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."

Comments

Re:Wow! What an innovative idea!

[Otter]

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.

sigh

[everphilski]

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.

Slashdot swamped with IDG Shills

[Frosty Piss]

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
inkslinger77
narramissic
jcatcw
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...

Estimating hydrazine mass by its thermal effects

[Cliff Stoll]

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.

Re:It's amazing that this was not done initially

[IndustrialComplex]

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.