How are satellites deployed to the right orbit from the ISS?

[THX1138]

I read that small satellites can be launched from the ISS using robotic arms but my expectation from having played KSP is that the orbit of the satellite will then be very similar to that of the ISS. Do satellites launched in this way have their own propulsion to adjust their orbits? I read that the film Gravity was unrealistic because the orbits of satellites are far lower than the ISS. Some of the satellites, called "CubeSats" are just four inches cubed! Even so, flicking it away with the robotic arm (I have no idea whether that's what they actually do - I would have expected the arm to move very slowly) will only affect the other side of the orbit.

Edited January 30, 2016 by THX1138

[Shpaget]

Cubesats rarely have propulsion, and the ones launched from ISS are even less likely to have it. Yes, they end up in practically the same orbit as ISS, gradually decay and reenter.

[Nibb31]

The ISS isn't used for routinely launching satellites. They sometimes eject something like a science cubesat, or the SuitSat, and you're right, it ends up on pretty much the same orbit as the ISS. However, they typically do this before a reboost so the experiment decays due to drag and the ISS is boosted to a higher orbit.

Gravity was unrealistic because satellites are typically in different inclinations. Altitude is not much of a problem, but different inclinations require a plane change, which requires a lot of dV. Hubble was in a completely different orbit to the ISS, so there was no way they could have rendezvous'd with the ISS with the dV of George's MMU.

[NovaSilisko]

They have deployed a lot of cubesats in recent times, actually. As Nibb said though, they do it just before they raise the orbit of the station to compensate for atmospheric drag, so as to avoid any collision concerns.

 

(re: Gravity, I just sort of made the assumption that they'd moved Hubble to the same orbit as ISS for easier maintenince, which IIRC was a real proposal at one point after Columbia, so the shuttle, if damaged, would still be able to retreat to the safety of the station)

Edited January 30, 2016 by NovaSilisko

[fredinno]

1 hour ago, NovaSilisko said:

They have deployed a lot of cubesats in recent times, actually. As Nibb said though, they do it just before they raise the orbit of the station to compensate for atmospheric drag, so as to avoid any collision concerns.

 

(re: Gravity, I just sort of made the assumption that they'd moved Hubble to the same orbit as ISS for easier maintenince, which IIRC was a real proposal at one point after Columbia, so the shuttle, if damaged, would still be able to retreat to the safety of the station)

You would need to put the Hubble inside the Shuttle, return it to Earth, then launch it again in the ISS' inclination- the OMS pods don't have enough delta v to do that plane change. 

Obviously, this is why it was never taken seriously.

[NovaSilisko]

You could do it with a solar-electric propulsion module docked to the rear of it, actually. It would take a long time, but it would be perfectly doable.

[fredinno]

31 minutes ago, NovaSilisko said:

You could do it with a solar-electric propulsion module docked to the rear of it, actually. It would take a long time, but it would be perfectly doable.

There is no big enough SEP tug, and there was no such large SEP tug then. It's not worth it, and Hubble is pretty old anyways.