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Space Technology

New Way of Extending Satellite Life Saves Millions 173

Posted by samzenpus
from the make-it-last dept.
coondoggie writes "A new technique to save aging satellites promises to save millions of dollars by extending the life of communications spacecraft. A process developed by researchers from Purdue University and Lockheed Martin has already saved $60 million for unnamed broadcasters by extending the service life of two communications satellites. In a nutshell the technique works by applying an advanced simulation and a method that equalizes the amount of propellant in satellite fuel tanks so that the satellite consumes all of the fuel before being retired from service. Some aging communications satellites are each equipped with four fuel tanks. If one of the tanks empties before the others, the satellite loses control and should be decommissioned, wasting the remaining fuel in the other tanks."
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New Way of Extending Satellite Life Saves Millions

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  • by UbuntuDupe (970646) * on Thursday September 06, 2007 @03:44PM (#20498473) Journal
    If there are four propellors with separate tanks, and one empties early, borrow from other tanks so you don't have to throw the whole thing out! What a brilliant idea! I think that's worthy of a patent.

    "A process for shifting resources from areas with a surplus to those that have run out ... on a satellite."

    Hey -- maybe if I act quickly I can get a patent on "sending a refueling pod"!

    (I don't know if this should count as funny, flamebait, or insighful.)
    • Re: (Score:2, Insightful)

      by Anonymous Coward
      (I don't know if this should count as funny, flamebait, or insighful.)

      None of the above. Your post was just stupid.

      This post, however, is insightful as fuck.
    • by Timesprout (579035) on Thursday September 06, 2007 @03:49PM (#20498533)
      I already tried to but apparently I needed 3 other patents to balance it out and now my application is just spinning wildly out of control.
    • by Chuckstar (799005) on Thursday September 06, 2007 @03:55PM (#20498633)
      My interpretation was that the difficulty is figuring out how much fuel is left in each tank in a weightless environment where each can be at dramatically different temperatures (one on the sun-side and one on the shade-side).
      • by Otter (3800) on Thursday September 06, 2007 @04:06PM (#20498787) Journal
        Looking at the paper (linked in the article), they're doing that and then using differential heating of the tanks to shift the fuel to rebalance them.

        Sure, it seemed likely that an idea that's obvious to the morons here has been nonetheless overlooked by decades of aerospace engineers, but this time that doesn't appear to be the case.

        • Re: (Score:2, Insightful)

          by dgatwood (11270)

          Sure, it seemed likely that an idea that's obvious to the morons here has been nonetheless overlooked by decades of aerospace engineers, but this time that doesn't appear to be the case.

          You're right. It's not an obvious solution that has been overlooked. It's a terribly overly complex and non-obvious solution to a relatively simple problem---precisely what I'd expect from an industry with multimillion dollar toilets.

          The obvious solution would be to just combine the output of all of the tanks and th

          • by enosys (705759) on Thursday September 06, 2007 @07:38PM (#20501217) Homepage
            The obvious solution would be to just combine the output of all of the tanks and then split it back off to the engines

            You mean create a single point of failure?

            • How is that better than "if any one tank is empty or fails to perform we're fucked"?
              • by HUADPE (903765)
                The tanks can refuel each other, so at the beginning of the mission you can easily fix the issue, the problem here is that it is difficult to tell if a tank is at 10% or 5%, so measuring where the fuel needs to go is very tricky.
          • Please read Apollo 13 and then get back to us. They had just such a cross-connected system, and when one of their several oxygen tanks blew out, they lost all their O2, rather than just some of it.
          • by sholden (12227)
            Except of course that sending a person up there to rework the plumbing will cost about a trillion dollars, whereas given the that the hardware is already up there, already has a ridiculous four fuel tanks and when one is empty we fail design, and (I assume) already has the hardware to do the fuel balancing the complicated heating way it seems a cheap way to get an extra 6 months of service from an expensive asset.
      • by Locutus (9039)
        Thanks, that sounds less like the "duh" comment I originally had. After all these years, I hope they are now launching systems with fuel balancing mechanisms in place and also a refueling dock. The dock would be just incase some drone can be launched from the ISS or a shuttle in the future.

