NASASpaceFlight.com Forum

General Discussion => Advanced Concepts => Topic started by: jpfulton314 on 09/29/2015 06:00 pm

Title: University of Sydney Student Claims to Develop Record Setting Ion Drive
Post by: jpfulton314 on 09/29/2015 06:00 pm
http://honisoit.com/2015/09/university-of-sydney-student-smashes-nasa-record-for-fuel-efficiency-mars-and-back-on-a-tank-of-fuel/ (http://honisoit.com/2015/09/university-of-sydney-student-smashes-nasa-record-for-fuel-efficiency-mars-and-back-on-a-tank-of-fuel/)

The most appealing aspect is that this drive uses commonly available materials, such as magnesium for fuel.
Title: Re: University of Sydney Student Claims to Develop Record Setting Ion Drive
Post by: rpapo on 09/29/2015 08:47 pm
Scavenging space junk for fuel, however, would only be worth it with a trash collector using a drive like this, and I am guessing that would not work very well in LEO.  The question is, how great is the thrust compared to the drag imposed by the upper fringes of the atmosphere?  The article said this drive had even less thrust than NASA's drive, and that is quite low already.
Title: Re: University of Sydney Student Claims to Develop Record Setting Ion Drive
Post by: Prober on 09/29/2015 10:56 pm
an educational model of an ion thruster ;)

http://forum.nasaspaceflight.com/index.php?topic=33141.msg1431024#msg1431024
Title: Re: University of Sydney Student Claims to Develop Record Setting Ion Drive
Post by: Prober on 09/29/2015 10:57 pm
Australian student smashes NASA’s fuel efficiency record

https://www.youtube.com/watch?v=zzXTp7mAb0g
Title: Re: University of Sydney Student Claims to Develop Record Setting Ion Drive
Post by: Impaler on 10/01/2015 06:13 am
It's just an arc-jet, one of the oldest and crudest forms of electric propulsion, if may be a better kind of arc-jet but it's not remotely deserving of being compared to the HiPEP.  Also the designs for next generations of ion thrusters blow past 20K seconds by using 4 grids, http://www.esa.int/gsp/ACT/doc/PRO/ACT-RPR-PRO-IAC2006-DS4G-C4.4.7.pdf thing is we don't NEED more ISP we need more thrust.

Simply measuring the speed at which stuff comes out the back of the device is NOT the way you calculate efficiency.  First the cosine loss of a wide code like spray of material significantly drops the efficiency.  Second their is no indication that all the material ejected is moving at this speed, given that he is using electric arcs to vaporize metal he is probably getting a range of velocities in what is basically a small messy explosion.  And finally their may be metal simply being splattered and adhering to the engine itself which would not only ruin the efficiency but rapidly ruin the engine too, remember Ion engines are useless unless they can operate for YEARS.

The whole article looks like massively over hyped, engines need to be tested in vacuum chamber, pendulum-stands to actually measure THRUST and then divide that over propellant consumption to determine efficiency.  By the methodology they use of measuring exhaust velocity you can call the LHC a billion times better then HiPEP because it ejects protons at near the speed of light.
Title: Re: University of Sydney Student Claims to Develop Record Setting Ion Drive
Post by: NovaSilisko on 10/01/2015 07:21 am
By the methodology they use of measuring exhaust velocity you can call the LHC a billion times better then HiPEP because it ejects protons at near the speed of light.

I have a small, handheld, low-thrust engine with an exhaust velocity of 299,792,458 m/s, powered by a few batteries...  ;)
Title: Re: University of Sydney Student Claims to Develop Record Setting Ion Drive
Post by: tea monster on 10/01/2015 12:54 pm
"It may not be ideal to launch a spacecraft off a planet, without some tweaking" LOL - like a few F1's strapped to the side to 'assist'  ;D ;D

Also, what is 'one tank of gas'? That could be a something the size of basketball or it could be an STS stage.
Title: Re: University of Sydney Student Claims to Develop Record Setting Ion Drive
Post by: Hanelyp on 10/01/2015 03:45 pm
It's just an arc-jet, ...
Based on what?  That class of device isn't known for getting anywhere near the reported class of exhaust velocity, being a temperature limited thermal expansion rocket.
Title: Re: University of Sydney Student Claims to Develop Record Setting Ion Drive
Post by: Prober on 10/01/2015 03:48 pm
It's just an arc-jet, one of the oldest and crudest forms of electric propulsion, if may be a better kind of arc-jet but it's not remotely deserving of being compared to the HiPEP.  Also the designs for next generations of ion thrusters blow past 20K seconds by using 4 grids, http://www.esa.int/gsp/ACT/doc/PRO/ACT-RPR-PRO-IAC2006-DS4G-C4.4.7.pdf thing is we don't NEED more ISP we need more thrust.

Simply measuring the speed at which stuff comes out the back of the device is NOT the way you calculate efficiency.  First the cosine loss of a wide code like spray of material significantly drops the efficiency.  Second their is no indication that all the material ejected is moving at this speed, given that he is using electric arcs to vaporize metal he is probably getting a range of velocities in what is basically a small messy explosion.  And finally their may be metal simply being splattered and adhering to the engine itself which would not only ruin the efficiency but rapidly ruin the engine too, remember Ion engines are useless unless they can operate for YEARS.

The whole article looks like massively over hyped, engines need to be tested in vacuum chamber, pendulum-stands to actually measure THRUST and then divide that over propellant consumption to determine efficiency.  By the methodology they use of measuring exhaust velocity you can call the LHC a billion times better then HiPEP because it ejects protons at near the speed of light.

a simple basic question: "It's just an arc-jet", if true why hasn't NASA used it?
Title: Re: University of Sydney Student Claims to Develop Record Setting Ion Drive
Post by: savuporo on 10/01/2015 04:54 pm
a simple basic question: "It's just an arc-jet", if true why hasn't NASA used it?
They have.
http://www.rocket.com/propulsion-systems/electric-propulsion
http://www.astronautix.com/engines/mr510.htm

Screen grab from http://descanso.jpl.nasa.gov/SciTechBook/series1/Goebel__cmprsd_opt.pdf

https://info.aiaa.org/Regions/Western/Orange_County/ASAT%20Conference%202014%20Presentations/Ellison_AIAA%20Electric%20Prop-Final.pdf

Quote
The arcjet continues to evolve progressing to  Lockheed’s A2100 satellites, and the MR-510 arcjet system (2.2-kW, 582-sec nominal Isp thrusters) for NSSK

In short, Arcjets ISP is limited by the heating available to around ~700

EDIT: Maybe i read the simple question wrong. If the question is, why havent they done it with magnesium, the answer is: various propellants for Arcjets have been tried through the history. Getting one to work and last beyond a benchtop experiment is a challenge, the electrodes erode fast
Title: Re: University of Sydney Student Claims to Develop Record Setting Ion Drive
Post by: Impaler on 10/03/2015 10:21 pm
Exactly, their are most likely huge drawbacks in practicality to this device, such as but not limited to...

Incredibly shot life span, possibly only a single firing
Excessively high voltage current needed
Inconsistent thrust production from one firing to the next
Excessive thruster mass leading to bad thrust to weight ratio

Generally when someone claims a 10 fold performance improvement in a laboratory bench variation of an established technology it is done by cratering multiple factors of performance that are necessary to make a practical working device.  Much like when you hear about new battery chemistry with is 10x denser, it's usually only last a handful of charge cycles and will spontaneously combust if you look at it funny.