6 ms·

This seems like a big deal. Assuming it could collect more than it needs to keep itself in orbit, it could refuel a tank and skip from atmospheric body to atmos

This seems like a big deal. Assuming it could collect more than it needs to keep itself in orbit, it could refuel a tank and skip from atmospheric body to atmospheric body. Something like this could make it to Neptune and back, though it might take an incredible amount of time. Still, atmospheric fuel scoops were still sci-fi until now, as far as I’m aware.

binarycoffee 9y ago
This is still very much sci-fi at the moment for anything flying above a 250 km earth orbit because atmospheric density decreases dramatically fast with altitude. The missions targeted by this technology are GOCE-like spacecrafts which by design must fly low and need an insane amount of propellant to compensate for the high atmospheric drag at such altitude.
- baybal2 9y ago
  This does not preclude the possibility of spacecraft doing repeated dips only on the perigee
  - binarycoffee 9y ago
    True, interesting idea. [Long edit] Thinking further about this idea, I realize this may even mitigate the catch 22 problem of very low orbits (<180km): the lower the orbit, the larger the drag and the required thrust power, meaning the solar arrays must be bigger, which in turn further increases the drag... Calculations suggests that with current solar array and thruster technology, flying lower than 150km with this concept is impossible. But with an elliptic orbit, energy from the solar arrays can be stored on the low-drag portion of the orbit too and used during the perigee dip, thus decreasing the requirements in terms of solar arrays area.
    - Cthulhu_ 9y ago
      I'm now imagining a craft that folds up its solar panels before dipping into the atmosphere to gather fuel / accelerate. I'm sure I've built that in KSP, :p.
      - greeneggs 9y ago
        Here's an example where the authors propose doing this for planetary gravity assists, e.g., instead of using Venus for a normal gravity assist, dig into its atmosphere. Everything would need to be folded up first. "Hypersonic Interplanetary Flight: Aero Gravity Assist" Al Bowers & Dan Banks, 2006 https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090008672.pdf https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/200900... Discussed in a podcast here: https://theorbitalmechanics.com/show-notes/al-bowers https://theorbitalmechanics.com/show-notes/al-bowers
      - msl 9y ago
        That is not particulary far-fetched either: the ISS already reorients its solar panels when not illuminated by the sun. They call it the "night glider mode" [1]. [1] https://en.wikipedia.org/wiki/Night_Glider_mode https://en.wikipedia.org/wiki/Night_Glider_mode
        sitkack 9y ago
        > The implementation of drag-reducing flight modes of the space station resulted in saving about 1,000 kg of orbital-maintenance propellant per year.
        zaarn 9y ago
        Night Glider sounds vaguely like some 80s TV show. I do hope everyone on board is required to wear non-functional sunglasses during night glide.
  - nbadg 9y ago
    This would have the added benefit of increased efficiency due to the Oberth effect; however, I'm still not sure you could use it for unassisted interplanetary flight. The last orbit, by definition, must occur before the craft passes Earth escape velocity -- the question is, in that last pass through perigee, can you get enough delta V to make it to another planet? Otherwise, you'd need supplemental propellant. It's still useful, it's just not something I would describe as "revolutionary" for interplanetary travel. Since the TWR of electric thrusters tends to be pretty abysmal, my gut is that you probably couldn't scale up the thruster well enough to bounce between planets without that supplemental propellant. That being said, as others have mentioned, this would be really quite interesting for stationkeeping at low orbital altitudes, particularly for small satellites.
- ckastner 9y ago
  > This is still very much sci-fi at the moment for anything flying above a 250 km earth orbit because atmospheric density decreases dramatically fast with altitude. One of my favorite takes on this concept was Poul Anderson's Tau Zero [1], which used a Bussard ramjet [2]. Apparently, in the 70s, in was thought that there was enough hydrogen surrounding our solar system to support interstellar travel. [1] https://en.wikipedia.org/wiki/Tau_Zero https://en.wikipedia.org/wiki/Tau_Zero [2] https://en.wikipedia.org/wiki/Bussard_ramjet https://en.wikipedia.org/wiki/Bussard_ramjet
  - gaius 9y ago
    How can you decelerate with a ramjet? Wouldn't your own exhaust push the matter you needed out of the way?
    - whatshisface 9y ago
      You could push the exhaust single-file in a highly focused beam, leaving most of the solid angle around you unpushed.
  - binarycoffee 9y ago
    Somewhat related is the E-sail [1] concept, a perhaps less ambitious but (probably) feasible idea to harness the momentum of solar wind particles with very long charged wires. [1] https://en.wikipedia.org/wiki/Electric_sail https://en.wikipedia.org/wiki/Electric_sail
  - wizardforhire 9y ago
    A personal favorite feature on federation vessels. http://memory-alpha.wikia.com/wiki/Bussard_collector http://memory-alpha.wikia.com/wiki/Bussard_collector
  - Retric 9y ago
    Bussard Ramjets can be useful for interstellar travel. The net thrust is not great, but for very long and relatively slow trips it let's you power a very large ship without dragging along as much fuel assuming you can get hydrogen only fusion to work.
- ProblemFactory 9y ago
  > The missions targeted by this technology are GOCE-like spacecrafts which by design must fly low Once the technology matures, it could be used by more missions. Flying low has its benefits: * Lower latency for communication satellites, * Better resolution for Earth imaging / spy satellites, * When the satellite fails, it quickly deorbits by itself. Until now, flying low has just not been economical, but if this thruster has similar lifetime to medium and high orbit satellites, then many more missions could choose lower orbits.
  - orbital-decay 9y ago
    >When the satellite fails, it quickly deorbits by itself. This also means that failure recovery will be quite tricky if possible at all. There are some downsides to other points too: such a satellite would work at very thin margins due to the thruster being inefficient with air as a propellant. Its ground swath width will be lower, coverage will be worse, requiring more ground stations (remote sensing is very often limited by the downlink bandwidth). Also, some kind of aerodynamic shape will be required, limiting its capabilities and power budget. (electric propulsion needs a lot of power itself)