        LoB
        • I hope they are now launching systems with fuel balancing mechanisms in place...
          Ummm...how about just one fuel tank?
          • Re: (Score:2, Insightful)

            by PachmanP (881352)
            Assuming you man one fuel and one oxidizer tank not just one tank (boom!), redundancy.
            Oh and more redundancy.
            And possibly a little backup.
          • by dgatwood (11270)

            Combining the output with a single unified fuel line would be a better idea than combining the tank. With one tank, if it ruptures, you're screwed. With four tanks and hardware to prevent backflow (either a traditional backflow prevention valve or a sensor coupled with a standard valve) all dumping into a single shared output line, you still get 3/4ths of your usable life if one tank fails.

          • by mikael (484)
            If it gets punctured or the control valve goes wonky, you lose all the fuel.

            If you have four fuel tanks, you still have at least three other tanks. They estimate the amount of fuel in each fuel tank is estimated by measuring the pressure of the fuel inside the tank. However, this is affected by the temperature of the fuel tank (caused by the orientation of the Sun relative to the satellite, which changes as the Earth rotates each day).

            Once they work out what amount of fuel remains in each fuel tank, they ha
            • If it gets punctured or the control valve goes wonky, you lose all the fuel.

              If you have four fuel tanks, you still have at least three other tanks.

              So any reasonble person would suspect. But in the design that they used, according to a more informative article at http://www.eurekalert.org/pub_releases/2007-09/pu- era090507.php [eurekalert.org],

              "The tanks are pressurized with the helium. If one tank runs out of fuel, the next time the valve in that tank is opened to ignite the rocket thrusters, the helium from that tank mixes with fuel going to the thrusters from the other tanks, preventing the thrusters from firing and shutting down the propulsion system."

              In other words, in this design, if one tank empties completely, it screws up the other three thrusters. The way they did it, four tanks do not increase reliability, they actually increase the likelyhood of failure.

        • by emarkp (67813)
          If only getting from LEO to geosync was that easy.
      • by toleraen (831634)
        Pretty close yeah. Here [eurekalert.org] is an article with a more detailed explanation.
      • That doesn't make sense. If pressure alone isn't enough to know, then a pressure and temp sensor on each tank should be enough to calculate the remaining fuel.
      • by griffjon (14945) <GriffJon@ g m a i l .com> on Thursday September 06, 2007 @04:31PM (#20499081) Homepage Journal
        I'm reminded of a quote by some NASA Scientist, on the NEAR probe: "We have no fuel on board, plus or minus 8 kilograms"
        • Re: (Score:3, Insightful)

          by datablaster (999781)
          Fuel=zero plus or minus 8kg. That pretty much sums up the level of uncertainty. It's easy from the comfort of terra firma, many degrees removed from actual work-day problem-solving about this to assume that there's a fuel gauge at least as accurate as on a car. Such is not the case. Obviously five decades of space technology is not enough time to have all the answers all the time.
          • by rts008 (812749) on Friday September 07, 2007 @12:26AM (#20503557) Journal
            Wish I had mod points for you for bringing me back down to Earth, so to speak. (why yes, that IS a selfish attitude!)

            My first thought when I read the summary was along the lines of this:
            WTF?!?!? We've been building semi's (18 wheelers) and satellites about the same amount of time- have the rocket scientists not heard of crossover fuel lines? (they connect left and right tanks and allow for equalization of the fuel level), then I thought...Hmmm...Space, the final frontier...Oh wait! Uhmmm atmospheric pressure, constant gravity from a predictable direction, reasonably constant temps and density- in a moderate range....none of this applies! WTF do we do now?

            I hereby revoke my armchair Astrophysics and Rocket Scientist privileges for a week.

            Mechanical/electrical engineering in space is no trivial thing. Obvious Earth-bound solutions seem to fail frequently when applied to cold vacuum with micro-gravity. It may not always seem to be so difficult from here, but up there it could be a whole new problem.

            Hopefully, even their most inaccurate 'fuel gauge' is better than the one in my car...I either have a quarter of a tank (when FULL) or it reads Empty below an actual 3/4 tank, and you have to use the odometer (Oh Sh*t!, was it reset last fuel-up?!?!?) to guesstimate what the real fuel level may be.

