1 Newton of constant ion thrust (~11 Dawn ion engines) could raise the ISS orbit by about 65 km per year.
Sounds about right. So a system like that could boost the ISS into a fairly stable very low medium Earth orbit (2000 km) in just 25 years.
It would require minor modifications to the ISS to attach them, and minimal additional power.
I don't think any modifications that require significant EVA activity are considered minor. You'd need many tons of xenon for a propellant, so all that mass would have to be carried up, not just the engines. At full thrust, the engines would be consuming 25 kW, which is fully one quarter the capacity of the solar panels that supply power to the ISS. Of course, these are eclipsed about a third of the time, and partly eclipsed half the time. So if the thrusters operate continuously, they will also be drawing heavily on the batteries, meaning they will likely have to be replaced more often than the current ~5 years. So it sounds to me like adding ion thrusters would have a profound impact on the ISS power systems.
Think of it as an experiment in reinventing the ISS:
1) Strap on at least one new Dawn like engine per year and keep spiraling the ISS out into new territory.
2) Slowly replace the astronauts with robots so the ISS requires less & less supplies/toilets over time.
<<The ISS is maintained in a nearly circular orbit with a minimum mean altitude of 278 km and a maximum of 460 km. The normal maximum altitude is 425 km to allow NASA Shuttle rendezvous missions. It is likely that, with the retirement of the shuttle, the nominal orbit of the space station will be raised in altitude. As the ISS constantly loses altitude because of a slight atmospheric drag, it needs to be boosted to a higher altitude several times each year. This boost can be performed by the station's two main engines on the Zvezda service module, a docked space shuttle, a Progress resupply vessel, or by ESA's ATV. It takes approximately two orbits (three hours) for the boost to a higher altitude to be completed.
On December 8, 2008, Ad Astra Company signed an agreement with NASA to arrange the placement and testing of a flight version of the VASIMR, the VF-200, on the International Space Station (ISS). This technology could allow station-keeping to be done more economically than at present. As of February 2011, its launch is anticipated to be in 2014, though it may be later. The Taurus II has been reported as the "top contender" for the launch vehicle. Since the available power from the ISS is less than 200 kW, the ISS VASIMR will include a trickle-charged battery system allowing for 15 min pulses of thrust. If the tests of VASIMR reboosting of the ISS goes according to plan, the increase in specific impulse could mean that the cost of fuel for altitude reboosting will be one-twentieth of the current $210 million annual cost. Hydrogen generated by the ISS as a by-product is currently vented into space but will be redirected to the VASIMR to act as the fuel in place of the current Argon.>>
<<The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is an electro-magnetic thruster for spacecraft propulsion. It uses radio waves to ionize and heat a propellant and magnetic fields to accelerate the resulting plasma to generate thrust. The method of heating plasma used in VASIMR was originally developed as a result of research into nuclear fusion. VASIMR is intended to bridge the gap between high-thrust, low-specific impulse propulsion systems and low-thrust, high-specific impulse systems. VASIMR is capable of functioning in either mode. Costa Rican scientist and former astronaut Franklin Chang-Diaz created the VASIMR concept and has been working on its development since 1977.
[It is] expected that the VX-200 engine would have a thrust level of 5 N. The specific power estimated at 1.5 kg/kW meant that this version of the VASIMR engine would weigh only about 300 kg. One of the remaining untested issues was potential vs actual thrust; that is, whether the hot plasma actually detached from the rocket. Another issue was waste heat management critical to allowing for continuous operation of VASIMR engine.
Between April and September 2009, tests were performed on the VX-200 prototype with fully integrated 2 Tesla superconducting magnets. They successfully expanded the power range of the VASIMR up to its full operational capability of 200 kW. The VF-200 flight-rated thruster consists of two 100 kW VASIMR units with opposite magnetic dipoles so that no net rotational torque is applied to the space station when the thrusters are firing. The VF-200-1 is the first flight unit and will be tested in space attached to the ISS. As of October 2010, Ad Astra Rocket Company is working toward utilizing VASIMR technology for space tug missions to help "clean up the ever-growing problem of space trash." They hope to have a first-generation commercial offering by 2014.
