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New Way of Extending Satellite Life Saves Millions
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."
borrow from other tanks
They didn't do that.
Actually, yeah it is. Real world engineering is rarely as simple and black and white as the armchair variety.
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.
What I'm listening to now on Pandora...
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.
coondoggie
inkslinger77
narramissic
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jpkunst
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...
If you want news from today, you have to come back tomorrow.
Nothing floats in microgravity. You can freely mix gases, liquids and solid materiials to the limits that surface tension allows. Watch this NASA video about liquids and gases in microgravity, consider that a number of fuel drops of various sizes may be bouncing around the fuel tank, possibly mixed with helium bubbles (used to pressurize some fuel tanks), and tell me what is supposed to float where and in which direction.
Unless one lighted one of the motors and accelerated the whole satellite long enough for all the fuel to coalesce on one side of the tank, that's just not going to work.
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.
... 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.
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
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.
If the tubes are pressurized fluid fuel, then they will equalize perfectly well, gravity or no gravity.
People in Soviet Russia, however, appear to be afflicted with amusing juxtapositions of the aforementioned situation
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.
Out of modpoints but really liked a post? 1BDkF6TtmmeZ3yqXbz9yhdYVqRYnwFoXDj
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 our bag of tricks.
Draper even produced a video of it available here
Worst...sig...ever!
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, wrapped with typical insulating materials as it would be on a satellite, filled it with various amounts of fluid and helium, stuck it in a vacuum chamber (to eliminate convection effects), and ran it through some heating and cooling cycles while measuring the temperature response.
There's a formula from thermodynamics (which I no longer remember) that relates the change in temperature to the energy added to a system, the mass of the system, and the thermodynamic properties of the materials in the system. In our experiment we knew the values of all of the variables within a certain error, and we were able to verify that the equation was accurately modeling the test. We were also able to invert the equation to solve for the mass of the propellant, and with some fancy analysis we determined the error range for that mass, given the error ranges of our other variables. (eg: the amount of energy going into the tanks depends on the voltage and current going to the heating elements, which the satellite telemetry could measure and report but not precisely, and the temperature could also be measured and reported but not precisely.)
What's really key in the end result isn't the mass of the propellant left in the tank; it's the error. As you noted, the traditional approach is bookkeeping, where the amount of fuel used for each burn is estimated, and over time the errors in that estimate add up. So, near the end of life, you know that you have 2 years worth of propellant, plus or minus six months. With the temperature-response approach, we were able to show that you can reduce the error to plus or minus two months (for example). With bookkeeping, the satellite has to be replaced at 2 years - six months, but with temperature-response it can be replaced at 2 years - two months: four additional months of service, which saves millions of dollars by delaying the new satellite.