More radiation at higher altitude since you're dipping more into the Van Allen Belts (specifically the South Atlantic Anomaly), but yeah, there probably is some merit to raising the orbit.
NASA has ready found a new optimum. None of us has anything to add to their operational decision making.
Quote from: Robotbeat on 12/13/2014 10:36 pmMore radiation at higher altitude since you're dipping more into the Van Allen Belts (specifically the South Atlantic Anomaly), but yeah, there probably is some merit to raising the orbit.The Van Allen belts do not get down to 500 km, but the SAA might be slightly more intense at the higher altitude, don't know for sure.Remember that HST is at 600 km, and our astronauts were fine there.
Yes, there is slightly more radiation at higher altitude, but the more pressing concern is that we can expect much higher densities of orbital debris, not all of which are trackable.
Quote from: Burninate on 12/14/2014 05:05 amYes, there is slightly more radiation at higher altitude, but the more pressing concern is that we can expect much higher densities of orbital debris, not all of which are trackable.Doesn't all debris at 500 km eventually make it to 400 km?
More radiation at higher altitude since you're dipping more into the Van Allen Belts (specifically the South Atlantic Anomaly), but yeah, there probably is some merit to raising the orbit. It also improves the business case for launching cubesats. It does, however, lower the resolution of optical instruments on Station (while increasing their field of view).
What would be the down side of moving up to 425 kilometers immediately?
One of the great cost drivers of the ISS program is the provision of propulsion to maintain the nominal ISS orbit. Right now, that nominal orbit is about 400 kilometers, and the Russian Progress vehicle supplies tons of propellant every year that is used to maintain the orbit.One of the constraints on the altitude is that Progress and Soyuz cannot easily operate above 400 kilometers altitude; however, the introduction of Soyuz-2 as a launcher for these vehicles would probably resolve this issue - unless there are avionics issues that preclude operation of the vehicle at higher altitudes. There is also an issue that Soyuz would have a slightly steeper re-entry, from, say, 500 kilometers altitude.The use of Soyuz-2 would allow Progress to carry as much cargo to 500 kilometers as it currently does to 400 kilometers on Soyuz-U; the cost in prop for Progress to raise its altitude by 100 km is about 100 - 200 kg; however, the launch vehicle could inject Progress to an initially higher altitude with no loss of cargo mass.There is probably a formula that could tell us the cost of raising the ISS orbit from 400 kilometers to 500 kilometers vs the savings in propellant at the higher altitude. There are also some additional benefits in operating at a higher altitude, including more time in sunlight, less orbital debris, less damage from debris due to slightly lower velocities at altitude, shorter rendezvous times, greater field of view for photography, less blockage by the Earth for science experiments, etc. Ground stations might gain an extra minute of visibility, which is important to the Russians.Gaining altitude does not have to happen all at once - the station could be raised to 425 kilometers to facilitate the current Soyuz and Progress operating regimes, and then the apogee could be raised to 500 kilometers, followed by the perigee, after the transition to the "MS" variants of these vehicles and Soyuz-2.Another issue is that the orbital inclination could be slightly reduced, since the station would be able to "see" farther north at a higher altitude.
Quote from: Robotbeat on 12/13/2014 10:36 pmMore radiation at higher altitude since you're dipping more into the Van Allen Belts (specifically the South Atlantic Anomaly), but yeah, there probably is some merit to raising the orbit. It also improves the business case for launching cubesats. It does, however, lower the resolution of optical instruments on Station (while increasing their field of view).As I understand the ISS mission is to reduce Radiation risks for BEO missions. This is their task. The ISS has had 10 plus years of research at the lower levels and should have an extensive database to work off of. It should be an easy progression of research to raise the orbit for further research. Remember deep space missions will not have the earths protections to hide in.
Actually, they are likely going to lower the orbit due to debris concerns and other issues. More sunlight is not necessarily a good thing as it leads to thermal issues.
I seem to remember someone from ISS management told that post-Shuttle raising orbit to where it is today doubled amount of DAMs they had to execute.