MadSci Network: Other
Query:

Re: Is a self contained working environment possible?

Date: Sun Jul 16 00:29:40 2000
Posted By: William A. Wheaton, Staff Scientist, IPAC, Infrared Processing Center
Area of science: Other
ID: 961702485.Ot
Message:

MAD Scientist: A Self-Contained Working Environment in Space

A Self-Contained Working Environment in Space

15 July 2000

Question:

Is a self contained working environment possible?

From: W.
Grade: 10-12
City: None State/Prov.: None Country: USA
Area: Other
Message ID Number: 961702485.Ot

I have this idea of an environment where astronauts can work safely. First for ex. repairing a telescope in space, can't they just contain the whole telescope with an airtight container, where conditions can be like inside a space shuttle; temporary life-support environment? Then space suits will not be needed as the astronauts will be working inside. What do you think?

Answer:

I believe your idea is certainly possible, and very likely to happen in the future; I hope fairly soon. The only reason it has not happened already is probably cost and lack of a specific need, by which I mean something required by a current mission that cannot be done any other way. With the development of the International Space Station (ISS) now progressing, I think such a facility is quite likely.

One important practical issue you may not appreciate, though, is that it is usually not easy to get large payloads like the Hubble Space Telescope (HST) from the orbit they are now in, to another one, say the ISS orbit. This means you cannot easily just haul everything to the hanger.

For example, if you will look at the JTrack web site, you will see both ISS and HST; CTL-click on the spacecraft icons to turn the orbit ground track on or off. The orbits are roughly fixed in space, while the Earth turns under them. Actually, in the JTrack figure, the orbits, Sun, and Earth shadow (shaded area) move (which way, do you think? -- remember the Sun has to rise in the East, and set in the West) while the map stays fixed; but of course really the Earth turns under the Sun. As you should be able to see from the orbit track, HST goes north and south of the Equator just about 30°. This means you can launch from Florida to HST by going due east (when the orbit track just touches Florida), which is the cheapest way to do it.

But the ISS orbit is quite different, it extends north and south to over 51°. One reason is so that most of the inhabited regions of the Earth are passed over by the Station, for climate and environmental observation purposes. Another is so that Russia can launch to and recover from the ISS, and be part of the project. Notice that the HST never passes over Russia (too far north). Can you see that this means it is impossible (well -- really just difficult, meaning very expensive) to reach the HST orbit from Russian territory?

If you wanted to get from the ISS orbit to the HST (or back), you would have to wait until you had arrived where the orbits cross. Then you have to match speeds by rocket power with the other orbit. The minimum crossing angle is actually (51.6° - 28.5°) = 23.1°, where I have taken the more accurate 51.6° and 28.5° inclination angles from the NORAD/GSCF page listed in the references below. Both HST and ISS are moving at nearly 8 km per sec, the characteristic speed for low-Earth orbits. A nice little trigonometry problem then shows that it takes about 3.2 km per sec -- really about (2*sin[23.1°/2])* 8 km/sec (hint: draw an isosceles triangle with 2 sides each 8 km/sec long, and a vertex angle of 23.1°, and then think about the base of it) -- to switch over from one orbit to the other.

Unfortunately, 3.2 km per sec is a lot in the space business. A specially designed space tug just might be able to do it at a feasible cost, ie, less than the cost of launching a whole space shuttle directly to HST. Of course the fuel for the tug has to come up from the ground, which is what makes it cost many thousands of dollars per kgm in orbit where you need it. However, there are a few further tricks one can play, which might reduce the cost, but which I have not space to go into here. If the tug is not practical, you would need to carry the hanger up with you, which is obviously far less much convenient. Perhaps it could be made of inflatable fabric.

REFERENCES:

Some places you may find interesting for further information:

  1. A nice display satellite positions "right now", the JTrack page is also very good for learning about how things move in low-Earth orbit.

  2. Somewhat out of date, but the best I've found, ISS reference information.

  3. NASA's main ISS page -- a little short on solid information, unfortunately.

  4. A very good reference to orbits and rockets, etc, is the classic Basics of Spaceflight. It is a whole book on-line book, though.

  5. Data from NORAD, distributed by GSCF, this page leads to the main US public reference for current satellite orbit data. Unfortunately it is a bit intimidating, and not too simple to decode. Proceeding bravely, click on "Access the catalog", and then "OIG Main page", followed by "Reports", then "Special Interest Group...". For the format ("TLE") of the elements, see the bottom of the "Reports" page, where there is an example. You'll have to refer to the JPL "Basics", above, to understand much of it, but the inclination is obvious.


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