            Yes, you all can laugh at me for this. My only semi-reasonable defense can be that I just walked in from work 10 minutes ago, after dealing with John Q Public and Josephine Sixpack for the last 10 hours. I mistakenly bit this worm, dunked the bobber, and now am caught...hook, line, and sinker.

            My bad, but I'm at least mouse/man enough to admit it!
        • by rbarreira (836272)
          Please explain how it's possible to have -8 kilograms of fuel :P Anti-fuel perhaps?
    • Re: (Score:2, Funny)

      by sentientbeing (688713)
      They should just put guns on the satellite. When the satellite passes overhead any ground-based fuel tanks it can blow them up, and the spaceship fuel tanks will fill up again.

      I thought everybody knew that.
    • by DrBuzzo (913503)
      Sending a refueling pod is not really that great an idea. These things are in geosynchronous orbit. A good portion of the cost is the launch itself. plus, given that they are not really designed for automated docking or anything (that would add a real lot of cost) you'd have to have the refuling craft somehow grab the satellite and refuel it. It would be just as cheap to launch another satellite than a satellite to refuel the original. Plus, technology advances... better amplifiers, more channels, mo
  • NSS?! (Score:3, Interesting)

    by Dread_ed (260158) on Thursday September 06, 2007 @03:47PM (#20498503) Homepage
    Pardon me if I don't cry out with excitement at this "discovery." It looks more like a built in obsolescence feature has been circumvented rather than an actual technical breakthrough.

    Seriously, who didn't learn the lesson of the limiting reagent in high school chemistry?
    • Re:NSS?! (Score:4, Funny)

      by Penguinisto (415985) on Thursday September 06, 2007 @03:53PM (#20498615) Journal

      Pardon me if I don't cry out with excitement at this "discovery." It looks more like a built in obsolescence feature has been circumvented rather than an actual technical breakthrough.

      Oh, great... so now Martin Marietta is gonna file a DMCA complaint and demand the arrest of...

      ...oh, wait; this ain't the computer field we're talking here, so common sense actually applies. My Bad.

      Good Show in either case!

      /P

    • Same propellant in each tank. But when one tank goes, the whole satellite goes. Note that they are only squeezing 6 months out of a 15 year satellite, or 3.3%. Not exactly planned obsolescence.
      • by Dread_ed (260158)
        That one tank is the limiting reagent. If it runs out the whole thing fails, regardless of the integrity of the communications equipment and the other 3 engines.

        My guess is future satelites will be built with (*GASP*) fuel gauges so that you don't have to have a freaking team of PHD guys trying to figure out which one will fail first and modeling how to use the other engines to compensate for the one that gets the most usage.

        Damn, with a brain trust idea like this someone might even think to put aysemetric
  • by the_skywise (189793) on Thursday September 06, 2007 @03:49PM (#20498531)
    ink jet cartridges...

    Oh wait... who am I kidding...
  • Who launches a multimillion satellite to space without making sure that it fully uses resources left onboard before retiring? Even if four separate fuel tanks are necessary, they can be just connected by small pipes and fuel can be redistributed with a pump powered by satellite's solar cells. It's not a rocket science!
    • by GweeDo (127172) on Thursday September 06, 2007 @03:58PM (#20498679) Homepage
      "It's not a rocket science!"

      But this time it really is!
    • Re: (Score:3, Informative)

      by DerekLyons (302214)
      But pipes can fail, so can pumps and so can fuel measuring devices (and all the associated power and control hardware). Thus the choice in the past has been to limit possible points of failure at a potential cost in satellite life.
       
       

      It's not a rocket science!

      Actually, yeah it is. Real world engineering is rarely as simple and black and white as the armchair variety.
      • by iamacat (583406)
        If a failure happens, we are no worse off than the current situation. So what's the catch?
        • by compro01 (777531)
          no, if a failure in terms of a clogged fuel line happens, it is not going to be when we expect it, unlike the known-and-planned-for "out of gas" failure, thus will definitely be worse.
        • If you *increase* the chance of a failure happening (which you do by adding the fuel transfer hardware, controls, etc...), then you are *worse* off than the current situation. That's the catch.
      • Re: (Score:2, Interesting)

        by ChrisMounce (1096567)
        I think an analogy to programming styles is appropriate here. Clever code is often lauded, just because so-and-so managed to write a one-liner that does <insert complex task here>. People compete to be clever (see those obfuscated C contests [ioccc.org]). Clever is impressive.