    - jccooper 9y ago
      "Quickly" in this context is probably still weeks, and you could carry a little backup system to kick it into higher orbit in case of trouble. But really, low-flying com or imaging sats are probably parts of large, "cheap" constellations and meant to be of limited lifespan.
    - alex_duf 9y ago
      >This also means that failure recovery will be quite tricky if possible at all Nowadays it's probably cheaper to send a new one than doing a whole Hubble like hot fix with a space shuttle
      - walrus01 9y ago
        failure recovery in the context of spacecraft usually means software-commands sent via TT&C (tracking, telemetry and control) channel to switch to another piece of hardware, part of the N+1 or 1+1 configuration on the spacecraft. It is incredibly exceptionally rare for a human to ever visit a satellite once in orbit. They did it a few times in the 1980s with the shuttle, including recovery of a satellite to prove it could be done, and there were the hubble servicing missions. But other than that no human has ever touched a satellite once it's in orbit.
- m_mueller 9y ago
  ISS is at 150km and needs costly refueling, right? Wouldn’t that be the most interesting applicaton in terms of cost savings?
  - exDM69 9y ago
    ISS is at 400+ km altitude where the atmosphere is really thin. It's also very heavy for low thrust electric propulsion.
    - Symmetry 9y ago
      Electric thrusters have a low thrust to weight ratio but there's nothing stopping you, in theory, from just scaling up. The ISS only experiences a little drag so an electric drive trying to zero that out doesn't need a huge thrust. There's some interest in adapting VASIMR for ISS station keeping. It would work, in theory, to just put a large number of Hall effect thrusters on the back but the piping would be infeasible.
    - duskwuff 9y ago
      It also needs resupply missions for food, air, and crew anyway. Reboost is almost a footnote.
pX0r 9y ago
"Sorry data, air may be the eventual oil." Trivia question: How many round-trips from Neptune would it take to cause a 1% dip in Earth's air content? Bonus question: Since the Earth is not making any more Xenon, are we losing some of this resource to the deep space every time we nudge a satellite?
- russdill 9y ago
  It's not Xenon you have to worry about, it's Helium. Once we run out we'll be too heavy and fall into the sun.
- wyattpeak 9y ago
  Xenon's very heavy, most of it would eventually come back down to Earth - probably sooner rather than later. Most of what we lose to deep space is hydrogen and helium. And almost none of that is from space missions, anyway, it's just Brownian motion.
  - alex_duf 9y ago
    Isn't it a matter of speed rather than mass? If the xenon is ejected faster than the escape velocity, it seems like it would get off Earth's gravity. In fact I think it would have to be roughly twice the escape velocity since the spacecraft is already going near it in one direction. According to Wikipedia[1] the exhaust velocity of an ion thruster is between 20 to 50 km/s when the Earth escape velocity is 11km/s [2] [1]: https://en.wikipedia.org/wiki/Ion_thruster https://en.wikipedia.org/wiki/Ion_thruster [2]: https://en.wikipedia.org/wiki/Escape_velocity https://en.wikipedia.org/wiki/Escape_velocity so I would assume most of it is lost in space
    - wyattpeak 9y ago
      Wow, you're right, I vastly underestimated the exhaust velocity. You'd still have to account for its interaction with the atmosphere, but my point is moot.
    - jtbayly 9y ago
      Velocity alone doesn't answer the question. Direction matters. My assumption (knowing nothing but basic Physics), is that the xenon is ejected in a direction slightly toward the earth, and mostly directly in the opposite direction of the current travel, because that's what would be necessary to counteract drag and keep a satellite on the same path. This means that if the satellite is going almost 11km/s one direction, the xenon will have that much less speed compared to the earth. And the trajectory will be slightly toward the earth. I would assume that makes it substantially more likely that the xenon falls back to earth.
SideburnsOfDoom 9y ago
> Assuming it could collect more than it needs to keep itself in orbit, it could refuel a tank That's not this device though, it looks like the "collected" air runs straight into the thruster, like the flow through a jet engine. No tank involved.
aetherspawn 9y ago
That's a cool thought. You could perhaps use the atmosphere of planets to accelerate at very high velocities with the energy stored between each body (which would be a lot .. ie 60 days of 24/7 solar harvesting). The question is whether the thrust you produce is roughly linear with the energy you expel? Or does it taper asymptotic? What if the power system on the craft is titanium batteries that are designed to deliver 1 MW for say 2 minutes? Will that give you the needed acceleration in a given planets atmosphere? What if you use planetary lasers and don't need batteries at all?
- zaarn 9y ago
  Solar light isn't that strong once you go beyond mars. Earth gets 1400 W/m^2, at Saturn only 16 W/m^2 and on Neptune maybe 1.5 W if you get lucky. 60 days of continous harvesting, assuming the spacecraft doesn't use any power (which is not true in reality), is about 2 kWh at Neptune. Not that much. Saturn would be 23 kWh.
  - aetherspawn 9y ago
    Yuck, that’s miserable.
    - zaarn 9y ago
      It's the inverse square law that bites you here as the same amount of energy gets stretched out into a larger sphere as it travels outwards (at earth the energy is 1.4kW for a square meter, when going outwards, this square meter gets stretched) Double the distance and you get 1/4th the energy. Saturn is 9AU or 9 times as far as earth; 1/81th the energy. (1400 / 9^2 = 17, so math checks out; roughly) We're quite lucky to be close enough for solar energy to be a viable source of energy. [*]: https://en.wikipedia.org/wiki/Inverse-square_law https://en.wikipedia.org/wiki/Inverse-square_law
      - blattimwind 9y ago
        > We're quite lucky to be close enough for solar energy to be a viable source of energy. If solar energy were not viable, this form would not exist.

