ISS Loses Orbit-Boosting Options

An anonymous reader writes "NewScientist reports is reporting that the International Space Station has lost some of its options when it comes to altitude-boosting due to several recent failures. From the article: 'The problems began on 19 April 2006, when the Russian Zvezda service module's main engines failed during a test. The failure may have been due to a sunshade cover that was not completely open, according to a station status report.'"

Re:Bring it back...

[anzev]

Great thoughts! I totally agree with you! However, the only problem is this station is huge! In fact, according to the NASA Mission Page [nasa.gov] it's 404,069 pounds with a width Across Solar Arrays of 240 feet. It's 146 feet long from Destiny Lab to Zvezda; 171 feet with a Progress docked and 90 feet high!

Whilst if you take a peek at the Shuttle info page [seds.org] you'll find that the cargo bay is 60 ft long, 15 ft in diameter. so there's almost no way you could get that station anywhere inside the orbiter. The only possible way to get it down, is the same way we got it up there in the first place. Which means dismantling it ! I found a nice array of photos showing the process here [nasa.gov].

I find [spaceprojects.com] the station has cost billions already and is a decade behind schedule. Here's a summary:
INITIAL DESIGN PAPERWORK -- $10 billion
HARDWARE -- $25 billion
SHUTTLE SERVICING COSTS -- $20 billion
MAINTENANCE -- $41 billion
YEAR 2001 COST OVERRUN (disclosed immediately AFTER the presidential election of 2000): $5 billion.

So, multiply this by two and you get the cost of bringing it down. Are you a tax payer? If so, I'm guessing you don't want to pay that :). Hope this clears the question of why they let sattelites burn up there too ... In case it doesn't, it costs [cato.org] around 2000 USD per pound to send a sattelite to space. It costs twice as much to recover it (sending an empty shuttle, a space walk, operating the hand, bringing it down) and we're taking a serious risk here, I mean, sending it up requires no humans, so if something goes wrong, we just blew up a few millions, but hey, if a shuttle explodes -- all hell breaks lose. So I say, leave them to burn out!

Re:1 in 10,000

[Antony T Curtis]

Probabilities of independent events are not cumulative... ...otherwise, a very large number of individuals who commute by car would have accumulated a probability of having an accident far in excess of 100% every year.

Concider this:

What is the probability that the next coin-flip comes up heads? 50%...
After I flip heads, what is the next probability for getting heads? It is still 50%.
The next coin flip getting heads? 50% again.

Now, the probability of three consequtive coin flips getting all heads is 12.5%

Re:1 in 10,000

[ScottLindner]

That's how probability works. You *cannot* guarantee an accident will not happen. You can only reduce the odds. You can only get close to 100% guarantee, but not actually achieve 100% guarantee. As you get closer to 100% the costs go up enormously. If you wanted to knock it down to 1:100,000 odds you will pay more than 10x the cost. And then.. it's still only a probability, and not a frequency. You interpretted it as a frequency of problems, and not a probability.

Even with this low probability, the ISS could get whacked once every day.. and the probably would still be 1:10000 with the procedure they are using today. Assuming they are modelling probability properly.

Chart of ISS Height

[sam5550]

A chart of the height of the ISS:

Getting lower... [heavens-above.com]

Re:Sucesses?

[A non-mouse Cow Herd]

The true use of the space station is that is shows that a long term spaceship can't be built in small sections over a long period of time without the whole assembly obsoleting itself or wearing out before it starts its main mission.

Even if that was true of ISS (which is a stretch at the very least), it doesn't prove it for the general case. In particular ISS is designed to be occupied and used while it is under construction, and designed to be serviced on orbit. If you were designing a deep space craft, you would make different choices.

For the sake of argument, presume that the spacestation had been designed to travel to mars. By adding high thrust ion engines and power plants, this could have been done.

Only if you completely redesigned most of it. ISS is designed for LEO. To make it work in deep space would require major changes. The thermal control, power and navigation systems are designed for LEO.

However an assembly as large as the space station and typical for the requirement, loses over a mile of altitude a day in earth orbit and will burn up in the atmosphere within 1 year of ceasing to re-adjust its orbit higher.

ISS loses ~100 meters/day when it is on the lower edge of it's nominal orbits. Maybe 200 meters if solar activity is really high. Incidentally, if it lost a mile per day, it would burn up in a matter of months or less, depending on the starting altitude.

What has been really learned is that complex space ships of conventional design will age too soon to be of much use other than to learn how fast things wear out and wear down in a space environment.

Not at all. Many of the original components are working fine, and the ones that have failed have definite, identifiable and fixable reasons for failing. Although ISS is an awfully expensive way of doing it, it does provide significant lessons in building long duration crewed spacecraft. Far better to learn these lessons in LEO rather than on the way to mars.

Re:Chart of ISS Height

[A non-mouse Cow Herd]

You can see the full history here [spaceref.com]

To answer the question, they could boost it somewhat higher, but have chosen not to. Lower orbits give leave more payload for visiting craft, although that must be weighed against extra fuel for reboosts. Reboosts also affect the launch windows for visiting craft. You might look at the graph the GP posted and think "OMG it's falling out of control" but that is not the case. It's at the current altitude because thats where they decided they wanted it. Reboosts are normally done with Progress and Shuttle engines, not the SM engines that failed.

They can't put it too high or it would be out of reach of the spacecraft that are supposed to service it. Even if they could reach it, you reduce the payload they can get there. Also, if you go too much higher you start hitting the lower edges of the Van Allen belts, which is bad for both the equipment and crew.

BTW: another good description of the recent failure can be found at http://www.thespacereview.com/article/619/1 [thespacereview.com]