any reason to? Setting aside the question of getting an operations team up to speed on how to run them... As I understand it... It could be tried. Nothing absolutely irrevocable was done. *However*, their heaters have been switched off for several years, and given their exposed position out on the scan platform, they're thoroughly frozen. They would probably work if warmed up again, but there are no guarantees. Repeated temperature cycles like that would undoubtedly kill them quickly, but after a single cycle there's a fair chance they'd still work. Signature"Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | henry@spsystems.net |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.