12
$\begingroup$

To throw away an investment in space infra-structure the size of the ISS seems an incredible waste. Even if there is only a limited chance of ever using it again, the probability of this happening should be multiplied with the gigantic investment itself in order to reach an assesment of the potential value of the long term storage investment.

In other words, if there is 10% chance of salvaging 30% of the investment, it is still worth billions. Another aspect of the value of a determined salvage operation is the learning experience. By using the existing NEXT ion engines and the station's existing solar power array, NASA or whoever does it might learn something about cost effective industrial space operations, which hopefully will come in handy one day .

If The ISS were boosted to a height of 5000 km , it would be stable for a very long time . Without airpressure in the modules, many of the processes of degeneration of materials would efectively end , except maybe the ageing of gaskets and pressure seals.

While NASA has a 2015 plan for using the Vasimir ion engine for experimenting with ISS orbit boost, this has never been a real practical plan for boosting the ISS to a stable orbit, but rather a way to get more funding for a PET project...The total drag on ISS is about 0.9 N , a single NEXT engine can push 0.25 , 6 ion engines together with ''normal'' chemical boosts for 10 more years could go along way towards a stable orbit. The NEXT program has build atleast 4 prototype engines , probably sitting on a shelf somewhere .. WHY not use them ?

$\endgroup$
  • $\begingroup$ You don't need an experimental NEXT. You can use an array of off-the-shelf Hall thrusters that are commonly used on geostationary satellites. E.g. an array of BPT-4000's which do a quarter of a Newton or even higher power, higher Isp commercial thrusters which can do a Newton each. The power supplies for those are commercial as well, and easier to develop. $\endgroup$ – Mark Adler May 24 '14 at 22:40
  • $\begingroup$ Hall thrusters has a limited lifetime from 6-10 thousand hours because of corosion , while NEXT has a dokumented record of 48.000 hours . On the other hand it might be cheaper and more efficient to use hall thrusters and exchange them when they burn out . The powersuply would be the ISS's own solar arrays which has a 200kw capacity. Much of this cacity is only used at peak demand . My point is , that such a ''mothballed'' station could be used in the future for specifik purposes of asembling larger structures , wich might otherwise never be build . $\endgroup$ – user3407 May 25 '14 at 12:18
  • 1
    $\begingroup$ No, that problem has been solved. We now have "immortal" Hall thrusters. $\endgroup$ – Mark Adler May 25 '14 at 16:54
  • $\begingroup$ Looks like going from 300 to 400 volts boosts ISP but reduces thrust. If drag is .9 newtons, the effective thrust of 6 .25 newton engines would be .6 newtons. Not sure the higher ISP would be worth it. $\endgroup$ – HopDavid May 26 '14 at 1:15
3
$\begingroup$

I don't know the characteristics of NEXT, this is just a prototype, right? But assuming

  • specific impulse around 3000 seconds,
  • the ISS mass to be 450 000 kg,
  • the delta-V required to boost from 400 km to 5000 km is around 1700 m/s.

we need around 27 tons of Xenon fuel to be delivered to 400 km orbit first.

That's more than a single Proton or a single Space Shuttle payload. The whole enterprise gets as expensive as to deliver a couple of new modules to the station.

While deorbiting the station only requires a single Progress, they say. A many times cheaper solution.

$\endgroup$
  • $\begingroup$ We dont need 27 ton of xenon to be delivered FIRST , just a few tons to get started with . The point is , that by starting now we keep all options open with a minimal investment . If we dont , we decide to throw the ISS away without investigating all the options . $\endgroup$ – user3407 May 25 '14 at 12:33
  • $\begingroup$ It doesn't matter. The price of bringing it in parts can only be higher. The bigger LV used the lower price per kilo. $\endgroup$ – horsh May 25 '14 at 12:44
  • $\begingroup$ What's the usual surplus of onboard propellants of the cargo delivery vehicles? I didn't check, but my guess would be their own thrusters could also be used to somewhat help with the needed orbital reboosts, and still keep enough for their own deorbit burn? $\endgroup$ – TildalWave May 25 '14 at 14:03
  • $\begingroup$ Progress: around 500kg their own (depends on how much has been consumed to arrive), and 580kg of resupply for the station. $\endgroup$ – horsh May 25 '14 at 17:37
  • $\begingroup$ ATV: up to 3910kg its own + to refuel Zvezda 860 kg. $\endgroup$ – horsh May 25 '14 at 17:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.