binarycoffee 9y ago

This is still very much sci-fi at the moment for anything flying above a 250 km earth orbit because atmospheric density decreases dramatically fast with altitude. The missions targeted by this technology are GOCE-like spacecrafts which by design must fly low and need an insane amount of propellant to compensate for the high atmospheric drag at such altitude.

baybal2 9y ago
This does not preclude the possibility of spacecraft doing repeated dips only on the perigee
- binarycoffee 9y ago
  True, interesting idea. [Long edit] Thinking further about this idea, I realize this may even mitigate the catch 22 problem of very low orbits (<180km): the lower the orbit, the larger the drag and the required thrust power, meaning the solar arrays must be bigger, which in turn further increases the drag... Calculations suggests that with current solar array and thruster technology, flying lower than 150km with this concept is impossible. But with an elliptic orbit, energy from the solar arrays can be stored on the low-drag portion of the orbit too and used during the perigee dip, thus decreasing the requirements in terms of solar arrays area.
  - Cthulhu_ 9y ago
    I'm now imagining a craft that folds up its solar panels before dipping into the atmosphere to gather fuel / accelerate. I'm sure I've built that in KSP, :p.
    - greeneggs 9y ago
      Here's an example where the authors propose doing this for planetary gravity assists, e.g., instead of using Venus for a normal gravity assist, dig into its atmosphere. Everything would need to be folded up first. "Hypersonic Interplanetary Flight: Aero Gravity Assist" Al Bowers & Dan Banks, 2006 https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090008672.pdf https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/200900... Discussed in a podcast here: https://theorbitalmechanics.com/show-notes/al-bowers https://theorbitalmechanics.com/show-notes/al-bowers
    - msl 9y ago
      That is not particulary far-fetched either: the ISS already reorients its solar panels when not illuminated by the sun. They call it the "night glider mode" [1]. [1] https://en.wikipedia.org/wiki/Night_Glider_mode https://en.wikipedia.org/wiki/Night_Glider_mode
      - sitkack 9y ago
        > The implementation of drag-reducing flight modes of the space station resulted in saving about 1,000 kg of orbital-maintenance propellant per year.
      - zaarn 9y ago
        Night Glider sounds vaguely like some 80s TV show. I do hope everyone on board is required to wear non-functional sunglasses during night glide.
- nbadg 9y ago
  This would have the added benefit of increased efficiency due to the Oberth effect; however, I'm still not sure you could use it for unassisted interplanetary flight. The last orbit, by definition, must occur before the craft passes Earth escape velocity -- the question is, in that last pass through perigee, can you get enough delta V to make it to another planet? Otherwise, you'd need supplemental propellant. It's still useful, it's just not something I would describe as "revolutionary" for interplanetary travel. Since the TWR of electric thrusters tends to be pretty abysmal, my gut is that you probably couldn't scale up the thruster well enough to bounce between planets without that supplemental propellant. That being said, as others have mentioned, this would be really quite interesting for stationkeeping at low orbital altitudes, particularly for small satellites.
ckastner 9y ago
> This is still very much sci-fi at the moment for anything flying above a 250 km earth orbit because atmospheric density decreases dramatically fast with altitude. One of my favorite takes on this concept was Poul Anderson's Tau Zero [1], which used a Bussard ramjet [2]. Apparently, in the 70s, in was thought that there was enough hydrogen surrounding our solar system to support interstellar travel. [1] https://en.wikipedia.org/wiki/Tau_Zero https://en.wikipedia.org/wiki/Tau_Zero [2] https://en.wikipedia.org/wiki/Bussard_ramjet https://en.wikipedia.org/wiki/Bussard_ramjet
- gaius 9y ago
