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Rocket scientists at Purdue University in west Lafayette, Indiana have come up with a new approach to plasma thrusters which will potentially increase their reliability and efficiency making them more suitable for softball sized nanosatellites, which are becoming more and more common.
Plasma thrusters have traditionally used one of two approaches to fuel. A solid propellant, usually Teflon (polytetrafluoroethylene, that is ablated and vaporized and then passed through a field that accelerates it.
The problem is that this ablation is a hit-and-miss process. The rate is difficult to control, and this can make the thrust non-uniform. Also, the Teflon surface sometimes breaks down and ejects debris in the form of macroparticles that interfere with the engine operation.
What's more, the igniter that triggers the flashover process can become damaged over time. All these problems ultimately limit the efficiency of the solid-fuel plasma thrusters to less than 15%.
The other common way is to store the propellant as a gas. This increases the efficiency of a plasma thruster by up to 70%.
But these systems are bulky and complex, and the gas itself has a significantly larger volume than an equivalent solid mass. That makes it hard to build into a nanosat.
According to lead author Adam Patel, these issues can be addressed by storing the propellant as a liquid, which "could potentially overcome several disadvantages associated with traditional pulsed plasma thruster devices"
The team has built and, using a vacuum chamber, tested a proof-of-principle micro-propulsion system fed by liquid propellant. The liquid they used was pentaphenyl trimethyl trisiloxane (C33H34O2Si3), a viscous liquid with low vapor pressure that is also an excellent dielectric.
The advantage of this kind of igniter is that the threshold voltage is always the same, and so the amount of energy required for flashover is always limited. This limits the potential damage to the flashover assembly over time.
In tests, Patel and co used the igniter for upwards of 1.5 million flashover events without observing any significant damage to the device. Other designs can sometimes fail after only 400 firing cycles.
The test device was able to generate an exhaust velocity of 32km/sec and 5.8 Newtons of thrust making it a potentially (not)solid option for future nanosats.
Reference
arxiv.org/abs/1907.00169 : Liquid-Fed Pulsed Plasma Thruster for Propelling Nanosatellites
(Score: 2) by Runaway1956 on Monday July 22 2019, @11:30AM (2 children)
Isn't that a fairly easy task? Everything is in a vacuum, so no conduction, or convection. Radiation isn't a huge problem. Everything I've read says that overheating is a bigger problem in space, than getting too cold. Getting too much sunlight is the greater danger, if I've got it right.
Of course, I've never seen any charts or anything, showing how quickly, or how slowly, heat is lost into space. If the typical comm satellite loses 1 degree per year, it seems you have a lot of time in which to correct cold fuel tanks. A single small solar power panel ought to take care of that.
(Score: 2) by VLM on Monday July 22 2019, @01:21PM
Passive thermal control is pretty old stuff now. In the 80s it was easy for any ham radio guy with standard HF gear to listen to the Russian RS-10 and RS-12 satellites which transmitted on HF bands in morse code, the transmissions were like "register name space value" format continuously (well, when the sat was overhead LOL) and you'd run the register number thru a formula and get the internal temperature of the satellite (or a zillion other sensors) and then you could graph it.
Modern sats are not so user friendly but do the same thing digitally using somewhat more obscure frequencies and modulation methods.
Anyway, yeah, its pretty much a solved problem for a long time and its within the range of hobby activity to receive, decode, and analyze satellite internal temps.
It kinda sucks that AMSAT and similar groups moved away from EZ-Sats like that and toward drastically higher performance but drastically harder to use sats. They really need an outreach program for, like, a HF PSK-31 telemetry transmitter.
(Score: 5, Informative) by ElizabethGreene on Monday July 22 2019, @03:30PM
Spacecraft thermal control volumes 1 and 2 are a fascinating read if you really want to know. The short version is that you need a sun shade, attitude control to keep the sunshade between you and the sun, thermal isolation between hot and cold components, and a way to generate heat to keep it from getting too cold.