The most important near-future application of VASIMR-powered spacecraft is transportation of cargo. Numerous studies have shown that, despite longer transit times, VASIMR-powered spacecraft will be much more efficient than traditional integrated chemical rockets at moving goods through space. An orbital transfer vehicle (OTV) — essentially a "space tug" — powered by a single VF-200 engine would be capable of transporting about 7 metric tons of cargo from low Earth orbit (LEO) to low Lunar orbit (LLO) with about a six month transit time. NASA envisages delivering about 34 metric tons of useful cargo to LLO in a single flight with a chemically propelled vehicle. To make that trip, about 60 metric tons of LOX-LH2 propellant would be burned. A comparable OTV would need to employ 5 VF-200 engines powered by a 1 MW solar array. To do the same job, such OTV would need to expend only about 8 metric tons of argon propellant. Total mass of such electric OTV would be in the range of 49 t (outbound & return fuel: 9 t, hardware: 6 t, cargo 34 t). The OTV transit times can be reduced by carrying lighter loads and/or expending more argon propellant with VASIMR throttled down to lower Isp. For instance, an empty OTV on the return trip to Earth covers the distance in about 23 days at optimal specific impulse of 5,000 s (50 kN·s/kg) or in about 14 days at Isp of 3,000 s (30 kN·s/kg). The total mass of the NASA specs' OTV (including structure, solar array, fuel tank, avionics, propellant and cargo) was assumed to be 100 metric tons (98.4 long tons; 110 short tons) allowing almost double the cargo capacity compared to chemically propelled vehicle but requiring even bigger solar arrays (or other source of power) capable of providing 2 MW.>>
A next-generation plasma rocket being developed by former NASA astronaut Franklin Chang Diaz called the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) has been touted as a way to get astronauts to Mars in weeks rather than months, as well as an innovative, cheap way to re-boost the International Space Station. But in a biting commentary posted on Space News and the Mars Society website, “Mars Direct” advocate Robert Zubrin calls VASIMR a “hoax” saying the engine “is neither revolutionary nor particularly promising. Rather, it is just another addition to the family of electric thrusters, which convert electric power to jet thrust, but are markedly inferior to the ones we already have,” adding, “There is thus no basis whatsoever for believing in the feasibility of Chang Diaz’s fantasy power system.”
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Zubrin has invited Chang Diaz to a formal public debate the VASIMR at a Mars Society convention in Dallas next month.
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk. — Garrison Keillor
A next-generation plasma rocket being developed by future NASA astronaut Cameron Diaz called the Magnetoplasma Action Specific Impulse MASI has been touted as a way to get owlice to Mars, Pennsylvania, in weeks (rather than the many months that it usually takes her), as well as an innovative, cheap way to re-boot owlice's office Work Station. But in a biting commentary posted on Space Gnus and the Marzipan Society website, advocate ZaSu Pitts calls MASI a “hoax” saying the engine “is neither revolutionary nor particularly promising. Rather, it is just another addition to the family of electronic bicycle thrusters, which convert Schweppervescence to bike thrust, but are markedly inferior to the ones we already have,” adding, “There is thus no basis whatsoever for believing in the feasibility of Cameron Diaz’s fantasy power system.” ZaSu Pitts has invited Cameron Diaz to a formal public debate the MASI at a Marzipan Society convention in the Dulles International Airport Zoo next month.
Say, that will come in handy until owlices thorny foot wound heals so she can peddle good again. And it can also be used to treat the pain--orally, of course Hic!
Earlier this month Russia's space agency Roscosmos caused an inadvertent media frenzy when deputy head Vitaly Davydov stated in a video that the International Space Station (ISS) would sink into the Pacific Ocean in 2020. But NASA officials say the statement about the roughly $150-billion, 15-nation partnership was premature.
Officially NASA, Roscosmos, and partners in Japan, Europe, and Canada have agreed to keep the station operational until at least 2020, but "that's only half the story," said NASA spokesperson Joshua Buck. "The international partners have been discussing extending the mission through 2028. At this point, there's no reason we wouldn't do that."
Still, at some point the mission will end, and the orbiting laboratory will be directed to plunge toward Earth. The station can't simply be left in orbit, or it will eventually fall from the skies on its own, raining debris over a wide swath of the planet and possibly endangering people on the ground. So what exactly will happen when we no longer need the biggest artificial space object in history?
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Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk. — Garrison Keillor
Hic!