  How can you decelerate with a ramjet? Wouldn't your own exhaust push the matter you needed out of the way?
  - whatshisface 9y ago
    You could push the exhaust single-file in a highly focused beam, leaving most of the solid angle around you unpushed.
- binarycoffee 9y ago
  Somewhat related is the E-sail [1] concept, a perhaps less ambitious but (probably) feasible idea to harness the momentum of solar wind particles with very long charged wires. [1] https://en.wikipedia.org/wiki/Electric_sail https://en.wikipedia.org/wiki/Electric_sail
- wizardforhire 9y ago
  A personal favorite feature on federation vessels. http://memory-alpha.wikia.com/wiki/Bussard_collector http://memory-alpha.wikia.com/wiki/Bussard_collector
- Retric 9y ago
  Bussard Ramjets can be useful for interstellar travel. The net thrust is not great, but for very long and relatively slow trips it let's you power a very large ship without dragging along as much fuel assuming you can get hydrogen only fusion to work.
ProblemFactory 9y ago
> The missions targeted by this technology are GOCE-like spacecrafts which by design must fly low Once the technology matures, it could be used by more missions. Flying low has its benefits: * Lower latency for communication satellites, * Better resolution for Earth imaging / spy satellites, * When the satellite fails, it quickly deorbits by itself. Until now, flying low has just not been economical, but if this thruster has similar lifetime to medium and high orbit satellites, then many more missions could choose lower orbits.
- orbital-decay 9y ago
  >When the satellite fails, it quickly deorbits by itself. This also means that failure recovery will be quite tricky if possible at all. There are some downsides to other points too: such a satellite would work at very thin margins due to the thruster being inefficient with air as a propellant. Its ground swath width will be lower, coverage will be worse, requiring more ground stations (remote sensing is very often limited by the downlink bandwidth). Also, some kind of aerodynamic shape will be required, limiting its capabilities and power budget. (electric propulsion needs a lot of power itself)
  - jccooper 9y ago
    "Quickly" in this context is probably still weeks, and you could carry a little backup system to kick it into higher orbit in case of trouble. But really, low-flying com or imaging sats are probably parts of large, "cheap" constellations and meant to be of limited lifespan.
  - alex_duf 9y ago
    >This also means that failure recovery will be quite tricky if possible at all Nowadays it's probably cheaper to send a new one than doing a whole Hubble like hot fix with a space shuttle
    - walrus01 9y ago
      failure recovery in the context of spacecraft usually means software-commands sent via TT&C (tracking, telemetry and control) channel to switch to another piece of hardware, part of the N+1 or 1+1 configuration on the spacecraft. It is incredibly exceptionally rare for a human to ever visit a satellite once in orbit. They did it a few times in the 1980s with the shuttle, including recovery of a satellite to prove it could be done, and there were the hubble servicing missions. But other than that no human has ever touched a satellite once it's in orbit.
m_mueller 9y ago
ISS is at 150km and needs costly refueling, right? Wouldn’t that be the most interesting applicaton in terms of cost savings?
- exDM69 9y ago
  ISS is at 400+ km altitude where the atmosphere is really thin. It's also very heavy for low thrust electric propulsion.
  - Symmetry 9y ago
    Electric thrusters have a low thrust to weight ratio but there's nothing stopping you, in theory, from just scaling up. The ISS only experiences a little drag so an electric drive trying to zero that out doesn't need a huge thrust. There's some interest in adapting VASIMR for ISS station keeping. It would work, in theory, to just put a large number of Hall effect thrusters on the back but the piping would be infeasible.
  - duskwuff 9y ago
    It also needs resupply missions for food, air, and crew anyway. Reboost is almost a footnote.