        But obvious stuff like writing easy-to-understand, well-documented code... that's just expected, no matter how hard it is to do in practice.
    • sigh (Score:5, Informative)

      by everphilski (877346) on Thursday September 06, 2007 @04:06PM (#20498797) Journal
      Who launches a multimillion satellite to space without making sure that it fully uses resources left onboard before retiring?

      It has lived its full life. It has reached the end of service. But wait, for a few hundred thousand or so in research/fuel shifting, we can net an extra six months in orbit and $50M in revenue. Do we do it? Do we? Of course.

      **that** is the situation. And yes, it is rocket science. Read the first page of the paper at least, they did something creative.
    • by Billosaur (927319)

      Pumping fuel in a zero-gravity environment is not like pumping gas at your gas station. More often, a secondary substance is needed to force the fuel to move, like helium. That also has to be kept aboard in pressurized tanks in a liquid state, which brings about its own set of problems. You also have to take into account the differential heating/cooling that takes place as the satellite rotates and moves about in its orbit, which adds stresses to the system. And let's not forget this all requires more mass

      • by iamacat (583406)
        How is pumping affected by lack of gravity besides lowering power requirements on the pump to overcome the same? If the fuel is a gas you don't actually need any pumps - pressure will equalize itself. If it's liquid, you will already need some way to get rid of empty space in the tank, otherwise you would have hard time getting globules floating around to the reaction chamber.
        • by IndustrialComplex (975015) on Thursday September 06, 2007 @05:52PM (#20499959)
          How is pumping affected by lack of gravity besides lowering power requirements on the pump to overcome the same? If the fuel is a gas you don't actually need any pumps - pressure will equalize itself. If it's liquid, you will already need some way to get rid of empty space in the tank, otherwise you would have hard time getting globules floating around to the reaction chamber.


          To give you an idea that there is indeed some difficulty here, I'll quote the article:

          "It took a year and a half of thermal pumping, carried out at different times, to accomplish the rebalancing".

          I'll give a small sample of a multitude of problems.

          Since you really aren't anchored to anything, you can't risk performing actions that would perturb your orientation. Change your orientation, and you will need to use fuel to get you back into position which defeats the purpose of equalizing your fuel since you used up what you would have saved.

          Remember, they problem of 'pumping' the fuel has been solved. It really is the difficulty of pumping the fuel when the needle is on 'E' and knowing that you won't run out between exits on the interstate.
          • by ookabooka (731013)
            Don't need fuel for orientation.

            Change your orientation, and you will need to use fuel to get you back into position which defeats the purpose of equalizing your fuel since you used up what you would have saved.

            Satellites often rotate themselves using gyroscopes. Imagine a large spherical weight inside a square box, you spin the sphere clockwise, box rotates counterclockwise, once you are at the orientation you desire, stop the spherical weight, box stops rotating as well. Theres a bit more finesse with th

    • by forkazoo (138186)

      Who launches a multimillion satellite to space without making sure that it fully uses resources left onboard before retiring? Even if four separate fuel tanks are necessary, they can be just connected by small pipes and fuel can be redistributed with a pump powered by satellite's solar cells. It's not a rocket science!

      Short answer : The pump will weight more than the wasted fuel, so your solution probably just shortened the lifetime instead of extending it.

      And, that's assuming that the pump doesn't break.

    • Ok that sounds easy. But do you even know how to pump fuel between two tanks? It's not so easy. In 0 G water does not flow down hill. If you open a drain it will not find the drain on it's own. It gets worse. There is no air to move heat so an empty tank could have a higher presure than a full tank. If you simply conectthem and open a valve fuel could flow the wrong way. How do you even know how much fuel is in the tank? Those float sensor in your car's gas tank don't work in space. All of these
  • Of course I haven't RTFA, but don't they connect the tanks on these things? That seems pretty obvious, and something they've been doing with airplane fuel tanks probably since they built the first plane with more than one tank.

    • by Amouth (879122)
      it might have occured on the second plane with more than 1 fuel tank..

      cause i could see them not doing it once.. then realizeing that was stupid and doing it for all the rest..
    • by harrkev (623093)

      Of course I haven't RTFA, but don't they connect the tanks on these things? That seems pretty obvious, and something they've been doing with airplane fuel tanks probably since they built the first plane with more than one tank.

