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Electric Propulsion and Space Solar technology Q&A
by
Raj2014
on 14 Nov, 2014 22:03
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Hello Everyone
Does anyone know:
1) Which electric propulsion produces the highest thrust?
2) Which electric propulsion has the highest fuel efficiency?
3) Which electric propulsion would be best to use to propel a manned spacecraft to Mars?
4) Which solar technology produces the highest electricity?
5) Which solar technology has the highest efficiency?
6) Which solar technology is the lightest?
Thank you.
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#1
by
Raj2014
on 18 Dec, 2014 23:12
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Hello everyone
I have been researching on electric propulsion and found information on magnetoplasmadynamic thruster. Apparently they offer higher fuel efficiency, exhaust speed and thrust out of all know electric propulsions. Does anyone know if there has been anymore research done recently and has NASA, or any other space organisation, consider using this type of propulsion for deep space travel?
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#2
by
Robotbeat
on 19 Dec, 2014 04:37
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MPD has lower /electrical/ efficiency than your typical ion thruster, which means it needs a heavier solar array a power processing unit.
A lot of the answers to your questions, like what type produces the most electricity (watts), depends on the scale, not the technology, so it's a weird bunch of questions to ask. But the lightest currently flying is Ultraflex, which can do about 150W/kg at 1AU. But IKAROS (Japanese solar sail/solar power sail experimental spacecraft) showed thin film solar arrays with super lightweight structure, so equivalent to about 1000W/kg at 1AU (and inverse square law besides that).
And the optimum Isp isn't always just as high as you can go. Higher exhaust velocity takes more power for the same thrust as lower exhaust velocity (because thrust is massFlowRate*velocity whereas exhaust power is .5*massFlowRate*velocity^2). And the longer you have to thrust, the higher the optimum is. The optimum exhaust velocity ("characteristic velocity") for a given thrusting time, specific power, and system electrical efficiency is usually close to:
velocity[m/s] = sqrt(2*(system specific power [W/kg])*efficiency[number, i.e. 0.5 for 50%]*thrustingTime[seconds])
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#3
by
Raj2014
on 19 Dec, 2014 08:54
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MPD has lower /electrical/ efficiency than your typical ion thruster, which means it needs a heavier solar array a power processing unit.
A lot of the answers to your questions, like what type produces the most electricity (watts), depends on the scale, not the technology, so it's a weird bunch of questions to ask. But the lightest currently flying is Ultraflex, which can do about 150W/kg at 1AU. But IKAROS (Japanese solar sail/solar power sail experimental spacecraft) showed thin film solar arrays with super lightweight structure, so equivalent to about 1000W/kg at 1AU (and inverse square law besides that).
And the optimum Isp isn't always just as high as you can go. Higher exhaust velocity takes more power for the same thrust as lower exhaust velocity (because thrust is massFlowRate*velocity whereas exhaust power is .5*massFlowRate*velocity^2). And the longer you have to thrust, the higher the optimum is. The optimum exhaust velocity ("characteristic velocity") for a given thrusting time, specific power, and system electrical efficiency is usually close to:
velocity[m/s] = sqrt(2*(system specific power [W/kg])*efficiency[number, i.e. 0.5 for 50%]*thrustingTime[seconds])
When you say MPD has lower /electrical/ efficiency than your typical ion thruster, in what way? I also read that NASA was working on an nuclear reactor called Project Prometheus, would this help produce a lot of thrust for electric propulsion?
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#4
by
enkarha
on 19 Dec, 2014 09:55
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MPD has lower /electrical/ efficiency than your typical ion thruster, which means it needs a heavier solar array a power processing unit.
A lot of the answers to your questions, like what type produces the most electricity (watts), depends on the scale, not the technology, so it's a weird bunch of questions to ask. But the lightest currently flying is Ultraflex, which can do about 150W/kg at 1AU. But IKAROS (Japanese solar sail/solar power sail experimental spacecraft) showed thin film solar arrays with super lightweight structure, so equivalent to about 1000W/kg at 1AU (and inverse square law besides that).
And the optimum Isp isn't always just as high as you can go. Higher exhaust velocity takes more power for the same thrust as lower exhaust velocity (because thrust is massFlowRate*velocity whereas exhaust power is .5*massFlowRate*velocity^2). And the longer you have to thrust, the higher the optimum is. The optimum exhaust velocity ("characteristic velocity") for a given thrusting time, specific power, and system electrical efficiency is usually close to:
velocity[m/s] = sqrt(2*(system specific power [W/kg])*efficiency[number, i.e. 0.5 for 50%]*thrustingTime[seconds])
When you say MPD has lower /electrical/ efficiency than your typical ion thruster, in what way? I also read that NASA was working on an nuclear reactor called Project Prometheus, would this help produce a lot of thrust for electric propulsion?
