5 ms·

In-orbit demonstration of an iodine electric propulsion system

136 points by jollybean 5y ago

tgbugs 5y ago
I look forward to seeing more methods sections which have a step that involves launching things into orbit. I bet that at some point the exact type of rocket that is used will cause variable results due to differences in the vibrational modes modifying payloads so that their behavior changes.
archermarks 5y ago
This is really cool. Electric propulsion for small satellites is a hot field and has been advancing rapidly, and this is no exception. The rising cost of Xenon is a real problem in the field right now so it's great to see the work being done on alternate propellants (it would be great if we knew more about SpaceX's thrusters, which run on Krypton). Doing some math, their total thrust efficiency seems to be around 29%, which is really good for a thruster of its size being ionized by RF power.
- 14 5y ago
  I was so excited by the possibility of an EmDrive engine for a bit it really seemed like everyone was trying and that there was maybe something to them. But also they would violate laws of physics so remained skeptical. Watched too much Star Trek as a kid I love to look at the skies and imagine humans travelling across the galaxy. One day.
- Robotbeat 5y ago
  There’s not much to know about SpaceX’s thrusters. They’re basic Hall Effect thrusters that run on a noble gas chemically identical to Xenon but slightly less efficient (since the mass of each singly ionized ion is lower for Krypton, so for the same mass of propellant, you have to ionize more atoms than you would for Xenon… plus the ionization energy per atom may be different) and much cheaper. You could run them on Argon, if you wanted. A Noble Gas is a Noble Gas, to first and second order. There’s no real reason we couldn’t run Xenon thrusters on Krypton except the lower density of Krypton means somewhat heavier tanks for the same mass of propellant.
  - dnautics 5y ago
    > A Noble Gas is a Noble Gas Probably not relevant for thrusters, but Xenon does make XeO2 and XeF6, and XeF4, and the other gases don't really do that (krypton does make KrF2)...
  - mrfusion 5y ago
    Why is it important to be a Nobel gas?
    - Robotbeat 5y ago
      1) won’t condense on the rest of your spacecraft. 2) won’t corrode your thruster as much. 3) Chemical and fire safety aren’t concerns. 4) Is a fluid already so doesn’t need to be heated to flow. Also, being monotomic makes it easier to model everything. A more complex molecule could have weird chemistry that ends up producing solid particles that impinge or maybe condense on your spacecraft (coating lenses, etc).
      - idiotsecant 5y ago
        None of these are really the primary reason why we use noble gasses. It has to do with the ionization energy of the gas, which tells us how much energy we have to spend per molecule to ionize the gas. https://en.wikipedia.org/wiki/Ionization_energy https://en.wikipedia.org/wiki/Ionization_energy
        Robotbeat 5y ago
        However noble gases don’t have the lowest ionization energy per unit molecular mass. Bismuth, Cesium, etc do significantly better on those metrics than even Xenon does, and Xenon is better than Krypton. http://aerospace.mtu.edu/__reports/Conference_Proceedings/2007_Ross_2.pdf http://aerospace.mtu.edu/__reports/Conference_Proceedings/20... EDIT: and iodine, ie the subject of this study, is also significantly better than Xenon in this metric: “ A possible alternative is iodine, which is much more abundant and cheaper than xenon and can be stored unpressurized as a solid. In addition, both atomic and diatomic iodine have a lower ionization threshold, and diatomic iodine has a relative mass that is almost twice that of xenon.”
- gorgoiler 5y ago
  …hot field…, hah. The cost of things is usually a function of labour and demand, but Xenon is in sufficiently low supply that building new engines is a better option than improving Xenon farming? Where does it come from?
  - ridgeguy 5y ago
    Xenon is a very minor trace component of air. It's collected as a byproduct during fractional cryo-distillation of air to make LOX and liquid nitrogen. [1] [1] https://en.wikipedia.org/wiki/Xenon#Occurrence_and_production https://en.wikipedia.org/wiki/Xenon#Occurrence_and_productio...
    - gorgoiler 5y ago
      > Worldwide production of xenon in 1998 was estimated at 5,000–7,000 m3 O2 annual production is 1e11kg presumably from 5e11 of air (20% of air is O2.) Xenon occurs 1:1e7 so that air should also yield 50,000kg by mass, or 8500m3 by volume. Sounds about right. I’m guessing then O2 buyers don’t care to subsidise the Xe market.
Scoundreller 5y ago
I can’t stop laughing at the company name the authors work at: “ThrustMe”…
aaronharnly 5y ago
I love that they supplied 4 citations for the opening assertion: "Propulsion is a critical subsystem of many spacecraft [1,2,3,4]". Glad I didn't have to take that on faith :)
- tubby12345 5y ago
  I work on compilers and I have lines in papers like "runtime performance is important for many heavily used services [1,2,3,4]". The reason you do this is to preempt some annoying reviewer whose area is some other dimension of the same problem (eg correctness).
- deleted 5y ago
  [deleted]
Symmetry 5y ago
A company doing similar work that I shared a startup incubator with for a while is Accion. They use a liquid salt so their propellant is sort of pre-ionized. https://accion-systems.com/our-technology/ https://accion-systems.com/our-technology/
kunstmord 5y ago
If anyone wants to read about EP in (a lot) more detail, here’s a great overview article: https://aip.scitation.org/doi/full/10.1063/5.0010134 https://aip.scitation.org/doi/full/10.1063/5.0010134

136 points by jollybean 5y ago

I look forward to seeing more methods sections which have a step that involves launching things into orbit. I bet that at some point the exact type of rocket that is used will cause variable results due to differences in the vibrational modes modifying payloads so that their behavior changes.

archermarks 5y ago

This is really cool. Electric propulsion for small satellites is a hot field and has been advancing rapidly, and this is no exception. The rising cost of Xenon is a real problem in the field right now so it's great to see the work being done on alternate propellants (it would be great if we knew more about SpaceX's thrusters, which run on Krypton). Doing some math, their total thrust efficiency seems to be around 29%, which is really good for a thruster of its size being ionized by RF power.