      No, you didn't RTFA, and it shows.

      Apparently, they DO connect them together. However, being space, the tanks do not automatically equalize the liquid fuel, even though they are connected. This scheme involves using data about the temperature of the tank to guestimate how much fuel i

  • by techpawn (969834) on Thursday September 06, 2007 @03:53PM (#20498613) Journal
    It really sounds like they just applied load balancing to the fuel tanks...
  • Y'know. $30 million?
  • I'm wondering why they haven't started using ion drives on satellites. They would have to be significantly cheaper to launch and should last significantly longer, which should more than make up the cost of using newer technology.
    • Ion drives are much heavier than chemical drives (which are basically just bottles). This is not a problem for long range systems, where the reduction in propellant mass more than makes up for it, but it might be on satellites, where the engines are only to make minor orbital corrections, and are a tiny part of the mass. You'd probably also need to add more solar panels if you wanted to be able to power an ion thruster. You'd also complicate the orbital calculations a lot (ion thrusters provide small amo
    • by dbIII (701233)
      They do use ion drives on some satellites.
  • The article claims that the process saved $60 million. However, according to the satellite life cycle they describe, it isn't a savings that was realized, but an unanticipated revenue above expectations. They extended the service life of the satellite, rather than helping it achieve its full lifespan.

    If I am wrong, I apologize, but this seems to be what they were describing.
    • by Chris Burke (6130)
      Helping the satellite reach its full life span, extending the life span of the satellite... what's the difference? Either way the result is the broadcast companies have to launch new satellites less often, and thus they save money.
    • Re: (Score:3, Insightful)

      by Rolgar (556636)
      The article is rather vague, saying that's how much they saved, but then how much revenue the satellites bring in over 6 months. If it's the later, that the income these satellites made, not what they saved. If they bring these down at the start of the 6 months instead of the end, they'd still earn the revenue by having the replacement satellites in place at the earlier date. Anyway, this doesn't really save much, it just allows them to push back the cost of launching the new satellites half a year. I s
  • How about thruster modules which can attach to satellites with a standardized mounting system? Then you could extend satellite life by having the old module detach itself and re-enter the atmosphere, letting the new module attach itself in its place. Alternatively, make the standardized mounting capable of supporting at least two modules, so that the old one can stay on and do station-keeping, while the new module docks. Perhaps a ring around the satellite's waist that the modules can clamp themselves to
    • by Bert64 (520050)
      Remember that these are communications satellites.... And they last 15 years usually...
      They could have built more expensive satellites in the first place, to last longer, but why bother? Communications technology changes a lot in 15 years, i wouldnt be surprised if many of the satelites up there werent even in active use for the full 15 years before being replaced with a more modern device.
  • by Frosty Piss (770223) on Thursday September 06, 2007 @04:08PM (#20498825)
    Looks like IDG (ComputerWorld, ITWorld, NetworkWorld...) is really hitting Slashdot HARD, either that or they have a deal with Slashdot. Here's a partial list of the shills that regularly show up and have almost 100% article acceptance rates:

    coondoggie [slashdot.com]
    inkslinger77 [slashdot.com]
    narramissic [slashdot.com]
    jcatcw [slashdot.com]
    jpkunst [slashdot.com]

    Looks like they spread out the work over a few shill user accounts, which is to be expected. If it's all OK and everything with the corporate ownership of Slashdot to be played by IDG, I suppose that's their business, but one would hope that they are actually getting PAID for being part of IDG's advertising program. And of course there should be disclosure so that visitors to Slashdot realize they are reading advertisements and not an article submitted by a "real" user...

    • Re: (Score:3, Interesting)

      by Soporific (595477)
      Well I would take jpkunst out of that list. But the others yeah, 30 stories with 3 comments? I don't get it either.