If you turn on a flashlight, the amount of mass it is losing relative to the speed of that mass is very low. It is mass efficient, it has a high Isp. But a lot of the energy you are actually using goes into useless heat. So you are not very energy efficient, and you need bigger nuclear power or solar power mass to fix that. Or you use LEDs instead, which is like going from MPD to some Kaufman thrusters or FEEPs. It's a problem, but not a huge one.
Ion thrusters are the same. Little mass usage, high energy usage. But not that high. Gains here are limited. FEEPs using indium already get >95% electrical efficiency but they have micronewton thrust.
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#5
by
Raj2014
on 19 Dec, 2014 13:39
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MPD has lower /electrical/ efficiency than your typical ion thruster, which means it needs a heavier solar array a power processing unit.
A lot of the answers to your questions, like what type produces the most electricity (watts), depends on the scale, not the technology, so it's a weird bunch of questions to ask. But the lightest currently flying is Ultraflex, which can do about 150W/kg at 1AU. But IKAROS (Japanese solar sail/solar power sail experimental spacecraft) showed thin film solar arrays with super lightweight structure, so equivalent to about 1000W/kg at 1AU (and inverse square law besides that).
And the optimum Isp isn't always just as high as you can go. Higher exhaust velocity takes more power for the same thrust as lower exhaust velocity (because thrust is massFlowRate*velocity whereas exhaust power is .5*massFlowRate*velocity^2). And the longer you have to thrust, the higher the optimum is. The optimum exhaust velocity ("characteristic velocity") for a given thrusting time, specific power, and system electrical efficiency is usually close to:
velocity[m/s] = sqrt(2*(system specific power [W/kg])*efficiency[number, i.e. 0.5 for 50%]*thrustingTime[seconds])
When you say MPD has lower /electrical/ efficiency than your typical ion thruster, in what way? I also read that NASA was working on an nuclear reactor called Project Prometheus, would this help produce a lot of thrust for electric propulsion?
If you turn on a flashlight, the amount of mass it is losing relative to the speed of that mass is very low. It is mass efficient, it has a high Isp. But a lot of the energy you are actually using goes into useless heat. So you are not very energy efficient, and you need bigger nuclear power or solar power mass to fix that. Or you use LEDs instead, which is like going from MPD to It's a problem, but not a huge one.
Ion thrusters are the same. Little mass usage, high energy usage. But not that high. Gains here are limited. FEEPs using indium already get >95% electrical efficiency but they have micronewton thrust.
Then why is NASA planning to use hall thrusters? Out of all the electric propulsions out there, which one has the highest thrust?
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#6
by
Jim
on 19 Dec, 2014 13:44
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Then why is NASA planning to use hall thrusters? Out of all the electric propulsions out there, which one has the highest thrust?
Because they work and are efficient for unmanned spacecraft. Electric propulsion is not useable for manned spacecraft at this time nor does NASA have the need for it.
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#7
by
DarkenedOne
on 19 Dec, 2014 15:51
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MPD has lower /electrical/ efficiency than your typical ion thruster, which means it needs a heavier solar array a power processing unit.
A lot of the answers to your questions, like what type produces the most electricity (watts), depends on the scale, not the technology, so it's a weird bunch of questions to ask. But the lightest currently flying is Ultraflex, which can do about 150W/kg at 1AU. But IKAROS (Japanese solar sail/solar power sail experimental spacecraft) showed thin film solar arrays with super lightweight structure, so equivalent to about 1000W/kg at 1AU (and inverse square law besides that).
And the optimum Isp isn't always just as high as you can go. Higher exhaust velocity takes more power for the same thrust as lower exhaust velocity (because thrust is massFlowRate*velocity whereas exhaust power is .5*massFlowRate*velocity^2). And the longer you have to thrust, the higher the optimum is. The optimum exhaust velocity ("characteristic velocity") for a given thrusting time, specific power, and system electrical efficiency is usually close to:
velocity[m/s] = sqrt(2*(system specific power [W/kg])*efficiency[number, i.e. 0.5 for 50%]*thrustingTime[seconds])
When you say MPD has lower /electrical/ efficiency than your typical ion thruster, in what way? I also read that NASA was working on an nuclear reactor called Project Prometheus, would this help produce a lot of thrust for electric propulsion?
If you turn on a flashlight, the amount of mass it is losing relative to the speed of that mass is very low. It is mass efficient, it has a high Isp. But a lot of the energy you are actually using goes into useless heat. So you are not very energy efficient, and you need bigger nuclear power or solar power mass to fix that. Or you use LEDs instead, which is like going from MPD to It's a problem, but not a huge one.
Ion thrusters are the same. Little mass usage, high energy usage. But not that high. Gains here are limited. FEEPs using indium already get >95% electrical efficiency but they have micronewton thrust.
Then why is NASA planning to use hall thrusters? Out of all the electric propulsions out there, which one has the highest thrust?