pX0r 9y ago

"Sorry data, air may be the eventual oil." Trivia question: How many round-trips from Neptune would it take to cause a 1% dip in Earth's air content? Bonus question: Since the Earth is not making any more Xenon, are we losing some of this resource to the deep space every time we nudge a satellite?

russdill 9y ago
It's not Xenon you have to worry about, it's Helium. Once we run out we'll be too heavy and fall into the sun.
wyattpeak 9y ago
Xenon's very heavy, most of it would eventually come back down to Earth - probably sooner rather than later. Most of what we lose to deep space is hydrogen and helium. And almost none of that is from space missions, anyway, it's just Brownian motion.
- alex_duf 9y ago
  Isn't it a matter of speed rather than mass? If the xenon is ejected faster than the escape velocity, it seems like it would get off Earth's gravity. In fact I think it would have to be roughly twice the escape velocity since the spacecraft is already going near it in one direction. According to Wikipedia[1] the exhaust velocity of an ion thruster is between 20 to 50 km/s when the Earth escape velocity is 11km/s [2] [1]: https://en.wikipedia.org/wiki/Ion_thruster https://en.wikipedia.org/wiki/Ion_thruster [2]: https://en.wikipedia.org/wiki/Escape_velocity https://en.wikipedia.org/wiki/Escape_velocity so I would assume most of it is lost in space
  - wyattpeak 9y ago
    Wow, you're right, I vastly underestimated the exhaust velocity. You'd still have to account for its interaction with the atmosphere, but my point is moot.
  - jtbayly 9y ago
    Velocity alone doesn't answer the question. Direction matters. My assumption (knowing nothing but basic Physics), is that the xenon is ejected in a direction slightly toward the earth, and mostly directly in the opposite direction of the current travel, because that's what would be necessary to counteract drag and keep a satellite on the same path. This means that if the satellite is going almost 11km/s one direction, the xenon will have that much less speed compared to the earth. And the trajectory will be slightly toward the earth. I would assume that makes it substantially more likely that the xenon falls back to earth.

SideburnsOfDoom 9y ago

> Assuming it could collect more than it needs to keep itself in orbit, it could refuel a tank That's not this device though, it looks like the "collected" air runs straight into the thruster, like the flow through a jet engine. No tank involved.

aetherspawn 9y ago

That's a cool thought. You could perhaps use the atmosphere of planets to accelerate at very high velocities with the energy stored between each body (which would be a lot .. ie 60 days of 24/7 solar harvesting). The question is whether the thrust you produce is roughly linear with the energy you expel? Or does it taper asymptotic? What if the power system on the craft is titanium batteries that are designed to deliver 1 MW for say 2 minutes? Will that give you the needed acceleration in a given planets atmosphere? What if you use planetary lasers and don't need batteries at all?

zaarn 9y ago
Solar light isn't that strong once you go beyond mars. Earth gets 1400 W/m^2, at Saturn only 16 W/m^2 and on Neptune maybe 1.5 W if you get lucky. 60 days of continous harvesting, assuming the spacecraft doesn't use any power (which is not true in reality), is about 2 kWh at Neptune. Not that much. Saturn would be 23 kWh.
- aetherspawn 9y ago
  Yuck, that’s miserable.
  - zaarn 9y ago
    It's the inverse square law that bites you here as the same amount of energy gets stretched out into a larger sphere as it travels outwards (at earth the energy is 1.4kW for a square meter, when going outwards, this square meter gets stretched) Double the distance and you get 1/4th the energy. Saturn is 9AU or 9 times as far as earth; 1/81th the energy. (1400 / 9^2 = 17, so math checks out; roughly) We're quite lucky to be close enough for solar energy to be a viable source of energy. [*]: https://en.wikipedia.org/wiki/Inverse-square_law https://en.wikipedia.org/wiki/Inverse-square_law
    - blattimwind 9y ago
      > We're quite lucky to be close enough for solar energy to be a viable source of energy. If solar energy were not viable, this form would not exist.