      ~S
    • by jadin (65295)
      Easier explanation? Perhaps they (IDG) figured out what appeals to /. and it's editors in a way to get a majority of their stories through the filters. But you know, tinfoil hat away.
  • by Anonymous Coward on Thursday September 06, 2007 @04:12PM (#20498881)
    With all the answers here from "Why not just have one tank?" to "Run a tube between them" to "God, they're so stupid!", I'm surprised that Lockheed Martin didn't just do an Ask Slashdot posting. Baby, Slashdot coulda saved you millions already. Call me.
  • Tricky business (Score:5, Interesting)

    by linuxwrangler (582055) on Thursday September 06, 2007 @04:13PM (#20498885)
    A friend of mine was hired to work on this project. It's actually pretty tricky. Attitude correction generally involves very brief "puffs" of jets. Of course they measure the fuel consumed in these brief blasts but over years the errors accumulate.

    You can't let it run out of fuel since you need enough fuel to deorbit it at end of life. But given the cost of a satellite, each extra month of life is worth millions.

    The fuel is floating around in microgravity so you can't weigh it. I'm not sure but I think the most promising technique involves looking at the rate of heating when the tank-heaters are on. But accurately correcting out the effects of solar-heating and the various forms of heat loss is still lots of work.
  • by dougwhitehead (573106) on Thursday September 06, 2007 @04:43PM (#20499225)
    Good Luck trying to get NASA to effect such a change. Maybe this publicity will help.

    I had another solution to the same problem, back about 1990. I worked for Contel, my job was to write an expert system to assist in dumping momentum (use propellent to counter build-up caused by attitude gyros spinning too fast) for the TDRSS satellite system. I asked why momentum builds up. Answer: solar wind against antenae. My suggestion was to build models of antenae configurations or solar array that would drive up or down the momentum as needed... in essence to sail back into normal configuration. The potential exists here to NOT USE PROPELLENT, extending the life of satellites dramatically.

    I talked to my bosses and to NASA. And basically, I was told to shut up and sit down. They had procedures for dumping momentum. As a sub-contractor we were PAID to dump momentum. And even though they re-orient the antennae array all of the time, they have no procedure to move the antennae to slow dump momentum during times of low utilization.

    In other words, NASA didn't want to deal with new ideas, and have to deal with the work associated with it, or overseeing the work in others. Everything is risky when you don't want to bother.

    This has since become one of my stories... the moral being that the tech solution is not necessarily the right solution.
    • Private space companies, who incidentally are booming and profitable with regards to satellite operations (because, unlike everything else done in space, they bring back real, measurable benefits to mankind), have great multi-million dollar incentives to keep costs down. You save the shareholders a million bucks with a bright idea? Congratulations, collect a $10,000 bonus. However, at NASA, the bureacracy exists to perpetuate itself and that does NOT happen by saving money, it happens by spending it. $1
    • Re: (Score:3, Informative)

      by cyclone96 (129449)
      In other words, NASA didn't want to deal with new ideas, and have to deal with the work associated with it, or overseeing the work in others. Everything is risky when you don't want to bother.

      That's too bad. I work for NASA...Draper Labs proposed doing the same thing with the International Space Station and we tried it out on the vehicle. Worked like a charm, desaturated the Control Moment Gyros and executed a 90 degree yaw maneuver to boot, no propellant used. Remarkable. It was a great tool to add to
    • Good Luck trying to get NASA to effect such a change. Maybe this publicity will help.

      Why would NASA be involved? This change is for the geosync commo birds, which are commercial/private not NASA.

      In other words, NASA didn't want to deal with new ideas, and have to deal with the work associated with it, or overseeing the work in others. Everything is risky when you don't want to bother.

      It's much more likely that NASA knew what is immediately obvious to me, and that you seem to have missed.

  • by Cliff Stoll (242915) on Thursday September 06, 2007 @05:27PM (#20499693) Homepage
    Geostationary spacecraft aren't as stationary as we'd like. Due to many forces (the earth's oblateness, tessoral harmonics in the earth's gravitational field, gravity from the moon and the sun), these spacecraft tend to drift, requiring occasional burns of small rockets to keep the spacecraft where it belongs.

    In the spacecraft, each of four tanks contains the fuel (hydrazine) and a pressurizing gas (typically helium). There's a system of pipes and valves to allow any tank to feed any of the sets of x-y-z rocket motors. Of course, valves are unreliable, so there's the usual redundancies and crosslinked fuel pipes.

