ISS and deorbit

[ar81]

ISS is at 354km and I know that non spherical gravity has a strong influence in ISS orbit.

How could ISS deorbit sooner? Due to atmospheric microdrag or due to non spherical gravity?

If you ask me, it looks like non spherical gravity, for microdrag should not be so powerful as an OMS engine and it take a lot of time to deorbit a shuttle.

How long ISS would take to deorbit if no bump takes place?

 

[Urwumpe]

Non-spherical gravity can't de-orbit the ISS at all, this effect on the orbit height is periodic and neutralized over the turn of one orbit (It can only change the orbit plane).

Sun and moon can de-orbit the ISS, but drag will be faster. Without reboosts, you can expect deorbit in ~12 months.

 

[joeybigO]

Just doing some basic math from the basics of spaceflight page.

Without any help or boost, the ISS would last about 496 revolutions.

My math could be jacked up too, I haven't used that math in about 3 or so years.
The constants come from internet fact finding. I used 2.0 on the Cd and a mass of 450 metric tons, and an area of 108 x 74 m. This could be bad data too.

 

[Urwumpe]

Sounds pretty bad as it is only one month of operation. Usual reboosts are about every two months.

 

[Scrooge McDuck]

Quote from this article:

Regular reboosts are needed to overcome the effects of residual atmospheric drag which makes the Station lose about 100 m in altitude per day.

 

[Urwumpe]

The altitude drop increases inverse exponentially with altitude. The lower the altitude, the higher the altitude drop per day.

 

[joeybigO]

my calculations were about 117.382 meters a day delta loss.

- Atmospheric Density Delta Height which was about 58 / delta velocity loss turned out -117 meters a day.

A much more accurate formula can be found by integrating the Atmospheric Density H calculation.

 

[GregBurch]

So wouldn't it make sense as a very high priority to build and install a solar-electric ion boost motor?

 

[Urwumpe]

So wouldn't it make sense as a very high priority to build and install a solar-electric ion boost motor?

You may calculate the power required to overcome drag.

For the ISS, it is pretty high and would weight a lot, as you would need to install a large array of thrusters somewhere. Also, you can only dock to the ISS while the thrusters are disabled as well as stay docked only when the thrusters are placed far away from the docking port.

Electrical engines are more useful for geostationary satellites where the forces are much lower and the solar power almost always available.

 

[GregBurch]

You may calculate the power required to overcome drag.

For the ISS, it is pretty high and would weight a lot, as you would need to install a large array of thrusters somewhere. Also, you can only dock to the ISS while the thrusters are disabled as well as stay docked only when the thrusters are placed far away from the docking port.

Electrical engines are more useful for geostationary satellites where the forces are much lower and the solar power almost always available.

Actually, being a math retard, I can't. Is the power required that much beyond what a solar/ion engine could do?

My idea was that thrusting at a low level would basically take place on a nearly-constant basis, pausing only for docking, undocking, EVA and science that requires drift.

 

[Spicer]

An ion engine on the back of the zvezda? That's actually a pretty cool idea! It would free up alot of weight on the ATV's and Progress craft for more essential items.

 

[SiberianTiger]

So wouldn't it make sense as a very high priority to build and install a solar-electric ion boost motor?

Hi Greg,
The only reason why the ISS operates now at the altitude like this is that it's a requirement for the Space Shutlle missions that ferry cargo (new modules, etc. to the station). Also, it needs to be very specially phased and tuned months before a shuttle mission blasts off - this are the routine tasks solved by TSUP-M ballisticians. Cannot point to the source, but I read that a substantial rise of the orbit is planned after the Shuttle retirement.

 

[SiberianTiger]

An ion engine on the back of the zvezda? That's actually a pretty cool idea! It would free up alot of weight on the ATV's and Progress craft for more essential items.

Would also require lots of solar power to operate, refitting the Zvezda's power lines and heck lots of $$$ for Xenon propellant, 'cause the mass to accelerate is quite different from the DeepSpace1's.

 

[chad_s]

http://www.heavens-above.com/IssHeight.aspx

 

[Urwumpe]

Actually, being a math retard, I can't. Is the power required that much beyond what a solar/ion engine could do?

My idea was that thrusting at a low level would basically take place on a nearly-constant basis, pausing only for docking, undocking, EVA and science that requires drift.

This paper might be interesting for you:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19640020179_1964020179.pdf

It is for a much older and smaller space station design, but you can get the idea. The conclusion itself in this paper, though, is pretty bad work, as it did not consider the limitations of the thrusters past their ISP.