14 5y ago
I was so excited by the possibility of an EmDrive engine for a bit it really seemed like everyone was trying and that there was maybe something to them. But also they would violate laws of physics so remained skeptical. Watched too much Star Trek as a kid I love to look at the skies and imagine humans travelling across the galaxy. One day.
Robotbeat 5y ago
There’s not much to know about SpaceX’s thrusters. They’re basic Hall Effect thrusters that run on a noble gas chemically identical to Xenon but slightly less efficient (since the mass of each singly ionized ion is lower for Krypton, so for the same mass of propellant, you have to ionize more atoms than you would for Xenon… plus the ionization energy per atom may be different) and much cheaper. You could run them on Argon, if you wanted. A Noble Gas is a Noble Gas, to first and second order. There’s no real reason we couldn’t run Xenon thrusters on Krypton except the lower density of Krypton means somewhat heavier tanks for the same mass of propellant.
- dnautics 5y ago
  > A Noble Gas is a Noble Gas Probably not relevant for thrusters, but Xenon does make XeO2 and XeF6, and XeF4, and the other gases don't really do that (krypton does make KrF2)...
- mrfusion 5y ago
  Why is it important to be a Nobel gas?
  - Robotbeat 5y ago
    1) won’t condense on the rest of your spacecraft. 2) won’t corrode your thruster as much. 3) Chemical and fire safety aren’t concerns. 4) Is a fluid already so doesn’t need to be heated to flow. Also, being monotomic makes it easier to model everything. A more complex molecule could have weird chemistry that ends up producing solid particles that impinge or maybe condense on your spacecraft (coating lenses, etc).
    - idiotsecant 5y ago
      None of these are really the primary reason why we use noble gasses. It has to do with the ionization energy of the gas, which tells us how much energy we have to spend per molecule to ionize the gas. https://en.wikipedia.org/wiki/Ionization_energy https://en.wikipedia.org/wiki/Ionization_energy
      - Robotbeat 5y ago
        However noble gases don’t have the lowest ionization energy per unit molecular mass. Bismuth, Cesium, etc do significantly better on those metrics than even Xenon does, and Xenon is better than Krypton. http://aerospace.mtu.edu/__reports/Conference_Proceedings/2007_Ross_2.pdf http://aerospace.mtu.edu/__reports/Conference_Proceedings/20... EDIT: and iodine, ie the subject of this study, is also significantly better than Xenon in this metric: “ A possible alternative is iodine, which is much more abundant and cheaper than xenon and can be stored unpressurized as a solid. In addition, both atomic and diatomic iodine have a lower ionization threshold, and diatomic iodine has a relative mass that is almost twice that of xenon.”
gorgoiler 5y ago
…hot field…, hah. The cost of things is usually a function of labour and demand, but Xenon is in sufficiently low supply that building new engines is a better option than improving Xenon farming? Where does it come from?
- ridgeguy 5y ago
  Xenon is a very minor trace component of air. It's collected as a byproduct during fractional cryo-distillation of air to make LOX and liquid nitrogen. [1] [1] https://en.wikipedia.org/wiki/Xenon#Occurrence_and_production https://en.wikipedia.org/wiki/Xenon#Occurrence_and_productio...
  - gorgoiler 5y ago
    > Worldwide production of xenon in 1998 was estimated at 5,000–7,000 m3 O2 annual production is 1e11kg presumably from 5e11 of air (20% of air is O2.) Xenon occurs 1:1e7 so that air should also yield 50,000kg by mass, or 8500m3 by volume. Sounds about right. I’m guessing then O2 buyers don’t care to subsidise the Xe market.

Scoundreller 5y ago

I can’t stop laughing at the company name the authors work at: “ThrustMe”…

aaronharnly 5y ago

I love that they supplied 4 citations for the opening assertion: "Propulsion is a critical subsystem of many spacecraft [1,2,3,4]". Glad I didn't have to take that on faith :)

tubby12345 5y ago
I work on compilers and I have lines in papers like "runtime performance is important for many heavily used services [1,2,3,4]". The reason you do this is to preempt some annoying reviewer whose area is some other dimension of the same problem (eg correctness).
deleted 5y ago
[deleted]

Symmetry 5y ago

A company doing similar work that I shared a startup incubator with for a while is Accion. They use a liquid salt so their propellant is sort of pre-ionized. https://accion-systems.com/our-technology/ https://accion-systems.com/our-technology/

kunstmord 5y ago

If anyone wants to read about EP in (a lot) more detail, here’s a great overview article: https://aip.scitation.org/doi/full/10.1063/5.0010134 https://aip.scitation.org/doi/full/10.1063/5.0010134