# What is the ISS maximum altitude?

I see two threats to the ISS as its altitude goes up:

1. Cosmic/solar radiation, which would endanger the crew and the electronics aboard.
2. Orbital debris, which would have higher relative speed and might increase danger.

Disregarding the fact that it would be impractical because of higher service cost, how high could we put the ISS while maintaining it safe?

Additionally, how high could we push it with current technology? (Perhaps using a better launch site like Kourou)

• ".. ISS as its altitude goes up: .. 2) Orbital debris, which would have higher relative speed and might increase danger." I'm pretty sure it is the opposite. As altitude rises, the orbital speed of satellites drops. As objects approach Earth from Solar orbit, they speed up due to Earth's gravity. Aug 6 '15 at 0:09
• @AndrewThompson Yes, but with distance it also gets more difficult to detect smaller debris, track and predict their orbits, so threat level actually goes up in that regard. Aug 6 '15 at 0:13
• @TildalWave "Yes, but with distance.." DYM distance from Earth (ground) based detectors? I thought they could not detect anything lower than around a meter in diameter.. Aug 6 '15 at 0:24
• @AndrewThompson No, they can detect debris down to roughly 1 centimeter in size at ISS altitude range (radar cross-section, not actual size - that's actually below half the Haystack wavelength at 3 cm, but Haystack Auxiliary Radar that is more suitable for tracking low altitude debris uses 1.8 cm). problem is, the smaller the debris, the more uncertain their mass and surface area (drag coefficient, momentum,...), and with it, more unreliable predicted orbit used for conjunction analysis. I.e. it fast becomes a risk management nightmare. Aug 6 '15 at 0:27
• The most debris heavy areas in space are around 800 km above Earth. The ISS actually orbits at the altitude it does in part because debris won't stay for very long. Orbital lifetime is in roughly the 1 year range at that altitude, which means that debris won't stick around for too long. Aug 6 '15 at 0:48

The official NASA ISS Familiarization Manual (used in crew training) states on page 1-3: (emphasis mine)

All of these IGAs, MOUs, SPIP volumes, and control centers are required to support a vehicle that, at Assembly Complete, is to be the largest man-made object ever to orbit the Earth. The ISS is to have

• A pressurized volume of 1200 cubic meters

• Mass of 419,000 kilograms

• Maximum power output of 110 kilowatts (kW), with a payload average power allocation of 30 kW

• A structure that measures 108.4 meters (truss length) by 74 meters (module length)

An orbital altitude of 370-460 km

• An orbital inclination of 51.6°

• A crew of six (three until Assembly Complete)

Rationale for these limits is given in section 1-5:

The orbit is bounded on the “high” end by equipment design limits and the ability of the ETOVs to reach the ISS; it is bounded on the “low” end by the requirement that the ISS must be able to miss a propellant resupply/reboost mission and still be above a defined safe minimum altitude by the next resupply/reboost mission.

(ETOV stands for Earth to Orbit Vehicle)

• I would love to hear about theses "Equipement design limits" but I guess this is the best answer we can get Aug 6 '15 at 22:25
• @Antzi The canonical data is given above. Aug 17 '16 at 8:19
• @Nathan Tuggy, the answer is fully provided above. The asker says he wants more, but i don't see what that is. How else can I proceed? Aug 17 '16 at 10:12
• Either wait for the asker to provide more on their own, or for someone else to ask them. Do not use answers for commenting. Aug 17 '16 at 10:14
• The answer is marked as accepted, so there is no need to proceed anymore. If I had to do it it would be with an other question like "what would be the first issue to rise if we spinner the ISS faster" Aug 17 '16 at 13:51

The driving factor for the ISS altitude is cheaper maintenance, and orbital debris mitigation. There is an optimal altitude for maintenance, which would actually be a bit higher than it is, because the ISS has to actively maintain its altitude by thrusting on a regular basis, while if it was higher that wouldn't be the case.

Orbital debris is the primary limiting factor to raising the altitude higher. See the below chart for the altitude of most orbital debris, from Wikipedia. Note that increasing the altitude only slightly dramatically increases the amount of debris.

Okay, so looking at the chart below, above 1600 would also be a good area. Let's take away the fact that this is harder to maintain, and would create more space debris. This, however brings one to the Van Allen belts, which start around 1000 km. The ISS doesn't really have the radiation shielding to manage that environment well, although it could be added.

Bottom line is, even if cost wasn't a factor, it still makes sense to have the ISS at or near the altitude it is currently orbiting, until the space debris can be removed, or better radiation shielding added.