    Stationkeeping in geosynchronous satellites requires precisely metered burns at just the right times. Shoot too much hydrazine, and the satellite moves out of the window, and everyone's TV reception goes to pot. Worse, you'll have to fire the rockets again and use more fuel to undo the damage from the previous burn. Too little hydrazine means that you'll need several burns, but these can only be done at certain times. If your first burn is insufficient, you may have to wait for a month (or sometimes six months) before you can fix it. (In fact, you seldom know the exact effects of a burn until doppler & tracking data is analyzed over the next days)

    Now, suppose the satellite is low on fuel -- it's near the end of a 15 year lifespan. Three tanks have a little liquid fuel. The fourth tank runs out. If you then simply mix the four tanks, the output fuel line will get a mix of hydrazine and helium. The two phases in the fuel line will cause the motor to sputter, flare, or fizzle. Bad news!

    So this is a non-trivial problem. And there's lots of money hanging on the answer.

    In the past, the amount of fuel in each tank was determined by simple book-keeping ... recording exactly how many grams of fuel was used in each burn. This is imprecise, because of the nature of propellant gauging by measuring pressure and timing burns. So every now and then, the four tanks of hydrozine would be rebalanced by connecting all the tanks together and letting the fuel equilibrate between 'em. Rebalancing the tanks is done by warming a tank and connecting it to the others. The amount of heat to put into a tank depends on how much fuel is in there, but you can't directly measure this ... you depend on book keeping.

    This paper sounds like they're relating the amount of heat put into a tank, and the tank's temperature. From this relationship, they're getting a better determination of the total hydrazine in each tank, and thus they can better balance the fuel in each tank.

    In short, they came up with a nice way to estimate the amount of hydrazine in each tank by measuring the thermal effects. It's a good idea. Might add a few months to the lifespans of some old spacecraft which were launched in the 1990's.

    • Why don't they just use a system with a collapsible fuel bladder inside of a pressurized tank? You could monitor the temperature and pressure inside the tank to see how much the gas had expanded to replace fuel volume.
    • Stop backing up your refutations of comments with facts, logic and comprehension. You're making us armchair engineers look bad ;)
    • This paper sounds like they're relating the amount of heat put into a tank, and the tank's temperature. From this relationship, they're getting a better determination of the total hydrazine in each tank, and thus they can better balance the fuel in each tank.

      Basically, yes. I did an internship with GE AstroSpace during the summer of 1991, and I worked with an engineer in their propulsion group testing exactly this concept. We had a small tank, which we covered with heating elements and temperature sensors

  • I read the headline and thought it meant it would save millions of people... Better imaging of flood areas, hurricane tracking, or something.

    Imagine my disappointment when I discovered it meant dollars...
    • by owlstead (636356)
      Yeah, I had the same thing. I thought it was weird when I read the headline. Maybe some all-important weather or communications satellite? Somehow I feel suckered in, I probably wouldn't have read the summary if the headline included " of dollars" at the end. And the only reason I joined in the discussion was to say this. You just beat me to it though, and I'm freshly out of mod points :(
  • yuck (Score:2, Funny)

    by Flunitrazepam (664690)
    who wants a Satellite flavored life saver, regardless of how long it lasts
  • by Kelz (611260) on Thursday September 06, 2007 @06:14PM (#20500219)
    Outside of a nutshell?

    Must be a pretty big nutshell to fit a commsat.
  • Because technology in communication seems to get better and better, wouldnt be better to replace a satellite with a better one? Or are we at the point in optomizeing communication that it would be better to keep an old fleet longer? All in all, it is pretty nice to have a long life span in communication satellites given that the typical time of life is usually anywhere from 5 years to 15.
  • Sounds familiar ... (Score:4, Interesting)

    by PhxBlue (562201) on Thursday September 06, 2007 @06:19PM (#20500297) Homepage Journal

    Some folks formerly at Schriever Air Force Base did something similar with Defense Satellite Communication Systems satellites, which saves the Air Force $5 million per year per satellite. There's more on that story here [af.mil].

  • by dashslotter (1093743) on Thursday September 06, 2007 @06:43PM (#20500573) Homepage
    Millions of what, satellite overlords?

"Mach was the greatest intellectual fraud in the last ten years." "What about X?" "I said `intellectual'." ;login, 9/1990

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