Asking which form of electric propulsion produces the highest thrust is like asking the same question for chemical rocket engines. One can always obtain more thrust out of a propulsion system by making it bigger.
The same does not hold true for specific impulse, aka. fuel efficiency. Chemical rocket engines are limited by the energy content of the fuel they consume. With electric propulsion power is provided by an external source, so the ISP that can be attained is limited by the external power source.
Typically electric propulsion systems are not used in situations where high thrust is required.
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#8
by
Robotbeat
on 19 Dec, 2014 21:03
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MPD is less electrically efficient, meaning for the same Isp and thrust, it requires more power, ie a solar array twice as big.
Hall thrusters are lower Isp, which is good if you only have a short time to thrust. See the characteristic equation I gave.
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#9
by
R7
on 20 Dec, 2014 15:03
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Hello Everyone
Does anyone know:
1) Which electric propulsion produces the highest thrust?
2) Which electric propulsion has the highest fuel efficiency?
3) Which electric propulsion would be best to use to propel a manned spacecraft to Mars?
4) Which solar technology produces the highest electricity?
5) Which solar technology has the highest efficiency?
6) Which solar technology is the lightest?
Thank you.
1) the one with lowest Isp, resistojet would be a good choice.
2) the one with photon exhaust
3) none at the moment. Something with variable thrust/Isp would be nice.
4) define "highest"
5) probably Fraunhofer Institute's latest record,
46% efficient multijunction cell.
6) a battle between thin films and concentrated solar power I guess.
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#10
by
Raj2014
on 20 Dec, 2014 17:23
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Hello Everyone
Does anyone know:
1) Which electric propulsion produces the highest thrust?
2) Which electric propulsion has the highest fuel efficiency?
3) Which electric propulsion would be best to use to propel a manned spacecraft to Mars?
4) Which solar technology produces the highest electricity?
5) Which solar technology has the highest efficiency?
6) Which solar technology is the lightest?
Thank you.
1) the one with lowest Isp, resistojet would be a good choice.
2) the one with photon exhaust
3) none at the moment. Something with variable thrust/Isp would be nice.
4) define "highest"
5) probably Fraunhofer Institute's latest record, 46% efficient multijunction cell.
6) a battle between thin films and concentrated solar power I guess.
In question 5, what I mean is, which solar panel can produce the highest amount of electricity. For question 3, do you think VASIMR would be a good propulsion to use?
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#11
by
baldusi
on 20 Dec, 2014 20:47
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Hello Everyone
Does anyone know:
1) Which electric propulsion produces the highest thrust?
2) Which electric propulsion has the highest fuel efficiency?
3) Which electric propulsion would be best to use to propel a manned spacecraft to Mars?
4) Which solar technology produces the highest electricity?
5) Which solar technology has the highest efficiency?
6) Which solar technology is the lightest?
Thank you.
1) the one with lowest Isp, resistojet would be a good choice.
2) the one with photon exhaust
3) none at the moment. Something with variable thrust/Isp would be nice.
4) define "highest"
5) probably Fraunhofer Institute's latest record, 46% efficient multijunction cell.
6) a battle between thin films and concentrated solar power I guess.
In question 5, what I mean is, which solar panel can produce the highest amount of electricity. For question 3, do you think VASIMR would be a good propulsion to use?
You mean per unit of weight, area, cost?
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#12
by
Raj2014
on 20 Dec, 2014 22:32
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Hello Everyone
Does anyone know:
1) Which electric propulsion produces the highest thrust?
2) Which electric propulsion has the highest fuel efficiency?
3) Which electric propulsion would be best to use to propel a manned spacecraft to Mars?
4) Which solar technology produces the highest electricity?
5) Which solar technology has the highest efficiency?
6) Which solar technology is the lightest?
Thank you.
1) the one with lowest Isp, resistojet would be a good choice.
2) the one with photon exhaust
3) none at the moment. Something with variable thrust/Isp would be nice.
4) define "highest"
5) probably Fraunhofer Institute's latest record, 46% efficient multijunction cell.
6) a battle between thin films and concentrated solar power I guess.
In question 5, what I mean is, which solar panel can produce the highest amount of electricity. For question 3, do you think VASIMR would be a good propulsion to use?
You mean per unit of weight, area, cost?
What I mean is, which solar panel is able to collect sunlight and convert it in to electricity, in terms of how much watts will it produce. The Fraunhofer Institute's record is 46% efficience on their solar panels. I read an article and watched a video showing solar panels can give between 50-300 kW. They are the ATK megaflex and DSS roll out solar array. Is this the highest?
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#13
by
baldusi
on 21 Dec, 2014 04:15
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So you mean total power? That depends on budget, mission risk, launching volume, mass margin and power requirements.
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#14
by
R7
on 21 Dec, 2014 09:24
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For question 3, do you think VASIMR would be a good propulsion to use?
If they get it to work as advertized, yes.